Rename InspectPackage method (#1713)

* Add new overload for options builder

* Refactor code

* Update ReleaseNotes.md

.github/workflows/ReleaseNotes.md

@@ -1,8 +1,20 @@
 * [Core] Added net7.0 builds (#1635, thanks to @YAJeff).
+* [Core] Added support for payload segments (#1585, thanks to @xljiulang)
 * [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!).
+* [Client] Added support for disabling packet fragmentation (required for i.e. AWS, #1690, thanks to @logicaloud).
+* [Client] Added new overloads for options builder.
+* [Client] Renamed _InspectPackage_ to _InspectPacketAsync_ (BREAKING CHANGE).
+* [ManagedClient] Exposed added and removed topics in _ManagedProcessFailedEventArgs_ (#1678, thanks to @scottbrogden-iheartmedia).
 * [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] 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).
+* [Server] Improved performance for retained message handling when subscribing using "DoNotSendOnSubscribe" or "SendAtSubscribeIfNewSubscriptionOnly" (#1661, thanks to @Int32Overflow).
+* [Server] Added support for changing the used TLS certificate while the server is running (#1652, thanks to @YAJeff). The certificate provider will now be invoked for every new connection!
+* [Server] Added a new API method which allows reading a single retained message without the need to processing the entire set of retained messages (#1659).
+* [Server] Added a new event (InterceptingClientEnqueueAsync) which allows intercepting when an application message is enqueued for a client (#1648).
+* [Server] Fixed race condition when handling connections which leads to stopped message transfers (#1677, thanks to @RazvanEmilR).
+* [Server] Fixed not delivered packets to other sessions if the _InterceptingClientEnqueueEvent_ is used and accepting the packet is denied (#1685, thanks to @RossHNPC).
+* [Server] Added missing user properties to subscribe and unsubscribe interceptor (#1702).

MQTTnet.sln.DotSettings

@@ -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>
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 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/WRAP_PARAMETERS_STYLE/@EntryValue">CHOP_IF_LONG</s:String>
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 	<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>

README.md

@@ -50,6 +50,22 @@ MQTTnet is a high performance .NET library for MQTT based communication. It prov
 * A custom message interceptor can be added which allows transforming or extending every received application message
 * Validate subscriptions and deny subscribing of certain topics depending on requesting clients
 
+## Getting Started
+
+MQTTnet is delivered via <b>NuGet</b> package manager. You can find the packages here: https://www.nuget.org/packages/MQTTnet/
+
+Use these command in the Package Manager console to install MQTTnet manually:
+```
+Install-Package MQTTnet
+```
+
+Samples for using MQTTnet are part of this repository. For starters these samples are recommended:
+
+- [Connect with a broker](https://github.com/dotnet/MQTTnet/blob/master/Samples/Client/Client_Connection_Samples.cs)
+- [Subscribing to data](https://github.com/dotnet/MQTTnet/blob/master/Samples/Client/Client_Subscribe_Samples.cs)
+- [Publishing data](https://github.com/dotnet/MQTTnet/blob/master/Samples/Client/Client_Publish_Samples.cs)
+- [Host own broker](https://github.com/dotnet/MQTTnet/blob/master/Samples/Server/Server_Simple_Samples.cs)
+
 ## Code of Conduct
 
 This project has adopted the code of conduct defined by the Contributor Covenant to clarify expected behavior in our community.

Samples/Client/Client_Connection_Samples.cs

@@ -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()
     {

Samples/Diagnostics/PackageInspection_Samples.cs

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

Samples/ManagedClient/Managed_Client_Simple_Samples.cs

@@ -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}");
         }
     }
 }

Samples/Program.cs

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

Samples/Server/Server_ASP_NET_Samples.cs

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

Samples/Server/Server_TLS_Samples.cs

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

Source/MQTTnet.AspNetCore.Tests/MqttConnectionContextTest.cs

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

Source/MQTTnet.AspNetCore.Tests/ReaderExtensionsTest.cs

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

Source/MQTTnet.AspnetCore/MqttWebSocketServerAdapter.cs

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

Source/MQTTnet.Benchmarks/ChannelAdapterBenchmark.cs

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

Source/MQTTnet.Benchmarks/SerializerBenchmark.cs

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

Source/MQTTnet.Extensions.ManagedClient/ApplicationMessageProcessedEventArgs.cs

@@ -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;
     }
-}
+}

Source/MQTTnet.Extensions.ManagedClient/ApplicationMessageSkippedEventArgs.cs

@@ -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; }
     }
-}
+}

Source/MQTTnet.Extensions.ManagedClient/ConnectingFailedEventArgs.cs

@@ -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; }
 

Source/MQTTnet.Extensions.ManagedClient/IManagedMqttClient.cs

@@ -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);
     }
 }

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

@@ -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>

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

@@ -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>

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttApplicationMessage.cs

@@ -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; }
     }
 }

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttApplicationMessageBuilder.cs

@@ -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
+            };
         }
     }
-}
+}

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClient.cs

@@ -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);
             }
         }
 

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClientExtensions.cs

@@ -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 });
         }
     }
 }

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClientOptions.cs

@@ -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;
     }

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClientOptionsBuilder.cs

@@ -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;

Source/MQTTnet.Extensions.ManagedClient/ManagedProcessFailedEventArgs.cs

@@ -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; }
+    }
+}

Source/MQTTnet.Extensions.ManagedClient/MqttFactoryExtensions.cs

@@ -10,54 +10,24 @@ 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)
-            {
-                throw new ArgumentNullException(nameof(factory));
-            }
+            if (factory == null) throw new ArgumentNullException(nameof(factory));
 
             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)
         {
-            if (factory == null)
-            {
-                throw new ArgumentNullException(nameof(factory));
-            }
+            if (factory == null) throw new ArgumentNullException(nameof(factory));
+            if (logger == null) throw new ArgumentNullException(nameof(logger));
 
-            if (logger == null)
-            {
-                throw new ArgumentNullException(nameof(logger));
-            }
-
-            return new NewManagedMqttClient(factory.CreateMqttClient(logger), logger);
-        }
-
-        public static ManagedMqttClientOptionsBuilder CreateManagedMqttClientOptionsBuilder(this MqttFactory factory)
-        {
-            return new ManagedMqttClientOptionsBuilder();
+            return new ManagedMqttClient(factory.CreateMqttClient(logger), logger);
         }
     }
 }

Source/MQTTnet.Extensions.ManagedClient/New/ApplicationMessagesManager.cs

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

Source/MQTTnet.Extensions.ManagedClient/New/Events/ApplicationMessageEnqueueingEventArgs.cs

@@ -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; }
-    }
-}

Source/MQTTnet.Extensions.ManagedClient/New/Events/ManagedProcessFailedEventArgs.cs

@@ -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; }
-    }
-}

Source/MQTTnet.Extensions.ManagedClient/New/Events/SubscribeProcessedEventArgs.cs

@@ -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; }
-    }
-}

Source/MQTTnet.Extensions.ManagedClient/New/Events/UnsubscribeProcessedEventArgs.cs

@@ -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; }
-    }
-}

Source/MQTTnet.Extensions.ManagedClient/New/MaintainConnectionResult.cs

@@ -1,15 +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.
-
-namespace MQTTnet.Extensions.ManagedClient
-{
-    public enum MaintainConnectionResult
-    {
-        NoChange,
-
-        ConnectedEstablished,
-
-        NotConnected
-    }
-}

Source/MQTTnet.Extensions.ManagedClient/New/ManagedMqttSubscription.cs

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

Source/MQTTnet.Extensions.ManagedClient/New/ManagedMqttSubscriptionsManager.cs

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

Source/MQTTnet.Extensions.ManagedClient/New/MqttConnectionManager.cs

@@ -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);
-        }
-    }
-}

Source/MQTTnet.Extensions.ManagedClient/New/NewManagedMqttClient.cs

@@ -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!
-        }
-    }
-}

Source/MQTTnet.Extensions.Rpc/MqttRpcClient.cs

@@ -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;

Source/MQTTnet.Extensions.WebSocket4Net/WebSocket4NetMqttClientAdapterFactory.cs

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

Source/MQTTnet.TestApp/ClientTest.cs

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

Source/MQTTnet.TestApp/PerformanceTest.cs

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

Source/MQTTnet.TestApp/ServerTest.cs

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

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

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

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

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

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

@@ -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 +20,79 @@ 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 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 +119,76 @@ 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 +199,18 @@ 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 +226,7 @@ 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 +266,6 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
         {
             using (var testEnvironment = CreateTestEnvironment())
             {
-                await testEnvironment.StartServer();
-
                 var unmanagedClient = testEnvironment.CreateClient();
                 var managedClient = await CreateManagedClientAsync(testEnvironment, unmanagedClient);
 
