Samples that show concurrent processing (#1803)

Samples that show concurrent processing with a limit and concurrent processing without auto ACK

.github/workflows/ReleaseNotes.md

@@ -1,9 +1,11 @@
-* [Core] Fixed a memory leak in _AsyncSignal_ implementation (#1586, thanks to @mario-zelger).
-* [Core] Fixed an issue with bounds handling in _MqttBufferReader_ (#1593).
-* [Core] Performance improvements and reduced memory usage due to improved buffer copies (#1599, thanks to @xljiulang).
-* [Server] Fix not properly reset statistics (#1587, thanks to @damikun).
-* [Server] Now using an empty string as the sender client ID for injected application messages (#1583, thanks to @xljiulang).
-* [Server] Improved memory usage for ASP.NET connections (#1582, thanks to @xljiulang).
-* [Server] Improved memory usage and performance for ASP.NET integration (#1596, thanks to @xljiulang).
-* [Server] Add support for interception of will messages (#1613).
-* [Server] Fixed wrong topic filter detections (#1615, thanks to @logicaloud).
+* [Client] Fixed _PlatformNotSupportedException_ when using Blazor (#1755, thanks to @Nickztar).
+* [Client] Added hot reload of client certificates (#1781).
+* [Client] Added several new option builders and aligned usage (#1781, BREAKING CHANGE!).
+* [Client] Added support for _RemoteCertificateValidationCallback_ for .NET 4.5.2, 4.6.1 and 4.8 (#1806, thanks to @troky).
+* [Client] Fixed wrong logging of obsolete feature when connection was not successful (#1801, thanks to @ramonsmits).
+* [Client] Fixed _NullReferenceException_ when performing several actions when not connected (#1800, thanks to @ramonsmits).
+* [RpcClient] Added support for passing custom parameters to topic generation context (#1798, thanks to @Temppus).
+* [Server] Fixed _NullReferenceException_ in retained messages management (#1762, thanks to @logicaloud).
+* [Server] Exposed new option which allows disabling packet fragmentation (#1753).
+* [Server] Expired sessions will no longer be used when a client connects (#1756).
+* [Server] Fixed an issue in connection handling for ASP.NET connections (#1819, thanks to @CZEMacLeod).

.github/workflows/ci.yml

@@ -3,7 +3,7 @@ name: CI
 on: [push, pull_request]
 
 env:
-  VERSION: "4.1.4.${{github.run_number}}"
+  VERSION: "4.3.0.${{github.run_number}}"
 
 jobs:
   build:
@@ -22,6 +22,7 @@ jobs:
           dotnet-version: |
             3.1.x
             6.0.x
+            7.0.x
 
       - name: Setup MSBuild
         uses: microsoft/setup-msbuild@v1.1

README.md

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

Samples/Client/Client_Connection_Samples.cs

@@ -16,6 +16,28 @@ namespace MQTTnet.Samples.Client;
 
 public static class Client_Connection_Samples
 {
+    public static async Task Clean_Disconnect()
+    {
+        /*
+         * This sample disconnects in a clean way. This will send a MQTT DISCONNECT packet
+         * to the server and close the connection afterwards.
+         *
+         * See sample _Connect_Client_ for more details.
+         */
+
+        var mqttFactory = new MqttFactory();
+
+        using (var mqttClient = mqttFactory.CreateMqttClient())
+        {
+            var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("broker.hivemq.com").Build();
+            await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
+
+            // This will send the DISCONNECT packet. Calling _Dispose_ without DisconnectAsync the 
+            // connection is closed in a "not clean" way. See MQTT specification for more details.
+            await mqttClient.DisconnectAsync(new MqttClientDisconnectOptionsBuilder().WithReason(MqttClientDisconnectOptionsReason.NormalDisconnection).Build());
+        }
+    }
+
     public static async Task Connect_Client()
     {
         /*
@@ -113,15 +135,15 @@ public static class Client_Connection_Samples
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
             var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("mqtt.fluux.io")
-                .WithTls(
+                .WithTlsOptions(
                     o =>
                     {
                         // The used public broker sometimes has invalid certificates. This sample accepts all
                         // certificates. This should not be used in live environments.
-                        o.CertificateValidationHandler = _ => true;
+                        o.WithCertificateValidationHandler(_ => true);
 
                         // The default value is determined by the OS. Set manually to force version.
-                        o.SslProtocol = SslProtocols.Tls12;
+                        o.WithSslProtocols(SslProtocols.Tls12);
                     })
                 .Build();
 
@@ -148,7 +170,7 @@ public static class Client_Connection_Samples
 
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
-            var mqttClientOptions = new MqttClientOptionsBuilder().WithWebSocketServer("broker.hivemq.com:8000/mqtt").Build();
+            var mqttClientOptions = new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.hivemq.com:8000/mqtt")).Build();
 
             var response = await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
 
@@ -170,7 +192,7 @@ public static class Client_Connection_Samples
 
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
-            var mqttClientOptions = new MqttClientOptionsBuilder().WithWebSocketServer("broker.hivemq.com:8000/mqtt").Build();
+            var mqttClientOptions = new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.hivemq.com:8000/mqtt")).Build();
 
             var response = await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
 
@@ -193,13 +215,11 @@ public static class Client_Connection_Samples
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
             var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8883)
-                .WithTls(
-                    o =>
-                    {
+                .WithTlsOptions(
+                    o => o.WithCertificateValidationHandler(
                         // The used public broker sometimes has invalid certificates. This sample accepts all
                         // certificates. This should not be used in live environments.
-                        o.CertificateValidationHandler = _ => true;
-                    })
+                        _ => true))
                 .Build();
 
             // In MQTTv5 the response contains much more information.
@@ -214,6 +234,31 @@ public static class Client_Connection_Samples
         }
     }
 
+    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 Disconnect_Clean()
     {
         /*
@@ -232,7 +277,7 @@ public static class Client_Connection_Samples
 
             // Calling _DisconnectAsync_ will send a DISCONNECT packet before closing the connection.
             // Using a reason code requires MQTT version 5.0.0!
-            await mqttClient.DisconnectAsync(MqttClientDisconnectReason.ImplementationSpecificError);
+            await mqttClient.DisconnectAsync(MqttClientDisconnectOptionsReason.ImplementationSpecificError);
         }
     }
 
@@ -269,18 +314,19 @@ public static class Client_Connection_Samples
         using (var mqttClient = mqttFactory.CreateMqttClient())
         {
             var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("mqtt.fluux.io", 8883)
-                .WithTls(
+                .WithTlsOptions(
                     o =>
                     {
-                        o.CertificateValidationHandler = eventArgs =>
-                        {
-                            eventArgs.Certificate.Subject.DumpToConsole();
-                            eventArgs.Certificate.GetExpirationDateString().DumpToConsole();
-                            eventArgs.Chain.ChainPolicy.RevocationMode.DumpToConsole();
-                            eventArgs.Chain.ChainStatus.DumpToConsole();
-                            eventArgs.SslPolicyErrors.DumpToConsole();
-                            return true;
-                        };
+                        o.WithCertificateValidationHandler(
+                            eventArgs =>
+                            {
+                                eventArgs.Certificate.Subject.DumpToConsole();
+                                eventArgs.Certificate.GetExpirationDateString().DumpToConsole();
+                                eventArgs.Chain.ChainPolicy.RevocationMode.DumpToConsole();
+                                eventArgs.Chain.ChainStatus.DumpToConsole();
+                                eventArgs.SslPolicyErrors.DumpToConsole();
+                                return true;
+                            });
                     })
                 .Build();
 
@@ -297,7 +343,7 @@ public static class Client_Connection_Samples
         /*
          * This sample sends a PINGREQ packet to the server and waits for a reply.
          *
-         * This is only supported in METTv5.0.0+.
+         * This is only supported in MQTTv5.0.0+.
          */
 
         var mqttFactory = new MqttFactory();
@@ -386,4 +432,4 @@ public static class Client_Connection_Samples
                 });
         }
     }
-}
+}

Samples/Client/Client_Subscribe_Samples.cs

@@ -5,6 +5,7 @@
 // ReSharper disable UnusedType.Global
 // ReSharper disable UnusedMember.Global
 // ReSharper disable InconsistentNaming
+// ReSharper disable UnusedMember.Local
 
 using MQTTnet.Client;
 using MQTTnet.Packets;
@@ -176,4 +177,60 @@ public static class Client_Subscribe_Samples
             response.DumpToConsole();
         }
     }
+
+    static void ConcurrentProcessingDisableAutoAcknowledge(CancellationToken shutdownToken, IMqttClient mqttClient)
+    {
+        /*
+         * This sample shows how to achieve concurrent processing and not have message AutoAcknowledged
+         * This to have a proper QoS1 (at-least-once) experience for what at least MQTT specification can provide
+         */
+        mqttClient.ApplicationMessageReceivedAsync += async ea =>
+        {
+            ea.AutoAcknowledge = false;
+
+            async Task ProcessAsync()
+            {
+                // DO YOUR WORK HERE!
+                await Task.Delay(1000, shutdownToken);
+                await ea.AcknowledgeAsync(shutdownToken);
+                // WARNING: If process failures are not transient the message will be retried on every restart of the client
+                //          A failed message will not be dispatched again to the client as MQTT does not have a NACK packet to let
+                //          the broker know processing failed
+                //
+                // Optionally: Use a framework like Polly to create a retry policy: https://github.com/App-vNext/Polly#retry
+            }
+
+            _ = Task.Run(ProcessAsync, shutdownToken);
+        };
+    }
+
+    static void ConcurrentProcessingWithLimit(CancellationToken shutdownToken, IMqttClient mqttClient)
+    {
+        /*
+         * This sample shows how to achieve concurrent processing, with:
+         * - a maximum concurrency limit based on Environment.ProcessorCount
+         */
+
+        var concurrent = new SemaphoreSlim(Environment.ProcessorCount);
+
+        mqttClient.ApplicationMessageReceivedAsync += async ea =>
+        {
+            await concurrent.WaitAsync(shutdownToken).ConfigureAwait(false);
+
+            async Task ProcessAsync()
+            {
+                try
+                {
+                    // DO YOUR WORK HERE!
+                    await Task.Delay(1000, shutdownToken);
+                }
+                finally
+                {
+                    concurrent.Release();
+                }
+            }
+
+            _ = Task.Run(ProcessAsync, shutdownToken);
+        };
+    }
 }

Samples/Diagnostics/PackageInspection_Samples.cs

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

Samples/Program.cs

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

Samples/Server/Server_ASP_NET_Samples.cs

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

Samples/Server/Server_Diagnostics_Samples.cs

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

Samples/Server/Server_Retained_Messages_Samples.cs

@@ -7,6 +7,8 @@
 // ReSharper disable InconsistentNaming
 
 using System.Text.Json;
+using MQTTnet.Packets;
+using MQTTnet.Protocol;
 
 namespace MQTTnet.Samples.Server;
 
@@ -32,7 +34,10 @@ public static class Server_Retained_Messages_Samples
             {
                 try
                 {
-                    eventArgs.LoadedRetainedMessages = await JsonSerializer.DeserializeAsync<List<MqttApplicationMessage>>(File.OpenRead(storePath));
+                    var models = await JsonSerializer.DeserializeAsync<List<MqttRetainedMessageModel>>(File.OpenRead(storePath)) ?? new List<MqttRetainedMessageModel>();
+                    var retainedMessages = models.Select(m => m.ToApplicationMessage()).ToList();
+
+                    eventArgs.LoadedRetainedMessages = retainedMessages;
                     Console.WriteLine("Retained messages loaded.");
                 }
                 catch (FileNotFoundException)
@@ -56,7 +61,9 @@ public static class Server_Retained_Messages_Samples
                     // used to write all retained messages to dedicated files etc. Then all files must be loaded and a full list
                     // of retained messages must be provided in the loaded event.
 
-                    var buffer = JsonSerializer.SerializeToUtf8Bytes(eventArgs.StoredRetainedMessages);
+                    var models = eventArgs.StoredRetainedMessages.Select(MqttRetainedMessageModel.Create);
+
+                    var buffer = JsonSerializer.SerializeToUtf8Bytes(models);
                     await File.WriteAllBytesAsync(storePath, buffer);
                     Console.WriteLine("Retained messages saved.");
                 }
@@ -79,4 +86,59 @@ public static class Server_Retained_Messages_Samples
             Console.ReadLine();
         }
     }
+
+    sealed class MqttRetainedMessageModel
+    {
+        public string? ContentType { get; set; }
+        public byte[]? CorrelationData { get; set; }
+        public byte[]? Payload { get; set; }
+        public MqttPayloadFormatIndicator PayloadFormatIndicator { get; set; }
+        public MqttQualityOfServiceLevel QualityOfServiceLevel { get; set; }
+        public string? ResponseTopic { get; set; }
+        public string? Topic { get; set; }
+        public List<MqttUserProperty>? UserProperties { get; set; }
+
+        public static MqttRetainedMessageModel Create(MqttApplicationMessage message)
+        {
+            if (message == null)
+            {
+                throw new ArgumentNullException(nameof(message));
+            }
+
+            return new MqttRetainedMessageModel
+            {
+                Topic = message.Topic,
+
+                // Create a copy of the buffer from the payload segment because 
+                // it cannot be serialized and deserialized with the JSON serializer.
+                Payload = message.PayloadSegment.ToArray(),
+                UserProperties = message.UserProperties,
+                ResponseTopic = message.ResponseTopic,
+                CorrelationData = message.CorrelationData,
+                ContentType = message.ContentType,
+                PayloadFormatIndicator = message.PayloadFormatIndicator,
+                QualityOfServiceLevel = message.QualityOfServiceLevel
+
+                // Other properties like "Retain" are not if interest in the storage.
+                // That's why a custom model makes sense.
+            };
+        }
+
+        public MqttApplicationMessage ToApplicationMessage()
+        {
+            return new MqttApplicationMessage
+            {
+                Topic = Topic,
+                PayloadSegment = new ArraySegment<byte>(Payload ?? Array.Empty<byte>()),
+                PayloadFormatIndicator = PayloadFormatIndicator,
+                ResponseTopic = ResponseTopic,
+                CorrelationData = CorrelationData,
+                ContentType = ContentType,
+                UserProperties = UserProperties,
+                QualityOfServiceLevel = QualityOfServiceLevel,
+                Dup = false,
+                Retain = true
+            };
+        }
+    }
 }

Samples/Server/Server_TLS_Samples.cs

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

Source/MQTTnet.AspNetCore.Tests/MqttConnectionContextTest.cs

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

Source/MQTTnet.AspNetCore.Tests/ReaderExtensionsTest.cs

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

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

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

Source/MQTTnet.AspnetCore/EndpointRouterExtensions.cs

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

Source/MQTTnet.AspnetCore/MQTTnet.AspNetCore.csproj

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

Source/MQTTnet.AspnetCore/MqttConnectionContext.cs

@@ -33,8 +33,11 @@ namespace MQTTnet.AspNetCore
             PacketFormatterAdapter = packetFormatterAdapter ?? throw new ArgumentNullException(nameof(packetFormatterAdapter));
             _connection = connection ?? throw new ArgumentNullException(nameof(connection));
 
