Samples that show concurrent processing (#1803)

Samples that show concurrent processing with a limit and concurrent processing without auto ACK

.github/workflows/ReleaseNotes.md

@@ -1,4 +1,11 @@
-* [Core] Add validation of maximum string lengths (#1718).
-* [Client] Added overloads for setting packet payload and will payload (#1720).
-* [Client] The proper connect result is now exposed in the _Disconnected_ event when authentication fails (#1139). 
-* [Server] Improved performance by changing internal locking strategy for subscriptions (#1716, thanks to @zeheng).
+* [Client] Fixed _PlatformNotSupportedException_ when using Blazor (#1755, thanks to @Nickztar).
+* [Client] Added hot reload of client certificates (#1781).
+* [Client] Added several new option builders and aligned usage (#1781, BREAKING CHANGE!).
+* [Client] Added support for _RemoteCertificateValidationCallback_ for .NET 4.5.2, 4.6.1 and 4.8 (#1806, thanks to @troky).
+* [Client] Fixed wrong logging of obsolete feature when connection was not successful (#1801, thanks to @ramonsmits).
+* [Client] Fixed _NullReferenceException_ when performing several actions when not connected (#1800, thanks to @ramonsmits).
+* [RpcClient] Added support for passing custom parameters to topic generation context (#1798, thanks to @Temppus).
+* [Server] Fixed _NullReferenceException_ in retained messages management (#1762, thanks to @logicaloud).
+* [Server] Exposed new option which allows disabling packet fragmentation (#1753).
+* [Server] Expired sessions will no longer be used when a client connects (#1756).
+* [Server] Fixed an issue in connection handling for ASP.NET connections (#1819, thanks to @CZEMacLeod).

.github/workflows/ci.yml

@@ -3,7 +3,7 @@ name: CI
 on: [push, pull_request]
 
 env:
-  VERSION: "4.2.1.${{github.run_number}}"
+  VERSION: "4.3.0.${{github.run_number}}"
 
 jobs:
   build:

Samples/Client/Client_Connection_Samples.cs

@@ -70,32 +70,6 @@ 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()
     {
@@ -161,15 +135,15 @@ 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 +170,7 @@ 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 +192,7 @@ 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 +215,11 @@ public static class Client_Connection_Samples
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
             var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8883)
-                .WithTls(
-                    o =>
-                    {
+                .WithTlsOptions(
+                    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 +234,31 @@ 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 +314,19 @@ 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 =>
-                        {
-                            eventArgs.Certificate.Subject.DumpToConsole();
-                            eventArgs.Certificate.GetExpirationDateString().DumpToConsole();
-                            eventArgs.Chain.ChainPolicy.RevocationMode.DumpToConsole();
-                            eventArgs.Chain.ChainStatus.DumpToConsole();
-                            eventArgs.SslPolicyErrors.DumpToConsole();
-                            return true;
-                        };
+                        o.WithCertificateValidationHandler(
+                            eventArgs =>
+                            {
+                                eventArgs.Certificate.Subject.DumpToConsole();
+                                eventArgs.Certificate.GetExpirationDateString().DumpToConsole();
+                                eventArgs.Chain.ChainPolicy.RevocationMode.DumpToConsole();
+                                eventArgs.Chain.ChainStatus.DumpToConsole();
+                                eventArgs.SslPolicyErrors.DumpToConsole();
+                                return true;
+                            });
                     })
                 .Build();
 
@@ -434,4 +432,4 @@ public static class Client_Connection_Samples
                 });
         }
     }
-}
+}

Samples/Client/Client_Subscribe_Samples.cs

@@ -5,6 +5,7 @@
 // ReSharper disable UnusedType.Global
 // ReSharper disable UnusedMember.Global
 // ReSharper disable InconsistentNaming
+// ReSharper disable UnusedMember.Local
 
 using MQTTnet.Client;
 using MQTTnet.Packets;
@@ -176,4 +177,60 @@ 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 += async 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);
+        };
+    }
+
+    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/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/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;
-            _output = connection.Transport.Output;
+            if (!(_connection is TcpConnection tcp) || tcp.IsConnected)
+            {
+                _input = connection.Transport.Input;
+                _output = connection.Transport.Output;
+            }
         }
 
         public long BytesReceived { get; private set; }

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.Rpc/IMqttRpcClient.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Protocol;
@@ -7,8 +8,8 @@ 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.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

@@ -92,18 +92,7 @@ namespace MQTTnet.Extensions.WebSocket4Net
             var webSocketVersion = WebSocketVersion.None;
             var receiveBufferSize = 0;
 
-            var certificates = new X509CertificateCollection();
-            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
-                }
-            }
+            var certificates = _webSocketOptions.TlsOptions?.ClientCertificatesProvider?.GetCertificates();
 
             _webSocket = new WebSocket(uri, subProtocol, cookies, customHeaders, userAgent, origin, webSocketVersion, proxy, sslProtocols, receiveBufferSize)
             {

Source/MQTTnet.TestApp/PublicBrokerTest.cs

@@ -20,7 +20,7 @@ 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,
@@ -29,7 +29,7 @@ namespace MQTTnet.TestApp
             };
 #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,
@@ -44,16 +44,16 @@ namespace MQTTnet.TestApp
 
             await ExecuteTestAsync(
                 "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",
-                new MqttClientOptionsBuilder().WithWebSocketServer("mqtt.eclipseprojects.io:443/mqtt")
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build());
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("mqtt.eclipseprojects.io:443/mqtt"))
+                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls13).Build());
             
             await ExecuteTestAsync("mqtt.eclipseprojects.io WS TLS13 (WebSocket4Net)",
-                new MqttClientOptionsBuilder().WithWebSocketServer("mqtt.eclipseprojects.io:443/mqtt")
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build(),
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("mqtt.eclipseprojects.io:443/mqtt"))
+                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls13).Build(),
                     true);
 #endif
 
@@ -68,12 +68,12 @@ namespace MQTTnet.TestApp
 
             await ExecuteTestAsync(
                 "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",
                 new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8883)
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build());
+                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls13).Build());
 #endif
 
             await ExecuteTestAsync(
@@ -81,21 +81,21 @@ namespace MQTTnet.TestApp
                 new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8885)
                     .WithCredentials("rw", "readwrite")
                     .WithProtocolVersion(MqttProtocolVersion.V311)
-                    .WithTls(unsafeTls12)
+                    .WithTlsOptions(unsafeTls12)
                     .Build());
 
             await ExecuteTestAsync(
                 "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(
                 "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(
                 "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(
             //     "test.mosquitto.org WS TLS12 (WebSocket4Net)",
@@ -109,30 +109,30 @@ namespace MQTTnet.TestApp
 
             await ExecuteTestAsync(
                 "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",
                 new MqttClientOptionsBuilder().WithTcpServer("broker.emqx.io", 8883)
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build());
+                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls13).Build());
 #endif
 
             await ExecuteTestAsync(
                 "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(
                 "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(
                 "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(
                 "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
@@ -142,11 +142,11 @@ namespace MQTTnet.TestApp
 
             await ExecuteTestAsync(
                 "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(
                 "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

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

@@ -421,7 +421,7 @@ 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;
 
@@ -454,7 +454,7 @@ 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);
 

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 +3,7 @@
 // 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 Microsoft.VisualStudio.TestTools.UnitTesting;
@@ -10,6 +11,7 @@ using MQTTnet.Client;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
 using MQTTnet.Internal;
+using MQTTnet.Packets;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
 
@@ -128,7 +130,7 @@ namespace MQTTnet.Tests.Clients.MqttClient
                 await client.DisconnectAsync(disconnectOptions);
 
                 await LongTestDelay();
-                
+
                 Assert.IsNotNull(eventArgs);
                 Assert.AreEqual(MqttDisconnectReasonCode.MessageRateTooHigh, eventArgs.ReasonCode);
             }
@@ -156,7 +158,7 @@ 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 +166,57 @@ namespace MQTTnet.Tests.Clients.MqttClient
                 Assert.AreEqual("test_value", eventArgs.UserProperties[0].Value);
             }
         }
+
+        [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 (MqttCommunicationException exception)
+            {
+                if (exception.Message == "The client is not connected.")
+                {
+                    return;
+                }
+            }
+
+            Assert.Fail();
+        }
     }
 }

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

@@ -296,7 +296,7 @@ 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 +507,7 @@ 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;
                 };
 

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/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($"MQTTnet.RPC/+/ping/{paramValue}");
+
+                responseSender.ApplicationMessageReceivedAsync += e => responseSender.PublishStringAsync(e.ApplicationMessage.Topic + "/response", "pong");
+
+                using (var rpcClient = await testEnvironment.ConnectRpcClient(new MqttRpcClientOptionsBuilder()
+                           .WithTopicGenerationStrategy(new TestParametersTopicGenerationStrategy()).Build()))
+                {
+                    var response = await rpcClient.ExecuteAsync(TimeSpan.FromSeconds(5), "ping", "", MqttQualityOfServiceLevel.AtMostOnce, parameters);
+
+                    Assert.AreEqual("pong", Encoding.UTF8.GetString(response));
+                }
+            }
+        }
+
         [TestMethod]
         public Task Execute_Success_With_QoS_0()
         {
@@ -222,5 +251,32 @@ namespace MQTTnet.Tests.Extensions
                 };
             }
         }
+
+        class TestParametersTopicGenerationStrategy : IMqttRpcClientTopicGenerationStrategy
+        {
+            internal const string ExpectedParamName = "test_param_name";
+
+            public MqttRpcTopicPair CreateRpcTopics(TopicGenerationContext context)
+            {
+                if (context.Parameters == null)
+                {
+                    throw new InvalidOperationException("Parameters dictionary expected to be not null");
+                }
+
+                if (!context.Parameters.TryGetValue(ExpectedParamName, out var paramValue))
+                {
+                    throw new InvalidOperationException($"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/Mockups/TestEnvironment.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
@@ -24,10 +25,9 @@ namespace MQTTnet.Tests.Mockups
     public sealed class TestEnvironment : IDisposable
     {
         readonly List<string> _clientErrors = new List<string>();
-        readonly List<IMqttClient> _clients = new List<IMqttClient>();
-
+        readonly ConcurrentBag<IMqttClient> _clients = new ConcurrentBag<IMqttClient>();
         readonly List<Exception> _exceptions = new List<Exception>();
-        readonly List<ILowLevelMqttClient> _lowLevelClients = new List<ILowLevelMqttClient>();
+        readonly ConcurrentBag<ILowLevelMqttClient> _lowLevelClients = new ConcurrentBag<ILowLevelMqttClient>();
         readonly MqttProtocolVersion _protocolVersion;
         readonly List<string> _serverErrors = new List<string>();
 
@@ -65,9 +65,12 @@ 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 +215,27 @@ namespace MQTTnet.Tests.Mockups
 
         public IMqttClient CreateClient()
         {
-            lock (_clients)
+            var logger = EnableLogger ? (IMqttNetLogger)ClientLogger : MqttNetNullLogger.Instance;
+            
+            var client = Factory.CreateMqttClient(logger);
+            client.ConnectingAsync += e =>
             {
-                var logger = EnableLogger ? (IMqttNetLogger)ClientLogger : new MqttNetNullLogger();
-
-                var client = Factory.CreateMqttClient(logger);
-                _clients.Add(client);
-
-                client.ConnectingAsync += e =>
+                if (TestContext != null)
                 {
-                    if (TestContext != null)
+                    var clientOptions = e.ClientOptions;
+                    var existingClientId = clientOptions.ClientId;
+                    if (existingClientId != null && !existingClientId.StartsWith(TestContext.TestName))
                     {
-                        var clientOptions = e.ClientOptions;
-                        var existingClientId = clientOptions.ClientId;
-                        if (existingClientId != null && !existingClientId.StartsWith(TestContext.TestName))
-                        {
-                            clientOptions.ClientId = TestContext.TestName + "_" + existingClientId;
-                        }
+                        clientOptions.ClientId = TestContext.TestName + "_" + existingClientId;
                     }
+                }
 
