Add new API for extended authentication

Add warning
Fix breaking changes
2026-10-15 17:00:03 +08:00 · 2023-05-07 18:27:11 +02:00 · 2023-05-06 14:17:39 +02:00 · 2023-05-06 13:09:02 +02:00 · 2023-05-06 13:03:13 +02:00 · 2023-05-06 12:49:41 +02:00
139 changed files with 3174 additions and 2915 deletions
@@ -1,8 +1,4 @@
-* [Core] Added net7.0 builds (#1635, thanks to @YAJeff).
-* [Client] Added support for passing MQTT v5 options (User properties etc.) for disconnects.
-* [Client] An internal exception is no longer caught silently when calling _DisconnectAsync_ to indicate that the disconnect is not clean (BREAKING CHANGE).
-* [Client] MQTTv5 features are now checked and an exception is thrown if they are used when using protocol version 3.1.1 and lower. These checks can be disabled in client options. (BREAKING CHANGE!).
-* [Server] Exposed MQTT v5 sent properties from the affected client in _ClientDisconnectedAsync_ event.
-* [Server] Fixed wrong client ID passed to _InterceptingUnsubscriptionEventArgs_ (#1631, thanks to @ghord). 
-* [Server] Exposed socket settings for TCP keep alive in TCP options (#1544).
-* [Server] Exposed server session items at server level and allow custom session items for injected application messages (#1638).
+* [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).
@@ -3,7 +3,7 @@ name: CI
 on: [push, pull_request]

 env:
-  VERSION: "4.2.0.${{github.run_number}}"
+  VERSION: "4.2.1.${{github.run_number}}"

 jobs:
  build:
@@ -1,67 +1,4 @@
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 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpCodeStyle/BRACES_FOR_FOR/@EntryValue">Required</s:String>
 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpCodeStyle/BRACES_FOR_FOREACH/@EntryValue">Required</s:String>
 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpCodeStyle/BRACES_FOR_IFELSE/@EntryValue">Required</s:String>
@@ -71,28 +8,23 @@
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/KEEP_EXISTING_INITIALIZER_ARRANGEMENT/@EntryValue">False</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/KEEP_EXISTING_INVOCATION_PARENS_ARRANGEMENT/@EntryValue">False</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/KEEP_EXISTING_PROPERTY_PATTERNS_ARRANGEMENT/@EntryValue">False</s:Boolean>
-	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/KEEP_EXISTING_SWITCH_EXPRESSION_ARRANGEMENT/@EntryValue">False</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/KEEP_USER_LINEBREAKS/@EntryValue">False</s:Boolean>
 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/PLACE_ACCESSORHOLDER_ATTRIBUTE_ON_SAME_LINE_EX/@EntryValue">NEVER</s:String>
-	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/PLACE_SIMPLE_ACCESSOR_ON_SINGLE_LINE/@EntryValue">False</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/PLACE_SIMPLE_ANONYMOUSMETHOD_ON_SINGLE_LINE/@EntryValue">False</s:Boolean>
 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/PLACE_SIMPLE_EMBEDDED_STATEMENT_ON_SAME_LINE/@EntryValue">NEVER</s:String>
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/PLACE_SIMPLE_INITIALIZER_ON_SINGLE_LINE/@EntryValue">False</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/PLACE_SIMPLE_PROPERTY_PATTERN_ON_SINGLE_LINE/@EntryValue">False</s:Boolean>
-	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/PLACE_WHILE_ON_NEW_LINE/@EntryValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/SPACE_WITHIN_METHOD_CALL_PARENTHESES/@EntryValue">False</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/SPACE_WITHIN_METHOD_PARENTHESES/@EntryValue">False</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/SPACE_WITHIN_PARENTHESES/@EntryValue">False</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/WRAP_AFTER_DECLARATION_LPAR/@EntryValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/WRAP_AFTER_INVOCATION_LPAR/@EntryValue">True</s:Boolean>
 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/WRAP_ARGUMENTS_STYLE/@EntryValue">CHOP_IF_LONG</s:String>
-	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/WRAP_ARRAY_INITIALIZER_STYLE/@EntryValue">CHOP_ALWAYS</s:String>
+	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/WRAP_ARRAY_INITIALIZER_STYLE/@EntryValue">CHOP_IF_LONG</s:String>
 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/WRAP_CHAINED_METHOD_CALLS/@EntryValue">CHOP_IF_LONG</s:String>
 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/WRAP_EXTENDS_LIST_STYLE/@EntryValue">CHOP_IF_LONG</s:String>
 	<s:Int64 x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/WRAP_LIMIT/@EntryValue">180</s:Int64>
-	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/WRAP_OBJECT_AND_COLLECTION_INITIALIZER_STYLE/@EntryValue">CHOP_ALWAYS</s:String>
 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/WRAP_PARAMETERS_STYLE/@EntryValue">CHOP_IF_LONG</s:String>
-	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/WRAP_PROPERTY_PATTERN/@EntryValue">CHOP_ALWAYS</s:String>
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/XmlDocFormatter/KeepUserLineBreaks/@EntryValue">True</s:Boolean>
 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/XmlDocFormatter/ProcessingInstructionAttributesFormat/@EntryValue">OnDifferentLines</s:String>
 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/XmlDocFormatter/TagAttributesFormat/@EntryValue">OnDifferentLines</s:String>
@@ -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.
@@ -70,6 +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()
    {
@@ -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)
        {
@@ -44,9 +44,9 @@ public sealed class Managed_Client_Simple_Samples
            Console.WriteLine("The managed MQTT client is connected.");
            
            // Wait until the queue is fully processed.
-            SpinWait.SpinUntil(() => managedMqttClient.EnqueuedApplicationMessagesCount == 0, 10000);
+            SpinWait.SpinUntil(() => managedMqttClient.PendingApplicationMessagesCount == 0, 10000);
            
-            Console.WriteLine($"Pending messages = {managedMqttClient.EnqueuedApplicationMessagesCount}");
+            Console.WriteLine($"Pending messages = {managedMqttClient.PendingApplicationMessagesCount}");
        }
    }
 }
@@ -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
@@ -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()
    {
@@ -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;
+            }
+        }
+    }
+}
@@ -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);
@@ -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);

@@ -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;
        }
    }
 }
@@ -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)
@@ -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);
            }
@@ -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++)
            {
@@ -15,12 +15,10 @@ namespace MQTTnet.Extensions.ManagedClient
        }

        public ManagedMqttApplicationMessage ApplicationMessage { get; }
-
+        
        /// <summary>
-        ///     Gets or sets the exception which was thrown while sending the message.
+        /// Then this is _null_ the message was processed successfully without any error.
        /// </summary>
        public Exception Exception { get; }
-
-        public bool HasFailed => Exception != null;
    }
-}
+}
@@ -6,13 +6,13 @@ using System;

 namespace MQTTnet.Extensions.ManagedClient
 {
-    public sealed class ApplicationMessageDroppedEventArgs : EventArgs
+    public sealed class ApplicationMessageSkippedEventArgs : EventArgs
    {
-        public ApplicationMessageDroppedEventArgs(ManagedMqttApplicationMessage applicationMessage)
+        public ApplicationMessageSkippedEventArgs(ManagedMqttApplicationMessage applicationMessage)
        {
            ApplicationMessage = applicationMessage ?? throw new ArgumentNullException(nameof(applicationMessage));
        }

        public ManagedMqttApplicationMessage ApplicationMessage { get; }
    }
-}
+}
@@ -1,7 +1,3 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
 using System;
 using MQTTnet.Client;

@@ -16,7 +12,7 @@ namespace MQTTnet.Extensions.ManagedClient
        }

        /// <summary>
-        ///     This is null when the server was not reachable and thus no MQTT response was transmitted.
+        /// This is null when the connection was failing and the server was not reachable.
        /// </summary>
        public MqttClientConnectResult ConnectResult { get; }

@@ -1,56 +1,52 @@
-// 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;
+using MQTTnet.Packets;

 namespace MQTTnet.Extensions.ManagedClient
 {
    public interface IManagedMqttClient : IDisposable
    {
-        event Func<ApplicationMessageDroppedEventArgs, Task> ApplicationMessageDroppedAsync;
-
-        event Func<EventArgs, Task> ApplicationMessageEnqueueingAsync;
-
        event Func<ApplicationMessageProcessedEventArgs, Task> ApplicationMessageProcessedAsync;
-
+        
        event Func<MqttApplicationMessageReceivedEventArgs, Task> ApplicationMessageReceivedAsync;
-
+        
+        event Func<ApplicationMessageSkippedEventArgs, Task> ApplicationMessageSkippedAsync;
+        
        event Func<MqttClientConnectedEventArgs, Task> ConnectedAsync;
-
+        
        event Func<ConnectingFailedEventArgs, Task> ConnectingFailedAsync;
-
+        
+        event Func<EventArgs, Task> ConnectionStateChangedAsync;
+        
        event Func<MqttClientDisconnectedEventArgs, Task> DisconnectedAsync;
-
-        event Func<SubscribeProcessedEventArgs, Task> SubscribeProcessedAsync;
-
-        event Func<UnsubscribeProcessedEventArgs, Task> UnsubscribeProcessedAsync;
-
-        int EnqueuedApplicationMessagesCount { get; }
-
+        
+        event Func<ManagedProcessFailedEventArgs, Task> SynchronizingSubscriptionsFailedAsync;
+        
        IMqttClient InternalClient { get; }
-
+        
        bool IsConnected { get; }
-
+        
        bool IsStarted { get; }
-
+        
        ManagedMqttClientOptions Options { get; }
-
+        
+        int PendingApplicationMessagesCount { get; }
+        
        Task EnqueueAsync(MqttApplicationMessage applicationMessage);
-
+        
        Task EnqueueAsync(ManagedMqttApplicationMessage applicationMessage);
-
+        
        Task PingAsync(CancellationToken cancellationToken = default);
-
+        
        Task StartAsync(ManagedMqttClientOptions options);
-
-        Task StopAsync(MqttClientDisconnectOptions options, CancellationToken cancellationToken);
-
-        Task SubscribeAsync(MqttClientSubscribeOptions options);
-
-        Task UnsubscribeAsync(MqttClientUnsubscribeOptions options);
+        
+        Task StopAsync(bool cleanDisconnect = true);
+        
+        Task SubscribeAsync(ICollection<MqttTopicFilter> topicFilters);
+        
+        Task UnsubscribeAsync(ICollection<string> topics);
    }
 }
@@ -4,8 +4,7 @@
        <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>
-
-        <LangVersion>7.3</LangVersion>
+        
        <AssemblyName>MQTTnet.Extensions.ManagedClient</AssemblyName>
        <RootNamespace>MQTTnet.Extensions.ManagedClient</RootNamespace>
        <GeneratePackageOnBuild>True</GeneratePackageOnBuild>
@@ -1,4 +0,0 @@
-<wpf:ResourceDictionary xml:space="preserve" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:s="clr-namespace:System;assembly=mscorlib" xmlns:ss="urn:shemas-jetbrains-com:settings-storage-xaml" xmlns:wpf="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
-	<s:Boolean x:Key="/Default/CodeInspection/NamespaceProvider/NamespaceFoldersToSkip/=new/@EntryIndexedValue">True</s:Boolean>
-	<s:Boolean x:Key="/Default/CodeInspection/NamespaceProvider/NamespaceFoldersToSkip/=new_005Cevents/@EntryIndexedValue">True</s:Boolean>
-	<s:Boolean x:Key="/Default/CodeInspection/NamespaceProvider/NamespaceFoldersToSkip/=new_005Coptions/@EntryIndexedValue">True</s:Boolean></wpf:ResourceDictionary>
@@ -6,16 +6,10 @@ using System;

 namespace MQTTnet.Extensions.ManagedClient
 {
-    public sealed class ManagedMqttApplicationMessage
+    public class ManagedMqttApplicationMessage
    {
-        public ManagedMqttApplicationMessage(string id, MqttApplicationMessage applicationMessage)
-        {
-            Id = id ?? throw new ArgumentNullException(nameof(id));
-            ApplicationMessage = applicationMessage ?? throw new ArgumentNullException(nameof(applicationMessage));
-        }
-        
-        public string Id { get; }
+        public Guid Id { get; set; } = Guid.NewGuid();

-        public MqttApplicationMessage ApplicationMessage { get; }
+        public MqttApplicationMessage ApplicationMessage { get; set; }
    }
 }
@@ -6,19 +6,15 @@ using System;

 namespace MQTTnet.Extensions.ManagedClient
 {
-    public sealed class ManagedMqttApplicationMessageBuilder
+    public class ManagedMqttApplicationMessageBuilder
    {
-        MqttApplicationMessage _applicationMessage;
-        string _id = Guid.NewGuid().ToString();
+        private Guid _id = Guid.NewGuid();
+        private MqttApplicationMessage _applicationMessage;

-        public ManagedMqttApplicationMessage Build()
+        public ManagedMqttApplicationMessageBuilder WithId(Guid id)
        {
-            if (_applicationMessage == null)
-            {
-                throw new InvalidOperationException("The ApplicationMessage cannot be null.");
-            }
-
-            return new ManagedMqttApplicationMessage(_id, _applicationMessage);
+            _id = id;
+            return this;
        }

        public ManagedMqttApplicationMessageBuilder WithApplicationMessage(MqttApplicationMessage applicationMessage)
@@ -29,10 +25,7 @@ namespace MQTTnet.Extensions.ManagedClient

        public ManagedMqttApplicationMessageBuilder WithApplicationMessage(Action<MqttApplicationMessageBuilder> builder)
        {
-            if (builder == null)
-            {
-                throw new ArgumentNullException(nameof(builder));
-            }
+            if (builder == null) throw new ArgumentNullException(nameof(builder));

            var internalBuilder = new MqttApplicationMessageBuilder();
            builder(internalBuilder);
@@ -41,16 +34,18 @@ namespace MQTTnet.Extensions.ManagedClient
            return this;
        }

-        public ManagedMqttApplicationMessageBuilder WithId(Guid id)
+        public ManagedMqttApplicationMessage Build()
        {
-            _id = id.ToString();
-            return this;
-        }
+            if (_applicationMessage == null)
+            {
+                throw new InvalidOperationException("The ApplicationMessage cannot be null.");
+            }

-        public ManagedMqttApplicationMessageBuilder WithId(string id)
-        {
-            _id = id ?? throw new ArgumentNullException(nameof(id));
-            return this;
+            return new ManagedMqttApplicationMessage
+            {
+                Id = _id,
+                ApplicationMessage = _applicationMessage
+            };
        }
    }
-}
+}
@@ -17,10 +17,10 @@ using MQTTnet.Server;

 namespace MQTTnet.Extensions.ManagedClient
 {
-    public sealed class ManagedMqttClient : Disposable
+    public sealed class ManagedMqttClient : Disposable, IManagedMqttClient
    {
        readonly AsyncEvent<ApplicationMessageProcessedEventArgs> _applicationMessageProcessedEvent = new AsyncEvent<ApplicationMessageProcessedEventArgs>();
-        readonly AsyncEvent<ApplicationMessageDroppedEventArgs> _applicationMessageSkippedEvent = new AsyncEvent<ApplicationMessageDroppedEventArgs>();
+        readonly AsyncEvent<ApplicationMessageSkippedEventArgs> _applicationMessageSkippedEvent = new AsyncEvent<ApplicationMessageSkippedEventArgs>();
        readonly AsyncEvent<ConnectingFailedEventArgs> _connectingFailedEvent = new AsyncEvent<ConnectingFailedEventArgs>();
        readonly AsyncEvent<EventArgs> _connectionStateChangedEvent = new AsyncEvent<EventArgs>();
        readonly AsyncEvent<ManagedProcessFailedEventArgs> _synchronizingSubscriptionsFailedEvent = new AsyncEvent<ManagedProcessFailedEventArgs>();
@@ -76,7 +76,7 @@ namespace MQTTnet.Extensions.ManagedClient
            _logger = logger.WithSource(nameof(ManagedMqttClient));
        }

-        public event Func<ApplicationMessageDroppedEventArgs, Task> ApplicationMessageSkippedAsync
+        public event Func<ApplicationMessageSkippedEventArgs, Task> ApplicationMessageSkippedAsync
        {
            add => _applicationMessageSkippedEvent.AddHandler(value);
            remove => _applicationMessageSkippedEvent.RemoveHandler(value);
@@ -118,18 +118,12 @@ namespace MQTTnet.Extensions.ManagedClient
            remove => InternalClient.DisconnectedAsync -= value;
        }

-        public event Func<SubscribeProcessedEventArgs, Task> SubscribeProcessedAsync;
-        
-        public event Func<UnsubscribeProcessedEventArgs, Task> UnsubscribeProcessedAsync;
-
-        public event Func<ManagedProcessFailedEventArgs, Task> SubscribedAsync
+        public event Func<ManagedProcessFailedEventArgs, Task> SynchronizingSubscriptionsFailedAsync
        {
            add => _synchronizingSubscriptionsFailedEvent.AddHandler(value);
            remove => _synchronizingSubscriptionsFailedEvent.RemoveHandler(value);
        }

-        public event Func<EventArgs, Task> ApplicationMessageEnqueued;
-
        public IMqttClient InternalClient { get; }

        public bool IsConnected => InternalClient.IsConnected;
@@ -170,7 +164,7 @@ namespace MQTTnet.Extensions.ManagedClient
            MqttTopicValidator.ThrowIfInvalid(applicationMessage.ApplicationMessage);

            ManagedMqttApplicationMessage removedMessage = null;
-            ApplicationMessageDroppedEventArgs applicationMessageDroppedEventArgs = null;
+            ApplicationMessageSkippedEventArgs applicationMessageSkippedEventArgs = null;

            try
            {
@@ -181,7 +175,7 @@ namespace MQTTnet.Extensions.ManagedClient
                        if (Options.PendingMessagesOverflowStrategy == MqttPendingMessagesOverflowStrategy.DropNewMessage)
                        {
                            _logger.Verbose("Skipping publish of new application message because internal queue is full.");
-                            applicationMessageDroppedEventArgs = new ApplicationMessageDroppedEventArgs(applicationMessage);
+                            applicationMessageSkippedEventArgs = new ApplicationMessageSkippedEventArgs(applicationMessage);
                            return;
                        }

@@ -189,7 +183,7 @@ namespace MQTTnet.Extensions.ManagedClient
                        {
                            removedMessage = _messageQueue.RemoveFirst();
                            _logger.Verbose("Removed oldest application message from internal queue because it is full.");
-                            applicationMessageDroppedEventArgs = new ApplicationMessageDroppedEventArgs(removedMessage);
+                            applicationMessageSkippedEventArgs = new ApplicationMessageSkippedEventArgs(removedMessage);
                        }
                    }

@@ -208,9 +202,9 @@ namespace MQTTnet.Extensions.ManagedClient
            }
            finally
            {
-                if (applicationMessageDroppedEventArgs != null && _applicationMessageSkippedEvent.HasHandlers)
+                if (applicationMessageSkippedEventArgs != null && _applicationMessageSkippedEvent.HasHandlers)
                {
-                    await _applicationMessageSkippedEvent.InvokeAsync(applicationMessageDroppedEventArgs).ConfigureAwait(false);
+                    await _applicationMessageSkippedEvent.InvokeAsync(applicationMessageSkippedEventArgs).ConfigureAwait(false);
                }
            }
        }
@@ -359,13 +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);
            }
        }

@@ -463,11 +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)
                    {
@@ -485,7 +481,7 @@ namespace MQTTnet.Extensions.ManagedClient
            }
            catch (Exception exception)
            {
-                await HandleSubscriptionExceptionAsync(exception).ConfigureAwait(false);
+                await HandleSubscriptionExceptionAsync(exception, topicFilters, null).ConfigureAwait(false);
            }
        }

@@ -597,6 +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())
@@ -613,7 +612,7 @@ namespace MQTTnet.Extensions.ManagedClient
            }
            catch (Exception exception)
            {
-                await HandleSubscriptionExceptionAsync(exception).ConfigureAwait(false);
+                await HandleSubscriptionExceptionAsync(exception, addedSubscriptions, removedSubscriptions).ConfigureAwait(false);
            }
        }

