Backport of: 2132 Fix support for enhanced authentication (#2171)

* Increase version

* Update release notes

* Adjust cancellation token handling

* Fix CI build

.editorconfig

@@ -40,7 +40,6 @@ dotnet_style_qualification_for_method = false:suggestion
 dotnet_style_qualification_for_property = false:suggestion
 
 # ReSharper properties
-resharper_autodetect_indent_settings = true
 resharper_default_private_modifier = implicit
 resharper_place_accessorholder_attribute_on_same_line = false
 resharper_use_indent_from_vs = false
@@ -61,7 +60,7 @@ resharper_web_config_wrong_module_highlighting = warning
 [*]
 charset = utf-8
 end_of_line = crlf
-trim_trailing_whitespace = false
+trim_trailing_whitespace = true
 insert_final_newline = false
 indent_style = space
 indent_size = 4

.github/workflows/ReleaseNotes.md

@@ -1,4 +1,3 @@
-* [Core] Add validation of maximum string lengths (#1718).
+* Client: Fixed wrong timeout for keep alive check (thanks to @Erw1nT, #2129)
-* [Client] Added overloads for setting packet payload and will payload (#1720).
+* Client: Fixed extended authentication (thanks to @chkr1011, #2132).
-* [Client] The proper connect result is now exposed in the _Disconnected_ event when authentication fails (#1139). 
+* Server: Fixed extended authentication (thanks to @chkr1011, #2132).
-* [Server] Improved performance by changing internal locking strategy for subscriptions (#1716, thanks to @zeheng).

.github/workflows/ci.yml

@@ -3,7 +3,7 @@ name: CI
 on: [push, pull_request]
 
 env:
-  VERSION: "4.2.1.${{github.run_number}}"
+  VERSION: "4.3.8.${{github.run_number}}"
 
 jobs:
   build:
@@ -12,12 +12,12 @@ jobs:
 
     steps:
       - name: Setup Windows SDK
-        uses: GuillaumeFalourd/setup-windows10-sdk-action@v1
+        uses: GuillaumeFalourd/setup-windows10-sdk-action@v2.4
         with:
           sdk-version: 18362
 
       - name: Setup .NET SDK
-        uses: actions/setup-dotnet@v1.9.0
+        uses: actions/setup-dotnet@v4
         with:
           dotnet-version: |
             3.1.x
@@ -28,7 +28,7 @@ jobs:
         uses: microsoft/setup-msbuild@v1.1
 
       - name: Checkout Code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Setup Signing Certificate
         run: |
@@ -42,23 +42,41 @@ jobs:
       - name: Build solution
         run: msbuild MQTTnet.sln /t:Build /p:Configuration="Release" /verbosity:m /p:FileVersion=${{ env.VERSION }} /p:AssemblyVersion=${{ env.VERSION }} /p:PackageVersion=${{ env.VERSION }} /p:SignAssembly=true /p:AssemblyOriginatorKeyFile=${{ github.workspace }}\certificate.snk
 
-      - name: Collect nuget Packages
-        uses: actions/upload-artifact@v2
-        with:
-          name: nuget Packages
-          path: |
-            **\*.nupkg
-            **\*.snupkg
-
       - name: Setup VSTest
         uses: darenm/Setup-VSTest@v1
 
       - name: Core Tests
-        run: vstest.console.exe Source\MQTTnet.Tests\bin\Release\net6.0\MQTTnet.Tests.dll
+        run: vstest.console.exe Source\MQTTnet.Tests\bin\Release\net7.0\MQTTnet.Tests.dll
 
       - name: ASP.NET Tests
         run: vstest.console.exe Source\MQTTnet.AspNetCore.Tests\bin\Release\netcoreapp3.1\MQTTnet.AspNetCore.Tests.dll
 
+      - name: Install sign CLI tool
+        run: dotnet tool install --tool-path . sign --version 0.9.0-beta.23127.3
+
+      - name: Sign nugets
+        shell: pwsh
+        run: >
+          ./sign code azure-key-vault `
+          "**/*.nupkg" `
+          --base-directory "${{ github.workspace }}/Source" `
+          --publisher-name "MQTTnet" `
+          --description "MQTTnet" `
+          --description-url "https://github.com/dotnet/MQTTnet" `
+          --azure-key-vault-tenant-id "${{ secrets.AZURE_TENANT_ID }}" `
+          --azure-key-vault-client-id "${{ secrets.AZURE_CLIENT_ID }}" `
+          --azure-key-vault-client-secret "${{ secrets.AZURE_CLIENT_SECRET }}" `
+          --azure-key-vault-certificate "${{ secrets.KEY_VAULT_CERTIFICATE_ID }}" `
+          --azure-key-vault-url "${{ secrets.KEY_VAULT_URL }}"
+
+      - name: Upload signed nuget packages
+        uses: actions/upload-artifact@v4
+        with:
+          name: signed-nugets
+          path: |
+            ${{ github.workspace }}/Source/**/*.nupkg
+            ${{ github.workspace }}/Source/**/*.snupkg
+
       - name: Publish MyGet nugets
         if: ${{ github.event_name == 'push' }}
-        run: dotnet nuget push **/*.nupkg -k ${{ secrets.MYGET_API_KEY }} -s https://www.myget.org/F/mqttnet/api/v3/index.json --skip-duplicate
+        run: dotnet nuget push ${{ github.workspace }}/Source/**/*.nupkg -k ${{ secrets.MYGET_API_KEY }} -s https://www.myget.org/F/mqttnet/api/v3/index.json --skip-duplicate

MQTTnet.sln

@@ -7,9 +7,11 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet", "Source\MQTTnet\M
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{B3F60ECB-45BA-4C66-8903-8BB89CA67998}"
 	ProjectSection(SolutionItems) = preProject
+		CODE-OF-CONDUCT.md = CODE-OF-CONDUCT.md
 		LICENSE = LICENSE
 		README.md = README.md
-		CODE-OF-CONDUCT.md = CODE-OF-CONDUCT.md
+		.github\workflows\ReleaseNotes.md = .github\workflows\ReleaseNotes.md
+		.github\workflows\ci.yml = .github\workflows\ci.yml
 	EndProjectSection
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.AspNetCore", "Source\MQTTnet.AspnetCore\MQTTnet.AspNetCore.csproj", "{F10C4060-F7EE-4A83-919F-FF723E72F94A}"
@@ -20,17 +22,19 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Extensions.ManagedC
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Extensions.WebSocket4Net", "Source\MQTTnet.Extensions.WebSocket4Net\MQTTnet.Extensions.WebSocket4Net.csproj", "{2BD01D53-4CA5-4142-BE8D-313876395E3E}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MQTTnet.Samples", "Samples\MQTTnet.Samples.csproj", "{71CF35F5-3327-4A91-AAF4-5340F6701771}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Samples", "Samples\MQTTnet.Samples.csproj", "{71CF35F5-3327-4A91-AAF4-5340F6701771}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MQTTnet.Tests", "Source\MQTTnet.Tests\MQTTnet.Tests.csproj", "{B270F32A-9F3E-42EE-A989-813E35E29ADB}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Tests", "Source\MQTTnet.Tests\MQTTnet.Tests.csproj", "{B270F32A-9F3E-42EE-A989-813E35E29ADB}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MQTTnet.AspNetCore.Tests", "Source\MQTTnet.AspNetCore.Tests\MQTTnet.AspNetCore.Tests.csproj", "{A238BBBF-C75F-482D-9CC3-BB34ABA9B675}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.AspNetCore.Tests", "Source\MQTTnet.AspNetCore.Tests\MQTTnet.AspNetCore.Tests.csproj", "{A238BBBF-C75F-482D-9CC3-BB34ABA9B675}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MQTTnet.Benchmarks", "Source\MQTTnet.Benchmarks\MQTTnet.Benchmarks.csproj", "{2F516E76-AAC4-4219-B7D1-34CDD3CFF381}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Benchmarks", "Source\MQTTnet.Benchmarks\MQTTnet.Benchmarks.csproj", "{2F516E76-AAC4-4219-B7D1-34CDD3CFF381}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MQTTnet.TestApp", "Source\MQTTnet.TestApp\MQTTnet.TestApp.csproj", "{175D5340-CC5B-4542-939D-4E7D15A0BC8D}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.TestApp", "Source\MQTTnet.TestApp\MQTTnet.TestApp.csproj", "{175D5340-CC5B-4542-939D-4E7D15A0BC8D}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MQTTnet.AspTestApp", "Source\MQTTnet.AspTestApp\MQTTnet.AspTestApp.csproj", "{72867E4C-4E15-4E8E-8FAB-AE9253286BBC}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.AspTestApp", "Source\MQTTnet.AspTestApp\MQTTnet.AspTestApp.csproj", "{72867E4C-4E15-4E8E-8FAB-AE9253286BBC}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Extensions.TopicTemplate", "Source\MQTTnet.Extensions.TopicTemplate\MQTTnet.Extensions.TopicTemplate.csproj", "{374D5861-F7A6-42A2-8CBE-040846000EF9}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -82,12 +86,14 @@ Global
 		{72867E4C-4E15-4E8E-8FAB-AE9253286BBC}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{72867E4C-4E15-4E8E-8FAB-AE9253286BBC}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{72867E4C-4E15-4E8E-8FAB-AE9253286BBC}.Release|Any CPU.Build.0 = Release|Any CPU
+		{374D5861-F7A6-42A2-8CBE-040846000EF9}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{374D5861-F7A6-42A2-8CBE-040846000EF9}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{374D5861-F7A6-42A2-8CBE-040846000EF9}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{374D5861-F7A6-42A2-8CBE-040846000EF9}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection
-	GlobalSection(NestedProjects) = preSolution
-	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {07536672-5CBC-4BE3-ACE0-708A431A7894}
 	EndGlobalSection

MQTTnet.sln.DotSettings

@@ -230,6 +230,7 @@
 	<s:String x:Key="/Default/CodeStyle/FileHeader/FileHeaderText/@EntryValue">Licensed to the .NET Foundation under one or more agreements.
 The .NET Foundation licenses this file to you under the MIT license.
 See the LICENSE file in the project root for more information.</s:String>
+	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EFeature_002EServices_002ECodeCleanup_002EFileHeader_002EFileHeaderSettingsMigrate/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ECSharpAttributeForSingleLineMethodUpgrade/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ECSharpKeepExistingMigration/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ECSharpPlaceEmbeddedOnSameLineMigration/@EntryIndexedValue">True</s:Boolean>
@@ -240,6 +241,7 @@ See the LICENSE file in the project root for more information.</s:String>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002ECSharpPlaceAttributeOnSameLineMigration/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002EMigrateBlankLinesAroundFieldToBlankLinesAroundProperty/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002EMigrateThisQualifierSettings/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/UserDictionary/Words/=catched/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=CONNACK/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=PINGREQ/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=PINGRESP/@EntryIndexedValue">True</s:Boolean>

Samples/Client/Client_Connection_Samples.cs

@@ -7,10 +7,14 @@
 // ReSharper disable InconsistentNaming
 
 using System.Security.Authentication;
+using System.Security.Cryptography.X509Certificates;
+using System.Text;
 using MQTTnet.Client;
 using MQTTnet.Extensions.WebSocket4Net;
 using MQTTnet.Formatter;
+using MQTTnet.Protocol;
 using MQTTnet.Samples.Helpers;
+using MQTTnet.Server;
 
 namespace MQTTnet.Samples.Client;
 
@@ -70,32 +74,6 @@ public static class Client_Connection_Samples
             await mqttClient.DisconnectAsync(mqttClientDisconnectOptions, CancellationToken.None);
         }
     }
-    
-    public static async Task Connect_With_Amazon_AWS()
-    {
-        /*
-         * This sample creates a simple MQTT client and connects to an Amazon Web Services broker.
-         *
-         * The broker requires special settings which are set here.
-         */
-
-        var mqttFactory = new MqttFactory();
-
-        using (var mqttClient = mqttFactory.CreateMqttClient())
-        {
-            var mqttClientOptions = new MqttClientOptionsBuilder()
-                .WithTcpServer("amazon.web.services.broker")
-                // Disabling packet fragmentation is very important!  
-                .WithoutPacketFragmentation()
-                .Build();
-            
-            await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
-
-            Console.WriteLine("The MQTT client is connected.");
-
-            await mqttClient.DisconnectAsync();
-        }
-    }
 
     public static async Task Connect_Client_Timeout()
     {
@@ -125,6 +103,105 @@ public static class Client_Connection_Samples
         }
     }
 
+    public static async Task Connect_Using_Extended_Authentication()
+    {
+        /*
+         * This sample uses enhanced (aka extended) authentication (Kerberos) when creating the connection.
+         */
+
+        /*
+         * Server part...
+         */
+
+        var mqttFactory = new MqttFactory();
+
+        var serverOptions = mqttFactory.CreateServerOptionsBuilder().WithDefaultEndpoint().Build();
+        var server = mqttFactory.CreateMqttServer(serverOptions);
+
+        server.ValidatingConnectionAsync += async args =>
+        {
+            if (args.AuthenticationMethod == "GS2-KRB5")
+            {
+                var result = await args.SendExtendedAuthenticationExchangeDataAsync(new MqttExtendedAuthenticationExchangeOptions());
+
+                Console.WriteLine($"Received AUTH data from client: {Encoding.UTF8.GetString(result.AuthenticationData)}");
+
+                var authOptions = mqttFactory.CreateMqttExtendedAuthenticationExchangeOptionsBuilder().WithAuthenticationData("reply context token").Build();
+
+                result = await args.SendExtendedAuthenticationExchangeDataAsync(authOptions);
+
+                Console.WriteLine($"Received AUTH data from client: {Encoding.UTF8.GetString(result.AuthenticationData)}");
+
+                args.ResponseAuthenticationData = "outcome of authentication"u8.ToArray();
+
+                // Authentication DONE!
+                args.ReasonCode = MqttConnectReasonCode.Success; // Also the default!
+            }
+            else
+            {
+                args.ReasonCode = MqttConnectReasonCode.BadAuthenticationMethod;
+            }
+        };
+
+        await server.StartAsync();
+
+        /*
+         * Client part...
+         */
+
+        var mqttClientFactory = new MqttFactory();
+
+        // Use Kerberos sample from the MQTT RFC.
+        var kerberosAuthenticationHandler = new SampleClientKerberosAuthenticationHandler();
+
+        var clientOptions = mqttClientFactory.CreateClientOptionsBuilder()
+            .WithTcpServer("localhost")
+            .WithProtocolVersion(MqttProtocolVersion.V500)
+            .WithExtendedAuthenticationExchangeHandler(kerberosAuthenticationHandler)
+            .WithAuthentication("GS2-KRB5", Array.Empty<byte>())
+            .Build();
+
+        var client = mqttClientFactory.CreateMqttClient();
+
+        var result = await client.ConnectAsync(clientOptions);
+
+        Console.WriteLine($"Client connect result: {result.ResultCode}");
+    }
+
+    class SampleClientKerberosAuthenticationHandler : IMqttExtendedAuthenticationExchangeHandler
+    {
+        private readonly Queue<byte[]> clientTokens = new Queue<byte[]>();
+
+        public SampleClientKerberosAuthenticationHandler()
+        {
+            // The Kerberos sample from the MQTT RFC sends two client tokens after the initial empty token.
+            clientTokens.Enqueue(Encoding.UTF8.GetBytes("initial context token"));
+            clientTokens.Enqueue(Array.Empty<byte>());
+        }
+
+        public async Task HandleRequestAsync(MqttExtendedAuthenticationExchangeContext context)
+        {
+            if (context.AuthenticationMethod != "GS2-KRB5")
+            {
+                throw new InvalidOperationException("Wrong authentication method");
+            }
+
+            Console.WriteLine($"Received AUTH data from server: {Encoding.UTF8.GetString(context.AuthenticationData)}");
+
+            if (!clientTokens.TryDequeue(out var clientToken))
+            {
+                throw new InvalidOperationException("No more client tokens available");
+            }
+
+            var sendOptions = new MqttExtendedAuthenticationExchangeData
+            {
+                AuthenticationData = clientToken
+            };
+
+            await context.Client.SendExtendedAuthenticationExchangeDataAsync(sendOptions);
+        }
+    }
+
     public static async Task Connect_Client_Using_MQTTv5()
     {
         /*
@@ -161,15 +238,15 @@ public static class Client_Connection_Samples
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
             var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("mqtt.fluux.io")
-                .WithTls(
+                .WithTlsOptions(
                     o =>
                     {
                         // The used public broker sometimes has invalid certificates. This sample accepts all
                         // certificates. This should not be used in live environments.
-                        o.CertificateValidationHandler = _ => true;
+                        o.WithCertificateValidationHandler(_ => true);
 
                         // The default value is determined by the OS. Set manually to force version.
-                        o.SslProtocol = SslProtocols.Tls12;
+                        o.WithSslProtocols(SslProtocols.Tls12);
                     })
                 .Build();
 
@@ -196,7 +273,7 @@ public static class Client_Connection_Samples
 
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
-            var mqttClientOptions = new MqttClientOptionsBuilder().WithWebSocketServer("broker.hivemq.com:8000/mqtt").Build();
+            var mqttClientOptions = new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.hivemq.com:8000/mqtt")).Build();
 
             var response = await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
 
@@ -218,7 +295,7 @@ public static class Client_Connection_Samples
 
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
-            var mqttClientOptions = new MqttClientOptionsBuilder().WithWebSocketServer("broker.hivemq.com:8000/mqtt").Build();
+            var mqttClientOptions = new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.hivemq.com:8000/mqtt")).Build();
 
             var response = await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
 
@@ -241,13 +318,11 @@ public static class Client_Connection_Samples
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
             var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8883)
-                .WithTls(
+                .WithTlsOptions(
-                    o =>
+                    o => o.WithCertificateValidationHandler(
-                    {
                         // The used public broker sometimes has invalid certificates. This sample accepts all
                         // certificates. This should not be used in live environments.
-                        o.CertificateValidationHandler = _ => true;
+                        _ => true))
-                    })
                 .Build();
 
             // In MQTTv5 the response contains much more information.
@@ -262,6 +337,31 @@ public static class Client_Connection_Samples
         }
     }
 
+    public static async Task Connect_With_Amazon_AWS()
+    {
+        /*
+         * This sample creates a simple MQTT client and connects to an Amazon Web Services broker.
+         *
+         * The broker requires special settings which are set here.
+         */
+
+        var mqttFactory = new MqttFactory();
+
+        using (var mqttClient = mqttFactory.CreateMqttClient())
+        {
+            var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("amazon.web.services.broker")
+                // Disabling packet fragmentation is very important!  
+                .WithoutPacketFragmentation()
+                .Build();
+
+            await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
+
+            Console.WriteLine("The MQTT client is connected.");
+
+            await mqttClient.DisconnectAsync();
+        }
+    }
+
     public static async Task Disconnect_Clean()
     {
         /*
@@ -317,18 +417,19 @@ public static class Client_Connection_Samples
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
             var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("mqtt.fluux.io", 8883)
-                .WithTls(
+                .WithTlsOptions(
                     o =>
                     {
-                        o.CertificateValidationHandler = eventArgs =>
+                        o.WithCertificateValidationHandler(
-                        {
+                            eventArgs =>
-                            eventArgs.Certificate.Subject.DumpToConsole();
+                            {
-                            eventArgs.Certificate.GetExpirationDateString().DumpToConsole();
+                                eventArgs.Certificate.Subject.DumpToConsole();
-                            eventArgs.Chain.ChainPolicy.RevocationMode.DumpToConsole();
+                                eventArgs.Certificate.GetExpirationDateString().DumpToConsole();
-                            eventArgs.Chain.ChainStatus.DumpToConsole();
+                                eventArgs.Chain.ChainPolicy.RevocationMode.DumpToConsole();
-                            eventArgs.SslPolicyErrors.DumpToConsole();
+                                eventArgs.Chain.ChainStatus.DumpToConsole();
-                            return true;
+                                eventArgs.SslPolicyErrors.DumpToConsole();
-                        };
+                                return true;
+                            });
                     })
                 .Build();
 
@@ -432,6 +533,59 @@ public static class Client_Connection_Samples
                         }
                     }
                 });
+
+            Console.WriteLine("Press <Enter> to exit");
+            Console.ReadLine();
         }
     }
-}
+
+    public static async Task ConnectTls_WithCaFile()
+    {
+        var mqttFactory = new MqttFactory();
+
+        X509Certificate2Collection caChain = new X509Certificate2Collection();
+        caChain.ImportFromPem(mosquitto_org); // from https://test.mosquitto.org/ssl/mosquitto.org.crt
+
+        using (var mqttClient = mqttFactory.CreateMqttClient())
+        {
+            var mqttClientOptions = new MqttClientOptionsBuilder()
+                .WithTcpServer("test.mosquitto.org", 8883)
+                .WithTlsOptions(new MqttClientTlsOptionsBuilder()
+                    .WithTrustChain(caChain) 
+                    .Build())
+                .Build();
+
+            var connAck = await mqttClient.ConnectAsync(mqttClientOptions);
+            Console.WriteLine("Connected to test.moquitto.org:8883 with CaFile mosquitto.org.crt: " + connAck.ResultCode);
+        }
+
+
+    }
+    const string mosquitto_org = @"
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
+";
+
+}

Samples/Client/Client_Subscribe_Samples.cs

@@ -5,8 +5,10 @@
 // ReSharper disable UnusedType.Global
 // ReSharper disable UnusedMember.Global
 // ReSharper disable InconsistentNaming
+// ReSharper disable UnusedMember.Local
 
 using MQTTnet.Client;
+using MQTTnet.Extensions.TopicTemplate;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
 using MQTTnet.Samples.Helpers;
@@ -15,6 +17,8 @@ namespace MQTTnet.Samples.Client;
 
 public static class Client_Subscribe_Samples
 {
+    static MqttTopicTemplate sampleTemplate = new MqttTopicTemplate("mqttnet/samples/topic/{id}");
+    
     public static async Task Handle_Received_Application_Message()
     {
         /*
@@ -41,11 +45,7 @@ public static class Client_Subscribe_Samples
             await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
 
             var mqttSubscribeOptions = mqttFactory.CreateSubscribeOptionsBuilder()
-                .WithTopicFilter(
+                .WithTopicTemplate(sampleTemplate.WithParameter("id", "2"))
-                    f =>
-                    {
-                        f.WithTopic("mqttnet/samples/topic/2");
-                    })
                 .Build();
 
             await mqttClient.SubscribeAsync(mqttSubscribeOptions, CancellationToken.None);
@@ -87,11 +87,8 @@ public static class Client_Subscribe_Samples
             await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
 
             var mqttSubscribeOptions = mqttFactory.CreateSubscribeOptionsBuilder()
-                .WithTopicFilter(
+                .WithTopicTemplate(
-                    f =>
+                    sampleTemplate.WithParameter("id", "1"))
-                    {
-                        f.WithTopic("mqttnet/samples/topic/1");
-                    })
                 .Build();
 
             var response = await mqttClient.SubscribeAsync(mqttSubscribeOptions, CancellationToken.None);
@@ -120,21 +117,12 @@ public static class Client_Subscribe_Samples
             // Create the subscribe options including several topics with different options.
             // It is also possible to all of these topics using a dedicated call of _SubscribeAsync_ per topic.
             var mqttSubscribeOptions = mqttFactory.CreateSubscribeOptionsBuilder()
-                .WithTopicFilter(
+                .WithTopicTemplate(
-                    f =>
+                    sampleTemplate.WithParameter("id", "1"))
-                    {
+                .WithTopicTemplate(
-                        f.WithTopic("mqttnet/samples/topic/1");
+                    sampleTemplate.WithParameter("id", "2"), noLocal: true)
-                    })
+                .WithTopicTemplate(
-                .WithTopicFilter(
+                    sampleTemplate.WithParameter("id", "3"), retainHandling: MqttRetainHandling.SendAtSubscribe)
-                    f =>
-                    {
-                        f.WithTopic("mqttnet/samples/topic/2").WithNoLocal();
-                    })
-                .WithTopicFilter(
-                    f =>
-                    {
-                        f.WithTopic("mqttnet/samples/topic/3").WithRetainHandling(MqttRetainHandling.SendAtSubscribe);
-                    })
                 .Build();
 
             var response = await mqttClient.SubscribeAsync(mqttSubscribeOptions, CancellationToken.None);
@@ -161,11 +149,7 @@ public static class Client_Subscribe_Samples
             await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
 
             var mqttSubscribeOptions = mqttFactory.CreateSubscribeOptionsBuilder()
-                .WithTopicFilter(
+                .WithTopicTemplate(sampleTemplate.WithParameter("id", "1"))
-                    f =>
-                    {
-                        f.WithTopic("mqttnet/samples/topic/1");
-                    })
                 .Build();
 
             var response = await mqttClient.SubscribeAsync(mqttSubscribeOptions, CancellationToken.None);
@@ -176,4 +160,62 @@ public static class Client_Subscribe_Samples
             response.DumpToConsole();
         }
     }
+
+    static void ConcurrentProcessingDisableAutoAcknowledge(CancellationToken shutdownToken, IMqttClient mqttClient)
+    {
+        /*
+         * This sample shows how to achieve concurrent processing and not have message AutoAcknowledged
+         * This to have a proper QoS1 (at-least-once) experience for what at least MQTT specification can provide
+         */
+        mqttClient.ApplicationMessageReceivedAsync += ea =>
+        {
+            ea.AutoAcknowledge = false;
+
+            async Task ProcessAsync()
+            {
+                // DO YOUR WORK HERE!
+                await Task.Delay(1000, shutdownToken);
+                await ea.AcknowledgeAsync(shutdownToken);
+                // WARNING: If process failures are not transient the message will be retried on every restart of the client
+                //          A failed message will not be dispatched again to the client as MQTT does not have a NACK packet to let
+                //          the broker know processing failed
+                //
+                // Optionally: Use a framework like Polly to create a retry policy: https://github.com/App-vNext/Polly#retry
+            }
+
+            _ = Task.Run(ProcessAsync, shutdownToken);
+
+            return Task.CompletedTask;
+        };
+    }
+
+    static void ConcurrentProcessingWithLimit(CancellationToken shutdownToken, IMqttClient mqttClient)
+    {
+        /*
+         * This sample shows how to achieve concurrent processing, with:
+         * - a maximum concurrency limit based on Environment.ProcessorCount
+         */
+
+        var concurrent = new SemaphoreSlim(Environment.ProcessorCount);
+
+        mqttClient.ApplicationMessageReceivedAsync += async ea =>
+        {
+            await concurrent.WaitAsync(shutdownToken).ConfigureAwait(false);
+
+            async Task ProcessAsync()
+            {
+                try
+                {
+                    // DO YOUR WORK HERE!
+                    await Task.Delay(1000, shutdownToken);
+                }
+                finally
+                {
+                    concurrent.Release();
+                }
+            }
+
+            _ = Task.Run(ProcessAsync, shutdownToken);
+        };
+    }
 }

Samples/MQTTnet.Samples.csproj

@@ -2,7 +2,7 @@
 
     <PropertyGroup>
         <OutputType>Exe</OutputType>
-        <TargetFramework>net6.0</TargetFramework>
+        <TargetFramework>net7.0</TargetFramework>
         <ImplicitUsings>enable</ImplicitUsings>
         <Nullable>enable</Nullable>
         <IsPackable>false</IsPackable>
@@ -17,6 +17,7 @@
         <ProjectReference Include="..\Source\MQTTnet.AspnetCore\MQTTnet.AspNetCore.csproj" />
         <ProjectReference Include="..\Source\MQTTnet.Extensions.ManagedClient\MQTTnet.Extensions.ManagedClient.csproj" />
         <ProjectReference Include="..\Source\MQTTnet.Extensions.Rpc\MQTTnet.Extensions.Rpc.csproj" />
+        <ProjectReference Include="..\Source\MQTTnet.Extensions.TopicTemplate\MQTTnet.Extensions.TopicTemplate.csproj" />
         <ProjectReference Include="..\Source\MQTTnet.Extensions.WebSocket4Net\MQTTnet.Extensions.WebSocket4Net.csproj" />
         <ProjectReference Include="..\Source\MQTTnet\MQTTnet.csproj" />
     </ItemGroup>

Samples/ManagedClient/Managed_Client_Subscribe_Samples.cs

@@ -0,0 +1,87 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+// ReSharper disable UnusedType.Global
+// ReSharper disable UnusedMember.Global
+// ReSharper disable InconsistentNaming
+
+using MQTTnet.Client;
+using MQTTnet.Extensions.ManagedClient;
+
+namespace MQTTnet.Samples.ManagedClient;
+
+public sealed class Managed_Client_Subscribe_Samples
+{
+    public static async Task Connect_Client()
+    {
+        /*
+         * This sample creates a simple managed MQTT client and connects to a public broker, subscribe to a topic and verifies subscription result.
+         *
+         * The managed client extends the existing _MqttClient_. It adds the following features.
+         * - Reconnecting when connection is lost.
+         * - Storing pending messages in an internal queue so that an enqueue is possible while the client remains not connected.
+         */
+
+        var mqttFactory = new MqttFactory();
+        var subscribed = false;
+
+        using (var managedMqttClient = mqttFactory.CreateManagedMqttClient())
+        {
+            var mqttClientOptions = new MqttClientOptionsBuilder()
+                .WithTcpServer("broker.hivemq.com")
+                .Build();
+
+            var managedMqttClientOptions = new ManagedMqttClientOptionsBuilder()
+                .WithClientOptions(mqttClientOptions)
+                .Build();
+
+            await managedMqttClient.StartAsync(managedMqttClientOptions);
+
+            // The application message is not sent. It is stored in an internal queue and
+            // will be sent when the client is connected.
+            await managedMqttClient.EnqueueAsync("Topic", "Payload");
+
+            Console.WriteLine("The managed MQTT client is connected.");
+
+            // Wait until the queue is fully processed.
+            SpinWait.SpinUntil(() => managedMqttClient.PendingApplicationMessagesCount == 0, 10000);
+
+            Console.WriteLine($"Pending messages = {managedMqttClient.PendingApplicationMessagesCount}");
+
+            managedMqttClient.SubscriptionsChangedAsync += args => SubscriptionsResultAsync(args, ref subscribed);
+            await managedMqttClient.SubscribeAsync("Topic").ConfigureAwait(false);
+
+            SpinWait.SpinUntil(() => subscribed, 1000);
+            Console.WriteLine($"Subscription properly done {subscribed}");
+        }
+    }
+
+    private static Task SubscriptionsResultAsync(SubscriptionsChangedEventArgs arg, ref bool subscribed)
+    {
+        foreach (var mqttClientSubscribeResult in arg.SubscribeResult)
+        {
+            Console.WriteLine($"Subscription reason {mqttClientSubscribeResult.ReasonString}");
+            foreach (var item in mqttClientSubscribeResult.Items)
+            {
+                Console.WriteLine($"For topic filter {item.TopicFilter}, result code: {item.ResultCode}");
+
+                if (item.TopicFilter.Topic == "Topic" && item.ResultCode == MqttClientSubscribeResultCode.GrantedQoS0 && !subscribed)
+                {
+                    subscribed = true;
+                }
+            }
+        }
+
+        foreach (var mqttClientUnsubscribeResult in arg.UnsubscribeResult)
+        {
+            Console.WriteLine($"Unsubscription reason {mqttClientUnsubscribeResult.ReasonString}");
+            foreach (var item in mqttClientUnsubscribeResult.Items)
+            {
+                Console.WriteLine($"For topic filter {item.TopicFilter}, result code: {item.ResultCode}");
+            }
+        }
+
+        return Task.CompletedTask;
+    }
+}

Samples/Server/Server_Retained_Messages_Samples.cs

@@ -7,6 +7,8 @@
 // ReSharper disable InconsistentNaming
 
 using System.Text.Json;
+using MQTTnet.Packets;
+using MQTTnet.Protocol;
 
 namespace MQTTnet.Samples.Server;
 
@@ -32,7 +34,10 @@ public static class Server_Retained_Messages_Samples
             {
                 try
                 {
-                    eventArgs.LoadedRetainedMessages = await JsonSerializer.DeserializeAsync<List<MqttApplicationMessage>>(File.OpenRead(storePath));
+                    var models = await JsonSerializer.DeserializeAsync<List<MqttRetainedMessageModel>>(File.OpenRead(storePath)) ?? new List<MqttRetainedMessageModel>();
+                    var retainedMessages = models.Select(m => m.ToApplicationMessage()).ToList();
+
+                    eventArgs.LoadedRetainedMessages = retainedMessages;
                     Console.WriteLine("Retained messages loaded.");
                 }
                 catch (FileNotFoundException)
@@ -56,7 +61,9 @@ public static class Server_Retained_Messages_Samples
                     // used to write all retained messages to dedicated files etc. Then all files must be loaded and a full list
                     // of retained messages must be provided in the loaded event.
 
-                    var buffer = JsonSerializer.SerializeToUtf8Bytes(eventArgs.StoredRetainedMessages);
+                    var models = eventArgs.StoredRetainedMessages.Select(MqttRetainedMessageModel.Create);
+
+                    var buffer = JsonSerializer.SerializeToUtf8Bytes(models);
                     await File.WriteAllBytesAsync(storePath, buffer);
                     Console.WriteLine("Retained messages saved.");
                 }
@@ -79,4 +86,59 @@ public static class Server_Retained_Messages_Samples
             Console.ReadLine();
         }
     }
+
+    sealed class MqttRetainedMessageModel
+    {
+        public string? ContentType { get; set; }
+        public byte[]? CorrelationData { get; set; }
+        public byte[]? Payload { get; set; }
+        public MqttPayloadFormatIndicator PayloadFormatIndicator { get; set; }
+        public MqttQualityOfServiceLevel QualityOfServiceLevel { get; set; }
+        public string? ResponseTopic { get; set; }
+        public string? Topic { get; set; }
+        public List<MqttUserProperty>? UserProperties { get; set; }
+
+        public static MqttRetainedMessageModel Create(MqttApplicationMessage message)
+        {
+            if (message == null)
+            {
+                throw new ArgumentNullException(nameof(message));
+            }
+
+            return new MqttRetainedMessageModel
+            {
+                Topic = message.Topic,
+
+                // Create a copy of the buffer from the payload segment because 
+                // it cannot be serialized and deserialized with the JSON serializer.
+                Payload = message.PayloadSegment.ToArray(),
+                UserProperties = message.UserProperties,
+                ResponseTopic = message.ResponseTopic,
+                CorrelationData = message.CorrelationData,
+                ContentType = message.ContentType,
+                PayloadFormatIndicator = message.PayloadFormatIndicator,
+                QualityOfServiceLevel = message.QualityOfServiceLevel
+
+                // Other properties like "Retain" are not if interest in the storage.
+                // That's why a custom model makes sense.
+            };
+        }
+
+        public MqttApplicationMessage ToApplicationMessage()
+        {
+            return new MqttApplicationMessage
+            {
+                Topic = Topic,
+                PayloadSegment = new ArraySegment<byte>(Payload ?? Array.Empty<byte>()),
+                PayloadFormatIndicator = PayloadFormatIndicator,
+                ResponseTopic = ResponseTopic,
+                CorrelationData = CorrelationData,
+                ContentType = ContentType,
+                UserProperties = UserProperties,
+                QualityOfServiceLevel = QualityOfServiceLevel,
+                Dup = false,
+                Retain = true
+            };
+        }
+    }
 }

Source/MQTTnet.AspNetCore.Tests/MqttConnectionContextTest.cs

@@ -48,7 +48,6 @@ namespace MQTTnet.AspNetCore.Tests
         {
             var mockup = new ConnectionHandlerMockup();
 
-
             using (var host = new WebHostBuilder().UseKestrel(kestrel => kestrel.ListenLocalhost(1883, listener => listener.Use((ctx, next) => mockup.OnConnectedAsync(ctx))))
                        .UseStartup<Startup>()
                        .ConfigureServices(

Source/MQTTnet.AspTestApp/MQTTnet.AspTestApp.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk.Web">
 
     <PropertyGroup>
-        <TargetFramework>net6.0</TargetFramework>
+        <TargetFramework>net7.0</TargetFramework>
         <Nullable>enable</Nullable>
         <ImplicitUsings>enable</ImplicitUsings>
         <IsPackable>false</IsPackable>

Source/MQTTnet.AspnetCore/Client/MqttClientConnectionContextFactory.cs

@@ -6,7 +6,6 @@ using MQTTnet.Adapter;
 using MQTTnet.AspNetCore.Client.Tcp;
 using MQTTnet.Formatter;
 using System;
-using System.Net;
 using MQTTnet.Client;
 using MQTTnet.Diagnostics;
 
@@ -22,8 +21,7 @@ namespace MQTTnet.AspNetCore.Client
             {
                 case MqttClientTcpOptions tcpOptions:
                     {
-                        var endpoint = new DnsEndPoint(tcpOptions.Server, tcpOptions.GetPort());
+                        var tcpConnection = new SocketConnection(tcpOptions.RemoteEndpoint);
-                        var tcpConnection = new TcpConnection(endpoint);
                         
                         var formatter = new MqttPacketFormatterAdapter(options.ProtocolVersion, new MqttBufferWriter(4096, 65535));
                         return new MqttConnectionContext(formatter, tcpConnection);

Source/MQTTnet.AspnetCore/Client/Tcp/SocketConnection.cs

@@ -15,15 +15,15 @@ using System.Threading.Tasks;
 
 namespace MQTTnet.AspNetCore.Client.Tcp
 {
-    public class TcpConnection : ConnectionContext
+    public sealed class SocketConnection : ConnectionContext
     {
-        private volatile bool _aborted;
+        volatile bool _aborted;
-        private readonly EndPoint _endPoint;
+        readonly EndPoint _endPoint;
-        private SocketSender _sender;
+        SocketSender _sender;
-        private SocketReceiver _receiver;
+        SocketReceiver _receiver;
 
-        private Socket _socket;
+        Socket _socket;
-        private IDuplexPipe _application;
+        IDuplexPipe _application;
 
         public bool IsConnected { get; private set; }
         public override string ConnectionId { get; set; }
@@ -31,12 +31,12 @@ namespace MQTTnet.AspNetCore.Client.Tcp
         public override IDictionary<object, object> Items { get; set; }
         public override IDuplexPipe Transport { get; set; }
 
-        public TcpConnection(EndPoint endPoint)
+        public SocketConnection(EndPoint endPoint)
         {
             _endPoint = endPoint;
         }
 
-        public TcpConnection(Socket socket)
+        public SocketConnection(Socket socket)
         {
             _socket = socket;
             _endPoint = socket.RemoteEndPoint;
@@ -87,7 +87,7 @@ namespace MQTTnet.AspNetCore.Client.Tcp
             IsConnected = true;
         }
 
-        private async Task ExecuteAsync()
+        async Task ExecuteAsync()
         {
             Exception sendError = null;
             try
@@ -114,7 +114,7 @@ namespace MQTTnet.AspNetCore.Client.Tcp
             }
             catch (Exception ex)
             {
-                Console.WriteLine($"Unexpected exception in {nameof(TcpConnection)}.{nameof(StartAsync)}: " + ex);
+                Console.WriteLine($"Unexpected exception in {nameof(SocketConnection)}.{nameof(StartAsync)}: " + ex);
             }
             finally
             {
@@ -122,7 +122,8 @@ namespace MQTTnet.AspNetCore.Client.Tcp
                 _application.Input.Complete(sendError);
             }
         }
-        private async Task DoReceive()
+
+        async Task DoReceive()
         {
             Exception error = null;
 
@@ -171,7 +172,7 @@ namespace MQTTnet.AspNetCore.Client.Tcp
             }
         }
 
-        private async Task ProcessReceives()
+        async Task ProcessReceives()
         {
             while (true)
             {
@@ -204,12 +205,12 @@ namespace MQTTnet.AspNetCore.Client.Tcp
             }
         }
 
-        private Exception ConnectionAborted()
+        Exception ConnectionAborted()
         {
             return new MqttCommunicationException("Connection Aborted");
         }
 
-        private async Task<Exception> DoSend()
+        async Task<Exception> DoSend()
         {
             Exception error = null;
 
@@ -240,7 +241,7 @@ namespace MQTTnet.AspNetCore.Client.Tcp
             return error;
         }
 
-        private async Task ProcessSends()
+        async Task ProcessSends()
         {
             while (true)
             {

Source/MQTTnet.AspnetCore/MQTTnet.AspNetCore.csproj

@@ -42,7 +42,7 @@
             <PackagePath>\</PackagePath>
         </None>
     </ItemGroup>
-    
+
     <ItemGroup>
         <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All" />
     </ItemGroup>
@@ -51,11 +51,11 @@
         <DefineConstants>RELEASE;NETSTANDARD2_0</DefineConstants>
     </PropertyGroup>
 
-    <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.1' or '$(TargetFramework)' == 'net5.0' or '$(TargetFramework)' == 'net6.0' or '$(TargetFramework)' == 'net7.0' ">
+    <ItemGroup Condition="'$(TargetFramework)' != 'netstandard2.0' and '$(TargetFramework)' != 'netcoreapp2.1' ">
         <FrameworkReference Include="Microsoft.AspNetCore.App" />
     </ItemGroup>
 
-    <ItemGroup Condition="'$(TargetFramework)' != 'netcoreapp3.1' and '$(TargetFramework)' != 'net5.0' and '$(TargetFramework)' != 'net6.0' and '$(TargetFramework)' != 'net7.0' ">
+    <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or '$(TargetFramework)' == 'netcoreapp2.1' ">
         <PackageReference Include="Microsoft.AspNetCore.Http.Connections" Version="1.1.0" />
     </ItemGroup>
 

Source/MQTTnet.AspnetCore/MqttConnectionContext.cs

@@ -33,8 +33,11 @@ namespace MQTTnet.AspNetCore
             PacketFormatterAdapter = packetFormatterAdapter ?? throw new ArgumentNullException(nameof(packetFormatterAdapter));
             _connection = connection ?? throw new ArgumentNullException(nameof(connection));
 
-            _input = connection.Transport.Input;
+            if (!(_connection is SocketConnection tcp) || tcp.IsConnected)
-            _output = connection.Transport.Output;
+            {
+                _input = connection.Transport.Input;
+                _output = connection.Transport.Output;
+            }
         }
 
         public long BytesReceived { get; private set; }
@@ -80,8 +83,6 @@ namespace MQTTnet.AspNetCore
             }
         }
 
-        public bool IsReadingPacket { get; private set; }
-
         public bool IsSecureConnection
         {
             get
@@ -108,7 +109,7 @@ namespace MQTTnet.AspNetCore
 
         public async Task ConnectAsync(CancellationToken cancellationToken)
         {
-            if (_connection is TcpConnection tcp && !tcp.IsConnected)
+            if (_connection is SocketConnection tcp && !tcp.IsConnected)
             {
                 await tcp.StartAsync().ConfigureAwait(false);
             }
@@ -161,11 +162,6 @@ namespace MQTTnet.AspNetCore
                                 BytesReceived += received;
                                 return packet;
                             }
-                            else
-                            {
-                                // we did receive something but the message is not yet complete
-                                IsReadingPacket = true;
-                            }
                         }
                         else if (readResult.IsCompleted)
                         {
@@ -186,12 +182,9 @@ namespace MQTTnet.AspNetCore
                 // completing the channel makes sure that there is no more data read after a protocol error
                 _input?.Complete(exception);
                 _output?.Complete(exception);
+
                 throw;
             }
-            finally
-            {
-                IsReadingPacket = false;
-            }
 
             cancellationToken.ThrowIfCancellationRequested();
             return null;