@@ -208,7 +282,7 @@ 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 +312,7 @@ 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 +328,7 @@ 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 +338,12 @@ 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 +353,7 @@ 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 +361,7 @@ 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 +371,7 @@ 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 +383,12 @@ 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 +413,7 @@ 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 +439,14 @@ 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 +456,7 @@ 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 +467,35 @@ 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 +518,7 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
 
     public class ManagedMqttClientTestStorage : IManagedMqttClientStorage
     {
-        IList<ManagedMqttApplicationMessage> _messages = new List<ManagedMqttApplicationMessage>();
+        IList<ManagedMqttApplicationMessage> _messages;
 
         public int GetMessageCount()
         {
@@ -483,6 +527,11 @@ namespace MQTTnet.Tests.Clients.ManagedMqttClient
 
         public Task<IList<ManagedMqttApplicationMessage>> LoadQueuedMessagesAsync()
         {
+            if (_messages == null)
+            {
+                _messages = new List<ManagedMqttApplicationMessage>();
+            }
+
             return Task.FromResult(_messages);
         }
 

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

@@ -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);
             }
@@ -150,6 +152,8 @@ namespace MQTTnet.Tests.Clients.MqttClient
 
                 // Perform a clean disconnect.
                 await client.DisconnectAsync(disconnectOptions);
+
+                await LongTestDelay();
                 
                 Assert.IsNotNull(eventArgs);
                 Assert.IsNotNull(eventArgs.UserProperties);

Source/MQTTnet.Tests/Diagnostics/PacketInspection_Tests.cs

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

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V3_Binary_Tests.cs

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

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V3_Tests.cs

@@ -2,7 +2,9 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Text;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Exceptions;
@@ -296,7 +298,7 @@ namespace MQTTnet.Tests.Formatter
                 PacketIdentifier = 123,
                 Dup = true,
                 Retain = true,
-                Payload = Encoding.ASCII.GetBytes("Payload"),
+                PayloadSegment = new ArraySegment<byte>(Encoding.ASCII.GetBytes("Payload")),
                 QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce,
                 Topic = "Topic",
                 ResponseTopic = "/Response",
@@ -320,7 +322,7 @@ namespace MQTTnet.Tests.Formatter
             Assert.AreEqual(publishPacket.PacketIdentifier, deserialized.PacketIdentifier);
             Assert.AreEqual(publishPacket.Dup, deserialized.Dup);
             Assert.AreEqual(publishPacket.Retain, deserialized.Retain);
-            CollectionAssert.AreEqual(publishPacket.Payload, deserialized.Payload);
+            CollectionAssert.AreEqual(publishPacket.PayloadSegment.ToArray(), deserialized.PayloadSegment.ToArray());
             Assert.AreEqual(publishPacket.QualityOfServiceLevel, deserialized.QualityOfServiceLevel);
             Assert.AreEqual(publishPacket.Topic, deserialized.Topic);
             Assert.AreEqual(null, deserialized.ResponseTopic); // Not supported in v3.1.1.

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V5_Tests.cs

@@ -2,7 +2,9 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Text;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Formatter;
@@ -257,7 +259,7 @@ namespace MQTTnet.Tests.Formatter
                 PacketIdentifier = 123,
                 Dup = true,
                 Retain = true,
-                Payload = Encoding.ASCII.GetBytes("Payload"),
+                PayloadSegment = new ArraySegment<byte>(Encoding.ASCII.GetBytes("Payload")),
                 QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce,
                 Topic = "Topic",
                 ResponseTopic = "/Response",
@@ -281,7 +283,7 @@ namespace MQTTnet.Tests.Formatter
             Assert.AreEqual(publishPacket.PacketIdentifier, deserialized.PacketIdentifier);
             Assert.AreEqual(publishPacket.Dup, deserialized.Dup);
             Assert.AreEqual(publishPacket.Retain, deserialized.Retain);
-            CollectionAssert.AreEqual(publishPacket.Payload, deserialized.Payload);
+            CollectionAssert.AreEqual(publishPacket.PayloadSegment.ToArray(), deserialized.PayloadSegment.ToArray());
             Assert.AreEqual(publishPacket.QualityOfServiceLevel, deserialized.QualityOfServiceLevel);
             Assert.AreEqual(publishPacket.Topic, deserialized.Topic);
             Assert.AreEqual(publishPacket.ResponseTopic, deserialized.ResponseTopic);

Source/MQTTnet.Tests/Mockups/TestApplicationMessageReceivedHandler.cs

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

Source/MQTTnet.Tests/Mockups/TestEnvironment.cs

@@ -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();
@@ -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)
@@ -340,18 +306,6 @@ namespace MQTTnet.Tests.Mockups
                 }
             }
 
-            foreach (var managedMqttClient in _managedClients)
-            {
-                try
-                {
-                    managedMqttClient.StopAsync().Wait();
-                }
-                finally
-                {
-                    managedMqttClient.Dispose();
-                }
-            }
-
             foreach (var lowLevelMqttClient in _lowLevelClients)
             {
                 lowLevelMqttClient.Dispose();
@@ -378,13 +332,6 @@ 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 +401,5 @@ namespace MQTTnet.Tests.Mockups
                 _exceptions.Add(exception);
             }
         }
-
-        Task ServerOnInterceptingPublishAsync(InterceptingPublishEventArgs arg)
-        {
-            lock (ServerReceivedApplicationMessages)
-            {
-                ServerReceivedApplicationMessages.Add(arg.ApplicationMessage);
-            }
-
-            return CompletedTask.Instance;
-        }
     }
 }

Source/MQTTnet.Tests/MqttApplicationMessageTest.cs

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

Source/MQTTnet.Tests/MqttPacketSerializationHelper.cs

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

Source/MQTTnet.Tests/Server/General.cs

@@ -954,7 +954,7 @@ namespace MQTTnet.Tests.Server
 
                 var client = testEnvironment.CreateClient();
 
-                client.InspectPackage += e =>
+                client.InspectPacketAsync += e =>
                 {
                     if (e.Buffer.Length > 0)
                     {

Source/MQTTnet.Tests/Server/MqttSubscriptionsManager_Tests.cs

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

Source/MQTTnet.Tests/Server/Publish_Tests.cs

@@ -1,58 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System.Threading.Tasks;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MQTTnet.Client;
-using MQTTnet.Formatter;
-using MQTTnet.Protocol;
-
-namespace MQTTnet.Tests.Server
-{
-    [TestClass]
-    public sealed class Publish_Tests : BaseTestClass
-    {
-        [TestMethod]
-        public async Task Return_Success_When_Subscribed()
-        {
-            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
-            {
-                await testEnvironment.StartServer();
-
-                var sender = await testEnvironment.ConnectClient();
-                var receiver = await testEnvironment.ConnectClient();
-
-                await receiver.SubscribeAsync("A");
-
-                // AtLeastOnce is required to get an ACK packet from the server.
-                var publishResult = await sender.PublishStringAsync("A", "Payload", MqttQualityOfServiceLevel.AtLeastOnce);
-                
-                Assert.AreEqual(MqttClientPublishReasonCode.Success, publishResult.ReasonCode);
-                
-                Assert.AreEqual(true, publishResult.IsSuccess);
-            }
-        }
-        
-        [TestMethod]
-        public async Task Return_NoMatchingSubscribers_When_Not_Subscribed()
-        {
-            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
-            {
-                await testEnvironment.StartServer();
-
-                var sender = await testEnvironment.ConnectClient();
-                var receiver = await testEnvironment.ConnectClient();
-             
-                await receiver.SubscribeAsync("A");
-
-                // AtLeastOnce is required to get an ACK packet from the server.
-                var publishResult = await sender.PublishStringAsync("B", "Payload", MqttQualityOfServiceLevel.AtLeastOnce);
-                
-                Assert.AreEqual(MqttClientPublishReasonCode.NoMatchingSubscribers, publishResult.ReasonCode);
-                
-                Assert.AreEqual(true, publishResult.IsSuccess);
-            }
-        }
-    }
-}