-            _input = connection.Transport.Input;
-            _output = connection.Transport.Output;
+            if (!(_connection is TcpConnection tcp) || tcp.IsConnected)
+            {
+                _input = connection.Transport.Input;
+                _output = connection.Transport.Output;
+            }
         }
 
         public long BytesReceived { get; private set; }
@@ -211,8 +214,17 @@ namespace MQTTnet.AspNetCore
                 {
                     var buffer = PacketFormatterAdapter.Encode(packet);
 
-                    WritePacketBuffer(_output, buffer);
-                    await _output.FlushAsync(cancellationToken).ConfigureAwait(false);
+                    if (buffer.Payload.Count == 0)
+                    {
+                        // zero copy
+                        // https://github.com/dotnet/runtime/blob/e31ddfdc4f574b26231233dc10c9a9c402f40590/src/libraries/System.IO.Pipelines/src/System/IO/Pipelines/StreamPipeWriter.cs#L279
+                        await _output.WriteAsync(buffer.Packet, cancellationToken).ConfigureAwait(false);
+                    }
+                    else
+                    {
+                        WritePacketBuffer(_output, buffer);
+                        await _output.FlushAsync(cancellationToken).ConfigureAwait(false);
+                    }
 
                     BytesSent += buffer.Length;
                 }

Source/MQTTnet.AspnetCore/MqttWebSocketServerAdapter.cs

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

Source/MQTTnet.Benchmarks/ChannelAdapterBenchmark.cs

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

Source/MQTTnet.Benchmarks/MQTTnet.Benchmarks.csproj

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

Source/MQTTnet.Benchmarks/MqttPacketReaderWriterBenchmark.cs

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

Source/MQTTnet.Benchmarks/SendPacketAsyncBenchmark.cs

@@ -0,0 +1,68 @@
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Jobs;
+using MQTTnet.Formatter;
+using System;
+using System.IO;
+using System.IO.Pipelines;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Benchmarks
+{
+    [SimpleJob(RuntimeMoniker.Net60)]
+    [RPlotExporter, RankColumn]
+    [MemoryDiagnoser]
+    public class SendPacketAsyncBenchmark : BaseBenchmark
+    {
+        MemoryStream stream;
+        MqttPacketBuffer buffer;
+
+        [GlobalSetup]
+        public void GlobalSetup()
+        {
+            stream = new MemoryStream(1024);
+            var packet = new ArraySegment<byte>(new byte[10]);
+            buffer = new MqttPacketBuffer(packet);
+        }
+
+        [Benchmark(Baseline = true)]
+        public async ValueTask Before()
+        {
+            stream.Position = 0;
+            var output = PipeWriter.Create(stream);
+
+            WritePacketBuffer(output, buffer);
+            await output.FlushAsync();
+        }
+
+        [Benchmark]
+        public async ValueTask After()
+        {
+            stream.Position = 0;
+            var output = PipeWriter.Create(stream);
+
+            if (buffer.Payload.Count == 0)
+            {
+                await output.WriteAsync(buffer.Packet).ConfigureAwait(false);
+            }
+            else
+            {
+                WritePacketBuffer(output, buffer);
+                await output.FlushAsync().ConfigureAwait(false);
+            }
+        }
+
+
+        static void WritePacketBuffer(PipeWriter output, MqttPacketBuffer buffer)
+        {
+            // copy MqttPacketBuffer's Packet and Payload to the same buffer block of PipeWriter
+            // MqttPacket will be transmitted within the bounds of a WebSocket frame after PipeWriter.FlushAsync
+
+            var span = output.GetSpan(buffer.Length);
+
+            buffer.Packet.AsSpan().CopyTo(span);
+            buffer.Payload.AsSpan().CopyTo(span.Slice(buffer.Packet.Count));
+
+            output.Advance(buffer.Length);
+        }
+    }
+}

Source/MQTTnet.Benchmarks/SerializerBenchmark.cs

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

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

@@ -1,8 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0</TargetFrameworks>
-        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461</TargetFrameworks>
+        <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0;net7.0</TargetFrameworks>
+        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461;net48</TargetFrameworks>
         <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' AND '$(MSBuildRuntimeType)' != 'Core' ">$(TargetFrameworks);uap10.0</TargetFrameworks>
         
         <AssemblyName>MQTTnet.Extensions.ManagedClient</AssemblyName>

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClient.cs

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

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClientOptions.cs

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

Source/MQTTnet.Extensions.ManagedClient/ManagedProcessFailedEventArgs.cs

@@ -2,17 +2,33 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using MQTTnet.Packets;
 using System;
+using System.Collections.Generic;
+using System.Linq;
 
 namespace MQTTnet.Extensions.ManagedClient
 {
     public class ManagedProcessFailedEventArgs : EventArgs
     {
-        public ManagedProcessFailedEventArgs(Exception exception)
+        public ManagedProcessFailedEventArgs(Exception exception, List<MqttTopicFilter> addedSubscriptions, List<string> removedSubscriptions)
         {
             Exception = exception ?? throw new ArgumentNullException(nameof(exception));
+
+            if (addedSubscriptions != null)
+            {
+                AddedSubscriptions = new List<string>(addedSubscriptions.Select(item => item.Topic));
+            }
+
+            if (removedSubscriptions != null)
+            {
+                RemovedSubscriptions = new List<string>(removedSubscriptions);
+            }
         }
 
         public Exception Exception { get; }
+
+        public List<string> AddedSubscriptions { get; }
+        public List<string> RemovedSubscriptions { get; }
     }
 }

Source/MQTTnet.Extensions.ManagedClient/MqttFactoryExtensions.cs

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

Source/MQTTnet.Extensions.Rpc/IMqttRpcClient.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Protocol;
@@ -7,8 +8,8 @@ namespace MQTTnet.Extensions.Rpc
 {
     public interface IMqttRpcClient : IDisposable
     {
-        Task<byte[]> ExecuteAsync(TimeSpan timeout, string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel);
+        Task<byte[]> ExecuteAsync(TimeSpan timeout, string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel, IDictionary<string,object> parameters = null);
         
-        Task<byte[]> ExecuteAsync(string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel, CancellationToken cancellationToken = default);
+        Task<byte[]> ExecuteAsync(string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel, IDictionary<string, object> parameters = null, CancellationToken cancellationToken = default);
     }
 }

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

@@ -1,8 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0</TargetFrameworks>
-        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461</TargetFrameworks>
+        <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0;net7.0</TargetFrameworks>
+        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461;net48</TargetFrameworks>
         <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' AND '$(MSBuildRuntimeType)' != 'Core' ">$(TargetFrameworks);uap10.0</TargetFrameworks>
         
         <AssemblyName>MQTTnet.Extensions.Rpc</AssemblyName>

Source/MQTTnet.Extensions.Rpc/MqttRpcClient.cs

@@ -4,10 +4,13 @@
 
 using System;
 using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Client;
 using MQTTnet.Exceptions;
+using MQTTnet.Formatter;
 using MQTTnet.Internal;
 using MQTTnet.Protocol;
 
@@ -17,9 +20,9 @@ namespace MQTTnet.Extensions.Rpc
     {
         readonly IMqttClient _mqttClient;
         readonly MqttRpcClientOptions _options;
-        
+
         readonly ConcurrentDictionary<string, AsyncTaskCompletionSource<byte[]>> _waitingCalls = new ConcurrentDictionary<string, AsyncTaskCompletionSource<byte[]>>();
-        
+
         public MqttRpcClient(IMqttClient mqttClient, MqttRpcClientOptions options)
         {
             _mqttClient = mqttClient ?? throw new ArgumentNullException(nameof(mqttClient));
@@ -40,13 +43,13 @@ namespace MQTTnet.Extensions.Rpc
             _waitingCalls.Clear();
         }
 
-        public async Task<byte[]> ExecuteAsync(TimeSpan timeout, string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel)
+        public async Task<byte[]> ExecuteAsync(TimeSpan timeout, string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel, IDictionary<string, object> parameters = null)
         {
             using (var timeoutToken = new CancellationTokenSource(timeout))
             {
                 try
                 {
-                    return await ExecuteAsync(methodName, payload, qualityOfServiceLevel, timeoutToken.Token).ConfigureAwait(false);
+                    return await ExecuteAsync(methodName, payload, qualityOfServiceLevel, parameters, timeoutToken.Token).ConfigureAwait(false);
                 }
                 catch (OperationCanceledException exception)
                 {
@@ -60,14 +63,14 @@ namespace MQTTnet.Extensions.Rpc
             }
         }
 
-        public async Task<byte[]> ExecuteAsync(string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel, CancellationToken cancellationToken = default)
+        public async Task<byte[]> ExecuteAsync(string methodName, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel, IDictionary<string, object> parameters = null, CancellationToken cancellationToken = default)
         {
             if (methodName == null)
             {
                 throw new ArgumentNullException(nameof(methodName));
             }
 
-            var context = new TopicGenerationContext(_mqttClient, _options, methodName, qualityOfServiceLevel);
+            var context = new TopicGenerationContext(_mqttClient, _options, methodName, parameters, qualityOfServiceLevel);
             var topicNames = _options.TopicGenerationStrategy.CreateRpcTopics(context);
 
             var requestTopic = topicNames.RequestTopic;
@@ -83,11 +86,14 @@ namespace MQTTnet.Extensions.Rpc
                 throw new MqttProtocolViolationException("RPC response topic is empty.");
             }
 
-            var requestMessage = new MqttApplicationMessageBuilder().WithTopic(requestTopic)
-                .WithPayload(payload)
-                .WithQualityOfServiceLevel(qualityOfServiceLevel)
-                .WithResponseTopic(responseTopic)
-                .Build();
+            var requestMessageBuilder = new MqttApplicationMessageBuilder().WithTopic(requestTopic).WithPayload(payload).WithQualityOfServiceLevel(qualityOfServiceLevel);
+
+            if (_mqttClient.Options.ProtocolVersion == MqttProtocolVersion.V500)
+            {
+                requestMessageBuilder.WithResponseTopic(responseTopic);
+            }
+
+            var requestMessage = requestMessageBuilder.Build();
 
             try
             {
@@ -115,7 +121,6 @@ namespace MQTTnet.Extensions.Rpc
             finally
             {
                 _waitingCalls.TryRemove(responseTopic, out _);
-
                 await _mqttClient.UnsubscribeAsync(responseTopic, CancellationToken.None).ConfigureAwait(false);
             }
         }
@@ -127,7 +132,8 @@ 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.Rpc/MqttRpcClientExtensions.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Generic;
 using System.Text;
 using System.Threading.Tasks;
 using MQTTnet.Protocol;
@@ -11,13 +12,13 @@ namespace MQTTnet.Extensions.Rpc
 {
     public static class MqttRpcClientExtensions
     {
-        public static Task<byte[]> ExecuteAsync(this IMqttRpcClient client, TimeSpan timeout, string methodName, string payload, MqttQualityOfServiceLevel qualityOfServiceLevel)
+        public static Task<byte[]> ExecuteAsync(this IMqttRpcClient client, TimeSpan timeout, string methodName, string payload, MqttQualityOfServiceLevel qualityOfServiceLevel, IDictionary<string,object> parameters = null)
         {
             if (client == null) throw new ArgumentNullException(nameof(client));
 
             var buffer = Encoding.UTF8.GetBytes(payload ?? string.Empty);
 
-            return client.ExecuteAsync(timeout, methodName, buffer, qualityOfServiceLevel);
+            return client.ExecuteAsync(timeout, methodName, buffer, qualityOfServiceLevel, parameters);
         }
     }
 }

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

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Generic;
 using MQTTnet.Client;
 using MQTTnet.Protocol;
 
@@ -10,9 +11,11 @@ namespace MQTTnet.Extensions.Rpc
 {
     public sealed class TopicGenerationContext
     {
-        public TopicGenerationContext(IMqttClient mqttClient, MqttRpcClientOptions options, string methodName, MqttQualityOfServiceLevel qualityOfServiceLevel)
+        public TopicGenerationContext(IMqttClient mqttClient, MqttRpcClientOptions options, string methodName,
+            IDictionary<string, object> parameters, MqttQualityOfServiceLevel qualityOfServiceLevel)
         {
             MethodName = methodName ?? throw new ArgumentNullException(nameof(methodName));
+            Parameters = parameters;
             QualityOfServiceLevel = qualityOfServiceLevel;
             MqttClient = mqttClient ?? throw new ArgumentNullException(nameof(mqttClient));
             Options = options ?? throw new ArgumentNullException(nameof(options));
@@ -20,6 +23,8 @@ namespace MQTTnet.Extensions.Rpc
 
         public string MethodName { get; }
 
+        public IDictionary<string, object> Parameters { get; }
+
         public IMqttClient MqttClient { get; }
 
         public MqttRpcClientOptions Options { get; }

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

@@ -1,8 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0</TargetFrameworks>
-        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461</TargetFrameworks>
+        <TargetFrameworks>netstandard1.3;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0;net6.0;net7.0</TargetFrameworks>
+        <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461;net48</TargetFrameworks>
         <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' AND '$(MSBuildRuntimeType)' != 'Core' ">$(TargetFrameworks);uap10.0</TargetFrameworks>
         
         <AssemblyName>MQTTnet.Extensions.WebSocket4Net</AssemblyName>

Source/MQTTnet.Extensions.WebSocket4Net/WebSocket4NetMqttChannel.cs

@@ -92,18 +92,7 @@ namespace MQTTnet.Extensions.WebSocket4Net
             var webSocketVersion = WebSocketVersion.None;
             var receiveBufferSize = 0;
 
-            var certificates = new X509CertificateCollection();
-            if (_webSocketOptions.TlsOptions?.Certificates != null)
-            {
-                foreach (var certificate in _webSocketOptions.TlsOptions.Certificates)
-                {
-#if WINDOWS_UWP
-                    certificates.Add(new X509Certificate(certificate));
-#else
-                    certificates.Add(certificate);
-#endif
-                }
-            }
+            var certificates = _webSocketOptions.TlsOptions?.ClientCertificatesProvider?.GetCertificates();
 
             _webSocket = new WebSocket(uri, subProtocol, cookies, customHeaders, userAgent, origin, webSocketVersion, proxy, sslProtocols, receiveBufferSize)
             {