-                    return CompletedTask.Instance;
-                };
-
-                return client;
-            }
+                return CompletedTask.Instance;
+            };
+            
+            _clients.Add(client);
+            
+            return client;
         }
 
         public MqttClientOptions CreateDefaultClientOptions()
@@ -250,13 +250,10 @@ namespace MQTTnet.Tests.Mockups
 
         public ILowLevelMqttClient CreateLowLevelClient()
         {
-            lock (_clients)
-            {
-                var client = Factory.CreateLowLevelMqttClient(ClientLogger);
-                _lowLevelClients.Add(client);
+            var client = Factory.CreateLowLevelMqttClient(ClientLogger);
+            _lowLevelClients.Add(client);
 
-                return client;
-            }
+            return client;
         }
 
         public MqttServer CreateServer(MqttServerOptions options)
@@ -277,7 +274,8 @@ 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;
                     }
                 }
 
@@ -291,12 +289,23 @@ namespace MQTTnet.Tests.Mockups
         {
             foreach (var mqttClient in _clients)
             {
-                mqttClient?.Dispose();
+                try
+                {
+                    //mqttClient.DisconnectAsync().GetAwaiter().GetResult();
+                }
+                catch
+                {
+                    // This can happen when the test already disconnected the client.
+                }
+                finally
+                {
+                    mqttClient?.Dispose();
+                }
             }
 
             foreach (var lowLevelMqttClient in _lowLevelClients)
             {
-                lowLevelMqttClient?.Dispose();
+                lowLevelMqttClient.Dispose();
             }
 
             try
@@ -371,13 +380,16 @@ namespace MQTTnet.Tests.Mockups
                 }
             }
 
-            lock (_clientErrors)
+            if (!IgnoreClientLogErrors)
             {
-                if (!IgnoreClientLogErrors && _clientErrors.Count > 0)
+                lock (_clientErrors)
                 {
-                    var message = $"Client(s) had {_clientErrors.Count} errors (${string.Join(Environment.NewLine, _clientErrors)})";
-                    Console.WriteLine(message);
-                    throw new Exception(message);
+                    if (_clientErrors.Count > 0)
+                    {
+                        var message = $"Client(s) had {_clientErrors.Count} errors (${string.Join(Environment.NewLine, _clientErrors)})";
+                        Console.WriteLine(message);
+                        throw new Exception(message);
+                    }
                 }
             }
         }

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/Server/General.cs

@@ -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);
             }
@@ -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 +1,445 @@
+#if !(NET452 || NET461)
+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;
+                }
+            }
+        }
+
+        class ClientTestHarness : IDisposable
+        {
+            readonly HotSwappableClientCertProvider _hotSwapClient = new HotSwappableClientCertProvider();
+            IMqttClient _client;
+
+            public string ClientId => _client.Options.ClientId;
+
+            public void ClearServerCerts()
+            {
+                _hotSwapClient.ClearServerCerts();
+            }
+
+            public Task Connect()
+            {
+                return Run_Client_Connection();
+            }
+
+            public void Dispose()
+            {
+                _client.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)
+            {
+                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");
+            }
+
+            public void WaitForDisconnect(TimeSpan timeout)
+            {
+                var timer = Stopwatch.StartNew();
+                while ((_client == null || _client.IsConnected) && timer.Elapsed < timeout)
+                {
+                    Thread.Sleep(5);
+                }
+            }
+
+            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(5);
+                }
+            }
+        }
+
+        class ServerTestHarness : IDisposable
+        {
+            readonly HotSwappableServerCertProvider _hotSwapServer = new HotSwappableServerCertProvider();
+
+            MqttServer _server;
+
+            public void ClearClientCerts()
+            {
+                _hotSwapServer.ClearClientCerts();
+            }
+
+            public void Dispose()
+            {
+                if (_server != null)
+                {
+                    _server.StopAsync().Wait();
+                    _server.Dispose();
+                }
+
+                if (_hotSwapServer != null)
+                {
+                    _hotSwapServer.Dispose();
+                }
+            }
+
+            public async Task ForceDisconnectAsync(ClientTestHarness client)
+            {
+                await _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 async 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);
+                await _server.StartAsync();
+            }
+        }
+
+        class HotSwappableClientCertProvider : IMqttClientCertificatesProvider
+        {
+            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 ClearServerCerts()
+            {
+                ServerCerts = new ConcurrentBag<X509Certificate2>();
+            }
+
+            public X509CertificateCollection GetCertificates()
+            {
+                return new X509Certificate2Collection(_certificates);
+            }
+
+            public void HotSwapCert()
+            {
+                var newCert = new X509Certificate2Collection(CreateSelfSignedCertificate("1.3.6.1.5.5.7.3.2"));
+                var oldCerts = Interlocked.Exchange(ref _certificates, newCert);
+            }
+
+            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;
+            }
+
+            void Dispose()
+            {
+                if (_certificates != null)
+                {
+                    foreach (var certs in _certificates)
+                    {
+#if !NET452
+                        certs.Dispose();
+#endif
+                    }
+                }
+            }
+        }
+
+        class HotSwappableServerCertProvider : ICertificateProvider, IDisposable
+        {
+            X509Certificate2 _certificate;
+            ConcurrentBag<X509Certificate2> ClientCerts = new ConcurrentBag<X509Certificate2>();
+
+            public HotSwappableServerCertProvider()
+            {
+                _certificate = CreateSelfSignedCertificate("1.3.6.1.5.5.7.3.1");
+            }
+
+            public void ClearClientCerts()
+            {
+                ClientCerts = new ConcurrentBag<X509Certificate2>();
+            }
+
+            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/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)]
@@ -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/Client/Authentication/MqttClientPartialAuthenticationResponse.cs

@@ -1,19 +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;
-using MQTTnet.Protocol;
-
-namespace MQTTnet.Client
-{
-    public sealed class MqttClientPartialAuthenticationResponse
-    {
-        public byte[] AuthenticationData { get; set; }
-
-        public MqttAuthenticateReasonCode ReasonCode { get; set; }
-
-        public List<MqttUserProperty> UserProperties { get; set; }
-    }
-}

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.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
-        /// </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>
+        /// Gets the result code.
+        /// MQTTv5 only.
         /// </summary>
         public MqttClientConnectResultCode ResultCode { get; internal set; }
 
         /// <summary>
-        ///     Gets whether the server supports retained messages.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// Gets a value indicating whether a session was already available or not.
+        /// 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 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.
+        /// Gets the client identifier which was chosen by the server.
+        /// MQTTv5 only.
         /// </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.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// Gets the authentication method.
+        /// MQTTv5 only.
         /// </summary>
-        public string ServerReference { get; internal set; }
-
-        public uint? SessionExpiryInterval { get; internal set; }
+        public string AuthenticationMethod { get; internal set; }
 
         /// <summary>
-        ///     Gets a value indicating whether the shared subscriptions are available or not.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// Gets the authentication data.
+        /// 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.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// Gets the reason string.
+        /// 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.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// Gets the response information.
+        /// 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.
-        ///     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.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// Gets an alternate server which should be used instead of the current one.
+        /// MQTTv5 only.
         /// </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.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// MQTTv5 only.
+        /// 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/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 +1,62 @@
+// 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.Packets;
+using MQTTnet.Protocol;
+
+namespace MQTTnet.Client
+{
+    public class MqttExtendedAuthenticationExchangeContext
+    {
+        public MqttExtendedAuthenticationExchangeContext(MqttAuthPacket authPacket, MqttClient client)
+        {
+            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));
+        }
+
+        /// <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; }
+    }
+}

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;
-
-        CancellationTokenSource _clientAlive;
+        bool _cleanDisconnectInitiated;
         volatile int _connectionStatus;
 
         // The value for this field can be set from two different enums.
@@ -41,6 +39,11 @@ namespace MQTTnet.Client
         int _disconnectReason;
         string _disconnectReasonString;
         List<MqttUserProperty> _disconnectUserProperties;
+
+        Task _keepAlivePacketsSenderTask;
+        DateTime _lastPacketSentTimestamp;
+
+        CancellationTokenSource _mqttClientAlive;
         MqttPacketDispatcher _packetDispatcher;
         Task _packetReceiverTask;
         AsyncQueue<MqttPublishPacket> _publishPacketReceiverQueue;
@@ -51,9 +54,6 @@ namespace MQTTnet.Client
             _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 +80,6 @@ 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);
@@ -122,14 +116,16 @@ 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.");
 
                 if (cancellationToken.CanBeCanceled)
                 {
-                    connectResult = await ConnectInternal(cancellationToken).ConfigureAwait(false);
+                    connectResult = await ConnectInternal(adapter, cancellationToken).ConfigureAwait(false);
                 }
                 else
                 {
@@ -137,10 +133,31 @@ 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");
@@ -194,7 +211,7 @@ 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
@@ -245,7 +262,7 @@ 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 +288,26 @@ 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();
 
-            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,
+                UserProperties = data.UserProperties
+            };
 
-            using (var timeout = new CancellationTokenSource(Options.Timeout))
-            {
-                return _authenticationHandler.ReAuthenticate(options, timeout.Token);
-            }
+            return Send(authPacket, cancellationToken);
         }
 
         public async Task<MqttClientSubscribeResult> SubscribeAsync(MqttClientSubscribeOptions options, CancellationToken cancellationToken = default)
@@ -304,13 +322,13 @@ 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 +366,7 @@ 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 +388,6 @@ 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)
@@ -431,22 +428,73 @@ namespace MQTTnet.Client
             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);
+
+                var receivedPacket = await Receive(cancellationToken).ConfigureAwait(false);
+
+                if (receivedPacket is MqttConnAckPacket connAckPacket)
+                {
+                    result = MqttClientResultFactory.ConnectResult.Create(connAckPacket, _adapter.PacketFormatterAdapter.ProtocolVersion);
+                }
+                else if (receivedPacket is MqttAuthPacket)
+                {
+                    throw new NotSupportedException("Extended authentication handler is not yet supported");
+                }
+                else if (receivedPacket == null)
+                {
+                    throw new MqttCommunicationException("Connection closed.");
+                }
+                else
+                {
+                    throw new InvalidOperationException($"Received an unexpected MQTT packet ({receivedPacket}).");
+                }
+            }
+            catch (Exception exception)
+            {
+                throw new MqttConnectingFailedException($"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();
-                _clientAlive = null;
+                _mqttClientAlive?.Dispose();
+                _mqttClientAlive = null;
 
                 _publishPacketReceiverQueue?.Dispose();
                 _publishPacketReceiverQueue = null;
 
-                _channelAdapter?.Dispose();
-                _channelAdapter = null;
+                _adapter?.Dispose();
+                _adapter = null;
 
                 _packetDispatcher?.Dispose();
                 _packetDispatcher = null;
@@ -458,29 +506,24 @@ 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 _adapter.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();
-                    _publishPacketReceiverQueue = new AsyncQueue<MqttPublishPacket>();
-
-                    _publishPacketReceiverTask = Task.Run(() => ProcessReceivedPublishPacketsLoop(clientAliveToken), clientAliveToken);
-                    _packetReceiverTask = Task.Run(() => ReceivePacketsLoop(clientAliveToken), clientAliveToken);
-
-                    _keepAliveHandler.Enable(connectResult);
+                    _publishPacketReceiverTask = Task.Run(() => ProcessReceivedPublishPackets(backgroundCancellationToken), backgroundCancellationToken);
+                    _packetReceiverTask = Task.Run(() => ReceivePacketsLoop(backgroundCancellationToken), backgroundCancellationToken);
                 }
 
                 return connectResult;
@@ -493,13 +536,13 @@ 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 +555,13 @@ 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).ConfigureAwait(false);
+                await Task.WhenAll(receiverTask, publishPacketReceiverTask, keepAliveTask).ConfigureAwait(false);
             }
             catch (Exception innerException)
             {
@@ -618,6 +660,17 @@ namespace MQTTnet.Client
             return CompletedTask.Instance;
         }
 
+        Task ProcessReceivedAuthPacket(MqttAuthPacket authPacket)
+        {
+            var extendedAuthenticationExchangeHandler = Options.ExtendedAuthenticationExchangeHandler;
+            if (extendedAuthenticationExchangeHandler != null)
+            {
+                return extendedAuthenticationExchangeHandler.HandleRequestAsync(new MqttExtendedAuthenticationExchangeContext(authPacket, this));
+            }
+
+            return CompletedTask.Instance;
+        }
+
         Task ProcessReceivedDisconnectPacket(MqttDisconnectPacket disconnectPacket)
         {
             _disconnectReason = (int)disconnectPacket.ReasonCode;
@@ -630,7 +683,7 @@ namespace MQTTnet.Client
             return DisconnectInternal(_packetReceiverTask, null, null);
         }
 
-        async Task ProcessReceivedPublishPacketsLoop(CancellationToken cancellationToken)
+        async Task ProcessReceivedPublishPackets(CancellationToken cancellationToken)
         {
             while (!cancellationToken.IsCancellationRequested)
             {
@@ -710,7 +763,7 @@ namespace MQTTnet.Client
 
         async Task<MqttPacket> Receive(CancellationToken cancellationToken)
         {
-            var packetTask = _channelAdapter.ReceivePacketAsync(cancellationToken);
+            var packetTask = _adapter.ReceivePacketAsync(cancellationToken);
 
             MqttPacket packet;
             if (packetTask.IsCompleted)
@@ -784,36 +837,15 @@ namespace MQTTnet.Client
             }
         }
 
-        internal async Task<TPacket> Receive<TPacket>(int packetIdentifier, CancellationToken cancellationToken) where TPacket : 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
+        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!
-            int packetIdentifier;
+            ushort packetIdentifier = 0;
             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))
             {
@@ -843,6 +875,15 @@ 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)
@@ -888,7 +929,7 @@ namespace MQTTnet.Client
             {
                 try
                 {
-                    _clientAlive?.Cancel(false);
+                    _mqttClientAlive?.Cancel(false);
                 }
                 catch (Exception exception)
                 {
@@ -917,31 +958,23 @@ namespace MQTTnet.Client
                 {
                     await ProcessReceivedDisconnectPacket(disconnectPacket).ConfigureAwait(false);
                 }
-                // else if (packet is MqttAuthPacket authPacket)
-                // {
-                //     await _authenticationHandler.HandleExtendedAuthentication(authPacket, new MqttInitialAuthenticationStrategy(_channelAdapter)).ConfigureAwait(false);
-                // }
+                else if (packet is MqttAuthPacket authPacket)
+                {
+                    await ProcessReceivedAuthPacket(authPacket).ConfigureAwait(false);
+                }
                 else if (packet is MqttPingRespPacket)
                 {
                     _packetDispatcher.TryDispatch(packet);
                 }
                 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.");
+                    throw new MqttProtocolViolationException("The PINGREQ Packet is sent from a Client to the Server only.");
                 }
                 else
                 {
                     if (!_packetDispatcher.TryDispatch(packet))
                     {
-                        throw new MqttProtocolViolationException($"Received unexpected {packet} packet.");
+                        throw new MqttProtocolViolationException($"Received packet '{packet}' at an unexpected time.");
                     }
                 }
             }
@@ -969,5 +1002,62 @@ namespace MQTTnet.Client
                 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 timeoutCancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken))
+                        {
+                            timeoutCancellationTokenSource.CancelAfter(Options.Timeout);
+                            await PingAsync(timeoutCancellationTokenSource.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;
+                }
+
+                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 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/MqttClientCertificateValidationEventArgs.cs

@@ -14,8 +14,14 @@ namespace MQTTnet.Client
 
         public X509Chain Chain { get; set; }
 
-        public SslPolicyErrors SslPolicyErrors { get; set; }
-
         public IMqttClientChannelOptions ClientOptions { get; set; }
+#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; set; }
     }
-}
+}

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

@@ -15,10 +15,14 @@ namespace MQTTnet.Client
     public sealed class MqttClientOptionsBuilder
     {
         readonly MqttClientOptions _options = new MqttClientOptions();
-        MqttClientWebSocketProxyOptions _proxyOptions;
+
+        [Obsolete] MqttClientWebSocketProxyOptions _proxyOptions;
 
         MqttClientTcpOptions _tcpOptions;
-        MqttClientOptionsBuilderTlsParameters _tlsParameters;
+        MqttClientTlsOptions _tlsOptions;
+
+        [Obsolete] MqttClientOptionsBuilderTlsParameters _tlsParameters;
+
         MqttClientWebSocketOptions _webSocketOptions;
 
         public MqttClientOptions Build()
@@ -28,11 +32,12 @@ namespace MQTTnet.Client
                 throw new InvalidOperationException("A channel must be set.");
             }
 
+            var tlsOptions = _tlsOptions;
             if (_tlsParameters != null)
             {
                 if (_tlsParameters?.UseTls == true)
                 {
-                    var tlsOptions = new MqttClientTlsOptions
+                    tlsOptions = new MqttClientTlsOptions
                     {
                         UseTls = true,
                         SslProtocol = _tlsParameters.SslProtocol,
@@ -40,28 +45,23 @@ namespace MQTTnet.Client
                         CertificateValidationHandler = _tlsParameters.CertificateValidationHandler,
                         IgnoreCertificateChainErrors = _tlsParameters.IgnoreCertificateChainErrors,
                         IgnoreCertificateRevocationErrors = _tlsParameters.IgnoreCertificateRevocationErrors,
-#if WINDOWS_UWP
-                        Certificates = _tlsParameters.Certificates?.Select(c => c.ToArray()).ToList(),
-#else
-                        Certificates = _tlsParameters.Certificates?.ToList(),
-#endif
-
+                        ClientCertificatesProvider = _tlsParameters.CertificatesProvider,
 #if NETCOREAPP3_1_OR_GREATER
                         ApplicationProtocols = _tlsParameters.ApplicationProtocols,
 #endif
                     };
-
-                    if (_tcpOptions != null)
-                    {
-                        _tcpOptions.TlsOptions = tlsOptions;
-                    }
-                    else if (_webSocketOptions != null)
-                    {
-                        _webSocketOptions.TlsOptions = tlsOptions;
-                    }
                 }
             }
 
+            if (_tcpOptions != null)
+            {
+                _tcpOptions.TlsOptions = tlsOptions;
+            }
+            else if (_webSocketOptions != null)
+            {
+                _webSocketOptions.TlsOptions = tlsOptions;
+            }
+
             if (_proxyOptions != null)
             {
                 if (_webSocketOptions == null)
@@ -79,7 +79,7 @@ namespace MQTTnet.Client
             return _options;
         }
 
-        public MqttClientOptionsBuilder WithAuthentication(string method, byte[] data = null)
+        public MqttClientOptionsBuilder WithAuthentication(string method, byte[] data)
         {
             _options.AuthenticationMethod = method;
             _options.AuthenticationData = data;
@@ -110,6 +110,7 @@ namespace MQTTnet.Client
             return this;
         }
 
+        [Obsolete("Use WithTcpServer(... configure) or WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithConnectionUri(Uri uri)
         {
             if (uri == null)
@@ -126,12 +127,16 @@ 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:
@@ -149,6 +154,7 @@ namespace MQTTnet.Client
             return this;
         }
 
+        [Obsolete("Use WithTcpServer(... configure) or WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithConnectionUri(string uri)
         {
             return WithConnectionUri(new Uri(uri, UriKind.Absolute));
@@ -177,6 +183,12 @@ namespace MQTTnet.Client
             return this;
         }
 
+        public MqttClientOptionsBuilder WithExtendedAuthenticationExchangeHandler(IMqttExtendedAuthenticationExchangeHandler handler)
+        {
+            _options.ExtendedAuthenticationExchangeHandler = handler;
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithKeepAlivePeriod(TimeSpan value)
         {
             _options.KeepAlivePeriod = value;
@@ -206,6 +218,16 @@ namespace MQTTnet.Client
             return this;
         }
 
+        /// <summary>
+        ///     The client will not throw an exception when the MQTT server responses 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 WithProtocolVersion(MqttProtocolVersion value)
         {
             if (value == MqttProtocolVersion.Unknown)
@@ -217,6 +239,7 @@ namespace MQTTnet.Client
             return this;
         }
 
+        [Obsolete("Use WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithProxy(
             string address,
             string username = null,
@@ -238,6 +261,7 @@ namespace MQTTnet.Client
             return this;
         }
 
+        [Obsolete("Use WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithProxy(Action<MqttClientWebSocketProxyOptions> optionsBuilder)
         {
             if (optionsBuilder == null)
@@ -308,17 +332,20 @@ 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 +362,26 @@ 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 +413,7 @@ namespace MQTTnet.Client
             return this;
         }
 
+        [Obsolete("Use WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithWebSocketServer(string uri, MqttClientOptionsBuilderWebSocketParameters parameters = null)
         {
             _webSocketOptions = new MqttClientWebSocketOptions
@@ -378,6 +426,21 @@ 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 +472,12 @@ 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/MqttClientTcpOptionsExtensions.cs

@@ -17,7 +17,7 @@ namespace MQTTnet.Client
                 return options.Port.Value;
             }
 
-            return !options.TlsOptions.UseTls ? 1883 : 8883;
+            return !(options.TlsOptions?.UseTls ?? false) ? 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;
 
@@ -23,18 +24,30 @@ namespace MQTTnet.Client
 
         public X509RevocationMode RevocationMode { get; set; } = X509RevocationMode.Online;
 
-#if WINDOWS_UWP
-        public List<byte[]> Certificates { get; set; }
-#else
-        public List<X509Certificate> Certificates { get; set; }
-#endif
+        /// <summary>
+        ///     Gets or sets the provider for certificates.
+        ///     This provider gets called whenever the client wants to connect
+        ///     with the server and requires certificates for authentication.
+        ///     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 System.Net.Security.CipherSuitesPolicy CipherSuitesPolicy { get; set; }
+        public List<SslApplicationProtocol> ApplicationProtocols { 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

Source/MQTTnet/Client/Options/MqttClientTlsOptionsBuilder.cs

@@ -0,0 +1,136 @@
+// 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 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
+    }
+}

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
     }
 }

Source/MQTTnet/Client/Options/MqttClientWebSocketOptionsBuilder.cs

@@ -0,0 +1,85 @@
+// 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.Net;
+
+namespace MQTTnet.Client
+{
+    public sealed class MqttClientWebSocketOptionsBuilder
+    {
+        readonly MqttClientWebSocketOptions _webSocketOptions = new MqttClientWebSocketOptions();
+
+        public MqttClientWebSocketOptions Build()
+        {
+            return _webSocketOptions;
+        }
+
+        public MqttClientWebSocketOptionsBuilder WithCookieContainer(CookieContainer cookieContainer)
+        {
+            _webSocketOptions.CookieContainer = cookieContainer;
+            return this;
+        }
+
+        public MqttClientWebSocketOptionsBuilder WithCookieContainer(ICredentials credentials)
+        {
+            _webSocketOptions.Credentials = credentials;
+            return this;
+        }
+
+        public MqttClientWebSocketOptionsBuilder WithProxyOptions(MqttClientWebSocketProxyOptions proxyOptions)
+        {
+            _webSocketOptions.ProxyOptions = proxyOptions;
+            return this;
+        }
+
+        public MqttClientWebSocketOptionsBuilder WithProxyOptions(Action<MqttClientWebSocketProxyOptionsBuilder> configure)
+        {
+            if (configure == null)
+            {
+                throw new ArgumentNullException(nameof(configure));
+            }
+
+            var proxyOptionsBuilder = new MqttClientWebSocketProxyOptionsBuilder();
+            configure.Invoke(proxyOptionsBuilder);
+
+            _webSocketOptions.ProxyOptions = proxyOptionsBuilder.Build();
+            return this;
+        }
+
+        public MqttClientWebSocketOptionsBuilder WithRequestHeaders(IDictionary<string, string> requestHeaders)
+        {
+            _webSocketOptions.RequestHeaders = requestHeaders;
+            return this;
+        }
+
+        public MqttClientWebSocketOptionsBuilder WithSubProtocols(ICollection<string> subProtocols)
+        {
+            _webSocketOptions.SubProtocols = subProtocols;
+            return this;
+        }
+
+        public MqttClientWebSocketOptionsBuilder WithUri(string uri)
+        {
+            _webSocketOptions.Uri = uri;
+            return this;
+        }
+
+#if !NETSTANDARD1_3
+        public MqttClientWebSocketOptionsBuilder WithKeepAliveInterval(TimeSpan keepAliveInterval)
+        {
+            _webSocketOptions.KeepAliveInterval = keepAliveInterval;
+            return this;
+        }
+#endif
+#if !WINDOWS_UWP && !NETSTANDARD1_3
+        public MqttClientWebSocketOptionsBuilder WithUseDefaultCredentials(bool useDefaultCredentials = true)
+        {
+            _webSocketOptions.UseDefaultCredentials = useDefaultCredentials;
+            return this;
+        }
+#endif
+    }
+}

Source/MQTTnet/Client/Options/MqttClientWebSocketProxyOptions.cs

@@ -16,6 +16,8 @@ namespace MQTTnet.Client
 
         public bool BypassOnLocal { get; set; }
 
+        public bool UseDefaultCredentials { get; set; }
+
         public string[] BypassList { get; set; }
     }
 }

Source/MQTTnet/Client/Options/MqttClientWebSocketProxyOptionsBuilder.cs

@@ -0,0 +1,67 @@
+// 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.Linq;
+
+namespace MQTTnet.Client
+{
+    public sealed class MqttClientWebSocketProxyOptionsBuilder
+    {
+        readonly MqttClientWebSocketProxyOptions _proxyOptions = new MqttClientWebSocketProxyOptions();
+
+        public MqttClientWebSocketProxyOptionsBuilder WithAddress(string address)
+        {
+            _proxyOptions.Address = address;
+            return this;
+        }
+        
+        public MqttClientWebSocketProxyOptionsBuilder WithUsername(string username)
+        {
+            _proxyOptions.Username = username;
+            return this;
+        }
+        
+        public MqttClientWebSocketProxyOptionsBuilder WithPassword(string password)
+        {
+            _proxyOptions.Password = password;
+            return this;
+        }
+        
+        public MqttClientWebSocketProxyOptionsBuilder WithDomain(string domain)
+        {
+            _proxyOptions.Domain = domain;
+            return this;
+        }
+        
+        public MqttClientWebSocketProxyOptionsBuilder WithBypassOnLocal(bool bypassOnLocal = true)
+        {
+            _proxyOptions.BypassOnLocal = bypassOnLocal;
+            return this;
+        }
+        
+        public MqttClientWebSocketProxyOptionsBuilder WithBypassList(string[] bypassList)
+        {
+            _proxyOptions.BypassList = bypassList;
+            return this;
+        }
+        
+        public MqttClientWebSocketProxyOptionsBuilder WithBypassList(IEnumerable<string> bypassList)
+        {
+            _proxyOptions.BypassList = bypassList?.ToArray();
+            return this;
+        }
+        
+        public MqttClientWebSocketProxyOptionsBuilder WithUseDefaultCredentials(bool useDefaultCredentials = true)
+        {
+            _proxyOptions.UseDefaultCredentials = useDefaultCredentials;
+            return this;
+        }
+        
+        public MqttClientWebSocketProxyOptions Build()
+        {
+            return _proxyOptions;
+        }
+    }
+}

Source/MQTTnet/Diagnostics/Runtime/TargetFrameworkProvider.cs

@@ -16,6 +16,8 @@ namespace MQTTnet.Diagnostics
                 return "net461";
 #elif NET472
                 return "net472";
+#elif NET48
+                return "net48";
 #elif NETSTANDARD1_3
                 return "netstandard1.3";
 #elif NETSTANDARD2_0

Source/MQTTnet/Formatter/MqttAuthPacketFactory.cs

@@ -1,37 +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 MQTTnet.Client;
-using MQTTnet.Packets;
-using MQTTnet.Protocol;
-
-namespace MQTTnet.Formatter
-{
-    public sealed class MqttAuthPacketFactory
-    {
-        public MqttAuthPacket CreateReAuthenticationPacket(MqttClientOptions clientOptions, MqttReAuthenticationOptions reAuthenticationOptions)
-        {
-            if (clientOptions == null)
-            {
-                throw new ArgumentNullException(nameof(clientOptions));
-            }
-
-            if (reAuthenticationOptions == null)
-            {
-                throw new ArgumentNullException(nameof(reAuthenticationOptions));
-            }
-
-            return new MqttAuthPacket
-            {
-                // The authentication method cannot change and must be always the same as long as the client is connected.
-                AuthenticationMethod = clientOptions.AuthenticationMethod,
-                ReasonCode = MqttAuthenticateReasonCode.ReAuthenticate,
-                AuthenticationData = reAuthenticationOptions.AuthenticationData,
-                UserProperties = reAuthenticationOptions.UserProperties,
-                ReasonString = null
-            };
-        }
-    }
-}

Source/MQTTnet/Formatter/MqttConnectReasonCodeConverter.cs

@@ -2,54 +2,12 @@
 // 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.Exceptions;
 using MQTTnet.Protocol;
 
 namespace MQTTnet.Formatter
 {
     public static class MqttConnectReasonCodeConverter
     {
-        public static MqttConnectReasonCode ToConnectReasonCode(MqttConnectReturnCode returnCode)
-        {
-            switch (returnCode)
-            {
-                case MqttConnectReturnCode.ConnectionAccepted:
-                {
-                    return MqttConnectReasonCode.Success;
-                }
-
-                case MqttConnectReturnCode.ConnectionRefusedUnacceptableProtocolVersion:
-                {
-                    return MqttConnectReasonCode.UnsupportedProtocolVersion;
-                }
-
-                case MqttConnectReturnCode.ConnectionRefusedBadUsernameOrPassword:
-                {
-                    return MqttConnectReasonCode.BadUserNameOrPassword;
-                }
-
-                case MqttConnectReturnCode.ConnectionRefusedIdentifierRejected:
-                {
-                    return MqttConnectReasonCode.ClientIdentifierNotValid;
-                }
-
-                case MqttConnectReturnCode.ConnectionRefusedServerUnavailable:
-                {
-                    return MqttConnectReasonCode.ServerUnavailable;
-                }
-
-                case MqttConnectReturnCode.ConnectionRefusedNotAuthorized:
-                {
-                    return MqttConnectReasonCode.NotAuthorized;
-                }
-
-                default:
-                {
-                    throw new MqttProtocolViolationException("Unable to convert connect reason code (MQTTv5) to return code (MQTTv3).");
-                }
-            }
-        }
-
         public static MqttConnectReturnCode ToConnectReturnCode(MqttConnectReasonCode reasonCode)
         {
             switch (reasonCode)
@@ -59,13 +17,13 @@ namespace MQTTnet.Formatter
                     return MqttConnectReturnCode.ConnectionAccepted;
                 }
 
-                case MqttConnectReasonCode.BadAuthenticationMethod:
                 case MqttConnectReasonCode.Banned:
                 case MqttConnectReasonCode.NotAuthorized:
                 {
                     return MqttConnectReturnCode.ConnectionRefusedNotAuthorized;
                 }
 
+                case MqttConnectReasonCode.BadAuthenticationMethod:
                 case MqttConnectReasonCode.BadUserNameOrPassword:
                 {
                     return MqttConnectReturnCode.ConnectionRefusedBadUsernameOrPassword;
@@ -75,12 +33,12 @@ namespace MQTTnet.Formatter
                 {
                     return MqttConnectReturnCode.ConnectionRefusedIdentifierRejected;
                 }
-                
+
                 case MqttConnectReasonCode.UnsupportedProtocolVersion:
                 {
                     return MqttConnectReturnCode.ConnectionRefusedUnacceptableProtocolVersion;
                 }
-                
+
                 case MqttConnectReasonCode.UseAnotherServer:
                 case MqttConnectReasonCode.ServerUnavailable:
                 case MqttConnectReasonCode.ServerBusy:
@@ -90,10 +48,7 @@ namespace MQTTnet.Formatter
                 }
 
                 default:
-                {
-                    // This is the most best matching value.
                     return MqttConnectReturnCode.ConnectionRefusedUnacceptableProtocolVersion;
-                }
             }
         }
     }

Source/MQTTnet/Formatter/MqttPacketFactories.cs

@@ -6,8 +6,6 @@ namespace MQTTnet.Formatter
 {
     public static class MqttPacketFactories
     {
-        public static MqttAuthPacketFactory Auth { get; } = new MqttAuthPacketFactory();
-        
         public static MqttConnAckPacketFactory ConnAck { get; } = new MqttConnAckPacketFactory();
         
         public static MqttConnectPacketFactory Connect { get; } = new MqttConnectPacketFactory();

Source/MQTTnet/Formatter/V5/MqttV5PacketDecoder.cs

@@ -130,6 +130,9 @@ namespace MQTTnet.Formatter.V5
                 MaximumQoS = MqttQualityOfServiceLevel.ExactlyOnce
             };
 
+            // Also set the return code of MQTT 3.1.1 for backward compatibility and debugging purposes.
+            packet.ReturnCode = MqttConnectReasonCodeConverter.ToConnectReturnCode(packet.ReasonCode);
+
             var propertiesReader = new MqttV5PropertiesReader(_bufferReader);
             while (propertiesReader.MoveNext())
             {

Source/MQTTnet/Implementations/MqttTcpChannel.Uwp.cs

@@ -6,8 +6,6 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
-using System.Linq;
-using System.Runtime.InteropServices.WindowsRuntime;
 using System.Security.Authentication;
 using System.Security.Cryptography.X509Certificates;
 using System.Threading;
@@ -18,6 +16,7 @@ using Windows.Security.Cryptography.Certificates;
 using MQTTnet.Channel;
 using MQTTnet.Client;
 using MQTTnet.Server;
+using System.Runtime.InteropServices.WindowsRuntime;
 
 namespace MQTTnet.Implementations
 {
@@ -126,17 +125,19 @@ namespace MQTTnet.Implementations
 
         private static Certificate LoadCertificate(IMqttClientChannelOptions options)
         {
-            if (options.TlsOptions.Certificates == null || !options.TlsOptions.Certificates.Any())
+            var certificates = options.TlsOptions?.ClientCertificatesProvider?.GetCertificates();
+
+            if (certificates == null || certificates.Count == 0)
             {
                 return null;
             }
 
-            if (options.TlsOptions.Certificates.Count > 1)
+            if (certificates.Count > 1)
             {
                 throw new NotSupportedException("Only one client certificate is supported when using 'uap10.0'.");
             }
 
-            return new Certificate(options.TlsOptions.Certificates.First().AsBuffer());
+            return new Certificate(certificates[0].Export(X509ContentType.Cert).AsBuffer());
         }
 
         private IEnumerable<ChainValidationResult> ResolveIgnorableServerCertificateErrors()

Source/MQTTnet/Implementations/MqttTcpChannel.cs

@@ -3,9 +3,6 @@
 // See the LICENSE file in the project root for more information.
 
 #if !WINDOWS_UWP
-using MQTTnet.Channel;
-using MQTTnet.Client;
-using MQTTnet.Exceptions;
 using System;
 using System.IO;
 using System.Net.Security;
@@ -14,6 +11,9 @@ using System.Runtime.ExceptionServices;
 using System.Security.Cryptography.X509Certificates;
 using System.Threading;
 using System.Threading.Tasks;
+using MQTTnet.Channel;
+using MQTTnet.Client;
+using MQTTnet.Exceptions;
 using MQTTnet.Internal;
 
 namespace MQTTnet.Implementations
@@ -73,7 +73,7 @@ namespace MQTTnet.Implementations
                 {
                     socket.Bind(_tcpOptions.LocalEndpoint);
                 }
-                
+
                 socket.ReceiveBufferSize = _tcpOptions.BufferSize;
                 socket.SendBufferSize = _tcpOptions.BufferSize;
                 socket.SendTimeout = (int)_clientOptions.Timeout.TotalMilliseconds;
@@ -100,6 +100,12 @@ namespace MQTTnet.Implementations
 
                 if (_tcpOptions.TlsOptions?.UseTls == true)
                 {
+                    var targetHost = _tcpOptions.TlsOptions.TargetHost;
+                    if (string.IsNullOrEmpty(targetHost))
+                    {
+                        targetHost = _tcpOptions.Server;
+                    }
+
                     var sslStream = new SslStream(networkStream, false, InternalUserCertificateValidationCallback);
                     try
                     {
@@ -111,14 +117,16 @@ namespace MQTTnet.Implementations
                             EnabledSslProtocols = _tcpOptions.TlsOptions.SslProtocol,
                             CertificateRevocationCheckMode =
  _tcpOptions.TlsOptions.IgnoreCertificateRevocationErrors ? X509RevocationMode.NoCheck : _tcpOptions.TlsOptions.RevocationMode,
-                            TargetHost = _tcpOptions.Server,
-                            CipherSuitesPolicy = _tcpOptions.TlsOptions.CipherSuitesPolicy
+                            TargetHost = targetHost,
+                            CipherSuitesPolicy = _tcpOptions.TlsOptions.CipherSuitesPolicy,
+                            EncryptionPolicy = _tcpOptions.TlsOptions.EncryptionPolicy,
+                            AllowRenegotiation = _tcpOptions.TlsOptions.AllowRenegotiation
                         };
 
                         await sslStream.AuthenticateAsClientAsync(sslOptions, cancellationToken).ConfigureAwait(false);
 #else
                         await sslStream.AuthenticateAsClientAsync(
-                                _tcpOptions.Server,
+                                targetHost,
                                 LoadCertificates(),
                                 _tcpOptions.TlsOptions.SslProtocol,
                                 !_tcpOptions.TlsOptions.IgnoreCertificateRevocationErrors)
@@ -290,18 +298,7 @@ namespace MQTTnet.Implementations
 
         X509CertificateCollection LoadCertificates()
         {
-            var certificates = new X509CertificateCollection();
-            if (_tcpOptions.TlsOptions.Certificates == null)
-            {
-                return certificates;
-            }
-
-            foreach (var certificate in _tcpOptions.TlsOptions.Certificates)
-            {
-                certificates.Add(certificate);
-            }
-
-            return certificates;
+            return _tcpOptions.TlsOptions.ClientCertificatesProvider?.GetCertificates();
         }
     }
 }

Source/MQTTnet/Implementations/MqttTcpServerListener.cs

@@ -231,6 +231,7 @@ namespace MQTTnet.Implementations
                     
                     using (var clientAdapter = new MqttChannelAdapter(tcpChannel, packetFormatterAdapter, _rootLogger))
                     {
+                        clientAdapter.AllowPacketFragmentation = _options.AllowPacketFragmentation;
                         await clientHandler(clientAdapter).ConfigureAwait(false);
                     }
                 }
@@ -255,6 +256,7 @@ namespace MQTTnet.Implementations
             {
                 try
                 {
+                    // ReSharper disable once MethodHasAsyncOverload
                     stream?.Dispose();
                     clientSocket?.Dispose();
                 }

Source/MQTTnet/Implementations/MqttWebSocketChannel.cs

@@ -155,14 +155,26 @@ namespace MQTTnet.Implementations
             throw new NotSupportedException("Proxies are not supported when using 'netstandard 1.3'.");
 #else
             var proxyUri = new Uri(_options.ProxyOptions.Address);
-
+            WebProxy webProxy;
+            
             if (!string.IsNullOrEmpty(_options.ProxyOptions.Username) && !string.IsNullOrEmpty(_options.ProxyOptions.Password))
             {
                 var credentials = new NetworkCredential(_options.ProxyOptions.Username, _options.ProxyOptions.Password, _options.ProxyOptions.Domain);
-                return new WebProxy(proxyUri, _options.ProxyOptions.BypassOnLocal, _options.ProxyOptions.BypassList, credentials);
+                webProxy = new WebProxy(proxyUri, _options.ProxyOptions.BypassOnLocal, _options.ProxyOptions.BypassList, credentials);
+            }
+            else
+            {
+                webProxy = new WebProxy(proxyUri, _options.ProxyOptions.BypassOnLocal, _options.ProxyOptions.BypassList);    
+            }
+            
+            if (_options.ProxyOptions.UseDefaultCredentials)
+            {
+                // Only update the property if required because setting it to false will alter
+                // the used credentials internally!
+                webProxy.UseDefaultCredentials = true;
             }
 
-            return new WebProxy(proxyUri, _options.ProxyOptions.BypassOnLocal, _options.ProxyOptions.BypassList);
+            return webProxy;
 #endif
         }
 
@@ -194,19 +206,35 @@ namespace MQTTnet.Implementations
                 clientWebSocket.Options.Cookies = _options.CookieContainer;
             }
 
-            if (_options.TlsOptions?.UseTls == true && _options.TlsOptions?.Certificates != null)
+            if (_options.TlsOptions?.UseTls == true)
             {
-                clientWebSocket.Options.ClientCertificates = new X509CertificateCollection();
-                foreach (var certificate in _options.TlsOptions.Certificates)
+                var certificates = _options.TlsOptions?.ClientCertificatesProvider?.GetCertificates();
+                if (certificates?.Count > 0)
                 {
-#if WINDOWS_UWP
-                    clientWebSocket.Options.ClientCertificates.Add(new X509Certificate(certificate));
-#else
-                    clientWebSocket.Options.ClientCertificates.Add(certificate);
-#endif
+                    clientWebSocket.Options.ClientCertificates = certificates;
                 }
             }
 
+#if !NETSTANDARD1_3
+#if !WINDOWS_UWP
+            // Only set the value if it is actually true. This property is not supported on all platforms
+            // and will throw a _PlatformNotSupported_ (i.e. WASM) exception when being used regardless of the actual value.
+            if (_options.UseDefaultCredentials)
+            {
+                clientWebSocket.Options.UseDefaultCredentials = _options.UseDefaultCredentials;
+            }
+
+            if (_options.KeepAliveInterval != WebSocket.DefaultKeepAliveInterval)
+            {
+                clientWebSocket.Options.KeepAliveInterval = _options.KeepAliveInterval;
+            }
+#endif
+#endif
+            if (_options.Credentials != null)
+            {
+                clientWebSocket.Options.Credentials = _options.Credentials;
+            }
+            
             var certificateValidationHandler = _options.TlsOptions?.CertificateValidationHandler;
             if (certificateValidationHandler != null)
             {
@@ -216,10 +244,20 @@ namespace MQTTnet.Implementations
                 throw new NotSupportedException("Remote certificate validation callback is not supported when using 'netstandard2.0'.");
 #elif WINDOWS_UWP
                 throw new NotSupportedException("Remote certificate validation callback is not supported when using 'uap10.0'.");
-#elif NET452
-                throw new NotSupportedException("Remote certificate validation callback is not supported when using 'net452'.");
-#elif NET461
-                throw new NotSupportedException("Remote certificate validation callback is not supported when using 'net461'.");
+#elif NET452 || NET461 || NET48
+                ServicePointManager.ServerCertificateValidationCallback += (sender, certificate, chain, sslPolicyErrors) => 
+                {
+                    var context = new MqttClientCertificateValidationEventArgs
+                    {
+                        Sender = sender,
+                        Certificate = certificate,
+                        Chain = chain,
+                        SslPolicyErrors = sslPolicyErrors,
+                        ClientOptions = _options
+                    };
+
+                    return certificateValidationHandler(context);
+                };
 #else
                 clientWebSocket.Options.RemoteCertificateValidationCallback = (sender, certificate, chain, sslPolicyErrors) =>
                 {
@@ -238,4 +276,4 @@ namespace MQTTnet.Implementations
             }
         }
     }
-}
+}

Source/MQTTnet/Internal/MqttTaskTimeout.cs

@@ -1,38 +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.Exceptions;
-
-namespace MQTTnet.Internal
-{
-    public static class MqttTaskTimeout
-    {
-        public static async Task WaitAsync(Func<CancellationToken, Task> action, TimeSpan timeout, CancellationToken cancellationToken)
-        {
-            if (action == null) throw new ArgumentNullException(nameof(action));
-
-            using (var timeoutCts = new CancellationTokenSource(timeout))
-            using (var linkedCts = CancellationTokenSource.CreateLinkedTokenSource(timeoutCts.Token, cancellationToken))
-            {
-                try
-                {
-                    await action(linkedCts.Token).ConfigureAwait(false);
-                }
-                catch (OperationCanceledException exception)
-                {
-                    var timeoutReached = timeoutCts.IsCancellationRequested && !cancellationToken.IsCancellationRequested;
-                    if (timeoutReached)
-                    {
-                        throw new MqttCommunicationTimedOutException(exception);
-                    }
-
-                    throw;
-                }
-            }
-        }
-    }
-}

Source/MQTTnet/MQTTnet.csproj

@@ -11,7 +11,7 @@
 
     <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>
         <LangVersion>7.3</LangVersion>
         <AssemblyName>MQTTnet</AssemblyName>

Source/MQTTnet/MQTTnet.csproj.DotSettings

@@ -1,5 +1,4 @@
 <wpf:ResourceDictionary xml:space="preserve" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:s="clr-namespace:System;assembly=mscorlib" xmlns:ss="urn:shemas-jetbrains-com:settings-storage-xaml" xmlns:wpf="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
-	<s:Boolean x:Key="/Default/CodeInspection/NamespaceProvider/NamespaceFoldersToSkip/=client_005Cauthentication/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeInspection/NamespaceProvider/NamespaceFoldersToSkip/=client_005Cconnecting/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeInspection/NamespaceProvider/NamespaceFoldersToSkip/=client_005Cdiagnostics/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeInspection/NamespaceProvider/NamespaceFoldersToSkip/=client_005Cdisconnecting/@EntryIndexedValue">True</s:Boolean>

Source/MQTTnet/MqttApplicationMessageExtensions.cs

@@ -4,6 +4,7 @@
 
 using System;
 using System.Text;
+using MQTTnet.Internal;
 
 namespace MQTTnet
 {
@@ -16,6 +17,16 @@ namespace MQTTnet
                 throw new ArgumentNullException(nameof(applicationMessage));
             }
 
+            if(applicationMessage.PayloadSegment == EmptyBuffer.ArraySegment)
+            {
+                return null;
+            }
+
+            if (applicationMessage.PayloadSegment.Array == null)
+            {
+                return null;
+            }
+
             var payloadSegment = applicationMessage.PayloadSegment;
             return Encoding.UTF8.GetString(payloadSegment.Array, payloadSegment.Offset, payloadSegment.Count);
         }

Source/MQTTnet/PacketDispatcher/IMqttPacketAwaitable.cs

@@ -9,7 +9,7 @@ namespace MQTTnet.PacketDispatcher
 {
     public interface IMqttPacketAwaitable : IDisposable
     {
-        int PacketIdentifier { get; }
+        MqttPacketAwaitableFilter Filter { get; }
         
         void Complete(MqttPacket packet);
 

Source/MQTTnet/PacketDispatcher/MqttPacketAwaitable.cs

@@ -16,13 +16,18 @@ namespace MQTTnet.PacketDispatcher
         readonly AsyncTaskCompletionSource<MqttPacket> _promise = new AsyncTaskCompletionSource<MqttPacket>();
         readonly MqttPacketDispatcher _owningPacketDispatcher;
 
-        public MqttPacketAwaitable(int packetPacketIdentifier, MqttPacketDispatcher owningPacketDispatcher)
+        public MqttPacketAwaitable(ushort packetIdentifier, MqttPacketDispatcher owningPacketDispatcher)
         {
-            PacketIdentifier = packetPacketIdentifier;
+            Filter = new MqttPacketAwaitableFilter
+            {
+                Type = typeof(TPacket),
+                Identifier = packetIdentifier
+            };
+            
             _owningPacketDispatcher = owningPacketDispatcher ?? throw new ArgumentNullException(nameof(owningPacketDispatcher));
         }
         
-        public int PacketIdentifier { get; }
+        public MqttPacketAwaitableFilter Filter { get; }
         
         public async Task<TPacket> WaitOneAsync(CancellationToken cancellationToken)
         {

Source/MQTTnet/PacketDispatcher/MqttPacketAwaitableFilter.cs

@@ -4,10 +4,12 @@
 
 using System;
 
-namespace MQTTnet.Server
+namespace MQTTnet.PacketDispatcher
 {
-    public sealed class ClientReAuthenticatingEventArgs : EventArgs
+    public sealed class MqttPacketAwaitableFilter
     {
+        public Type Type { get; set; }
         
+        public ushort Identifier { get; set; }
     }
 }

Source/MQTTnet/PacketDispatcher/MqttPacketDispatcher.cs

@@ -10,15 +10,11 @@ namespace MQTTnet.PacketDispatcher
 {
     public sealed class MqttPacketDispatcher : IDisposable
     {
-        public const int PingRespPacketFakeIdentifier = 2147483647;
-        public const int AuthPacketFakeIdentifier = 2147483646;
-        public const int SuccessAuthPacketFakeIdentifier = 2147483647;
-        
         readonly List<IMqttPacketAwaitable> _waiters = new List<IMqttPacketAwaitable>();
 
         bool _isDisposed;
 
-        public MqttPacketAwaitable<TResponsePacket> AddAwaitable<TResponsePacket>(int packetIdentifier) where TResponsePacket : MqttPacket
+        public MqttPacketAwaitable<TResponsePacket> AddAwaitable<TResponsePacket>(ushort packetIdentifier) where TResponsePacket : MqttPacket
         {
             var awaitable = new MqttPacketAwaitable<TResponsePacket>(packetIdentifier, this);
 
@@ -103,21 +99,15 @@ namespace MQTTnet.PacketDispatcher
                 throw new ArgumentNullException(nameof(packet));
             }
 
-            var identifier = 0;
+            ushort identifier = 0;
             if (packet is MqttPacketWithIdentifier packetWithIdentifier)
             {
                 identifier = packetWithIdentifier.PacketIdentifier;
             }
-            else if (packet is MqttPingRespPacket)
-            {
-                identifier = PingRespPacketFakeIdentifier;
-            }
-            else
-            {
-                throw new InvalidOperationException($"Cannot dispatch {packet.GetRfcName()} packet.");
-            }
-            
+
+            var packetType = packet.GetType();
             var waiters = new List<IMqttPacketAwaitable>();
+
             lock (_waiters)
             {
                 ThrowIfDisposed();
@@ -125,8 +115,11 @@ namespace MQTTnet.PacketDispatcher
                 for (var i = _waiters.Count - 1; i >= 0; i--)
                 {
                     var entry = _waiters[i];
-                    
-                    if (entry.PacketIdentifier != identifier)
+
+                    // Note: The PingRespPacket will also arrive here and has NO identifier but there
+                    // is code which waits for it. So the code must be able to deal with filters which
+                    // are referring to the type only (identifier is 0)!
+                    if (entry.Filter.Type != packetType || entry.Filter.Identifier != identifier)
                     {
                         continue;
                     }

Source/MQTTnet/Packets/MqttConnAckPacket.cs

@@ -28,7 +28,7 @@ namespace MQTTnet.Packets
         public MqttQualityOfServiceLevel MaximumQoS { get; set; }
 
         /// <summary>
-        ///     The return code is only used in MQTTv 5.0.0 and higher.
+        ///     Added in MQTTv5.
         /// </summary>
         public MqttConnectReasonCode ReasonCode { get; set; }
 
@@ -39,16 +39,13 @@ namespace MQTTnet.Packets
         public string ResponseInformation { get; set; }
 
         public bool RetainAvailable { get; set; }
-
-        /// <summary>
-        ///     The return code is only used in MQTTv 3.1.1 and lower.
-        /// </summary>
+        
         public MqttConnectReturnCode ReturnCode { get; set; }
 
         public ushort ServerKeepAlive { get; set; }
 
         public string ServerReference { get; set; }
-
+        
         public uint SessionExpiryInterval { get; set; }
 
         public bool SharedSubscriptionAvailable { get; set; }

Source/MQTTnet/Packets/MqttDisconnectPacket.cs

@@ -36,7 +36,7 @@ namespace MQTTnet.Packets
 
         public override string ToString()
         {
-            return $"Disconnect: [ReasonCode={ReasonCode}]";
+            return $"Disconnect: [ReasonCode={ReasonCode}] [ReasonString={ReasonString}] [ServerReference={ServerReference}] [SessionExpiryInterval={SessionExpiryInterval}]";
         }
     }
 }

Source/MQTTnet/Packets/MqttUserPropertiesBuilder.cs

@@ -1,24 +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;
-
-namespace MQTTnet.Packets
-{
-    public sealed class MqttUserPropertiesBuilder
-    {
-        readonly List<MqttUserProperty> _properties = new List<MqttUserProperty>();
-
-        public List<MqttUserProperty> Build()
-        {
-            return _properties;
-        }
-
-        public MqttUserPropertiesBuilder With(string name, string value = "")
-        {
-            _properties.Add(new MqttUserProperty(name, value));
-            return this;
-        }
-    }
-}

Source/MQTTnet/Server/Events/ClientConnectedEventArgs.cs

@@ -4,26 +4,33 @@
 
 using System;
 using System.Collections;
+using System.Collections.Generic;
 using MQTTnet.Formatter;
+using MQTTnet.Packets;
 
 namespace MQTTnet.Server
 {
     public sealed class ClientConnectedEventArgs : EventArgs
     {
-        public ClientConnectedEventArgs(string clientId, string userName, MqttProtocolVersion protocolVersion, string endpoint, IDictionary sessionItems)
+        readonly MqttConnectPacket _connectPacket;
+
+        public ClientConnectedEventArgs(MqttConnectPacket connectPacket, MqttProtocolVersion protocolVersion, string endpoint, IDictionary sessionItems)
         {
-            ClientId = clientId ?? throw new ArgumentNullException(nameof(clientId));
-            UserName = userName;
+            _connectPacket = connectPacket ?? throw new ArgumentNullException(nameof(connectPacket));
             ProtocolVersion = protocolVersion;
             Endpoint = endpoint;
             SessionItems = sessionItems ?? throw new ArgumentNullException(nameof(sessionItems));
         }
 
+        public byte[] AuthenticationData => _connectPacket.AuthenticationData;
+
+        public string AuthenticationMethod => _connectPacket.AuthenticationMethod;
+
         /// <summary>
         ///     Gets the client identifier of the connected client.
         ///     Hint: This identifier needs to be unique over all used clients / devices on the broker to avoid connection issues.
         /// </summary>
-        public string ClientId { get; }
+        public string ClientId => _connectPacket.ClientId;
 
         /// <summary>
         ///     Gets the endpoint of the connected client.
@@ -43,6 +50,12 @@ namespace MQTTnet.Server
         /// <summary>
         ///     Gets the user name of the connected client.
         /// </summary>
-        public string UserName { get; }
+        public string UserName => _connectPacket.Username;
+
+        /// <summary>
+        ///     Gets the user properties sent by the client.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// </summary>
+        public List<MqttUserProperty> UserProperties => _connectPacket?.UserProperties;
     }
 }

Source/MQTTnet/Server/Events/PartialAuthenticationResponse.cs

@@ -1,19 +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;
-using MQTTnet.Protocol;
-
-namespace MQTTnet.Server
-{
-    public sealed class PartialAuthenticationResponse
-    {
-        public byte[] AuthenticationData { get; set; }
-
-        public MqttAuthenticateReasonCode ReasonCode { get; set; }
-
-        public List<MqttUserProperty> UserProperties { get; set; }
-    }
-}

Source/MQTTnet/Server/Events/ValidatingConnectionEventArgs.cs

@@ -7,10 +7,7 @@ using System.Collections;
 using System.Collections.Generic;
 using System.Security.Cryptography.X509Certificates;
 using System.Text;
-using System.Threading;
-using System.Threading.Tasks;
 using MQTTnet.Adapter;
-using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
 using MQTTnet.Internal;
 using MQTTnet.Packets;
@@ -22,12 +19,11 @@ namespace MQTTnet.Server
     {
         readonly MqttConnectPacket _connectPacket;
 
-        public ValidatingConnectionEventArgs(MqttConnectPacket connectPacket, IMqttChannelAdapter clientAdapter, IDictionary sessionItems, CancellationToken cancellationToken)
+        public ValidatingConnectionEventArgs(MqttConnectPacket connectPacket, IMqttChannelAdapter clientAdapter, IDictionary sessionItems)
         {
             _connectPacket = connectPacket ?? throw new ArgumentNullException(nameof(connectPacket));
             ChannelAdapter = clientAdapter ?? throw new ArgumentNullException(nameof(clientAdapter));
             SessionItems = sessionItems ?? throw new ArgumentNullException(nameof(sessionItems));
-            CancellationToken = cancellationToken;
         }
 
         /// <summary>
@@ -48,11 +44,6 @@ namespace MQTTnet.Server
         /// </summary>
         public string AuthenticationMethod => _connectPacket.AuthenticationMethod;
 
-        /// <summary>
-        ///     Gets a cancellation token which is being canceled as soon as the transport connection is closed.
-        /// </summary>
-        public CancellationToken CancellationToken { get; }
-
         /// <summary>
         ///     Gets the channel adapter. This can be a _MqttConnectionContext_ (used in ASP.NET), a _MqttChannelAdapter_ (used for
         ///     TCP or WebSockets) or a custom implementation.
@@ -198,51 +189,5 @@ namespace MQTTnet.Server
         ///     A value of 0 indicates that the value is not used.
         /// </summary>
         public uint WillDelayInterval => _connectPacket.WillDelayInterval;
-
-        public async Task<PartialAuthenticationResponse> ReceiveAuthenticationDataAsync(CancellationToken cancellationToken = default)
-        {
-            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 new PartialAuthenticationResponse
-                {
-                    ReasonCode = authPacket.ReasonCode,
-                    AuthenticationData = authPacket.AuthenticationData,
-                    UserProperties = authPacket.UserProperties
-                };
-            }
-
-            if (receivePacket == null)
-            {
-                throw new MqttCommunicationException("The client closed the connection.");
-            }
-
-            throw new MqttProtocolViolationException("Expected an AUTH packet from the client.");
-        }
-
-        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 = new MqttAuthPacket
-            {
-                AuthenticationMethod = AuthenticationMethod,
-                AuthenticationData = authenticationData,
-                UserProperties = userProperties,
-                ReasonCode = reasonCode,
-                ReasonString = reasonString
-            };
-
-            return ChannelAdapter.SendPacketAsync(authPacket, cancellationToken);
-        }
     }
 }

Source/MQTTnet/Server/Internal/MqttClient.cs

@@ -95,15 +95,16 @@ namespace MQTTnet.Server
             {
                 var cancellationToken = _cancellationToken.Token;
                 IsRunning = true;
-
-                _ = Task.Factory.StartNew(() => SendPacketsLoop(cancellationToken), cancellationToken, TaskCreationOptions.PreferFairness, TaskScheduler.Default)
-                    .ConfigureAwait(false);
+                
+                _ = Task.Factory.StartNew(() => SendPacketsLoop(cancellationToken), cancellationToken, TaskCreationOptions.PreferFairness, TaskScheduler.Default).ConfigureAwait(false);
 
                 await ReceivePackagesLoop(cancellationToken).ConfigureAwait(false);
             }
             finally
             {
                 IsRunning = false;
+                
+                Session.DisconnectedTimestamp = DateTime.UtcNow;
 
                 _cancellationToken?.TryCancel();
                 _cancellationToken?.Dispose();
@@ -177,22 +178,6 @@ namespace MQTTnet.Server
             return CompletedTask.Instance;
         }
 
-        async Task HandleIncomingAuthPacket(MqttAuthPacket authPacket)
-        {
-            if (authPacket.ReasonCode != MqttAuthenticateReasonCode.ReAuthenticate)
-            {
-                throw new MqttProtocolViolationException("Clients are only allowed to send AUTH packets after connecting for re authentication.");
-            }
-
-            // We have to handle the re authentication in another task because we rely on the package retrieval.
-            _ = Task.Run(
-                async () =>
-                {
-                    var eventArgs = new ClientReAuthenticatingEventArgs();
-                    await _eventContainer.ClientReAuthenticatingEvent.InvokeAsync(eventArgs);
-                });
-        }
-
         void HandleIncomingPingReqPacket()
         {
             // See: The Server MUST send a PINGRESP packet in response to a PINGREQ packet [MQTT-3.12.4-1].
@@ -453,13 +438,9 @@ namespace MQTTnet.Server
                         DisconnectPacket = disconnectPacket;
                         return;
                     }
-                    else if (currentPacket is MqttAuthPacket authPacket)
-                    {
-                        await HandleIncomingAuthPacket(authPacket);
-                    }
                     else
                     {
-                        throw new MqttProtocolViolationException("Packet not allowed.");
+                        throw new MqttProtocolViolationException("Packet not allowed");
                     }
                 }
             }

Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs

@@ -34,7 +34,7 @@ namespace MQTTnet.Server
 
         // The _sessions dictionary contains all session, the _subscriberSessions hash set contains subscriber sessions only.
         // See the MqttSubscription object for a detailed explanation.
-        readonly Dictionary<string, MqttSession> _sessions = new Dictionary<string, MqttSession>(4096);
+        readonly MqttSessionsStorage _sessionsStorage = new MqttSessionsStorage();
 
         readonly ReaderWriterLockSlim _sessionsManagementLock = new ReaderWriterLockSlim();
         readonly HashSet<MqttSession> _subscriberSessions = new HashSet<MqttSession>();
@@ -58,7 +58,7 @@ namespace MQTTnet.Server
             _eventContainer = eventContainer ?? throw new ArgumentNullException(nameof(eventContainer));
         }
 
-        public async Task CloseAllConnectionsAsync()
+        public async Task CloseAllConnections()
         {
             List<MqttClient> connections;
             lock (_clients)
@@ -78,21 +78,16 @@ namespace MQTTnet.Server
             _logger.Verbose("Deleting session for client '{0}'.", clientId);
 
             MqttClient connection;
-
             lock (_clients)
             {
                 _clients.TryGetValue(clientId, out connection);
             }
 
             MqttSession session;
-
             _sessionsManagementLock.EnterWriteLock();
             try
             {
-                _sessions.TryGetValue(clientId, out session);
-                _sessions.Remove(clientId);
-
-                if (session != null)
+                if (_sessionsStorage.TryRemoveSession(clientId, out session))
                 {
                     _subscriberSessions.Remove(session);
                 }
@@ -111,7 +106,7 @@ namespace MQTTnet.Server
             }
             catch (Exception exception)
             {
-                _logger.Error(exception, $"Error while deleting session '{clientId}'.");
+                _logger.Error(exception, "Error while deleting session '{0}'", clientId);
             }
 
             try
@@ -124,12 +119,12 @@ namespace MQTTnet.Server
             }
             catch (Exception exception)
             {
-                _logger.Error(exception, $"Error while executing session deleted event for session '{clientId}'.");
+                _logger.Error(exception, "Error while executing session deleted event for session '{0}'", clientId);
             }
 
             session?.Dispose();
 
-            _logger.Verbose("Session for client '{0}' deleted.", clientId);
+            _logger.Verbose("Session of client '{0}' deleted", clientId);
         }
 
         public async Task<DispatchApplicationMessageResult> DispatchApplicationMessage(
@@ -269,20 +264,14 @@ namespace MQTTnet.Server
             _sessionsManagementLock.EnterWriteLock();
             try
             {
-                foreach (var sessionItem in _sessions)
-                {
-                    sessionItem.Value.Dispose();
-                }
+                _sessionsStorage.Dispose();
             }
             finally
             {
                 _sessionsManagementLock.ExitWriteLock();
             }
 
-            if (_sessionsManagementLock != null)
-            {
-                _sessionsManagementLock.Dispose();
-            }
+            _sessionsManagementLock?.Dispose();
         }
 
         public MqttClient GetClient(string id)
@@ -306,17 +295,17 @@ namespace MQTTnet.Server
             }
         }
 
-        public Task<IList<MqttClientStatus>> GetClientStatusesAsync()
+        public Task<IList<MqttClientStatus>> GetClientsStatus()
         {
             var result = new List<MqttClientStatus>();
 
             lock (_clients)
             {
-                foreach (var connection in _clients.Values)
+                foreach (var client in _clients.Values)
                 {
-                    var clientStatus = new MqttClientStatus(connection)
+                    var clientStatus = new MqttClientStatus(client)
                     {
-                        Session = new MqttSessionStatus(connection.Session)
+                        Session = new MqttSessionStatus(client.Session)
                     };
 
                     result.Add(clientStatus);
@@ -326,16 +315,16 @@ namespace MQTTnet.Server
             return Task.FromResult((IList<MqttClientStatus>)result);
         }
 
-        public Task<IList<MqttSessionStatus>> GetSessionStatusAsync()
+        public Task<IList<MqttSessionStatus>> GetSessionsStatus()
         {
             var result = new List<MqttSessionStatus>();
 
             _sessionsManagementLock.EnterReadLock();
             try
             {
-                foreach (var sessionItem in _sessions)
+                foreach (var session in _sessionsStorage.ReadAllSessions())
                 {
-                    var sessionStatus = new MqttSessionStatus(sessionItem.Value);
+                    var sessionStatus = new MqttSessionStatus(session);
                     result.Add(sessionStatus);
                 }
             }
@@ -360,7 +349,7 @@ namespace MQTTnet.Server
                     return;
                 }
 
-                var validatingConnectionEventArgs = await ValidateConnection(connectPacket, channelAdapter, cancellationToken).ConfigureAwait(false);
+                var validatingConnectionEventArgs = await ValidateConnection(connectPacket, channelAdapter).ConfigureAwait(false);
                 var connAckPacket = MqttPacketFactories.ConnAck.Create(validatingConnectionEventArgs);
 
                 if (validatingConnectionEventArgs.ReasonCode != MqttConnectReasonCode.Success)
@@ -377,9 +366,7 @@ namespace MQTTnet.Server
 
                 if (_eventContainer.ClientConnectedEvent.HasHandlers)
                 {
-                    var eventArgs = new ClientConnectedEventArgs(
-                        connectPacket.ClientId,
-                        connectPacket.Username,
+                    var eventArgs = new ClientConnectedEventArgs(connectPacket,
                         channelAdapter.PacketFormatterAdapter.ProtocolVersion,
                         channelAdapter.Endpoint,
                         client.Session.Items);
@@ -397,7 +384,7 @@ namespace MQTTnet.Server
             }
             catch (Exception exception)
             {
-                _logger.Error(exception, $"Error while validating client {channelAdapter.Endpoint}. {exception.Message}");
+                _logger.Error(exception, exception.Message);
             }
             finally
             {
@@ -486,7 +473,7 @@ namespace MQTTnet.Server
         {
             if (!_options.EnablePersistentSessions)
             {
-                _sessions.Clear();
+                _sessionsStorage.Clear();
             }
         }
 
@@ -586,45 +573,49 @@ namespace MQTTnet.Server
                     MqttSession session;
 
                     // Create a new session (if required).
-                    if (!_sessions.TryGetValue(connectPacket.ClientId, out oldSession))
+                    if (!_sessionsStorage.TryGetSession(connectPacket.ClientId, out oldSession))
                     {
-                        session = CreateSession(connectPacket.ClientId, validatingConnectionEventArgs.SessionItems, sessionShouldPersist);
+                        session = CreateSession(connectPacket, validatingConnectionEventArgs, sessionShouldPersist);
                     }
                     else
                     {
                         if (connectPacket.CleanSession)
                         {
-                            _logger.Verbose("Deleting existing session of client '{0}' due to clean start.", connectPacket.ClientId);
+                            _logger.Verbose("Deleting existing session of client '{0}' due to clean start", connectPacket.ClientId);
                             _subscriberSessions.Remove(oldSession);
-                            session = CreateSession(connectPacket.ClientId, validatingConnectionEventArgs.SessionItems, sessionShouldPersist);
+                            session = CreateSession(connectPacket, validatingConnectionEventArgs, sessionShouldPersist);
                         }
                         else
                         {
-                            _logger.Verbose("Reusing existing session of client '{0}'.", connectPacket.ClientId);
+                            _logger.Verbose("Reusing existing session of client '{0}'", connectPacket.ClientId);
                             session = oldSession;
                             oldSession = null;
 
                             // Session persistence could change for MQTT 5 clients that reconnect with different SessionExpiryInterval
                             session.IsPersistent = sessionShouldPersist;
-                            connAckPacket.IsSessionPresent = true;
+                            session.DisconnectedTimestamp = null;
                             session.Recover();
+                            
+                            connAckPacket.IsSessionPresent = true;
                         }
                     }
 
-                    _sessions[connectPacket.ClientId] = session;
-
+                    _sessionsStorage.UpdateSession(connectPacket.ClientId, session);
+                    
                     // Create a new client (always required).
-                    _clients.TryGetValue(connectPacket.ClientId, out oldClient);
-                    if (oldClient != null)
+                    lock (_clients)
                     {
-                        // This will stop the current client from sending and receiving but remains the connection active
-                        // for a later DISCONNECT packet.
-                        oldClient.IsTakenOver = true;
+                        _clients.TryGetValue(connectPacket.ClientId, out oldClient);
+                        if (oldClient != null)
+                        {
+                            // This will stop the current client from sending and receiving but remains the connection active
+                            // for a later DISCONNECT packet.
+                            oldClient.IsTakenOver = true;
+                        }
+
+                        client = CreateClient(connectPacket, channelAdapter, session);
+                        _clients[connectPacket.ClientId] = client;
                     }
-
-                    client = CreateClient(connectPacket, channelAdapter, session);
-
-                    _clients[connectPacket.ClientId] = client;
                 }
                 finally
                 {
@@ -656,11 +647,14 @@ namespace MQTTnet.Server
             return client;
         }
 
-        MqttSession CreateSession(string clientId, IDictionary sessionItems, bool isPersistent)
+        MqttSession CreateSession(MqttConnectPacket connectPacket, ValidatingConnectionEventArgs validatingConnectionEventArgs, bool isPersistent)
         {
-            _logger.Verbose("Created new session for client '{0}'.", clientId);
+            _logger.Verbose("Created new session for client '{0}'", connectPacket.ClientId);
 
-            return new MqttSession(clientId, isPersistent, sessionItems, _options, _eventContainer, _retainedMessagesManager, this);
+            return new MqttSession(connectPacket, validatingConnectionEventArgs.SessionItems, _options, _eventContainer, _retainedMessagesManager, this)
+            {
+                IsPersistent = isPersistent
+            };
         }
 
         async Task FireApplicationMessageNotConsumedEvent(MqttApplicationMessage applicationMessage, string senderId)
@@ -679,7 +673,7 @@ namespace MQTTnet.Server
             _sessionsManagementLock.EnterReadLock();
             try
             {
-                if (!_sessions.TryGetValue(clientId, out var session))
+                if (!_sessionsStorage.TryGetSession(clientId, out var session))
                 {
                     throw new InvalidOperationException($"Client session '{clientId}' is unknown.");
                 }
@@ -719,11 +713,11 @@ namespace MQTTnet.Server
             return null;
         }
 
-        async Task<ValidatingConnectionEventArgs> ValidateConnection(MqttConnectPacket connectPacket, IMqttChannelAdapter channelAdapter, CancellationToken cancellationToken)
+        async Task<ValidatingConnectionEventArgs> ValidateConnection(MqttConnectPacket connectPacket, IMqttChannelAdapter channelAdapter)
         {
             // TODO: Load session items from persisted sessions in the future.
             var sessionItems = new ConcurrentDictionary<object, object>();
-            var eventArgs = new ValidatingConnectionEventArgs(connectPacket, channelAdapter, sessionItems, cancellationToken);
+            var eventArgs = new ValidatingConnectionEventArgs(connectPacket, channelAdapter, sessionItems);
             await _eventContainer.ValidatingConnectionEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
 
             // Check the client ID and set a random one if supported.

Source/MQTTnet/Server/Internal/MqttClientSubscriptionsManager.cs

@@ -162,10 +162,7 @@ namespace MQTTnet.Server
 
         public void Dispose()
         {
-            if (_subscriptionsLock != null)
-            {
-                _subscriptionsLock.Dispose();
-            }
+            _subscriptionsLock?.Dispose();
         }
 
         public async Task<SubscribeResult> Subscribe(MqttSubscribePacket subscribePacket, CancellationToken cancellationToken)

Source/MQTTnet/Server/Internal/MqttRetainedMessagesManager.cs

@@ -134,9 +134,9 @@ namespace MQTTnet.Server
                 {
                     return Task.FromResult(message);
                 }
-
-                return null;
             }
+
+            return Task.FromResult<MqttApplicationMessage>(null);
         }
 
         public async Task ClearMessages()

Source/MQTTnet/Server/Internal/MqttServerEventContainer.cs

@@ -17,14 +17,11 @@ namespace MQTTnet.Server
 
         public AsyncEvent<ClientDisconnectedEventArgs> ClientDisconnectedEvent { get; } = new AsyncEvent<ClientDisconnectedEventArgs>();
 
-        public AsyncEvent<ClientReAuthenticatingEventArgs> ClientReAuthenticatingEvent { get; } = new AsyncEvent<ClientReAuthenticatingEventArgs>();
-
         public AsyncEvent<ClientSubscribedTopicEventArgs> ClientSubscribedTopicEvent { get; } = new AsyncEvent<ClientSubscribedTopicEventArgs>();
 
         public AsyncEvent<ClientUnsubscribedTopicEventArgs> ClientUnsubscribedTopicEvent { get; } = new AsyncEvent<ClientUnsubscribedTopicEventArgs>();
 
-        public AsyncEvent<InterceptingClientApplicationMessageEnqueueEventArgs> InterceptingClientEnqueueEvent { get; } =
-            new AsyncEvent<InterceptingClientApplicationMessageEnqueueEventArgs>();
+        public AsyncEvent<InterceptingClientApplicationMessageEnqueueEventArgs> InterceptingClientEnqueueEvent { get; } = new AsyncEvent<InterceptingClientApplicationMessageEnqueueEventArgs>();
 
         public AsyncEvent<InterceptingPacketEventArgs> InterceptingInboundPacketEvent { get; } = new AsyncEvent<InterceptingPacketEventArgs>();
 

Source/MQTTnet/Server/Internal/MqttSession.cs

@@ -21,6 +21,7 @@ namespace MQTTnet.Server
         readonly MqttPacketBus _packetBus = new MqttPacketBus();
         readonly MqttPacketIdentifierProvider _packetIdentifierProvider = new MqttPacketIdentifierProvider();
 
+        readonly MqttConnectPacket _connectPacket;
         readonly MqttServerOptions _serverOptions;
         readonly MqttClientSubscriptionsManager _subscriptionsManager;
 
@@ -31,18 +32,16 @@ namespace MQTTnet.Server
         HashSet<string> _subscribedTopics;
 
         public MqttSession(
-            string clientId,
-            bool isPersistent,
+            MqttConnectPacket connectPacket,
             IDictionary items,
             MqttServerOptions serverOptions,
             MqttServerEventContainer eventContainer,
             MqttRetainedMessagesManager retainedMessagesManager,
             MqttClientSessionsManager clientSessionsManager)
         {
-            Id = clientId ?? throw new ArgumentNullException(nameof(clientId));
-            IsPersistent = isPersistent;
             Items = items ?? throw new ArgumentNullException(nameof(items));
 
+            _connectPacket = connectPacket ?? throw new ArgumentNullException(nameof(connectPacket));
             _serverOptions = serverOptions ?? throw new ArgumentNullException(nameof(serverOptions));
             _clientSessionsManager = clientSessionsManager ?? throw new ArgumentNullException(nameof(clientSessionsManager));
 
@@ -50,10 +49,14 @@ namespace MQTTnet.Server
         }
 
         public DateTime CreatedTimestamp { get; } = DateTime.UtcNow;
+        
+        public DateTime? DisconnectedTimestamp { get; set; }
 
         public bool HasSubscribedTopics => _subscribedTopics != null && _subscribedTopics.Count > 0;
 
-        public string Id { get; }
+        public uint ExpiryInterval => _connectPacket.SessionExpiryInterval;
+        
+        public string Id => _connectPacket.ClientId;
 
         /// <summary>
         ///     Session should persist if CleanSession was set to false (Mqtt3) or if SessionExpiryInterval != 0 (Mqtt5)

Source/MQTTnet/Server/Internal/MqttSessionsStorage.cs

@@ -0,0 +1,93 @@
+// 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.Collections.ObjectModel;
+using System.Linq;
+
+namespace MQTTnet.Server
+{
+    public sealed class MqttSessionsStorage
+    {
+        readonly Dictionary<string, MqttSession> _sessions = new Dictionary<string, MqttSession>(4096);
+
+        public void Clear()
+        {
+            // Make sure that the sessions are also getting disposed!
+            // This object can be reused after disposing.
+            Dispose();
+        }
+
+        public void Dispose()
+        {
+            foreach (var sessionItem in _sessions)
+            {
+                sessionItem.Value.Dispose();
+            }
+
+            _sessions.Clear();
+        }
+
+        public IReadOnlyCollection<MqttSession> ReadAllSessions()
+        {
+            return new ReadOnlyCollection<MqttSession>(_sessions.Values.ToList());
+        }
+
+        public bool TryGetSession(string id, out MqttSession session)
+        {
+            if (id == null)
+            {
+                throw new ArgumentNullException(nameof(id));
+            }
+
+            if (!_sessions.TryGetValue(id, out session))
+            {
+                return false;
+            }
+
+            // If the Session Expiry Interval is 0xFFFFFFFF (UINT_MAX), the Session does not expire.
+            if (session.ExpiryInterval > 0 && session.ExpiryInterval != uint.MaxValue)
+            {
+                if (session.DisconnectedTimestamp.HasValue)
+                {
+                    if (DateTime.UtcNow > session.DisconnectedTimestamp.Value.AddSeconds(session.ExpiryInterval))
+                    {
+                        TryRemoveSession(id, out var oldSession);
+                        oldSession?.Dispose();
+                        return false;
+                    }
+                }
+            }
+
+            return true;
+        }
+
+        public bool TryRemoveSession(string id, out MqttSession session)
+        {
+            if (id == null)
+            {
+                throw new ArgumentNullException(nameof(id));
+            }
+
+            if (_sessions.TryGetValue(id, out session))
+            {
+                _sessions.Remove(id);
+                return true;
+            }
+
+            return false;
+        }
+
+        public void UpdateSession(string id, MqttSession session)
+        {
+            if (id == null)
+            {
+                throw new ArgumentNullException(nameof(id));
+            }
+
+            _sessions[id] = session;
+        }
+    }
+}

Source/MQTTnet/Server/MqttServer.cs

@@ -73,12 +73,6 @@ namespace MQTTnet.Server
             remove => _eventContainer.ClientDisconnectedEvent.RemoveHandler(value);
         }
 
-        public event Func<ClientReAuthenticatingEventArgs, Task> ClientReAuthenticatingAsync
-        {
-            add => _eventContainer.ClientReAuthenticatingEvent.AddHandler(value);
-            remove => _eventContainer.ClientReAuthenticatingEvent.RemoveHandler(value);
-        }
-
         public event Func<ClientSubscribedTopicEventArgs, Task> ClientSubscribedTopicAsync
         {
             add => _eventContainer.ClientSubscribedTopicEvent.AddHandler(value);
@@ -206,7 +200,14 @@ namespace MQTTnet.Server
         {
             ThrowIfNotStarted();
 
-            return _clientSessionsManager.GetClientStatusesAsync();
+            return _clientSessionsManager.GetClientsStatus();
+        }
+
+        public Task<IList<MqttApplicationMessage>> GetRetainedMessagesAsync()
+        {
+            ThrowIfNotStarted();
+
+            return _retainedMessagesManager.GetMessages();
         }
 
         public Task<MqttApplicationMessage> GetRetainedMessageAsync(string topic)
@@ -221,18 +222,11 @@ namespace MQTTnet.Server
             return _retainedMessagesManager.GetMessage(topic);
         }
 
-        public Task<IList<MqttApplicationMessage>> GetRetainedMessagesAsync()
-        {
-            ThrowIfNotStarted();
-
-            return _retainedMessagesManager.GetMessages();
-        }
-
         public Task<IList<MqttSessionStatus>> GetSessionsAsync()
         {
             ThrowIfNotStarted();
 
-            return _clientSessionsManager.GetSessionStatusAsync();
+            return _clientSessionsManager.GetSessionsStatus();
         }
 
         public Task InjectApplicationMessage(InjectedMqttApplicationMessage injectedApplicationMessage, CancellationToken cancellationToken = default)
@@ -298,7 +292,7 @@ namespace MQTTnet.Server
 
                 _cancellationTokenSource.Cancel(false);
 
-                await _clientSessionsManager.CloseAllConnectionsAsync().ConfigureAwait(false);
+                await _clientSessionsManager.CloseAllConnections().ConfigureAwait(false);
 
                 foreach (var adapter in _adapters)
                 {

Source/MQTTnet/Server/Options/MqttServerOptionsBuilder.cs

@@ -131,6 +131,18 @@ namespace MQTTnet.Server
             return this;
         }
 
+        /// <summary>
+        ///     Usually the MQTT packets can be send partially to improve memory allocations.
+        ///     This is done by using multiple TCP packets or WebSocket frames etc.
+        ///     Unfortunately not all clients do support this and will close the connection when receiving partial packets.
+        /// </summary>
+        public MqttServerOptionsBuilder WithoutPacketFragmentation()
+        {
+            _options.DefaultEndpointOptions.AllowPacketFragmentation = false;
+            _options.TlsEndpointOptions.AllowPacketFragmentation = false;
+            return this;
+        }
+
         public MqttServerOptionsBuilder WithPersistentSessions(bool value = true)
         {
             _options.EnablePersistentSessions = value;

Source/MQTTnet/Server/Options/MqttServerTcpEndpointBaseOptions.cs

@@ -23,6 +23,14 @@ namespace MQTTnet.Server
         /// </summary>
         public bool? KeepAlive { get; set; }
 
+        /// <summary>
+        ///     Usually the MQTT packets can be send partially. This is done by using multiple TCP packets
+        ///     or WebSocket frames etc. Unfortunately not all clients do support this feature and
+        ///     will close the connection when receiving such packets. If such clients are connecting to this
+        ///     server the flag must be set to _false_.
+        /// </summary>
+        public bool AllowPacketFragmentation { get; set; } = true;
+
         /// <summary>
         ///     Gets or sets the TCP keep alive interval.
         ///     The value _null_ indicates that the OS and framework defaults should be used.

Source/MQTTnet/Server/Status/MqttSessionStatus.cs

@@ -21,6 +21,10 @@ namespace MQTTnet.Server
 
         public DateTime CreatedTimestamp => _session.CreatedTimestamp;
 
+        public DateTime? DisconnectedTimestamp => _session.DisconnectedTimestamp;
+
+        public uint ExpiryInterval => _session.ExpiryInterval;
+
         public string Id => _session.Id;
 
         public IDictionary Items => _session.Items;