Source/MQTTnet.AspnetCore/MqttHostedServer.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
@@ -14,20 +15,52 @@ namespace MQTTnet.AspNetCore
 {
     public sealed class MqttHostedServer : MqttServer, IHostedService
     {
-        public MqttHostedServer(MqttServerOptions options, IEnumerable<IMqttServerAdapter> adapters, IMqttNetLogger logger) 
+        readonly MqttFactory _mqttFactory;
-            : base(options, adapters, logger)
+#if NETCOREAPP3_1_OR_GREATER
+        readonly IHostApplicationLifetime _hostApplicationLifetime;
+        public MqttHostedServer(IHostApplicationLifetime hostApplicationLifetime, MqttFactory mqttFactory,
+            MqttServerOptions options, IEnumerable<IMqttServerAdapter> adapters, IMqttNetLogger logger) : base(
+            options,
+            adapters,
+            logger)
         {
+            _mqttFactory = mqttFactory ?? throw new ArgumentNullException(nameof(mqttFactory));
+            _hostApplicationLifetime = hostApplicationLifetime;
         }
-
+#else
-        public Task StartAsync(CancellationToken cancellationToken)
+        public MqttHostedServer(MqttFactory mqttFactory,
+            MqttServerOptions options, IEnumerable<IMqttServerAdapter> adapters, IMqttNetLogger logger) : base(
+            options,
+            adapters,
+            logger)
         {
-            _ =  StartAsync();
+            _mqttFactory = mqttFactory ?? throw new ArgumentNullException(nameof(mqttFactory));
-            return Task.CompletedTask;
+        }
+#endif
+
+
+        public async Task StartAsync(CancellationToken cancellationToken)
+        {
+            // The yield makes sure that the hosted service is considered up and running.
+            await Task.Yield();
+#if NETCOREAPP3_1_OR_GREATER
+            _hostApplicationLifetime.ApplicationStarted.Register(OnStarted);
+#else
+            _ = StartAsync();
+#endif
+
         }
 
         public Task StopAsync(CancellationToken cancellationToken)
         {
-            return StopAsync();
+            return StopAsync(_mqttFactory.CreateMqttServerStopOptionsBuilder().Build());
         }
+
+#if NETCOREAPP3_1_OR_GREATER
+        private void OnStarted()
+        {
+            _ = StartAsync();
+        }
+#endif
     }
 }

Source/MQTTnet.AspnetCore/ServiceCollectionExtensions.cs

@@ -4,6 +4,7 @@
 
 using System;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
 using Microsoft.Extensions.Hosting;
 using MQTTnet.Adapter;
 using MQTTnet.Diagnostics;
@@ -14,86 +15,71 @@ namespace MQTTnet.AspNetCore
 {
     public static class ServiceCollectionExtensions
     {
-        public static IServiceCollection AddMqttServer(this IServiceCollection serviceCollection, Action<MqttServerOptionsBuilder> configure = null)
-        {
-            if (serviceCollection is null)
-            {
-                throw new ArgumentNullException(nameof(serviceCollection));
-            }
-
-            serviceCollection.AddMqttConnectionHandler();
-            serviceCollection.AddHostedMqttServer(configure);
-            
-            return serviceCollection;
-        }
-
         public static IServiceCollection AddHostedMqttServer(this IServiceCollection services, MqttServerOptions options)
         {
-            if (options == null) throw new ArgumentNullException(nameof(options));
+            if (services == null)
+            {
+                throw new ArgumentNullException(nameof(services));
+            }
+
+            if (options == null)
+            {
+                throw new ArgumentNullException(nameof(options));
+            }
 
             services.AddSingleton(options);
-
             services.AddHostedMqttServer();
 
             return services;
         }
 
-        public static IServiceCollection AddHostedMqttServer(this IServiceCollection services, Action<MqttServerOptionsBuilder> configure = null)
+        public static IServiceCollection AddHostedMqttServer(this IServiceCollection services, Action<MqttServerOptionsBuilder> configure)
         {
-            services.AddSingleton(s =>
+            if (services == null)
             {
-                var serverOptionsBuilder = new MqttServerOptionsBuilder();
+                throw new ArgumentNullException(nameof(services));
-                configure?.Invoke(serverOptionsBuilder);
+            }
-                return serverOptionsBuilder.Build();
-            });
 
-            services.AddHostedMqttServer();
+            var serverOptionsBuilder = new MqttServerOptionsBuilder();
 
-            return services;
+            configure?.Invoke(serverOptionsBuilder);
+
+            var options = serverOptionsBuilder.Build();
+
+            return AddHostedMqttServer(services, options);
+        }
+
+        public static void AddHostedMqttServer(this IServiceCollection services)
+        {
+            // The user may have these services already registered.
+            services.TryAddSingleton<IMqttNetLogger>(MqttNetNullLogger.Instance);
+            services.TryAddSingleton(new MqttFactory());
+
+            services.AddSingleton<MqttHostedServer>();
+            services.AddSingleton<IHostedService>(s => s.GetService<MqttHostedServer>());
+            services.AddSingleton<MqttServer>(s => s.GetService<MqttHostedServer>());
         }
 
         public static IServiceCollection AddHostedMqttServerWithServices(this IServiceCollection services, Action<AspNetMqttServerOptionsBuilder> configure)
         {
-            services.AddSingleton(s =>
+            if (services == null)
             {
-                var builder = new AspNetMqttServerOptionsBuilder(s);
+                throw new ArgumentNullException(nameof(services));
-                configure(builder);
+            }
-                return builder.Build();
+
-            });
+            services.AddSingleton(
+                s =>
+                {
+                    var builder = new AspNetMqttServerOptionsBuilder(s);
+                    configure(builder);
+                    return builder.Build();
+                });
 
             services.AddHostedMqttServer();
 
             return services;
         }
 
-        static IServiceCollection AddHostedMqttServer(this IServiceCollection services)
-        {
-            var logger = new MqttNetEventLogger();
-
-            services.AddSingleton<IMqttNetLogger>(logger);
-            services.AddSingleton<MqttHostedServer>();
-            services.AddSingleton<IHostedService>(s => s.GetService<MqttHostedServer>());
-            services.AddSingleton<MqttServer>(s => s.GetService<MqttHostedServer>());
-
-            return services;
-        }
-
-        public static IServiceCollection AddMqttWebSocketServerAdapter(this IServiceCollection services)
-        {
-            services.AddSingleton<MqttWebSocketServerAdapter>();
-            services.AddSingleton<IMqttServerAdapter>(s => s.GetService<MqttWebSocketServerAdapter>());
-
-            return services;
-        }
-
-        public static IServiceCollection AddMqttTcpServerAdapter(this IServiceCollection services)
-        {
-            services.AddSingleton<MqttTcpServerAdapter>();
-            services.AddSingleton<IMqttServerAdapter>(s => s.GetService<MqttTcpServerAdapter>());
-
-            return services;
-        }
-
         public static IServiceCollection AddMqttConnectionHandler(this IServiceCollection services)
         {
             services.AddSingleton<MqttConnectionHandler>();
@@ -101,5 +87,44 @@ namespace MQTTnet.AspNetCore
 
             return services;
         }
+
+        public static void AddMqttLogger(this IServiceCollection services, IMqttNetLogger logger)
+        {
+            if (services == null)
+            {
+                throw new ArgumentNullException(nameof(services));
+            }
+
+            services.AddSingleton(logger);
+        }
+
+        public static IServiceCollection AddMqttServer(this IServiceCollection serviceCollection, Action<MqttServerOptionsBuilder> configure = null)
+        {
+            if (serviceCollection is null)
+            {
+                throw new ArgumentNullException(nameof(serviceCollection));
+            }
+
+            serviceCollection.AddMqttConnectionHandler();
+            serviceCollection.AddHostedMqttServer(configure);
+
+            return serviceCollection;
+        }
+
+        public static IServiceCollection AddMqttTcpServerAdapter(this IServiceCollection services)
+        {
+            services.AddSingleton<MqttTcpServerAdapter>();
+            services.AddSingleton<IMqttServerAdapter>(s => s.GetService<MqttTcpServerAdapter>());
+
+            return services;
+        }
+
+        public static IServiceCollection AddMqttWebSocketServerAdapter(this IServiceCollection services)
+        {
+            services.AddSingleton<MqttWebSocketServerAdapter>();
+            services.AddSingleton<IMqttServerAdapter>(s => s.GetService<MqttWebSocketServerAdapter>());
+
+            return services;
+        }
     }
-}
+}

Source/MQTTnet.Benchmarks/TcpPipesBenchmark.cs

@@ -29,12 +29,12 @@ namespace MQTTnet.Benchmarks
 
             var task = Task.Run(() => server.AcceptSocket());
 
-            var clientConnection = new TcpConnection(new IPEndPoint(IPAddress.Loopback, 1883));
+            var clientConnection = new SocketConnection(new IPEndPoint(IPAddress.Loopback, 1883));
 
             clientConnection.StartAsync().GetAwaiter().GetResult();
             _client = clientConnection.Transport;
 
-            var serverConnection = new TcpConnection(task.GetAwaiter().GetResult());
+            var serverConnection = new SocketConnection(task.GetAwaiter().GetResult());
             serverConnection.StartAsync().GetAwaiter().GetResult();
             _server = serverConnection.Transport;
         }

Source/MQTTnet.Extensions.ManagedClient/IManagedMqttClient.cs

@@ -25,6 +25,8 @@ namespace MQTTnet.Extensions.ManagedClient
         
         event Func<ManagedProcessFailedEventArgs, Task> SynchronizingSubscriptionsFailedAsync;
         
+        event Func<SubscriptionsChangedEventArgs, Task> SubscriptionsChangedAsync;
+        
         IMqttClient InternalClient { get; }
         
         bool IsConnected { get; }
@@ -45,8 +47,8 @@ namespace MQTTnet.Extensions.ManagedClient
         
         Task StopAsync(bool cleanDisconnect = true);
         
-        Task SubscribeAsync(ICollection<MqttTopicFilter> topicFilters);
+        Task SubscribeAsync(IEnumerable<MqttTopicFilter> topicFilters);
         
-        Task UnsubscribeAsync(ICollection<string> topics);
+        Task UnsubscribeAsync(IEnumerable<string> topics);
     }
 }

Source/MQTTnet.Extensions.ManagedClient/InterceptingPublishMessageEventArgs.cs

@@ -0,0 +1,20 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+
+namespace MQTTnet.Extensions.ManagedClient
+{
+    public sealed class InterceptingPublishMessageEventArgs : EventArgs
+    {
+        public InterceptingPublishMessageEventArgs(ManagedMqttApplicationMessage applicationMessage)
+        {
+            ApplicationMessage = applicationMessage ?? throw new ArgumentNullException(nameof(applicationMessage));
+        }
+
+        public ManagedMqttApplicationMessage ApplicationMessage { get; }
+
+        public bool AcceptPublish { get; set; } = true;
+    }
+}

Source/MQTTnet.Extensions.ManagedClient/MQTTnet.Extensions.ManagedClient.csproj

@@ -2,7 +2,7 @@
 
     <PropertyGroup>
         <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0;net7.0</TargetFrameworks>
-        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461</TargetFrameworks>
+        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461;net48</TargetFrameworks>
         <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' AND '$(MSBuildRuntimeType)' != 'Core' ">$(TargetFrameworks);uap10.0</TargetFrameworks>
         
         <AssemblyName>MQTTnet.Extensions.ManagedClient</AssemblyName>

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClient.cs

@@ -19,15 +19,17 @@ namespace MQTTnet.Extensions.ManagedClient
 {
     public sealed class ManagedMqttClient : Disposable, IManagedMqttClient
     {
+        readonly MqttNetSourceLogger _logger;
+
+        readonly AsyncEvent<InterceptingPublishMessageEventArgs> _interceptingPublishMessageEvent = new AsyncEvent<InterceptingPublishMessageEventArgs>();
         readonly AsyncEvent<ApplicationMessageProcessedEventArgs> _applicationMessageProcessedEvent = new AsyncEvent<ApplicationMessageProcessedEventArgs>();
         readonly AsyncEvent<ApplicationMessageSkippedEventArgs> _applicationMessageSkippedEvent = new AsyncEvent<ApplicationMessageSkippedEventArgs>();
         readonly AsyncEvent<ConnectingFailedEventArgs> _connectingFailedEvent = new AsyncEvent<ConnectingFailedEventArgs>();
         readonly AsyncEvent<EventArgs> _connectionStateChangedEvent = new AsyncEvent<EventArgs>();
         readonly AsyncEvent<ManagedProcessFailedEventArgs> _synchronizingSubscriptionsFailedEvent = new AsyncEvent<ManagedProcessFailedEventArgs>();
-        
+        readonly AsyncEvent<SubscriptionsChangedEventArgs> _subscriptionsChangedEvent = new AsyncEvent<SubscriptionsChangedEventArgs>();
-        readonly MqttNetSourceLogger _logger;
-        readonly BlockingQueue<ManagedMqttApplicationMessage> _messageQueue = new BlockingQueue<ManagedMqttApplicationMessage>();
 
+        readonly BlockingQueue<ManagedMqttApplicationMessage> _messageQueue = new BlockingQueue<ManagedMqttApplicationMessage>();
         readonly AsyncLock _messageQueueLock = new AsyncLock();
 
         /// <summary>
@@ -81,13 +83,19 @@ namespace MQTTnet.Extensions.ManagedClient
             add => _applicationMessageSkippedEvent.AddHandler(value);
             remove => _applicationMessageSkippedEvent.RemoveHandler(value);
         }
-        
+
         public event Func<ApplicationMessageProcessedEventArgs, Task> ApplicationMessageProcessedAsync
         {
             add => _applicationMessageProcessedEvent.AddHandler(value);
             remove => _applicationMessageProcessedEvent.RemoveHandler(value);
         }
 
+        public event Func<InterceptingPublishMessageEventArgs, Task> InterceptPublishMessageAsync
+        {
+            add => _interceptingPublishMessageEvent.AddHandler(value);
+            remove => _interceptingPublishMessageEvent.RemoveHandler(value);
+        }
+
         public event Func<MqttApplicationMessageReceivedEventArgs, Task> ApplicationMessageReceivedAsync
         {
             add => InternalClient.ApplicationMessageReceivedAsync += value;
@@ -124,6 +132,12 @@ namespace MQTTnet.Extensions.ManagedClient
             remove => _synchronizingSubscriptionsFailedEvent.RemoveHandler(value);
         }
 
+        public event Func<SubscriptionsChangedEventArgs, Task> SubscriptionsChangedAsync
+        {
+            add => _subscriptionsChangedEvent.AddHandler(value);
+            remove => _subscriptionsChangedEvent.RemoveHandler(value);
+        }
+
         public IMqttClient InternalClient { get; }
 
         public bool IsConnected => InternalClient.IsConnected;
@@ -133,7 +147,7 @@ namespace MQTTnet.Extensions.ManagedClient
         public ManagedMqttClientOptions Options { get; private set; }
 
         public int PendingApplicationMessagesCount => _messageQueue.Count;
-        
+
         public async Task EnqueueAsync(MqttApplicationMessage applicationMessage)
         {
             ThrowIfDisposed();
@@ -261,7 +275,7 @@ namespace MQTTnet.Extensions.ManagedClient
             ThrowIfDisposed();
 
             _isCleanDisconnect = cleanDisconnect;
-            
+
             StopPublishing();
             StopMaintainingConnection();
 
@@ -274,7 +288,7 @@ namespace MQTTnet.Extensions.ManagedClient
             }
         }
 
-        public Task SubscribeAsync(ICollection<MqttTopicFilter> topicFilters)
+        public Task SubscribeAsync(IEnumerable<MqttTopicFilter> topicFilters)
         {
             ThrowIfDisposed();
 
@@ -302,7 +316,7 @@ namespace MQTTnet.Extensions.ManagedClient
             return CompletedTask.Instance;
         }
 
-        public Task UnsubscribeAsync(ICollection<string> topics)
+        public Task UnsubscribeAsync(IEnumerable<string> topics)
         {
             ThrowIfDisposed();
 
@@ -353,6 +367,13 @@ namespace MQTTnet.Extensions.ManagedClient
             return remainingTime < TimeSpan.Zero ? TimeSpan.Zero : remainingTime;
         }
 
+        CancellationTokenSource NewTimeoutToken(CancellationToken linkedToken)
+        {
+            var newTimeoutToken = CancellationTokenSource.CreateLinkedTokenSource(linkedToken);
+            newTimeoutToken.CancelAfter(Options.ClientOptions.Timeout);
+            return newTimeoutToken;
+        }
+
         async Task HandleSubscriptionExceptionAsync(Exception exception, List<MqttTopicFilter> addedSubscriptions, List<string> removedSubscriptions)
         {
             _logger.Warning(exception, "Synchronizing subscriptions failed.");
@@ -363,6 +384,14 @@ namespace MQTTnet.Extensions.ManagedClient
             }
         }
 
+        async Task HandleSubscriptionsResultAsync(SendSubscribeUnsubscribeResult subscribeUnsubscribeResult)
+        {
+            if (_subscriptionsChangedEvent.HasHandlers)
+            {
+                await _subscriptionsChangedEvent.InvokeAsync(new SubscriptionsChangedEventArgs(subscribeUnsubscribeResult.SubscribeResults, subscribeUnsubscribeResult.UnsubscribeResults)).ConfigureAwait(false);
+            }
+        }
+
         async Task MaintainConnectionAsync(CancellationToken cancellationToken)
         {
             try
@@ -387,7 +416,7 @@ namespace MQTTnet.Extensions.ManagedClient
                     {
                         if (_isCleanDisconnect)
                         {
-                            using (var disconnectTimeout = new CancellationTokenSource(Options.ClientOptions.Timeout))
+                            using (var disconnectTimeout = NewTimeoutToken(CancellationToken.None))
                             {
                                 await InternalClient.DisconnectAsync(new MqttClientDisconnectOptions(), disconnectTimeout.Token).ConfigureAwait(false);
                             }
@@ -437,7 +466,7 @@ namespace MQTTnet.Extensions.ManagedClient
 
                     cancellationToken.ThrowIfCancellationRequested();
 
-                    await TryPublishQueuedMessageAsync(message).ConfigureAwait(false);
+                    await TryPublishQueuedMessageAsync(message, cancellationToken).ConfigureAwait(false);
                 }
             }
             catch (OperationCanceledException)
@@ -453,7 +482,7 @@ namespace MQTTnet.Extensions.ManagedClient
             }
         }
 
-        async Task PublishReconnectSubscriptionsAsync()
+        async Task PublishReconnectSubscriptionsAsync(CancellationToken cancellationToken)
         {
             _logger.Info("Publishing subscriptions at reconnect");
 
@@ -464,6 +493,7 @@ namespace MQTTnet.Extensions.ManagedClient
                 if (_reconnectSubscriptions.Any())
                 {
                     topicFilters = new List<MqttTopicFilter>();
+                    SendSubscribeUnsubscribeResult subscribeUnsubscribeResult;
 
                     foreach (var sub in _reconnectSubscriptions)
                     {
@@ -471,12 +501,14 @@ namespace MQTTnet.Extensions.ManagedClient
 
                         if (topicFilters.Count == Options.MaxTopicFiltersInSubscribeUnsubscribePackets)
                         {
-                            await SendSubscribeUnsubscribe(topicFilters, null).ConfigureAwait(false);
+                            subscribeUnsubscribeResult = await SendSubscribeUnsubscribe(topicFilters, null, cancellationToken).ConfigureAwait(false);
                             topicFilters.Clear();
+                            await HandleSubscriptionsResultAsync(subscribeUnsubscribeResult).ConfigureAwait(false);
                         }
                     }
 
-                    await SendSubscribeUnsubscribe(topicFilters, null).ConfigureAwait(false);
+                    subscribeUnsubscribeResult = await SendSubscribeUnsubscribe(topicFilters, null, cancellationToken).ConfigureAwait(false);
+                    await HandleSubscriptionsResultAsync(subscribeUnsubscribeResult).ConfigureAwait(false);
                 }
             }
             catch (Exception exception)
@@ -492,6 +524,7 @@ namespace MQTTnet.Extensions.ManagedClient
             while (await _subscriptionsQueuedSignal.WaitAsync(GetRemainingTime(endTime), cancellationToken).ConfigureAwait(false))
             {
                 List<MqttTopicFilter> subscriptions;
+                SendSubscribeUnsubscribeResult subscribeUnsubscribeResult;
                 HashSet<string> unsubscriptions;
 
                 lock (_subscriptions)
@@ -527,12 +560,14 @@ namespace MQTTnet.Extensions.ManagedClient
 
                     if (addedTopicFilters.Count == Options.MaxTopicFiltersInSubscribeUnsubscribePackets)
                     {
-                        await SendSubscribeUnsubscribe(addedTopicFilters, null).ConfigureAwait(false);
+                        subscribeUnsubscribeResult = await SendSubscribeUnsubscribe(addedTopicFilters, null, cancellationToken).ConfigureAwait(false);
                         addedTopicFilters.Clear();
+                        await HandleSubscriptionsResultAsync(subscribeUnsubscribeResult).ConfigureAwait(false);
                     }
                 }
 
-                await SendSubscribeUnsubscribe(addedTopicFilters, null).ConfigureAwait(false);
+                subscribeUnsubscribeResult = await SendSubscribeUnsubscribe(addedTopicFilters, null, cancellationToken).ConfigureAwait(false);
+                await HandleSubscriptionsResultAsync(subscribeUnsubscribeResult).ConfigureAwait(false);
 
                 var removedTopicFilters = new List<string>();
                 foreach (var unSub in unsubscriptions)
@@ -541,12 +576,14 @@ namespace MQTTnet.Extensions.ManagedClient
 
                     if (removedTopicFilters.Count == Options.MaxTopicFiltersInSubscribeUnsubscribePackets)
                     {
-                        await SendSubscribeUnsubscribe(null, removedTopicFilters).ConfigureAwait(false);
+                        subscribeUnsubscribeResult = await SendSubscribeUnsubscribe(null, removedTopicFilters, cancellationToken).ConfigureAwait(false);
                         removedTopicFilters.Clear();
+                        await HandleSubscriptionsResultAsync(subscribeUnsubscribeResult).ConfigureAwait(false);
                     }
                 }
 
-                await SendSubscribeUnsubscribe(null, removedTopicFilters).ConfigureAwait(false);
+                subscribeUnsubscribeResult = await SendSubscribeUnsubscribe(null, removedTopicFilters, cancellationToken).ConfigureAwait(false);
+                await HandleSubscriptionsResultAsync(subscribeUnsubscribeResult).ConfigureAwait(false);
             }
         }
 
@@ -560,7 +597,7 @@ namespace MQTTnet.Extensions.ManagedClient
             MqttClientConnectResult connectResult = null;
             try
             {
-                using (var connectTimeout = new CancellationTokenSource(Options.ClientOptions.Timeout))
+                using (var connectTimeout = NewTimeoutToken(cancellationToken))
                 {
                     connectResult = await InternalClient.ConnectAsync(Options.ClientOptions, connectTimeout.Token).ConfigureAwait(false);
                 }
@@ -579,8 +616,10 @@ namespace MQTTnet.Extensions.ManagedClient
             }
         }
 
-        async Task SendSubscribeUnsubscribe(List<MqttTopicFilter> addedSubscriptions, List<string> removedSubscriptions)
+        async Task<SendSubscribeUnsubscribeResult> SendSubscribeUnsubscribe(List<MqttTopicFilter> addedSubscriptions, List<string> removedSubscriptions, CancellationToken cancellationToken)
         {
+            var subscribeResults = new List<MqttClientSubscribeResult>();
+            var unsubscribeResults = new List<MqttClientUnsubscribeResult>();
             try
             {
                 if (removedSubscriptions != null && removedSubscriptions.Any())
@@ -592,7 +631,11 @@ namespace MQTTnet.Extensions.ManagedClient
                         unsubscribeOptionsBuilder.WithTopicFilter(removedSubscription);
                     }
 
-                    await InternalClient.UnsubscribeAsync(unsubscribeOptionsBuilder.Build()).ConfigureAwait(false);
+                    using (var unsubscribeTimeout = NewTimeoutToken(cancellationToken))
+                    {
+                        var unsubscribeResult = await InternalClient.UnsubscribeAsync(unsubscribeOptionsBuilder.Build(), unsubscribeTimeout.Token).ConfigureAwait(false);
+                        unsubscribeResults.Add(unsubscribeResult);
+                    }
 
                     //clear because these worked, maybe the subscribe below will fail, only report those
                     removedSubscriptions.Clear();
@@ -607,13 +650,19 @@ namespace MQTTnet.Extensions.ManagedClient
                         subscribeOptionsBuilder.WithTopicFilter(addedSubscription);
                     }
 
-                    await InternalClient.SubscribeAsync(subscribeOptionsBuilder.Build()).ConfigureAwait(false);
+                    using (var subscribeTimeout = NewTimeoutToken(cancellationToken))
+                    {
+                        var subscribeResult = await InternalClient.SubscribeAsync(subscribeOptionsBuilder.Build(), subscribeTimeout.Token).ConfigureAwait(false);
+                        subscribeResults.Add(subscribeResult);
+                    }
                 }
             }
             catch (Exception exception)
             {
                 await HandleSubscriptionExceptionAsync(exception, addedSubscriptions, removedSubscriptions).ConfigureAwait(false);
             }
+
+            return new SendSubscribeUnsubscribeResult(subscribeResults, unsubscribeResults);
         }
 
         void StartPublishing()
@@ -659,7 +708,7 @@ namespace MQTTnet.Extensions.ManagedClient
             {
                 var oldConnectionState = InternalClient.IsConnected;
                 var connectionState = await ReconnectIfRequiredAsync(cancellationToken).ConfigureAwait(false);
-                
+
                 if (connectionState == ReconnectionResult.NotConnected)
                 {
                     StopPublishing();
@@ -667,7 +716,7 @@ namespace MQTTnet.Extensions.ManagedClient
                 }
                 else if (connectionState == ReconnectionResult.Reconnected)
                 {
-                    await PublishReconnectSubscriptionsAsync().ConfigureAwait(false);
+                    await PublishReconnectSubscriptionsAsync(cancellationToken).ConfigureAwait(false);
                     StartPublishing();
                 }
                 else if (connectionState == ReconnectionResult.Recovered)
@@ -697,12 +746,26 @@ namespace MQTTnet.Extensions.ManagedClient
             }
         }
 
-        async Task TryPublishQueuedMessageAsync(ManagedMqttApplicationMessage message)
+        async Task TryPublishQueuedMessageAsync(ManagedMqttApplicationMessage message, CancellationToken cancellationToken)
         {
             Exception transmitException = null;
+            bool acceptPublish = true;
             try
             {
-                await InternalClient.PublishAsync(message.ApplicationMessage).ConfigureAwait(false);
+                if (_interceptingPublishMessageEvent.HasHandlers)
+                {
+                    var interceptEventArgs = new InterceptingPublishMessageEventArgs(message);
+                    await _interceptingPublishMessageEvent.InvokeAsync(interceptEventArgs).ConfigureAwait(false);
+                    acceptPublish = interceptEventArgs.AcceptPublish;
+                }
+
+                if (acceptPublish)
+                {
+                    using (var publishTimeout = NewTimeoutToken(cancellationToken))
+                    {
+                        await InternalClient.PublishAsync(message.ApplicationMessage, publishTimeout.Token).ConfigureAwait(false);
+                    }
+                }
 
                 using (await _messageQueueLock.EnterAsync().ConfigureAwait(false)) //lock to avoid conflict with this.PublishAsync
                 {

Source/MQTTnet.Extensions.ManagedClient/SendSubscribeUnsubscribeResult.cs

@@ -0,0 +1,23 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using MQTTnet.Client;
+
+namespace MQTTnet.Extensions.ManagedClient
+{
+    public sealed class SendSubscribeUnsubscribeResult
+    {
+        public SendSubscribeUnsubscribeResult(List<MqttClientSubscribeResult> subscribeResults, List<MqttClientUnsubscribeResult> unsubscribeResults)
+        {
+            SubscribeResults = subscribeResults ?? throw new ArgumentNullException(nameof(subscribeResults));
+            UnsubscribeResults = unsubscribeResults ?? throw new ArgumentNullException(nameof(unsubscribeResults));
+        }
+        
+        public List<MqttClientSubscribeResult> SubscribeResults { get; private set; }
+        
+        public List<MqttClientUnsubscribeResult> UnsubscribeResults { get; private set; }
+    }
+}

Source/MQTTnet.Extensions.ManagedClient/SubscriptionsChangedEventArgs.cs

@@ -0,0 +1,23 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using MQTTnet.Client;
+using System;
+using System.Collections.Generic;
+
+namespace MQTTnet.Extensions.ManagedClient
+{
+    public sealed class SubscriptionsChangedEventArgs : EventArgs
+    {
+        public SubscriptionsChangedEventArgs(List<MqttClientSubscribeResult> subscribeResult, List<MqttClientUnsubscribeResult> unsubscribeResult)
+        {
+            SubscribeResult = subscribeResult ?? throw new ArgumentNullException(nameof(subscribeResult));
+            UnsubscribeResult = unsubscribeResult ?? throw new ArgumentNullException(nameof(unsubscribeResult));
+        }
+
+        public List<MqttClientSubscribeResult> SubscribeResult { get; }
+
+        public List<MqttClientUnsubscribeResult> UnsubscribeResult { get; }
+    }
+}

Source/MQTTnet.Extensions.Rpc/IMqttRpcClient.cs

@@ -1,4 +1,9 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
 using System;
+using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Protocol;
@@ -7,8 +12,8 @@ namespace MQTTnet.Extensions.Rpc
 {
     public interface IMqttRpcClient : IDisposable
     {
-        Task<byte[]> ExecuteAsync(TimeSpan timeout, string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel);
+        Task<byte[]> ExecuteAsync(TimeSpan timeout, string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel, IDictionary<string,object> parameters = null);
         
-        Task<byte[]> ExecuteAsync(string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel, CancellationToken cancellationToken = default);
+        Task<byte[]> ExecuteAsync(string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel, IDictionary<string, object> parameters = null, CancellationToken cancellationToken = default);
     }
 }

Source/MQTTnet.Extensions.Rpc/MQTTnet.Extensions.Rpc.csproj

@@ -2,7 +2,7 @@
 
     <PropertyGroup>
         <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0;net7.0</TargetFrameworks>
-        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461</TargetFrameworks>
+        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461;net48</TargetFrameworks>
         <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' AND '$(MSBuildRuntimeType)' != 'Core' ">$(TargetFrameworks);uap10.0</TargetFrameworks>
         
         <AssemblyName>MQTTnet.Extensions.Rpc</AssemblyName>

Source/MQTTnet.Extensions.Rpc/MqttRpcClient.cs

@@ -4,6 +4,7 @@
 
 using System;
 using System.Collections.Concurrent;
+using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
@@ -42,13 +43,13 @@ namespace MQTTnet.Extensions.Rpc
             _waitingCalls.Clear();
         }
 
-        public async Task<byte[]> ExecuteAsync(TimeSpan timeout, string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel)
+        public async Task<byte[]> ExecuteAsync(TimeSpan timeout, string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel, IDictionary<string, object> parameters = null)
         {
             using (var timeoutToken = new CancellationTokenSource(timeout))
             {
                 try
                 {
-                    return await ExecuteAsync(methodName, payload, qualityOfServiceLevel, timeoutToken.Token).ConfigureAwait(false);
+                    return await ExecuteAsync(methodName, payload, qualityOfServiceLevel, parameters, timeoutToken.Token).ConfigureAwait(false);
                 }
                 catch (OperationCanceledException exception)
                 {
@@ -62,14 +63,14 @@ namespace MQTTnet.Extensions.Rpc
             }
         }
 
-        public async Task<byte[]> ExecuteAsync(string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel, CancellationToken cancellationToken = default)
+        public async Task<byte[]> ExecuteAsync(string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel, IDictionary<string, object> parameters = null, CancellationToken cancellationToken = default)
         {
             if (methodName == null)
             {
                 throw new ArgumentNullException(nameof(methodName));
             }
 
-            var context = new TopicGenerationContext(_mqttClient, _options, methodName, qualityOfServiceLevel);
+            var context = new TopicGenerationContext(_mqttClient, _options, methodName, parameters, qualityOfServiceLevel);
             var topicNames = _options.TopicGenerationStrategy.CreateRpcTopics(context);
 
             var requestTopic = topicNames.RequestTopic;

Source/MQTTnet.Extensions.Rpc/MqttRpcClientExtensions.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Generic;
 using System.Text;
 using System.Threading.Tasks;
 using MQTTnet.Protocol;
@@ -11,13 +12,13 @@ namespace MQTTnet.Extensions.Rpc
 {
     public static class MqttRpcClientExtensions
     {
-        public static Task<byte[]> ExecuteAsync(this IMqttRpcClient client, TimeSpan timeout, string methodName, string payload, MqttQualityOfServiceLevel qualityOfServiceLevel)
+        public static Task<byte[]> ExecuteAsync(this IMqttRpcClient client, TimeSpan timeout, string methodName, string payload, MqttQualityOfServiceLevel qualityOfServiceLevel, IDictionary<string,object> parameters = null)
         {
             if (client == null) throw new ArgumentNullException(nameof(client));
 
             var buffer = Encoding.UTF8.GetBytes(payload ?? string.Empty);
 
-            return client.ExecuteAsync(timeout, methodName, buffer, qualityOfServiceLevel);
+            return client.ExecuteAsync(timeout, methodName, buffer, qualityOfServiceLevel, parameters);
         }
     }
 }

Source/MQTTnet.Extensions.Rpc/Options/TopicGeneration/TopicGenerationContext.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Generic;
 using MQTTnet.Client;
 using MQTTnet.Protocol;
 
@@ -10,9 +11,11 @@ namespace MQTTnet.Extensions.Rpc
 {
     public sealed class TopicGenerationContext
     {
-        public TopicGenerationContext(IMqttClient mqttClient, MqttRpcClientOptions options, string methodName, MqttQualityOfServiceLevel qualityOfServiceLevel)
+        public TopicGenerationContext(IMqttClient mqttClient, MqttRpcClientOptions options, string methodName,
+            IDictionary<string, object> parameters, MqttQualityOfServiceLevel qualityOfServiceLevel)
         {
             MethodName = methodName ?? throw new ArgumentNullException(nameof(methodName));
+            Parameters = parameters;
             QualityOfServiceLevel = qualityOfServiceLevel;
             MqttClient = mqttClient ?? throw new ArgumentNullException(nameof(mqttClient));
             Options = options ?? throw new ArgumentNullException(nameof(options));
@@ -20,6 +23,8 @@ namespace MQTTnet.Extensions.Rpc
 
         public string MethodName { get; }
 
+        public IDictionary<string, object> Parameters { get; }
+
         public IMqttClient MqttClient { get; }
 
         public MqttRpcClientOptions Options { get; }

Source/MQTTnet.Extensions.TopicTemplate/MQTTnet.Extensions.TopicTemplate.csproj

@@ -0,0 +1,73 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0;net7.0</TargetFrameworks>
+        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461;net48</TargetFrameworks>
+        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' AND '$(MSBuildRuntimeType)' != 'Core' ">$(TargetFrameworks);uap10.0</TargetFrameworks>
+        
+        <AssemblyName>MQTTnet.Extensions.TopicTemplate</AssemblyName>
+        <RootNamespace>MQTTnet.Extensions.TopicTemplate</RootNamespace>
+        <GeneratePackageOnBuild>True</GeneratePackageOnBuild>
+        <Company>The contributors of MQTTnet</Company>
+        <Product>MQTTnet</Product>
+        <Description>
+           Provides mqtt topic templating logic to support dispatch,
+           routing and similar functionality based on the well known moustache syntax (AsyncAPI compatible).
+        </Description>
+		<PackageReadmeFile>README.md</PackageReadmeFile>
+        <Authors>The contributors of MQTTnet</Authors>
+        <PackageId>MQTTnet.Extensions.TopicTemplate</PackageId>
+        <SignAssembly>false</SignAssembly>
+        <DelaySign>false</DelaySign>
+        <PublishRepositoryUrl>true</PublishRepositoryUrl>
+        <IncludeSymbols>true</IncludeSymbols>
+        <SymbolPackageFormat>snupkg</SymbolPackageFormat>
+        <Copyright>Copyright (c) .NET Foundation and Contributors</Copyright>
+        <PackageProjectUrl>https://github.com/dotnet/MQTTnet</PackageProjectUrl>
+        <RepositoryUrl>https://github.com/dotnet/MQTTnet.git</RepositoryUrl>
+        <RepositoryType>git</RepositoryType>
+        <PackageTags>MQTT Message Queue Telemetry MQTTClient Messaging Routing AsyncAPI Template</PackageTags>
+        <NeutralLanguage>en-US</NeutralLanguage>
+        <PackageIcon>nuget.png</PackageIcon>
+        <EmbedUntrackedSources>true</EmbedUntrackedSources>
+        <ContinuousIntegrationBuild>true</ContinuousIntegrationBuild>
+        <PackageLicenseExpression>MIT</PackageLicenseExpression>
+        <PackageReleaseNotes>For release notes please go to MQTTnet release notes (https://www.nuget.org/packages/MQTTnet/).</PackageReleaseNotes>
+        <GenerateDocumentationFile>true</GenerateDocumentationFile>
+        <NoWarn>1591;NETSDK1138</NoWarn>
+    </PropertyGroup>
+
+    <PropertyGroup Condition="'$(TargetFramework)' == 'uap10.0'">
+        <CopyLocalLockFileAssemblies>false</CopyLocalLockFileAssemblies>
+        <NugetTargetMoniker>UAP,Version=v10.0</NugetTargetMoniker>
+        <TargetPlatformIdentifier>UAP</TargetPlatformIdentifier>
+        <TargetPlatformVersion>10.0.18362.0</TargetPlatformVersion>
+        <TargetPlatformMinVersion>10.0.10240.0</TargetPlatformMinVersion>
+        <TargetFrameworkIdentifier>.NETCore</TargetFrameworkIdentifier>
+        <TargetFrameworkVersion>v5.0</TargetFrameworkVersion>
+        <DefineConstants>$(DefineConstants);WINDOWS_UWP</DefineConstants>
+        <DefaultLanguage>en</DefaultLanguage>
+        <LanguageTargets>$(MSBuildExtensionsPath)\Microsoft\WindowsXaml\v$(VisualStudioVersion)\Microsoft.Windows.UI.Xaml.CSharp.targets</LanguageTargets>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <None Include="README.md">
+            <Pack>True</Pack>
+            <PackagePath>\</PackagePath>
+        </None>
+        <None Include="..\..\Images\nuget.png">
+            <Pack>True</Pack>
+            <PackagePath>\</PackagePath>
+        </None>
+    </ItemGroup>
+    
+    <ItemGroup>
+        <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All" />
+        <PackageReference Include="System.ValueTuple" Version="4.5.0" />
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\MQTTnet\MQTTnet.csproj" />
+    </ItemGroup>
+
+</Project>