Source/MQTTnet.Extensions.WebSocket4Net/WebSocket4NetMqttClientAdapterFactory.cs

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

Source/MQTTnet.TestApp/ClientTest.cs

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

Source/MQTTnet.TestApp/MQTTnet.TestApp.csproj

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

Source/MQTTnet.TestApp/PerformanceTest.cs

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

Source/MQTTnet.TestApp/PublicBrokerTest.cs

@@ -20,7 +20,7 @@ namespace MQTTnet.TestApp
         {
 #if NET5_0_OR_GREATER
             // TLS13 is only available in Net5.0
-            var unsafeTls13 = new MqttClientOptionsBuilderTlsParameters
+            var unsafeTls13 = new MqttClientTlsOptions
             {
                 UseTls = true,
                 SslProtocol = SslProtocols.Tls13,
@@ -29,7 +29,7 @@ namespace MQTTnet.TestApp
             };
 #endif
             // Also defining TLS12 for servers that don't seem no to support TLS13.
-            var unsafeTls12 = new MqttClientOptionsBuilderTlsParameters
+            var unsafeTls12 = new MqttClientTlsOptions
             {
                 UseTls = true,
                 SslProtocol = SslProtocols.Tls12,
@@ -44,16 +44,16 @@ namespace MQTTnet.TestApp
 
             await ExecuteTestAsync(
                 "mqtt.eclipseprojects.io WS",
-                new MqttClientOptionsBuilder().WithWebSocketServer("mqtt.eclipseprojects.io:80/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build());
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("mqtt.eclipseprojects.io:80/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
 #if NET5_0_OR_GREATER
             await ExecuteTestAsync("mqtt.eclipseprojects.io WS TLS13",
-                new MqttClientOptionsBuilder().WithWebSocketServer("mqtt.eclipseprojects.io:443/mqtt")
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build());
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("mqtt.eclipseprojects.io:443/mqtt"))
+                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls13).Build());
             
             await ExecuteTestAsync("mqtt.eclipseprojects.io WS TLS13 (WebSocket4Net)",
-                new MqttClientOptionsBuilder().WithWebSocketServer("mqtt.eclipseprojects.io:443/mqtt")
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build(),
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("mqtt.eclipseprojects.io:443/mqtt"))
+                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls13).Build(),
                     true);
 #endif
 
@@ -68,12 +68,12 @@ namespace MQTTnet.TestApp
 
             await ExecuteTestAsync(
                 "test.mosquitto.org TCP TLS12",
-                new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8883).WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+                new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8883).WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls12).Build());
 
 #if NET5_0_OR_GREATER
             await ExecuteTestAsync("test.mosquitto.org TCP TLS13",
                 new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8883)
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build());
+                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls13).Build());
 #endif
 
             await ExecuteTestAsync(
@@ -81,21 +81,21 @@ namespace MQTTnet.TestApp
                 new MqttClientOptionsBuilder().WithTcpServer("test.mosquitto.org", 8885)
                     .WithCredentials("rw", "readwrite")
                     .WithProtocolVersion(MqttProtocolVersion.V311)
-                    .WithTls(unsafeTls12)
+                    .WithTlsOptions(unsafeTls12)
                     .Build());
 
             await ExecuteTestAsync(
                 "test.mosquitto.org WS",
-                new MqttClientOptionsBuilder().WithWebSocketServer("test.mosquitto.org:8080/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build());
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("test.mosquitto.org:8080/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
             await ExecuteTestAsync(
                 "test.mosquitto.org WS (WebSocket4Net)",
-                new MqttClientOptionsBuilder().WithWebSocketServer("test.mosquitto.org:8080/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build(),
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("test.mosquitto.org:8080/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).Build(),
                 true);
 
             await ExecuteTestAsync(
                 "test.mosquitto.org WS TLS12",
-                new MqttClientOptionsBuilder().WithWebSocketServer("test.mosquitto.org:8081/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("test.mosquitto.org:8081/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls12).Build());
 
             // await ExecuteTestAsync(
             //     "test.mosquitto.org WS TLS12 (WebSocket4Net)",
@@ -109,30 +109,30 @@ namespace MQTTnet.TestApp
 
             await ExecuteTestAsync(
                 "broker.emqx.io TCP TLS12",
-                new MqttClientOptionsBuilder().WithTcpServer("broker.emqx.io", 8883).WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+                new MqttClientOptionsBuilder().WithTcpServer("broker.emqx.io", 8883).WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls12).Build());
 
 #if NET5_0_OR_GREATER
             await ExecuteTestAsync("broker.emqx.io TCP TLS13",
                 new MqttClientOptionsBuilder().WithTcpServer("broker.emqx.io", 8883)
-                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls13).Build());
+                    .WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls13).Build());
 #endif
 
             await ExecuteTestAsync(
                 "broker.emqx.io WS",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.emqx.io:8083/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build());
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.emqx.io:8083/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
             await ExecuteTestAsync(
                 "broker.emqx.io WS (WebSocket4Net)",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.emqx.io:8084/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build(),
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.emqx.io:8084/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).Build(),
                 true);
 
             await ExecuteTestAsync(
                 "broker.emqx.io WS TLS12",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.emqx.io:8084/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build());
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.emqx.io:8084/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls12).Build());
 
             await ExecuteTestAsync(
                 "broker.emqx.io WS TLS12 (WebSocket4Net)",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.emqx.io:8084/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).WithTls(unsafeTls12).Build(),
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.emqx.io:8084/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).WithTlsOptions(unsafeTls12).Build(),
                 true);
 
             // broker.hivemq.com
@@ -142,11 +142,11 @@ namespace MQTTnet.TestApp
 
             await ExecuteTestAsync(
                 "broker.hivemq.com WS",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.hivemq.com:8000/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build());
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.hivemq.com:8000/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).Build());
 
             await ExecuteTestAsync(
                 "broker.hivemq.com WS (WebSocket4Net)",
-                new MqttClientOptionsBuilder().WithWebSocketServer("broker.hivemq.com:8000/mqtt").WithProtocolVersion(MqttProtocolVersion.V311).Build(),
+                new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("broker.hivemq.com:8000/mqtt")).WithProtocolVersion(MqttProtocolVersion.V311).Build(),
                 true);
 
             // mqtt.swifitch.cz: Does not seem to operate any more

Source/MQTTnet.TestApp/ServerTest.cs

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

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

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

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

@@ -17,11 +17,43 @@ using MQTTnet.Protocol;
 using MQTTnet.Server;
 using MQTTnet.Tests.Mockups;
 
-namespace MQTTnet.Tests.Client
+namespace MQTTnet.Tests.Clients.ManagedMqttClient
 {
     [TestClass]
     public sealed class ManagedMqttClient_Tests : BaseTestClass
     {
+        [TestMethod]
+        public async Task Expose_Custom_Connection_Error()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                var server = await testEnvironment.StartServer();
+                
+                server.ValidatingConnectionAsync += args =>
+                {
+                    args.ReasonCode = MqttConnectReasonCode.BadUserNameOrPassword;
+                    return CompletedTask.Instance;
+                };
+
+                var managedClient = testEnvironment.Factory.CreateManagedMqttClient();
+
+                MqttClientDisconnectedEventArgs disconnectedArgs = null;
+                managedClient.DisconnectedAsync += args =>
+                {
+                    disconnectedArgs = args;
+                    return CompletedTask.Instance;
+                };
+                
+                var clientOptions = testEnvironment.Factory.CreateManagedMqttClientOptionsBuilder().WithClientOptions(testEnvironment.CreateDefaultClientOptions()).Build();
+                await managedClient.StartAsync(clientOptions);
+
+                await LongTestDelay();
+
+                Assert.IsNotNull(disconnectedArgs);
+                Assert.AreEqual(MqttClientConnectResultCode.BadUserNameOrPassword, disconnectedArgs.ConnectResult.ResultCode);
+            }
+        }
+        
         [TestMethod]
         public async Task Receive_While_Not_Cleanly_Disconnected()
         {
@@ -164,7 +196,7 @@ namespace MQTTnet.Tests.Client
                     .Build();
 
                 var dyingClient = testEnvironment.CreateClient();
-                var dyingManagedClient = new ManagedMqttClient(dyingClient, testEnvironment.ClientLogger);
+                var dyingManagedClient = new MQTTnet.Extensions.ManagedClient.ManagedMqttClient(dyingClient, testEnvironment.ClientLogger);
 
                 await dyingManagedClient.StartAsync(new ManagedMqttClientOptionsBuilder().WithClientOptions(clientOptions).Build());
 
@@ -199,7 +231,7 @@ namespace MQTTnet.Tests.Client
             {
                 var server = await testEnvironment.StartServer();
 
-                var managedClient = new ManagedMqttClient(testEnvironment.CreateClient(), new MqttNetEventLogger());
+                var managedClient = new MQTTnet.Extensions.ManagedClient.ManagedMqttClient(testEnvironment.CreateClient(), new MqttNetEventLogger());
                 var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("localhost", testEnvironment.ServerPort);
 
                 var connected = GetConnectedTask(managedClient);
@@ -226,7 +258,7 @@ namespace MQTTnet.Tests.Client
 
                 await testEnvironment.StartServer();
 
-                var managedClient = new ManagedMqttClient(testEnvironment.CreateClient(), new MqttNetEventLogger());
+                var managedClient = new MQTTnet.Extensions.ManagedClient.ManagedMqttClient(testEnvironment.CreateClient(), new MqttNetEventLogger());
                 var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("localhost", testEnvironment.ServerPort);
                 var storage = new ManagedMqttClientTestStorage();
 
@@ -389,7 +421,7 @@ namespace MQTTnet.Tests.Client
                 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 });
+                await sendingClient.PublishAsync(new MqttApplicationMessage { Topic = "topic", PayloadSegment = new ArraySegment<byte>( new byte[] { 1 }), Retain = true });
 
                 var subscribeTime = DateTime.UtcNow;
 
@@ -422,7 +454,7 @@ namespace MQTTnet.Tests.Client
                 //wait a bit for the subscription to become established
                 await Task.Delay(500);
 
-                await sendingClient.PublishAsync(new MqttApplicationMessage { Topic = "topic", Payload = new byte[] { 1 }, Retain = true });
+                await sendingClient.PublishAsync(new MqttApplicationMessage { Topic = "topic", PayloadSegment = new ArraySegment<byte>(new byte[] { 1 }), Retain = true });
 
                 var messages = await SetupReceivingOfMessages(managedClient, 1);
 
@@ -439,7 +471,7 @@ namespace MQTTnet.Tests.Client
             }
         }
 
-        async Task<ManagedMqttClient> CreateManagedClientAsync(
+        async Task<MQTTnet.Extensions.ManagedClient.ManagedMqttClient> CreateManagedClientAsync(
             TestEnvironment testEnvironment,
             IMqttClient underlyingClient = null,
             TimeSpan? connectionCheckInterval = null,
@@ -456,7 +488,7 @@ namespace MQTTnet.Tests.Client
             // at connection check intervals
             managedOptions.ConnectionCheckInterval = connectionCheckInterval ?? TimeSpan.FromSeconds(0.1);
 
-            var managedClient = new ManagedMqttClient(underlyingClient ?? testEnvironment.CreateClient(), new MqttNetEventLogger());
+            var managedClient = new MQTTnet.Extensions.ManagedClient.ManagedMqttClient(underlyingClient ?? testEnvironment.CreateClient(), new MqttNetEventLogger());
 
             var connected = GetConnectedTask(managedClient);
 
@@ -473,7 +505,7 @@ namespace MQTTnet.Tests.Client
         ///         name="managedClient" />
         ///     has connected
         /// </summary>
-        Task GetConnectedTask(ManagedMqttClient managedClient)
+        Task GetConnectedTask(MQTTnet.Extensions.ManagedClient.ManagedMqttClient managedClient)
         {
             var connected = new TaskCompletionSource<bool>();
 
@@ -495,7 +527,7 @@ namespace MQTTnet.Tests.Client
         ///         name="expectedNumberOfMessages" />
         ///     have been received
         /// </summary>
-        Task<List<MqttApplicationMessage>> SetupReceivingOfMessages(ManagedMqttClient managedClient, int expectedNumberOfMessages)
+        Task<List<MqttApplicationMessage>> SetupReceivingOfMessages(MQTTnet.Extensions.ManagedClient.ManagedMqttClient managedClient, int expectedNumberOfMessages)
         {
             var receivedMessages = new List<MqttApplicationMessage>();
             var result = new AsyncTaskCompletionSource<List<MqttApplicationMessage>>();

