1612 mqttserver subscription to similar base and subtopic with wildcards fails (#1622)

Bumps [Newtonsoft.Json](https://github.com/JamesNK/Newtonsoft.Json) from 13.0.1 to 13.0.2.
- [Release notes](https://github.com/JamesNK/Newtonsoft.Json/releases)
- [Commits](https://github.com/JamesNK/Newtonsoft.Json/compare/13.0.1...13.0.2)

---
updated-dependencies:
- dependency-name: Newtonsoft.Json
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/ReleaseNotes.md

@@ -0,0 +1,9 @@
+* [Core] Fixed a memory leak in _AsyncSignal_ implementation (#1586, thanks to @mario-zelger).
+* [Core] Fixed an issue with bounds handling in _MqttBufferReader_ (#1593).
+* [Core] Performance improvements and reduced memory usage due to improved buffer copies (#1599, thanks to @xljiulang).
+* [Server] Fix not properly reset statistics (#1587, thanks to @damikun).
+* [Server] Now using an empty string as the sender client ID for injected application messages (#1583, thanks to @xljiulang).
+* [Server] Improved memory usage for ASP.NET connections (#1582, thanks to @xljiulang).
+* [Server] Improved memory usage and performance for ASP.NET integration (#1596, thanks to @xljiulang).
+* [Server] Add support for interception of will messages (#1613).
+* [Server] Fixed wrong topic filter detections (#1615, thanks to @logicaloud).

.github/workflows/ci.yml

@@ -3,7 +3,7 @@ name: CI
 on: [push, pull_request]
 
 env:
-  VERSION: "4.1.0.${{github.run_number}}"
+  VERSION: "4.1.4.${{github.run_number}}"
 
 jobs:
   build:
@@ -60,8 +60,4 @@ jobs:
 
       - name: Publish MyGet nugets
         if: ${{ github.event_name == 'push' }}
-        run: dotnet nuget push **/*.nupkg -k ${{ secrets.MYGET_API_KEY }} -s https://www.myget.org/F/mqttnet/api/v3/index.json --skip-duplicate
-
-#      - name: Publish nugets
-#        if: ${{ github.event_name == 'push' && github.ref == 'refs/heads/master' }}
-#        run: dotnet nuget push **/*.nupkg -k ${{ secrets.NUGET_API_KEY }} -s https://api.nuget.org/v3/index.json --skip-duplicate
+        run: dotnet nuget push **/*.nupkg -k ${{ secrets.MYGET_API_KEY }} -s https://www.myget.org/F/mqttnet/api/v3/index.json --skip-duplicate

MQTTnet.sln.DotSettings

@@ -210,6 +210,7 @@
         </Or>
       </Entry.Match>
         <Entry.SortBy>
+            <Access Order="Public Internal Protected Private" />
             <Name />
         </Entry.SortBy>
     </Entry>
@@ -239,6 +240,14 @@ See the LICENSE file in the project root for more information.</s:String>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002ECSharpPlaceAttributeOnSameLineMigration/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002EMigrateBlankLinesAroundFieldToBlankLinesAroundProperty/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002EMigrateThisQualifierSettings/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/UserDictionary/Words/=CONNACK/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=PINGREQ/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/UserDictionary/Words/=PINGRESP/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/UserDictionary/Words/=PUBACK/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/UserDictionary/Words/=PUBCOMP/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/UserDictionary/Words/=PUBREC/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/UserDictionary/Words/=PUBREL/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/UserDictionary/Words/=SUBACK/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=Tnet/@EntryIndexedValue">True</s:Boolean>
-	<s:Boolean x:Key="/Default/UserDictionary/Words/=unsub/@EntryIndexedValue">True</s:Boolean></wpf:ResourceDictionary>
+	<s:Boolean x:Key="/Default/UserDictionary/Words/=unsub/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/UserDictionary/Words/=UNSUBACK/@EntryIndexedValue">True</s:Boolean></wpf:ResourceDictionary>

README.md

@@ -4,7 +4,7 @@
 </p>
 
 [![NuGet Badge](https://buildstats.info/nuget/MQTTnet)](https://www.nuget.org/packages/MQTTnet)
-[![CI](https://github.com/dotnet/MQTTnet/actions/workflows/ci.yml/badge.svg)](https://github.com/dotnet/MQTTnet/actions/workflows/ci.yml)
+[![CI](https://github.com/dotnet/MQTTnet/actions/workflows/ci.yml/badge.svg?branch=master)](https://github.com/dotnet/MQTTnet/actions/workflows/ci.yml)
 [![MyGet](https://img.shields.io/myget/mqttnet/v/mqttnet?color=orange&label=MyGet-Preview)](https://www.myget.org/feed/mqttnet/package/nuget/MQTTnet)
 ![Size](https://img.shields.io/github/repo-size/dotnet/MQTTnet.svg)
 [![Join the chat at https://gitter.im/MQTTnet/community](https://badges.gitter.im/MQTTnet/community.svg)](https://gitter.im/MQTTnet/community?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
@@ -12,7 +12,7 @@
 
 # MQTTnet
 
-MQTTnet is a high performance .NET library for MQTT based communication. It provides a MQTT client and a MQTT server (broker) and supports the MQTT protocol up to version 5.
+MQTTnet is a high performance .NET library for MQTT based communication. It provides a MQTT client and a MQTT server (broker) and supports the MQTT protocol up to version 5. It is compatible with mostly any supported .NET Framework version and CPU architecture.
 
 ## Features
 
@@ -50,39 +50,6 @@ MQTTnet is a high performance .NET library for MQTT based communication. It prov
 * A custom message interceptor can be added which allows transforming or extending every received application message
 * Validate subscriptions and deny subscribing of certain topics depending on requesting clients
 
-## Supported frameworks
-
-| Framwork           | Version     |
-| ------------------ | ----------- |
-|.NET                | 5.0+        |
-|.NET Framework      | 4.5.2+      |
-|.NET Standard       | 1.3+        |
-|.NET Core           | 1.1+        |
-|.NET Core App       | 1.1+        |
-| Mono               | 5.2+        |
-| UWP                | 10.0.10240+ |
-| Xamarin.Android    | 7.5+        |
-| Xamarin.iOS        | 10.14+      |
-| Blazor WebAssembly | 3.2.0+      |
-
-## References
-
-This library is used in the following projects:
-
-* Azure Functions MQTT Bindings, <https://github.com/keesschollaart81/CaseOnline.Azure.WebJobs.Extensions.Mqtt>)
-* HA4IoT (Open Source Home Automation system for .NET, <https://github.com/chkr1011/HA4IoT>)
-* MQTT Client Rx (Wrapper for Reactive Extensions, <https://github.com/1iveowl/MQTTClient.rx>)
-* MQTT Client Rx (Managed Client Wrapper for Reactive Extensions, <https://github.com/mmuecke/RxMQTTnet>)
-* MQTT Tester (MQTT client test app for [Android](https://play.google.com/store/apps/details?id=com.liveowl.mqtttester) and [iOS](https://itunes.apple.com/us/app/mqtt-tester/id1278621826?mt=8))
-* MQTTnet App (Cross platform client application for MQTT debugging, inspection etc., <https://github.com/chkr1011/MQTTnetApp>)
-* Wirehome.Core (Open Source Home Automation system for .NET Core, <https://github.com/chkr1011/Wirehome.Core>)
-* SparkplugNet (Sparkplug library for .Net, <https://github.com/SeppPenner/SparkplugNet>)
-* Silverback (Framework to build event-driven applications - support for MQTT, Kafka & RabbitMQ) <https://github.com/BEagle1984/silverback>
-
-Further projects using this project can be found under https://github.com/dotnet/MQTTnet/network/dependents.
-
-If you use this library and want to see your project here please create a pull request.
-
 ## Code of Conduct
 
 This project has adopted the code of conduct defined by the Contributor Covenant to clarify expected behavior in our community.

Samples/Client/Client_Connection_Samples.cs

@@ -10,7 +10,7 @@ using System.Security.Authentication;
 using MQTTnet.Client;
 using MQTTnet.Extensions.WebSocket4Net;
 using MQTTnet.Formatter;
-using MQTTnet.Samples.Shared;
+using MQTTnet.Samples.Helpers;
 
 namespace MQTTnet.Samples.Client;
 
@@ -119,7 +119,7 @@ public static class Client_Connection_Samples
                         // The used public broker sometimes has invalid certificates. This sample accepts all
                         // certificates. This should not be used in live environments.
                         o.CertificateValidationHandler = _ => true;
-                        
+
                         // The default value is determined by the OS. Set manually to force version.
                         o.SslProtocol = SslProtocols.Tls12;
                     })
@@ -134,15 +134,17 @@ public static class Client_Connection_Samples
         }
     }
 
-    public static async Task Connect_Client_Using_WebSockets()
+    public static async Task Connect_Client_Using_WebSocket4Net()
     {
         /*
          * This sample creates a simple MQTT client and connects to a public broker using a WebSocket connection.
+         * Instead of the .NET implementation of WebSockets the implementation from WebSocket4Net is used. It provides more
+         * encryption algorithms and supports more platforms.
          * 
          * This is a modified version of the sample _Connect_Client_! See other sample for more details.
          */
 
-        var mqttFactory = new MqttFactory();
+        var mqttFactory = new MqttFactory().UseWebSocket4Net();
 
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
@@ -155,18 +157,16 @@ public static class Client_Connection_Samples
             response.DumpToConsole();
         }
     }
-    
-    public static async Task Connect_Client_Using_WebSocket4Net()
+
+    public static async Task Connect_Client_Using_WebSockets()
     {
         /*
          * This sample creates a simple MQTT client and connects to a public broker using a WebSocket connection.
-         * Instead of the .NET implementation of WebSockets the implementaion from WebSocket4Net is used. It provides more
-         * encryption algorithms and supports more platforms.
          * 
          * This is a modified version of the sample _Connect_Client_! See other sample for more details.
          */
 
-        var mqttFactory = new MqttFactory().UseWebSocket4Net();
+        var mqttFactory = new MqttFactory();
 
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
@@ -206,7 +206,7 @@ public static class Client_Connection_Samples
             using (var timeout = new CancellationTokenSource(5000))
             {
                 var response = await mqttClient.ConnectAsync(mqttClientOptions, timeout.Token);
-                
+
                 Console.WriteLine("The MQTT client is connected.");
 
                 response.DumpToConsole();
@@ -214,6 +214,49 @@ public static class Client_Connection_Samples
         }
     }
 
+    public static async Task Disconnect_Clean()
+    {
+        /*
+         * This sample disconnects from the server with sending a DISCONNECT packet.
+         * This way of disconnecting is treated as a clean disconnect which will not
+         * trigger sending the last will etc.
+         */
+
+        var mqttFactory = new MqttFactory();
+
+        using (var mqttClient = mqttFactory.CreateMqttClient())
+        {
+            var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("broker.hivemq.com").Build();
+
+            await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
+
+            // Calling _DisconnectAsync_ will send a DISCONNECT packet before closing the connection.
+            // Using a reason code requires MQTT version 5.0.0!
+            await mqttClient.DisconnectAsync(MqttClientDisconnectReason.ImplementationSpecificError);
+        }
+    }
+
+    public static async Task Disconnect_Non_Clean()
+    {
+        /*
+         * This sample disconnects from the server without sending a DISCONNECT packet.
+         * This way of disconnecting is treated as a non clean disconnect which will
+         * trigger sending the last will etc.
+         */
+
+        var mqttFactory = new MqttFactory();
+
+        var mqttClient = mqttFactory.CreateMqttClient();
+
+        var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("broker.hivemq.com").Build();
+
+        await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
+
+        // Calling _Dispose_ or use of a _using_ statement will close the transport connection
+        // without sending a DISCONNECT packet to the server.
+        mqttClient.Dispose();
+    }
+
     public static async Task Inspect_Certificate_Validation_Errors()
     {
         /*
@@ -248,7 +291,7 @@ public static class Client_Connection_Samples
             }
         }
     }
-    
+
     public static async Task Ping_Server()
     {
         /*
@@ -321,14 +364,12 @@ public static class Client_Connection_Samples
                     {
                         try
                         {
-                            // This code will also do the very first connect! So no call to _ConnectAsync_ is required
-                            // in the first place.
-                            if (!mqttClient.IsConnected)
+                            // This code will also do the very first connect! So no call to _ConnectAsync_ is required in the first place.
+                            if (!await mqttClient.TryPingAsync())
                             {
                                 await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
 
                                 // Subscribe to topics when session is clean etc.
-
                                 Console.WriteLine("The MQTT client is connected.");
                             }
                         }
@@ -345,4 +386,4 @@ public static class Client_Connection_Samples
                 });
         }
     }
-}
+}

Samples/Client/Client_Publish_Samples.cs

@@ -40,6 +40,53 @@ public static class Client_Publish_Samples
 
             await mqttClient.PublishAsync(applicationMessage, CancellationToken.None);
 
+            await mqttClient.DisconnectAsync();
+            
+            Console.WriteLine("MQTT application message is published.");
+        }
+    }
+    
+    public static async Task Publish_Multiple_Application_Messages()
+    {
+        /*
+         * This sample pushes multiple simple application message including a topic and a payload.
+         *
+         * See sample _Publish_Application_Message_ for more details.
+         */
+
+        var mqttFactory = new MqttFactory();
+
+        using (var mqttClient = mqttFactory.CreateMqttClient())
+        {
+            var mqttClientOptions = new MqttClientOptionsBuilder()
+                .WithTcpServer("broker.hivemq.com")
+                .Build();
+
+            await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
+
+            var applicationMessage = new MqttApplicationMessageBuilder()
+                .WithTopic("samples/temperature/living_room")
+                .WithPayload("19.5")
+                .Build();
+
+            await mqttClient.PublishAsync(applicationMessage, CancellationToken.None);
+            
+            applicationMessage = new MqttApplicationMessageBuilder()
+                .WithTopic("samples/temperature/living_room")
+                .WithPayload("20.0")
+                .Build();
+            
+            await mqttClient.PublishAsync(applicationMessage, CancellationToken.None);
+
+            applicationMessage = new MqttApplicationMessageBuilder()
+                .WithTopic("samples/temperature/living_room")
+                .WithPayload("21.0")
+                .Build();
+            
+            await mqttClient.PublishAsync(applicationMessage, CancellationToken.None);
+
+            await mqttClient.DisconnectAsync();
+            
             Console.WriteLine("MQTT application message is published.");
         }
     }

Samples/Client/Client_Subscribe_Samples.cs

@@ -7,7 +7,9 @@
 // ReSharper disable InconsistentNaming
 
 using MQTTnet.Client;
-using MQTTnet.Samples.Shared;
+using MQTTnet.Packets;
+using MQTTnet.Protocol;
+using MQTTnet.Samples.Helpers;
 
 namespace MQTTnet.Samples.Client;
 
@@ -23,9 +25,7 @@ public static class Client_Subscribe_Samples
 
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
-            var mqttClientOptions = new MqttClientOptionsBuilder()
-                .WithTcpServer("broker.hivemq.com")
-                .Build();
+            var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("broker.hivemq.com").Build();
 
             // Setup message handling before connecting so that queued messages
             // are also handled properly. When there is no event handler attached all
@@ -41,7 +41,11 @@ public static class Client_Subscribe_Samples
             await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
 
             var mqttSubscribeOptions = mqttFactory.CreateSubscribeOptionsBuilder()
-                .WithTopicFilter(f => { f.WithTopic("mqttnet/samples/topic/2"); })
+                .WithTopicFilter(
+                    f =>
+                    {
+                        f.WithTopic("mqttnet/samples/topic/2");
+                    })
                 .Build();
 
             await mqttClient.SubscribeAsync(mqttSubscribeOptions, CancellationToken.None);
@@ -53,6 +57,95 @@ public static class Client_Subscribe_Samples
         }
     }
 
+    public static async Task Send_Responses()
+    {
+        /*
+         * This sample subscribes to a topic and sends a response to the broker. This requires at least QoS level 1 to work!
+         */
+
+        var mqttFactory = new MqttFactory();
+
+        using (var mqttClient = mqttFactory.CreateMqttClient())
+        {
+            mqttClient.ApplicationMessageReceivedAsync += delegate(MqttApplicationMessageReceivedEventArgs args)
+            {
+                // Do some work with the message...
+
+                // Now respond to the broker with a reason code other than success.
+                args.ReasonCode = MqttApplicationMessageReceivedReasonCode.ImplementationSpecificError;
+                args.ResponseReasonString = "That did not work!";
+
+                // User properties require MQTT v5!
+                args.ResponseUserProperties.Add(new MqttUserProperty("My", "Data"));
+
+                // Now the broker will resend the message again.
+                return Task.CompletedTask;
+            };
+
+            var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("broker.hivemq.com").Build();
+
+            await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
+
+            var mqttSubscribeOptions = mqttFactory.CreateSubscribeOptionsBuilder()
+                .WithTopicFilter(
+                    f =>
+                    {
+                        f.WithTopic("mqttnet/samples/topic/1");
+                    })
+                .Build();
+
+            var response = await mqttClient.SubscribeAsync(mqttSubscribeOptions, CancellationToken.None);
+
+            Console.WriteLine("MQTT client subscribed to topic.");
+
+            // The response contains additional data sent by the server after subscribing.
+            response.DumpToConsole();
+        }
+    }
+
+    public static async Task Subscribe_Multiple_Topics()
+    {
+        /*
+         * This sample subscribes to several topics in a single request.
+         */
+
+        var mqttFactory = new MqttFactory();
+
+        using (var mqttClient = mqttFactory.CreateMqttClient())
+        {
+            var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("broker.hivemq.com").Build();
+
+            await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
+
+            // Create the subscribe options including several topics with different options.
+            // It is also possible to all of these topics using a dedicated call of _SubscribeAsync_ per topic.
+            var mqttSubscribeOptions = mqttFactory.CreateSubscribeOptionsBuilder()
+                .WithTopicFilter(
+                    f =>
+                    {
+                        f.WithTopic("mqttnet/samples/topic/1");
+                    })
+                .WithTopicFilter(
+                    f =>
+                    {
+                        f.WithTopic("mqttnet/samples/topic/2").WithNoLocal();
+                    })
+                .WithTopicFilter(
+                    f =>
+                    {
+                        f.WithTopic("mqttnet/samples/topic/3").WithRetainHandling(MqttRetainHandling.SendAtSubscribe);
+                    })
+                .Build();
+
+            var response = await mqttClient.SubscribeAsync(mqttSubscribeOptions, CancellationToken.None);
+
+            Console.WriteLine("MQTT client subscribed to topics.");
+
+            // The response contains additional data sent by the server after subscribing.
+            response.DumpToConsole();
+        }
+    }
+
     public static async Task Subscribe_Topic()
     {
         /*
@@ -63,14 +156,16 @@ public static class Client_Subscribe_Samples
 
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
-            var mqttClientOptions = new MqttClientOptionsBuilder()
-                .WithTcpServer("broker.hivemq.com")
-                .Build();
+            var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("broker.hivemq.com").Build();
 
             await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
 
             var mqttSubscribeOptions = mqttFactory.CreateSubscribeOptionsBuilder()
-                .WithTopicFilter(f => { f.WithTopic("mqttnet/samples/topic/1"); })
+                .WithTopicFilter(
+                    f =>
+                    {
+                        f.WithTopic("mqttnet/samples/topic/1");
+                    })
                 .Build();
 
             var response = await mqttClient.SubscribeAsync(mqttSubscribeOptions, CancellationToken.None);

Samples/Diagnostics/Logger_Samples.cs

@@ -8,7 +8,6 @@
 
 using System.Text;
 using MQTTnet.Diagnostics;
-using MQTTnet.Samples.Shared;
 
 namespace MQTTnet.Samples.Diagnostics;
 
@@ -23,7 +22,9 @@ public static class Logger_Samples
 
         var mqttFactory = new MqttFactory(new MyLogger());
 
-        var mqttClientOptions = mqttFactory.CreateClientOptionsBuilder().WithTcpServer("broker.hivemq.com").Build();
+        var mqttClientOptions = mqttFactory.CreateClientOptionsBuilder()
+            .WithTcpServer("broker.hivemq.com")
+            .Build();
 
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
@@ -31,31 +32,13 @@ public static class Logger_Samples
 
             Console.WriteLine("MQTT client is connected.");
 
-            var mqttClientDisconnectOptions = mqttFactory.CreateClientDisconnectOptionsBuilder().Build();
+            var mqttClientDisconnectOptions = mqttFactory.CreateClientDisconnectOptionsBuilder()
+                .Build();
 
             await mqttClient.DisconnectAsync(mqttClientDisconnectOptions, CancellationToken.None);
         }
     }
 
-    public static async Task Log_To_Console()
-    {
-        /*
-       * This sample covers the creation of a custom logger which is used to log to the console.
-       */
-
-        var mqttFactory = new MqttFactory(new ConsoleLogger());
-
-        var mqttClientOptions = mqttFactory.CreateClientOptionsBuilder().WithTcpServer("broker.hivemq.com").Build();
-
-        using (var mqttClient = mqttFactory.CreateMqttClient())
-        {
-            await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
-
-            Console.WriteLine("MQTT client is connected. Press any key to exit.");
-            Console.ReadKey(true);
-        }
-    }
-
     public static async Task Use_Event_Logger()
     {
         /*
@@ -81,7 +64,9 @@ public static class Logger_Samples
 
         var mqttFactory = new MqttFactory(mqttEventLogger);
 
-        var mqttClientOptions = mqttFactory.CreateClientOptionsBuilder().WithTcpServer("broker.hivemq.com").Build();
+        var mqttClientOptions = mqttFactory.CreateClientOptionsBuilder()
+            .WithTcpServer("broker.hivemq.com")
+            .Build();
 
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
@@ -89,7 +74,8 @@ public static class Logger_Samples
 
             Console.WriteLine("MQTT client is connected.");
 
-            var mqttClientDisconnectOptions = mqttFactory.CreateClientDisconnectOptionsBuilder().Build();
+            var mqttClientDisconnectOptions = mqttFactory.CreateClientDisconnectOptionsBuilder()
+                .Build();
 
             await mqttClient.DisconnectAsync(mqttClientDisconnectOptions, CancellationToken.None);
         }
@@ -97,7 +83,7 @@ public static class Logger_Samples
 
     sealed class MyLogger : IMqttNetLogger
     {
-        public bool IsEnabled { get; } = true;
+        public bool IsEnabled { get; set; } = true;
 
         public void Publish(MqttNetLogLevel logLevel, string source, string message, object[] parameters, Exception exception)
         {

Samples/Helpers/ObjectExtensions.cs

@@ -4,7 +4,7 @@
 
 using System.Text.Json;
 
-namespace MQTTnet.Samples.Shared;
+namespace MQTTnet.Samples.Helpers;
 
 internal static class ObjectExtensions
 {

Samples/MQTTnet.Samples.csproj

@@ -9,12 +9,10 @@
         <DisableImplicitAspNetCoreAnalyzers>true</DisableImplicitAspNetCoreAnalyzers>
         <EnableNETAnalyzers>false</EnableNETAnalyzers>
         <EnforceCodeStyleInBuild>false</EnforceCodeStyleInBuild>
-        <NoWarn>1591</NoWarn>
+        <NoWarn>1591;NETSDK1138</NoWarn>
     </PropertyGroup>
 
     <ItemGroup>
-        <PackageReference Include="Microsoft.CodeAnalysis.Compilers" Version="4.0.1" />
-        <PackageReference Include="Microsoft.Net.Compilers" Version="4.0.1" />
 
         <ProjectReference Include="..\Source\MQTTnet.AspnetCore\MQTTnet.AspNetCore.csproj" />
         <ProjectReference Include="..\Source\MQTTnet.Extensions.ManagedClient\MQTTnet.Extensions.ManagedClient.csproj" />

Samples/Program.cs

@@ -8,7 +8,6 @@ Console.WriteLine("Welcome to MQTTnet samples!");
 Console.WriteLine();
 
 var sampleClasses = Assembly.GetExecutingAssembly().GetExportedTypes().OrderBy(c => c.Name).ToList();
-sampleClasses.RemoveAll(c => c.Namespace.Contains(".Shared"));
 
 var index = 0;
 foreach (var sampleClass in sampleClasses)

Samples/Server/Server_Intercepting_Samples.cs

@@ -0,0 +1,47 @@
+// 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
+// ReSharper disable EmptyConstructor
+// ReSharper disable MemberCanBeMadeStatic.Local
+
+using MQTTnet.Internal;
+using MQTTnet.Server;
+
+namespace MQTTnet.Samples.Server;
+
+public static class Server_Intercepting_Samples
+{
+    public static async Task Intercept_Application_Messages()
+    {
+        /*
+         * This sample starts a simple MQTT server which manipulate all processed application messages.
+         * Please see _Server_Simple_Samples_ for more details on how to start a server.
+         */
+
+        var mqttFactory = new MqttFactory();
+        var mqttServerOptions = new MqttServerOptionsBuilder().WithDefaultEndpoint().Build();
+
+        using (var mqttServer = mqttFactory.CreateMqttServer(mqttServerOptions))
+        {
+            mqttServer.InterceptingPublishAsync += args =>
+            {
+                // Here we only change the topic of the received application message.
+                // but also changing the payload etc. is required. Changing the QoS after
+                // transmitting is not supported and makes no sense at all.
+                args.ApplicationMessage.Topic += "/manipulated";
+
+                return CompletedTask.Instance;
+            };
+
+            await mqttServer.StartAsync();
+
+            Console.WriteLine("Press Enter to exit.");
+            Console.ReadLine();
+            await mqttServer.StopAsync();
+        }
+    }
+}

Samples/Server/Server_Simple_Samples.cs

@@ -6,8 +6,8 @@
 // ReSharper disable UnusedMember.Global
 // ReSharper disable InconsistentNaming
 
+using MQTTnet.Diagnostics;
 using MQTTnet.Protocol;
-using MQTTnet.Samples.Shared;
 using MQTTnet.Server;
 
 namespace MQTTnet.Samples.Server;
@@ -170,4 +170,50 @@ public static class Server_Simple_Samples
         await server.StartAsync();
         return server;
     }
+
+    class ConsoleLogger : IMqttNetLogger
+    {
+        readonly object _consoleSyncRoot = new();
+
+        public bool IsEnabled => true;
+
+        public void Publish(MqttNetLogLevel logLevel, string source, string message, object[]? parameters, Exception? exception)
+        {
+            var foregroundColor = ConsoleColor.White;
+            switch (logLevel)
+            {
+                case MqttNetLogLevel.Verbose:
+                    foregroundColor = ConsoleColor.White;
+                    break;
+
+                case MqttNetLogLevel.Info:
+                    foregroundColor = ConsoleColor.Green;
+                    break;
+
+                case MqttNetLogLevel.Warning:
+                    foregroundColor = ConsoleColor.DarkYellow;
+                    break;
+
+                case MqttNetLogLevel.Error:
+                    foregroundColor = ConsoleColor.Red;
+                    break;
+            }
+
+            if (parameters?.Length > 0)
+            {
+                message = string.Format(message, parameters);
+            }
+
+            lock (_consoleSyncRoot)
+            {
+                Console.ForegroundColor = foregroundColor;
+                Console.WriteLine(message);
+
+                if (exception != null)
+                {
+                    Console.WriteLine(exception);
+                }
+            }
+        }
+    }
 }

Samples/Shared/ConsoleLogger.cs

@@ -1,53 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using MQTTnet.Diagnostics;
-
-namespace MQTTnet.Samples.Shared;
-
-public sealed class ConsoleLogger : IMqttNetLogger
-{
-    readonly object _consoleSyncRoot = new();
-
-    public bool IsEnabled => true;
-
-    public void Publish(MqttNetLogLevel logLevel, string source, string message, object[]? parameters, Exception? exception)
-    {
-        var foregroundColor = ConsoleColor.White;
-        switch (logLevel)
-        {
-            case MqttNetLogLevel.Verbose:
-                foregroundColor = ConsoleColor.White;
-                break;
-
-            case MqttNetLogLevel.Info:
-                foregroundColor = ConsoleColor.Green;
-                break;
-
-            case MqttNetLogLevel.Warning:
-                foregroundColor = ConsoleColor.DarkYellow;
-                break;
-
-            case MqttNetLogLevel.Error:
-                foregroundColor = ConsoleColor.Red;
-                break;
-        }
-
-        if (parameters?.Length > 0)
-        {
-            message = string.Format(message, parameters);
-        }
-
-        lock (_consoleSyncRoot)
-        {
-            Console.ForegroundColor = foregroundColor;
-            Console.WriteLine(message);
-
-            if (exception != null)
-            {
-                Console.WriteLine(exception);
-            }
-        }
-    }
-}