Source/MQTTnet.Extensions.TopicTemplate/MqttTopicTemplate.cs

@@ -0,0 +1,357 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text.RegularExpressions;
+using System.Threading;
+using MQTTnet.Protocol;
+
+namespace MQTTnet.Extensions.TopicTemplate
+{
+    /// <summary>
+    ///     A topic template is an MQTT topic filter string that may contain
+    ///     segments in curly braces called parameters. This well-known
+    ///     'moustache' syntax also matches AsyncAPI Channel Address Expressions.
+    ///     The topic template is designed to support dynamic subscription/publication,
+    ///     message-topic matching and routing. It is intended to be more safe and
+    ///     convenient than String.Format() for aforementioned purposes.
+    /// </summary>
+    /// <example>
+    ///     topic/subtopic/{parameter}/{otherParameter}
+    /// </example>
+    public sealed class MqttTopicTemplate : IEquatable<MqttTopicTemplate>
+    {
+        static readonly Regex MoustacheRegex = new Regex("{([^/]+?)}", RegexOptions.Compiled);
+        
+        readonly string[] _parameterSegments;
+        
+        string _topicFilter;
+        
+        /// <summary>
+        ///     Create a topic template from an mqtt topic filter with moustache placeholders.
+        /// </summary>
+        /// <param
+        ///     name="topicTemplate">
+        /// </param>
+        /// <exception
+        ///     cref="ArgumentNullException">
+        /// </exception>
+        public MqttTopicTemplate(string topicTemplate)
+        {
+            if (topicTemplate == null)
+            {
+                throw new ArgumentNullException(nameof(topicTemplate));
+            }
+            
+            MqttTopicValidator.ThrowIfInvalidSubscribe(topicTemplate);
+            
+            Template = topicTemplate;
+            _parameterSegments = topicTemplate.Split(MqttTopicFilterComparer.LevelSeparator)
+                .Select(segment => MoustacheRegex.Match(segment).Groups[1].Value)
+                .Select(s => s.Length > 0 ? s : null)
+                .ToArray();
+        }
+        
+        /// <summary>
+        ///     Yield the template parameter names.
+        /// </summary>
+        public IEnumerable<string> Parameters => _parameterSegments.Where(s => s != null);
+        
+        /// <summary>
+        ///     The topic template string representation, e.g. A/B/{foo}/D.
+        /// </summary>
+        public string Template { get; }
+        
+        /// <summary>
+        ///     The topic template as an MQTT topic filter (+ substituted for all parameters). If the template
+        ///     ends with a multi-level wildcard (hash), this will be reflected here.
+        /// </summary>
+        public string TopicFilter
+        {
+            get
+            {
+                LazyInitializer.EnsureInitialized(ref _topicFilter, () => MoustacheRegex.Replace(Template, MqttTopicFilterComparer.SingleLevelWildcard.ToString()));
+                return _topicFilter;
+            }
+        }
+        
+        /// <summary>
+        ///     Return the topic filter of this template, ending with a multi-level wildcard (hash).
+        /// </summary>
+        public string TopicTreeRootFilter
+        {
+            get
+            {
+                var filter = TopicFilter;
+                // append slash if neccessary
+                if (filter.Length > 0 && !filter.EndsWith(MqttTopicFilterComparer.LevelSeparator.ToString()) &&
+                    !filter.EndsWith(MqttTopicFilterComparer.MultiLevelWildcard.ToString()))
+                {
+                    filter += MqttTopicFilterComparer.LevelSeparator;
+                }
+                
+                // append hash if neccessary
+                if (!filter.EndsWith(MqttTopicFilterComparer.MultiLevelWildcard.ToString()))
+                {
+                    filter += MqttTopicFilterComparer.MultiLevelWildcard;
+                }
+                
+                return filter;
+            }
+        }
+        
+        public bool Equals(MqttTopicTemplate other)
+        {
+            return other != null && Template == other.Template;
+        }
+        
+        public override bool Equals(object obj)
+        {
+            if (ReferenceEquals(null, obj))
+            {
+                return false;
+            }
+            
+            if (ReferenceEquals(this, obj))
+            {
+                return true;
+            }
+            
+            if (obj.GetType() != GetType())
+            {
+                return false;
+            }
+            
+            return Equals((MqttTopicTemplate)obj);
+        }
+        
+        /// <summary>
+        ///     Determine the shortest common prefix of the given templates. Partial segments
+        ///     are not returned.
+        /// </summary>
+        /// <param
+        ///     name="templates">
+        ///     topic templates
+        /// </param>
+        /// <returns></returns>
+        public static MqttTopicTemplate FindCanonicalPrefix(IEnumerable<MqttTopicTemplate> templates)
+        {
+            string root = null;
+            
+            string CommonPrefix(string a, string b)
+            {
+                var maxIndex = Math.Min(a.Length, b.Length) - 1;
+                for (var i = 0; i <= maxIndex; i++)
+                {
+                    if (a[i] != b[i])
+                    {
+                        return a.Substring(0, i);
+                    }
+                }
+                
+                return a.Substring(0, maxIndex+1);
+            }
+            
+            foreach (string topic in from template in templates select template.Template)
+            {
+                root = root == null ? topic : CommonPrefix(root, topic);
+            }
+            
+            if (string.IsNullOrEmpty(root))
+                return new MqttTopicTemplate(MqttTopicFilterComparer.MultiLevelWildcard.ToString());
+            
+            if (root.Contains(MqttTopicFilterComparer.LevelSeparator) &&
+                !root.EndsWith(MqttTopicFilterComparer.LevelSeparator.ToString()) &&
+                !root.EndsWith("}"))
+            {
+                root = root.Substring(0, root.LastIndexOf(MqttTopicFilterComparer.LevelSeparator)+1);
+            }
+            
+            if (root.EndsWith(MqttTopicFilterComparer.LevelSeparator.ToString()))
+                root += MqttTopicFilterComparer.SingleLevelWildcard;
+
+            return new MqttTopicTemplate(root);
+        }
+        
+        public override int GetHashCode()
+        {
+            return Template.GetHashCode();
+        }
+        
+        /// <summary>
+        ///     Test if this topic template matches a given topic.
+        /// </summary>
+        /// <param
+        ///     name="topic">
+        ///     a fully specified topic
+        /// </param>
+        /// <param
+        ///     name="subtree">
+        ///     true to match including the subtree (multi-level wildcard)
+        /// </param>
+        /// <returns>true iff the topic matches the template's filter</returns>
+        /// <exception
+        ///     cref="InvalidOperationException">
+        /// </exception>
+        /// <exception
+        ///     cref="ArgumentException">
+        ///     if the topic is invalid
+        /// </exception>
+        public bool MatchesTopic(string topic, bool subtree = false)
+        {
+            var comparison = MqttTopicFilterComparer.Compare(topic, subtree ? TopicTreeRootFilter : TopicFilter);
+            if (comparison == MqttTopicFilterCompareResult.FilterInvalid)
+            {
+                throw new InvalidOperationException("Invalid filter");
+            }
+            
+            if (comparison == MqttTopicFilterCompareResult.TopicInvalid)
+            {
+                throw new ArgumentException("Invalid topic", nameof(topic));
+            }
+            
+            return comparison == MqttTopicFilterCompareResult.IsMatch;
+        }
+        
+        /// <summary>
+        ///     Extract the parameter values from a topic corresponding to the template
+        ///     parameters. The topic has to match this template.
+        /// </summary>
+        /// <param
+        ///     name="topic">
+        ///     the topic
+        /// </param>
+        /// <returns>an enumeration of (parameter, index, value)</returns>
+        public IEnumerable<(string parameter, int index, string value)> ParseParameterValues(string topic)
+        {
+            if (!MatchesTopic(topic))
+            {
+                throw new ArgumentException("the topic has to match this template", nameof(topic));
+            }
+            
+            return parseParameterValuesInternal(topic);
+        }
+        
+        /// <summary>
+        ///     Extract the parameter values from the message topic corresponding to the template
+        ///     parameters. The message topic has to match this topic template.
+        /// </summary>
+        /// <param
+        ///     name="message">
+        ///     the message
+        /// </param>
+        /// <returns>an enumeration of (parameter, index, value)</returns>
+        public IEnumerable<(string parameter, int index, string value)> ParseParameterValues(MqttApplicationMessage message)
+        {
+            return ParseParameterValues(message.Topic);
+        }
+        
+        /// <summary>
+        ///     Try to set a parameter to a given value. If the parameter is not present,
+        ///     this is returned. The value must not contain slashes.
+        /// </summary>
+        /// <param
+        ///     name="parameter">
+        ///     a template parameter
+        /// </param>
+        /// <param
+        ///     name="value">
+        ///     a string
+        /// </param>
+        /// <returns></returns>
+        public MqttTopicTemplate TrySetParameter(string parameter, string value)
+        {
+            if (parameter != null && _parameterSegments.Contains(parameter))
+            {
+                return WithParameter(parameter, value);
+            }
+            
+            return this;
+        }
+        
+        /// <summary>
+        ///     Replace the given parameter with a single-level wildcard (plus sign).
+        /// </summary>
+        /// <param
+        ///     name="parameter">
+        ///     parameter name
+        /// </param>
+        /// <returns>the topic template (without the parameter)</returns>
+        public MqttTopicTemplate WithoutParameter(string parameter)
+        {
+            if (string.IsNullOrEmpty(parameter) || !_parameterSegments.Contains(parameter))
+            {
+                throw new ArgumentException("topic template parameter must exist.");
+            }
+            
+            return ReplaceInternal(parameter, MqttTopicFilterComparer.SingleLevelWildcard.ToString());
+        }
+        
+        /// <summary>
+        ///     Substitute a parameter with a given value, thus removing the parameter. If the parameter is not present,
+        ///     the method trows. The value must not contain slashes or wildcards.
+        /// </summary>
+        /// <param
+        ///     name="parameter">
+        ///     a template parameter
+        /// </param>
+        /// <param
+        ///     name="value">
+        ///     a string
+        /// </param>
+        /// <exception
+        ///     cref="ArgumentException">
+        ///     when the parameter is not present
+        /// </exception>
+        /// <returns>the topic template (without the parameter)</returns>
+        public MqttTopicTemplate WithParameter(string parameter, string value)
+        {
+            if (value == null || string.IsNullOrEmpty(parameter) || !_parameterSegments.Contains(parameter) ||
+                value.Contains(MqttTopicFilterComparer.LevelSeparator) ||
+                value.Contains(MqttTopicFilterComparer.SingleLevelWildcard) ||
+                value.Contains(MqttTopicFilterComparer.MultiLevelWildcard))
+            {
+                throw new ArgumentException("parameter must exist and value must not contain slashes or wildcard.");
+            }
+            
+            return ReplaceInternal(parameter, value);
+        }
+        
+        private MqttTopicTemplate ReplaceInternal(string parameter, string value)
+        {
+            var moustache = "{" + parameter + "}";
+            return new MqttTopicTemplate(Template.Replace(moustache, value));
+        }
+        
+        /// <summary>
+        ///     Reuse parameters as they are extracted using another topic template on this template
+        ///     when the parameter name matches. Useful
+        ///     for compatibility routing.
+        /// </summary>
+        /// <param
+        ///     name="parameters">
+        /// </param>
+        /// <returns></returns>
+        public MqttTopicTemplate WithParameterValuesFrom(IEnumerable<(string parameter, int index, string value)> parameters)
+        {
+            return parameters.Aggregate(this, (t, p) => t.TrySetParameter(p.parameter, p.value));
+        }
+        
+        IEnumerable<(string parameter, int index, string value)> parseParameterValuesInternal(string topic)
+        {
+            // because we have a match, we know the segment array is at least the template's length
+            var segments = topic.Split(MqttTopicFilterComparer.LevelSeparator);
+            for (var i = 0; i < _parameterSegments.Length; i++)
+            {
+                var name = _parameterSegments[i];
+                if (name != null)
+                {
+                    yield return (name, i, segments[i]);
+                }
+            }
+        }
+    }
+}

Source/MQTTnet.Extensions.TopicTemplate/README.md

@@ -0,0 +1,79 @@
+# MQTTNet.Extensions.TopicTemplate
+
+Provides mqtt topic templating logic to support dispatch, routing and
+similar functionality based on the well known moustache syntax, aka
+AsyncAPI dynamic channel address.
+
+Generating and parsing MQTT topics and topic filters is often done in
+an ad-hoc fashion, leading to error-prone code and subtly introduced
+showstoppers like forgetting to strip a slash from a parameter.  To
+remedy, this extension aids you write safe, maintainable logic
+for topic generation, routing and dispatch.
+
+
+## How it works
+
+The package lets you write MQTTNet code like:
+```csharp
+var template = new MqttTopicTemplate("App/v1/{sender}/message");
+
+var filter = new MqttTopicFilterBuilder()
+    .WithTopicTemplate(template) // (1)
+    .WithAtLeastOnceQoS()
+    .WithNoLocal()
+    .Build();
+
+// filter.Topic == "App/v1/+/message"
+
+var myTopic = template
+    .WithParameter("sender", "me, myself & i"); // (2)
+
+var message = new MqttApplicationMessageBuilder()
+    .WithTopicTemplate(  // (3)
+        myTopic)
+    .WithPayload("Hello!")
+    .Build();
+
+// message.Topic == "App/v1/me, myself & i/message"
+
+Assert.IsTrue(message.MatchesTopicTemplate(template)); // (4)
+```
+
+At (1), the parameter "sender" was automatically replaced by a plus sign
+(single level wildcard) because the caller is creating a topic filter.
+
+Using the same template (they are immutable), you can send
+a message. At (2), we replace the parameter with a known value.
+If that value contained a level separator or topic filter only
+characters, we'd get an ArgumentException. If we forgot to replace
+the parameter "sender" (e.g. when placing template not myTopic),
+we would be prevented from sending at (3).
+
+On the receiving side, a message can be matched to a template
+using code like at (4).
+
+These daily tasks become much safer and easier to code than 
+string.Format() and Split() allow for. More elaborate computation is supported
+too. You could extract the sender using the template or route
+messages based on topic content.
+
+## Features
+
+- Safe handling of topic parameters in moustache syntax
+- Simplifies topic generation and parsing logic
+- Match topics and extract the values of their parameters
+- Translate between topic templates to ease dynamic routing
+- Derive a canonical topic filter from a bunch of templates
+- Integrates with MQTTNet message, subscription and filter builders
+- Extension method friendly (sealed class with one public ctor)
+
+## Additional documentation
+
+- Some of the [unit tests](https://github.com/dotnet/MQTTnet/blob/master/Source/MQTTnet.Tests/Extensions/MqttTopicTemplate_Tests.cs) are instructive
+- Some examples feature the extension, e.g. TopicGenerator, Client_Subscribe_Samples
+
+## Feedback
+
+Report any issues with the main project on https://github.com/dotnet/MQTTnet/issues
+
+

Source/MQTTnet.Extensions.TopicTemplate/TopicTemplateExtensions.cs

@@ -0,0 +1,190 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Linq;
+using MQTTnet.Client;
+using MQTTnet.Packets;
+using MQTTnet.Protocol;
+
+namespace MQTTnet.Extensions.TopicTemplate
+{
+    public static class TopicTemplateExtensions
+    {
+        /// <summary>
+        ///     Modify this message builder to respond to a given message. The
+        ///     message's response topic and correlation data are included
+        ///     in the message builder.
+        /// </summary>
+        /// <param
+        ///     name="builder">
+        ///     a message builder
+        /// </param>
+        /// <param
+        ///     name="message">
+        ///     a message with a response topic
+        /// </param>
+        /// <returns>a message builder</returns>
+        /// <see
+        ///     cref="BuildResponse" />
+        public static MqttApplicationMessageBuilder AsResponseTo(this MqttApplicationMessageBuilder builder, MqttApplicationMessage message)
+        {
+            if (!string.IsNullOrEmpty(message.ResponseTopic))
+            {
+                throw new ArgumentException("message does not have a response topic");
+            }
+
+            return builder.WithTopic(message.ResponseTopic).WithCorrelationData(message.CorrelationData);
+        }
+
+        /// <summary>
+        ///     Set the filter topic according to the template, with
+        ///     remaining template parameters substituted by single-level
+        ///     wildcard.
+        /// </summary>
+        /// <param
+        ///     name="topicTemplate">
+        ///     a topic template
+        /// </param>
+        /// <param
+        ///     name="subscribeTreeRoot">
+        ///     whether to subscribe to the whole topic tree
+        /// </param>
+        /// <returns>the modified topic filter</returns>
+        public static MqttTopicFilterBuilder BuildFilter(this MqttTopicTemplate topicTemplate, bool subscribeTreeRoot = false)
+        {
+            return new MqttTopicFilterBuilder().WithTopicTemplate(topicTemplate, subscribeTreeRoot);
+        }
+
+        /// <summary>
+        ///     Create a message builder from this template. The template must not have
+        ///     remaining parameters. 
+        /// </summary>
+        /// <param
+        ///     name="topicTemplate">
+        ///     a parameterless topic template
+        /// </param>
+        /// <returns>a new message builder</returns>
+        /// <exception
+        ///     cref="ArgumentException">
+        ///     if the topic template has parameters
+        /// </exception>
+        public static MqttApplicationMessageBuilder BuildMessage(this MqttTopicTemplate topicTemplate)
+        {
+            return new MqttApplicationMessageBuilder().WithTopicTemplate(topicTemplate);
+        }
+        
+        /// <summary>
+        ///     Return a message builder to respond to this message. The
+        ///     message's response topic and correlation data are included
+        ///     in the response message builder.
+        /// </summary>
+        /// <param
+        ///     name="message">
+        ///     a message with a response topic
+        /// </param>
+        /// <returns>a message builder</returns>
+        /// <see
+        ///     cref="AsResponseTo" />
+        public static MqttApplicationMessageBuilder BuildResponse(this MqttApplicationMessage message)
+        {
+            return new MqttApplicationMessageBuilder().AsResponseTo(message);
+        }
+
+        /// <summary>
+        ///     Return whether the message matches the given topic template.
+        /// </summary>
+        /// <param
+        ///     name="message">
+        ///     a message
+        /// </param>
+        /// <param
+        ///     name="topicTemplate">
+        ///     a topic template
+        /// </param>
+        /// <param
+        ///     name="subtree">
+        ///     whether to include the topic subtree
+        /// </param>
+        /// <returns></returns>
+        public static bool MatchesTopicTemplate(this MqttApplicationMessage message, MqttTopicTemplate topicTemplate, bool subtree = false)
+        {
+            return topicTemplate.MatchesTopic(message.Topic, subtree);
+        }
+
+        /// <summary>
+        ///     Set the filter topic according to the template, with
+        ///     template parameters substituted by a single-level
+        ///     wildcard.
+        /// </summary>
+        /// <param
+        ///     name="builder">
+        ///     a filter builder
+        /// </param>
+        /// <param
+        ///     name="topicTemplate">
+        ///     a topic template
+        /// </param>
+        /// <param
+        ///     name="subscribeTreeRoot">
+        ///     whether to subscribe to the whole topic tree
+        /// </param>
+        /// <returns>the modified topic filter</returns>
+        public static MqttTopicFilterBuilder WithTopicTemplate(this MqttTopicFilterBuilder builder, MqttTopicTemplate topicTemplate, bool subscribeTreeRoot = false)
+        {
+            return builder.WithTopic(subscribeTreeRoot ? topicTemplate.TopicTreeRootFilter : topicTemplate.TopicFilter);
+        }
+
+        /// <summary>
+        /// Set the subscription to the template's topic filter.
+        /// </summary>
+        /// <returns>the builder</returns>
+        public static MqttClientSubscribeOptionsBuilder WithTopicTemplate(
+            this MqttClientSubscribeOptionsBuilder builder,
+            MqttTopicTemplate topicTemplate,
+            MqttQualityOfServiceLevel qualityOfServiceLevel = MqttQualityOfServiceLevel.AtMostOnce,
+            bool noLocal = false,
+            bool retainAsPublished = false,
+            MqttRetainHandling retainHandling = MqttRetainHandling.SendAtSubscribe)
+        {
+            return builder.WithTopicFilter(
+                new MqttTopicFilter
+                {
+                    Topic = topicTemplate.TopicFilter,
+                    QualityOfServiceLevel = qualityOfServiceLevel,
+                    NoLocal = noLocal,
+                    RetainAsPublished = retainAsPublished,
+                    RetainHandling = retainHandling
+                });
+        }
+        
+        /// <summary>
+        ///     Set the publication topic according to the topic template. The template
+        ///     must not have remaining (unset) parameters or contain wildcards.
+        /// </summary>
+        /// <param
+        ///     name="builder">
+        ///     a message builder
+        /// </param>
+        /// <param
+        ///     name="topicTemplate">
+        ///     a parameterless topic template
+        /// </param>
+        /// <returns>the modified message builder</returns>
+        /// <exception
+        ///     cref="ArgumentException">
+        ///     if the topic template has parameters
+        /// </exception>
+        public static MqttApplicationMessageBuilder WithTopicTemplate(this MqttApplicationMessageBuilder builder, MqttTopicTemplate topicTemplate)
+        {
+            if (topicTemplate.Parameters.Any())
+            {
+                throw new ArgumentException("topic templates must be parameter-less when sending " + topicTemplate.Template);
+            }
+
+            MqttTopicValidator.ThrowIfInvalid(topicTemplate.Template);
+            return builder.WithTopic(topicTemplate.Template);
+        }
+    }
+}

Source/MQTTnet.Extensions.WebSocket4Net/MQTTnet.Extensions.WebSocket4Net.csproj

@@ -2,7 +2,7 @@
 
     <PropertyGroup>
         <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0;net7.0</TargetFrameworks>
-        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461</TargetFrameworks>
+        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461;net48</TargetFrameworks>
         <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' AND '$(MSBuildRuntimeType)' != 'Core' ">$(TargetFrameworks);uap10.0</TargetFrameworks>
         
         <AssemblyName>MQTTnet.Extensions.WebSocket4Net</AssemblyName>

Source/MQTTnet.Extensions.WebSocket4Net/WebSocket4NetMqttChannel.cs

@@ -47,13 +47,13 @@ namespace MQTTnet.Extensions.WebSocket4Net
             var uri = _webSocketOptions.Uri;
             if (!uri.StartsWith("ws://", StringComparison.OrdinalIgnoreCase) && !uri.StartsWith("wss://", StringComparison.OrdinalIgnoreCase))
             {
-                if (_webSocketOptions.TlsOptions?.UseTls == false)
+                if (_webSocketOptions.TlsOptions?.UseTls == true)
                 {
-                    uri = "ws://" + uri;
+                    uri = "wss://" + uri;
                 }
                 else
                 {
-                    uri = "wss://" + uri;
+                    uri = "ws://" + uri;
                 }
             }
             
@@ -76,7 +76,7 @@ namespace MQTTnet.Extensions.WebSocket4Net
             List<KeyValuePair<string, string>> customHeaders = null;
             if (_webSocketOptions.RequestHeaders != null)
             {
-                customHeaders = _webSocketOptions.RequestHeaders.Select(i => new KeyValuePair<string, string>(i.Key, i.Value)).ToList();
+                customHeaders = _webSocketOptions.RequestHeaders.ToList();
             }
 
             EndPoint proxy = null;
@@ -92,18 +92,7 @@ namespace MQTTnet.Extensions.WebSocket4Net
             var webSocketVersion = WebSocketVersion.None;
             var receiveBufferSize = 0;
 
-            var certificates = new X509CertificateCollection();
+            var certificates = _webSocketOptions.TlsOptions?.ClientCertificatesProvider?.GetCertificates();
-            if (_webSocketOptions.TlsOptions?.Certificates != null)
-            {
-                foreach (var certificate in _webSocketOptions.TlsOptions.Certificates)
-                {
-#if WINDOWS_UWP
-                    certificates.Add(new X509Certificate(certificate));
-#else
-                    certificates.Add(certificate);
-#endif
-                }
-            }
 
             _webSocket = new WebSocket(uri, subProtocol, cookies, customHeaders, userAgent, origin, webSocketVersion, proxy, sslProtocols, receiveBufferSize)
             {

Source/MQTTnet.TestApp/ClientTest.cs

@@ -4,6 +4,7 @@
 
 using MQTTnet.Client;
 using System;
+using System.Net;
 using System.Text;
 using System.Threading.Tasks;
 using MQTTnet.Diagnostics;
@@ -27,7 +28,7 @@ namespace MQTTnet.TestApp
                 {
                     ChannelOptions = new MqttClientTcpOptions
                     {
-                        Server = "127.0.0.1"
+                        RemoteEndpoint = new DnsEndPoint("127.0.0.1", 0)
                     }
                 };
 

Source/MQTTnet.TestApp/MQTTnet.TestApp.csproj

@@ -10,6 +10,7 @@
         <EnforceCodeStyleInBuild>false</EnforceCodeStyleInBuild>
         <DisableImplicitAspNetCoreAnalyzers>true</DisableImplicitAspNetCoreAnalyzers>
         <NoWarn>1591;NETSDK1138</NoWarn>
+        <LangVersion>7.3</LangVersion>
     </PropertyGroup>
 
     <ItemGroup>
@@ -20,6 +21,7 @@
         <ProjectReference Include="..\..\Source\MQTTnet.Extensions.ManagedClient\MQTTnet.Extensions.ManagedClient.csproj" />
         <ProjectReference Include="..\..\Source\MQTTnet.Extensions.WebSocket4Net\MQTTnet.Extensions.WebSocket4Net.csproj" />
         <ProjectReference Include="..\..\Source\MQTTnet\MQTTnet.csproj" />
+        <ProjectReference Include="..\MQTTnet.Extensions.TopicTemplate\MQTTnet.Extensions.TopicTemplate.csproj" />
     </ItemGroup>
 
 </Project>

Source/MQTTnet.TestApp/ManagedClientTest.cs

@@ -7,6 +7,7 @@ using System.Threading.Tasks;
 using System.IO;
 using Newtonsoft.Json;
 using System.Collections.Generic;
+using System.Net;
 using MQTTnet.Client;
 using MQTTnet.Extensions.ManagedClient;
 using MQTTnet.Internal;
@@ -28,7 +29,7 @@ namespace MQTTnet.TestApp
                     Credentials = new RandomPassword(),
                     ChannelOptions = new MqttClientTcpOptions
                     {
-                        Server = "broker.hivemq.com"
+                        RemoteEndpoint = new DnsEndPoint("broker.hivemq.com", 0)
                     }
                 },
 

Source/MQTTnet.TestApp/PerformanceTest.cs

@@ -5,13 +5,13 @@
 using System;
 using System.Diagnostics;
 using System.Linq;
+using System.Net;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Client;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
-using MqttClient = MQTTnet.Client.MqttClient;
 
 namespace MQTTnet.TestApp
 {
@@ -25,7 +25,7 @@ namespace MQTTnet.TestApp
                 {
                     ChannelOptions = new MqttClientTcpOptions
                     {
-                        Server = "127.0.0.1"
+                        RemoteEndpoint = new DnsEndPoint("127.0.0.1", 0)
                     },
                     CleanSession = true
                 };
@@ -71,7 +71,7 @@ namespace MQTTnet.TestApp
                 {
                     ChannelOptions = new MqttClientTcpOptions
                     {
-                        Server = "127.0.0.1"
+                        RemoteEndpoint = new DnsEndPoint("127.0.0.1", 0)
                     }
                 };
 
@@ -114,7 +114,10 @@ namespace MQTTnet.TestApp
             {
                 var options = new MqttClientOptions
                 {
-                    ChannelOptions = new MqttClientTcpOptions { Server = "localhost" },
+                    ChannelOptions = new MqttClientTcpOptions
+                    {
+                        RemoteEndpoint = new DnsEndPoint("localhost", 0)
+                    },
                     ClientId = "Client1",
                     CleanSession = true
                 };
@@ -218,7 +221,7 @@ namespace MQTTnet.TestApp
                 {
                     ChannelOptions = new MqttClientTcpOptions
                     {
-                        Server = "127.0.0.1"
+                        RemoteEndpoint = new DnsEndPoint("127.0.0.1", 0)
                     },
                     CleanSession = true
                 };
@@ -269,7 +272,7 @@ namespace MQTTnet.TestApp
                 {
                     ChannelOptions = new MqttClientTcpOptions
                     {
-                        Server = "127.0.0.1"
+                        RemoteEndpoint = new DnsEndPoint("127.0.0.1", 0)
                     },
                     CleanSession = true
                 };
@@ -320,7 +323,7 @@ namespace MQTTnet.TestApp
                 {
                     ChannelOptions = new MqttClientTcpOptions
                     {
-                        Server = "127.0.0.1"
+                        RemoteEndpoint = new DnsEndPoint("127.0.0.1", 0)
                     },
                     CleanSession = true
                 };

Source/MQTTnet.TestApp/PublicBrokerTest.cs

@@ -20,143 +20,155 @@ namespace MQTTnet.TestApp
         {
 #if NET5_0_OR_GREATER
             // TLS13 is only available in Net5.0
-            var unsafeTls13 = new MqttClientOptionsBuilderTlsParameters
+            var unsafeTls13 = new MqttClientTlsOptions
             {
                 UseTls = true,
                 SslProtocol = SslProtocols.Tls13,
                 // Don't use this in production code. This handler simply allows any invalid certificate to work.
-                CertificateValidationHandler = w => true
+                AllowUntrustedCertificates = true,
+                IgnoreCertificateChainErrors = true,
+                CertificateValidationHandler = _ => true
             };
 #endif
             // Also defining TLS12 for servers that don't seem no to support TLS13.
-            var unsafeTls12 = new MqttClientOptionsBuilderTlsParameters
+            var unsafeTls12 = new MqttClientTlsOptions
             {
                 UseTls = true,
                 SslProtocol = SslProtocols.Tls12,
                 // Don't use this in production code. This handler simply allows any invalid certificate to work.
-                CertificateValidationHandler = w => true
+                AllowUntrustedCertificates = true,
+                IgnoreCertificateChainErrors = true,
+                CertificateValidationHandler = _ => true
             };
 
             // mqtt.eclipseprojects.io
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "mqtt.eclipseprojects.io TCP",
                 new MqttClientOptionsBuilder().WithTcpServer("mqtt.eclipseprojects.io", 1883).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "mqtt.eclipseprojects.io WS",
-                new MqttClientOptionsBuilder().WithWebSocketServer("mqtt.eclipseprojects.io:80/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build());
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("mqtt.eclipseprojects.io:80/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
 #if NET5_0_OR_GREATER
-            await ExecuteTestAsync("mqtt.eclipseprojects.io WS TLS13",
+            await ExecuteTestsAsync("mqtt.eclipseprojects.io WS TLS13",
-                new MqttClientOptionsBuilder().WithWebSocketServer("mqtt.eclipseprojects.io:443/mqtt")
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("mqtt.eclipseprojects.io:443/mqtt"))
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build());
+                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls13).Build());
             
-            await ExecuteTestAsync("mqtt.eclipseprojects.io WS TLS13 (WebSocket4Net)",
+            await ExecuteTestsAsync("mqtt.eclipseprojects.io WS TLS13 (WebSocket4Net)",
-                new MqttClientOptionsBuilder().WithWebSocketServer("mqtt.eclipseprojects.io:443/mqtt")
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("mqtt.eclipseprojects.io:443/mqtt"))
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build(),
+                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls13).Build(),
                     true);
 #endif
 
             // test.mosquitto.org
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "test.mosquitto.org TCP",
                 new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 1883).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "test.mosquitto.org TCP - Authenticated",
                 new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 1884).WithCredentials("rw", "readwrite").WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "test.mosquitto.org TCP TLS12",
-                new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8883).WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+                new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8883).WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls12).Build());
 
 #if NET5_0_OR_GREATER
-            await ExecuteTestAsync("test.mosquitto.org TCP TLS13",
+            await ExecuteTestsAsync("test.mosquitto.org TCP TLS13",
                 new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8883)
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build());
+                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls13).Build());
 #endif
 
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "test.mosquitto.org TCP TLS12 - Authenticated",
                 new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8885)
                     .WithCredentials("rw", "readwrite")
                     .WithProtocolVersion(MqttProtocolVersion.V311)
-                    .WithTls(unsafeTls12)
+                    .WithTlsOptions(unsafeTls12)
                     .Build());
 
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "test.mosquitto.org WS",
-                new MqttClientOptionsBuilder().WithWebSocketServer("test.mosquitto.org:8080/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build());
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("test.mosquitto.org:8080/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "test.mosquitto.org WS (WebSocket4Net)",
-                new MqttClientOptionsBuilder().WithWebSocketServer("test.mosquitto.org:8080/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build(),
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("test.mosquitto.org:8080/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).Build(),
                 true);
 
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "test.mosquitto.org WS TLS12",
-                new MqttClientOptionsBuilder().WithWebSocketServer("test.mosquitto.org:8081/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("test.mosquitto.org:8081/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls12).Build());
 
-            // await ExecuteTestAsync(
+            await ExecuteTestsAsync(
-            //     "test.mosquitto.org WS TLS12 (WebSocket4Net)",
+                "test.mosquitto.org WS TLS12 (WebSocket4Net)",
-            //     new MqttClientOptionsBuilder().WithWebSocketServer("test.mosquitto.org:8081/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build(),
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("test.mosquitto.org:8081/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls12).Build(),
-            //     true);
+                true);
 
             // broker.emqx.io
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "broker.emqx.io TCP",
                 new MqttClientOptionsBuilder().WithTcpServer("broker.emqx.io", 1883).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "broker.emqx.io TCP TLS12",
-                new MqttClientOptionsBuilder().WithTcpServer("broker.emqx.io", 8883).WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+                new MqttClientOptionsBuilder().WithTcpServer("broker.emqx.io", 8883).WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls12).Build());
 
 #if NET5_0_OR_GREATER
-            await ExecuteTestAsync("broker.emqx.io TCP TLS13",
+            await ExecuteTestsAsync("broker.emqx.io TCP TLS13",
                 new MqttClientOptionsBuilder().WithTcpServer("broker.emqx.io", 8883)
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build());
+                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls13).Build());
 #endif
 
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "broker.emqx.io WS",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.emqx.io:8083/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build());
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.emqx.io:8083/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "broker.emqx.io WS (WebSocket4Net)",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.emqx.io:8084/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build(),
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.emqx.io:8084/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).Build(),
                 true);
 
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "broker.emqx.io WS TLS12",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.emqx.io:8084/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.emqx.io:8084/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls12).Build());
 
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "broker.emqx.io WS TLS12 (WebSocket4Net)",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.emqx.io:8084/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build(),
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.emqx.io:8084/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls12).Build(),
                 true);
 
             // broker.hivemq.com
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "broker.hivemq.com TCP",
                 new MqttClientOptionsBuilder().WithTcpServer("broker.hivemq.com", 1883).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "broker.hivemq.com WS",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.hivemq.com:8000/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build());
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.hivemq.com:8000/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync(
+            await ExecuteTestsAsync(
                 "broker.hivemq.com WS (WebSocket4Net)",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.hivemq.com:8000/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build(),
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.hivemq.com:8000/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).Build(),
                 true);
 
             // mqtt.swifitch.cz: Does not seem to operate any more
-
             // cloudmqtt.com: Cannot test because it does not offer a free plan any more.
 
             Write("Finished.", ConsoleColor.White);
             Console.ReadLine();
         }
 
+        static async Task ExecuteTestsAsync(string name, MqttClientOptions options, bool useWebSocket4Net = false)
+        {
+            options.ProtocolVersion = MqttProtocolVersion.V311;
+            await ExecuteTestAsync(name + " V3.1.1", options, useWebSocket4Net);
+
+            options.ProtocolVersion = MqttProtocolVersion.V500;
+            await ExecuteTestAsync(name + " V5.0.0", options, useWebSocket4Net);
+        }
+        
         static async Task ExecuteTestAsync(string name, MqttClientOptions options, bool useWebSocket4Net = false)
         {
             try
@@ -197,9 +209,10 @@ namespace MQTTnet.TestApp
 
                 Write("[OK]\n", ConsoleColor.Green);
             }
-            catch (Exception e)
+            catch (Exception exception)
             {
-                Write("[FAILED] " + e.Message + "\n", ConsoleColor.Red);
+                Write("[FAILED]" + Environment.NewLine, ConsoleColor.Red);
+                Write(exception + Environment.NewLine, ConsoleColor.Red);
             }
         }
 

Source/MQTTnet.TestApp/TopicGenerator.cs

@@ -1,6 +1,6 @@
 using System;
 using System.Collections.Generic;
-using System.Text;
+using MQTTnet.Extensions.TopicTemplate;
 
 namespace MQTTnet.TestApp
 {
@@ -17,6 +17,8 @@ namespace MQTTnet.TestApp
             singleWildcardTopicsByPublisher = new Dictionary<string, List<string>>();
             multiWildcardTopicsByPublisher = new Dictionary<string, List<string>>();
 
+            MqttTopicTemplate baseTemplate = new MqttTopicTemplate("{publisher}/{building}/{level}/{sensor}");
+
             // Find some reasonable distribution across three topic levels
             var topicsPerLevel = (int)Math.Pow(numTopicsPerPublisher, (1.0 / 3.0));
 
@@ -40,25 +42,37 @@ namespace MQTTnet.TestApp
                 int publisherTopicCount = 0;
 
                 var publisherName = "pub" + p;
+                var publisherTemplate = baseTemplate
+                    .WithParameter("publisher", publisherName);
                 for (var l1 = 0; l1 < numLevel1Topics; ++l1)
                 {
+                    var l1Template = publisherTemplate
+                        .WithParameter("building", "building" + (l1 + 1));
                     for (var l2 = 0; l2 < numLevel2Topics; ++l2)
                     {
+                        var l2Template = l1Template
+                            .WithParameter("level", "level" + (l2 + 1));
                         for (var l3 = 0; l3 < maxNumLevel3Topics; ++l3)
                         {
                             if (publisherTopicCount >= numTopicsPerPublisher)
                                 break;
 
-                            var topic = string.Format("{0}/building{1}/level{2}/sensor{3}", publisherName, l1 + 1, l2 + 1, l3 + 1);
+                            var topic = l2Template
+                                .WithParameter("sensor", "sensor" + (l3 + 1))
+                                .TopicFilter;
                             AddPublisherTopic(publisherName, topic, topicsByPublisher);
 
                             if (l2 == 0)
                             {
-                                var singleWildcardTopic = string.Format("{0}/building{1}/+/sensor{2}", publisherName, l1 + 1, l3 + 1);
+                                var singleWildcardTopic = l1Template
+                                        .WithParameter("sensor", "sensor" + (l3 + 1))
+                                        .TopicFilter;
                                 AddPublisherTopic(publisherName, singleWildcardTopic, singleWildcardTopicsByPublisher);
                                 if (l1 == 0)
                                 {
-                                    var multiWildcardTopic = string.Format("{0}/+/level{1}/+", publisherName, l3 + 1);
+                                    var multiWildcardTopic = publisherTemplate
+                                        .WithParameter("sensor", "sensor" + (l3 + 1))
+                                        .TopicFilter;
                                     AddPublisherTopic(publisherName, multiWildcardTopic, multiWildcardTopicsByPublisher);
                                 }
                             }

Source/MQTTnet.Tests/Clients/LowLevelMqttClient/LowLevelMqttClient_Tests.cs

@@ -13,6 +13,7 @@ using MQTTnet.Exceptions;
 using MQTTnet.LowLevelClient;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
+using MQTTnet.Server;
 
 namespace MQTTnet.Tests.Clients.LowLevelMqttClient
 {

Source/MQTTnet.Tests/Clients/ManagedMqttClient/ManagedMqttClient_Tests.cs

@@ -13,6 +13,7 @@ using MQTTnet.Diagnostics;
 using MQTTnet.Extensions.ManagedClient;
 using MQTTnet.Formatter;
 using MQTTnet.Internal;
+using MQTTnet.Packets;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
 using MQTTnet.Tests.Mockups;
@@ -22,99 +23,6 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
     [TestClass]
     public sealed class ManagedMqttClient_Tests : BaseTestClass
     {
-        [TestMethod]
-        public async Task Expose_Custom_Connection_Error()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                var server = await testEnvironment.StartServer();
-                
-                server.ValidatingConnectionAsync += args =>
-                {
-                    args.ReasonCode = MqttConnectReasonCode.BadUserNameOrPassword;
-                    return CompletedTask.Instance;
-                };
-
-                var managedClient = testEnvironment.Factory.CreateManagedMqttClient();
-
-                MqttClientDisconnectedEventArgs disconnectedArgs = null;
-                managedClient.DisconnectedAsync += args =>
-                {
-                    disconnectedArgs = args;
-                    return CompletedTask.Instance;
-                };
-                
-                var clientOptions = testEnvironment.Factory.CreateManagedMqttClientOptionsBuilder().WithClientOptions(testEnvironment.CreateDefaultClientOptions()).Build();
-                await managedClient.StartAsync(clientOptions);
-
-                await LongTestDelay();
-
-                Assert.IsNotNull(disconnectedArgs);
-                Assert.AreEqual(MqttClientConnectResultCode.BadUserNameOrPassword, disconnectedArgs.ConnectResult.ResultCode);
-            }
-        }
-        
-        [TestMethod]
-        public async Task Receive_While_Not_Cleanly_Disconnected()
-        {
-            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
-            {
-                await testEnvironment.StartServer(o => o.WithPersistentSessions());
-
-                var senderClient = await testEnvironment.ConnectClient();
-
-                // Prepare managed client.
-                var managedClient = testEnvironment.Factory.CreateManagedMqttClient();
-                await managedClient.SubscribeAsync("#");
-                var receivedMessages = testEnvironment.CreateApplicationMessageHandler(managedClient);
-                
-                var managedClientOptions = new ManagedMqttClientOptions
-                {
-                    ClientOptions = testEnvironment.Factory.CreateClientOptionsBuilder()
-                        .WithTcpServer("127.0.0.1", testEnvironment.ServerPort)
-                        .WithClientId(nameof(Receive_While_Not_Cleanly_Disconnected) + "_managed")
-                        .WithCleanSession(false)
-                        .Build()
-                };
-
-                await managedClient.StartAsync(managedClientOptions);
-                await LongTestDelay();
-                await LongTestDelay();
-                
-                // Send test data.
-                await senderClient.PublishStringAsync("topic1");
-                await LongTestDelay();
-                await LongTestDelay();
-                
-                receivedMessages.AssertReceivedCountEquals(1);
-
-                // Stop the managed client but keep session at server (not clean disconnect required).
-                await managedClient.StopAsync(false);
-                await LongTestDelay();
-                
-                // Send new messages in the meantime.
-                await senderClient.PublishStringAsync("topic2", qualityOfServiceLevel: MqttQualityOfServiceLevel.ExactlyOnce);
-                await LongTestDelay();
-                
-                // Start the managed client, it should receive the new message.
-                await managedClient.StartAsync(managedClientOptions);
-                await LongTestDelay();
-                
-                receivedMessages.AssertReceivedCountEquals(2);
-                
-                // Stop and start again, no new message should be received.
-                for (var i = 0; i < 3; i++)
-                {
-                    await managedClient.StopAsync(false);
-                    await LongTestDelay();
-                    await managedClient.StartAsync(managedClientOptions);
-                    await LongTestDelay();
-                }
-
-                receivedMessages.AssertReceivedCountEquals(2);
-            }
-        }
-
         [TestMethod]
         public async Task Connect_To_Invalid_Server()
         {
@@ -181,6 +89,38 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
             }
         }
 
+        [TestMethod]
+        public async Task Expose_Custom_Connection_Error()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                var server = await testEnvironment.StartServer();
+
+                server.ValidatingConnectionAsync += args =>
+                {
+                    args.ReasonCode = MqttConnectReasonCode.BadUserNameOrPassword;
+                    return CompletedTask.Instance;
+                };
+
+                var managedClient = testEnvironment.Factory.CreateManagedMqttClient();
+
+                MqttClientDisconnectedEventArgs disconnectedArgs = null;
+                managedClient.DisconnectedAsync += args =>
+                {
+                    disconnectedArgs = args;
+                    return CompletedTask.Instance;
+                };
+
+                var clientOptions = testEnvironment.Factory.CreateManagedMqttClientOptionsBuilder().WithClientOptions(testEnvironment.CreateDefaultClientOptions()).Build();
+                await managedClient.StartAsync(clientOptions);
+
+                await LongTestDelay();
+
+                Assert.IsNotNull(disconnectedArgs);
+                Assert.AreEqual(MqttClientConnectResultCode.BadUserNameOrPassword, disconnectedArgs.ConnectResult.ResultCode);
+            }
+        }
+
         [TestMethod]
         public async Task ManagedClients_Will_Message_Send()
         {
@@ -224,6 +164,67 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
             }
         }
 
+        [TestMethod]
+        public async Task Receive_While_Not_Cleanly_Disconnected()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                await testEnvironment.StartServer(o => o.WithPersistentSessions());
+
+                var senderClient = await testEnvironment.ConnectClient();
+
+                // Prepare managed client.
+                var managedClient = testEnvironment.Factory.CreateManagedMqttClient();
+                await managedClient.SubscribeAsync("#");
+                var receivedMessages = testEnvironment.CreateApplicationMessageHandler(managedClient);
+
+                var managedClientOptions = new ManagedMqttClientOptions
+                {
+                    ClientOptions = testEnvironment.Factory.CreateClientOptionsBuilder()
+                        .WithTcpServer("127.0.0.1", testEnvironment.ServerPort)
+                        .WithClientId(nameof(Receive_While_Not_Cleanly_Disconnected) + "_managed")
+                        .WithCleanSession(false)
+                        .Build()
+                };
+
+                await managedClient.StartAsync(managedClientOptions);
+                await LongTestDelay();
+                await LongTestDelay();
+
+                // Send test data.
+                await senderClient.PublishStringAsync("topic1");
+                await LongTestDelay();
+                await LongTestDelay();
+
+                receivedMessages.AssertReceivedCountEquals(1);
+
+                // Stop the managed client but keep session at server (not clean disconnect required).
+                await managedClient.StopAsync(false);
+                await LongTestDelay();
+
+                // Send new messages in the meantime.
+                await senderClient.PublishStringAsync("topic2", qualityOfServiceLevel: MqttQualityOfServiceLevel.ExactlyOnce);
+                await LongTestDelay();
+
+                // Start the managed client, it should receive the new message.
+                await managedClient.StartAsync(managedClientOptions);
+                await LongTestDelay();
+
+                receivedMessages.AssertReceivedCountEquals(2);
+
+                // Stop and start again, no new message should be received.
+                for (var i = 0; i < 3; i++)
+                {
+                    await managedClient.StopAsync(false);
+                    await LongTestDelay();
+                    await managedClient.StartAsync(managedClientOptions);
+                    await LongTestDelay();
+                }
+
+                receivedMessages.AssertReceivedCountEquals(2);
+            }
+        }
+
         [TestMethod]
         public async Task Start_Stop()
         {
@@ -375,7 +376,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
                 var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1", testEnvironment.ServerPort);
 
                 var receivedManagedMessages = new List<MqttApplicationMessage>();
-                
+
                 var managedClient = testEnvironment.Factory.CreateManagedMqttClient(testEnvironment.CreateClient());
                 managedClient.ApplicationMessageReceivedAsync += e =>
                 {
@@ -403,7 +404,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
                 // Make sure that it gets received after subscribing again.
                 await managedClient.SubscribeAsync("topic");
                 await LongTestDelay();
-                
+
                 Assert.AreEqual(2, receivedManagedMessages.Count);
             }
         }
@@ -421,7 +422,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
                 var receivingClient = await CreateManagedClientAsync(testEnvironment, null, connectionCheckInterval);
                 var sendingClient = await testEnvironment.ConnectClient();
 