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

@@ -0,0 +1,222 @@
+// 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 Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Client;
+using MQTTnet.Exceptions;
+using MQTTnet.Formatter;
+using MQTTnet.Internal;
+using MQTTnet.Packets;
+using MQTTnet.Protocol;
+using MQTTnet.Server;
+
+namespace MQTTnet.Tests.Clients.MqttClient
+{
+    [TestClass]
+    public sealed class MqttClient_Connection_Tests : BaseTestClass
+    {
+        [TestMethod]
+        [ExpectedException(typeof(MqttCommunicationException))]
+        public async Task Connect_To_Invalid_Server_Port_Not_Opened()
+        {
+            var client = new MqttFactory().CreateMqttClient();
+            using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(5)))
+            {
+                await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1", 12345).Build(), timeout.Token);
+            }
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(OperationCanceledException))]
+        public async Task Connect_To_Invalid_Server_Wrong_IP()
+        {
+            var client = new MqttFactory().CreateMqttClient();
+            using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(2)))
+            {
+                await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("1.2.3.4").Build(), timeout.Token);
+            }
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(MqttCommunicationException))]
+        public async Task Connect_To_Invalid_Server_Wrong_Protocol()
+        {
+            var client = new MqttFactory().CreateMqttClient();
+            await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("http://127.0.0.1", 12345).WithTimeout(TimeSpan.FromSeconds(2)).Build());
+        }
+
+        [TestMethod]
+        public async Task ConnectTimeout_Throws_Exception()
+        {
+            var factory = new MqttFactory();
+            using (var client = factory.CreateMqttClient())
+            {
+                var disconnectHandlerCalled = false;
+                try
+                {
+                    client.DisconnectedAsync += args =>
+                    {
+                        disconnectHandlerCalled = true;
+                        return CompletedTask.Instance;
+                    };
+
+                    await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("1.2.3.4").Build());
+
+                    Assert.Fail("Must fail!");
+                }
+                catch (Exception exception)
+                {
+                    Assert.IsNotNull(exception);
+                    Assert.IsInstanceOfType(exception, typeof(MqttCommunicationException));
+                }
+
+                await LongTestDelay(); // disconnected handler is called async
+                Assert.IsTrue(disconnectHandlerCalled);
+            }
+        }
+
+        [TestMethod]
+        public async Task Disconnect_Clean()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                var server = await testEnvironment.StartServer();
+
+                ClientDisconnectedEventArgs eventArgs = null;
+                server.ClientDisconnectedAsync += args =>
+                {
+                    eventArgs = args;
+                    return CompletedTask.Instance;
+                };
+
+                var client = await testEnvironment.ConnectClient();
+
+                var disconnectOptions = testEnvironment.Factory.CreateClientDisconnectOptionsBuilder().WithReason(MqttClientDisconnectOptionsReason.MessageRateTooHigh).Build();
+
+                // Perform a clean disconnect.
+                await client.DisconnectAsync(disconnectOptions);
+
+                await LongTestDelay();
+
+                Assert.IsNotNull(eventArgs);
+                Assert.AreEqual(MqttClientDisconnectType.Clean, eventArgs.DisconnectType);
+            }
+        }
+
+        [TestMethod]
+        public async Task Disconnect_Clean_With_Custom_Reason()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                var server = await testEnvironment.StartServer();
+
+                ClientDisconnectedEventArgs eventArgs = null;
+                server.ClientDisconnectedAsync += args =>
+                {
+                    eventArgs = args;
+                    return CompletedTask.Instance;
+                };
+
+                var client = await testEnvironment.ConnectClient();
+
+                var disconnectOptions = testEnvironment.Factory.CreateClientDisconnectOptionsBuilder().WithReason(MqttClientDisconnectOptionsReason.MessageRateTooHigh).Build();
+
+                // Perform a clean disconnect.
+                await client.DisconnectAsync(disconnectOptions);
+
+                await LongTestDelay();
+
+                Assert.IsNotNull(eventArgs);
+                Assert.AreEqual(MqttDisconnectReasonCode.MessageRateTooHigh, eventArgs.ReasonCode);
+            }
+        }
+
+        [TestMethod]
+        public async Task Disconnect_Clean_With_User_Properties()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                var server = await testEnvironment.StartServer();
+
+                ClientDisconnectedEventArgs eventArgs = null;
+                server.ClientDisconnectedAsync += args =>
+                {
+                    eventArgs = args;
+                    return CompletedTask.Instance;
+                };
+
+                var client = await testEnvironment.ConnectClient();
+
+                var disconnectOptions = testEnvironment.Factory.CreateClientDisconnectOptionsBuilder().WithUserProperty("test_name", "test_value").Build();
+
+                // Perform a clean disconnect.
+                await client.DisconnectAsync(disconnectOptions);
+
+                await LongTestDelay();
+
+                Assert.IsNotNull(eventArgs);
+                Assert.IsNotNull(eventArgs.UserProperties);
+                Assert.AreEqual(1, eventArgs.UserProperties.Count);
+                Assert.AreEqual("test_name", eventArgs.UserProperties[0].Name);
+                Assert.AreEqual("test_value", eventArgs.UserProperties[0].Value);
+            }
+        }
+
+        [TestMethod]
+        public async Task Return_Non_Success()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                var server = await testEnvironment.StartServer();
+
+                server.ValidatingConnectionAsync += args =>
+                {
+                    args.ResponseUserProperties = new List<MqttUserProperty>
+                    {
+                        new MqttUserProperty("Property", "Value")
+                    };
+
+                    args.ReasonCode = MqttConnectReasonCode.QuotaExceeded;
+
+                    return CompletedTask.Instance;
+                };
+
+                var client = testEnvironment.CreateClient();
+
+                var response = await client.ConnectAsync(testEnvironment.CreateDefaultClientOptionsBuilder().WithoutThrowOnNonSuccessfulConnectResponse().Build());
+
+                Assert.IsNotNull(response);
+                Assert.AreEqual(MqttClientConnectResultCode.QuotaExceeded, response.ResultCode);
+                Assert.AreEqual(response.UserProperties[0].Name, "Property");
+                Assert.AreEqual(response.UserProperties[0].Value, "Value");
+            }
+        }
+
+        [TestMethod]
+        public async Task Throw_Proper_Exception_When_Not_Connected()
+        {
+            try
+            {
+                var mqttFactory = new MqttFactory();
+                using (var mqttClient = mqttFactory.CreateMqttClient())
+                {
+                    await mqttClient.SubscribeAsync("test", MqttQualityOfServiceLevel.AtLeastOnce);
+                }
+            }
+            catch (MqttCommunicationException exception)
+            {
+                if (exception.Message == "The client is not connected.")
+                {
+                    return;
+                }
+            }
+
+            Assert.Fail();
+        }
+    }
+}

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

@@ -21,7 +21,7 @@ using MQTTnet.Tests.Mockups;
 
 // ReSharper disable InconsistentNaming
 
-namespace MQTTnet.Tests.Client
+namespace MQTTnet.Tests.Clients.MqttClient
 {
     [TestClass]
     public sealed class MqttClient_Tests : BaseTestClass
@@ -71,60 +71,34 @@ namespace MQTTnet.Tests.Client
         }
 
         [TestMethod]
-        [ExpectedException(typeof(MqttCommunicationException))]
-        public async Task Connect_To_Invalid_Server_Port_Not_Opened()
+        public async Task Connect_Disconnect_Connect()
         {
-            var client = new MqttFactory().CreateMqttClient();
-            await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1", 12345).WithTimeout(TimeSpan.FromSeconds(5)).Build());
-        }
-
-        [TestMethod]
-        [ExpectedException(typeof(OperationCanceledException))]
-        public async Task Connect_To_Invalid_Server_Wrong_IP()
-        {
-            var client = new MqttFactory().CreateMqttClient();
-            using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(2)))
+            using (var testEnvironment = CreateTestEnvironment())
             {
-                await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("1.2.3.4").Build(), timeout.Token);
+                await testEnvironment.StartServer();
+
+                var clientOptions = testEnvironment.CreateDefaultClientOptions();
+                var client = testEnvironment.CreateClient();
+
+                await client.ConnectAsync(clientOptions);
+                await client.DisconnectAsync();
+                await client.ConnectAsync(clientOptions);
             }
         }
-
+        
         [TestMethod]
-        [ExpectedException(typeof(MqttCommunicationException))]
-        public async Task Connect_To_Invalid_Server_Wrong_Protocol()
+        [ExpectedException(typeof(InvalidOperationException))]
+        public async Task Connect_Multiple_Times_Should_Fail()
         {
-            var client = new MqttFactory().CreateMqttClient();
-            await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("http://127.0.0.1", 12345).WithTimeout(TimeSpan.FromSeconds(2)).Build());
-        }
-
-        [TestMethod]
-        public async Task ConnectTimeout_Throws_Exception()
-        {
-            var factory = new MqttFactory();
-            using (var client = factory.CreateMqttClient())
+            using (var testEnvironment = CreateTestEnvironment())
             {
-                var disconnectHandlerCalled = false;
-                try
-                {
-                    client.DisconnectedAsync += args =>
-                    {
-                        disconnectHandlerCalled = true;
-                        return CompletedTask.Instance;
-                    };
+                await testEnvironment.StartServer();
 
-                    await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("1.2.3.4").Build());
+                var clientOptions = testEnvironment.CreateDefaultClientOptions();
+                var client = testEnvironment.CreateClient();
 
-                    Assert.Fail("Must fail!");
-                }
-                catch (Exception exception)
-                {
-                    Assert.IsNotNull(exception);
-                    Assert.IsInstanceOfType(exception, typeof(MqttCommunicationException));
-                    //Assert.IsInstanceOfType(exception.InnerException, typeof(SocketException));
-                }
-
-                await LongTestDelay(); // disconnected handler is called async
-                Assert.IsTrue(disconnectHandlerCalled);
+                await client.ConnectAsync(clientOptions);
+                await client.ConnectAsync(clientOptions);
             }
         }
 
@@ -322,7 +296,7 @@ namespace MQTTnet.Tests.Client
 
                 Assert.IsNotNull(receivedMessage);
                 Assert.AreEqual("A", receivedMessage.Topic);
-                Assert.AreEqual(null, receivedMessage.Payload);
+                Assert.AreEqual(null, receivedMessage.PayloadSegment.Array);
             }
         }
 
@@ -533,7 +507,7 @@ namespace MQTTnet.Tests.Client
 
                 client2.ApplicationMessageReceivedAsync += e =>
                 {
-                    client2TopicResults.Add(Encoding.UTF8.GetString(e.ApplicationMessage.Payload));
+                    client2TopicResults.Add(Encoding.UTF8.GetString(e.ApplicationMessage.PayloadSegment.ToArray()));
                     return CompletedTask.Instance;
                 };
 

Source/MQTTnet.Tests/Clients/MqttClientOptionsBuilder_Tests.cs

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

Source/MQTTnet.Tests/Diagnostics/PacketInspection_Tests.cs

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

Source/MQTTnet.Tests/Extension_Tests.cs

@@ -1,98 +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 System.Threading;
-using System.Threading.Tasks;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MQTTnet.Exceptions;
-using MQTTnet.Internal;
-
-namespace MQTTnet.Tests
-{
-    [TestClass]
-    public class Extension_Tests
-    {
-        [ExpectedException(typeof(MqttCommunicationTimedOutException))]
-        [TestMethod]
-        public async Task TimeoutAfter()
-        {
-            await MqttTaskTimeout.WaitAsync(ct => Task.Delay(TimeSpan.FromMilliseconds(500), ct),
-                TimeSpan.FromMilliseconds(100), CancellationToken.None);
-        }
-
-        [ExpectedException(typeof(MqttCommunicationTimedOutException))]
-        [TestMethod]
-        public async Task TimeoutAfterWithResult()
-        {
-            await MqttTaskTimeout.WaitAsync(
-                ct => Task.Delay(TimeSpan.FromMilliseconds(500), ct).ContinueWith(t => 5, ct),
-                TimeSpan.FromMilliseconds(100), CancellationToken.None);
-        }
-        
-        [TestMethod]
-        public async Task TimeoutAfterWithInnerException()
-        {
-            try
-            {
-                await MqttTaskTimeout.WaitAsync(ct => Task.Run(() =>
-                {
-                    var iis = new int[0];
-                    iis[1] = 0;
-                }, ct), TimeSpan.FromSeconds(1), CancellationToken.None);
-
-                Assert.Fail();
-            }
-            catch (Exception e)
-            {
-                Assert.IsTrue(e is IndexOutOfRangeException);
-            }
-        }
-
-        [TestMethod]
-        public async Task TimeoutAfterWithInnerExceptionWithResult()
-        {
-            try
-            {
-                await MqttTaskTimeout.WaitAsync(ct => Task.Run(() =>
-                {
-                    var iis = new int[0];
-                    iis[1] = 0;
-                    return iis[0];
-                }, ct), TimeSpan.FromSeconds(1), CancellationToken.None);
-
-                Assert.Fail();
-            }
-            catch (Exception e)
-            {
-                Assert.IsTrue(e is IndexOutOfRangeException);
-            }
-        }
-
-        [TestMethod]
-        public async Task TimeoutAfterMemoryUsage()
-        {
-            var initialMemory = GC.GetTotalMemory(true);
-
-            var tasks = Enumerable.Range(0, 100000)
-                .Select(i =>
-                {
-                    return MqttTaskTimeout.WaitAsync(ct => Task.Delay(TimeSpan.FromMilliseconds(1), ct),
-                        TimeSpan.FromMinutes(1), CancellationToken.None);
-                });
-
-            await Task.WhenAll(tasks);
-            AssertIsLess(initialMemory + 2_000_000, GC.GetTotalMemory(true));
-        }
-
-        static void AssertIsLess(long bound, long actual)
-        {
-            if (bound < actual)
-            {
-                Assert.Fail($"value must be less than {bound:N0} but is {actual:N0}");
-            }
-        }
-    }
-}

Source/MQTTnet.Tests/Extensions/Rpc_Tests.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Generic;
 using System.Text;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
@@ -45,6 +46,34 @@ namespace MQTTnet.Tests.Extensions
             }
         }
 
+        [TestMethod]
+        public async Task Execute_Success_Parameters_Propagated_Correctly()
+        {
+            var paramValue = "123";
+            var parameters = new Dictionary<string, object>
+            {
+                { TestParametersTopicGenerationStrategy.ExpectedParamName, "123" },
+            };
+
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                await testEnvironment.StartServer();
+
+                var responseSender = await testEnvironment.ConnectClient(new MqttClientOptionsBuilder());
+                await responseSender.SubscribeAsync($"MQTTnet.RPC/+/ping/{paramValue}");
+
+                responseSender.ApplicationMessageReceivedAsync += e => responseSender.PublishStringAsync(e.ApplicationMessage.Topic + "/response", "pong");
+
+                using (var rpcClient = await testEnvironment.ConnectRpcClient(new MqttRpcClientOptionsBuilder()
+                           .WithTopicGenerationStrategy(new TestParametersTopicGenerationStrategy()).Build()))
+                {
+                    var response = await rpcClient.ExecuteAsync(TimeSpan.FromSeconds(5), "ping", "", MqttQualityOfServiceLevel.AtMostOnce, parameters);
+
+                    Assert.AreEqual("pong", Encoding.UTF8.GetString(response));
+                }
+            }
+        }
+
         [TestMethod]
         public Task Execute_Success_With_QoS_0()
         {
@@ -222,5 +251,32 @@ namespace MQTTnet.Tests.Extensions
                 };
             }
         }
+
+        class TestParametersTopicGenerationStrategy : IMqttRpcClientTopicGenerationStrategy
+        {
+            internal const string ExpectedParamName = "test_param_name";
+
+            public MqttRpcTopicPair CreateRpcTopics(TopicGenerationContext context)
+            {
+                if (context.Parameters == null)
+                {
+                    throw new InvalidOperationException("Parameters dictionary expected to be not null");
+                }
+
+                if (!context.Parameters.TryGetValue(ExpectedParamName, out var paramValue))
+                {
+                    throw new InvalidOperationException($"Parameter with name {ExpectedParamName} not present");
+                }
+
+                var requestTopic = $"MQTTnet.RPC/{Guid.NewGuid():N}/{context.MethodName}/{paramValue}";
+                var responseTopic = requestTopic + "/response";
+
+                return new MqttRpcTopicPair
+                {
+                    RequestTopic = requestTopic,
+                    ResponseTopic = responseTopic
+                };
+            }
+        }
     }
 }

Source/MQTTnet.Tests/Extensions/WebSocket4Net_Tests.cs

@@ -23,7 +23,7 @@ namespace MQTTnet.Tests.Extensions
 
             using (var client = factory.CreateMqttClient())
             {
-                var options = new MqttClientOptionsBuilder().WithWebSocketServer("ws://a.b/mqtt").WithTimeout(TimeSpan.FromSeconds(2)).Build();
+                var options = new MqttClientOptionsBuilder().WithWebSocketServer(o => o.WithUri("ws://a.b/mqtt")).WithTimeout(TimeSpan.FromSeconds(2)).Build();
                 await client.ConnectAsync(options).ConfigureAwait(false);
             }
         }

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;
@@ -76,7 +78,7 @@ namespace MQTTnet.Tests.Formatter
             Assert.IsNull(deserialized.UserProperties); // Not supported in v3.1.1
         }
         
-                [TestMethod]
+        [TestMethod]
         public void Serialize_Full_MqttConnAckPacket_V310()
         {
             var connAckPacket = new MqttConnAckPacket
@@ -296,7 +298,7 @@ namespace MQTTnet.Tests.Formatter
                 PacketIdentifier = 123,
                 Dup = true,
                 Retain = true,
-                Payload = Encoding.ASCII.GetBytes("Payload"),
+                PayloadSegment = new ArraySegment<byte>(Encoding.ASCII.GetBytes("Payload")),
                 QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce,
                 Topic = "Topic",
                 ResponseTopic = "/Response",
@@ -320,7 +322,7 @@ namespace MQTTnet.Tests.Formatter
             Assert.AreEqual(publishPacket.PacketIdentifier, deserialized.PacketIdentifier);
             Assert.AreEqual(publishPacket.Dup, deserialized.Dup);
             Assert.AreEqual(publishPacket.Retain, deserialized.Retain);
-            CollectionAssert.AreEqual(publishPacket.Payload, deserialized.Payload);
+            CollectionAssert.AreEqual(publishPacket.PayloadSegment.ToArray(), deserialized.PayloadSegment.ToArray());
             Assert.AreEqual(publishPacket.QualityOfServiceLevel, deserialized.QualityOfServiceLevel);
             Assert.AreEqual(publishPacket.Topic, deserialized.Topic);
             Assert.AreEqual(null, deserialized.ResponseTopic); // Not supported in v3.1.1.