Source/MQTTnet.Tests/Server/Publishing_Tests.cs

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

Source/MQTTnet.Tests/Server/Security_Tests.cs

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

Source/MQTTnet.Tests/Server/Subscribe_Tests.cs

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

Source/MQTTnet.Tests/Server/Subscription_TopicHash_Tests.cs

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

Source/MQTTnet.Tests/Server/Tls_Tests.cs

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

Source/MQTTnet.Tests/Server/Unsubscribe_Tests.cs

@@ -2,10 +2,14 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
+using MQTTnet.Formatter;
+using MQTTnet.Internal;
 using MQTTnet.Protocol;
+using MQTTnet.Server;
 
 namespace MQTTnet.Tests.Server
 {
@@ -28,5 +32,28 @@ namespace MQTTnet.Tests.Server
                 await client.UnsubscribeAsync("#");
             }
         }
+
+        [TestMethod]
+        public async Task Intercept_Unsubscribe_With_User_Properties()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                var server = await testEnvironment.StartServer();
+
+                InterceptingUnsubscriptionEventArgs eventArgs = null;
+                server.InterceptingUnsubscriptionAsync += e =>
+                {
+                    eventArgs = e;
+                    return CompletedTask.Instance;
+                };
+
+                var client = await testEnvironment.ConnectClient();
+
+                var unsubscribeOptions = testEnvironment.Factory.CreateUnsubscribeOptionsBuilder().WithTopicFilter("X").WithUserProperty("A", "1").Build();
+                await client.UnsubscribeAsync(unsubscribeOptions);
+
+                CollectionAssert.AreEqual(unsubscribeOptions.UserProperties.ToList(), eventArgs.UserProperties);
+            }
+        }
     }
 }

Source/MQTTnet.Tests/TopicFilterComparer_Tests.cs

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

Source/MQTTnet/Adapter/MqttChannelAdapter.cs

@@ -27,18 +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;

Source/MQTTnet/Client/Connecting/MqttClientConnectResult.cs

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

Source/MQTTnet/Client/Disconnecting/MqttClientDisconnectOptions.cs

@@ -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;
 

Source/MQTTnet/Client/IMqttClient.cs

@@ -15,7 +15,7 @@ namespace MQTTnet.Client
 
         event Func<MqttClientDisconnectedEventArgs, Task> DisconnectedAsync;
 
-        event Func<InspectMqttPacketEventArgs, Task> InspectPackage;
+        event Func<InspectMqttPacketEventArgs, Task> InspectPacketAsync;
 
         bool IsConnected { get; }
 

Source/MQTTnet/Client/MqttClient.cs

@@ -87,13 +87,13 @@ namespace MQTTnet.Client
             remove => _disconnectedEvent.RemoveHandler(value);
         }
 
-        public event Func<InspectMqttPacketEventArgs, Task> InspectPackage
+        public event Func<InspectMqttPacketEventArgs, Task> InspectPacketAsync
         {
             add => _inspectPacketEvent.AddHandler(value);
             remove => _inspectPacketEvent.RemoveHandler(value);
         }
 
-        public bool IsConnected => _adapter != null && (MqttClientConnectionStatus)_connectionStatus == MqttClientConnectionStatus.Connected;
+        public bool IsConnected => (MqttClientConnectionStatus)_connectionStatus == MqttClientConnectionStatus.Connected;
 
         public MqttClientOptions Options { get; private set; }
 
@@ -116,7 +116,7 @@ namespace MQTTnet.Client
 
                 if (_connectingEvent.HasHandlers)
                 {
-                    await _connectingEvent.InvokeAsync(new MqttClientConnectingEventArgs(options)).ConfigureAwait(false);
+                    await _connectingEvent.InvokeAsync(new MqttClientConnectingEventArgs(options));
                 }
 
                 Cleanup();
@@ -174,10 +174,7 @@ namespace MQTTnet.Client
             {
                 _disconnectReason = (int)MqttClientDisconnectOptionsReason.UnspecifiedError;
 
-                if (!(exception is OperationCanceledException))
-                {
-                    _logger.Error(exception, "Error while connecting with server.");
-                }
+                _logger.Error(exception, "Error while connecting with server.");
 
                 await DisconnectInternalAsync(null, exception, connectResult).ConfigureAwait(false);
 
@@ -491,9 +488,9 @@ namespace MQTTnet.Client
 
             using (var effectiveCancellationToken = CancellationTokenSource.CreateLinkedTokenSource(backgroundCancellationToken, cancellationToken))
             {
-                _logger.Verbose("Trying to connect with server '{0}'.", Options.ChannelOptions);
+                _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("Connection with server established");
 
                 _publishPacketReceiverQueue?.Dispose();
                 _publishPacketReceiverQueue = new AsyncQueue<MqttPublishPacket>();
@@ -600,8 +597,7 @@ namespace MQTTnet.Client
                         connectionStatus = curStatus;
                         break;
                 }
-            }
-            while (true);
+            } while (true);
         }
 
         void EnqueueReceivedPublishPacket(MqttPublishPacket publishPacket)
@@ -729,7 +725,6 @@ namespace MQTTnet.Client
         async Task<TResponsePacket> SendAndReceiveAsync<TResponsePacket>(MqttPacket requestPacket, CancellationToken cancellationToken) where TResponsePacket : MqttPacket
         {
             cancellationToken.ThrowIfCancellationRequested();
-            ThrowIfNoAdapter();
 
             ushort packetIdentifier = 0;
             if (requestPacket is MqttPacketWithIdentifier packetWithIdentifier)
@@ -768,9 +763,9 @@ namespace MQTTnet.Client
         Task SendAsync(MqttPacket packet, CancellationToken cancellationToken)
         {
             cancellationToken.ThrowIfCancellationRequested();
-            ThrowIfNoAdapter();
 
             _lastPacketSentTimestamp = DateTime.UtcNow;
+
             return _adapter.SendPacketAsync(packet, cancellationToken);
         }
 
@@ -782,16 +777,6 @@ 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)

Source/MQTTnet/Client/Options/MqttClientOptions.cs

@@ -24,6 +24,14 @@ namespace MQTTnet.Client
         /// </summary>
         public string AuthenticationMethod { get; set; }
 
+        /// <summary>
+        ///     Usually the MQTT packets can be send partially. This is done by using multiple TCP packets
+        ///     or WebSocket frames etc. Unfortunately not all 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;
+
         public IMqttClientChannelOptions ChannelOptions { get; set; }
 
         /// <summary>
@@ -214,4 +222,4 @@ namespace MQTTnet.Client
         /// </summary>
         public int WriterBufferSizeMax { get; set; } = 65535;
     }
-}
+}

Source/MQTTnet/Client/Options/MqttClientOptionsBuilder.cs

@@ -75,7 +75,7 @@ namespace MQTTnet.Client
             _options.ChannelOptions = (IMqttClientChannelOptions)_tcpOptions ?? _webSocketOptions;
 
             MqttClientOptionsValidator.ThrowIfNotSupported(_options);
-            
+
             return _options;
         }
 
@@ -86,12 +86,24 @@ namespace MQTTnet.Client
             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;
@@ -188,6 +200,18 @@ 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 +290,7 @@ namespace MQTTnet.Client
 
             return this;
         }
-        
+
         public MqttClientOptionsBuilder WithTcpServer(Action<MqttClientTcpOptions> optionsBuilder)
         {
             if (optionsBuilder == null)
@@ -373,6 +397,18 @@ 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 +420,33 @@ namespace MQTTnet.Client
             _options.WillPayload = willPayload;
             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 +455,20 @@ namespace MQTTnet.Client
             _options.WillRetain = willRetain;
             return this;
         }
-        
-        public MqttClientOptionsBuilder WithWillContentType(string willContentType)
+
+        public MqttClientOptionsBuilder WithWillTopic(string willTopic)
         {
-            _options.WillContentType = willContentType;
+            _options.WillTopic = willTopic;
             return this;
         }
-        
-        public MqttClientOptionsBuilder WithWillCorrelationData(byte[] willCorrelationData)
-        {
-            _options.WillCorrelationData = willCorrelationData;
-            return this;
-        }
-        
-        public MqttClientOptionsBuilder WithWillResponseTopic(string willResponseTopic)
-        {
-            _options.WillResponseTopic = willResponseTopic;
-            return this;
-        }
-        
-        public MqttClientOptionsBuilder WithWillPayloadFormatIndicator(MqttPayloadFormatIndicator willPayloadFormatIndicator)
-        {
-            _options.WillPayloadFormatIndicator = willPayloadFormatIndicator;
-            return this;
-        }
-        
+
         public MqttClientOptionsBuilder WithWillUserProperty(string name, string value)
         {
             if (_options.WillUserProperties == null)
             {
                 _options.WillUserProperties = new List<MqttUserProperty>();
             }
-            
+
             _options.WillUserProperties.Add(new MqttUserProperty(name, value));
             return this;
         }

Source/MQTTnet/Client/Publishing/MqttClientPublishResult.cs

@@ -34,7 +34,7 @@ namespace MQTTnet.Client
         ///     Gets or sets the reason code.
         ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
-        public MqttClientPublishReasonCode ReasonCode { get; }
+        public MqttClientPublishReasonCode ReasonCode { get; } = MqttClientPublishReasonCode.Success;
 
         /// <summary>
         ///     Gets or sets the reason string.