-                await sendingClient.PublishAsync(new MqttApplicationMessage { Topic = "topic", Payload = new byte[] { 1 }, Retain = true });
+                await sendingClient.PublishAsync(new MqttApplicationMessage { Topic = "topic", PayloadSegment = new ArraySegment<byte>(new byte[] { 1 }), Retain = true });
 
                 var subscribeTime = DateTime.UtcNow;
 
@@ -437,6 +438,109 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
             }
         }
 
+
+        [TestMethod]
+        public async Task ManagedClients_CanInterceptPublishedMessage_PreventingPublish()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                await testEnvironment.StartServer();
+
+                var receivedMessagesCount = 0;
+                var interceptedMessagesCount = 0;
+
+                var clientOptions = new MqttClientOptionsBuilder()
+                    .WithTcpServer("127.0.0.1", testEnvironment.ServerPort)
+                    .Build();
+
+                var sendingClient = testEnvironment.CreateClient();
+                var sendingManagedClient = new MQTTnet.Extensions.ManagedClient.ManagedMqttClient(sendingClient, testEnvironment.ClientLogger);
+
+                await sendingManagedClient.StartAsync(new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).Build());
+
+                // Wait until the managed client is fully set up and running.
+                await Task.Delay(1000);
+
+                var receivingClient = await testEnvironment.ConnectClient();
+
+                receivingClient.ApplicationMessageReceivedAsync += e =>
+                {
+                    Interlocked.Increment(ref receivedMessagesCount);
+                    return CompletedTask.Instance;
+                };
+                sendingManagedClient.InterceptPublishMessageAsync += e =>
+                {
+                    Interlocked.Increment(ref interceptedMessagesCount);
+                    e.AcceptPublish = false;
+                    return CompletedTask.Instance;
+                };
+
+                await receivingClient.SubscribeAsync("My/last/will");
+
+                // Wait for arrival of the will message at the receiver.
+                await Task.Delay(5000);
+
+                await sendingManagedClient.EnqueueAsync("My/last/will", "hello world");
+
+                // Wait for arrival of the will message at the receiver.
+                await Task.Delay(5000);
+
+                Assert.AreEqual(0, receivedMessagesCount);
+                Assert.AreEqual(1, interceptedMessagesCount);
+            }
+        }
+
+        [TestMethod]
+        public async Task ManagedClients_CanInterceptPublishedMessage_AllowingPublish()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                await testEnvironment.StartServer();
+
+                var receivedMessagesCount = 0;
+                var interceptedMessagesCount = 0;
+
+                var clientOptions = new MqttClientOptionsBuilder()
+                    .WithTcpServer("127.0.0.1", testEnvironment.ServerPort)
+                    .Build();
+
+                var sendingClient = testEnvironment.CreateClient();
+                var sendingManagedClient = new MQTTnet.Extensions.ManagedClient.ManagedMqttClient(sendingClient, testEnvironment.ClientLogger);
+
+                await sendingManagedClient.StartAsync(new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).Build());
+
+                // Wait until the managed client is fully set up and running.
+                await Task.Delay(1000);
+
+                var receivingClient = await testEnvironment.ConnectClient();
+
+                receivingClient.ApplicationMessageReceivedAsync += e =>
+                {
+                    Interlocked.Increment(ref receivedMessagesCount);
+                    return CompletedTask.Instance;
+                };
+                sendingManagedClient.InterceptPublishMessageAsync += e =>
+                {
+                    Interlocked.Increment(ref interceptedMessagesCount);
+                    e.AcceptPublish = true;
+                    return CompletedTask.Instance;
+                };
+
+                await receivingClient.SubscribeAsync("My/last/will");
+
+                // Wait for arrival of the will message at the receiver.
+                await Task.Delay(5000);
+
+                await sendingManagedClient.EnqueueAsync("My/last/will", "hello world");
+
+                // Wait for arrival of the will message at the receiver.
+                await Task.Delay(5000);
+
+                Assert.AreEqual(1, receivedMessagesCount);
+                Assert.AreEqual(1, interceptedMessagesCount);
+            }
+        }
+
         // This case also serves as a regression test for the previous behavior which re-published
         // each and every existing subscriptions with every new subscription that was made
         // (causing performance problems and having the visible symptom of retained messages being received again)
@@ -454,7 +558,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
                 //wait a bit for the subscription to become established
                 await Task.Delay(500);
 
-                await sendingClient.PublishAsync(new MqttApplicationMessage { Topic = "topic", Payload = new byte[] { 1 }, Retain = true });
+                await sendingClient.PublishAsync(new MqttApplicationMessage { Topic = "topic", PayloadSegment = new ArraySegment<byte>(new byte[] { 1 }), Retain = true });
 
                 var messages = await SetupReceivingOfMessages(managedClient, 1);
 
@@ -471,16 +575,154 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
             }
         }
 
+        [TestMethod]
+        public async Task Subscribe_Does_Not_Hang_On_Server_Stop()
+        {
+            var timeout = TimeSpan.FromSeconds(2);
+            var testTimeout = TimeSpan.FromSeconds(timeout.TotalSeconds * 2);
+            const string topic = "test_topic_2";
+            using (var testEnvironment = CreateTestEnvironment())
+            using (var managedClient = await CreateManagedClientAsync(testEnvironment, timeout: timeout))
+            {
+                testEnvironment.IgnoreClientLogErrors = true;
+                bool reject = true;
+                var receivedOnServer = new SemaphoreSlim(0, 1);
+                var failedOnClient = new SemaphoreSlim(0, 1);
+                testEnvironment.Server.InterceptingInboundPacketAsync += e =>
+                {
+                    if (e.Packet is MqttSubscribePacket)
+                    {
+                        if (reject)
+                        {
+                            e.ProcessPacket = false;
+                        }
+                        receivedOnServer.Release();
+                    }
+
+                    return CompletedTask.Instance;
+                };
+                managedClient.SynchronizingSubscriptionsFailedAsync += e =>
+                {
+                    failedOnClient.Release();
+                    return CompletedTask.Instance;
+                };
+
+                await managedClient.SubscribeAsync(topic);
+                Assert.IsTrue(await receivedOnServer.WaitAsync(testTimeout));
+                Assert.IsTrue(await failedOnClient.WaitAsync(testTimeout));
+
+                reject = false;
+                await managedClient.SubscribeAsync(topic);
+                Assert.IsTrue(await receivedOnServer.WaitAsync(testTimeout));
+            }
+        }
+
+        [TestMethod]
+        public async Task Unsubscribe_Does_Not_Hang_On_Server_Stop()
+        {
+            var timeout = TimeSpan.FromSeconds(2);
+            var testTimeout = TimeSpan.FromSeconds(timeout.TotalSeconds * 2);
+            const string topic = "test_topic_2";
+            using (var testEnvironment = CreateTestEnvironment())
+            using (var managedClient = await CreateManagedClientAsync(testEnvironment, timeout: timeout))
+            {
+                testEnvironment.IgnoreClientLogErrors = true;
+                bool reject = true;
+                var receivedOnServer = new SemaphoreSlim(0, 1);
+                var failedOnClient = new SemaphoreSlim(0, 1);
+                testEnvironment.Server.InterceptingInboundPacketAsync += e =>
+                {
+                    if (e.Packet is MqttUnsubscribePacket)
+                    {
+                        if (reject)
+                        {
+                            e.ProcessPacket = false;
+                        }
+                        receivedOnServer.Release();
+                    }
+                    else if (e.Packet is MqttSubscribePacket)
+                    {
+                        receivedOnServer.Release();
+                    }
+
+                    return CompletedTask.Instance;
+                };
+                managedClient.SynchronizingSubscriptionsFailedAsync += e =>
+                {
+                    failedOnClient.Release();
+                    return CompletedTask.Instance;
+                };
+
+                await managedClient.SubscribeAsync(topic);
+                Assert.IsTrue(await receivedOnServer.WaitAsync(testTimeout));
+
+                await managedClient.UnsubscribeAsync(topic);
+                Assert.IsTrue(await receivedOnServer.WaitAsync(testTimeout));
+                Assert.IsTrue(await failedOnClient.WaitAsync(testTimeout));
+
+                reject = false;
+                await managedClient.UnsubscribeAsync(topic);
+                Assert.IsTrue(await receivedOnServer.WaitAsync(testTimeout));
+            }
+        }
+
+        [TestMethod]
+        public async Task Publish_Does_Not_Hang_On_Server_Error()
+        {
+            var timeout = TimeSpan.FromSeconds(2);
+            var testTimeout = TimeSpan.FromSeconds(timeout.TotalSeconds * 2);
+
+            const string topic = "test_topic_42";
+
+            using (var testEnvironment = CreateTestEnvironment())
+            using (var managedClient = await CreateManagedClientAsync(testEnvironment, timeout: timeout))
+            {
+                testEnvironment.IgnoreClientLogErrors = true;
+                bool reject = true;
+                var receivedOnServer = new TaskCompletionSource<object>();
+                managedClient.ApplicationMessageProcessedAsync += e => Task.FromResult(reject &= e.Exception is null);
+                testEnvironment.Server.InterceptingInboundPacketAsync += e =>
+                {
+                    if (e.Packet is MqttPublishPacket)
+                    {
+                        if (reject)
+                        {
+                            e.ProcessPacket = false;
+                        }
+                        else
+                        {
+                            receivedOnServer.TrySetResult(null);
+                        }
+                    }
+
+                    return CompletedTask.Instance;
+                };
+
+                await managedClient.EnqueueAsync(new MqttApplicationMessage { Topic = topic, PayloadSegment = new ArraySegment<byte>(new byte[] { 1 }), Retain = true, QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce });
+
+                var timeoutTask = Task.Delay(testTimeout);
+
+                var firstDone = await Task.WhenAny(receivedOnServer.Task, timeoutTask);
+                Assert.AreEqual(receivedOnServer.Task, firstDone, "Client is hung on publish!");
+            }
+        }
+
         async Task<MQTTnet.Extensions.ManagedClient.ManagedMqttClient> CreateManagedClientAsync(
             TestEnvironment testEnvironment,
             IMqttClient underlyingClient = null,
             TimeSpan? connectionCheckInterval = null,
-            string host = "localhost")
+            string host = "localhost",
+            TimeSpan? timeout = null)
         {
             await testEnvironment.StartServer();
 
             var clientOptions = new MqttClientOptionsBuilder().WithTcpServer(host, testEnvironment.ServerPort);
 
+            if (timeout != null)
+            {
+                clientOptions.WithTimeout(timeout.Value);
+            }
+
             var managedOptions = new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).Build();
 
             // Use a short connection check interval so that subscription operations are performed quickly

Source/MQTTnet.Tests/Clients/MqttClient/Extended_Authentication_Tests.cs

@@ -1,159 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Text;
-using System.Threading;
-using System.Threading.Tasks;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MQTTnet.Client;
-using MQTTnet.Formatter;
-using MQTTnet.Internal;
-using MQTTnet.Packets;
-using MQTTnet.Protocol;
-
-namespace MQTTnet.Tests.Clients.MqttClient
-{
-    [TestClass]
-    public sealed class Extended_Authentication_Tests : BaseTestClass
-    {
-        [TestMethod]
-        public async Task ReAuthenticate()
-        {
-            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
-            {
-                var server = await testEnvironment.StartServer();
-                
-                server.ValidatingConnectionAsync += async args =>
-                {
-                    using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(10)))
-                    {
-                        // Just do a simple custom authentication.
-                        await args.SendAuthenticationDataAsync(MqttAuthenticateReasonCode.ContinueAuthentication, cancellationToken: timeout.Token);
-                        var clientResponse = await args.ReceiveAuthenticationDataAsync(timeout.Token);
-                        CollectionAssert.AreEqual(clientResponse.AuthenticationData, Encoding.ASCII.GetBytes("TOKEN"));
-
-                        var userProperties = new MqttUserPropertiesBuilder().With("x", "y").Build();
-                        await args.SendAuthenticationDataAsync(MqttAuthenticateReasonCode.ContinueAuthentication, cancellationToken: timeout.Token, userProperties: userProperties);
-                        
-                        args.ReasonCode = MqttConnectReasonCode.Success;
-                    }
-                };
-
-                server.ClientReAuthenticatingAsync += args =>
-                {
-                    
-                    return CompletedTask.Instance;
-                };
-                
-                var client = testEnvironment.CreateClient();
-                client.ExtendedAuthenticationExchangeAsync += async args =>
-                {
-                    await args.SendAuthenticationDataAsync(MqttAuthenticateReasonCode.ContinueAuthentication, Encoding.ASCII.GetBytes("TOKEN"));
-
-                    var serverResponse = await args.ReceiveAuthenticationDataAsync(CancellationToken.None);
-                    Assert.IsNotNull(serverResponse.UserProperties);
-                    Assert.AreEqual("x", serverResponse.UserProperties[0].Name);
-                    Assert.AreEqual("y", serverResponse.UserProperties[0].Value);
-                };
-
-                var clientOptions = testEnvironment.CreateDefaultClientOptionsBuilder().WithTimeout(TimeSpan.FromSeconds(10)).WithAuthentication("CUSTOM").Build();
-                await client.ConnectAsync(clientOptions);
-
-                await LongTestDelay();
-
-                await client.ReAuthenticateAsync();
-
-                await LongTestDelay();
-
-                var pingResult = await client.TryPingAsync();
-                
-                Assert.IsTrue(pingResult);
-            }
-        }
-        
-        [TestMethod]
-        public async Task Use_Extended_Authentication()
-        {
-            var initialContextToken = Encoding.ASCII.GetBytes("initial context token");
-            var replyContextToken = Encoding.ASCII.GetBytes("reply context token");
-            var outcomeOfAuthentication = Encoding.ASCII.GetBytes("outcome of authentication");
-
-            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
-            {
-                var server = await testEnvironment.StartServer();
-                
-                /*
-                Sample flow from RFC:
-                
-                1. Client to Server CONNECT Authentication Method="GS2-KRB5"
-                2. Server to Client AUTH rc=0x18 Authentication Method="GS2-KRB5"
-                3. Client to Server AUTH rc=0x18 Authentication Method="GS2-KRB5" Authentication Data=initial context token
-                4. Server to Client AUTH rc=0x18 Authentication Method="GS2-KRB5" Authentication Data=reply context token
-                5. Client to Server AUTH rc=0x18 Authentication Method="GS2-KRB5"
-                6. Server to Client CONNACK rc=0 Authentication Method="GS2-KRB5" Authentication Data=outcome of authentication
-                 */
-
-                server.ValidatingConnectionAsync += async args =>
-                {
-                    using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(10)))
-                    {
-                        // 1.
-                        if (args.AuthenticationMethod != "GS2-KRB5")
-                        {
-                            args.ReasonCode = MqttConnectReasonCode.BadAuthenticationMethod;
-                            return;
-                        }
-
-                        // 2.
-                        await args.SendAuthenticationDataAsync(MqttAuthenticateReasonCode.ContinueAuthentication, cancellationToken: timeout.Token);
-
-                        // 3.
-                        var clientResponse = await args.ReceiveAuthenticationDataAsync(timeout.Token);
-                        CollectionAssert.AreEqual(clientResponse.AuthenticationData, initialContextToken);
-                        Assert.AreEqual(MqttAuthenticateReasonCode.ContinueAuthentication, clientResponse.ReasonCode);
-
-                        // 4.
-                        await args.SendAuthenticationDataAsync(MqttAuthenticateReasonCode.ContinueAuthentication, replyContextToken, cancellationToken: timeout.Token);
-
-                        // 5.
-                        clientResponse = await args.ReceiveAuthenticationDataAsync(timeout.Token);
-                        Assert.AreEqual(clientResponse.AuthenticationData, null);
-                        Assert.AreEqual(MqttAuthenticateReasonCode.ContinueAuthentication, clientResponse.ReasonCode);
-
-                        // 6.
-                        args.ResponseAuthenticationData = outcomeOfAuthentication;
-                        args.ReasonCode = MqttConnectReasonCode.Success;
-                    }
-                };
-
-                var client = testEnvironment.CreateClient();
-                client.ExtendedAuthenticationExchangeAsync += async args =>
-                {
-                    if (args.AuthenticationMethod != "GS2-KRB5")
-                    {
-                        Assert.Fail("Authentication method is wrong.");
-                    }
-
-                    // 2. THE FACT THAT THE SERVER SENDS THE AUTH PACKET WILL TRIGGER THIS EVENT SO THE INITIAL DATA IS IN THE EVENT ARGS!
-                    Assert.AreEqual(MqttAuthenticateReasonCode.ContinueAuthentication, args.ReasonCode);
-                    
-                    // 3.
-                    await args.SendAuthenticationDataAsync(MqttAuthenticateReasonCode.ContinueAuthentication, initialContextToken);
-
-                    // 4.
-                    var serverResponse = await args.ReceiveAuthenticationDataAsync(CancellationToken.None);
-                    CollectionAssert.AreEqual(serverResponse.AuthenticationData, replyContextToken);
-                    Assert.AreEqual(MqttAuthenticateReasonCode.ContinueAuthentication, serverResponse.ReasonCode);
-                    
-                    // 5.
-                    await args.SendAuthenticationDataAsync(MqttAuthenticateReasonCode.ContinueAuthentication);
-                };
-
-                var clientOptions = testEnvironment.CreateDefaultClientOptionsBuilder().WithTimeout(TimeSpan.FromSeconds(10)).WithAuthentication("GS2-KRB5").Build();
-                await client.ConnectAsync(clientOptions);
-            }
-        }
-    }
-}

Source/MQTTnet.Tests/Clients/MqttClient/MqttClient_Connection_Tests.cs

@@ -3,6 +3,8 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Generic;
+using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
@@ -10,6 +12,7 @@ using MQTTnet.Client;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
 using MQTTnet.Internal;
+using MQTTnet.Packets;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
 
@@ -63,7 +66,7 @@ namespace MQTTnet.Tests.Clients.MqttClient
                         return CompletedTask.Instance;
                     };
 
-                    await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("1.2.3.4").Build());
+                    await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1").Build());
 
                     Assert.Fail("Must fail!");
                 }
@@ -128,7 +131,7 @@ namespace MQTTnet.Tests.Clients.MqttClient
                 await client.DisconnectAsync(disconnectOptions);
 
                 await LongTestDelay();
-                
+
                 Assert.IsNotNull(eventArgs);
                 Assert.AreEqual(MqttDisconnectReasonCode.MessageRateTooHigh, eventArgs.ReasonCode);
             }
@@ -156,7 +159,7 @@ namespace MQTTnet.Tests.Clients.MqttClient
                 await client.DisconnectAsync(disconnectOptions);
 
                 await LongTestDelay();
-                
+
                 Assert.IsNotNull(eventArgs);
                 Assert.IsNotNull(eventArgs.UserProperties);
                 Assert.AreEqual(1, eventArgs.UserProperties.Count);
@@ -164,5 +167,174 @@ namespace MQTTnet.Tests.Clients.MqttClient
                 Assert.AreEqual("test_value", eventArgs.UserProperties[0].Value);
             }
         }
+
+        class TestClientKerberosAuthenticationHandler : IMqttExtendedAuthenticationExchangeHandler
+        {
+            public static IReadOnlyList<string> ServerTokens { get; } = new List<string>()
+            {
+                string.Empty,
+                "reply context token"
+            };
+
+            public static IReadOnlyList<string> ClientTokens { get; } = new List<string>()
+            {
+                string.Empty,
+                "initial context token",
+                string.Empty
+            };
+
+            int tokenCursor;
+
+            public async Task HandleRequestAsync(MqttExtendedAuthenticationExchangeContext context)
+            {
+                if (context.AuthenticationMethod != "GS2-KRB5")
+                {
+                    throw new InvalidOperationException("Wrong authentication method");
+                }
+
+                Assert.IsTrue(tokenCursor < ServerTokens.Count, "No more server tokens were expected.");
+                var expectedToken = ServerTokens[tokenCursor++];
+                Assert.AreEqual(expectedToken, Encoding.UTF8.GetString(context.AuthenticationData));
+
+                var sendOptions = new MqttExtendedAuthenticationExchangeData
+                {
+                    AuthenticationData = Encoding.UTF8.GetBytes(ClientTokens[tokenCursor])
+                };
+
+                await context.Client.SendExtendedAuthenticationExchangeDataAsync(sendOptions, context.CancellationToken);
+            }
+        }
+
+        [TestMethod]
+        public async Task Use_Extended_Authentication()
+        {
+            // Use Kerberos sample from the MQTT RFC.
+            var kerberosAuthenticationHandler = new TestClientKerberosAuthenticationHandler();
+
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                var server = await testEnvironment.StartServer();
+
+                server.ValidatingConnectionAsync += async args =>
+                {
+                    if (args.AuthenticationMethod == "GS2-KRB5")
+                    {
+                        var authenticationData = args.AuthenticationData;
+                        string expectedToken;
+                        int tokenCursor;
+                        for (tokenCursor = 0; tokenCursor < TestClientKerberosAuthenticationHandler.ServerTokens.Count; tokenCursor++)
+                        {
+                            expectedToken = TestClientKerberosAuthenticationHandler.ClientTokens[tokenCursor];
+                            Assert.AreEqual(expectedToken, Encoding.UTF8.GetString(authenticationData), "The received client token is not correct.");
+
+                            var serverToken = TestClientKerberosAuthenticationHandler.ServerTokens[tokenCursor];
+                            var authOptions = testEnvironment.Factory.CreateMqttExtendedAuthenticationExchangeOptionsBuilder().WithAuthenticationData(serverToken).Build();
+                            var result = await args.SendExtendedAuthenticationExchangeDataAsync(authOptions);
+
+                            authenticationData = result.AuthenticationData;
+                        }
+
+                        expectedToken = TestClientKerberosAuthenticationHandler.ClientTokens[tokenCursor];
+                        Assert.AreEqual(expectedToken, Encoding.UTF8.GetString(authenticationData), "The received client token is not correct.");
+                        args.ResponseAuthenticationData = Encoding.UTF8.GetBytes("outcome of authentication");
+                        args.ReasonCode = MqttConnectReasonCode.Success;
+                        args.ReasonString = "Authentication successful";
+                    }
+                    else
+                    {
+                        args.ReasonCode = MqttConnectReasonCode.BadAuthenticationMethod;
+                    }
+                };
+
+                var clientOptions = testEnvironment.CreateDefaultClientOptionsBuilder().WithAuthentication("GS2-KRB5", new byte[0]).WithExtendedAuthenticationExchangeHandler(kerberosAuthenticationHandler);
+                var client = await testEnvironment.ConnectClient(clientOptions);
+
+                Assert.IsTrue(client.IsConnected);
+            }
+        }
+
+        [TestMethod]
+        public async Task No_Unobserved_Exception()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                testEnvironment.IgnoreClientLogErrors = true;
+
+                var client = testEnvironment.CreateClient();
+                var options = new MqttClientOptionsBuilder().WithTcpServer("1.2.3.4").WithTimeout(TimeSpan.FromSeconds(2)).Build();
+
+                try
+                {
+                    using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(0.5)))
+                    {
+                        await client.ConnectAsync(options, timeout.Token);
+                    }
+                }
+                catch (OperationCanceledException)
+                {
+                }
+
+                client.Dispose();
+
+                // These delays and GC calls are required in order to make calling the finalizer reproducible.
+                GC.Collect();
+                GC.WaitForPendingFinalizers();
+                await LongTestDelay();
+                await LongTestDelay();
+                await LongTestDelay();
+            }
+        }
+
+        [TestMethod]
+        public async Task Return_Non_Success()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                var server = await testEnvironment.StartServer();
+
+                server.ValidatingConnectionAsync += args =>
+                {
+                    args.ResponseUserProperties = new List<MqttUserProperty>
+                    {
+                        new MqttUserProperty("Property", "Value")
+                    };
+
+                    args.ReasonCode = MqttConnectReasonCode.QuotaExceeded;
+
+                    return CompletedTask.Instance;
+                };
+
+                var client = testEnvironment.CreateClient();
+
+                var response = await client.ConnectAsync(testEnvironment.CreateDefaultClientOptionsBuilder().WithoutThrowOnNonSuccessfulConnectResponse().Build());
+
+                Assert.IsNotNull(response);
+                Assert.AreEqual(MqttClientConnectResultCode.QuotaExceeded, response.ResultCode);
+                Assert.AreEqual(response.UserProperties[0].Name, "Property");
+                Assert.AreEqual(response.UserProperties[0].Value, "Value");
+            }
+        }
+
+        [TestMethod]
+        public async Task Throw_Proper_Exception_When_Not_Connected()
+        {
+            try
+            {
+                var mqttFactory = new MqttFactory();
+                using (var mqttClient = mqttFactory.CreateMqttClient())
+                {
+                    await mqttClient.SubscribeAsync("test", MqttQualityOfServiceLevel.AtLeastOnce);
+                }
+            }
+            catch (MqttClientNotConnectedException exception)
+            {
+                if (exception.Message == "The MQTT client is not connected.")
+                {
+                    return;
+                }
+            }
+
+            Assert.Fail();
+        }
     }
 }

Source/MQTTnet.Tests/Clients/MqttClient/MqttClient_Tests.cs

@@ -6,6 +6,7 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using System.Net;
 using System.Net.Sockets;
 using System.Text;
 using System.Threading;
@@ -17,6 +18,7 @@ using MQTTnet.Formatter;
 using MQTTnet.Internal;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
+using MQTTnet.Server;
 using MQTTnet.Tests.Mockups;
 
 // ReSharper disable InconsistentNaming
@@ -85,7 +87,7 @@ namespace MQTTnet.Tests.Clients.MqttClient
                 await client.ConnectAsync(clientOptions);
             }
         }
-        
+
         [TestMethod]
         [ExpectedException(typeof(InvalidOperationException))]
         public async Task Connect_Multiple_Times_Should_Fail()
@@ -296,7 +298,7 @@ namespace MQTTnet.Tests.Clients.MqttClient
 
                 Assert.IsNotNull(receivedMessage);
                 Assert.AreEqual("A", receivedMessage.Topic);
-                Assert.AreEqual(null, receivedMessage.Payload);
+                Assert.AreEqual(null, receivedMessage.PayloadSegment.Array);
             }
         }
 
@@ -507,7 +509,7 @@ namespace MQTTnet.Tests.Clients.MqttClient
 
                 client2.ApplicationMessageReceivedAsync += e =>
                 {
-                    client2TopicResults.Add(Encoding.UTF8.GetString(e.ApplicationMessage.Payload));
+                    client2TopicResults.Add(Encoding.UTF8.GetString(e.ApplicationMessage.PayloadSegment.ToArray()));
                     return CompletedTask.Instance;
                 };
 
@@ -747,8 +749,8 @@ namespace MQTTnet.Tests.Clients.MqttClient
                 {
                     if (e.ApplicationMessage.Topic == "request")
                     {
-                        // Use AtMostOnce here because with QoS 1 or even QoS 2 the process waits for 
+                        // Use AtMostOnce here because with QoS 1 or even QoS 2 the process waits for
-                        // the ACK etc. The problem is that the SpinUntil below only waits until the 
+                        // the ACK etc. The problem is that the SpinUntil below only waits until the
                         // flag is set. It does not wait until the client has sent the ACK
                         await client2.PublishStringAsync("reply");
                     }
@@ -924,5 +926,54 @@ namespace MQTTnet.Tests.Clients.MqttClient
                 Assert.IsFalse(disconnectedFired);
             }
         }
+
+        [TestMethod]
+        public void Backward_compatible_TCP_options()
+        {
+            var options = new MqttClientOptionsBuilder().WithTcpServer("host", 3).Build();
+
+            Assert.AreEqual("host", ((MqttClientTcpOptions)options.ChannelOptions).Server);
+            Assert.AreEqual(3, ((MqttClientTcpOptions)options.ChannelOptions).Port);
+
+            options = new MqttClientOptions
+            {
+                ChannelOptions = new MqttClientTcpOptions
+                {
+                    Server = "host",
+                    Port = 3
+                }
+            };
+
+            Assert.AreEqual("host:3", options.ChannelOptions.ToString());
+            Assert.AreEqual("host", ((MqttClientTcpOptions)options.ChannelOptions).Server);
+            Assert.AreEqual(3, ((MqttClientTcpOptions)options.ChannelOptions).Port);
+
+            options = new MqttClientOptionsBuilder().WithEndPoint(new DnsEndPoint("host", 3)).Build();
+            Assert.AreEqual("Unspecified/host:3", options.ChannelOptions.ToString());
+            Assert.AreEqual("host", ((MqttClientTcpOptions)options.ChannelOptions).Server);
+            Assert.AreEqual(3, ((MqttClientTcpOptions)options.ChannelOptions).Port);
+
+            options = new MqttClientOptionsBuilder().WithTcpServer("host").Build();
+
+            Assert.AreEqual("host", ((MqttClientTcpOptions)options.ChannelOptions).Server);
+            Assert.AreEqual(1883, ((MqttClientTcpOptions)options.ChannelOptions).Port);
+            Assert.AreEqual("Unspecified/host:1883", options.ChannelOptions.ToString());
+
+            options = new MqttClientOptionsBuilder().WithTlsOptions(o => o.UseTls()).WithTcpServer("host").Build();
+
+            Assert.AreEqual("host", ((MqttClientTcpOptions)options.ChannelOptions).Server);
+            Assert.AreEqual(8883, ((MqttClientTcpOptions)options.ChannelOptions).Port);
+
+            options = new MqttClientOptions
+            {
+                ChannelOptions = new MqttClientTcpOptions
+                {
+                    Server = "host"
+                }
+            };
+
+            Assert.AreEqual("host", ((MqttClientTcpOptions)options.ChannelOptions).Server);
+            Assert.AreEqual(null, ((MqttClientTcpOptions)options.ChannelOptions).Port);
+        }
     }
 }

Source/MQTTnet.Tests/Extension_Tests.cs

@@ -1,98 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Linq;
-using System.Threading;
-using System.Threading.Tasks;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MQTTnet.Exceptions;
-using MQTTnet.Internal;
-
-namespace MQTTnet.Tests
-{
-    [TestClass]
-    public class Extension_Tests
-    {
-        [ExpectedException(typeof(MqttCommunicationTimedOutException))]
-        [TestMethod]
-        public async Task TimeoutAfter()
-        {
-            await MqttTaskTimeout.WaitAsync(ct => Task.Delay(TimeSpan.FromMilliseconds(500), ct),
-                TimeSpan.FromMilliseconds(100), CancellationToken.None);
-        }
-
-        [ExpectedException(typeof(MqttCommunicationTimedOutException))]
-        [TestMethod]
-        public async Task TimeoutAfterWithResult()
-        {
-            await MqttTaskTimeout.WaitAsync(
-                ct => Task.Delay(TimeSpan.FromMilliseconds(500), ct).ContinueWith(t => 5, ct),
-                TimeSpan.FromMilliseconds(100), CancellationToken.None);
-        }
-        
-        [TestMethod]
-        public async Task TimeoutAfterWithInnerException()
-        {
-            try
-            {
-                await MqttTaskTimeout.WaitAsync(ct => Task.Run(() =>
-                {
-                    var iis = new int[0];
-                    iis[1] = 0;
-                }, ct), TimeSpan.FromSeconds(1), CancellationToken.None);
-
-                Assert.Fail();
-            }
-            catch (Exception e)
-            {
-                Assert.IsTrue(e is IndexOutOfRangeException);
-            }
-        }
-
-        [TestMethod]
-        public async Task TimeoutAfterWithInnerExceptionWithResult()
-        {
-            try
-            {
-                await MqttTaskTimeout.WaitAsync(ct => Task.Run(() =>
-                {
-                    var iis = new int[0];
-                    iis[1] = 0;
-                    return iis[0];
-                }, ct), TimeSpan.FromSeconds(1), CancellationToken.None);
-
-                Assert.Fail();
-            }
-            catch (Exception e)
-            {
-                Assert.IsTrue(e is IndexOutOfRangeException);
-            }
-        }
-
-        [TestMethod]
-        public async Task TimeoutAfterMemoryUsage()
-        {
-            var initialMemory = GC.GetTotalMemory(true);
-
-            var tasks = Enumerable.Range(0, 100000)
-                .Select(i =>
-                {
-                    return MqttTaskTimeout.WaitAsync(ct => Task.Delay(TimeSpan.FromMilliseconds(1), ct),
-                        TimeSpan.FromMinutes(1), CancellationToken.None);
-                });
-
-            await Task.WhenAll(tasks);
-            AssertIsLess(initialMemory + 2_000_000, GC.GetTotalMemory(true));
-        }
-
-        static void AssertIsLess(long bound, long actual)
-        {
-            if (bound < actual)
-            {
-                Assert.Fail($"value must be less than {bound:N0} but is {actual:N0}");
-            }
-        }
-    }
-}

Source/MQTTnet.Tests/Extensions/MqttTopicTemplate_Tests.cs

@@ -0,0 +1,273 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Linq;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Exceptions;
+using MQTTnet.Extensions.TopicTemplate;
+
+namespace MQTTnet.Tests.Extensions
+{
+    [TestClass]
+    public sealed class MqttTopicTemplate_Tests
+    {
+        [TestMethod]
+        public void BasicOps()
+        {
+            var template = new MqttTopicTemplate("A/B/{param}/D");
+            Assert.AreEqual("A/B/C/D", template.WithParameter("param", "C").Template);
+            Assert.AreEqual("A/B/+/D", template.WithoutParameter("param").Template);
+            Assert.AreEqual("A/B/+/D", template.TopicFilter);
+            Assert.AreEqual("A/B/+/D/#", template.TopicTreeRootFilter);
+
+            // corner cases
+            Assert.AreEqual("#", new MqttTopicTemplate("#").TopicFilter);
+            Assert.AreEqual("+", new MqttTopicTemplate("+").TopicFilter);
+            Assert.AreEqual("/", new MqttTopicTemplate("/").TopicFilter);
+        }
+
+        [TestMethod]
+        public void BasicOpsWithHash()
+        {
+            var template = new MqttTopicTemplate("A/B/{param}/D/#");
+            Assert.AreEqual("A/B/C/D/#", template.WithParameter("param", "C").Template);
+            Assert.AreEqual("A/B/+/D/#", template.WithoutParameter("param").Template);
+            Assert.AreEqual("A/B/+/D/#", template.TopicFilter);
+            Assert.AreEqual("A/B/+/D/#", template.TopicTreeRootFilter);
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(ArgumentException))]
+        public void RejectsReservedChars1()
+        {
+            var template = new MqttTopicTemplate("A/B/{foo}/D");
+            template.WithParameter("foo", "a#");
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(ArgumentException))]
+        public void RejectsReservedChars2()
+        {
+            var template = new MqttTopicTemplate("A/B/{foo}/D");
+            template.WithParameter("foo", "a+b");
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(ArgumentException))]
+        public void RejectsReservedChars3()
+        {
+            var template = new MqttTopicTemplate("A/B/{foo}/D");
+            template.WithParameter("foo", "a/b");
+        }
+        
+        [TestMethod]
+        public void AcceptsEmptyValue()
+        {
+            var template = new MqttTopicTemplate("A/B/{foo}/D");
+            template.WithParameter("foo", "");
+        }
+        
+        [TestMethod]
+        [ExpectedException(typeof(MqttProtocolViolationException))]
+        public void RejectsEmptyTemplate()
+        {
+            var _ = new MqttTopicTemplate("");
+        }
+        
+        [TestMethod]
+        [ExpectedException(typeof(ArgumentNullException))]
+        public void RejectsNullTemplate()
+        {
+            var _ = new MqttTopicTemplate(null);
+        }
+
+        
+        [TestMethod]
+        public void IgnoresEmptyParameters()
+        {
+            var template = new MqttTopicTemplate("A/B/{}/D");
+            Assert.IsFalse(template.Parameters.Any());
+        }
+        
+        [TestMethod]
+        public void AcceptsValidTopics()
+        {
+            _ = new MqttTopicTemplate("A");
+            _ = new MqttTopicTemplate("/");
+            _ = new MqttTopicTemplate("/A");
+            _ = new MqttTopicTemplate("A/#");
+            _ = new MqttTopicTemplate("$SYS/#");
+            _ = new MqttTopicTemplate("////");
+            _ = new MqttTopicTemplate("A/B/{foo}/D/");
+        }
+
+        [TestMethod]
+        public void DynamicRoutingSupport()
+        {
+            var v1template = new MqttTopicTemplate("A/v1/{id}/F");
+            var v2template = new MqttTopicTemplate("A/v2/foo/{id}/{bar}");
+            var incoming_v1_topic = "A/v1/32/F";
+
+            var compat_v2_topic = v2template
+                .WithParameterValuesFrom(
+                    v1template.ParseParameterValues(incoming_v1_topic))
+                .WithParameter("bar", "unknown");
+
+            // id: 32 was relocated and bar: unknown added
+            Assert.AreEqual("A/v2/foo/32/unknown", compat_v2_topic.Template);
+        }
+
+        [TestMethod]
+        public void SubscriptionSupport()
+        {
+            var template = new MqttTopicTemplate("A/v1/{param}/F");
+            var filter = template.BuildFilter()
+                .WithAtLeastOnceQoS()
+                .WithNoLocal()
+                .Build();
+            Assert.AreEqual("A/v1/+/F", filter.Topic);
+        }
+
+        [TestMethod]
+        public void SubscriptionSupport2()
+        {
+            var template = new MqttTopicTemplate("A/v1/{param}/F");
+            
+            var subscribeOptions = new MqttFactory().CreateSubscribeOptionsBuilder()
+                .WithTopicTemplate(template)
+                .WithSubscriptionIdentifier(5)
+                .Build();
+            Assert.AreEqual("A/v1/+/F", subscribeOptions.TopicFilters[0].Topic);
+        }
+
+        [TestMethod]
+        public void SendAndSubscribeSupport()
+        {
+            var template = new MqttTopicTemplate("App/v1/{sender}/message");
+
+            var filter = new MqttTopicFilterBuilder()
+                .WithTopicTemplate(template)
+                .WithAtLeastOnceQoS()
+                .WithNoLocal()
+                .Build();
+
+            Assert.AreEqual("App/v1/+/message", filter.Topic);
+
+            var myTopic = template.WithParameter("sender", "me, myself & i");
+
+            var message = new MqttApplicationMessageBuilder()
+                .WithTopicTemplate(
+                    myTopic)
+                .WithPayload("Hello!")
+                .Build();
+
+            Assert.IsTrue(message.MatchesTopicTemplate(template));
+        }
+
+        [TestMethod]
+        public void SendAndSubscribeSupport2()
+        {
+            var template = new MqttTopicTemplate("App/v1/{sender}/message");
+            Assert.ThrowsException<ArgumentException>(() => 
+                template.BuildMessage());
+        }
+
+        [TestMethod]
+        public void CanonicalPrefixFilter()
+        {
+            var template1 = new MqttTopicTemplate("A/v1/{param}/F");
+            var template2 = new MqttTopicTemplate("A/v1/E/F");
+            var template3 = new MqttTopicTemplate("A/v1/E/F/G/H");
+            var canonicalFilter = MqttTopicTemplate.FindCanonicalPrefix(new[] { template1, template2, template3 });
+            // possible improvement: Assert.AreEqual("A/v1/+/F", canonicalFilter.TopicFilter);
+            Assert.AreEqual("A/v1/+", canonicalFilter.TopicFilter);
+            Assert.AreEqual("A/v1/+/#", canonicalFilter.TopicTreeRootFilter);
+            
+            var template2b = new MqttTopicTemplate("A/v1/E/X");
+            canonicalFilter = MqttTopicTemplate.FindCanonicalPrefix(new[] { template1, template2, template3, template2b });
+            Assert.AreEqual("A/v1/+", canonicalFilter.Template);
+            Assert.AreEqual("A/v1/+", canonicalFilter.TopicFilter);
+            Assert.AreEqual("A/v1/+/#", canonicalFilter.TopicTreeRootFilter);
+
+
+            var template4 = new MqttTopicTemplate("A/v2/{prefix}");
+            var canonicalFilter2 = MqttTopicTemplate.FindCanonicalPrefix(new[] { template1, template2, template3, template4 });
+            Assert.AreEqual("A/+", canonicalFilter2.TopicFilter);
+            Assert.AreEqual("A/+/#", canonicalFilter2.TopicTreeRootFilter);
+        }
+        
+        [TestMethod]
+        public void CanonicalPrefixFilterSimple1()
+        {
+            var template = MqttTopicTemplate.FindCanonicalPrefix(new[]
+            {
+                new MqttTopicTemplate("A"),
+                new MqttTopicTemplate("B")
+            });
+            Assert.AreEqual("#", template.TopicFilter);
+            Assert.AreEqual("#", template.Template);
+        }
+        
+        [TestMethod]
+        public void CanonicalPrefixFilterSimple2()
+        {
+            var template = MqttTopicTemplate.FindCanonicalPrefix(new[]
+            {
+                new MqttTopicTemplate("A/v1/{param}/F/"),
+                new MqttTopicTemplate("A/v1/E/X")
+            });
+            Assert.AreEqual("A/v1/+", template.TopicFilter);
+        }
+        
+        [TestMethod]
+        public void CanonicalPrefixFilterSimple3()
+        {
+            var template = MqttTopicTemplate.FindCanonicalPrefix(new[]
+            {
+                new MqttTopicTemplate("A/v1/{param}/F"),
+                new MqttTopicTemplate("A/v1/{param}/F/X")
+            });
+            Assert.AreEqual("A/v1/+/+", template.TopicFilter);
+            Assert.AreEqual("A/v1/{param}/+", template.Template);
+        }
+        
+        [TestMethod]
+        public void CanonicalPrefixFilterSimple4()
+        {
+            var template = MqttTopicTemplate.FindCanonicalPrefix(new[]
+            {
+                new MqttTopicTemplate("A/v1/{param}/FFA"),
+                new MqttTopicTemplate("A/v1/{param}/FX")
+            });
+            Assert.AreEqual("A/v1/+/+", template.TopicFilter);
+            Assert.AreEqual("A/v1/{param}/+", template.Template);
+        }
+        
+        
+        [TestMethod]
+        public void CanonicalPrefixFilterSimple5()
+        {
+            var template = MqttTopicTemplate.FindCanonicalPrefix(new[]
+            {
+                new MqttTopicTemplate("A/v1/E/F/G/H"),
+                new MqttTopicTemplate("A/v2/{param}")
+            });
+            Assert.AreEqual("A/+", template.TopicFilter);
+            Assert.AreEqual("A/+/#", template.TopicTreeRootFilter);
+        }
+        
+        [TestMethod]
+        public void CanonicalPrefixFilterSimple6()
+        {
+            var template = MqttTopicTemplate.FindCanonicalPrefix(new[]
+            {
+                new MqttTopicTemplate("A/{version}/E/F/G/H"),
+                new MqttTopicTemplate("A/{version}/{param}")
+            });
+            Assert.AreEqual("A/+/+", template.TopicFilter);
+            Assert.AreEqual("A/+/+/#", template.TopicTreeRootFilter);
+        }
+    }
+}