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V5_Tests.cs

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

Source/MQTTnet.Tests/Formatter/MqttPacketWriter_Tests.cs

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

Source/MQTTnet.Tests/MQTTnet.Tests.csproj

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

Source/MQTTnet.Tests/Mockups/TestApplicationMessageReceivedHandler.cs

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

Source/MQTTnet.Tests/Mockups/TestEnvironment.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
@@ -24,10 +25,9 @@ namespace MQTTnet.Tests.Mockups
     public sealed class TestEnvironment : IDisposable
     {
         readonly List<string> _clientErrors = new List<string>();
-        readonly List<IMqttClient> _clients = new List<IMqttClient>();
-
+        readonly ConcurrentBag<IMqttClient> _clients = new ConcurrentBag<IMqttClient>();
         readonly List<Exception> _exceptions = new List<Exception>();
-        readonly List<ILowLevelMqttClient> _lowLevelClients = new List<ILowLevelMqttClient>();
+        readonly ConcurrentBag<ILowLevelMqttClient> _lowLevelClients = new ConcurrentBag<ILowLevelMqttClient>();
         readonly MqttProtocolVersion _protocolVersion;
         readonly List<string> _serverErrors = new List<string>();
 
@@ -65,9 +65,12 @@ namespace MQTTnet.Tests.Mockups
 
                 if (e.LogMessage.Level == MqttNetLogLevel.Error)
                 {
-                    lock (_clientErrors)
+                    if (!IgnoreClientLogErrors)
                     {
-                        _clientErrors.Add(e.LogMessage.ToString());
+                        lock (_clientErrors)
+                        {
+                            _clientErrors.Add(e.LogMessage.ToString());
+                        }
                     }
                 }
             };
@@ -212,41 +215,45 @@ namespace MQTTnet.Tests.Mockups
 
         public IMqttClient CreateClient()
         {
-            lock (_clients)
+            var logger = EnableLogger ? (IMqttNetLogger)ClientLogger : MqttNetNullLogger.Instance;
+            
+            var client = Factory.CreateMqttClient(logger);
+            client.ConnectingAsync += e =>
             {
-                var logger = EnableLogger ? (IMqttNetLogger)ClientLogger : new MqttNetNullLogger();
-
-                var client = Factory.CreateMqttClient(logger);
-                _clients.Add(client);
-
-                client.ConnectingAsync += e =>
+                if (TestContext != null)
                 {
-                    if (TestContext != null)
+                    var clientOptions = e.ClientOptions;
+                    var existingClientId = clientOptions.ClientId;
+                    if (existingClientId != null && !existingClientId.StartsWith(TestContext.TestName))
                     {
-                        var clientOptions = e.ClientOptions;
-                        var existingClientId = clientOptions.ClientId;
-                        if (existingClientId != null && !existingClientId.StartsWith(TestContext.TestName))
-                        {
-                            clientOptions.ClientId = TestContext.TestName + "_" + existingClientId;
-                        }
+                        clientOptions.ClientId = TestContext.TestName + "_" + existingClientId;
                     }
+                }
 
-                    return CompletedTask.Instance;
-                };
+                return CompletedTask.Instance;
+            };
+            
+            _clients.Add(client);
+            
+            return client;
+        }
 
-                return client;
-            }
+        public MqttClientOptions CreateDefaultClientOptions()
+        {
+            return CreateDefaultClientOptionsBuilder().Build();
+        }
+
+        public MqttClientOptionsBuilder CreateDefaultClientOptionsBuilder()
+        {
+            return Factory.CreateClientOptionsBuilder().WithProtocolVersion(_protocolVersion).WithTcpServer("127.0.0.1", ServerPort).WithClientId(TestContext.TestName + "_" + Guid.NewGuid());
         }
 
         public ILowLevelMqttClient CreateLowLevelClient()
         {
-            lock (_clients)
-            {
-                var client = Factory.CreateLowLevelMqttClient(ClientLogger);
-                _lowLevelClients.Add(client);
+            var client = Factory.CreateLowLevelMqttClient(ClientLogger);
+            _lowLevelClients.Add(client);
 
-                return client;
-            }
+            return client;
         }
 
         public MqttServer CreateServer(MqttServerOptions options)
@@ -373,13 +380,16 @@ namespace MQTTnet.Tests.Mockups
                 }
             }
 
-            lock (_clientErrors)
+            if (!IgnoreClientLogErrors)
             {
-                if (!IgnoreClientLogErrors && _clientErrors.Count > 0)
+                lock (_clientErrors)
                 {
-                    var message = $"Client(s) had {_clientErrors.Count} errors (${string.Join(Environment.NewLine, _clientErrors)})";
-                    Console.WriteLine(message);
-                    throw new Exception(message);
+                    if (_clientErrors.Count > 0)
+                    {
+                        var message = $"Client(s) had {_clientErrors.Count} errors (${string.Join(Environment.NewLine, _clientErrors)})";
+                        Console.WriteLine(message);
+                        throw new Exception(message);
+                    }
                 }
             }
         }

Source/MQTTnet.Tests/MqttApplicationMessageBuilder_Tests.cs

@@ -4,6 +4,7 @@
 
 using System;
 using System.IO;
+using System.Linq;
 using System.Text;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Protocol;
@@ -11,7 +12,7 @@ using MQTTnet.Protocol;
 namespace MQTTnet.Tests
 {
     [TestClass]
-    public class MqttApplicationMessageBuilder_Tests
+    public sealed class MqttApplicationMessageBuilder_Tests
     {
         [TestMethod]
         public void CreateApplicationMessage_TopicOnly()
@@ -29,7 +30,7 @@ namespace MQTTnet.Tests
             Assert.AreEqual("xyz", message.Topic);
             Assert.IsFalse(message.Retain);
             Assert.AreEqual(MqttQualityOfServiceLevel.AtMostOnce, message.QualityOfServiceLevel);
-            Assert.AreEqual(Encoding.UTF8.GetString(message.Payload), "00:06:00");
+            Assert.AreEqual(Encoding.UTF8.GetString(message.PayloadSegment.ToArray()), "00:06:00");
         }
 
         [TestMethod]
@@ -41,7 +42,7 @@ namespace MQTTnet.Tests
             Assert.AreEqual("123", message.Topic);
             Assert.IsFalse(message.Retain);
             Assert.AreEqual(MqttQualityOfServiceLevel.AtMostOnce, message.QualityOfServiceLevel);
-            Assert.AreEqual(Encoding.UTF8.GetString(message.Payload), "Hello");
+            Assert.AreEqual(Encoding.UTF8.GetString(message.PayloadSegment.ToArray()), "Hello");
         }
 
         [TestMethod]

Source/MQTTnet.Tests/MqttApplicationMessageTest.cs

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

Source/MQTTnet.Tests/MqttApplicationMessageValidator_Tests.cs

@@ -0,0 +1,44 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Formatter;
+
+namespace MQTTnet.Tests
+{
+    [TestClass]
+    public sealed class MqttApplicationMessageValidator_Tests
+    {
+        [TestMethod]
+        [ExpectedException(typeof(NotSupportedException))]
+        public void Succeed_When_Using_TopicAlias_And_MQTT_311()
+        {
+            MqttApplicationMessageValidator.ThrowIfNotSupported(new MqttApplicationMessageBuilder().WithTopicAlias(1).Build(), MqttProtocolVersion.V311);
+        }
+
+        [TestMethod]
+        public void Succeed_When_Using_TopicAlias_And_MQTT_500()
+        {
+            MqttApplicationMessageValidator.ThrowIfNotSupported(new MqttApplicationMessageBuilder().WithTopicAlias(1).Build(), MqttProtocolVersion.V500);
+        }
+
+        [TestMethod]
+        public void Succeed_When_Using_UserProperties_And_MQTT_500()
+        {
+            MqttApplicationMessageValidator.ThrowIfNotSupported(
+                new MqttApplicationMessageBuilder().WithTopic("A").WithUserProperty("User", "Property").Build(),
+                MqttProtocolVersion.V500);
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(NotSupportedException))]
+        public void Succeed_When_Using_WillUserProperties_And_MQTT_311()
+        {
+            MqttApplicationMessageValidator.ThrowIfNotSupported(
+                new MqttApplicationMessageBuilder().WithTopic("B").WithUserProperty("User", "Property").Build(),
+                MqttProtocolVersion.V311);
+        }
+    }
+}

Source/MQTTnet.Tests/MqttClientOptionsValidator_Tests.cs

@@ -0,0 +1,54 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Client;
+using MQTTnet.Formatter;
+
+namespace MQTTnet.Tests
+{
+    [TestClass]
+    public sealed class MqttClientOptionsValidator_Tests
+    {
+        [TestMethod]
+        public void Succeed_When_Using_UserProperties_And_MQTT_500()
+        {
+            new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V500).WithUserProperty("User", "Property").WithTcpServer("FAKE").Build();
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(NotSupportedException))]
+        public void Succeed_When_Using_WillUserProperties_And_MQTT_311()
+        {
+            new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V311).WithWillUserProperty("User", "Property").WithTcpServer("FAKE").Build();
+        }
+
+        [TestMethod]
+        public void Succeed_When_Using_WillUserProperties_And_MQTT_500()
+        {
+            new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V500).WithWillUserProperty("User", "Property").WithTcpServer("FAKE").Build();
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(NotSupportedException))]
+        public void Throw_When_Using_UserProperties_And_MQTT_311()
+        {
+            new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V311).WithUserProperty("User", "Property").WithTcpServer("FAKE").Build();
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(NotSupportedException))]
+        public void Throw_When_Using_WithRequestResponseInformation_And_MQTT_311()
+        {
+            new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V311).WithRequestResponseInformation().WithTcpServer("FAKE").Build();
+        }
+
+        [TestMethod]
+        public void Throw_When_Using_WithRequestResponseInformation_And_MQTT_500()
+        {
+            new MqttClientOptionsBuilder().WithProtocolVersion(MqttProtocolVersion.V500).WithRequestResponseInformation().WithTcpServer("FAKE").Build();
+        }
+    }
+}

Source/MQTTnet.Tests/MqttPacketSerializationHelper.cs

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

Source/MQTTnet.Tests/MqttPacketWriter_Tests.cs

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

Source/MQTTnet.Tests/MqttTopicValidator_Tests.cs

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

Source/MQTTnet.Tests/Server/General.cs

@@ -598,8 +598,7 @@ namespace MQTTnet.Tests.Server
                 // c
                 var c1 = await testEnvironment.ConnectClient(clientOptionsBuilder);
 
-                await Task.Delay(500);
-
+                await LongTestDelay();
                 var flow = string.Join(string.Empty, events);
                 Assert.AreEqual("c", flow);
 
@@ -607,10 +606,8 @@ namespace MQTTnet.Tests.Server
                 // Connect client with same client ID. Should disconnect existing client.
                 var c2 = await testEnvironment.ConnectClient(clientOptionsBuilder);
 
-                await Task.Delay(500);
-
+                await LongTestDelay();
                 flow = string.Join(string.Empty, events);
-
                 Assert.AreEqual("cdc", flow);
 
                 c2.ApplicationMessageReceivedAsync += e =>
@@ -628,27 +625,27 @@ namespace MQTTnet.Tests.Server
                 // r
                 await c2.PublishStringAsync("topic");
 
-                await Task.Delay(500);
-
+                await LongTestDelay();
                 flow = string.Join(string.Empty, events);
                 Assert.AreEqual("cdcr", flow);
 
                 // nothing
 
                 Assert.AreEqual(false, c1.IsConnected);
-                await c1.DisconnectAsync();
+                await c1.TryDisconnectAsync();
                 Assert.AreEqual(false, c1.IsConnected);
 
-                await Task.Delay(500);
+                await LongTestDelay();
 
                 // d
                 Assert.AreEqual(true, c2.IsConnected);
                 await c2.DisconnectAsync();
 
-                await Task.Delay(500);
+                await LongTestDelay();
 
                 await server.StopAsync();
 
+                await LongTestDelay();
                 flow = string.Join(string.Empty, events);
                 Assert.AreEqual("cdcrd", flow);
             }
@@ -852,11 +849,11 @@ namespace MQTTnet.Tests.Server
                     return CompletedTask.Instance;
                 };
 
-                await Task.Delay(100);
-
+                // Stopping the server should disconnect the connection with the client
+                // which, it turn, will fire the disconnected event at the client.
                 await server.StopAsync();
 
-                await Task.Delay(100);
+                await LongTestDelay();
 
                 Assert.AreEqual(1, disconnectCalled);
             }
@@ -954,7 +951,7 @@ namespace MQTTnet.Tests.Server
 
                 var client = testEnvironment.CreateClient();
 
-                client.InspectPackage += e =>
+                client.InspectPacketAsync += e =>
                 {
                     if (e.Buffer.Length > 0)
                     {