@@ -3,9 +3,8 @@
 // See the LICENSE file in the project root for more information.

 using System;
-using System.Threading;
+using System.Collections.Generic;
 using System.Threading.Tasks;
-using MQTTnet.Client;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;

@@ -39,35 +38,6 @@ namespace MQTTnet.Extensions.ManagedClient
            return managedMqttClient.EnqueueAsync(applicationMessage);
        }

-        public static Task StopAsync(this IManagedMqttClient managedMqttClient, bool isClean = true, CancellationToken cancellationToken = default)
-        {
-            if (managedMqttClient == null)
-            {
-                throw new ArgumentNullException(nameof(managedMqttClient));
-            }
-
-            return managedMqttClient.StopAsync(new MqttClientDisconnectOptions
-            {
-                IsClean = isClean
-            }, cancellationToken);
-        }
-        
-        public static Task SubscribeAsync(this IManagedMqttClient managedMqttClient, MqttTopicFilter topicFilter)
-        {
-            if (managedMqttClient == null)
-            {
-                throw new ArgumentNullException(nameof(managedMqttClient));
-            }
-
-            if (topicFilter == null)
-            {
-                throw new ArgumentNullException(nameof(topicFilter));
-            }
-
-            var subscribeOptions = new MqttClientSubscribeOptionsBuilder().WithTopicFilter(topicFilter).Build();
-            return managedMqttClient.SubscribeAsync(subscribeOptions);
-        }
-
        public static Task SubscribeAsync(
            this IManagedMqttClient managedMqttClient,
            string topic,
@@ -83,8 +53,11 @@ namespace MQTTnet.Extensions.ManagedClient
                throw new ArgumentNullException(nameof(topic));
            }

-            var subscribeOptions = new MqttClientSubscribeOptionsBuilder().WithTopicFilter(topic, qualityOfServiceLevel).Build();
-            return managedMqttClient.SubscribeAsync(subscribeOptions);
+            return managedMqttClient.SubscribeAsync(
+                new List<MqttTopicFilter>
+                {
+                    new MqttTopicFilterBuilder().WithTopic(topic).WithQualityOfServiceLevel(qualityOfServiceLevel).Build()
+                });
        }

        public static Task UnsubscribeAsync(this IManagedMqttClient managedMqttClient, string topic)
@@ -99,8 +72,7 @@ namespace MQTTnet.Extensions.ManagedClient
                throw new ArgumentNullException(nameof(topic));
            }

-            var unsubscribeOptions = new MqttClientUnsubscribeOptionsBuilder().WithTopicFilter(topic).Build();
-            return managedMqttClient.UnsubscribeAsync(unsubscribeOptions);
+            return managedMqttClient.UnsubscribeAsync(new List<string> { topic });
        }
    }
 }
@@ -10,15 +10,6 @@ namespace MQTTnet.Extensions.ManagedClient
 {
    public sealed class ManagedMqttClientOptions
    {
-        public ManagedMqttClientOptions()
-        {
-        }
-
-        public ManagedMqttClientOptions(MqttClientOptions clientOptions)
-        {
-            ClientOptions = clientOptions;
-        }
-        
        public MqttClientOptions ClientOptions { get; set; }

        public TimeSpan AutoReconnectDelay { get; set; } = TimeSpan.FromSeconds(5);
@@ -33,7 +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;
    }
@@ -8,7 +8,7 @@ using MQTTnet.Server;

 namespace MQTTnet.Extensions.ManagedClient
 {
-    public sealed class ManagedMqttClientOptionsBuilder
+    public class ManagedMqttClientOptionsBuilder
    {
        readonly ManagedMqttClientOptions _options = new ManagedMqttClientOptions();
        MqttClientOptionsBuilder _clientOptionsBuilder;
@@ -0,0 +1,34 @@
+// 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.Packets;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace MQTTnet.Extensions.ManagedClient
+{
+    public class ManagedProcessFailedEventArgs : EventArgs
+    {
+        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; }
+    }
+}
@@ -10,21 +10,6 @@ namespace MQTTnet.Extensions.ManagedClient
 {
    public static class MqttFactoryExtensions
    {
-        public static IManagedMqttClient CreateManagedMqttClient(this MqttFactory factory, IMqttClient mqttClient, IMqttNetLogger logger)
-        {
-            if (factory == null)
-            {
-                throw new ArgumentNullException(nameof(factory));
-            }
-
-            if (mqttClient == null)
-            {
-                return new NewManagedMqttClient(factory.CreateMqttClient(), logger);
-            }
-
-            return new NewManagedMqttClient(mqttClient, logger);
-        }
-
        public static IManagedMqttClient CreateManagedMqttClient(this MqttFactory factory, IMqttClient mqttClient = null)
        {
            if (factory == null)
@@ -34,10 +19,10 @@ namespace MQTTnet.Extensions.ManagedClient

            if (mqttClient == null)
            {
-                return new NewManagedMqttClient(factory.CreateMqttClient(), factory.DefaultLogger);
+                return new ManagedMqttClient(factory.CreateMqttClient(), factory.DefaultLogger);
            }

-            return new NewManagedMqttClient(mqttClient, factory.DefaultLogger);
+            return new ManagedMqttClient(mqttClient, factory.DefaultLogger);
        }

        public static IManagedMqttClient CreateManagedMqttClient(this MqttFactory factory, IMqttNetLogger logger)
@@ -52,10 +37,10 @@ namespace MQTTnet.Extensions.ManagedClient
                throw new ArgumentNullException(nameof(logger));
            }

-            return new NewManagedMqttClient(factory.CreateMqttClient(logger), logger);
+            return new ManagedMqttClient(factory.CreateMqttClient(logger), logger);
        }

-        public static ManagedMqttClientOptionsBuilder CreateManagedMqttClientOptionsBuilder(this MqttFactory factory)
+        public static ManagedMqttClientOptionsBuilder CreateManagedMqttClientOptionsBuilder(this MqttFactory _)
        {
            return new ManagedMqttClientOptionsBuilder();
        }
@@ -1,95 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Collections.Generic;
-using System.Threading.Tasks;
-using MQTTnet.Client;
-using MQTTnet.Diagnostics;
-using MQTTnet.Internal;
-
-namespace MQTTnet.Extensions.ManagedClient
-{
-    public sealed class ApplicationMessagesManager
-    {
-        readonly MqttNetSourceLogger _logger;
-
-        readonly Queue<ManagedMqttApplicationMessage> _messageQueue = new Queue<ManagedMqttApplicationMessage>();
-        readonly IMqttClient _mqttClient;
-
-        public ApplicationMessagesManager(IMqttClient mqttClient, IMqttNetLogger logger)
-        {
-            _mqttClient = mqttClient ?? throw new ArgumentNullException(nameof(mqttClient));
-
-            if (logger == null)
-            {
-                throw new ArgumentNullException(nameof(logger));
-            }
-
-            _logger = logger.WithSource<ApplicationMessagesManager>();
-        }
-
-        public AsyncEvent<ApplicationMessageDroppedEventArgs> ApplicationMessageDroppedEvent { get; } = new AsyncEvent<ApplicationMessageDroppedEventArgs>();
-
-        public AsyncEvent<ApplicationMessageEnqueueingEventArgs> ApplicationMessageEnqueueingEvent { get; } = new AsyncEvent<ApplicationMessageEnqueueingEventArgs>();
-
-        public int EnqueuedApplicationMessagesCount
-        {
-            get
-            {
-                lock (_messageQueue)
-                {
-                    return _messageQueue.Count;
-                }
-            }
-        }
-
-        public void Dequeue()
-        {
-            lock (_messageQueue)
-            {
-                _messageQueue.Dequeue();
-            }
-        }
-
-        public async Task Enqueue(ManagedMqttApplicationMessage applicationMessage)
-        {
-            if (applicationMessage == null)
-            {
-                throw new ArgumentNullException(nameof(applicationMessage));
-            }
-
-            // Fire the event first so that the handler can make sure that this message is 
-            // properly backed up in a suitable storage.
-            if (ApplicationMessageEnqueueingEvent.HasHandlers)
-            {
-                var eventArgs = new ApplicationMessageEnqueueingEventArgs(applicationMessage, 0);
-                await ApplicationMessageEnqueueingEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
-            }
-
-            lock (_messageQueue)
-            {
-                
-                // TODO: Drop if too much!
-                
-                _messageQueue.Enqueue(applicationMessage);
-            }
-        }
-
-        public bool TryPeek(out ManagedMqttApplicationMessage applicationMessage)
-        {
-            lock (_messageQueue)
-            {
-                if (_messageQueue.Count == 0)
-                {
-                    applicationMessage = null;
-                    return false;
-                }
-
-                applicationMessage = _messageQueue.Peek();
-                return true;
-            }
-        }
-    }
-}
@@ -1,21 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-
-namespace MQTTnet.Extensions.ManagedClient
-{
-    public sealed class ApplicationMessageEnqueueingEventArgs : EventArgs
-    {
-        public ApplicationMessageEnqueueingEventArgs(ManagedMqttApplicationMessage applicationMessage, ushort packetIdentifier)
-        {
-            ApplicationMessage = applicationMessage ?? throw new ArgumentNullException(nameof(applicationMessage));
-            PacketIdentifier = packetIdentifier;
-        }
-
-        public ManagedMqttApplicationMessage ApplicationMessage { get; }
-
-        public ushort PacketIdentifier { get; }
-    }
-}
@@ -1,18 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-
-namespace MQTTnet.Extensions.ManagedClient
-{
-    public class ManagedProcessFailedEventArgs : EventArgs
-    {
-        public ManagedProcessFailedEventArgs(Exception exception)
-        {
-            Exception = exception ?? throw new ArgumentNullException(nameof(exception));
-        }
-
-        public Exception Exception { get; }
-    }
-}
@@ -1,27 +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.Client;
-using MQTTnet.Packets;
-
-namespace MQTTnet.Extensions.ManagedClient
-{
-    public sealed class SubscribeProcessedEventArgs : EventArgs
-    {
-        public SubscribeProcessedEventArgs(MqttClientSubscribeOptions options, MqttClientSubscribeResultCode result, IReadOnlyCollection<MqttUserProperty> userProperties)
-        {
-            Options = options ?? throw new ArgumentNullException(nameof(options));
-            Result = result;
-            UserProperties = userProperties;
-        }
-
-        public MqttClientSubscribeOptions Options { get; }
-
-        public MqttClientSubscribeResultCode Result { get; }
-
-        public IReadOnlyCollection<MqttUserProperty> UserProperties { get; }
-    }
-}
@@ -1,27 +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.Client;
-using MQTTnet.Packets;
-
-namespace MQTTnet.Extensions.ManagedClient
-{
-    public sealed class UnsubscribeProcessedEventArgs : EventArgs
-    {
-        public UnsubscribeProcessedEventArgs(MqttClientUnsubscribeOptions options, MqttClientUnsubscribeResultCode result, IReadOnlyCollection<MqttUserProperty> userProperties)
-        {
-            Options = options ?? throw new ArgumentNullException(nameof(options));
-            Result = result;
-            UserProperties = userProperties;
-        }
-
-        public MqttClientUnsubscribeOptions Options { get; }
-
-        public MqttClientUnsubscribeResultCode Result { get; }
-
-        public IReadOnlyCollection<MqttUserProperty> UserProperties { get; }
-    }
-}
@@ -1,35 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Linq;
-using MQTTnet.Client;
-
-namespace MQTTnet.Extensions.ManagedClient
-{
-    public sealed class ManagedMqttSubscription
-    {
-        public ManagedMqttSubscription(MqttClientSubscribeOptions subscribeOptions)
-        {
-            SubscribeOptions = subscribeOptions ?? throw new ArgumentNullException(nameof(subscribeOptions));
-
-            Topic = subscribeOptions.TopicFilters.First().Topic;
-        }
-
-        public bool IsObsolete => UnsubscribeOptions != null;
-
-        public bool IsPending { get; set; } = true;
-
-        public MqttClientSubscribeOptions SubscribeOptions { get; }
-
-        public string Topic { get; }
-
-        public MqttClientUnsubscribeOptions UnsubscribeOptions { get; private set; }
-
-        public void MarkAsUnsubscribed(MqttClientUnsubscribeOptions options)
-        {
-            UnsubscribeOptions = options ?? throw new ArgumentNullException(nameof(options));
-        }
-    }
-}
@@ -1,155 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Threading;
-using System.Threading.Tasks;
-using MQTTnet.Client;
-using MQTTnet.Diagnostics;
-using MQTTnet.Internal;
-using MQTTnet.Protocol;
-
-namespace MQTTnet.Extensions.ManagedClient
-{
-    public sealed class ManagedMqttSubscriptionsManager
-    {
-        readonly MqttNetSourceLogger _logger;
-        readonly IMqttClient _mqttClient;
-        
-        // Do not use a dictionary in order to preserve subscription ordering (retained messages).
-        readonly List<ManagedMqttSubscription> _subscriptions = new List<ManagedMqttSubscription>();
-
-        public ManagedMqttSubscriptionsManager(IMqttClient mqttClient, IMqttNetLogger logger)
-        {
-            _mqttClient = mqttClient ?? throw new ArgumentNullException(nameof(mqttClient));
-
-            if (logger == null)
-            {
-                throw new ArgumentNullException(nameof(logger));
-            }
-
-            _logger = logger.WithSource<ManagedMqttSubscriptionsManager>();
-        }
-
-        public AsyncEvent<SubscribeProcessedEventArgs> SubscribeProcessedEvent { get; } = new AsyncEvent<SubscribeProcessedEventArgs>();
-
-        public AsyncEvent<UnsubscribeProcessedEventArgs> UnsubscribeProcessedEvent { get; } = new AsyncEvent<UnsubscribeProcessedEventArgs>();
-
-        public void ResubscribeAll()
-        {
-            lock (_subscriptions)
-            {
-                foreach (var subscription in _subscriptions)
-                {
-                    subscription.IsPending = true;
-                }
-            }
-        }
-
-        public void Subscribe(MqttClientSubscribeOptions options)
-        {
-            if (options == null)
-            {
-                throw new ArgumentNullException(nameof(options));
-            }
-
-            if (options.TopicFilters.Count > 1)
-            {
-                throw new NotSupportedException("The managed client only supports subscribing to one topic at the same time.");
-            }
-
-            var topic = options.TopicFilters.First().Topic;
-            
-            lock (_subscriptions)
-            {
-                MqttTopicValidator.ThrowIfInvalidSubscribe(topic);
-
-                _subscriptions.RemoveAll(s => s.Topic.Equals(topic));
-                _subscriptions.Add(new ManagedMqttSubscription(options));
-            }
-        }
-
-        public async Task Synchronize(CancellationToken cancellationToken)
-        {
-            // TODO: Remember real changes.
-
-            List<ManagedMqttSubscription> pendingSubscriptions;
-            List<ManagedMqttSubscription> obsoleteSubscriptions;
-            lock (_subscriptions)
-            {
-                pendingSubscriptions = _subscriptions.Where(s => s.IsPending).ToList();
-                obsoleteSubscriptions = _subscriptions.Where(s => s.IsObsolete).ToList();
-            }
-
-            if (pendingSubscriptions.Count == 0 && obsoleteSubscriptions.Count == 0)
-            {
-                _logger.Verbose("No subscriptions to synchronize");
-                return;
-            }
-
-            foreach (var subscription in pendingSubscriptions)
-            {
-                var subscribeResult = await _mqttClient.SubscribeAsync(subscription.SubscribeOptions, cancellationToken).ConfigureAwait(false);
-                subscription.IsPending = false;
-                await FireSubscribeProcessedEvent(subscription, subscribeResult).ConfigureAwait(false);
-            }
-
-            foreach (var subscription in obsoleteSubscriptions)
-            {
-                var unsubscribeResult = await _mqttClient.UnsubscribeAsync(subscription.UnsubscribeOptions, cancellationToken).ConfigureAwait(false);
-                lock (_subscriptions)
-                {
-                    _subscriptions.Remove(subscription);
-                }
-
-                await FireUnsubscribeProcessedEvent(subscription, unsubscribeResult).ConfigureAwait(false);
-            }
-        }
-
-        public void Unsubscribe(MqttClientUnsubscribeOptions options)
-        {
-            if (options == null)
-            {
-                throw new ArgumentNullException(nameof(options));
-            }
-
-            lock (_subscriptions)
-            {
-                var topic = options.TopicFilters.First();
-                var existingSubscription = _subscriptions.FirstOrDefault(s => s.Topic.Equals(topic));
-
-                if (existingSubscription != null)
-                {
-                    existingSubscription.MarkAsUnsubscribed(options);
-                }
-            }
-        }
-
-        async Task FireSubscribeProcessedEvent(ManagedMqttSubscription subscription, MqttClientSubscribeResult subscribeResult)
-        {
-            _logger.Info("Subscribed topic '{0}'.", subscription.Topic);
-
-            if (SubscribeProcessedEvent.HasHandlers)
-            {
-                var resultCode = subscribeResult?.Items.First().ResultCode ?? MqttClientSubscribeResultCode.UnspecifiedError;
-                var eventArgs = new SubscribeProcessedEventArgs(subscription.SubscribeOptions, resultCode, subscribeResult?.UserProperties);
-                await SubscribeProcessedEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
-            }
-        }
-
-        async Task FireUnsubscribeProcessedEvent(ManagedMqttSubscription subscription, MqttClientUnsubscribeResult unsubscribeResult)
-        {
-            _logger.Info("Unsubscribed topic '{0}'.", subscription.Topic);
-
-            if (UnsubscribeProcessedEvent.HasHandlers)
-            {
-                var resultCode = unsubscribeResult?.Items.First().ResultCode ?? MqttClientUnsubscribeResultCode.UnspecifiedError;
-                var eventArgs = new UnsubscribeProcessedEventArgs(subscription.UnsubscribeOptions, resultCode, unsubscribeResult?.UserProperties);
-                await UnsubscribeProcessedEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
-            }
-        }
-    }
-}
@@ -1,103 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Threading;
-using System.Threading.Tasks;
-using MQTTnet.Client;
-using MQTTnet.Diagnostics;
-using MQTTnet.Internal;
-
-namespace MQTTnet.Extensions.ManagedClient
-{
-    public sealed class MqttConnectionManager
-    {
-        readonly MqttNetSourceLogger _logger;
-        readonly IMqttClient _mqttClient;
-
-        bool _wasConnected;
-
-        public MqttConnectionManager(IMqttClient mqttClient, IMqttNetLogger logger)
-        {
-            _mqttClient = mqttClient ?? throw new ArgumentNullException(nameof(mqttClient));
-
-            if (logger == null)
-            {
-                throw new ArgumentNullException(nameof(logger));
-            }
-
-            _logger = logger.WithSource<MqttConnectionManager>();
-
-            _mqttClient.DisconnectedAsync += OnClientDisconnected;
-        }
-
-        public AsyncEvent<MqttClientConnectedEventArgs> ConnectedEvent { get; } = new AsyncEvent<MqttClientConnectedEventArgs>();
-
-        public AsyncEvent<ConnectingFailedEventArgs> ConnectingFailedEvent { get; } = new AsyncEvent<ConnectingFailedEventArgs>();
-
-        public AsyncEvent<MqttClientDisconnectedEventArgs> DisconnectedEvent { get; } = new AsyncEvent<MqttClientDisconnectedEventArgs>();
-
-        public async Task<MaintainConnectionResult> MaintainConnection(ManagedMqttClientOptions options, CancellationToken cancellationToken)
-        {
-            cancellationToken.ThrowIfCancellationRequested();
-            
-            if (_wasConnected)
-            {
-                try
-                {
-                    // The only valid way for testing the connection is to send a PING. So we start with this
-                    // in order to check if reconnecting etc. is require or not.
-                    await _mqttClient.PingAsync(cancellationToken).ConfigureAwait(false);
-
-                    // The client is properly connection. No further action required.
-                    return MaintainConnectionResult.NoChange;
-                }
-                catch (Exception exception)
-                {
-                    _logger.Error(exception, "Error while checking connection.");
-                }
-            }
-
-            MqttClientConnectResult connectResult = null;
-            try
-            {
-                // The PING was not successful so that there is no working connection. So we connect.
-                connectResult = await _mqttClient.ConnectAsync(options.ClientOptions, cancellationToken).ConfigureAwait(false);
-
-                _wasConnected = true;
-                _logger.Info("Connected.");
-
-                if (ConnectedEvent.HasHandlers)
-                {
-                    var eventArgs = new MqttClientConnectedEventArgs(connectResult);
-                    await ConnectedEvent.TryInvokeAsync(eventArgs, _logger).ConfigureAwait(false);
-                }
-
-                return MaintainConnectionResult.ConnectedEstablished;
-            }
-            catch (Exception exception)
-            {
-                if (!(exception is OperationCanceledException))
-                {
-                    _logger.Error(exception, "Error while connecting.");
-                }
-
-                if (ConnectingFailedEvent.HasHandlers)
-                {
-                    var eventArgs = new ConnectingFailedEventArgs(connectResult, exception);
-                    await ConnectingFailedEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
-                }
-            }
-
-            _wasConnected = false;
-            return MaintainConnectionResult.NotConnected;
-        }
-
-        Task OnClientDisconnected(MqttClientDisconnectedEventArgs arg)
-        {
-            _wasConnected = false;
-            return DisconnectedEvent?.InvokeAsync(arg);
-        }
-    }
-}
@@ -1,309 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Threading;
-using System.Threading.Tasks;
-using MQTTnet.Client;
-using MQTTnet.Diagnostics;
-using MQTTnet.Internal;
-
-namespace MQTTnet.Extensions.ManagedClient
-{
-    public sealed class NewManagedMqttClient : Disposable, IManagedMqttClient
-    {
-        readonly AsyncEvent<ApplicationMessageProcessedEventArgs> _applicationMessageProcessedEvent = new AsyncEvent<ApplicationMessageProcessedEventArgs>();
-        readonly ApplicationMessagesManager _applicationMessagesManager;
-        readonly MqttConnectionManager _connectionManager;
-        readonly AsyncEvent<EventArgs> _isConnectedChangedEvent = new AsyncEvent<EventArgs>();
-        readonly MqttNetSourceLogger _logger;
-        readonly ManagedMqttSubscriptionsManager _subscriptionsManager;
-
-        readonly ManualResetEventSlim _workSignal = new ManualResetEventSlim();
-
-        CancellationTokenSource _workerCancellationToken;
-        Task _workerTask;
-
-        public NewManagedMqttClient(IMqttClient mqttClient, IMqttNetLogger logger)
-        {
-            InternalClient = mqttClient ?? throw new ArgumentNullException(nameof(mqttClient));
-
-            if (logger == null)
-            {
-                throw new ArgumentNullException(nameof(logger));
-            }
-
-            InternalClient.DisconnectedAsync += OnInternalClientDisconnected;
-
-            _logger = logger.WithSource(nameof(NewManagedMqttClient));
-
-            _connectionManager = new MqttConnectionManager(mqttClient, logger);
-            _subscriptionsManager = new ManagedMqttSubscriptionsManager(mqttClient, logger);
-            _applicationMessagesManager = new ApplicationMessagesManager(mqttClient, logger);
-
-            // TODO: Start timer for periodical connection checking.
-        }
-
-        public event Func<EventArgs, Task> ApplicationMessageEnqueueingAsync
-        {
-            add => _applicationMessagesManager.ApplicationMessageEnqueueingEvent.AddHandler(value);
-            remove => _applicationMessagesManager.ApplicationMessageEnqueueingEvent.RemoveHandler(value);
-        }
-
-        public event Func<ApplicationMessageProcessedEventArgs, Task> ApplicationMessageProcessedAsync
-        {
-            add => _applicationMessageProcessedEvent.AddHandler(value);
-            remove => _applicationMessageProcessedEvent.RemoveHandler(value);
-        }
-
-        public event Func<MqttApplicationMessageReceivedEventArgs, Task> ApplicationMessageReceivedAsync
-        {
-            add => InternalClient.ApplicationMessageReceivedAsync += value;
-            remove => InternalClient.ApplicationMessageReceivedAsync += value;
-        }
-
-        public event Func<ApplicationMessageDroppedEventArgs, Task> ApplicationMessageDroppedAsync
-        {
-            add => _applicationMessagesManager.ApplicationMessageDroppedEvent.AddHandler(value);
-            remove => _applicationMessagesManager.ApplicationMessageDroppedEvent.RemoveHandler(value);
-        }
-
-        public event Func<MqttClientConnectedEventArgs, Task> ConnectedAsync
-        {
-            add => _connectionManager.ConnectedEvent.AddHandler(value);
-            remove => _connectionManager.ConnectedEvent.RemoveHandler(value);
-        }
-
-        public event Func<ConnectingFailedEventArgs, Task> ConnectingFailedAsync
-        {
-            add => _connectionManager.ConnectingFailedEvent.AddHandler(value);
-            remove => _connectionManager.ConnectingFailedEvent.RemoveHandler(value);
-        }
-
-        public event Func<MqttClientDisconnectedEventArgs, Task> DisconnectedAsync
-        {
-            add => _connectionManager.DisconnectedEvent.AddHandler(value);
-            remove => _connectionManager.DisconnectedEvent.RemoveHandler(value);
-        }
-
-        public event Func<SubscribeProcessedEventArgs, Task> SubscribeProcessedAsync
-        {
-            add => _subscriptionsManager.SubscribeProcessedEvent.AddHandler(value);
-            remove => _subscriptionsManager.SubscribeProcessedEvent.RemoveHandler(value);
-        }
-
-        public event Func<UnsubscribeProcessedEventArgs, Task> UnsubscribeProcessedAsync
-        {
-            add => _subscriptionsManager.UnsubscribeProcessedEvent.AddHandler(value);
-            remove => _subscriptionsManager.UnsubscribeProcessedEvent.RemoveHandler(value);
-        }
-
-        public IMqttClient InternalClient { get; }
-
-        public bool IsConnected { get; private set; }
-
-        public bool IsStarted { get; private set; }
-
-        public ManagedMqttClientOptions Options { get; private set; }
-
-        public int EnqueuedApplicationMessagesCount => _applicationMessagesManager.EnqueuedApplicationMessagesCount;
-
-        public Task EnqueueAsync(MqttApplicationMessage applicationMessage)
-        {
-            return EnqueueAsync(new ManagedMqttApplicationMessage(Guid.NewGuid().ToString(), applicationMessage));
-        }
-
-        public async Task EnqueueAsync(ManagedMqttApplicationMessage applicationMessage)
-        {
-            if (applicationMessage == null)
-            {
-                throw new ArgumentNullException(nameof(applicationMessage));
-            }
-
-            await _applicationMessagesManager.Enqueue(applicationMessage).ConfigureAwait(false);
-            _workSignal.Set();
-        }
-
-        public Task PingAsync(CancellationToken cancellationToken = default)
-        {
-            return InternalClient.PingAsync(cancellationToken);
-        }
-
-        public Task StartAsync(ManagedMqttClientOptions options)
-        {
-            Options = options ?? throw new ArgumentNullException(nameof(options));
-
-            _workerCancellationToken = new CancellationTokenSource();
-
-            _workerTask = Task.Factory.StartNew(
-                () => WorkerLoop(_workerCancellationToken.Token),
-                _workerCancellationToken.Token,
-                TaskCreationOptions.PreferFairness,
-                TaskScheduler.Default);
-
-            _workSignal.Set();
-
-            return CompletedTask.Instance;
-        }
-
-        public async Task StopAsync(MqttClientDisconnectOptions options, CancellationToken cancellationToken = default)
-        {
-            if (options == null)
-            {
-                throw new ArgumentNullException(nameof(options));
-            }
-
-            // TODO: Send proper Disconnect signal.
-
-            try
-            {
-                await InternalClient.DisconnectAsync(options, cancellationToken).ConfigureAwait(false);
-            }
-            catch (Exception exception)
-            {
-                _logger.Error(exception, "Error while disconnecting.");
-            }
-
-            _workerCancellationToken?.Cancel(false);
-            _workerCancellationToken?.Dispose();
-
-            _workerCancellationToken = null;
-
-            if (_workerTask != null)
-            {
-            }
-        }
-
-        public Task SubscribeAsync(MqttClientSubscribeOptions options)
-        {
-            ThrowIfDisposed();
-
-            _subscriptionsManager.Subscribe(options);
-            _workSignal.Set();
-
-            return CompletedTask.Instance;
-        }
-
-        public Task UnsubscribeAsync(MqttClientUnsubscribeOptions options)
-        {
-            ThrowIfDisposed();
-
-            _subscriptionsManager.Unsubscribe(options);
-            _workSignal.Set();
-
-            return CompletedTask.Instance;
-        }
-
-        protected override void Dispose(bool disposing)
-        {
-            base.Dispose(disposing);
-
-            if (disposing)
-            {
-            }
-        }
-
-        Task OnInternalClientDisconnected(MqttClientDisconnectedEventArgs eventArgs)
-        {
-            _workSignal.Set();
-            return CompletedTask.Instance;
-        }
-
-        async Task UpdateConnectionStatus(MaintainConnectionResult maintainConnectionResult)
-        {
-            var isConnected = maintainConnectionResult != MaintainConnectionResult.NotConnected;
-
-            if (IsConnected.Equals(isConnected))
-            {
-                return;
-            }
-
-            IsConnected = isConnected;
-
-            if (_isConnectedChangedEvent.HasHandlers)
-            {
-                await _isConnectedChangedEvent.InvokeAsync(EventArgs.Empty).ConfigureAwait(false);
-            }
-        }
-
-        async Task WorkerLoop(CancellationToken cancellationToken)
-        {
-            try
-            {
-                IsStarted = true;
-
-                while (!cancellationToken.IsCancellationRequested)
-                {
-                    _workSignal.Wait(cancellationToken);
-                    _workSignal.Reset();
-
-                    var maintainConnectionResult = await _connectionManager.MaintainConnection(Options, cancellationToken).ConfigureAwait(false);
-                    await UpdateConnectionStatus(maintainConnectionResult).ConfigureAwait(false);
-
-                    if (maintainConnectionResult == MaintainConnectionResult.ConnectedEstablished && Options.ClientOptions.CleanSession)
-                    {
-                        // Since the session is clean the server will now know any subscription so that
-                        // we have to subscribe to all of them again.
-                        _subscriptionsManager.ResubscribeAll();
-                    }
-
-                    if (IsConnected)
-                    {
-                        await _subscriptionsManager.Synchronize(cancellationToken).ConfigureAwait(false);
-                    }
-
-                    if (IsConnected)
-                    {
-                        // TODO: Move into pending messages manager + locking.
-                        while (_applicationMessagesManager.TryPeek(out var nextPendingMessage))
-                        {
-                            Exception processingException = null;
-                            try
-                            {
-                                _logger.Verbose("Publishing managed application message {0}.", nextPendingMessage.Id);
-
-                                await InternalClient.PublishAsync(nextPendingMessage.ApplicationMessage, cancellationToken).ConfigureAwait(false);
-
-                                // The message was delivered successfully. So we can get rid of it.
-                                _applicationMessagesManager.Dequeue();
-                            }
-                            catch (Exception exception)
-                            {
-                                processingException = exception;
-                            }
-                            finally
-                            {
-                                if (_applicationMessageProcessedEvent.HasHandlers)
-                                {
-                                    var eventArgs = new ApplicationMessageProcessedEventArgs(nextPendingMessage, processingException);
-                                    await _applicationMessageProcessedEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
-                                }
-                            }
-                        }
-                    }
-                }
-            }
-            catch (OperationCanceledException)
-            {
-            }
-#if !NETSTANDARD1_3
-            catch (ThreadAbortException)
-            {
-            }
-#endif
-            catch (Exception exception)
-            {
-                _logger.Error(exception, "Error while maintaining connection.");
-            }
-            finally
-            {
-                IsStarted = false;
-
-                await UpdateConnectionStatus(MaintainConnectionResult.NotConnected).ConfigureAwait(false);
-            }
-
-            // TODO: Disconnected!
-        }
-    }
-}
@@ -4,6 +4,7 @@

 using System;
 using System.Collections.Concurrent;
+using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Client;
@@ -119,7 +120,6 @@ namespace MQTTnet.Extensions.Rpc
            finally
            {
                _waitingCalls.TryRemove(responseTopic, out _);
-
                await _mqttClient.UnsubscribeAsync(responseTopic, CancellationToken.None).ConfigureAwait(false);
            }
        }
@@ -131,7 +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;
@@ -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:
@@ -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();
@@ -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
                };

@@ -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;
                };

@@ -1,178 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Threading;
-using System.Threading.Tasks;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MQTTnet.Extensions.ManagedClient;
-using MQTTnet.Internal;
-
-namespace MQTTnet.Tests.ManagedMqttClient
-{
-    [TestClass]
-    public sealed class ManagedMqttClient_Event_Tests : BaseTestClass
-    {
-        [TestMethod]
-        public async Task Connecting_Should_Fire_Event()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                await testEnvironment.StartServer();
-
-                var managedClient = testEnvironment.CreateManagedClient();
-
-                var eventFired = false;
-                managedClient.ConnectedAsync += e =>
-                {
-                    eventFired = true;
-                    return CompletedTask.Instance;
-                };
-
-                await managedClient.StartAsync(testEnvironment.CreateDefaultManagedMqttClientOptions());
-
-                await LongTestDelay();
-
-                Assert.IsTrue(eventFired);
-            }
-        }
-
-        [TestMethod]
-        public async Task Connecting_To_Invalid_Server_Should_Fire_Event()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                testEnvironment.IgnoreClientLogErrors = true;
-
-                var managedClient = testEnvironment.CreateManagedMqttClient();
-
-                ConnectingFailedEventArgs connectingFailedEventArgs = null;
-                managedClient.ConnectingFailedAsync += args =>
-                {
-                    connectingFailedEventArgs = args;
-                    return CompletedTask.Instance;
-                };
-
-                await managedClient.StartAsync(
-                    new ManagedMqttClientOptions
-                    {
-                        ClientOptions = testEnvironment.Factory.CreateClientOptionsBuilder().WithTimeout(TimeSpan.FromSeconds(2)).WithTcpServer("wrong_server", 1234).Build()
-                    });
-
-                SpinWait.SpinUntil(() => connectingFailedEventArgs != null, 10000);
-
-                // The wrong server must be reported in general.
-                Assert.IsNotNull(connectingFailedEventArgs);
-                Assert.IsNotNull(connectingFailedEventArgs.Exception);
-                Assert.IsNull(connectingFailedEventArgs.ConnectResult);
-            }
-        }
-
-        [TestMethod]
-        public async Task Disconnect_Should_Fire_Event()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                var server = await testEnvironment.StartServer();
-
-                var managedClient = testEnvironment.CreateManagedClient();
-
-                var eventFired = false;
-                managedClient.DisconnectedAsync += e =>
-                {
-                    eventFired = true;
-                    return CompletedTask.Instance;
-                };
-
-                await managedClient.StartAsync(testEnvironment.CreateDefaultManagedMqttClientOptions());
-
-                await LongTestDelay();
-
-                await server.StopAsync();
-
-                await LongTestDelay();
-
-                Assert.IsTrue(eventFired);
-            }
-        }
-
-        [TestMethod]
-        public async Task Enqueueing_Should_Fire_Event()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                await testEnvironment.StartServer();
-
-                var managedClient = testEnvironment.CreateManagedClient();
-
-                var eventFired = false;
-                managedClient.ApplicationMessageEnqueueingAsync += e =>
-                {
-                    eventFired = true;
-                    return CompletedTask.Instance;
-                };
-
-                await managedClient.EnqueueAsync("A");
-
-                Assert.IsTrue(eventFired);
-            }
-        }
-
-        [TestMethod]
-        public async Task Subscription_Should_Fire_Event()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                await testEnvironment.StartServer();
-
-                var managedClient = testEnvironment.CreateManagedClient();
-
-                await managedClient.SubscribeAsync("A");
-
-                var eventFired = false;
-                managedClient.SubscribeProcessedAsync += e =>
-                {
-                    eventFired = e.Options.TopicFilters[0].Topic == "A";
-                    return CompletedTask.Instance;
-                };
-
-                await managedClient.StartAsync(testEnvironment.CreateDefaultManagedMqttClientOptions());
-
-                await LongTestDelay();
-
-                Assert.IsTrue(eventFired);
-            }
-        }
-
-        [TestMethod]
-        public async Task Unsubscription_Should_Fire_Event()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                await testEnvironment.StartServer();
-
-                var managedClient = testEnvironment.CreateManagedClient();
-
-                await managedClient.SubscribeAsync("A");
-
-                var eventFired = false;
-                managedClient.UnsubscribeProcessedAsync += e =>
-                {
-                    eventFired = e.Options.TopicFilters[0] == "A";
-                    return CompletedTask.Instance;
-                };
-
-                await managedClient.StartAsync(testEnvironment.CreateDefaultManagedMqttClientOptions());
-
-                await LongTestDelay();
-
-                await managedClient.UnsubscribeAsync("A");
-
-                await LongTestDelay();
-
-                Assert.IsTrue(eventFired);
-            }
-        }
-    }
-}
@@ -1,135 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System.Collections.Generic;
-using System.Linq;
-using System.Threading.Tasks;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MQTTnet.Extensions.ManagedClient;
-using MQTTnet.Implementations;
-using MQTTnet.Internal;
-using MQTTnet.Server;
-
-namespace MQTTnet.Tests.ManagedMqttClient
-{
-    [TestClass]
-    public sealed class ManagedMqttClient_Messages_Tests : BaseTestClass
-    {
-        [TestMethod]
-        public async Task Drop_New_Messages_On_Full_Queue()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                await testEnvironment.StartServer();
-
-                var managedClient = testEnvironment.CreateManagedMqttClient();
-
-                var clientOptions = new ManagedMqttClientOptionsBuilder().WithClientOptions(o => o.WithTcpServer("localhost"))
-                    .WithMaxPendingMessages(5)
-                    .WithPendingMessagesOverflowStrategy(MqttPendingMessagesOverflowStrategy.DropNewMessage);
-
-                await managedClient.StartAsync(clientOptions.Build());
-
-                await managedClient.EnqueueAsync("1");
-                await managedClient.EnqueueAsync("2");
-                await managedClient.EnqueueAsync("3");
-                await managedClient.EnqueueAsync("4");
-                await managedClient.EnqueueAsync("5");
-                await managedClient.EnqueueAsync("6");
-                await managedClient.EnqueueAsync("7");
-                await managedClient.EnqueueAsync("8");
-
-                Assert.AreEqual(5, managedClient.EnqueuedApplicationMessagesCount);
-            }
-        }
-
-        [TestMethod]
-        public async Task Drop_Old_Messages_On_Full_Queue()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                await testEnvironment.StartServer();
-
-                var managedClient = testEnvironment.CreateManagedMqttClient();
-
-                var clientOptions = new ManagedMqttClientOptionsBuilder().WithClientOptions(o => o.WithTcpServer("localhost"))
-                    .WithMaxPendingMessages(5)
-                    .WithPendingMessagesOverflowStrategy(MqttPendingMessagesOverflowStrategy.DropOldestQueuedMessage);
-
-                await managedClient.StartAsync(clientOptions.Build());
-
-                await managedClient.EnqueueAsync("1");
-                await managedClient.EnqueueAsync("2");
-                await managedClient.EnqueueAsync("3");
-                await managedClient.EnqueueAsync("4");
-                await managedClient.EnqueueAsync("5");
-                await managedClient.EnqueueAsync("6");
-                await managedClient.EnqueueAsync("7");
-                await managedClient.EnqueueAsync("8");
-
-                Assert.AreEqual(5, managedClient.EnqueuedApplicationMessagesCount);
-            }
-        }
-
-        [TestMethod]
-        public async Task Preserve_Order_Of_Subscriptions()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                var server = await testEnvironment.StartServer();
-
-                // Prepare the retained messages.
-                await server.InjectApplicationMessage(testEnvironment.Factory.CreateApplicationMessageBuilder().WithTopic("A").WithPayload("P").WithRetainFlag().Build());
-                await server.InjectApplicationMessage(testEnvironment.Factory.CreateApplicationMessageBuilder().WithTopic("B").WithPayload("P").WithRetainFlag().Build());
-                await server.InjectApplicationMessage(testEnvironment.Factory.CreateApplicationMessageBuilder().WithTopic("C").WithPayload("P").WithRetainFlag().Build());
-                await server.InjectApplicationMessage(testEnvironment.Factory.CreateApplicationMessageBuilder().WithTopic("3").WithPayload("P").WithRetainFlag().Build());
-                await server.InjectApplicationMessage(testEnvironment.Factory.CreateApplicationMessageBuilder().WithTopic("2").WithPayload("P").WithRetainFlag().Build());
-                await server.InjectApplicationMessage(testEnvironment.Factory.CreateApplicationMessageBuilder().WithTopic("1").WithPayload("P").WithRetainFlag().Build());
-
-                // Subscribe to the retained messages in a defined order.
-                var managedClient = testEnvironment.CreateManagedMqttClient();
-
-                var applicationMessages = new List<MqttApplicationMessage>();
-                managedClient.ApplicationMessageReceivedAsync += e =>
-                {
-                    applicationMessages.Add(e.ApplicationMessage);
-                    return CompletedTask.Instance;
-                };
-
-                await managedClient.SubscribeAsync("B");
-                await managedClient.SubscribeAsync("C");
-                await managedClient.SubscribeAsync("A");
-                await managedClient.SubscribeAsync("2");
-                await managedClient.SubscribeAsync("1");
-                await managedClient.SubscribeAsync("3");
-
-                await managedClient.StartAsync(testEnvironment.CreateDefaultManagedMqttClientOptions()).ConfigureAwait(false);
-
-                await LongTestDelay();
-
-                var order = string.Join(string.Empty, applicationMessages.Select(a => a.Topic));
-
-                Assert.AreEqual("BCA213", order);
-            }
-        }
-
-        [TestMethod]
-        public async Task Publish()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                testEnvironment.TrackServerReceivedApplicationMessages = true;
-                await testEnvironment.StartServer();
-
-                var managedClient = await testEnvironment.StartManagedClient();
-
-                await managedClient.EnqueueAsync(testEnvironment.Factory.CreateApplicationMessageBuilder().WithTopic("TEST").Build());
-
-                await LongTestDelay();
-
-                Assert.AreEqual(1, testEnvironment.ServerReceivedApplicationMessages.Count);
-            }
-        }
-    }
-}
@@ -9,6 +9,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
+using MQTTnet.Diagnostics;
 using MQTTnet.Extensions.ManagedClient;
 using MQTTnet.Formatter;
 using MQTTnet.Internal;
@@ -19,17 +20,111 @@ using MQTTnet.Tests.Mockups;
 namespace MQTTnet.Tests.Clients.ManagedMqttClient
 {
    [TestClass]
-    public sealed class ManagedMqttClient_Connection_Tests : BaseTestClass
+    public sealed class ManagedMqttClient_Tests : BaseTestClass
    {
+        [TestMethod]
+        public async Task Expose_Custom_Connection_Error()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                var server = await testEnvironment.StartServer();
+                
+                server.ValidatingConnectionAsync += args =>
+                {
+                    args.ReasonCode = MqttConnectReasonCode.BadUserNameOrPassword;
+                    return CompletedTask.Instance;
+                };
+
+                var managedClient = testEnvironment.Factory.CreateManagedMqttClient();
+
+                MqttClientDisconnectedEventArgs disconnectedArgs = null;
+                managedClient.DisconnectedAsync += args =>
+                {
+                    disconnectedArgs = args;
+                    return CompletedTask.Instance;
+                };
+                
+                var clientOptions = testEnvironment.Factory.CreateManagedMqttClientOptionsBuilder().WithClientOptions(testEnvironment.CreateDefaultClientOptions()).Build();
+                await managedClient.StartAsync(clientOptions);
+
+                await LongTestDelay();
+
+                Assert.IsNotNull(disconnectedArgs);
+                Assert.AreEqual(MqttClientConnectResultCode.BadUserNameOrPassword, disconnectedArgs.ConnectResult.ResultCode);
+            }
+        }
+        
+        [TestMethod]
+        public async Task Receive_While_Not_Cleanly_Disconnected()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                await testEnvironment.StartServer(o => o.WithPersistentSessions());
+
+                var senderClient = await testEnvironment.ConnectClient();
+
+                // Prepare managed client.
+                var managedClient = testEnvironment.Factory.CreateManagedMqttClient();
+                await managedClient.SubscribeAsync("#");
+                var receivedMessages = testEnvironment.CreateApplicationMessageHandler(managedClient);
+                
+                var managedClientOptions = new ManagedMqttClientOptions
+                {
+                    ClientOptions = testEnvironment.Factory.CreateClientOptionsBuilder()
+                        .WithTcpServer("127.0.0.1", testEnvironment.ServerPort)
+                        .WithClientId(nameof(Receive_While_Not_Cleanly_Disconnected) + "_managed")
+                        .WithCleanSession(false)
+                        .Build()
+                };
+
+                await managedClient.StartAsync(managedClientOptions);
+                await LongTestDelay();
+                await LongTestDelay();
+                
+                // Send test data.
+                await senderClient.PublishStringAsync("topic1");
+                await LongTestDelay();
+                await LongTestDelay();
+                
+                receivedMessages.AssertReceivedCountEquals(1);
+
+                // Stop the managed client but keep session at server (not clean disconnect required).
+                await managedClient.StopAsync(false);
+                await LongTestDelay();
+                
+                // Send new messages in the meantime.
+                await senderClient.PublishStringAsync("topic2", qualityOfServiceLevel: MqttQualityOfServiceLevel.ExactlyOnce);
+                await LongTestDelay();
+                
+                // Start the managed client, it should receive the new message.
+                await managedClient.StartAsync(managedClientOptions);
+                await LongTestDelay();
+                
+                receivedMessages.AssertReceivedCountEquals(2);
+                
+                // Stop and start again, no new message should be received.
+                for (var i = 0; i < 3; i++)
+                {
+                    await managedClient.StopAsync(false);
+                    await LongTestDelay();
+                    await managedClient.StartAsync(managedClientOptions);
+                    await LongTestDelay();
+                }
+
+                receivedMessages.AssertReceivedCountEquals(2);
+            }
+        }
+
        [TestMethod]
        public async Task Connect_To_Invalid_Server()
        {
            using (var testEnvironment = CreateTestEnvironment())
            {
-                await testEnvironment.StartServer();
-                await LongTestDelay();
+                testEnvironment.IgnoreClientLogErrors = true;

-                var managedClient = testEnvironment.Factory.CreateManagedMqttClient(testEnvironment.CreateClient());
+                var mqttClient = testEnvironment.CreateClient();
+
+                var managedClient = testEnvironment.Factory.CreateManagedMqttClient(mqttClient);

                ConnectingFailedEventArgs connectingFailedEventArgs = null;
                managedClient.ConnectingFailedAsync += args =>
@@ -56,63 +151,76 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
        }

        [TestMethod]
-        public async Task Receive_While_Not_Cleanly_Disconnected()
+        public async Task Drop_New_Messages_On_Full_Queue()
        {
-            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            var factory = new MqttFactory();
+            var managedClient = factory.CreateManagedMqttClient();
+            try
            {
-                await testEnvironment.StartServer(o => o.WithPersistentSessions());
+                var clientOptions = new ManagedMqttClientOptionsBuilder().WithMaxPendingMessages(5)
+                    .WithPendingMessagesOverflowStrategy(MqttPendingMessagesOverflowStrategy.DropNewMessage);

-                var senderClient = await testEnvironment.ConnectClient();
+                clientOptions.WithClientOptions(o => o.WithTcpServer("localhost"));

-                // Prepare managed client.
-                var managedClient = testEnvironment.Factory.CreateManagedMqttClient();
-                await managedClient.SubscribeAsync("#");
-                var receivedMessages = testEnvironment.CreateApplicationMessageHandler(managedClient);
+                await managedClient.StartAsync(clientOptions.Build());

-                var managedClientOptions = new ManagedMqttClientOptions
+                await managedClient.EnqueueAsync("1");
+                await managedClient.EnqueueAsync("2");
+                await managedClient.EnqueueAsync("3");
+                await managedClient.EnqueueAsync("4");
+                await managedClient.EnqueueAsync("5");
+                await managedClient.EnqueueAsync("6");
+                await managedClient.EnqueueAsync("7");
+                await managedClient.EnqueueAsync("8");
+
+                Assert.AreEqual(5, managedClient.PendingApplicationMessagesCount);
+            }
+            finally
+            {
+                await managedClient.StopAsync();
+            }
+        }
+
+        [TestMethod]
+        public async Task ManagedClients_Will_Message_Send()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                await testEnvironment.StartServer();
+
+                var receivedMessagesCount = 0;
+
+                var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1", testEnvironment.ServerPort)
+                    .WithWillTopic("My/last/will")
+                    .WithWillQualityOfServiceLevel(MqttQualityOfServiceLevel.AtMostOnce)
+                    .Build();
+
+                var dyingClient = testEnvironment.CreateClient();
+                var dyingManagedClient = new MQTTnet.Extensions.ManagedClient.ManagedMqttClient(dyingClient, testEnvironment.ClientLogger);
+
+                await dyingManagedClient.StartAsync(new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).Build());
+
+                // Wait until the managed client is fully set up and running.
+                await Task.Delay(1000);
+
+                var receivingClient = await testEnvironment.ConnectClient();
+
+                receivingClient.ApplicationMessageReceivedAsync += e =>
                {
-                    ClientOptions = testEnvironment.Factory.CreateClientOptionsBuilder()
-                        .WithTcpServer("127.0.0.1", testEnvironment.ServerPort)
-                        .WithClientId(nameof(Receive_While_Not_Cleanly_Disconnected) + "_managed")
-                        .WithCleanSession(false)
-                        .Build()
+                    Interlocked.Increment(ref receivedMessagesCount);
+                    return CompletedTask.Instance;
                };

-                await managedClient.StartAsync(managedClientOptions);
-                await LongTestDelay();
-                await LongTestDelay();
+                await receivingClient.SubscribeAsync("My/last/will");

-                // Send test data.
-                await senderClient.PublishStringAsync("topic1");
-                await LongTestDelay();
-                await LongTestDelay();
+                // Disposing the client will not sent a DISCONNECT packet so that connection is terminated
+                // which will lead to the will publish.
+                dyingManagedClient.Dispose();

-                receivedMessages.AssertReceivedCountEquals(1);
+                // Wait for arrival of the will message at the receiver.
+                await Task.Delay(5000);

-                // Stop the managed client but keep session at server (not clean disconnect required).
-                await managedClient.StopAsync(false);
-                await LongTestDelay();
-
-                // Send new messages in the meantime.
-                await senderClient.PublishStringAsync("topic2", qualityOfServiceLevel: MqttQualityOfServiceLevel.ExactlyOnce);
-                await LongTestDelay();
-
-                // Start the managed client, it should receive the new message.
-                await managedClient.StartAsync(managedClientOptions);
-                await LongTestDelay();
-
-                receivedMessages.AssertReceivedCountEquals(2);
-
-                // Stop and start again, no new message should be received.
-                for (var i = 0; i < 3; i++)
-                {
-                    await managedClient.StopAsync(false);
-                    await LongTestDelay();
-                    await managedClient.StartAsync(managedClientOptions);
-                    await LongTestDelay();
-                }
-
-                receivedMessages.AssertReceivedCountEquals(2);
+                Assert.AreEqual(1, receivedMessagesCount);
            }
        }

@@ -123,18 +231,18 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
            {
                var server = await testEnvironment.StartServer();

-                var managedClient = testEnvironment.CreateManagedClient();
+                var managedClient = new MQTTnet.Extensions.ManagedClient.ManagedMqttClient(testEnvironment.CreateClient(), new MqttNetEventLogger());
                var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("localhost", testEnvironment.ServerPort);

                var connected = GetConnectedTask(managedClient);

-                await managedClient.StartAsync(testEnvironment.CreateDefaultManagedMqttClientOptions());
+                await managedClient.StartAsync(new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).Build());

                await connected;

                await managedClient.StopAsync();

-                await LongTestDelay();
+                await Task.Delay(500);

                Assert.AreEqual(0, (await server.GetClientsAsync()).Count);
            }
@@ -150,7 +258,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient

                await testEnvironment.StartServer();

-                var managedClient = testEnvironment.CreateManagedClient();
+                var managedClient = new MQTTnet.Extensions.ManagedClient.ManagedMqttClient(testEnvironment.CreateClient(), new MqttNetEventLogger());
                var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("localhost", testEnvironment.ServerPort);
                var storage = new ManagedMqttClientTestStorage();

@@ -190,8 +298,6 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
        {
            using (var testEnvironment = CreateTestEnvironment())
            {
-                await testEnvironment.StartServer();
-
                var unmanagedClient = testEnvironment.CreateClient();
                var managedClient = await CreateManagedClientAsync(testEnvironment, unmanagedClient);

@@ -208,7 +314,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
                await managedClient.SubscribeAsync("unsubscribedThenSubscribed");

                //wait a bit for the subscriptions to become established before the messages are published
-                await LongTestDelay();
+                await Task.Delay(500);

                var sendingClient = await testEnvironment.ConnectClient();

@@ -238,7 +344,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
                await connected;

                // wait a bit so that the managed client can reestablish the subscriptions
-                await LongTestDelay();
+                await Task.Delay(500);

                received = SetupReceivingOfMessages(managedClient, 2);

@@ -254,7 +360,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
        {
            using (var testEnvironment = CreateTestEnvironment())
            {
-                var server = await testEnvironment.StartServer().ConfigureAwait(false);
+                await testEnvironment.StartServer().ConfigureAwait(false);

                var sendingClient = await testEnvironment.ConnectClient().ConfigureAwait(false);
                await sendingClient.PublishStringAsync("topic", "A", retain: true);
@@ -264,12 +370,12 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient

                await sendingClient.DisconnectAsync();

-                // Prepare retained messages.
-                await server.InjectApplicationMessage(testEnvironment.Factory.CreateApplicationMessageBuilder().WithTopic("topic").WithPayload("payload").WithRetainFlag().Build());
-
                // Now use the managed client and check if subscriptions get cleared properly.
-                var receivedManagedMessages = new List<MqttApplicationMessage>();

+                var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1", testEnvironment.ServerPort);
+
+                var receivedManagedMessages = new List<MqttApplicationMessage>();
+                
                var managedClient = testEnvironment.Factory.CreateManagedMqttClient(testEnvironment.CreateClient());
                managedClient.ApplicationMessageReceivedAsync += e =>
                {
@@ -279,10 +385,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient

                await managedClient.SubscribeAsync("topic");

-                var managedClientOptions = testEnvironment.CreateDefaultManagedMqttClientOptions();
-                managedClientOptions.ClientOptions.CleanSession = false;
-                await managedClient.StartAsync(managedClientOptions);
-
+                await managedClient.StartAsync(new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).WithAutoReconnectDelay(TimeSpan.FromSeconds(0.5)).Build());
                await LongTestDelay();

                Assert.AreEqual(1, receivedManagedMessages.Count);
@@ -290,8 +393,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
                await managedClient.StopAsync();
                await LongTestDelay();

-                await managedClient.StartAsync(managedClientOptions);
-
+                await managedClient.StartAsync(new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).WithAutoReconnectDelay(TimeSpan.FromSeconds(0.5)).Build());
                await LongTestDelay();

                // After reconnect and then some delay, the retained message must not be received,
@@ -301,7 +403,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
                // Make sure that it gets received after subscribing again.
                await managedClient.SubscribeAsync("topic");
                await LongTestDelay();
-
+                
                Assert.AreEqual(2, receivedManagedMessages.Count);
            }
        }
@@ -313,13 +415,12 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
        {
            using (var testEnvironment = CreateTestEnvironment())
            {
-                await testEnvironment.StartServer();
-
                // Use a long connection check interval to verify that the subscriptions
                // do not depend on the connection check interval anymore
                var connectionCheckInterval = TimeSpan.FromSeconds(10);
                var receivingClient = await CreateManagedClientAsync(testEnvironment, null, connectionCheckInterval);
                var sendingClient = await testEnvironment.ConnectClient();
+
                await sendingClient.PublishAsync(new MqttApplicationMessage { Topic = "topic", Payload = new byte[] { 1 }, Retain = true });

                var subscribeTime = DateTime.UtcNow;
@@ -344,9 +445,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
        {
            using (var testEnvironment = CreateTestEnvironment())
            {
-                await testEnvironment.StartServer();
-
-                var managedClient = testEnvironment.CreateManagedClient();
+                var managedClient = await CreateManagedClientAsync(testEnvironment);

                var sendingClient = await testEnvironment.ConnectClient();

@@ -372,52 +471,14 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
            }
        }

-        [TestMethod]
-        public async Task Will_Message_Send()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                await testEnvironment.StartServer();
-
-                // Prepare the receiving client.
-                var receivedMessagesCount = 0;
-
-                var receivingClient = await testEnvironment.ConnectClient();
-                receivingClient.ApplicationMessageReceivedAsync += e =>
-                {
-                    Interlocked.Increment(ref receivedMessagesCount);
-                    return CompletedTask.Instance;
-                };
-
-                await receivingClient.SubscribeAsync("My/last/will");
-
-                // Prepare the managed client.
-                var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1", testEnvironment.ServerPort).WithWillTopic("My/last/will").Build();
-
-                var dyingClient = testEnvironment.CreateClient();
-                var dyingManagedClient = testEnvironment.CreateManagedMqttClient(dyingClient);
-                await dyingManagedClient.StartAsync(new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).Build());
-
-                // Wait until the managed client is fully set up and running.
-                await LongTestDelay();
-
-                // Disposing the client will not sent a DISCONNECT packet so that connection is terminated
-                // which will lead to the will publish.
-                dyingManagedClient.Dispose();
-
-                // Wait for arrival of the will message at the receiver.
-                await LongTestDelay();
-
-                Assert.AreEqual(1, receivedMessagesCount);
-            }
-        }
-
-        static async Task<IManagedMqttClient> CreateManagedClientAsync(
+        async Task<MQTTnet.Extensions.ManagedClient.ManagedMqttClient> CreateManagedClientAsync(
            TestEnvironment testEnvironment,
            IMqttClient underlyingClient = null,
            TimeSpan? connectionCheckInterval = null,
            string host = "localhost")
        {
+            await testEnvironment.StartServer();
+
            var clientOptions = new MqttClientOptionsBuilder().WithTcpServer(host, testEnvironment.ServerPort);

            var managedOptions = new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).Build();
@@ -427,7 +488,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
            // at connection check intervals
            managedOptions.ConnectionCheckInterval = connectionCheckInterval ?? TimeSpan.FromSeconds(0.1);

-            var managedClient = testEnvironment.CreateManagedMqttClient(underlyingClient ?? testEnvironment.CreateClient());
+            var managedClient = new MQTTnet.Extensions.ManagedClient.ManagedMqttClient(underlyingClient ?? testEnvironment.CreateClient(), new MqttNetEventLogger());

            var connected = GetConnectedTask(managedClient);

@@ -438,20 +499,35 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
            return managedClient;
        }

-        static Task GetConnectedTask(IManagedMqttClient managedClient)
+        /// <summary>
+        ///     Returns a task that will finish when the
+        ///     <paramref
+        ///         name="managedClient" />
+        ///     has connected
+        /// </summary>
+        Task GetConnectedTask(MQTTnet.Extensions.ManagedClient.ManagedMqttClient managedClient)
        {
-            var promise = new TaskCompletionSource<bool>();
+            var connected = new TaskCompletionSource<bool>();

            managedClient.ConnectedAsync += e =>
            {
-                promise.TrySetResult(true);
+                connected.TrySetResult(true);
                return CompletedTask.Instance;
            };

-            return promise.Task;
+            return connected.Task;
        }

-        static Task<List<MqttApplicationMessage>> SetupReceivingOfMessages(IManagedMqttClient managedClient, int expectedNumberOfMessages)
+        /// <summary>
+        ///     Returns a task that will return the messages received on
+        ///     <paramref
+        ///         name="managedClient" />
+        ///     when
+        ///     <paramref
+        ///         name="expectedNumberOfMessages" />
+        ///     have been received
+        /// </summary>
+        Task<List<MqttApplicationMessage>> SetupReceivingOfMessages(MQTTnet.Extensions.ManagedClient.ManagedMqttClient managedClient, int expectedNumberOfMessages)
        {
            var receivedMessages = new List<MqttApplicationMessage>();
            var result = new AsyncTaskCompletionSource<List<MqttApplicationMessage>>();
@@ -474,7 +550,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient

    public class ManagedMqttClientTestStorage : IManagedMqttClientStorage
    {
-        IList<ManagedMqttApplicationMessage> _messages = new List<ManagedMqttApplicationMessage>();
+        IList<ManagedMqttApplicationMessage> _messages;

        public int GetMessageCount()
        {
@@ -483,6 +559,11 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient

        public Task<IList<ManagedMqttApplicationMessage>> LoadQueuedMessagesAsync()
        {
+            if (_messages == null)
+            {
+                _messages = new List<ManagedMqttApplicationMessage>();
+            }
+
            return Task.FromResult(_messages);
        }

@@ -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);
+            }
+        }
+    }
+}
@@ -99,6 +99,8 @@ namespace MQTTnet.Tests.Clients.MqttClient
                // Perform a clean disconnect.
                await client.DisconnectAsync(disconnectOptions);

+                await LongTestDelay();
+
                Assert.IsNotNull(eventArgs);
                Assert.AreEqual(MqttClientDisconnectType.Clean, eventArgs.DisconnectType);
            }
@@ -125,6 +127,8 @@ namespace MQTTnet.Tests.Clients.MqttClient
                // Perform a clean disconnect.
                await client.DisconnectAsync(disconnectOptions);

+                await LongTestDelay();
+                
                Assert.IsNotNull(eventArgs);
                Assert.AreEqual(MqttDisconnectReasonCode.MessageRateTooHigh, eventArgs.ReasonCode);
            }
@@ -150,6 +154,8 @@ namespace MQTTnet.Tests.Clients.MqttClient

                // Perform a clean disconnect.
                await client.DisconnectAsync(disconnectOptions);
+
+                await LongTestDelay();
                
                Assert.IsNotNull(eventArgs);
                Assert.IsNotNull(eventArgs.UserProperties);
@@ -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;
@@ -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();
            }
        }
@@ -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.
@@ -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);
@@ -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();

@@ -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()
@@ -2,8 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.

-#region
-
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -21,8 +19,6 @@ using MQTTnet.LowLevelClient;
 using MQTTnet.Protocol;
 using MQTTnet.Server;

-#endregion
-
 namespace MQTTnet.Tests.Mockups
 {
    public sealed class TestEnvironment : IDisposable
@@ -32,7 +28,6 @@ namespace MQTTnet.Tests.Mockups

        readonly List<Exception> _exceptions = new List<Exception>();
        readonly List<ILowLevelMqttClient> _lowLevelClients = new List<ILowLevelMqttClient>();
-        readonly List<IManagedMqttClient> _managedClients = new List<IManagedMqttClient>();
        readonly MqttProtocolVersion _protocolVersion;
        readonly List<string> _serverErrors = new List<string>();

@@ -94,12 +89,8 @@ namespace MQTTnet.Tests.Mockups

        public int ServerPort { get; set; }

-        public List<MqttApplicationMessage> ServerReceivedApplicationMessages { get; } = new List<MqttApplicationMessage>();
-
        public TestContext TestContext { get; }

-        public bool TrackServerReceivedApplicationMessages { get; set; }
-
        public Task<IMqttClient> ConnectClient()
        {
            return ConnectClient(Factory.CreateClientOptionsBuilder().WithProtocolVersion(_protocolVersion));
@@ -247,11 +238,6 @@ namespace MQTTnet.Tests.Mockups
            }
        }

-        public ManagedMqttClientOptions CreateDefaultManagedMqttClientOptions()
-        {
-            return Factory.CreateManagedMqttClientOptionsBuilder().WithClientOptions(Factory.CreateClientOptionsBuilder().WithTcpServer("127.0.0.1", ServerPort).Build()).Build();
-        }
-
        public MqttClientOptions CreateDefaultClientOptions()
        {
            return CreateDefaultClientOptionsBuilder().Build();
@@ -259,7 +245,7 @@ namespace MQTTnet.Tests.Mockups

        public MqttClientOptionsBuilder CreateDefaultClientOptionsBuilder()
        {
-            return Factory.CreateClientOptionsBuilder().WithProtocolVersion(_protocolVersion).WithTcpServer("127.0.0.1", ServerPort);
+            return Factory.CreateClientOptionsBuilder().WithProtocolVersion(_protocolVersion).WithTcpServer("127.0.0.1", ServerPort).WithClientId(TestContext.TestName + "_" + Guid.NewGuid());
        }

        public ILowLevelMqttClient CreateLowLevelClient()
@@ -273,21 +259,6 @@ namespace MQTTnet.Tests.Mockups
            }
        }

-        public IManagedMqttClient CreateManagedClient()
-        {
-            return Factory.CreateManagedMqttClient(CreateClient());
-        }
-
-        public IManagedMqttClient CreateManagedMqttClient()
-        {
-            return Factory.CreateManagedMqttClient(CreateClient(), ClientLogger);
-        }
-
-        public IManagedMqttClient CreateManagedMqttClient(IMqttClient client)
-        {
-            return Factory.CreateManagedMqttClient(client, ClientLogger);
-        }
-
        public MqttServer CreateServer(MqttServerOptions options)
        {
            if (Server != null)
@@ -299,11 +270,6 @@ namespace MQTTnet.Tests.Mockups

            Server = Factory.CreateMqttServer(options, logger);

-            if (TrackServerReceivedApplicationMessages)
-            {
-                Server.InterceptingPublishAsync += ServerOnInterceptingPublishAsync;
-            }
-
            Server.ValidatingConnectionAsync += e =>
            {
                if (TestContext != null)
@@ -311,8 +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}).");
                    }
                }

@@ -326,35 +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();
-                }
-            }
-
-            foreach (var managedMqttClient in _managedClients)
-            {
-                try
-                {
-                    managedMqttClient.StopAsync().Wait();
-                }
-                finally
-                {
-                    managedMqttClient.Dispose();
-                }
+                mqttClient?.Dispose();
            }

            foreach (var lowLevelMqttClient in _lowLevelClients)
            {
-                lowLevelMqttClient.Dispose();
+                lowLevelMqttClient?.Dispose();
            }

            try
@@ -378,13 +320,6 @@ namespace MQTTnet.Tests.Mockups
            }
        }

-        public async Task<IManagedMqttClient> StartManagedClient()
-        {
-            var managedClient = Factory.CreateManagedMqttClient(CreateClient());
-            await managedClient.StartAsync(CreateDefaultManagedMqttClientOptions());
-            return managedClient;
-        }
-
        public Task<MqttServer> StartServer()
        {
            return StartServer(Factory.CreateServerOptionsBuilder());
@@ -454,15 +389,5 @@ namespace MQTTnet.Tests.Mockups
                _exceptions.Add(exception);
            }
        }
-
-        Task ServerOnInterceptingPublishAsync(InterceptingPublishEventArgs arg)
-        {
-            lock (ServerReceivedApplicationMessages)
-            {
-                ServerReceivedApplicationMessages.Add(arg.ApplicationMessage);
-            }
-
-            return CompletedTask.Instance;
-        }
    }
 }
@@ -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));
+        }
+    }
+}
@@ -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();
            }
        }
@@ -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);
        }
    }
@@ -954,7 +954,7 @@ namespace MQTTnet.Tests.Server

                var client = testEnvironment.CreateClient();

-                client.InspectPackage += e =>
+                client.InspectPacketAsync += e =>
                {
                    if (e.Buffer.Length > 0)
                    {
@@ -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);
        }
    }
@@ -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);
-            }
-        }
-    }
-}
@@ -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);
+            }
+        }
    }
 }
@@ -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);
            }
        }
@@ -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()
        {
@@ -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)
@@ -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
@@ -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);
+            }
+        }
    }
 }
@@ -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)
            {
@@ -27,18 +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();

-        Statistics _statistics;     // mutable struct, don't make readonly!
+        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));

@@ -64,6 +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();
@@ -126,7 +127,7 @@ namespace MQTTnet.Adapter

            try
            {
-                _packetInspector?.BeginReceivePacket();
+                PacketInspector?.BeginReceivePacket();

                ReceivedMqttPacket receivedPacket;
                var receivedPacketTask = ReceiveAsync(cancellationToken);
@@ -144,7 +145,7 @@ namespace MQTTnet.Adapter
                    return null;
                }

-                _packetInspector?.EndReceivePacket();
+                PacketInspector?.EndReceivePacket();

                Interlocked.Add(ref _statistics._bytesSent, receivedPacket.TotalLength);

@@ -180,7 +181,10 @@ namespace MQTTnet.Adapter
            return null;
        }

-        public void ResetStatistics() => _statistics.Reset();
+        public void ResetStatistics()
+        {
+            _statistics.Reset();
+        }

        public async Task SendPacketAsync(MqttPacket packet, CancellationToken cancellationToken)
        {
@@ -197,18 +201,18 @@ 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.Packet, false, cancellationToken).ConfigureAwait(false);
-                        await _channel.WriteAsync(packetBuffer.Payload, true, cancellationToken).ConfigureAwait(false);
+                        await _channel.WriteAsync(packetBuffer.Join(), true, cancellationToken).ConfigureAwait(false);
                    }
                    else
                    {
-                        await _channel.WriteAsync(packetBuffer.Packet, true, cancellationToken).ConfigureAwait(false);
+                        await _channel.WriteAsync(packetBuffer.Packet, false, cancellationToken).ConfigureAwait(false);
+                        await _channel.WriteAsync(packetBuffer.Payload, true, cancellationToken).ConfigureAwait(false);
                    }

                    Interlocked.Add(ref _statistics._bytesReceived, packetBuffer.Length);
@@ -270,7 +274,7 @@ namespace MQTTnet.Adapter
                    return 0;
                }

-                _packetInspector?.FillReceiveBuffer(_singleByteBuffer);
+                PacketInspector?.FillReceiveBuffer(_singleByteBuffer);

                encodedByte = _singleByteBuffer[0];

@@ -309,7 +313,7 @@ namespace MQTTnet.Adapter
                {
                    return ReadFixedHeaderResult.ConnectionClosed;
                }
-               
+
                if (cancellationToken.IsCancellationRequested)
                {
                    return ReadFixedHeaderResult.Canceled;
@@ -323,7 +327,7 @@ namespace MQTTnet.Adapter
                totalBytesRead += bytesRead;
            }

-            _packetInspector?.FillReceiveBuffer(buffer);
+            PacketInspector?.FillReceiveBuffer(buffer);

            var hasRemainingLength = buffer[1] != 0;
            if (!hasRemainingLength)
@@ -407,7 +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);
@@ -455,7 +459,7 @@ namespace MQTTnet.Adapter
            throw new MqttCommunicationException(exception);
        }

-        private struct Statistics
+        struct Statistics
        {
            public long _bytesReceived;
            public long _bytesSent;
@@ -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; }
+    }
+}
@@ -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);
+        }
+    }
+}
@@ -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; }
+    }
+}
@@ -12,25 +12,25 @@ namespace MQTTnet.Client
    {
        /// <summary>
        ///     Gets the client identifier which was chosen by the server.
-        ///     MQTTv5 only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public string AssignedClientIdentifier { get; internal set; }

        /// <summary>
        ///     Gets the authentication data.
-        ///     MQTTv5 only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public byte[] AuthenticationData { get; internal set; }

        /// <summary>
        ///     Gets the authentication method.
-        ///     MQTTv5 only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public string AuthenticationMethod { get; internal set; }

        /// <summary>
        ///     Gets a value indicating whether a session was already available or not.
-        ///     MQTTv5 only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public bool IsSessionPresent { get; internal set; }

@@ -38,13 +38,13 @@ namespace MQTTnet.Client

        /// <summary>
        ///     Gets the maximum QoS which is supported by the server.
-        ///     MQTTv5 only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public MqttQualityOfServiceLevel MaximumQoS { get; internal set; }

        /// <summary>
        ///     Gets the reason string.
-        ///     MQTTv5 only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public string ReasonString { get; internal set; }

@@ -52,19 +52,19 @@ namespace MQTTnet.Client

        /// <summary>
        ///     Gets the response information.
-        ///     MQTTv5 only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public string ResponseInformation { get; internal set; }

        /// <summary>
        ///     Gets the result code.
-        ///     MQTTv5 only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public MqttClientConnectResultCode ResultCode { get; internal set; }

        /// <summary>
        ///     Gets whether the server supports retained messages.
-        ///     MQTTv5 only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public bool RetainAvailable { get; internal set; }

@@ -78,7 +78,7 @@ namespace MQTTnet.Client

        /// <summary>
        ///     Gets an alternate server which should be used instead of the current one.
-        ///     MQTTv5 only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public string ServerReference { get; internal set; }

@@ -86,19 +86,19 @@ namespace MQTTnet.Client

        /// <summary>
        ///     Gets a value indicating whether the shared subscriptions are available or not.
-        ///     MQTTv5 only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public bool SharedSubscriptionAvailable { get; internal set; }

        /// <summary>
        ///     Gets a value indicating whether the subscription identifiers are available or not.
-        ///     MQTTv5 only.
+        ///     <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.
-        ///     MQTTv5 only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public ushort TopicAliasMaximum { get; internal set; }

@@ -109,13 +109,13 @@ 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.
-        ///     MQTTv5 only.
+        ///     <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.
-        ///     MQTTv5 only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public bool WildcardSubscriptionAvailable { get; internal set; }
    }
@@ -9,14 +9,9 @@ namespace MQTTnet.Client
 {
    public sealed class MqttClientDisconnectOptions
    {
-        /// <summary>
-        /// Gets or sets whether this disconnect is a clean disconnect.
-        /// </summary>
-        public bool IsClean { get; set; }
-        
        /// <summary>
        ///     Gets or sets the reason code.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public MqttClientDisconnectOptionsReason Reason { get; set; } = MqttClientDisconnectOptionsReason.NormalDisconnection;

@@ -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);
-    }
-}
@@ -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; }
-    }
-}
@@ -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; }
-    }
-}
@@ -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);

@@ -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);
+        }
+    }
+}
@@ -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>();
+    }
+}
@@ -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");
+            }
+        }
+    }
+}
@@ -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();
+    }
+}
@@ -7,6 +7,7 @@ using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Adapter;
+using MQTTnet.Client.Internal;
 using MQTTnet.Diagnostics;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
@@ -20,25 +21,19 @@ namespace MQTTnet.Client
    public sealed class MqttClient : Disposable, IMqttClient
    {
        readonly IMqttClientAdapterFactory _adapterFactory;
-        readonly AsyncEvent<MqttApplicationMessageReceivedEventArgs> _applicationMessageReceivedEvent = new AsyncEvent<MqttApplicationMessageReceivedEventArgs>();
-
-        readonly MqttClientPublishResultFactory _clientPublishResultFactory = new MqttClientPublishResultFactory();
-        readonly MqttClientSubscribeResultFactory _clientSubscribeResultFactory = new MqttClientSubscribeResultFactory();
-        readonly MqttClientUnsubscribeResultFactory _clientUnsubscribeResultFactory = new MqttClientUnsubscribeResultFactory();
-
-        readonly AsyncEvent<MqttClientConnectedEventArgs> _connectedEvent = new AsyncEvent<MqttClientConnectedEventArgs>();
-        readonly AsyncEvent<MqttClientConnectingEventArgs> _connectingEvent = new AsyncEvent<MqttClientConnectingEventArgs>();
-        readonly AsyncEvent<MqttClientDisconnectedEventArgs> _disconnectedEvent = new AsyncEvent<MqttClientDisconnectedEventArgs>();
+        readonly MqttClientAuthenticationHandler _authenticationHandler;
        readonly object _disconnectLock = new object();
-        readonly AsyncEvent<InspectMqttPacketEventArgs> _inspectPacketEvent = new AsyncEvent<InspectMqttPacketEventArgs>();
+        readonly MqttClientEvents _events = new MqttClientEvents();
+        readonly MqttClientKeepAliveHandler _keepAliveHandler;
        readonly MqttNetSourceLogger _logger;
-
        readonly MqttPacketIdentifierProvider _packetIdentifierProvider = new MqttPacketIdentifierProvider();
        readonly IMqttNetLogger _rootLogger;

-        IMqttChannelAdapter _adapter;
+        IMqttChannelAdapter _channelAdapter;

-        bool _cleanDisconnectInitiated;
+        internal bool _cleanDisconnectInitiated;
+
+        CancellationTokenSource _clientAlive;
        volatile int _connectionStatus;

        // The value for this field can be set from two different enums.
@@ -46,11 +41,6 @@ namespace MQTTnet.Client
        int _disconnectReason;
        string _disconnectReasonString;
        List<MqttUserProperty> _disconnectUserProperties;
-
-        Task _keepAlivePacketsSenderTask;
-        DateTime _lastPacketSentTimestamp;
-
-        CancellationTokenSource _mqttClientAlive;
        MqttPacketDispatcher _packetDispatcher;
        Task _packetReceiverTask;
        AsyncQueue<MqttPublishPacket> _publishPacketReceiverQueue;
@@ -61,39 +51,48 @@ namespace MQTTnet.Client
            _adapterFactory = channelFactory ?? throw new ArgumentNullException(nameof(channelFactory));
            _rootLogger = logger ?? throw new ArgumentNullException(nameof(logger));
            _logger = logger.WithSource(nameof(MqttClient));
+
+            _authenticationHandler = new MqttClientAuthenticationHandler(this, logger);
+            _keepAliveHandler = new MqttClientKeepAliveHandler(this, logger);
        }

        public event Func<MqttApplicationMessageReceivedEventArgs, Task> ApplicationMessageReceivedAsync
        {
-            add => _applicationMessageReceivedEvent.AddHandler(value);
-            remove => _applicationMessageReceivedEvent.RemoveHandler(value);
+            add => _events.ApplicationMessageReceivedEvent.AddHandler(value);
+            remove => _events.ApplicationMessageReceivedEvent.RemoveHandler(value);
        }

        public event Func<MqttClientConnectedEventArgs, Task> ConnectedAsync
        {
-            add => _connectedEvent.AddHandler(value);
-            remove => _connectedEvent.RemoveHandler(value);
+            add => _events.ConnectedEvent.AddHandler(value);
+            remove => _events.ConnectedEvent.RemoveHandler(value);
        }

        public event Func<MqttClientConnectingEventArgs, Task> ConnectingAsync
        {
-            add => _connectingEvent.AddHandler(value);
-            remove => _connectingEvent.RemoveHandler(value);
+            add => _events.ConnectingEvent.AddHandler(value);
+            remove => _events.ConnectingEvent.RemoveHandler(value);
        }

        public event Func<MqttClientDisconnectedEventArgs, Task> DisconnectedAsync
        {
-            add => _disconnectedEvent.AddHandler(value);
-            remove => _disconnectedEvent.RemoveHandler(value);
+            add => _events.DisconnectedEvent.AddHandler(value);
+            remove => _events.DisconnectedEvent.RemoveHandler(value);
        }

-        public event Func<InspectMqttPacketEventArgs, Task> InspectPackage
+        public event Func<MqttExtendedAuthenticationExchangeEventArgs, Task> ExtendedAuthenticationExchangeAsync
        {
-            add => _inspectPacketEvent.AddHandler(value);
-            remove => _inspectPacketEvent.RemoveHandler(value);
+            add => _authenticationHandler.AddHandler(value);
+            remove => _authenticationHandler.RemoveHandler(value);
        }

-        public bool IsConnected => _adapter != null && (MqttClientConnectionStatus)_connectionStatus == MqttClientConnectionStatus.Connected;
+        public event Func<InspectMqttPacketEventArgs, Task> InspectPacketAsync
+        {
+            add => _events.InspectPacketEvent.AddHandler(value);
+            remove => _events.InspectPacketEvent.RemoveHandler(value);
+        }
+
+        public bool IsConnected => (MqttClientConnectionStatus)_connectionStatus == MqttClientConnectionStatus.Connected;

        public MqttClientOptions Options { get; private set; }

@@ -114,21 +113,19 @@ namespace MQTTnet.Client
            {
                Options = options;

-                if (_connectingEvent.HasHandlers)
+                if (_events.ConnectingEvent.HasHandlers)
                {
-                    await _connectingEvent.InvokeAsync(new MqttClientConnectingEventArgs(options)).ConfigureAwait(false);
+                    await _events.ConnectingEvent.InvokeAsync(new MqttClientConnectingEventArgs(options));
                }

                Cleanup();

                _packetIdentifierProvider.Reset();
                _packetDispatcher = new MqttPacketDispatcher();
+                _clientAlive = new CancellationTokenSource();

-                _mqttClientAlive = new CancellationTokenSource();
-                var mqttClientAliveToken = _mqttClientAlive.Token;
-
-                var adapter = _adapterFactory.CreateClientAdapter(options, new MqttPacketInspector(_inspectPacketEvent, _rootLogger), _rootLogger);
-                _adapter = adapter;
+                var adapter = _adapterFactory.CreateClientAdapter(options, new MqttPacketInspector(_events.InspectPacketEvent, _rootLogger), _rootLogger);
+                _channelAdapter = adapter;

                if (cancellationToken.CanBeCanceled)
                {
@@ -144,42 +141,26 @@ namespace MQTTnet.Client
                    }
                }

-                _lastPacketSentTimestamp = DateTime.UtcNow;
-
-                var keepAliveInterval = Options.KeepAlivePeriod;
-                if (connectResult.ServerKeepAlive > 0)
-                {
-                    _logger.Info($"Using keep alive value ({connectResult.ServerKeepAlive}) sent from the server.");
-                    keepAliveInterval = TimeSpan.FromSeconds(connectResult.ServerKeepAlive);
-                }
-
-                if (keepAliveInterval != TimeSpan.Zero)
-                {
-                    _keepAlivePacketsSenderTask = Task.Run(() => TrySendKeepAliveMessagesAsync(mqttClientAliveToken), mqttClientAliveToken);
-                }
-
                CompareExchangeConnectionStatus(MqttClientConnectionStatus.Connected, MqttClientConnectionStatus.Connecting);

-                _logger.Info("Connected.");
+                _logger.Info("Connected");

-                if (_connectedEvent.HasHandlers)
-                {
-                    var eventArgs = new MqttClientConnectedEventArgs(connectResult);
-                    await _connectedEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
-                }
+                await OnConnected(connectResult).ConfigureAwait(false);

                return connectResult;
            }
            catch (Exception exception)
            {
-                _disconnectReason = (int)MqttClientDisconnectOptionsReason.UnspecifiedError;
-
-                if (!(exception is OperationCanceledException))
+                if (exception is MqttConnectingFailedException connectingFailedException)
                {
-                    _logger.Error(exception, "Error while connecting with server.");
+                    connectResult = connectingFailedException.Result;
                }

-                await DisconnectInternalAsync(null, exception, connectResult).ConfigureAwait(false);
+                _disconnectReason = (int)MqttClientDisconnectOptionsReason.UnspecifiedError;
+
+                _logger.Error(exception, "Error while connecting with server");
+
+                await DisconnectInternal(null, exception, connectResult).ConfigureAwait(false);

                throw;
            }
@@ -213,7 +194,7 @@ namespace MQTTnet.Client

                if (Options.ValidateFeatures)
                {
-                    MqttClientDisconnectOptionsValidator.ThrowIfNotSupported(options, _adapter.PacketFormatterAdapter.ProtocolVersion);
+                    MqttClientDisconnectOptionsValidator.ThrowIfNotSupported(options, _channelAdapter.PacketFormatterAdapter.ProtocolVersion);
                }

                // Sending the DISCONNECT may fail due to connection issues. The resulting exception
@@ -222,19 +203,19 @@ namespace MQTTnet.Client

                if (cancellationToken.CanBeCanceled)
                {
-                    await SendAsync(disconnectPacket, cancellationToken).ConfigureAwait(false);
+                    await Send(disconnectPacket, cancellationToken).ConfigureAwait(false);
                }
                else
                {
                    using (var timeout = new CancellationTokenSource(Options.Timeout))
                    {
-                        await SendAsync(disconnectPacket, timeout.Token).ConfigureAwait(false);
+                        await Send(disconnectPacket, timeout.Token).ConfigureAwait(false);
                    }
                }
            }
            finally
            {
-                await DisconnectCoreAsync(null, null, null, clientWasConnected).ConfigureAwait(false);
+                await DisconnectCore(null, null, null, clientWasConnected).ConfigureAwait(false);
            }
        }

@@ -242,13 +223,13 @@ namespace MQTTnet.Client
        {
            if (cancellationToken.CanBeCanceled)
            {
-                await SendAndReceiveAsync<MqttPingRespPacket>(MqttPingReqPacket.Instance, cancellationToken).ConfigureAwait(false);
+                await Request<MqttPingRespPacket>(MqttPingReqPacket.Instance, cancellationToken).ConfigureAwait(false);
            }
            else
            {
                using (var timeout = new CancellationTokenSource(Options.Timeout))
                {
-                    await SendAndReceiveAsync<MqttPingRespPacket>(MqttPingReqPacket.Instance, timeout.Token).ConfigureAwait(false);
+                    await Request<MqttPingRespPacket>(MqttPingReqPacket.Instance, timeout.Token).ConfigureAwait(false);
                }
            }
        }
@@ -264,7 +245,7 @@ namespace MQTTnet.Client

            if (Options.ValidateFeatures)
            {
-                MqttApplicationMessageValidator.ThrowIfNotSupported(applicationMessage, _adapter.PacketFormatterAdapter.ProtocolVersion);
+                MqttApplicationMessageValidator.ThrowIfNotSupported(applicationMessage, _channelAdapter.PacketFormatterAdapter.ProtocolVersion);
            }

            var publishPacket = MqttPacketFactories.Publish.Create(applicationMessage);
@@ -277,11 +258,11 @@ namespace MQTTnet.Client
                }
                case MqttQualityOfServiceLevel.AtLeastOnce:
                {
-                    return PublishAtLeastOnceAsync(publishPacket, cancellationToken);
+                    return PublishAtLeastOnce(publishPacket, cancellationToken);
                }
                case MqttQualityOfServiceLevel.ExactlyOnce:
                {
-                    return PublishExactlyOnceAsync(publishPacket, cancellationToken);
+                    return PublishExactlyOnce(publishPacket, cancellationToken);
                }
                default:
                {
@@ -290,26 +271,25 @@ namespace MQTTnet.Client
            }
        }

-        public Task SendExtendedAuthenticationExchangeDataAsync(MqttExtendedAuthenticationExchangeData data, CancellationToken cancellationToken = default)
+        public Task ReAuthenticateAsync(MqttReAuthenticationOptions options, CancellationToken cancellationToken = default)
        {
-            if (data == null)
+            if (options == null)
            {
-                throw new ArgumentNullException(nameof(data));
+                throw new ArgumentNullException(nameof(options));
            }

            ThrowIfDisposed();
            ThrowIfNotConnected();

-            var authPacket = new MqttAuthPacket
+            if (cancellationToken.CanBeCanceled)
            {
-                // This must always be equal to the value from the CONNECT packet. So we use it here to ensure that.
-                AuthenticationMethod = Options.AuthenticationMethod,
-                AuthenticationData = data.AuthenticationData,
-                ReasonString = data.ReasonString,
-                UserProperties = data.UserProperties
-            };
+                return _authenticationHandler.ReAuthenticate(options, cancellationToken);
+            }

-            return SendAsync(authPacket, cancellationToken);
+            using (var timeout = new CancellationTokenSource(Options.Timeout))
+            {
+                return _authenticationHandler.ReAuthenticate(options, timeout.Token);
+            }
        }

        public async Task<MqttClientSubscribeResult> SubscribeAsync(MqttClientSubscribeOptions options, CancellationToken cancellationToken = default)
@@ -326,7 +306,7 @@ namespace MQTTnet.Client

            if (Options.ValidateFeatures)
            {
-                MqttClientSubscribeOptionsValidator.ThrowIfNotSupported(options, _adapter.PacketFormatterAdapter.ProtocolVersion);
+                MqttClientSubscribeOptionsValidator.ThrowIfNotSupported(options, _channelAdapter.PacketFormatterAdapter.ProtocolVersion);
            }

            ThrowIfDisposed();
@@ -338,17 +318,17 @@ namespace MQTTnet.Client
            MqttSubAckPacket subAckPacket;
            if (cancellationToken.CanBeCanceled)
            {
-                subAckPacket = await SendAndReceiveAsync<MqttSubAckPacket>(subscribePacket, cancellationToken).ConfigureAwait(false);
+                subAckPacket = await Request<MqttSubAckPacket>(subscribePacket, cancellationToken).ConfigureAwait(false);
            }
            else
            {
                using (var timeout = new CancellationTokenSource(Options.Timeout))
                {
-                    subAckPacket = await SendAndReceiveAsync<MqttSubAckPacket>(subscribePacket, timeout.Token).ConfigureAwait(false);
+                    subAckPacket = await Request<MqttSubAckPacket>(subscribePacket, timeout.Token).ConfigureAwait(false);
                }
            }

-            return _clientSubscribeResultFactory.Create(subscribePacket, subAckPacket);
+            return MqttClientResultFactory.SubscribeResult.Create(subscribePacket, subAckPacket);
        }

        public async Task<MqttClientUnsubscribeResult> UnsubscribeAsync(MqttClientUnsubscribeOptions options, CancellationToken cancellationToken = default)
@@ -368,7 +348,7 @@ namespace MQTTnet.Client

            if (Options.ValidateFeatures)
            {
-                MqttClientUnsubscribeOptionsValidator.ThrowIfNotSupported(options, _adapter.PacketFormatterAdapter.ProtocolVersion);
+                MqttClientUnsubscribeOptionsValidator.ThrowIfNotSupported(options, _channelAdapter.PacketFormatterAdapter.ProtocolVersion);
            }

            var unsubscribePacket = MqttPacketFactories.Unsubscribe.Create(options);
@@ -377,17 +357,38 @@ namespace MQTTnet.Client
            MqttUnsubAckPacket unsubAckPacket;
            if (cancellationToken.CanBeCanceled)
            {
-                unsubAckPacket = await SendAndReceiveAsync<MqttUnsubAckPacket>(unsubscribePacket, cancellationToken).ConfigureAwait(false);
+                unsubAckPacket = await Request<MqttUnsubAckPacket>(unsubscribePacket, cancellationToken).ConfigureAwait(false);
            }
            else
            {
                using (var timeout = new CancellationTokenSource(Options.Timeout))
                {
-                    unsubAckPacket = await SendAndReceiveAsync<MqttUnsubAckPacket>(unsubscribePacket, timeout.Token).ConfigureAwait(false);
+                    unsubAckPacket = await Request<MqttUnsubAckPacket>(unsubscribePacket, timeout.Token).ConfigureAwait(false);
                }
            }

-            return _clientUnsubscribeResultFactory.Create(unsubscribePacket, unsubAckPacket);
+            return MqttClientResultFactory.UnsubscribeResult.Create(unsubscribePacket, unsubAckPacket);
+        }
+
+        internal Task DisconnectInternalAsync(Task sender, Exception exception, MqttClientConnectResult connectResult)
+        {
+            var clientWasConnected = IsConnected;
+
+            if (!DisconnectIsPendingOrFinished())
+            {
+                return DisconnectCore(sender, exception, connectResult, clientWasConnected);
+            }
+
+            return CompletedTask.Instance;
+        }
+
+        internal Task Send(MqttPacket packet, CancellationToken cancellationToken)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+
+            _keepAliveHandler.TrackSentPacket();
+
+            return _channelAdapter.SendPacketAsync(packet, cancellationToken);
        }

        protected override void Dispose(bool disposing)
@@ -411,7 +412,7 @@ namespace MQTTnet.Client
                if (!eventArgs.ProcessingFailed)
                {
                    var pubAckPacket = MqttPacketFactories.PubAck.Create(eventArgs);
-                    return SendAsync(pubAckPacket, cancellationToken);
+                    return Send(pubAckPacket, cancellationToken);
                }
            }
            else if (eventArgs.PublishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
@@ -419,7 +420,7 @@ namespace MQTTnet.Client
                if (!eventArgs.ProcessingFailed)
                {
                    var pubRecPacket = MqttPacketFactories.PubRec.Create(eventArgs);
-                    return SendAsync(pubRecPacket, cancellationToken);
+                    return Send(pubRecPacket, cancellationToken);
                }
            }
            else
@@ -430,50 +431,22 @@ namespace MQTTnet.Client
            return CompletedTask.Instance;
        }

-        async Task<MqttClientConnectResult> AuthenticateAsync(MqttClientOptions options, CancellationToken cancellationToken)
-        {
-            MqttClientConnectResult result;
-
-            try
-            {
-                var connectPacket = MqttPacketFactories.Connect.Create(options);
-
-                var connAckPacket = await SendAndReceiveAsync<MqttConnAckPacket>(connectPacket, cancellationToken).ConfigureAwait(false);
-
-                var clientConnectResultFactory = new MqttClientConnectResultFactory();
-                result = clientConnectResultFactory.Create(connAckPacket, _adapter.PacketFormatterAdapter.ProtocolVersion);
-            }
-            catch (Exception exception)
-            {
-                throw new MqttConnectingFailedException($"Error while authenticating. {exception.Message}", exception, null);
-            }
-
-            if (result.ResultCode != MqttClientConnectResultCode.Success)
-            {
-                throw new MqttConnectingFailedException($"Connecting with MQTT server failed ({result.ResultCode}).", null, result);
-            }
-
-            _logger.Verbose("Authenticated MQTT connection with server established.");
-
-            return result;
-        }
-
        void Cleanup()
        {
            try
            {
-                _mqttClientAlive?.Cancel(false);
+                _clientAlive?.Cancel(false);
            }
            finally
            {
-                _mqttClientAlive?.Dispose();
-                _mqttClientAlive = null;
+                _clientAlive?.Dispose();
+                _clientAlive = null;

                _publishPacketReceiverQueue?.Dispose();
                _publishPacketReceiverQueue = null;

-                _adapter?.Dispose();
-                _adapter = null;
+                _channelAdapter?.Dispose();
+                _channelAdapter = null;

                _packetDispatcher?.Dispose();
                _packetDispatcher = null;
@@ -487,37 +460,46 @@ namespace MQTTnet.Client

        async Task<MqttClientConnectResult> ConnectInternal(CancellationToken cancellationToken)
        {
-            var backgroundCancellationToken = _mqttClientAlive.Token;
+            var clientAliveToken = _clientAlive.Token;

-            using (var effectiveCancellationToken = CancellationTokenSource.CreateLinkedTokenSource(backgroundCancellationToken, cancellationToken))
+            using (var effectiveCancellationToken = CancellationTokenSource.CreateLinkedTokenSource(clientAliveToken, cancellationToken))
            {
-                _logger.Verbose("Trying to connect with server '{0}'.", Options.ChannelOptions);
-                await _adapter.ConnectAsync(effectiveCancellationToken.Token).ConfigureAwait(false);
-                _logger.Verbose("Connection with server established.");
+                _logger.Verbose("Trying to connect with server '{0}'", Options.ChannelOptions);

-                _publishPacketReceiverQueue?.Dispose();
-                _publishPacketReceiverQueue = new AsyncQueue<MqttPublishPacket>();
+                await _channelAdapter.ConnectAsync(effectiveCancellationToken.Token).ConfigureAwait(false);

-                _publishPacketReceiverTask = Task.Run(() => ProcessReceivedPublishPackets(backgroundCancellationToken), backgroundCancellationToken);
-                _packetReceiverTask = Task.Run(() => TryReceivePacketsAsync(backgroundCancellationToken), backgroundCancellationToken);
+                _logger.Verbose("Connection with server established");

-                return await AuthenticateAsync(Options, effectiveCancellationToken.Token).ConfigureAwait(false);
+                var connectResult = await _authenticationHandler.Authenticate(_channelAdapter, Options, effectiveCancellationToken.Token).ConfigureAwait(false);
+
+                if (connectResult.ResultCode == MqttClientConnectResultCode.Success)
+                {
+                    _publishPacketReceiverQueue?.Dispose();
+                    _publishPacketReceiverQueue = new AsyncQueue<MqttPublishPacket>();
+
+                    _publishPacketReceiverTask = Task.Run(() => ProcessReceivedPublishPacketsLoop(clientAliveToken), clientAliveToken);
+                    _packetReceiverTask = Task.Run(() => ReceivePacketsLoop(clientAliveToken), clientAliveToken);
+
+                    _keepAliveHandler.Enable(connectResult);
+                }
+
+                return connectResult;
            }
        }

-        async Task DisconnectCoreAsync(Task sender, Exception exception, MqttClientConnectResult connectResult, bool clientWasConnected)
+        async Task DisconnectCore(Task sender, Exception exception, MqttClientConnectResult connectResult, bool clientWasConnected)
        {
            TryInitiateDisconnect();

            try
            {
-                if (_adapter != null)
+                if (_channelAdapter != null)
                {
                    _logger.Verbose("Disconnecting [Timeout={0}]", Options.Timeout);

                    using (var timeout = new CancellationTokenSource(Options.Timeout))
                    {
-                        await _adapter.DisconnectAsync(timeout.Token).ConfigureAwait(false);
+                        await _channelAdapter.DisconnectAsync(timeout.Token).ConfigureAwait(false);
                    }
                }

@@ -534,9 +516,10 @@ namespace MQTTnet.Client

                var receiverTask = _packetReceiverTask.WaitAsync(sender, _logger);
                var publishPacketReceiverTask = _publishPacketReceiverTask.WaitAsync(sender, _logger);
-                var keepAliveTask = _keepAlivePacketsSenderTask.WaitAsync(sender, _logger);

-                await Task.WhenAll(receiverTask, publishPacketReceiverTask, keepAliveTask).ConfigureAwait(false);
+                _keepAliveHandler.Disable();
+
+                await Task.WhenAll(receiverTask, publishPacketReceiverTask).ConfigureAwait(false);
            }
            catch (Exception innerException)
            {
@@ -560,17 +543,17 @@ namespace MQTTnet.Client

                // This handler must be executed in a new thread because otherwise a dead lock may happen
                // when trying to reconnect in that handler etc.
-                Task.Run(() => _disconnectedEvent.InvokeAsync(eventArgs)).RunInBackground(_logger);
+                Task.Run(() => _events.DisconnectedEvent.InvokeAsync(eventArgs)).RunInBackground(_logger);
            }
        }

-        Task DisconnectInternalAsync(Task sender, Exception exception, MqttClientConnectResult connectResult)
+        Task DisconnectInternal(Task sender, Exception exception, MqttClientConnectResult connectResult)
        {
            var clientWasConnected = IsConnected;

            if (!DisconnectIsPendingOrFinished())
            {
-                return DisconnectCoreAsync(sender, exception, connectResult, clientWasConnected);
+                return DisconnectCore(sender, exception, connectResult, clientWasConnected);
            }

            return CompletedTask.Instance;
@@ -600,8 +583,7 @@ namespace MQTTnet.Client
                        connectionStatus = curStatus;
                        break;
                }
-            }
-            while (true);
+            } while (true);
        }

        void EnqueueReceivedPublishPacket(MqttPublishPacket publishPacket)
@@ -616,21 +598,21 @@ namespace MQTTnet.Client
            }
        }

-        async Task<MqttApplicationMessageReceivedEventArgs> HandleReceivedApplicationMessageAsync(MqttPublishPacket publishPacket)
+        async Task<MqttApplicationMessageReceivedEventArgs> HandleReceivedApplicationMessage(MqttPublishPacket publishPacket)
        {
            var applicationMessage = MqttApplicationMessageFactory.Create(publishPacket);
            var eventArgs = new MqttApplicationMessageReceivedEventArgs(Options.ClientId, applicationMessage, publishPacket, AcknowledgeReceivedPublishPacket);
-            await _applicationMessageReceivedEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
+            await _events.ApplicationMessageReceivedEvent.InvokeAsync(eventArgs).ConfigureAwait(false);

            return eventArgs;
        }

-        Task ProcessReceivedAuthPacket(MqttAuthPacket authPacket)
+        Task OnConnected(MqttClientConnectResult connectResult)
        {
-            var extendedAuthenticationExchangeHandler = Options.ExtendedAuthenticationExchangeHandler;
-            if (extendedAuthenticationExchangeHandler != null)
+            if (_events.ConnectedEvent.HasHandlers)
            {
-                return extendedAuthenticationExchangeHandler.HandleRequestAsync(new MqttExtendedAuthenticationExchangeContext(authPacket, this));
+                var eventArgs = new MqttClientConnectedEventArgs(connectResult);
+                return _events.ConnectedEvent.InvokeAsync(eventArgs);
            }

            return CompletedTask.Instance;
@@ -645,10 +627,10 @@ namespace MQTTnet.Client
            // Also dispatch disconnect to waiting threads to generate a proper exception.
            _packetDispatcher.Dispose(new MqttClientUnexpectedDisconnectReceivedException(disconnectPacket));

-            return DisconnectInternalAsync(_packetReceiverTask, null, null);
+            return DisconnectInternal(_packetReceiverTask, null, null);
        }

-        async Task ProcessReceivedPublishPackets(CancellationToken cancellationToken)
+        async Task ProcessReceivedPublishPacketsLoop(CancellationToken cancellationToken)
        {
            while (!cancellationToken.IsCancellationRequested)
            {
@@ -661,7 +643,7 @@ namespace MQTTnet.Client
                    }

                    var publishPacket = publishPacketDequeueResult.Item;
-                    var eventArgs = await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false);
+                    var eventArgs = await HandleReceivedApplicationMessage(publishPacket).ConfigureAwait(false);

                    if (eventArgs.AutoAcknowledge)
                    {
@@ -685,7 +667,7 @@ namespace MQTTnet.Client
                // The packet is unknown. Probably due to a restart of the client.
                // So wen send this to the server to trigger a full resend of the message.
                var pubRelPacket = MqttPacketFactories.PubRel.Create(pubRecPacket, MqttApplicationMessageReceivedReasonCode.PacketIdentifierNotFound);
-                return SendAsync(pubRelPacket, cancellationToken);
+                return Send(pubRelPacket, cancellationToken);
            }

            return CompletedTask.Instance;
@@ -694,54 +676,150 @@ namespace MQTTnet.Client
        Task ProcessReceivedPubRelPacket(MqttPubRelPacket pubRelPacket, CancellationToken cancellationToken)
        {
            var pubCompPacket = MqttPacketFactories.PubComp.Create(pubRelPacket, MqttApplicationMessageReceivedReasonCode.Success);
-            return SendAsync(pubCompPacket, cancellationToken);
+            return Send(pubCompPacket, cancellationToken);
        }

-        async Task<MqttClientPublishResult> PublishAtLeastOnceAsync(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
+        async Task<MqttClientPublishResult> PublishAtLeastOnce(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
        {
            publishPacket.PacketIdentifier = _packetIdentifierProvider.GetNextPacketIdentifier();

-            var pubAckPacket = await SendAndReceiveAsync<MqttPubAckPacket>(publishPacket, cancellationToken).ConfigureAwait(false);
-            return _clientPublishResultFactory.Create(pubAckPacket);
+            var pubAckPacket = await Request<MqttPubAckPacket>(publishPacket, cancellationToken).ConfigureAwait(false);
+            return MqttClientResultFactory.PublishResult.Create(pubAckPacket);
        }

        async Task<MqttClientPublishResult> PublishAtMostOnce(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
        {
            // No packet identifier is used for QoS 0 [3.3.2.2 Packet Identifier]
-            await SendAsync(publishPacket, cancellationToken).ConfigureAwait(false);
+            await Send(publishPacket, cancellationToken).ConfigureAwait(false);

-            return _clientPublishResultFactory.Create(null);
+            return MqttClientResultFactory.PublishResult.Create(null);
        }

-        async Task<MqttClientPublishResult> PublishExactlyOnceAsync(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
+        async Task<MqttClientPublishResult> PublishExactlyOnce(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
        {
            publishPacket.PacketIdentifier = _packetIdentifierProvider.GetNextPacketIdentifier();

-            var pubRecPacket = await SendAndReceiveAsync<MqttPubRecPacket>(publishPacket, cancellationToken).ConfigureAwait(false);
+            var pubRecPacket = await Request<MqttPubRecPacket>(publishPacket, cancellationToken).ConfigureAwait(false);

            var pubRelPacket = MqttPacketFactories.PubRel.Create(pubRecPacket, MqttApplicationMessageReceivedReasonCode.Success);

-            var pubCompPacket = await SendAndReceiveAsync<MqttPubCompPacket>(pubRelPacket, cancellationToken).ConfigureAwait(false);
+            var pubCompPacket = await Request<MqttPubCompPacket>(pubRelPacket, cancellationToken).ConfigureAwait(false);

-            return _clientPublishResultFactory.Create(pubRecPacket, pubCompPacket);
+            return MqttClientResultFactory.PublishResult.Create(pubRecPacket, pubCompPacket);
        }

-        async Task<TResponsePacket> SendAndReceiveAsync<TResponsePacket>(MqttPacket requestPacket, CancellationToken cancellationToken) where TResponsePacket : MqttPacket
+        async Task<MqttPacket> Receive(CancellationToken cancellationToken)
+        {
+            var packetTask = _channelAdapter.ReceivePacketAsync(cancellationToken);
+
+            MqttPacket packet;
+            if (packetTask.IsCompleted)
+            {
+                packet = packetTask.Result;
+            }
+            else
+            {
+                packet = await packetTask.ConfigureAwait(false);
+            }
+
+            return packet;
+        }
+
+        async Task ReceivePacketsLoop(CancellationToken cancellationToken)
+        {
+            try
+            {
+                _logger.Verbose("Start receiving packets.");
+
+                while (!cancellationToken.IsCancellationRequested)
+                {
+                    var packet = await Receive(cancellationToken).ConfigureAwait(false);
+
+                    if (cancellationToken.IsCancellationRequested)
+                    {
+                        return;
+                    }
+
+                    if (packet == null)
+                    {
+                        await DisconnectInternal(_packetReceiverTask, null, null).ConfigureAwait(false);
+
+                        return;
+                    }
+
+                    await TryProcessReceivedPacket(packet, cancellationToken).ConfigureAwait(false);
+                }
+            }
+            catch (Exception exception)
+            {
+                if (_cleanDisconnectInitiated)
+                {
+                    return;
+                }
+
+                if (exception is AggregateException aggregateException)
+                {
+                    exception = aggregateException.GetBaseException();
+                }
+
+                if (exception is OperationCanceledException)
+                {
+                }
+                else if (exception is MqttCommunicationException)
+                {
+                    _logger.Warning(exception, "Communication error while receiving packets.");
+                }
+                else
+                {
+                    _logger.Error(exception, "Error while receiving packets.");
+                }
+
+                _packetDispatcher.FailAll(exception);
+
+                await DisconnectInternal(_packetReceiverTask, exception, null).ConfigureAwait(false);
+            }
+            finally
+            {
+                _logger.Verbose("Stopped receiving packets.");
+            }
+        }
+
+        internal async Task<TPacket> Receive<TPacket>(int packetIdentifier, CancellationToken cancellationToken) where TPacket : MqttPacket
+        {
+            using (var packetAwaitable = _packetDispatcher.AddAwaitable<TPacket>(packetIdentifier))
+            {
+                return await packetAwaitable.WaitOneAsync(cancellationToken);
+            }
+        }
+        
+        internal async Task<TResponsePacket> Request<TResponsePacket>(MqttPacket requestPacket, CancellationToken cancellationToken) where TResponsePacket : MqttPacket
        {
            cancellationToken.ThrowIfCancellationRequested();
-            ThrowIfNoAdapter();

-            ushort packetIdentifier = 0;
+            // Some packets are a direct response to another packet but have no packet identifier for correlation!
+            int packetIdentifier;
            if (requestPacket is MqttPacketWithIdentifier packetWithIdentifier)
            {
                packetIdentifier = packetWithIdentifier.PacketIdentifier;
            }
+            else if (requestPacket is MqttPingReqPacket)
+            {
+                packetIdentifier = MqttPacketDispatcher.PingRespPacketFakeIdentifier;
+            }
+            else if (requestPacket is MqttAuthPacket)
+            {
+                packetIdentifier = MqttPacketDispatcher.AuthPacketFakeIdentifier;
+            }
+            else
+            {
+                throw new MqttProtocolViolationException($"Expecting a response for packet {requestPacket.GetRfcName()} is not supported.");
+            }

            using (var packetAwaitable = _packetDispatcher.AddAwaitable<TResponsePacket>(packetIdentifier))
            {
                try
                {
-                    await SendAsync(requestPacket, cancellationToken).ConfigureAwait(false);
+                    await Send(requestPacket, cancellationToken).ConfigureAwait(false);
                }
                catch (Exception exception)
                {
@@ -765,15 +843,6 @@ namespace MQTTnet.Client
            }
        }

-        Task SendAsync(MqttPacket packet, CancellationToken cancellationToken)
-        {
-            cancellationToken.ThrowIfCancellationRequested();
-            ThrowIfNoAdapter();
-
-            _lastPacketSentTimestamp = DateTime.UtcNow;
-            return _adapter.SendPacketAsync(packet, cancellationToken);
-        }
-
        void ThrowIfConnected(string message)
        {
            if (IsConnected)
@@ -782,16 +851,6 @@ namespace MQTTnet.Client
            }
        }

-        void ThrowIfNoAdapter()
-        {
-            // Having no adapter indicates that the connection is closed or still being created.
-            // Thus the client is disconnected.
-            if (_adapter == null)
-            {
-                ThrowNotConnected();
-            }
-        }
-
        void ThrowIfNotConnected()
        {
            if (!IsConnected)
@@ -829,7 +888,7 @@ namespace MQTTnet.Client
            {
                try
                {
-                    _mqttClientAlive?.Cancel(false);
+                    _clientAlive?.Cancel(false);
                }
                catch (Exception exception)
                {
@@ -838,7 +897,7 @@ namespace MQTTnet.Client
            }
        }

-        async Task TryProcessReceivedPacketAsync(MqttPacket packet, CancellationToken cancellationToken)
+        async Task TryProcessReceivedPacket(MqttPacket packet, CancellationToken cancellationToken)
        {
            try
            {
@@ -858,23 +917,31 @@ namespace MQTTnet.Client
                {
                    await ProcessReceivedDisconnectPacket(disconnectPacket).ConfigureAwait(false);
                }
-                else if (packet is MqttAuthPacket authPacket)
-                {
-                    await ProcessReceivedAuthPacket(authPacket).ConfigureAwait(false);
-                }
+                // else if (packet is MqttAuthPacket authPacket)
+                // {
+                //     await _authenticationHandler.HandleExtendedAuthentication(authPacket, new MqttInitialAuthenticationStrategy(_channelAdapter)).ConfigureAwait(false);
+                // }
                else if (packet is MqttPingRespPacket)
                {
                    _packetDispatcher.TryDispatch(packet);
                }
                else if (packet is MqttPingReqPacket)
                {
-                    throw new MqttProtocolViolationException("The PINGREQ Packet is sent from a Client to the Server only.");
+                    throw new MqttProtocolViolationException("The PINGREQ packet can only be sent from client to server.");
+                }
+                else if (packet is MqttConnAckPacket)
+                {
+                    throw new MqttProtocolViolationException("The CONNACK packet can only be send while connecting.");
+                }
+                else if (packet is MqttConnectPacket)
+                {
+                    throw new MqttProtocolViolationException("The CONNECT packet can only be sent from client to server.");
                }
                else
                {
                    if (!_packetDispatcher.TryDispatch(packet))
                    {
-                        throw new MqttProtocolViolationException($"Received packet '{packet}' at an unexpected time.");
+                        throw new MqttProtocolViolationException($"Received unexpected {packet} packet.");
                    }
                }
            }
@@ -899,133 +966,7 @@ namespace MQTTnet.Client

                _packetDispatcher.FailAll(exception);

-                await DisconnectInternalAsync(_packetReceiverTask, exception, null).ConfigureAwait(false);
-            }
-        }
-
-        async Task TryReceivePacketsAsync(CancellationToken cancellationToken)
-        {
-            try
-            {
-                _logger.Verbose("Start receiving packets.");
-
-                while (!cancellationToken.IsCancellationRequested)
-                {
-                    MqttPacket packet;
-                    var packetTask = _adapter.ReceivePacketAsync(cancellationToken);
-
-                    if (packetTask.IsCompleted)
-                    {
-                        packet = packetTask.Result;
-                    }
-                    else
-                    {
-                        packet = await packetTask.ConfigureAwait(false);
-                    }
-
-                    if (cancellationToken.IsCancellationRequested)
-                    {
-                        return;
-                    }
-
-                    if (packet == null)
-                    {
-                        await DisconnectInternalAsync(_packetReceiverTask, null, null).ConfigureAwait(false);
-
-                        return;
-                    }
-
-                    await TryProcessReceivedPacketAsync(packet, cancellationToken).ConfigureAwait(false);
-                }
-            }
-            catch (Exception exception)
-            {
-                if (_cleanDisconnectInitiated)
-                {
-                    return;
-                }
-
-                if (exception is AggregateException aggregateException)
-                {
-                    exception = aggregateException.GetBaseException();
-                }
-
-                if (exception is OperationCanceledException)
-                {
-                }
-                else if (exception is MqttCommunicationException)
-                {
-                    _logger.Warning(exception, "Communication error while receiving packets.");
-                }
-                else
-                {
-                    _logger.Error(exception, "Error while receiving packets.");
-                }
-
-                _packetDispatcher.FailAll(exception);
-
-                await DisconnectInternalAsync(_packetReceiverTask, exception, null).ConfigureAwait(false);
-            }
-            finally
-            {
-                _logger.Verbose("Stopped receiving packets.");
-            }
-        }
-
-        async Task TrySendKeepAliveMessagesAsync(CancellationToken cancellationToken)
-        {
-            try
-            {
-                _logger.Verbose("Start sending keep alive packets.");
-
-                var keepAlivePeriod = Options.KeepAlivePeriod;
-
-                while (!cancellationToken.IsCancellationRequested)
-                {
-                    // Values described here: [MQTT-3.1.2-24].
-                    var timeWithoutPacketSent = DateTime.UtcNow - _lastPacketSentTimestamp;
-
-                    if (timeWithoutPacketSent > keepAlivePeriod)
-                    {
-                        using (var timeoutCancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken))
-                        {
-                            timeoutCancellationTokenSource.CancelAfter(Options.Timeout);
-                            await PingAsync(timeoutCancellationTokenSource.Token).ConfigureAwait(false);
-                        }
-                    }
-
-                    // Wait a fixed time in all cases. Calculation of the remaining time is complicated
-                    // due to some edge cases and was buggy in the past. Now we wait several ms because the
-                    // min keep alive value is one second so that the server will wait 1.5 seconds for a PING
-                    // packet.
-                    await Task.Delay(250, cancellationToken).ConfigureAwait(false);
-                }
-            }
-            catch (Exception exception)
-            {
-                if (_cleanDisconnectInitiated)
-                {
-                    return;
-                }
-
-                if (exception is OperationCanceledException)
-                {
-                    return;
-                }
-                else if (exception is MqttCommunicationException)
-                {
-                    _logger.Warning(exception, "Communication error while sending/receiving keep alive packets.");
-                }
-                else
-                {
-                    _logger.Error(exception, "Error exception while sending/receiving keep alive packets.");
-                }
-
-                await DisconnectInternalAsync(_keepAlivePacketsSenderTask, exception, null).ConfigureAwait(false);
-            }
-            finally
-            {
-                _logger.Verbose("Stopped sending keep alive packets.");
+                await DisconnectInternal(_packetReceiverTask, exception, null).ConfigureAwait(false);
            }
        }
    }
@@ -14,6 +14,8 @@ namespace MQTTnet.Client
 {
    public static class MqttClientExtensions
    {
+        static readonly MqttReAuthenticationOptions EmptyReAuthenticationOptions = new MqttReAuthenticationOptions();
+
        public static Task DisconnectAsync(
            this IMqttClient client,
            MqttClientDisconnectOptionsReason reason = MqttClientDisconnectOptionsReason.NormalDisconnection,
@@ -77,6 +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)
@@ -88,16 +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)
@@ -12,6 +12,14 @@ 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.
        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
@@ -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.
@@ -92,6 +98,11 @@ namespace MQTTnet.Client
        /// </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.
@@ -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.

@@ -75,23 +75,35 @@ 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;
@@ -165,12 +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;
@@ -188,6 +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)
@@ -266,7 +284,7 @@ namespace MQTTnet.Client

            return this;
        }
-        
+
        public MqttClientOptionsBuilder WithTcpServer(Action<MqttClientTcpOptions> optionsBuilder)
        {
            if (optionsBuilder == null)
@@ -373,6 +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;
@@ -384,27 +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;
        }

@@ -413,38 +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;
        }
@@ -10,11 +10,7 @@ namespace MQTTnet.Client
 {
    public sealed class MqttClientSubscribeResult
    {
-        public MqttClientSubscribeResult(
-            ushort packetIdentifier,
-            IReadOnlyCollection<MqttClientSubscribeResultItem> items,
-            string reasonString,
-            IReadOnlyCollection<MqttUserProperty> userProperties)
+        public MqttClientSubscribeResult(ushort packetIdentifier, IReadOnlyCollection<MqttClientSubscribeResultItem> items, string reasonString, IReadOnlyCollection<MqttUserProperty> userProperties)
        {
            PacketIdentifier = packetIdentifier;
            Items = items ?? throw new ArgumentNullException(nameof(items));
@@ -23,26 +19,25 @@ namespace MQTTnet.Client
        }

        /// <summary>
-        ///     Gets the result for every topic filter item.
+        /// 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.
+        /// Gets the user properties which were part of the SUBACK packet.
+        /// <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
-        public ushort PacketIdentifier { get; }
-
+        public IReadOnlyCollection<MqttUserProperty> UserProperties { get; }
+        
        /// <summary>
-        ///     Gets the reason string.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// Gets the reason string.
+        /// <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
        public string ReasonString { get; }

        /// <summary>
-        ///     Gets the user properties which were part of the SUBACK packet.
-        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// Gets the packet identifier which was used.
        /// </summary>
-        public IReadOnlyCollection<MqttUserProperty> UserProperties { get; }
+        public ushort PacketIdentifier { get; }
    }
 }
@@ -27,4 +27,4 @@ namespace MQTTnet.Client
        /// </summary>
        public MqttClientSubscribeResultCode ResultCode { get; }
    }
-}
+}
@@ -42,6 +42,6 @@ namespace MQTTnet.Client
        ///     Gets the user properties which were part of the UNSUBACK packet.
        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
        /// </summary>
-        public IReadOnlyCollection<MqttUserProperty> UserProperties { get; }
+        public IReadOnlyCollection<MqttUserProperty> UserProperties { get; set; }
    }
 }
@@ -101,13 +101,6 @@ namespace MQTTnet.Diagnostics

            logger.Publish(logLevel, message, new object[] { parameter1, parameter2 }, exception);
        }
-        
-        public static MqttNetSourceLogger WithSource<TSource>(this IMqttNetLogger logger)
-        {
-            if (logger == null) throw new ArgumentNullException(nameof(logger));
-
-            return new MqttNetSourceLogger(logger, typeof(TSource).Name);
-        }

        public static void Verbose<TParameter1>(this MqttNetSourceLogger logger, string message, TParameter1 parameter1)
        {
@@ -19,7 +19,7 @@ namespace MQTTnet.Formatter
            return new MqttApplicationMessage
            {
                Topic = publishPacket.Topic,
-                Payload = publishPacket.Payload,
+                PayloadSegment = publishPacket.PayloadSegment,
                QualityOfServiceLevel = publishPacket.QualityOfServiceLevel,
                Retain = publishPacket.Retain,
                Dup = publishPacket.Dup,
@@ -0,0 +1,37 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using MQTTnet.Client;
+using MQTTnet.Packets;
+using MQTTnet.Protocol;
+
+namespace MQTTnet.Formatter
+{
+    public sealed class MqttAuthPacketFactory
+    {
+        public MqttAuthPacket CreateReAuthenticationPacket(MqttClientOptions clientOptions, MqttReAuthenticationOptions reAuthenticationOptions)
+        {
+            if (clientOptions == null)
+            {
+                throw new ArgumentNullException(nameof(clientOptions));
+            }
+
+            if (reAuthenticationOptions == null)
+            {
+                throw new ArgumentNullException(nameof(reAuthenticationOptions));
+            }
+
+            return new MqttAuthPacket
+            {
+                // The authentication method cannot change and must be always the same as long as the client is connected.
+                AuthenticationMethod = clientOptions.AuthenticationMethod,
+                ReasonCode = MqttAuthenticateReasonCode.ReAuthenticate,
+                AuthenticationData = reAuthenticationOptions.AuthenticationData,
+                UserProperties = reAuthenticationOptions.UserProperties,
+                ReasonString = null
+            };
+        }
+    }
+}
@@ -19,7 +19,8 @@ namespace MQTTnet.Formatter
    /// </summary>
    public sealed class MqttBufferWriter
    {
-        public const uint VariableByteIntegerMaxValue = 268435455;
+        const uint VariableByteIntegerMaxValue = 268435455;
+        const int EncodedStringMaxLength = 65535;

        readonly int _maxBufferSize;

@@ -112,25 +113,7 @@ namespace MQTTnet.Formatter
            WriteBinary(propertyWriter._buffer, 0, propertyWriter.Length);
        }

-        public void WriteBinary(byte[] buffer, int offset, int count)
-        {
-            if (buffer == null)
-            {
-                throw new ArgumentNullException(nameof(buffer));
-            }
-
-            if (count == 0)
-            {
-                return;
-            }
-
-            EnsureAdditionalCapacity(count);
-
-            MqttMemoryHelper.Copy(buffer, offset, _buffer, _position, count);
-            IncreasePosition(count);
-        }
-
-        public void WriteBinaryData(byte[] value)
+        public void WriteBinary(byte[] value)
        {
            if (value == null || value.Length == 0)
            {
@@ -155,6 +138,24 @@ namespace MQTTnet.Formatter
            }
        }

+        public void WriteBinary(byte[] buffer, int offset, int count)
+        {
+            if (buffer == null)
+            {
+                throw new ArgumentNullException(nameof(buffer));
+            }
+
+            if (count == 0)
+            {
+                return;
+            }
+
+            EnsureAdditionalCapacity(count);
+
+            MqttMemoryHelper.Copy(buffer, offset, _buffer, _position, count);
+            IncreasePosition(count);
+        }
+
        public void WriteByte(byte @byte)
        {
            EnsureAdditionalCapacity(1);
@@ -186,6 +187,13 @@ namespace MQTTnet.Formatter

                var writtenBytes = Encoding.UTF8.GetBytes(value, 0, value.Length, _buffer, _position + 2);

+                // From RFC: 1.5.4 UTF-8 Encoded String
+                // Unless stated otherwise all UTF-8 encoded strings can have any length in the range 0 to 65,535 bytes.
+                if (writtenBytes > EncodedStringMaxLength)
+                {
+                    throw new MqttProtocolViolationException($"The maximum string length is 65535. The current string has a length of {writtenBytes}.");
+                }
+
                _buffer[_position] = (byte)(writtenBytes >> 8);
                _buffer[_position + 1] = (byte)writtenBytes;

@@ -273,8 +281,7 @@ namespace MQTTnet.Formatter
                newBufferLength *= 2;
            }

-            // Array.Resize will create a new array and copy the existing
-            // data to the new one.
+            // Array.Resize will create a new array and copy the existing data to the new one.
            Array.Resize(ref _buffer, newBufferLength);
        }

@@ -285,6 +292,8 @@ namespace MQTTnet.Formatter

            if (_position > Length)
            {
+                // Also extend the position because we reached the end of the 
+                // pre allocated buffer.
                Length = _position;
            }
        }
@@ -59,6 +59,8 @@ namespace MQTTnet.Formatter
                    return MqttConnectReturnCode.ConnectionAccepted;
                }

+                case MqttConnectReasonCode.BadAuthenticationMethod:
+                case MqttConnectReasonCode.Banned:
                case MqttConnectReasonCode.NotAuthorized:
                {
                    return MqttConnectReturnCode.ConnectionRefusedNotAuthorized;
@@ -73,12 +75,13 @@ namespace MQTTnet.Formatter
                {
                    return MqttConnectReturnCode.ConnectionRefusedIdentifierRejected;
                }
-
+                
                case MqttConnectReasonCode.UnsupportedProtocolVersion:
                {
                    return MqttConnectReturnCode.ConnectionRefusedUnacceptableProtocolVersion;
                }
-
+                
+                case MqttConnectReasonCode.UseAnotherServer:
                case MqttConnectReasonCode.ServerUnavailable:
                case MqttConnectReasonCode.ServerBusy:
                case MqttConnectReasonCode.ServerMoved:
@@ -88,7 +91,8 @@ namespace MQTTnet.Formatter

                default:
                {
-                    throw new MqttProtocolViolationException("Unable to convert connect reason code (MQTTv5) to return code (MQTTv3).");
+                    // This is the most best matching value.
+                    return MqttConnectReturnCode.ConnectionRefusedUnacceptableProtocolVersion;
                }
            }
        }
@@ -6,6 +6,8 @@ namespace MQTTnet.Formatter
 {
    public static class MqttPacketFactories
    {
+        public static MqttAuthPacketFactory Auth { get; } = new MqttAuthPacketFactory();
+        
        public static MqttConnAckPacketFactory ConnAck { get; } = new MqttConnAckPacketFactory();
        
        public static MqttConnectPacketFactory Connect { get; } = new MqttConnectPacketFactory();
@@ -31,10 +31,14 @@ namespace MQTTnet.Formatter

        public MqttProtocolVersion ProtocolVersion { get; private set; } = MqttProtocolVersion.Unknown;

+        public void Cleanup()
+        {
+            _bufferWriter.Cleanup();
+        }
+
        public MqttPacket Decode(ReceivedMqttPacket receivedMqttPacket)
        {
            ThrowIfFormatterNotSet();
-
            return _formatter.Decode(receivedMqttPacket);
        }

@@ -50,11 +54,6 @@ namespace MQTTnet.Formatter
            return _formatter.Encode(packet);
        }

-        public void Cleanup()
-        {
-            _bufferWriter.Cleanup();
-        }
-
        public static IMqttPacketFormatter GetMqttPacketFormatter(MqttProtocolVersion protocolVersion, MqttBufferWriter bufferWriter)
        {
            if (protocolVersion == MqttProtocolVersion.Unknown)
@@ -98,7 +97,7 @@ namespace MQTTnet.Formatter
            // Remove the mosquitto try_private flag (MQTT 3.1.1 Bridge).
            // This flag is accepted but not yet used.
            protocolLevel &= 0x7F;
-            
+
            if (protocolName == "MQTT")
            {
                if (protocolLevel == 5)
@@ -16,7 +16,7 @@ namespace MQTTnet.Formatter
            return new MqttPublishPacket
            {
                Topic = publishPacket.Topic,
-                Payload = publishPacket.Payload,
+                PayloadSegment = publishPacket.PayloadSegment, 
                Retain = publishPacket.Retain,
                QualityOfServiceLevel = publishPacket.QualityOfServiceLevel,
                Dup = publishPacket.Dup,
@@ -36,7 +36,7 @@ namespace MQTTnet.Formatter
            var packet = new MqttPublishPacket
            {
                Topic = applicationMessage.Topic,
-                Payload = applicationMessage.Payload,
+                PayloadSegment = applicationMessage.PayloadSegment, 
                QualityOfServiceLevel = applicationMessage.QualityOfServiceLevel,
                Retain = applicationMessage.Retain,
                Dup = applicationMessage.Dup,
@@ -65,10 +65,16 @@ namespace MQTTnet.Formatter
                throw new MqttProtocolViolationException("The CONNECT packet contains no will message (WillFlag).");
            }

+            ArraySegment<byte> willMessageBuffer = default;
+            if (connectPacket.WillMessage?.Length > 0)
+            {
+                willMessageBuffer = new ArraySegment<byte>(connectPacket.WillMessage);
+            }
+
            var packet = new MqttPublishPacket
            {
                Topic = connectPacket.WillTopic,
-                Payload = connectPacket.WillMessage,
+                PayloadSegment = willMessageBuffer,
                QualityOfServiceLevel = connectPacket.WillQoS,
                Retain = connectPacket.WillRetain,
                ContentType = connectPacket.WillContentType,
@@ -54,12 +54,12 @@ namespace MQTTnet.Formatter.V3
                    return DecodePubRelPacket(receivedMqttPacket.Body);
                case MqttControlPacketType.PubComp:
                    return DecodePubCompPacket(receivedMqttPacket.Body);
-                
+
                case MqttControlPacketType.PingReq:
                    return MqttPingReqPacket.Instance;
                case MqttControlPacketType.PingResp:
                    return MqttPingRespPacket.Instance;
-                
+
                case MqttControlPacketType.Connect:
                    return DecodeConnectPacket(receivedMqttPacket.Body);
                case MqttControlPacketType.ConnAck:
@@ -73,7 +73,7 @@ namespace MQTTnet.Formatter.V3
                    }
                case MqttControlPacketType.Disconnect:
                    return DisconnectPacket;
-                
+
                case MqttControlPacketType.Subscribe:
                    return DecodeSubscribePacket(receivedMqttPacket.Body);
                case MqttControlPacketType.SubAck:
@@ -103,9 +103,10 @@ namespace MQTTnet.Formatter.V3
            var remainingLength = (uint)(_bufferWriter.Length - 5);

            var publishPacket = packet as MqttPublishPacket;
-            if (publishPacket?.Payload != null)
+            var payloadSegment = publishPacket?.PayloadSegment;
+            if (payloadSegment != null)
            {
-                remainingLength += (uint)publishPacket.Payload.Length;
+                remainingLength += (uint)payloadSegment.Value.Count;
            }

            var remainingLengthSize = MqttBufferWriter.GetVariableByteIntegerSize(remainingLength);
@@ -119,18 +120,13 @@ namespace MQTTnet.Formatter.V3
            _bufferWriter.WriteVariableByteInteger(remainingLength);

            var buffer = _bufferWriter.GetBuffer();
-
            var firstSegment = new ArraySegment<byte>(buffer, headerOffset, _bufferWriter.Length - headerOffset);

-            if (publishPacket?.Payload != null)
-            {
-                var payloadSegment = new ArraySegment<byte>(publishPacket.Payload, 0, publishPacket.Payload.Length);
-                return new MqttPacketBuffer(firstSegment, payloadSegment);
-            }
-
-            return new MqttPacketBuffer(firstSegment);
+            return payloadSegment == null
+                ? new MqttPacketBuffer(firstSegment)
+                : new MqttPacketBuffer(firstSegment, payloadSegment.Value);
        }
-        
+
        MqttPacket DecodeConnAckPacket(ArraySegment<byte> body)
        {
            ThrowIfBodyIsEmpty(body);
@@ -177,7 +173,7 @@ namespace MQTTnet.Formatter.V3

            var tryPrivate = (protocolVersion & 0x80) > 0;
            protocolVersion &= 0x7F;
-            
+
            if (protocolVersion != 3 && protocolVersion != 4)
            {
                throw new MqttProtocolViolationException("MQTT protocol version do not match MQTT v3.");
@@ -282,7 +278,7 @@ namespace MQTTnet.Formatter.V3

            if (!_bufferReader.EndOfStream)
            {
-                packet.Payload = _bufferReader.ReadRemainingData();
+                packet.PayloadSegment = new ArraySegment<byte>(_bufferReader.ReadRemainingData());
            }

            return packet;
@@ -421,7 +417,7 @@ namespace MQTTnet.Formatter.V3
            {
                protocolVersion |= 0x80;
            }
-            
+
            bufferWriter.WriteByte((byte)protocolVersion);

            byte connectFlags = 0x0;
@@ -463,7 +459,7 @@ namespace MQTTnet.Formatter.V3
            if (packet.WillFlag)
            {
                bufferWriter.WriteString(packet.WillTopic);
-                bufferWriter.WriteBinaryData(packet.WillMessage);
+                bufferWriter.WriteBinary(packet.WillMessage);
            }

            if (packet.Username != null)
@@ -473,7 +469,7 @@ namespace MQTTnet.Formatter.V3

            if (packet.Password != null)
            {
-                bufferWriter.WriteBinaryData(packet.Password);
+                bufferWriter.WriteBinary(packet.Password);
            }

            return MqttBufferWriter.BuildFixedHeader(MqttControlPacketType.Connect);
@@ -525,7 +521,7 @@ namespace MQTTnet.Formatter.V3
            if (packet.WillFlag)
            {
                bufferWriter.WriteString(packet.WillTopic);
-                bufferWriter.WriteBinaryData(packet.WillMessage);
+                bufferWriter.WriteBinary(packet.WillMessage);
            }

            if (packet.Username != null)
@@ -535,7 +531,7 @@ namespace MQTTnet.Formatter.V3

            if (packet.Password != null)
            {
-                bufferWriter.WriteBinaryData(packet.Password);
+                bufferWriter.WriteBinary(packet.Password);
            }

            return MqttBufferWriter.BuildFixedHeader(MqttControlPacketType.Connect);
@@ -528,7 +528,7 @@ namespace MQTTnet.Formatter.V5

            if (!_bufferReader.EndOfStream)
            {
-                packet.Payload = _bufferReader.ReadRemainingData();
+                packet.PayloadSegment = new ArraySegment<byte>(_bufferReader.ReadRemainingData());
            }

            return packet;
--- a/Show More
+++ b/Show More
Author	SHA1	Message	Date
Christian	df0b268a08	Add new API for extended authentication	2023-05-07 18:27:11 +02:00
Christian	addf812d58	Add warning	2023-05-06 14:17:39 +02:00
Christian	533b8e22c2	Fix breaking changes	2023-05-06 13:09:02 +02:00
Christian	3aaf101b3b	Merge branch 'master' into 1681-misleading-signature-of-mqttclientconnectasync-mqttclientconnectresultcode-expected-but-throws-exception	2023-05-06 13:03:13 +02:00
Christian	449624fd72	Expose proper connect result in clients Disconnected event (#1728 )	2023-05-06 12:49:41 +02:00
Christian	99f4f46062	Add new overloads for packet payload and will payload (#1721 )	2023-05-04 22:19:06 +02:00
henry Zeheng Feng Christian	b08d11c069	replace lock/semaphore by readerwriterlockslim to avoid lock contenti… (#1716 ) * 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>	2023-05-01 13:53:15 +02:00
Christian	ac41e838ec	Merge branch 'master' of https://github.com/dotnet/MQTTnet	2023-05-01 12:20:26 +02:00
Christian	836ddf3bbc	Update version	2023-05-01 12:20:20 +02:00
Christian	0e815c626c	Add validation of string lengths (#1718 )	2023-05-01 12:03:23 +02:00
Christian	9d9076ba77	Fix build	2023-04-29 13:47:38 +02:00
Christian	af1c151e8e	Merge branch 'master' into 1681-misleading-signature-of-mqttclientconnectasync-mqttclientconnectresultcode-expected-but-throws-exception	2023-04-29 12:45:17 +02:00
Christian	4b7d035e9e	Reset release notes	2023-04-29 12:37:36 +02:00
Christian	cb3c44f48d	Rename InspectPackage method (#1713 )	2023-04-23 13:57:59 +02:00
Christian	8b3b9d33de	Add overloads for options builder (#1711 ) * Add new overload for options builder * Refactor code * Update ReleaseNotes.md	2023-04-11 22:11:16 +02:00
scottbrogden-iheartmediaandChristian	59d99509c8	Notify what subscription topics failed as part of the SynchronizingSu… (#1678 ) * Notify what subscription topics failed as part of the SynchronizingSubscriptionsFailedAsync callback * Update ReleaseNotes.md --------- Co-authored-by: Christian <6939810+chkr1011@users.noreply.github.com>	2023-04-08 14:03:58 +02:00
RossHNPCandChristian	2933b76237	ClientMessageQueueInterceptor continues with subscription processing. (#1685 ) * ClientMessageQueueInterceptor continues with subscription processing. * Update readme --------- Co-authored-by: Christian <6939810+chkr1011@users.noreply.github.com>	2023-04-06 17:55:33 +02:00
ChristianandMichi	36c6d8974e	Allow disabling of packet fragmentation (#1709 ) * Add compatibility option for AWS * Fix UWP build * Fix comment in MqttClientOptions (#1706) * Refactor naming * Fix wrong option value --------- Co-authored-by: Michi <michael@volz.dev>	2023-04-06 17:54:36 +02:00
Christian	d6cab76728	Add user properties to event args to interceptors for subscribing and unsubscribing (#1707 ) Add user properties to event args	2023-04-06 17:31:42 +02:00
Christian	b4f740f338	Update readme	2023-04-05 22:12:58 +02:00
Christian	202e299f65	Move code into dedicated components	2023-03-08 17:04:44 +01:00
Christian	a004de25ac	Fix unit test	2023-02-22 21:46:33 +01:00
Christian	129348c07b	Refactor connection creation	2023-02-22 21:45:40 +01:00
老九	d0584413ca	Add PayloadSegmentable feature (#1585 )	2023-02-22 20:53:55 +01:00
Christian	ba57537108	Fix running state handling in server (#1680 ) Fix running state handling	2023-02-17 21:17:31 +01:00
Christian	6dcb110737	Add InterceptingClientEnqueueAsync event (#1679 )	2023-02-17 19:13:06 +01:00
Christian	b599a832da	Add new method for reading a single retained message (#1676 )	2023-02-15 19:46:37 +01:00
Christian	9cbd5dd778	Update ReleaseNotes.md	2023-01-28 13:08:24 +01:00
Christian	ed31c51237	Code cleanup	2023-01-28 13:08:21 +01:00
Christian	e01707d25e	Improve samples	2023-01-28 13:08:08 +01:00
Jeffery MichaelandJeff Scherrer	73f118fe1c	Moved the usage of certificate provider into the server listener (#1652 ) * Moved the usage of certificate provider into the server listener so that each connection has the posibility of receiving a new SSL cert. * Removed warning from unused field. * Reduced changeds on original codebase. --------- Co-authored-by: Jeff Scherrer <Jeff.Scherrer@vw.com>	2023-01-28 12:18:31 +01:00
Int32Overflow	0234918f30	Performance impact fix (#1661 )	2023-01-28 12:12:20 +01:00
Jeffery Michael	c90ba7e061	Fixed broken UWP build (#1655 ) Added compiler declaritive to check for WINDOWS_UWP on IsAssignableFrom call.	2023-01-28 12:02:22 +01:00