Add new API for extended authentication

* replace lock/semaphore by readerwriterlockslim to avoid lock contention while dispatch messages

* Update MqttClientSubscriptionsManager.cs

removed comment out codes

* Update ReleaseNotes.md

---------

Co-authored-by: Zeheng Feng <hf944813@broadcom.com>
Co-authored-by: Christian <6939810+chkr1011@users.noreply.github.com>

.github/workflows/ReleaseNotes.md

@@ -1,9 +1,4 @@
-* [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).
+* [Core] Add validation of maximum string lengths (#1718).
+* [Client] Added overloads for setting packet payload and will payload (#1720).
+* [Client] The proper connect result is now exposed in the _Disconnected_ event when authentication fails (#1139). 
+* [Server] Improved performance by changing internal locking strategy for subscriptions (#1716, thanks to @zeheng).

.github/workflows/ci.yml

@@ -3,7 +3,7 @@ name: CI
 on: [push, pull_request]
 
 env:
-  VERSION: "4.1.4.${{github.run_number}}"
+  VERSION: "4.2.1.${{github.run_number}}"
 
 jobs:
   build:
@@ -22,6 +22,7 @@ jobs:
           dotnet-version: |
             3.1.x
             6.0.x
+            7.0.x
 
       - name: Setup MSBuild
         uses: microsoft/setup-msbuild@v1.1

README.md

@@ -50,6 +50,22 @@ 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
 
+## Getting Started
+
+MQTTnet is delivered via <b>NuGet</b> package manager. You can find the packages here: https://www.nuget.org/packages/MQTTnet/
+
+Use these command in the Package Manager console to install MQTTnet manually:
+```
+Install-Package MQTTnet
+```
+
+Samples for using MQTTnet are part of this repository. For starters these samples are recommended:
+
+- [Connect with a broker](https://github.com/dotnet/MQTTnet/blob/master/Samples/Client/Client_Connection_Samples.cs)
+- [Subscribing to data](https://github.com/dotnet/MQTTnet/blob/master/Samples/Client/Client_Subscribe_Samples.cs)
+- [Publishing data](https://github.com/dotnet/MQTTnet/blob/master/Samples/Client/Client_Publish_Samples.cs)
+- [Host own broker](https://github.com/dotnet/MQTTnet/blob/master/Samples/Server/Server_Simple_Samples.cs)
+
 ## 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

@@ -16,6 +16,28 @@ namespace MQTTnet.Samples.Client;
 
 public static class Client_Connection_Samples
 {
+    public static async Task Clean_Disconnect()
+    {
+        /*
+         * This sample disconnects in a clean way. This will send a MQTT DISCONNECT packet
+         * to the server and close the connection afterwards.
+         *
+         * See sample _Connect_Client_ 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);
+
+            // This will send the DISCONNECT packet. Calling _Dispose_ without DisconnectAsync the 
+            // connection is closed in a "not clean" way. See MQTT specification for more details.
+            await mqttClient.DisconnectAsync(new MqttClientDisconnectOptionsBuilder().WithReason(MqttClientDisconnectOptionsReason.NormalDisconnection).Build());
+        }
+    }
+
     public static async Task Connect_Client()
     {
         /*
@@ -48,6 +70,32 @@ public static class Client_Connection_Samples
             await mqttClient.DisconnectAsync(mqttClientDisconnectOptions, CancellationToken.None);
         }
     }
+    
+    public static async Task Connect_With_Amazon_AWS()
+    {
+        /*
+         * This sample creates a simple MQTT client and connects to an Amazon Web Services broker.
+         *
+         * The broker requires special settings which are set here.
+         */
+
+        var mqttFactory = new MqttFactory();
+
+        using (var mqttClient = mqttFactory.CreateMqttClient())
+        {
+            var mqttClientOptions = new MqttClientOptionsBuilder()
+                .WithTcpServer("amazon.web.services.broker")
+                // Disabling packet fragmentation is very important!  
+                .WithoutPacketFragmentation()
+                .Build();
+            
+            await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
+
+            Console.WriteLine("The MQTT client is connected.");
+
+            await mqttClient.DisconnectAsync();
+        }
+    }
 
     public static async Task Connect_Client_Timeout()
     {
@@ -232,7 +280,7 @@ public static class Client_Connection_Samples
 
             // 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);
+            await mqttClient.DisconnectAsync(MqttClientDisconnectOptionsReason.ImplementationSpecificError);
         }
     }
 
@@ -297,7 +345,7 @@ public static class Client_Connection_Samples
         /*
          * This sample sends a PINGREQ packet to the server and waits for a reply.
          *
-         * This is only supported in METTv5.0.0+.
+         * This is only supported in MQTTv5.0.0+.
          */
 
         var mqttFactory = new MqttFactory();

Samples/Diagnostics/PackageInspection_Samples.cs

@@ -26,7 +26,7 @@ public static class PackageInspection_Samples
                 .WithTcpServer("broker.hivemq.com")
                 .Build();
             
-            mqttClient.InspectPackage += OnInspectPackage;
+            mqttClient.InspectPacketAsync += OnInspectPacket;
             
             await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
             
@@ -39,7 +39,7 @@ public static class PackageInspection_Samples
         }
     }
 
-    static Task OnInspectPackage(InspectMqttPacketEventArgs eventArgs)
+    static Task OnInspectPacket(InspectMqttPacketEventArgs eventArgs)
     {
         if (eventArgs.Direction == MqttPacketFlowDirection.Inbound)
         {

Samples/Program.cs

@@ -4,7 +4,13 @@
 
 using System.Reflection;
 
-Console.WriteLine("Welcome to MQTTnet samples!");
+Console.BackgroundColor = ConsoleColor.White;
+Console.BackgroundColor = ConsoleColor.Red;
+Console.Title = "Samples - MQTTnet";
+Console.WriteLine("----------------------------------------------");
+Console.WriteLine("-         Welcome to MQTTnet samples!        -");
+Console.WriteLine("----------------------------------------------");
+Console.ResetColor();
 Console.WriteLine();
 
 var sampleClasses = Assembly.GetExecutingAssembly().GetExportedTypes().OrderBy(c => c.Name).ToList();
@@ -16,7 +22,11 @@ foreach (var sampleClass in sampleClasses)
     index++;
 }
 
+Console.WriteLine();
+Console.ForegroundColor = ConsoleColor.Green;
 Console.Write("Please choose sample class (press Enter to continue): ");
+Console.ResetColor();
+
 var input = Console.ReadLine();
 var selectedIndex = int.Parse(input ?? "0");
 var selectedSampleClass = sampleClasses[selectedIndex];
@@ -29,12 +39,19 @@ foreach (var sampleMethod in sampleMethods)
     index++;
 }
 
+Console.WriteLine();
+Console.ForegroundColor = ConsoleColor.Green;
 Console.Write("Please choose sample (press Enter to continue): ");
+Console.ResetColor();
+
 input = Console.ReadLine();
 selectedIndex = int.Parse(input ?? "0");
 var selectedSampleMethod = sampleMethods[selectedIndex];
 
+Console.WriteLine();
+Console.ForegroundColor = ConsoleColor.White;
 Console.WriteLine("Executing sample...");
+Console.ResetColor();
 Console.WriteLine();
 
 try

Samples/Server/Server_ASP_NET_Samples.cs

@@ -17,7 +17,7 @@ using MQTTnet.Server;
 
 namespace MQTTnet.Samples.Server;
 
-public static class Server_Asp_Net_Samples
+public static class Server_ASP_NET_Samples
 {
     public static Task Start_Server_With_WebSockets_Support()
     {

Samples/Server/Server_Diagnostics_Samples.cs

@@ -0,0 +1,53 @@
+// 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.Internal;
+using MQTTnet.Packets;
+using MQTTnet.Server;
+
+namespace MQTTnet.Samples.Server;
+
+// ReSharper disable UnusedType.Global
+// ReSharper disable UnusedMember.Global
+// ReSharper disable InconsistentNaming
+// ReSharper disable EmptyConstructor
+// ReSharper disable MemberCanBeMadeStatic.Local
+
+public static class Server_Diagnostics_Samples
+{
+    public static async Task Get_Notified_When_Client_Received_Message()
+    {
+        /*
+         * This sample starts a MQTT server and attaches an event which gets fired whenever
+         * a client received and acknowledged a PUBLISH packet.
+         */
+        
+        var mqttFactory = new MqttFactory();
+        var mqttServerOptions = new MqttServerOptionsBuilder().WithDefaultEndpoint().Build();
+        
+        using (var mqttServer = mqttFactory.CreateMqttServer(mqttServerOptions))
+        {
+            // Attach the event handler.
+            mqttServer.ClientAcknowledgedPublishPacketAsync += e =>
+            {
+                Console.WriteLine($"Client '{e.ClientId}' acknowledged packet {e.PublishPacket.PacketIdentifier} with topic '{e.PublishPacket.Topic}'");
+                
+                // It is also possible to read additional data from the client response. This requires casting the response packet.
+                var qos1AcknowledgePacket = e.AcknowledgePacket as MqttPubAckPacket;
+                Console.WriteLine($"QoS 1 reason code: {qos1AcknowledgePacket?.ReasonCode}");
+                
+                var qos2AcknowledgePacket = e.AcknowledgePacket as MqttPubCompPacket;
+                Console.WriteLine($"QoS 2 reason code: {qos1AcknowledgePacket?.ReasonCode}");
+                return CompletedTask.Instance;
+            };
+            
+            await mqttServer.StartAsync();
+
+            Console.WriteLine("Press Enter to exit.");
+            Console.ReadLine();
+
+            await mqttServer.StopAsync();
+        }
+    }
+}

Samples/Server/Server_TLS_Samples.cs

@@ -0,0 +1,75 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+// ReSharper disable UnusedType.Global
+// ReSharper disable UnusedMember.Global
+// ReSharper disable InconsistentNaming
+
+using System.Net;
+using System.Security.Cryptography;
+using System.Security.Cryptography.X509Certificates;
+using MQTTnet.Server;
+
+namespace MQTTnet.Samples.Server;
+
+public static class Server_TLS_Samples
+{
+    public static async Task Run_Server_With_Self_Signed_Certificate()
+    {
+        /*
+         * This sample starts a simple MQTT server which will accept any TCP connection.
+         * It also has an encrypted connection using a self signed TLS certificate.
+         *
+         * See sample "Run_Minimal_Server" for more details.
+         */
+
+        var mqttFactory = new MqttFactory();
+
+        // This certificate is self signed so that
+        var certificate = CreateSelfSignedCertificate("1.3.6.1.5.5.7.3.1");
+        
+        var mqttServerOptions = new MqttServerOptionsBuilder().WithEncryptionCertificate(certificate).WithEncryptedEndpoint().Build();
+
+        using (var mqttServer = mqttFactory.CreateMqttServer(mqttServerOptions))
+        {
+            await mqttServer.StartAsync();
+
+            Console.WriteLine("Press Enter to exit.");
+            Console.ReadLine();
+
+            // Stop and dispose the MQTT server if it is no longer needed!
+            await mqttServer.StopAsync();
+        }
+    }
+
+    static X509Certificate2 CreateSelfSignedCertificate(string oid)
+    {
+        var sanBuilder = new SubjectAlternativeNameBuilder();
+        sanBuilder.AddIpAddress(IPAddress.Loopback);
+        sanBuilder.AddIpAddress(IPAddress.IPv6Loopback);
+        sanBuilder.AddDnsName("localhost");
+
+        using (var rsa = RSA.Create())
+        {
+            var certRequest = new CertificateRequest("CN=localhost", rsa, HashAlgorithmName.SHA512, RSASignaturePadding.Pkcs1);
+
+            certRequest.CertificateExtensions.Add(
+                new X509KeyUsageExtension(X509KeyUsageFlags.DataEncipherment | X509KeyUsageFlags.KeyEncipherment | X509KeyUsageFlags.DigitalSignature, false));
+
+            certRequest.CertificateExtensions.Add(new X509EnhancedKeyUsageExtension(new OidCollection { new(oid) }, false));
+
+            certRequest.CertificateExtensions.Add(sanBuilder.Build());
+
+            using (var certificate = certRequest.CreateSelfSigned(DateTimeOffset.Now.AddMinutes(-10), DateTimeOffset.Now.AddMinutes(10)))
+            {
+                var pfxCertificate = new X509Certificate2(
+                    certificate.Export(X509ContentType.Pfx),
+                    (string)null!,
+                    X509KeyStorageFlags.MachineKeySet | X509KeyStorageFlags.Exportable);
+
+                return pfxCertificate;
+            }
+        }
+    }
+}

Source/MQTTnet.AspNetCore.Tests/MqttConnectionContextTest.cs

@@ -103,7 +103,7 @@ namespace MQTTnet.AspNetCore.Tests
             connection.Transport = pipe;
             var ctx = new MqttConnectionContext(serializer, connection);
 
-            await ctx.SendPacketAsync(new MqttPublishPacket { Payload = new byte[20_000] }, CancellationToken.None).ConfigureAwait(false);
+            await ctx.SendPacketAsync(new MqttPublishPacket { PayloadSegment = new ArraySegment<byte>(new byte[20_000]) }, CancellationToken.None).ConfigureAwait(false);
 
             var readResult = await pipe.Send.Reader.ReadAsync();
             Assert.IsTrue(readResult.Buffer.Length > 20000);

Source/MQTTnet.AspNetCore.Tests/ReaderExtensionsTest.cs

@@ -19,7 +19,7 @@ namespace MQTTnet.AspNetCore.Tests
         {
             var serializer = new MqttPacketFormatterAdapter(MqttProtocolVersion.V311, new MqttBufferWriter(4096, 65535));
 
-            var buffer = serializer.Encode(new MqttPublishPacket {Topic = "a", Payload = new byte[5]}).Join();
+            var buffer = serializer.Encode(new MqttPublishPacket {Topic = "a", PayloadSegment = new byte[5]}).Join();
 
             var sequence = new ReadOnlySequence<byte>(buffer.Array, buffer.Offset, buffer.Count);
 

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

@@ -44,7 +44,7 @@ namespace MQTTnet.AspNetCore.Client.Tcp
             _sender = new SocketSender(_socket, PipeScheduler.ThreadPool);
             _receiver = new SocketReceiver(_socket, PipeScheduler.ThreadPool);
         }
-#if NETCOREAPP3_1 || NET5_0_OR_GREATER
+#if NETCOREAPP3_1_OR_GREATER
         public override ValueTask DisposeAsync()
 #else
         public Task DisposeAsync()
@@ -57,7 +57,7 @@ namespace MQTTnet.AspNetCore.Client.Tcp
 
             _socket?.Dispose();
 
-#if NETCOREAPP3_1 || NET5_0_OR_GREATER
+#if NETCOREAPP3_1_OR_GREATER
 
             return base.DisposeAsync();
         }

Source/MQTTnet.AspnetCore/EndpointRouterExtensions.cs

@@ -3,7 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 
-#if NETCOREAPP3_1 || NET5_0_OR_GREATER
+#if NETCOREAPP3_1_OR_GREATER
 
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Routing;

Source/MQTTnet.AspnetCore/MQTTnet.AspNetCore.csproj

@@ -1,7 +1,7 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFrameworks>netstandard2.0;netcoreapp2.1;netcoreapp3.1;net5.0;net6.0</TargetFrameworks>
+        <TargetFrameworks>netstandard2.0;netcoreapp2.1;netcoreapp3.1;net5.0;net6.0;net7.0</TargetFrameworks>
 
         <AssemblyName>MQTTnet.AspNetCore</AssemblyName>
         <RootNamespace>MQTTnet.AspNetCore</RootNamespace>
@@ -51,11 +51,11 @@
         <DefineConstants>RELEASE;NETSTANDARD2_0</DefineConstants>
     </PropertyGroup>
 
-    <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.1' or '$(TargetFramework)' == 'net5.0' or '$(TargetFramework)' == 'net6.0' ">
+    <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.1' or '$(TargetFramework)' == 'net5.0' or '$(TargetFramework)' == 'net6.0' or '$(TargetFramework)' == 'net7.0' ">
         <FrameworkReference Include="Microsoft.AspNetCore.App" />
     </ItemGroup>
 
-    <ItemGroup Condition="'$(TargetFramework)' != 'netcoreapp3.1' and '$(TargetFramework)' != 'net5.0' and '$(TargetFramework)' != 'net6.0' ">
+    <ItemGroup Condition="'$(TargetFramework)' != 'netcoreapp3.1' and '$(TargetFramework)' != 'net5.0' and '$(TargetFramework)' != 'net6.0' and '$(TargetFramework)' != 'net7.0' ">
         <PackageReference Include="Microsoft.AspNetCore.Http.Connections" Version="1.1.0" />
     </ItemGroup>
 

Source/MQTTnet.AspnetCore/MqttConnectionContext.cs

@@ -211,8 +211,17 @@ namespace MQTTnet.AspNetCore
                 {
                     var buffer = PacketFormatterAdapter.Encode(packet);
 
-                    WritePacketBuffer(_output, buffer);
-                    await _output.FlushAsync(cancellationToken).ConfigureAwait(false);
+                    if (buffer.Payload.Count == 0)
+                    {
+                        // zero copy
+                        // https://github.com/dotnet/runtime/blob/e31ddfdc4f574b26231233dc10c9a9c402f40590/src/libraries/System.IO.Pipelines/src/System/IO/Pipelines/StreamPipeWriter.cs#L279
+                        await _output.WriteAsync(buffer.Packet, cancellationToken).ConfigureAwait(false);
+                    }
+                    else
+                    {
+                        WritePacketBuffer(_output, buffer);
+                        await _output.FlushAsync(cancellationToken).ConfigureAwait(false);
+                    }
 
                     BytesSent += buffer.Length;
                 }

Source/MQTTnet.AspnetCore/MqttWebSocketServerAdapter.cs

@@ -2,38 +2,34 @@
 // 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.Http;
-using MQTTnet.Adapter;
-using MQTTnet.Formatter;
-using MQTTnet.Implementations;
-using MQTTnet.Server;
 using System;
 using System.Net.WebSockets;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Http;
+using MQTTnet.Adapter;
 using MQTTnet.Diagnostics;
+using MQTTnet.Formatter;
+using MQTTnet.Implementations;
+using MQTTnet.Server;
 
 namespace MQTTnet.AspNetCore
 {
     public sealed class MqttWebSocketServerAdapter : IMqttServerAdapter
     {
-        IMqttNetLogger _logger = new MqttNetNullLogger();
-        
+        IMqttNetLogger _logger = MqttNetNullLogger.Instance;
+
         public Func<IMqttChannelAdapter, Task> ClientHandler { get; set; }
 
-        public Task StartAsync(MqttServerOptions options, IMqttNetLogger logger)
+        public void Dispose()
         {
-            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
-            return Task.CompletedTask;
-        }
-
-        public Task StopAsync()
-        {
-            return Task.CompletedTask;
         }
 
         public async Task RunWebSocketConnectionAsync(WebSocket webSocket, HttpContext httpContext)
         {
-            if (webSocket == null) throw new ArgumentNullException(nameof(webSocket));
+            if (webSocket == null)
+            {
+                throw new ArgumentNullException(nameof(webSocket));
+            }
 
             var endpoint = $"{httpContext.Connection.RemoteIpAddress}:{httpContext.Connection.RemotePort}";
 
@@ -48,7 +44,7 @@ namespace MQTTnet.AspNetCore
                     var formatter = new MqttPacketFormatterAdapter(new MqttBufferWriter(4096, 65535));
                     var channel = new MqttWebSocketChannel(webSocket, endpoint, isSecureConnection, clientCertificate);
 
-                    using (var channelAdapter = new MqttChannelAdapter(channel, formatter, null, _logger))
+                    using (var channelAdapter = new MqttChannelAdapter(channel, formatter, _logger))
                     {
                         await clientHandler(channelAdapter).ConfigureAwait(false);
                     }
@@ -60,8 +56,15 @@ namespace MQTTnet.AspNetCore
             }
         }
 
-        public void Dispose()
+        public Task StartAsync(MqttServerOptions options, IMqttNetLogger logger)
         {
+            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+            return Task.CompletedTask;
+        }
+
+        public Task StopAsync()
+        {
+            return Task.CompletedTask;
         }
     }
 }

Source/MQTTnet.Benchmarks/ChannelAdapterBenchmark.cs

@@ -73,7 +73,7 @@ namespace MQTTnet.Benchmarks
 
             var channel = new MemoryMqttChannel(_stream);
 
-            _channelAdapter = new MqttChannelAdapter(channel, serializer, null, new MqttNetEventLogger());
+            _channelAdapter = new MqttChannelAdapter(channel, serializer, new MqttNetEventLogger());
         }
 
         static byte[] Join(params ArraySegment<byte>[] chunks)