Source/MQTTnet.Tests/Extensions/Rpc_Tests.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Generic;
 using System.Text;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
@@ -45,6 +46,34 @@ namespace MQTTnet.Tests.Extensions
             }
         }
 
+        [TestMethod]
+        public async Task Execute_Success_Parameters_Propagated_Correctly()
+        {
+            var paramValue = "123";
+            var parameters = new Dictionary<string, object>
+            {
+                { TestParametersTopicGenerationStrategy.ExpectedParamName, "123" }
+            };
+
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                await testEnvironment.StartServer();
+
+                var responseSender = await testEnvironment.ConnectClient(new MqttClientOptionsBuilder());
+                await responseSender.SubscribeAsync($"MQTTnet.RPC/+/ping/{paramValue}");
+
+                responseSender.ApplicationMessageReceivedAsync += e => responseSender.PublishStringAsync(e.ApplicationMessage.Topic + "/response", "pong");
+
+                using (var rpcClient = await testEnvironment.ConnectRpcClient(new MqttRpcClientOptionsBuilder()
+                           .WithTopicGenerationStrategy(new TestParametersTopicGenerationStrategy()).Build()))
+                {
+                    var response = await rpcClient.ExecuteAsync(TimeSpan.FromSeconds(5), "ping", "", MqttQualityOfServiceLevel.AtMostOnce, parameters);
+
+                    Assert.AreEqual("pong", Encoding.UTF8.GetString(response));
+                }
+            }
+        }
+
         [TestMethod]
         public Task Execute_Success_With_QoS_0()
         {
@@ -135,7 +164,7 @@ namespace MQTTnet.Tests.Extensions
 
                 using (var rpcClient = new MqttRpcClient(requestSender, new MqttRpcClientOptionsBuilder().Build()))
                 {
-                    var response = await rpcClient.ExecuteAsync(TimeSpan.FromSeconds(2), "ping", "", MqttQualityOfServiceLevel.AtMostOnce);
+                    await rpcClient.ExecuteAsync(TimeSpan.FromSeconds(2), "ping", "", MqttQualityOfServiceLevel.AtMostOnce);
                 }
             }
         }
@@ -222,5 +251,32 @@ namespace MQTTnet.Tests.Extensions
                 };
             }
         }
+
+        class TestParametersTopicGenerationStrategy : IMqttRpcClientTopicGenerationStrategy
+        {
+            internal const string ExpectedParamName = "test_param_name";
+
+            public MqttRpcTopicPair CreateRpcTopics(TopicGenerationContext context)
+            {
+                if (context.Parameters == null)
+                {
+                    throw new InvalidOperationException("Parameters dictionary expected to be not null");
+                }
+
+                if (!context.Parameters.TryGetValue(ExpectedParamName, out var paramValue))
+                {
+                    throw new InvalidOperationException($"Parameter with name {ExpectedParamName} not present");
+                }
+
+                var requestTopic = $"MQTTnet.RPC/{Guid.NewGuid():N}/{context.MethodName}/{paramValue}";
+                var responseTopic = requestTopic + "/response";
+
+                return new MqttRpcTopicPair
+                {
+                    RequestTopic = requestTopic,
+                    ResponseTopic = responseTopic
+                };
+            }
+        }
     }
 }

Source/MQTTnet.Tests/Extensions/WebSocket4Net_Tests.cs

@@ -23,7 +23,7 @@ namespace MQTTnet.Tests.Extensions
 
             using (var client = factory.CreateMqttClient())
             {
-                var options = new MqttClientOptionsBuilder().WithWebSocketServer("ws://a.b/mqtt").WithTimeout(TimeSpan.FromSeconds(2)).Build();
+                var options = new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("ws://a.b/mqtt")).WithTimeout(TimeSpan.FromSeconds(2)).Build();
                 await client.ConnectAsync(options).ConfigureAwait(false);
             }
         }

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V3_Tests.cs

@@ -78,7 +78,7 @@ namespace MQTTnet.Tests.Formatter
             Assert.IsNull(deserialized.UserProperties); // Not supported in v3.1.1
         }
         
-                [TestMethod]
+        [TestMethod]
         public void Serialize_Full_MqttConnAckPacket_V310()
         {
             var connAckPacket = new MqttConnAckPacket

Source/MQTTnet.Tests/Internal/CrossPlatformSocket_Tests.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Net.Sockets;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
@@ -17,7 +18,7 @@ namespace MQTTnet.Tests.Internal
         [TestMethod]
         public async Task Connect_Send_Receive()
         {
-            var crossPlatformSocket = new CrossPlatformSocket();
+            var crossPlatformSocket = new CrossPlatformSocket(ProtocolType.Tcp);
             await crossPlatformSocket.ConnectAsync("www.google.de", 80, CancellationToken.None);
 
             var requestBuffer = Encoding.UTF8.GetBytes("GET / HTTP/1.1\r\nHost: www.google.de\r\n\r\n");
@@ -36,7 +37,7 @@ namespace MQTTnet.Tests.Internal
         [ExpectedException(typeof(OperationCanceledException))]
         public async Task Try_Connect_Invalid_Host()
         {
-            var crossPlatformSocket = new CrossPlatformSocket();
+            var crossPlatformSocket = new CrossPlatformSocket(ProtocolType.Tcp);
 
             var cancellationToken = new CancellationTokenSource(TimeSpan.FromSeconds(5));
             cancellationToken.Token.Register(() => crossPlatformSocket.Dispose());
@@ -65,7 +66,7 @@ namespace MQTTnet.Tests.Internal
         [TestMethod]
         public void Set_Options()
         {
-            var crossPlatformSocket = new CrossPlatformSocket();
+            var crossPlatformSocket = new CrossPlatformSocket(ProtocolType.Tcp);
 
             Assert.IsFalse(crossPlatformSocket.ReuseAddress);
             crossPlatformSocket.ReuseAddress = true;

Source/MQTTnet.Tests/MQTTnet.Tests.csproj

@@ -1,7 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFrameworks>net452;net461;net48;netcoreapp3.1;net6.0;net7.0</TargetFrameworks>
+        <TargetFrameworks>netcoreapp3.1;net7.0</TargetFrameworks>
+        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net48</TargetFrameworks>
         <IsPackable>false</IsPackable>
         <LangVersion>7.3</LangVersion>
         <EnableNETAnalyzers>false</EnableNETAnalyzers>
@@ -20,6 +21,7 @@
         <ProjectReference Include="..\..\Source\MQTTnet.Extensions.ManagedClient\MQTTnet.Extensions.ManagedClient.csproj" />
         <ProjectReference Include="..\..\Source\MQTTnet.Extensions.Rpc\MQTTnet.Extensions.Rpc.csproj" />
         <ProjectReference Include="..\..\Source\MQTTnet\MQTTnet.csproj" />
+        <ProjectReference Include="..\MQTTnet.Extensions.TopicTemplate\MQTTnet.Extensions.TopicTemplate.csproj" />
         <ProjectReference Include="..\MQTTnet.Extensions.WebSocket4Net\MQTTnet.Extensions.WebSocket4Net.csproj" />
     </ItemGroup>
 

Source/MQTTnet.Tests/MQTTv5/Client_Tests.cs

@@ -273,7 +273,7 @@ namespace MQTTnet.Tests.MQTTv5
                 Assert.AreEqual(applicationMessage.ResponseTopic, receivedMessage.ResponseTopic);
                 Assert.AreEqual(applicationMessage.MessageExpiryInterval, receivedMessage.MessageExpiryInterval);
                 CollectionAssert.AreEqual(applicationMessage.CorrelationData, receivedMessage.CorrelationData);
-                CollectionAssert.AreEqual(applicationMessage.Payload, receivedMessage.Payload);
+                CollectionAssert.AreEqual(applicationMessage.PayloadSegment.ToArray(), receivedMessage.PayloadSegment.ToArray());
                 CollectionAssert.AreEqual(applicationMessage.UserProperties, receivedMessage.UserProperties);
             }
         }

Source/MQTTnet.Tests/MQTTv5/Server_Tests.cs

@@ -10,6 +10,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Internal;
 using MQTTnet.Protocol;
+using MQTTnet.Server;
 
 namespace MQTTnet.Tests.MQTTv5
 {

Source/MQTTnet.Tests/Mockups/TestEnvironment.cs

@@ -25,7 +25,6 @@ namespace MQTTnet.Tests.Mockups
     {
         readonly List<string> _clientErrors = new List<string>();
         readonly List<IMqttClient> _clients = new List<IMqttClient>();
-
         readonly List<Exception> _exceptions = new List<Exception>();
         readonly List<ILowLevelMqttClient> _lowLevelClients = new List<ILowLevelMqttClient>();
         readonly MqttProtocolVersion _protocolVersion;
@@ -40,6 +39,8 @@ namespace MQTTnet.Tests.Mockups
             _protocolVersion = protocolVersion;
             TestContext = testContext;
 
+            TaskScheduler.UnobservedTaskException += TrackUnobservedTaskException;
+
             ServerLogger.LogMessagePublished += (s, e) =>
             {
                 if (Debugger.IsAttached)
@@ -65,9 +66,12 @@ namespace MQTTnet.Tests.Mockups
 
                 if (e.LogMessage.Level == MqttNetLogLevel.Error)
                 {
-                    lock (_clientErrors)
+                    if (!IgnoreClientLogErrors)
                     {
-                        _clientErrors.Add(e.LogMessage.ToString());
+                        lock (_clientErrors)
+                        {
+                            _clientErrors.Add(e.LogMessage.ToString());
+                        }
                     }
                 }
             };
@@ -212,30 +216,31 @@ namespace MQTTnet.Tests.Mockups
 
         public IMqttClient CreateClient()
         {
+            var logger = EnableLogger ? (IMqttNetLogger)ClientLogger : MqttNetNullLogger.Instance;
+
+            var client = Factory.CreateMqttClient(logger);
+
+            client.ConnectingAsync += e =>
+            {
+                if (TestContext != null)
+                {
+                    var clientOptions = e.ClientOptions;
+                    var existingClientId = clientOptions.ClientId;
+                    if (existingClientId != null && !existingClientId.StartsWith(TestContext.TestName))
+                    {
+                        clientOptions.ClientId = TestContext.TestName + "_" + existingClientId;
+                    }
+                }
+
+                return CompletedTask.Instance;
+            };
+
             lock (_clients)
             {
-                var logger = EnableLogger ? (IMqttNetLogger)ClientLogger : new MqttNetNullLogger();
-
-                var client = Factory.CreateMqttClient(logger);
                 _clients.Add(client);
-
-                client.ConnectingAsync += e =>
-                {
-                    if (TestContext != null)
-                    {
-                        var clientOptions = e.ClientOptions;
-                        var existingClientId = clientOptions.ClientId;
-                        if (existingClientId != null && !existingClientId.StartsWith(TestContext.TestName))
-                        {
-                            clientOptions.ClientId = TestContext.TestName + "_" + existingClientId;
-                        }
-                    }
-
-                    return CompletedTask.Instance;
-                };
-
-                return client;
             }
+
+            return client;
         }
 
         public MqttClientOptions CreateDefaultClientOptions()
@@ -245,18 +250,22 @@ namespace MQTTnet.Tests.Mockups
 
         public MqttClientOptionsBuilder CreateDefaultClientOptionsBuilder()
         {
-            return Factory.CreateClientOptionsBuilder().WithProtocolVersion(_protocolVersion).WithTcpServer("127.0.0.1", ServerPort).WithClientId(TestContext.TestName + "_" + Guid.NewGuid());
+            return Factory.CreateClientOptionsBuilder()
+                .WithProtocolVersion(_protocolVersion)
+                .WithTcpServer("127.0.0.1", ServerPort)
+                .WithClientId(TestContext.TestName + "_" + Guid.NewGuid());
         }
 
         public ILowLevelMqttClient CreateLowLevelClient()
         {
-            lock (_clients)
+            var client = Factory.CreateLowLevelMqttClient(ClientLogger);
-            {
-                var client = Factory.CreateLowLevelMqttClient(ClientLogger);
-                _lowLevelClients.Add(client);
 
-                return client;
+            lock (_lowLevelClients)
+            {
+                _lowLevelClients.Add(client);
             }
+
+            return client;
         }
 
         public MqttServer CreateServer(MqttServerOptions options)
@@ -277,7 +286,8 @@ namespace MQTTnet.Tests.Mockups
                     // Null is used when the client id is assigned from the server!
                     if (!string.IsNullOrEmpty(e.ClientId) && !e.ClientId.StartsWith(TestContext.TestName))
                     {
-                        Assert.Fail($"Client ID does not start with test name ({TestContext.TestName}).");
+                        TrackException(new InvalidOperationException($"Invalid client ID used ({e.ClientId}). It must start with UnitTest name."));
+                        e.ReasonCode = MqttConnectReasonCode.ClientIdentifierNotValid;
                     }
                 }
 
@@ -289,34 +299,68 @@ namespace MQTTnet.Tests.Mockups
 
         public void Dispose()
         {
-            foreach (var mqttClient in _clients)
-            {
-                mqttClient?.Dispose();
-            }
-
-            foreach (var lowLevelMqttClient in _lowLevelClients)
-            {
-                lowLevelMqttClient?.Dispose();
-            }
-
             try
             {
-                Server?.StopAsync().GetAwaiter().GetResult();
+                lock (_clients)
-            }
+                {
-            catch
+                    foreach (var mqttClient in _clients)
-            {
+                    {
-                // This can happen when the test already stopped the server.
+                        try
+                        {
+                            //mqttClient.DisconnectAsync().GetAwaiter().GetResult();
+                        }
+                        catch
+                        {
+                            // This can happen when the test already disconnected the client.
+                        }
+                        finally
+                        {
+                            mqttClient?.Dispose();
+                        }
+                    }
+
+                    _clients.Clear();
+                }
+
+                lock (_lowLevelClients)
+                {
+                    foreach (var lowLevelMqttClient in _lowLevelClients)
+                    {
+                        lowLevelMqttClient.Dispose();
+                    }
+
+                    _lowLevelClients.Clear();
+                }
+
+                try
+                {
+                    Server?.StopAsync().GetAwaiter().GetResult();
+                }
+                catch
+                {
+                    // This can happen when the test already stopped the server.
+                }
+                finally
+                {
+                    Server?.Dispose();
+                }
+
+                Server = null;
+
+                ThrowIfLogErrors();
+
+                GC.Collect();
+                GC.WaitForFullGCComplete();
+                GC.WaitForPendingFinalizers();
+                
+                if (_exceptions.Any())
+                {
+                    throw new Exception($"{_exceptions.Count} exceptions tracked.\r\n" + string.Join(Environment.NewLine, _exceptions));
+                }
             }
             finally
             {
-                Server?.Dispose();
+                TaskScheduler.UnobservedTaskException -= TrackUnobservedTaskException;
-            }
-
-            ThrowIfLogErrors();
-
-            if (_exceptions.Any())
-            {
-                throw new Exception($"{_exceptions.Count} exceptions tracked.\r\n" + string.Join(Environment.NewLine, _exceptions));
             }
         }
 
@@ -333,7 +377,7 @@ namespace MQTTnet.Tests.Mockups
 
             var options = optionsBuilder.Build();
             var server = CreateServer(options);
-            await server.StartAsync();
+            await server.StartAsync().ConfigureAwait(false);
 
             // The OS has chosen the port to we have to properly expose it to the tests.
             ServerPort = options.DefaultEndpointOptions.Port;
@@ -361,33 +405,49 @@ namespace MQTTnet.Tests.Mockups
 
         public void ThrowIfLogErrors()
         {
-            lock (_serverErrors)
+            if (!IgnoreServerLogErrors)
             {
-                if (!IgnoreServerLogErrors && _serverErrors.Count > 0)
+                lock (_serverErrors)
                 {
-                    var message = $"Server had {_serverErrors.Count} errors (${string.Join(Environment.NewLine, _serverErrors)}).";
+                    if (_serverErrors.Count > 0)
-                    Console.WriteLine(message);
+                    {
-                    throw new Exception(message);
+                        var message = $"Server had {_serverErrors.Count} errors (${string.Join(Environment.NewLine, _serverErrors)}).";
+                        Console.WriteLine(message);
+                        throw new Exception(message);
+                    }
                 }
             }
 
-            lock (_clientErrors)
+            if (!IgnoreClientLogErrors)
             {
-                if (!IgnoreClientLogErrors && _clientErrors.Count > 0)
+                lock (_clientErrors)
                 {
-                    var message = $"Client(s) had {_clientErrors.Count} errors (${string.Join(Environment.NewLine, _clientErrors)})";
+                    if (_clientErrors.Count > 0)
-                    Console.WriteLine(message);
+                    {
-                    throw new Exception(message);
+                        var message = $"Client(s) had {_clientErrors.Count} errors (${string.Join(Environment.NewLine, _clientErrors)})";
+                        Console.WriteLine(message);
+                        throw new Exception(message);
+                    }
                 }
             }
         }
 
         public void TrackException(Exception exception)
         {
+            if (exception == null)
+            {
+                return;
+            }
+
             lock (_exceptions)
             {
                 _exceptions.Add(exception);
             }
         }
+
+        void TrackUnobservedTaskException(object sender, UnobservedTaskExceptionEventArgs e)
+        {
+            TrackException(e.Exception);
+        }
     }
 }

Source/MQTTnet.Tests/MqttApplicationMessageBuilder_Tests.cs

@@ -4,6 +4,7 @@
 
 using System;
 using System.IO;
+using System.Linq;
 using System.Text;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Protocol;
@@ -11,7 +12,7 @@ using MQTTnet.Protocol;
 namespace MQTTnet.Tests
 {
     [TestClass]
-    public class MqttApplicationMessageBuilder_Tests
+    public sealed class MqttApplicationMessageBuilder_Tests
     {
         [TestMethod]
         public void CreateApplicationMessage_TopicOnly()
@@ -29,7 +30,7 @@ namespace MQTTnet.Tests
             Assert.AreEqual("xyz", message.Topic);
             Assert.IsFalse(message.Retain);
             Assert.AreEqual(MqttQualityOfServiceLevel.AtMostOnce, message.QualityOfServiceLevel);
-            Assert.AreEqual(Encoding.UTF8.GetString(message.Payload), "00:06:00");
+            Assert.AreEqual(Encoding.UTF8.GetString(message.PayloadSegment.ToArray()), "00:06:00");
         }
 
         [TestMethod]
@@ -41,7 +42,7 @@ namespace MQTTnet.Tests
             Assert.AreEqual("123", message.Topic);
             Assert.IsFalse(message.Retain);
             Assert.AreEqual(MqttQualityOfServiceLevel.AtMostOnce, message.QualityOfServiceLevel);
-            Assert.AreEqual(Encoding.UTF8.GetString(message.Payload), "Hello");
+            Assert.AreEqual(Encoding.UTF8.GetString(message.PayloadSegment.ToArray()), "Hello");
         }
 
         [TestMethod]

Source/MQTTnet.Tests/MqttApplicationMessageTest.cs

@@ -1,3 +1,5 @@
+#pragma warning disable CS0618 // Type or member is obsolete
+
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using System;
 using System.Collections.Generic;
@@ -8,7 +10,7 @@ using System.Threading.Tasks;
 namespace MQTTnet.Tests
 {
     [TestClass]
-    public class MqttApplicationMessageTest
+    public sealed class MqttApplicationMessageTest
     {
         [TestMethod]
         public void PayloadSegment()
@@ -17,32 +19,27 @@ namespace MQTTnet.Tests
             Assert.AreEqual(0, message.Payload.Length);
             Assert.AreEqual(0, message.PayloadSegment.Count);
 
-            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsTrue(ReferenceEquals(message.Payload, message.PayloadSegment.Array));
-            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
 
             message.Payload = new byte[] { 1, 2 };
             Assert.AreEqual(2, message.Payload.Length);
             Assert.AreEqual(2, message.PayloadSegment.Count);
-            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsTrue(ReferenceEquals(message.Payload, message.PayloadSegment.Array));
-            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
 
             message.Payload = new byte[] { 1, 2, 3 };
             Assert.AreEqual(3, message.Payload.Length);
             Assert.AreEqual(3, message.PayloadSegment.Count);
-            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsTrue(ReferenceEquals(message.Payload, message.PayloadSegment.Array));
-            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
 
             message.PayloadSegment = new ArraySegment<byte>(new byte[] { 1, 2, 3 });
             Assert.AreEqual(3, message.Payload.Length);
             Assert.AreEqual(3, message.PayloadSegment.Count);
-            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsTrue(ReferenceEquals(message.Payload, message.PayloadSegment.Array));
-            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
 
             message.PayloadSegment = new ArraySegment<byte>(new byte[] { 1, 2, 3 }, 1, 1);
             Assert.AreEqual(1, message.Payload.Length);
             Assert.AreEqual(1, message.PayloadSegment.Count);
-            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsFalse(ReferenceEquals(message.Payload, message.PayloadSegment.Array));
-            Assert.IsFalse(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
         }
     }
 }

Source/MQTTnet.Tests/MqttTcpChannel_Tests.cs

@@ -2,13 +2,13 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MQTTnet.Implementations;
 using System;
 using System.Net;
 using System.Net.Sockets;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Implementations;
 
 namespace MQTTnet.Tests
 {
@@ -18,62 +18,68 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Dispose_Channel_While_Used()
         {
-            var ct = new CancellationTokenSource();
+            using (var ct = new CancellationTokenSource())
-            var serverSocket = new CrossPlatformSocket(AddressFamily.InterNetwork);
-
-            try
             {
-                serverSocket.Bind(new IPEndPoint(IPAddress.Any, 50001));
+                using (var serverSocket = new CrossPlatformSocket(AddressFamily.InterNetwork, ProtocolType.Tcp))
-                serverSocket.Listen(0);
-
-#pragma warning disable 4014
-                Task.Run(async () =>
-#pragma warning restore 4014
                 {
-                    while (!ct.IsCancellationRequested)
+                    try
                     {
-                        var client = await serverSocket.AcceptAsync();
+                        serverSocket.Bind(new IPEndPoint(IPAddress.Any, 50001));
-                        var data = new byte[] { 128 };
+                        serverSocket.Listen(0);
-                        await client.SendAsync(new ArraySegment<byte>(data), SocketFlags.None);
-                    }
-                }, ct.Token);
 
-                var clientSocket = new CrossPlatformSocket(AddressFamily.InterNetwork);
-                await clientSocket.ConnectAsync("localhost", 50001, CancellationToken.None);
-
-                var tcpChannel = new MqttTcpChannel(clientSocket.GetStream(), "test", null);
-
-                await Task.Delay(100, ct.Token);
-
-                var buffer = new byte[1];
-                await tcpChannel.ReadAsync(buffer, 0, 1, ct.Token);
-
-                Assert.AreEqual(128, buffer[0]);
-
-                // This block should fail after dispose.
 #pragma warning disable 4014
-                Task.Run(() =>
+                        Task.Run(
+                            async () =>
 #pragma warning restore 4014
-                {
+                            {
-                    Task.Delay(200, ct.Token);
+                                while (!ct.IsCancellationRequested)
-                    tcpChannel.Dispose();
+                                {
-                }, ct.Token);
+                                    var client = await serverSocket.AcceptAsync(ct.Token);
+                                    var data = new byte[] { 128 };
+                                    await client.SendAsync(new ArraySegment<byte>(data), SocketFlags.None);
+                                }
+                            },
+                            ct.Token);
 
-                try
+                        var clientSocket = new CrossPlatformSocket(AddressFamily.InterNetwork, ProtocolType.Tcp);
-                {
+                        await clientSocket.ConnectAsync("localhost", 50001, CancellationToken.None);
-                    await tcpChannel.ReadAsync(buffer, 0, 1, CancellationToken.None);
+
+                        var tcpChannel = new MqttTcpChannel(clientSocket.GetStream(), "test", null);
+
+                        await Task.Delay(100, ct.Token);
+
+                        var buffer = new byte[1];
+                        await tcpChannel.ReadAsync(buffer, 0, 1, ct.Token);
+
+                        Assert.AreEqual(128, buffer[0]);
+
+                        // This block should fail after dispose.
+#pragma warning disable 4014
+                        Task.Run(
+                            () =>
+#pragma warning restore 4014
+                            {
+                                Task.Delay(200, ct.Token);
+                                tcpChannel.Dispose();
+                            },
+                            ct.Token);
+
+                        try
+                        {
+                            await tcpChannel.ReadAsync(buffer, 0, 1, CancellationToken.None);
+                        }
+                        catch (Exception exception)
+                        {
+                            Assert.IsInstanceOfType(exception, typeof(SocketException));
+                            Assert.AreEqual(SocketError.OperationAborted, ((SocketException)exception).SocketErrorCode);
+                        }
+                    }
+                    finally
+                    {
+                        ct.Cancel(false);
+                    }
                 }
-                catch (Exception exception)
-                {
-                    Assert.IsInstanceOfType(exception, typeof(SocketException));
-                    Assert.AreEqual(SocketError.OperationAborted, ((SocketException)exception).SocketErrorCode);
-                }
-            }
-            finally
-            {
-                ct.Cancel(false);
-                serverSocket.Dispose();
             }
         }
     }
-}
+}

Source/MQTTnet.Tests/Server/Connection_Tests.cs

@@ -23,7 +23,7 @@ namespace MQTTnet.Tests.Server
             {
                 await testEnvironment.StartServer(new MqttServerOptionsBuilder().WithDefaultCommunicationTimeout(TimeSpan.FromSeconds(1)));
 
-                var client = new CrossPlatformSocket(AddressFamily.InterNetwork);
+                var client = new CrossPlatformSocket(AddressFamily.InterNetwork, ProtocolType.Tcp);
                 await client.ConnectAsync("localhost", testEnvironment.ServerPort, CancellationToken.None);
 
                 // Don't send anything. The server should close the connection.
@@ -54,7 +54,7 @@ namespace MQTTnet.Tests.Server
 
                 // Send an invalid packet and ensure that the server will close the connection and stay in a waiting state
                 // forever. This is security related.
-                var client = new CrossPlatformSocket(AddressFamily.InterNetwork);
+                var client = new CrossPlatformSocket(AddressFamily.InterNetwork, ProtocolType.Tcp);
                 await client.ConnectAsync("localhost", testEnvironment.ServerPort, CancellationToken.None);
 
                 var buffer = Encoding.UTF8.GetBytes("Garbage");

Source/MQTTnet.Tests/Server/General.cs

@@ -303,7 +303,7 @@ namespace MQTTnet.Tests.Server
                 var server = await testEnvironment.StartServer();
                 server.InterceptingPublishAsync += e =>
                 {
-                    e.ApplicationMessage.Payload = Encoding.ASCII.GetBytes("extended");
+                    e.ApplicationMessage.PayloadSegment = new ArraySegment<byte>(Encoding.ASCII.GetBytes("extended"));
                     return CompletedTask.Instance;
                 };
 
@@ -314,7 +314,7 @@ namespace MQTTnet.Tests.Server
                 var isIntercepted = false;
                 c2.ApplicationMessageReceivedAsync += e =>
                 {
-                    isIntercepted = string.Compare("extended", Encoding.UTF8.GetString(e.ApplicationMessage.Payload), StringComparison.Ordinal) == 0;
+                    isIntercepted = string.Compare("extended", Encoding.UTF8.GetString(e.ApplicationMessage.PayloadSegment.ToArray()), StringComparison.Ordinal) == 0;
                     return CompletedTask.Instance;
                 };
 
@@ -425,7 +425,7 @@ namespace MQTTnet.Tests.Server
                             new MqttApplicationMessage
                             {
                                 Topic = "/test/1",
-                                Payload = Encoding.UTF8.GetBytes("true"),
+                                PayloadSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes("true")),
                                 QualityOfServiceLevel = MqttQualityOfServiceLevel.ExactlyOnce
                             })
                         {
@@ -598,8 +598,7 @@ namespace MQTTnet.Tests.Server
                 // c
                 var c1 = await testEnvironment.ConnectClient(clientOptionsBuilder);
 
-                await Task.Delay(500);
+                await LongTestDelay();
-
                 var flow = string.Join(string.Empty, events);
                 Assert.AreEqual("c", flow);
 
@@ -607,10 +606,8 @@ namespace MQTTnet.Tests.Server
                 // Connect client with same client ID. Should disconnect existing client.
                 var c2 = await testEnvironment.ConnectClient(clientOptionsBuilder);
 
-                await Task.Delay(500);
+                await LongTestDelay();
-
                 flow = string.Join(string.Empty, events);
-
                 Assert.AreEqual("cdc", flow);
 
                 c2.ApplicationMessageReceivedAsync += e =>
@@ -628,8 +625,7 @@ namespace MQTTnet.Tests.Server
                 // r
                 await c2.PublishStringAsync("topic");
 
-                await Task.Delay(500);
+                await LongTestDelay();
-
                 flow = string.Join(string.Empty, events);
                 Assert.AreEqual("cdcr", flow);
 
@@ -639,16 +635,17 @@ namespace MQTTnet.Tests.Server
                 await c1.TryDisconnectAsync();
                 Assert.AreEqual(false, c1.IsConnected);
 
-                await Task.Delay(500);
+                await LongTestDelay();
 
                 // d
                 Assert.AreEqual(true, c2.IsConnected);
                 await c2.DisconnectAsync();
 
-                await Task.Delay(500);
+                await LongTestDelay();
 
                 await server.StopAsync();
 
+                await LongTestDelay();
                 flow = string.Join(string.Empty, events);
                 Assert.AreEqual("cdcrd", flow);
             }
@@ -783,7 +780,7 @@ namespace MQTTnet.Tests.Server
                 var client1 = await testEnvironment.ConnectClient();
                 client1.ApplicationMessageReceivedAsync += e =>
                 {
-                    receivedBody = e.ApplicationMessage.Payload;
+                    receivedBody = e.ApplicationMessage.PayloadSegment.ToArray();
                     return CompletedTask.Instance;
                 };
 
@@ -852,11 +849,11 @@ namespace MQTTnet.Tests.Server
                     return CompletedTask.Instance;
                 };
 
-                await Task.Delay(100);
+                // Stopping the server should disconnect the connection with the client
-
+                // which, it turn, will fire the disconnected event at the client.
                 await server.StopAsync();
 
-                await Task.Delay(100);
+                await LongTestDelay();
 
                 Assert.AreEqual(1, disconnectCalled);
             }

Source/MQTTnet.Tests/Server/HotSwapCerts_Tests.cs

@@ -0,0 +1,426 @@
+#if !(NET452 || NET461 || NET48)
+using System;
+using System.Collections.Concurrent;
+using System.Diagnostics;
+using System.Linq;
+using System.Net;
+using System.Net.Security;
+using System.Security.Authentication;
+using System.Security.Cryptography;
+using System.Security.Cryptography.X509Certificates;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Certificates;
+using MQTTnet.Client;
+using MQTTnet.Formatter;
+using MQTTnet.Protocol;
+using MQTTnet.Server;
+
+namespace MQTTnet.Tests.Server
+{
+    // missing certificate builder api means tests won't work for older frameworks
+
+    [TestClass]
+    public sealed class HotSwapCerts_Tests
+    {
+        static readonly TimeSpan DefaultTimeout = TimeSpan.FromSeconds(10);
+
+        [TestMethod]
+        public async Task ClientCertChangeWithoutServerUpdateFailsReconnect()
+        {
+            using (var server = new ServerTestHarness())
+            using (var client01 = new ClientTestHarness())
+            {
+                server.InstallNewClientCert(client01.GetCurrentClientCert());
+                client01.InstallNewServerCert(server.GetCurrentServerCert());
+
+                await server.StartServer();
+
+                await client01.Connect();
+
+                client01.WaitForConnectOrFail(DefaultTimeout);
+
+                client01.HotSwapClientCert();
+                server.ForceDisconnectAsync(client01).Wait(DefaultTimeout);
+                client01.WaitForDisconnectOrFail(DefaultTimeout);
+
+                client01.WaitForConnectToFail(DefaultTimeout);
+            }
+        }
+
+        [TestMethod]
+        public async Task ClientCertChangeWithServerUpdateAcceptsReconnect()
+        {
+            using (var server = new ServerTestHarness())
+            using (var client01 = new ClientTestHarness())
+            {
+                server.InstallNewClientCert(client01.GetCurrentClientCert());
+                client01.InstallNewServerCert(server.GetCurrentServerCert());
+
+                await server.StartServer();
+
+                await client01.Connect();
+
+                client01.WaitForConnectOrFail(DefaultTimeout);
+
+                client01.HotSwapClientCert();
+                server.ForceDisconnectAsync(client01).Wait(DefaultTimeout);
+                client01.WaitForDisconnectOrFail(DefaultTimeout);
+
+                server.InstallNewClientCert(client01.GetCurrentClientCert());
+
+                client01.WaitForConnectOrFail(DefaultTimeout);
+            }
+        }
+
+        [TestMethod]
+        public async Task ServerCertChangeWithClientCertUpdateAllowsReconnect()
+        {
+            using (var server = new ServerTestHarness())
+            using (var client01 = new ClientTestHarness())
+            {
+                server.InstallNewClientCert(client01.GetCurrentClientCert());
+                client01.InstallNewServerCert(server.GetCurrentServerCert());
+
+                await server.StartServer();
+                await client01.Connect();
+
+                client01.WaitForConnectOrFail(DefaultTimeout);
+                server.HotSwapServerCert();
+
+                server.ForceDisconnectAsync(client01).Wait(DefaultTimeout);
+                client01.WaitForDisconnectOrFail(DefaultTimeout);
+                client01.InstallNewServerCert(server.GetCurrentServerCert());
+
+                client01.WaitForConnectOrFail(DefaultTimeout);
+            }
+        }
+
+        [TestMethod]
+        public async Task ServerCertChangeWithoutClientCertUpdateFailsReconnect()
+        {
+            using (var server = new ServerTestHarness())
+            using (var client01 = new ClientTestHarness())
+            {
+                server.InstallNewClientCert(client01.GetCurrentClientCert());
+                client01.InstallNewServerCert(server.GetCurrentServerCert());
+
+                await server.StartServer();
+                await client01.Connect();
+
+                client01.WaitForConnectOrFail(DefaultTimeout);
+                server.HotSwapServerCert();
+
+                server.ForceDisconnectAsync(client01).Wait(DefaultTimeout);
+                client01.WaitForDisconnectOrFail(DefaultTimeout);
+
+                client01.WaitForConnectToFail(DefaultTimeout);
+            }
+        }
+
+        static X509Certificate2 CreateSelfSignedCertificate(string oid)
+        {
+            var sanBuilder = new SubjectAlternativeNameBuilder();
+            sanBuilder.AddIpAddress(IPAddress.Loopback);
+            sanBuilder.AddIpAddress(IPAddress.IPv6Loopback);
+            sanBuilder.AddDnsName("localhost");
+
+            using (var rsa = RSA.Create())
+            {
+                var certRequest = new CertificateRequest("CN=localhost", rsa, HashAlgorithmName.SHA512, RSASignaturePadding.Pkcs1);
+
+                certRequest.CertificateExtensions.Add(
+                    new X509KeyUsageExtension(X509KeyUsageFlags.DataEncipherment | X509KeyUsageFlags.KeyEncipherment | X509KeyUsageFlags.DigitalSignature, false));
+
+                certRequest.CertificateExtensions.Add(new X509EnhancedKeyUsageExtension(new OidCollection { new Oid(oid) }, false));
+
+                certRequest.CertificateExtensions.Add(sanBuilder.Build());
+
+                using (var certificate = certRequest.CreateSelfSigned(DateTimeOffset.Now.AddMinutes(-10), DateTimeOffset.Now.AddMinutes(10)))
+                {
+                    var pfxCertificate = new X509Certificate2(
+                        certificate.Export(X509ContentType.Pfx),
+                        (string)null,
+                        X509KeyStorageFlags.MachineKeySet | X509KeyStorageFlags.Exportable);
+
+                    return pfxCertificate;
+                }
+            }
+        }
+
+        sealed class ClientTestHarness : IDisposable
+        {
+            readonly HotSwappableClientCertProvider _hotSwapClient = new HotSwappableClientCertProvider();
+
+            IMqttClient _client;
+
+            public string ClientId => _client.Options.ClientId;
+
+            public Task Connect()
+            {
+                return Run_Client_Connection();
+            }
+
+            public void Dispose()
+            {
+                _client.Dispose();
+                _hotSwapClient.Dispose();
+            }
+
+            public X509Certificate2 GetCurrentClientCert()
+            {
+                var result = _hotSwapClient.GetCertificates()[0];
+                return new X509Certificate2(result);
+            }
+
+            public void HotSwapClientCert()
+            {
+                _hotSwapClient.HotSwapCert();
+            }
+
+            public void InstallNewServerCert(X509Certificate2 serverCert)
+            {
+                _hotSwapClient.InstallNewServerCert(serverCert);
+            }
+
+            public void WaitForConnectOrFail(TimeSpan timeout)
+            {
+                Thread.Sleep(100);
+
+                if (!_client.IsConnected)
+                {
+                    _client.ReconnectAsync().Wait(timeout);
+                }
+
+                WaitForConnect(timeout);
+
+                Assert.IsNotNull(_client, "Client was never initialized");
+                Assert.IsTrue(_client.IsConnected, $"Client connection failed after {timeout}");
+            }
+
+            public void WaitForConnectToFail(TimeSpan timeout)
+            {
+                Assert.IsFalse(_client.IsConnected, "Client should be disconnected before waiting for connect.");
+
+                WaitForConnect(timeout);
+
+                Assert.IsNotNull(_client, "Client was never initialized");
+                Assert.IsFalse(_client.IsConnected, "Client connection success but test wanted fail");
+            }
+
+            void WaitForDisconnect(TimeSpan timeout)
+            {
+                var timer = Stopwatch.StartNew();
+                while ((_client == null || _client.IsConnected) && timer.Elapsed < timeout)
+                {
+                    Thread.Sleep(100);
+                }
+            }
+
+            public void WaitForDisconnectOrFail(TimeSpan timeout)
+            {
+                WaitForDisconnect(timeout);
+
+                Assert.IsNotNull(_client, "Client was never initialized");
+                Assert.IsFalse(_client.IsConnected, $"Client connection should have disconnected after {timeout}");
+            }
+
+            async Task Run_Client_Connection()
+            {
+                var optionsBuilder = new MqttClientOptionsBuilder()
+                    .WithTlsOptions(
+                        o => o.WithClientCertificatesProvider(_hotSwapClient)
+                            .WithCertificateValidationHandler(_hotSwapClient.OnCertificateValidation)
+                            .WithSslProtocols(SslProtocols.Tls12))
+                    .WithTcpServer("localhost")
+                    .WithCleanSession()
+                    .WithProtocolVersion(MqttProtocolVersion.V500);
+
+                var mqttClientOptions = optionsBuilder.Build();
+
+                var factory = new MqttFactory();
+                var mqttClient = factory.CreateMqttClient();
+                _client = mqttClient;
+
+                await mqttClient.ConnectAsync(mqttClientOptions);
+            }
+
+            void WaitForConnect(TimeSpan timeout)
+            {
+                var timer = Stopwatch.StartNew();
+                while ((_client == null || !_client.IsConnected) && timer.Elapsed < timeout)
+                {
+                    Thread.Sleep(100);
+                }
+            }
+        }
+
+        sealed class ServerTestHarness : IDisposable
+        {
+            readonly HotSwappableServerCertProvider _hotSwapServer = new HotSwappableServerCertProvider();
+
+            MqttServer _server;
+
+            public void Dispose()
+            {
+                if (_server != null)
+                {
+                    _server.StopAsync().Wait();
+                    _server.Dispose();
+                }
+
+                _hotSwapServer?.Dispose();
+            }
+
+            public Task ForceDisconnectAsync(ClientTestHarness client)
+            {
+                return _server.DisconnectClientAsync(client.ClientId, MqttDisconnectReasonCode.UnspecifiedError);
+            }
+
+            public X509Certificate2 GetCurrentServerCert()
+            {
+                return _hotSwapServer.GetCertificate();
+            }
+
+            public void HotSwapServerCert()
+            {
+                _hotSwapServer.HotSwapCert();
+            }
+
+            public void InstallNewClientCert(X509Certificate2 serverCert)
+            {
+                _hotSwapServer.InstallNewClientCert(serverCert);
+            }
+
+            public Task StartServer()
+            {
+                var mqttFactory = new MqttFactory();
+
+                var mqttServerOptions = new MqttServerOptionsBuilder().WithEncryptionCertificate(_hotSwapServer)
+                    .WithRemoteCertificateValidationCallback(_hotSwapServer.RemoteCertificateValidationCallback)
+                    .WithEncryptedEndpoint()
+                    .Build();
+
+                mqttServerOptions.TlsEndpointOptions.ClientCertificateRequired = true;
+
+                _server = mqttFactory.CreateMqttServer(mqttServerOptions);
+                return _server.StartAsync();
+            }
+        }
+
+        class HotSwappableClientCertProvider : IMqttClientCertificatesProvider, IDisposable
+        {
+            X509Certificate2Collection _certificates;
+            ConcurrentBag<X509Certificate2> _serverCerts = new ConcurrentBag<X509Certificate2>();
+
+            public HotSwappableClientCertProvider()
+            {
+                _certificates = new X509Certificate2Collection(CreateSelfSignedCertificate("1.3.6.1.5.5.7.3.2"));
+            }
+            
+            public void Dispose()
+            {
+                if (_certificates != null)
+                {
+                    foreach (var certs in _certificates)
+                    {
+#if !NET452
+                        certs.Dispose();
+#endif
+                    }
+                }
+            }
+
+            public X509CertificateCollection GetCertificates()
+            {
+                return new X509Certificate2Collection(_certificates);
+            }
+
+            public void HotSwapCert()
+            {
+                _certificates = new X509Certificate2Collection(CreateSelfSignedCertificate("1.3.6.1.5.5.7.3.2"));
+            }
+
+            public void InstallNewServerCert(X509Certificate2 serverCert)
+            {
+                _serverCerts.Add(serverCert);
+            }
+
+            public bool OnCertificateValidation(MqttClientCertificateValidationEventArgs certContext)
+            {
+                var serverCerts = _serverCerts.ToArray();
+
+                var providedCert = certContext.Certificate.GetRawCertData();
+                for (int i = 0, n = serverCerts.Length; i < n; i++)
+                {
+                    var currentcert = serverCerts[i];
+
+                    if (currentcert.RawData.SequenceEqual(providedCert))
+                    {
+                        return true;
+                    }
+                }
+
+                return false;
+            }
+        }
+
+        sealed class HotSwappableServerCertProvider : ICertificateProvider, IDisposable
+        {
+            readonly ConcurrentBag<X509Certificate2> _clientCerts = new ConcurrentBag<X509Certificate2>();
+            X509Certificate2 _certificate;
+
+            public HotSwappableServerCertProvider()
+            {
+                _certificate = CreateSelfSignedCertificate("1.3.6.1.5.5.7.3.1");
+            }
+
+            public void Dispose()
+            {
+#if !NET452
+                _certificate.Dispose();
+#endif
+            }
+
+            public X509Certificate2 GetCertificate()
+            {
+                return _certificate;
+            }
+
+            public void HotSwapCert()
+            {
+                var newCert = CreateSelfSignedCertificate("1.3.6.1.5.5.7.3.1");
+                var oldCert = Interlocked.Exchange(ref _certificate, newCert);
+#if !NET452
+                oldCert.Dispose();
+#endif
+            }
+
+            public void InstallNewClientCert(X509Certificate2 certificate)
+            {
+                _clientCerts.Add(certificate);
+            }
+
+            public bool RemoteCertificateValidationCallback(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
+            {
+                var serverCerts = _clientCerts.ToArray();
+
+                var providedCert = certificate.GetRawCertData();
+                for (int i = 0, n = serverCerts.Length; i < n; i++)
+                {
+                    var currentCert = serverCerts[i];
+
+                    if (currentCert.RawData.SequenceEqual(providedCert))
+                    {
+                        return true;
+                    }
+                }
+
+                return false;
+            }
+        }
+    }
+}
+
+#endif