Source/MQTTnet.Tests/Server/HotSwapCerts_Tests.cs

@@ -0,0 +1,445 @@
+#if !(NET452 || NET461)
+using System;
+using System.Collections.Concurrent;
+using System.Diagnostics;
+using System.Linq;
+using System.Net;
+using System.Net.Security;
+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.Protocol;
+using MQTTnet.Server;
+
+namespace MQTTnet.Tests.Server
+{
+    // missing certificate builder api means tests won't work for older frameworks
+
+    [TestClass]
+    public sealed class HotSwapCerts_Tests
+    {
+        static readonly TimeSpan DefaultTimeout = TimeSpan.FromSeconds(10);
+
+        [TestMethod]
+        public async Task ClientCertChangeWithoutServerUpdateFailsReconnect()
+        {
+            using (var server = new ServerTestHarness())
+            using (var client01 = new ClientTestHarness())
+            {
+                server.InstallNewClientCert(client01.GetCurrentClientCert());
+                client01.InstallNewServerCert(server.GetCurrentServerCert());
+
+                await server.StartServer();
+
+                await client01.Connect();
+
+                client01.WaitForConnectOrFail(DefaultTimeout);
+
+                client01.HotSwapClientCert();
+                server.ForceDisconnectAsync(client01).Wait(DefaultTimeout);
+                client01.WaitForDisconnectOrFail(DefaultTimeout);
+
+                client01.WaitForConnectToFail(DefaultTimeout);
+            }
+        }
+
+        [TestMethod]
+        public async Task ClientCertChangeWithServerUpdateAcceptsReconnect()
+        {
+            using (var server = new ServerTestHarness())
+            using (var client01 = new ClientTestHarness())
+            {
+                server.InstallNewClientCert(client01.GetCurrentClientCert());
+                client01.InstallNewServerCert(server.GetCurrentServerCert());
+
+                await server.StartServer();
+
+                await client01.Connect();
+
+                client01.WaitForConnectOrFail(DefaultTimeout);
+
+                client01.HotSwapClientCert();
+                server.ForceDisconnectAsync(client01).Wait(DefaultTimeout);
+                client01.WaitForDisconnectOrFail(DefaultTimeout);
+
+                server.InstallNewClientCert(client01.GetCurrentClientCert());
+
+                client01.WaitForConnectOrFail(DefaultTimeout);
+            }
+        }
+
+        [TestMethod]
+        public async Task ServerCertChangeWithClientCertUpdateAllowsReconnect()
+        {
+            using (var server = new ServerTestHarness())
+            using (var client01 = new ClientTestHarness())
+            {
+                server.InstallNewClientCert(client01.GetCurrentClientCert());
+                client01.InstallNewServerCert(server.GetCurrentServerCert());
+
+                await server.StartServer();
+                await client01.Connect();
+
+                client01.WaitForConnectOrFail(DefaultTimeout);
+                server.HotSwapServerCert();
+
+                server.ForceDisconnectAsync(client01).Wait(DefaultTimeout);
+                client01.WaitForDisconnectOrFail(DefaultTimeout);
+                client01.InstallNewServerCert(server.GetCurrentServerCert());
+
+                client01.WaitForConnectOrFail(DefaultTimeout);
+            }
+        }
+
+        [TestMethod]
+        public async Task ServerCertChangeWithoutClientCertUpdateFailsReconnect()
+        {
+            using (var server = new ServerTestHarness())
+            using (var client01 = new ClientTestHarness())
+            {
+                server.InstallNewClientCert(client01.GetCurrentClientCert());
+                client01.InstallNewServerCert(server.GetCurrentServerCert());
+
+                await server.StartServer();
+                await client01.Connect();
+
+                client01.WaitForConnectOrFail(DefaultTimeout);
+                server.HotSwapServerCert();
+
+                server.ForceDisconnectAsync(client01).Wait(DefaultTimeout);
+                client01.WaitForDisconnectOrFail(DefaultTimeout);
+
+                client01.WaitForConnectToFail(DefaultTimeout);
+            }
+        }
+
+        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(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;
+                }
+            }
+        }
+
+        class ClientTestHarness : IDisposable
+        {
+            readonly HotSwappableClientCertProvider _hotSwapClient = new HotSwappableClientCertProvider();
+            IMqttClient _client;
+
+            public string ClientId => _client.Options.ClientId;
+
+            public void ClearServerCerts()
+            {
+                _hotSwapClient.ClearServerCerts();
+            }
+
+            public Task Connect()
+            {
+                return Run_Client_Connection();
+            }
+
+            public void Dispose()
+            {
+                _client.Dispose();
+            }
+
+            public X509Certificate2 GetCurrentClientCert()
+            {
+                var result = _hotSwapClient.GetCertificates()[0];
+                return new X509Certificate2(result);
+            }
+
+            public void HotSwapClientCert()
+            {
+                _hotSwapClient.HotSwapCert();
+            }
+
+            public void InstallNewServerCert(X509Certificate2 serverCert)
+            {
+                _hotSwapClient.InstallNewServerCert(serverCert);
+            }
+
+            public void WaitForConnectOrFail(TimeSpan timeout)
+            {
+                if (!_client.IsConnected)
+                {
+                    _client.ReconnectAsync().Wait(timeout);
+                }
+
+                WaitForConnect(timeout);
+
+                Assert.IsNotNull(_client, "Client was never initialized");
+                Assert.IsTrue(_client.IsConnected, $"Client connection failed after {timeout}");
+            }
+
+            public void WaitForConnectToFail(TimeSpan timeout)
+            {
+                Assert.IsFalse(_client.IsConnected, "Client should be disconnected before waiting for connect.");
+
+                WaitForConnect(timeout);
+
+                Assert.IsNotNull(_client, "Client was never initialized");
+                Assert.IsFalse(_client.IsConnected, "Client connection success but test wanted fail");
+            }
+
+            public void WaitForDisconnect(TimeSpan timeout)
+            {
+                var timer = Stopwatch.StartNew();
+                while ((_client == null || _client.IsConnected) && timer.Elapsed < timeout)
+                {
+                    Thread.Sleep(5);
+                }
+            }
+
+            public void WaitForDisconnectOrFail(TimeSpan timeout)
+            {
+                WaitForDisconnect(timeout);
+
+                Assert.IsNotNull(_client, "Client was never initialized");
+                Assert.IsFalse(_client.IsConnected, $"Client connection should have disconnected after {timeout}");
+            }
+
+            async Task Run_Client_Connection()
+            {
+                var optionsBuilder = new MqttClientOptionsBuilder()
+                    .WithTlsOptions(
+                        o => o.WithClientCertificatesProvider(_hotSwapClient)
+                            .WithCertificateValidationHandler(_hotSwapClient.OnCertificateValidation)
+                            .WithSslProtocols(SslProtocols.Tls12))
+                    .WithTcpServer("localhost")
+                    .WithCleanSession()
+                    .WithProtocolVersion(MqttProtocolVersion.V500);
+
+                var mqttClientOptions = optionsBuilder.Build();
+
+                var factory = new MqttFactory();
+                var mqttClient = factory.CreateMqttClient();
+                _client = mqttClient;
+
+                await mqttClient.ConnectAsync(mqttClientOptions);
+            }
+
+            void WaitForConnect(TimeSpan timeout)
+            {
+                var timer = Stopwatch.StartNew();
+                while ((_client == null || !_client.IsConnected) && timer.Elapsed < timeout)
+                {
+                    Thread.Sleep(5);
+                }
+            }
+        }
+
+        class ServerTestHarness : IDisposable
+        {
+            readonly HotSwappableServerCertProvider _hotSwapServer = new HotSwappableServerCertProvider();
+
+            MqttServer _server;
+
+            public void ClearClientCerts()
+            {
+                _hotSwapServer.ClearClientCerts();
+            }
+
+            public void Dispose()
+            {
+                if (_server != null)
+                {
+                    _server.StopAsync().Wait();
+                    _server.Dispose();
+                }
+
+                if (_hotSwapServer != null)
+                {
+                    _hotSwapServer.Dispose();
+                }
+            }
+
+            public async Task ForceDisconnectAsync(ClientTestHarness client)
+            {
+                await _server.DisconnectClientAsync(client.ClientId, MqttDisconnectReasonCode.UnspecifiedError);
+            }
+
+            public X509Certificate2 GetCurrentServerCert()
+            {
+                return _hotSwapServer.GetCertificate();
+            }
+
+            public void HotSwapServerCert()
+            {
+                _hotSwapServer.HotSwapCert();
+            }
+
+            public void InstallNewClientCert(X509Certificate2 serverCert)
+            {
+                _hotSwapServer.InstallNewClientCert(serverCert);
+            }
+
+            public async Task StartServer()
+            {
+                var mqttFactory = new MqttFactory();
+
+                var mqttServerOptions = new MqttServerOptionsBuilder().WithEncryptionCertificate(_hotSwapServer)
+                    .WithRemoteCertificateValidationCallback(_hotSwapServer.RemoteCertificateValidationCallback)
+                    .WithEncryptedEndpoint()
+                    .Build();
+
+                mqttServerOptions.TlsEndpointOptions.ClientCertificateRequired = true;
+                _server = mqttFactory.CreateMqttServer(mqttServerOptions);
+                await _server.StartAsync();
+            }
+        }
+
+        class HotSwappableClientCertProvider : IMqttClientCertificatesProvider
+        {
+            X509Certificate2Collection _certificates;
+            ConcurrentBag<X509Certificate2> ServerCerts = new ConcurrentBag<X509Certificate2>();
+
+            public HotSwappableClientCertProvider()
+            {
+                _certificates = new X509Certificate2Collection(CreateSelfSignedCertificate("1.3.6.1.5.5.7.3.2"));
+            }
+
+            public void ClearServerCerts()
+            {
+                ServerCerts = new ConcurrentBag<X509Certificate2>();
+            }
+
+            public X509CertificateCollection GetCertificates()
+            {
+                return new X509Certificate2Collection(_certificates);
+            }
+
+            public void HotSwapCert()
+            {
+                var newCert = new X509Certificate2Collection(CreateSelfSignedCertificate("1.3.6.1.5.5.7.3.2"));
+                var oldCerts = Interlocked.Exchange(ref _certificates, newCert);
+            }
+
+            public void InstallNewServerCert(X509Certificate2 serverCert)
+            {
+                ServerCerts.Add(serverCert);
+            }
+
+            public bool OnCertificateValidation(MqttClientCertificateValidationEventArgs certContext)
+            {
+                var serverCerts = ServerCerts.ToArray();
+
+                var providedCert = certContext.Certificate.GetRawCertData();
+                for (int i = 0, n = serverCerts.Length; i < n; i++)
+                {
+                    var currentcert = serverCerts[i];
+
+                    if (currentcert.RawData.SequenceEqual(providedCert))
+                    {
+                        return true;
+                    }
+                }
+
+                return false;
+            }
+
+            void Dispose()
+            {
+                if (_certificates != null)
+                {
+                    foreach (var certs in _certificates)
+                    {
+#if !NET452
+                        certs.Dispose();
+#endif
+                    }
+                }
+            }
+        }
+
+        class HotSwappableServerCertProvider : ICertificateProvider, IDisposable
+        {
+            X509Certificate2 _certificate;
+            ConcurrentBag<X509Certificate2> ClientCerts = new ConcurrentBag<X509Certificate2>();
+
+            public HotSwappableServerCertProvider()
+            {
+                _certificate = CreateSelfSignedCertificate("1.3.6.1.5.5.7.3.1");
+            }
+
+            public void ClearClientCerts()
+            {
+                ClientCerts = new ConcurrentBag<X509Certificate2>();
+            }
+
+            public void Dispose()
+            {
+#if !NET452
+                _certificate.Dispose();
+#endif
+            }
+
+            public X509Certificate2 GetCertificate()
+            {
+                return _certificate;
+            }
+
+            public void HotSwapCert()
+            {
+                var newCert = CreateSelfSignedCertificate("1.3.6.1.5.5.7.3.1");
+                var oldCert = Interlocked.Exchange(ref _certificate, newCert);
+#if !NET452
+                oldCert.Dispose();
+#endif
+            }
+
+            public void InstallNewClientCert(X509Certificate2 certificate)
+            {
+                ClientCerts.Add(certificate);
+            }
+
+            public bool RemoteCertificateValidationCallback(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
+            {
+                var serverCerts = ClientCerts.ToArray();
+
+                var providedCert = certificate.GetRawCertData();
+                for (int i = 0, n = serverCerts.Length; i < n; i++)
+                {
+                    var currentCert = serverCerts[i];
+
+                    if (currentCert.RawData.SequenceEqual(providedCert))
+                    {
+                        return true;
+                    }
+                }
+
+                return false;
+            }
+        }
+    }
+}
+
+#endif

Source/MQTTnet.Tests/Server/MqttRetainedMessageManager_Tests.cs

@@ -0,0 +1,25 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Tests.Server
+{
+    [TestClass]
+    public sealed class MqttRetainedMessageManager_Tests
+    {
+        [TestMethod]
+        public async Task MqttRetainedMessageManager_GetUndefinedTopic()
+        {
+            var logger = new Mockups.TestLogger();
+            var eventContainer = new MQTTnet.Server.MqttServerEventContainer();
+            var retainedMessagesManager = new MQTTnet.Server.MqttRetainedMessagesManager(eventContainer, logger);
+            var task = retainedMessagesManager.GetMessage("undefined");
+            Assert.IsNotNull(task, "Task should not be null");
+            var result = await task;
+            Assert.IsNull(result, "Null result expected");
+        }
+    }
+}

Source/MQTTnet.Tests/Server/MqttSubscriptionsManager_Tests.cs

@@ -221,14 +221,17 @@ namespace MQTTnet.Tests.Server
             var eventContainer = new MqttServerEventContainer();
             var clientSessionManager = new MqttClientSessionsManager(options, retainedMessagesManager, eventContainer, logger);
 
-            var session = new MqttSession("", false, new ConcurrentDictionary<object, object>(), options, eventContainer, retainedMessagesManager, clientSessionManager);
+            var session = new MqttSession(new MqttConnectPacket
+            {
+                ClientId = ""
+            }, new ConcurrentDictionary<object, object>(), options, eventContainer, retainedMessagesManager, clientSessionManager);
 
             _subscriptionsManager = new MqttClientSubscriptionsManager(session, new MqttServerEventContainer(), retainedMessagesManager, clientSessionManager);
         }
 
         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/Session_Tests.cs

@@ -70,6 +70,28 @@ namespace MQTTnet.Tests.Server
             }
         }
 
+        [TestMethod]
+        public async Task Do_Not_Use_Expired_Session()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                await testEnvironment.StartServer(o => o.WithPersistentSessions());
+
+                var c1 = await testEnvironment.ConnectClient(o => o.WithClientId("Client1").WithCleanSession(false).WithSessionExpiryInterval(3));
+
+                // Kill the client connection and ensure that the session will stay there but is expired after 3 seconds!
+                c1.Dispose();
+
+                await Task.Delay(TimeSpan.FromSeconds(6));
+
+                c1 = testEnvironment.CreateClient();
+                var options = testEnvironment.CreateDefaultClientOptionsBuilder().WithClientId("Client1").WithCleanSession(false).WithSessionExpiryInterval(3).Build();
+
+                var connectResult = await c1.ConnectAsync(options);
+                Assert.AreEqual(false, connectResult.IsSessionPresent);
+            }
+        }
+
         [TestMethod]
         public async Task Fire_Deleted_Event()
         {
@@ -121,7 +143,7 @@ namespace MQTTnet.Tests.Server
                 Assert.AreEqual(true, session.Items["can_subscribe_x"]);
             }
         }
-        
+
         [TestMethod]
         [DataRow(MqttProtocolVersion.V310)]
         [DataRow(MqttProtocolVersion.V311)]
@@ -134,16 +156,12 @@ namespace MQTTnet.Tests.Server
 
                 await testEnvironment.StartServer();
 