Source/MQTTnet.Benchmarks/MQTTnet.Benchmarks.csproj

@@ -4,7 +4,7 @@
         <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
         <OutputType>Exe</OutputType>
         <DebugType>Full</DebugType>
-        <TargetFrameworks>net6.0</TargetFrameworks>
+        <TargetFrameworks>net6.0;net7.0</TargetFrameworks>
         <LangVersion>7.2</LangVersion>
         <IsPackable>false</IsPackable>
         <EnableNETAnalyzers>false</EnableNETAnalyzers>
@@ -26,6 +26,10 @@
         <PackageReference Include="System.IO.Pipelines" Version="5.0.0" />
     </ItemGroup>
 
+    <ItemGroup Condition="'$(TargetFramework)' == 'net7.0'">
+        <PackageReference Include="System.IO.Pipelines" Version="7.0.0" />
+    </ItemGroup>
+
     <ItemGroup>
         <ProjectReference Include="..\..\Source\MQTTnet.AspnetCore\MQTTnet.AspNetCore.csproj" />
         <ProjectReference Include="..\MQTTnet.Tests\MQTTnet.Tests.csproj" />

Source/MQTTnet.Benchmarks/MqttPacketReaderWriterBenchmark.cs

@@ -30,17 +30,17 @@ namespace MQTTnet.Benchmarks
             
             var writer = new MqttBufferWriter(4096, 65535);
             writer.WriteString("A relative short string.");
-            writer.WriteBinaryData(_demoPayload);
+            writer.WriteBinary(_demoPayload);
             writer.WriteByte(0x01);
             writer.WriteByte(0x02);
             writer.WriteVariableByteInteger(5647382);
             writer.WriteString("A relative short string.");
             writer.WriteVariableByteInteger(8574489);
-            writer.WriteBinaryData(_demoPayload);
+            writer.WriteBinary(_demoPayload);
             writer.WriteByte(2);
             writer.WriteByte(0x02);
             writer.WriteString("fjgffiogfhgfhoihgoireghreghreguhreguireoghreouighreouighreughreguiorehreuiohruiorehreuioghreug");
-            writer.WriteBinaryData(_demoPayload);
+            writer.WriteBinary(_demoPayload);
 
             _readPayload = new ArraySegment<byte>(writer.GetBuffer(), 0, writer.Length).ToArray();
         }
@@ -83,11 +83,11 @@ namespace MQTTnet.Benchmarks
                 writer.WriteVariableByteInteger(5647382);
                 writer.WriteString("A relative short string.");
                 writer.WriteVariableByteInteger(8574589);
-                writer.WriteBinaryData(_demoPayload);
+                writer.WriteBinary(_demoPayload);
                 writer.WriteByte(2);
                 writer.WriteByte(0x02);
                 writer.WriteString("fjgffiogfhgfhoihgoireghreghreguhreguireoghreouighreouighreughreguiorehreuiohruiorehreuioghreug");
-                writer.WriteBinaryData(_demoPayload);
+                writer.WriteBinary(_demoPayload);
 
                 writer.Reset(0);
             }

Source/MQTTnet.Benchmarks/SendPacketAsyncBenchmark.cs

@@ -0,0 +1,68 @@
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Jobs;
+using MQTTnet.Formatter;
+using System;
+using System.IO;
+using System.IO.Pipelines;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Benchmarks
+{
+    [SimpleJob(RuntimeMoniker.Net60)]
+    [RPlotExporter, RankColumn]
+    [MemoryDiagnoser]
+    public class SendPacketAsyncBenchmark : BaseBenchmark
+    {
+        MemoryStream stream;
+        MqttPacketBuffer buffer;
+
+        [GlobalSetup]
+        public void GlobalSetup()
+        {
+            stream = new MemoryStream(1024);
+            var packet = new ArraySegment<byte>(new byte[10]);
+            buffer = new MqttPacketBuffer(packet);
+        }
+
+        [Benchmark(Baseline = true)]
+        public async ValueTask Before()
+        {
+            stream.Position = 0;
+            var output = PipeWriter.Create(stream);
+
+            WritePacketBuffer(output, buffer);
+            await output.FlushAsync();
+        }
+
+        [Benchmark]
+        public async ValueTask After()
+        {
+            stream.Position = 0;
+            var output = PipeWriter.Create(stream);
+
+            if (buffer.Payload.Count == 0)
+            {
+                await output.WriteAsync(buffer.Packet).ConfigureAwait(false);
+            }
+            else
+            {
+                WritePacketBuffer(output, buffer);
+                await output.FlushAsync().ConfigureAwait(false);
+            }
+        }
+
+
+        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.Benchmarks/SerializerBenchmark.cs

@@ -54,7 +54,7 @@ namespace MQTTnet.Benchmarks
         public void Deserialize_10000_Messages()
         {
             var channel = new BenchmarkMqttChannel(_serializedPacket);
-            var reader = new MqttChannelAdapter(channel, new MqttPacketFormatterAdapter(new MqttBufferWriter(4096, 65535)), null, new MqttNetEventLogger());
+            var reader = new MqttChannelAdapter(channel, new MqttPacketFormatterAdapter(new MqttBufferWriter(4096, 65535)), new MqttNetEventLogger());
 
             for (var i = 0; i < 10000; i++)
             {

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

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0</TargetFrameworks>
+        <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0;net7.0</TargetFrameworks>
         <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461</TargetFrameworks>
         <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' AND '$(MSBuildRuntimeType)' != 'Core' ">$(TargetFrameworks);uap10.0</TargetFrameworks>
         

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClient.cs

@@ -353,13 +353,13 @@ namespace MQTTnet.Extensions.ManagedClient
             return remainingTime < TimeSpan.Zero ? TimeSpan.Zero : remainingTime;
         }
 
-        async Task HandleSubscriptionExceptionAsync(Exception exception)
+        async Task HandleSubscriptionExceptionAsync(Exception exception, List<MqttTopicFilter> addedSubscriptions, List<string> removedSubscriptions)
         {
             _logger.Warning(exception, "Synchronizing subscriptions failed.");
 
             if (_synchronizingSubscriptionsFailedEvent.HasHandlers)
             {
-                await _synchronizingSubscriptionsFailedEvent.InvokeAsync(new ManagedProcessFailedEventArgs(exception)).ConfigureAwait(false);
+                await _synchronizingSubscriptionsFailedEvent.InvokeAsync(new ManagedProcessFailedEventArgs(exception, addedSubscriptions, removedSubscriptions)).ConfigureAwait(false);
             }
         }
 
@@ -457,11 +457,13 @@ namespace MQTTnet.Extensions.ManagedClient
         {
             _logger.Info("Publishing subscriptions at reconnect");
 
+            List<MqttTopicFilter> topicFilters = null;
+
             try
             {
                 if (_reconnectSubscriptions.Any())
                 {
-                    var topicFilters = new List<MqttTopicFilter>();
+                    topicFilters = new List<MqttTopicFilter>();
 
                     foreach (var sub in _reconnectSubscriptions)
                     {
@@ -479,7 +481,7 @@ namespace MQTTnet.Extensions.ManagedClient
             }
             catch (Exception exception)
             {
-                await HandleSubscriptionExceptionAsync(exception).ConfigureAwait(false);
+                await HandleSubscriptionExceptionAsync(exception, topicFilters, null).ConfigureAwait(false);
             }
         }
 
@@ -591,6 +593,9 @@ namespace MQTTnet.Extensions.ManagedClient
                     }
 
                     await InternalClient.UnsubscribeAsync(unsubscribeOptionsBuilder.Build()).ConfigureAwait(false);
+
+                    //clear because these worked, maybe the subscribe below will fail, only report those
+                    removedSubscriptions.Clear();
                 }
 
                 if (addedSubscriptions != null && addedSubscriptions.Any())
@@ -607,7 +612,7 @@ namespace MQTTnet.Extensions.ManagedClient
             }
             catch (Exception exception)
             {
-                await HandleSubscriptionExceptionAsync(exception).ConfigureAwait(false);
+                await HandleSubscriptionExceptionAsync(exception, addedSubscriptions, removedSubscriptions).ConfigureAwait(false);
             }
         }
 

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClientOptions.cs

@@ -24,7 +24,7 @@ namespace MQTTnet.Extensions.ManagedClient
 
         /// <summary>
         /// Defines the maximum amount of topic filters which will be sent in a SUBSCRIBE/UNSUBSCRIBE packet.
-        /// Amazon AWS limits this number to 8. The default is int.MaxValue.
+        /// Amazon Web Services (AWS) limits this number to 8. The default is int.MaxValue.
         /// </summary>
         public int MaxTopicFiltersInSubscribeUnsubscribePackets { get; set; } = int.MaxValue;
     }

Source/MQTTnet.Extensions.ManagedClient/ManagedProcessFailedEventArgs.cs

@@ -2,17 +2,33 @@
 // 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.Packets;
 using System;
+using System.Collections.Generic;
+using System.Linq;
 
 namespace MQTTnet.Extensions.ManagedClient
 {
     public class ManagedProcessFailedEventArgs : EventArgs
     {
-        public ManagedProcessFailedEventArgs(Exception exception)
+        public ManagedProcessFailedEventArgs(Exception exception, List<MqttTopicFilter> addedSubscriptions, List<string> removedSubscriptions)
         {
             Exception = exception ?? throw new ArgumentNullException(nameof(exception));
+
+            if (addedSubscriptions != null)
+            {
+                AddedSubscriptions = new List<string>(addedSubscriptions.Select(item => item.Topic));
+            }
+
+            if (removedSubscriptions != null)
+            {
+                RemovedSubscriptions = new List<string>(removedSubscriptions);
+            }
         }
 
         public Exception Exception { get; }
+
+        public List<string> AddedSubscriptions { get; }
+        public List<string> RemovedSubscriptions { get; }
     }
 }

Source/MQTTnet.Extensions.ManagedClient/MqttFactoryExtensions.cs

@@ -12,22 +12,37 @@ namespace MQTTnet.Extensions.ManagedClient
     {
         public static IManagedMqttClient CreateManagedMqttClient(this MqttFactory factory, IMqttClient mqttClient = null)
         {
-            if (factory == null) throw new ArgumentNullException(nameof(factory));
+            if (factory == null)
+            {
+                throw new ArgumentNullException(nameof(factory));
+            }
 
             if (mqttClient == null)
             {
-                return new ManagedMqttClient(factory.CreateMqttClient(), factory.DefaultLogger);    
+                return new ManagedMqttClient(factory.CreateMqttClient(), factory.DefaultLogger);
             }
-            
+
             return new ManagedMqttClient(mqttClient, factory.DefaultLogger);
         }
-        
+
         public static IManagedMqttClient CreateManagedMqttClient(this MqttFactory factory, IMqttNetLogger logger)
         {
-            if (factory == null) throw new ArgumentNullException(nameof(factory));
-            if (logger == null) throw new ArgumentNullException(nameof(logger));
+            if (factory == null)
+            {
+                throw new ArgumentNullException(nameof(factory));
+            }
+
+            if (logger == null)
+            {
+                throw new ArgumentNullException(nameof(logger));
+            }
 
             return new ManagedMqttClient(factory.CreateMqttClient(logger), logger);
         }
+
+        public static ManagedMqttClientOptionsBuilder CreateManagedMqttClientOptionsBuilder(this MqttFactory _)
+        {
+            return new ManagedMqttClientOptionsBuilder();
+        }
     }
 }

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

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0</TargetFrameworks>
+        <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0;net7.0</TargetFrameworks>
         <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461</TargetFrameworks>
         <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' AND '$(MSBuildRuntimeType)' != 'Core' ">$(TargetFrameworks);uap10.0</TargetFrameworks>
         

Source/MQTTnet.Extensions.Rpc/MqttRpcClient.cs

@@ -4,10 +4,12 @@
 
 using System;
 using System.Collections.Concurrent;
+using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Client;
 using MQTTnet.Exceptions;
+using MQTTnet.Formatter;
 using MQTTnet.Internal;
 using MQTTnet.Protocol;
 
@@ -17,9 +19,9 @@ namespace MQTTnet.Extensions.Rpc
     {
         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));
@@ -83,11 +85,14 @@ namespace MQTTnet.Extensions.Rpc
                 throw new MqttProtocolViolationException("RPC response topic is empty.");
             }
 
-            var requestMessage = new MqttApplicationMessageBuilder().WithTopic(requestTopic)
-                .WithPayload(payload)
-                .WithQualityOfServiceLevel(qualityOfServiceLevel)
-                .WithResponseTopic(responseTopic)
-                .Build();
+            var requestMessageBuilder = new MqttApplicationMessageBuilder().WithTopic(requestTopic).WithPayload(payload).WithQualityOfServiceLevel(qualityOfServiceLevel);
+
+            if (_mqttClient.Options.ProtocolVersion == MqttProtocolVersion.V500)
+            {
+                requestMessageBuilder.WithResponseTopic(responseTopic);
+            }
+
+            var requestMessage = requestMessageBuilder.Build();
 
             try
             {
@@ -115,7 +120,6 @@ namespace MQTTnet.Extensions.Rpc
             finally
             {
                 _waitingCalls.TryRemove(responseTopic, out _);
-
                 await _mqttClient.UnsubscribeAsync(responseTopic, CancellationToken.None).ConfigureAwait(false);
             }
         }
@@ -127,7 +131,8 @@ namespace MQTTnet.Extensions.Rpc
                 return CompletedTask.Instance;
             }
 
-            awaitable.TrySetResult(eventArgs.ApplicationMessage.Payload);
+            var payloadBuffer = eventArgs.ApplicationMessage.PayloadSegment.ToArray();
+            awaitable.TrySetResult(payloadBuffer);
 
             // Set this message to handled to that other code can avoid execution etc.
             eventArgs.IsHandled = true;

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

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0</TargetFrameworks>
+        <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0;net7.0</TargetFrameworks>
         <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461</TargetFrameworks>
         <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' AND '$(MSBuildRuntimeType)' != 'Core' ">$(TargetFrameworks);uap10.0</TargetFrameworks>
         

Source/MQTTnet.Extensions.WebSocket4Net/WebSocket4NetMqttClientAdapterFactory.cs

@@ -27,8 +27,10 @@ namespace MQTTnet.Extensions.WebSocket4Net
                     return new MqttChannelAdapter(
                         new MqttTcpChannel(options),
                         new MqttPacketFormatterAdapter(options.ProtocolVersion, new MqttBufferWriter(options.WriterBufferSize, options.WriterBufferSizeMax)),
-                        packetInspector,
-                        logger);
+                        logger)
+                    {
+                        PacketInspector = packetInspector
+                    };
                 }
 
                 case MqttClientWebSocketOptions webSocketOptions:
@@ -36,8 +38,10 @@ namespace MQTTnet.Extensions.WebSocket4Net
                     return new MqttChannelAdapter(
                         new WebSocket4NetMqttChannel(options, webSocketOptions),
                         new MqttPacketFormatterAdapter(options.ProtocolVersion, new MqttBufferWriter(options.WriterBufferSize, options.WriterBufferSizeMax)),
-                        packetInspector,
-                        logger);
+                        logger)
+                    {
+                        PacketInspector = packetInspector
+                    };
                 }
 
                 default:

Source/MQTTnet.TestApp/ClientTest.cs

@@ -33,9 +33,18 @@ namespace MQTTnet.TestApp
 
                 client.ApplicationMessageReceivedAsync += e =>
                 {
+                    var payloadText = string.Empty;
+                    if (e.ApplicationMessage.PayloadSegment.Count > 0)
+                    {
+                        payloadText = Encoding.UTF8.GetString(
+                            e.ApplicationMessage.PayloadSegment.Array,
+                            e.ApplicationMessage.PayloadSegment.Offset,
+                            e.ApplicationMessage.PayloadSegment.Count);
+                    }
+                    
                     Console.WriteLine("### RECEIVED APPLICATION MESSAGE ###");
                     Console.WriteLine($"+ Topic = {e.ApplicationMessage.Topic}");
-                    Console.WriteLine($"+ Payload = {Encoding.UTF8.GetString(e.ApplicationMessage.Payload)}");
+                    Console.WriteLine($"+ Payload = {payloadText}");
                     Console.WriteLine($"+ QoS = {e.ApplicationMessage.QualityOfServiceLevel}");
                     Console.WriteLine($"+ Retain = {e.ApplicationMessage.Retain}");
                     Console.WriteLine();

Source/MQTTnet.TestApp/MQTTnet.TestApp.csproj

@@ -1,9 +1,9 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
         <OutputType>Exe</OutputType>
         <DebugType>Full</DebugType>
-        <TargetFrameworks>net5.0;net6.0</TargetFrameworks>
+        <TargetFrameworks>net5.0;net6.0;net7.0</TargetFrameworks>
         <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461</TargetFrameworks>
         <IsPackable>false</IsPackable>
         <EnableNETAnalyzers>false</EnableNETAnalyzers>

Source/MQTTnet.TestApp/PerformanceTest.cs

@@ -196,7 +196,7 @@ namespace MQTTnet.TestApp
             return new MqttApplicationMessage
             {
                 Topic = "A/B/C",
-                Payload = Encoding.UTF8.GetBytes(Payload),
+                PayloadSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes(Payload)),
                 QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce
             };
         }
@@ -229,7 +229,7 @@ namespace MQTTnet.TestApp
                 var message = new MqttApplicationMessage
                 {
                     Topic = "A/B/C",
-                    Payload = Encoding.UTF8.GetBytes("Hello World"),
+                    PayloadSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes("Hello World")),
                     QualityOfServiceLevel = MqttQualityOfServiceLevel.ExactlyOnce
                 };
 
@@ -280,7 +280,7 @@ namespace MQTTnet.TestApp
                 var message = new MqttApplicationMessage
                 {
                     Topic = "A/B/C",
-                    Payload = Encoding.UTF8.GetBytes("Hello World"),
+                    PayloadSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes("Hello World")),
                     QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce
                 };
 
@@ -331,7 +331,7 @@ namespace MQTTnet.TestApp
                 var message = new MqttApplicationMessage
                 {
                     Topic = "A/B/C",
-                    Payload = Encoding.UTF8.GetBytes("Hello World"),
+                    PayloadSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes("Hello World")),
                     QualityOfServiceLevel = MqttQualityOfServiceLevel.AtMostOnce
                 };
 

Source/MQTTnet.TestApp/ServerTest.cs

@@ -5,6 +5,7 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using MQTTnet.Diagnostics;
@@ -100,7 +101,7 @@ namespace MQTTnet.TestApp
                     {
                         // Replace the payload with the timestamp. But also extending a JSON 
                         // based payload with the timestamp is a suitable use case.
-                        e.ApplicationMessage.Payload = Encoding.UTF8.GetBytes(DateTime.Now.ToString("O"));
+                        e.ApplicationMessage.PayloadSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes(DateTime.Now.ToString("O")));
                     }
 
                     if (e.ApplicationMessage.Topic == "not_allowed_topic")
@@ -143,10 +144,16 @@ namespace MQTTnet.TestApp
                 
                 mqttServer.InterceptingPublishAsync += e =>
                 {
-                    MqttNetConsoleLogger.PrintToConsole(
-                        $"'{e.ClientId}' reported '{e.ApplicationMessage.Topic}' > '{Encoding.UTF8.GetString(e.ApplicationMessage.Payload ?? new byte[0])}'",
-                        ConsoleColor.Magenta);
+                    var payloadText = string.Empty;
+                    if (e.ApplicationMessage.PayloadSegment.Count > 0)
+                    {
+                        payloadText = Encoding.UTF8.GetString(
+                            e.ApplicationMessage.PayloadSegment.Array,
+                            e.ApplicationMessage.PayloadSegment.Offset,
+                            e.ApplicationMessage.PayloadSegment.Count);
+                    }
                     
+                    MqttNetConsoleLogger.PrintToConsole($"'{e.ClientId}' reported '{e.ApplicationMessage.Topic}' > '{payloadText}'", ConsoleColor.Magenta);
                     return CompletedTask.Instance;
                 };
 

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

@@ -14,7 +14,7 @@ using MQTTnet.LowLevelClient;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
 
-namespace MQTTnet.Tests.Client
+namespace MQTTnet.Tests.Clients.LowLevelMqttClient
 {
     [TestClass]
     public sealed class LowLevelMqttClient_Tests : BaseTestClass

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

@@ -17,11 +17,43 @@ using MQTTnet.Protocol;
 using MQTTnet.Server;
 using MQTTnet.Tests.Mockups;
 