Source/MQTTnet.AspNetCore.Tests/MQTTnet.AspNetCore.Tests.csproj

@@ -12,8 +12,6 @@
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.2.0" />
         <PackageReference Include="MSTest.TestAdapter" Version="2.2.10" />
         <PackageReference Include="MSTest.TestFramework" Version="2.2.10" />
-        <PackageReference Include="Microsoft.CodeAnalysis.Compilers" Version="4.0.1" />
-        <PackageReference Include="Microsoft.Net.Compilers" Version="4.0.1" />
     </ItemGroup>
 
     <ItemGroup Condition=" '$(TargetFramework)' == 'netcoreapp3.1' ">

Source/MQTTnet.AspNetCore.Tests/Mockups/ConnectionContextMockup.cs

@@ -1,26 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System.Collections.Generic;
-using System.IO.Pipelines;
-using Microsoft.AspNetCore.Connections;
-using Microsoft.AspNetCore.Http.Features;
-
-namespace MQTTnet.AspNetCore.Tests.Mockups
-{
-    public class ConnectionContextMockup : ConnectionContext
-    {
-        public override string ConnectionId { get; set; }
-
-        public override IFeatureCollection Features { get; }
-
-        public override IDictionary<object, object> Items { get; set; }
-        public override IDuplexPipe Transport { get; set; }
-
-        public ConnectionContextMockup()
-        {
-            //Transport = new DefaultConnectionContext
-        }
-    }
-}

Source/MQTTnet.AspNetCore.Tests/Mockups/ConnectionHandlerMockup.cs

@@ -2,20 +2,24 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using Microsoft.AspNetCore.Connections;
-using MQTTnet.Adapter;
-using MQTTnet.Formatter;
-using MQTTnet.Server;
 using System;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Connections;
+using MQTTnet.Adapter;
 using MQTTnet.Diagnostics;
+using MQTTnet.Formatter;
+using MQTTnet.Server;
 
 namespace MQTTnet.AspNetCore.Tests.Mockups
 {
-    public class ConnectionHandlerMockup: IMqttServerAdapter
+    public sealed class ConnectionHandlerMockup : IMqttServerAdapter
     {
-        public TaskCompletionSource<MqttConnectionContext> Context { get; } = new TaskCompletionSource<MqttConnectionContext>();
         public Func<IMqttChannelAdapter, Task> ClientHandler { get; set; }
+        public TaskCompletionSource<MqttConnectionContext> Context { get; } = new TaskCompletionSource<MqttConnectionContext>();
+
+        public void Dispose()
+        {
+        }
 
         public async Task OnConnectedAsync(ConnectionContext connection)
         {
@@ -42,9 +46,5 @@ namespace MQTTnet.AspNetCore.Tests.Mockups
         {
             return Task.CompletedTask;
         }
-
-        public void Dispose()
-        {
-        }
     }
-}
+}

Source/MQTTnet.AspNetCore.Tests/Mockups/DuplexPipeMockup.cs

@@ -6,7 +6,7 @@ using System.IO.Pipelines;
 
 namespace MQTTnet.AspNetCore.Tests.Mockups
 {
-    public class DuplexPipeMockup : IDuplexPipe
+    public sealed class DuplexPipeMockup : IDuplexPipe
     {
         public DuplexPipeMockup()
         {
@@ -20,9 +20,8 @@ namespace MQTTnet.AspNetCore.Tests.Mockups
 
         PipeWriter IDuplexPipe.Output => Send.Writer;
 
+        public Pipe Receive { get; } 
 
-        public Pipe Receive { get; set; } 
-
-        public Pipe Send { get; set; }
+        public Pipe Send { get; }
     }
 }

Source/MQTTnet.AspNetCore.Tests/Mockups/LimitedMemoryPool.cs

@@ -6,7 +6,7 @@ using System.Buffers;
 
 namespace MQTTnet.AspNetCore.Tests.Mockups
 {
-    public class LimitedMemoryPool : MemoryPool<byte>
+    public sealed class LimitedMemoryPool : MemoryPool<byte>
     {
         protected override void Dispose(bool disposing)
         {

Source/MQTTnet.AspNetCore.Tests/Mockups/MemoryOwner.cs

@@ -7,9 +7,9 @@ using System.Buffers;
 
 namespace MQTTnet.AspNetCore.Tests.Mockups
 {
-    public class MemoryOwner : IMemoryOwner<byte>
+    public sealed class MemoryOwner : IMemoryOwner<byte>
     {
-        private readonly byte[] _raw;
+        readonly byte[] _raw;
 
         public MemoryOwner(int size)
         {
@@ -27,11 +27,11 @@ namespace MQTTnet.AspNetCore.Tests.Mockups
             Memory = _raw;
         }
 
+        public Memory<byte> Memory { get; }
+
         public void Dispose()
         {
             ArrayPool<byte>.Shared.Return(_raw);
         }
-
-        public Memory<byte> Memory { get; }
     }
 }

Source/MQTTnet.AspNetCore.Tests/MqttConnectionContextTest.cs

@@ -2,44 +2,29 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using Microsoft.AspNetCore.Builder;
-using Microsoft.AspNetCore.Connections;
-using Microsoft.AspNetCore.Hosting;
-using Microsoft.Extensions.DependencyInjection;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-
 using System;
 using System.Net;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Connections;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Adapter;
 using MQTTnet.AspNetCore.Tests.Mockups;
+using MQTTnet.Client;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
 using MQTTnet.Packets;
-using MQTTnet.Client;
 using MQTTnet.Protocol;
-using MQTTnet.Tests.Extensions;
+using MQTTnet.Tests.Helpers;
 
 namespace MQTTnet.AspNetCore.Tests
 {
     [TestClass]
     public class MqttConnectionContextTest
     {
-        [TestMethod]
-        public async Task TestReceivePacketAsyncThrowsWhenReaderCompleted()
-        {
-            var serializer = new MqttPacketFormatterAdapter(MqttProtocolVersion.V311, new MqttBufferWriter(4096, 65535));
-            var pipe = new DuplexPipeMockup();
-            var connection = new DefaultConnectionContext();
-            connection.Transport = pipe;
-            var ctx = new MqttConnectionContext(serializer, connection);
-
-            pipe.Receive.Writer.Complete();
-
-            await Assert.ThrowsExceptionAsync<MqttCommunicationException>(() => ctx.ReceivePacketAsync(CancellationToken.None));
-        }
-
         [TestMethod]
         public async Task TestCorruptedConnectPacket()
         {
@@ -49,13 +34,43 @@ namespace MQTTnet.AspNetCore.Tests
             var connection = new DefaultConnectionContext();
             connection.Transport = pipe;
             var ctx = new MqttConnectionContext(serializer, connection);
-            
-            await pipe.Receive.Writer.WriteAsync(writer.AddMqttHeader(MqttControlPacketType.Connect, new byte[0]));
+
+            await pipe.Receive.Writer.WriteAsync(writer.AddMqttHeader(MqttControlPacketType.Connect, Array.Empty<byte>()));
 
             await Assert.ThrowsExceptionAsync<MqttProtocolViolationException>(() => ctx.ReceivePacketAsync(CancellationToken.None));
 
             // the first exception should complete the pipes so if someone tries to use the connection after that it should throw immidiatly
-            await Assert.ThrowsExceptionAsync<InvalidOperationException>(() =>  ctx.ReceivePacketAsync(CancellationToken.None));
+            await Assert.ThrowsExceptionAsync<InvalidOperationException>(() => ctx.ReceivePacketAsync(CancellationToken.None));
+        }
+
+        [TestMethod]
+        public async Task TestEndpoint()
+        {
+            var mockup = new ConnectionHandlerMockup();
+
+
+            using (var host = new WebHostBuilder().UseKestrel(kestrel => kestrel.ListenLocalhost(1883, listener => listener.Use((ctx, next) => mockup.OnConnectedAsync(ctx))))
+                       .UseStartup<Startup>()
+                       .ConfigureServices(
+                           (hostContext, services) =>
+                           {
+                               services.AddHostedMqttServer(o => o.WithoutDefaultEndpoint());
+                               services.AddSingleton<IMqttServerAdapter>(mockup);
+                           })
+                       .Build())
+
+            using (var client = new MqttFactory().CreateMqttClient())
+            {
+                host.Start();
+                await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost").Build(), CancellationToken.None);
+
+                var ctx = await mockup.Context.Task;
+#if NETCOREAPP3_1
+                var ep = IPEndPoint.Parse(ctx.Endpoint);
+                Assert.IsNotNull(ep);
+#endif
+                Assert.IsNotNull(ctx);
+            }
         }
 
         // COMMENTED OUT DUE TO DEAD LOCK? OR VERY VERY SLOW PERFORMANCE ON LOCAL DEV MACHINE. TEST WAS STILL RUNNING AFTER SEVERAL MINUTES!
@@ -78,7 +93,7 @@ namespace MQTTnet.AspNetCore.Tests
 
         //    await Task.WhenAll(tasks).ConfigureAwait(false);
         //}
-        
+
         [TestMethod]
         public async Task TestLargePacket()
         {
@@ -94,43 +109,25 @@ namespace MQTTnet.AspNetCore.Tests
             Assert.IsTrue(readResult.Buffer.Length > 20000);
         }
 
-        private class Startup 
+        [TestMethod]
+        public async Task TestReceivePacketAsyncThrowsWhenReaderCompleted()
+        {
+            var serializer = new MqttPacketFormatterAdapter(MqttProtocolVersion.V311, new MqttBufferWriter(4096, 65535));
+            var pipe = new DuplexPipeMockup();
+            var connection = new DefaultConnectionContext();
+            connection.Transport = pipe;
+            var ctx = new MqttConnectionContext(serializer, connection);
+
+            pipe.Receive.Writer.Complete();
+
+            await Assert.ThrowsExceptionAsync<MqttCommunicationException>(() => ctx.ReceivePacketAsync(CancellationToken.None));
+        }
+
+        class Startup
         {
             public void Configure(IApplicationBuilder app)
-            { 
+            {
             }
         }
-
-        [TestMethod]
-        public async Task TestEndpoint()
-        {
-            var mockup = new ConnectionHandlerMockup();
-
-
-            using (var host = new WebHostBuilder()
-                .UseKestrel(kestrel => kestrel.ListenLocalhost(1883, listener => listener.Use((ctx, next) => mockup.OnConnectedAsync(ctx))))
-                .UseStartup<Startup>()
-                .ConfigureServices((hostContext, services) =>
-                {
-                    services.AddHostedMqttServer(o => o.WithoutDefaultEndpoint());
-                    services.AddSingleton<IMqttServerAdapter>(mockup);
-                })
-                .Build())
-                
-            using (var client = new MqttFactory().CreateMqttClient())
-            {
-                host.Start();
-                await client.ConnectAsync(new MqttClientOptionsBuilder()
-                    .WithTcpServer("localhost")
-                    .Build(), CancellationToken.None);
-
-                var ctx = await mockup.Context.Task;
-#if NETCOREAPP3_1
-                var ep = IPEndPoint.Parse(ctx.Endpoint);
-                Assert.IsNotNull(ep);
-#endif
-                Assert.IsNotNull(ctx);
-            }               
-        }
     }
-}
+}

Source/MQTTnet.AspNetCore.Tests/ReaderExtensionsTest.cs

@@ -12,7 +12,7 @@ using MQTTnet.Packets;
 namespace MQTTnet.AspNetCore.Tests
 {
     [TestClass]
-    public class ReaderExtensionsTest
+    public sealed class ReaderExtensionsTest
     {
         [TestMethod]
         public void TestTryDeserialize()

Source/MQTTnet.AspTestApp/MQTTnet.AspTestApp.csproj

@@ -8,17 +8,15 @@
         <DisableImplicitAspNetCoreAnalyzers>true</DisableImplicitAspNetCoreAnalyzers>
         <EnableNETAnalyzers>false</EnableNETAnalyzers>
         <EnforceCodeStyleInBuild>false</EnforceCodeStyleInBuild>
+        <NoWarn>1591;NETSDK1138</NoWarn>
     </PropertyGroup>
 
     <ItemGroup>
-        <ProjectReference Include="..\..\Source\MQTTnet.AspnetCore\MQTTnet.AspNetCore.csproj"/>
-
-        <PackageReference Include="Microsoft.CodeAnalysis.Compilers" Version="4.0.1" />
-        <PackageReference Include="Microsoft.Net.Compilers" Version="4.0.1" />
+        <ProjectReference Include="..\..\Source\MQTTnet.AspnetCore\MQTTnet.AspNetCore.csproj" />
     </ItemGroup>
 
     <ItemGroup>
-        <Folder Include="wwwroot\"/>
+        <Folder Include="wwwroot\" />
     </ItemGroup>
 
 </Project>

Source/MQTTnet.AspnetCore/MQTTnet.AspNetCore.csproj

@@ -32,7 +32,8 @@
         <DisableImplicitAspNetCoreAnalyzers>true</DisableImplicitAspNetCoreAnalyzers>
         <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
         <GenerateDocumentationFile>true</GenerateDocumentationFile>
-        <NoWarn>1591</NoWarn>
+        <NoWarn>1591;NETSDK1138</NoWarn>
+        <LangVersion>7.3</LangVersion>
     </PropertyGroup>
 
     <ItemGroup>

Source/MQTTnet.AspnetCore/MqttConnectionContext.cs

@@ -2,38 +2,59 @@
 // 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.IO.Pipelines;
+using System.Net;
+using System.Security.Cryptography.X509Certificates;
+using System.Threading;
+using System.Threading.Tasks;
 using Microsoft.AspNetCore.Connections;
 using Microsoft.AspNetCore.Http.Connections.Features;
+using Microsoft.AspNetCore.Http.Features;
 using MQTTnet.Adapter;
 using MQTTnet.AspNetCore.Client.Tcp;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
-using MQTTnet.Packets;
-using System;
-using System.IO.Pipelines;
-using System.Security.Cryptography.X509Certificates;
-using System.Threading;
-using System.Threading.Tasks;
 using MQTTnet.Internal;
+using MQTTnet.Packets;
 
 namespace MQTTnet.AspNetCore
 {
     public sealed class MqttConnectionContext : IMqttChannelAdapter
     {
+        readonly ConnectionContext _connection;
         readonly AsyncLock _writerLock = new AsyncLock();
-        
+
         PipeReader _input;
         PipeWriter _output;
-        
+
         public MqttConnectionContext(MqttPacketFormatterAdapter packetFormatterAdapter, ConnectionContext connection)
         {
             PacketFormatterAdapter = packetFormatterAdapter ?? throw new ArgumentNullException(nameof(packetFormatterAdapter));
-            Connection = connection ?? throw new ArgumentNullException(nameof(connection));
+            _connection = connection ?? throw new ArgumentNullException(nameof(connection));
 
-            if (Connection.Transport != null)
+            _input = connection.Transport.Input;
+            _output = connection.Transport.Output;
+        }
+
+        public long BytesReceived { get; private set; }
+
+        public long BytesSent { get; private set; }
+
+        public X509Certificate2 ClientCertificate
+        {
+            get
             {
-                _input = Connection.Transport.Input;
-                _output = Connection.Transport.Output;
+                // mqtt over tcp
+                var tlsFeature = _connection.Features.Get<ITlsConnectionFeature>();
+                if (tlsFeature != null)
+                {
+                    return tlsFeature.ClientCertificate;
+                }
+
+                // mqtt over websocket
+                var httpFeature = _connection.Features.Get<IHttpContextFeature>();
+                return httpFeature?.HttpContext?.Connection.ClientCertificate;
             }
         }
 
@@ -41,47 +62,59 @@ namespace MQTTnet.AspNetCore
         {
             get
             {
-#if NETCOREAPP3_1
-                if (Connection?.RemoteEndPoint != null)
+                // mqtt over tcp 
+#if NETCOREAPP3_1_OR_GREATER
+                if (_connection.RemoteEndPoint != null)
                 {
-                    return Connection.RemoteEndPoint.ToString();
+                    return _connection.RemoteEndPoint.ToString();
                 }
 #endif
-                var connection = Http?.HttpContext?.Connection;
-                if (connection == null)
+                // mqtt over websocket
+                var httpFeature = _connection.Features.Get<IHttpConnectionFeature>();
+                if (httpFeature?.RemoteIpAddress != null)
                 {
-                    return Connection.ConnectionId;
+                    return new IPEndPoint(httpFeature.RemoteIpAddress, httpFeature.RemotePort).ToString();
                 }
 
-                return $"{connection.RemoteIpAddress}:{connection.RemotePort}";
+                return null;
             }
         }
 
-        public bool IsSecureConnection => Http?.HttpContext?.Request?.IsHttps ?? false;
-
-        public X509Certificate2 ClientCertificate => Http?.HttpContext?.Connection?.ClientCertificate;
-
-        public ConnectionContext Connection { get; }
-        
-        public MqttPacketFormatterAdapter PacketFormatterAdapter { get; }
-
-        public long BytesSent { get; set; }
-
-        public long BytesReceived { get; set; }
-
         public bool IsReadingPacket { get; private set; }
 
-        IHttpContextFeature Http => Connection.Features.Get<IHttpContextFeature>();
+        public bool IsSecureConnection
+        {
+            get
+            {
+                // mqtt over tcp
+                var tlsFeature = _connection.Features.Get<ITlsConnectionFeature>();
+                if (tlsFeature != null)
+                {
+                    return true;
+                }
+
+                // mqtt over websocket
+                var httpFeature = _connection.Features.Get<IHttpContextFeature>();
+                if (httpFeature?.HttpContext != null)
+                {
+                    return httpFeature.HttpContext.Request.IsHttps;
+                }
+
+                return false;
+            }
+        }
+
+        public MqttPacketFormatterAdapter PacketFormatterAdapter { get; }
 
         public async Task ConnectAsync(CancellationToken cancellationToken)
         {
-            if (Connection is TcpConnection tcp && !tcp.IsConnected)
+            if (_connection is TcpConnection tcp && !tcp.IsConnected)
             {
                 await tcp.StartAsync().ConfigureAwait(false);
             }
 
-            _input = Connection.Transport.Input;
-            _output = Connection.Transport.Output;
+            _input = _connection.Transport.Input;
+            _output = _connection.Transport.Output;
         }
 
         public Task DisconnectAsync(CancellationToken cancellationToken)
@@ -92,16 +125,19 @@ namespace MQTTnet.AspNetCore
             return Task.CompletedTask;
         }
 
+        public void Dispose()
+        {
+            _writerLock.Dispose();
+        }
+
         public async Task<MqttPacket> ReceivePacketAsync(CancellationToken cancellationToken)
         {
-            var input = Connection.Transport.Input;
-
             try
             {
                 while (!cancellationToken.IsCancellationRequested)
                 {
                     ReadResult readResult;
-                    var readTask = input.ReadAsync(cancellationToken);
+                    var readTask = _input.ReadAsync(cancellationToken);
                     if (readTask.IsCompleted)
                     {
                         readResult = readTask.Result;
@@ -141,15 +177,15 @@ namespace MQTTnet.AspNetCore
                         // The buffer was sliced up to where it was consumed, so we can just advance to the start.
                         // We mark examined as buffer.End so that if we didn't receive a full frame, we'll wait for more data
                         // before yielding the read again.
-                        input.AdvanceTo(consumed, observed);
+                        _input.AdvanceTo(consumed, observed);
                     }
                 }
             }
-            catch (Exception e)
+            catch (Exception exception)
             {
                 // completing the channel makes sure that there is no more data read after a protocol error
-                _input?.Complete(e);
-                _output?.Complete(e);
+                _input?.Complete(exception);
+                _output?.Complete(exception);
                 throw;
             }
             finally
@@ -169,25 +205,35 @@ namespace MQTTnet.AspNetCore
 
         public async Task SendPacketAsync(MqttPacket packet, CancellationToken cancellationToken)
         {
-            var formatter = PacketFormatterAdapter;
-            
-            using (await _writerLock.WaitAsync(cancellationToken).ConfigureAwait(false))
+            using (await _writerLock.EnterAsync(cancellationToken).ConfigureAwait(false))
             {
-                var buffer = formatter.Encode(packet);
-                var msg = buffer.Join().AsMemory();
-                var output = _output;
-                var result = await output.WriteAsync(msg, cancellationToken).ConfigureAwait(false);
-                if (result.IsCompleted)
+                try
                 {
-                    BytesSent += msg.Length;
-                }
+                    var buffer = PacketFormatterAdapter.Encode(packet);
 
-                PacketFormatterAdapter.Cleanup();
+                    WritePacketBuffer(_output, buffer);
+                    await _output.FlushAsync(cancellationToken).ConfigureAwait(false);
+
+                    BytesSent += buffer.Length;
+                }
+                finally
+                {
+                    PacketFormatterAdapter.Cleanup();
+                }
             }
         }
 
-        public void Dispose()
+        static void WritePacketBuffer(PipeWriter output, MqttPacketBuffer buffer)
         {
+            // copy MqttPacketBuffer's Packet and Payload to the same buffer block of PipeWriter
+            // MqttPacket will be transmitted within the bounds of a WebSocket frame after PipeWriter.FlushAsync
+
+            var span = output.GetSpan(buffer.Length);
+
+            buffer.Packet.AsSpan().CopyTo(span);
+            buffer.Payload.AsSpan().CopyTo(span.Slice(buffer.Packet.Count));
+
+            output.Advance(buffer.Length);
         }
     }
-}
+}

Source/MQTTnet.AspnetCore/ReaderExtensions.cs

@@ -2,21 +2,23 @@
 // 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.Buffers;
 using MQTTnet.Adapter;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
 using MQTTnet.Packets;
+using System;
+using System.Buffers;
+using System.Linq;
+using System.Runtime.InteropServices;
 
 namespace MQTTnet.AspNetCore
 {
     public static class ReaderExtensions
     {
-        public static bool TryDecode(this MqttPacketFormatterAdapter formatter, 
-            in ReadOnlySequence<byte> input, 
-            out MqttPacket packet, 
-            out SequencePosition consumed, 
+        public static bool TryDecode(this MqttPacketFormatterAdapter formatter,
+            in ReadOnlySequence<byte> input,
+            out MqttPacket packet,
+            out SequencePosition consumed,
             out SequencePosition observed,
             out int bytesRead)
         {
@@ -33,22 +35,22 @@ namespace MQTTnet.AspNetCore
                 return false;
             }
 
-            var fixedHeader = copy.First.Span[0];
-            if (!TryReadBodyLength(ref copy, out int headerLength, out var bodyLength))
+            if (!TryReadBodyLength(ref copy, out var headerLength, out var bodyLength))
             {
                 return false;
             }
 
+            var fixedHeader = copy.First.Span[0];
+            copy = copy.Slice(headerLength);
             if (copy.Length < bodyLength)
             {
                 return false;
             }
 
             var bodySlice = copy.Slice(0, bodyLength);
-            var buffer = bodySlice.GetMemory().ToArray();
-            
-            var receivedMqttPacket = new ReceivedMqttPacket(fixedHeader, new ArraySegment<byte>(buffer, 0, buffer.Length), buffer.Length + 2);
-
+            var bodySegment = GetArraySegment(ref bodySlice); 
+    
+            var receivedMqttPacket = new ReceivedMqttPacket(fixedHeader, bodySegment, headerLength + bodyLength);
             if (formatter.ProtocolVersion == MqttProtocolVersion.Unknown)
             {
                 formatter.DetectProtocolVersion(receivedMqttPacket);
@@ -61,18 +63,41 @@ namespace MQTTnet.AspNetCore
             return true;
         }
 
-        static ReadOnlyMemory<byte> GetMemory(this in ReadOnlySequence<byte> input)
+        static ArraySegment<byte> GetArraySegment(ref ReadOnlySequence<byte> input)
         {
-            if (input.IsSingleSegment)
+            if (input.IsSingleSegment && MemoryMarshal.TryGetArray(input.First, out var segment))
             {
-                return input.First;
+                return segment;
             }
 
             // Should be rare
-            return input.ToArray();
+            var array = input.ToArray();
+            return new ArraySegment<byte>(array);
         }
 
         static bool TryReadBodyLength(ref ReadOnlySequence<byte> input, out int headerLength, out int bodyLength)
+        {
+            var valueSequence = input.Slice(0, Math.Min(5, input.Length));
+            if (valueSequence.IsSingleSegment)
+            {
+                var valueSpan =
+#if NET5_0_OR_GREATER
+                    valueSequence.FirstSpan;
+#else
+                    valueSequence.First.Span;
+#endif
+                return TryReadBodyLength(valueSpan, out headerLength, out bodyLength);
+            }
+            else
+            {
+                Span<byte> valueSpan = stackalloc byte[8];
+                valueSequence.CopyTo(valueSpan);
+                valueSpan = valueSpan.Slice(0, (int)valueSequence.Length);
+                return TryReadBodyLength(valueSpan, out headerLength, out bodyLength);
+            }
+        }
+
+        static bool TryReadBodyLength(ReadOnlySpan<byte> span, out int headerLength, out int bodyLength)
         {
             // Alorithm taken from https://docs.oasis-open.org/mqtt/mqtt/v3.1.1/errata01/os/mqtt-v3.1.1-errata01-os-complete.html.
             var multiplier = 1;
@@ -81,33 +106,35 @@ namespace MQTTnet.AspNetCore
             var index = 1;
             headerLength = 0;
             bodyLength = 0;
-            
-            var temp = input.Slice(0, Math.Min(5, input.Length)).GetMemory().Span;
 
             do
             {
-                if (index == temp.Length)
+                if (index == span.Length)
                 {
                     return false;
                 }
 
-                encodedByte = temp[index];
+                encodedByte = span[index];
                 index++;
 
                 value += (byte)(encodedByte & 127) * multiplier;
                 if (multiplier > 128 * 128 * 128)
                 {
-                    throw new MqttProtocolViolationException($"Remaining length is invalid (Data={string.Join(",", temp.Slice(1, index).ToArray())}).");
+                    ThrowProtocolViolationException(span, index);
                 }
 
                 multiplier *= 128;
             } while ((encodedByte & 128) != 0);
 
-            input = input.Slice(index);
-
             headerLength = index;
             bodyLength = value;
             return true;
         }
+
+
+        static void ThrowProtocolViolationException(ReadOnlySpan<byte> valueSpan, int index)
+        {
+            throw new MqttProtocolViolationException($"Remaining length is invalid (Data={string.Join(",", valueSpan.Slice(1, index).ToArray())}).");
+        }
     }
 }

Source/MQTTnet.Benchmarks/AsyncLockBenchmark.cs

@@ -0,0 +1,66 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Jobs;
+using MQTTnet.Internal;
+
+namespace MQTTnet.Benchmarks
+{
+    [SimpleJob(RuntimeMoniker.Net60)]
+    [MemoryDiagnoser]
+    public class AsyncLockBenchmark : BaseBenchmark
+    {
+        [Benchmark]
+        public async Task Synchronize_100_Tasks()
+        {
+            const int tasksCount = 100;
+
+            var tasks = new Task[tasksCount];
+            var asyncLock = new AsyncLock();
+            var globalI = 0;
+
+            for (var i = 0; i < tasksCount; i++)
+            {
+                tasks[i] = Task.Run(
+                    async () =>
+                    {
+                        using (await asyncLock.EnterAsync().ConfigureAwait(false))
+                        {
+                            var localI = globalI;
+                            await Task.Delay(5).ConfigureAwait(false); // Increase the chance for wrong data.
+                            localI++;
+                            globalI = localI;
+                        }
+                    });
+            }
+
+            await Task.WhenAll(tasks).ConfigureAwait(false);
+
+            if (globalI != tasksCount)
+            {
+                throw new Exception($"Code is broken ({globalI})!");
+            }
+        }
+        
+        [Benchmark]
+        public async Task Wait_100_000_Times()
+        {
+            var asyncLock = new AsyncLock();
+
+            using (var cancellationToken = new CancellationTokenSource())
+            {
+                for (var i = 0; i < 100000; i++)
+                {
+                    using (await asyncLock.EnterAsync(cancellationToken.Token).ConfigureAwait(false))
+                    {
+                    }
+                }
+            }
+        }
+    }
+}

Source/MQTTnet.Benchmarks/BaseBenchmark.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.
+
 namespace MQTTnet.Benchmarks
 {
     public abstract class BaseBenchmark