Source/MQTTnet.Tests/Server/MqttRetainedMessageManager_Tests.cs

@@ -0,0 +1,25 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Tests.Server
+{
+    [TestClass]
+    public sealed class MqttRetainedMessageManager_Tests
+    {
+        [TestMethod]
+        public async Task MqttRetainedMessageManager_GetUndefinedTopic()
+        {
+            var logger = new Mockups.TestLogger();
+            var eventContainer = new MQTTnet.Server.MqttServerEventContainer();
+            var retainedMessagesManager = new MQTTnet.Server.MqttRetainedMessagesManager(eventContainer, logger);
+            var task = retainedMessagesManager.GetMessage("undefined");
+            Assert.IsNotNull(task, "Task should not be null");
+            var result = await task;
+            Assert.IsNull(result, "Null result expected");
+        }
+    }
+}

Source/MQTTnet.Tests/Server/MqttSubscriptionsManager_Tests.cs

@@ -221,7 +221,10 @@ namespace MQTTnet.Tests.Server
             var eventContainer = new MqttServerEventContainer();
             var clientSessionManager = new MqttClientSessionsManager(options, retainedMessagesManager, eventContainer, logger);
 
-            var session = new MqttSession("", false, new ConcurrentDictionary<object, object>(), options, eventContainer, retainedMessagesManager, clientSessionManager);
+            var session = new MqttSession(new MqttConnectPacket
+            {
+                ClientId = ""
+            }, new ConcurrentDictionary<object, object>(), options, eventContainer, retainedMessagesManager, clientSessionManager);
 
             _subscriptionsManager = new MqttClientSubscriptionsManager(session, new MqttServerEventContainer(), retainedMessagesManager, clientSessionManager);
         }

Source/MQTTnet.Tests/Server/Publishing_Tests.cs

@@ -8,6 +8,7 @@ using MQTTnet.Client;
 using MQTTnet.Formatter;
 using MQTTnet.Internal;
 using MQTTnet.Protocol;
+using MQTTnet.Server;
 
 namespace MQTTnet.Tests.Server
 {

Source/MQTTnet.Tests/Server/Session_Tests.cs

@@ -70,6 +70,28 @@ namespace MQTTnet.Tests.Server
             }
         }
 
+        [TestMethod]
+        public async Task Do_Not_Use_Expired_Session()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                await testEnvironment.StartServer(o => o.WithPersistentSessions());
+
+                var c1 = await testEnvironment.ConnectClient(o => o.WithClientId("Client1").WithCleanSession(false).WithSessionExpiryInterval(3));
+
+                // Kill the client connection and ensure that the session will stay there but is expired after 3 seconds!
+                c1.Dispose();
+
+                await Task.Delay(TimeSpan.FromSeconds(6));
+
+                c1 = testEnvironment.CreateClient();
+                var options = testEnvironment.CreateDefaultClientOptionsBuilder().WithClientId("Client1").WithCleanSession(false).WithSessionExpiryInterval(3).Build();
+
+                var connectResult = await c1.ConnectAsync(options);
+                Assert.AreEqual(false, connectResult.IsSessionPresent);
+            }
+        }
+
         [TestMethod]
         public async Task Fire_Deleted_Event()
         {
@@ -121,7 +143,7 @@ namespace MQTTnet.Tests.Server
                 Assert.AreEqual(true, session.Items["can_subscribe_x"]);
             }
         }
-        
+
         [TestMethod]
         [DataRow(MqttProtocolVersion.V310)]
         [DataRow(MqttProtocolVersion.V311)]
@@ -134,16 +156,12 @@ namespace MQTTnet.Tests.Server
 
                 await testEnvironment.StartServer();
 
-                var options = new MqttClientOptionsBuilder().WithClientId("1").WithTimeout(TimeSpan.FromSeconds(1)).WithProtocolVersion(protocolVersion);
+                var options = new MqttClientOptionsBuilder().WithClientId("1").WithTimeout(TimeSpan.FromSeconds(10)).WithProtocolVersion(protocolVersion);
 
                 var hasReceive = false;
-
                 void OnReceive()
                 {
-                    if (!hasReceive)
+                    hasReceive = true;
-                    {
-                        hasReceive = true;
-                    }
                 }
 
                 // Try to connect 50 clients at the same time.
@@ -152,7 +170,7 @@ namespace MQTTnet.Tests.Server
                 var connectedClients = clients.Where(c => c?.TryPingAsync().GetAwaiter().GetResult() == true).ToList();
 
                 await LongTestDelay();
-                
+
                 Assert.AreEqual(1, connectedClients.Count);
 
                 var option2 = new MqttClientOptionsBuilder().WithClientId("2").WithKeepAlivePeriod(TimeSpan.FromSeconds(10));
@@ -164,7 +182,7 @@ namespace MQTTnet.Tests.Server
                 Assert.AreEqual(true, hasReceive);
             }
         }
- 
+
         [DataTestMethod]
         [DataRow(MqttQualityOfServiceLevel.ExactlyOnce)]
         [DataRow(MqttQualityOfServiceLevel.AtLeastOnce)]
@@ -265,7 +283,7 @@ namespace MQTTnet.Tests.Server
 
                 server.InterceptingPublishAsync += e =>
                 {
-                    e.ApplicationMessage.Payload = Encoding.UTF8.GetBytes(e.SessionItems["default_payload"] as string ?? string.Empty);
+                    e.ApplicationMessage.PayloadSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes(e.SessionItems["default_payload"] as string ?? string.Empty));
                     return CompletedTask.Instance;
                 };
 
@@ -355,8 +373,8 @@ namespace MQTTnet.Tests.Server
                     onReceive();
                     return CompletedTask.Instance;
                 };
-                
+
-                using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(5)))
+                using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(30)))
                 {
                     await client.SubscribeAsync("aaa", MqttQualityOfServiceLevel.AtMostOnce, timeout.Token).ConfigureAwait(false);
                 }

Source/MQTTnet.Tests/Server/Subscription_TopicHash_Tests.cs

@@ -557,7 +557,7 @@ namespace MQTTnet.Tests.Server
             var eventContainer = new MqttServerEventContainer();
             var retainedMessagesManager = new MqttRetainedMessagesManager(eventContainer, logger);
             var sessionManager = new MqttClientSessionsManager(serverOptions, retainedMessagesManager, eventContainer, logger);
-            _clientSession = new MqttSession(clientId, false, new Dictionary<object, object>(), serverOptions, eventContainer, retainedMessagesManager, sessionManager);
+            _clientSession = new MqttSession(new MqttConnectPacket{ ClientId = clientId }, new Dictionary<object, object>(), serverOptions, eventContainer, retainedMessagesManager, sessionManager);
 
             List<string> topicsToSubscribe;
 

Source/MQTTnet.Tests/Server/Tls_Tests.cs

@@ -101,7 +101,7 @@ namespace MQTTnet.Tests.Server
                 new MqttApplicationMessage
                 {
                     Topic = "TestTopic1",
-                    Payload = new byte[] { 1, 2, 3, 4 }
+                    PayloadSegment = new ArraySegment<byte>(new byte[] { 1, 2, 3, 4 })
                 });
 
             await testEnvironment.Server.InjectApplicationMessage(
@@ -109,7 +109,7 @@ namespace MQTTnet.Tests.Server
                     new MqttApplicationMessage
                     {
                         Topic = "TestTopic1",
-                        Payload = new byte[] { 1, 2, 3, 4 }
+                        PayloadSegment = new ArraySegment<byte>(new byte[] { 1, 2, 3, 4 })
                     }));
 
             certificateProvider.CurrentCertificate = CreateCertificate(secondOid);
@@ -137,7 +137,7 @@ namespace MQTTnet.Tests.Server
                 new MqttApplicationMessage
                 {
                     Topic = "TestTopic2",
-                    Payload = new byte[] { 1, 2, 3, 4 }
+                    PayloadSegment = new ArraySegment<byte>(new byte[] { 1, 2, 3, 4 })
                 });
 
             await testEnvironment.Server.InjectApplicationMessage(
@@ -145,7 +145,7 @@ namespace MQTTnet.Tests.Server
                     new MqttApplicationMessage
                     {
                         Topic = "TestTopic2",
-                        Payload = new byte[] { 1, 2, 3, 4 }
+                        PayloadSegment = new ArraySegment<byte>(new byte[] { 1, 2, 3, 4 })
                     }));
 
             // Ensure first client still works
@@ -153,7 +153,7 @@ namespace MQTTnet.Tests.Server
                 new MqttApplicationMessage
                 {
                     Topic = "TestTopic1",
-                    Payload = new byte[] { 1, 2, 3, 4 }
+                    PayloadSegment = new ArraySegment<byte>(new byte[] { 1, 2, 3, 4 })
                 });
 
             await testEnvironment.Server.InjectApplicationMessage(
@@ -161,7 +161,7 @@ namespace MQTTnet.Tests.Server
                     new MqttApplicationMessage
                     {
                         Topic = "TestTopic1",
-                        Payload = new byte[] { 1, 2, 3, 4 }
+                        PayloadSegment = new ArraySegment<byte>(new byte[] { 1, 2, 3, 4 })
                     }));
 
             await Task.Delay(1000);
@@ -178,12 +178,10 @@ namespace MQTTnet.Tests.Server
             var clientOptionsBuilder = testEnvironment.Factory.CreateClientOptionsBuilder();
             clientOptionsBuilder.WithClientId(Guid.NewGuid().ToString())
                 .WithTcpServer("localhost", 8883)
-                .WithTls(
+                .WithTlsOptions(
-                    tls =>
+                    o =>
                     {
-                        tls.UseTls = true;
+                        o.WithSslProtocols(SslProtocols.Tls12).WithCertificateValidationHandler(certValidator);
-                        tls.SslProtocol = SslProtocols.Tls12;
-                        tls.CertificateValidationHandler = certValidator;
                     });
 
             var clientOptions = clientOptionsBuilder.Build();

Source/MQTTnet.Tests/TopicGenerator.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using MQTTnet.Extensions.TopicTemplate;
 
 namespace MQTTnet.Tests
 {
@@ -31,31 +32,43 @@ namespace MQTTnet.Tests
             {
                 maxNumLevel3Topics = 1;
             }
+            
+            MqttTopicTemplate baseTemplate = new MqttTopicTemplate("{publisher}/{building}/{level}/{sensor}");
 
             for (var p = 0; p < numPublishers; ++p)
             {
                 int publisherTopicCount = 0;
                 var publisherName = "pub" + p;
+                var publisherTemplate = baseTemplate
+                    .WithParameter("publisher", publisherName);
+                
                 for (var l1 = 0; l1 < numLevel1Topics; ++l1)
                 {
+                    var l1Template = publisherTemplate.WithParameter("building", "building" + (l1 + 1));
                     for (var l2 = 0; l2 < numLevel2Topics; ++l2)
                     {
+                        var l2Template = l1Template.WithParameter("level", "level" + (l2 + 1));
                         for (var l3 = 0; l3 < maxNumLevel3Topics; ++l3)
                         {
                             if (publisherTopicCount >= numTopicsPerPublisher)
                                 break;
 
-                            var topic = string.Format("{0}/building{1}/level{2}/sensor{3}", publisherName, l1 + 1, l2 + 1, l3 + 1);
+                            var l3Template = l2Template
-                            AddPublisherTopic(publisherName, topic, topicsByPublisher);
+                                .WithParameter("sensor", "sensor" + (l3 + 1));
+                            AddPublisherTopic(publisherName, l3Template.TopicFilter, topicsByPublisher);
 
                             if (l2 == 0)
                             {
-                                var singleWildcardTopic = string.Format("{0}/building{1}/+/sensor{2}", publisherName, l1 + 1, l3 + 1);
+                                var singleWildcardTopic = l1Template
+                                    .WithParameter("sensor", "sensor" + (l3 + 1))
+                                    .TopicFilter;
                                 AddPublisherTopic(publisherName, singleWildcardTopic, singleWildcardTopicsByPublisher);
                             }
                             if ((l1 == 0) && (l3 == 0))
                             {
-                                var multiWildcardTopic = string.Format("{0}/+/level{1}/+", publisherName, l2 + 1);
+                                var multiWildcardTopic = publisherTemplate
+                                    .WithParameter("level", "level" + (l2 + 1))
+                                    .TopicFilter;
                                 AddPublisherTopic(publisherName, multiWildcardTopic, multiWildcardTopicsByPublisher);
                             }
 

Source/MQTTnet/Adapter/IMqttChannelAdapter.cs

@@ -25,8 +25,6 @@ namespace MQTTnet.Adapter
 
         long BytesReceived { get; }
 
-        bool IsReadingPacket { get; }
-
         Task ConnectAsync(CancellationToken cancellationToken);
 
         Task DisconnectAsync(CancellationToken cancellationToken);

Source/MQTTnet/Adapter/IMqttServerAdapter.cs

@@ -14,6 +14,7 @@ namespace MQTTnet.Adapter
         Func<IMqttChannelAdapter, Task> ClientHandler { get; set; }
 
         Task StartAsync(MqttServerOptions options, IMqttNetLogger logger);
+
         Task StopAsync();
     }
 }

Source/MQTTnet/Adapter/MqttChannelAdapter.cs

@@ -26,9 +26,7 @@ namespace MQTTnet.Adapter
         readonly IMqttChannel _channel;
         readonly byte[] _fixedHeaderBuffer = new byte[2];
         readonly MqttNetSourceLogger _logger;
-
         readonly byte[] _singleByteBuffer = new byte[1];
-
         readonly AsyncLock _syncRoot = new AsyncLock();
 
         Statistics _statistics; // mutable struct, don't make readonly!
@@ -47,6 +45,8 @@ namespace MQTTnet.Adapter
             _logger = logger.WithSource(nameof(MqttChannelAdapter));
         }
 
+        public bool AllowPacketFragmentation { get; set; } = true;
+
         public long BytesReceived => Volatile.Read(ref _statistics._bytesReceived);
 
         public long BytesSent => Volatile.Read(ref _statistics._bytesSent);
@@ -55,16 +55,12 @@ namespace MQTTnet.Adapter
 
         public string Endpoint => _channel.Endpoint;
 
-        public bool IsReadingPacket { get; private set; }
-
         public bool IsSecureConnection => _channel.IsSecureConnection;
 
         public MqttPacketFormatterAdapter PacketFormatterAdapter { get; }
 
         public MqttPacketInspector PacketInspector { get; set; }
 
-        public bool AllowPacketFragmentation { get; set; } = true;
-
         public async Task ConnectAsync(CancellationToken cancellationToken)
         {
             cancellationToken.ThrowIfCancellationRequested();
@@ -78,12 +74,30 @@ namespace MQTTnet.Adapter
                  * block forever. Even a cancellation token is not supported properly.
                  */
 
-                var connectTask = _channel.ConnectAsync(cancellationToken);
-
                 var timeout = new TaskCompletionSource<object>();
                 using (cancellationToken.Register(() => timeout.TrySetResult(null)))
                 {
+                    var connectTask = Task.Run(
+                        async () =>
+                        {
+                            try
+                            {
+                                await _channel.ConnectAsync(cancellationToken).ConfigureAwait(false);
+                            }
+                            catch
+                            {
+                                // If the timeout is already reached the exception is no longer of interest and
+                                // must be catched. Otherwise it will arrive at the TaskScheduler.UnobservedTaskException.
+                                if (!timeout.Task.IsCompleted)
+                                {
+                                    throw;
+                                }
+                            }
+                        },
+                        CancellationToken.None);
+
                     await Task.WhenAny(connectTask, timeout.Task).ConfigureAwait(false);
+
                     if (timeout.Task.IsCompleted && !connectTask.IsCompleted)
                     {
                         throw new OperationCanceledException("MQTT connect canceled.", cancellationToken);
@@ -127,7 +141,8 @@ namespace MQTTnet.Adapter
 
             try
             {
-                PacketInspector?.BeginReceivePacket();
+                var localPacketInspector = PacketInspector;
+                localPacketInspector?.BeginReceivePacket();
 
                 ReceivedMqttPacket receivedPacket;
                 var receivedPacketTask = ReceiveAsync(cancellationToken);
@@ -145,7 +160,10 @@ namespace MQTTnet.Adapter
                     return null;
                 }
 
-                PacketInspector?.EndReceivePacket();
+                if (localPacketInspector != null)
+                {
+                    await localPacketInspector.EndReceivePacket().ConfigureAwait(false);
+                }
 
                 Interlocked.Add(ref _statistics._bytesSent, receivedPacket.TotalLength);
 
@@ -201,10 +219,15 @@ namespace MQTTnet.Adapter
                 try
                 {
                     var packetBuffer = PacketFormatterAdapter.Encode(packet);
-                    PacketInspector?.BeginSendPacket(packetBuffer);
 
-                    _logger.Verbose("TX ({0} bytes) >>> {1}", packetBuffer.Length, packet);
+                    var localPacketInspector = PacketInspector;
+                    if (localPacketInspector != null)
+                    {
+                        await localPacketInspector.BeginSendPacket(packetBuffer).ConfigureAwait(false);    
+                    }
                     
+                    _logger.Verbose("TX ({0} bytes) >>> {1}", packetBuffer.Length, packet);
+
                     if (packetBuffer.Payload.Count == 0 || !AllowPacketFragmentation)
                     {
                         await _channel.WriteAsync(packetBuffer.Join(), true, cancellationToken).ConfigureAwait(false);
@@ -373,53 +396,45 @@ namespace MQTTnet.Adapter
                 return ReceivedMqttPacket.Empty;
             }
 
-            IsReadingPacket = true;
+            var fixedHeader = readFixedHeaderResult.FixedHeader;
-            try
+            if (fixedHeader.RemainingLength == 0)
             {
-                var fixedHeader = readFixedHeaderResult.FixedHeader;
+                return new ReceivedMqttPacket(fixedHeader.Flags, EmptyBuffer.ArraySegment, 2);
-                if (fixedHeader.RemainingLength == 0)
+            }
+
+            var bodyLength = fixedHeader.RemainingLength;
+            var body = new byte[bodyLength];
+
+            var bodyOffset = 0;
+            var chunkSize = Math.Min(ReadBufferSize, bodyLength);
+
+            do
+            {
+                var bytesLeft = body.Length - bodyOffset;
+                if (chunkSize > bytesLeft)
                 {
-                    return new ReceivedMqttPacket(fixedHeader.Flags, EmptyBuffer.ArraySegment, 2);
+                    chunkSize = bytesLeft;
                 }
 
-                var bodyLength = fixedHeader.RemainingLength;
+                var readBytes = await _channel.ReadAsync(body, bodyOffset, chunkSize, cancellationToken).ConfigureAwait(false);
-                var body = new byte[bodyLength];
 
-                var bodyOffset = 0;
+                if (cancellationToken.IsCancellationRequested)
-                var chunkSize = Math.Min(ReadBufferSize, bodyLength);
-
-                do
                 {
-                    var bytesLeft = body.Length - bodyOffset;
+                    return ReceivedMqttPacket.Empty;
-                    if (chunkSize > bytesLeft)
+                }
-                    {
-                        chunkSize = bytesLeft;
-                    }
 
-                    var readBytes = await _channel.ReadAsync(body, bodyOffset, chunkSize, cancellationToken).ConfigureAwait(false);
+                if (readBytes == 0)
+                {
+                    return ReceivedMqttPacket.Empty;
+                }
 
-                    if (cancellationToken.IsCancellationRequested)
+                bodyOffset += readBytes;
-                    {
+            } while (bodyOffset < bodyLength);
-                        return ReceivedMqttPacket.Empty;
-                    }
 
-                    if (readBytes == 0)
+            PacketInspector?.FillReceiveBuffer(body);
-                    {
-                        return ReceivedMqttPacket.Empty;
-                    }
 
-                    bodyOffset += readBytes;
+            var bodySegment = new ArraySegment<byte>(body, 0, bodyLength);
-                } while (bodyOffset < bodyLength);
+            return new ReceivedMqttPacket(fixedHeader.Flags, bodySegment, fixedHeader.TotalLength);
-
-                PacketInspector?.FillReceiveBuffer(body);
-
-                var bodySegment = new ArraySegment<byte>(body, 0, bodyLength);
-                return new ReceivedMqttPacket(fixedHeader.Flags, bodySegment, fixedHeader.TotalLength);
-            }
-            finally
-            {
-                IsReadingPacket = false;
-            }
         }
 
         static bool WrapAndThrowException(Exception exception)

Source/MQTTnet/Adapter/MqttPacketInspector.cs

@@ -4,6 +4,7 @@
 
 using System;
 using System.IO;
+using System.Threading.Tasks;
 using MQTTnet.Diagnostics;
 using MQTTnet.Formatter;
 using MQTTnet.Internal;
@@ -12,16 +13,20 @@ namespace MQTTnet.Adapter
 {
     public sealed class MqttPacketInspector
     {
-        readonly MqttNetSourceLogger _logger;
         readonly AsyncEvent<InspectMqttPacketEventArgs> _asyncEvent;
-        
+        readonly MqttNetSourceLogger _logger;
+
         MemoryStream _receivedPacketBuffer;
-        
+
         public MqttPacketInspector(AsyncEvent<InspectMqttPacketEventArgs> asyncEvent, IMqttNetLogger logger)
         {
             _asyncEvent = asyncEvent ?? throw new ArgumentNullException(nameof(asyncEvent));
-            
+
-            if (logger == null) throw new ArgumentNullException(nameof(logger));
+            if (logger == null)
+            {
+                throw new ArgumentNullException(nameof(logger));
+            }
+
             _logger = logger.WithSource(nameof(MqttPacketInspector));
         }
 
@@ -36,28 +41,15 @@ namespace MQTTnet.Adapter
             {
                 _receivedPacketBuffer = new MemoryStream();
             }
-            
+
             _receivedPacketBuffer?.SetLength(0);
         }
 
-        public void EndReceivePacket()
+        public Task BeginSendPacket(MqttPacketBuffer buffer)
         {
             if (!_asyncEvent.HasHandlers)
             {
-                return;
+                return CompletedTask.Instance;
-            }
-
-            var buffer = _receivedPacketBuffer.ToArray();
-            _receivedPacketBuffer.SetLength(0);
-
-            InspectPacket(buffer, MqttPacketFlowDirection.Inbound);
-        }
-
-        public void BeginSendPacket(MqttPacketBuffer buffer)
-        {
-            if (!_asyncEvent.HasHandlers)
-            {
-                return;
             }
 
             // Create a copy of the actual packet so that the inspector gets no access
@@ -65,7 +57,20 @@ namespace MQTTnet.Adapter
             // intended for debugging etc. so that this is OK.
             var bufferCopy = buffer.ToArray();
 
-            InspectPacket(bufferCopy, MqttPacketFlowDirection.Outbound);
+            return InspectPacket(bufferCopy, MqttPacketFlowDirection.Outbound);
+        }
+
+        public Task EndReceivePacket()
+        {
+            if (!_asyncEvent.HasHandlers)
+            {
+                return CompletedTask.Instance;
+            }
+
+            var buffer = _receivedPacketBuffer.ToArray();
+            _receivedPacketBuffer.SetLength(0);
+
+            return InspectPacket(buffer, MqttPacketFlowDirection.Inbound);
         }
 
         public void FillReceiveBuffer(byte[] buffer)
@@ -74,16 +79,16 @@ namespace MQTTnet.Adapter
             {
                 return;
             }
-            
+
             _receivedPacketBuffer?.Write(buffer, 0, buffer.Length);
         }
 
-        void InspectPacket(byte[] buffer, MqttPacketFlowDirection direction)
+        async Task InspectPacket(byte[] buffer, MqttPacketFlowDirection direction)
         {
             try
             {
                 var eventArgs = new InspectMqttPacketEventArgs(direction, buffer);
-                _asyncEvent.InvokeAsync(eventArgs).GetAwaiter().GetResult();
+                await _asyncEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
             }
             catch (Exception exception)
             {

Source/MQTTnet/Client/Authentication/MqttExtendedAuthenticationExchangeEventArgs.cs

@@ -1,111 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Collections.Generic;
-using System.Threading;
-using System.Threading.Tasks;
-using MQTTnet.Client.Internal;
-using MQTTnet.Exceptions;
-using MQTTnet.Packets;
-using MQTTnet.Protocol;
-
-namespace MQTTnet.Client
-{
-    public sealed class MqttExtendedAuthenticationExchangeEventArgs : EventArgs
-    {
-        static readonly IReadOnlyCollection<MqttUserProperty> EmptyUserProperties = new List<MqttUserProperty>();
-
-        readonly IMqttAuthenticationTransportStrategy _transportStrategy;
-
-        public MqttExtendedAuthenticationExchangeEventArgs(MqttAuthPacket authPacket, IMqttAuthenticationTransportStrategy transportStrategy)
-        {
-            if (authPacket == null)
-            {
-                throw new ArgumentNullException(nameof(authPacket));
-            }
-
-            _transportStrategy = transportStrategy ?? throw new ArgumentNullException(nameof(transportStrategy));
-
-            ReasonCode = authPacket.ReasonCode;
-            ReasonString = authPacket.ReasonString;
-            AuthenticationMethod = authPacket.AuthenticationMethod;
-            AuthenticationData = authPacket.AuthenticationData;
-            UserProperties = authPacket.UserProperties ?? EmptyUserProperties;
-        }
-
-        /// <summary>
-        ///     Gets the authentication data.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
-        /// </summary>
-        public byte[] AuthenticationData { get; }
-
-        /// <summary>
-        ///     Gets the authentication method.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
-        /// </summary>
-        public string AuthenticationMethod { get; }
-
-        /// <summary>
-        ///     Gets the reason code.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
-        /// </summary>
-        public MqttAuthenticateReasonCode ReasonCode { get; }
-
-        /// <summary>
-        ///     Gets the reason string.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
-        /// </summary>
-        public string ReasonString { get; }
-
-        // /// <summary>
-        // ///     Gets the response which will be sent to the server.
-        // /// </summary>
-        // public MqttExtendedAuthenticationExchangeResponse Response { get; } = new MqttExtendedAuthenticationExchangeResponse();
-
-        /// <summary>
-        ///     Gets or sets the user properties.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
-        /// </summary>
-        public IReadOnlyCollection<MqttUserProperty> UserProperties { get; }
-
-        public async Task<MqttClientPartialAuthenticationResponse> ReceiveAuthenticationDataAsync(CancellationToken cancellationToken)
-        {
-            var receivePacket = await _transportStrategy.ReceivePacketAsync(AuthenticationMethod, cancellationToken).ConfigureAwait(false);
-            if (receivePacket == null)
-            {
-                throw new MqttCommunicationException("The client closed the connection.");
-            }
-
-            return new MqttClientPartialAuthenticationResponse
-            {
-                ReasonCode = receivePacket.ReasonCode,
-                AuthenticationData = receivePacket.AuthenticationData,
-                UserProperties = receivePacket.UserProperties
-            };
-        }
-
-        public Task SendAuthenticationDataAsync(
-            MqttAuthenticateReasonCode reasonCode,
-            byte[] authenticationData = null,
-            string reasonString = null,
-            List<MqttUserProperty> userProperties = null,
-            CancellationToken cancellationToken = default)
-        {
-            // The authentication method will never change so we must use the already known one [MQTT-4.12.0-5].
-            //var authPacket = MqttPacketFactories.Auth.Create(AuthenticationMethod, reasonCode);
-
-            var authPacket = new MqttAuthPacket
-            {
-                AuthenticationMethod = AuthenticationMethod,
-                AuthenticationData = authenticationData,
-                UserProperties = userProperties,
-                ReasonCode = reasonCode,
-                ReasonString = reasonString
-            };
-
-            return _transportStrategy.SendPacketAsync(authPacket, cancellationToken);
-        }
-    }
-}

Source/MQTTnet/Client/Authentication/MqttReAuthenticationOptions.cs

@@ -1,28 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System.Collections.Generic;
-using MQTTnet.Packets;
-
-namespace MQTTnet.Client
-{
-    public sealed class MqttReAuthenticationOptions
-    {
-        /// <summary>
-        ///     Gets or sets the authentication data.
-        ///     Authentication data is binary information used to transmit multiple iterations of cryptographic secrets of protocol
-        ///     steps.
-        ///     The content of the authentication data is highly dependent on the specific implementation of the authentication
-        ///     method.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
-        /// </summary>
-        public byte[] AuthenticationData { get; set; }
-
-        /// <summary>
-        ///     Gets or sets the user properties.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
-        /// </summary>
-        public List<MqttUserProperty> UserProperties { get; set; }
-    }
-}

Source/MQTTnet/Client/Connecting/MqttClientConnectResult.cs

@@ -11,112 +11,110 @@ namespace MQTTnet.Client
     public sealed class MqttClientConnectResult
     {
         /// <summary>
-        ///     Gets the client identifier which was chosen by the server.
+        /// Gets the result code.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// MQTTv5 only.
-        /// </summary>
-        public string AssignedClientIdentifier { get; internal set; }
-
-        /// <summary>
-        ///     Gets the authentication data.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
-        /// </summary>
-        public byte[] AuthenticationData { get; internal set; }
-
-        /// <summary>
-        ///     Gets the authentication method.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
-        /// </summary>
-        public string AuthenticationMethod { get; internal set; }
-
-        /// <summary>
-        ///     Gets a value indicating whether a session was already available or not.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
-        /// </summary>
-        public bool IsSessionPresent { get; internal set; }
-
-        public uint? MaximumPacketSize { get; internal set; }
-
-        /// <summary>
-        ///     Gets the maximum QoS which is supported by the server.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
-        /// </summary>
-        public MqttQualityOfServiceLevel MaximumQoS { get; internal set; }
-
-        /// <summary>
-        ///     Gets the reason string.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
-        /// </summary>
-        public string ReasonString { get; internal set; }
-
-        public ushort? ReceiveMaximum { get; internal set; }
-
-        /// <summary>
-        ///     Gets the response information.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
-        /// </summary>
-        public string ResponseInformation { get; internal set; }
-
-        /// <summary>
-        ///     Gets the result code.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public MqttClientConnectResultCode ResultCode { get; internal set; }
 
         /// <summary>
-        ///     Gets whether the server supports retained messages.
+        /// Gets a value indicating whether a session was already available or not.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// MQTTv5 only.
+        /// </summary>
+        public bool IsSessionPresent { get; internal set; }
+
+        /// <summary>
+        /// Gets a value indicating whether wildcards can be used in subscriptions at the current server.
+        /// MQTTv5 only.
+        /// </summary>
+        public bool WildcardSubscriptionAvailable { get; internal set; }
+
+        /// <summary>
+        /// Gets whether the server supports retained messages.
+        /// MQTTv5 only.
         /// </summary>
         public bool RetainAvailable { get; internal set; }
 
         /// <summary>
-        ///     MQTTv5 only.
+        /// Gets the client identifier which was chosen by the server.
-        ///     Gets the keep alive interval which was chosen by the server instead of the
+        /// MQTTv5 only.
-        ///     keep alive interval from the client CONNECT packet.
-        ///     A value of 0 indicates that the feature is not used.
         /// </summary>
-        public ushort ServerKeepAlive { get; internal set; }
+        public string AssignedClientIdentifier { get; internal set; }
 
         /// <summary>
-        ///     Gets an alternate server which should be used instead of the current one.
+        /// Gets the authentication method.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// MQTTv5 only.
         /// </summary>
-        public string ServerReference { get; internal set; }
+        public string AuthenticationMethod { get; internal set; }
-
-        public uint? SessionExpiryInterval { get; internal set; }
 
         /// <summary>
-        ///     Gets a value indicating whether the shared subscriptions are available or not.
+        /// Gets the authentication data.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// MQTTv5 only.
         /// </summary>
-        public bool SharedSubscriptionAvailable { get; internal set; }
+        public byte[] AuthenticationData { get; internal set; }
+
+        public uint? MaximumPacketSize { get; internal set; }
 
         /// <summary>
-        ///     Gets a value indicating whether the subscription identifiers are available or not.
+        /// Gets the reason string.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// MQTTv5 only.
         /// </summary>
-        public bool SubscriptionIdentifiersAvailable { get; internal set; }
+        public string ReasonString { get; internal set; }
+
+        public ushort? ReceiveMaximum { get; internal set; }
+        
+        /// <summary>
+        /// Gets the maximum QoS which is supported by the server.
+        /// MQTTv5 only.
+        /// </summary>
+        public MqttQualityOfServiceLevel MaximumQoS { get; internal set; }
 
         /// <summary>
-        ///     Gets the maximum value for a topic alias. 0 means not supported.
+        /// Gets the response information.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// MQTTv5 only.
+        /// </summary>
+        public string ResponseInformation { get; internal set; }
+
+        /// <summary>
+        /// Gets the maximum value for a topic alias. 0 means not supported.
+        /// MQTTv5 only.
         /// </summary>
         public ushort TopicAliasMaximum { get; internal set; }
 
         /// <summary>
-        ///     Gets the user properties.
+        /// Gets an alternate server which should be used instead of the current one.
-        ///     In MQTT 5, user properties are basic UTF-8 string key-value pairs that you can append to almost every type of MQTT
+        /// MQTTv5 only.
-        ///     packet.
-        ///     As long as you don’t exceed the maximum message size, you can use an unlimited number of user properties to add
-        ///     metadata to MQTT messages and pass information between publisher, broker, and subscriber.
-        ///     The feature is very similar to the HTTP header concept.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
-        public List<MqttUserProperty> UserProperties { get; internal set; }
+        public string ServerReference { get; internal set; }
 
         /// <summary>
-        ///     Gets a value indicating whether wildcards can be used in subscriptions at the current server.
+        /// MQTTv5 only.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// Gets the keep alive interval which was chosen by the server instead of the
+        /// keep alive interval from the client CONNECT packet.
+        /// A value of 0 indicates that the feature is not used.
         /// </summary>
-        public bool WildcardSubscriptionAvailable { get; internal set; }
+        public ushort ServerKeepAlive { get; internal set; }
+
+        public uint? SessionExpiryInterval { get; internal set; }
+
+        /// <summary>
+        /// Gets a value indicating whether the subscription identifiers are available or not.
+        /// MQTTv5 only.
+        /// </summary>
+        public bool SubscriptionIdentifiersAvailable { get; internal set; }
+
+        /// <summary>
+        /// Gets a value indicating whether the shared subscriptions are available or not.
+        /// MQTTv5 only.
+        /// </summary>
+        public bool SharedSubscriptionAvailable { get; internal set; }
+
+        /// <summary>
+        /// Gets the user properties.
+        /// In MQTT 5, user properties are basic UTF-8 string key-value pairs that you can append to almost every type of MQTT packet.
+        /// As long as you don’t exceed the maximum message size, you can use an unlimited number of user properties to add metadata to MQTT messages and pass information between publisher, broker, and subscriber.
+        /// The feature is very similar to the HTTP header concept.
+        /// MQTTv5 only.
+        /// </summary>
+        public List<MqttUserProperty> UserProperties { get; internal set; }
     }
-}
+}

Source/MQTTnet/Client/Exceptions/MqttClientUnexpectedDisconnectReceivedException.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
 using MQTTnet.Exceptions;
 using MQTTnet.Packets;
@@ -11,8 +12,9 @@ namespace MQTTnet.Client
 {
     public sealed class MqttClientUnexpectedDisconnectReceivedException : MqttCommunicationException
     {
-        public MqttClientUnexpectedDisconnectReceivedException(MqttDisconnectPacket disconnectPacket) 
+        public MqttClientUnexpectedDisconnectReceivedException(MqttDisconnectPacket disconnectPacket, Exception innerExcpetion = null) : base(
-            : base($"Unexpected DISCONNECT (Reason code={disconnectPacket.ReasonCode}) received.")
+            $"Unexpected DISCONNECT (Reason code={disconnectPacket.ReasonCode}) received.",
+            innerExcpetion)
         {
             ReasonCode = disconnectPacket.ReasonCode;
             SessionExpiryInterval = disconnectPacket.SessionExpiryInterval;
@@ -23,12 +25,12 @@ namespace MQTTnet.Client
 
         public MqttDisconnectReasonCode? ReasonCode { get; }
 
-        public uint? SessionExpiryInterval { get; }
-
         public string ReasonString { get; }
 
-        public List<MqttUserProperty> UserProperties { get; }
-
         public string ServerReference { get; }
+
+        public uint? SessionExpiryInterval { get; }
+
+        public List<MqttUserProperty> UserProperties { get; }
     }
-}
+}

Source/MQTTnet/Client/ExtendedAuthenticationExchange/IMqttExtendedAuthenticationExchangeHandler.cs

@@ -0,0 +1,13 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Threading.Tasks;
+
+namespace MQTTnet.Client
+{
+    public interface IMqttExtendedAuthenticationExchangeHandler
+    {
+        Task HandleRequestAsync(MqttExtendedAuthenticationExchangeContext context);
+    }
+}

Source/MQTTnet/Client/ExtendedAuthenticationExchange/MqttExtendedAuthenticationExchangeContext.cs

@@ -0,0 +1,69 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using MQTTnet.Packets;
+using MQTTnet.Protocol;
+
+namespace MQTTnet.Client
+{
+    public class MqttExtendedAuthenticationExchangeContext
+    {
+        public MqttExtendedAuthenticationExchangeContext(MqttAuthPacket authPacket, MqttClient client, CancellationToken cancellationToken)
+        {
+            if (authPacket == null) throw new ArgumentNullException(nameof(authPacket));
+
+            ReasonCode = authPacket.ReasonCode;
+            ReasonString = authPacket.ReasonString;
+            AuthenticationMethod = authPacket.AuthenticationMethod;
+            AuthenticationData = authPacket.AuthenticationData;
+            UserProperties = authPacket.UserProperties;
+
+            Client = client ?? throw new ArgumentNullException(nameof(client));
+            CancellationToken = cancellationToken;
+        }
+
+        /// <summary>
+        /// Gets the reason code.
+        /// Hint: MQTT 5 feature only.
+        /// </summary>
+        public MqttAuthenticateReasonCode ReasonCode { get; }
+
+        /// <summary>
+        /// Gets the reason string.
+        /// Hint: MQTT 5 feature only.
+        /// </summary>
+        public string ReasonString { get; }
+
+        /// <summary>
+        /// Gets the authentication method.
+        /// Hint: MQTT 5 feature only.
+        /// </summary>
+        public string AuthenticationMethod { get; }
+
+        /// <summary>
+        /// Gets the authentication data.
+        /// Hint: MQTT 5 feature only.
+        /// </summary>
+        public byte[] AuthenticationData { get; }
+
+        /// <summary>
+        /// Gets the user properties.
+        /// In MQTT 5, user properties are basic UTF-8 string key-value pairs that you can append to almost every type of MQTT packet.
+        /// As long as you don’t exceed the maximum message size, you can use an unlimited number of user properties to add metadata to MQTT messages and pass information between publisher, broker, and subscriber.
+        /// The feature is very similar to the HTTP header concept.
+        /// Hint: MQTT 5 feature only.
+        /// </summary>
+        public List<MqttUserProperty> UserProperties { get; }
+
+        public MqttClient Client { get; }
+
+        /// <summary>
+        /// The cancellation token passed to the operation being authenticated (e.g. ConnectAsync).
+        /// </summary>
+        public CancellationToken CancellationToken { get; }
+    }
+}

Source/MQTTnet/Client/ExtendedAuthenticationExchange/MqttExtendedAuthenticationExchangeData.cs

@@ -0,0 +1,42 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Generic;
+using MQTTnet.Packets;
+using MQTTnet.Protocol;
+
+namespace MQTTnet.Client
+{
+    public class MqttExtendedAuthenticationExchangeData
+    {
+        /// <summary>
+        /// Gets or sets the reason code.
+        /// Hint: MQTT 5 feature only.
+        /// </summary>
+        public MqttAuthenticateReasonCode ReasonCode { get; set; }
+
+        /// <summary>
+        /// Gets or sets the reason string.
+        /// Hint: MQTT 5 feature only.
+        /// </summary>
+        public string ReasonString { get; set; }
+
+        /// <summary>
+        /// Gets or sets the authentication data.
+        /// Authentication data is binary information used to transmit multiple iterations of cryptographic secrets of protocol steps.
+        /// The content of the authentication data is highly dependent on the specific implementation of the authentication method.
+        /// Hint: MQTT 5 feature only.
+        /// </summary>
+        public byte[] AuthenticationData { get; set; }
+
+        /// <summary>
+        /// Gets or sets the user properties.
+        /// In MQTT 5, user properties are basic UTF-8 string key-value pairs that you can append to almost every type of MQTT packet.
+        /// As long as you don’t exceed the maximum message size, you can use an unlimited number of user properties to add metadata to MQTT messages and pass information between publisher, broker, and subscriber.
+        /// The feature is very similar to the HTTP header concept.
+        /// Hint: MQTT 5 feature only.
+        /// </summary>
+        public List<MqttUserProperty> UserProperties { get; }
+    }
+}

Source/MQTTnet/Client/IMqttClient.cs

@@ -8,15 +8,13 @@ namespace MQTTnet.Client
     public interface IMqttClient : IDisposable
     {
         event Func<MqttApplicationMessageReceivedEventArgs, Task> ApplicationMessageReceivedAsync;
-
+        
         event Func<MqttClientConnectedEventArgs, Task> ConnectedAsync;
 
         event Func<MqttClientConnectingEventArgs, Task> ConnectingAsync;
 
         event Func<MqttClientDisconnectedEventArgs, Task> DisconnectedAsync;
 
-        event Func<MqttExtendedAuthenticationExchangeEventArgs, Task> ExtendedAuthenticationExchangeAsync;
-
         event Func<InspectMqttPacketEventArgs, Task> InspectPacketAsync;
 
         bool IsConnected { get; }
@@ -31,7 +29,7 @@ namespace MQTTnet.Client
 
         Task<MqttClientPublishResult> PublishAsync(MqttApplicationMessage applicationMessage, CancellationToken cancellationToken = default);
 
-        Task ReAuthenticateAsync(MqttReAuthenticationOptions options, CancellationToken cancellationToken = default);
+        Task SendExtendedAuthenticationExchangeDataAsync(MqttExtendedAuthenticationExchangeData data, CancellationToken cancellationToken = default);
 
         Task<MqttClientSubscribeResult> SubscribeAsync(MqttClientSubscribeOptions options, CancellationToken cancellationToken = default);
 