-namespace MQTTnet.Tests.Client
+namespace MQTTnet.Tests.Clients.ManagedMqttClient
 {
     [TestClass]
     public sealed class ManagedMqttClient_Tests : BaseTestClass
     {
+        [TestMethod]
+        public async Task Expose_Custom_Connection_Error()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                var server = await testEnvironment.StartServer();
+                
+                server.ValidatingConnectionAsync += args =>
+                {
+                    args.ReasonCode = MqttConnectReasonCode.BadUserNameOrPassword;
+                    return CompletedTask.Instance;
+                };
+
+                var managedClient = testEnvironment.Factory.CreateManagedMqttClient();
+
+                MqttClientDisconnectedEventArgs disconnectedArgs = null;
+                managedClient.DisconnectedAsync += args =>
+                {
+                    disconnectedArgs = args;
+                    return CompletedTask.Instance;
+                };
+                
+                var clientOptions = testEnvironment.Factory.CreateManagedMqttClientOptionsBuilder().WithClientOptions(testEnvironment.CreateDefaultClientOptions()).Build();
+                await managedClient.StartAsync(clientOptions);
+
+                await LongTestDelay();
+
+                Assert.IsNotNull(disconnectedArgs);
+                Assert.AreEqual(MqttClientConnectResultCode.BadUserNameOrPassword, disconnectedArgs.ConnectResult.ResultCode);
+            }
+        }
+        
         [TestMethod]
         public async Task Receive_While_Not_Cleanly_Disconnected()
         {
@@ -164,7 +196,7 @@ namespace MQTTnet.Tests.Client
                     .Build();
 
                 var dyingClient = testEnvironment.CreateClient();
-                var dyingManagedClient = new ManagedMqttClient(dyingClient, testEnvironment.ClientLogger);
+                var dyingManagedClient = new MQTTnet.Extensions.ManagedClient.ManagedMqttClient(dyingClient, testEnvironment.ClientLogger);
 
                 await dyingManagedClient.StartAsync(new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).Build());
 
@@ -199,7 +231,7 @@ namespace MQTTnet.Tests.Client
             {
                 var server = await testEnvironment.StartServer();
 
-                var managedClient = new ManagedMqttClient(testEnvironment.CreateClient(), new MqttNetEventLogger());
+                var managedClient = new MQTTnet.Extensions.ManagedClient.ManagedMqttClient(testEnvironment.CreateClient(), new MqttNetEventLogger());
                 var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("localhost", testEnvironment.ServerPort);
 
                 var connected = GetConnectedTask(managedClient);
@@ -226,7 +258,7 @@ namespace MQTTnet.Tests.Client
 
                 await testEnvironment.StartServer();
 
-                var managedClient = new ManagedMqttClient(testEnvironment.CreateClient(), new MqttNetEventLogger());
+                var managedClient = new MQTTnet.Extensions.ManagedClient.ManagedMqttClient(testEnvironment.CreateClient(), new MqttNetEventLogger());
                 var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("localhost", testEnvironment.ServerPort);
                 var storage = new ManagedMqttClientTestStorage();
 
@@ -439,7 +471,7 @@ namespace MQTTnet.Tests.Client
             }
         }
 
-        async Task<ManagedMqttClient> CreateManagedClientAsync(
+        async Task<MQTTnet.Extensions.ManagedClient.ManagedMqttClient> CreateManagedClientAsync(
             TestEnvironment testEnvironment,
             IMqttClient underlyingClient = null,
             TimeSpan? connectionCheckInterval = null,
@@ -456,7 +488,7 @@ namespace MQTTnet.Tests.Client
             // at connection check intervals
             managedOptions.ConnectionCheckInterval = connectionCheckInterval ?? TimeSpan.FromSeconds(0.1);
 
-            var managedClient = new ManagedMqttClient(underlyingClient ?? testEnvironment.CreateClient(), new MqttNetEventLogger());
+            var managedClient = new MQTTnet.Extensions.ManagedClient.ManagedMqttClient(underlyingClient ?? testEnvironment.CreateClient(), new MqttNetEventLogger());
 
             var connected = GetConnectedTask(managedClient);
 
@@ -473,7 +505,7 @@ namespace MQTTnet.Tests.Client
         ///         name="managedClient" />
         ///     has connected
         /// </summary>
-        Task GetConnectedTask(ManagedMqttClient managedClient)
+        Task GetConnectedTask(MQTTnet.Extensions.ManagedClient.ManagedMqttClient managedClient)
         {
             var connected = new TaskCompletionSource<bool>();
 
@@ -495,7 +527,7 @@ namespace MQTTnet.Tests.Client
         ///         name="expectedNumberOfMessages" />
         ///     have been received
         /// </summary>
-        Task<List<MqttApplicationMessage>> SetupReceivingOfMessages(ManagedMqttClient managedClient, int expectedNumberOfMessages)
+        Task<List<MqttApplicationMessage>> SetupReceivingOfMessages(MQTTnet.Extensions.ManagedClient.ManagedMqttClient managedClient, int expectedNumberOfMessages)
         {
             var receivedMessages = new List<MqttApplicationMessage>();
             var result = new AsyncTaskCompletionSource<List<MqttApplicationMessage>>();

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

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

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

@@ -0,0 +1,168 @@
+// 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 Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Client;
+using MQTTnet.Exceptions;
+using MQTTnet.Formatter;
+using MQTTnet.Internal;
+using MQTTnet.Protocol;
+using MQTTnet.Server;
+
+namespace MQTTnet.Tests.Clients.MqttClient
+{
+    [TestClass]
+    public sealed class MqttClient_Connection_Tests : BaseTestClass
+    {
+        [TestMethod]
+        [ExpectedException(typeof(MqttCommunicationException))]
+        public async Task Connect_To_Invalid_Server_Port_Not_Opened()
+        {
+            var client = new MqttFactory().CreateMqttClient();
+            using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(5)))
+            {
+                await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1", 12345).Build(), timeout.Token);
+            }
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(OperationCanceledException))]
+        public async Task Connect_To_Invalid_Server_Wrong_IP()
+        {
+            var client = new MqttFactory().CreateMqttClient();
+            using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(2)))
+            {
+                await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("1.2.3.4").Build(), timeout.Token);
+            }
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(MqttCommunicationException))]
+        public async Task Connect_To_Invalid_Server_Wrong_Protocol()
+        {
+            var client = new MqttFactory().CreateMqttClient();
+            await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("http://127.0.0.1", 12345).WithTimeout(TimeSpan.FromSeconds(2)).Build());
+        }
+
+        [TestMethod]
+        public async Task ConnectTimeout_Throws_Exception()
+        {
+            var factory = new MqttFactory();
+            using (var client = factory.CreateMqttClient())
+            {
+                var disconnectHandlerCalled = false;
+                try
+                {
+                    client.DisconnectedAsync += args =>
+                    {
+                        disconnectHandlerCalled = true;
+                        return CompletedTask.Instance;
+                    };
+
+                    await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("1.2.3.4").Build());
+
+                    Assert.Fail("Must fail!");
+                }
+                catch (Exception exception)
+                {
+                    Assert.IsNotNull(exception);
+                    Assert.IsInstanceOfType(exception, typeof(MqttCommunicationException));
+                }
+
+                await LongTestDelay(); // disconnected handler is called async
+                Assert.IsTrue(disconnectHandlerCalled);
+            }
+        }
+
+        [TestMethod]
+        public async Task Disconnect_Clean()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                var server = await testEnvironment.StartServer();
+
+                ClientDisconnectedEventArgs eventArgs = null;
+                server.ClientDisconnectedAsync += args =>
+                {
+                    eventArgs = args;
+                    return CompletedTask.Instance;
+                };
+
+                var client = await testEnvironment.ConnectClient();
+
+                var disconnectOptions = testEnvironment.Factory.CreateClientDisconnectOptionsBuilder().WithReason(MqttClientDisconnectOptionsReason.MessageRateTooHigh).Build();
+
+                // Perform a clean disconnect.
+                await client.DisconnectAsync(disconnectOptions);
+
+                await LongTestDelay();
+
+                Assert.IsNotNull(eventArgs);
+                Assert.AreEqual(MqttClientDisconnectType.Clean, eventArgs.DisconnectType);
+            }
+        }
+
+        [TestMethod]
+        public async Task Disconnect_Clean_With_Custom_Reason()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                var server = await testEnvironment.StartServer();
+
+                ClientDisconnectedEventArgs eventArgs = null;
+                server.ClientDisconnectedAsync += args =>
+                {
+                    eventArgs = args;
+                    return CompletedTask.Instance;
+                };
+
+                var client = await testEnvironment.ConnectClient();
+
+                var disconnectOptions = testEnvironment.Factory.CreateClientDisconnectOptionsBuilder().WithReason(MqttClientDisconnectOptionsReason.MessageRateTooHigh).Build();
+
+                // Perform a clean disconnect.
+                await client.DisconnectAsync(disconnectOptions);
+
+                await LongTestDelay();
+                
+                Assert.IsNotNull(eventArgs);
+                Assert.AreEqual(MqttDisconnectReasonCode.MessageRateTooHigh, eventArgs.ReasonCode);
+            }
+        }
+
+        [TestMethod]
+        public async Task Disconnect_Clean_With_User_Properties()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                var server = await testEnvironment.StartServer();
+
+                ClientDisconnectedEventArgs eventArgs = null;
+                server.ClientDisconnectedAsync += args =>
+                {
+                    eventArgs = args;
+                    return CompletedTask.Instance;
+                };
+
+                var client = await testEnvironment.ConnectClient();
+
+                var disconnectOptions = testEnvironment.Factory.CreateClientDisconnectOptionsBuilder().WithUserProperty("test_name", "test_value").Build();
+
+                // Perform a clean disconnect.
+                await client.DisconnectAsync(disconnectOptions);
+
+                await LongTestDelay();
+                
+                Assert.IsNotNull(eventArgs);
+                Assert.IsNotNull(eventArgs.UserProperties);
+                Assert.AreEqual(1, eventArgs.UserProperties.Count);
+                Assert.AreEqual("test_name", eventArgs.UserProperties[0].Name);
+                Assert.AreEqual("test_value", eventArgs.UserProperties[0].Value);
+            }
+        }
+    }
+}

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

@@ -21,7 +21,7 @@ using MQTTnet.Tests.Mockups;
 
 // ReSharper disable InconsistentNaming
 
-namespace MQTTnet.Tests.Client
+namespace MQTTnet.Tests.Clients.MqttClient
 {
     [TestClass]
     public sealed class MqttClient_Tests : BaseTestClass
@@ -71,60 +71,34 @@ namespace MQTTnet.Tests.Client
         }
 
         [TestMethod]
-        [ExpectedException(typeof(MqttCommunicationException))]
-        public async Task Connect_To_Invalid_Server_Port_Not_Opened()
+        public async Task Connect_Disconnect_Connect()
         {
-            var client = new MqttFactory().CreateMqttClient();
-            await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1", 12345).WithTimeout(TimeSpan.FromSeconds(5)).Build());
-        }
-
-        [TestMethod]
-        [ExpectedException(typeof(OperationCanceledException))]
-        public async Task Connect_To_Invalid_Server_Wrong_IP()
-        {
-            var client = new MqttFactory().CreateMqttClient();
-            using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(2)))
+            using (var testEnvironment = CreateTestEnvironment())
             {
-                await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("1.2.3.4").Build(), timeout.Token);
+                await testEnvironment.StartServer();
+
+                var clientOptions = testEnvironment.CreateDefaultClientOptions();
+                var client = testEnvironment.CreateClient();
+
+                await client.ConnectAsync(clientOptions);
+                await client.DisconnectAsync();
+                await client.ConnectAsync(clientOptions);
             }
         }
-
+        
         [TestMethod]
-        [ExpectedException(typeof(MqttCommunicationException))]
-        public async Task Connect_To_Invalid_Server_Wrong_Protocol()
+        [ExpectedException(typeof(InvalidOperationException))]
+        public async Task Connect_Multiple_Times_Should_Fail()
         {
-            var client = new MqttFactory().CreateMqttClient();
-            await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("http://127.0.0.1", 12345).WithTimeout(TimeSpan.FromSeconds(2)).Build());
-        }
-
-        [TestMethod]
-        public async Task ConnectTimeout_Throws_Exception()
-        {
-            var factory = new MqttFactory();
-            using (var client = factory.CreateMqttClient())
+            using (var testEnvironment = CreateTestEnvironment())
             {
-                var disconnectHandlerCalled = false;
-                try
-                {
-                    client.DisconnectedAsync += args =>
-                    {
-                        disconnectHandlerCalled = true;
-                        return CompletedTask.Instance;
-                    };
+                await testEnvironment.StartServer();
 
-                    await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("1.2.3.4").Build());
+                var clientOptions = testEnvironment.CreateDefaultClientOptions();
+                var client = testEnvironment.CreateClient();
 
-                    Assert.Fail("Must fail!");
-                }
-                catch (Exception exception)
-                {
-                    Assert.IsNotNull(exception);
-                    Assert.IsInstanceOfType(exception, typeof(MqttCommunicationException));
-                    //Assert.IsInstanceOfType(exception.InnerException, typeof(SocketException));
-                }
-
-                await LongTestDelay(); // disconnected handler is called async
-                Assert.IsTrue(disconnectHandlerCalled);
+                await client.ConnectAsync(clientOptions);
+                await client.ConnectAsync(clientOptions);
             }
         }
 

Source/MQTTnet.Tests/Clients/MqttClientOptionsBuilder_Tests.cs

@@ -6,9 +6,8 @@ using System.Linq;
 using System.Text;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
-using MQTTnet.Extensions;
 
-namespace MQTTnet.Tests.Client
+namespace MQTTnet.Tests.Clients
 {
     [TestClass]
     public class MqttClientOptionsBuilder_Tests

Source/MQTTnet.Tests/Diagnostics/PacketInspection_Tests.cs

@@ -30,7 +30,7 @@ namespace MQTTnet.Tests.Diagnostics
 
                     var packets = new List<string>();
                     
-                    mqttClient.InspectPackage += eventArgs =>
+                    mqttClient.InspectPacketAsync += eventArgs =>
                     {
                         packets.Add(eventArgs.Direction + ":" + Convert.ToBase64String(eventArgs.Buffer));
                         return CompletedTask.Instance;

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V3_Binary_Tests.cs

@@ -111,7 +111,7 @@ namespace MQTTnet.Tests.Formatter
                 PacketIdentifier = 123,
                 Dup = true,
                 Retain = true,
-                Payload = Encoding.ASCII.GetBytes("HELLO"),
+                PayloadSegment = new ArraySegment<byte>(Encoding.ASCII.GetBytes("HELLO")),
                 QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce,
                 Topic = "A/B/C"
             };
@@ -318,10 +318,9 @@ namespace MQTTnet.Tests.Formatter
             var publishPacket = new MqttPublishPacket
             {
                 Topic = "abcdefghijklmnopqrstuvwxyz0123456789",
-                Payload = payload
+                PayloadSegment = new ArraySegment<byte>(payload)
             };
 
-
             var serializationHelper = new MqttPacketSerializationHelper();
 
             var buffer = serializationHelper.Encode(publishPacket);
@@ -329,17 +328,17 @@ namespace MQTTnet.Tests.Formatter
 
             Assert.IsNotNull(publishPacketCopy);
             Assert.AreEqual(publishPacket.Topic, publishPacketCopy.Topic);
-            CollectionAssert.AreEqual(publishPacket.Payload, publishPacketCopy.Payload);
+            CollectionAssert.AreEqual(publishPacket.PayloadSegment.ToArray(), publishPacketCopy.PayloadSegment.ToArray());
 
             // Now modify the payload and test again.
-            publishPacket.Payload = Encoding.UTF8.GetBytes("MQTT");
+            publishPacket.PayloadSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes("MQTT"));
 
             buffer = serializationHelper.Encode(publishPacket);
             var publishPacketCopy2 = serializationHelper.Decode(buffer) as MqttPublishPacket;
 
             Assert.IsNotNull(publishPacketCopy2);
             Assert.AreEqual(publishPacket.Topic, publishPacketCopy2.Topic);
-            CollectionAssert.AreEqual(publishPacket.Payload, publishPacketCopy2.Payload);
+            CollectionAssert.AreEqual(publishPacket.PayloadSegment.ToArray(), publishPacketCopy2.PayloadSegment.ToArray());
         }
 
         [TestMethod]
@@ -463,7 +462,7 @@ namespace MQTTnet.Tests.Formatter
                 PacketIdentifier = 123,
                 Dup = true,
                 Retain = true,
-                Payload = Encoding.ASCII.GetBytes("HELLO"),
+                PayloadSegment = new ArraySegment<byte>(Encoding.ASCII.GetBytes("HELLO")),
                 QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce,
                 Topic = "A/B/C"
             };
@@ -567,7 +566,6 @@ namespace MQTTnet.Tests.Formatter
                     using (var adapter = new MqttChannelAdapter(
                                channel,
                                new MqttPacketFormatterAdapter(protocolVersion, new MqttBufferWriter(4096, 65535)),
-                               null,
                                new MqttNetEventLogger()))
                     {
                         var receivedPacket = adapter.ReceivePacketAsync(CancellationToken.None).GetAwaiter().GetResult();
@@ -583,19 +581,12 @@ namespace MQTTnet.Tests.Formatter
         MqttProtocolVersion DeserializeAndDetectVersion(MqttPacketFormatterAdapter packetFormatterAdapter, byte[] buffer)
         {
             var channel = new MemoryMqttChannel(buffer);
-            var adapter = new MqttChannelAdapter(channel, packetFormatterAdapter, null, new MqttNetEventLogger());
+            var adapter = new MqttChannelAdapter(channel, packetFormatterAdapter, new MqttNetEventLogger());
 
             adapter.ReceivePacketAsync(CancellationToken.None).GetAwaiter().GetResult();
             return packetFormatterAdapter.ProtocolVersion;
         }
 
-        MqttBufferReader ReaderFactory(byte[] data)
-        {
-            var reader = new MqttBufferReader();
-            reader.SetBuffer(data, 0, data.Length);
-            return reader;
-        }
-
         TPacket Roundtrip<TPacket>(TPacket packet, MqttProtocolVersion protocolVersion = MqttProtocolVersion.V311, MqttBufferWriter bufferWriter = null) where TPacket : MqttPacket
         {
             var writer = bufferWriter ?? WriterFactory();
@@ -604,7 +595,7 @@ namespace MQTTnet.Tests.Formatter
 
             using (var channel = new MemoryMqttChannel(buffer.Join().ToArray()))
             {
-                var adapter = new MqttChannelAdapter(channel, new MqttPacketFormatterAdapter(protocolVersion, new MqttBufferWriter(4096, 65535)), null, new MqttNetEventLogger());
+                var adapter = new MqttChannelAdapter(channel, new MqttPacketFormatterAdapter(protocolVersion, new MqttBufferWriter(4096, 65535)), new MqttNetEventLogger());
                 return (TPacket)adapter.ReceivePacketAsync(CancellationToken.None).GetAwaiter().GetResult();
             }
         }

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V3_Tests.cs

@@ -2,7 +2,9 @@
 // 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 Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Exceptions;
@@ -296,7 +298,7 @@ namespace MQTTnet.Tests.Formatter
                 PacketIdentifier = 123,
                 Dup = true,
                 Retain = true,
-                Payload = Encoding.ASCII.GetBytes("Payload"),
+                PayloadSegment = new ArraySegment<byte>(Encoding.ASCII.GetBytes("Payload")),
                 QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce,
                 Topic = "Topic",
                 ResponseTopic = "/Response",
@@ -320,7 +322,7 @@ namespace MQTTnet.Tests.Formatter
             Assert.AreEqual(publishPacket.PacketIdentifier, deserialized.PacketIdentifier);
             Assert.AreEqual(publishPacket.Dup, deserialized.Dup);
             Assert.AreEqual(publishPacket.Retain, deserialized.Retain);
-            CollectionAssert.AreEqual(publishPacket.Payload, deserialized.Payload);
+            CollectionAssert.AreEqual(publishPacket.PayloadSegment.ToArray(), deserialized.PayloadSegment.ToArray());
             Assert.AreEqual(publishPacket.QualityOfServiceLevel, deserialized.QualityOfServiceLevel);
             Assert.AreEqual(publishPacket.Topic, deserialized.Topic);
             Assert.AreEqual(null, deserialized.ResponseTopic); // Not supported in v3.1.1.

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V5_Tests.cs

@@ -2,7 +2,9 @@
 // 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 Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Formatter;
@@ -257,7 +259,7 @@ namespace MQTTnet.Tests.Formatter
                 PacketIdentifier = 123,
                 Dup = true,
                 Retain = true,
-                Payload = Encoding.ASCII.GetBytes("Payload"),
+                PayloadSegment = new ArraySegment<byte>(Encoding.ASCII.GetBytes("Payload")),
                 QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce,
                 Topic = "Topic",
                 ResponseTopic = "/Response",
@@ -281,7 +283,7 @@ namespace MQTTnet.Tests.Formatter
             Assert.AreEqual(publishPacket.PacketIdentifier, deserialized.PacketIdentifier);
             Assert.AreEqual(publishPacket.Dup, deserialized.Dup);
             Assert.AreEqual(publishPacket.Retain, deserialized.Retain);
-            CollectionAssert.AreEqual(publishPacket.Payload, deserialized.Payload);
+            CollectionAssert.AreEqual(publishPacket.PayloadSegment.ToArray(), deserialized.PayloadSegment.ToArray());
             Assert.AreEqual(publishPacket.QualityOfServiceLevel, deserialized.QualityOfServiceLevel);
             Assert.AreEqual(publishPacket.Topic, deserialized.Topic);
             Assert.AreEqual(publishPacket.ResponseTopic, deserialized.ResponseTopic);

Source/MQTTnet.Tests/Formatter/MqttPacketWriter_Tests.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Linq;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
 
 namespace MQTTnet.Tests.Formatter
@@ -47,23 +48,32 @@ namespace MQTTnet.Tests.Formatter
             Assert.AreEqual(1234U, reader.ReadVariableByteInteger());
             Assert.AreEqual(9876U, reader.ReadVariableByteInteger());
         }
+        
+        [TestMethod]
+        [ExpectedException(typeof(MqttProtocolViolationException))]
+        public void Throw_If_String_Too_Long()
+        {
+            var writer = new MqttBufferWriter(4096, 65535);
+            
+            writer.WriteString(string.Empty.PadLeft(65536));
+        }
 
         [TestMethod]
         public void Write_And_Read_Multiple_Times()
         {
             var writer = new MqttBufferWriter(4096, 65535);
             writer.WriteString("A relative short string.");
-            writer.WriteBinaryData(new byte[1234]);
+            writer.WriteBinary(new byte[1234]);
             writer.WriteByte(0x01);
             writer.WriteByte(0x02);
             writer.WriteVariableByteInteger(5647382);
             writer.WriteString("A relative short string.");
             writer.WriteVariableByteInteger(8574489);
-            writer.WriteBinaryData(new byte[48]);
+            writer.WriteBinary(new byte[48]);
             writer.WriteByte(2);
             writer.WriteByte(0x02);
             writer.WriteString("fjgffiogfhgfhoihgoireghreghreguhreguireoghreouighreouighreughreguiorehreuiohruiorehreuioghreug");
-            writer.WriteBinaryData(new byte[3]);
+            writer.WriteBinary(new byte[3]);
 
             var readPayload = new ArraySegment<byte>(writer.GetBuffer(), 0, writer.Length).ToArray();
 

Source/MQTTnet.Tests/MQTTnet.Tests.csproj

@@ -1,7 +1,7 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFrameworks>net452;net461;net48;netcoreapp3.1;net6.0</TargetFrameworks>
+        <TargetFrameworks>net452;net461;net48;netcoreapp3.1;net6.0;net7.0</TargetFrameworks>
         <IsPackable>false</IsPackable>
         <LangVersion>7.3</LangVersion>
         <EnableNETAnalyzers>false</EnableNETAnalyzers>

Source/MQTTnet.Tests/Mockups/TestApplicationMessageReceivedHandler.cs

@@ -51,10 +51,7 @@ namespace MQTTnet.Tests.Mockups
 
         public void AssertReceivedCountEquals(int expectedCount)
         {
-            lock (_receivedEventArgs)
-            {
-                Assert.AreEqual(expectedCount, _receivedEventArgs.Count);
-            }
+            Assert.AreEqual(expectedCount, Count);
         }
 
         public string GeneratePayloadSequence()

Source/MQTTnet.Tests/Mockups/TestEnvironment.cs

@@ -238,6 +238,16 @@ namespace MQTTnet.Tests.Mockups
             }
         }
 
+        public MqttClientOptions CreateDefaultClientOptions()
+        {
+            return CreateDefaultClientOptionsBuilder().Build();
+        }
+
+        public MqttClientOptionsBuilder CreateDefaultClientOptionsBuilder()
+        {
+            return Factory.CreateClientOptionsBuilder().WithProtocolVersion(_protocolVersion).WithTcpServer("127.0.0.1", ServerPort).WithClientId(TestContext.TestName + "_" + Guid.NewGuid());
+        }
+
         public ILowLevelMqttClient CreateLowLevelClient()
         {
             lock (_clients)
@@ -267,8 +277,7 @@ namespace MQTTnet.Tests.Mockups
                     // Null is used when the client id is assigned from the server!
                     if (!string.IsNullOrEmpty(e.ClientId) && !e.ClientId.StartsWith(TestContext.TestName))
                     {
-                        TrackException(new InvalidOperationException($"Invalid client ID used ({e.ClientId}). It must start with UnitTest name."));
-                        e.ReasonCode = MqttConnectReasonCode.ClientIdentifierNotValid;
+                        Assert.Fail($"Client ID does not start with test name ({TestContext.TestName}).");
                     }
                 }
 
@@ -282,23 +291,12 @@ namespace MQTTnet.Tests.Mockups
         {
             foreach (var mqttClient in _clients)
             {
-                try
-                {
-                    //mqttClient.DisconnectAsync().GetAwaiter().GetResult();
-                }
-                catch
-                {
-                    // This can happen when the test already disconnected the client.
-                }
-                finally
-                {
-                    mqttClient?.Dispose();
-                }
+                mqttClient?.Dispose();
             }
 
             foreach (var lowLevelMqttClient in _lowLevelClients)
             {
-                lowLevelMqttClient.Dispose();
+                lowLevelMqttClient?.Dispose();
             }
 
             try

Source/MQTTnet.Tests/MqttApplicationMessageTest.cs

@@ -0,0 +1,48 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Tests
+{
+    [TestClass]
+    public class MqttApplicationMessageTest
+    {
+        [TestMethod]
+        public void PayloadSegment()
+        {
+            var message = new MqttApplicationMessage();
+            Assert.AreEqual(0, message.Payload.Length);
+            Assert.AreEqual(0, message.PayloadSegment.Count);
+
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
+
+            message.Payload = new byte[] { 1, 2 };
+            Assert.AreEqual(2, message.Payload.Length);
+            Assert.AreEqual(2, message.PayloadSegment.Count);
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
+
+            message.Payload = new byte[] { 1, 2, 3 };
+            Assert.AreEqual(3, message.Payload.Length);
+            Assert.AreEqual(3, message.PayloadSegment.Count);
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
+
+            message.PayloadSegment = new ArraySegment<byte>(new byte[] { 1, 2, 3 });
+            Assert.AreEqual(3, message.Payload.Length);
+            Assert.AreEqual(3, message.PayloadSegment.Count);
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
+
+            message.PayloadSegment = new ArraySegment<byte>(new byte[] { 1, 2, 3 }, 1, 1);
+            Assert.AreEqual(1, message.Payload.Length);
+            Assert.AreEqual(1, message.PayloadSegment.Count);
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsFalse(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
+        }
+    }
+}

Source/MQTTnet.Tests/MqttApplicationMessageValidator_Tests.cs

@@ -0,0 +1,44 @@
+// 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 Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Formatter;
+
+namespace MQTTnet.Tests
+{
+    [TestClass]
+    public sealed class MqttApplicationMessageValidator_Tests
+    {
+        [TestMethod]
+        [ExpectedException(typeof(NotSupportedException))]
+        public void Succeed_When_Using_TopicAlias_And_MQTT_311()
+        {
+            MqttApplicationMessageValidator.ThrowIfNotSupported(new MqttApplicationMessageBuilder().WithTopicAlias(1).Build(), MqttProtocolVersion.V311);
+        }
+
+        [TestMethod]
+        public void Succeed_When_Using_TopicAlias_And_MQTT_500()
+        {
+            MqttApplicationMessageValidator.ThrowIfNotSupported(new MqttApplicationMessageBuilder().WithTopicAlias(1).Build(), MqttProtocolVersion.V500);
+        }
+
+        [TestMethod]
+        public void Succeed_When_Using_UserProperties_And_MQTT_500()
+        {
+            MqttApplicationMessageValidator.ThrowIfNotSupported(
+                new MqttApplicationMessageBuilder().WithTopic("A").WithUserProperty("User", "Property").Build(),
+                MqttProtocolVersion.V500);
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(NotSupportedException))]
+        public void Succeed_When_Using_WillUserProperties_And_MQTT_311()
+        {
+            MqttApplicationMessageValidator.ThrowIfNotSupported(
+                new MqttApplicationMessageBuilder().WithTopic("B").WithUserProperty("User", "Property").Build(),
+                MqttProtocolVersion.V311);
+        }
+    }
+}

Source/MQTTnet.Tests/MqttClientOptionsValidator_Tests.cs

@@ -0,0 +1,54 @@
+// 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 Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Client;
+using MQTTnet.Formatter;
+
+namespace MQTTnet.Tests
+{
+    [TestClass]
+    public sealed class MqttClientOptionsValidator_Tests
+    {
+        [TestMethod]
+        public void Succeed_When_Using_UserProperties_And_MQTT_500()
+        {
+            new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V500).WithUserProperty("User", "Property").WithTcpServer("FAKE").Build();
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(NotSupportedException))]
+        public void Succeed_When_Using_WillUserProperties_And_MQTT_311()
+        {
+            new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V311).WithWillUserProperty("User", "Property").WithTcpServer("FAKE").Build();
+        }
+
+        [TestMethod]
+        public void Succeed_When_Using_WillUserProperties_And_MQTT_500()
+        {
+            new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V500).WithWillUserProperty("User", "Property").WithTcpServer("FAKE").Build();
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(NotSupportedException))]
+        public void Throw_When_Using_UserProperties_And_MQTT_311()
+        {
+            new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V311).WithUserProperty("User", "Property").WithTcpServer("FAKE").Build();
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(NotSupportedException))]
+        public void Throw_When_Using_WithRequestResponseInformation_And_MQTT_311()
+        {
+            new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V311).WithRequestResponseInformation().WithTcpServer("FAKE").Build();
+        }
+
+        [TestMethod]
+        public void Throw_When_Using_WithRequestResponseInformation_And_MQTT_500()
+        {
+            new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V500).WithRequestResponseInformation().WithTcpServer("FAKE").Build();
+        }
+    }
+}

Source/MQTTnet.Tests/MqttPacketSerializationHelper.cs

@@ -31,7 +31,7 @@ namespace MQTTnet.Tests
             {
                 var formatterAdapter = new MqttPacketFormatterAdapter(_protocolVersion, new MqttBufferWriter(4096, 65535));
 
-                var adapter = new MqttChannelAdapter(channel, formatterAdapter, null, MqttNetNullLogger.Instance);
+                var adapter = new MqttChannelAdapter(channel, formatterAdapter, MqttNetNullLogger.Instance);
                 return adapter.ReceivePacketAsync(CancellationToken.None).GetAwaiter().GetResult();
             }
         }

Source/MQTTnet.Tests/MqttPacketWriter_Tests.cs

@@ -24,10 +24,10 @@ namespace MQTTnet.Tests
             writer.WriteString("1234567890");
             Assert.AreEqual(10 + 2, writer.Length);
 
-            writer.WriteBinaryData(new byte[300]);
+            writer.WriteBinary(new byte[300]);
             Assert.AreEqual(300 + 2 + 12, writer.Length);
 
-            writer.WriteBinaryData(new byte[5000]);
+            writer.WriteBinary(new byte[5000]);
             Assert.AreEqual(5000 + 2 + 300 + 2 + 12, writer.Length);
         }
     }

Source/MQTTnet.Tests/MqttTopicValidator_Tests.cs

@@ -9,19 +9,13 @@ using MQTTnet.Protocol;
 namespace MQTTnet.Tests
 {
     [TestClass]
-    public class MqttTopicValidator_Tests
+    public sealed class MqttTopicValidator_Tests
     {
-        [TestMethod]
-        public void Valid_Topic()
-        {
-            MqttTopicValidator.ThrowIfInvalid("/a/b/c");
-        }
-
         [TestMethod]
         [ExpectedException(typeof(MqttProtocolViolationException))]
-        public void Invalid_Topic_Plus()
+        public void Invalid_Topic_Empty()
         {
-            MqttTopicValidator.ThrowIfInvalid("/a/+/c");
+            MqttTopicValidator.ThrowIfInvalid(string.Empty);
         }
 
         [TestMethod]
@@ -33,9 +27,15 @@ namespace MQTTnet.Tests
 
         [TestMethod]
         [ExpectedException(typeof(MqttProtocolViolationException))]
-        public void Invalid_Topic_Empty()
+        public void Invalid_Topic_Plus()
         {
-            MqttTopicValidator.ThrowIfInvalid(string.Empty);
+            MqttTopicValidator.ThrowIfInvalid("/a/+/c");
+        }
+
+        [TestMethod]
+        public void Valid_Topic()
+        {
+            MqttTopicValidator.ThrowIfInvalid("/a/b/c");
         }
     }
-}
+}

Source/MQTTnet.Tests/Server/General.cs

@@ -636,7 +636,7 @@ namespace MQTTnet.Tests.Server
                 // nothing
 
                 Assert.AreEqual(false, c1.IsConnected);
-                await c1.DisconnectAsync();
+                await c1.TryDisconnectAsync();
                 Assert.AreEqual(false, c1.IsConnected);
 
                 await Task.Delay(500);
@@ -954,7 +954,7 @@ namespace MQTTnet.Tests.Server
 
                 var client = testEnvironment.CreateClient();
 
-                client.InspectPackage += e =>
+                client.InspectPacketAsync += e =>
                 {
                     if (e.Buffer.Length > 0)
                     {

Source/MQTTnet.Tests/Server/MqttSubscriptionsManager_Tests.cs

@@ -228,7 +228,7 @@ namespace MQTTnet.Tests.Server
 
         CheckSubscriptionsResult CheckSubscriptions(string topic, MqttQualityOfServiceLevel applicationMessageQoSLevel, string senderClientId)
         {
-            MqttSubscription.CalculateTopicHash(topic, out var topicHash, out _, out _);
+            MqttTopicHash.Calculate(topic, out var topicHash, out _, out _);
             return _subscriptionsManager.CheckSubscriptions(topic, topicHash, applicationMessageQoSLevel, senderClientId);
         }
     }

Source/MQTTnet.Tests/Server/Publish_Tests.cs

@@ -1,58 +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.Threading.Tasks;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MQTTnet.Client;
-using MQTTnet.Formatter;
-using MQTTnet.Protocol;
-
-namespace MQTTnet.Tests.Server
-{
-    [TestClass]
-    public sealed class Publish_Tests : BaseTestClass
-    {
-        [TestMethod]
-        public async Task Return_Success_When_Subscribed()
-        {
-            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
-            {
-                await testEnvironment.StartServer();
-
-                var sender = await testEnvironment.ConnectClient();
-                var receiver = await testEnvironment.ConnectClient();
-
-                await receiver.SubscribeAsync("A");
-
-                // AtLeastOnce is required to get an ACK packet from the server.
-                var publishResult = await sender.PublishStringAsync("A", "Payload", MqttQualityOfServiceLevel.AtLeastOnce);
-                
-                Assert.AreEqual(MqttClientPublishReasonCode.Success, publishResult.ReasonCode);
-                
-                Assert.AreEqual(true, publishResult.IsSuccess);
-            }
-        }
-        
-        [TestMethod]
-        public async Task Return_NoMatchingSubscribers_When_Not_Subscribed()
-        {
-            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
-            {
-                await testEnvironment.StartServer();
-
-                var sender = await testEnvironment.ConnectClient();
-                var receiver = await testEnvironment.ConnectClient();
-             
-                await receiver.SubscribeAsync("A");
-
-                // AtLeastOnce is required to get an ACK packet from the server.
-                var publishResult = await sender.PublishStringAsync("B", "Payload", MqttQualityOfServiceLevel.AtLeastOnce);
-                
-                Assert.AreEqual(MqttClientPublishReasonCode.NoMatchingSubscribers, publishResult.ReasonCode);
-                
-                Assert.AreEqual(true, publishResult.IsSuccess);
-            }
-        }
-    }
-}

Source/MQTTnet.Tests/Server/Publishing_Tests.cs

@@ -5,6 +5,8 @@
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
+using MQTTnet.Formatter;
+using MQTTnet.Internal;
 using MQTTnet.Protocol;
 
 namespace MQTTnet.Tests.Server
@@ -27,5 +29,118 @@ namespace MQTTnet.Tests.Server
                 await client.PublishStringAsync("test", qualityOfServiceLevel: MqttQualityOfServiceLevel.AtLeastOnce);
             }
         }
+
+        [TestMethod]
+        public async Task Return_NoMatchingSubscribers_When_Not_Subscribed()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                await testEnvironment.StartServer();
+
+                var sender = await testEnvironment.ConnectClient();
+                var receiver = await testEnvironment.ConnectClient();
+
+                await receiver.SubscribeAsync("A");
+
+                // AtLeastOnce is required to get an ACK packet from the server.
+                var publishResult = await sender.PublishStringAsync("B", "Payload", MqttQualityOfServiceLevel.AtLeastOnce);
+
+                Assert.AreEqual(MqttClientPublishReasonCode.NoMatchingSubscribers, publishResult.ReasonCode);
+
+                Assert.AreEqual(true, publishResult.IsSuccess);
+            }
+        }
+
+        [TestMethod]
+        public async Task Return_Success_When_Subscribed()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                await testEnvironment.StartServer();
+
+                var sender = await testEnvironment.ConnectClient();
+                var receiver = await testEnvironment.ConnectClient();
+
+                await receiver.SubscribeAsync("A");
+
+                // AtLeastOnce is required to get an ACK packet from the server.
+                var publishResult = await sender.PublishStringAsync("A", "Payload", MqttQualityOfServiceLevel.AtLeastOnce);
+
+                Assert.AreEqual(MqttClientPublishReasonCode.Success, publishResult.ReasonCode);
+
+                Assert.AreEqual(true, publishResult.IsSuccess);
+            }
+        }
+
+        [TestMethod]
+        public async Task Intercept_Client_Enqueue()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                var server = await testEnvironment.StartServer();
+                
+                var sender = await testEnvironment.ConnectClient();
+                
+                var receiver = await testEnvironment.ConnectClient();
+                await receiver.SubscribeAsync("A");
+                var receivedMessages = testEnvironment.CreateApplicationMessageHandler(receiver);
+                
+                await sender.PublishStringAsync("A", "Payload", MqttQualityOfServiceLevel.AtLeastOnce);
+
+                await LongTestDelay();
+                
+                receivedMessages.AssertReceivedCountEquals(1);
+                
+                server.InterceptingClientEnqueueAsync += e =>
+                {
+                    e.AcceptEnqueue = false;
+                    return CompletedTask.Instance;
+                };
+                
+                await sender.PublishStringAsync("A", "Payload", MqttQualityOfServiceLevel.AtLeastOnce);
+
+                await LongTestDelay();
+                
+                // Do not increase because the internal enqueue to the target client is not accepted!
+                receivedMessages.AssertReceivedCountEquals(1);
+            }
+        }
+
+        [TestMethod]
+        public async Task Intercept_Client_Enqueue_Multiple_Clients_Subscribed_Messages_Are_Filtered()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                var server = await testEnvironment.StartServer();
+
+                var sender = await testEnvironment.ConnectClient();
+
+                var receiverOne = await testEnvironment.ConnectClient(o => o.WithClientId("One"));
+                await receiverOne.SubscribeAsync("A");
+                var receivedMessagesOne = testEnvironment.CreateApplicationMessageHandler(receiverOne);
+
+                var receiverTwo = await testEnvironment.ConnectClient(o => o.WithClientId("Two"));
+                await receiverTwo.SubscribeAsync("A");
+                var receivedMessagesTwo = testEnvironment.CreateApplicationMessageHandler(receiverTwo);
+
+                var receiverThree = await testEnvironment.ConnectClient(o => o.WithClientId("Three"));
+                await receiverThree.SubscribeAsync("A");
+                var receivedMessagesThree = testEnvironment.CreateApplicationMessageHandler(receiverThree);
+
+                server.InterceptingClientEnqueueAsync += e =>
+                {
+                    if (e.ReceiverClientId.Contains("Two")) e.AcceptEnqueue = false;
+                    return CompletedTask.Instance;
+                };
+
+                await sender.PublishStringAsync("A", "Payload", MqttQualityOfServiceLevel.AtLeastOnce);
+
+                await LongTestDelay();
+
+                receivedMessagesOne.AssertReceivedCountEquals(1);
+                receivedMessagesTwo.AssertReceivedCountEquals(0);
+                receivedMessagesThree.AssertReceivedCountEquals(1);
+            }
+        }
     }
 }

Source/MQTTnet.Tests/Server/Security_Tests.cs

@@ -164,7 +164,7 @@ namespace MQTTnet.Tests.Server
 
                 var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1", testEnvironment.ServerPort).WithCredentials(userName, password).Build();
 
-                var ex = await Assert.ThrowsExceptionAsync<MqttConnectingFailedException>(async () => await client.ConnectAsync(clientOptions));
+                var ex = await Assert.ThrowsExceptionAsync<MqttConnectingFailedException>(() => client.ConnectAsync(clientOptions));
                 Assert.AreEqual(MqttClientConnectResultCode.BadUserNameOrPassword, ex.Result.ResultCode);
             }
         }

Source/MQTTnet.Tests/Server/Subscribe_Tests.cs

@@ -62,7 +62,7 @@ namespace MQTTnet.Tests.Server
                 }
             }
         }
-        
+
         [TestMethod]
         public async Task Deny_Invalid_Topic()
         {
@@ -90,6 +90,29 @@ namespace MQTTnet.Tests.Server
             }
         }
 
+        [TestMethod]
+        public async Task Intercept_Subscribe_With_User_Properties()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                var server = await testEnvironment.StartServer();
+
+                InterceptingSubscriptionEventArgs eventArgs = null;
+                server.InterceptingSubscriptionAsync += e =>
+                {
+                    eventArgs = e;
+                    return CompletedTask.Instance;
+                };
+
+                var client = await testEnvironment.ConnectClient();
+
+                var subscribeOptions = testEnvironment.Factory.CreateSubscribeOptionsBuilder().WithTopicFilter("X").WithUserProperty("A", "1").Build();
+                await client.SubscribeAsync(subscribeOptions);
+
+                CollectionAssert.AreEqual(subscribeOptions.UserProperties.ToList(), eventArgs.UserProperties);
+            }
+        }
+
         [TestMethod]
         [ExpectedException(typeof(MqttClientDisconnectedException))]
         public async Task Disconnect_While_Subscribing()
@@ -105,7 +128,7 @@ namespace MQTTnet.Tests.Server
                 await client.SubscribeAsync("#");
             }
         }
-        
+
         [TestMethod]
         public async Task Enqueue_Message_After_Subscription()
         {

Source/MQTTnet.Tests/Server/Subscription_TopicHash_Tests.cs

@@ -47,7 +47,7 @@ namespace MQTTnet.Tests.Server
                 var topics = t.Value;
                 foreach (var topic in topics)
                 {
-                    MqttSubscription.CalculateTopicHash(topic, out var topicHash, out var hashMask, out var hasWildcard);
+                    MqttTopicHash.Calculate(topic, out var topicHash, out var hashMask, out var hasWildcard);
 
                     bucketDepths.TryGetValue(topicHash, out var currentValue);
                     ++currentValue;
@@ -96,7 +96,7 @@ namespace MQTTnet.Tests.Server
         {
             var topic = "asdfasdf/asdfasdf/asdfasdf/asdfasdf/asdfas/dfaf/assfdgsdfgdf/#";
 
-            MqttSubscription.CalculateTopicHash(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
+            MqttTopicHash.Calculate(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
 
             Assert.IsTrue(topicHasWildcard, "Wildcard not detected");
         }
@@ -110,7 +110,7 @@ namespace MQTTnet.Tests.Server
         {
             var topic = "asdfasdf/asdfasdf/asdfasdf/asdfasdf/asdfas/dfaf/assfdgsdfgdf/+";
 
-            MqttSubscription.CalculateTopicHash(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
+            MqttTopicHash.Calculate(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
 
             Assert.IsTrue(topicHasWildcard, "Wildcard not detected");
         }
@@ -150,7 +150,7 @@ namespace MQTTnet.Tests.Server
 
             // UInt64 is limited to 8 levels
 
-            MqttSubscription.CalculateTopicHash(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
+            MqttTopicHash.Calculate(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
 
             Assert.IsTrue(topicHasWildcard, "Wildcard not detected");
 
@@ -212,7 +212,7 @@ namespace MQTTnet.Tests.Server
 
             var topic = sb.ToString();
 
-            MqttSubscription.CalculateTopicHash(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
+            MqttTopicHash.Calculate(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
 
             Assert.IsFalse(topicHasWildcard, "Wildcard detected when not present");
 
@@ -269,7 +269,7 @@ namespace MQTTnet.Tests.Server
 
             var topic = sb.ToString();
 
-            MqttSubscription.CalculateTopicHash(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
+            MqttTopicHash.Calculate(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
 
             Assert.IsTrue(topicHasWildcard, "Wildcard not detected");
 
@@ -319,7 +319,7 @@ namespace MQTTnet.Tests.Server
             var l3 = "#";
             var topic = $"{l0}/{l1}/{l2}/{l3}";
 
-            MqttSubscription.CalculateTopicHash(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
+            MqttTopicHash.Calculate(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
 
             Assert.IsTrue(topicHasWildcard, "Wildcard not detected");
 
@@ -354,7 +354,7 @@ namespace MQTTnet.Tests.Server
             var l3 = "prop1";
             var topic = $"{l0}/{l1}/{l2}/{l3}";
 
-            MqttSubscription.CalculateTopicHash(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
+            MqttTopicHash.Calculate(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
 
             Assert.IsFalse(topicHasWildcard, "Wildcard detected when not wildcard present");
 
@@ -447,7 +447,7 @@ namespace MQTTnet.Tests.Server
             var l3 = "prop1";
             var topic = $"{l0}/{l1}/{l2}/{l3}";
 
-            MqttSubscription.CalculateTopicHash(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
+            MqttTopicHash.Calculate(topic, out var topicHash, out var topicHashMask, out var topicHasWildcard);
 
             Assert.IsTrue(topicHasWildcard, "Wildcard not detected");
 
@@ -475,7 +475,7 @@ namespace MQTTnet.Tests.Server
 
         void CheckTopicHash(string topic, ulong expectedHash, ulong expectedHashMask)
         {
-            MqttSubscription.CalculateTopicHash(topic, out var topicHash, out var hashMask, out var hasWildcard);
+            MqttTopicHash.Calculate(topic, out var topicHash, out var hashMask, out var hasWildcard);
 
             Console.WriteLine();
             Console.WriteLine("Topic: " + topic);
@@ -501,7 +501,7 @@ namespace MQTTnet.Tests.Server
                 {
                     var topicToFind = topicsToFind[countDown];
 
-                    MqttSubscription.CalculateTopicHash(topicToFind, out var topicHash, out _, out _);
+                    MqttTopicHash.Calculate(topicToFind, out var topicHash, out _, out _);
 
                     clientSession.TryCheckSubscriptions(topicToFind, topicHash, MqttQualityOfServiceLevel.AtMostOnce, "OtherClient", out var result);
                     if (result.IsSubscribed)

Source/MQTTnet.Tests/Server/Tls_Tests.cs

@@ -0,0 +1,204 @@
+#if !WINDOWS_UWP && (NET48_OR_GREATER || NET5_0_OR_GREATER)
+using System;
+using System.Linq;
+using System.Net;
+using System.Security.Authentication;
+using System.Security.Cryptography;
+using System.Security.Cryptography.X509Certificates;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Certificates;
+using MQTTnet.Client;
+using MQTTnet.Formatter;
+using MQTTnet.Server;
+using MQTTnet.Tests.Mockups;
+
+namespace MQTTnet.Tests.Server
+{
+    [TestClass]
+    public sealed class Tls_Tests : BaseTestClass
+    {
+        static X509Certificate2 CreateCertificate(string oid)
+        {
+            var sanBuilder = new SubjectAlternativeNameBuilder();
+            sanBuilder.AddIpAddress(IPAddress.Loopback);
+            sanBuilder.AddIpAddress(IPAddress.IPv6Loopback);
+            sanBuilder.AddDnsName("localhost");
+            
+            using (var rsa = RSA.Create())
+            {
+                var certRequest = new CertificateRequest("CN=localhost", rsa, HashAlgorithmName.SHA512, RSASignaturePadding.Pkcs1);
+
+                certRequest.CertificateExtensions.Add(
+                    new X509KeyUsageExtension(X509KeyUsageFlags.DataEncipherment | X509KeyUsageFlags.KeyEncipherment | X509KeyUsageFlags.DigitalSignature, false));
+
+                certRequest.CertificateExtensions.Add(new X509EnhancedKeyUsageExtension(new OidCollection { new Oid(oid) }, false));
+
+                certRequest.CertificateExtensions.Add(sanBuilder.Build());
+
+                using (var certificate = certRequest.CreateSelfSigned(DateTimeOffset.Now.AddMinutes(-10), DateTimeOffset.Now.AddMinutes(10)))
+                {
+                    var pfxCertificate = new X509Certificate2(
+                        certificate.Export(X509ContentType.Pfx),
+                        (string)null,
+                        X509KeyStorageFlags.MachineKeySet | X509KeyStorageFlags.Exportable);
+
+                    return pfxCertificate;
+                }
+            }
+        }
+
+        [TestMethod]
+        public async Task Tls_Swap_Test()
+        {
+            var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500);
+            var serverOptionsBuilder = testEnvironment.Factory.CreateServerOptionsBuilder();
+
+            var firstOid = "1.3.6.1.5.5.7.3.1";
+            var secondOid = "1.3.6.1.5.5.7.3.2";
+
+            var certificateProvider = new CertificateProvider
+            {
+                CurrentCertificate = CreateCertificate(firstOid)
+            };
+
+            serverOptionsBuilder.WithoutDefaultEndpoint().WithEncryptedEndpoint().WithEncryptionSslProtocol(SslProtocols.Tls12).WithEncryptionCertificate(certificateProvider);
+
+            var serverOptions = serverOptionsBuilder.Build();
+
+            var server = testEnvironment.CreateServer(serverOptions);
+
+            var publishedCount = 0;
+            server.InterceptingPublishAsync += args =>
+            {
+                Interlocked.Increment(ref publishedCount);
+
+                return Task.CompletedTask;
+            };
+
+            await server.StartAsync();
+
+            var firstClient = await ConnectClientAsync(
+                testEnvironment,
+                args =>
+                {
+                    Assert.AreEqual(firstOid, ((X509Certificate2)args.Certificate).Extensions.OfType<X509EnhancedKeyUsageExtension>().First().EnhancedKeyUsages[0].Value);
+                    return true;
+                });
+
+            var firstClientReceivedCount = 0;
+            firstClient.ApplicationMessageReceivedAsync += args =>
+            {
+                Interlocked.Increment(ref firstClientReceivedCount);
+
+                return Task.CompletedTask;
+            };
+
+            await firstClient.SubscribeAsync("TestTopic1");
+
+            await firstClient.PublishAsync(
+                new MqttApplicationMessage
+                {
+                    Topic = "TestTopic1",
+                    Payload = new byte[] { 1, 2, 3, 4 }
+                });
+
+            await testEnvironment.Server.InjectApplicationMessage(
+                new InjectedMqttApplicationMessage(
+                    new MqttApplicationMessage
+                    {
+                        Topic = "TestTopic1",
+                        Payload = new byte[] { 1, 2, 3, 4 }
+                    }));
+
+            certificateProvider.CurrentCertificate = CreateCertificate(secondOid);
+
+            // Validate that the certificate was switched
+            var secondClient = await ConnectClientAsync(
+                testEnvironment,
+                args =>
+                {
+                    Assert.AreEqual(secondOid, ((X509Certificate2)args.Certificate).Extensions.OfType<X509EnhancedKeyUsageExtension>().First().EnhancedKeyUsages[0].Value);
+                    return true;
+                });
+
+            var secondClientReceivedCount = 0;
+            secondClient.ApplicationMessageReceivedAsync += args =>
+            {
+                Interlocked.Increment(ref secondClientReceivedCount);
+
+                return Task.CompletedTask;
+            };
+
+            await secondClient.SubscribeAsync("TestTopic2");
+
+            await firstClient.PublishAsync(
+                new MqttApplicationMessage
+                {
+                    Topic = "TestTopic2",
+                    Payload = new byte[] { 1, 2, 3, 4 }
+                });
+
+            await testEnvironment.Server.InjectApplicationMessage(
+                new InjectedMqttApplicationMessage(
+                    new MqttApplicationMessage
+                    {
+                        Topic = "TestTopic2",
+                        Payload = new byte[] { 1, 2, 3, 4 }
+                    }));
+
+            // Ensure first client still works
+            await firstClient.PublishAsync(
+                new MqttApplicationMessage
+                {
+                    Topic = "TestTopic1",
+                    Payload = new byte[] { 1, 2, 3, 4 }
+                });
+
+            await testEnvironment.Server.InjectApplicationMessage(
+                new InjectedMqttApplicationMessage(
+                    new MqttApplicationMessage
+                    {
+                        Topic = "TestTopic1",
+                        Payload = new byte[] { 1, 2, 3, 4 }
+                    }));
+
+            await Task.Delay(1000);
+
+            Assert.AreEqual(6, publishedCount);
+            Assert.AreEqual(4, firstClientReceivedCount);
+            Assert.AreEqual(2, secondClientReceivedCount);
+
+            await server.StopAsync();
+        }
+
+        static async Task<IMqttClient> ConnectClientAsync(TestEnvironment testEnvironment, Func<MqttClientCertificateValidationEventArgs, bool> certValidator)
+        {
+            var clientOptionsBuilder = testEnvironment.Factory.CreateClientOptionsBuilder();
+            clientOptionsBuilder.WithClientId(Guid.NewGuid().ToString())
+                .WithTcpServer("localhost", 8883)
+                .WithTls(
+                    tls =>
+                    {
+                        tls.UseTls = true;
+                        tls.SslProtocol = SslProtocols.Tls12;
+                        tls.CertificateValidationHandler = certValidator;
+                    });
+
+            var clientOptions = clientOptionsBuilder.Build();
+            return await testEnvironment.ConnectClient(clientOptions);
+        }
+        
+        sealed class CertificateProvider : ICertificateProvider
+        {
+            public X509Certificate2 CurrentCertificate { get; set; }
+
+            public X509Certificate2 GetCertificate()
+            {
+                return CurrentCertificate;
+            }
+        }
+    }
+}
+#endif

Source/MQTTnet.Tests/Server/Unsubscribe_Tests.cs

@@ -2,10 +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.Linq;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
+using MQTTnet.Formatter;
+using MQTTnet.Internal;
 using MQTTnet.Protocol;
+using MQTTnet.Server;
 
 namespace MQTTnet.Tests.Server
 {
@@ -28,5 +32,28 @@ namespace MQTTnet.Tests.Server
                 await client.UnsubscribeAsync("#");
             }
         }
+
+        [TestMethod]
+        public async Task Intercept_Unsubscribe_With_User_Properties()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                var server = await testEnvironment.StartServer();
+
+                InterceptingUnsubscriptionEventArgs eventArgs = null;
+                server.InterceptingUnsubscriptionAsync += e =>
+                {
+                    eventArgs = e;
+                    return CompletedTask.Instance;
+                };
+
+                var client = await testEnvironment.ConnectClient();
+
+                var unsubscribeOptions = testEnvironment.Factory.CreateUnsubscribeOptionsBuilder().WithTopicFilter("X").WithUserProperty("A", "1").Build();
+                await client.UnsubscribeAsync(unsubscribeOptions);
+
+                CollectionAssert.AreEqual(unsubscribeOptions.UserProperties.ToList(), eventArgs.UserProperties);
+            }
+        }
     }
 }

Source/MQTTnet.Tests/TopicFilterComparer_Tests.cs

@@ -150,18 +150,8 @@ namespace MQTTnet.Tests
         {
             Assert.AreEqual(expectedResult, MqttTopicFilterComparer.Compare(topic, filter));
 
-            ulong topicHash;
-            ulong topicHashMask;
-            bool topicHasWildcard;
-
-            MqttSubscription.CalculateTopicHash(topic, out topicHash, out topicHashMask, out topicHasWildcard);
-
-
-            ulong filterTopicHash;
-            ulong filterTopicHashMask;
-            bool filterTopicHasWildcard;
-
-            MqttSubscription.CalculateTopicHash(filter, out filterTopicHash, out filterTopicHashMask, out filterTopicHasWildcard);
+            MqttTopicHash.Calculate(topic, out var topicHash, out _, out _);
+            MqttTopicHash.Calculate(filter, out var filterTopicHash, out var filterTopicHashMask, out _);
 
             if (expectedResult == MqttTopicFilterCompareResult.IsMatch)
             {

Source/MQTTnet/Adapter/MqttChannelAdapter.cs

@@ -27,19 +27,15 @@ namespace MQTTnet.Adapter
         readonly byte[] _fixedHeaderBuffer = new byte[2];
         readonly MqttNetSourceLogger _logger;
 
-        readonly MqttPacketInspector _packetInspector;
-
         readonly byte[] _singleByteBuffer = new byte[1];
 
         readonly AsyncLock _syncRoot = new AsyncLock();
 
-        long _bytesReceived;
-        long _bytesSent;
+        Statistics _statistics; // mutable struct, don't make readonly!
 
-        public MqttChannelAdapter(IMqttChannel channel, MqttPacketFormatterAdapter packetFormatterAdapter, MqttPacketInspector packetInspector, IMqttNetLogger logger)
+        public MqttChannelAdapter(IMqttChannel channel, MqttPacketFormatterAdapter packetFormatterAdapter, IMqttNetLogger logger)
         {
             _channel = channel ?? throw new ArgumentNullException(nameof(channel));
-            _packetInspector = packetInspector;
 
             PacketFormatterAdapter = packetFormatterAdapter ?? throw new ArgumentNullException(nameof(packetFormatterAdapter));
 
@@ -51,9 +47,9 @@ namespace MQTTnet.Adapter
             _logger = logger.WithSource(nameof(MqttChannelAdapter));
         }
 
-        public long BytesReceived => Interlocked.Read(ref _bytesReceived);
+        public long BytesReceived => Volatile.Read(ref _statistics._bytesReceived);
 
-        public long BytesSent => Interlocked.Read(ref _bytesSent);
+        public long BytesSent => Volatile.Read(ref _statistics._bytesSent);
 
         public X509Certificate2 ClientCertificate => _channel.ClientCertificate;
 
@@ -65,6 +61,10 @@ namespace MQTTnet.Adapter
 
         public MqttPacketFormatterAdapter PacketFormatterAdapter { get; }
 
+        public MqttPacketInspector PacketInspector { get; set; }
+
+        public bool AllowPacketFragmentation { get; set; } = true;
+
         public async Task ConnectAsync(CancellationToken cancellationToken)
         {
             cancellationToken.ThrowIfCancellationRequested();
@@ -127,7 +127,7 @@ namespace MQTTnet.Adapter
 
             try
             {
-                _packetInspector?.BeginReceivePacket();
+                PacketInspector?.BeginReceivePacket();
 
                 ReceivedMqttPacket receivedPacket;
                 var receivedPacketTask = ReceiveAsync(cancellationToken);
@@ -145,9 +145,9 @@ namespace MQTTnet.Adapter
                     return null;
                 }
 
-                _packetInspector?.EndReceivePacket();
+                PacketInspector?.EndReceivePacket();
 
-                Interlocked.Add(ref _bytesSent, receivedPacket.TotalLength);
+                Interlocked.Add(ref _statistics._bytesSent, receivedPacket.TotalLength);
 
                 if (PacketFormatterAdapter.ProtocolVersion == MqttProtocolVersion.Unknown)
                 {
@@ -183,8 +183,7 @@ namespace MQTTnet.Adapter
 
         public void ResetStatistics()
         {
-            Interlocked.Exchange(ref _bytesReceived, 0L);
-            Interlocked.Exchange(ref _bytesSent, 0L);
+            _statistics.Reset();
         }
 
         public async Task SendPacketAsync(MqttPacket packet, CancellationToken cancellationToken)
@@ -202,21 +201,21 @@ namespace MQTTnet.Adapter
                 try
                 {
                     var packetBuffer = PacketFormatterAdapter.Encode(packet);
-                    _packetInspector?.BeginSendPacket(packetBuffer);
+                    PacketInspector?.BeginSendPacket(packetBuffer);
 
                     _logger.Verbose("TX ({0} bytes) >>> {1}", packetBuffer.Length, packet);
-
-                    if (packetBuffer.Payload.Count > 0)
+                    
+                    if (packetBuffer.Payload.Count == 0 || !AllowPacketFragmentation)
+                    {
+                        await _channel.WriteAsync(packetBuffer.Join(), true, cancellationToken).ConfigureAwait(false);
+                    }
+                    else
                     {
                         await _channel.WriteAsync(packetBuffer.Packet, false, cancellationToken).ConfigureAwait(false);
                         await _channel.WriteAsync(packetBuffer.Payload, true, cancellationToken).ConfigureAwait(false);
                     }
-                    else
-                    {
-                        await _channel.WriteAsync(packetBuffer.Packet, true, cancellationToken).ConfigureAwait(false);
-                    }
 
-                    Interlocked.Add(ref _bytesReceived, packetBuffer.Length);
+                    Interlocked.Add(ref _statistics._bytesReceived, packetBuffer.Length);
                 }
                 catch (Exception exception)
                 {
@@ -275,7 +274,7 @@ namespace MQTTnet.Adapter
                     return 0;
                 }
 
-                _packetInspector?.FillReceiveBuffer(_singleByteBuffer);
+                PacketInspector?.FillReceiveBuffer(_singleByteBuffer);
 
                 encodedByte = _singleByteBuffer[0];
 
@@ -314,7 +313,7 @@ namespace MQTTnet.Adapter
                 {
                     return ReadFixedHeaderResult.ConnectionClosed;
                 }
-               
+
                 if (cancellationToken.IsCancellationRequested)
                 {
                     return ReadFixedHeaderResult.Canceled;
@@ -328,7 +327,7 @@ namespace MQTTnet.Adapter
                 totalBytesRead += bytesRead;
             }
 
-            _packetInspector?.FillReceiveBuffer(buffer);
+            PacketInspector?.FillReceiveBuffer(buffer);
 
             var hasRemainingLength = buffer[1] != 0;
             if (!hasRemainingLength)
@@ -412,7 +411,7 @@ namespace MQTTnet.Adapter
                     bodyOffset += readBytes;
                 } while (bodyOffset < bodyLength);
 
-                _packetInspector?.FillReceiveBuffer(body);
+                PacketInspector?.FillReceiveBuffer(body);
 
                 var bodySegment = new ArraySegment<byte>(body, 0, bodyLength);
                 return new ReceivedMqttPacket(fixedHeader.Flags, bodySegment, fixedHeader.TotalLength);
@@ -459,5 +458,17 @@ namespace MQTTnet.Adapter
 
             throw new MqttCommunicationException(exception);
         }
+
+        struct Statistics
+        {
+            public long _bytesReceived;
+            public long _bytesSent;
+
+            public void Reset()
+            {
+                Volatile.Write(ref _bytesReceived, 0);
+                Volatile.Write(ref _bytesSent, 0);
+            }
+        }
     }
 }

Source/MQTTnet/Adapter/MqttPacketInspector.cs

@@ -82,12 +82,7 @@ namespace MQTTnet.Adapter
         {
             try
             {
-                var eventArgs = new InspectMqttPacketEventArgs
-                {
-                    Buffer = buffer,
-                    Direction = direction
-                };
-
+                var eventArgs = new InspectMqttPacketEventArgs(direction, buffer);
                 _asyncEvent.InvokeAsync(eventArgs).GetAwaiter().GetResult();
             }
             catch (Exception exception)

Source/MQTTnet/Client/Authentication/MqttClientPartialAuthenticationResponse.cs

@@ -0,0 +1,19 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Generic;
+using MQTTnet.Packets;
+using MQTTnet.Protocol;
+
+namespace MQTTnet.Client
+{
+    public sealed class MqttClientPartialAuthenticationResponse
+    {
+        public byte[] AuthenticationData { get; set; }
+
+        public MqttAuthenticateReasonCode ReasonCode { get; set; }
+
+        public List<MqttUserProperty> UserProperties { get; set; }
+    }
+}

Source/MQTTnet/Client/Authentication/MqttExtendedAuthenticationExchangeEventArgs.cs

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

Source/MQTTnet/Client/Authentication/MqttReAuthenticationOptions.cs

@@ -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.Collections.Generic;
+using MQTTnet.Packets;
+
+namespace MQTTnet.Client
+{
+    public sealed class MqttReAuthenticationOptions
+    {
+        /// <summary>
+        ///     Gets or sets the authentication data.
+        ///     Authentication data is binary information used to transmit multiple iterations of cryptographic secrets of protocol
+        ///     steps.
+        ///     The content of the authentication data is highly dependent on the specific implementation of the authentication
+        ///     method.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// </summary>
+        public byte[] AuthenticationData { get; set; }
+
+        /// <summary>
+        ///     Gets or sets the user properties.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// </summary>
+        public List<MqttUserProperty> UserProperties { get; set; }
+    }
+}

Source/MQTTnet/Client/Connecting/MqttClientConnectResult.cs

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

Source/MQTTnet/Client/Connecting/MqttClientConnectedEventArgs.cs

@@ -15,7 +15,7 @@ namespace MQTTnet.Client
 
         /// <summary>
         ///     Gets the authentication result.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public MqttClientConnectResult ConnectResult { get; }
     }

Source/MQTTnet/Client/Disconnecting/MqttClientDisconnectOptions.cs

@@ -2,20 +2,35 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Collections.Generic;
+using MQTTnet.Packets;
+
 namespace MQTTnet.Client
 {
     public sealed class MqttClientDisconnectOptions
     {
         /// <summary>
-        /// Gets or sets the reason code.
-        /// Hint: MQTT 5 feature only.
+        ///     Gets or sets the reason code.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
-        public MqttClientDisconnectReason Reason { get; set; } = MqttClientDisconnectReason.NormalDisconnection;
+        public MqttClientDisconnectOptionsReason Reason { get; set; } = MqttClientDisconnectOptionsReason.NormalDisconnection;
 
         /// <summary>
-        /// Gets or sets the reason string.
-        /// Hint: MQTT 5 feature only.
+        ///     Gets or sets the reason string.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public string ReasonString { get; set; }
+
+        /// <summary>
+        ///     Gets or sets the session expiry interval.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// </summary>
+        public uint SessionExpiryInterval { get; set; }
+
+        /// <summary>
+        ///     Gets or sets the user properties.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// </summary>
+        public List<MqttUserProperty> UserProperties { get; set; }
     }
-}
+}

Source/MQTTnet/Client/Disconnecting/MqttClientDisconnectOptionsBuilder.cs

@@ -2,32 +2,62 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Collections.Generic;
+using MQTTnet.Packets;
+
 namespace MQTTnet.Client
 {
     public sealed class MqttClientDisconnectOptionsBuilder
     {
-        MqttClientDisconnectReason _reason = MqttClientDisconnectReason.NormalDisconnection;
+        MqttClientDisconnectOptionsReason _reason = MqttClientDisconnectOptionsReason.NormalDisconnection;
         string _reasonString;
-        
-        public MqttClientDisconnectOptionsBuilder WithReasonString(string value)
-        {
-            _reasonString = value;
-            return this;
-        }
-        
-        public MqttClientDisconnectOptionsBuilder WithReason(MqttClientDisconnectReason value)
-        {
-            _reason = value;
-            return this;
-        }
-        
+        uint _sessionExpiryInterval;
+        List<MqttUserProperty> _userProperties;
+
         public MqttClientDisconnectOptions Build()
         {
             return new MqttClientDisconnectOptions
             {
                 Reason = _reason,
-                ReasonString = _reasonString
+                ReasonString = _reasonString,
+                UserProperties = _userProperties,
+                SessionExpiryInterval = _sessionExpiryInterval
             };
         }
+
+        public MqttClientDisconnectOptionsBuilder WithReason(MqttClientDisconnectOptionsReason value)
+        {
+            _reason = value;
+            return this;
+        }
+
+        public MqttClientDisconnectOptionsBuilder WithReasonString(string value)
+        {
+            _reasonString = value;
+            return this;
+        }
+
+        public MqttClientDisconnectOptionsBuilder WithSessionExpiryInterval(uint value)
+        {
+            _sessionExpiryInterval = value;
+            return this;
+        }
+
+        public MqttClientDisconnectOptionsBuilder WithUserProperties(List<MqttUserProperty> userProperties)
+        {
+            _userProperties = userProperties;
+            return this;
+        }
+
+        public MqttClientDisconnectOptionsBuilder WithUserProperty(string name, string value)
+        {
+            if (_userProperties == null)
+            {
+                _userProperties = new List<MqttUserProperty>();
+            }
+
+            _userProperties.Add(new MqttUserProperty(name, value));
+            return this;
+        }
     }
 }

Source/MQTTnet/Client/Disconnecting/MqttClientDisconnectOptionsReason.cs

@@ -0,0 +1,27 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace MQTTnet.Client
+{
+    /// <summary>
+    /// This enum only contains values which are valid when a client sends the reason to the server.
+    /// </summary>
+    public enum MqttClientDisconnectOptionsReason
+    {
+        NormalDisconnection = 0,
+        DisconnectWithWillMessage = 4,
+        UnspecifiedError = 128,
+        MalformedPacket = 129,
+        ProtocolError = 130,
+        ImplementationSpecificError = 131,
+        TopicNameInvalid = 144,
+        ReceiveMaximumExceeded = 147,
+        TopicAliasInvalid = 148,
+        PacketTooLarge = 149,
+        MessageRateTooHigh = 150,
+        QuotaExceeded = 151,
+        AdministrativeAction = 152,
+        PayloadFormatInvalid = 153
+    }
+}

Source/MQTTnet/Client/Disconnecting/MqttClientDisconnectOptionsValidator.cs

@@ -0,0 +1,42 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Linq;
+using MQTTnet.Formatter;
+
+namespace MQTTnet.Client
+{
+    public static class MqttClientDisconnectOptionsValidator
+    {
+        public static void ThrowIfNotSupported(MqttClientDisconnectOptions options, MqttProtocolVersion protocolVersion)
+        {
+            if (options == null)
+            {
+                throw new ArgumentNullException(nameof(options));
+            }
+
+            if (protocolVersion == MqttProtocolVersion.V500)
+            {
+                // Everything is supported.
+                return;
+            }
+
+            if (options.ReasonString?.Any() == true)
+            {
+                Throw(nameof(options.ReasonString));
+            }
+
+            if (options.Reason != MqttClientDisconnectOptionsReason.NormalDisconnection)
+            {
+                Throw(nameof(options.Reason));
+            }
+        }
+
+        static void Throw(string featureName)
+        {
+            throw new NotSupportedException($"Feature {featureName} requires MQTT version 5.0.0.");
+        }
+    }
+}

Source/MQTTnet/Client/Disconnecting/MqttClientDisconnectedEventArgs.cs

@@ -3,27 +3,47 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Generic;
+using MQTTnet.Packets;
 
 namespace MQTTnet.Client
 {
     public sealed class MqttClientDisconnectedEventArgs : EventArgs
     {
-        public bool ClientWasConnected { get; internal set; }
+        public MqttClientDisconnectedEventArgs(
+            bool clientWasConnected,
+            MqttClientConnectResult connectResult,
+            MqttClientDisconnectReason reason,
+            string reasonString,
+            List<MqttUserProperty> userProperties,
+            Exception exception)
+        {
+            ClientWasConnected = clientWasConnected;
+            ConnectResult = connectResult;
+            Exception = exception;
+            Reason = reason;
+            ReasonString = reasonString;
+            UserProperties = userProperties;
+        }
 
-        public Exception Exception { get; internal set; }
+        public bool ClientWasConnected { get; }
 
         /// <summary>
-        /// Gets the authentication result.
-        /// Hint: MQTT 5 feature only.
+        ///     Gets the authentication result.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
-        public MqttClientConnectResult ConnectResult { get; internal set; }
+        public MqttClientConnectResult ConnectResult { get; }
+
+        public Exception Exception { get; }
 
         /// <summary>
-        /// Gets or sets the reason.
-        /// Hint: MQTT 5 feature only.
+        ///     Gets or sets the reason.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
-        public MqttClientDisconnectReason Reason { get; internal set; }
-        
-        public string ReasonString { get; internal set; }
+        public MqttClientDisconnectReason Reason { get; }
+
+        public string ReasonString { get; }
+
+        public List<MqttUserProperty> UserProperties { get; }
     }
-}
+}

Source/MQTTnet/Client/ExtendedAuthenticationExchange/IMqttExtendedAuthenticationExchangeHandler.cs

@@ -1,13 +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.Threading.Tasks;
-
-namespace MQTTnet.Client
-{
-    public interface IMqttExtendedAuthenticationExchangeHandler
-    {
-        Task HandleRequestAsync(MqttExtendedAuthenticationExchangeContext context);
-    }
-}

Source/MQTTnet/Client/ExtendedAuthenticationExchange/MqttExtendedAuthenticationExchangeContext.cs

@@ -1,62 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Collections.Generic;
-using MQTTnet.Packets;
-using MQTTnet.Protocol;
-
-namespace MQTTnet.Client
-{
-    public class MqttExtendedAuthenticationExchangeContext
-    {
-        public MqttExtendedAuthenticationExchangeContext(MqttAuthPacket authPacket, MqttClient client)
-        {
-            if (authPacket == null) throw new ArgumentNullException(nameof(authPacket));
-
-            ReasonCode = authPacket.ReasonCode;
-            ReasonString = authPacket.ReasonString;
-            AuthenticationMethod = authPacket.AuthenticationMethod;
-            AuthenticationData = authPacket.AuthenticationData;
-            UserProperties = authPacket.UserProperties;
-
-            Client = client ?? throw new ArgumentNullException(nameof(client));
-        }
-
-        /// <summary>
-        /// Gets the reason code.
-        /// Hint: MQTT 5 feature only.
-        /// </summary>
-        public MqttAuthenticateReasonCode ReasonCode { get; }
-
-        /// <summary>
-        /// Gets the reason string.
-        /// Hint: MQTT 5 feature only.
-        /// </summary>
-        public string ReasonString { get; }
-
-        /// <summary>
-        /// Gets the authentication method.
-        /// Hint: MQTT 5 feature only.
-        /// </summary>
-        public string AuthenticationMethod { get; }
-
-        /// <summary>
-        /// Gets the authentication data.
-        /// Hint: MQTT 5 feature only.
-        /// </summary>
-        public byte[] AuthenticationData { get; }
-
-        /// <summary>
-        /// Gets the user properties.
-        /// In MQTT 5, user properties are basic UTF-8 string key-value pairs that you can append to almost every type of MQTT packet.
-        /// As long as you don’t exceed the maximum message size, you can use an unlimited number of user properties to add metadata to MQTT messages and pass information between publisher, broker, and subscriber.
-        /// The feature is very similar to the HTTP header concept.
-        /// Hint: MQTT 5 feature only.
-        /// </summary>
-        public List<MqttUserProperty> UserProperties { get; }
-
-        public MqttClient Client { get; }
-    }
-}

Source/MQTTnet/Client/ExtendedAuthenticationExchange/MqttExtendedAuthenticationExchangeData.cs

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

Source/MQTTnet/Client/IMqttClient.cs

@@ -8,14 +8,16 @@ namespace MQTTnet.Client
     public interface IMqttClient : IDisposable
     {
         event Func<MqttApplicationMessageReceivedEventArgs, Task> ApplicationMessageReceivedAsync;
-        
+
         event Func<MqttClientConnectedEventArgs, Task> ConnectedAsync;
 
         event Func<MqttClientConnectingEventArgs, Task> ConnectingAsync;
 
         event Func<MqttClientDisconnectedEventArgs, Task> DisconnectedAsync;
 
-        event Func<InspectMqttPacketEventArgs, Task> InspectPackage;
+        event Func<MqttExtendedAuthenticationExchangeEventArgs, Task> ExtendedAuthenticationExchangeAsync;
+
+        event Func<InspectMqttPacketEventArgs, Task> InspectPacketAsync;
 
         bool IsConnected { get; }
 
@@ -29,7 +31,7 @@ namespace MQTTnet.Client
 
         Task<MqttClientPublishResult> PublishAsync(MqttApplicationMessage applicationMessage, CancellationToken cancellationToken = default);
 
-        Task SendExtendedAuthenticationExchangeDataAsync(MqttExtendedAuthenticationExchangeData data, CancellationToken cancellationToken = default);
+        Task ReAuthenticateAsync(MqttReAuthenticationOptions options, CancellationToken cancellationToken = default);
 
         Task<MqttClientSubscribeResult> SubscribeAsync(MqttClientSubscribeOptions options, CancellationToken cancellationToken = default);
 

Source/MQTTnet/Client/Internal/MqttClientAuthenticationHandler.cs

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

Source/MQTTnet/Client/Internal/MqttClientEvents.cs

@@ -0,0 +1,18 @@
+// 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;
+using MQTTnet.Internal;
+
+namespace MQTTnet.Client.Internal
+{
+    public sealed class MqttClientEvents
+    {
+        public AsyncEvent<MqttApplicationMessageReceivedEventArgs> ApplicationMessageReceivedEvent { get; } = new AsyncEvent<MqttApplicationMessageReceivedEventArgs>();
+        public AsyncEvent<MqttClientConnectedEventArgs> ConnectedEvent { get; } = new AsyncEvent<MqttClientConnectedEventArgs>();
+        public AsyncEvent<MqttClientConnectingEventArgs> ConnectingEvent { get; } = new AsyncEvent<MqttClientConnectingEventArgs>();
+        public AsyncEvent<MqttClientDisconnectedEventArgs> DisconnectedEvent { get; } = new AsyncEvent<MqttClientDisconnectedEventArgs>();
+        public AsyncEvent<InspectMqttPacketEventArgs> InspectPacketEvent { get; } = new AsyncEvent<InspectMqttPacketEventArgs>();
+    }
+}

Source/MQTTnet/Client/Internal/MqttClientKeepAliveHandler.cs

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

Source/MQTTnet/Client/Internal/MqttClientResultFactory.cs

@@ -0,0 +1,14 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace MQTTnet.Client.Internal
+{
+    public static class MqttClientResultFactory
+    {
+        public static readonly MqttClientConnectResultFactory ConnectResult = new MqttClientConnectResultFactory();
+        public static readonly MqttClientPublishResultFactory PublishResult = new MqttClientPublishResultFactory();
+        public static readonly MqttClientSubscribeResultFactory SubscribeResult = new MqttClientSubscribeResultFactory();
+        public static readonly MqttClientUnsubscribeResultFactory UnsubscribeResult = new MqttClientUnsubscribeResultFactory();
+    }
+}

Source/MQTTnet/Client/MqttClientExtensions.cs

@@ -14,20 +14,30 @@ namespace MQTTnet.Client
 {
     public static class MqttClientExtensions
     {
-        public static Task DisconnectAsync(this IMqttClient client, MqttClientDisconnectReason reason = MqttClientDisconnectReason.NormalDisconnection, string reasonString = null)
+        static readonly MqttReAuthenticationOptions EmptyReAuthenticationOptions = new MqttReAuthenticationOptions();
+
+        public static Task DisconnectAsync(
+            this IMqttClient client,
+            MqttClientDisconnectOptionsReason reason = MqttClientDisconnectOptionsReason.NormalDisconnection,
+            string reasonString = null,
+            uint sessionExpiryInterval = 0,
+            List<MqttUserProperty> userProperties = null,
+            CancellationToken cancellationToken = default)
         {
             if (client == null)
             {
                 throw new ArgumentNullException(nameof(client));
             }
 
-            return client.DisconnectAsync(
-                new MqttClientDisconnectOptions
-                {
-                    Reason = reason,
-                    ReasonString = reasonString
-                },
-                CancellationToken.None);
+            var disconnectOptions = new MqttClientDisconnectOptions
+            {
+                Reason = reason,
+                ReasonString = reasonString,
+                SessionExpiryInterval = sessionExpiryInterval,
+                UserProperties = userProperties
+            };
+
+            return client.DisconnectAsync(disconnectOptions, cancellationToken);
         }
 
         public static Task<MqttClientPublishResult> PublishBinaryAsync(
@@ -69,6 +79,11 @@ namespace MQTTnet.Client
             return mqttClient.PublishBinaryAsync(topic, payloadBuffer, qualityOfServiceLevel, retain, cancellationToken);
         }
 
+        public static Task ReAuthenticateAsync(this IMqttClient client, CancellationToken cancellationToken = default)
+        {
+            return client.ReAuthenticateAsync(EmptyReAuthenticationOptions, cancellationToken);
+        }
+
         public static Task ReconnectAsync(this IMqttClient client, CancellationToken cancellationToken = default)
         {
             if (client.Options == null)
@@ -80,16 +95,6 @@ namespace MQTTnet.Client
             return client.ConnectAsync(client.Options, cancellationToken);
         }
 
-        public static Task SendExtendedAuthenticationExchangeDataAsync(this IMqttClient client, MqttExtendedAuthenticationExchangeData data)
-        {
-            if (client == null)
-            {
-                throw new ArgumentNullException(nameof(client));
-            }
-
-            return client.SendExtendedAuthenticationExchangeDataAsync(data, CancellationToken.None);
-        }
-
         public static Task<MqttClientSubscribeResult> SubscribeAsync(this IMqttClient mqttClient, MqttTopicFilter topicFilter, CancellationToken cancellationToken = default)
         {
             if (mqttClient == null)
@@ -128,6 +133,29 @@ namespace MQTTnet.Client
             return mqttClient.SubscribeAsync(subscribeOptions, cancellationToken);
         }
 
+        public static async Task<bool> TryDisconnectAsync(
+            this IMqttClient client,
+            MqttClientDisconnectOptionsReason reason = MqttClientDisconnectOptionsReason.NormalDisconnection,
+            string reasonString = null)
+        {
+            if (client == null)
+            {
+                throw new ArgumentNullException(nameof(client));
+            }
+
+            try
+            {
+                await client.DisconnectAsync(reason, reasonString).ConfigureAwait(false);
+                return true;
+            }
+            catch
+            {
+                // Ignore all errors.
+            }
+
+            return false;
+        }
+
         public static async Task<bool> TryPingAsync(this IMqttClient client, CancellationToken cancellationToken = default)
         {
             if (client == null)

Source/MQTTnet/Client/Options/MqttClientOptions.cs

@@ -12,15 +12,23 @@ namespace MQTTnet.Client
 {
     public sealed class MqttClientOptions
     {
+        /// <summary>
+        ///     Usually the MQTT packets can be send partially. This is done by using multiple TCP packets
+        ///     or WebSocket frames etc. Unfortunately not all brokers (like Amazon Web Services (AWS)) do support this feature and
+        ///     will close the connection when receiving such packets. If such a service is used this flag must
+        ///     be set to _false_.
+        /// </summary>
+        public bool AllowPacketFragmentation { get; set; } = true;
+
         /// <summary>
         ///     Gets or sets the authentication data.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public byte[] AuthenticationData { get; set; }
 
         /// <summary>
         ///     Gets or sets the authentication method.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public string AuthenticationMethod { get; set; }
 
@@ -45,9 +53,7 @@ namespace MQTTnet.Client
         public string ClientId { get; set; } = Guid.NewGuid().ToString("N");
 
         public IMqttClientCredentialsProvider Credentials { get; set; }
-
-        public IMqttExtendedAuthenticationExchangeHandler ExtendedAuthenticationExchangeHandler { get; set; }
-
+        
         /// <summary>
         ///     Gets or sets the keep alive period.
         ///     The connection is normally left open by the client so that is can send and receive data at any time.
@@ -58,6 +64,10 @@ namespace MQTTnet.Client
         /// </summary>
         public TimeSpan KeepAlivePeriod { get; set; } = TimeSpan.FromSeconds(15);
 
+        /// <summary>
+        ///     Gets or sets the maximum packet size.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// </summary>
         public uint MaximumPacketSize { get; set; }
 
         public MqttProtocolVersion ProtocolVersion { get; set; } = MqttProtocolVersion.V311;
@@ -65,27 +75,34 @@ namespace MQTTnet.Client
         /// <summary>
         ///     Gets or sets the receive maximum.
         ///     This gives the maximum length of the receive messages.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public ushort ReceiveMaximum { get; set; }
 
         /// <summary>
         ///     Gets or sets the request problem information.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public bool RequestProblemInformation { get; set; } = true;
 
         /// <summary>
         ///     Gets or sets the request response information.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public bool RequestResponseInformation { get; set; }
 
         /// <summary>
         ///     Gets or sets the session expiry interval.
         ///     The time after a session expires when it's not actively used.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public uint SessionExpiryInterval { get; set; }
 
+        /// <summary>
+        ///     Gets or sets whether an exception should be thrown when the server has sent a non success ACK packet.
+        /// </summary>
+        public bool ThrowOnNonSuccessfulResponseFromServer { get; set; } = true;
+
         /// <summary>
         ///     Gets or sets the timeout which will be applied at socket level and internal operations.
         ///     The default value is the same as for sockets in .NET in general.
@@ -95,6 +112,7 @@ namespace MQTTnet.Client
         /// <summary>
         ///     Gets or sets the topic alias maximum.
         ///     This gives the maximum length of the topic alias.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public ushort TopicAliasMaximum { get; set; }
 
@@ -103,8 +121,10 @@ namespace MQTTnet.Client
         ///     client.
         ///     If successful, this means that loop detection will be more effective and that retained messages will be propagated
         ///     correctly.
-        ///     Not all brokers support this feature so it may be necessary to set it to false if your bridge does not connect
-        ///     properly.
+        ///     <remarks>
+        ///         Not all brokers support this feature so it may be necessary to set it to false if your bridge does not
+        ///         connect properly.
+        ///     </remarks>
         /// </summary>
         public bool TryPrivate { get; set; } = true;
 
@@ -115,28 +135,41 @@ namespace MQTTnet.Client
         ///     As long as you don’t exceed the maximum message size, you can use an unlimited number of user properties to add
         ///     metadata to MQTT messages and pass information between publisher, broker, and subscriber.
         ///     The feature is very similar to the HTTP header concept.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public List<MqttUserProperty> UserProperties { get; set; }
 
+        /// <summary>
+        ///     When this feature is enabled the client will check if used properties are supported in the selected protocol
+        ///     version.
+        ///     This feature can be validated if an application message is generated one time but sent via different protocol
+        ///     versions.
+        ///     Default values are applied if the validation is off and features are not supported.
+        /// </summary>
+        public bool ValidateFeatures { get; set; } = true;
+
         /// <summary>
         ///     Gets or sets the content type of the will message.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public string WillContentType { get; set; }
 
         /// <summary>
         ///     Gets or sets the correlation data of the will message.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public byte[] WillCorrelationData { get; set; }
 
         /// <summary>
         ///     Gets or sets the will delay interval.
         ///     This is the time between the client disconnect and the time the will message will be sent.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public uint WillDelayInterval { get; set; }
 
         /// <summary>
         ///     Gets or sets the message expiry interval of the will message.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public uint WillMessageExpiryInterval { get; set; }
 
@@ -147,8 +180,9 @@ namespace MQTTnet.Client
 
         /// <summary>
         ///     Gets or sets the payload format indicator of the will message.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
-        public MqttPayloadFormatIndicator WillPayloadFormatIndicator { get; set; }
+        public MqttPayloadFormatIndicator WillPayloadFormatIndicator { get; set; } = MqttPayloadFormatIndicator.Unspecified;
 
         /// <summary>
         ///     Gets or sets the QoS level of the will message.
@@ -157,6 +191,7 @@ namespace MQTTnet.Client
 
         /// <summary>
         ///     Gets or sets the response topic of the will message.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public string WillResponseTopic { get; set; }
 
@@ -172,6 +207,7 @@ namespace MQTTnet.Client
 
         /// <summary>
         ///     Gets or sets the user properties of the will message.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public List<MqttUserProperty> WillUserProperties { get; set; }
 

Source/MQTTnet/Client/Options/MqttClientOptionsBuilder.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// 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.
 
@@ -46,7 +46,7 @@ namespace MQTTnet.Client
                         Certificates = _tlsParameters.Certificates?.ToList(),
 #endif
 
-#if NETCOREAPP3_1 || NET5_0_OR_GREATER
+#if NETCOREAPP3_1_OR_GREATER
                         ApplicationProtocols = _tlsParameters.ApplicationProtocols,
 #endif
                     };
@@ -74,22 +74,36 @@ namespace MQTTnet.Client
 
             _options.ChannelOptions = (IMqttClientChannelOptions)_tcpOptions ?? _webSocketOptions;
 
+            MqttClientOptionsValidator.ThrowIfNotSupported(_options);
+
             return _options;
         }
 
-        public MqttClientOptionsBuilder WithAuthentication(string method, byte[] data)
+        public MqttClientOptionsBuilder WithAuthentication(string method, byte[] data = null)
         {
             _options.AuthenticationMethod = method;
             _options.AuthenticationData = data;
             return this;
         }
 
+        /// <summary>
+        ///     Clean session is used in MQTT versions below 5.0.0. It is the same as setting "CleanStart".
+        /// </summary>
         public MqttClientOptionsBuilder WithCleanSession(bool value = true)
         {
             _options.CleanSession = value;
             return this;
         }
 
+        /// <summary>
+        ///     Clean start is used in MQTT versions 5.0.0 and higher. It is the same as setting "CleanSession".
+        /// </summary>
+        public MqttClientOptionsBuilder WithCleanStart(bool value = true)
+        {
+            _options.CleanSession = value;
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithClientId(string value)
         {
             _options.ClientId = value;
@@ -163,12 +177,6 @@ namespace MQTTnet.Client
             return this;
         }
 
-        public MqttClientOptionsBuilder WithExtendedAuthenticationExchangeHandler(IMqttExtendedAuthenticationExchangeHandler handler)
-        {
-            _options.ExtendedAuthenticationExchangeHandler = handler;
-            return this;
-        }
-
         public MqttClientOptionsBuilder WithKeepAlivePeriod(TimeSpan value)
         {
             _options.KeepAlivePeriod = value;
@@ -186,6 +194,18 @@ namespace MQTTnet.Client
             return WithKeepAlivePeriod(TimeSpan.Zero);
         }
 
+        /// <summary>
+        ///     Usually the MQTT packets can be send partially. This is done by using multiple TCP packets
+        ///     or WebSocket frames etc. Unfortunately not all brokers (like Amazon Web Services (AWS)) do support this feature and
+        ///     will close the connection when receiving such packets. If such a service is used this flag must
+        ///     be set to _true_.
+        /// </summary>
+        public MqttClientOptionsBuilder WithoutPacketFragmentation()
+        {
+            _options.AllowPacketFragmentation = false;
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithProtocolVersion(MqttProtocolVersion value)
         {
             if (value == MqttProtocolVersion.Unknown)
@@ -264,7 +284,7 @@ namespace MQTTnet.Client
 
             return this;
         }
-        
+
         public MqttClientOptionsBuilder WithTcpServer(Action<MqttClientTcpOptions> optionsBuilder)
         {
             if (optionsBuilder == null)
@@ -337,16 +357,6 @@ namespace MQTTnet.Client
 
         public MqttClientOptionsBuilder WithUserProperty(string name, string value)
         {
-            if (name is null)
-            {
-                throw new ArgumentNullException(nameof(name));
-            }
-
-            if (value is null)
-            {
-                throw new ArgumentNullException(nameof(value));
-            }
-
             if (_options.UserProperties == null)
             {
                 _options.UserProperties = new List<MqttUserProperty>();
@@ -381,6 +391,18 @@ namespace MQTTnet.Client
             return this;
         }
 
+        public MqttClientOptionsBuilder WithWillContentType(string willContentType)
+        {
+            _options.WillContentType = willContentType;
+            return this;
+        }
+
+        public MqttClientOptionsBuilder WithWillCorrelationData(byte[] willCorrelationData)
+        {
+            _options.WillCorrelationData = willCorrelationData;
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithWillDelayInterval(uint willDelayInterval)
         {
             _options.WillDelayInterval = willDelayInterval;
@@ -392,27 +414,45 @@ namespace MQTTnet.Client
             _options.WillPayload = willPayload;
             return this;
         }
-        
+
+        public MqttClientOptionsBuilder WithWillPayload(ArraySegment<byte> willPayload)
+        {
+            if (willPayload.Count == 0)
+            {
+                _options.WillPayload = null;
+                return this;
+            }
+
+            _options.WillPayload = willPayload.ToArray();
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithWillPayload(string willPayload)
         {
             if (string.IsNullOrEmpty(willPayload))
             {
                 return WithWillPayload((byte[])null);
             }
-            
+
             _options.WillPayload = Encoding.UTF8.GetBytes(willPayload);
             return this;
         }
 
+        public MqttClientOptionsBuilder WithWillPayloadFormatIndicator(MqttPayloadFormatIndicator willPayloadFormatIndicator)
+        {
+            _options.WillPayloadFormatIndicator = willPayloadFormatIndicator;
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithWillQualityOfServiceLevel(MqttQualityOfServiceLevel willQualityOfServiceLevel)
         {
             _options.WillQualityOfServiceLevel = willQualityOfServiceLevel;
             return this;
         }
 
-        public MqttClientOptionsBuilder WithWillTopic(string willTopic)
+        public MqttClientOptionsBuilder WithWillResponseTopic(string willResponseTopic)
         {
-            _options.WillTopic = willTopic;
+            _options.WillResponseTopic = willResponseTopic;
             return this;
         }
 
@@ -421,38 +461,20 @@ namespace MQTTnet.Client
             _options.WillRetain = willRetain;
             return this;
         }
-        
-        public MqttClientOptionsBuilder WithWillContentType(string willContentType)
+
+        public MqttClientOptionsBuilder WithWillTopic(string willTopic)
         {
-            _options.WillContentType = willContentType;
+            _options.WillTopic = willTopic;
             return this;
         }
-        
-        public MqttClientOptionsBuilder WithWillCorrelationData(byte[] willCorrelationData)
-        {
-            _options.WillCorrelationData = willCorrelationData;
-            return this;
-        }
-        
-        public MqttClientOptionsBuilder WithWillResponseTopic(string willResponseTopic)
-        {
-            _options.WillResponseTopic = willResponseTopic;
-            return this;
-        }
-        
-        public MqttClientOptionsBuilder WithWillPayloadFormatIndicator(MqttPayloadFormatIndicator willPayloadFormatIndicator)
-        {
-            _options.WillPayloadFormatIndicator = willPayloadFormatIndicator;
-            return this;
-        }
-        
+
         public MqttClientOptionsBuilder WithWillUserProperty(string name, string value)
         {
             if (_options.WillUserProperties == null)
             {
                 _options.WillUserProperties = new List<MqttUserProperty>();
             }
-            
+
             _options.WillUserProperties.Add(new MqttUserProperty(name, value));
             return this;
         }

Source/MQTTnet/Client/Options/MqttClientOptionsBuilderTlsParameters.cs

@@ -4,7 +4,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Net.Security;
 using System.Security.Authentication;
 using System.Security.Cryptography.X509Certificates;
 
@@ -13,10 +12,10 @@ namespace MQTTnet.Client
     public sealed class MqttClientOptionsBuilderTlsParameters
     {
         public bool UseTls { get; set; }
-        
+
         public Func<MqttClientCertificateValidationEventArgs, bool> CertificateValidationHandler { get; set; }
 
-#if NET48 || NETCOREAPP3_1 || NET5 || NET6
+#if NET48 || NETCOREAPP3_1_OR_GREATER
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12 | SslProtocols.Tls13;
 #else
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12 | (SslProtocols)0x00003000 /*Tls13*/;
@@ -28,14 +27,14 @@ namespace MQTTnet.Client
         public IEnumerable<X509Certificate> Certificates { get; set; }
 #endif
 
-#if NETCOREAPP3_1 || NET5_0_OR_GREATER
-        public List<SslApplicationProtocol> ApplicationProtocols { get;set; }
+#if NETCOREAPP3_1_OR_GREATER
+        public List<System.Net.Security.SslApplicationProtocol> ApplicationProtocols { get; set; }
 #endif
 
-	    public bool AllowUntrustedCertificates { get; set; }
+        public bool AllowUntrustedCertificates { get; set; }
 
         public bool IgnoreCertificateChainErrors { get; set; }
 
         public bool IgnoreCertificateRevocationErrors { get; set; }
     }
-}
+}

Source/MQTTnet/Client/Options/MqttClientOptionsValidator.cs

@@ -0,0 +1,114 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Linq;
+using MQTTnet.Formatter;
+using MQTTnet.Protocol;
+
+namespace MQTTnet.Client
+{
+    public static class MqttClientOptionsValidator
+    {
+        public static void ThrowIfNotSupported(MqttClientOptions options)
+        {
+            if (options == null)
+            {
+                throw new ArgumentNullException(nameof(options));
+            }
+
+            if (options.ProtocolVersion == MqttProtocolVersion.V500)
+            {
+                // Everything is supported.
+                return;
+            }
+            
+            if (options.WillContentType?.Any() == true)
+            {
+                Throw(nameof(options.WillContentType));
+            }
+
+            if (options.UserProperties?.Any() == true)
+            {
+                Throw(nameof(options.UserProperties));
+            }
+
+            if (options.RequestProblemInformation)
+            {
+                // Since this value is a boolean and true by default, validation would
+                // require a nullable boolean.
+                //Throw(nameof(options.RequestProblemInformation));
+            }
+
+            if (options.RequestResponseInformation)
+            {
+                Throw(nameof(options.RequestResponseInformation));
+            }
+
+            if (options.ReceiveMaximum > 0)
+            {
+                Throw(nameof(options.ReceiveMaximum));
+            }
+            
+            if (options.MaximumPacketSize > 0)
+            {
+                Throw(nameof(options.MaximumPacketSize));
+            }
+
+            // Authentication relevant properties.
+            
+            if (options.AuthenticationData?.Any() == true)
+            {
+                Throw(nameof(options.AuthenticationData));
+            }
+
+            if (options.AuthenticationMethod?.Any() == true)
+            {
+                Throw(nameof(options.AuthenticationMethod));
+            }
+
+            // Will relevant properties.
+            
+            if (options.WillPayloadFormatIndicator != MqttPayloadFormatIndicator.Unspecified)
+            {
+                Throw(nameof(options.WillPayloadFormatIndicator));
+            }
+
+            if (options.WillContentType?.Any() == true)
+            {
+                Throw(nameof(options.WillContentType));
+            }
+
+            if (options.WillCorrelationData?.Any() == true)
+            {
+                Throw(nameof(options.WillCorrelationData));
+            }
+            
+            if (options.WillResponseTopic?.Any() == true)
+            {
+                Throw(nameof(options.WillResponseTopic));
+            }
+            
+            if (options.WillDelayInterval > 0)
+            {
+                Throw(nameof(options.WillDelayInterval));
+            }
+            
+            if (options.WillMessageExpiryInterval > 0)
+            {
+                Throw(nameof(options.WillMessageExpiryInterval));
+            }
+            
+            if (options.WillUserProperties?.Any() == true)
+            {
+                Throw(nameof(options.WillUserProperties));
+            }
+        }
+
+        static void Throw(string featureName)
+        {
+            throw new NotSupportedException($"Feature {featureName} requires MQTT version 5.0.0.");
+        }
+    }
+}

Source/MQTTnet/Client/Options/MqttClientTlsOptions.cs

@@ -29,13 +29,13 @@ namespace MQTTnet.Client
         public List<X509Certificate> Certificates { get; set; }
 #endif
 
-#if NETCOREAPP3_1 || NET5_0_OR_GREATER
+#if NETCOREAPP3_1_OR_GREATER
         public List<System.Net.Security.SslApplicationProtocol> ApplicationProtocols { get; set; }
         
         public System.Net.Security.CipherSuitesPolicy CipherSuitesPolicy { get; set; }
 #endif
 
-#if NET48 || NETCOREAPP3_1 || NET5 || NET6
+#if NET48 || NETCOREAPP3_1_OR_GREATER
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12 | SslProtocols.Tls13;
 #else
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12 | (SslProtocols)0x00003000 /*Tls13*/;

Source/MQTTnet/Client/Publishing/MqttClientPublishResult.cs

@@ -9,9 +9,18 @@ namespace MQTTnet.Client
 {
     public sealed class MqttClientPublishResult
     {
+        public MqttClientPublishResult(ushort? packetIdentifier, MqttClientPublishReasonCode reasonCode, string reasonString, IReadOnlyCollection<MqttUserProperty> userProperties)
+        {
+            PacketIdentifier = packetIdentifier;
+            ReasonCode = reasonCode;
+            ReasonString = reasonString;
+            UserProperties = userProperties;
+        }
+
         /// <summary>
         ///     Returns if the overall status of the publish is a success. This can be the reason code _Success_ or
-        ///     _NoMatchingSubscribers_. _NoMatchingSubscribers_ usually indicates only that no other client is interested in the topic but overall transmit
+        ///     _NoMatchingSubscribers_. _NoMatchingSubscribers_ usually indicates only that no other client is interested in the
+        ///     topic but overall transmit
         ///     to the server etc. was a success.
         /// </summary>
         public bool IsSuccess => ReasonCode == MqttClientPublishReasonCode.Success || ReasonCode == MqttClientPublishReasonCode.NoMatchingSubscribers;
@@ -19,19 +28,19 @@ namespace MQTTnet.Client
         /// <summary>
         ///     Gets the packet identifier which was used for this publish.
         /// </summary>
-        public ushort? PacketIdentifier { get; set; }
+        public ushort? PacketIdentifier { get; }
 
         /// <summary>
         ///     Gets or sets the reason code.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
-        public MqttClientPublishReasonCode ReasonCode { get; set; } = MqttClientPublishReasonCode.Success;
+        public MqttClientPublishReasonCode ReasonCode { get; }
 
         /// <summary>
         ///     Gets or sets the reason string.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
-        public string ReasonString { get; set; }
+        public string ReasonString { get; }
 
         /// <summary>
         ///     Gets or sets the user properties.
@@ -40,8 +49,8 @@ namespace MQTTnet.Client
         ///     As long as you don’t exceed the maximum message size, you can use an unlimited number of user properties to add
         ///     metadata to MQTT messages and pass information between publisher, broker, and subscriber.
         ///     The feature is very similar to the HTTP header concept.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
-        public IReadOnlyCollection<MqttUserProperty> UserProperties { get; internal set; }
+        public IReadOnlyCollection<MqttUserProperty> UserProperties { get; }
     }
 }

Source/MQTTnet/Client/Publishing/MqttClientPublishResultFactory.cs

@@ -10,25 +10,23 @@ namespace MQTTnet.Client
 {
     public sealed class MqttClientPublishResultFactory
     {
-        static readonly MqttClientPublishResult EmptySuccessResult = new MqttClientPublishResult();
         static readonly IReadOnlyCollection<MqttUserProperty> EmptyUserProperties = new List<MqttUserProperty>();
+        static readonly MqttClientPublishResult AtMostOnceSuccessResult = new MqttClientPublishResult(null, MqttClientPublishReasonCode.Success, null, EmptyUserProperties);
 
         public MqttClientPublishResult Create(MqttPubAckPacket pubAckPacket)
         {
             // QoS 0 has no response. So we treat it as a success always.
             if (pubAckPacket == null)
             {
-                return EmptySuccessResult;
+                return AtMostOnceSuccessResult;
             }
 
-            var result = new MqttClientPublishResult
-            {
+            var result = new MqttClientPublishResult(
+                pubAckPacket.PacketIdentifier,
                 // Both enums have the same values. So it can be easily converted.
-                ReasonCode = (MqttClientPublishReasonCode)(int)pubAckPacket.ReasonCode,
-                PacketIdentifier = pubAckPacket.PacketIdentifier,
-                ReasonString = pubAckPacket.ReasonString,
-                UserProperties = pubAckPacket.UserProperties ?? EmptyUserProperties
-            };
+                (MqttClientPublishReasonCode)(int)pubAckPacket.ReasonCode,
+                pubAckPacket.ReasonString,
+                pubAckPacket.UserProperties ?? EmptyUserProperties);
 
             return result;
         }
@@ -37,43 +35,28 @@ namespace MQTTnet.Client
         {
             if (pubRecPacket == null || pubCompPacket == null)
             {
-                return new MqttClientPublishResult
-                {
-                    ReasonCode = MqttClientPublishReasonCode.UnspecifiedError
-                };
+                var packetIdentifier = pubRecPacket?.PacketIdentifier ?? pubCompPacket?.PacketIdentifier;
+                return new MqttClientPublishResult(packetIdentifier, MqttClientPublishReasonCode.ImplementationSpecificError, null, EmptyUserProperties);
             }
 
-            MqttClientPublishResult result;
-
             // The PUBCOMP is the last packet in QoS 2. So we use the results from that instead of PUBREC.
             if (pubCompPacket.ReasonCode == MqttPubCompReasonCode.PacketIdentifierNotFound)
             {
-                result = new MqttClientPublishResult
-                {
-                    PacketIdentifier = pubCompPacket.PacketIdentifier,
-                    ReasonCode = MqttClientPublishReasonCode.UnspecifiedError,
-                    ReasonString = pubCompPacket.ReasonString,
-                    UserProperties = pubCompPacket.UserProperties ?? EmptyUserProperties
-                };
-
-                return result;
+                return new MqttClientPublishResult(
+                    pubCompPacket.PacketIdentifier,
+                    MqttClientPublishReasonCode.UnspecifiedError,
+                    pubCompPacket.ReasonString,
+                    pubCompPacket.UserProperties ?? EmptyUserProperties);
             }
 
-            result = new MqttClientPublishResult
-            {
-                PacketIdentifier = pubCompPacket.PacketIdentifier,
-                ReasonCode = MqttClientPublishReasonCode.Success,
-                ReasonString = pubCompPacket.ReasonString,
-                UserProperties = pubCompPacket.UserProperties ?? EmptyUserProperties
-            };
-
+            var reasonCode = MqttClientPublishReasonCode.Success;
             if (pubRecPacket.ReasonCode != MqttPubRecReasonCode.Success)
             {
                 // Both enums share the same values.
-                result.ReasonCode = (MqttClientPublishReasonCode)pubRecPacket.ReasonCode;
+                reasonCode = (MqttClientPublishReasonCode)pubRecPacket.ReasonCode;
             }
 
-            return result;
+            return new MqttClientPublishResult(pubCompPacket.PacketIdentifier, reasonCode, null, pubCompPacket.UserProperties ?? EmptyUserProperties);
         }
     }
 }

Source/MQTTnet/Client/Subscribing/MqttClientSubscribeOptions.cs

@@ -10,27 +10,31 @@ namespace MQTTnet.Client
     public sealed class MqttClientSubscribeOptions
     {
         /// <summary>
-        /// Gets or sets a list of topic filters the client wants to subscribe to.
-        /// Topic filters can include regular topics or wild cards.
-        /// </summary>
-        public List<MqttTopicFilter> TopicFilters { get; set; } = new List<MqttTopicFilter>();
-
-        /// <summary>
-        /// Gets or sets the subscription identifier.
-        /// The client can specify a subscription identifier when subscribing.
-        /// The broker will establish and store the mapping relationship between this subscription and subscription identifier when successfully create or modify subscription.
-        /// The broker will return the subscription identifier associated with this PUBLISH packet and the PUBLISH packet to the client when need to forward PUBLISH packets matching this subscription to this client.
-        /// Hint: MQTT 5 feature only.
+        ///     Gets or sets the subscription identifier.
+        ///     The client can specify a subscription identifier when subscribing.
+        ///     The broker will establish and store the mapping relationship between this subscription and subscription identifier
+        ///     when successfully create or modify subscription.
+        ///     The broker will return the subscription identifier associated with this PUBLISH packet and the PUBLISH packet to
+        ///     the client when need to forward PUBLISH packets matching this subscription to this client.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public uint SubscriptionIdentifier { get; set; }
 
         /// <summary>
-        /// Gets or sets the user properties.
-        /// In MQTT 5, user properties are basic UTF-8 string key-value pairs that you can append to almost every type of MQTT packet.
-        /// As long as you don’t exceed the maximum message size, you can use an unlimited number of user properties to add metadata to MQTT messages and pass information between publisher, broker, and subscriber.
-        /// The feature is very similar to the HTTP header concept.
-        /// Hint: MQTT 5 feature only.
+        ///     Gets or sets a list of topic filters the client wants to subscribe to.
+        ///     Topic filters can include regular topics or wild cards.
+        /// </summary>
+        public List<MqttTopicFilter> TopicFilters { get; set; } = new List<MqttTopicFilter>();
+
+        /// <summary>
+        ///     Gets or sets the user properties.
+        ///     In MQTT 5, user properties are basic UTF-8 string key-value pairs that you can append to almost every type of MQTT
+        ///     packet.
+        ///     As long as you don’t exceed the maximum message size, you can use an unlimited number of user properties to add
+        ///     metadata to MQTT messages and pass information between publisher, broker, and subscriber.
+        ///     The feature is very similar to the HTTP header concept.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public List<MqttUserProperty> UserProperties { get; set; }
     }
-}
+}

Source/MQTTnet/Client/Subscribing/MqttClientSubscribeOptionsBuilder.cs

@@ -14,26 +14,9 @@ namespace MQTTnet.Client
     {
         readonly MqttClientSubscribeOptions _subscribeOptions = new MqttClientSubscribeOptions();
 
-        /// <summary>
-        /// Adds the user property to the subscribe options.
-        /// Hint: MQTT 5 feature only.
-        /// </summary>
-        /// <param name="name">The property name.</param>
-        /// <param name="value">The property value.</param>
-        /// <returns>A new instance of the <see cref="MqttApplicationMessageBuilder"/> class.</returns>
-        public MqttClientSubscribeOptionsBuilder WithUserProperty(string name, string value)
+        public MqttClientSubscribeOptions Build()
         {
-            if (name == null) throw new ArgumentNullException(nameof(name));
-            if (value == null) throw new ArgumentNullException(nameof(value));
-
-            if (_subscribeOptions.UserProperties == null)
-            {
-                _subscribeOptions.UserProperties = new List<MqttUserProperty>();
-            }
-
-            _subscribeOptions.UserProperties.Add(new MqttUserProperty(name, value));
-
-            return this;
+            return _subscribeOptions;
         }
 
         public MqttClientSubscribeOptionsBuilder WithSubscriptionIdentifier(uint subscriptionIdentifier)
@@ -42,7 +25,7 @@ namespace MQTTnet.Client
             {
                 throw new MqttProtocolViolationException("Subscription identifier cannot be 0.");
             }
-            
+
             _subscribeOptions.SubscriptionIdentifier = subscriptionIdentifier;
             return this;
         }
@@ -54,19 +37,23 @@ namespace MQTTnet.Client
             bool retainAsPublished = false,
             MqttRetainHandling retainHandling = MqttRetainHandling.SendAtSubscribe)
         {
-            return WithTopicFilter(new MqttTopicFilter
-            {
-                Topic = topic,
-                QualityOfServiceLevel = qualityOfServiceLevel,
-                NoLocal = noLocal,
-                RetainAsPublished = retainAsPublished,
-                RetainHandling = retainHandling
-            });
+            return WithTopicFilter(
+                new MqttTopicFilter
+                {
+                    Topic = topic,
+                    QualityOfServiceLevel = qualityOfServiceLevel,
+                    NoLocal = noLocal,
+                    RetainAsPublished = retainAsPublished,
+                    RetainHandling = retainHandling
+                });
         }
 
         public MqttClientSubscribeOptionsBuilder WithTopicFilter(Action<MqttTopicFilterBuilder> topicFilterBuilder)
         {
-            if (topicFilterBuilder == null) throw new ArgumentNullException(nameof(topicFilterBuilder));
+            if (topicFilterBuilder == null)
+            {
+                throw new ArgumentNullException(nameof(topicFilterBuilder));
+            }
 
             var internalTopicFilterBuilder = new MqttTopicFilterBuilder();
             topicFilterBuilder(internalTopicFilterBuilder);
@@ -76,14 +63,20 @@ namespace MQTTnet.Client
 
         public MqttClientSubscribeOptionsBuilder WithTopicFilter(MqttTopicFilterBuilder topicFilterBuilder)
         {
-            if (topicFilterBuilder == null) throw new ArgumentNullException(nameof(topicFilterBuilder));
+            if (topicFilterBuilder == null)
+            {
+                throw new ArgumentNullException(nameof(topicFilterBuilder));
+            }
 
             return WithTopicFilter(topicFilterBuilder.Build());
         }
 
         public MqttClientSubscribeOptionsBuilder WithTopicFilter(MqttTopicFilter topicFilter)
         {
-            if (topicFilter == null) throw new ArgumentNullException(nameof(topicFilter));
+            if (topicFilter == null)
+            {
+                throw new ArgumentNullException(nameof(topicFilter));
+            }
 
             if (_subscribeOptions.TopicFilters == null)
             {
@@ -95,9 +88,20 @@ namespace MQTTnet.Client
             return this;
         }
 
-        public MqttClientSubscribeOptions Build()
+        /// <summary>
+        ///     Adds the user property to the subscribe options.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// </summary>
+        public MqttClientSubscribeOptionsBuilder WithUserProperty(string name, string value)
         {
-            return _subscribeOptions;
+            if (_subscribeOptions.UserProperties == null)
+            {
+                _subscribeOptions.UserProperties = new List<MqttUserProperty>();
+            }
+
+            _subscribeOptions.UserProperties.Add(new MqttUserProperty(name, value));
+
+            return this;
         }
     }
-}
+}

Source/MQTTnet/Client/Subscribing/MqttClientSubscribeOptionsValidator.cs

@@ -0,0 +1,58 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Linq;
+using MQTTnet.Formatter;
+using MQTTnet.Protocol;
+
+namespace MQTTnet.Client
+{
+    public static class MqttClientSubscribeOptionsValidator
+    {
+        public static void ThrowIfNotSupported(MqttClientSubscribeOptions options, MqttProtocolVersion protocolVersion)
+        {
+            if (options == null)
+            {
+                throw new ArgumentNullException(nameof(options));
+            }
+            
+            if (protocolVersion == MqttProtocolVersion.V500)
+            {
+                // Everything is supported.
+                return;
+            }
+
+            if (options.UserProperties?.Any() == true)
+            {
+                Throw(nameof(options.UserProperties));
+            }
+            
+            if (options.SubscriptionIdentifier != 0)
+            {
+                Throw(nameof(options.SubscriptionIdentifier));
+            }
+            
+            if (options.TopicFilters?.Any(t => t.NoLocal) == true)
+            {
+                Throw("NoLocal");
+            }
+            
+            if (options.TopicFilters?.Any(t => t.RetainAsPublished) == true)
+            {
+                Throw("RetainAsPublished");
+            }
+            
+            if (options.TopicFilters?.Any(t => t.RetainHandling != MqttRetainHandling.SendAtSubscribe) == true)
+            {
+                Throw("RetainHandling");
+            }
+        }
+        
+        static void Throw(string featureName)
+        {
+            throw new NotSupportedException($"Feature {featureName} requires MQTT version 5.0.0.");
+        }
+    }
+}

Source/MQTTnet/Client/Subscribing/MqttClientSubscribeResult.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
 using MQTTnet.Packets;
 
@@ -9,23 +10,34 @@ namespace MQTTnet.Client
 {
     public sealed class MqttClientSubscribeResult
     {
-        public IReadOnlyCollection<MqttClientSubscribeResultItem> Items { get; internal set; }
+        public MqttClientSubscribeResult(ushort packetIdentifier, IReadOnlyCollection<MqttClientSubscribeResultItem> items, string reasonString, IReadOnlyCollection<MqttUserProperty> userProperties)
+        {
+            PacketIdentifier = packetIdentifier;
+            Items = items ?? throw new ArgumentNullException(nameof(items));
+            ReasonString = reasonString;
+            UserProperties = userProperties ?? throw new ArgumentNullException(nameof(userProperties));
+        }
+
+        /// <summary>
+        /// Gets the result for every topic filter item.
+        /// </summary>
+        public IReadOnlyCollection<MqttClientSubscribeResultItem> Items { get; }
         
         /// <summary>
         /// Gets the user properties which were part of the SUBACK packet.
-        /// MQTTv5 only.
+        /// <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
-        public IReadOnlyCollection<MqttUserProperty> UserProperties { get; internal set; }
+        public IReadOnlyCollection<MqttUserProperty> UserProperties { get; }
         
         /// <summary>
         /// Gets the reason string.
-        /// MQTTv5 only.
+        /// <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
-        public string ReasonString { get; internal set; }
+        public string ReasonString { get; }
 
         /// <summary>
         /// Gets the packet identifier which was used.
         /// </summary>
-        public ushort PacketIdentifier { get; internal set; }
+        public ushort PacketIdentifier { get; }
     }
 }

Source/MQTTnet/Client/Subscribing/MqttClientSubscribeResultFactory.cs

@@ -16,42 +16,35 @@ namespace MQTTnet.Client
 
         public MqttClientSubscribeResult Create(MqttSubscribePacket subscribePacket, MqttSubAckPacket subAckPacket)
         {
-            if (subscribePacket == null) throw new ArgumentNullException(nameof(subscribePacket));
-            if (subAckPacket == null) throw new ArgumentNullException(nameof(subAckPacket));
-            
+            if (subscribePacket == null)
+            {
+                throw new ArgumentNullException(nameof(subscribePacket));
+            }
+
+            if (subAckPacket == null)
+            {
+                throw new ArgumentNullException(nameof(subAckPacket));
+            }
+
             // MQTTv5.0.0 handling.
             if (subAckPacket.ReasonCodes.Any() && subAckPacket.ReasonCodes.Count != subscribePacket.TopicFilters.Count)
             {
-                throw new MqttProtocolViolationException(
-                    "The reason codes are not matching the topic filters [MQTT-3.9.3-1].");
+                throw new MqttProtocolViolationException("The reason codes are not matching the topic filters [MQTT-3.9.3-1].");
             }
-            
+
             var items = new List<MqttClientSubscribeResultItem>();
             for (var i = 0; i < subscribePacket.TopicFilters.Count; i++)
             {
                 items.Add(CreateSubscribeResultItem(i, subscribePacket, subAckPacket));
             }
-            
-            var result = new MqttClientSubscribeResult
-            {
-                PacketIdentifier = subAckPacket.PacketIdentifier,
-                ReasonString = subAckPacket.ReasonString,
-                UserProperties = subAckPacket.UserProperties ?? EmptyUserProperties,
-                Items = items
-            };
-            
-            return result;
+
+            return new MqttClientSubscribeResult(subAckPacket.PacketIdentifier, items, subAckPacket.ReasonString, subAckPacket.UserProperties ?? EmptyUserProperties);
         }
 
         static MqttClientSubscribeResultItem CreateSubscribeResultItem(int index, MqttSubscribePacket subscribePacket, MqttSubAckPacket subAckPacket)
         {
-            var resultCode = (MqttClientSubscribeResultCode) subAckPacket.ReasonCodes[index];
-
-            return new MqttClientSubscribeResultItem
-            {
-                TopicFilter = subscribePacket.TopicFilters[index],
-                ResultCode = resultCode,
-            };
+            var resultCode = (MqttClientSubscribeResultCode)subAckPacket.ReasonCodes[index];
+            return new MqttClientSubscribeResultItem(subscribePacket.TopicFilters[index], resultCode);
         }
     }
 }

Source/MQTTnet/Client/Subscribing/MqttClientSubscribeResultItem.cs

@@ -2,22 +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 System;
 using MQTTnet.Packets;
 
 namespace MQTTnet.Client
 {
     public sealed class MqttClientSubscribeResultItem
     {
+        public MqttClientSubscribeResultItem(MqttTopicFilter topicFilter, MqttClientSubscribeResultCode resultCode)
+        {
+            TopicFilter = topicFilter ?? throw new ArgumentNullException(nameof(topicFilter));
+            ResultCode = resultCode;
+        }
+
         /// <summary>
         /// Gets or sets the topic filter.
         /// The topic filter can contain topics and wildcards.
         /// </summary>
-        public MqttTopicFilter TopicFilter { get; internal set; }
+        public MqttTopicFilter TopicFilter { get; }
 
         /// <summary>
         /// Gets or sets the result code.
-        /// Hint: MQTT 5 feature only.
+        /// <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
-        public MqttClientSubscribeResultCode ResultCode { get; internal set; }
+        public MqttClientSubscribeResultCode ResultCode { get; }
     }
 }

Source/MQTTnet/Client/Unsubscribing/MqttClientUnsubscribeOptions.cs

@@ -10,18 +10,20 @@ namespace MQTTnet.Client
     public sealed class MqttClientUnsubscribeOptions
     {
         /// <summary>
-        /// Gets or sets a list of topic filters the client wants to unsubscribe from.
-        /// Topic filters can include regular topics or wild cards.
+        ///     Gets or sets a list of topic filters the client wants to unsubscribe from.
+        ///     Topic filters can include regular topics or wild cards.
         /// </summary>
         public List<string> TopicFilters { get; set; } = new List<string>();
 
         /// <summary>
-        /// Gets or sets the user properties.
-        /// In MQTT 5, user properties are basic UTF-8 string key-value pairs that you can append to almost every type of MQTT packet.
-        /// As long as you don’t exceed the maximum message size, you can use an unlimited number of user properties to add metadata to MQTT messages and pass information between publisher, broker, and subscriber.
-        /// The feature is very similar to the HTTP header concept.
-        /// Hint: MQTT 5 feature only.
+        ///     Gets or sets the user properties.
+        ///     In MQTT 5, user properties are basic UTF-8 string key-value pairs that you can append to almost every type of MQTT
+        ///     packet.
+        ///     As long as you don’t exceed the maximum message size, you can use an unlimited number of user properties to add
+        ///     metadata to MQTT messages and pass information between publisher, broker, and subscriber.
+        ///     The feature is very similar to the HTTP header concept.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
-        public List<MqttUserProperty> UserProperties { get; set; } = new List<MqttUserProperty>();
+        public List<MqttUserProperty> UserProperties { get; set; }
     }
-}
+}