-                var options = new MqttClientOptionsBuilder().WithClientId("1").WithTimeout(TimeSpan.FromSeconds(1)).WithProtocolVersion(protocolVersion);
+                var options = new MqttClientOptionsBuilder().WithClientId("1").WithTimeout(TimeSpan.FromSeconds(10)).WithProtocolVersion(protocolVersion);
 
                 var hasReceive = false;
-
                 void OnReceive()
                 {
-                    if (!hasReceive)
-                    {
-                        hasReceive = true;
-                    }
+                    hasReceive = true;
                 }
 
                 // Try to connect 50 clients at the same time.
@@ -152,7 +170,7 @@ namespace MQTTnet.Tests.Server
                 var connectedClients = clients.Where(c => c?.TryPingAsync().GetAwaiter().GetResult() == true).ToList();
 
                 await LongTestDelay();
-                
+
                 Assert.AreEqual(1, connectedClients.Count);
 
                 var option2 = new MqttClientOptionsBuilder().WithClientId("2").WithKeepAlivePeriod(TimeSpan.FromSeconds(10));
@@ -164,7 +182,7 @@ namespace MQTTnet.Tests.Server
                 Assert.AreEqual(true, hasReceive);
             }
         }
- 
+
         [DataTestMethod]
         [DataRow(MqttQualityOfServiceLevel.ExactlyOnce)]
         [DataRow(MqttQualityOfServiceLevel.AtLeastOnce)]
@@ -355,8 +373,8 @@ namespace MQTTnet.Tests.Server
                     onReceive();
                     return CompletedTask.Instance;
                 };
-                
-                using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(5)))
+
+                using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(30)))
                 {
                     await client.SubscribeAsync("aaa", MqttQualityOfServiceLevel.AtMostOnce, timeout.Token).ConfigureAwait(false);
                 }

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)
@@ -557,7 +557,7 @@ namespace MQTTnet.Tests.Server
             var eventContainer = new MqttServerEventContainer();
             var retainedMessagesManager = new MqttRetainedMessagesManager(eventContainer, logger);
             var sessionManager = new MqttClientSessionsManager(serverOptions, retainedMessagesManager, eventContainer, logger);
-            _clientSession = new MqttSession(clientId, false, new Dictionary<object, object>(), serverOptions, eventContainer, retainedMessagesManager, sessionManager);
+            _clientSession = new MqttSession(new MqttConnectPacket{ ClientId = clientId }, new Dictionary<object, object>(), serverOptions, eventContainer, retainedMessagesManager, sessionManager);
 
             List<string> topicsToSubscribe;
 

Source/MQTTnet.Tests/Server/Tls_Tests.cs

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

Source/MQTTnet.Tests/Server/Unsubscribe_Tests.cs

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

Source/MQTTnet.Tests/TopicFilterComparer_Tests.cs

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

Source/MQTTnet/Adapter/MqttChannelAdapter.cs

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

Source/MQTTnet/Adapter/MqttPacketInspector.cs

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

Source/MQTTnet/Client/Connecting/MqttClientConnectedEventArgs.cs

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

Source/MQTTnet/Client/Disconnecting/MqttClientDisconnectOptions.cs

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

Source/MQTTnet/Client/Disconnecting/MqttClientDisconnectOptionsBuilder.cs

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

Source/MQTTnet/Client/Disconnecting/MqttClientDisconnectOptionsReason.cs

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

Source/MQTTnet/Client/Disconnecting/MqttClientDisconnectOptionsValidator.cs

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

Source/MQTTnet/Client/Disconnecting/MqttClientDisconnectedEventArgs.cs

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

Source/MQTTnet/Client/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/Internal/MqttClientEvents.cs

@@ -0,0 +1,18 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using MQTTnet.Diagnostics;
+using MQTTnet.Internal;
+
+namespace MQTTnet.Client.Internal
+{
+    public sealed class MqttClientEvents
+    {
+        public AsyncEvent<MqttApplicationMessageReceivedEventArgs> ApplicationMessageReceivedEvent { get; } = new AsyncEvent<MqttApplicationMessageReceivedEventArgs>();
+        public AsyncEvent<MqttClientConnectedEventArgs> ConnectedEvent { get; } = new AsyncEvent<MqttClientConnectedEventArgs>();
+        public AsyncEvent<MqttClientConnectingEventArgs> ConnectingEvent { get; } = new AsyncEvent<MqttClientConnectingEventArgs>();
+        public AsyncEvent<MqttClientDisconnectedEventArgs> DisconnectedEvent { get; } = new AsyncEvent<MqttClientDisconnectedEventArgs>();
+        public AsyncEvent<InspectMqttPacketEventArgs> InspectPacketEvent { get; } = new AsyncEvent<InspectMqttPacketEventArgs>();
+    }
+}

Source/MQTTnet/Client/Internal/MqttClientResultFactory.cs

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

Source/MQTTnet/Client/MqttClient.cs

@@ -3,9 +3,11 @@
 // 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.Adapter;
+using MQTTnet.Client.Internal;
 using MQTTnet.Diagnostics;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
@@ -19,30 +21,29 @@ namespace MQTTnet.Client
     public sealed class MqttClient : Disposable, IMqttClient
     {
         readonly IMqttClientAdapterFactory _adapterFactory;
-        readonly AsyncEvent<MqttApplicationMessageReceivedEventArgs> _applicationMessageReceivedEvent = new AsyncEvent<MqttApplicationMessageReceivedEventArgs>();
 
-        readonly MqttClientPublishResultFactory _clientPublishResultFactory = new MqttClientPublishResultFactory();
-        readonly MqttClientSubscribeResultFactory _clientSubscribeResultFactory = new MqttClientSubscribeResultFactory();
-        readonly MqttClientUnsubscribeResultFactory _clientUnsubscribeResultFactory = new MqttClientUnsubscribeResultFactory();
-
-        readonly AsyncEvent<MqttClientConnectedEventArgs> _connectedEvent = new AsyncEvent<MqttClientConnectedEventArgs>();
-        readonly AsyncEvent<MqttClientConnectingEventArgs> _connectingEvent = new AsyncEvent<MqttClientConnectingEventArgs>();
-        readonly AsyncEvent<MqttClientDisconnectedEventArgs> _disconnectedEvent = new AsyncEvent<MqttClientDisconnectedEventArgs>();
         readonly object _disconnectLock = new object();
-        readonly AsyncEvent<InspectMqttPacketEventArgs> _inspectPacketEvent = new AsyncEvent<InspectMqttPacketEventArgs>();
+        readonly MqttClientEvents _events = new MqttClientEvents();
         readonly MqttNetSourceLogger _logger;
 
         readonly MqttPacketIdentifierProvider _packetIdentifierProvider = new MqttPacketIdentifierProvider();
         readonly IMqttNetLogger _rootLogger;
 
         IMqttChannelAdapter _adapter;
-        CancellationTokenSource _backgroundCancellationTokenSource;
+
         bool _cleanDisconnectInitiated;
         volatile int _connectionStatus;
-        MqttClientDisconnectReason _disconnectReason;
+
+        // The value for this field can be set from two different enums.
+        // They contain the same values but the set is reduced in one case.
+        int _disconnectReason;
         string _disconnectReasonString;
+        List<MqttUserProperty> _disconnectUserProperties;
+
         Task _keepAlivePacketsSenderTask;
         DateTime _lastPacketSentTimestamp;
+
+        CancellationTokenSource _mqttClientAlive;
         MqttPacketDispatcher _packetDispatcher;
         Task _packetReceiverTask;
         AsyncQueue<MqttPublishPacket> _publishPacketReceiverQueue;
@@ -57,52 +58,42 @@ namespace MQTTnet.Client
 
         public event Func<MqttApplicationMessageReceivedEventArgs, Task> ApplicationMessageReceivedAsync
         {
-            add => _applicationMessageReceivedEvent.AddHandler(value);
-            remove => _applicationMessageReceivedEvent.RemoveHandler(value);
+            add => _events.ApplicationMessageReceivedEvent.AddHandler(value);
+            remove => _events.ApplicationMessageReceivedEvent.RemoveHandler(value);
         }
 
         public event Func<MqttClientConnectedEventArgs, Task> ConnectedAsync
         {
-            add => _connectedEvent.AddHandler(value);
-            remove => _connectedEvent.RemoveHandler(value);
+            add => _events.ConnectedEvent.AddHandler(value);
+            remove => _events.ConnectedEvent.RemoveHandler(value);
         }
 
         public event Func<MqttClientConnectingEventArgs, Task> ConnectingAsync
         {
-            add => _connectingEvent.AddHandler(value);
-            remove => _connectingEvent.RemoveHandler(value);
+            add => _events.ConnectingEvent.AddHandler(value);
+            remove => _events.ConnectingEvent.RemoveHandler(value);
         }
 
         public event Func<MqttClientDisconnectedEventArgs, Task> DisconnectedAsync
         {
-            add => _disconnectedEvent.AddHandler(value);
-            remove => _disconnectedEvent.RemoveHandler(value);
+            add => _events.DisconnectedEvent.AddHandler(value);
+            remove => _events.DisconnectedEvent.RemoveHandler(value);
         }
 
-        public event Func<InspectMqttPacketEventArgs, Task> InspectPackage
+        public event Func<InspectMqttPacketEventArgs, Task> InspectPacketAsync
         {
-            add => _inspectPacketEvent.AddHandler(value);
-            remove => _inspectPacketEvent.RemoveHandler(value);
+            add => _events.InspectPacketEvent.AddHandler(value);
+            remove => _events.InspectPacketEvent.RemoveHandler(value);
         }
-        
+
         public bool IsConnected => (MqttClientConnectionStatus)_connectionStatus == MqttClientConnectionStatus.Connected;
 
         public MqttClientOptions Options { get; private set; }
 
         public async Task<MqttClientConnectResult> ConnectAsync(MqttClientOptions options, CancellationToken cancellationToken = default)
         {
-            if (options == null)
-            {
-                throw new ArgumentNullException(nameof(options));
-            }
-
-            if (options.ChannelOptions == null)
-            {
-                throw new ArgumentException("ChannelOptions are not set.");
-            }
-
+            ThrowIfOptionsInvalid(options);
             ThrowIfConnected("It is not allowed to connect with a server after the connection is established.");
-
             ThrowIfDisposed();
 
             if (CompareExchangeConnectionStatus(MqttClientConnectionStatus.Connecting, MqttClientConnectionStatus.Disconnected) != MqttClientConnectionStatus.Disconnected)
@@ -116,33 +107,41 @@ namespace MQTTnet.Client
             {
                 Options = options;
 
-                if (_connectingEvent.HasHandlers)
+                if (_events.ConnectingEvent.HasHandlers)
                 {
-                    await _connectingEvent.InvokeAsync(new MqttClientConnectingEventArgs(options));
+                    await _events.ConnectingEvent.InvokeAsync(new MqttClientConnectingEventArgs(options));
                 }
 
+                Cleanup();
+
                 _packetIdentifierProvider.Reset();
                 _packetDispatcher = new MqttPacketDispatcher();
 
-                _backgroundCancellationTokenSource = new CancellationTokenSource();
-                var backgroundCancellationToken = _backgroundCancellationTokenSource.Token;
+                _mqttClientAlive = new CancellationTokenSource();
+                var mqttClientAliveToken = _mqttClientAlive.Token;
 
-                var adapter = _adapterFactory.CreateClientAdapter(options, new MqttPacketInspector(_inspectPacketEvent, _rootLogger), _rootLogger);
-                _adapter = adapter;
+                var adapter = _adapterFactory.CreateClientAdapter(options, new MqttPacketInspector(_events.InspectPacketEvent, _rootLogger), _rootLogger);
+                _adapter = adapter ?? throw new InvalidOperationException("The adapter factory did not provide an adapter.");
 
-                using (var effectiveCancellationToken = CancellationTokenSource.CreateLinkedTokenSource(backgroundCancellationToken, cancellationToken))
+                if (cancellationToken.CanBeCanceled)
                 {
-                    _logger.Verbose("Trying to connect with server '{0}'.", options.ChannelOptions);
-                    await adapter.ConnectAsync(effectiveCancellationToken.Token).ConfigureAwait(false);
-                    _logger.Verbose("Connection with server established.");
+                    connectResult = await ConnectInternal(adapter, cancellationToken).ConfigureAwait(false);
+                }
+                else
+                {
+                    // Fall back to the general timeout specified in the options if the user passed
+                    // CancellationToken.None or similar.
+                    using (var timeout = new CancellationTokenSource(Options.Timeout))
+                    {
+                        connectResult = await ConnectInternal(adapter, timeout.Token).ConfigureAwait(false);
+                    }
+                }
 
-                    _publishPacketReceiverQueue?.Dispose();
-                    _publishPacketReceiverQueue = new AsyncQueue<MqttPublishPacket>();
-                    _publishPacketReceiverTask = Task.Run(() => ProcessReceivedPublishPackets(backgroundCancellationToken), backgroundCancellationToken);
-
-                    _packetReceiverTask = Task.Run(() => TryReceivePacketsAsync(backgroundCancellationToken), backgroundCancellationToken);
-
-                    connectResult = await AuthenticateAsync(options, effectiveCancellationToken.Token).ConfigureAwait(false);
+                if (connectResult.ResultCode != MqttClientConnectResultCode.Success)
+                {
+                    _logger.Warning("Connecting failed: {0}", connectResult.ResultCode);
+                    await DisconnectInternal(null, null, connectResult).ConfigureAwait(false);
+                    return connectResult;
                 }
 
                 _lastPacketSentTimestamp = DateTime.UtcNow;
@@ -150,34 +149,35 @@ namespace MQTTnet.Client
                 var keepAliveInterval = Options.KeepAlivePeriod;
                 if (connectResult.ServerKeepAlive > 0)
                 {
-                    _logger.Info($"Using keep alive value ({connectResult.ServerKeepAlive}) sent from the server.");
+                    _logger.Info($"Using keep alive value ({connectResult.ServerKeepAlive}) sent from the server");
                     keepAliveInterval = TimeSpan.FromSeconds(connectResult.ServerKeepAlive);
                 }
 
                 if (keepAliveInterval != TimeSpan.Zero)
                 {
-                    _keepAlivePacketsSenderTask = Task.Run(() => TrySendKeepAliveMessagesAsync(backgroundCancellationToken), backgroundCancellationToken);
+                    _keepAlivePacketsSenderTask = Task.Run(() => TrySendKeepAliveMessages(mqttClientAliveToken), mqttClientAliveToken);
                 }
 