Source/MQTTnet/Client/Internal/MqttClientAuthenticationHandler.cs

@@ -1,225 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Threading;
-using System.Threading.Tasks;
-using MQTTnet.Adapter;
-using MQTTnet.Diagnostics;
-using MQTTnet.Exceptions;
-using MQTTnet.Formatter;
-using MQTTnet.Internal;
-using MQTTnet.Packets;
-using MQTTnet.Protocol;
-
-namespace MQTTnet.Client.Internal
-{
-    public sealed class MqttInitialAuthenticationStrategy : IMqttAuthenticationTransportStrategy
-    {
-        readonly IMqttChannelAdapter _channelAdapter;
-
-        public MqttInitialAuthenticationStrategy(IMqttChannelAdapter channelAdapter)
-        {
-            _channelAdapter = channelAdapter ?? throw new ArgumentNullException(nameof(channelAdapter));
-        }
-
-
-        public Task SendPacketAsync(MqttAuthPacket authPacket, CancellationToken cancellationToken)
-        {
-            if (authPacket == null)
-            {
-                throw new ArgumentNullException(nameof(authPacket));
-            }
-
-            return _channelAdapter.SendPacketAsync(authPacket, cancellationToken);
-        }
-
-        public async Task<MqttAuthPacket> ReceivePacketAsync(string authenticationMethod, CancellationToken cancellationToken)
-        {
-            if (authenticationMethod == null)
-            {
-                throw new ArgumentNullException(nameof(authenticationMethod));
-            }
-
-            var receivePacket = await _channelAdapter.ReceivePacketAsync(cancellationToken).ConfigureAwait(false);
-            if (receivePacket is MqttAuthPacket authPacket)
-            {
-                if (!string.Equals(authPacket.AuthenticationMethod, authenticationMethod, StringComparison.Ordinal))
-                {
-                    throw new MqttProtocolViolationException("The authentication method is not allowed to change while authenticating.");
-                }
-
-                return authPacket;
-            }
-
-            if (receivePacket == null)
-            {
-                throw new MqttCommunicationException("The server closed the connection.");
-            }
-
-            throw new MqttProtocolViolationException("Expected an AUTH packet from the client.");
-        }
-    }
-    
-    public interface IMqttAuthenticationTransportStrategy
-    {
-        Task SendPacketAsync(MqttAuthPacket authPacket, CancellationToken cancellationToken);
-        
-        Task<MqttAuthPacket> ReceivePacketAsync(string authenticationMethod, CancellationToken cancellationToken);
-    }
-    
-    public sealed class MqttClientAuthenticationHandler
-    {
-        readonly MqttClient _client;
-
-        readonly AsyncEvent<MqttExtendedAuthenticationExchangeEventArgs> _extendedAuthenticationExchangeEvent = new AsyncEvent<MqttExtendedAuthenticationExchangeEventArgs>();
-        readonly MqttNetSourceLogger _logger;
-
-        public MqttClientAuthenticationHandler(MqttClient client, IMqttNetLogger logger)
-        {
-            if (logger == null)
-            {
-                throw new ArgumentNullException(nameof(logger));
-            }
-
-            _client = client ?? throw new ArgumentNullException(nameof(client));
-            _logger = logger.WithSource(nameof(MqttClientAuthenticationHandler));
-        }
-
-        public void AddHandler(Func<MqttExtendedAuthenticationExchangeEventArgs, Task> handler)
-        {
-            _extendedAuthenticationExchangeEvent.AddHandler(handler);
-        }
-
-        public async Task<MqttClientConnectResult> Authenticate(IMqttChannelAdapter channelAdapter, MqttClientOptions options, CancellationToken cancellationToken)
-        {
-            if (channelAdapter == null)
-            {
-                throw new ArgumentNullException(nameof(channelAdapter));
-            }
-
-            if (options == null)
-            {
-                throw new ArgumentNullException(nameof(options));
-            }
-
-            // From the RFC:
-            // The CONNACK packet is the packet sent by the Server in response to a CONNECT packet received from a Client.
-            // The Server MUST send a CONNACK with a 0x00 (Success) Reason Code before sending any Packet other than AUTH [MQTT-3.2.0-1].
-            // The Server MUST NOT send more than one CONNACK in a Network Connection [MQTT-3.2.0-2].
-
-            MqttClientConnectResult result;
-
-            try
-            {
-                // Send the CONNECT packet..
-                var connectPacket = MqttPacketFactories.Connect.Create(options);
-                await _client.Send(connectPacket, cancellationToken).ConfigureAwait(false);
-
-                // Wait for the CONNACK packet...
-                MqttConnAckPacket connAckPacket = null;
-                while (!cancellationToken.IsCancellationRequested)
-                {
-                    var receivedPacket = await channelAdapter.ReceivePacketAsync(cancellationToken).ConfigureAwait(false);
-
-                    if (receivedPacket is MqttAuthPacket initialAuthPacket)
-                    {
-                        // MQTT v3.1.1 cannot send an AUTH packet.
-                        // If the Server requires additional information to complete the authentication, it can send an AUTH packet to the Client.
-                        // This packet MUST contain a Reason Code of 0x18 (Continue authentication)
-                        if (initialAuthPacket.ReasonCode != MqttAuthenticateReasonCode.ContinueAuthentication)
-                        {
-                            throw new MqttProtocolViolationException("Wrong reason code received [MQTT-4.12.0-2].");
-                        }
-
-                        //var response = await HandleExtendedAuthentication(authPacket, channelAdapter).ConfigureAwait(false);
-                        await HandleExtendedAuthentication(initialAuthPacket, new MqttInitialAuthenticationStrategy(channelAdapter)).ConfigureAwait(false);
-                    }
-                    else if (receivedPacket is MqttConnAckPacket connAckPacketBuffer)
-                    {
-                        connAckPacket = connAckPacketBuffer;
-                        
-                        // The CONNACK packet is the last packet when authenticating so there is no further AUTH packet allowed!
-                        break;
-                    }
-                    else
-                    {
-                        throw new MqttProtocolViolationException($"Received {receivedPacket.GetRfcName()} while authenticating.");
-                    }
-                }
-
-                cancellationToken.ThrowIfCancellationRequested();
-
-                // If the initial CONNECT packet included an Authentication Method property then all AUTH packets,
-                // and any successful CONNACK packet MUST include an Authentication Method Property with the same
-                // value as in the CONNECT packet [MQTT-4.12.0-5].
-                if (!string.IsNullOrEmpty(connectPacket.AuthenticationMethod))
-                {
-                    if (!string.Equals(connectPacket.AuthenticationMethod, connAckPacket?.AuthenticationMethod))
-                    {
-                        throw new MqttProtocolViolationException("The CONNACK packet does not have the same authentication method as the CONNECT packet.");
-                    }
-                }
-
-                result = MqttClientResultFactory.ConnectResult.Create(connAckPacket, channelAdapter.PacketFormatterAdapter.ProtocolVersion);
-            }
-            catch (Exception exception)
-            {
-                throw new MqttConnectingFailedException($"Error while authenticating. {exception.Message}", exception, null);
-            }
-
-            // This is no feature. It is basically a backward compatibility option and should be removed in the future.
-            // The client should not throw any exception if the transport layer connection was successful and the server
-            // did send a proper ACK packet.
-            if (options.ThrowOnNonSuccessfulResponseFromServer)
-            {
-                _logger.Warning(
-                    "Client will now throw an _MqttConnectingFailedException_. This is obsolete and will be removed in the future. Consider setting _ThrowOnNonSuccessfulResponseFromServer=False_ in client options.");
-
-                if (result.ResultCode != MqttClientConnectResultCode.Success)
-                {
-                    throw new MqttConnectingFailedException($"Connecting with MQTT server failed ({result.ResultCode}).", null, result);
-                }
-            }
-
-            _logger.Verbose("Authenticated MQTT connection with server established.");
-
-            return result;
-        }
-
-        public Task HandleExtendedAuthentication(MqttAuthPacket initialAuthPacket, IMqttAuthenticationTransportStrategy transportStrategy)
-        {
-            ValidateEventHandler();
-
-            var eventArgs = new MqttExtendedAuthenticationExchangeEventArgs(initialAuthPacket, transportStrategy);
-            return _extendedAuthenticationExchangeEvent.InvokeAsync(eventArgs);
-        }
-
-        void ValidateEventHandler()
-        {
-            if (!_extendedAuthenticationExchangeEvent.HasHandlers)
-            {
-                throw new InvalidOperationException("Cannot handle extended authentication without attached event handler.");
-            }
-        }
-        
-        public void RemoveHandler(Func<MqttExtendedAuthenticationExchangeEventArgs, Task> handler)
-        {
-            _extendedAuthenticationExchangeEvent.RemoveHandler(handler);
-        }
-
-        public async Task ReAuthenticate(MqttReAuthenticationOptions options, CancellationToken cancellationToken)
-        {
-            ValidateEventHandler();
-            
-            var authPacket = MqttPacketFactories.Auth.CreateReAuthenticationPacket(_client.Options, options);
-
-            
-            
-            // Sending the AUTH packet will trigger the re authentication and the event handler will
-            // handle the details.
-            await _client.Send(authPacket, cancellationToken).ConfigureAwait(false);
-        }
-    }
-}

Source/MQTTnet/Client/Internal/MqttClientKeepAliveHandler.cs

@@ -1,126 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Threading;
-using System.Threading.Tasks;
-using MQTTnet.Diagnostics;
-using MQTTnet.Exceptions;
-
-namespace MQTTnet.Client.Internal
-{
-    public sealed class MqttClientKeepAliveHandler
-    {
-        readonly MqttClient _client;
-        readonly MqttNetSourceLogger _logger;
-
-        CancellationTokenSource _cancellationToken;
-        TimeSpan _keepAliveInterval;
-        Task _keepAlivePacketsSenderTask;
-        DateTime _lastPacketSentTimestamp;
-
-        public MqttClientKeepAliveHandler(MqttClient client, IMqttNetLogger logger)
-        {
-            _client = client ?? throw new ArgumentNullException(nameof(client));
-            _logger = logger.WithSource(nameof(MqttClientKeepAliveHandler));
-        }
-
-        public void Disable()
-        {
-            try
-            {
-                _cancellationToken?.Cancel(false);
-            }
-            finally
-            {
-                _cancellationToken?.Dispose();
-                _cancellationToken = null;
-            }
-        }
-
-        public void Enable(MqttClientConnectResult connectResult)
-        {
-            if (connectResult == null)
-            {
-                throw new ArgumentNullException(nameof(connectResult));
-            }
-
-            _keepAliveInterval = _client.Options.KeepAlivePeriod;
-
-            if (connectResult.ServerKeepAlive > 0)
-            {
-                _logger.Info("Using keep alive value {0} sent from the server", connectResult.ServerKeepAlive);
-                _keepAliveInterval = TimeSpan.FromSeconds(connectResult.ServerKeepAlive);
-            }
-
-            if (_keepAliveInterval == TimeSpan.Zero)
-            {
-                return;
-            }
-
-            _cancellationToken = new CancellationTokenSource();
-            _keepAlivePacketsSenderTask = Task.Run(() => SendKeepAliveMessagesLoop(_cancellationToken.Token), _cancellationToken.Token);
-        }
-
-        public void TrackSentPacket()
-        {
-            // Only use UTC to avoid performance hit by loading current time zone all the time.
-            _lastPacketSentTimestamp = DateTime.UtcNow;
-        }
-
-        async Task SendKeepAliveMessagesLoop(CancellationToken cancellationToken)
-        {
-            try
-            {
-                _logger.Verbose("Start sending keep alive packets.");
-
-                while (!cancellationToken.IsCancellationRequested)
-                {
-                    // Values described here: [MQTT-3.1.2-24].
-                    var timeWithoutPacketSent = DateTime.UtcNow - _lastPacketSentTimestamp;
-
-                    if (timeWithoutPacketSent > _keepAliveInterval)
-                    {
-                        using (var timeout = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken))
-                        {
-                            timeout.CancelAfter(_client.Options.Timeout);
-                            await _client.PingAsync(timeout.Token).ConfigureAwait(false);
-                        }
-                    }
-
-                    // Wait a fixed time in all cases. Calculation of the remaining time is complicated
-                    // due to some edge cases and was buggy in the past. Now we wait several ms because the
-                    // min keep alive value is one second so that the server will wait 1.5 seconds for a PING packet.
-                    await Task.Delay(250, cancellationToken).ConfigureAwait(false);
-                }
-            }
-            catch (Exception exception)
-            {
-                if (_client._cleanDisconnectInitiated)
-                {
-                    return;
-                }
-
-                if (exception is OperationCanceledException)
-                {
-                    return;
-                }
-                else if (exception is MqttCommunicationException)
-                {
-                    _logger.Warning(exception, "Communication error while sending/receiving keep alive packets");
-                }
-                else
-                {
-                    _logger.Error(exception, "Error exception while sending/receiving keep alive packets");
-                }
-
-                await _client.DisconnectInternalAsync(_keepAlivePacketsSenderTask, exception, null).ConfigureAwait(false);
-            }
-            finally
-            {
-                _logger.Verbose("Stopped sending keep alive packets");
-            }
-        }
-    }
-}

Source/MQTTnet/Client/MqttClient.cs

@@ -21,19 +21,17 @@ namespace MQTTnet.Client
     public sealed class MqttClient : Disposable, IMqttClient
     {
         readonly IMqttClientAdapterFactory _adapterFactory;
-        readonly MqttClientAuthenticationHandler _authenticationHandler;
+
         readonly object _disconnectLock = new object();
         readonly MqttClientEvents _events = new MqttClientEvents();
-        readonly MqttClientKeepAliveHandler _keepAliveHandler;
         readonly MqttNetSourceLogger _logger;
+
         readonly MqttPacketIdentifierProvider _packetIdentifierProvider = new MqttPacketIdentifierProvider();
         readonly IMqttNetLogger _rootLogger;
 
-        IMqttChannelAdapter _channelAdapter;
+        IMqttChannelAdapter _adapter;
 
-        internal bool _cleanDisconnectInitiated;
+        bool _cleanDisconnectInitiated;
-
-        CancellationTokenSource _clientAlive;
         volatile int _connectionStatus;
 
         // The value for this field can be set from two different enums.
@@ -41,19 +39,22 @@ namespace MQTTnet.Client
         int _disconnectReason;
         string _disconnectReasonString;
         List<MqttUserProperty> _disconnectUserProperties;
+
+        Task _keepAlivePacketsSenderTask;
+        DateTime _lastPacketSentTimestamp;
+
+        CancellationTokenSource _mqttClientAlive;
         MqttPacketDispatcher _packetDispatcher;
         Task _packetReceiverTask;
         AsyncQueue<MqttPublishPacket> _publishPacketReceiverQueue;
         Task _publishPacketReceiverTask;
+        MqttDisconnectPacket _unexpectedDisconnectPacket;
 
         public MqttClient(IMqttClientAdapterFactory channelFactory, IMqttNetLogger logger)
         {
             _adapterFactory = channelFactory ?? throw new ArgumentNullException(nameof(channelFactory));
             _rootLogger = logger ?? throw new ArgumentNullException(nameof(logger));
             _logger = logger.WithSource(nameof(MqttClient));
-
-            _authenticationHandler = new MqttClientAuthenticationHandler(this, logger);
-            _keepAliveHandler = new MqttClientKeepAliveHandler(this, logger);
         }
 
         public event Func<MqttApplicationMessageReceivedEventArgs, Task> ApplicationMessageReceivedAsync
@@ -80,12 +81,6 @@ namespace MQTTnet.Client
             remove => _events.DisconnectedEvent.RemoveHandler(value);
         }
 
-        public event Func<MqttExtendedAuthenticationExchangeEventArgs, Task> ExtendedAuthenticationExchangeAsync
-        {
-            add => _authenticationHandler.AddHandler(value);
-            remove => _authenticationHandler.RemoveHandler(value);
-        }
-
         public event Func<InspectMqttPacketEventArgs, Task> InspectPacketAsync
         {
             add => _events.InspectPacketEvent.AddHandler(value);
@@ -94,6 +89,8 @@ namespace MQTTnet.Client
 
         public bool IsConnected => (MqttClientConnectionStatus)_connectionStatus == MqttClientConnectionStatus.Connected;
 
+        bool IsConnecting => (MqttClientConnectionStatus)_connectionStatus == MqttClientConnectionStatus.Connecting;
+
         public MqttClientOptions Options { get; private set; }
 
         public async Task<MqttClientConnectResult> ConnectAsync(MqttClientOptions options, CancellationToken cancellationToken = default)
@@ -122,14 +119,18 @@ namespace MQTTnet.Client
 
                 _packetIdentifierProvider.Reset();
                 _packetDispatcher = new MqttPacketDispatcher();
-                _clientAlive = new CancellationTokenSource();
+
+                _mqttClientAlive = new CancellationTokenSource();
+                var mqttClientAliveToken = _mqttClientAlive.Token;
 
                 var adapter = _adapterFactory.CreateClientAdapter(options, new MqttPacketInspector(_events.InspectPacketEvent, _rootLogger), _rootLogger);
-                _channelAdapter = adapter;
+                _adapter = adapter ?? throw new InvalidOperationException("The adapter factory did not provide an adapter.");
+
+                _unexpectedDisconnectPacket = null;
 
                 if (cancellationToken.CanBeCanceled)
                 {
-                    connectResult = await ConnectInternal(cancellationToken).ConfigureAwait(false);
+                    connectResult = await ConnectInternal(adapter, cancellationToken).ConfigureAwait(false);
                 }
                 else
                 {
@@ -137,10 +138,31 @@ namespace MQTTnet.Client
                     // CancellationToken.None or similar.
                     using (var timeout = new CancellationTokenSource(Options.Timeout))
                     {
-                        connectResult = await ConnectInternal(timeout.Token).ConfigureAwait(false);
+                        connectResult = await ConnectInternal(adapter, timeout.Token).ConfigureAwait(false);
                     }
                 }
 
+                if (connectResult.ResultCode != MqttClientConnectResultCode.Success)
+                {
+                    _logger.Warning("Connecting failed: {0}", connectResult.ResultCode);
+                    await DisconnectInternal(null, null, connectResult).ConfigureAwait(false);
+                    return connectResult;
+                }
+
+                _lastPacketSentTimestamp = DateTime.UtcNow;
+
+                var keepAliveInterval = Options.KeepAlivePeriod;
+                if (connectResult.ServerKeepAlive > 0)
+                {
+                    _logger.Info($"Using keep alive value ({connectResult.ServerKeepAlive}) sent from the server");
+                    keepAliveInterval = TimeSpan.FromSeconds(connectResult.ServerKeepAlive);
+                }
+
+                if (keepAliveInterval != TimeSpan.Zero)
+                {
+                    _keepAlivePacketsSenderTask = Task.Run(() => TrySendKeepAliveMessages(mqttClientAliveToken), mqttClientAliveToken);
+                }
+
                 CompareExchangeConnectionStatus(MqttClientConnectionStatus.Connected, MqttClientConnectionStatus.Connecting);
 
                 _logger.Info("Connected");
@@ -194,11 +216,11 @@ namespace MQTTnet.Client
 
                 if (Options.ValidateFeatures)
                 {
-                    MqttClientDisconnectOptionsValidator.ThrowIfNotSupported(options, _channelAdapter.PacketFormatterAdapter.ProtocolVersion);
+                    MqttClientDisconnectOptionsValidator.ThrowIfNotSupported(options, _adapter.PacketFormatterAdapter.ProtocolVersion);
                 }
 
                 // Sending the DISCONNECT may fail due to connection issues. The resulting exception
-                // must be throw to let the caller know that the disconnect is not a clean one.
+                // must be thrown to let the caller know that the disconnect was not clean.
                 var disconnectPacket = MqttPacketFactories.Disconnect.Create(options);
 
                 if (cancellationToken.CanBeCanceled)
@@ -221,6 +243,11 @@ namespace MQTTnet.Client
 
         public async Task PingAsync(CancellationToken cancellationToken = default)
         {
+            cancellationToken.ThrowIfCancellationRequested();
+
+            ThrowIfDisposed();
+            ThrowIfNotConnected();
+
             if (cancellationToken.CanBeCanceled)
             {
                 await Request<MqttPingRespPacket>(MqttPingReqPacket.Instance, cancellationToken).ConfigureAwait(false);
@@ -245,7 +272,7 @@ namespace MQTTnet.Client
 
             if (Options.ValidateFeatures)
             {
-                MqttApplicationMessageValidator.ThrowIfNotSupported(applicationMessage, _channelAdapter.PacketFormatterAdapter.ProtocolVersion);
+                MqttApplicationMessageValidator.ThrowIfNotSupported(applicationMessage, _adapter.PacketFormatterAdapter.ProtocolVersion);
             }
 
             var publishPacket = MqttPacketFactories.Publish.Create(applicationMessage);
@@ -271,25 +298,27 @@ namespace MQTTnet.Client
             }
         }
 
-        public Task ReAuthenticateAsync(MqttReAuthenticationOptions options, CancellationToken cancellationToken = default)
+        public Task SendExtendedAuthenticationExchangeDataAsync(MqttExtendedAuthenticationExchangeData data, CancellationToken cancellationToken = default)
         {
-            if (options == null)
+            if (data == null)
             {
-                throw new ArgumentNullException(nameof(options));
+                throw new ArgumentNullException(nameof(data));
             }
 
             ThrowIfDisposed();
-            ThrowIfNotConnected();
+            ThrowIfNotConnectedOrConnecting();
 
-            if (cancellationToken.CanBeCanceled)
+            var authPacket = new MqttAuthPacket
             {
-                return _authenticationHandler.ReAuthenticate(options, cancellationToken);
+                // This must always be equal to the value from the CONNECT packet. So we use it here to ensure that.
-            }
+                AuthenticationMethod = Options.AuthenticationMethod,
+                AuthenticationData = data.AuthenticationData,
+                ReasonString = data.ReasonString,
+                ReasonCode = data.ReasonCode,
+                UserProperties = data.UserProperties
+            };
 
-            using (var timeout = new CancellationTokenSource(Options.Timeout))
+            return Send(authPacket, cancellationToken);
-            {
-                return _authenticationHandler.ReAuthenticate(options, timeout.Token);
-            }
         }
 
         public async Task<MqttClientSubscribeResult> SubscribeAsync(MqttClientSubscribeOptions options, CancellationToken cancellationToken = default)
@@ -304,14 +333,14 @@ namespace MQTTnet.Client
                 MqttTopicValidator.ThrowIfInvalidSubscribe(topicFilter.Topic);
             }
 
-            if (Options.ValidateFeatures)
-            {
-                MqttClientSubscribeOptionsValidator.ThrowIfNotSupported(options, _channelAdapter.PacketFormatterAdapter.ProtocolVersion);
-            }
-
             ThrowIfDisposed();
             ThrowIfNotConnected();
 
+            if (Options.ValidateFeatures)
+            {
+                MqttClientSubscribeOptionsValidator.ThrowIfNotSupported(options, _adapter.PacketFormatterAdapter.ProtocolVersion);
+            }
+
             var subscribePacket = MqttPacketFactories.Subscribe.Create(options);
             subscribePacket.PacketIdentifier = _packetIdentifierProvider.GetNextPacketIdentifier();
 
@@ -348,7 +377,7 @@ namespace MQTTnet.Client
 
             if (Options.ValidateFeatures)
             {
-                MqttClientUnsubscribeOptionsValidator.ThrowIfNotSupported(options, _channelAdapter.PacketFormatterAdapter.ProtocolVersion);
+                MqttClientUnsubscribeOptionsValidator.ThrowIfNotSupported(options, _adapter.PacketFormatterAdapter.ProtocolVersion);
             }
 
             var unsubscribePacket = MqttPacketFactories.Unsubscribe.Create(options);
@@ -370,27 +399,6 @@ namespace MQTTnet.Client
             return MqttClientResultFactory.UnsubscribeResult.Create(unsubscribePacket, unsubAckPacket);
         }
 
-        internal Task DisconnectInternalAsync(Task sender, Exception exception, MqttClientConnectResult connectResult)
-        {
-            var clientWasConnected = IsConnected;
-
-            if (!DisconnectIsPendingOrFinished())
-            {
-                return DisconnectCore(sender, exception, connectResult, clientWasConnected);
-            }
-
-            return CompletedTask.Instance;
-        }
-
-        internal Task Send(MqttPacket packet, CancellationToken cancellationToken)
-        {
-            cancellationToken.ThrowIfCancellationRequested();
-
-            _keepAliveHandler.TrackSentPacket();
-
-            return _channelAdapter.SendPacketAsync(packet, cancellationToken);
-        }
-
         protected override void Dispose(bool disposing)
         {
             if (disposing)
@@ -403,50 +411,116 @@ namespace MQTTnet.Client
 
         Task AcknowledgeReceivedPublishPacket(MqttApplicationMessageReceivedEventArgs eventArgs, CancellationToken cancellationToken)
         {
-            if (eventArgs.PublishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
+            switch (eventArgs.PublishPacket.QualityOfServiceLevel)
             {
-                // no response required
+                case MqttQualityOfServiceLevel.AtMostOnce:
-            }
-            else if (eventArgs.PublishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtLeastOnce)
-            {
-                if (!eventArgs.ProcessingFailed)
                 {
-                    var pubAckPacket = MqttPacketFactories.PubAck.Create(eventArgs);
+                    // no response required
-                    return Send(pubAckPacket, cancellationToken);
+                    break;
                 }
-            }
+                case MqttQualityOfServiceLevel.AtLeastOnce:
-            else if (eventArgs.PublishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
-            {
-                if (!eventArgs.ProcessingFailed)
                 {
-                    var pubRecPacket = MqttPacketFactories.PubRec.Create(eventArgs);
+                    if (!eventArgs.ProcessingFailed)
-                    return Send(pubRecPacket, cancellationToken);
+                    {
+                        var pubAckPacket = MqttPacketFactories.PubAck.Create(eventArgs);
+                        return Send(pubAckPacket, cancellationToken);
+                    }
+
+                    break;
+                }
+                case MqttQualityOfServiceLevel.ExactlyOnce:
+                {
+                    if (!eventArgs.ProcessingFailed)
+                    {
+                        var pubRecPacket = MqttPacketFactories.PubRec.Create(eventArgs);
+                        return Send(pubRecPacket, cancellationToken);
+                    }
+
+                    break;
+                }
+                default:
+                {
+                    throw new MqttProtocolViolationException("Received a not supported QoS level.");
                 }
-            }
-            else
-            {
-                throw new MqttProtocolViolationException("Received a not supported QoS level.");
             }
 
             return CompletedTask.Instance;
         }
 
+        async Task<MqttClientConnectResult> Authenticate(IMqttChannelAdapter channelAdapter, MqttClientOptions options, CancellationToken cancellationToken)
+        {
+            MqttClientConnectResult result;
+
+            try
+            {
+                var connectPacket = MqttPacketFactories.Connect.Create(options);
+                await Send(connectPacket, cancellationToken).ConfigureAwait(false);
+
+                for (; ; )
+                {
+                    cancellationToken.ThrowIfCancellationRequested();
+
+                    var receivedPacket = await Receive(cancellationToken).ConfigureAwait(false);
+
+                    if (receivedPacket is MqttAuthPacket authPacket)
+                    {
+                        await ProcessReceivedAuthPacket(authPacket, cancellationToken).ConfigureAwait(false);
+                        continue;
+                    }
+
+                    if (receivedPacket is MqttConnAckPacket connAckPacket)
+                    {
+                        result = MqttClientResultFactory.ConnectResult.Create(connAckPacket, channelAdapter.PacketFormatterAdapter.ProtocolVersion);
+                        break;
+                    }
+
+                    if (receivedPacket != null)
+                    {
+                        throw new MqttProtocolViolationException($"Received other packet than CONNACK or AUTH while connecting ({receivedPacket}).");
+                    }
+
+                    throw new MqttCommunicationException("Connection closed.");
+                }
+            }
+            catch (Exception exception)
+            {
+                throw new MqttConnectingFailedException($"Error while authenticating. {exception.Message}", exception, null);
+            }
+
+            // This is no feature. It is basically a backward compatibility option and should be removed in the future.
+            // The client should not throw any exception if the transport layer connection was successful and the server
+            // did send a proper ACK packet with a non success response.
+            if (options.ThrowOnNonSuccessfulConnectResponse)
+            {
+                if (result.ResultCode != MqttClientConnectResultCode.Success)
+                {
+                    _logger.Warning(
+                        "Client will now throw an _MqttConnectingFailedException_. This is obsolete and will be removed in the future. Consider setting _ThrowOnNonSuccessfulResponseFromServer=False_ in client options.");
+                    throw new MqttConnectingFailedException($"Connecting with MQTT server failed ({result.ResultCode}).", null, result);
+                }
+            }
+
+            _logger.Verbose("Authenticated MQTT connection with server established.");
+
+            return result;
+        }
+
         void Cleanup()
         {
             try
             {
-                _clientAlive?.Cancel(false);
+                _mqttClientAlive?.Cancel(false);
             }
             finally
             {
-                _clientAlive?.Dispose();
+                _mqttClientAlive?.Dispose();
-                _clientAlive = null;
+                _mqttClientAlive = null;
 
                 _publishPacketReceiverQueue?.Dispose();
                 _publishPacketReceiverQueue = null;
 
-                _channelAdapter?.Dispose();
+                _adapter?.Dispose();
-                _channelAdapter = null;
+                _adapter = null;
 
                 _packetDispatcher?.Dispose();
                 _packetDispatcher = null;
@@ -458,29 +532,24 @@ namespace MQTTnet.Client
             return (MqttClientConnectionStatus)Interlocked.CompareExchange(ref _connectionStatus, (int)value, (int)comparand);
         }
 
-        async Task<MqttClientConnectResult> ConnectInternal(CancellationToken cancellationToken)
+        async Task<MqttClientConnectResult> ConnectInternal(IMqttChannelAdapter channelAdapter, CancellationToken cancellationToken)
         {
-            var clientAliveToken = _clientAlive.Token;
+            var backgroundCancellationToken = _mqttClientAlive.Token;
 
-            using (var effectiveCancellationToken = CancellationTokenSource.CreateLinkedTokenSource(clientAliveToken, cancellationToken))
+            using (var effectiveCancellationToken = CancellationTokenSource.CreateLinkedTokenSource(backgroundCancellationToken, cancellationToken))
             {
                 _logger.Verbose("Trying to connect with server '{0}'", Options.ChannelOptions);
-
+                await channelAdapter.ConnectAsync(effectiveCancellationToken.Token).ConfigureAwait(false);
-                await _channelAdapter.ConnectAsync(effectiveCancellationToken.Token).ConfigureAwait(false);
-
                 _logger.Verbose("Connection with server established");
 
-                var connectResult = await _authenticationHandler.Authenticate(_channelAdapter, Options, effectiveCancellationToken.Token).ConfigureAwait(false);
+                _publishPacketReceiverQueue?.Dispose();
+                _publishPacketReceiverQueue = new AsyncQueue<MqttPublishPacket>();
 
+                var connectResult = await Authenticate(channelAdapter, Options, effectiveCancellationToken.Token).ConfigureAwait(false);
                 if (connectResult.ResultCode == MqttClientConnectResultCode.Success)
                 {
-                    _publishPacketReceiverQueue?.Dispose();
+                    _publishPacketReceiverTask = Task.Run(() => ProcessReceivedPublishPackets(backgroundCancellationToken), backgroundCancellationToken);
-                    _publishPacketReceiverQueue = new AsyncQueue<MqttPublishPacket>();
+                    _packetReceiverTask = Task.Run(() => ReceivePacketsLoop(backgroundCancellationToken), backgroundCancellationToken);
-
-                    _publishPacketReceiverTask = Task.Run(() => ProcessReceivedPublishPacketsLoop(clientAliveToken), clientAliveToken);
-                    _packetReceiverTask = Task.Run(() => ReceivePacketsLoop(clientAliveToken), clientAliveToken);
-
-                    _keepAliveHandler.Enable(connectResult);
                 }
 
                 return connectResult;
@@ -493,13 +562,13 @@ namespace MQTTnet.Client
 
             try
             {
-                if (_channelAdapter != null)
+                if (_adapter != null)
                 {
                     _logger.Verbose("Disconnecting [Timeout={0}]", Options.Timeout);
 
                     using (var timeout = new CancellationTokenSource(Options.Timeout))
                     {
-                        await _channelAdapter.DisconnectAsync(timeout.Token).ConfigureAwait(false);
+                        await _adapter.DisconnectAsync(timeout.Token).ConfigureAwait(false);
                     }
                 }
 
@@ -512,14 +581,13 @@ namespace MQTTnet.Client
 
             try
             {
-                _packetDispatcher.Dispose(new MqttClientDisconnectedException(exception));
+                _packetDispatcher?.Dispose(new MqttClientDisconnectedException(exception));
 
                 var receiverTask = _packetReceiverTask.WaitAsync(sender, _logger);
                 var publishPacketReceiverTask = _publishPacketReceiverTask.WaitAsync(sender, _logger);
+                var keepAliveTask = _keepAlivePacketsSenderTask.WaitAsync(sender, _logger);
 
-                _keepAliveHandler.Disable();
+                await Task.WhenAll(receiverTask, publishPacketReceiverTask, keepAliveTask).ConfigureAwait(false);
-
-                await Task.WhenAll(receiverTask, publishPacketReceiverTask).ConfigureAwait(false);
             }
             catch (Exception innerException)
             {
@@ -541,8 +609,8 @@ namespace MQTTnet.Client
                     _disconnectUserProperties,
                     exception);
 
-                // This handler must be executed in a new thread because otherwise a dead lock may happen
+                // This handler must be executed in a new thread to prevent a deadlock
-                // when trying to reconnect in that handler etc.
+                // that may occur when attempting to reconnect within that handler, etc.
                 Task.Run(() => _events.DisconnectedEvent.InvokeAsync(eventArgs)).RunInBackground(_logger);
             }
         }
@@ -551,12 +619,9 @@ namespace MQTTnet.Client
         {
             var clientWasConnected = IsConnected;
 
-            if (!DisconnectIsPendingOrFinished())
+            return !DisconnectIsPendingOrFinished() ?
-            {
+                DisconnectCore(sender, exception, connectResult, clientWasConnected)
-                return DisconnectCore(sender, exception, connectResult, clientWasConnected);
+                : CompletedTask.Instance;
-            }
-
-            return CompletedTask.Instance;
         }
 
         bool DisconnectIsPendingOrFinished()
@@ -609,13 +674,46 @@ namespace MQTTnet.Client
 
         Task OnConnected(MqttClientConnectResult connectResult)
         {
-            if (_events.ConnectedEvent.HasHandlers)
+            if (!_events.ConnectedEvent.HasHandlers)
             {
-                var eventArgs = new MqttClientConnectedEventArgs(connectResult);
+                return CompletedTask.Instance;
-                return _events.ConnectedEvent.InvokeAsync(eventArgs);
             }
 
-            return CompletedTask.Instance;
+            var eventArgs = new MqttClientConnectedEventArgs(connectResult);
+            return _events.ConnectedEvent.InvokeAsync(eventArgs);
+        }
+
+        Task ProcessReceivedAuthPacket(MqttAuthPacket authPacket, CancellationToken cancellationToken)
+        {
+            var extendedAuthenticationExchangeHandler = Options.ExtendedAuthenticationExchangeHandler;
+            if (extendedAuthenticationExchangeHandler == null)
+            {
+                // From RFC:
+                // The Client can close the connection at any point in this process. It MAY send a DISCONNECT packet before doing so.
+                // The Server can reject the authentication at any point in this process. It MAY send a CONNACK with a Reason Code of
+                // 0x80 or above as described in section 4.13, and MUST close the Network Connection [MQTT-4.12.0-4].
+                //
+                // If the re-authentication fails, the Client or Server SHOULD send DISCONNECT with an appropriate Reason Code
+                // as described in section 4.13, and MUST close the Network Connection [MQTT-4.12.1-2].
+                //
+                // Since we have no handler there is no chance to fulfil the initial authentication or re-authentication requests.
+
+                if (IsConnecting)
+                {
+                    throw new MqttCommunicationException("No handler was provided to handle the extended authentication exchange.");
+                }
+
+                _ = DisconnectAsync(new MqttClientDisconnectOptions
+                {
+                    Reason = MqttClientDisconnectOptionsReason.ImplementationSpecificError,
+                    ReasonString = "Unable to handle AUTH packet"
+                },
+                cancellationToken);
+
+                return CompletedTask.Instance;
+            }
+
+            return extendedAuthenticationExchangeHandler.HandleRequestAsync(new MqttExtendedAuthenticationExchangeContext(authPacket, this, cancellationToken));
         }
 
         Task ProcessReceivedDisconnectPacket(MqttDisconnectPacket disconnectPacket)
@@ -623,14 +721,15 @@ namespace MQTTnet.Client
             _disconnectReason = (int)disconnectPacket.ReasonCode;
             _disconnectReasonString = disconnectPacket.ReasonString;
             _disconnectUserProperties = disconnectPacket.UserProperties;
+            _unexpectedDisconnectPacket = disconnectPacket;
 
             // Also dispatch disconnect to waiting threads to generate a proper exception.
-            _packetDispatcher.Dispose(new MqttClientUnexpectedDisconnectReceivedException(disconnectPacket));
+            _packetDispatcher.Dispose(new MqttClientUnexpectedDisconnectReceivedException(disconnectPacket, null));
 
             return DisconnectInternal(_packetReceiverTask, null, null);
         }
 
-        async Task ProcessReceivedPublishPacketsLoop(CancellationToken cancellationToken)
+        async Task ProcessReceivedPublishPackets(CancellationToken cancellationToken)
         {
             while (!cancellationToken.IsCancellationRequested)
             {
@@ -650,27 +749,30 @@ namespace MQTTnet.Client
                         await eventArgs.AcknowledgeAsync(cancellationToken).ConfigureAwait(false);
                     }
                 }
+                catch (ObjectDisposedException)
+                {
+                }
                 catch (OperationCanceledException)
                 {
                 }
                 catch (Exception exception)
                 {
-                    _logger.Error(exception, "Error while handling application message.");
+                    _logger.Error(exception, "Error while handling application message");
                 }
             }
         }
 
         Task ProcessReceivedPubRecPacket(MqttPubRecPacket pubRecPacket, CancellationToken cancellationToken)
         {
-            if (!_packetDispatcher.TryDispatch(pubRecPacket))
+            if (_packetDispatcher.TryDispatch(pubRecPacket))
             {
-                // The packet is unknown. Probably due to a restart of the client.
+                return CompletedTask.Instance;
-                // So wen send this to the server to trigger a full resend of the message.
-                var pubRelPacket = MqttPacketFactories.PubRel.Create(pubRecPacket, MqttApplicationMessageReceivedReasonCode.PacketIdentifierNotFound);
-                return Send(pubRelPacket, cancellationToken);
             }
 
-            return CompletedTask.Instance;
+            // The packet is unknown, probably due to a restart of the client.
+            // So we send this to the server to trigger a full resend of the message.
+            var pubRelPacket = MqttPacketFactories.PubRel.Create(pubRecPacket, MqttApplicationMessageReceivedReasonCode.PacketIdentifierNotFound);
+            return Send(pubRelPacket, cancellationToken);
         }
 
         Task ProcessReceivedPubRelPacket(MqttPubRelPacket pubRelPacket, CancellationToken cancellationToken)
@@ -689,10 +791,27 @@ namespace MQTTnet.Client
 
         async Task<MqttClientPublishResult> PublishAtMostOnce(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
         {
-            // No packet identifier is used for QoS 0 [3.3.2.2 Packet Identifier]
+            try
-            await Send(publishPacket, cancellationToken).ConfigureAwait(false);
+            {
+                // No packet identifier is used for QoS 0 [3.3.2.2 Packet Identifier]
+                await Send(publishPacket, cancellationToken).ConfigureAwait(false);
 
-            return MqttClientResultFactory.PublishResult.Create(null);
+                return MqttClientResultFactory.PublishResult.Create(null);
+            }
+            catch (Exception exception)
+            {
+                // We have to check if the server has sent a disconnect packet in response to the published message.
+                // Since we are in QoS 0 we do not get a direct response via an PUBACK packet and thus basically no
+                // feedback at all.
+                var localUnexpectedDisconnectPacket = _unexpectedDisconnectPacket;
+
+                if (localUnexpectedDisconnectPacket != null)
+                {
+                    throw new MqttClientUnexpectedDisconnectReceivedException(localUnexpectedDisconnectPacket, exception);
+                }
+
+                throw;
+            }
         }
 
         async Task<MqttClientPublishResult> PublishExactlyOnce(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
@@ -710,7 +829,7 @@ namespace MQTTnet.Client
 
         async Task<MqttPacket> Receive(CancellationToken cancellationToken)
         {
-            var packetTask = _channelAdapter.ReceivePacketAsync(cancellationToken);
+            var packetTask = _adapter.ReceivePacketAsync(cancellationToken);
 
             MqttPacket packet;
             if (packetTask.IsCompleted)
@@ -729,7 +848,7 @@ namespace MQTTnet.Client
         {
             try
             {
-                _logger.Verbose("Start receiving packets.");
+                _logger.Verbose("Start receiving packets");
 
                 while (!cancellationToken.IsCancellationRequested)
                 {
@@ -767,53 +886,33 @@ namespace MQTTnet.Client
                 }
                 else if (exception is MqttCommunicationException)
                 {
-                    _logger.Warning(exception, "Communication error while receiving packets.");
+                    _logger.Warning(exception, "Communication error while receiving packets");
                 }
                 else
                 {
-                    _logger.Error(exception, "Error while receiving packets.");
+                    _logger.Error(exception, "Error while receiving packets");
                 }
 
-                _packetDispatcher.FailAll(exception);
+                // The packet dispatcher is set to null when the client is being disposed so it may already being gone!
+                _packetDispatcher?.FailAll(exception);
 
                 await DisconnectInternal(_packetReceiverTask, exception, null).ConfigureAwait(false);
             }
             finally
             {
-                _logger.Verbose("Stopped receiving packets.");
+                _logger.Verbose("Stopped receiving packets");
             }
         }
 
-        internal async Task<TPacket> Receive<TPacket>(int packetIdentifier, CancellationToken cancellationToken) where TPacket : MqttPacket
+        async Task<TResponsePacket> Request<TResponsePacket>(MqttPacket requestPacket, CancellationToken cancellationToken) where TResponsePacket : MqttPacket
-        {
-            using (var packetAwaitable = _packetDispatcher.AddAwaitable<TPacket>(packetIdentifier))
-            {
-                return await packetAwaitable.WaitOneAsync(cancellationToken);
-            }
-        }
-        
-        internal async Task<TResponsePacket> Request<TResponsePacket>(MqttPacket requestPacket, CancellationToken cancellationToken) where TResponsePacket : MqttPacket
         {
             cancellationToken.ThrowIfCancellationRequested();
 
-            // Some packets are a direct response to another packet but have no packet identifier for correlation!
+            ushort packetIdentifier = 0;
-            int packetIdentifier;
             if (requestPacket is MqttPacketWithIdentifier packetWithIdentifier)
             {
                 packetIdentifier = packetWithIdentifier.PacketIdentifier;
             }
-            else if (requestPacket is MqttPingReqPacket)
-            {
-                packetIdentifier = MqttPacketDispatcher.PingRespPacketFakeIdentifier;
-            }
-            else if (requestPacket is MqttAuthPacket)
-            {
-                packetIdentifier = MqttPacketDispatcher.AuthPacketFakeIdentifier;
-            }
-            else
-            {
-                throw new MqttProtocolViolationException($"Expecting a response for packet {requestPacket.GetRfcName()} is not supported.");
-            }
 
             using (var packetAwaitable = _packetDispatcher.AddAwaitable<TResponsePacket>(packetIdentifier))
             {
@@ -823,7 +922,7 @@ namespace MQTTnet.Client
                 }
                 catch (Exception exception)
                 {
-                    _logger.Warning(exception, "Error when sending request packet ({0}).", requestPacket.GetType().Name);
+                    _logger.Warning(exception, "Error when sending {0} request packet", requestPacket.GetType().Name);
                     packetAwaitable.Fail(exception);
                 }
 