Source/MQTTnet.Benchmarks/ChannelAdapterBenchmark.cs

@@ -2,54 +2,25 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using BenchmarkDotNet.Attributes;
-using MQTTnet.Adapter;
-using MQTTnet.Internal;
-using MQTTnet.Packets;
 using System;
 using System.IO;
 using System.Threading;
+using BenchmarkDotNet.Attributes;
+using MQTTnet.Adapter;
 using MQTTnet.Diagnostics;
 using MQTTnet.Formatter;
+using MQTTnet.Packets;
 using MQTTnet.Tests.Mockups;
 
 namespace MQTTnet.Benchmarks
 {
     [MemoryDiagnoser]
-    public sealed class ChannelAdapterBenchmark
+    public sealed class ChannelAdapterBenchmark : BaseBenchmark
     {
         MqttChannelAdapter _channelAdapter;
         int _iterations;
-        MemoryStream _stream;
         MqttPublishPacket _packet;
-
-        [GlobalSetup]
-        public void Setup()
-        {
-            _packet = new MqttPublishPacket
-            {
-                Topic = "A"
-            };
-
-            var serializer = new MqttPacketFormatterAdapter(MqttProtocolVersion.V311, new MqttBufferWriter(4096, 65535));
-            
-            var serializedPacket = Join(serializer.Encode(_packet).Join());
-
-            _iterations = 10000;
-
-            _stream = new MemoryStream(_iterations * serializedPacket.Length);
-
-            for (var i = 0; i < _iterations; i++)
-            {
-                _stream.Write(serializedPacket, 0, serializedPacket.Length);
-            }
-
-            _stream.Position = 0;
-
-            var channel = new MemoryMqttChannel(_stream);
-            
-            _channelAdapter = new MqttChannelAdapter(channel, serializer, null, new MqttNetEventLogger());
-        }
+        MemoryStream _stream;
 
         [Benchmark]
         public void Receive_10000_Messages()
@@ -77,6 +48,34 @@ namespace MQTTnet.Benchmarks
             _stream.Position = 0;
         }
 
+        [GlobalSetup]
+        public void Setup()
+        {
+            _packet = new MqttPublishPacket
+            {
+                Topic = "A"
+            };
+
+            var serializer = new MqttPacketFormatterAdapter(MqttProtocolVersion.V311, new MqttBufferWriter(4096, 65535));
+
+            var serializedPacket = Join(serializer.Encode(_packet).Join());
+
+            _iterations = 10000;
+
+            _stream = new MemoryStream(_iterations * serializedPacket.Length);
+
+            for (var i = 0; i < _iterations; i++)
+            {
+                _stream.Write(serializedPacket, 0, serializedPacket.Length);
+            }
+
+            _stream.Position = 0;
+
+            var channel = new MemoryMqttChannel(_stream);
+
+            _channelAdapter = new MqttChannelAdapter(channel, serializer, null, new MqttNetEventLogger());
+        }
+
         static byte[] Join(params ArraySegment<byte>[] chunks)
         {
             var buffer = new MemoryStream();
@@ -88,4 +87,4 @@ namespace MQTTnet.Benchmarks
             return buffer.ToArray();
         }
     }
-}
+}

Source/MQTTnet.Benchmarks/Configurations/AllowNonOptimized.cs

@@ -1,22 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using BenchmarkDotNet.Jobs;
-using BenchmarkDotNet.Validators;
-
-namespace MQTTnet.Benchmarks.Configurations
-{
-    /// <summary>
-    /// this options may be used to run benchmarks in debugmode and attach a performance profiler
-    /// https://benchmarkdotnet.org/Configs/Configs.htm
-    /// </summary>
-    public class AllowNonOptimized : BaseConfig
-    {
-        public AllowNonOptimized()
-        {
-            AddValidator(JitOptimizationsValidator.DontFailOnError); // ALLOW NON-OPTIMIZED DLLS
-            AddJob(Job.InProcess);
-        }
-    }
-}

Source/MQTTnet.Benchmarks/Configurations/BaseConfig.cs

@@ -1,19 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using BenchmarkDotNet.Configs;
-using System.Linq;
-
-namespace MQTTnet.Benchmarks.Configurations
-{
-    public class BaseConfig : ManualConfig
-    {
-        public BaseConfig()
-        {
-            AddLogger(DefaultConfig.Instance.GetLoggers().ToArray()); // manual config has no loggers by default
-            AddExporter(DefaultConfig.Instance.GetExporters().ToArray()); // manual config has no exporters by default
-            AddColumnProvider(DefaultConfig.Instance.GetColumnProviders().ToArray()); // manual config has no columns by default
-        }
-    }
-}

Source/MQTTnet.Benchmarks/Configurations/RuntimeCompareConfig.cs

@@ -1,19 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using BenchmarkDotNet.Environments;
-using BenchmarkDotNet.Jobs;
-using BenchmarkDotNet.Toolchains.CsProj;
-
-namespace MQTTnet.Benchmarks.Configurations
-{
-    public class RuntimeCompareConfig : BaseConfig
-    {
-        public RuntimeCompareConfig()
-        {
-            AddJob(Job.Default.WithRuntime(ClrRuntime.Net48));
-            AddJob(Job.Default.WithRuntime(CoreRuntime.Core50).WithToolchain(CsProjCoreToolchain.NetCoreApp50));
-        }
-    }
-}

Source/MQTTnet.Benchmarks/LoggerBenchmark.cs

@@ -11,7 +11,7 @@ namespace MQTTnet.Benchmarks
     [SimpleJob(RuntimeMoniker.Net60)]
     [RPlotExporter]
     [MemoryDiagnoser]
-    public class LoggerBenchmark
+    public class LoggerBenchmark : BaseBenchmark
     {
         MqttNetNullLogger _nullLogger;
         MqttNetSourceLogger _sourceNullLogger;

Source/MQTTnet.Benchmarks/MQTTnet.Benchmarks.csproj

@@ -1,25 +1,23 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
+        <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
         <OutputType>Exe</OutputType>
         <DebugType>Full</DebugType>
-        <TargetFrameworks>net5.0;net6.0</TargetFrameworks>
+        <TargetFrameworks>net6.0</TargetFrameworks>
         <LangVersion>7.2</LangVersion>
         <IsPackable>false</IsPackable>
         <EnableNETAnalyzers>false</EnableNETAnalyzers>
         <EnforceCodeStyleInBuild>false</EnforceCodeStyleInBuild>
         <DisableImplicitAspNetCoreAnalyzers>true</DisableImplicitAspNetCoreAnalyzers>
+        <NoWarn>1591;NETSDK1138</NoWarn>
     </PropertyGroup>
 
     <ItemGroup>
-        <PackageReference Include="BenchmarkDotNet" Version="0.13.1" />
+        <PackageReference Include="BenchmarkDotNet" Version="0.13.2" />
         <PackageReference Include="Microsoft.AspNetCore" Version="2.2.0" />
     </ItemGroup>
-
-    <ItemGroup Condition="'$(TargetFramework)' != 'net5.0'">
-        <PackageReference Include="System.IO.Pipelines" Version="4.7.2" />
-    </ItemGroup>
-
+    
     <ItemGroup Condition="'$(TargetFramework)' == 'net5.0'">
         <PackageReference Include="System.IO.Pipelines" Version="5.0.0" />
     </ItemGroup>
@@ -30,9 +28,6 @@
 
     <ItemGroup>
         <ProjectReference Include="..\..\Source\MQTTnet.AspnetCore\MQTTnet.AspNetCore.csproj" />
-
-        <PackageReference Include="Microsoft.CodeAnalysis.Compilers" Version="4.0.1" />
-        <PackageReference Include="Microsoft.Net.Compilers" Version="4.0.1" />
         <ProjectReference Include="..\MQTTnet.Tests\MQTTnet.Tests.csproj" />
     </ItemGroup>
 

Source/MQTTnet.Benchmarks/MemoryCopyBenchmark.cs

@@ -0,0 +1,40 @@
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Jobs;
+using System;
+
+
+namespace MQTTnet.Benchmarks
+{
+    [SimpleJob(RuntimeMoniker.Net60)]
+    [RPlotExporter, RankColumn]
+    [MemoryDiagnoser]
+    public class MemoryCopyBenchmark
+    {
+        const int max_length = 1024 * 8;
+        private byte[] source;
+        private byte[] target;
+
+        [Params(64 - 1, 128 - 1, 256 - 1, 512 - 1, 1024 - 1, 2048 - 1, 5096 - 1)]
+        public int Length { get; set; }
+
+        [GlobalSetup]
+        public void Setup()
+        {
+            source = new byte[max_length];
+            target = new byte[max_length];
+        }
+
+        [Benchmark(Baseline = true)]
+        public void Array_Copy()
+        {
+            Array.Copy(source, 0, target, 0, Length);
+        }
+
+        [Benchmark]
+        public void Memory_Copy()
+        {
+            MQTTnet.Internal.MqttMemoryHelper.Copy(source, 0, target, 0, Length);
+        }
+
+    }
+}

Source/MQTTnet.Benchmarks/MessageDeliveryBenchmark.cs

@@ -1,5 +1,8 @@
+// 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 BenchmarkDotNet.Attributes;
-using BenchmarkDotNet.Jobs;
 using MQTTnet.Client;
 using MQTTnet.Server;
 using System;
@@ -8,14 +11,10 @@ using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 
-
 namespace MQTTnet.Benchmarks
 {
-    /// <summary>
-    /// Create a number of topics, publish, subscribe, and wait for response
-    /// </summary>
     [MemoryDiagnoser]
-    public class MessageDeliveryBenchmark
+    public class MessageDeliveryBenchmark : BaseBenchmark
     {
         List<MqttApplicationMessage> _topicPublishMessages;
 

Source/MQTTnet.Benchmarks/MessageProcessingBenchmark.cs

@@ -12,7 +12,7 @@ namespace MQTTnet.Benchmarks
     [SimpleJob(RuntimeMoniker.Net60)]
     [RPlotExporter, RankColumn]
     [MemoryDiagnoser]
-    public class MessageProcessingBenchmark
+    public class MessageProcessingBenchmark : BaseBenchmark
     {
         MqttServer _mqttServer;
         IMqttClient _mqttClient;

Source/MQTTnet.Benchmarks/MessageProcessingMqttConnectionContextBenchmark.cs

@@ -15,7 +15,7 @@ namespace MQTTnet.Benchmarks
 {
     [SimpleJob(RuntimeMoniker.Net60)]
     [MemoryDiagnoser]
-    public class MessageProcessingMqttConnectionContextBenchmark
+    public class MessageProcessingMqttConnectionContextBenchmark : BaseBenchmark
     {
         IWebHost _host;
         IMqttClient _mqttClient;

Source/MQTTnet.Benchmarks/MqttBufferReaderBenchmark.cs

@@ -0,0 +1,43 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Text;
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Jobs;
+using MQTTnet.Formatter;
+
+namespace MQTTnet.Benchmarks
+{
+    [SimpleJob(RuntimeMoniker.Net60)]
+    [MemoryDiagnoser]
+    public class MqttBufferReaderBenchmark
+    {
+        byte[] _buffer;
+        int _bufferLength;
+
+        [GlobalSetup]
+        public void GlobalSetup()
+        {
+            var writer = new MqttBufferWriter(1024, 1024);
+            writer.WriteString("hgfjkdfkjlghfdjghdfljkdfhgdlkjfshgsldkfjghsdflkjghdsflkjhrstiuoghlkfjbhnfbutghjoiöjhklötnbhtroliöuhbjntluiobkjzbhtdrlskbhtruhjkfthgbkftgjhgfiklhotriuöhbjtrsioöbtrsötrhträhtrühjtriüoätrhjtsrölbktrbnhtrulöbionhströloubinströoliubhnsöotrunbtöroisntröointröioujhgötiohjgötorshjnbgtöorihbnjtröoihbjntröobntröoibntrjhötrohjbtröoihntröoibnrtoiöbtrjnboöitrhjtnriohötrhjtöroihjtroöihjtroösibntsroönbotöirsbntöoihjntröoihntroöbtrboöitrnhoöitrhjntröoishbnjtröosbhtröbntriohjtröoijtöoitbjöotibjnhöotirhbjntroöibhnjrtoöibnhtroöibnhtörsbnhtöoirbnhtöroibntoörhjnbträöbtrbträbtrbtirbätrsibohjntrsöiobthnjiohjsrtoib");
+
+            _buffer = writer.GetBuffer();
+            _bufferLength = writer.Length;
+        }
+
+        [Benchmark]
+        public void Use_Span()
+        {
+            var span = _buffer.AsSpan(0, _bufferLength);
+            Encoding.UTF8.GetString(span);
+        }
+        
+        [Benchmark]
+        public void Use_Encoding()
+        {
+            Encoding.UTF8.GetString(_buffer, 0, _bufferLength);
+        }
+    }
+}

Source/MQTTnet.Benchmarks/MqttPacketReaderWriterBenchmark.cs

@@ -1,7 +1,10 @@
+// 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 BenchmarkDotNet.Attributes;
 using BenchmarkDotNet.Jobs;
-using MQTTnet.AspNetCore;
 using MQTTnet.Formatter;
 using MQTTnet.Tests.Mockups;
 
@@ -9,7 +12,7 @@ namespace MQTTnet.Benchmarks
 {
     [SimpleJob(RuntimeMoniker.Net60)]
     [MemoryDiagnoser]
-    public class MqttPacketReaderWriterBenchmark
+    public class MqttPacketReaderWriterBenchmark : BaseBenchmark
     {
         readonly byte[] _demoPayload = new byte[1024];
         

Source/MQTTnet.Benchmarks/MqttTcpChannelBenchmark.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 BenchmarkDotNet.Attributes;
 using MQTTnet.Channel;
 using MQTTnet.Implementations;
@@ -16,7 +17,7 @@ namespace MQTTnet.Benchmarks
 {
     [SimpleJob(RuntimeMoniker.Net60)]
     [MemoryDiagnoser]
-    public sealed class MqttTcpChannelBenchmark
+    public class MqttTcpChannelBenchmark : BaseBenchmark
     {
         MqttServer _mqttServer;
         IMqttChannel _serverChannel;
@@ -70,8 +71,8 @@ namespace MQTTnet.Benchmarks
 
             while (read < expected)
             {
-                var readresult = await _clientChannel.ReadAsync(new byte[size], 0, size, CancellationToken.None).ConfigureAwait(false);
-                read += readresult;
+                var readResult = await _clientChannel.ReadAsync(new byte[size], 0, size, CancellationToken.None).ConfigureAwait(false);
+                read += readResult;
             }
         }
 
@@ -79,9 +80,11 @@ namespace MQTTnet.Benchmarks
         {
             await Task.Yield();
 
+            var buffer = new ArraySegment<byte>(new byte[size]);
+            
             for (var i = 0; i < iterations; i++)
             {
-                await _serverChannel.WriteAsync(new byte[size], 0, size, CancellationToken.None).ConfigureAwait(false);
+                await _serverChannel.WriteAsync(buffer, true, CancellationToken.None).ConfigureAwait(false);
             }
         }
     }

Source/MQTTnet.Benchmarks/Program.cs

@@ -3,81 +3,140 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Generic;
+using System.Linq;
+using BenchmarkDotNet.Loggers;
 using BenchmarkDotNet.Running;
-using MQTTnet.Benchmarks.Configurations;
 using MQTTnet.Diagnostics;
 
 namespace MQTTnet.Benchmarks
 {
     public static class Program
     {
-        public static void Main(string[] args)
-        {
-            Console.WriteLine($"MQTTnet - Benchmarks ({TargetFrameworkProvider.TargetFramework})");
-            Console.WriteLine("--------------------------------------------------------");
-            Console.WriteLine("1 = MessageProcessingBenchmark");
-            Console.WriteLine("2 = SerializerBenchmark");
-            Console.WriteLine("3 = LoggerBenchmark");
-            Console.WriteLine("4 = TopicFilterComparerBenchmark");
-            Console.WriteLine("5 = ChannelAdapterBenchmark");
-            Console.WriteLine("6 = MqttTcpChannelBenchmark");
-            Console.WriteLine("7 = TcpPipesBenchmark");
-            Console.WriteLine("8 = MessageProcessingMqttConnectionContextBenchmark");
-            Console.WriteLine("9 = ServerProcessingBenchmark");
-            Console.WriteLine("a = MqttPacketReaderWriterBenchmark");
-            Console.WriteLine("b = RoundtripBenchmark");
-            Console.WriteLine("c = SubscribeBenchmark");
-            Console.WriteLine("d = UnsubscribeBenchmark");
-            Console.WriteLine("e = MessageDeliveryBenchmark");
+        static int _selectedBenchmarkIndex;
+        static List<Type> _benchmarks;
 
-            var pressedKey = Console.ReadKey(true);
-            switch (pressedKey.KeyChar)
+        public static void Main(string[] arguments)
+        {
+            _benchmarks = CollectBenchmarks();
+            HandleArguments(arguments);
+
+            while (true)
             {
-                case '1':
-                    BenchmarkRunner.Run<MessageProcessingBenchmark>();
-                    break;
-                case '2':
-                    BenchmarkRunner.Run<SerializerBenchmark>();
-                    break;
-                case '3':
-                    BenchmarkRunner.Run<LoggerBenchmark>();
-                    break;
-                case '4':
-                    BenchmarkRunner.Run<TopicFilterComparerBenchmark>();
-                    break;
-                case '5':
-                    BenchmarkRunner.Run<ChannelAdapterBenchmark>();
-                    break;
-                case '6':
-                    BenchmarkRunner.Run<MqttTcpChannelBenchmark>();
-                    break;
-                case '7':
-                    BenchmarkRunner.Run<TcpPipesBenchmark>();
-                    break;
-                case '8':
-                    BenchmarkRunner.Run<MessageProcessingMqttConnectionContextBenchmark>(new RuntimeCompareConfig());
-                    break;
-                case '9':
-                    BenchmarkRunner.Run<ServerProcessingBenchmark>();
-                    break;
-                case 'a':
-                    BenchmarkRunner.Run(typeof(MqttPacketReaderWriterBenchmark));
-                    break;
-                case 'b':
-                    BenchmarkRunner.Run<RoundtripProcessingBenchmark>();
-                    break;
-                case 'c':
-                    BenchmarkRunner.Run<SubscribeBenchmark>();
-                    break;
-                case 'd':
-                    BenchmarkRunner.Run<UnsubscribeBenchmark>();
-                    break;
-                case 'e':
-                    BenchmarkRunner.Run<MessageDeliveryBenchmark>();
+                RenderMenu();
+
+                var key = Console.ReadKey(true);
+
+                if (key.Key == ConsoleKey.DownArrow)
+                {
+                    _selectedBenchmarkIndex++;
+                    if (_selectedBenchmarkIndex > _benchmarks.Count - 1)
+                    {
+                        _selectedBenchmarkIndex = 0;
+                    }
+                }
+                else if (key.Key == ConsoleKey.UpArrow)
+                {
+                    _selectedBenchmarkIndex--;
+                    if (_selectedBenchmarkIndex < 0)
+                    {
+                        _selectedBenchmarkIndex = _benchmarks.Count - 1;
+                    }
+                }
+                else if (key.Key == ConsoleKey.Escape)
+                {
+                    Environment.Exit(0);
+                }
+                else if (key.Key == ConsoleKey.Enter)
+                {
                     break;
+                }
             }
 
+            BenchmarkRunner.Run(_benchmarks[_selectedBenchmarkIndex]);
+
+            Console.ForegroundColor = ConsoleColor.Yellow;
+            Console.WriteLine("Press any key to exit");
             Console.ReadLine();
         }
+
+        static List<Type> CollectBenchmarks()
+        {
+            var benchmarks = new List<Type>();
+
+            var types = typeof(Program).Assembly.GetExportedTypes();
+            foreach (var type in types)
+            {
+                if (typeof(BaseBenchmark).IsAssignableFrom(type))
+                {
+                    if (type != typeof(BaseBenchmark))
+                    {
+                        benchmarks.Add(type);        
+                    }
+                }
+            }
+
+            return benchmarks.OrderBy(b => b.Name).ToList();
+        }
+
+        static void HandleArguments(string[] arguments)
+        {
+            if (arguments.Length == 0)
+            {
+                return;
+            }
+
+            // Allow for preselection to avoid developer frustration.
+            
+            if (int.TryParse(arguments[0], out var benchmarkIndex))
+            {
+                _selectedBenchmarkIndex = benchmarkIndex;
+                return;
+            }
+
+            _selectedBenchmarkIndex = _benchmarks.FindIndex(b => b.Name.Equals(arguments[0]));
+
+            if (_selectedBenchmarkIndex < 0)
+            {
+                _selectedBenchmarkIndex = 0;
+            }
+
+            if (_selectedBenchmarkIndex > _benchmarks.Count - 1)
+            {
+                _selectedBenchmarkIndex = _benchmarks.Count - 1;
+            }
+        }
+
+        static void RenderMenu()
+        {
+            Console.Clear();
+
+            Console.WriteLine($"MQTTnet - Benchmarks ({TargetFrameworkProvider.TargetFramework})");
+            Console.WriteLine("-----------------------------------------------");
+            Console.ForegroundColor = ConsoleColor.Yellow;
+            Console.WriteLine("Press arrow keys for benchmark selection");
+            Console.WriteLine("Press Enter for benchmark execution");
+            Console.WriteLine("Press Esc for exit");
+            Console.ForegroundColor = ConsoleColor.White;
+            Console.WriteLine();
+
+            for (var index = 0; index < _benchmarks.Count; index++)
+            {
+                var benchmark = _benchmarks[index];
+
+                if (_selectedBenchmarkIndex == index)
+                {
+                    Console.Write("-> ");
+                }
+                else
+                {
+                    Console.Write("   ");
+                }
+
+                Console.WriteLine(benchmark.Name);
+            }
+
+            Console.WriteLine();
+        }
     }
-}
+}

Source/MQTTnet.Benchmarks/ReaderExtensionsBenchmark.cs

@@ -0,0 +1,240 @@
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Jobs;
+using MQTTnet.Adapter;
+using MQTTnet.AspNetCore;
+using MQTTnet.Exceptions;
+using MQTTnet.Formatter;
+using MQTTnet.Packets;
+using System;
+using System.Buffers;
+using System.IO;
+using System.IO.Pipelines;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Benchmarks
+{
+    [SimpleJob(RuntimeMoniker.Net60)]
+    [RPlotExporter, RankColumn]
+    [MemoryDiagnoser]
+    public class ReaderExtensionsBenchmark
+    {
+        MqttPacketFormatterAdapter mqttPacketFormatter;
+        MemoryStream stream;
+
+        [GlobalSetup]
+        public void GlobalSetup()
+        {
+            mqttPacketFormatter = new MqttPacketFormatterAdapter(MqttProtocolVersion.V311, new MqttBufferWriter(4096, 65535));
+            var mqttMessage = new MqttApplicationMessageBuilder()
+            .WithTopic("topic")
+            .WithPayload(new byte[10 * 1024])
+            .Build();
+
+            var packet = MqttPacketFactories.Publish.Create(mqttMessage);
+
+            var buffer = mqttPacketFormatter.Encode(packet);
+            stream = new MemoryStream();
+            stream.Write(buffer.Packet);
+            stream.Write(buffer.Payload);
+            mqttPacketFormatter.Cleanup();
+        }
+
+        [Benchmark(Baseline = true)]
+        public async Task Before()
+        {
+            stream.Position = 0;
+            var input = PipeReader.Create(stream);
+
+            while (true)
+            {
+                ReadResult readResult;
+                var readTask = input.ReadAsync();
+                if (readTask.IsCompleted)
+                {
+                    readResult = readTask.Result;
+                }
+                else
+                {
+                    readResult = await readTask.ConfigureAwait(false);
+                }
+
+                var buffer = readResult.Buffer;
+
+                var consumed = buffer.Start;
+                var observed = buffer.Start;
+
+                try
+                {
+                    if (!buffer.IsEmpty)
+                    {
+                        if (ReaderExtensions_Before.TryDecode(mqttPacketFormatter, buffer, out var packet, out consumed, out observed, out var received))
+                        {
+                            break;
+                        }
+                    }
+                    else if (readResult.IsCompleted)
+                    {
+                        throw new MqttCommunicationException("Connection Aborted");
+                    }
+                }
+                finally
+                {
+                    // The buffer was sliced up to where it was consumed, so we can just advance to the start.
+                    // We mark examined as buffer.End so that if we didn't receive a full frame, we'll wait for more data
+                    // before yielding the read again.
+                    input.AdvanceTo(consumed, observed);
+                }
+            }
+        }
+
+        [Benchmark]
+        public async Task After()
+        {
+            stream.Position = 0;
+            var input = PipeReader.Create(stream);
+
+            while (true)
+            {
+                ReadResult readResult;
+                var readTask = input.ReadAsync();
+                if (readTask.IsCompleted)
+                {
+                    readResult = readTask.Result;
+                }
+                else
+                {
+                    readResult = await readTask.ConfigureAwait(false);
+                }
+
+                var buffer = readResult.Buffer;
+
+                var consumed = buffer.Start;
+                var observed = buffer.Start;
+
+                try
+                {
+                    if (!buffer.IsEmpty)
+                    {
+                        if (ReaderExtensions.TryDecode(mqttPacketFormatter, buffer, out var packet, out consumed, out observed, out var received))
+                        {
+                            break;
+                        }
+                    }
+                    else if (readResult.IsCompleted)
+                    {
+                        throw new MqttCommunicationException("Connection Aborted");
+                    }
+                }
+                finally
+                {
+                    // The buffer was sliced up to where it was consumed, so we can just advance to the start.
+                    // We mark examined as buffer.End so that if we didn't receive a full frame, we'll wait for more data
+                    // before yielding the read again.
+                    input.AdvanceTo(consumed, observed);
+                }
+            }
+        }
+
+        public static class ReaderExtensions_Before
+        {
+            public static bool TryDecode(MqttPacketFormatterAdapter formatter,
+                in ReadOnlySequence<byte> input,
+                out MqttPacket packet,
+                out SequencePosition consumed,
+                out SequencePosition observed,
+                out int bytesRead)
+            {
+                if (formatter == null) throw new ArgumentNullException(nameof(formatter));
+
+                packet = null;
+                consumed = input.Start;
+                observed = input.End;
+                bytesRead = 0;
+                var copy = input;
+
+                if (copy.Length < 2)
+                {
+                    return false;
+                }
+
+                var fixedHeader = copy.First.Span[0];
+                if (!TryReadBodyLength(ref copy, out int headerLength, out var bodyLength))
+                {
+                    return false;
+                }
+
+                if (copy.Length < bodyLength)
+                {
+                    return false;
+                }
+
+                var bodySlice = copy.Slice(0, bodyLength);
+                var buffer = GetMemory(bodySlice).ToArray();
+
+                var receivedMqttPacket = new ReceivedMqttPacket(fixedHeader, new ArraySegment<byte>(buffer, 0, buffer.Length), buffer.Length + 2);
+
+                if (formatter.ProtocolVersion == MqttProtocolVersion.Unknown)
+                {
+                    formatter.DetectProtocolVersion(receivedMqttPacket);
+                }
+
+                packet = formatter.Decode(receivedMqttPacket);
+                consumed = bodySlice.End;
+                observed = bodySlice.End;
+                bytesRead = headerLength + bodyLength;
+                return true;
+            }
+
+            static ReadOnlyMemory<byte> GetMemory(in ReadOnlySequence<byte> input)
+            {
+                if (input.IsSingleSegment)
+                {
+                    return input.First;
+                }
+
+                // Should be rare
+                return input.ToArray();
+            }
+
+            static bool TryReadBodyLength(ref ReadOnlySequence<byte> input, out int headerLength, out int bodyLength)
+            {
+                // Alorithm taken from https://docs.oasis-open.org/mqtt/mqtt/v3.1.1/errata01/os/mqtt-v3.1.1-errata01-os-complete.html.
+                var multiplier = 1;
+                var value = 0;
+                byte encodedByte;
+                var index = 1;
+                headerLength = 0;
+                bodyLength = 0;
+
+                var temp = GetMemory(input.Slice(0, Math.Min(5, input.Length))).Span;
+
+                do
+                {
+                    if (index == temp.Length)
+                    {
+                        return false;
+                    }
+
+                    encodedByte = temp[index];
+                    index++;
+
+                    value += (byte)(encodedByte & 127) * multiplier;
+                    if (multiplier > 128 * 128 * 128)
+                    {
+                        throw new MqttProtocolViolationException($"Remaining length is invalid (Data={string.Join(",", temp.Slice(1, index).ToArray())}).");
+                    }
+
+                    multiplier *= 128;
+                } while ((encodedByte & 128) != 0);
+
+                input = input.Slice(index);
+
+                headerLength = index;
+                bodyLength = value;
+                return true;
+            }
+        }
+
+    }
+}

Source/MQTTnet.Benchmarks/RoundtripProcessingBenchmark.cs

@@ -8,7 +8,7 @@ namespace MQTTnet.Benchmarks
     [SimpleJob(RuntimeMoniker.Net60)]
     [RPlotExporter, RankColumn]
     [MemoryDiagnoser]
-    public class RoundtripProcessingBenchmark
+    public class RoundtripProcessingBenchmark : BaseBenchmark
     {
         [GlobalSetup]
         public void GlobalSetup()

Source/MQTTnet.Benchmarks/SerializerBenchmark.cs

@@ -104,7 +104,7 @@ namespace MQTTnet.Benchmarks
                 return Task.FromResult(count);
             }
 
-            public Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+            public Task WriteAsync(ArraySegment<byte> buffer, bool isEndOfPacket, CancellationToken cancellationToken)
             {
                 throw new NotSupportedException();
             }

Source/MQTTnet.Benchmarks/ServerProcessingBenchmark.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 BenchmarkDotNet.Attributes;
 using BenchmarkDotNet.Jobs;
 using MQTTnet.Tests.Mockups;
@@ -8,7 +12,7 @@ namespace MQTTnet.Benchmarks
     [SimpleJob(RuntimeMoniker.Net60)]
     [RPlotExporter, RankColumn]
     [MemoryDiagnoser]
-    public class ServerProcessingBenchmark
+    public class ServerProcessingBenchmark : BaseBenchmark
     {
         [GlobalSetup]
         public void GlobalSetup()

Source/MQTTnet.Benchmarks/SubscribeBenchmark.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 BenchmarkDotNet.Attributes;
 using BenchmarkDotNet.Jobs;
 using MQTTnet.Client;
@@ -8,7 +12,7 @@ using System.Linq;
 namespace MQTTnet.Benchmarks
 {
     [MemoryDiagnoser]
-    public class SubscribeBenchmark
+    public class SubscribeBenchmark : BaseBenchmark
     {
         MqttServer _mqttServer;
         IMqttClient _mqttClient;

Source/MQTTnet.Benchmarks/TcpPipesBenchmark.cs

@@ -15,7 +15,7 @@ namespace MQTTnet.Benchmarks
 {
     [SimpleJob(RuntimeMoniker.Net60)]
     [MemoryDiagnoser]
-    public class TcpPipesBenchmark
+    public class TcpPipesBenchmark : BaseBenchmark
     {
         IDuplexPipe _client;
         IDuplexPipe _server;

Source/MQTTnet.Benchmarks/TopicFilterComparerBenchmark.cs

@@ -11,7 +11,7 @@ namespace MQTTnet.Benchmarks
     [SimpleJob(RuntimeMoniker.Net60)]
     [RPlotExporter]
     [MemoryDiagnoser]
-    public class TopicFilterComparerBenchmark
+    public class TopicFilterComparerBenchmark : BaseBenchmark
     {
         static readonly char[] TopicLevelSeparator = { '/' };
 

Source/MQTTnet.Benchmarks/TopicGenerator.cs

@@ -1,31 +1,30 @@
 using System;
 using System.Collections.Generic;
-using System.Text;
 
 namespace MQTTnet.Benchmarks
 {
     public class TopicGenerator
     {
         public static void Generate(
-           int numPublishers, int numTopicsPerPublisher,
-           out Dictionary<string, List<string>> topicsByPublisher,
-           out Dictionary<string, List<string>> singleWildcardTopicsByPublisher,
-           out Dictionary<string, List<string>> multiWildcardTopicsByPublisher
-           )
+            int numPublishers,
+            int numTopicsPerPublisher,
+            out Dictionary<string, List<string>> topicsByPublisher,
+            out Dictionary<string, List<string>> singleWildcardTopicsByPublisher,
+            out Dictionary<string, List<string>> multiWildcardTopicsByPublisher)
         {
             topicsByPublisher = new Dictionary<string, List<string>>();
             singleWildcardTopicsByPublisher = new Dictionary<string, List<string>>();
             multiWildcardTopicsByPublisher = new Dictionary<string, List<string>>();
 
             // Find some reasonable distribution across three topic levels
-            var topicsPerLevel = (int)Math.Pow(numTopicsPerPublisher, (1.0 / 3.0));
+            var topicsPerLevel = (int)Math.Pow(numTopicsPerPublisher, 1.0 / 3.0);
             if (topicsPerLevel <= 0)
             {
                 topicsPerLevel = 1;
             }
 
-            int numLevel1Topics = topicsPerLevel;
-            int numLevel2Topics = topicsPerLevel;
+            var numLevel1Topics = topicsPerLevel;
+            var numLevel2Topics = topicsPerLevel;
 
             var maxNumLevel3Topics = 1 + (int)((double)numTopicsPerPublisher / numLevel1Topics / numLevel2Topics);
             if (maxNumLevel3Topics <= 0)
@@ -35,7 +34,7 @@ namespace MQTTnet.Benchmarks
 
             for (var p = 0; p < numPublishers; ++p)
             {
-                int publisherTopicCount = 0;
+                var publisherTopicCount = 0;
                 var publisherName = "pub" + p;
                 for (var l1 = 0; l1 < numLevel1Topics; ++l1)
                 {
@@ -44,19 +43,22 @@ namespace MQTTnet.Benchmarks
                         for (var l3 = 0; l3 < maxNumLevel3Topics; ++l3)
                         {
                             if (publisherTopicCount >= numTopicsPerPublisher)
+                            {
                                 break;
+                            }
 
-                            var topic = string.Format("{0}/building{1}/level{2}/sensor{3}", publisherName, l1 + 1, l2 + 1, l3 + 1);
+                            var topic = $"{publisherName}/building{l1 + 1}/level{l2 + 1}/sensor{l3 + 1}";
                             AddPublisherTopic(publisherName, topic, topicsByPublisher);
 
                             if (l2 == 0)
                             {
-                                var singleWildcardTopic = string.Format("{0}/building{1}/+/sensor{2}", publisherName, l1 + 1, l3 + 1);
+                                var singleWildcardTopic = $"{publisherName}/building{l1 + 1}/+/sensor{l3 + 1}";
                                 AddPublisherTopic(publisherName, singleWildcardTopic, singleWildcardTopicsByPublisher);
                             }
-                            if ((l1 == 0) && (l3 == 0))
+
+                            if (l1 == 0 && l3 == 0)
                             {
-                                var multiWildcardTopic = string.Format("{0}/+/level{1}/+", publisherName, l2 + 1);
+                                var multiWildcardTopic = $"{publisherName}/+/level{l2 + 1}/+";
                                 AddPublisherTopic(publisherName, multiWildcardTopic, multiWildcardTopicsByPublisher);
                             }
 
@@ -75,7 +77,8 @@ namespace MQTTnet.Benchmarks
                 topicList = new List<string>();
                 topicsByPublisher.Add(publisherName, topicList);
             }
+
             topicList.Add(topic);
         }
     }
-}
+}

Source/MQTTnet.Benchmarks/UnsubscribeBenchmark.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 BenchmarkDotNet.Attributes;
 using MQTTnet.Client;
 using MQTTnet.Server;
@@ -7,7 +11,7 @@ using System.Linq;
 namespace MQTTnet.Benchmarks
 {
     [MemoryDiagnoser]
-    public class UnsubscribeBenchmark
+    public class UnsubscribeBenchmark : BaseBenchmark 
     {
         MqttServer _mqttServer;
         IMqttClient _mqttClient;

Source/MQTTnet.Benchmarks/packages.config

@@ -1,54 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<packages>
-  <package id="BenchmarkDotNet" version="0.10.14" targetFramework="net462" />
-  <package id="BenchmarkDotNet.Core" version="0.10.14" targetFramework="net462" />
-  <package id="BenchmarkDotNet.Toolchains.Roslyn" version="0.10.14" targetFramework="net462" />
-  <package id="Microsoft.CodeAnalysis.Analyzers" version="1.1.0" targetFramework="net462" />
-  <package id="Microsoft.CodeAnalysis.Common" version="2.6.1" targetFramework="net462" />
-  <package id="Microsoft.CodeAnalysis.CSharp" version="2.6.1" targetFramework="net462" />
-  <package id="Microsoft.DotNet.InternalAbstractions" version="1.0.0" targetFramework="net462" />
-  <package id="Microsoft.DotNet.PlatformAbstractions" version="1.1.1" targetFramework="net462" />
-  <package id="Microsoft.Win32.Registry" version="4.3.0" targetFramework="net462" />
-  <package id="System.AppContext" version="4.3.0" targetFramework="net462" />
-  <package id="System.Collections" version="4.3.0" targetFramework="net462" />
-  <package id="System.Collections.Concurrent" version="4.3.0" targetFramework="net462" />
-  <package id="System.Collections.Immutable" version="1.3.1" targetFramework="net462" />
-  <package id="System.Console" version="4.3.0" targetFramework="net462" />
-  <package id="System.Diagnostics.Debug" version="4.3.0" targetFramework="net462" />
-  <package id="System.Diagnostics.FileVersionInfo" version="4.3.0" targetFramework="net462" />
-  <package id="System.Diagnostics.StackTrace" version="4.3.0" targetFramework="net462" />
-  <package id="System.Diagnostics.Tools" version="4.3.0" targetFramework="net462" />
-  <package id="System.Dynamic.Runtime" version="4.3.0" targetFramework="net462" />
-  <package id="System.Globalization" version="4.3.0" targetFramework="net462" />
-  <package id="System.IO.Compression" version="4.3.0" targetFramework="net462" />
-  <package id="System.IO.FileSystem" version="4.3.0" targetFramework="net462" />
-  <package id="System.IO.FileSystem.Primitives" version="4.3.0" targetFramework="net462" />
-  <package id="System.Linq" version="4.3.0" targetFramework="net462" />
-  <package id="System.Linq.Expressions" version="4.3.0" targetFramework="net462" />
-  <package id="System.Reflection" version="4.3.0" targetFramework="net462" />
-  <package id="System.Reflection.Metadata" version="1.4.2" targetFramework="net462" />
-  <package id="System.Resources.ResourceManager" version="4.3.0" targetFramework="net462" />
-  <package id="System.Runtime" version="4.3.0" targetFramework="net462" />
-  <package id="System.Runtime.Extensions" version="4.3.0" targetFramework="net462" />
-  <package id="System.Runtime.InteropServices" version="4.3.0" targetFramework="net462" />
-  <package id="System.Runtime.Numerics" version="4.3.0" targetFramework="net462" />
-  <package id="System.Security.Cryptography.Algorithms" version="4.3.0" targetFramework="net462" />
-  <package id="System.Security.Cryptography.Encoding" version="4.3.0" targetFramework="net462" />
-  <package id="System.Security.Cryptography.Primitives" version="4.3.0" targetFramework="net462" />
-  <package id="System.Security.Cryptography.X509Certificates" version="4.3.0" targetFramework="net462" />
-  <package id="System.Text.Encoding" version="4.3.0" targetFramework="net462" />
-  <package id="System.Text.Encoding.CodePages" version="4.3.0" targetFramework="net462" />
-  <package id="System.Text.Encoding.Extensions" version="4.3.0" targetFramework="net462" />
-  <package id="System.Threading" version="4.3.0" targetFramework="net462" />
-  <package id="System.Threading.Tasks" version="4.3.0" targetFramework="net462" />
-  <package id="System.Threading.Tasks.Extensions" version="4.3.0" targetFramework="net462" />
-  <package id="System.Threading.Tasks.Parallel" version="4.3.0" targetFramework="net462" />
-  <package id="System.Threading.Thread" version="4.3.0" targetFramework="net462" />
-  <package id="System.ValueTuple" version="4.3.0" targetFramework="net462" />
-  <package id="System.Xml.ReaderWriter" version="4.3.0" targetFramework="net462" />
-  <package id="System.Xml.XDocument" version="4.3.0" targetFramework="net462" />
-  <package id="System.Xml.XmlDocument" version="4.3.0" targetFramework="net462" />
-  <package id="System.Xml.XmlSerializer" version="4.3.0" targetFramework="net462" />
-  <package id="System.Xml.XPath" version="4.3.0" targetFramework="net462" />
-  <package id="System.Xml.XPath.XDocument" version="4.3.0" targetFramework="net462" />
-</packages>

Source/MQTTnet.Extensions.ManagedClient/IManagedMqttClient.cs

@@ -43,7 +43,7 @@ namespace MQTTnet.Extensions.ManagedClient
         
         Task StartAsync(ManagedMqttClientOptions options);
         
-        Task StopAsync();
+        Task StopAsync(bool cleanDisconnect = true);
         
         Task SubscribeAsync(ICollection<MqttTopicFilter> topicFilters);
         

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

@@ -33,7 +33,7 @@
         <PackageReleaseNotes>For release notes please go to MQTTnet release notes (https://www.nuget.org/packages/MQTTnet/).</PackageReleaseNotes>
         <DisableImplicitAspNetCoreAnalyzers>true</DisableImplicitAspNetCoreAnalyzers>
         <GenerateDocumentationFile>true</GenerateDocumentationFile>
-        <NoWarn>1591</NoWarn>
+        <NoWarn>1591;NETSDK1138</NoWarn>
     </PropertyGroup>
 
     <PropertyGroup Condition="'$(TargetFramework)' == 'uap10.0'">

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClient.cs

@@ -62,6 +62,7 @@ namespace MQTTnet.Extensions.ManagedClient
         CancellationTokenSource _publishingCancellationToken;
 
         ManagedMqttClientStorageManager _storageManager;
+        bool _isCleanDisconnect;
 
         public ManagedMqttClient(IMqttClient mqttClient, IMqttNetLogger logger)
         {
@@ -160,14 +161,14 @@ namespace MQTTnet.Extensions.ManagedClient
                 throw new InvalidOperationException("call StartAsync before publishing messages");
             }
 
-            MqttTopicValidator.ThrowIfInvalid(applicationMessage.ApplicationMessage.Topic);
+            MqttTopicValidator.ThrowIfInvalid(applicationMessage.ApplicationMessage);
 
             ManagedMqttApplicationMessage removedMessage = null;
             ApplicationMessageSkippedEventArgs applicationMessageSkippedEventArgs = null;
 
             try
             {
-                using (await _messageQueueLock.WaitAsync(CancellationToken.None).ConfigureAwait(false))
+                using (await _messageQueueLock.EnterAsync().ConfigureAwait(false))
                 {
                     if (_messageQueue.Count >= Options.MaxPendingMessages)
                     {
@@ -255,10 +256,12 @@ namespace MQTTnet.Extensions.ManagedClient
             _logger.Info("Started");
         }
 
-        public async Task StopAsync()
+        public async Task StopAsync(bool cleanDisconnect = true)
         {
             ThrowIfDisposed();
 
+            _isCleanDisconnect = cleanDisconnect;
+            
             StopPublishing();
             StopMaintainingConnection();
 
@@ -296,7 +299,7 @@ namespace MQTTnet.Extensions.ManagedClient
 
             _subscriptionsQueuedSignal.Release();
 
-            return Task.FromResult(0);
+            return CompletedTask.Instance;
         }
 
         public Task UnsubscribeAsync(ICollection<string> topics)
@@ -319,7 +322,7 @@ namespace MQTTnet.Extensions.ManagedClient
 
             _subscriptionsQueuedSignal.Release();
 
-            return Task.FromResult(0);
+            return CompletedTask.Instance;
         }
 
         protected override void Dispose(bool disposing)
@@ -382,9 +385,12 @@ namespace MQTTnet.Extensions.ManagedClient
                 {
                     try
                     {
-                        using (var disconnectTimeout = new CancellationTokenSource(Options.ClientOptions.Timeout))
+                        if (_isCleanDisconnect)
                         {
-                            await InternalClient.DisconnectAsync(new MqttClientDisconnectOptions(), disconnectTimeout.Token).ConfigureAwait(false);
+                            using (var disconnectTimeout = new CancellationTokenSource(Options.ClientOptions.Timeout))
+                            {
+                                await InternalClient.DisconnectAsync(new MqttClientDisconnectOptions(), disconnectTimeout.Token).ConfigureAwait(false);
+                            }
                         }
                     }
                     catch (OperationCanceledException)
@@ -693,7 +699,7 @@ namespace MQTTnet.Extensions.ManagedClient
             {
                 await InternalClient.PublishAsync(message.ApplicationMessage).ConfigureAwait(false);
 
-                using (await _messageQueueLock.WaitAsync(CancellationToken.None).ConfigureAwait(false)) //lock to avoid conflict with this.PublishAsync
+                using (await _messageQueueLock.EnterAsync().ConfigureAwait(false)) //lock to avoid conflict with this.PublishAsync
                 {
                     // While publishing this message, this.PublishAsync could have booted this
                     // message off the queue to make room for another (when using a cap
@@ -724,7 +730,7 @@ namespace MQTTnet.Extensions.ManagedClient
                     //contradict the expected behavior of QoS 1 and 2, that's also true
                     //for the usage of a message queue cap, so it's still consistent
                     //with prior behavior in that way.
-                    using (await _messageQueueLock.WaitAsync(CancellationToken.None).ConfigureAwait(false)) //lock to avoid conflict with this.PublishAsync
+                    using (await _messageQueueLock.EnterAsync().ConfigureAwait(false)) //lock to avoid conflict with this.PublishAsync
                     {
                         _messageQueue.RemoveFirst(i => i.Id.Equals(message.Id));
 

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClientStorageManager.cs

@@ -34,7 +34,7 @@ namespace MQTTnet.Extensions.ManagedClient
         {
             if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
 
-            using (await _messagesLock.WaitAsync(CancellationToken.None).ConfigureAwait(false))
+            using (await _messagesLock.EnterAsync().ConfigureAwait(false))
             {
                 _messages.Add(applicationMessage);
                 await SaveAsync().ConfigureAwait(false);
@@ -45,7 +45,7 @@ namespace MQTTnet.Extensions.ManagedClient
         {
             if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
 
-            using (await _messagesLock.WaitAsync(CancellationToken.None).ConfigureAwait(false))
+            using (await _messagesLock.EnterAsync().ConfigureAwait(false))
             {
                 var index = _messages.IndexOf(applicationMessage);
                 if (index == -1)

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

@@ -33,7 +33,8 @@
         <PackageReleaseNotes>For release notes please go to MQTTnet release notes (https://www.nuget.org/packages/MQTTnet/).</PackageReleaseNotes>
         <DisableImplicitAspNetCoreAnalyzers>true</DisableImplicitAspNetCoreAnalyzers>
         <GenerateDocumentationFile>true</GenerateDocumentationFile>
-        <NoWarn>1591</NoWarn>
+        <NoWarn>1591;NETSDK1138</NoWarn>
+        <LangVersion>7.3</LangVersion>
     </PropertyGroup>
 
     <PropertyGroup Condition="'$(TargetFramework)' == 'uap10.0'">

Source/MQTTnet.Extensions.Rpc/MqttFactoryExtensions.cs

@@ -11,10 +11,12 @@ namespace MQTTnet.Extensions.Rpc
     {
         public static IMqttRpcClient CreateMqttRpcClient(this MqttFactory factory, IMqttClient mqttClient)
         {
-            return factory.CreateMqttRpcClient(mqttClient, new MqttRpcClientOptions
-            {
-                TopicGenerationStrategy = new DefaultMqttRpcClientTopicGenerationStrategy()
-            });
+            return factory.CreateMqttRpcClient(
+                mqttClient,
+                new MqttRpcClientOptions
+                {
+                    TopicGenerationStrategy = new DefaultMqttRpcClientTopicGenerationStrategy()
+                });
         }
 
         public static IMqttRpcClient CreateMqttRpcClient(this MqttFactory _, IMqttClient mqttClient, MqttRpcClientOptions rpcClientOptions)

Source/MQTTnet.Extensions.Rpc/MqttRpcClient.cs

@@ -2,23 +2,24 @@
 // 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 MQTTnet.Exceptions;
-using MQTTnet.Protocol;
 using System;
 using System.Collections.Concurrent;
 using System.Threading;
 using System.Threading.Tasks;
-using MQTTnet.Implementations;
+using MQTTnet.Client;
+using MQTTnet.Exceptions;
+using MQTTnet.Internal;
+using MQTTnet.Protocol;
 
 namespace MQTTnet.Extensions.Rpc
 {
     public sealed class MqttRpcClient : IMqttRpcClient
     {
-        readonly ConcurrentDictionary<string, TaskCompletionSource<byte[]>> _waitingCalls = new ConcurrentDictionary<string, TaskCompletionSource<byte[]>>();
         readonly IMqttClient _mqttClient;
         readonly MqttRpcClientOptions _options;
         
+        readonly ConcurrentDictionary<string, AsyncTaskCompletionSource<byte[]>> _waitingCalls = new ConcurrentDictionary<string, AsyncTaskCompletionSource<byte[]>>();
+        
         public MqttRpcClient(IMqttClient mqttClient, MqttRpcClientOptions options)
         {
             _mqttClient = mqttClient ?? throw new ArgumentNullException(nameof(mqttClient));
@@ -27,6 +28,18 @@ namespace MQTTnet.Extensions.Rpc
             _mqttClient.ApplicationMessageReceivedAsync += HandleApplicationMessageReceivedAsync;
         }
 
+        public void Dispose()
+        {
+            _mqttClient.ApplicationMessageReceivedAsync -= HandleApplicationMessageReceivedAsync;
+
+            foreach (var tcs in _waitingCalls)
+            {
+                tcs.Value.TrySetCanceled();
+            }
+
+            _waitingCalls.Clear();
+        }
+
         public async Task<byte[]> ExecuteAsync(TimeSpan timeout, string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel)
         {
             using (var timeoutToken = new CancellationTokenSource(timeout))
@@ -49,15 +62,13 @@ namespace MQTTnet.Extensions.Rpc
 
         public async Task<byte[]> ExecuteAsync(string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel, CancellationToken cancellationToken = default)
         {
-            if (methodName == null) throw new ArgumentNullException(nameof(methodName));
-            
-            var topicNames = _options.TopicGenerationStrategy.CreateRpcTopics(new TopicGenerationContext
+            if (methodName == null)
             {
-                MethodName = methodName,
-                QualityOfServiceLevel = qualityOfServiceLevel,
-                MqttClient = _mqttClient,
-                Options = _options
-            });
+                throw new ArgumentNullException(nameof(methodName));
+            }
+
+            var context = new TopicGenerationContext(_mqttClient, _options, methodName, qualityOfServiceLevel);
+            var topicNames = _options.TopicGenerationStrategy.CreateRpcTopics(context);
 
             var requestTopic = topicNames.RequestTopic;
             var responseTopic = topicNames.ResponseTopic;
@@ -72,8 +83,7 @@ namespace MQTTnet.Extensions.Rpc
                 throw new MqttProtocolViolationException("RPC response topic is empty.");
             }
 
-            var requestMessage = new MqttApplicationMessageBuilder()
-                .WithTopic(requestTopic)
+            var requestMessage = new MqttApplicationMessageBuilder().WithTopic(requestTopic)
                 .WithPayload(payload)
                 .WithQualityOfServiceLevel(qualityOfServiceLevel)
                 .WithResponseTopic(responseTopic)
@@ -81,25 +91,23 @@ namespace MQTTnet.Extensions.Rpc
 
             try
             {
-#if NET452
-                var awaitable = new TaskCompletionSource<byte[]>();
-#else
-                var awaitable = new TaskCompletionSource<byte[]>(TaskCreationOptions.RunContinuationsAsynchronously);
-#endif
+                var awaitable = new AsyncTaskCompletionSource<byte[]>();
 
                 if (!_waitingCalls.TryAdd(responseTopic, awaitable))
                 {
                     throw new InvalidOperationException();
                 }
 
-                var subscribeOptions = new MqttClientSubscribeOptionsBuilder()
-                    .WithTopicFilter(responseTopic, qualityOfServiceLevel)
-                    .Build();
+                var subscribeOptions = new MqttClientSubscribeOptionsBuilder().WithTopicFilter(responseTopic, qualityOfServiceLevel).Build();
 
                 await _mqttClient.SubscribeAsync(subscribeOptions, cancellationToken).ConfigureAwait(false);
                 await _mqttClient.PublishAsync(requestMessage, cancellationToken).ConfigureAwait(false);
 
-                using (cancellationToken.Register(() => { awaitable.TrySetCanceled(); }))
+                using (cancellationToken.Register(
+                           () =>
+                           {
+                               awaitable.TrySetCanceled();
+                           }))
                 {
                     return await awaitable.Task.ConfigureAwait(false);
                 }
@@ -107,8 +115,8 @@ namespace MQTTnet.Extensions.Rpc
             finally
             {
                 _waitingCalls.TryRemove(responseTopic, out _);
-                
-                await _mqttClient.UnsubscribeAsync(responseTopic).ConfigureAwait(false);
+
+                await _mqttClient.UnsubscribeAsync(responseTopic, CancellationToken.None).ConfigureAwait(false);
             }
         }
 
@@ -116,31 +124,15 @@ namespace MQTTnet.Extensions.Rpc
         {
             if (!_waitingCalls.TryRemove(eventArgs.ApplicationMessage.Topic, out var awaitable))
             {
-                return PlatformAbstractionLayer.CompletedTask;
+                return CompletedTask.Instance;
             }
 
-#if NET452
-            Task.Run(() => awaitable.TrySetResult(eventArgs.ApplicationMessage.Payload));
-#else
             awaitable.TrySetResult(eventArgs.ApplicationMessage.Payload);
-#endif
 
             // Set this message to handled to that other code can avoid execution etc.
             eventArgs.IsHandled = true;
 
-            return PlatformAbstractionLayer.CompletedTask;
-        }
-
-        public void Dispose()
-        {
-            _mqttClient.ApplicationMessageReceivedAsync -= HandleApplicationMessageReceivedAsync;
-
-            foreach (var tcs in _waitingCalls)
-            {
-                tcs.Value.TrySetCanceled();
-            }
-
-            _waitingCalls.Clear();
+            return CompletedTask.Instance;
         }
     }
 }

Source/MQTTnet.Extensions.Rpc/Options/MqttRpcClientOptionsBuilder.cs

@@ -10,13 +10,6 @@ namespace MQTTnet.Extensions.Rpc
     {
         IMqttRpcClientTopicGenerationStrategy _topicGenerationStrategy = new DefaultMqttRpcClientTopicGenerationStrategy();
 
-        public MqttRpcClientOptionsBuilder WithTopicGenerationStrategy(IMqttRpcClientTopicGenerationStrategy value)
-        {
-            _topicGenerationStrategy = value ?? throw new ArgumentNullException(nameof(value));
-
-            return this;
-        }
-
         public MqttRpcClientOptions Build()
         {
             return new MqttRpcClientOptions
@@ -24,5 +17,12 @@ namespace MQTTnet.Extensions.Rpc
                 TopicGenerationStrategy = _topicGenerationStrategy
             };
         }
+
+        public MqttRpcClientOptionsBuilder WithTopicGenerationStrategy(IMqttRpcClientTopicGenerationStrategy value)
+        {
+            _topicGenerationStrategy = value ?? throw new ArgumentNullException(nameof(value));
+
+            return this;
+        }
     }
-}
+}

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

@@ -10,6 +10,11 @@ namespace MQTTnet.Extensions.Rpc
     {
         public MqttRpcTopicPair CreateRpcTopics(TopicGenerationContext context)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
             if (context.MethodName.Contains("/") || context.MethodName.Contains("+") || context.MethodName.Contains("#"))
             {
                 throw new ArgumentException("The method name cannot contain /, + or #.");

Source/MQTTnet.Extensions.Rpc/Options/TopicGeneration/TopicGenerationContext.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 MQTTnet.Client;
 using MQTTnet.Protocol;
 
@@ -9,20 +10,29 @@ namespace MQTTnet.Extensions.Rpc
 {
     public sealed class TopicGenerationContext
     {
-        public string MethodName { get; set; }
+        public TopicGenerationContext(IMqttClient mqttClient, MqttRpcClientOptions options, string methodName, MqttQualityOfServiceLevel qualityOfServiceLevel)
+        {
+            MethodName = methodName ?? throw new ArgumentNullException(nameof(methodName));
+            QualityOfServiceLevel = qualityOfServiceLevel;
+            MqttClient = mqttClient ?? throw new ArgumentNullException(nameof(mqttClient));
+            Options = options ?? throw new ArgumentNullException(nameof(options));
+        }
+
+        public string MethodName { get; }
+
+        public IMqttClient MqttClient { get; }
+
+        public MqttRpcClientOptions Options { get; }
 
         /// <summary>
-        /// Gets or sets the quality of service level.
-        /// The Quality of Service (QoS) level is an agreement between the sender of a message and the receiver of a message that defines the guarantee of delivery for a specific message.
-        /// There are 3 QoS levels in MQTT:
-        /// - At most once  (0): Message gets delivered no time, once or multiple times.
-        /// - At least once (1): Message gets delivered at least once (one time or more often).
-        /// - Exactly once  (2): Message gets delivered exactly once (It's ensured that the message only comes once).
+        ///     Gets or sets the quality of service level.
+        ///     The Quality of Service (QoS) level is an agreement between the sender of a message and the receiver of a message
+        ///     that defines the guarantee of delivery for a specific message.
+        ///     There are 3 QoS levels in MQTT:
+        ///     - At most once  (0): Message gets delivered no time, once or multiple times.
+        ///     - At least once (1): Message gets delivered at least once (one time or more often).
+        ///     - Exactly once  (2): Message gets delivered exactly once (It's ensured that the message only comes once).
         /// </summary>
-        public MqttQualityOfServiceLevel QualityOfServiceLevel { get; set; }
-
-        public IMqttClient MqttClient { get; set; }
-
-        public MqttRpcClientOptions Options { get; set; }
+        public MqttQualityOfServiceLevel QualityOfServiceLevel { get; }
     }
-}
+}

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

@@ -33,7 +33,8 @@
         <PackageReleaseNotes>For release notes please go to MQTTnet release notes (https://www.nuget.org/packages/MQTTnet/).</PackageReleaseNotes>
         <DisableImplicitAspNetCoreAnalyzers>true</DisableImplicitAspNetCoreAnalyzers>
         <GenerateDocumentationFile>true</GenerateDocumentationFile>
-        <NoWarn>1591</NoWarn>
+        <NoWarn>1591;NETSDK1138</NoWarn>
+        <LangVersion>7.3</LangVersion>
     </PropertyGroup>
 
     <PropertyGroup Condition="'$(TargetFramework)' == 'uap10.0'">

Source/MQTTnet.Extensions.WebSocket4Net/MqttFactoryExtensions.cs

@@ -10,9 +10,12 @@ namespace MQTTnet.Extensions.WebSocket4Net
     {
         public static MqttFactory UseWebSocket4Net(this MqttFactory mqttFactory)
         {
-            if (mqttFactory == null) throw new ArgumentNullException(nameof(mqttFactory));
+            if (mqttFactory == null)
+            {
+                throw new ArgumentNullException(nameof(mqttFactory));
+            }
 
             return mqttFactory.UseClientAdapterFactory(new WebSocket4NetMqttClientAdapterFactory());
         }
     }
-}
+}

Source/MQTTnet.Extensions.WebSocket4Net/WebSocket4NetMqttChannel.cs

@@ -5,6 +5,7 @@
 using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Net;
 using System.Security.Authentication;
@@ -14,16 +15,17 @@ using System.Threading.Tasks;
 using MQTTnet.Channel;
 using MQTTnet.Client;
 using MQTTnet.Exceptions;
+using MQTTnet.Internal;
 using SuperSocket.ClientEngine;
 using WebSocket4Net;
+using DataReceivedEventArgs = WebSocket4Net.DataReceivedEventArgs;
 
 namespace MQTTnet.Extensions.WebSocket4Net
 {
     public sealed class WebSocket4NetMqttChannel : IMqttChannel
     {
-        readonly BlockingCollection<byte> _receiveBuffer = new BlockingCollection<byte>();
-
         readonly MqttClientOptions _clientOptions;
+        readonly BlockingCollection<byte> _receiveBuffer = new BlockingCollection<byte>();
         readonly MqttClientWebSocketOptions _webSocketOptions;
 
         WebSocket _webSocket;
@@ -34,13 +36,13 @@ namespace MQTTnet.Extensions.WebSocket4Net
             _webSocketOptions = webSocketOptions ?? throw new ArgumentNullException(nameof(webSocketOptions));
         }
 
+        public X509Certificate2 ClientCertificate { get; }
+
         public string Endpoint => _webSocketOptions.Uri;
 
         public bool IsSecureConnection { get; private set; }
 
-        public X509Certificate2 ClientCertificate { get; }
-
-        public async Task ConnectAsync(CancellationToken cancellationToken)
+        public Task ConnectAsync(CancellationToken cancellationToken)
         {
             var uri = _webSocketOptions.Uri;
             if (!uri.StartsWith("ws://", StringComparison.OrdinalIgnoreCase) && !uri.StartsWith("wss://", StringComparison.OrdinalIgnoreCase))
@@ -54,11 +56,13 @@ namespace MQTTnet.Extensions.WebSocket4Net
                     uri = "wss://" + uri;
                 }
             }
+            
+            IsSecureConnection = uri.StartsWith("wss://", StringComparison.OrdinalIgnoreCase);
 
-#if NET48 || NETCOREAPP3_1 || NET5 || NET6
-            var sslProtocols = _webSocketOptions?.TlsOptions?.SslProtocol ?? SslProtocols.Tls12 | SslProtocols.Tls13;
+#if NET48 || NETCOREAPP3_0_OR_GREATER
+            var sslProtocols = _webSocketOptions.TlsOptions?.SslProtocol ?? SslProtocols.Tls12 | SslProtocols.Tls13;
 #else
-            var sslProtocols = _webSocketOptions?.TlsOptions?.SslProtocol ?? SslProtocols.Tls12 | (SslProtocols)0x00003000 /*Tls13*/;
+            var sslProtocols = _webSocketOptions.TlsOptions?.SslProtocol ?? SslProtocols.Tls12 | (SslProtocols)0x00003000 /*Tls13*/;
 #endif
 
             var subProtocol = _webSocketOptions.SubProtocols.FirstOrDefault() ?? string.Empty;
@@ -89,7 +93,7 @@ namespace MQTTnet.Extensions.WebSocket4Net
             var receiveBufferSize = 0;
 
             var certificates = new X509CertificateCollection();
-            if (_webSocketOptions?.TlsOptions?.Certificates != null)
+            if (_webSocketOptions.TlsOptions?.Certificates != null)
             {
                 foreach (var certificate in _webSocketOptions.TlsOptions.Certificates)
                 {
@@ -106,15 +110,13 @@ namespace MQTTnet.Extensions.WebSocket4Net
                 NoDelay = true,
                 Security =
                 {
-                    AllowUnstrustedCertificate = _webSocketOptions?.TlsOptions?.AllowUntrustedCertificates == true,
-                    AllowCertificateChainErrors = _webSocketOptions?.TlsOptions?.IgnoreCertificateChainErrors == true,
+                    AllowUnstrustedCertificate = _webSocketOptions.TlsOptions?.AllowUntrustedCertificates == true,
+                    AllowCertificateChainErrors = _webSocketOptions.TlsOptions?.IgnoreCertificateChainErrors == true,
                     Certificates = certificates
                 }
             };
 
-            await ConnectInternalAsync(cancellationToken).ConfigureAwait(false);
-            
-            IsSecureConnection = uri.StartsWith("wss://", StringComparison.OrdinalIgnoreCase);
+            return ConnectInternalAsync(cancellationToken);
         }
 
         public Task DisconnectAsync(CancellationToken cancellationToken)
@@ -123,8 +125,21 @@ namespace MQTTnet.Extensions.WebSocket4Net
             {
                 _webSocket.Close();
             }
-            
-            return Task.FromResult(0);
+
+            return CompletedTask.Instance;
+        }
+
+        public void Dispose()
+        {
+            if (_webSocket == null)
+            {
+                return;
+            }
+
+            _webSocket.DataReceived -= OnDataReceived;
+            _webSocket.Error -= OnError;
+            _webSocket.Dispose();
+            _webSocket = null;
         }
 
         public Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
@@ -154,36 +169,10 @@ namespace MQTTnet.Extensions.WebSocket4Net
             return Task.FromResult(readBytes);
         }
 
-        public Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+        public Task WriteAsync(ArraySegment<byte> buffer, bool isEndOfPacket, CancellationToken cancellationToken)
         {
-            _webSocket.Send(buffer, offset, count);
-            return Task.FromResult(0);
-        }
-
-        public void Dispose()
-        {
-            if (_webSocket == null)
-            {
-                return;
-            }
-
-            _webSocket.DataReceived -= OnDataReceived;
-            _webSocket.Error -= OnError;
-            _webSocket.Dispose();
-            _webSocket = null;
-        }
-
-        static void OnError(object sender, ErrorEventArgs e)
-        {
-            System.Diagnostics.Debug.Write(e.Exception.ToString());
-        }
-
-        void OnDataReceived(object sender, DataReceivedEventArgs e)
-        {
-            foreach (var @byte in e.Data)
-            {
-                _receiveBuffer.Add(@byte);
-            }
+            _webSocket.Send(buffer.Array, buffer.Offset, buffer.Count);
+            return CompletedTask.Instance;
         }
 
         async Task ConnectInternalAsync(CancellationToken cancellationToken)
@@ -191,44 +180,50 @@ namespace MQTTnet.Extensions.WebSocket4Net
             _webSocket.Error += OnError;
             _webSocket.DataReceived += OnDataReceived;
 
-            var taskCompletionSource = new TaskCompletionSource<Exception>();
+            var promise = new AsyncTaskCompletionSource<bool>();
 
             void ErrorHandler(object sender, ErrorEventArgs e)
             {
-                taskCompletionSource.TrySetResult(e.Exception);
+                promise.TrySetException(e.Exception);
             }
 
-            void SuccessHandler(object sender, EventArgs e)
+            void OpenedHandler(object sender, EventArgs e)
             {
-                taskCompletionSource.TrySetResult(null);
+                promise.TrySetResult(true);
+            }
+
+            void ClosedHandler(object sender, EventArgs e)
+            {
+                promise.TrySetException(new MqttCommunicationException("Connection closed."));
             }
 
             try
             {
-                _webSocket.Opened += SuccessHandler;
+                _webSocket.Opened += OpenedHandler;
+                _webSocket.Closed += ClosedHandler;
                 _webSocket.Error += ErrorHandler;
 
-#pragma warning disable AsyncFixer02 // Long-running or blocking operations inside an async method
-                _webSocket.Open();
-#pragma warning restore AsyncFixer02 // Long-running or blocking operations inside an async method
-
-                using (var timeoutCts = new CancellationTokenSource(_clientOptions.Timeout))
-                using (var linkedCts = CancellationTokenSource.CreateLinkedTokenSource(timeoutCts.Token, cancellationToken))
+                using (var timeout = new CancellationTokenSource(_clientOptions.Timeout))
+                using (var linkedCts = CancellationTokenSource.CreateLinkedTokenSource(timeout.Token, cancellationToken))
                 {
-                    using (linkedCts.Token.Register(() => taskCompletionSource.TrySetCanceled()))
+                    using (linkedCts.Token.Register(() => promise.TrySetCanceled()))
                     {
                         try
                         {
-                            await taskCompletionSource.Task.ConfigureAwait(false);
+                            // OpenAsync does basically the same but without support for a cancellation token.
+                            // So we do it on our own!
+                            _webSocket.Open();
+
+                            await promise.Task.ConfigureAwait(false);
                         }
                         catch (Exception exception)
                         {
-                            var timeoutReached = timeoutCts.IsCancellationRequested && !cancellationToken.IsCancellationRequested;
+                            var timeoutReached = timeout.IsCancellationRequested && !cancellationToken.IsCancellationRequested;
                             if (timeoutReached)
                             {
                                 throw new MqttCommunicationTimedOutException(exception);
                             }
-                            
+
                             if (exception is AuthenticationException authenticationException)
                             {
                                 throw new MqttCommunicationException(authenticationException.InnerException);
@@ -250,9 +245,23 @@ namespace MQTTnet.Extensions.WebSocket4Net
             }
             finally
             {
-                _webSocket.Opened -= SuccessHandler;
+                _webSocket.Opened -= OpenedHandler;
+                _webSocket.Closed -= ClosedHandler;
                 _webSocket.Error -= ErrorHandler;
             }
         }
+
+        void OnDataReceived(object sender, DataReceivedEventArgs e)
+        {
+            foreach (var @byte in e.Data)
+            {
+                _receiveBuffer.Add(@byte);
+            }
+        }
+
+        static void OnError(object sender, ErrorEventArgs e)
+        {
+            Debug.Write(e.Exception.ToString());
+        }
     }
-}
+}

Source/MQTTnet.Extensions.WebSocket4Net/WebSocket4NetMqttClientAdapterFactory.cs

@@ -2,12 +2,12 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using MQTTnet.Adapter;
-using MQTTnet.Formatter;
-using MQTTnet.Implementations;
 using System;
+using MQTTnet.Adapter;
 using MQTTnet.Client;
 using MQTTnet.Diagnostics;
+using MQTTnet.Formatter;
+using MQTTnet.Implementations;
 
 namespace MQTTnet.Extensions.WebSocket4Net
 {
@@ -15,7 +15,10 @@ namespace MQTTnet.Extensions.WebSocket4Net
     {
         public IMqttChannelAdapter CreateClientAdapter(MqttClientOptions options, MqttPacketInspector packetInspector, IMqttNetLogger logger)
         {
-            if (options == null) throw new ArgumentNullException(nameof(options));
+            if (options == null)
+            {
+                throw new ArgumentNullException(nameof(options));
+            }
 
             switch (options.ChannelOptions)
             {
@@ -23,7 +26,7 @@ namespace MQTTnet.Extensions.WebSocket4Net
                 {
                     return new MqttChannelAdapter(
                         new MqttTcpChannel(options),
-                        new MqttPacketFormatterAdapter(options.ProtocolVersion, new MqttBufferWriter(4096, 65535)),
+                        new MqttPacketFormatterAdapter(options.ProtocolVersion, new MqttBufferWriter(options.WriterBufferSize, options.WriterBufferSizeMax)),
                         packetInspector,
                         logger);
                 }
@@ -32,16 +35,16 @@ namespace MQTTnet.Extensions.WebSocket4Net
                 {
                     return new MqttChannelAdapter(
                         new WebSocket4NetMqttChannel(options, webSocketOptions),
-                        new MqttPacketFormatterAdapter(options.ProtocolVersion, new MqttBufferWriter(4068, 65535)), 
+                        new MqttPacketFormatterAdapter(options.ProtocolVersion, new MqttBufferWriter(options.WriterBufferSize, options.WriterBufferSizeMax)),
                         packetInspector,
                         logger);
                 }
 
                 default:
-                    {
-                        throw new NotSupportedException();
-                    }
+                {
+                    throw new NotSupportedException();
+                }
             }
         }
     }
-}
+}

Source/MQTTnet.TestApp/AsyncLockTest.cs

@@ -0,0 +1,28 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Threading;
+using System.Threading.Tasks;
+using MQTTnet.Internal;
+
+namespace MQTTnet.TestApp
+{
+    public sealed class AsyncLockTest
+    {
+        public async Task Run()
+        {
+            var asyncLock = new AsyncLock();
+
+            using (var cancellationToken = new CancellationTokenSource())
+            {
+                for (var i = 0; i < 100000; i++)
+                {
+                    using (await asyncLock.EnterAsync(cancellationToken.Token).ConfigureAwait(false))
+                    {
+                    }
+                } 
+            }
+        }
+    }
+}

Source/MQTTnet.TestApp/ClientTest.cs

@@ -7,7 +7,7 @@ using System;
 using System.Text;
 using System.Threading.Tasks;
 using MQTTnet.Diagnostics;
-using MQTTnet.Implementations;
+using MQTTnet.Internal;
 using MQTTnet.Protocol;
 
 namespace MQTTnet.TestApp
@@ -40,7 +40,7 @@ namespace MQTTnet.TestApp
                     Console.WriteLine($"+ Retain = {e.ApplicationMessage.Retain}");
                     Console.WriteLine();
                     
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 client.ConnectedAsync += async e =>

Source/MQTTnet.TestApp/MQTTnet.TestApp.csproj

@@ -9,12 +9,11 @@
         <EnableNETAnalyzers>false</EnableNETAnalyzers>
         <EnforceCodeStyleInBuild>false</EnforceCodeStyleInBuild>
         <DisableImplicitAspNetCoreAnalyzers>true</DisableImplicitAspNetCoreAnalyzers>
+        <NoWarn>1591;NETSDK1138</NoWarn>
     </PropertyGroup>
 
     <ItemGroup>
-        <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
-        <PackageReference Include="Microsoft.CodeAnalysis.Compilers" Version="4.0.1" />
-        <PackageReference Include="Microsoft.Net.Compilers" Version="4.0.1" />
+        <PackageReference Include="Newtonsoft.Json" Version="13.0.2" />
     </ItemGroup>
 
     <ItemGroup>

Source/MQTTnet.TestApp/ManagedClientTest.cs

@@ -9,7 +9,7 @@ using Newtonsoft.Json;
 using System.Collections.Generic;
 using MQTTnet.Client;
 using MQTTnet.Extensions.ManagedClient;
-using MQTTnet.Implementations;
+using MQTTnet.Internal;
 using MQTTnet.Protocol;
 
 namespace MQTTnet.TestApp
@@ -42,7 +42,7 @@ namespace MQTTnet.TestApp
                 managedClient.ApplicationMessageReceivedAsync += e =>
                 {
                     Console.WriteLine(">> RECEIVED: " + e.ApplicationMessage.Topic);
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await managedClient.StartAsync(options);
@@ -85,7 +85,7 @@ namespace MQTTnet.TestApp
             public Task SaveQueuedMessagesAsync(IList<ManagedMqttApplicationMessage> messages)
             {
                 File.WriteAllText(Filename, JsonConvert.SerializeObject(messages));
-                return Task.FromResult(0);
+                return CompletedTask.Instance;
             }
 
             public Task<IList<ManagedMqttApplicationMessage>> LoadQueuedMessagesAsync()

Source/MQTTnet.TestApp/MessageThroughputTest.cs

@@ -5,6 +5,7 @@ using System;
 using System.Threading;
 using System.Threading.Tasks;
 using System.Linq;
+using MQTTnet.Internal;
 
 namespace MQTTnet.TestApp
 {
@@ -124,7 +125,7 @@ namespace MQTTnet.TestApp
             {
                 _cancellationTokenSource.Cancel();
             }
-            return Implementations.PlatformAbstractionLayer.CompletedTask;
+            return CompletedTask.Instance;
         }
 
         public async Task Cleanup()

Source/MQTTnet.TestApp/Program.cs

@@ -28,6 +28,7 @@ namespace MQTTnet.TestApp
             Console.WriteLine("c = Start QoS 0 benchmark");
             Console.WriteLine("d = Start server with logging");
             Console.WriteLine("e = Start Message Throughput Test");
+            Console.WriteLine("f = Start AsyncLock Test");
 
             var pressedKey = Console.ReadKey(true);
             if (pressedKey.KeyChar == '1')
@@ -88,6 +89,10 @@ namespace MQTTnet.TestApp
             {
                 Task.Run(new MessageThroughputTest().Run);
             }
+            else if (pressedKey.KeyChar == 'f')
+            {
+                Task.Run(new AsyncLockTest().Run);
+            }
 
             Thread.Sleep(Timeout.Infinite);
         }

Source/MQTTnet.TestApp/PublicBrokerTest.cs

@@ -2,13 +2,14 @@
 // 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.Security.Authentication;
 using System.Threading;
 using System.Threading.Tasks;
+using MQTTnet.Client;
+using MQTTnet.Extensions.WebSocket4Net;
 using MQTTnet.Formatter;
-using MQTTnet.Implementations;
+using MQTTnet.Internal;
 using MQTTnet.Protocol;
 
 namespace MQTTnet.TestApp
@@ -17,10 +18,6 @@ namespace MQTTnet.TestApp
     {
         public static async Task RunAsync()
         {
-            // MqttNetConsoleLogger.ForwardToConsole();
-
-            // For most of these connections to work, set output target to Net5.0.            
-
 #if NET5_0_OR_GREATER
             // TLS13 is only available in Net5.0
             var unsafeTls13 = new MqttClientOptionsBuilderTlsParameters
@@ -31,7 +28,6 @@ namespace MQTTnet.TestApp
                 CertificateValidationHandler = w => true
             };
 #endif
-
             // Also defining TLS12 for servers that don't seem no to support TLS13.
             var unsafeTls12 = new MqttClientOptionsBuilderTlsParameters
             {
@@ -42,33 +38,37 @@ namespace MQTTnet.TestApp
             };
 
             // mqtt.eclipseprojects.io
-            await ExecuteTestAsync("mqtt.eclipseprojects.io TCP",
-                    new MqttClientOptionsBuilder().WithTcpServer("mqtt.eclipseprojects.io", 1883)
-                        .WithProtocolVersion(MqttProtocolVersion.V311).Build());
+            await ExecuteTestAsync(
+                "mqtt.eclipseprojects.io TCP",
+                new MqttClientOptionsBuilder().WithTcpServer("mqtt.eclipseprojects.io", 1883).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync("mqtt.eclipseprojects.io WS",
-                new MqttClientOptionsBuilder().WithWebSocketServer("mqtt.eclipseprojects.io:80/mqtt")
-                    .WithProtocolVersion(MqttProtocolVersion.V311).Build());
+            await ExecuteTestAsync(
+                "mqtt.eclipseprojects.io WS",
+                new MqttClientOptionsBuilder().WithWebSocketServer("mqtt.eclipseprojects.io:80/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
 #if NET5_0_OR_GREATER
             await ExecuteTestAsync("mqtt.eclipseprojects.io WS TLS13",
                 new MqttClientOptionsBuilder().WithWebSocketServer("mqtt.eclipseprojects.io:443/mqtt")
                     .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build());
+            
+            await ExecuteTestAsync("mqtt.eclipseprojects.io WS TLS13 (WebSocket4Net)",
+                new MqttClientOptionsBuilder().WithWebSocketServer("mqtt.eclipseprojects.io:443/mqtt")
+                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build(),
+                    true);
 #endif
 
             // test.mosquitto.org
-            await ExecuteTestAsync("test.mosquitto.org TCP",
-                new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 1883)
-                    .WithProtocolVersion(MqttProtocolVersion.V311).Build());
+            await ExecuteTestAsync(
+                "test.mosquitto.org TCP",
+                new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 1883).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync("test.mosquitto.org TCP - Authenticated",
-                new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 1884)
-                    .WithCredentials("rw", "readwrite")
-                    .WithProtocolVersion(MqttProtocolVersion.V311).Build());
+            await ExecuteTestAsync(
+                "test.mosquitto.org TCP - Authenticated",
+                new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 1884).WithCredentials("rw", "readwrite").WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync("test.mosquitto.org TCP TLS12",
-                new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8883)
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+            await ExecuteTestAsync(
+                "test.mosquitto.org TCP TLS12",
+                new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8883).WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
 
 #if NET5_0_OR_GREATER
             await ExecuteTestAsync("test.mosquitto.org TCP TLS13",
@@ -76,27 +76,40 @@ namespace MQTTnet.TestApp
                     .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build());
 #endif
 
-            await ExecuteTestAsync("test.mosquitto.org TCP TLS12 - Authenticated",
+            await ExecuteTestAsync(
+                "test.mosquitto.org TCP TLS12 - Authenticated",
                 new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8885)
                     .WithCredentials("rw", "readwrite")
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+                    .WithProtocolVersion(MqttProtocolVersion.V311)
+                    .WithTls(unsafeTls12)
+                    .Build());
 
-            await ExecuteTestAsync("test.mosquitto.org WS",
-                new MqttClientOptionsBuilder().WithWebSocketServer("test.mosquitto.org:8080/mqtt")
-                    .WithProtocolVersion(MqttProtocolVersion.V311).Build());
+            await ExecuteTestAsync(
+                "test.mosquitto.org WS",
+                new MqttClientOptionsBuilder().WithWebSocketServer("test.mosquitto.org:8080/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync("test.mosquitto.org WS TLS12",
-                new MqttClientOptionsBuilder().WithWebSocketServer("test.mosquitto.org:8081/mqtt")
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+            await ExecuteTestAsync(
+                "test.mosquitto.org WS (WebSocket4Net)",
+                new MqttClientOptionsBuilder().WithWebSocketServer("test.mosquitto.org:8080/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build(),
+                true);
+
+            await ExecuteTestAsync(
+                "test.mosquitto.org WS TLS12",
+                new MqttClientOptionsBuilder().WithWebSocketServer("test.mosquitto.org:8081/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+
+            // await ExecuteTestAsync(
+            //     "test.mosquitto.org WS TLS12 (WebSocket4Net)",
+            //     new MqttClientOptionsBuilder().WithWebSocketServer("test.mosquitto.org:8081/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build(),
+            //     true);
 
             // broker.emqx.io
-            await ExecuteTestAsync("broker.emqx.io TCP",
-                new MqttClientOptionsBuilder().WithTcpServer("broker.emqx.io", 1883)
-                     .WithProtocolVersion(MqttProtocolVersion.V311).Build());
+            await ExecuteTestAsync(
+                "broker.emqx.io TCP",
+                new MqttClientOptionsBuilder().WithTcpServer("broker.emqx.io", 1883).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync("broker.emqx.io TCP TLS12",
-                new MqttClientOptionsBuilder().WithTcpServer("broker.emqx.io", 8883)
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+            await ExecuteTestAsync(
+                "broker.emqx.io TCP TLS12",
+                new MqttClientOptionsBuilder().WithTcpServer("broker.emqx.io", 8883).WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
 
 #if NET5_0_OR_GREATER
             await ExecuteTestAsync("broker.emqx.io TCP TLS13",
@@ -104,23 +117,37 @@ namespace MQTTnet.TestApp
                     .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build());
 #endif
 
-            await ExecuteTestAsync("broker.emqx.io WS",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.emqx.io:8083/mqtt")
-                    .WithProtocolVersion(MqttProtocolVersion.V311).Build());
+            await ExecuteTestAsync(
+                "broker.emqx.io WS",
+                new MqttClientOptionsBuilder().WithWebSocketServer("broker.emqx.io:8083/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync("broker.emqx.io WS TLS12",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.emqx.io:8084/mqtt")
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+            await ExecuteTestAsync(
+                "broker.emqx.io WS (WebSocket4Net)",
+                new MqttClientOptionsBuilder().WithWebSocketServer("broker.emqx.io:8084/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build(),
+                true);
 
+            await ExecuteTestAsync(
+                "broker.emqx.io WS TLS12",
+                new MqttClientOptionsBuilder().WithWebSocketServer("broker.emqx.io:8084/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+
+            await ExecuteTestAsync(
+                "broker.emqx.io WS TLS12 (WebSocket4Net)",
+                new MqttClientOptionsBuilder().WithWebSocketServer("broker.emqx.io:8084/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build(),
+                true);
 
             // broker.hivemq.com
-            await ExecuteTestAsync("broker.hivemq.com TCP",
-                new MqttClientOptionsBuilder().WithTcpServer("broker.hivemq.com", 1883)
-                    .WithProtocolVersion(MqttProtocolVersion.V311).Build());
+            await ExecuteTestAsync(
+                "broker.hivemq.com TCP",
+                new MqttClientOptionsBuilder().WithTcpServer("broker.hivemq.com", 1883).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
-            await ExecuteTestAsync("broker.hivemq.com WS",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.hivemq.com:8000/mqtt")
-                    .WithProtocolVersion(MqttProtocolVersion.V311).Build());
+            await ExecuteTestAsync(
+                "broker.hivemq.com WS",
+                new MqttClientOptionsBuilder().WithWebSocketServer("broker.hivemq.com:8000/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build());
+
+            await ExecuteTestAsync(
+                "broker.hivemq.com WS (WebSocket4Net)",
+                new MqttClientOptionsBuilder().WithWebSocketServer("broker.hivemq.com:8000/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build(),
+                true);
 
             // mqtt.swifitch.cz: Does not seem to operate any more
 
@@ -130,36 +157,43 @@ namespace MQTTnet.TestApp
             Console.ReadLine();
         }
 
-        static async Task ExecuteTestAsync(string name, MqttClientOptions options)
+        static async Task ExecuteTestAsync(string name, MqttClientOptions options, bool useWebSocket4Net = false)
         {
             try
             {
                 Write("Testing '" + name + "'... ", ConsoleColor.Gray);
+
                 var factory = new MqttFactory();
-                //factory.UseWebSocket4Net();
-                var client = factory.CreateMqttClient();
-                var topic = Guid.NewGuid().ToString();
-
-                MqttApplicationMessage receivedMessage = null;
-                client.ApplicationMessageReceivedAsync += e =>
+                if (useWebSocket4Net)
                 {
-                    receivedMessage = e.ApplicationMessage;
-                    return PlatformAbstractionLayer.CompletedTask;
-                };
-
-                await client.ConnectAsync(options);
-                await client.SubscribeAsync(topic, MqttQualityOfServiceLevel.AtLeastOnce);
-                await client.PublishStringAsync(topic, "Hello_World", MqttQualityOfServiceLevel.AtLeastOnce);
-
-                SpinWait.SpinUntil(() => receivedMessage != null, 5000);
-
-                if (receivedMessage?.Topic != topic || receivedMessage?.ConvertPayloadToString() != "Hello_World")
-                {
-                    throw new Exception("Message invalid.");
+                    factory.UseWebSocket4Net();
                 }
 
-                await client.UnsubscribeAsync(topic);
-                await client.DisconnectAsync();
+                using (var client = factory.CreateMqttClient())
+                {
+                    MqttApplicationMessage receivedMessage = null;
+                    client.ApplicationMessageReceivedAsync += e =>
+                    {
+                        receivedMessage = e.ApplicationMessage;
+                        return CompletedTask.Instance;
+                    };
+
+                    await client.ConnectAsync(options).ConfigureAwait(false);
+
+                    var topic = Guid.NewGuid().ToString();
+                    await client.SubscribeAsync(topic, MqttQualityOfServiceLevel.AtLeastOnce).ConfigureAwait(false);
+                    await client.PublishStringAsync(topic, "Hello_World", MqttQualityOfServiceLevel.AtLeastOnce).ConfigureAwait(false);
+
+                    SpinWait.SpinUntil(() => receivedMessage != null, 5000);
+
+                    if (receivedMessage?.Topic != topic || receivedMessage?.ConvertPayloadToString() != "Hello_World")
+                    {
+                        throw new Exception("Message invalid.");
+                    }
+
+                    await client.UnsubscribeAsync(topic).ConfigureAwait(false);
+                    await client.DisconnectAsync().ConfigureAwait(false);
+                }
 
                 Write("[OK]\n", ConsoleColor.Green);
             }
@@ -174,6 +208,5 @@ namespace MQTTnet.TestApp
             Console.ForegroundColor = color;
             Console.Write(message);
         }
-
     }
-}
+}

Source/MQTTnet.TestApp/ServerTest.cs

@@ -4,13 +4,11 @@
 
 using System;
 using System.Collections.Generic;
-using System.Diagnostics;
 using System.IO;
 using System.Text;
 using System.Threading.Tasks;
 using MQTTnet.Diagnostics;
-using MQTTnet.Extensions.ManagedClient;
-using MQTTnet.Implementations;
+using MQTTnet.Internal;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
 using Newtonsoft.Json;
@@ -69,13 +67,13 @@ namespace MQTTnet.TestApp
                     }
 
                     File.WriteAllText(Filename, JsonConvert.SerializeObject(e.StoredRetainedMessages));
-                    return Task.FromResult(0);
+                    return CompletedTask.Instance;
                 };
                 
                 mqttServer.RetainedMessagesClearedAsync += e =>
                 {
                     File.Delete(Filename);
-                    return Task.FromResult(0);
+                    return CompletedTask.Instance;
                 };
                 
                 mqttServer.LoadingRetainedMessageAsync += e =>
@@ -93,7 +91,7 @@ namespace MQTTnet.TestApp
 
                     e.LoadedRetainedMessages = retainedMessages;
 
-                    return Task.FromResult(0);
+                    return CompletedTask.Instance;
                 };
 
                 mqttServer.InterceptingPublishAsync += e =>
@@ -111,7 +109,7 @@ namespace MQTTnet.TestApp
                         e.CloseConnection = true;
                     }
 
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
                 
                 mqttServer.ValidatingConnectionAsync += e =>
@@ -124,7 +122,7 @@ namespace MQTTnet.TestApp
                         }
                     }
 
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 mqttServer.InterceptingSubscriptionAsync += e =>
@@ -140,7 +138,7 @@ namespace MQTTnet.TestApp
                         e.CloseConnection = true;
                     }
 
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
                 
                 mqttServer.InterceptingPublishAsync += e =>
@@ -149,7 +147,7 @@ namespace MQTTnet.TestApp
                         $"'{e.ClientId}' reported '{e.ApplicationMessage.Topic}' > '{Encoding.UTF8.GetString(e.ApplicationMessage.Payload ?? new byte[0])}'",
                         ConsoleColor.Magenta);
                     
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 //options.ApplicationMessageInterceptor = c =>
@@ -177,7 +175,7 @@ namespace MQTTnet.TestApp
                 mqttServer.ClientConnectedAsync += e =>
                 {
                     Console.Write("Client disconnected event fired.");
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await mqttServer.StartAsync();

Source/MQTTnet.Tests/Client/LowLevelMqttClient_Tests.cs

@@ -64,7 +64,7 @@ namespace MQTTnet.Tests.Client
 
             await client.ConnectAsync(options, CancellationToken.None).ConfigureAwait(false);
         }
-        
+
         [TestMethod]
         [ExpectedException(typeof(MqttCommunicationException))]
         public async Task Connect_To_Wrong_Host()
@@ -80,6 +80,8 @@ namespace MQTTnet.Tests.Client
         {
             using (var testEnvironment = CreateTestEnvironment())
             {
+                testEnvironment.IgnoreServerLogErrors = true;
+
                 testEnvironment.ServerPort = 8364;
                 var server = await testEnvironment.StartServer();
 
@@ -116,6 +118,8 @@ namespace MQTTnet.Tests.Client
         {
             using (var testEnvironment = CreateTestEnvironment())
             {
+                testEnvironment.IgnoreServerLogErrors = true;
+
                 var server = await testEnvironment.StartServer();
 
                 using (var lowLevelClient = testEnvironment.CreateLowLevelClient())
@@ -123,7 +127,7 @@ namespace MQTTnet.Tests.Client
                     Assert.IsFalse(lowLevelClient.IsConnected);
 
                     var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1", testEnvironment.ServerPort).WithTimeout(TimeSpan.FromSeconds(1)).Build();
-                    
+
                     await lowLevelClient.ConnectAsync(clientOptions, CancellationToken.None);
 
                     Assert.IsTrue(lowLevelClient.IsConnected);
@@ -148,7 +152,7 @@ namespace MQTTnet.Tests.Client
                     catch
                     {
                     }
-           
+
                     Assert.IsFalse(lowLevelClient.IsConnected);
                 }
             }

Source/MQTTnet.Tests/Client/ManagedMqttClient_Tests.cs

@@ -11,18 +11,78 @@ using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
 using MQTTnet.Diagnostics;
 using MQTTnet.Extensions.ManagedClient;
-using MQTTnet.Implementations;
+using MQTTnet.Formatter;
 using MQTTnet.Internal;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
 using MQTTnet.Tests.Mockups;
-using MqttClient = MQTTnet.Client.MqttClient;
 
 namespace MQTTnet.Tests.Client
 {
     [TestClass]
     public sealed class ManagedMqttClient_Tests : BaseTestClass
     {
+        [TestMethod]
+        public async Task Receive_While_Not_Cleanly_Disconnected()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                await testEnvironment.StartServer(o => o.WithPersistentSessions());
+
+                var senderClient = await testEnvironment.ConnectClient();
+
+                // Prepare managed client.
+                var managedClient = testEnvironment.Factory.CreateManagedMqttClient();
+                await managedClient.SubscribeAsync("#");
+                var receivedMessages = testEnvironment.CreateApplicationMessageHandler(managedClient);
+                
+                var managedClientOptions = new ManagedMqttClientOptions
+                {
+                    ClientOptions = testEnvironment.Factory.CreateClientOptionsBuilder()
+                        .WithTcpServer("127.0.0.1", testEnvironment.ServerPort)
+                        .WithClientId(nameof(Receive_While_Not_Cleanly_Disconnected) + "_managed")
+                        .WithCleanSession(false)
+                        .Build()
+                };
+
+                await managedClient.StartAsync(managedClientOptions);
+                await LongTestDelay();
+                await LongTestDelay();
+                
+                // Send test data.
+                await senderClient.PublishStringAsync("topic1");
+                await LongTestDelay();
+                await LongTestDelay();
+                
+                receivedMessages.AssertReceivedCountEquals(1);
+
+                // Stop the managed client but keep session at server (not clean disconnect required).
+                await managedClient.StopAsync(false);
+                await LongTestDelay();
+                
+                // Send new messages in the meantime.
+                await senderClient.PublishStringAsync("topic2", qualityOfServiceLevel: MqttQualityOfServiceLevel.ExactlyOnce);
+                await LongTestDelay();
+                
+                // Start the managed client, it should receive the new message.
+                await managedClient.StartAsync(managedClientOptions);
+                await LongTestDelay();
+                
+                receivedMessages.AssertReceivedCountEquals(2);
+                
+                // Stop and start again, no new message should be received.
+                for (var i = 0; i < 3; i++)
+                {
+                    await managedClient.StopAsync(false);
+                    await LongTestDelay();
+                    await managedClient.StartAsync(managedClientOptions);
+                    await LongTestDelay();
+                }
+
+                receivedMessages.AssertReceivedCountEquals(2);
+            }
+        }
+
         [TestMethod]
         public async Task Connect_To_Invalid_Server()
         {
@@ -35,11 +95,10 @@ namespace MQTTnet.Tests.Client
                 var managedClient = testEnvironment.Factory.CreateManagedMqttClient(mqttClient);
 
                 ConnectingFailedEventArgs connectingFailedEventArgs = null;
-
                 managedClient.ConnectingFailedAsync += args =>
                 {
                     connectingFailedEventArgs = args;
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await managedClient.StartAsync(
@@ -117,7 +176,7 @@ namespace MQTTnet.Tests.Client
                 receivingClient.ApplicationMessageReceivedAsync += e =>
                 {
                     Interlocked.Increment(ref receivedMessagesCount);
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await receivingClient.SubscribeAsync("My/last/will");
@@ -272,16 +331,10 @@ namespace MQTTnet.Tests.Client
                 await testEnvironment.StartServer().ConfigureAwait(false);
 
                 var sendingClient = await testEnvironment.ConnectClient().ConfigureAwait(false);
-                await sendingClient.PublishAsync(
-                    new MqttApplicationMessage
-                    {
-                        Topic = "topic",
-                        Payload = new byte[] { 1 },
-                        Retain = true
-                    });
+                await sendingClient.PublishStringAsync("topic", "A", retain: true);
 
                 // Wait a bit for the retained message to be available
-                await Task.Delay(1000);
+                await LongTestDelay();
 
                 await sendingClient.DisconnectAsync();
 
@@ -290,28 +343,26 @@ namespace MQTTnet.Tests.Client
                 var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1", testEnvironment.ServerPort);
 
                 var receivedManagedMessages = new List<MqttApplicationMessage>();
-                var managedClient = new ManagedMqttClient(testEnvironment.CreateClient(), new MqttNetEventLogger());
+                
+                var managedClient = testEnvironment.Factory.CreateManagedMqttClient(testEnvironment.CreateClient());
                 managedClient.ApplicationMessageReceivedAsync += e =>
                 {
                     receivedManagedMessages.Add(e.ApplicationMessage);
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await managedClient.SubscribeAsync("topic");
 
-                await managedClient.StartAsync(new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).WithAutoReconnectDelay(TimeSpan.FromSeconds(1)).Build());
-
-                await Task.Delay(1000);
+                await managedClient.StartAsync(new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).WithAutoReconnectDelay(TimeSpan.FromSeconds(0.5)).Build());
+                await LongTestDelay();
 
                 Assert.AreEqual(1, receivedManagedMessages.Count);
 
                 await managedClient.StopAsync();
+                await LongTestDelay();
 
-                await Task.Delay(500);
-
-                await managedClient.StartAsync(new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).WithAutoReconnectDelay(TimeSpan.FromSeconds(1)).Build());
-
-                await Task.Delay(1000);
+                await managedClient.StartAsync(new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).WithAutoReconnectDelay(TimeSpan.FromSeconds(0.5)).Build());
+                await LongTestDelay();
 
                 // After reconnect and then some delay, the retained message must not be received,
                 // showing that the subscriptions were cleared
@@ -319,7 +370,8 @@ namespace MQTTnet.Tests.Client
 
                 // Make sure that it gets received after subscribing again.
                 await managedClient.SubscribeAsync("topic");
-                await Task.Delay(500);
+                await LongTestDelay();
+                
                 Assert.AreEqual(2, receivedManagedMessages.Count);
             }
         }
@@ -428,7 +480,7 @@ namespace MQTTnet.Tests.Client
             managedClient.ConnectedAsync += e =>
             {
                 connected.TrySetResult(true);
-                return PlatformAbstractionLayer.CompletedTask;
+                return CompletedTask.Instance;
             };
 
             return connected.Task;
@@ -457,7 +509,7 @@ namespace MQTTnet.Tests.Client
                     result.TrySetResult(receivedMessages);
                 }
 
-                return PlatformAbstractionLayer.CompletedTask;
+                return CompletedTask.Instance;
             };
 
             return result.Task;
@@ -486,7 +538,7 @@ namespace MQTTnet.Tests.Client
         public Task SaveQueuedMessagesAsync(IList<ManagedMqttApplicationMessage> messages)
         {
             _messages = messages;
-            return Task.FromResult(0);
+            return CompletedTask.Instance;
         }
     }
 }

Source/MQTTnet.Tests/Client/MqttClient_Tests.cs

@@ -14,15 +14,17 @@ using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
-using MQTTnet.Implementations;
+using MQTTnet.Internal;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
 using MQTTnet.Tests.Mockups;
 
+// ReSharper disable InconsistentNaming
+
 namespace MQTTnet.Tests.Client
 {
     [TestClass]
-    public sealed class Client_Tests : BaseTestClass
+    public sealed class MqttClient_Tests : BaseTestClass
     {
         [DataTestMethod]
         [DataRow(MqttQualityOfServiceLevel.ExactlyOnce)]
@@ -56,7 +58,7 @@ namespace MQTTnet.Tests.Client
                     }
 
                     _ = InvokeInternal();
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 var publishes = Task.WhenAll(publisher.PublishStringAsync("a", null, qos), publisher.PublishStringAsync("b", null, qos));
@@ -107,7 +109,7 @@ namespace MQTTnet.Tests.Client
                     client.DisconnectedAsync += args =>
                     {
                         disconnectHandlerCalled = true;
-                        return PlatformAbstractionLayer.CompletedTask;
+                        return CompletedTask.Instance;
                     };
 
                     await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("1.2.3.4").Build());
@@ -121,7 +123,7 @@ namespace MQTTnet.Tests.Client
                     //Assert.IsInstanceOfType(exception.InnerException, typeof(SocketException));
                 }
 
-                await Task.Delay(100); // disconnected handler is called async
+                await LongTestDelay(); // disconnected handler is called async
                 Assert.IsTrue(disconnectHandlerCalled);
             }
         }
@@ -136,7 +138,7 @@ namespace MQTTnet.Tests.Client
                 client.DisconnectedAsync += e =>
                 {
                     ex = e.Exception;
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 try
@@ -145,6 +147,7 @@ namespace MQTTnet.Tests.Client
                 }
                 catch
                 {
+                    // Ignore errors.
                 }
 
                 await Task.Delay(500);
@@ -167,7 +170,7 @@ namespace MQTTnet.Tests.Client
                 server.InterceptingPublishAsync += c =>
                 {
                     i++;
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await client.SendAsync(
@@ -208,7 +211,7 @@ namespace MQTTnet.Tests.Client
                 client.DisconnectedAsync += e =>
                 {
                     handlerFired = true;
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await server.StopAsync();
@@ -239,10 +242,10 @@ namespace MQTTnet.Tests.Client
 
                 for (var i = 0; i < 98; i++)
                 {
-                    Assert.IsFalse(clients[i].IsConnected, $"clients[{i}] is not connected");
+                    Assert.IsFalse(clients[i].TryPingAsync().GetAwaiter().GetResult(), $"clients[{i}] is not connected");
                 }
 
-                Assert.IsTrue(clients[99].IsConnected);
+                Assert.IsTrue(clients[99].TryPingAsync().GetAwaiter().GetResult());
 
                 Assert.AreEqual(1, clientStatus.Count);
                 Assert.AreEqual(1, sessionStatus.Count);
@@ -252,7 +255,7 @@ namespace MQTTnet.Tests.Client
                 receiveClient.ApplicationMessageReceivedAsync += e =>
                 {
                     receivedPayload = e.ApplicationMessage.ConvertPayloadToString();
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await receiveClient.SubscribeAsync("x");
@@ -310,7 +313,7 @@ namespace MQTTnet.Tests.Client
                 receiver.ApplicationMessageReceivedAsync += e =>
                 {
                     receivedMessage = e.ApplicationMessage;
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await sender.PublishAsync(message.Build(), CancellationToken.None);
@@ -332,7 +335,7 @@ namespace MQTTnet.Tests.Client
 
                 var client = await testEnvironment.ConnectClient();
 
-                Assert.IsTrue(client.IsConnected);
+                Assert.IsTrue(client.TryPingAsync().GetAwaiter().GetResult());
             }
         }
 
@@ -343,11 +346,11 @@ namespace MQTTnet.Tests.Client
             {
                 await testEnvironment.StartServer();
                 var client = await testEnvironment.ConnectClient();
-                Assert.IsTrue(client.IsConnected);
+                Assert.IsTrue(client.TryPingAsync().GetAwaiter().GetResult());
 
                 await client.DisconnectAsync();
 
-                Assert.IsFalse(client.IsConnected);
+                Assert.IsFalse(client.TryPingAsync().GetAwaiter().GetResult());
             }
         }
 
@@ -453,7 +456,7 @@ namespace MQTTnet.Tests.Client
                         receivedValues.Add(value);
                     }
 
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 }
 
                 client1.ApplicationMessageReceivedAsync += Handler1;
@@ -531,7 +534,7 @@ namespace MQTTnet.Tests.Client
                 client2.ApplicationMessageReceivedAsync += e =>
                 {
                     client2TopicResults.Add(Encoding.UTF8.GetString(e.ApplicationMessage.Payload));
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await client2.SubscribeAsync(client2Topic);
@@ -566,7 +569,7 @@ namespace MQTTnet.Tests.Client
                         receivedMessages.Add(e.ApplicationMessage);
                     }
 
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await client1.SubscribeAsync("a");
@@ -591,17 +594,17 @@ namespace MQTTnet.Tests.Client
                 var client = await testEnvironment.ConnectClient();
 
                 await Task.Delay(500);
-                Assert.IsTrue(client.IsConnected);
+                Assert.IsTrue(await client.TryPingAsync());
 
                 await server.StopAsync();
                 await Task.Delay(500);
-                Assert.IsFalse(client.IsConnected);
+                Assert.IsFalse(await client.TryPingAsync());
 
                 await server.StartAsync();
                 await Task.Delay(500);
 
                 await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1", testEnvironment.ServerPort).Build());
-                Assert.IsTrue(client.IsConnected);
+                Assert.IsTrue(await client.TryPingAsync());
             }
         }
 
@@ -637,6 +640,7 @@ namespace MQTTnet.Tests.Client
                 }
                 catch
                 {
+                    // Ignore errors.
                 }
 
                 SpinWait.SpinUntil(() => tries >= maxTries, 10000);
@@ -656,11 +660,11 @@ namespace MQTTnet.Tests.Client
                 var client = await testEnvironment.ConnectClient();
 
                 await Task.Delay(500);
-                Assert.IsTrue(client.IsConnected);
+                Assert.IsTrue(client.TryPingAsync().GetAwaiter().GetResult());
 
                 await server.StopAsync();
                 await Task.Delay(500);
-                Assert.IsFalse(client.IsConnected);
+                Assert.IsFalse(client.TryPingAsync().GetAwaiter().GetResult());
 
                 for (var i = 0; i < 5; i++)
                 {
@@ -671,6 +675,7 @@ namespace MQTTnet.Tests.Client
                     }
                     catch
                     {
+                        // Ignore errors.
                     }
                 }
 
@@ -678,7 +683,7 @@ namespace MQTTnet.Tests.Client
                 await Task.Delay(500);
 
                 await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1", testEnvironment.ServerPort).Build());
-                Assert.IsTrue(client.IsConnected);
+                await client.PingAsync();
             }
         }
 
@@ -723,7 +728,7 @@ namespace MQTTnet.Tests.Client
                         replies.Add(eventArgs.ApplicationMessage.Topic);
                     }
 
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 }
 
                 client2.ApplicationMessageReceivedAsync += Handler2;
@@ -761,7 +766,7 @@ namespace MQTTnet.Tests.Client
                         replyReceived = true;
                     }
 
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 client2.ApplicationMessageReceivedAsync += async e =>
@@ -812,7 +817,7 @@ namespace MQTTnet.Tests.Client
                         replyReceived = true;
                     }
 
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await client.PublishStringAsync("request", null, MqttQualityOfServiceLevel.AtLeastOnce);
@@ -828,14 +833,14 @@ namespace MQTTnet.Tests.Client
         {
             using (var testEnvironment = new TestEnvironment(TestContext))
             {
-                var server = await testEnvironment.StartServer();
+                await testEnvironment.StartServer();
                 var client = await testEnvironment.ConnectClient();
 
-                Assert.IsTrue(client.IsConnected);
+                Assert.IsTrue(client.TryPingAsync().GetAwaiter().GetResult());
                 client.DisconnectedAsync += e =>
                 {
                     Assert.IsTrue(e.ClientWasConnected);
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await client.DisconnectAsync();
@@ -851,11 +856,11 @@ namespace MQTTnet.Tests.Client
                 var server = await testEnvironment.StartServer();
                 var client = await testEnvironment.ConnectClient();
 
-                Assert.IsTrue(client.IsConnected);
+                Assert.IsTrue(client.TryPingAsync().GetAwaiter().GetResult());
                 client.DisconnectedAsync += e =>
                 {
                     Assert.IsTrue(e.ClientWasConnected);
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await server.StopAsync();
@@ -892,7 +897,7 @@ namespace MQTTnet.Tests.Client
                         receivedMessages.Add(e.ApplicationMessage);
                     }
 
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost", testEnvironment.ServerPort).Build());
@@ -917,14 +922,14 @@ namespace MQTTnet.Tests.Client
                 client1.DisconnectedAsync += c =>
                 {
                     disconnectedFired = true;
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 var messageReceived = false;
                 client1.ApplicationMessageReceivedAsync += e =>
                 {
                     messageReceived = true;
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await client1.SubscribeAsync(new MqttTopicFilterBuilder().WithTopic("topic1").WithExactlyOnceQoS().Build());
@@ -941,7 +946,7 @@ namespace MQTTnet.Tests.Client
                 await Task.Delay(500);
 
                 Assert.IsTrue(messageReceived);
-                Assert.IsTrue(client1.IsConnected);
+                Assert.IsTrue(client1.TryPingAsync().GetAwaiter().GetResult());
                 Assert.IsFalse(disconnectedFired);
             }
         }

Source/MQTTnet.Tests/Diagnostics/PacketInspection_Tests.cs

@@ -7,7 +7,7 @@ using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MQTTnet.Implementations;
+using MQTTnet.Internal;
 
 namespace MQTTnet.Tests.Diagnostics
 {
@@ -33,7 +33,7 @@ namespace MQTTnet.Tests.Diagnostics
                     mqttClient.InspectPackage += eventArgs =>
                     {
                         packets.Add(eventArgs.Direction + ":" + Convert.ToBase64String(eventArgs.Buffer));
-                        return PlatformAbstractionLayer.CompletedTask;
+                        return CompletedTask.Instance;
                     };
                 
                     await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);

Source/MQTTnet.Tests/Extensions/Rpc_Tests.cs

@@ -6,67 +6,93 @@ using System;
 using System.Text;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MQTTnet.Tests.Mockups;
 using MQTTnet.Client;
 using MQTTnet.Exceptions;
 using MQTTnet.Extensions.Rpc;
-using MQTTnet.Protocol;
 using MQTTnet.Formatter;
-using MQTTnet.Implementations;
+using MQTTnet.Internal;
+using MQTTnet.Protocol;
+using MQTTnet.Tests.Mockups;
 
-namespace MQTTnet.Tests
+namespace MQTTnet.Tests.Extensions
 {
     [TestClass]
-    public sealed class RPC_Tests : BaseTestClass
+    public sealed class Rpc_Tests : BaseTestClass
     {
+        [TestMethod]
+        public async Task Execute_Success_MQTT_V5_Mixed_Clients()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                await testEnvironment.StartServer();
+                var responseSender = await testEnvironment.ConnectClient();
+                await responseSender.SubscribeAsync("MQTTnet.RPC/+/ping");
+
+                responseSender.ApplicationMessageReceivedAsync += async e =>
+                {
+                    Assert.IsNull(e.ApplicationMessage.ResponseTopic);
+                    await responseSender.PublishStringAsync(e.ApplicationMessage.Topic + "/response", "pong");
+                };
+
+                var requestSender = await testEnvironment.ConnectClient(new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V500));
+
+                using (var rpcClient = new MqttRpcClient(requestSender, new MqttRpcClientOptionsBuilder().Build()))
+                {
+                    var response = await rpcClient.ExecuteAsync(TimeSpan.FromSeconds(5), "ping", "", MqttQualityOfServiceLevel.AtMostOnce);
+
+                    Assert.AreEqual("pong", Encoding.UTF8.GetString(response));
+                }
+            }
+        }
+
         [TestMethod]
         public Task Execute_Success_With_QoS_0()
         {
             return Execute_Success(MqttQualityOfServiceLevel.AtMostOnce, MqttProtocolVersion.V311);
         }
 
-        [TestMethod]
-        public Task Execute_Success_With_QoS_1()
-        {
-            return Execute_Success(MqttQualityOfServiceLevel.AtLeastOnce, MqttProtocolVersion.V311);
-        }
-
-        [TestMethod]
-        public Task Execute_Success_With_QoS_2()
-        {
-            return Execute_Success(MqttQualityOfServiceLevel.ExactlyOnce, MqttProtocolVersion.V311);
-        }
-
         [TestMethod]
         public Task Execute_Success_With_QoS_0_MQTT_V5()
         {
             return Execute_Success(MqttQualityOfServiceLevel.AtMostOnce, MqttProtocolVersion.V500);
         }
 
-        [TestMethod]
-        public Task Execute_Success_With_QoS_1_MQTT_V5()
-        {
-            return Execute_Success(MqttQualityOfServiceLevel.AtLeastOnce, MqttProtocolVersion.V500);
-        }
-
-        [TestMethod]
-        public Task Execute_Success_With_QoS_2_MQTT_V5()
-        {
-            return Execute_Success(MqttQualityOfServiceLevel.ExactlyOnce, MqttProtocolVersion.V500);
-        }
-
         [TestMethod]
         public Task Execute_Success_With_QoS_0_MQTT_V5_Use_ResponseTopic()
         {
             return Execute_Success_MQTT_V5(MqttQualityOfServiceLevel.AtMostOnce);
         }
 
+        [TestMethod]
+        public Task Execute_Success_With_QoS_1()
+        {
+            return Execute_Success(MqttQualityOfServiceLevel.AtLeastOnce, MqttProtocolVersion.V311);
+        }
+
+        [TestMethod]
+        public Task Execute_Success_With_QoS_1_MQTT_V5()
+        {
+            return Execute_Success(MqttQualityOfServiceLevel.AtLeastOnce, MqttProtocolVersion.V500);
+        }
+
         [TestMethod]
         public Task Execute_Success_With_QoS_1_MQTT_V5_Use_ResponseTopic()
         {
             return Execute_Success_MQTT_V5(MqttQualityOfServiceLevel.AtLeastOnce);
         }
 
+        [TestMethod]
+        public Task Execute_Success_With_QoS_2()
+        {
+            return Execute_Success(MqttQualityOfServiceLevel.ExactlyOnce, MqttProtocolVersion.V311);
+        }
+
+        [TestMethod]
+        public Task Execute_Success_With_QoS_2_MQTT_V5()
+        {
+            return Execute_Success(MqttQualityOfServiceLevel.ExactlyOnce, MqttProtocolVersion.V500);
+        }
+
         [TestMethod]
         public Task Execute_Success_With_QoS_2_MQTT_V5_Use_ResponseTopic()
         {
@@ -89,6 +115,31 @@ namespace MQTTnet.Tests
             }
         }
 
+        [TestMethod]
+        [ExpectedException(typeof(MqttCommunicationTimedOutException))]
+        public async Task Execute_Timeout_MQTT_V5_Mixed_Clients()
+        {
+            using (var testEnvironment = new TestEnvironment(TestContext))
+            {
+                await testEnvironment.StartServer();
+                var responseSender = await testEnvironment.ConnectClient();
+                await responseSender.SubscribeAsync("MQTTnet.RPC/+/ping");
+
+                responseSender.ApplicationMessageReceivedAsync += async e =>
+                {
+                    Assert.IsNull(e.ApplicationMessage.ResponseTopic);
+                    await CompletedTask.Instance;
+                };
+
+                var requestSender = await testEnvironment.ConnectClient(new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V500));
+
+                using (var rpcClient = new MqttRpcClient(requestSender, new MqttRpcClientOptionsBuilder().Build()))
+                {
+                    var response = await rpcClient.ExecuteAsync(TimeSpan.FromSeconds(2), "ping", "", MqttQualityOfServiceLevel.AtMostOnce);
+                }
+            }
+        }
+
         [TestMethod]
         [ExpectedException(typeof(MqttCommunicationTimedOutException))]
         public async Task Execute_With_Custom_Topic_Names()
@@ -97,14 +148,24 @@ namespace MQTTnet.Tests
             {
                 await testEnvironment.StartServer();
 
-                var requestSender = await testEnvironment.ConnectClient();
-
                 var rpcClient = await testEnvironment.ConnectRpcClient(new MqttRpcClientOptionsBuilder().WithTopicGenerationStrategy(new TestTopicStrategy()).Build());
 
                 await rpcClient.ExecuteAsync(TimeSpan.FromSeconds(2), "ping", "", MqttQualityOfServiceLevel.AtMostOnce);
             }
         }
 
+        [TestMethod]
+        public void Use_Factory()
+        {
+            var factory = new MqttFactory();
+            using (var client = factory.CreateMqttClient())
+            {
+                var rpcClient = factory.CreateMqttRpcClient(client);
+
+                Assert.IsNotNull(rpcClient);
+            }
+        }
+
         async Task Execute_Success(MqttQualityOfServiceLevel qosLevel, MqttProtocolVersion protocolVersion)
         {
             using (var testEnvironment = CreateTestEnvironment())
@@ -150,57 +211,6 @@ namespace MQTTnet.Tests
             }
         }
 
-        [TestMethod]
-        public async Task Execute_Success_MQTT_V5_Mixed_Clients()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                await testEnvironment.StartServer();
-                var responseSender = await testEnvironment.ConnectClient();
-                await responseSender.SubscribeAsync("MQTTnet.RPC/+/ping", MqttQualityOfServiceLevel.AtMostOnce);
-
-                responseSender.ApplicationMessageReceivedAsync += async e =>
-                {
-                    Assert.IsNull(e.ApplicationMessage.ResponseTopic);
-                    await responseSender.PublishStringAsync(e.ApplicationMessage.Topic + "/response", "pong");
-                };
-
-                var requestSender = await testEnvironment.ConnectClient(new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V500));
-
-                using (var rpcClient = new MqttRpcClient(requestSender, new MqttRpcClientOptionsBuilder().Build()))
-                {
-                    var response = await rpcClient.ExecuteAsync(TimeSpan.FromSeconds(5), "ping", "", MqttQualityOfServiceLevel.AtMostOnce);
-
-                    Assert.AreEqual("pong", Encoding.UTF8.GetString(response));
-                }
-            }
-        }
-
-        [TestMethod]
-        [ExpectedException(typeof(MqttCommunicationTimedOutException))]
-        public async Task Execute_Timeout_MQTT_V5_Mixed_Clients()
-        {
-            using (var testEnvironment = new TestEnvironment(TestContext))
-            {
-                await testEnvironment.StartServer();
-                var responseSender = await testEnvironment.ConnectClient();
-                await responseSender.SubscribeAsync("MQTTnet.RPC/+/ping", MqttQualityOfServiceLevel.AtMostOnce);
-
-                responseSender.ApplicationMessageReceivedAsync += async e =>
-                {
-                    Assert.IsNull(e.ApplicationMessage.ResponseTopic);
-                    await PlatformAbstractionLayer.CompletedTask;
-                };
-
-                var requestSender = await testEnvironment.ConnectClient(new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V500));
-
-                using (var rpcClient = new MqttRpcClient(requestSender, new MqttRpcClientOptionsBuilder().Build()))
-                {
-                    var response = await rpcClient.ExecuteAsync(TimeSpan.FromSeconds(2), "ping", "", MqttQualityOfServiceLevel.AtMostOnce);
-                }
-            }
-        }
-
         class TestTopicStrategy : IMqttRpcClientTopicGenerationStrategy
         {
             public MqttRpcTopicPair CreateRpcTopics(TopicGenerationContext context)
@@ -213,4 +223,4 @@ namespace MQTTnet.Tests
             }
         }
     }
-}
+}

Source/MQTTnet.Tests/Extensions/WebSocket4Net_Tests.cs

@@ -0,0 +1,51 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Client;
+using MQTTnet.Exceptions;
+using MQTTnet.Extensions.WebSocket4Net;
+using MQTTnet.Tests.Helpers;
+
+namespace MQTTnet.Tests.Extensions
+{
+    [TestClass]
+    public sealed class WebSocket4Net_Tests
+    {
+        [TestMethod]
+        [ExpectedException(typeof(MqttCommunicationException))]
+        public async Task Connect_Failed_With_Invalid_Server()
+        {
+            var factory = new MqttFactory().UseWebSocket4Net();
+
+            using (var client = factory.CreateMqttClient())
+            {
+                var options = new MqttClientOptionsBuilder().WithWebSocketServer("ws://a.b/mqtt").WithTimeout(TimeSpan.FromSeconds(2)).Build();
+                await client.ConnectAsync(options).ConfigureAwait(false);
+            }
+        }
+
+        [TestMethod]
+        public void Use_Correct_Adapter()
+        {
+            // Should not throw exception
+            var factory = new MqttFactory().UseWebSocket4Net();
+            using (var client = factory.CreateMqttClient())
+            {
+                var adapterFactory = client.GetFieldValue("_adapterFactory");
+
+                Assert.IsInstanceOfType(adapterFactory, typeof(WebSocket4NetMqttClientAdapterFactory));
+            }
+        }
+
+        [TestMethod]
+        public void Use_WebSocket4Net()
+        {
+            // Should not throw exception
+            new MqttFactory().UseWebSocket4Net();
+        }
+    }
+}

Source/MQTTnet.Tests/Factory/MqttFactory_Tests.cs

@@ -8,7 +8,7 @@ using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Diagnostics;
 using MQTTnet.Extensions.ManagedClient;
-using MQTTnet.Implementations;
+using MQTTnet.Internal;
 using MQTTnet.Server;
 
 namespace MQTTnet.Tests.Factory
@@ -56,7 +56,7 @@ namespace MQTTnet.Tests.Factory
                 managedClient.ConnectingFailedAsync += e =>
                 {
                     tcs.TrySetResult(null);
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
                 
                 await Task.WhenAny(Task.Delay(managedClient.Options.ClientOptions.Timeout), tcs.Task);

Source/MQTTnet.Tests/Formatter/MqttBufferReader_Tests.cs

@@ -0,0 +1,310 @@
+// 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.IO;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Exceptions;
+using MQTTnet.Formatter;
+
+namespace MQTTnet.Tests.Formatter
+{
+    [TestClass]
+    public sealed class MqttBufferReader_Tests
+    {
+        [TestMethod]
+        [ExpectedException(typeof(MqttProtocolViolationException), "Expected at least 4 bytes but there are only 3 bytes")]
+        public void Fire_Exception_If_Not_Enough_Data()
+        {
+            var buffer = new byte[] { 0, 1, 2 };
+
+            var reader = new MqttBufferReader();
+
+            reader.SetBuffer(buffer, 0, 3);
+
+            // 1 byte is missing.
+            reader.ReadFourByteInteger();
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(MqttProtocolViolationException), "Expected at least 4 bytes but there are only 3 bytes")]
+        public void Fire_Exception_If_Not_Enough_Data_With_Longer_Buffer()
+        {
+            var buffer = new byte[] { 0, 1, 2, 3, 4, 5, 6 };
+
+            var reader = new MqttBufferReader();
+
+            reader.SetBuffer(buffer, 0, 3);
+
+            // 1 byte is missing.
+            reader.ReadFourByteInteger();
+        }
+
+        [TestMethod]
+        public void Is_EndOfStream_Without_Buffer()
+        {
+            var reader = new MqttBufferReader();
+
+            Assert.IsTrue(reader.EndOfStream);
+            Assert.AreEqual(0, reader.BytesLeft);
+        }
+
+        [TestMethod]
+        public void Read_Remaining_Data_From_Larger_Buffer()
+        {
+            var buffer = new byte[] { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+
+            var reader = new MqttBufferReader();
+
+            // The used buffer contains more data than used!
+            reader.SetBuffer(buffer, 0, 5);
+
+            // This should only read 5 bytes even if more data is in the buffer
+            // due to custom bounds.
+            var remainingData = reader.ReadRemainingData();
+
+            Assert.IsTrue(reader.EndOfStream);
+            Assert.AreEqual(0, reader.BytesLeft);
+            Assert.AreEqual(5, remainingData.Length);
+        }
+
+        [TestMethod]
+        public void Read_Various_Positions_and_Offsets()
+        {
+            const int NumBufferElements = 1000;
+            const int NumTestSequences = 10000;
+
+            const string TestString = "The quick brown fox jumps over the lazy dog.";
+
+            var rndSeed = Environment.TickCount;
+            // rndSeed = ...; // assign random seed here if there is an error so that it can be repeated
+            var rnd = new Random(rndSeed);
+            // rndSeed is printed when an assert fails
+
+            var bufferElements = new List<ElementReference>();
+
+            byte[] elementBuffer;
+
+            // Fill a buffer with strings or numbers in big endian format
+            using (var ms = new MemoryStream())
+            {
+                using (var bw = new BinaryWriter(ms))
+                {
+                    var bufferOffset = 0;
+
+                    for (var i = 0; i < NumBufferElements; i++)
+                    {
+                        var nextElementType = (ElementReference.BufferElementType)rnd.Next(ElementReference.NumBufferElementTypes);
+
+                        byte[] elementBytes = null;
+                        uint elementNumberValue = 0; // all element number values fit into uint
+                        string elementStringValue = null;
+                        var elementSize = 0;
+
+                        var alreadyBigEndian = false;
+                        switch (nextElementType)
+                        {
+                            case ElementReference.BufferElementType.Byte:
+                                var byteValue = (byte)i;
+                                elementNumberValue = byteValue;
+                                elementSize = sizeof(byte);
+                                elementBytes = new byte[1] { byteValue };
+                                alreadyBigEndian = true; // nothing to swap
+                                break;
+                            case ElementReference.BufferElementType.TwoByteInt:
+                                var ushortValue = (ushort)i;
+                                elementNumberValue = ushortValue;
+                                elementSize = sizeof(ushort);
+                                elementBytes = BitConverter.GetBytes(ushortValue);
+                                break;
+                            case ElementReference.BufferElementType.FourByteInt:
+                                var uintValue = (uint)i;
+                                elementNumberValue = uintValue;
+                                elementSize = sizeof(uint);
+                                elementBytes = BitConverter.GetBytes(uintValue);
+                                break;
+                            case ElementReference.BufferElementType.VariableSizeInt:
+                            {
+                                elementNumberValue = (uint)i;
+                                var writer = new MqttBufferWriter(4, 4);
+                                writer.WriteVariableByteInteger(elementNumberValue);
+                                elementSize = writer.Length;
+                                elementBytes = new byte[elementSize];
+                                var buffer = writer.GetBuffer();
+                                Array.Copy(buffer, elementBytes, elementSize);
+                                alreadyBigEndian = true; // nothing to swap
+                            }
+                                break;
+                            case ElementReference.BufferElementType.String:
+                            {
+                                var stringLen = rnd.Next(TestString.Length);
+                                elementStringValue = TestString.Substring(0, stringLen); // could be empty
+                                var writer = new MqttBufferWriter(stringLen + 1, stringLen + 1);
+                                writer.WriteString(elementStringValue);
+                                elementSize = writer.Length;
+                                elementBytes = new byte[elementSize];
+                                var buffer = writer.GetBuffer();
+                                Array.Copy(buffer, elementBytes, elementSize);
+                                alreadyBigEndian = true; // nothing to swap
+                            }
+                                break;
+                        }
+
+                        if (BitConverter.IsLittleEndian && !alreadyBigEndian)
+                        {
+                            Array.Reverse(elementBytes);
+                        }
+
+                        bw.Write(elementBytes);
+                        bufferElements.Add(new ElementReference(nextElementType, elementSize, elementNumberValue, elementStringValue, bufferOffset));
+                        bufferOffset += elementSize;
+                    }
+
+                    elementBuffer = ms.ToArray();
+                }
+            }
+
+            for (var i = 0; i < NumTestSequences; i++)
+            {
+                var firstElementIndex = rnd.Next(NumBufferElements - 1);
+                // segmentElementIndex will be < NumBufferElements - 1, which means there is at least one byte left for segment element count
+                var elementCount = rnd.Next(NumBufferElements - firstElementIndex) + 1;
+                var lastElementIndex = firstElementIndex + elementCount - 1;
+                // Use element index to get buffer offsets
+                var lastElement = bufferElements[lastElementIndex];
+                var segmentStartPosition = bufferElements[firstElementIndex].BufferOffset;
+                var segmentEndPosition = lastElement.BufferOffset + lastElement.Size;
+                var segmentLength = segmentEndPosition - segmentStartPosition;
+
+                var reader = new MqttBufferReader();
+                reader.SetBuffer(elementBuffer, segmentStartPosition, segmentLength);
+
+                // read all elements in the buffer segment; values should be as expected              
+                for (var n = 0; n < elementCount; n++)
+                {
+                    var element = bufferElements[firstElementIndex + n];
+                    uint elementNumberValue = 0;
+                    string elementStringValue = null;
+
+                    var expectedPosition = element.BufferOffset - segmentStartPosition;
+                    Assert.AreEqual(expectedPosition, reader.Position);
+
+                    switch (element.Type)
+                    {
+                        case ElementReference.BufferElementType.Byte:
+                        {
+                            elementNumberValue = reader.ReadByte();
+                        }
+                            break;
+                        case ElementReference.BufferElementType.TwoByteInt:
+                        {
+                            elementNumberValue = reader.ReadTwoByteInteger();
+                        }
+                            break;
+                        case ElementReference.BufferElementType.FourByteInt:
+                        {
+                            elementNumberValue = reader.ReadFourByteInteger();
+                        }
+                            break;
+                        case ElementReference.BufferElementType.VariableSizeInt:
+                        {
+                            elementNumberValue = reader.ReadVariableByteInteger();
+                        }
+                            break;
+                        case ElementReference.BufferElementType.String:
+                        {
+                            elementStringValue = reader.ReadString();
+                        }
+                            break;
+                    }
+
+                    if (elementStringValue != null)
+                    {
+                        Assert.AreEqual(elementStringValue, element.StringValue, $"'{elementStringValue}' not equal '{element.StringValue}' with random seed {rndSeed}.");
+                    }
+                    else
+                    {
+                        Assert.AreEqual(elementNumberValue, element.NumberValue, $"{elementNumberValue} not equal {element.NumberValue} with random seed {rndSeed}.");
+                    }
+                }
+
+                // confirm end of stream
+                Assert.AreEqual(0, reader.BytesLeft, "BytesLeft not zero as expected with random seed " + rndSeed);
+                Assert.IsTrue(reader.EndOfStream, "Not end of stream as expected with random seed " + rndSeed);
+            }
+        }
+
+        [TestMethod]
+        public void Report_Correct_Length_For_Full_Buffer()
+        {
+            var buffer = new byte[] { 5, 6, 7, 8, 9 };
+
+            var reader = new MqttBufferReader();
+            reader.SetBuffer(buffer, 0, 5);
+
+            Assert.IsFalse(reader.EndOfStream);
+            Assert.AreEqual(5, reader.BytesLeft);
+        }
+
+        [TestMethod]
+        public void Report_Correct_Length_For_Partial_End_Buffer()
+        {
+            var buffer = new byte[] { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+
+            var reader = new MqttBufferReader();
+
+            // The used buffer contains more data than used!
+            reader.SetBuffer(buffer, 5, 5);
+
+            Assert.IsFalse(reader.EndOfStream);
+            Assert.AreEqual(5, reader.BytesLeft);
+        }
+
+        [TestMethod]
+        public void Report_Correct_Length_For_Partial_Start_Buffer()
+        {
+            var buffer = new byte[] { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+
+            var reader = new MqttBufferReader();
+
+            // The used buffer contains more data than used!
+            reader.SetBuffer(buffer, 0, 5);
+
+            Assert.IsFalse(reader.EndOfStream);
+            Assert.AreEqual(5, reader.BytesLeft);
+        }
+
+
+        // Helper class to build up a reference to elements of various types in a buffer
+        class ElementReference
+        {
+            public enum BufferElementType
+            {
+                Byte,
+                TwoByteInt,
+                FourByteInt,
+                VariableSizeInt,
+                String
+            }
+
+            public const int NumBufferElementTypes = 5;
+
+            public ElementReference(BufferElementType type, int size, uint numberValue, string stringValue, int bufferOffset)
+            {
+                Type = type;
+                Size = size;
+                NumberValue = numberValue;
+                StringValue = stringValue;
+                BufferOffset = bufferOffset;
+            }
+
+            public int BufferOffset { get; }
+            public uint NumberValue { get; }
+            public int Size { get; }
+            public string StringValue { get; }
+            public BufferElementType Type { get; }
+        }
+    }
+}

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V3_Binary_Tests.cs

@@ -13,13 +13,12 @@ using MQTTnet.Adapter;
 using MQTTnet.Diagnostics;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
-using MQTTnet.Internal;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
-using MQTTnet.Tests.Extensions;
+using MQTTnet.Tests.Helpers;
 using MQTTnet.Tests.Mockups;
 
-namespace MQTTnet.Tests
+namespace MQTTnet.Tests.Formatter
 {
     [TestClass]
     public sealed class MqttPacketSerialization_V3_Binary_Tests

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V3_Tests.cs

@@ -10,7 +10,7 @@ using MQTTnet.Formatter;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
 
-namespace MQTTnet.Tests
+namespace MQTTnet.Tests.Formatter
 {
     [TestClass]
     public sealed class MqttPacketSerialization_V3_Tests

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V5_Tests.cs

@@ -9,7 +9,7 @@ using MQTTnet.Formatter;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
 
-namespace MQTTnet.Tests
+namespace MQTTnet.Tests.Formatter
 {
     [TestClass]
     public sealed class MqttPacketSerialization_V5_Tests

Source/MQTTnet.Tests/Helpers/MqttClientExtensions.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 MQTTnet.Client;
+using MQTTnet.Tests.Mockups;
+
+namespace MQTTnet.Tests.Helpers
+{
+    public static class MqttClientExtensions
+    {
+        public static TestApplicationMessageReceivedHandler TrackReceivedMessages(this IMqttClient client)
+        {
+            if (client == null)
+            {
+                throw new ArgumentNullException(nameof(client));
+            }
+
+            return new TestApplicationMessageReceivedHandler(client);
+        }
+    }
+}

Source/MQTTnet.Tests/Helpers/MqttPacketWriterExtensions.cs

@@ -5,7 +5,7 @@
 using MQTTnet.Formatter;
 using MQTTnet.Protocol;
 
-namespace MQTTnet.Tests.Extensions
+namespace MQTTnet.Tests.Helpers
 {
     public static class MqttPacketWriterExtensions
     {

Source/MQTTnet.Tests/Helpers/ReflectionExtensions.cs

@@ -0,0 +1,28 @@
+// 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.Reflection;
+
+namespace MQTTnet.Tests.Helpers
+{
+    public static class ReflectionExtensions
+    {
+        public static object GetFieldValue(this object source, string fieldName)
+        {
+            if (source == null)
+            {
+                throw new ArgumentNullException(nameof(source));
+            }
+
+            var field = source.GetType().GetField(fieldName, BindingFlags.Instance | BindingFlags.NonPublic);
+            if (field == null)
+            {
+                throw new ArgumentException($"Field {fieldName} not found.");
+            }
+            
+            return field.GetValue(source);
+        }
+    }
+}

Source/MQTTnet.Tests/Internal/AsyncEvent_Tests.cs

@@ -6,7 +6,6 @@ using System;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MQTTnet.Implementations;
 using MQTTnet.Internal;
 
 namespace MQTTnet.Tests.Internal
@@ -16,6 +15,28 @@ namespace MQTTnet.Tests.Internal
     {
         int _testEventAsyncCount;
 
+        [TestMethod]
+        public async Task Attach_and_Detach_Sync_And_Async_EventHandler()
+        {
+            var testClass = new TestClass();
+
+            testClass.TestEventAsync += OnTestEventAsync;
+            testClass.TestEvent += OnTestEvent;
+
+            await testClass.FireEventAsync(EventArgs.Empty);
+            Assert.AreEqual(2, _testEventAsyncCount);
+
+            testClass.TestEvent -= OnTestEvent;
+
+            await testClass.FireEventAsync(EventArgs.Empty);
+            Assert.AreEqual(3, _testEventAsyncCount);
+
+            testClass.TestEventAsync -= OnTestEventAsync;
+
+            await testClass.FireEventAsync(EventArgs.Empty);
+            Assert.AreEqual(3, _testEventAsyncCount);
+        }
+
         [TestMethod]
         public async Task Attach_EventHandler()
         {
@@ -28,6 +49,19 @@ namespace MQTTnet.Tests.Internal
             Assert.AreEqual(1, _testEventAsyncCount);
         }
 
+        [TestMethod]
+        public async Task Attach_Sync_And_Async_EventHandler()
+        {
+            var testClass = new TestClass();
+
+            testClass.TestEventAsync += OnTestEventAsync;
+            testClass.TestEvent += OnTestEvent;
+
+            await testClass.FireEventAsync(EventArgs.Empty);
+
+            Assert.AreEqual(2, _testEventAsyncCount);
+        }
+
         [TestMethod]
         public async Task Detach_EventHandler()
         {
@@ -41,22 +75,62 @@ namespace MQTTnet.Tests.Internal
             Assert.AreEqual(0, _testEventAsyncCount);
         }
 
+        [TestMethod]
+        public void Has_Handlers()
+        {
+            var testClass = new TestClass();
+            testClass.TestEventAsync += OnTestEventAsync;
+
+            Assert.AreEqual(true, testClass.HasTestHandlers);
+        }
+
+        [TestMethod]
+        public void No_Handlers()
+        {
+            var testClass = new TestClass();
+
+            Assert.AreEqual(false, testClass.HasTestHandlers);
+        }
+
+        [TestMethod]
+        public void Remove_Handlers()
+        {
+            var testClass = new TestClass();
+            testClass.TestEventAsync += OnTestEventAsync;
+            testClass.TestEventAsync -= OnTestEventAsync;
+
+            Assert.AreEqual(false, testClass.HasTestHandlers);
+        }
+
+        void OnTestEvent(EventArgs arg)
+        {
+            Interlocked.Increment(ref _testEventAsyncCount);
+        }
+
         Task OnTestEventAsync(EventArgs arg)
         {
             Interlocked.Increment(ref _testEventAsyncCount);
-            return PlatformAbstractionLayer.CompletedTask;
+            return CompletedTask.Instance;
         }
 
         sealed class TestClass
         {
             readonly AsyncEvent<EventArgs> _testEvent = new AsyncEvent<EventArgs>();
 
+            public event Action<EventArgs> TestEvent
+            {
+                add => _testEvent.AddHandler(value);
+                remove => _testEvent.RemoveHandler(value);
+            }
+
             public event Func<EventArgs, Task> TestEventAsync
             {
                 add => _testEvent.AddHandler(value);
                 remove => _testEvent.RemoveHandler(value);
             }
 
+            public bool HasTestHandlers => _testEvent.HasHandlers;
+
             public Task FireEventAsync(EventArgs eventArgs)
             {
                 return _testEvent.InvokeAsync(eventArgs);

Source/MQTTnet.Tests/Internal/AsyncLock_Tests.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Diagnostics;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
@@ -11,8 +12,186 @@ using MQTTnet.Internal;
 namespace MQTTnet.Tests.Internal
 {
     [TestClass]
-    public class AsyncLock_Tests
+    public sealed class AsyncLock_Tests
     {
+        [TestMethod]
+        public async Task Cancellation_Of_Awaiter()
+        {
+            var @lock = new AsyncLock();
+
+            // This call will not yet "release" the lock due to missing _using_.
+            var releaser = await @lock.EnterAsync().ConfigureAwait(false);
+
+            var counter = 0;
+
+            Debug.WriteLine("Prepared locked lock.");
+
+            _ = Task.Run(
+                async () =>
+                {
+                    // SHOULD GET TIMEOUT!
+                    using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(1)))
+                    {
+                        using (await @lock.EnterAsync(timeout.Token))
+                        {
+                            Debug.WriteLine("Task 1 incremented");
+                            counter++;
+                        }
+                    }
+                });
+
+            _ = Task.Run(
+                async () =>
+                {
+                    // SHOULD GET TIMEOUT!
+                    using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(2)))
+                    {
+                        using (await @lock.EnterAsync(timeout.Token))
+                        {
+                            Debug.WriteLine("Task 2 incremented");
+                            counter++;
+                        }
+                    }
+                });
+
+            _ = Task.Run(
+                async () =>
+                {
+                    // SHOULD GET TIMEOUT!
+                    using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(3)))
+                    {
+                        using (await @lock.EnterAsync(timeout.Token))
+                        {
+                            Debug.WriteLine("Task 3 incremented");
+                            counter++;
+                        }
+                    }
+                });
+
+            _ = Task.Run(
+                async () =>
+                {
+                    using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(4)))
+                    {
+                        using (await @lock.EnterAsync(timeout.Token))
+                        {
+                            Debug.WriteLine("Task 4 incremented");
+                            counter++;
+                        }
+                    }
+                });
+
+            _ = Task.Run(
+                async () =>
+                {
+                    using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(5)))
+                    {
+                        using (await @lock.EnterAsync(timeout.Token))
+                        {
+                            Debug.WriteLine("Task 5 incremented");
+                            counter++;
+                        }
+                    }
+                });
+
+            _ = Task.Run(
+                async () =>
+                {
+                    using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(6)))
+                    {
+                        using (await @lock.EnterAsync(timeout.Token))
+                        {
+                            Debug.WriteLine("Task 6 incremented");
+                            counter++;
+                        }
+                    }
+                });
+
+            Debug.WriteLine("Delay before release...");
+            await Task.Delay(TimeSpan.FromSeconds(3.1));
+            releaser.Dispose();
+
+            Debug.WriteLine("Wait for all tasks...");
+            await Task.Delay(TimeSpan.FromSeconds(6.1));
+
+            Assert.AreEqual(3, counter);
+        }
+
+        [TestMethod]
+        public void Lock_Parallel_Tasks()
+        {
+            const int taskCount = 50;
+            
+            var @lock = new AsyncLock();
+            
+            var tasks = new Task[taskCount];
+            var globalI = 0;
+            for (var i = 0; i < taskCount; i++)
+            {
+#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+                tasks[i] = Task.Run(
+                    async () =>
+                    {
+                        using (await @lock.EnterAsync())
+                        {
+                            var localI = globalI;
+                            await Task.Delay(5); // Increase the chance for wrong data.
+                            localI++;
+                            globalI = localI;
+                        }
+                    });
+#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+            }
+
+            Task.WaitAll(tasks);
+            Assert.AreEqual(taskCount, globalI);
+        }
+
+        [TestMethod]
+        public void Lock_10_Parallel_Tasks_With_Dispose_Doesnt_Lockup()
+        {
+            const int ThreadsCount = 10;
+
+            var threads = new Task[ThreadsCount];
+            var @lock = new AsyncLock();
+            var globalI = 0;
+            for (var i = 0; i < ThreadsCount; i++)
+            {
+#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+                threads[i] = Task.Run(
+                        async () =>
+                        {
+                            using (await @lock.EnterAsync())
+                            {
+                                var localI = globalI;
+                                await Task.Delay(10); // Increase the chance for wrong data.
+                                localI++;
+                                globalI = localI;
+                            }
+                        })
+                    .ContinueWith(
+                        x =>
+                        {
+                            if (globalI == 5)
+                            {
+                                @lock.Dispose();
+                                @lock = new AsyncLock();
+                            }
+
+                            if (x.Exception != null)
+                            {
+                                Debug.WriteLine(x.Exception.GetBaseException().GetType().Name);
+                            }
+                        });
+#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+            }
+
+            Task.WaitAll(threads);
+
+            // Expect only 6 because the others are failing due to disposal (if (globalI == 5)).
+            Assert.AreEqual(6, globalI);
+        }
+
         [TestMethod]
         public async Task Lock_Serial_Calls()
         {
@@ -21,7 +200,7 @@ namespace MQTTnet.Tests.Internal
             var @lock = new AsyncLock();
             for (var i = 0; i < 100; i++)
             {
-                using (await @lock.WaitAsync(CancellationToken.None).ConfigureAwait(false))
+                using (await @lock.EnterAsync().ConfigureAwait(false))
                 {
                     sum++;
                 }
@@ -37,66 +216,76 @@ namespace MQTTnet.Tests.Internal
             var @lock = new AsyncLock();
 
             // This call will never "release" the lock due to missing _using_.
-            await @lock.WaitAsync(CancellationToken.None).ConfigureAwait(false);
+            await @lock.EnterAsync().ConfigureAwait(false);
 
             using (var cts = new CancellationTokenSource(TimeSpan.FromSeconds(3)))
             {
-                await @lock.WaitAsync(cts.Token).ConfigureAwait(false);
+                await @lock.EnterAsync(cts.Token).ConfigureAwait(false);
             }
         }
 
-        //[TestMethod]
-        //public async Task Test_Cancellation_With_Later_Access()
-        //{
-        //    var @lock = new AsyncLock();
-
-        //    var releaser = await @lock.WaitAsync().ConfigureAwait(false);
-
-        //    try
-        //    {
-        //        using (var cts = new CancellationTokenSource(TimeSpan.FromSeconds(3)))
-        //        {
-        //            await @lock.WaitAsync(cts.Token).ConfigureAwait(false);
-        //        }
-        //    }
-        //    catch (OperationCanceledException)
-        //    {
-        //    }
-            
-        //    releaser.Dispose();
-
-        //    using (await @lock.WaitAsync().ConfigureAwait(false))
-        //    {
-        //        // When the method finished, the thread got access.
-        //    }
-        //}
-
         [TestMethod]
-        public void Lock_10_Parallel_Tasks()
+        public async Task Test_Cancellation_With_Later_Access()
         {
-            const int ThreadsCount = 10;
+            var asyncLock = new AsyncLock();
 
-            var threads = new Task[ThreadsCount];
-            var @lock = new AsyncLock();
-            var globalI = 0;
-            for (var i = 0; i < ThreadsCount; i++)
+            var releaser = await asyncLock.EnterAsync().ConfigureAwait(false);
+
+            try
             {
-#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
-                threads[i] = Task.Run(async () =>
+                using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(3)))
                 {
-                    using (var releaser = await @lock.WaitAsync(CancellationToken.None))
-                    {
-                        var localI = globalI;
-                        await Task.Delay(10); // Increase the chance for wrong data.
-                        localI++;
-                        globalI = localI;
-                    }
-                });
-#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+                    await asyncLock.EnterAsync(timeout.Token).ConfigureAwait(false);
+                }
+
+                Assert.Fail("Exception should be thrown!");
+            }
+            catch (OperationCanceledException)
+            {
             }
 
-            Task.WaitAll(threads);
-            Assert.AreEqual(ThreadsCount, globalI);
+            releaser.Dispose();
+
+            using (await asyncLock.EnterAsync(CancellationToken.None).ConfigureAwait(false))
+            {
+                // When the method finished, the thread got access.
+            }
+        }
+
+        [TestMethod]
+        public async Task Use_After_Cancellation()
+        {
+            var @lock = new AsyncLock();
+
+            // This call will not yet "release" the lock due to missing _using_.
+            var releaser = await @lock.EnterAsync().ConfigureAwait(false);
+
+            try
+            {
+                using (var cts = new CancellationTokenSource(TimeSpan.FromSeconds(3)))
+                {
+                    await @lock.EnterAsync(cts.Token).ConfigureAwait(false);
+                }
+            }
+            catch (OperationCanceledException)
+            {
+                // Expected exception!
+            }
+
+            releaser.Dispose();
+
+            // Regular usage after cancellation.
+            using (await @lock.EnterAsync().ConfigureAwait(false))
+            {
+            }
+
+            using (await @lock.EnterAsync().ConfigureAwait(false))
+            {
+            }
+
+            using (await @lock.EnterAsync().ConfigureAwait(false))
+            {
+            }
         }
     }
-}
+}

Source/MQTTnet.Tests/Internal/AsyncSignal_Tests.cs

@@ -0,0 +1,128 @@
+// 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.Diagnostics;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Internal;
+
+namespace MQTTnet.Tests.Internal
+{
+    [TestClass]
+    public sealed class AsyncSignal_Tests
+    {
+        [TestMethod]
+        [ExpectedException(typeof(TaskCanceledException))]
+        public async Task Cancel_If_No_Signal()
+        {
+            var asyncSignal = new AsyncSignal();
+
+            using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(2)))
+            {
+                await asyncSignal.WaitAsync(timeout.Token);
+
+                Assert.Fail("There is no signal. So we must fail here!");
+            }
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(ObjectDisposedException))]
+        public async Task Dispose_Properly()
+        {
+            var asyncSignal = new AsyncSignal();
+
+            // The timeout will not be reached but another task will kill the async signal.
+            using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(999)))
+            {
+                _ = Task.Run(
+                    async () =>
+                    {
+                        await Task.Delay(2000, CancellationToken.None);
+                        asyncSignal.Dispose();
+                    },
+                    CancellationToken.None);
+
+                await asyncSignal.WaitAsync(timeout.Token);
+
+                Assert.Fail("There is no signal. So we must fail here!");
+            }
+        }
+
+        [TestMethod]
+        public async Task Reset_Signal()
+        {
+            var asyncSignal = new AsyncSignal();
+
+            // WaitAsync should fail because no signal is available.
+            for (var i = 0; i < 10; i++)
+            {
+                try
+                {
+                    using (var timeout = new CancellationTokenSource(TimeSpan.FromMilliseconds(100)))
+                    {
+                        await asyncSignal.WaitAsync(timeout.Token);
+                    }
+                    
+                    Assert.Fail("This must fail because the signal is not yet set.");
+                }
+                catch (OperationCanceledException)
+                {
+                }
+                
+                asyncSignal.Set();
+                
+                // WaitAsync should return directly because the signal is available.
+                await asyncSignal.WaitAsync();
+            }
+        }
+
+        [TestMethod]
+        public async Task Signal()
+        {
+            var asyncSignal = new AsyncSignal();
+
+            // The timeout will not be reached but another task will kill the async signal.
+            using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(3)))
+            {
+                var stopwatch = Stopwatch.StartNew();
+
+                _ = Task.Run(
+                    async () =>
+                    {
+                        await Task.Delay(1000, CancellationToken.None);
+                        asyncSignal.Set();
+                    },
+                    CancellationToken.None);
+
+                await asyncSignal.WaitAsync(timeout.Token);
+
+                stopwatch.Stop();
+
+                Assert.IsTrue(stopwatch.ElapsedMilliseconds > 900);
+            }
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(InvalidOperationException))]
+        public async Task Fail_For_Two_Waiters()
+        {
+            var asyncSignal = new AsyncSignal();
+
+            // This thread will wait properly because it is the first waiter.
+            _ = Task.Run(
+                async () =>
+                {
+                    await asyncSignal.WaitAsync();
+                },
+                CancellationToken.None);
+
+            await Task.Delay(1000);
+            
+            // Now the current thread must fail because there is already a waiter.
+            await asyncSignal.WaitAsync();
+        }
+    }
+}

Source/MQTTnet.Tests/Internal/MqttPacketBusItem_Tests.cs

@@ -0,0 +1,43 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Internal;
+using MQTTnet.Packets;
+
+namespace MQTTnet.Tests.Internal
+{
+    [TestClass]
+    public sealed class MqttPacketBusItem_Tests
+    {
+        [TestMethod]
+        public void Fire_Completed_Event()
+        {
+            var eventFired = false;
+
+            var item = new MqttPacketBusItem(new MqttPublishPacket());
+            item.Completed += (_, __) =>
+            {
+                eventFired = true;
+            };
+
+            item.Complete();
+
+            Assert.IsTrue(eventFired);
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(TaskCanceledException))]
+        public async Task Wait_Packet_Bus_Item_After_Already_Canceled()
+        {
+            var item = new MqttPacketBusItem(new MqttPublishPacket());
+
+            // Finish the item before the actual 
+            item.Cancel();
+
+            await item.WaitAsync();
+        }
+    }
+}

Source/MQTTnet.Tests/Internal/MqttPacketBus_Tests.cs

@@ -13,69 +13,26 @@ namespace MQTTnet.Tests.Internal
 {
     [TestClass]
     public sealed class MqttPacketBus_Tests
-    {
-        [TestMethod]
-        [ExpectedException(typeof(OperationCanceledException))]
-        public async Task Wait_With_Empty_Bus()
-        {
-            var bus = new MqttPacketBus();
-
-            using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(1)))
-            {
-                await bus.DequeueItemAsync(timeout.Token);
-            }
-        }
-        
-        [TestMethod]
-        public async Task Fill_From_Different_Task()
-        {
-            const int MessageCount = 500;
-
-            var delayRandom = new Random();
-            
-            var bus = new MqttPacketBus();
-
-            _ = Task.Run(
-                () =>
-                {
-                    for (int i = 0; i < MessageCount; i++)
-                    {
-                        bus.EnqueueItem(new MqttPacketBusItem(MqttPingReqPacket.Instance), MqttPacketBusPartition.Health);
-                        
-                        Thread.Sleep(delayRandom.Next(0, 10));
-                    }
-                });
-            
-            for (var i = 0; i < MessageCount; i++)
-            {
-                using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(10)))
-                {
-                    await bus.DequeueItemAsync(timeout.Token);
-                }    
-            }
-            
-            Assert.AreEqual(0, bus.TotalItemsCount);
-        }
-        
+    {       
         [TestMethod]
         public void Alternate_Priorities()
         {
             var bus = new MqttPacketBus();
-            
+
             bus.EnqueueItem(new MqttPacketBusItem(new MqttPublishPacket()), MqttPacketBusPartition.Data);
             bus.EnqueueItem(new MqttPacketBusItem(new MqttPublishPacket()), MqttPacketBusPartition.Data);
             bus.EnqueueItem(new MqttPacketBusItem(new MqttPublishPacket()), MqttPacketBusPartition.Data);
-            
+
             bus.EnqueueItem(new MqttPacketBusItem(new MqttSubAckPacket()), MqttPacketBusPartition.Control);
             bus.EnqueueItem(new MqttPacketBusItem(new MqttSubAckPacket()), MqttPacketBusPartition.Control);
             bus.EnqueueItem(new MqttPacketBusItem(new MqttSubAckPacket()), MqttPacketBusPartition.Control);
-            
+
             bus.EnqueueItem(new MqttPacketBusItem(new MqttPingRespPacket()), MqttPacketBusPartition.Health);
             bus.EnqueueItem(new MqttPacketBusItem(new MqttPingRespPacket()), MqttPacketBusPartition.Health);
             bus.EnqueueItem(new MqttPacketBusItem(new MqttPingRespPacket()), MqttPacketBusPartition.Health);
 
             Assert.AreEqual(9, bus.TotalItemsCount);
-            
+
             Assert.IsInstanceOfType(bus.DequeueItemAsync(CancellationToken.None).Result.Packet, typeof(MqttPublishPacket));
             Assert.IsInstanceOfType(bus.DequeueItemAsync(CancellationToken.None).Result.Packet, typeof(MqttSubAckPacket));
             Assert.IsInstanceOfType(bus.DequeueItemAsync(CancellationToken.None).Result.Packet, typeof(MqttPingRespPacket));
@@ -85,33 +42,10 @@ namespace MQTTnet.Tests.Internal
             Assert.IsInstanceOfType(bus.DequeueItemAsync(CancellationToken.None).Result.Packet, typeof(MqttPublishPacket));
             Assert.IsInstanceOfType(bus.DequeueItemAsync(CancellationToken.None).Result.Packet, typeof(MqttSubAckPacket));
             Assert.IsInstanceOfType(bus.DequeueItemAsync(CancellationToken.None).Result.Packet, typeof(MqttPingRespPacket));
-            
+
             Assert.AreEqual(0, bus.TotalItemsCount);
         }
-        
-        [TestMethod]
-        public void Export_Packets_Without_Dequeue()
-        {
-            var bus = new MqttPacketBus();
 
-            bus.EnqueueItem(new MqttPacketBusItem(new MqttPublishPacket()), MqttPacketBusPartition.Data);
-            bus.EnqueueItem(new MqttPacketBusItem(new MqttPublishPacket()), MqttPacketBusPartition.Data);
-            bus.EnqueueItem(new MqttPacketBusItem(new MqttPublishPacket()), MqttPacketBusPartition.Data);
-            
-            Assert.AreEqual(3, bus.TotalItemsCount);
-
-            var exportedPackets = bus.ExportPackets(MqttPacketBusPartition.Control);
-            Assert.AreEqual(0, exportedPackets.Count);
-            
-            exportedPackets = bus.ExportPackets(MqttPacketBusPartition.Health);
-            Assert.AreEqual(0, exportedPackets.Count);
-            
-            exportedPackets = bus.ExportPackets(MqttPacketBusPartition.Data);
-            Assert.AreEqual(3, exportedPackets.Count);
-            
-            Assert.AreEqual(3, bus.TotalItemsCount);
-        }
-        
         [TestMethod]
         public void Await_Single_Packet()
         {
@@ -121,31 +55,97 @@ namespace MQTTnet.Tests.Internal
 
             var item1 = new MqttPacketBusItem(new MqttPublishPacket());
             var item2 = new MqttPacketBusItem(new MqttPublishPacket());
-            
+
             var item3 = new MqttPacketBusItem(new MqttPublishPacket());
-            item3.Delivered += (_, __) =>
+            item3.Completed += (_, __) =>
             {
                 delivered = true;
             };
-            
+
             bus.EnqueueItem(item1, MqttPacketBusPartition.Data);
             bus.EnqueueItem(item2, MqttPacketBusPartition.Data);
             bus.EnqueueItem(item3, MqttPacketBusPartition.Data);
-            
+
             Assert.IsFalse(delivered);
 
-            bus.DequeueItemAsync(CancellationToken.None).Result.MarkAsDelivered();
-            
+            bus.DequeueItemAsync(CancellationToken.None).Result.Complete();
+
             Assert.IsFalse(delivered);
-            
-            bus.DequeueItemAsync(CancellationToken.None).Result.MarkAsDelivered();
-            
+
+            bus.DequeueItemAsync(CancellationToken.None).Result.Complete();
+
             Assert.IsFalse(delivered);
-            
-            bus.DequeueItemAsync(CancellationToken.None).Result.MarkAsDelivered();
-            
+
+            bus.DequeueItemAsync(CancellationToken.None).Result.Complete();
+
             // The third packet has the event attached.
             Assert.IsTrue(delivered);
         }
+
+        [TestMethod]
+        public void Export_Packets_Without_Dequeue()
+        {
+            var bus = new MqttPacketBus();
+
+            bus.EnqueueItem(new MqttPacketBusItem(new MqttPublishPacket()), MqttPacketBusPartition.Data);
+            bus.EnqueueItem(new MqttPacketBusItem(new MqttPublishPacket()), MqttPacketBusPartition.Data);
+            bus.EnqueueItem(new MqttPacketBusItem(new MqttPublishPacket()), MqttPacketBusPartition.Data);
+
+            Assert.AreEqual(3, bus.TotalItemsCount);
+
+            var exportedPackets = bus.ExportPackets(MqttPacketBusPartition.Control);
+            Assert.AreEqual(0, exportedPackets.Count);
+
+            exportedPackets = bus.ExportPackets(MqttPacketBusPartition.Health);
+            Assert.AreEqual(0, exportedPackets.Count);
+
+            exportedPackets = bus.ExportPackets(MqttPacketBusPartition.Data);
+            Assert.AreEqual(3, exportedPackets.Count);
+
+            Assert.AreEqual(3, bus.TotalItemsCount);
+        }
+
+        [TestMethod]
+        public async Task Fill_From_Different_Task()
+        {
+            const int MessageCount = 500;
+
+            var delayRandom = new Random();
+
+            var bus = new MqttPacketBus();
+
+            _ = Task.Run(
+                () =>
+                {
+                    for (var i = 0; i < MessageCount; i++)
+                    {
+                        bus.EnqueueItem(new MqttPacketBusItem(MqttPingReqPacket.Instance), MqttPacketBusPartition.Health);
+
+                        Thread.Sleep(delayRandom.Next(0, 10));
+                    }
+                });
+
+            for (var i = 0; i < MessageCount; i++)
+            {
+                using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(10)))
+                {
+                    await bus.DequeueItemAsync(timeout.Token);
+                }
+            }
+
+            Assert.AreEqual(0, bus.TotalItemsCount);
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(TaskCanceledException))]
+        public async Task Wait_With_Empty_Bus()
+        {
+            var bus = new MqttPacketBus();
+
+            using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(1)))
+            {
+                await bus.DequeueItemAsync(timeout.Token);
+            }
+        }
     }
 }

Source/MQTTnet.Tests/MQTTnet.Tests.csproj

@@ -1,27 +1,26 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFrameworks>net452;net461;netcoreapp3.1;net6.0</TargetFrameworks>
+        <TargetFrameworks>net452;net461;net48;netcoreapp3.1;net6.0</TargetFrameworks>
         <IsPackable>false</IsPackable>
         <LangVersion>7.3</LangVersion>
         <EnableNETAnalyzers>false</EnableNETAnalyzers>
         <EnforceCodeStyleInBuild>false</EnforceCodeStyleInBuild>
         <DisableImplicitAspNetCoreAnalyzers>true</DisableImplicitAspNetCoreAnalyzers>
+        <NoWarn>1591;NETSDK1138</NoWarn>
     </PropertyGroup>
 
     <ItemGroup>
         <PackageReference Include="MSTest.TestAdapter" Version="2.2.10" />
         <PackageReference Include="MSTest.TestFramework" Version="2.2.10" />
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.2.0" />
-
-        <PackageReference Include="Microsoft.CodeAnalysis.Compilers" Version="4.0.1" />
-        <PackageReference Include="Microsoft.Net.Compilers" Version="4.0.1" />
     </ItemGroup>
 
     <ItemGroup>
         <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.WebSocket4Net\MQTTnet.Extensions.WebSocket4Net.csproj" />
     </ItemGroup>
 
 </Project>

Source/MQTTnet.Tests/MQTTv5/Client_Tests.cs

@@ -8,10 +8,9 @@ using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
 using MQTTnet.Formatter;
-using MQTTnet.Implementations;
+using MQTTnet.Internal;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
-using MQTTnet.Tests.Mockups;
 
 namespace MQTTnet.Tests.MQTTv5
 {
@@ -43,7 +42,7 @@ namespace MQTTnet.Tests.MQTTv5
                 client.ApplicationMessageReceivedAsync += e =>
                 {
                     receivedMessage = e.ApplicationMessage;
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 await client.PublishAsync(new MqttApplicationMessageBuilder()
@@ -155,7 +154,7 @@ namespace MQTTnet.Tests.MQTTv5
                 var result = await client.PublishStringAsync("a", "b", MqttQualityOfServiceLevel.AtLeastOnce);
                 await client.DisconnectAsync();
 
-                Assert.AreEqual(MqttClientPublishReasonCode.Success, result.ReasonCode);
+                Assert.AreEqual(MqttClientPublishReasonCode.NoMatchingSubscribers, result.ReasonCode);
             }
         }
 
@@ -170,7 +169,7 @@ namespace MQTTnet.Tests.MQTTv5
                 var result = await client.PublishStringAsync("a", "b", MqttQualityOfServiceLevel.ExactlyOnce);
                 await client.DisconnectAsync();
 
-                Assert.AreEqual(MqttClientPublishReasonCode.Success, result.ReasonCode);
+                Assert.AreEqual(MqttClientPublishReasonCode.NoMatchingSubscribers, result.ReasonCode);
             }
         }
 
@@ -245,7 +244,7 @@ namespace MQTTnet.Tests.MQTTv5
                 receiver.ApplicationMessageReceivedAsync += e =>
                 {
                     receivedMessage = e.ApplicationMessage;
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 var sender = await testEnvironment.ConnectClient(new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V500));

Source/MQTTnet.Tests/MQTTv5/Server_Tests.cs

@@ -8,7 +8,7 @@ using MQTTnet.Formatter;
 using MQTTnet.Tests.Mockups;
 using System.Threading;
 using System.Threading.Tasks;
-using MQTTnet.Implementations;
+using MQTTnet.Internal;
 using MQTTnet.Protocol;
 
 namespace MQTTnet.Tests.MQTTv5
@@ -31,15 +31,15 @@ namespace MQTTnet.Tests.MQTTv5
                 c1.ApplicationMessageReceivedAsync += e =>
                 {
                     Interlocked.Increment(ref receivedMessagesCount);
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
                 
                 await c1.SubscribeAsync(new MqttTopicFilterBuilder().WithTopic("#").Build());
 
                 var c2 = await testEnvironment.ConnectClient(clientOptions);
-                c2.Dispose(); // Dispose will not send a DISCONNECT pattern first so the will message must be sent.
+                c2.Dispose(); // Dispose will not send a DISCONNECT packet first so the will message must be sent.
 
-                await Task.Delay(1000);
+                await LongTestDelay();
 
                 Assert.AreEqual(1, receivedMessagesCount);
             }
@@ -171,11 +171,53 @@ namespace MQTTnet.Tests.MQTTv5
                 // Session should be present
 
                 Assert.IsTrue(!result3.IsSessionPresent, "Session is present when it should not");
-
             }
         }
 
-        MqttClientOptions CreateClientOptions(TestEnvironment testEnvironment, string clientId, bool cleanSession, uint sessionExpiryInterval)
+        [TestMethod]
+        public async Task Disconnect_with_Reason()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                var disconnectReason = MqttClientDisconnectReason.UnspecifiedError;
+
+                string testClientId = null;
+
+                await testEnvironment.StartServer();
+
+                testEnvironment.Server.ClientConnectedAsync += e =>
+                {
+                    testClientId = e.ClientId;
+                    return CompletedTask.Instance;
+                };
+
+                var client = await testEnvironment.ConnectClient(new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V500));
+
+                client.DisconnectedAsync += e =>
+                {
+                    disconnectReason = e.Reason;
+                    return CompletedTask.Instance;
+                };
+
+                await LongTestDelay();
+
+                // Test client should be connected now
+
+                Assert.IsTrue(testClientId != null);
+
+                // Have the server disconnect the client with AdministrativeAction reason
+
+                await testEnvironment.Server.DisconnectClientAsync(testClientId, MqttDisconnectReasonCode.AdministrativeAction);
+
+                await LongTestDelay();
+
+                // The reason should be returned to the client in the DISCONNECT packet
+
+                Assert.AreEqual(MqttClientDisconnectReason.AdministrativeAction, disconnectReason);
+            }
+        }
+
+        static MqttClientOptions CreateClientOptions(TestEnvironment testEnvironment, string clientId, bool cleanSession, uint sessionExpiryInterval)
         {
             return testEnvironment.Factory.CreateClientOptionsBuilder()
                 .WithProtocolVersion(MqttProtocolVersion.V500)

Source/MQTTnet.Tests/Mockups/MemoryMqttChannel.cs

@@ -2,11 +2,13 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.IO;
 using System.Security.Cryptography.X509Certificates;
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Channel;
+using MQTTnet.Internal;
 
 namespace MQTTnet.Tests.Mockups
 {
@@ -32,12 +34,12 @@ namespace MQTTnet.Tests.Mockups
 
         public Task ConnectAsync(CancellationToken cancellationToken)
         {
-            return Task.FromResult(0);
+            return CompletedTask.Instance;
         }
 
         public Task DisconnectAsync(CancellationToken cancellationToken)
         {
-            return Task.FromResult(0);
+            return CompletedTask.Instance;
         }
 
         public Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
@@ -45,9 +47,9 @@ namespace MQTTnet.Tests.Mockups
             return _stream.ReadAsync(buffer, offset, count, cancellationToken);
         }
 
-        public Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+        public Task WriteAsync(ArraySegment<byte> buffer, bool isEndOfPacket, CancellationToken cancellationToken)
         {
-            return _stream.WriteAsync(buffer, offset, count, cancellationToken);
+            return _stream.WriteAsync(buffer.Array, buffer.Offset, buffer.Count, cancellationToken);
         }
 
         public void Dispose()

Source/MQTTnet.Tests/Mockups/TestApplicationMessageReceivedHandler.cs

@@ -2,12 +2,14 @@
 // 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;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
-using MQTTnet.Implementations;
+using MQTTnet.Internal;
 
 namespace MQTTnet.Tests.Mockups
 {
@@ -17,7 +19,23 @@ namespace MQTTnet.Tests.Mockups
 
         public TestApplicationMessageReceivedHandler(IMqttClient mqttClient)
         {
-            mqttClient.ApplicationMessageReceivedAsync += MqttClientOnApplicationMessageReceivedAsync;
+            if (mqttClient == null)
+            {
+                throw new ArgumentNullException(nameof(mqttClient));
+            }
+
+            mqttClient.ApplicationMessageReceivedAsync += OnApplicationMessageReceivedAsync;
+        }
+
+        public int Count
+        {
+            get
+            {
+                lock (_receivedEventArgs)
+                {
+                    return _receivedEventArgs.Count;
+                }
+            }
         }
 
         public List<MqttApplicationMessageReceivedEventArgs> ReceivedEventArgs
@@ -39,14 +57,32 @@ namespace MQTTnet.Tests.Mockups
             }
         }
 
-        Task MqttClientOnApplicationMessageReceivedAsync(MqttApplicationMessageReceivedEventArgs eventArgs)
+        public string GeneratePayloadSequence()
+        {
+            var sequence = new StringBuilder();
+
+            lock (_receivedEventArgs)
+            {
+                foreach (var receivedEventArg in _receivedEventArgs)
+                {
+                    var payload = receivedEventArg.ApplicationMessage.ConvertPayloadToString();
+
+                    // An empty payload is not part of the sequence!
+                    sequence.Append(payload);
+                }
+            }
+
+            return sequence.ToString();
+        }
+
+        Task OnApplicationMessageReceivedAsync(MqttApplicationMessageReceivedEventArgs eventArgs)
         {
             lock (_receivedEventArgs)
             {
                 _receivedEventArgs.Add(eventArgs);
             }
 
-            return PlatformAbstractionLayer.CompletedTask;
+            return CompletedTask.Instance;
         }
     }
 }

Source/MQTTnet.Tests/Mockups/TestEnvironment.cs

@@ -11,9 +11,10 @@ using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
 using MQTTnet.Diagnostics;
+using MQTTnet.Extensions.ManagedClient;
 using MQTTnet.Extensions.Rpc;
 using MQTTnet.Formatter;
-using MQTTnet.Implementations;
+using MQTTnet.Internal;
 using MQTTnet.LowLevelClient;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
@@ -109,7 +110,7 @@ namespace MQTTnet.Tests.Mockups
             configureOptions.Invoke(optionsBuilder);
 
             var options = optionsBuilder.Build();
-            
+
             var client = CreateClient();
 
             if (timeout == TimeSpan.Zero)
@@ -137,7 +138,7 @@ namespace MQTTnet.Tests.Mockups
             options = options.WithTcpServer("127.0.0.1", ServerPort);
 
             var client = CreateClient();
-            
+
             if (timeout == TimeSpan.Zero)
             {
                 await client.ConnectAsync(options.Build()).ConfigureAwait(false);
@@ -161,7 +162,7 @@ namespace MQTTnet.Tests.Mockups
             }
 
             var client = CreateClient();
-            
+
             if (timeout == TimeSpan.Zero)
             {
                 await client.ConnectAsync(options).ConfigureAwait(false);
@@ -199,6 +200,16 @@ namespace MQTTnet.Tests.Mockups
             return new TestApplicationMessageReceivedHandler(mqttClient);
         }
 
+        public TestApplicationMessageReceivedHandler CreateApplicationMessageHandler(IManagedMqttClient managedClient)
+        {
+            if (managedClient == null)
+            {
+                throw new ArgumentNullException(nameof(managedClient));
+            }
+
+            return new TestApplicationMessageReceivedHandler(managedClient.InternalClient);
+        }
+
         public IMqttClient CreateClient()
         {
             lock (_clients)
@@ -220,7 +231,7 @@ namespace MQTTnet.Tests.Mockups
                         }
                     }
 
-                    return PlatformAbstractionLayer.CompletedTask;
+                    return CompletedTask.Instance;
                 };
 
                 return client;
@@ -261,7 +272,7 @@ namespace MQTTnet.Tests.Mockups
                     }
                 }
 
-                return PlatformAbstractionLayer.CompletedTask;
+                return CompletedTask.Instance;
             };
 
             return Server;
@@ -325,7 +336,7 @@ namespace MQTTnet.Tests.Mockups
             var options = optionsBuilder.Build();
             var server = CreateServer(options);
             await server.StartAsync();
-            
+
             // The OS has chosen the port to we have to properly expose it to the tests.
             ServerPort = options.DefaultEndpointOptions.Port;
             return server;
@@ -344,7 +355,7 @@ namespace MQTTnet.Tests.Mockups
             var options = optionsBuilder.Build();
             var server = CreateServer(options);
             await server.StartAsync();
-            
+
             // The OS has chosen the port to we have to properly expose it to the tests.
             ServerPort = options.DefaultEndpointOptions.Port;
             return server;

Source/MQTTnet.Tests/Protocol_Tests.cs

@@ -8,27 +8,48 @@ using MQTTnet.Formatter;
 namespace MQTTnet.Tests
 {
     [TestClass]
-    public class Protocol_Tests
+    public sealed class Protocol_Tests
     {
         [TestMethod]
         public void Encode_Four_Byte_Integer()
         {
             var writer = new MqttBufferWriter(4, 4);
-            
+
             for (uint value = 0; value < 268435455; value++)
             {
                 writer.WriteVariableByteInteger(value);
-                
+
                 var buffer = writer.GetBuffer();
-                
+
                 var reader = new MqttBufferReader();
                 reader.SetBuffer(buffer, 0, writer.Length);
                 var checkValue = reader.ReadVariableByteInteger();
 
                 Assert.AreEqual(value, checkValue);
-                
+
+                writer.Reset(0);
+            }
+        }
+
+        [TestMethod]
+        public void Encode_Two_Byte_Integer()
+        {
+            var writer = new MqttBufferWriter(2, 2);
+
+            for (ushort value = 0; value < ushort.MaxValue; value++)
+            {
+                writer.WriteTwoByteInteger(value);
+
+                var buffer = writer.GetBuffer();
+
+                var reader = new MqttBufferReader();
+                reader.SetBuffer(buffer, 0, writer.Length);
+                var checkValue = reader.ReadTwoByteInteger();
+
+                Assert.AreEqual(value, checkValue);
+
                 writer.Reset(0);
             }
         }
     }
-}
+}