                 CompareExchangeConnectionStatus(MqttClientConnectionStatus.Connected, MqttClientConnectionStatus.Connecting);
 
-                _logger.Info("Connected.");
+                _logger.Info("Connected");
 
-                if (_connectedEvent.HasHandlers)
-                {
-                    var eventArgs = new MqttClientConnectedEventArgs(connectResult);
-                    await _connectedEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
-                }
+                await OnConnected(connectResult).ConfigureAwait(false);
 
                 return connectResult;
             }
             catch (Exception exception)
             {
-                _disconnectReason = MqttClientDisconnectReason.UnspecifiedError;
+                if (exception is MqttConnectingFailedException connectingFailedException)
+                {
+                    connectResult = connectingFailedException.Result;
+                }
 
-                _logger.Error(exception, "Error while connecting with server.");
+                _disconnectReason = (int)MqttClientDisconnectOptionsReason.UnspecifiedError;
 
-                await DisconnectInternalAsync(null, exception, connectResult).ConfigureAwait(false);
+                _logger.Error(exception, "Error while connecting with server");
+
+                await DisconnectInternal(null, exception, connectResult).ConfigureAwait(false);
 
                 throw;
             }
@@ -193,6 +193,7 @@ namespace MQTTnet.Client
             ThrowIfDisposed();
 
             var clientWasConnected = IsConnected;
+
             if (DisconnectIsPendingOrFinished())
             {
                 return;
@@ -200,18 +201,38 @@ namespace MQTTnet.Client
 
             try
             {
-                _disconnectReason = MqttClientDisconnectReason.NormalDisconnection;
+                if (!clientWasConnected)
+                {
+                    ThrowNotConnected();
+                }
+
+                _disconnectReason = (int)options.Reason;
                 _cleanDisconnectInitiated = true;
 
-                if (clientWasConnected)
+                if (Options.ValidateFeatures)
                 {
-                    var disconnectPacket = MqttPacketFactories.Disconnect.Create(options);
-                    await SendAsync(disconnectPacket, cancellationToken).ConfigureAwait(false);
+                    MqttClientDisconnectOptionsValidator.ThrowIfNotSupported(options, _adapter.PacketFormatterAdapter.ProtocolVersion);
+                }
+
+                // Sending the DISCONNECT may fail due to connection issues. The resulting exception
+                // must be throw to let the caller know that the disconnect is not a clean one.
+                var disconnectPacket = MqttPacketFactories.Disconnect.Create(options);
+
+                if (cancellationToken.CanBeCanceled)
+                {
+                    await Send(disconnectPacket, cancellationToken).ConfigureAwait(false);
+                }
+                else
+                {
+                    using (var timeout = new CancellationTokenSource(Options.Timeout))
+                    {
+                        await Send(disconnectPacket, timeout.Token).ConfigureAwait(false);
+                    }
                 }
             }
             finally
             {
-                await DisconnectCoreAsync(null, null, null, clientWasConnected).ConfigureAwait(false);
+                await DisconnectCore(null, null, null, clientWasConnected).ConfigureAwait(false);
             }
         }
 
@@ -219,13 +240,13 @@ namespace MQTTnet.Client
         {
             if (cancellationToken.CanBeCanceled)
             {
-                await SendAndReceiveAsync<MqttPingRespPacket>(MqttPingReqPacket.Instance, cancellationToken).ConfigureAwait(false);
+                await Request<MqttPingRespPacket>(MqttPingReqPacket.Instance, cancellationToken).ConfigureAwait(false);
             }
             else
             {
                 using (var timeout = new CancellationTokenSource(Options.Timeout))
                 {
-                    await SendAndReceiveAsync<MqttPingRespPacket>(MqttPingReqPacket.Instance, timeout.Token).ConfigureAwait(false);
+                    await Request<MqttPingRespPacket>(MqttPingReqPacket.Instance, timeout.Token).ConfigureAwait(false);
                 }
             }
         }
@@ -239,6 +260,11 @@ namespace MQTTnet.Client
             ThrowIfDisposed();
             ThrowIfNotConnected();
 
+            if (Options.ValidateFeatures)
+            {
+                MqttApplicationMessageValidator.ThrowIfNotSupported(applicationMessage, _adapter.PacketFormatterAdapter.ProtocolVersion);
+            }
+
             var publishPacket = MqttPacketFactories.Publish.Create(applicationMessage);
 
             switch (applicationMessage.QualityOfServiceLevel)
@@ -249,11 +275,11 @@ namespace MQTTnet.Client
                 }
                 case MqttQualityOfServiceLevel.AtLeastOnce:
                 {
-                    return PublishAtLeastOnceAsync(publishPacket, cancellationToken);
+                    return PublishAtLeastOnce(publishPacket, cancellationToken);
                 }
                 case MqttQualityOfServiceLevel.ExactlyOnce:
                 {
-                    return PublishExactlyOnceAsync(publishPacket, cancellationToken);
+                    return PublishExactlyOnce(publishPacket, cancellationToken);
                 }
                 default:
                 {
@@ -281,7 +307,7 @@ namespace MQTTnet.Client
                 UserProperties = data.UserProperties
             };
 
-            return SendAsync(authPacket, cancellationToken);
+            return Send(authPacket, cancellationToken);
         }
 
         public async Task<MqttClientSubscribeResult> SubscribeAsync(MqttClientSubscribeOptions options, CancellationToken cancellationToken = default)
@@ -298,13 +324,29 @@ namespace MQTTnet.Client
 
             ThrowIfDisposed();
             ThrowIfNotConnected();
+            
+            if (Options.ValidateFeatures)
+            {
+                MqttClientSubscribeOptionsValidator.ThrowIfNotSupported(options, _adapter.PacketFormatterAdapter.ProtocolVersion);
+            }
 
             var subscribePacket = MqttPacketFactories.Subscribe.Create(options);
             subscribePacket.PacketIdentifier = _packetIdentifierProvider.GetNextPacketIdentifier();
 
-            var subAckPacket = await SendAndReceiveAsync<MqttSubAckPacket>(subscribePacket, cancellationToken).ConfigureAwait(false);
+            MqttSubAckPacket subAckPacket;
+            if (cancellationToken.CanBeCanceled)
+            {
+                subAckPacket = await Request<MqttSubAckPacket>(subscribePacket, cancellationToken).ConfigureAwait(false);
+            }
+            else
+            {
+                using (var timeout = new CancellationTokenSource(Options.Timeout))
+                {
+                    subAckPacket = await Request<MqttSubAckPacket>(subscribePacket, timeout.Token).ConfigureAwait(false);
+                }
+            }
 
-            return _clientSubscribeResultFactory.Create(subscribePacket, subAckPacket);
+            return MqttClientResultFactory.SubscribeResult.Create(subscribePacket, subAckPacket);
         }
 
         public async Task<MqttClientUnsubscribeResult> UnsubscribeAsync(MqttClientUnsubscribeOptions options, CancellationToken cancellationToken = default)
@@ -314,15 +356,36 @@ namespace MQTTnet.Client
                 throw new ArgumentNullException(nameof(options));
             }
 
+            foreach (var topicFilter in options.TopicFilters)
+            {
+                MqttTopicValidator.ThrowIfInvalidSubscribe(topicFilter);
+            }
+
             ThrowIfDisposed();
             ThrowIfNotConnected();
 
+            if (Options.ValidateFeatures)
+            {
+                MqttClientUnsubscribeOptionsValidator.ThrowIfNotSupported(options, _adapter.PacketFormatterAdapter.ProtocolVersion);
+            }
+
             var unsubscribePacket = MqttPacketFactories.Unsubscribe.Create(options);
             unsubscribePacket.PacketIdentifier = _packetIdentifierProvider.GetNextPacketIdentifier();
 
-            var unsubAckPacket = await SendAndReceiveAsync<MqttUnsubAckPacket>(unsubscribePacket, cancellationToken).ConfigureAwait(false);
+            MqttUnsubAckPacket unsubAckPacket;
+            if (cancellationToken.CanBeCanceled)
+            {
+                unsubAckPacket = await Request<MqttUnsubAckPacket>(unsubscribePacket, cancellationToken).ConfigureAwait(false);
+            }
+            else
+            {
+                using (var timeout = new CancellationTokenSource(Options.Timeout))
+                {
+                    unsubAckPacket = await Request<MqttUnsubAckPacket>(unsubscribePacket, timeout.Token).ConfigureAwait(false);
+                }
+            }
 
-            return _clientUnsubscribeResultFactory.Create(unsubscribePacket, unsubAckPacket);
+            return MqttClientResultFactory.UnsubscribeResult.Create(unsubscribePacket, unsubAckPacket);
         }
 
         protected override void Dispose(bool disposing)
@@ -346,7 +409,7 @@ namespace MQTTnet.Client
                 if (!eventArgs.ProcessingFailed)
                 {
                     var pubAckPacket = MqttPacketFactories.PubAck.Create(eventArgs);
-                    return SendAsync(pubAckPacket, cancellationToken);
+                    return Send(pubAckPacket, cancellationToken);
                 }
             }
             else if (eventArgs.PublishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
@@ -354,7 +417,7 @@ namespace MQTTnet.Client
                 if (!eventArgs.ProcessingFailed)
                 {
                     var pubRecPacket = MqttPacketFactories.PubRec.Create(eventArgs);
-                    return SendAsync(pubRecPacket, cancellationToken);
+                    return Send(pubRecPacket, cancellationToken);
                 }
             }
             else
@@ -365,27 +428,50 @@ namespace MQTTnet.Client
             return CompletedTask.Instance;
         }
 
-        async Task<MqttClientConnectResult> AuthenticateAsync(MqttClientOptions options, CancellationToken cancellationToken)
+        async Task<MqttClientConnectResult> Authenticate(IMqttChannelAdapter channelAdapter, MqttClientOptions options, CancellationToken cancellationToken)
         {
             MqttClientConnectResult result;
 
             try
             {
                 var connectPacket = MqttPacketFactories.Connect.Create(options);
+                await Send(connectPacket, cancellationToken).ConfigureAwait(false);
 
-                var connAckPacket = await SendAndReceiveAsync<MqttConnAckPacket>(connectPacket, cancellationToken).ConfigureAwait(false);
+                var receivedPacket = await Receive(cancellationToken).ConfigureAwait(false);
 
-                var clientConnectResultFactory = new MqttClientConnectResultFactory();
-                result = clientConnectResultFactory.Create(connAckPacket, options.ProtocolVersion);
+                if (receivedPacket is MqttConnAckPacket connAckPacket)
+                {
+                    result = MqttClientResultFactory.ConnectResult.Create(connAckPacket, _adapter.PacketFormatterAdapter.ProtocolVersion);
+                }
+                else if (receivedPacket is MqttAuthPacket)
+                {
+                    throw new NotSupportedException("Extended authentication handler is not yet supported");
+                }
+                else if (receivedPacket == null)
+                {
+                    throw new MqttCommunicationException("Connection closed.");
+                }
+                else
+                {
+                    throw new InvalidOperationException($"Received an unexpected MQTT packet ({receivedPacket}).");
+                }
             }
             catch (Exception exception)
             {
                 throw new MqttConnectingFailedException($"Error while authenticating. {exception.Message}", exception, null);
             }
 
-            if (result.ResultCode != MqttClientConnectResultCode.Success)
+            // This is no feature. It is basically a backward compatibility option and should be removed in the future.
+            // The client should not throw any exception if the transport layer connection was successful and the server
+            // did send a proper ACK packet with a non success response.
+            if (options.ThrowOnNonSuccessfulConnectResponse)
             {
-                throw new MqttConnectingFailedException($"Connecting with MQTT server failed ({result.ResultCode}).", null, result);
+                if (result.ResultCode != MqttClientConnectResultCode.Success)
+                {
+                    _logger.Warning(
+                        "Client will now throw an _MqttConnectingFailedException_. This is obsolete and will be removed in the future. Consider setting _ThrowOnNonSuccessfulResponseFromServer=False_ in client options.");
+                    throw new MqttConnectingFailedException($"Connecting with MQTT server failed ({result.ResultCode}).", null, result);
+                }
             }
 
             _logger.Verbose("Authenticated MQTT connection with server established.");
@@ -397,19 +483,19 @@ namespace MQTTnet.Client
         {
             try
             {
-                _backgroundCancellationTokenSource?.Cancel(false);
+                _mqttClientAlive?.Cancel(false);
             }
             finally
             {
-                _backgroundCancellationTokenSource?.Dispose();
-                _backgroundCancellationTokenSource = null;
+                _mqttClientAlive?.Dispose();
+                _mqttClientAlive = null;
 
                 _publishPacketReceiverQueue?.Dispose();
                 _publishPacketReceiverQueue = null;
 
                 _adapter?.Dispose();
                 _adapter = null;
-                
+
                 _packetDispatcher?.Dispose();
                 _packetDispatcher = null;
             }
@@ -420,7 +506,31 @@ namespace MQTTnet.Client
             return (MqttClientConnectionStatus)Interlocked.CompareExchange(ref _connectionStatus, (int)value, (int)comparand);
         }
 
-        async Task DisconnectCoreAsync(Task sender, Exception exception, MqttClientConnectResult connectResult, bool clientWasConnected)
+        async Task<MqttClientConnectResult> ConnectInternal(IMqttChannelAdapter channelAdapter, CancellationToken cancellationToken)
+        {
+            var backgroundCancellationToken = _mqttClientAlive.Token;
+
+            using (var effectiveCancellationToken = CancellationTokenSource.CreateLinkedTokenSource(backgroundCancellationToken, cancellationToken))
+            {
+                _logger.Verbose("Trying to connect with server '{0}'", Options.ChannelOptions);
+                await _adapter.ConnectAsync(effectiveCancellationToken.Token).ConfigureAwait(false);
+                _logger.Verbose("Connection with server established");
+
+                _publishPacketReceiverQueue?.Dispose();
+                _publishPacketReceiverQueue = new AsyncQueue<MqttPublishPacket>();
+
+                var connectResult = await Authenticate(channelAdapter, Options, effectiveCancellationToken.Token).ConfigureAwait(false);
+                if (connectResult.ResultCode == MqttClientConnectResultCode.Success)
+                {
+                    _publishPacketReceiverTask = Task.Run(() => ProcessReceivedPublishPackets(backgroundCancellationToken), backgroundCancellationToken);
+                    _packetReceiverTask = