Restore behavior of _Server_ and _Port_ in client options (#2009)

* Restore old server and port behavior

* Fix unit test

.editorconfig

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

.github/workflows/ReleaseNotes.md

@@ -1,5 +1 @@
-* [Client] Exposed the _EndPoint_ type to support other endpoint types (like Unix Domain Sockets) in client options (#1919).
-* [ManagedClient] Added support for intercepting (and cancelling) publish messages (#1915, thanks to @hannasm).
-* [Server] Added new events for delivered and dropped messages (#1866, thanks to @kallayj).
-* [Server] The server will no longer treat a client which is receiving a large payload as alive. The packet must be received completely within the keep alive boundaries (BREAKING CHANGE!, #1883).
-* [Server] Fixed "service not registered" exception in ASP.NET integration (#1889).
+* [Client] Restored _Server_ and _Port_ behavior of client options (#2005).

.github/workflows/ci.yml

@@ -3,7 +3,7 @@ name: CI
 on: [push, pull_request]
 
 env:
-  VERSION: "4.3.3.${{github.run_number}}"
+  VERSION: "4.3.6.${{github.run_number}}"
 
 jobs:
   build:

MQTTnet.sln

@@ -7,9 +7,9 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet", "Source\MQTTnet\M
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{B3F60ECB-45BA-4C66-8903-8BB89CA67998}"
 	ProjectSection(SolutionItems) = preProject
+		CODE-OF-CONDUCT.md = CODE-OF-CONDUCT.md
 		LICENSE = LICENSE
 		README.md = README.md
-		CODE-OF-CONDUCT.md = CODE-OF-CONDUCT.md
 	EndProjectSection
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.AspNetCore", "Source\MQTTnet.AspnetCore\MQTTnet.AspNetCore.csproj", "{F10C4060-F7EE-4A83-919F-FF723E72F94A}"
@@ -20,17 +20,19 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Extensions.ManagedC
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Extensions.WebSocket4Net", "Source\MQTTnet.Extensions.WebSocket4Net\MQTTnet.Extensions.WebSocket4Net.csproj", "{2BD01D53-4CA5-4142-BE8D-313876395E3E}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MQTTnet.Samples", "Samples\MQTTnet.Samples.csproj", "{71CF35F5-3327-4A91-AAF4-5340F6701771}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Samples", "Samples\MQTTnet.Samples.csproj", "{71CF35F5-3327-4A91-AAF4-5340F6701771}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MQTTnet.Tests", "Source\MQTTnet.Tests\MQTTnet.Tests.csproj", "{B270F32A-9F3E-42EE-A989-813E35E29ADB}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Tests", "Source\MQTTnet.Tests\MQTTnet.Tests.csproj", "{B270F32A-9F3E-42EE-A989-813E35E29ADB}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MQTTnet.AspNetCore.Tests", "Source\MQTTnet.AspNetCore.Tests\MQTTnet.AspNetCore.Tests.csproj", "{A238BBBF-C75F-482D-9CC3-BB34ABA9B675}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.AspNetCore.Tests", "Source\MQTTnet.AspNetCore.Tests\MQTTnet.AspNetCore.Tests.csproj", "{A238BBBF-C75F-482D-9CC3-BB34ABA9B675}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MQTTnet.Benchmarks", "Source\MQTTnet.Benchmarks\MQTTnet.Benchmarks.csproj", "{2F516E76-AAC4-4219-B7D1-34CDD3CFF381}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Benchmarks", "Source\MQTTnet.Benchmarks\MQTTnet.Benchmarks.csproj", "{2F516E76-AAC4-4219-B7D1-34CDD3CFF381}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MQTTnet.TestApp", "Source\MQTTnet.TestApp\MQTTnet.TestApp.csproj", "{175D5340-CC5B-4542-939D-4E7D15A0BC8D}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.TestApp", "Source\MQTTnet.TestApp\MQTTnet.TestApp.csproj", "{175D5340-CC5B-4542-939D-4E7D15A0BC8D}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MQTTnet.AspTestApp", "Source\MQTTnet.AspTestApp\MQTTnet.AspTestApp.csproj", "{72867E4C-4E15-4E8E-8FAB-AE9253286BBC}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.AspTestApp", "Source\MQTTnet.AspTestApp\MQTTnet.AspTestApp.csproj", "{72867E4C-4E15-4E8E-8FAB-AE9253286BBC}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Extensions.TopicTemplate", "Source\MQTTnet.Extensions.TopicTemplate\MQTTnet.Extensions.TopicTemplate.csproj", "{374D5861-F7A6-42A2-8CBE-040846000EF9}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -82,12 +84,14 @@ Global
 		{72867E4C-4E15-4E8E-8FAB-AE9253286BBC}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{72867E4C-4E15-4E8E-8FAB-AE9253286BBC}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{72867E4C-4E15-4E8E-8FAB-AE9253286BBC}.Release|Any CPU.Build.0 = Release|Any CPU
+		{374D5861-F7A6-42A2-8CBE-040846000EF9}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{374D5861-F7A6-42A2-8CBE-040846000EF9}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{374D5861-F7A6-42A2-8CBE-040846000EF9}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{374D5861-F7A6-42A2-8CBE-040846000EF9}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection
-	GlobalSection(NestedProjects) = preSolution
-	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {07536672-5CBC-4BE3-ACE0-708A431A7894}
 	EndGlobalSection

Samples/ManagedClient/Managed_Client_Subscribe_Samples.cs

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

Source/MQTTnet.AspTestApp/MQTTnet.AspTestApp.csproj

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

Source/MQTTnet.AspnetCore/MQTTnet.AspNetCore.csproj

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

Source/MQTTnet.AspnetCore/ServiceCollectionExtensions.cs

@@ -40,13 +40,10 @@ namespace MQTTnet.AspNetCore
                 throw new ArgumentNullException(nameof(services));
             }
 
-            if (configure == null)
-            {
-                throw new ArgumentNullException(nameof(configure));
-            }
-
             var serverOptionsBuilder = new MqttServerOptionsBuilder();
-            configure.Invoke(serverOptionsBuilder);
+
+            configure?.Invoke(serverOptionsBuilder);
+
             var options = serverOptionsBuilder.Build();
 
             return AddHostedMqttServer(services, options);

Source/MQTTnet.Extensions.ManagedClient/IManagedMqttClient.cs

@@ -25,6 +25,8 @@ namespace MQTTnet.Extensions.ManagedClient
         
         event Func<ManagedProcessFailedEventArgs, Task> SynchronizingSubscriptionsFailedAsync;
         
+        event Func<SubscriptionsChangedEventArgs, Task> SubscriptionsChangedAsync;
+        
         IMqttClient InternalClient { get; }
         
         bool IsConnected { get; }

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClient.cs

@@ -19,16 +19,17 @@ namespace MQTTnet.Extensions.ManagedClient
 {
     public sealed class ManagedMqttClient : Disposable, IManagedMqttClient
     {
+        readonly MqttNetSourceLogger _logger;
+
         readonly AsyncEvent<InterceptingPublishMessageEventArgs> _interceptingPublishMessageEvent = new AsyncEvent<InterceptingPublishMessageEventArgs>();
         readonly AsyncEvent<ApplicationMessageProcessedEventArgs> _applicationMessageProcessedEvent = new AsyncEvent<ApplicationMessageProcessedEventArgs>();
         readonly AsyncEvent<ApplicationMessageSkippedEventArgs> _applicationMessageSkippedEvent = new AsyncEvent<ApplicationMessageSkippedEventArgs>();
         readonly AsyncEvent<ConnectingFailedEventArgs> _connectingFailedEvent = new AsyncEvent<ConnectingFailedEventArgs>();
         readonly AsyncEvent<EventArgs> _connectionStateChangedEvent = new AsyncEvent<EventArgs>();
         readonly AsyncEvent<ManagedProcessFailedEventArgs> _synchronizingSubscriptionsFailedEvent = new AsyncEvent<ManagedProcessFailedEventArgs>();
-        
-        readonly MqttNetSourceLogger _logger;
-        readonly BlockingQueue<ManagedMqttApplicationMessage> _messageQueue = new BlockingQueue<ManagedMqttApplicationMessage>();
+        readonly AsyncEvent<SubscriptionsChangedEventArgs> _subscriptionsChangedEvent = new AsyncEvent<SubscriptionsChangedEventArgs>();
 
+        readonly BlockingQueue<ManagedMqttApplicationMessage> _messageQueue = new BlockingQueue<ManagedMqttApplicationMessage>();
         readonly AsyncLock _messageQueueLock = new AsyncLock();
 
         /// <summary>
@@ -82,21 +83,19 @@ namespace MQTTnet.Extensions.ManagedClient
             add => _applicationMessageSkippedEvent.AddHandler(value);
             remove => _applicationMessageSkippedEvent.RemoveHandler(value);
         }
-        
+
         public event Func<ApplicationMessageProcessedEventArgs, Task> ApplicationMessageProcessedAsync
         {
             add => _applicationMessageProcessedEvent.AddHandler(value);
             remove => _applicationMessageProcessedEvent.RemoveHandler(value);
         }
 
-
         public event Func<InterceptingPublishMessageEventArgs, Task> InterceptPublishMessageAsync
         {
             add => _interceptingPublishMessageEvent.AddHandler(value);
             remove => _interceptingPublishMessageEvent.RemoveHandler(value);
         }
 
-
         public event Func<MqttApplicationMessageReceivedEventArgs, Task> ApplicationMessageReceivedAsync
         {
             add => InternalClient.ApplicationMessageReceivedAsync += value;
@@ -133,6 +132,12 @@ namespace MQTTnet.Extensions.ManagedClient
             remove => _synchronizingSubscriptionsFailedEvent.RemoveHandler(value);
         }
 
+        public event Func<SubscriptionsChangedEventArgs, Task> SubscriptionsChangedAsync
+        {
+            add => _subscriptionsChangedEvent.AddHandler(value);
+            remove => _subscriptionsChangedEvent.RemoveHandler(value);
+        }
+
         public IMqttClient InternalClient { get; }
 
         public bool IsConnected => InternalClient.IsConnected;
@@ -142,7 +147,7 @@ namespace MQTTnet.Extensions.ManagedClient
         public ManagedMqttClientOptions Options { get; private set; }
 
         public int PendingApplicationMessagesCount => _messageQueue.Count;
-        
+
         public async Task EnqueueAsync(MqttApplicationMessage applicationMessage)
         {
             ThrowIfDisposed();
@@ -270,7 +275,7 @@ namespace MQTTnet.Extensions.ManagedClient
             ThrowIfDisposed();
 
             _isCleanDisconnect = cleanDisconnect;
-            
+
             StopPublishing();
             StopMaintainingConnection();
 
@@ -362,6 +367,13 @@ namespace MQTTnet.Extensions.ManagedClient
             return remainingTime < TimeSpan.Zero ? TimeSpan.Zero : remainingTime;
         }
 
+        CancellationTokenSource NewTimeoutToken(CancellationToken linkedToken)
+        {
+            var newTimeoutToken = CancellationTokenSource.CreateLinkedTokenSource(linkedToken);
+            newTimeoutToken.CancelAfter(Options.ClientOptions.Timeout);
+            return newTimeoutToken;
+        }
+
         async Task HandleSubscriptionExceptionAsync(Exception exception, List<MqttTopicFilter> addedSubscriptions, List<string> removedSubscriptions)
         {
             _logger.Warning(exception, "Synchronizing subscriptions failed.");
@@ -372,6 +384,14 @@ namespace MQTTnet.Extensions.ManagedClient
             }
         }
 
+        async Task HandleSubscriptionsResultAsync(SendSubscribeUnsubscribeResult subscribeUnsubscribeResult)
+        {
+            if (_subscriptionsChangedEvent.HasHandlers)
+            {
+                await _subscriptionsChangedEvent.InvokeAsync(new SubscriptionsChangedEventArgs(subscribeUnsubscribeResult.SubscribeResults, subscribeUnsubscribeResult.UnsubscribeResults)).ConfigureAwait(false);
+            }
+        }
+
         async Task MaintainConnectionAsync(CancellationToken cancellationToken)
         {
             try
@@ -396,7 +416,7 @@ namespace MQTTnet.Extensions.ManagedClient
                     {
                         if (_isCleanDisconnect)
                         {
-                            using (var disconnectTimeout = new CancellationTokenSource(Options.ClientOptions.Timeout))
+                            using (var disconnectTimeout = NewTimeoutToken(CancellationToken.None))
                             {
                                 await InternalClient.DisconnectAsync(new MqttClientDisconnectOptions(), disconnectTimeout.Token).ConfigureAwait(false);
                             }
@@ -446,7 +466,7 @@ namespace MQTTnet.Extensions.ManagedClient
 
                     cancellationToken.ThrowIfCancellationRequested();
 
-                    await TryPublishQueuedMessageAsync(message).ConfigureAwait(false);
+                    await TryPublishQueuedMessageAsync(message, cancellationToken).ConfigureAwait(false);
                 }
             }
             catch (OperationCanceledException)
@@ -462,7 +482,7 @@ namespace MQTTnet.Extensions.ManagedClient
             }
         }
 
-        async Task PublishReconnectSubscriptionsAsync()
+        async Task PublishReconnectSubscriptionsAsync(CancellationToken cancellationToken)
         {
             _logger.Info("Publishing subscriptions at reconnect");
 
@@ -473,6 +493,7 @@ namespace MQTTnet.Extensions.ManagedClient
                 if (_reconnectSubscriptions.Any())
                 {
                     topicFilters = new List<MqttTopicFilter>();
+                    SendSubscribeUnsubscribeResult subscribeUnsubscribeResult;
 
                     foreach (var sub in _reconnectSubscriptions)
                     {
@@ -480,12 +501,14 @@ namespace MQTTnet.Extensions.ManagedClient
 
                         if (topicFilters.Count == Options.MaxTopicFiltersInSubscribeUnsubscribePackets)
                         {
-                            await SendSubscribeUnsubscribe(topicFilters, null).ConfigureAwait(false);
+                            subscribeUnsubscribeResult = await SendSubscribeUnsubscribe(topicFilters, null, cancellationToken).ConfigureAwait(false);
                             topicFilters.Clear();
+                            await HandleSubscriptionsResultAsync(subscribeUnsubscribeResult).ConfigureAwait(false);
                         }
                     }
 
-                    await SendSubscribeUnsubscribe(topicFilters, null).ConfigureAwait(false);
+                    subscribeUnsubscribeResult = await SendSubscribeUnsubscribe(topicFilters, null, cancellationToken).ConfigureAwait(false);
+                    await HandleSubscriptionsResultAsync(subscribeUnsubscribeResult).ConfigureAwait(false);
                 }
             }
             catch (Exception exception)
@@ -501,6 +524,7 @@ namespace MQTTnet.Extensions.ManagedClient
             while (await _subscriptionsQueuedSignal.WaitAsync(GetRemainingTime(endTime), cancellationToken).ConfigureAwait(false))
             {
                 List<MqttTopicFilter> subscriptions;
+                SendSubscribeUnsubscribeResult subscribeUnsubscribeResult;
                 HashSet<string> unsubscriptions;
 
                 lock (_subscriptions)
@@ -536,12 +560,14 @@ namespace MQTTnet.Extensions.ManagedClient
 
                     if (addedTopicFilters.Count == Options.MaxTopicFiltersInSubscribeUnsubscribePackets)
                     {
-                        await SendSubscribeUnsubscribe(addedTopicFilters, null).ConfigureAwait(false);
+                        subscribeUnsubscribeResult = await SendSubscribeUnsubscribe(addedTopicFilters, null, cancellationToken).ConfigureAwait(false);
                         addedTopicFilters.Clear();
+                        await HandleSubscriptionsResultAsync(subscribeUnsubscribeResult).ConfigureAwait(false);
                     }
                 }
 
-                await SendSubscribeUnsubscribe(addedTopicFilters, null).ConfigureAwait(false);
+                subscribeUnsubscribeResult = await SendSubscribeUnsubscribe(addedTopicFilters, null, cancellationToken).ConfigureAwait(false);
+                await HandleSubscriptionsResultAsync(subscribeUnsubscribeResult).ConfigureAwait(false);
 
                 var removedTopicFilters = new List<string>();
                 foreach (var unSub in unsubscriptions)
@@ -550,12 +576,14 @@ namespace MQTTnet.Extensions.ManagedClient
 
                     if (removedTopicFilters.Count == Options.MaxTopicFiltersInSubscribeUnsubscribePackets)
                     {
-                        await SendSubscribeUnsubscribe(null, removedTopicFilters).ConfigureAwait(false);
+                        subscribeUnsubscribeResult = await SendSubscribeUnsubscribe(null, removedTopicFilters, cancellationToken).ConfigureAwait(false);
                         removedTopicFilters.Clear();
+                        await HandleSubscriptionsResultAsync(subscribeUnsubscribeResult).ConfigureAwait(false);
                     }
                 }
 
-                await SendSubscribeUnsubscribe(null, removedTopicFilters).ConfigureAwait(false);
+                subscribeUnsubscribeResult = await SendSubscribeUnsubscribe(null, removedTopicFilters, cancellationToken).ConfigureAwait(false);
+                await HandleSubscriptionsResultAsync(subscribeUnsubscribeResult).ConfigureAwait(false);
             }
         }
 
@@ -569,7 +597,7 @@ namespace MQTTnet.Extensions.ManagedClient
             MqttClientConnectResult connectResult = null;
             try
             {
-                using (var connectTimeout = new CancellationTokenSource(Options.ClientOptions.Timeout))
+                using (var connectTimeout = NewTimeoutToken(cancellationToken))
                 {
                     connectResult = await InternalClient.ConnectAsync(Options.ClientOptions, connectTimeout.Token).ConfigureAwait(false);
                 }
@@ -588,8 +616,10 @@ namespace MQTTnet.Extensions.ManagedClient
             }
         }
 
-        async Task SendSubscribeUnsubscribe(List<MqttTopicFilter> addedSubscriptions, List<string> removedSubscriptions)
+        async Task<SendSubscribeUnsubscribeResult> SendSubscribeUnsubscribe(List<MqttTopicFilter> addedSubscriptions, List<string> removedSubscriptions, CancellationToken cancellationToken)
         {
+            var subscribeResults = new List<MqttClientSubscribeResult>();
+            var unsubscribeResults = new List<MqttClientUnsubscribeResult>();
             try
             {
                 if (removedSubscriptions != null && removedSubscriptions.Any())
@@ -601,7 +631,11 @@ namespace MQTTnet.Extensions.ManagedClient
                         unsubscribeOptionsBuilder.WithTopicFilter(removedSubscription);
                     }
 
-                    await InternalClient.UnsubscribeAsync(unsubscribeOptionsBuilder.Build()).ConfigureAwait(false);
+                    using (var unsubscribeTimeout = NewTimeoutToken(cancellationToken))
+                    {
+                        var unsubscribeResult = await InternalClient.UnsubscribeAsync(unsubscribeOptionsBuilder.Build(), unsubscribeTimeout.Token).ConfigureAwait(false);
+                        unsubscribeResults.Add(unsubscribeResult);
+                    }
 
                     //clear because these worked, maybe the subscribe below will fail, only report those
                     removedSubscriptions.Clear();
@@ -616,13 +650,19 @@ namespace MQTTnet.Extensions.ManagedClient
                         subscribeOptionsBuilder.WithTopicFilter(addedSubscription);
                     }
 
-                    await InternalClient.SubscribeAsync(subscribeOptionsBuilder.Build()).ConfigureAwait(false);
+                    using (var subscribeTimeout = NewTimeoutToken(cancellationToken))
+                    {
+                        var subscribeResult = await InternalClient.SubscribeAsync(subscribeOptionsBuilder.Build(), subscribeTimeout.Token).ConfigureAwait(false);
+                        subscribeResults.Add(subscribeResult);
+                    }
                 }
             }
             catch (Exception exception)
             {
                 await HandleSubscriptionExceptionAsync(exception, addedSubscriptions, removedSubscriptions).ConfigureAwait(false);
             }
+
+            return new SendSubscribeUnsubscribeResult(subscribeResults, unsubscribeResults);
         }
 
         void StartPublishing()
@@ -668,7 +708,7 @@ namespace MQTTnet.Extensions.ManagedClient
             {
                 var oldConnectionState = InternalClient.IsConnected;
                 var connectionState = await ReconnectIfRequiredAsync(cancellationToken).ConfigureAwait(false);
-                
+
                 if (connectionState == ReconnectionResult.NotConnected)
                 {
                     StopPublishing();
@@ -676,7 +716,7 @@ namespace MQTTnet.Extensions.ManagedClient
                 }
                 else if (connectionState == ReconnectionResult.Reconnected)
                 {
-                    await PublishReconnectSubscriptionsAsync().ConfigureAwait(false);
+                    await PublishReconnectSubscriptionsAsync(cancellationToken).ConfigureAwait(false);
                     StartPublishing();
                 }
                 else if (connectionState == ReconnectionResult.Recovered)
@@ -706,7 +746,7 @@ namespace MQTTnet.Extensions.ManagedClient
             }
         }
 
-        async Task TryPublishQueuedMessageAsync(ManagedMqttApplicationMessage message)
+        async Task TryPublishQueuedMessageAsync(ManagedMqttApplicationMessage message, CancellationToken cancellationToken)
         {
             Exception transmitException = null;
             bool acceptPublish = true;
@@ -721,7 +761,10 @@ namespace MQTTnet.Extensions.ManagedClient
 
                 if (acceptPublish)
                 {
-                    await InternalClient.PublishAsync(message.ApplicationMessage).ConfigureAwait(false);
+                    using (var publishTimeout = NewTimeoutToken(cancellationToken))
+                    {
+                        await InternalClient.PublishAsync(message.ApplicationMessage, publishTimeout.Token).ConfigureAwait(false);
+                    }
                 }
 
                 using (await _messageQueueLock.EnterAsync().ConfigureAwait(false)) //lock to avoid conflict with this.PublishAsync

Source/MQTTnet.Extensions.ManagedClient/SendSubscribeUnsubscribeResult.cs

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

Source/MQTTnet.Extensions.ManagedClient/SubscriptionsChangedEventArgs.cs

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

Source/MQTTnet.Extensions.Rpc/IMqttRpcClient.cs

@@ -1,3 +1,7 @@
+// 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;

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

@@ -0,0 +1,69 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0;net7.0</TargetFrameworks>
+        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461;net48</TargetFrameworks>
+        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' AND '$(MSBuildRuntimeType)' != 'Core' ">$(TargetFrameworks);uap10.0</TargetFrameworks>
+        
+        <AssemblyName>MQTTnet.Extensions.TopicTemplate</AssemblyName>
+        <RootNamespace>MQTTnet.Extensions.TopicTemplate</RootNamespace>
+        <GeneratePackageOnBuild>True</GeneratePackageOnBuild>
+        <Company>The contributors of MQTTnet</Company>
+        <Product>MQTTnet</Product>
+        <Description>
+           This is an extension library which provides mqtt topic templating logic to support dispatch,
+           routing and similar functionality based on the well known moustache syntax, aka
+           AsyncAPI dynamic channel address.
+        </Description>
+        <Authors>The contributors of MQTTnet</Authors>
+        <PackageId>MQTTnet.Extensions.TopicTemplate</PackageId>
+        <SignAssembly>false</SignAssembly>
+        <DelaySign>false</DelaySign>
+        <PublishRepositoryUrl>true</PublishRepositoryUrl>
+        <IncludeSymbols>true</IncludeSymbols>
+        <SymbolPackageFormat>snupkg</SymbolPackageFormat>
+        <Copyright>Copyright (c) .NET Foundation and Contributors</Copyright>
+        <PackageProjectUrl>https://github.com/dotnet/MQTTnet</PackageProjectUrl>
+        <RepositoryUrl>https://github.com/dotnet/MQTTnet.git</RepositoryUrl>
+        <RepositoryType>git</RepositoryType>
+        <PackageTags>MQTT Message Queue Telemetry MQTTClient Messaging Routing AsyncAPI Template</PackageTags>
+        <NeutralLanguage>en-US</NeutralLanguage>
+        <PackageIcon>nuget.png</PackageIcon>
+        <EmbedUntrackedSources>true</EmbedUntrackedSources>
+        <ContinuousIntegrationBuild>true</ContinuousIntegrationBuild>
+        <PackageLicenseExpression>MIT</PackageLicenseExpression>
+        <PackageReleaseNotes>For release notes please go to MQTTnet release notes (https://www.nuget.org/packages/MQTTnet/).</PackageReleaseNotes>
+        <GenerateDocumentationFile>true</GenerateDocumentationFile>
+        <NoWarn>1591;NETSDK1138</NoWarn>
+    </PropertyGroup>
+
+    <PropertyGroup Condition="'$(TargetFramework)' == 'uap10.0'">
+        <CopyLocalLockFileAssemblies>false</CopyLocalLockFileAssemblies>
+        <NugetTargetMoniker>UAP,Version=v10.0</NugetTargetMoniker>
+        <TargetPlatformIdentifier>UAP</TargetPlatformIdentifier>
+        <TargetPlatformVersion>10.0.18362.0</TargetPlatformVersion>
+        <TargetPlatformMinVersion>10.0.10240.0</TargetPlatformMinVersion>
+        <TargetFrameworkIdentifier>.NETCore</TargetFrameworkIdentifier>
+        <TargetFrameworkVersion>v5.0</TargetFrameworkVersion>
+        <DefineConstants>$(DefineConstants);WINDOWS_UWP</DefineConstants>
+        <DefaultLanguage>en</DefaultLanguage>
+        <LanguageTargets>$(MSBuildExtensionsPath)\Microsoft\WindowsXaml\v$(VisualStudioVersion)\Microsoft.Windows.UI.Xaml.CSharp.targets</LanguageTargets>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <None Include="..\..\Images\nuget.png">
+            <Pack>True</Pack>
+            <PackagePath>\</PackagePath>
+        </None>
+    </ItemGroup>
+    
+    <ItemGroup>
+        <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All" />
+        <PackageReference Include="System.ValueTuple" Version="4.5.0" />
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\MQTTnet\MQTTnet.csproj" />
+    </ItemGroup>
+
+</Project>

Source/MQTTnet.Extensions.TopicTemplate/MqttTopicTemplate.cs

@@ -0,0 +1,345 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text.RegularExpressions;
+using System.Threading;
+using MQTTnet.Protocol;
+
+namespace MQTTnet.Extensions.TopicTemplate
+{
+    /// <summary>
+    ///     A topic template is an MQTT topic filter string that may contain
+    ///     segments in curly braces called parameters. This well-known
+    ///     'moustache' syntax also matches AsyncAPI Channel Address Expressions.
+    ///     The topic template is designed to support dynamic subscription/publication,
+    ///     message-topic matching and routing. It is intended to be more convenient
+    ///     than String.Format() for aforementioned purposes.
+    /// </summary>
+    /// <example>
+    ///     topic/subtopic/{parameter}/{otherParameter}
+    /// </example>
+    public sealed class MqttTopicTemplate : IEquatable<MqttTopicTemplate>
+    {
+        static readonly Regex MoustacheRegex = new Regex("{([^/]+?)}", RegexOptions.Compiled);
+        
+        readonly string[] _parameterSegments;
+        
+        string _topicFilter;
+        
+        /// <summary>
+        ///     Create a topic template from an mqtt topic filter with moustache placeholders.
+        /// </summary>
+        /// <param
+        ///     name="topicTemplate">
+        /// </param>
+        /// <exception
+        ///     cref="ArgumentNullException">
+        /// </exception>
+        public MqttTopicTemplate(string topicTemplate)
+        {
+            if (topicTemplate == null)
+            {
+                throw new ArgumentNullException(nameof(topicTemplate));
+            }
+            
+            MqttTopicValidator.ThrowIfInvalidSubscribe(topicTemplate);
+            
+            Template = topicTemplate;
+            _parameterSegments = topicTemplate.Split(MqttTopicFilterComparer.LevelSeparator)
+                .Select(segment => MoustacheRegex.Match(segment).Groups[1].Value)
+                .Select(s => s.Length > 0 ? s : null)
+                .ToArray();
+        }
+        
+        /// <summary>
+        ///     Yield the template parameter names.
+        /// </summary>
+        public IEnumerable<string> Parameters => _parameterSegments.Where(s => s != null);
+        
+        /// <summary>
+        ///     The topic template string representation, e.g. A/B/{foo}/D.
+        /// </summary>
+        public string Template { get; }
+        
+        /// <summary>
+        ///     The topic template as an MQTT topic filter (+ substituted for all parameters). If the template
+        ///     ends with a multi-level wildcard (hash), this will be reflected here.
+        /// </summary>
+        public string TopicFilter
+        {
+            get
+            {
+                LazyInitializer.EnsureInitialized(ref _topicFilter, () => MoustacheRegex.Replace(Template, MqttTopicFilterComparer.SingleLevelWildcard.ToString()));
+                return _topicFilter;
+            }
+        }
+        
+        /// <summary>
+        ///     Return the topic filter of this template, ending with a multi-level wildcard (hash).
+        /// </summary>
+        public string TopicTreeRootFilter
+        {
+            get
+            {
+                var filter = TopicFilter;
+                // append slash if neccessary
+                if (filter.Length > 0 && !filter.EndsWith(MqttTopicFilterComparer.LevelSeparator.ToString()) &&
+                    !filter.EndsWith(MqttTopicFilterComparer.MultiLevelWildcard.ToString()))
+                {
+                    filter += MqttTopicFilterComparer.LevelSeparator;
+                }
+                
+                // append hash if neccessary
+                if (!filter.EndsWith(MqttTopicFilterComparer.MultiLevelWildcard.ToString()))
+                {
+                    filter += MqttTopicFilterComparer.MultiLevelWildcard;
+                }
+                
+                return filter;
+            }
+        }
+        
+        public bool Equals(MqttTopicTemplate other)
+        {
+            return other != null && Template == other.Template;
+        }
+        
+        public override bool Equals(object obj)
+        {
+            if (ReferenceEquals(null, obj))
+            {
+                return false;
+            }
+            
+            if (ReferenceEquals(this, obj))
+            {
+                return true;
+            }
+            
+            if (obj.GetType() != GetType())
+            {
+                return false;
+            }
+            
+            return Equals((MqttTopicTemplate)obj);
+        }
+        
+        /// <summary>
+        ///     Determine the shortest common prefix of the given templates. Partial segments
+        ///     are not returned.
+        /// </summary>
+        /// <param
+        ///     name="templates">
+        ///     topic templates
+        /// </param>
+        /// <returns></returns>
+        public static MqttTopicTemplate FindCanonicalPrefix(IEnumerable<MqttTopicTemplate> templates)
+        {
+            string root = null;
+            
+            string CommonPrefix(string a, string b)
+            {
+                var maxIndex = Math.Min(a.Length, b.Length) - 1;
+                for (var i = 0; i <= maxIndex; i++)
+                {
+                    if (a[i] != b[i])
+                    {
+                        return a.Substring(0, i);
+                    }
+                }
+                
+                return a.Substring(0, maxIndex+1);
+            }
+            
+            foreach (string topic in from template in templates select template.Template)
+            {
+                root = root == null ? topic : CommonPrefix(root, topic);
+            }
+            
+            if (string.IsNullOrEmpty(root))
+                return new MqttTopicTemplate(MqttTopicFilterComparer.MultiLevelWildcard.ToString());
+            
+            if (root.Contains(MqttTopicFilterComparer.LevelSeparator) &&
+                !root.EndsWith(MqttTopicFilterComparer.LevelSeparator.ToString()) &&
+                !root.EndsWith("}"))
+            {
+                root = root.Substring(0, root.LastIndexOf(MqttTopicFilterComparer.LevelSeparator)+1);
+            }
+            
+            if (root.EndsWith(MqttTopicFilterComparer.LevelSeparator.ToString()))
+                root += MqttTopicFilterComparer.SingleLevelWildcard;
+
+            return new MqttTopicTemplate(root);
+        }
+        
+        public override int GetHashCode()
+        {
+            return Template.GetHashCode();
+        }
+        
+        /// <summary>
+        ///     Test if this topic template matches a given topic.
+        /// </summary>
+        /// <param
+        ///     name="topic">
+        ///     a fully specified topic
+        /// </param>
+        /// <param
+        ///     name="subtree">
+        ///     true to match including the subtree (multi-level wildcard)
+        /// </param>
+        /// <returns>true iff the topic matches the template's filter</returns>
+        /// <exception
+        ///     cref="InvalidOperationException">
+        /// </exception>
+        /// <exception
+        ///     cref="ArgumentException">
+        ///     if the topic is invalid
+        /// </exception>
+        public bool MatchesTopic(string topic, bool subtree = false)
+        {
+            var comparison = MqttTopicFilterComparer.Compare(topic, subtree ? TopicTreeRootFilter : TopicFilter);
+            if (comparison == MqttTopicFilterCompareResult.FilterInvalid)
+            {
+                throw new InvalidOperationException("Invalid filter");
+            }
+            
+            if (comparison == MqttTopicFilterCompareResult.TopicInvalid)
+            {
+                throw new ArgumentException("Invalid topic", nameof(topic));
+            }
+            
+            return comparison == MqttTopicFilterCompareResult.IsMatch;
+        }
+        
+        /// <summary>
+        ///     Extract the parameter values from a topic corresponding to the template
+        ///     parameters. The topic has to match this template.
+        /// </summary>
+        /// <param
+        ///     name="topic">
+        ///     the topic
+        /// </param>
+        /// <returns>an enumeration of (parameter, index, value)</returns>
+        public IEnumerable<(string parameter, int index, string value)> ParseParameterValues(string topic)
+        {
+            if (!MatchesTopic(topic))
+            {
+                throw new ArgumentException("the topic has to match this template", nameof(topic));
+            }
+            
+            return parseParameterValuesInternal(topic);
+        }
+        
+        /// <summary>
+        ///     Extract the parameter values from the message topic corresponding to the template
+        ///     parameters. The message topic has to match this topic template.
+        /// </summary>
+        /// <param
+        ///     name="message">
+        ///     the message
+        /// </param>
+        /// <returns>an enumeration of (parameter, index, value)</returns>
+        public IEnumerable<(string parameter, int index, string value)> ParseParameterValues(MqttApplicationMessage message)
+        {
+            return ParseParameterValues(message.Topic);
+        }
+        
+        /// <summary>
+        ///     Try to set a parameter to a given value. If the parameter is not present,
+        ///     this is returned. The value must not contain slashes.
+        /// </summary>
+        /// <param
+        ///     name="parameter">
+        ///     a template parameter
+        /// </param>
+        /// <param
+        ///     name="value">
+        ///     a string
+        /// </param>
+        /// <returns></returns>
+        public MqttTopicTemplate TrySetParameter(string parameter, string value)
+        {
+            if (parameter != null && _parameterSegments.Contains(parameter))
+            {
+                return WithParameter(parameter, value);
+            }
+            
+            return this;
+        }
+        
+        /// <summary>
+        ///     Replace the given parameter with a single-level wildcard (plus sign).
+        /// </summary>
+        /// <param
+        ///     name="parameter">
+        ///     parameter name
+        /// </param>
+        /// <returns>the topic template (without the parameter)</returns>
+        public MqttTopicTemplate WithoutParameter(string parameter)
+        {
+            return WithParameter(parameter, MqttTopicFilterComparer.SingleLevelWildcard.ToString());
+        }
+        
+        /// <summary>
+        ///     Substitute a parameter with a given value, thus removing the parameter. If the parameter is not present,
+        ///     the method trows. The value must not contain slashes.
+        /// </summary>
+        /// <param
+        ///     name="parameter">
+        ///     a template parameter
+        /// </param>
+        /// <param
+        ///     name="value">
+        ///     a string
+        /// </param>
+        /// <exception
+        ///     cref="ArgumentException">
+        ///     when the parameter is not present
+        /// </exception>
+        /// <returns>the topic template (without the parameter)</returns>
+        public MqttTopicTemplate WithParameter(string parameter, string value)
+        {
+            if (value == null || string.IsNullOrEmpty(parameter) || !_parameterSegments.Contains(parameter) || value.Contains(MqttTopicFilterComparer.LevelSeparator) ||
+                value.Contains(MqttTopicFilterComparer.MultiLevelWildcard))
+            {
+                throw new ArgumentException("parameter must exist and value must not contain slashes.");
+            }
+            
+            var moustache = "{" + parameter + "}";
+            return new MqttTopicTemplate(Template.Replace(moustache, value));
+        }
+        
+        /// <summary>
+        ///     Reuse parameters as they are extracted using another topic template on this template
+        ///     when the parameter name matches. Useful
+        ///     for compatibility routing.
+        /// </summary>
+        /// <param
+        ///     name="parameters">
+        /// </param>
+        /// <returns></returns>
+        public MqttTopicTemplate WithParameterValuesFrom(IEnumerable<(string parameter, int index, string value)> parameters)
+        {
+            return parameters.Aggregate(this, (t, p) => t.TrySetParameter(p.parameter, p.value));
+        }
+        
+        IEnumerable<(string parameter, int index, string value)> parseParameterValuesInternal(string topic)
+        {
+            // because we have a match, we know the segment array is at least the template's length
+            var segments = topic.Split(MqttTopicFilterComparer.LevelSeparator);
+            for (var i = 0; i < _parameterSegments.Length; i++)
+            {
+                var name = _parameterSegments[i];
+                if (name != null)
+                {
+                    yield return (name, i, segments[i]);
+                }
+            }
+        }
+    }
+}

Source/MQTTnet.Extensions.TopicTemplate/TopicTemplateExtensions.cs

@@ -0,0 +1,147 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Linq;
+using MQTTnet.Protocol;
+
+namespace MQTTnet.Extensions.TopicTemplate
+{
+    public static class TopicTemplateExtensions
+    {
+        /// <summary>
+        ///     Modify this message builder to respond to a given message. The
+        ///     message's response topic and correlation data are included
+        ///     in the message builder.
+        /// </summary>
+        /// <param
+        ///     name="builder">
+        ///     a message builder
+        /// </param>
+        /// <param
+        ///     name="message">
+        ///     a message with a response topic
+        /// </param>
+        /// <returns>a message builder</returns>
+        /// <see
+        ///     cref="BuildResponse" />
+        public static MqttApplicationMessageBuilder AsResponseTo(this MqttApplicationMessageBuilder builder, MqttApplicationMessage message)
+        {
+            if (!string.IsNullOrEmpty(message.ResponseTopic))
+            {
+                throw new ArgumentException("message does not have a response topic");
+            }
+
+            return builder.WithTopic(message.ResponseTopic).WithCorrelationData(message.CorrelationData);
+        }
+
+        /// <summary>
+        ///     Set the filter topic according to the template, with
+        ///     remaining template parameters substituted by single-level
+        ///     wildcard.
+        /// </summary>
+        /// <param
+        ///     name="topicTemplate">
+        ///     a topic template
+        /// </param>
+        /// <param
+        ///     name="subscribeTreeRoot">
+        ///     whether to subscribe to the whole topic tree
+        /// </param>
+        /// <returns>the modified topic filter</returns>
+        public static MqttTopicFilterBuilder BuildFilter(this MqttTopicTemplate topicTemplate, bool subscribeTreeRoot = false)
+        {
+            return new MqttTopicFilterBuilder().WithTopicTemplate(topicTemplate, subscribeTreeRoot);
+        }
+
+        /// <summary>
+        ///     Return a message builder to respond to this message. The
+        ///     message's response topic and correlation data are included
+        ///     in the response message builder.
+        /// </summary>
+        /// <param
+        ///     name="message">
+        ///     a message with a response topic
+        /// </param>
+        /// <returns>a message builder</returns>
+        /// <see
+        ///     cref="AsResponseTo" />
+        public static MqttApplicationMessageBuilder BuildResponse(this MqttApplicationMessage message)
+        {
+            return new MqttApplicationMessageBuilder().AsResponseTo(message);
+        }
+
+        /// <summary>
+        ///     Return whether the message matches the given topic template.
+        /// </summary>
+        /// <param
+        ///     name="message">
+        ///     a message
+        /// </param>
+        /// <param
+        ///     name="topicTemplate">
+        ///     a topic template
+        /// </param>
+        /// <param
+        ///     name="subtree">
+        ///     whether to include the topic subtree
+        /// </param>
+        /// <returns></returns>
+        public static bool MatchesTopicTemplate(this MqttApplicationMessage message, MqttTopicTemplate topicTemplate, bool subtree = false)
+        {
+            return topicTemplate.MatchesTopic(message.Topic, subtree);
+        }
+
+        /// <summary>
+        ///     Set the filter topic according to the template, with
+        ///     template parameters substituted by a single-level
+        ///     wildcard.
+        /// </summary>
+        /// <param
+        ///     name="builder">
+        ///     a filter builder
+        /// </param>
+        /// <param
+        ///     name="topicTemplate">
+        ///     a topic template
+        /// </param>
+        /// <param
+        ///     name="subscribeTreeRoot">
+        ///     whether to subscribe to the whole topic tree
+        /// </param>
+        /// <returns>the modified topic filter</returns>
+        public static MqttTopicFilterBuilder WithTopicTemplate(this MqttTopicFilterBuilder builder, MqttTopicTemplate topicTemplate, bool subscribeTreeRoot = false)
+        {
+            return builder.WithTopic(subscribeTreeRoot ? topicTemplate.TopicTreeRootFilter : topicTemplate.TopicFilter);
+        }
+
+        /// <summary>
+        ///     Set the publication topic according to the topic template. The template
+        ///     must not have remaining (unset) parameters or contain wildcards.
+        /// </summary>
+        /// <param
+        ///     name="builder">
+        ///     a message builder
+        /// </param>
+        /// <param
+        ///     name="topicTemplate">
+        ///     a parameterless topic template
+        /// </param>
+        /// <returns>the modified message builder</returns>
+        /// <exception
+        ///     cref="ArgumentException">
+        ///     if the topic template has parameters
+        /// </exception>
+        public static MqttApplicationMessageBuilder WithTopicTemplate(this MqttApplicationMessageBuilder builder, MqttTopicTemplate topicTemplate)
+        {
+            if (topicTemplate.Parameters.Any())
+            {
+                throw new ArgumentException("topic templates must be parameter-less when sending " + topicTemplate.Template);
+            }
+
+            MqttTopicValidator.ThrowIfInvalid(topicTemplate.Template);
+            return builder.WithTopic(topicTemplate.Template);
+        }
+    }
+}

Source/MQTTnet.Extensions.WebSocket4Net/WebSocket4NetMqttChannel.cs

@@ -76,7 +76,7 @@ namespace MQTTnet.Extensions.WebSocket4Net
             List<KeyValuePair<string, string>> customHeaders = null;
             if (_webSocketOptions.RequestHeaders != null)
             {
-                customHeaders = _webSocketOptions.RequestHeaders.Select(i => new KeyValuePair<string, string>(i.Key, i.Value)).ToList();
+                customHeaders = _webSocketOptions.RequestHeaders.ToList();
             }
 
             EndPoint proxy = null;

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

@@ -13,6 +13,7 @@ using MQTTnet.Diagnostics;
 using MQTTnet.Extensions.ManagedClient;
 using MQTTnet.Formatter;
 using MQTTnet.Internal;
+using MQTTnet.Packets;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
 using MQTTnet.Tests.Mockups;
@@ -574,16 +575,154 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
             }
         }
 
+        [TestMethod]
+        public async Task Subscribe_Does_Not_Hang_On_Server_Stop()
+        {
+            var timeout = TimeSpan.FromSeconds(2);
+            var testTimeout = TimeSpan.FromSeconds(timeout.TotalSeconds * 2);
+            const string topic = "test_topic_2";
+            using (var testEnvironment = CreateTestEnvironment())
+            using (var managedClient = await CreateManagedClientAsync(testEnvironment, timeout: timeout))
+            {
+                testEnvironment.IgnoreClientLogErrors = true;
+                bool reject = true;
+                var receivedOnServer = new SemaphoreSlim(0, 1);
+                var failedOnClient = new SemaphoreSlim(0, 1);
+                testEnvironment.Server.InterceptingInboundPacketAsync += e =>
+                {
+                    if (e.Packet is MqttSubscribePacket)
+                    {
+                        if (reject)
+                        {
+                            e.ProcessPacket = false;
+                        }
+                        receivedOnServer.Release();
+                    }
+
+                    return CompletedTask.Instance;
+                };
+                managedClient.SynchronizingSubscriptionsFailedAsync += e =>
+                {
+                    failedOnClient.Release();
+                    return CompletedTask.Instance;
+                };
+
+                await managedClient.SubscribeAsync(topic);
+                Assert.IsTrue(await receivedOnServer.WaitAsync(testTimeout));
+                Assert.IsTrue(await failedOnClient.WaitAsync(testTimeout));
+
+                reject = false;
+                await managedClient.SubscribeAsync(topic);
+                Assert.IsTrue(await receivedOnServer.WaitAsync(testTimeout));
+            }
+        }
+
+        [TestMethod]
+        public async Task Unsubscribe_Does_Not_Hang_On_Server_Stop()
+        {
+            var timeout = TimeSpan.FromSeconds(2);
+            var testTimeout = TimeSpan.FromSeconds(timeout.TotalSeconds * 2);
+            const string topic = "test_topic_2";
+            using (var testEnvironment = CreateTestEnvironment())
+            using (var managedClient = await CreateManagedClientAsync(testEnvironment, timeout: timeout))
+            {
+                testEnvironment.IgnoreClientLogErrors = true;
+                bool reject = true;
+                var receivedOnServer = new SemaphoreSlim(0, 1);
+                var failedOnClient = new SemaphoreSlim(0, 1);
+                testEnvironment.Server.InterceptingInboundPacketAsync += e =>
+                {
+                    if (e.Packet is MqttUnsubscribePacket)
+                    {
+                        if (reject)
+                        {
+                            e.ProcessPacket = false;
+                        }
+                        receivedOnServer.Release();
+                    }
+                    else if (e.Packet is MqttSubscribePacket)
+                    {
+                        receivedOnServer.Release();
+                    }
+
+                    return CompletedTask.Instance;
+                };
+                managedClient.SynchronizingSubscriptionsFailedAsync += e =>
+                {
+                    failedOnClient.Release();
+                    return CompletedTask.Instance;
+                };
+
+                await managedClient.SubscribeAsync(topic);
+                Assert.IsTrue(await receivedOnServer.WaitAsync(testTimeout));
+
+                await managedClient.UnsubscribeAsync(topic);
+                Assert.IsTrue(await receivedOnServer.WaitAsync(testTimeout));
+                Assert.IsTrue(await failedOnClient.WaitAsync(testTimeout));
+
+                reject = false;
+                await managedClient.UnsubscribeAsync(topic);
+                Assert.IsTrue(await receivedOnServer.WaitAsync(testTimeout));
+            }
+        }
+
+        [TestMethod]
+        public async Task Publish_Does_Not_Hang_On_Server_Error()
+        {
+            var timeout = TimeSpan.FromSeconds(2);
+            var testTimeout = TimeSpan.FromSeconds(timeout.TotalSeconds * 2);
+
+            const string topic = "test_topic_42";
+
+            using (var testEnvironment = CreateTestEnvironment())
+            using (var managedClient = await CreateManagedClientAsync(testEnvironment, timeout: timeout))
+            {
+                testEnvironment.IgnoreClientLogErrors = true;
+                bool reject = true;
+                var receivedOnServer = new TaskCompletionSource<object>();
+                managedClient.ApplicationMessageProcessedAsync += e => Task.FromResult(reject &= e.Exception is null);
+                testEnvironment.Server.InterceptingInboundPacketAsync += e =>
+                {
+                    if (e.Packet is MqttPublishPacket)
+                    {
+                        if (reject)
+                        {
+                            e.ProcessPacket = false;
+                        }
+                        else
+                        {
+                            receivedOnServer.TrySetResult(null);
+                        }
+                    }
+
+                    return CompletedTask.Instance;
+                };
+
+                await managedClient.EnqueueAsync(new MqttApplicationMessage { Topic = topic, PayloadSegment = new ArraySegment<byte>(new byte[] { 1 }), Retain = true, QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce });
+
+                var timeoutTask = Task.Delay(testTimeout);
+
+                var firstDone = await Task.WhenAny(receivedOnServer.Task, timeoutTask);
+                Assert.AreEqual(receivedOnServer.Task, firstDone, "Client is hung on publish!");
+            }
+        }
+
         async Task<MQTTnet.Extensions.ManagedClient.ManagedMqttClient> CreateManagedClientAsync(
             TestEnvironment testEnvironment,
             IMqttClient underlyingClient = null,
             TimeSpan? connectionCheckInterval = null,
-            string host = "localhost")
+            string host = "localhost",
+            TimeSpan? timeout = null)
         {
             await testEnvironment.StartServer();
 
             var clientOptions = new MqttClientOptionsBuilder().WithTcpServer(host, testEnvironment.ServerPort);
 
+            if (timeout != null)
+            {
+                clientOptions.WithTimeout(timeout.Value);
+            }
+
             var managedOptions = new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).Build();
 
             // Use a short connection check interval so that subscription operations are performed quickly

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

@@ -65,7 +65,7 @@ namespace MQTTnet.Tests.Clients.MqttClient
                         return CompletedTask.Instance;
                     };
 
-                    await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("1.2.3.4").Build());
+                    await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1").Build());
 
                     Assert.Fail("Must fail!");
                 }
@@ -175,7 +175,7 @@ namespace MQTTnet.Tests.Clients.MqttClient
                 testEnvironment.IgnoreClientLogErrors = true;
 
                 var client = testEnvironment.CreateClient();
-                var options = new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1").WithTimeout(TimeSpan.FromSeconds(2)).Build();
+                var options = new MqttClientOptionsBuilder().WithTcpServer("1.2.3.4").WithTimeout(TimeSpan.FromSeconds(2)).Build();
 
                 try
                 {
@@ -240,9 +240,9 @@ namespace MQTTnet.Tests.Clients.MqttClient
                     await mqttClient.SubscribeAsync("test", MqttQualityOfServiceLevel.AtLeastOnce);
                 }
             }
-            catch (MqttCommunicationException exception)
+            catch (MqttClientNotConnectedException exception)
             {
-                if (exception.Message == "The client is not connected.")
+                if (exception.Message == "The MQTT client is not connected.")
                 {
                     return;
                 }

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

@@ -6,6 +6,7 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using System.Net;
 using System.Net.Sockets;
 using System.Text;
 using System.Threading;
@@ -86,7 +87,7 @@ namespace MQTTnet.Tests.Clients.MqttClient
                 await client.ConnectAsync(clientOptions);
             }
         }
-        
+
         [TestMethod]
         [ExpectedException(typeof(InvalidOperationException))]
         public async Task Connect_Multiple_Times_Should_Fail()
@@ -748,8 +749,8 @@ namespace MQTTnet.Tests.Clients.MqttClient
                 {
                     if (e.ApplicationMessage.Topic == "request")
                     {
-                        // Use AtMostOnce here because with QoS 1 or even QoS 2 the process waits for 
-                        // the ACK etc. The problem is that the SpinUntil below only waits until the 
+                        // Use AtMostOnce here because with QoS 1 or even QoS 2 the process waits for
+                        // the ACK etc. The problem is that the SpinUntil below only waits until the
                         // flag is set. It does not wait until the client has sent the ACK
                         await client2.PublishStringAsync("reply");
                     }
@@ -925,5 +926,54 @@ namespace MQTTnet.Tests.Clients.MqttClient
                 Assert.IsFalse(disconnectedFired);
             }
         }
+
+        [TestMethod]
+        public void Backward_compatible_TCP_options()
+        {
+            var options = new MqttClientOptionsBuilder().WithTcpServer("host", 3).Build();
+
+            Assert.AreEqual("host", ((MqttClientTcpOptions)options.ChannelOptions).Server);
+            Assert.AreEqual(3, ((MqttClientTcpOptions)options.ChannelOptions).Port);
+
+            options = new MqttClientOptions
+            {
+                ChannelOptions = new MqttClientTcpOptions
+                {
+                    Server = "host",
+                    Port = 3
+                }
+            };
+
+            Assert.AreEqual("host:3", options.ChannelOptions.ToString());
+            Assert.AreEqual("host", ((MqttClientTcpOptions)options.ChannelOptions).Server);
+            Assert.AreEqual(3, ((MqttClientTcpOptions)options.ChannelOptions).Port);
+
+            options = new MqttClientOptionsBuilder().WithEndPoint(new DnsEndPoint("host", 3)).Build();
+            Assert.AreEqual("Unspecified/host:3", options.ChannelOptions.ToString());
+            Assert.AreEqual("host", ((MqttClientTcpOptions)options.ChannelOptions).Server);
+            Assert.AreEqual(3, ((MqttClientTcpOptions)options.ChannelOptions).Port);
+
+            options = new MqttClientOptionsBuilder().WithTcpServer("host").Build();
+
+            Assert.AreEqual("host", ((MqttClientTcpOptions)options.ChannelOptions).Server);
+            Assert.AreEqual(1883, ((MqttClientTcpOptions)options.ChannelOptions).Port);
+            Assert.AreEqual("Unspecified/host:1883", options.ChannelOptions.ToString());
+
+            options = new MqttClientOptionsBuilder().WithTlsOptions(o => o.UseTls()).WithTcpServer("host").Build();
+
+            Assert.AreEqual("host", ((MqttClientTcpOptions)options.ChannelOptions).Server);
+            Assert.AreEqual(8883, ((MqttClientTcpOptions)options.ChannelOptions).Port);
+
+            options = new MqttClientOptions
+            {
+                ChannelOptions = new MqttClientTcpOptions
+                {
+                    Server = "host"
+                }
+            };
+
+            Assert.AreEqual("host", ((MqttClientTcpOptions)options.ChannelOptions).Server);
+            Assert.AreEqual(null, ((MqttClientTcpOptions)options.ChannelOptions).Port);
+        }
     }
 }

Source/MQTTnet.Tests/Extensions/MqttTopicTemplate_Tests.cs

@@ -0,0 +1,213 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Linq;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Exceptions;
+using MQTTnet.Extensions.TopicTemplate;
+
+namespace MQTTnet.Tests.Extensions
+{
+    [TestClass]
+    public sealed class MqttTopicTemplate_Tests
+    {
+        [TestMethod]
+        public void BasicOps()
+        {
+            var template = new MqttTopicTemplate("A/B/{param}/D");
+            Assert.AreEqual("A/B/C/D", template.WithParameter("param", "C").Template);
+            Assert.AreEqual("A/B/+/D", template.WithoutParameter("param").Template);
+            Assert.AreEqual("A/B/+/D", template.TopicFilter);
+            Assert.AreEqual("A/B/+/D/#", template.TopicTreeRootFilter);
+
+            // corner cases
+            Assert.AreEqual("#", new MqttTopicTemplate("#").TopicFilter);
+            Assert.AreEqual("+", new MqttTopicTemplate("+").TopicFilter);
+            Assert.AreEqual("/", new MqttTopicTemplate("/").TopicFilter);
+        }
+
+        [TestMethod]
+        public void BasicOpsWithHash()
+        {
+            var template = new MqttTopicTemplate("A/B/{param}/D/#");
+            Assert.AreEqual("A/B/C/D/#", template.WithParameter("param", "C").Template);
+            Assert.AreEqual("A/B/+/D/#", template.WithoutParameter("param").Template);
+            Assert.AreEqual("A/B/+/D/#", template.TopicFilter);
+            Assert.AreEqual("A/B/+/D/#", template.TopicTreeRootFilter);
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(ArgumentException))]
+        public void RejectsReservedChars1()
+        {
+            var template = new MqttTopicTemplate("A/B/{foo}/D");
+            template.WithParameter("foo", "a#");
+        }
+        
+        [TestMethod]
+        [ExpectedException(typeof(MqttProtocolViolationException))]
+        public void RejectsEmptyTemplate()
+        {
+            var _ = new MqttTopicTemplate("");
+        }
+        
+        [TestMethod]
+        [ExpectedException(typeof(ArgumentNullException))]
+        public void RejectsNullTemplate()
+        {
+            var _ = new MqttTopicTemplate(null);
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(ArgumentException))]
+        public void RejectsReservedChars2()
+        {
+            var template = new MqttTopicTemplate("A/B/{foo}/D");
+            template.WithParameter("foo", "e/f");
+        }
+        
+        [TestMethod]
+        public void IgnoresEmptyParameters()
+        {
+            var template = new MqttTopicTemplate("A/B/{}/D");
+            Assert.IsFalse(template.Parameters.Any());
+        }
+        
+        [TestMethod]
+        public void AcceptsValidTopics()
+        {
+            _ = new MqttTopicTemplate("A");
+            _ = new MqttTopicTemplate("/");
+            _ = new MqttTopicTemplate("/A");
+            _ = new MqttTopicTemplate("A/#");
+            _ = new MqttTopicTemplate("$SYS/#");
+            _ = new MqttTopicTemplate("////");
+            _ = new MqttTopicTemplate("A/B/{foo}/D/");
+        }
+
+        [TestMethod]
+        public void DynamicRoutingSupport()
+        {
+            var v1template = new MqttTopicTemplate("A/v1/{id}/F");
+            var v2template = new MqttTopicTemplate("A/v2/foo/{id}/{bar}");
+            var incoming_v1_topic = "A/v1/32/F";
+
+            var compat_v2_topic = v2template
+                .WithParameterValuesFrom(
+                    v1template.ParseParameterValues(incoming_v1_topic))
+                .WithParameter("bar", "unknown");
+
+            // id: 32 was relocated and bar: unknown added
+            Assert.AreEqual("A/v2/foo/32/unknown", compat_v2_topic.Template);
+        }
+
+        [TestMethod]
+        public void SubscriptionSupport()
+        {
+            var template = new MqttTopicTemplate("A/v1/{param}/F");
+            var filter = template.BuildFilter()
+                .WithAtLeastOnceQoS()
+                .WithNoLocal()
+                .Build();
+            Assert.AreEqual("A/v1/+/F", filter.Topic);
+        }
+
+        [TestMethod]
+        public void CanonicalPrefixFilter()
+        {
+            var template1 = new MqttTopicTemplate("A/v1/{param}/F");
+            var template2 = new MqttTopicTemplate("A/v1/E/F");
+            var template3 = new MqttTopicTemplate("A/v1/E/F/G/H");
+            var canonicalFilter = MqttTopicTemplate.FindCanonicalPrefix(new[] { template1, template2, template3 });
+            // possible improvement: Assert.AreEqual("A/v1/+/F", canonicalFilter.TopicFilter);
+            Assert.AreEqual("A/v1/+", canonicalFilter.TopicFilter);
+            Assert.AreEqual("A/v1/+/#", canonicalFilter.TopicTreeRootFilter);
+            
+            var template2b = new MqttTopicTemplate("A/v1/E/X");
+            canonicalFilter = MqttTopicTemplate.FindCanonicalPrefix(new[] { template1, template2, template3, template2b });
+            Assert.AreEqual("A/v1/+", canonicalFilter.Template);
+            Assert.AreEqual("A/v1/+", canonicalFilter.TopicFilter);
+            Assert.AreEqual("A/v1/+/#", canonicalFilter.TopicTreeRootFilter);
+
+
+            var template4 = new MqttTopicTemplate("A/v2/{prefix}");
+            var canonicalFilter2 = MqttTopicTemplate.FindCanonicalPrefix(new[] { template1, template2, template3, template4 });
+            Assert.AreEqual("A/+", canonicalFilter2.TopicFilter);
+            Assert.AreEqual("A/+/#", canonicalFilter2.TopicTreeRootFilter);
+        }
+        
+        [TestMethod]
+        public void CanonicalPrefixFilterSimple1()
+        {
+            var template = MqttTopicTemplate.FindCanonicalPrefix(new[]
+            {
+                new MqttTopicTemplate("A"),
+                new MqttTopicTemplate("B")
+            });
+            Assert.AreEqual("#", template.TopicFilter);
+            Assert.AreEqual("#", template.Template);
+        }
+        
+        [TestMethod]
+        public void CanonicalPrefixFilterSimple2()
+        {
+            var template = MqttTopicTemplate.FindCanonicalPrefix(new[]
+            {
+                new MqttTopicTemplate("A/v1/{param}/F/"),
+                new MqttTopicTemplate("A/v1/E/X")
+            });
+            Assert.AreEqual("A/v1/+", template.TopicFilter);
+        }
+        
+        [TestMethod]
+        public void CanonicalPrefixFilterSimple3()
+        {
+            var template = MqttTopicTemplate.FindCanonicalPrefix(new[]
+            {
+                new MqttTopicTemplate("A/v1/{param}/F"),
+                new MqttTopicTemplate("A/v1/{param}/F/X")
+            });
+            Assert.AreEqual("A/v1/+/+", template.TopicFilter);
+            Assert.AreEqual("A/v1/{param}/+", template.Template);
+        }
+        
+        [TestMethod]
+        public void CanonicalPrefixFilterSimple4()
+        {
+            var template = MqttTopicTemplate.FindCanonicalPrefix(new[]
+            {
+                new MqttTopicTemplate("A/v1/{param}/FFA"),
+                new MqttTopicTemplate("A/v1/{param}/FX")
+            });
+            Assert.AreEqual("A/v1/+/+", template.TopicFilter);
+            Assert.AreEqual("A/v1/{param}/+", template.Template);
+        }
+        
+        
+        [TestMethod]
+        public void CanonicalPrefixFilterSimple5()
+        {
+            var template = MqttTopicTemplate.FindCanonicalPrefix(new[]
+            {
+                new MqttTopicTemplate("A/v1/E/F/G/H"),
+                new MqttTopicTemplate("A/v2/{param}")
+            });
+            Assert.AreEqual("A/+", template.TopicFilter);
+            Assert.AreEqual("A/+/#", template.TopicTreeRootFilter);
+        }
+        
+        [TestMethod]
+        public void CanonicalPrefixFilterSimple6()
+        {
+            var template = MqttTopicTemplate.FindCanonicalPrefix(new[]
+            {
+                new MqttTopicTemplate("A/{version}/E/F/G/H"),
+                new MqttTopicTemplate("A/{version}/{param}")
+            });
+            Assert.AreEqual("A/+/+", template.TopicFilter);
+            Assert.AreEqual("A/+/+/#", template.TopicTreeRootFilter);
+        }
+    }
+}

Source/MQTTnet.Tests/Internal/CrossPlatformSocket_Tests.cs

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

Source/MQTTnet.Tests/MQTTnet.Tests.csproj

@@ -21,6 +21,7 @@
         <ProjectReference Include="..\..\Source\MQTTnet.Extensions.ManagedClient\MQTTnet.Extensions.ManagedClient.csproj" />
         <ProjectReference Include="..\..\Source\MQTTnet.Extensions.Rpc\MQTTnet.Extensions.Rpc.csproj" />
         <ProjectReference Include="..\..\Source\MQTTnet\MQTTnet.csproj" />
+        <ProjectReference Include="..\MQTTnet.Extensions.TopicTemplate\MQTTnet.Extensions.TopicTemplate.csproj" />
         <ProjectReference Include="..\MQTTnet.Extensions.WebSocket4Net\MQTTnet.Extensions.WebSocket4Net.csproj" />
     </ItemGroup>
 

Source/MQTTnet.Tests/MqttTcpChannel_Tests.cs

@@ -19,7 +19,7 @@ namespace MQTTnet.Tests
         public async Task Dispose_Channel_While_Used()
         {
             var ct = new CancellationTokenSource();
-            var serverSocket = new CrossPlatformSocket(AddressFamily.InterNetwork);
+            var serverSocket = new CrossPlatformSocket(AddressFamily.InterNetwork, ProtocolType.Tcp);
 
             try
             {
@@ -38,7 +38,7 @@ namespace MQTTnet.Tests
                     }
                 }, ct.Token);
 
-                var clientSocket = new CrossPlatformSocket(AddressFamily.InterNetwork);
+                var clientSocket = new CrossPlatformSocket(AddressFamily.InterNetwork, ProtocolType.Tcp);
                 await clientSocket.ConnectAsync("localhost", 50001, CancellationToken.None);
 
                 var tcpChannel = new MqttTcpChannel(clientSocket.GetStream(), "test", null);

Source/MQTTnet.Tests/Server/Connection_Tests.cs

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

Source/MQTTnet/Adapter/MqttChannelAdapter.cs

@@ -141,7 +141,8 @@ namespace MQTTnet.Adapter
 
             try
             {
-                PacketInspector?.BeginReceivePacket();
+                var localPacketInspector = PacketInspector;
+                localPacketInspector?.BeginReceivePacket();
 
                 ReceivedMqttPacket receivedPacket;
                 var receivedPacketTask = ReceiveAsync(cancellationToken);
@@ -159,7 +160,10 @@ namespace MQTTnet.Adapter
                     return null;
                 }
 
-                PacketInspector?.EndReceivePacket();
+                if (localPacketInspector != null)
+                {
+                    await localPacketInspector.EndReceivePacket().ConfigureAwait(false);
+                }
 
                 Interlocked.Add(ref _statistics._bytesSent, receivedPacket.TotalLength);
 
@@ -215,8 +219,13 @@ namespace MQTTnet.Adapter
                 try
                 {
                     var packetBuffer = PacketFormatterAdapter.Encode(packet);
-                    PacketInspector?.BeginSendPacket(packetBuffer);
 
+                    var localPacketInspector = PacketInspector;
+                    if (localPacketInspector != null)
+                    {
+                        await localPacketInspector.BeginSendPacket(packetBuffer).ConfigureAwait(false);    
+                    }
+                    
                     _logger.Verbose("TX ({0} bytes) >>> {1}", packetBuffer.Length, packet);
 
                     if (packetBuffer.Payload.Count == 0 || !AllowPacketFragmentation)

Source/MQTTnet/Adapter/MqttPacketInspector.cs

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

Source/MQTTnet/Client/Exceptions/MqttClientUnexpectedDisconnectReceivedException.cs

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

Source/MQTTnet/Client/MqttClient.cs

@@ -48,6 +48,7 @@ namespace MQTTnet.Client
         Task _packetReceiverTask;
         AsyncQueue<MqttPublishPacket> _publishPacketReceiverQueue;
         Task _publishPacketReceiverTask;
+        MqttDisconnectPacket _unexpectedDisconnectPacket;
 
         public MqttClient(IMqttClientAdapterFactory channelFactory, IMqttNetLogger logger)
         {
@@ -123,6 +124,8 @@ namespace MQTTnet.Client
                 var adapter = _adapterFactory.CreateClientAdapter(options, new MqttPacketInspector(_events.InspectPacketEvent, _rootLogger), _rootLogger);
                 _adapter = adapter ?? throw new InvalidOperationException("The adapter factory did not provide an adapter.");
 
+                _unexpectedDisconnectPacket = null;
+
                 if (cancellationToken.CanBeCanceled)
                 {
                     connectResult = await ConnectInternal(adapter, cancellationToken).ConfigureAwait(false);
@@ -215,7 +218,7 @@ namespace MQTTnet.Client
                 }
 
                 // Sending the DISCONNECT may fail due to connection issues. The resulting exception
-                // must be throw to let the caller know that the disconnect is not a clean one.
+                // must be thrown to let the caller know that the disconnect was not clean.
                 var disconnectPacket = MqttPacketFactories.Disconnect.Create(options);
 
                 if (cancellationToken.CanBeCanceled)
@@ -239,7 +242,7 @@ namespace MQTTnet.Client
         public async Task PingAsync(CancellationToken cancellationToken = default)
         {
             cancellationToken.ThrowIfCancellationRequested();
-            
+
             ThrowIfDisposed();
             ThrowIfNotConnected();
 
@@ -330,7 +333,7 @@ namespace MQTTnet.Client
 
             ThrowIfDisposed();
             ThrowIfNotConnected();
-            
+
             if (Options.ValidateFeatures)
             {
                 MqttClientSubscribeOptionsValidator.ThrowIfNotSupported(options, _adapter.PacketFormatterAdapter.ProtocolVersion);
@@ -406,29 +409,37 @@ namespace MQTTnet.Client
 
         Task AcknowledgeReceivedPublishPacket(MqttApplicationMessageReceivedEventArgs eventArgs, CancellationToken cancellationToken)
         {
-            if (eventArgs.PublishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
+            switch (eventArgs.PublishPacket.QualityOfServiceLevel)
             {
-                // no response required
-            }
-            else if (eventArgs.PublishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtLeastOnce)
-            {
-                if (!eventArgs.ProcessingFailed)
+                case MqttQualityOfServiceLevel.AtMostOnce:
                 {
-                    var pubAckPacket = MqttPacketFactories.PubAck.Create(eventArgs);
-                    return Send(pubAckPacket, cancellationToken);
+                    // no response required
+                    break;
                 }
-            }
-            else if (eventArgs.PublishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
-            {
-                if (!eventArgs.ProcessingFailed)
+                case MqttQualityOfServiceLevel.AtLeastOnce:
                 {
-                    var pubRecPacket = MqttPacketFactories.PubRec.Create(eventArgs);
-                    return Send(pubRecPacket, cancellationToken);
+                    if (!eventArgs.ProcessingFailed)
+                    {
+                        var pubAckPacket = MqttPacketFactories.PubAck.Create(eventArgs);
+                        return Send(pubAckPacket, cancellationToken);
+                    }
+
+                    break;
+                }
+                case MqttQualityOfServiceLevel.ExactlyOnce:
+                {
+                    if (!eventArgs.ProcessingFailed)
+                    {
+                        var pubRecPacket = MqttPacketFactories.PubRec.Create(eventArgs);
+                        return Send(pubRecPacket, cancellationToken);
+                    }
+
+                    break;
+                }
+                default:
+                {
+                    throw new MqttProtocolViolationException("Received a not supported QoS level.");
                 }
-            }
-            else
-            {
-                throw new MqttProtocolViolationException("Received a not supported QoS level.");
             }
 
             return CompletedTask.Instance;
@@ -445,21 +456,25 @@ namespace MQTTnet.Client
 
                 var receivedPacket = await Receive(cancellationToken).ConfigureAwait(false);
 
-                if (receivedPacket is MqttConnAckPacket connAckPacket)
+                switch (receivedPacket)
                 {
-                    result = MqttClientResultFactory.ConnectResult.Create(connAckPacket, channelAdapter.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($"Received an unexpected MQTT packet ({receivedPacket}).");
+                    case MqttConnAckPacket connAckPacket:
+                    {
+                        result = MqttClientResultFactory.ConnectResult.Create(connAckPacket, channelAdapter.PacketFormatterAdapter.ProtocolVersion);
+                        break;
+                    }
+                    case MqttAuthPacket _:
+                    {
+                        throw new NotSupportedException("Extended authentication handler is not yet supported");
+                    }
+                    case null:
+                    {
+                        throw new MqttCommunicationException("Connection closed.");
+                    }
+                    default:
+                    {
+                        throw new InvalidOperationException($"Received an unexpected MQTT packet ({receivedPacket}).");
+                    }
                 }
             }
             catch (Exception exception)
@@ -589,8 +604,8 @@ namespace MQTTnet.Client
                     _disconnectUserProperties,
                     exception);
 
-                // This handler must be executed in a new thread because otherwise a dead lock may happen
-                // when trying to reconnect in that handler etc.
+                // This handler must be executed in a new thread to prevent a deadlock
+                // that may occur when attempting to reconnect within that handler, etc.
                 Task.Run(() => _events.DisconnectedEvent.InvokeAsync(eventArgs)).RunInBackground(_logger);
             }
         }
@@ -599,12 +614,9 @@ namespace MQTTnet.Client
         {
             var clientWasConnected = IsConnected;
 
-            if (!DisconnectIsPendingOrFinished())
-            {
-                return DisconnectCore(sender, exception, connectResult, clientWasConnected);
-            }
-
-            return CompletedTask.Instance;
+            return !DisconnectIsPendingOrFinished() ?
+                DisconnectCore(sender, exception, connectResult, clientWasConnected)
+                : CompletedTask.Instance;
         }
 
         bool DisconnectIsPendingOrFinished()
@@ -657,24 +669,19 @@ namespace MQTTnet.Client
 
         Task OnConnected(MqttClientConnectResult connectResult)
         {
-            if (_events.ConnectedEvent.HasHandlers)
+            if (!_events.ConnectedEvent.HasHandlers)
             {
-                var eventArgs = new MqttClientConnectedEventArgs(connectResult);
-                return _events.ConnectedEvent.InvokeAsync(eventArgs);
+                return CompletedTask.Instance;
             }
 
-            return CompletedTask.Instance;
+            var eventArgs = new MqttClientConnectedEventArgs(connectResult);
+            return _events.ConnectedEvent.InvokeAsync(eventArgs);
         }
 
         Task ProcessReceivedAuthPacket(MqttAuthPacket authPacket)
         {
             var extendedAuthenticationExchangeHandler = Options.ExtendedAuthenticationExchangeHandler;
-            if (extendedAuthenticationExchangeHandler != null)
-            {
-                return extendedAuthenticationExchangeHandler.HandleRequestAsync(new MqttExtendedAuthenticationExchangeContext(authPacket, this));
-            }
-
-            return CompletedTask.Instance;
+            return extendedAuthenticationExchangeHandler != null ? extendedAuthenticationExchangeHandler.HandleRequestAsync(new MqttExtendedAuthenticationExchangeContext(authPacket, this)) : CompletedTask.Instance;
         }
 
         Task ProcessReceivedDisconnectPacket(MqttDisconnectPacket disconnectPacket)
@@ -682,9 +689,10 @@ namespace MQTTnet.Client
             _disconnectReason = (int)disconnectPacket.ReasonCode;
             _disconnectReasonString = disconnectPacket.ReasonString;
             _disconnectUserProperties = disconnectPacket.UserProperties;
+            _unexpectedDisconnectPacket = disconnectPacket;
 
             // Also dispatch disconnect to waiting threads to generate a proper exception.
-            _packetDispatcher.Dispose(new MqttClientUnexpectedDisconnectReceivedException(disconnectPacket));
+            _packetDispatcher.Dispose(new MqttClientUnexpectedDisconnectReceivedException(disconnectPacket, null));
 
             return DisconnectInternal(_packetReceiverTask, null, null);
         }
@@ -724,15 +732,15 @@ namespace MQTTnet.Client
 
         Task ProcessReceivedPubRecPacket(MqttPubRecPacket pubRecPacket, CancellationToken cancellationToken)
         {
-            if (!_packetDispatcher.TryDispatch(pubRecPacket))
+            if (_packetDispatcher.TryDispatch(pubRecPacket))
             {
-                // The packet is unknown. Probably due to a restart of the client.
-                // So wen send this to the server to trigger a full resend of the message.
-                var pubRelPacket = MqttPacketFactories.PubRel.Create(pubRecPacket, MqttApplicationMessageReceivedReasonCode.PacketIdentifierNotFound);
-                return Send(pubRelPacket, cancellationToken);
+                return CompletedTask.Instance;
             }
 
-            return CompletedTask.Instance;
+            // The packet is unknown, probably due to a restart of the client.
+            // So we send this to the server to trigger a full resend of the message.
+            var pubRelPacket = MqttPacketFactories.PubRel.Create(pubRecPacket, MqttApplicationMessageReceivedReasonCode.PacketIdentifierNotFound);
+            return Send(pubRelPacket, cancellationToken);
         }
 
         Task ProcessReceivedPubRelPacket(MqttPubRelPacket pubRelPacket, CancellationToken cancellationToken)
@@ -751,10 +759,27 @@ namespace MQTTnet.Client
 
         async Task<MqttClientPublishResult> PublishAtMostOnce(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
         {
-            // No packet identifier is used for QoS 0 [3.3.2.2 Packet Identifier]
-            await Send(publishPacket, cancellationToken).ConfigureAwait(false);
+            try
+            {
+                // No packet identifier is used for QoS 0 [3.3.2.2 Packet Identifier]
+                await Send(publishPacket, cancellationToken).ConfigureAwait(false);
 
-            return MqttClientResultFactory.PublishResult.Create(null);
+                return MqttClientResultFactory.PublishResult.Create(null);
+            }
+            catch (Exception exception)
+            {
+                // We have to check if the server has sent a disconnect packet in response to the published message.
+                // Since we are in QoS 0 we do not get a direct response via an PUBACK packet and thus basically no
+                // feedback at all.
+                var localUnexpectedDisconnectPacket = _unexpectedDisconnectPacket;
+
+                if (localUnexpectedDisconnectPacket != null)
+                {
+                    throw new MqttClientUnexpectedDisconnectReceivedException(localUnexpectedDisconnectPacket, exception);
+                }
+
+                throw;
+            }
         }
 
         async Task<MqttClientPublishResult> PublishExactlyOnce(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
@@ -930,7 +955,7 @@ namespace MQTTnet.Client
 
         static void ThrowNotConnected()
         {
-            throw new MqttCommunicationException("The client is not connected.");
+            throw new MqttClientNotConnectedException();
         }
 
         void TryInitiateDisconnect()
@@ -952,39 +977,36 @@ namespace MQTTnet.Client
         {
             try
             {
-                if (packet is MqttPublishPacket publishPacket)
+                switch (packet)
                 {
-                    EnqueueReceivedPublishPacket(publishPacket);
-                }
-                else if (packet is MqttPubRecPacket pubRecPacket)
-                {
-                    await ProcessReceivedPubRecPacket(pubRecPacket, cancellationToken).ConfigureAwait(false);
-                }
-                else if (packet is MqttPubRelPacket pubRelPacket)
-                {
-                    await ProcessReceivedPubRelPacket(pubRelPacket, cancellationToken).ConfigureAwait(false);
-                }
-                else if (packet is MqttDisconnectPacket disconnectPacket)
-                {
-                    await ProcessReceivedDisconnectPacket(disconnectPacket).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 is sent from a client to the server only.");
-                }
-                else
-                {
-                    if (!_packetDispatcher.TryDispatch(packet))
+                    case MqttPublishPacket publishPacket:
+                        EnqueueReceivedPublishPacket(publishPacket);
+                        break;
+                    case MqttPubRecPacket pubRecPacket:
+                        await ProcessReceivedPubRecPacket(pubRecPacket, cancellationToken).ConfigureAwait(false);
+                        break;
+                    case MqttPubRelPacket pubRelPacket:
+                        await ProcessReceivedPubRelPacket(pubRelPacket, cancellationToken).ConfigureAwait(false);
+                        break;
+                    case MqttDisconnectPacket disconnectPacket:
+                        await ProcessReceivedDisconnectPacket(disconnectPacket).ConfigureAwait(false);
+                        break;
+                    case MqttAuthPacket authPacket:
+                        await ProcessReceivedAuthPacket(authPacket).ConfigureAwait(false);
+                        break;
+                    case MqttPingRespPacket _:
+                        _packetDispatcher.TryDispatch(packet);
+                        break;
+                    case MqttPingReqPacket _:
+                        throw new MqttProtocolViolationException("The PINGREQ Packet is sent from a client to the server only.");
+                    default:
                     {
-                        throw new MqttProtocolViolationException($"Received packet '{packet}' at an unexpected time.");
+                        if (!_packetDispatcher.TryDispatch(packet))
+                        {
+                            throw new MqttProtocolViolationException($"Received packet '{packet}' at an unexpected time.");
+                        }
+
+                        break;
                     }
                 }
             }
@@ -995,19 +1017,19 @@ namespace MQTTnet.Client
                     return;
                 }
 
-                if (exception is OperationCanceledException)
+                switch (exception)
                 {
-                }
-                else if (exception is MqttCommunicationException)
-                {
-                    _logger.Warning(exception, "Communication error while receiving packets");
-                }
-                else
-                {
-                    _logger.Error(exception, "Error while processing received {0} packet", packet.GetType().Name);
+                    case OperationCanceledException _:
+                        break;
+                    case MqttCommunicationException _:
+                        _logger.Warning(exception, "Communication error while receiving packets");
+                        break;
+                    default:
+                        _logger.Error(exception, "Error while processing received {0} packet", packet.GetType().Name);
+                        break;
                 }
 
-                // The packet dispatcher may already be gone due to disconnect etc!
+                // The packet dispatcher may already be gone due to disconnect etc.!
                 _packetDispatcher?.FailAll(exception);
 
                 await DisconnectInternal(_packetReceiverTask, exception, null).ConfigureAwait(false);
@@ -1050,17 +1072,16 @@ namespace MQTTnet.Client
                     return;
                 }
 
-                if (exception is OperationCanceledException)
+                switch (exception)
                 {
-                    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");
+                    case OperationCanceledException _:
+                        return;
+                    case MqttCommunicationException _:
+                        _logger.Warning(exception, "Communication error while sending/receiving keep alive packets");
+                        break;
+                    default:
+                        _logger.Error(exception, "Error exception while sending/receiving keep alive packets");
+                        break;
                 }
 
                 await DisconnectInternal(_keepAlivePacketsSenderTask, exception, null).ConfigureAwait(false);
@@ -1071,4 +1092,4 @@ namespace MQTTnet.Client
             }
         }
     }
-}
+}

Source/MQTTnet/Client/Options/MqttClientCertificateSelectionEventArgs.cs

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

Source/MQTTnet/Client/Options/MqttClientCertificateValidationEventArgs.cs

@@ -10,11 +10,20 @@ namespace MQTTnet.Client
 {
     public sealed class MqttClientCertificateValidationEventArgs : EventArgs
     {
-        public X509Certificate Certificate { get; set; }
+        public MqttClientCertificateValidationEventArgs(X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors, IMqttClientChannelOptions clientOptions)
+        {
+            Certificate = certificate;
+            Chain = chain;
+            SslPolicyErrors = sslPolicyErrors;
+            ClientOptions = clientOptions ?? throw new ArgumentNullException(nameof(clientOptions));
+        }
 
-        public X509Chain Chain { get; set; }
+        public X509Certificate Certificate { get; }
+
+        public X509Chain Chain { get; }
+
+        public IMqttClientChannelOptions ClientOptions { get; }
 
-        public IMqttClientChannelOptions ClientOptions { get; set; }
 #if NET452 || NET461 || NET48
         /// <summary>
         ///     Can be a host string name or an object derived from WebRequest.
@@ -22,6 +31,6 @@ namespace MQTTnet.Client
         public object Sender { get; set; }
 #endif
 
-        public SslPolicyErrors SslPolicyErrors { get; set; }
+        public SslPolicyErrors SslPolicyErrors { get; }
     }
 }

Source/MQTTnet/Client/Options/MqttClientOptionsBuilder.cs

@@ -8,6 +8,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Net;
+using System.Net.Sockets;
 using System.Text;
 using MQTTnet.Formatter;
 using MQTTnet.Packets;
@@ -18,14 +19,14 @@ namespace MQTTnet.Client
     public sealed class MqttClientOptionsBuilder
     {
         readonly MqttClientOptions _options = new MqttClientOptions();
+        int? _port;
 
         [Obsolete] MqttClientWebSocketProxyOptions _proxyOptions;
+        EndPoint _remoteEndPoint;
 
         MqttClientTcpOptions _tcpOptions;
         MqttClientTlsOptions _tlsOptions;
-        EndPoint _remoteEndPoint;
-        int? _port;
-        
+
         [Obsolete] MqttClientOptionsBuilderTlsParameters _tlsParameters;
 
         MqttClientWebSocketOptions _webSocketOptions;
@@ -78,18 +79,33 @@ namespace MQTTnet.Client
                     {
                         if (_port.HasValue)
                         {
-                            _remoteEndPoint = new DnsEndPoint(dns.Host, _port.Value);
+                            _remoteEndPoint = new DnsEndPoint(dns.Host, _port.Value, dns.AddressFamily);
                         }
                         else
                         {
-                            _remoteEndPoint = new DnsEndPoint(dns.Host, tlsOptions?.UseTls == false ? MqttPorts.Default : MqttPorts.Secure);
+                            _remoteEndPoint = new DnsEndPoint(dns.Host, tlsOptions?.UseTls == false ? MqttPorts.Default : MqttPorts.Secure, dns.AddressFamily);
+                        }
+                    }
+                }
+
+                if (_remoteEndPoint is IPEndPoint ip)
+                {
+                    if (ip.Port == 0)
+                    {
+                        if (_port.HasValue)
+                        {
+                            _remoteEndPoint = new IPEndPoint(ip.Address, _port.Value);
+                        }
+                        else
+                        {
+                            _remoteEndPoint = new IPEndPoint(ip.Address, tlsOptions?.UseTls == false ? MqttPorts.Default : MqttPorts.Secure);
                         }
                     }
                 }
 
                 if (_tcpOptions.RemoteEndpoint == null)
                 {
-                    _tcpOptions.RemoteEndpoint = _remoteEndPoint;    
+                    _tcpOptions.RemoteEndpoint = _remoteEndPoint;
                 }
             }
             else if (_webSocketOptions != null)
@@ -114,6 +130,12 @@ namespace MQTTnet.Client
             return _options;
         }
 
+        public MqttClientOptionsBuilder WithAddressFamily(AddressFamily addressFamily)
+        {
+            _tcpOptions.AddressFamily = addressFamily;
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithAuthentication(string method, byte[] data)
         {
             _options.AuthenticationMethod = method;
@@ -145,7 +167,6 @@ namespace MQTTnet.Client
             return this;
         }
 
-        [Obsolete("Use WithTcpServer(... configure) or WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithConnectionUri(Uri uri)
         {
             if (uri == null)
@@ -189,7 +210,6 @@ 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));
@@ -218,6 +238,14 @@ namespace MQTTnet.Client
             return this;
         }
 
+        public MqttClientOptionsBuilder WithEndPoint(EndPoint endPoint)
+        {
+            _remoteEndPoint = endPoint ?? throw new ArgumentNullException(nameof(endPoint));
+            _tcpOptions = new MqttClientTcpOptions();
+
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithExtendedAuthenticationExchangeHandler(IMqttExtendedAuthenticationExchangeHandler handler)
         {
             _options.ExtendedAuthenticationExchangeHandler = handler;
@@ -254,7 +282,7 @@ namespace MQTTnet.Client
         }
 
         /// <summary>
-        ///     The client will not throw an exception when the MQTT server responses with a non success ACK packet.
+        ///     The client will not throw an exception when the MQTT server responds with a non success ACK packet.
         ///     This will become the default behavior in future versions of the library.
         /// </summary>
         public MqttClientOptionsBuilder WithoutThrowOnNonSuccessfulConnectResponse()
@@ -263,6 +291,12 @@ namespace MQTTnet.Client
             return this;
         }
 
+        public MqttClientOptionsBuilder WithProtocolType(ProtocolType protocolType)
+        {
+            _tcpOptions.ProtocolType = protocolType;
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithProtocolVersion(MqttProtocolVersion value)
         {
             if (value == MqttProtocolVersion.Unknown)
@@ -333,25 +367,22 @@ namespace MQTTnet.Client
             return this;
         }
 
-        public MqttClientOptionsBuilder WithTcpServer(string server, int? port = null)
+        public MqttClientOptionsBuilder WithTcpServer(string host, int? port = null, AddressFamily addressFamily = AddressFamily.Unspecified)
         {
+            if (host == null)
+            {
+                throw new ArgumentNullException(nameof(host));
+            }
+
             _tcpOptions = new MqttClientTcpOptions();
 
             // The value 0 will be updated when building the options.
             // This a backward compatibility feature.
-            _remoteEndPoint = new DnsEndPoint(server, port ?? 0);
+            _remoteEndPoint = new DnsEndPoint(host, port ?? 0, addressFamily);
             _port = port;
 
             return this;
         }
-        
-        public MqttClientOptionsBuilder WithEndPoint(EndPoint endPoint)
-        {
-            _remoteEndPoint = endPoint ?? throw new ArgumentNullException(nameof(endPoint));
-            _tcpOptions = new MqttClientTcpOptions();
-
-            return this;
-        }
 
         public MqttClientOptionsBuilder WithTcpServer(Action<MqttClientTcpOptions> optionsBuilder)
         {

Source/MQTTnet/Client/Options/MqttClientTcpOptions.cs

@@ -2,13 +2,16 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Net;
 using System.Net.Sockets;
+using MQTTnet.Protocol;
 
 namespace MQTTnet.Client
 {
     public sealed class MqttClientTcpOptions : IMqttClientChannelOptions
     {
+        EndPoint _remoteEndpoint;
         public AddressFamily AddressFamily { get; set; } = AddressFamily.Unspecified;
 
         public int BufferSize { get; set; } = 8192;
@@ -20,6 +23,12 @@ namespace MQTTnet.Client
         /// </summary>
         public bool? DualMode { get; set; }
 
+        [Obsolete("Use RemoteEndpoint or MqttClientOptionsBuilder instead.")]
+        public int? Port { get; set; }
+
+        [Obsolete("Use RemoteEndpoint or MqttClientOptionsBuilder instead.")]
+        public string Server { get; set; }
+
         public LingerOption LingerState { get; set; } = new LingerOption(true, 0);
 
         /// <summary>
@@ -28,15 +37,70 @@ namespace MQTTnet.Client
         /// </summary>
         public EndPoint LocalEndpoint { get; set; }
 
+        /// <summary>
+        ///     Enables or disables the Nagle algorithm for the socket.
+        ///     This is only supported for TCP.
+        ///     For other protocol types the value is ignored.
+        ///     Default: true
+        /// </summary>
         public bool NoDelay { get; set; } = true;
 
-        public EndPoint RemoteEndpoint { get; set; }
+        /// <summary>
+        ///     The MQTT transport is usually TCP but when using other endpoint types like
+        ///     unix sockets it must be changed (IP for unix sockets).
+        /// </summary>
+        public ProtocolType ProtocolType { get; set; } = ProtocolType.Tcp;
+
+        public EndPoint RemoteEndpoint
+        {
+            get => _remoteEndpoint;
+            set
+            {
+                _remoteEndpoint = value;
+
+                if (_remoteEndpoint is DnsEndPoint dnsEndPoint)
+                {
+                    Server = dnsEndPoint.Host;
+                    Port = dnsEndPoint.Port;
+                }
+                else if (_remoteEndpoint is IPEndPoint ipEndPoint)
+                {
+                    Server = ipEndPoint.Address.ToString();
+                    Port = ipEndPoint.Port;
+                }
+            }
+        }
 
         public MqttClientTlsOptions TlsOptions { get; set; } = new MqttClientTlsOptions();
 
         public override string ToString()
         {
-            return RemoteEndpoint?.ToString() ?? string.Empty;
+            if (RemoteEndpoint != null)
+            {
+                return RemoteEndpoint.ToString();
+            }
+
+            if (!string.IsNullOrEmpty(Server))
+            {
+                return $"{Server}:{GetPort()}";
+            }
+
+            return string.Empty;
+        }
+
+        int GetPort()
+        {
+            if (Port.HasValue)
+            {
+                return Port.Value;
+            }
+
+            if (TlsOptions?.UseTls == true)
+            {
+                return MqttPorts.Secure;
+            }
+
+            return MqttPorts.Default;
         }
     }
 }

Source/MQTTnet/Client/Options/MqttClientTlsOptions.cs

@@ -14,6 +14,8 @@ namespace MQTTnet.Client
     {
         public Func<MqttClientCertificateValidationEventArgs, bool> CertificateValidationHandler { get; set; }
 
+        public Func<MqttClientCertificateSelectionEventArgs, X509Certificate> CertificateSelectionHandler { get; set; }
+
         public bool UseTls { get; set; }
 
         public bool IgnoreCertificateRevocationErrors { get; set; }

Source/MQTTnet/Client/Options/MqttClientTlsOptionsBuilder.cs

@@ -49,6 +49,17 @@ namespace MQTTnet.Client
             return this;
         }
 
+        public MqttClientTlsOptionsBuilder WithCertificateSelectionHandler(Func<MqttClientCertificateSelectionEventArgs, X509Certificate> certificateSelectionHandler)
+        {
+            if (certificateSelectionHandler == null)
+            {
+                throw new ArgumentNullException(nameof(certificateSelectionHandler));
+            }
+
+            _tlsOptions.CertificateSelectionHandler = certificateSelectionHandler;
+            return this;
+        }
+
         public MqttClientTlsOptionsBuilder WithClientCertificates(IEnumerable<X509Certificate2> certificates)
         {
             if (certificates == null)

Source/MQTTnet/Exceptions/MqttClientNotConnectedException.cs

@@ -0,0 +1,19 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+
+namespace MQTTnet.Exceptions
+{
+    public class MqttClientNotConnectedException : MqttCommunicationException
+    {
+        public MqttClientNotConnectedException() : base("The MQTT client is not connected.")
+        {
+        }
+
+        public MqttClientNotConnectedException(Exception innerException) : base("The MQTT client is not connected.", innerException)
+        {
+        }
+    }
+}

Source/MQTTnet/Formatter/V5/MqttV5PacketDecoder.cs

@@ -220,7 +220,7 @@ namespace MQTTnet.Formatter.V5
             var packet = new MqttConnectPacket
             {
                 // If the Request Problem Information is absent, the value of 1 is used.
-                RequestProblemInformation = true 
+                RequestProblemInformation = true
             };
 
             var protocolName = _bufferReader.ReadString();
@@ -352,7 +352,16 @@ namespace MQTTnet.Formatter.V5
 
         MqttPacket DecodeDisconnectPacket(ArraySegment<byte> body)
         {
-            ThrowIfBodyIsEmpty(body);
+            // From RFC: 3.14.2.1 Disconnect Reason Code
+            // Byte 1 in the Variable Header is the Disconnect Reason Code.
+            // If the Remaining Length is less than 1 the value of 0x00 (Normal disconnection) is used.
+            if (body.Count == 0)
+            {
+                return new MqttDisconnectPacket
+                {
+                    ReasonCode = MqttDisconnectReasonCode.NormalDisconnection
+                };
+            }
 
             _bufferReader.SetBuffer(body.Array, body.Offset, body.Count);
 
@@ -386,7 +395,7 @@ namespace MQTTnet.Formatter.V5
 
             return packet;
         }
-        
+
         MqttPacket DecodePubAckPacket(ArraySegment<byte> body)
         {
             ThrowIfBodyIsEmpty(body);
@@ -724,7 +733,7 @@ namespace MQTTnet.Formatter.V5
             packet.UserProperties = propertiesReader.CollectedUserProperties;
 
             packet.ReasonCodes = new List<MqttUnsubscribeReasonCode>(_bufferReader.BytesLeft);
-            
+
             while (!_bufferReader.EndOfStream)
             {
                 var reasonCode = (MqttUnsubscribeReasonCode)_bufferReader.ReadByte();
@@ -770,4 +779,4 @@ namespace MQTTnet.Formatter.V5
             }
         }
     }
-}
+}

Source/MQTTnet/Formatter/V5/MqttV5PacketEncoder.cs

@@ -279,7 +279,7 @@ namespace MQTTnet.Formatter.V5
             _propertiesWriter.WriteReasonString(packet.ReasonString);
             _propertiesWriter.WriteUserProperties(packet.UserProperties);
 
-            if (_bufferWriter.Length > 0 || packet.ReasonCode != MqttPubAckReasonCode.Success)
+            if (_propertiesWriter.Length > 0 || packet.ReasonCode != MqttPubAckReasonCode.Success)
             {
                 _bufferWriter.WriteByte((byte)packet.ReasonCode);
                 _propertiesWriter.WriteTo(_bufferWriter);
@@ -375,7 +375,7 @@ namespace MQTTnet.Formatter.V5
 
             _bufferWriter.WriteTwoByteInteger(packet.PacketIdentifier);
 
-            if (_bufferWriter.Length > 0 || packet.ReasonCode != MqttPubRecReasonCode.Success)
+            if (_propertiesWriter.Length > 0 || packet.ReasonCode != MqttPubRecReasonCode.Success)
             {
                 _bufferWriter.WriteByte((byte)packet.ReasonCode);
                 _propertiesWriter.WriteTo(_bufferWriter);
@@ -534,4 +534,4 @@ namespace MQTTnet.Formatter.V5
             }
         }
     }
-}
+}

Source/MQTTnet/Implementations/CrossPlatformSocket.cs

@@ -22,20 +22,20 @@ namespace MQTTnet.Implementations
 
         NetworkStream _networkStream;
 
-        public CrossPlatformSocket(AddressFamily addressFamily)
+        public CrossPlatformSocket(AddressFamily addressFamily, ProtocolType protocolType)
         {
-            _socket = new Socket(addressFamily, SocketType.Stream, ProtocolType.Tcp);
+            _socket = new Socket(addressFamily, SocketType.Stream, protocolType);
 
 #if !NET5_0_OR_GREATER
             _socketDisposeAction = _socket.Dispose;
 #endif
         }
 
-        public CrossPlatformSocket()
+        public CrossPlatformSocket(ProtocolType protocolType)
         {
             // Having this constructor is important because avoiding the address family as parameter
             // will make use of dual mode in the .net framework.
-            _socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
+            _socket = new Socket(SocketType.Stream, protocolType);
 
 #if !NET5_0_OR_GREATER
             _socketDisposeAction = _socket.Dispose;
@@ -202,9 +202,28 @@ namespace MQTTnet.Implementations
                 using (cancellationToken.Register(_socketDisposeAction))
                 {
 #if NET452 || NET461
-                    await Task.Factory.FromAsync(_socket.BeginConnect, _socket.EndConnect, endPoint, null).ConfigureAwait(false);
+                    // This is a fix for Mono which behaves differently than dotnet.
+                    // The connection will not be established when the DNS endpoint is used.
+                    if (endPoint is DnsEndPoint dns && dns.AddressFamily == AddressFamily.Unspecified)
+                    {
+                        await Task.Factory.FromAsync(_socket.BeginConnect, _socket.EndConnect, dns.Host, dns.Port, null).ConfigureAwait(false);
+                    }
+                    else
+                    {
+                        await Task.Factory.FromAsync(_socket.BeginConnect, _socket.EndConnect, endPoint, null).ConfigureAwait(false);
+                    }
 #else
-                    await _socket.ConnectAsync(endPoint).ConfigureAwait(false);
+
+                    // This is a fix for Mono which behaves differently than dotnet.
+                    // The connection will not be established when the DNS endpoint is used.
+                    if (endPoint is DnsEndPoint dns && dns.AddressFamily == AddressFamily.Unspecified)
+                    {
+                        await _socket.ConnectAsync(dns.Host, dns.Port).ConfigureAwait(false);
+                    }
+                    else
+                    {
+                        await _socket.ConnectAsync(endPoint).ConfigureAwait(false);
+                    }
 #endif
                 }
 #endif

Source/MQTTnet/Implementations/MqttTcpChannel.cs

@@ -16,6 +16,7 @@ using MQTTnet.Channel;
 using MQTTnet.Client;
 using MQTTnet.Exceptions;
 using MQTTnet.Internal;
+using MQTTnet.Protocol;
 
 namespace MQTTnet.Implementations
 {
@@ -63,11 +64,11 @@ namespace MQTTnet.Implementations
             {
                 if (_tcpOptions.AddressFamily == AddressFamily.Unspecified)
                 {
-                    socket = new CrossPlatformSocket();
+                    socket = new CrossPlatformSocket(_tcpOptions.ProtocolType);
                 }
                 else
                 {
-                    socket = new CrossPlatformSocket(_tcpOptions.AddressFamily);
+                    socket = new CrossPlatformSocket(_tcpOptions.AddressFamily, _tcpOptions.ProtocolType);
                 }
 
                 if (_tcpOptions.LocalEndpoint != null)
@@ -78,7 +79,12 @@ namespace MQTTnet.Implementations
                 socket.ReceiveBufferSize = _tcpOptions.BufferSize;
                 socket.SendBufferSize = _tcpOptions.BufferSize;
                 socket.SendTimeout = (int)_clientOptions.Timeout.TotalMilliseconds;
-                socket.NoDelay = _tcpOptions.NoDelay;
+
+                if (_tcpOptions.ProtocolType == ProtocolType.Tcp)
+                {
+                    // Other protocol types do not support the Nagle algorithm.
+                    socket.NoDelay = _tcpOptions.NoDelay;
+                }
 
                 if (socket.LingerState != null)
                 {
@@ -93,6 +99,29 @@ namespace MQTTnet.Implementations
                     socket.DualMode = _tcpOptions.DualMode.Value;
                 }
 
+                // This block is only for backward compatibility.
+                if (_tcpOptions.RemoteEndpoint == null && !string.IsNullOrEmpty(_tcpOptions.Server))
+                {
+                    int port;
+                    if (_tcpOptions.Port.HasValue)
+                    {
+                        port = _tcpOptions.Port.Value;
+                    }
+                    else
+                    {
+                        if (_tcpOptions.TlsOptions?.UseTls == true)
+                        {
+                            port = MqttPorts.Secure;
+                        }
+                        else
+                        {
+                            port = MqttPorts.Default;
+                        }
+                    }
+
+                    _tcpOptions.RemoteEndpoint = new DnsEndPoint(_tcpOptions.Server, port, AddressFamily.Unspecified);
+                }
+
                 await socket.ConnectAsync(_tcpOptions.RemoteEndpoint, cancellationToken).ConfigureAwait(false);
 
                 cancellationToken.ThrowIfCancellationRequested();
@@ -106,10 +135,29 @@ namespace MQTTnet.Implementations
                     {
                         if (_tcpOptions.RemoteEndpoint is DnsEndPoint dns)
                         {
-                            targetHost = dns.Host;    
+                            targetHost = dns.Host;
                         }
                     }
-                    var sslStream = new SslStream(networkStream, false, InternalUserCertificateValidationCallback);
+
+                    SslStream sslStream;
+                    if (_tcpOptions.TlsOptions.CertificateSelectionHandler != null)
+                    {
+                        sslStream = new SslStream(
+                            networkStream,
+                            false,
+                            InternalUserCertificateValidationCallback,
+                            InternalUserCertificateSelectionCallback);
+                    }
+                    else
+                    {
+                        // Use a different constructor depending on the options for MQTTnet so that we do not have
+                        // to copy the exact same behavior of the selection handler.
+                        sslStream = new SslStream(
+                            networkStream,
+                            false,
+                            InternalUserCertificateValidationCallback);
+                    }
+
                     try
                     {
 #if NETCOREAPP3_1_OR_GREATER
@@ -134,9 +182,7 @@ namespace MQTTnet.Implementations
                             {
                                 TrustMode = X509ChainTrustMode.CustomRootTrust,
                                 VerificationFlags = X509VerificationFlags.IgnoreEndRevocationUnknown,
-                                RevocationMode = _tcpOptions.TlsOptions.IgnoreCertificateRevocationErrors
-                                    ? X509RevocationMode.NoCheck
-                                    : _tcpOptions.TlsOptions.RevocationMode
+                                RevocationMode = _tcpOptions.TlsOptions.IgnoreCertificateRevocationErrors ? X509RevocationMode.NoCheck : _tcpOptions.TlsOptions.RevocationMode
                             };
 
                             sslOptions.CertificateChainPolicy.CustomTrustStore.AddRange(_tcpOptions.TlsOptions.TrustChain);
@@ -292,19 +338,34 @@ namespace MQTTnet.Implementations
             }
         }
 
+        X509Certificate InternalUserCertificateSelectionCallback(
+            object sender,
+            string targetHost,
+            X509CertificateCollection localCertificates,
+            X509Certificate remoteCertificate,
+            string[] acceptableIssuers)
+        {
+            var certificateSelectionHandler = _tcpOptions?.TlsOptions?.CertificateSelectionHandler;
+            if (certificateSelectionHandler != null)
+            {
+                var eventArgs = new MqttClientCertificateSelectionEventArgs(targetHost, localCertificates, remoteCertificate, acceptableIssuers, _tcpOptions);
+                return certificateSelectionHandler(eventArgs);
+            }
+
+            if (localCertificates?.Count > 0)
+            {
+                return localCertificates[0];
+            }
+
+            return null;
+        }
+
         bool InternalUserCertificateValidationCallback(object sender, X509Certificate x509Certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
         {
             var certificateValidationHandler = _tcpOptions?.TlsOptions?.CertificateValidationHandler;
             if (certificateValidationHandler != null)
             {
-                var eventArgs = new MqttClientCertificateValidationEventArgs
-                {
-                    Certificate = x509Certificate,
-                    Chain = chain,
-                    SslPolicyErrors = sslPolicyErrors,
-                    ClientOptions = _tcpOptions
-                };
-
+                var eventArgs = new MqttClientCertificateValidationEventArgs(x509Certificate, chain, sslPolicyErrors, _tcpOptions);
                 return certificateValidationHandler(eventArgs);
             }
 

Source/MQTTnet/Implementations/MqttTcpServerListener.cs

@@ -27,7 +27,7 @@ namespace MQTTnet.Implementations
         readonly MqttServerOptions _serverOptions;
         readonly MqttServerTcpEndpointBaseOptions _options;
         readonly MqttServerTlsTcpEndpointOptions _tlsOptions;
-        
+
         CrossPlatformSocket _socket;
         IPEndPoint _localEndPoint;
 
@@ -65,7 +65,7 @@ namespace MQTTnet.Implementations
 
                 _logger.Info("Starting TCP listener (Endpoint={0}, TLS={1})", _localEndPoint, _tlsOptions?.CertificateProvider != null);
 
-                _socket = new CrossPlatformSocket(_addressFamily);
+                _socket = new CrossPlatformSocket(_addressFamily, ProtocolType.Tcp);
 
                 // Usage of socket options is described here: https://docs.microsoft.com/en-us/dotnet/api/system.net.sockets.socket.setsocketoption?view=netcore-2.2
                 if (_options.ReuseAddress)
@@ -87,33 +87,33 @@ namespace MQTTnet.Implementations
                 {
                     _socket.KeepAlive = _options.KeepAlive.Value;
                 }
-                
+
                 if (_options.TcpKeepAliveInterval.HasValue)
                 {
                     _socket.TcpKeepAliveInterval = _options.TcpKeepAliveInterval.Value;
                 }
-                
+
                 if (_options.TcpKeepAliveRetryCount.HasValue)
                 {
                     _socket.TcpKeepAliveInterval = _options.TcpKeepAliveRetryCount.Value;
                 }
-                
+
                 if (_options.TcpKeepAliveTime.HasValue)
                 {
                     _socket.TcpKeepAliveTime = _options.TcpKeepAliveTime.Value;
                 }
-                
+
                 _socket.Bind(_localEndPoint);
-                
+
                 // Get the local endpoint back from the socket. The port may have changed.
                 // This can happen when port 0 is used. Then the OS will choose the next free port.
                 _localEndPoint = (IPEndPoint)_socket.LocalEndPoint;
                 _options.Port = _localEndPoint.Port;
-                
+
                 _socket.Listen(_options.ConnectionBacklog);
-                
+
                 _logger.Verbose("TCP listener started (Endpoint={0})", _localEndPoint);
-                
+
                 Task.Run(() => AcceptClientConnectionsAsync(cancellationToken), cancellationToken).RunInBackground(_logger);
 
                 return true;
@@ -183,7 +183,7 @@ namespace MQTTnet.Implementations
                 clientSocket.NoDelay = _options.NoDelay;
                 stream = clientSocket.GetStream();
                 var clientCertificate = _tlsOptions?.CertificateProvider?.GetCertificate();
-                
+
                 if (clientCertificate != null)
                 {
                     if (!clientCertificate.HasPrivateKey)
@@ -228,7 +228,7 @@ namespace MQTTnet.Implementations
                     var tcpChannel = new MqttTcpChannel(stream, remoteEndPoint, clientCertificate);
                     var bufferWriter = new MqttBufferWriter(_serverOptions.WriterBufferSize, _serverOptions.WriterBufferSizeMax);
                     var packetFormatterAdapter = new MqttPacketFormatterAdapter(bufferWriter);
-                    
+
                     using (var clientAdapter = new MqttChannelAdapter(tcpChannel, packetFormatterAdapter, _rootLogger))
                     {
                         clientAdapter.AllowPacketFragmentation = _options.AllowPacketFragmentation;

Source/MQTTnet/Implementations/MqttWebSocketChannel.cs

@@ -109,7 +109,7 @@ namespace MQTTnet.Implementations
             // A single WebSocket data frame can contain multiple or partial MQTT Control Packets. The receiver MUST NOT assume that MQTT Control Packets are aligned on WebSocket frame boundaries [MQTT-6.0.0-2].
             await _webSocket.SendAsync(buffer, WebSocketMessageType.Binary, isEndOfPacket, cancellationToken).ConfigureAwait(false);
 #else
-            // The lock is required because the client will throw an exception if _SendAsync_ is 
+            // The lock is required because the client will throw an exception if _SendAsync_ is
             // called from multiple threads at the same time. But this issue only happens with several
             // framework versions.
             if (_sendLock == null)
@@ -156,7 +156,7 @@ namespace MQTTnet.Implementations
 #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);
@@ -164,9 +164,9 @@ namespace MQTTnet.Implementations
             }
             else
             {
-                webProxy = new WebProxy(proxyUri, _options.ProxyOptions.BypassOnLocal, _options.ProxyOptions.BypassList);    
+                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
@@ -234,7 +234,7 @@ namespace MQTTnet.Implementations
             {
                 clientWebSocket.Options.Credentials = _options.Credentials;
             }
-            
+
             var certificateValidationHandler = _options.TlsOptions?.CertificateValidationHandler;
             if (certificateValidationHandler != null)
             {
@@ -245,15 +245,11 @@ namespace MQTTnet.Implementations
 #elif WINDOWS_UWP
                 throw new NotSupportedException("Remote certificate validation callback is not supported when using 'uap10.0'.");
 #elif NET452 || NET461 || NET48
-                ServicePointManager.ServerCertificateValidationCallback += (sender, certificate, chain, sslPolicyErrors) => 
+                ServicePointManager.ServerCertificateValidationCallback += (sender, certificate, chain, sslPolicyErrors) =>
                 {
-                    var context = new MqttClientCertificateValidationEventArgs
+                    var context = new MqttClientCertificateValidationEventArgs(certificate, chain, sslPolicyErrors, _options)
                     {
-                        Sender = sender,
-                        Certificate = certificate,
-                        Chain = chain,
-                        SslPolicyErrors = sslPolicyErrors,
-                        ClientOptions = _options
+                        Sender = sender
                     };
 
                     return certificateValidationHandler(context);
@@ -262,17 +258,16 @@ namespace MQTTnet.Implementations
                 clientWebSocket.Options.RemoteCertificateValidationCallback = (sender, certificate, chain, sslPolicyErrors) =>
                 {
                     // TODO: Find a way to add client options to same callback. Problem is that they have a different type.
-                    var context = new MqttClientCertificateValidationEventArgs
-                    {
-                        Certificate = certificate,
-                        Chain = chain,
-                        SslPolicyErrors = sslPolicyErrors,
-                        ClientOptions = _options
-                    };
-
+                    var context = new MqttClientCertificateValidationEventArgs(certificate, chain, sslPolicyErrors, _options);
                     return certificateValidationHandler(context);
                 };
 #endif
+
+                var certificateSelectionHandler = _options.TlsOptions?.CertificateSelectionHandler;
+                if (certificateSelectionHandler != null)
+                {
+                    throw new NotSupportedException("Remote certificate selection callback is not supported for WebSocket connections.");
+                }
             }
         }
     }

Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs

@@ -257,7 +257,12 @@ namespace MQTTnet.Server
 
                     if (matchingSubscribersCount == 0)
                     {
-                        reasonCode = (int)MqttPubAckReasonCode.NoMatchingSubscribers;
+                        if (reasonCode == (int)MqttPubAckReasonCode.Success)
+                        {
+                            // Only change the value if it was success. Otherwise, we would hide an error or not authorized status.
+                            reasonCode = (int)MqttPubAckReasonCode.NoMatchingSubscribers;
+                        }
+
                         await FireApplicationMessageNotConsumedEvent(applicationMessage, senderId).ConfigureAwait(false);
                     }
                 }

Source/MQTTnet/Server/Internal/MqttServerKeepAliveMonitor.cs

@@ -57,7 +57,7 @@ namespace MQTTnet.Server
                 while (!cancellationToken.IsCancellationRequested)
                 {
                     TryProcessClients();
-                    Sleep(_options.KeepAliveMonitorInterval);
+                    Sleep(_options.KeepAliveOptions.MonitorInterval);
                 }
             }
             catch (OperationCanceledException)