Source/MQTTnet/Client/Subscribing/MqttClientSubscribeResult.cs

@@ -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; }
     }
 }

Source/MQTTnet/Client/Subscribing/MqttClientSubscribeResultItem.cs

@@ -27,4 +27,4 @@ namespace MQTTnet.Client
         /// </summary>
         public MqttClientSubscribeResultCode ResultCode { get; }
     }
-}
+}

Source/MQTTnet/Client/Unsubscribing/MqttClientUnsubscribeResult.cs

@@ -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; }
     }
 }

Source/MQTTnet/Diagnostics/Logger/MqttNetSourceLoggerExtensions.cs

@@ -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)
         {

Source/MQTTnet/Formatter/MqttApplicationMessageFactory.cs

@@ -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,

Source/MQTTnet/Formatter/MqttPublishPacketFactory.cs

@@ -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,

Source/MQTTnet/Formatter/V3/MqttV3PacketFormatter.cs

@@ -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;

Source/MQTTnet/Formatter/V5/MqttV5PacketDecoder.cs

@@ -528,7 +528,7 @@ namespace MQTTnet.Formatter.V5
 
             if (!_bufferReader.EndOfStream)
             {
-                packet.Payload = _bufferReader.ReadRemainingData();
+                packet.PayloadSegment = new ArraySegment<byte>(_bufferReader.ReadRemainingData());
             }
 
             return packet;

Source/MQTTnet/Formatter/V5/MqttV5PacketEncoder.cs

@@ -37,9 +37,11 @@ namespace MQTTnet.Formatter.V5
             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);
@@ -53,18 +55,13 @@ namespace MQTTnet.Formatter.V5
             _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);
         }
-        
+
         byte EncodeAuthPacket(MqttAuthPacket packet)
         {
             _bufferWriter.WriteByte((byte)packet.ReasonCode);

Source/MQTTnet/Implementations/MqttClientAdapterFactory.cs

@@ -40,7 +40,12 @@ namespace MQTTnet.Implementations
 
             var bufferWriter = new MqttBufferWriter(options.WriterBufferSize, options.WriterBufferSizeMax);
             var packetFormatterAdapter = new MqttPacketFormatterAdapter(options.ProtocolVersion, bufferWriter);
-            return new MqttChannelAdapter(channel, packetFormatterAdapter, packetInspector, logger);
+
+            return new MqttChannelAdapter(channel, packetFormatterAdapter, logger)
+            {
+                AllowPacketFragmentation = options.AllowPacketFragmentation,
+                PacketInspector = packetInspector
+            };
         }
     }
 }

Source/MQTTnet/Implementations/MqttTcpServerAdapter.Uwp.cs

@@ -95,7 +95,7 @@ namespace MQTTnet.Implementations
                     var packetFormatterAdapter = new MqttPacketFormatterAdapter(bufferWriter);
                     var tcpChannel = new MqttTcpChannel(args.Socket, clientCertificate, _options);
 
-                    using (var clientAdapter = new MqttChannelAdapter(tcpChannel, packetFormatterAdapter, null, _rootLogger))
+                    using (var clientAdapter = new MqttChannelAdapter(tcpChannel, packetFormatterAdapter, _rootLogger))
                     {
                         await clientHandler(clientAdapter).ConfigureAwait(false);
                     }

Source/MQTTnet/Implementations/MqttTcpServerAdapter.cs

@@ -1,44 +1,51 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
-
 #if !WINDOWS_UWP
-using MQTTnet.Adapter;
-using MQTTnet.Diagnostics;
-using MQTTnet.Server;
 using System;
 using System.Collections.Generic;
 using System.Net;
 using System.Net.Sockets;
-using System.Security.Cryptography.X509Certificates;
 using System.Threading;
 using System.Threading.Tasks;
+using MQTTnet.Adapter;
+using MQTTnet.Diagnostics;
 using MQTTnet.Internal;
+using MQTTnet.Server;
 
 namespace MQTTnet.Implementations
 {
     public sealed class MqttTcpServerAdapter : IMqttServerAdapter
     {
         readonly List<MqttTcpServerListener> _listeners = new List<MqttTcpServerListener>();
+        
+        CancellationTokenSource _cancellationTokenSource;
 
         MqttServerOptions _serverOptions;
-        CancellationTokenSource _cancellationTokenSource;
-        
+
         public Func<IMqttChannelAdapter, Task> ClientHandler { get; set; }
 
         public bool TreatSocketOpeningErrorAsWarning { get; set; }
 
+        public void Dispose()
+        {
+            Cleanup();
+        }
+
         public Task StartAsync(MqttServerOptions options, IMqttNetLogger logger)
         {
-            if (_cancellationTokenSource != null) throw new InvalidOperationException("Server is already started.");
+            if (_cancellationTokenSource != null)
+            {
+                throw new InvalidOperationException("Server is already started.");
+            }
 
             _serverOptions = options;
-            
+
             _cancellationTokenSource = new CancellationTokenSource();
 
             if (options.DefaultEndpointOptions.IsEnabled)
             {
-                RegisterListeners(options.DefaultEndpointOptions, null, logger, _cancellationTokenSource.Token);
+                RegisterListeners(options.DefaultEndpointOptions, logger, _cancellationTokenSource.Token);
             }
 
             if (options.TlsEndpointOptions?.IsEnabled == true)
@@ -48,13 +55,7 @@ namespace MQTTnet.Implementations
                     throw new ArgumentException("TLS certificate is not set.");
                 }
 
-                var tlsCertificate = options.TlsEndpointOptions.CertificateProvider.GetCertificate();
-                if (!tlsCertificate.HasPrivateKey)
-                {
-                    throw new InvalidOperationException("The certificate for TLS encryption must contain the private key.");
-                }
-
-                RegisterListeners(options.TlsEndpointOptions, tlsCertificate, logger, _cancellationTokenSource.Token);
+                RegisterListeners(options.TlsEndpointOptions, logger, _cancellationTokenSource.Token);
             }
 
             return CompletedTask.Instance;
@@ -66,11 +67,6 @@ namespace MQTTnet.Implementations
             return CompletedTask.Instance;
         }
 
-        public void Dispose()
-        {
-            Cleanup();
-        }
-
         void Cleanup()
         {
             try
@@ -91,11 +87,22 @@ namespace MQTTnet.Implementations
             }
         }
 
-        void RegisterListeners(MqttServerTcpEndpointBaseOptions tcpEndpointOptions, X509Certificate2 tlsCertificate, IMqttNetLogger logger, CancellationToken cancellationToken)
+        Task OnClientAcceptedAsync(IMqttChannelAdapter channelAdapter)
+        {
+            var clientHandler = ClientHandler;
+            if (clientHandler == null)
+            {
+                return CompletedTask.Instance;
+            }
+
+            return clientHandler(channelAdapter);
+        }
+
+        void RegisterListeners(MqttServerTcpEndpointBaseOptions tcpEndpointOptions, IMqttNetLogger logger, CancellationToken cancellationToken)
         {
             if (!tcpEndpointOptions.BoundInterNetworkAddress.Equals(IPAddress.None))
             {
-                var listenerV4 = new MqttTcpServerListener(AddressFamily.InterNetwork, _serverOptions, tcpEndpointOptions, tlsCertificate, logger)
+                var listenerV4 = new MqttTcpServerListener(AddressFamily.InterNetwork, _serverOptions, tcpEndpointOptions, logger)
                 {
                     ClientHandler = OnClientAcceptedAsync
                 };
@@ -108,7 +115,7 @@ namespace MQTTnet.Implementations
 
             if (!tcpEndpointOptions.BoundInterNetworkV6Address.Equals(IPAddress.None))
             {
-                var listenerV6 = new MqttTcpServerListener(AddressFamily.InterNetworkV6, _serverOptions, tcpEndpointOptions, tlsCertificate, logger)
+                var listenerV6 = new MqttTcpServerListener(AddressFamily.InterNetworkV6, _serverOptions, tcpEndpointOptions, logger)
                 {
                     ClientHandler = OnClientAcceptedAsync
                 };
@@ -119,17 +126,6 @@ namespace MQTTnet.Implementations
                 }
             }
         }
-
-        Task OnClientAcceptedAsync(IMqttChannelAdapter channelAdapter)
-        {
-            var clientHandler = ClientHandler;
-            if (clientHandler == null)
-            {
-                return CompletedTask.Instance;
-            }
-
-            return clientHandler(channelAdapter);
-        }
     }
 }
 #endif

Source/MQTTnet/Implementations/MqttTcpServerListener.cs

@@ -27,8 +27,7 @@ namespace MQTTnet.Implementations
         readonly MqttServerOptions _serverOptions;
         readonly MqttServerTcpEndpointBaseOptions _options;
         readonly MqttServerTlsTcpEndpointOptions _tlsOptions;
-        readonly X509Certificate2 _tlsCertificate;
-
+        
         CrossPlatformSocket _socket;
         IPEndPoint _localEndPoint;
 
@@ -36,13 +35,11 @@ namespace MQTTnet.Implementations
             AddressFamily addressFamily,
             MqttServerOptions serverOptions,
             MqttServerTcpEndpointBaseOptions tcpEndpointOptions,
-            X509Certificate2 tlsCertificate,
             IMqttNetLogger logger)
         {
             _addressFamily = addressFamily;
             _serverOptions = serverOptions ?? throw new ArgumentNullException(nameof(serverOptions));
             _options = tcpEndpointOptions ?? throw new ArgumentNullException(nameof(tcpEndpointOptions));
-            _tlsCertificate = tlsCertificate;
             _rootLogger = logger;
             _logger = logger.WithSource(nameof(MqttTcpServerListener));
 
@@ -66,7 +63,7 @@ namespace MQTTnet.Implementations
 
                 _localEndPoint = new IPEndPoint(boundIp, _options.Port);
 
-                _logger.Info("Starting TCP listener (Endpoint='{0}', TLS={1}).", _localEndPoint, _tlsCertificate != null);
+                _logger.Info("Starting TCP listener (Endpoint={0}, TLS={1})", _localEndPoint, _tlsOptions?.CertificateProvider != null);
 
                 _socket = new CrossPlatformSocket(_addressFamily);
 
@@ -115,7 +112,7 @@ namespace MQTTnet.Implementations
                 
                 _socket.Listen(_options.ConnectionBacklog);
                 
-                _logger.Verbose("TCP listener started (Endpoint='{0}'.", _localEndPoint);
+                _logger.Verbose("TCP listener started (Endpoint={0})", _localEndPoint);
                 
                 Task.Run(() => AcceptClientConnectionsAsync(cancellationToken), cancellationToken).RunInBackground(_logger);
 
@@ -128,7 +125,7 @@ namespace MQTTnet.Implementations
                     throw;
                 }
 
-                _logger.Warning(exception, "Error while creating listener socket for local end point '{0}'.", _localEndPoint);
+                _logger.Warning(exception, "Error while starting TCP listener (Endpoint={0})", _localEndPoint);
                 return false;
             }
         }
@@ -136,10 +133,6 @@ namespace MQTTnet.Implementations
         public void Dispose()
         {
             _socket?.Dispose();
-
-#if !NET452
-            _tlsCertificate?.Dispose();
-#endif
         }
 
         async Task AcceptClientConnectionsAsync(CancellationToken cancellationToken)
@@ -170,7 +163,7 @@ namespace MQTTnet.Implementations
                         }
                     }
 
-                    _logger.Error(exception, "Error while accepting connection at TCP listener {0} TLS={1}.", _localEndPoint, _tlsCertificate != null);
+                    _logger.Error(exception, "Error while accepting TCP connection (Endpoint={0})", _localEndPoint);
                     await Task.Delay(TimeSpan.FromSeconds(1), cancellationToken).ConfigureAwait(false);
                 }
             }
@@ -185,24 +178,26 @@ namespace MQTTnet.Implementations
             {
                 remoteEndPoint = clientSocket.RemoteEndPoint.ToString();
 
-                _logger.Verbose("Client '{0}' accepted by TCP listener '{1}, {2}'.",
-                    remoteEndPoint,
-                    _localEndPoint,
-                    _addressFamily == AddressFamily.InterNetwork ? "ipv4" : "ipv6");
+                _logger.Verbose("TCP client '{0}' accepted (Local endpoint={1})", remoteEndPoint, _localEndPoint);
 
                 clientSocket.NoDelay = _options.NoDelay;
                 stream = clientSocket.GetStream();
-                X509Certificate2 clientCertificate = null;
-
-                if (_tlsCertificate != null)
+                var clientCertificate = _tlsOptions?.CertificateProvider?.GetCertificate();
+                
+                if (clientCertificate != null)
                 {
+                    if (!clientCertificate.HasPrivateKey)
+                    {
+                        throw new InvalidOperationException("The certificate for TLS encryption must contain the private key.");
+                    }
+
                     var sslStream = new SslStream(stream, false, _tlsOptions.RemoteCertificateValidationCallback);
 
                     #if NETCOREAPP3_1_OR_GREATER
                         await sslStream.AuthenticateAsServerAsync(
-                            new SslServerAuthenticationOptions()
+                            new SslServerAuthenticationOptions
                             {
-                                ServerCertificate = _tlsCertificate,
+                                ServerCertificate = clientCertificate,
                                 ClientCertificateRequired = _tlsOptions.ClientCertificateRequired,
                                 EnabledSslProtocols = _tlsOptions.SslProtocol,
                                 CertificateRevocationCheckMode = _tlsOptions.CheckCertificateRevocation ? X509RevocationMode.Online : X509RevocationMode.NoCheck,
@@ -211,7 +206,7 @@ namespace MQTTnet.Implementations
                             }).ConfigureAwait(false);
                     #else
                         await sslStream.AuthenticateAsServerAsync(
-                            _tlsCertificate,
+                            clientCertificate,
                             _tlsOptions.ClientCertificateRequired,
                             _tlsOptions.SslProtocol,
                             _tlsOptions.CheckCertificateRevocation).ConfigureAwait(false);
@@ -234,7 +229,7 @@ namespace MQTTnet.Implementations
                     var bufferWriter = new MqttBufferWriter(_serverOptions.WriterBufferSize, _serverOptions.WriterBufferSizeMax);
                     var packetFormatterAdapter = new MqttPacketFormatterAdapter(bufferWriter);
                     
-                    using (var clientAdapter = new MqttChannelAdapter(tcpChannel, packetFormatterAdapter, null, _rootLogger))
+                    using (var clientAdapter = new MqttChannelAdapter(tcpChannel, packetFormatterAdapter, _rootLogger))
                     {
                         await clientHandler(clientAdapter).ConfigureAwait(false);
                     }
@@ -254,7 +249,7 @@ namespace MQTTnet.Implementations
                     return;
                 }
 
-                _logger.Error(exception, "Error while handling client connection.");
+                _logger.Error(exception, "Error while handling TCP client connection");
             }
             finally
             {
@@ -269,10 +264,7 @@ namespace MQTTnet.Implementations
                 }
             }
 
-            _logger.Verbose("Client '{0}' disconnected at TCP listener '{1}, {2}'.",
-                remoteEndPoint,
-                _localEndPoint,
-                _addressFamily == AddressFamily.InterNetwork ? "ipv4" : "ipv6");
+            _logger.Verbose("TCP client '{0}' disconnected (Local endpoint={1})", remoteEndPoint, _localEndPoint);
         }
     }
 }

Source/MQTTnet/Implementations/MqttWebSocketChannel.cs

@@ -63,7 +63,7 @@ namespace MQTTnet.Implementations
 
                 await clientWebSocket.ConnectAsync(new Uri(uri), cancellationToken).ConfigureAwait(false);
             }
-            catch (Exception)
+            catch
             {
                 // Prevent a memory leak when always creating new instance which will fail while connecting.
                 clientWebSocket.Dispose();
@@ -103,7 +103,7 @@ namespace MQTTnet.Implementations
         public async Task WriteAsync(ArraySegment<byte> buffer, bool isEndOfPacket, CancellationToken cancellationToken)
         {
             cancellationToken.ThrowIfCancellationRequested();
-            
+
 #if NET5_0_OR_GREATER
             // MQTT Control Packets MUST be sent in WebSocket binary data frames. If any other type of data frame is received the recipient MUST close the Network Connection [MQTT-6.0.0-1].
             // A single WebSocket data frame can contain multiple or partial MQTT Control Packets. The receiver MUST NOT assume that MQTT Control Packets are aligned on WebSocket frame boundaries [MQTT-6.0.0-2].

Source/MQTTnet/Internal/AsyncQueue.cs

@@ -37,7 +37,7 @@ namespace MQTTnet.Internal
 
                 _isDisposed = true;
 
-#if !NETSTANDARD1_3
+#if !NETSTANDARD1_3 && !WINDOWS_UWP
                 if (typeof(IDisposable).IsAssignableFrom(typeof(TItem)))
                 {
                     while (_queue.TryDequeue(out TItem item))

Source/MQTTnet/LowLevelClient/ILowLevelMqttClient.cs

@@ -9,7 +9,7 @@ namespace MQTTnet.LowLevelClient
 {
     public interface ILowLevelMqttClient : IDisposable
     {
-        event Func<InspectMqttPacketEventArgs, Task> InspectPackage;
+        event Func<InspectMqttPacketEventArgs, Task> InspectPacketAsync;
         
         bool IsConnected { get; }
         

Source/MQTTnet/LowLevelClient/LowLevelMqttClient.cs

@@ -32,7 +32,7 @@ namespace MQTTnet.LowLevelClient
             _logger = logger.WithSource(nameof(LowLevelMqttClient));
         }
 
-        public event Func<InspectMqttPacketEventArgs, Task> InspectPackage
+        public event Func<InspectMqttPacketEventArgs, Task> InspectPacketAsync
         {
             add => _inspectPacketEvent.AddHandler(value);
             remove => _inspectPacketEvent.RemoveHandler(value);
@@ -52,13 +52,19 @@ namespace MQTTnet.LowLevelClient
                 throw new InvalidOperationException("Low level MQTT client is already connected. Disconnect first before connecting again.");
             }
 
-            var newAdapter = _clientAdapterFactory.CreateClientAdapter(options, new MqttPacketInspector(_inspectPacketEvent, _rootLogger), _rootLogger);
+            MqttPacketInspector packetInspector = null;
+            if (_inspectPacketEvent.HasHandlers)
+            {
+                packetInspector = new MqttPacketInspector(_inspectPacketEvent, _rootLogger);
+            }
+
+            var newAdapter = _clientAdapterFactory.CreateClientAdapter(options, packetInspector, _rootLogger);
 
             try
             {
-                _logger.Verbose("Trying to connect with server '{0}'.", options.ChannelOptions);
+                _logger.Verbose("Trying to connect with server '{0}'", options.ChannelOptions);
                 await newAdapter.ConnectAsync(cancellationToken).ConfigureAwait(false);
-                _logger.Verbose("Connection with server established.");
+                _logger.Verbose("Connection with server established");
             }
             catch (Exception)
             {

Source/MQTTnet/MqttApplicationMessage.cs

@@ -2,14 +2,19 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using System.Collections.Generic;
+using MQTTnet.Internal;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
+using System;
+using System.Collections.Generic;
 
 namespace MQTTnet
 {
     public sealed class MqttApplicationMessage
     {
+        byte[] _payloadCache;
+        ArraySegment<byte> _payloadSegment = EmptyBuffer.ArraySegment;
+
         /// <summary>
         ///     Gets or sets the content type.
         ///     The content type must be a UTF-8 encoded string. The content type value identifies the kind of UTF-8 encoded
@@ -48,10 +53,53 @@ namespace MQTTnet
         public uint MessageExpiryInterval { get; set; }
 
         /// <summary>
-        ///     Gets or sets the payload.
-        ///     The payload is the data bytes sent via the MQTT protocol.
+        /// Gets or sets the payload.
+        /// The payload is the data bytes sent via the MQTT protocol.
         /// </summary>
-        public byte[] Payload { get; set; }
+        [Obsolete("Use PayloadSegment instead. This property will be removed in a future release.")]
+        public byte[] Payload
+        {
+            get
+            {
+                if (_payloadSegment.Array == null)
+                {
+                    return null;
+                }
+                
+                // just reference from _payloadSegment.Array
+                if (_payloadSegment.Count == _payloadSegment.Array.Length)
+                {
+                    return _payloadSegment.Array;
+                }
+
+                // copy from _payloadSegment
+                if (_payloadCache == null)
+                {
+                    _payloadCache = new byte[_payloadSegment.Count];
+                    MqttMemoryHelper.Copy(_payloadSegment.Array, _payloadSegment.Offset, _payloadCache, 0, _payloadCache.Length);
+                }
+
+                return _payloadCache;
+            }
+            set
+            {
+                _payloadCache = null;
+                _payloadSegment = value == null || value.Length == 0 ? EmptyBuffer.ArraySegment : new ArraySegment<byte>(value);
+            }
+        }
+
+        /// <summary>
+        /// Get or set ArraySegment style of Payload.
+        /// </summary>
+        public ArraySegment<byte> PayloadSegment
+        {
+            get => _payloadSegment;
+            set
+            {
+                _payloadCache = null;
+                _payloadSegment = value;
+            }
+        }
 
         /// <summary>
         ///     Gets or sets the payload format indicator.

Source/MQTTnet/MqttApplicationMessageBuilder.cs

@@ -2,13 +2,16 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using MQTTnet.Exceptions;
+using MQTTnet.Internal;
+using MQTTnet.Packets;
+using MQTTnet.Protocol;
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Runtime.InteropServices;
 using System.Text;
-using MQTTnet.Exceptions;
-using MQTTnet.Packets;
-using MQTTnet.Protocol;
 
 namespace MQTTnet
 {
@@ -17,7 +20,8 @@ namespace MQTTnet
         string _contentType;
         byte[] _correlationData;
         uint _messageExpiryInterval;
-        byte[] _payload;
+        ArraySegment<byte> _payloadSegment;
+
         MqttPayloadFormatIndicator _payloadFormatIndicator;
         MqttQualityOfServiceLevel _qualityOfServiceLevel = MqttQualityOfServiceLevel.AtMostOnce;
         string _responseTopic;
@@ -37,7 +41,7 @@ namespace MQTTnet
             var applicationMessage = new MqttApplicationMessage
             {
                 Topic = _topic,
-                Payload = _payload,
+                PayloadSegment = _payloadSegment,
                 QualityOfServiceLevel = _qualityOfServiceLevel,
                 Retain = _retain,
                 ContentType = _contentType,
@@ -85,7 +89,15 @@ namespace MQTTnet
 
         public MqttApplicationMessageBuilder WithPayload(byte[] payload)
         {
-            _payload = payload;
+            _payloadSegment = payload == null || payload.Length == 0
+                ? EmptyBuffer.ArraySegment
+                : new ArraySegment<byte>(payload);
+            return this;
+        }
+
+        public MqttApplicationMessageBuilder WithPayloadSegment(ArraySegment<byte> payloadSegment)
+        {
+            _payloadSegment = payloadSegment;
             return this;
         }
 
@@ -93,70 +105,73 @@ namespace MQTTnet
         {
             if (payload == null)
             {
-                _payload = null;
-                return this;
+                return WithPayload(default(byte[]));
             }
 
-            _payload = payload as byte[] ?? payload.ToArray();
+            if (payload is byte[] byteArray)
+            {
+                return WithPayload(byteArray);
+            }
 
-            return this;
+            if (payload is ArraySegment<byte> arraySegment)
+            {
+                return WithPayloadSegment(arraySegment);
+            }
+
+            return WithPayload(payload.ToArray());
         }
 
         public MqttApplicationMessageBuilder WithPayload(Stream payload)
         {
-            if (payload == null)
-            {
-                _payload = null;
-                return this;
-            }
-
-            return WithPayload(payload, payload.Length - payload.Position);
+            return payload == null
+                ? WithPayload(default(byte[]))
+                : WithPayload(payload, payload.Length - payload.Position);
         }
 
         public MqttApplicationMessageBuilder WithPayload(Stream payload, long length)
         {
-            if (payload == null)
+            if (payload == null || length == 0)
             {
-                _payload = null;
-                return this;
+                return WithPayload(default(byte[]));
             }
 
-            if (payload.Length == 0)
+            var payloadBuffer = new byte[length];
+            var totalRead = 0;
+            do
             {
-                _payload = null;
-            }
-            else
-            {
-                _payload = new byte[length];
-
-                var totalRead = 0;
-                do
+                var bytesRead = payload.Read(payloadBuffer, totalRead, payloadBuffer.Length - totalRead);
+                if (bytesRead == 0)
                 {
-                    var bytesRead = payload.Read(_payload, totalRead, _payload.Length - totalRead);
-                    if (bytesRead == 0)
-                    {
-                        break;
-                    }
+                    break;
+                }
 
-                    totalRead += bytesRead;
-                } while (totalRead < length);
-            }
+                totalRead += bytesRead;
+            } while (totalRead < length);
 
-            return this;
+            return WithPayload(payloadBuffer);
         }
 
         public MqttApplicationMessageBuilder WithPayload(string payload)
         {
-            if (payload == null)
+            if (string.IsNullOrEmpty(payload))
             {
-                _payload = null;
-                return this;
+                return WithPayload(default(byte[]));
             }
 
-            _payload = string.IsNullOrEmpty(payload) ? null : Encoding.UTF8.GetBytes(payload);
-            return this;
+            var payloadBuffer = Encoding.UTF8.GetBytes(payload);
+            return WithPayload(payloadBuffer);
         }
 
+
+#if NETCOREAPP3_1_OR_GREATER || NETSTANDARD2_1
+        public MqttApplicationMessageBuilder WithPayloadSegment(ReadOnlyMemory<byte> payloadSegment)
+        {
+            return MemoryMarshal.TryGetArray(payloadSegment, out var segment)
+                ? WithPayloadSegment(segment)
+                : WithPayload(payloadSegment.ToArray());
+        }
+#endif
+
         /// <summary>
         ///     Adds the payload format indicator to the message.
         ///     <remarks>MQTT 5.0.0+ feature.</remarks>

Source/MQTTnet/MqttApplicationMessageExtensions.cs

@@ -11,19 +11,13 @@ namespace MQTTnet
     {
         public static string ConvertPayloadToString(this MqttApplicationMessage applicationMessage)
         {
-            if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
-
-            if (applicationMessage.Payload == null)
+            if (applicationMessage == null)
             {
-                return null;
+                throw new ArgumentNullException(nameof(applicationMessage));
             }
 
-            if (applicationMessage.Payload.Length == 0)
-            {
-                return string.Empty;
-            }
-
-            return Encoding.UTF8.GetString(applicationMessage.Payload, 0, applicationMessage.Payload.Length);
+            var payloadSegment = applicationMessage.PayloadSegment;
+            return Encoding.UTF8.GetString(payloadSegment.Array, payloadSegment.Offset, payloadSegment.Count);
         }
     }
 }

Source/MQTTnet/Packets/MqttPublishPacket.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
 using MQTTnet.Protocol;
 
@@ -17,10 +18,10 @@ namespace MQTTnet.Packets
 
         public uint MessageExpiryInterval { get; set; }
 
-        public byte[] Payload { get; set; }
-
         public MqttPayloadFormatIndicator PayloadFormatIndicator { get; set; } = MqttPayloadFormatIndicator.Unspecified;
 
+        public ArraySegment<byte> PayloadSegment { get; set; }
+
         public MqttQualityOfServiceLevel QualityOfServiceLevel { get; set; } = MqttQualityOfServiceLevel.AtMostOnce;
 
         public string ResponseTopic { get; set; }
@@ -38,7 +39,7 @@ namespace MQTTnet.Packets
         public override string ToString()
         {
             return
-                $"Publish: [Topic={Topic}] [Payload.Length={Payload?.Length}] [QoSLevel={QualityOfServiceLevel}] [Dup={Dup}] [Retain={Retain}] [PacketIdentifier={PacketIdentifier}]";
+                $"Publish: [Topic={Topic}] [PayloadLength={PayloadSegment.Count}] [QoSLevel={QualityOfServiceLevel}] [Dup={Dup}] [Retain={Retain}] [PacketIdentifier={PacketIdentifier}]";
         }
     }
 }

Source/MQTTnet/Server/Events/InterceptingClientApplicationMessageEnqueueEventArgs.cs

@@ -0,0 +1,35 @@
+// 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.Server
+{
+    public sealed class InterceptingClientApplicationMessageEnqueueEventArgs : EventArgs
+    {
+        public InterceptingClientApplicationMessageEnqueueEventArgs(string senderClientId, string receiverClientId, MqttApplicationMessage applicationMessage)
+        {
+            SenderClientId = senderClientId ?? throw new ArgumentNullException(nameof(senderClientId));
+            ReceiverClientId = receiverClientId ?? throw new ArgumentNullException(nameof(receiverClientId));
+            ApplicationMessage = applicationMessage ?? throw new ArgumentNullException(nameof(applicationMessage));
+        }
+
+        /// <summary>
+        ///     Gets or sets whether the enqueue of the application message should be performed or not.
+        ///     If set to _False_ the client will not receive the application message.
+        /// </summary>
+        public bool AcceptEnqueue { get; set; } = true;
+
+        public MqttApplicationMessage ApplicationMessage { get; }
+
+        /// <summary>
+        ///     Indicates if the connection with the sender should be closed.
+        /// </summary>
+        public bool CloseSenderConnection { get; set; }
+
+        public string ReceiverClientId { get; }
+
+        public string SenderClientId { get; }
+    }
+}

Source/MQTTnet/Server/Events/InterceptingSubscriptionEventArgs.cs

@@ -16,12 +16,14 @@ namespace MQTTnet.Server
             CancellationToken cancellationToken,
             string clientId,
             MqttSessionStatus session,
-            MqttTopicFilter topicFilter)
+            MqttTopicFilter topicFilter,
+            List<MqttUserProperty> userProperties)
         {
             CancellationToken = cancellationToken;
             ClientId = clientId;
             Session = session;
             TopicFilter = topicFilter;
+            UserProperties = userProperties;
         }
 
         /// <summary>
@@ -75,6 +77,7 @@ namespace MQTTnet.Server
 
         /// <summary>
         ///     Gets or sets the user properties.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public List<MqttUserProperty> UserProperties { get; set; }
     }

Source/MQTTnet/Server/Events/InterceptingUnsubscriptionEventArgs.cs

@@ -4,18 +4,21 @@
 
 using System;
 using System.Collections;
+using System.Collections.Generic;
 using System.Threading;
+using MQTTnet.Packets;
 
 namespace MQTTnet.Server
 {
     public sealed class InterceptingUnsubscriptionEventArgs : EventArgs
     {
-        public InterceptingUnsubscriptionEventArgs(CancellationToken cancellationToken, string clientId, IDictionary sessionItems, string topic)
+        public InterceptingUnsubscriptionEventArgs(CancellationToken cancellationToken, string clientId, IDictionary sessionItems, string topic, List<MqttUserProperty> userProperties)
         {
             CancellationToken = cancellationToken;
             ClientId = clientId;
             SessionItems = sessionItems;
             Topic = topic;
+            UserProperties = userProperties;
         }
 
         /// <summary>
@@ -59,5 +62,11 @@ namespace MQTTnet.Server
         ///     separator).
         /// </summary>
         public string Topic { get; }
+
+        /// <summary>
+        ///     Gets or sets the user properties.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// </summary>
+        public List<MqttUserProperty> UserProperties { get; set; }
     }
 }

Source/MQTTnet/Server/Internal/MqttClient.cs

@@ -94,10 +94,9 @@ namespace MQTTnet.Server
             try
             {
                 var cancellationToken = _cancellationToken.Token;
-
-                _ = Task.Factory.StartNew(() => SendPacketsLoop(cancellationToken), cancellationToken, TaskCreationOptions.PreferFairness, TaskScheduler.Default).ConfigureAwait(false);
-
                 IsRunning = true;
+                
+                _ = Task.Factory.StartNew(() => SendPacketsLoop(cancellationToken), cancellationToken, TaskCreationOptions.PreferFairness, TaskScheduler.Default).ConfigureAwait(false);
 
                 await ReceivePackagesLoop(cancellationToken).ConfigureAwait(false);
             }

Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs

@@ -179,7 +179,7 @@ namespace MQTTnet.Server
                     }
 
                     // Calculate application message topic hash once for subscription checks
-                    MqttSubscription.CalculateTopicHash(applicationMessage.Topic, out var topicHash, out _, out _);
+                    MqttTopicHash.Calculate(applicationMessage.Topic, out var topicHash, out _, out _);
 
                     foreach (var session in subscriberSessions)
                     {
@@ -199,6 +199,18 @@ namespace MQTTnet.Server
                         {
                             continue;
                         }
+                        
+                        if (_eventContainer.InterceptingClientEnqueueEvent.HasHandlers)
+                        {
+                            var eventArgs = new InterceptingClientApplicationMessageEnqueueEventArgs(senderId, session.Id, applicationMessage);
+                            await _eventContainer.InterceptingClientEnqueueEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
+
+                            if (!eventArgs.AcceptEnqueue)
+                            {
+                                // Continue checking the other subscriptions
+                                continue;
+                            }
+                        }
 
                         var publishPacketCopy = MqttPacketFactories.Publish.Create(applicationMessage);
                         publishPacketCopy.QualityOfServiceLevel = checkSubscriptionsResult.QualityOfServiceLevel;
@@ -219,10 +231,10 @@ namespace MQTTnet.Server
                             publishPacketCopy.Retain = false;
                         }
 
-                        session.EnqueueDataPacket(new MqttPacketBusItem(publishPacketCopy));
                         matchingSubscribersCount++;
 
-                        _logger.Verbose("Client '{0}': Queued PUBLISH packet with topic '{1}'.", session.Id, applicationMessage.Topic);
+                        session.EnqueueDataPacket(new MqttPacketBusItem(publishPacketCopy));
+                        _logger.Verbose("Client '{0}': Queued PUBLISH packet with topic '{1}'", session.Id, applicationMessage.Topic);
                     }
 
                     if (matchingSubscribersCount == 0)
@@ -233,7 +245,7 @@ namespace MQTTnet.Server
                 }
                 catch (Exception exception)
                 {
-                    _logger.Error(exception, "Unhandled exception while processing next queued application message.");
+                    _logger.Error(exception, "Error while processing next queued application message");
                 }
             }
 
@@ -592,13 +604,8 @@ namespace MQTTnet.Server
 
                     if (_eventContainer.ClientDisconnectedEvent.HasHandlers)
                     {
-                        var eventArgs = new ClientDisconnectedEventArgs(
-                            oldClient.Id,
-                            null,
-                            MqttClientDisconnectType.Takeover,
-                            oldClient.Endpoint,
-                            oldClient.Session.Items);
-                        
+                        var eventArgs = new ClientDisconnectedEventArgs(oldClient.Id, null, MqttClientDisconnectType.Takeover, oldClient.Endpoint, oldClient.Session.Items);
+
                         await _eventContainer.ClientDisconnectedEvent.TryInvokeAsync(eventArgs, _logger).ConfigureAwait(false);
                     }
                 }

Source/MQTTnet/Server/Internal/MqttClientSubscriptionsManager.cs

@@ -177,15 +177,15 @@ namespace MQTTnet.Server
             // lower one.
             foreach (var topicFilterItem in subscribePacket.TopicFilters.OrderByDescending(f => f.QualityOfServiceLevel))
             {
-                var subscriptionEventArgs = await InterceptSubscribe(topicFilterItem, cancellationToken).ConfigureAwait(false);
-                var topicFilter = subscriptionEventArgs.TopicFilter;
-                var processSubscription = subscriptionEventArgs.ProcessSubscription && subscriptionEventArgs.Response.ReasonCode <= MqttSubscribeReasonCode.GrantedQoS2;
+                var interceptorEventArgs = await InterceptSubscribe(topicFilterItem, subscribePacket.UserProperties, cancellationToken).ConfigureAwait(false);
+                var topicFilter = interceptorEventArgs.TopicFilter;
+                var processSubscription = interceptorEventArgs.ProcessSubscription && interceptorEventArgs.Response.ReasonCode <= MqttSubscribeReasonCode.GrantedQoS2;
 
-                result.UserProperties = subscriptionEventArgs.UserProperties;
-                result.ReasonString = subscriptionEventArgs.ReasonString;
-                result.ReasonCodes.Add(subscriptionEventArgs.Response.ReasonCode);
+                result.UserProperties = interceptorEventArgs.UserProperties;
+                result.ReasonString = interceptorEventArgs.ReasonString;
+                result.ReasonCodes.Add(interceptorEventArgs.Response.ReasonCode);
 
-                if (subscriptionEventArgs.CloseConnection)
+                if (interceptorEventArgs.CloseConnection)
                 {
                     // When any of the interceptor calls leads to a connection close the connection
                     // must be closed. So do not revert to false!
@@ -197,7 +197,7 @@ namespace MQTTnet.Server
                     continue;
                 }
 
-                var createSubscriptionResult = CreateSubscription(topicFilter, subscribePacket.SubscriptionIdentifier, subscriptionEventArgs.Response.ReasonCode);
+                var createSubscriptionResult = CreateSubscription(topicFilter, subscribePacket.SubscriptionIdentifier, interceptorEventArgs.Response.ReasonCode);
 
                 addedSubscriptions.Add(topicFilter.Topic);
                 finalTopicFilters.Add(topicFilter);
@@ -238,12 +238,13 @@ namespace MQTTnet.Server
                 {
                     _subscriptions.TryGetValue(topicFilter, out var existingSubscription);
 
-                    var interceptorContext = await InterceptUnsubscribe(topicFilter, existingSubscription, cancellationToken).ConfigureAwait(false);
-                    var acceptUnsubscription = interceptorContext.Response.ReasonCode == MqttUnsubscribeReasonCode.Success;
+                    var interceptorEventArgs = await InterceptUnsubscribe(topicFilter, existingSubscription, unsubscribePacket.UserProperties, cancellationToken).ConfigureAwait(false);
+                    var acceptUnsubscription = interceptorEventArgs.Response.ReasonCode == MqttUnsubscribeReasonCode.Success;
 
-                    result.ReasonCodes.Add(interceptorContext.Response.ReasonCode);
+                    result.UserProperties = interceptorEventArgs.UserProperties;
+                    result.ReasonCodes.Add(interceptorEventArgs.Response.ReasonCode);
 
-                    if (interceptorContext.CloseConnection)
+                    if (interceptorEventArgs.CloseConnection)
                     {
                         // When any of the interceptor calls leads to a connection close the connection
                         // must be closed. So do not revert to false!
@@ -255,7 +256,7 @@ namespace MQTTnet.Server
                         continue;
                     }
 
-                    if (interceptorContext.ProcessUnsubscription)
+                    if (interceptorEventArgs.ProcessUnsubscription)
                     {
                         _subscriptions.Remove(topicFilter);
 
@@ -342,7 +343,7 @@ namespace MQTTnet.Server
 
             using (_subscriptionsLock.EnterAsync(CancellationToken.None).GetAwaiter().GetResult())
             {
-                MqttSubscription.CalculateTopicHash(topicFilter.Topic, out var topicHash, out var topicHashMask, out var hasWildcard);
+                MqttTopicHash.Calculate(topicFilter.Topic, out var topicHash, out _, out var hasWildcard);
 
                 if (_subscriptions.TryGetValue(topicFilter.Topic, out var existingSubscription))
                 {
@@ -403,6 +404,18 @@ namespace MQTTnet.Server
             CreateSubscriptionResult createSubscriptionResult,
             SubscribeResult subscribeResult)
         {
+            if (createSubscriptionResult.Subscription.RetainHandling == MqttRetainHandling.DoNotSendOnSubscribe)
+            {
+                // This is a MQTT V5+ feature.
+                return;
+            }
+
+            if (createSubscriptionResult.Subscription.RetainHandling == MqttRetainHandling.SendAtSubscribeIfNewSubscriptionOnly && !createSubscriptionResult.IsNewSubscription)
+            {
+                // This is a MQTT V5+ feature.
+                return;
+            }
+
             for (var index = retainedMessages.Count - 1; index >= 0; index--)
             {
                 var retainedMessage = retainedMessages[index];
@@ -411,18 +424,6 @@ namespace MQTTnet.Server
                     continue;
                 }
 
-                if (createSubscriptionResult.Subscription.RetainHandling == MqttRetainHandling.DoNotSendOnSubscribe)
-                {
-                    // This is a MQTT V5+ feature.
-                    continue;
-                }
-
-                if (createSubscriptionResult.Subscription.RetainHandling == MqttRetainHandling.SendAtSubscribeIfNewSubscriptionOnly && !createSubscriptionResult.IsNewSubscription)
-                {
-                    // This is a MQTT V5+ feature.
-                    continue;
-                }
-
                 if (MqttTopicFilterComparer.Compare(retainedMessage.Topic, createSubscriptionResult.Subscription.Topic) != MqttTopicFilterCompareResult.IsMatch)
                 {
                     continue;
@@ -452,9 +453,12 @@ namespace MQTTnet.Server
             }
         }
 
-        async Task<InterceptingSubscriptionEventArgs> InterceptSubscribe(MqttTopicFilter topicFilter, CancellationToken cancellationToken)
+        async Task<InterceptingSubscriptionEventArgs> InterceptSubscribe(
+            MqttTopicFilter topicFilter,
+            List<MqttUserProperty> userProperties,
+            CancellationToken cancellationToken)
         {
-            var eventArgs = new InterceptingSubscriptionEventArgs(cancellationToken, _session.Id, new MqttSessionStatus(_session), topicFilter);
+            var eventArgs = new InterceptingSubscriptionEventArgs(cancellationToken, _session.Id, new MqttSessionStatus(_session), topicFilter, userProperties);
 
             if (topicFilter.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
             {
@@ -481,9 +485,13 @@ namespace MQTTnet.Server
             return eventArgs;
         }
 
-        async Task<InterceptingUnsubscriptionEventArgs> InterceptUnsubscribe(string topicFilter, MqttSubscription mqttSubscription, CancellationToken cancellationToken)
+        async Task<InterceptingUnsubscriptionEventArgs> InterceptUnsubscribe(
+            string topicFilter,
+            MqttSubscription mqttSubscription,
+            List<MqttUserProperty> userProperties,
+            CancellationToken cancellationToken)
         {
-            var clientUnsubscribingTopicEventArgs = new InterceptingUnsubscriptionEventArgs(cancellationToken, _session.Id, _session.Items, topicFilter)
+            var clientUnsubscribingTopicEventArgs = new InterceptingUnsubscriptionEventArgs(cancellationToken, _session.Id, _session.Items, topicFilter, userProperties)
             {
                 Response =
                 {