@@ -835,7 +934,7 @@ namespace MQTTnet.Client
                 {
                     if (exception is MqttCommunicationTimedOutException)
                     {
-                        _logger.Warning("Timeout while waiting for response packet ({0}).", typeof(TResponsePacket).Name);
+                        _logger.Warning("Timeout while waiting for {0} response packet", typeof(TResponsePacket).Name);
                     }
 
                     throw;
@@ -843,6 +942,15 @@ namespace MQTTnet.Client
             }
         }
 
+        Task Send(MqttPacket packet, CancellationToken cancellationToken)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+
+            _lastPacketSentTimestamp = DateTime.UtcNow;
+
+            return _adapter.SendPacketAsync(packet, cancellationToken);
+        }
+
         void ThrowIfConnected(string message)
         {
             if (IsConnected)
@@ -859,6 +967,14 @@ namespace MQTTnet.Client
             }
         }
 
+        void ThrowIfNotConnectedOrConnecting()
+        {
+            if (!(IsConnected || IsConnecting))
+            {
+                ThrowNotConnectedOrConnecting();
+            }
+        }
+
         static void ThrowIfOptionsInvalid(MqttClientOptions options)
         {
             if (options == null)
@@ -879,7 +995,12 @@ namespace MQTTnet.Client
 
         static void ThrowNotConnected()
         {
-            throw new MqttCommunicationException("The client is not connected.");
+            throw new MqttClientNotConnectedException();
+        }
+
+        static void ThrowNotConnectedOrConnecting()
+        {
+            throw new MqttCommunicationException("The MQTT client is not connected or connecting.");
         }
 
         void TryInitiateDisconnect()
@@ -888,11 +1009,11 @@ namespace MQTTnet.Client
             {
                 try
                 {
-                    _clientAlive?.Cancel(false);
+                    _mqttClientAlive?.Cancel(false);
                 }
                 catch (Exception exception)
                 {
-                    _logger.Warning(exception, "Error while initiating disconnect.");
+                    _logger.Warning(exception, "Error while initiating disconnect");
                 }
             }
         }
@@ -901,47 +1022,36 @@ namespace MQTTnet.Client
         {
             try
             {
-                if (packet is MqttPublishPacket publishPacket)
+                switch (packet)
                 {
-                    EnqueueReceivedPublishPacket(publishPacket);
+                    case MqttPublishPacket publishPacket:
-                }
+                        EnqueueReceivedPublishPacket(publishPacket);
-                else if (packet is MqttPubRecPacket pubRecPacket)
+                        break;
-                {
+                    case MqttPubRecPacket pubRecPacket:
-                    await ProcessReceivedPubRecPacket(pubRecPacket, cancellationToken).ConfigureAwait(false);
+                        await ProcessReceivedPubRecPacket(pubRecPacket, cancellationToken).ConfigureAwait(false);
-                }
+                        break;
-                else if (packet is MqttPubRelPacket pubRelPacket)
+                    case MqttPubRelPacket pubRelPacket:
-                {
+                        await ProcessReceivedPubRelPacket(pubRelPacket, cancellationToken).ConfigureAwait(false);
-                    await ProcessReceivedPubRelPacket(pubRelPacket, cancellationToken).ConfigureAwait(false);
+                        break;
-                }
+                    case MqttDisconnectPacket disconnectPacket:
-                else if (packet is MqttDisconnectPacket disconnectPacket)
+                        await ProcessReceivedDisconnectPacket(disconnectPacket).ConfigureAwait(false);
-                {
+                        break;
-                    await ProcessReceivedDisconnectPacket(disconnectPacket).ConfigureAwait(false);
+                    case MqttAuthPacket authPacket:
-                }
+                        await ProcessReceivedAuthPacket(authPacket, cancellationToken).ConfigureAwait(false);
-                // else if (packet is MqttAuthPacket authPacket)
+                        break;
-                // {
+                    case MqttPingRespPacket _:
-                //     await _authenticationHandler.HandleExtendedAuthentication(authPacket, new MqttInitialAuthenticationStrategy(_channelAdapter)).ConfigureAwait(false);
+                        _packetDispatcher.TryDispatch(packet);
-                // }
+                        break;
-                else if (packet is MqttPingRespPacket)
+                    case MqttPingReqPacket _:
-                {
+                        throw new MqttProtocolViolationException("The PINGREQ Packet is sent from a client to the server only.");
-                    _packetDispatcher.TryDispatch(packet);
+                    default:
-                }
-                else if (packet is MqttPingReqPacket)
-                {
-                    throw new MqttProtocolViolationException("The PINGREQ packet can only be sent from client to server.");
-                }
-                else if (packet is MqttConnAckPacket)
-                {
-                    throw new MqttProtocolViolationException("The CONNACK packet can only be send while connecting.");
-                }
-                else if (packet is MqttConnectPacket)
-                {
-                    throw new MqttProtocolViolationException("The CONNECT packet can only be sent from client to server.");
-                }
-                else
-                {
-                    if (!_packetDispatcher.TryDispatch(packet))
                     {
-                        throw new MqttProtocolViolationException($"Received unexpected {packet} packet.");
+                        if (!_packetDispatcher.TryDispatch(packet))
+                        {
+                            throw new MqttProtocolViolationException($"Received packet '{packet}' at an unexpected time.");
+                        }
+
+                        break;
                     }
                 }
             }
@@ -952,22 +1062,82 @@ namespace MQTTnet.Client
                     return;
                 }
 
-                if (exception is OperationCanceledException)
+                switch (exception)
                 {
-                }
+                    case OperationCanceledException _:
-                else if (exception is MqttCommunicationException)
+                        break;
-                {
+                    case MqttCommunicationException _:
-                    _logger.Warning(exception, "Communication error while receiving packets.");
+                        _logger.Warning(exception, "Communication error while receiving packets");
-                }
+                        break;
-                else
+                    default:
-                {
+                        _logger.Error(exception, "Error while processing received {0} packet", packet.GetType().Name);
-                    _logger.Error(exception, $"Error while processing received packet ({packet.GetType().Name}).");
+                        break;
                 }
 
-                _packetDispatcher.FailAll(exception);
+                // The packet dispatcher may already be gone due to disconnect etc.!
+                _packetDispatcher?.FailAll(exception);
 
                 await DisconnectInternal(_packetReceiverTask, exception, null).ConfigureAwait(false);
             }
         }
+
+        async Task TrySendKeepAliveMessages(CancellationToken cancellationToken)
+        {
+            try
+            {
+                _logger.Verbose("Start sending keep alive packets");
+
+                var keepAlivePeriod = Options.KeepAlivePeriod;
+
+                while (!cancellationToken.IsCancellationRequested)
+                {
+                    // Values described here: [MQTT-3.1.2-24].
+                    var timeWithoutPacketSent = DateTime.UtcNow - _lastPacketSentTimestamp;
+
+                    if (timeWithoutPacketSent > keepAlivePeriod)
+                    {
+                        using (var pingTimeout = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken))
+                        {
+                            // We already reached the keep alive timeout. Due to the RFC part [MQTT-3.1.2-24] the server will wait another
+                            // 1/2 of the keep alive time. So we can also use this value as the timeout.
+                            pingTimeout.CancelAfter((int)(keepAlivePeriod.TotalMilliseconds / 2));
+
+                            await PingAsync(pingTimeout.Token).ConfigureAwait(false);
+                        }
+                    }
+
+                    // Wait a fixed time in all cases. Calculation of the remaining time is complicated
+                    // due to some edge cases and was buggy in the past. Now we wait several ms because the
+                    // min keep alive value is one second so that the server will wait 1.5 seconds for a PING
+                    // packet.
+                    await Task.Delay(250, cancellationToken).ConfigureAwait(false);
+                }
+            }
+            catch (Exception exception)
+            {
+                if (_cleanDisconnectInitiated)
+                {
+                    return;
+                }
+
+                switch (exception)
+                {
+                    case OperationCanceledException _:
+                        return;
+                    case MqttCommunicationException _:
+                        _logger.Warning(exception, "Communication error while sending/receiving keep alive packets");
+                        break;
+                    default:
+                        _logger.Error(exception, "Error exception while sending/receiving keep alive packets");
+                        break;
+                }
+
+                await DisconnectInternal(_keepAlivePacketsSenderTask, exception, null).ConfigureAwait(false);
+            }
+            finally
+            {
+                _logger.Verbose("Stopped sending keep alive packets");
+            }
+        }
     }
 }

Source/MQTTnet/Client/MqttClientExtensions.cs

@@ -14,8 +14,6 @@ namespace MQTTnet.Client
 {
     public static class MqttClientExtensions
     {
-        static readonly MqttReAuthenticationOptions EmptyReAuthenticationOptions = new MqttReAuthenticationOptions();
-
         public static Task DisconnectAsync(
             this IMqttClient client,
             MqttClientDisconnectOptionsReason reason = MqttClientDisconnectOptionsReason.NormalDisconnection,
@@ -79,11 +77,6 @@ namespace MQTTnet.Client
             return mqttClient.PublishBinaryAsync(topic, payloadBuffer, qualityOfServiceLevel, retain, cancellationToken);
         }
 
-        public static Task ReAuthenticateAsync(this IMqttClient client, CancellationToken cancellationToken = default)
-        {
-            return client.ReAuthenticateAsync(EmptyReAuthenticationOptions, cancellationToken);
-        }
-
         public static Task ReconnectAsync(this IMqttClient client, CancellationToken cancellationToken = default)
         {
             if (client.Options == null)
@@ -95,6 +88,16 @@ namespace MQTTnet.Client
             return client.ConnectAsync(client.Options, cancellationToken);
         }
 
+        public static Task SendExtendedAuthenticationExchangeDataAsync(this IMqttClient client, MqttExtendedAuthenticationExchangeData data)
+        {
+            if (client == null)
+            {
+                throw new ArgumentNullException(nameof(client));
+            }
+
+            return client.SendExtendedAuthenticationExchangeDataAsync(data, CancellationToken.None);
+        }
+
         public static Task<MqttClientSubscribeResult> SubscribeAsync(this IMqttClient mqttClient, MqttTopicFilter topicFilter, CancellationToken cancellationToken = default)
         {
             if (mqttClient == null)

Source/MQTTnet/Client/Options/DefaultMqttCertificatesProvider.cs

@@ -0,0 +1,36 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Generic;
+using System.Security.Cryptography.X509Certificates;
+
+namespace MQTTnet.Client
+{
+    public sealed class DefaultMqttCertificatesProvider : IMqttClientCertificatesProvider
+    {
+        readonly X509Certificate2Collection _certificates;
+
+        public DefaultMqttCertificatesProvider(X509Certificate2Collection certificates)
+        {
+            _certificates = certificates;
+        }
+
+        public DefaultMqttCertificatesProvider(IEnumerable<X509Certificate> certificates)
+        {
+            if (certificates != null)
+            {
+                _certificates = new X509Certificate2Collection();
+                foreach (var certificate in certificates)
+                {
+                    _certificates.Add(certificate);
+                }
+            }
+        }
+
+        public X509CertificateCollection GetCertificates()
+        {
+            return _certificates;
+        }
+    }
+}

Source/MQTTnet/Client/Options/IMqttClientCertificatesProvider.cs

@@ -0,0 +1,11 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace MQTTnet.Client
+{
+    public interface IMqttClientCertificatesProvider
+    {
+        System.Security.Cryptography.X509Certificates.X509CertificateCollection GetCertificates();
+    }
+}

Source/MQTTnet/Client/Options/MqttClientCertificateSelectionEventArgs.cs

@@ -0,0 +1,36 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Security.Cryptography.X509Certificates;
+
+namespace MQTTnet.Client
+{
+    public sealed class MqttClientCertificateSelectionEventArgs : EventArgs
+    {
+        public MqttClientCertificateSelectionEventArgs(
+            string targetHost,
+            X509CertificateCollection localCertificates,
+            X509Certificate remoteCertificate,
+            string[] acceptableIssuers,
+            MqttClientTcpOptions tcpOptions)
+        {
+            TargetHost = targetHost;
+            LocalCertificates = localCertificates;
+            RemoveCertificate = remoteCertificate;
+            AcceptableIssuers = acceptableIssuers;
+            TcpOptions = tcpOptions ?? throw new ArgumentNullException(nameof(tcpOptions));
+        }
+
+        public string[] AcceptableIssuers { get; }
+
+        public X509CertificateCollection LocalCertificates { get; }
+
+        public X509Certificate RemoveCertificate { get; }
+
+        public string TargetHost { get; }
+
+        public MqttClientTcpOptions TcpOptions { get; }
+    }
+}

Source/MQTTnet/Client/Options/MqttClientCertificateValidationEventArgs.cs

@@ -10,12 +10,27 @@ namespace MQTTnet.Client
 {
     public sealed class MqttClientCertificateValidationEventArgs : EventArgs
     {
-        public X509Certificate Certificate { get; set; }
+        public MqttClientCertificateValidationEventArgs(X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors, IMqttClientChannelOptions clientOptions)
+        {
+            Certificate = certificate;
+            Chain = chain;
+            SslPolicyErrors = sslPolicyErrors;
+            ClientOptions = clientOptions ?? throw new ArgumentNullException(nameof(clientOptions));
+        }
 
-        public X509Chain Chain { get; set; }
+        public X509Certificate Certificate { get; }
 
-        public SslPolicyErrors SslPolicyErrors { get; set; }
+        public X509Chain Chain { get; }
 
-        public IMqttClientChannelOptions ClientOptions { get; set; }
+        public IMqttClientChannelOptions ClientOptions { get; }
+
+#if NET452 || NET461 || NET48
+        /// <summary>
+        ///     Can be a host string name or an object derived from WebRequest.
+        /// </summary>
+        public object Sender { get; set; }
+#endif
+
+        public SslPolicyErrors SslPolicyErrors { get; }
     }
-}
+}

Source/MQTTnet/Client/Options/MqttClientOptions.cs

@@ -53,7 +53,9 @@ namespace MQTTnet.Client
         public string ClientId { get; set; } = Guid.NewGuid().ToString("N");
 
         public IMqttClientCredentialsProvider Credentials { get; set; }
-        
+
+        public IMqttExtendedAuthenticationExchangeHandler ExtendedAuthenticationExchangeHandler { get; set; }
+
         /// <summary>
         ///     Gets or sets the keep alive period.
         ///     The connection is normally left open by the client so that is can send and receive data at any time.
@@ -101,7 +103,7 @@ namespace MQTTnet.Client
         /// <summary>
         ///     Gets or sets whether an exception should be thrown when the server has sent a non success ACK packet.
         /// </summary>
-        public bool ThrowOnNonSuccessfulResponseFromServer { get; set; } = true;
+        public bool ThrowOnNonSuccessfulConnectResponse { get; set; } = true;
 
         /// <summary>
         ///     Gets or sets the timeout which will be applied at socket level and internal operations.

Source/MQTTnet/Client/Options/MqttClientOptionsBuilder.cs

@@ -2,9 +2,13 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#pragma warning disable CS0612 // Type or member is obsolete
+
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Net;
+using System.Net.Sockets;
 using System.Text;
 using MQTTnet.Formatter;
 using MQTTnet.Packets;
@@ -15,10 +19,16 @@ namespace MQTTnet.Client
     public sealed class MqttClientOptionsBuilder
     {
         readonly MqttClientOptions _options = new MqttClientOptions();
-        MqttClientWebSocketProxyOptions _proxyOptions;
+        int? _port;
+
+        [Obsolete] MqttClientWebSocketProxyOptions _proxyOptions;
+        EndPoint _remoteEndPoint;
 
         MqttClientTcpOptions _tcpOptions;
-        MqttClientOptionsBuilderTlsParameters _tlsParameters;
+        MqttClientTlsOptions _tlsOptions;
+
+        [Obsolete] MqttClientOptionsBuilderTlsParameters _tlsParameters;
+
         MqttClientWebSocketOptions _webSocketOptions;
 
         public MqttClientOptions Build()
@@ -28,11 +38,17 @@ namespace MQTTnet.Client
                 throw new InvalidOperationException("A channel must be set.");
             }
 
+            // The user can specify the TCP options with already configured TLS options
+            // or start with TLS settings not knowing which transport will be used (depending
+            // on the order of called methods from the builder).
+            // The builder prefers the explicitly set TLS options!
+            var tlsOptions = _tlsOptions ?? _tcpOptions?.TlsOptions;
+
             if (_tlsParameters != null)
             {
                 if (_tlsParameters?.UseTls == true)
                 {
-                    var tlsOptions = new MqttClientTlsOptions
+                    tlsOptions = new MqttClientTlsOptions
                     {
                         UseTls = true,
                         SslProtocol = _tlsParameters.SslProtocol,
@@ -40,26 +56,61 @@ namespace MQTTnet.Client
                         CertificateValidationHandler = _tlsParameters.CertificateValidationHandler,
                         IgnoreCertificateChainErrors = _tlsParameters.IgnoreCertificateChainErrors,
                         IgnoreCertificateRevocationErrors = _tlsParameters.IgnoreCertificateRevocationErrors,
-#if WINDOWS_UWP
+                        ClientCertificatesProvider = _tlsParameters.CertificatesProvider,
-                        Certificates = _tlsParameters.Certificates?.Select(c => c.ToArray()).ToList(),
-#else
-                        Certificates = _tlsParameters.Certificates?.ToList(),
-#endif
-
 #if NETCOREAPP3_1_OR_GREATER
                         ApplicationProtocols = _tlsParameters.ApplicationProtocols,
 #endif
                     };
+                }
+            }
 
-                    if (_tcpOptions != null)
+            if (_tcpOptions != null)
+            {
+                _tcpOptions.TlsOptions = tlsOptions;
+
+                if (_remoteEndPoint == null)
+                {
+                    throw new ArgumentException("No endpoint is set.");
+                }
+
+                if (_remoteEndPoint is DnsEndPoint dns)
+                {
+                    if (dns.Port == 0)
                     {
-                        _tcpOptions.TlsOptions = tlsOptions;
+                        if (_port.HasValue)
-                    }
+                        {
-                    else if (_webSocketOptions != null)
+                            _remoteEndPoint = new DnsEndPoint(dns.Host, _port.Value, dns.AddressFamily);
-                    {
+                        }
-                        _webSocketOptions.TlsOptions = tlsOptions;
+                        else
+                        {
+                            _remoteEndPoint = new DnsEndPoint(dns.Host, tlsOptions?.UseTls == false ? MqttPorts.Default : MqttPorts.Secure, dns.AddressFamily);
+                        }
                     }
                 }
+
+                if (_remoteEndPoint is IPEndPoint ip)
+                {
+                    if (ip.Port == 0)
+                    {
+                        if (_port.HasValue)
+                        {
+                            _remoteEndPoint = new IPEndPoint(ip.Address, _port.Value);
+                        }
+                        else
+                        {
+                            _remoteEndPoint = new IPEndPoint(ip.Address, tlsOptions?.UseTls == false ? MqttPorts.Default : MqttPorts.Secure);
+                        }
+                    }
+                }
+
+                if (_tcpOptions.RemoteEndpoint == null)
+                {
+                    _tcpOptions.RemoteEndpoint = _remoteEndPoint;
+                }
+            }
+            else if (_webSocketOptions != null)
+            {
+                _webSocketOptions.TlsOptions = tlsOptions;
             }
 
             if (_proxyOptions != null)
@@ -79,7 +130,13 @@ namespace MQTTnet.Client
             return _options;
         }
 
-        public MqttClientOptionsBuilder WithAuthentication(string method, byte[] data = null)
+        public MqttClientOptionsBuilder WithAddressFamily(AddressFamily addressFamily)
+        {
+            _tcpOptions.AddressFamily = addressFamily;
+            return this;
+        }
+
+        public MqttClientOptionsBuilder WithAuthentication(string method, byte[] data)
         {
             _options.AuthenticationMethod = method;
             _options.AuthenticationData = data;
@@ -126,12 +183,16 @@ namespace MQTTnet.Client
                     break;
 
                 case "mqtts":
-                    WithTcpServer(uri.Host, port).WithTls();
+                    WithTcpServer(uri.Host, port)
+                        .WithTlsOptions(
+                            o =>
+                            {
+                            });
                     break;
 
                 case "ws":
                 case "wss":
-                    WithWebSocketServer(uri.ToString());
+                    WithWebSocketServer(o => o.WithUri(uri.ToString()));
                     break;
 
                 default:
@@ -177,6 +238,20 @@ namespace MQTTnet.Client
             return this;
         }
 
+        public MqttClientOptionsBuilder WithEndPoint(EndPoint endPoint)
+        {
+            _remoteEndPoint = endPoint ?? throw new ArgumentNullException(nameof(endPoint));
+            _tcpOptions = new MqttClientTcpOptions();
+
+            return this;
+        }
+
+        public MqttClientOptionsBuilder WithExtendedAuthenticationExchangeHandler(IMqttExtendedAuthenticationExchangeHandler handler)
+        {
+            _options.ExtendedAuthenticationExchangeHandler = handler;
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithKeepAlivePeriod(TimeSpan value)
         {
             _options.KeepAlivePeriod = value;
@@ -206,6 +281,22 @@ namespace MQTTnet.Client
             return this;
         }
 
+        /// <summary>
+        ///     The client will not throw an exception when the MQTT server responds with a non success ACK packet.
+        ///     This will become the default behavior in future versions of the library.
+        /// </summary>
+        public MqttClientOptionsBuilder WithoutThrowOnNonSuccessfulConnectResponse()
+        {
+            _options.ThrowOnNonSuccessfulConnectResponse = false;
+            return this;
+        }
+
+        public MqttClientOptionsBuilder WithProtocolType(ProtocolType protocolType)
+        {
+            _tcpOptions.ProtocolType = protocolType;
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithProtocolVersion(MqttProtocolVersion value)
         {
             if (value == MqttProtocolVersion.Unknown)
@@ -217,6 +308,7 @@ namespace MQTTnet.Client
             return this;
         }
 
+        [Obsolete("Use WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithProxy(
             string address,
             string username = null,
@@ -238,6 +330,7 @@ namespace MQTTnet.Client
             return this;
         }
 
+        [Obsolete("Use WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithProxy(Action<MqttClientWebSocketProxyOptions> optionsBuilder)
         {
             if (optionsBuilder == null)
@@ -274,13 +367,19 @@ namespace MQTTnet.Client
             return this;
         }
 
-        public MqttClientOptionsBuilder WithTcpServer(string server, int? port = null)
+        public MqttClientOptionsBuilder WithTcpServer(string host, int? port = null, AddressFamily addressFamily = AddressFamily.Unspecified)
         {
-            _tcpOptions = new MqttClientTcpOptions
+            if (host == null)
             {
-                Server = server,
+                throw new ArgumentNullException(nameof(host));
-                Port = port
+            }
-            };
+
+            _tcpOptions = new MqttClientTcpOptions();
+
+            // The value 0 will be updated when building the options.
+            // This a backward compatibility feature.
+            _remoteEndPoint = new DnsEndPoint(host, port ?? 0, addressFamily);
+            _port = port;
 
             return this;
         }
@@ -308,17 +407,20 @@ namespace MQTTnet.Client
             return this;
         }
 
+        [Obsolete("Use WithTlsOptions(... configure) instead.")]
         public MqttClientOptionsBuilder WithTls(MqttClientOptionsBuilderTlsParameters parameters)
         {
             _tlsParameters = parameters;
             return this;
         }
 
+        [Obsolete("Use WithTlsOptions(... configure) instead.")]
         public MqttClientOptionsBuilder WithTls()
         {
             return WithTls(new MqttClientOptionsBuilderTlsParameters { UseTls = true });
         }
 
+        [Obsolete("Use WithTlsOptions(... configure) instead.")]
         public MqttClientOptionsBuilder WithTls(Action<MqttClientOptionsBuilderTlsParameters> optionsBuilder)
         {
             if (optionsBuilder == null)
@@ -335,6 +437,26 @@ namespace MQTTnet.Client
             return this;
         }
 
+        public MqttClientOptionsBuilder WithTlsOptions(MqttClientTlsOptions tlsOptions)
+        {
+            _tlsOptions = tlsOptions;
+            return this;
+        }
+
+        public MqttClientOptionsBuilder WithTlsOptions(Action<MqttClientTlsOptionsBuilder> configure)
+        {
+            if (configure == null)
+            {
+                throw new ArgumentNullException(nameof(configure));
+            }
+
+            var builder = new MqttClientTlsOptionsBuilder();
+            configure.Invoke(builder);
+
+            _tlsOptions = builder.Build();
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithTopicAliasMaximum(ushort topicAliasMaximum)
         {
             _options.TopicAliasMaximum = topicAliasMaximum;
@@ -366,6 +488,7 @@ namespace MQTTnet.Client
             return this;
         }
 
+        [Obsolete("Use WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithWebSocketServer(string uri, MqttClientOptionsBuilderWebSocketParameters parameters = null)
         {
             _webSocketOptions = new MqttClientWebSocketOptions
@@ -378,6 +501,21 @@ namespace MQTTnet.Client
             return this;
         }
 
+        public MqttClientOptionsBuilder WithWebSocketServer(Action<MqttClientWebSocketOptionsBuilder> configure)
+        {
+            if (configure == null)
+            {
+                throw new ArgumentNullException(nameof(configure));
+            }
+
+            var webSocketOptionsBuilder = new MqttClientWebSocketOptionsBuilder();
+            configure.Invoke(webSocketOptionsBuilder);
+
+            _webSocketOptions = webSocketOptionsBuilder.Build();
+            return this;
+        }
+
+        [Obsolete("Use WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithWebSocketServer(Action<MqttClientWebSocketOptions> optionsBuilder)
         {
             if (optionsBuilder == null)
@@ -409,6 +547,12 @@ namespace MQTTnet.Client
             return this;
         }
 
+        public MqttClientOptionsBuilder WithWillMessageExpiryInterval(uint willMessageExpiryInterval)
+        {
+            _options.WillMessageExpiryInterval = willMessageExpiryInterval;
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithWillPayload(byte[] willPayload)
         {
             _options.WillPayload = willPayload;

Source/MQTTnet/Client/Options/MqttClientOptionsBuilderTlsParameters.cs

@@ -5,12 +5,14 @@
 using System;
 using System.Collections.Generic;
 using System.Security.Authentication;
-using System.Security.Cryptography.X509Certificates;
 
 namespace MQTTnet.Client
 {
+    [Obsolete("Use methods from MqttClientOptionsBuilder instead.")]
     public sealed class MqttClientOptionsBuilderTlsParameters
     {
+        IEnumerable<System.Security.Cryptography.X509Certificates.X509Certificate> _obsoleteCertificates;
+
         public bool UseTls { get; set; }
 
         public Func<MqttClientCertificateValidationEventArgs, bool> CertificateValidationHandler { get; set; }
@@ -24,7 +26,24 @@ namespace MQTTnet.Client
 #if WINDOWS_UWP
         public IEnumerable<IEnumerable<byte>> Certificates { get; set; }
 #else
-        public IEnumerable<X509Certificate> Certificates { get; set; }
+        [Obsolete("Use CertificatesProvider instead.")]
+        public IEnumerable<System.Security.Cryptography.X509Certificates.X509Certificate> Certificates
+        {
+            get => _obsoleteCertificates;
+            set
+            {
+                _obsoleteCertificates = value;
+
+                if (value == null)
+                {
+                    CertificatesProvider = null;
+                }
+                else
+                {
+                    CertificatesProvider = new DefaultMqttCertificatesProvider(value);
+                }
+            }
+        }
 #endif
 
 #if NETCOREAPP3_1_OR_GREATER
@@ -36,5 +55,7 @@ namespace MQTTnet.Client
         public bool IgnoreCertificateChainErrors { get; set; }
 
         public bool IgnoreCertificateRevocationErrors { get; set; }
+
+        public IMqttClientCertificatesProvider CertificatesProvider { get; set; }
     }
 }

Source/MQTTnet/Client/Options/MqttClientOptionsBuilderWebSocketParameters.cs

@@ -2,11 +2,13 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
 using System.Net;
 
 namespace MQTTnet.Client
 {
+    [Obsolete("Use dedicated methods in MqttClientOptionsBuilder.")]
     public class MqttClientOptionsBuilderWebSocketParameters
     {
         public IDictionary<string, string> RequestHeaders { get; set; }

Source/MQTTnet/Client/Options/MqttClientOptionsValidator.cs

@@ -68,8 +68,13 @@ namespace MQTTnet.Client
                 Throw(nameof(options.AuthenticationMethod));
             }
 
+            if (options.ExtendedAuthenticationExchangeHandler != null)
+            {
+                Throw(nameof(options.ExtendedAuthenticationExchangeHandler));
+            }
+
             // Will relevant properties.
-            
+
             if (options.WillPayloadFormatIndicator != MqttPayloadFormatIndicator.Unspecified)
             {
                 Throw(nameof(options.WillPayloadFormatIndicator));

Source/MQTTnet/Client/Options/MqttClientTcpOptions.cs

@@ -2,43 +2,105 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Net;
 using System.Net.Sockets;
+using MQTTnet.Protocol;
 
 namespace MQTTnet.Client
 {
     public sealed class MqttClientTcpOptions : IMqttClientChannelOptions
     {
+        EndPoint _remoteEndpoint;
         public AddressFamily AddressFamily { get; set; } = AddressFamily.Unspecified;
 
-        /// <summary>
-        /// Gets the local endpoint (network card) which is used by the client.
-        /// Set it to _null_ to let the OS select the network card.
-        /// </summary>
-        public EndPoint LocalEndpoint { get; set; }
-        
         public int BufferSize { get; set; } = 8192;
 
         /// <summary>
-        /// Gets or sets whether the underlying socket should run in dual mode.
+        ///     Gets or sets whether the underlying socket should run in dual mode.
-        /// Leaving this _null_ will avoid setting this value at socket level.
+        ///     Leaving this _null_ will avoid setting this value at socket level.
-        /// Setting this a value other than _null_ will throw an exception when only IPv4 is supported on the machine.
+        ///     Setting this a value other than _null_ will throw an exception when only IPv4 is supported on the machine.
         /// </summary>
         public bool? DualMode { get; set; }
 
+        [Obsolete("Use RemoteEndpoint or MqttClientOptionsBuilder instead.")]
+        public int? Port { get; set; }
+
+        [Obsolete("Use RemoteEndpoint or MqttClientOptionsBuilder instead.")]
+        public string Server { get; set; }
+
         public LingerOption LingerState { get; set; } = new LingerOption(true, 0);
 
+        /// <summary>
+        ///     Gets the local endpoint (network card) which is used by the client.
+        ///     Set it to _null_ to let the OS select the network card.
+        /// </summary>
+        public EndPoint LocalEndpoint { get; set; }
+
+        /// <summary>
+        ///     Enables or disables the Nagle algorithm for the socket.
+        ///     This is only supported for TCP.
+        ///     For other protocol types the value is ignored.
+        ///     Default: true
+        /// </summary>
         public bool NoDelay { get; set; } = true;
 
-        public int? Port { get; set; }
+        /// <summary>
-        
+        ///     The MQTT transport is usually TCP but when using other endpoint types like
-        public string Server { get; set; }
+        ///     unix sockets it must be changed (IP for unix sockets).
+        /// </summary>
+        public ProtocolType ProtocolType { get; set; } = ProtocolType.Tcp;
+
+        public EndPoint RemoteEndpoint
+        {
+            get => _remoteEndpoint;
+            set
+            {
+                _remoteEndpoint = value;
+
+                if (_remoteEndpoint is DnsEndPoint dnsEndPoint)
+                {
+                    Server = dnsEndPoint.Host;
+                    Port = dnsEndPoint.Port;
+                }
+                else if (_remoteEndpoint is IPEndPoint ipEndPoint)
+                {
+                    Server = ipEndPoint.Address.ToString();
+                    Port = ipEndPoint.Port;
+                }
+            }
+        }
 
         public MqttClientTlsOptions TlsOptions { get; set; } = new MqttClientTlsOptions();
 
         public override string ToString()
         {
-            return Server + ":" + this.GetPort();
+            if (RemoteEndpoint != null)
+            {
+                return RemoteEndpoint.ToString();
+            }
+
+            if (!string.IsNullOrEmpty(Server))
+            {
+                return $"{Server}:{GetPort()}";
+            }
+
+            return string.Empty;
+        }
+
+        int GetPort()
+        {
+            if (Port.HasValue)
+            {
+                return Port.Value;
+            }
+
+            if (TlsOptions?.UseTls == true)
+            {
+                return MqttPorts.Secure;
+            }
+
+            return MqttPorts.Default;
         }
     }
 }

Source/MQTTnet/Client/Options/MqttClientTcpOptionsExtensions.cs

@@ -1,23 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-
-namespace MQTTnet.Client
-{
-    public static class MqttClientTcpOptionsExtensions
-    {
-        public static int GetPort(this MqttClientTcpOptions options)
-        {
-            if (options == null) throw new ArgumentNullException(nameof(options));
-
-            if (options.Port.HasValue)
-            {
-                return options.Port.Value;
-            }
-
-            return !options.TlsOptions.UseTls ? 1883 : 8883;
-        }
-    }
-}

Source/MQTTnet/Client/Options/MqttClientTlsOptions.cs

@@ -4,6 +4,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Net.Security;
 using System.Security.Authentication;
 using System.Security.Cryptography.X509Certificates;
 
@@ -13,6 +14,8 @@ namespace MQTTnet.Client
     {
         public Func<MqttClientCertificateValidationEventArgs, bool> CertificateValidationHandler { get; set; }
 
+        public Func<MqttClientCertificateSelectionEventArgs, X509Certificate> CertificateSelectionHandler { get; set; }
+
         public bool UseTls { get; set; }
 
         public bool IgnoreCertificateRevocationErrors { get; set; }
@@ -23,22 +26,39 @@ namespace MQTTnet.Client
 
         public X509RevocationMode RevocationMode { get; set; } = X509RevocationMode.Online;
 
-#if WINDOWS_UWP
+        /// <summary>
-        public List<byte[]> Certificates { get; set; }
+        ///     Gets or sets the provider for certificates.
-#else
+        ///     This provider gets called whenever the client wants to connect
-        public List<X509Certificate> Certificates { get; set; }
+        ///     with the server and requires certificates for authentication.
-#endif
+        ///     The implementation may return different certificates each time.
+        /// </summary>
+        public IMqttClientCertificatesProvider ClientCertificatesProvider { get; set; }
 
 #if NETCOREAPP3_1_OR_GREATER
-        public List<System.Net.Security.SslApplicationProtocol> ApplicationProtocols { get; set; }
+        public List<SslApplicationProtocol> ApplicationProtocols { get; set; }
-        
+
-        public System.Net.Security.CipherSuitesPolicy CipherSuitesPolicy { get; set; }
+        public CipherSuitesPolicy CipherSuitesPolicy { get; set; }
+
+        public EncryptionPolicy EncryptionPolicy { get; set; } = EncryptionPolicy.RequireEncryption;
+
+        public bool AllowRenegotiation { get; set; } = true;
 #endif
 
+        /// <summary>
+        ///     Gets or sets the target host.
+        ///     If the value is null or empty the same host as the TCP socket host will be used.
+        /// </summary>
+        public string TargetHost { get; set; }
+
 #if NET48 || NETCOREAPP3_1_OR_GREATER
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12 | SslProtocols.Tls13;
+
 #else
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12 | (SslProtocols)0x00003000 /*Tls13*/;
 #endif
+
+#if NET7_0_OR_GREATER
+        public X509Certificate2Collection TrustChain { get; set; }
+#endif
     }
 }

Source/MQTTnet/Client/Options/MqttClientTlsOptionsBuilder.cs

@@ -0,0 +1,156 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Security.Authentication;
+using System.Security.Cryptography.X509Certificates;
+#if NETCOREAPP3_1_OR_GREATER
+using System.Net.Security;
+#endif
+
+namespace MQTTnet.Client
+{
+    public sealed class MqttClientTlsOptionsBuilder
+    {
+        readonly MqttClientTlsOptions _tlsOptions = new MqttClientTlsOptions
+        {
+            // If someone used this builder the change is very very high that TLS
+            // should be actually used.
+            UseTls = true
+        };
+
+        public MqttClientTlsOptions Build()
+        {
+            return _tlsOptions;
+        }
+
+        public MqttClientTlsOptionsBuilder UseTls(bool useTls = true)
+        {
+            _tlsOptions.UseTls = useTls;
+            return this;
+        }
+
+        public MqttClientTlsOptionsBuilder WithAllowUntrustedCertificates(bool allowUntrustedCertificates = true)
+        {
+            _tlsOptions.AllowUntrustedCertificates = allowUntrustedCertificates;
+            return this;
+        }
+
+        public MqttClientTlsOptionsBuilder WithCertificateValidationHandler(Func<MqttClientCertificateValidationEventArgs, bool> certificateValidationHandler)
+        {
+            if (certificateValidationHandler == null)
+            {
+                throw new ArgumentNullException(nameof(certificateValidationHandler));
+            }
+
+            _tlsOptions.CertificateValidationHandler = certificateValidationHandler;
+            return this;
+        }
+
+        public MqttClientTlsOptionsBuilder WithCertificateSelectionHandler(Func<MqttClientCertificateSelectionEventArgs, X509Certificate> certificateSelectionHandler)
+        {
+            if (certificateSelectionHandler == null)
+            {
+                throw new ArgumentNullException(nameof(certificateSelectionHandler));
+            }
+
+            _tlsOptions.CertificateSelectionHandler = certificateSelectionHandler;
+            return this;
+        }
+
+        public MqttClientTlsOptionsBuilder WithClientCertificates(IEnumerable<X509Certificate2> certificates)
+        {
+            if (certificates == null)
+            {
+                throw new ArgumentNullException(nameof(certificates));
+            }
+
+            _tlsOptions.ClientCertificatesProvider = new DefaultMqttCertificatesProvider(certificates);
+            return this;
+        }
+
+        public MqttClientTlsOptionsBuilder WithClientCertificates(X509Certificate2Collection certificates)
+        {
+            if (certificates == null)
+            {
+                throw new ArgumentNullException(nameof(certificates));
+            }
+
+            _tlsOptions.ClientCertificatesProvider = new DefaultMqttCertificatesProvider(certificates);
+            return this;
+        }
+
+        public MqttClientTlsOptionsBuilder WithClientCertificatesProvider(IMqttClientCertificatesProvider clientCertificatesProvider)
+        {
+            _tlsOptions.ClientCertificatesProvider = clientCertificatesProvider;
+            return this;
+        }
+
+        public MqttClientTlsOptionsBuilder WithIgnoreCertificateChainErrors(bool ignoreCertificateChainErrors = true)
+        {
+            _tlsOptions.IgnoreCertificateChainErrors = ignoreCertificateChainErrors;
+            return this;
+        }
+
+        public MqttClientTlsOptionsBuilder WithIgnoreCertificateRevocationErrors(bool ignoreCertificateRevocationErrors = true)
+        {
+            _tlsOptions.IgnoreCertificateRevocationErrors = ignoreCertificateRevocationErrors;
+            return this;
+        }
+
+        public MqttClientTlsOptionsBuilder WithRevocationMode(X509RevocationMode revocationMode)
+        {
+            _tlsOptions.RevocationMode = revocationMode;
+            return this;
+        }
+
+        public MqttClientTlsOptionsBuilder WithSslProtocols(SslProtocols sslProtocols)
+        {
+            _tlsOptions.SslProtocol = sslProtocols;
+            return this;
+        }
+
+        public MqttClientTlsOptionsBuilder WithTargetHost(string targetHost)
+        {
+            _tlsOptions.TargetHost = targetHost;
+            return this;
+        }
+
+#if NETCOREAPP3_1_OR_GREATER
+        public MqttClientTlsOptionsBuilder WithAllowRenegotiation(bool allowRenegotiation = true)
+        {
+            _tlsOptions.AllowRenegotiation = allowRenegotiation;
+            return this;
+        }
+
+        public MqttClientTlsOptionsBuilder WithApplicationProtocols(List<SslApplicationProtocol> applicationProtocols)
+        {
+            _tlsOptions.ApplicationProtocols = applicationProtocols;
+            return this;
+        }
+
+        public MqttClientTlsOptionsBuilder WithCipherSuitesPolicy(CipherSuitesPolicy cipherSuitePolicy)
+        {
+            _tlsOptions.CipherSuitesPolicy = cipherSuitePolicy;
+            return this;
+        }
+
+        public MqttClientTlsOptionsBuilder WithCipherSuitesPolicy(EncryptionPolicy encryptionPolicy)
+        {
+            _tlsOptions.EncryptionPolicy = encryptionPolicy;
+            return this;
+        }
+#endif
+
+#if NET7_0_OR_GREATER
+        public MqttClientTlsOptionsBuilder WithTrustChain(X509Certificate2Collection chain)
+        {
+            _tlsOptions.TrustChain = chain;
+            return this;
+        }
+
+#endif
+    }
+}

Source/MQTTnet/Client/Options/MqttClientWebSocketOptions.cs

@@ -2,15 +2,19 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
 using System.Net;
+using System.Net.WebSockets;
 
 namespace MQTTnet.Client
 {
     public sealed class MqttClientWebSocketOptions : IMqttClientChannelOptions
     {
         public CookieContainer CookieContainer { get; set; }
-        
+
+        public ICredentials Credentials { get; set; }
+
         public MqttClientWebSocketProxyOptions ProxyOptions { get; set; }
 
         public IDictionary<string, string> RequestHeaders { get; set; }
@@ -18,12 +22,34 @@ namespace MQTTnet.Client
         public ICollection<string> SubProtocols { get; set; } = new List<string> { "mqtt" };
 
         public MqttClientTlsOptions TlsOptions { get; set; } = new MqttClientTlsOptions();
-        
+
         public string Uri { get; set; }
 
         public override string ToString()
         {
             return Uri;
         }
+
+#if !NETSTANDARD1_3
+#if !WINDOWS_UWP
+        /// <summary>
+        ///     Gets or sets the keep alive interval for the Web Socket connection.
+        ///     This is not related to the keep alive interval for the MQTT protocol.
+        /// </summary>
+        public TimeSpan KeepAliveInterval { get; set; } = WebSocket.DefaultKeepAliveInterval;
+
+        /// <summary>
+        ///     Gets or sets whether the default (system) credentials should be used when connecting via Web Socket connection.
+        ///     This is not related to the credentials which are used for the MQTT protocol.
+        /// </summary>
+        public bool UseDefaultCredentials { get; set; }
+#else
+        /// <summary>
+        ///     Gets or sets the keep alive interval for the Web Socket connection.
+        ///     This is not related to the keep alive interval for the MQTT protocol.
+        /// </summary>
+        public TimeSpan KeepAliveInterval { get; set; } = TimeSpan.FromSeconds(30);
+#endif
+#endif
     }
 }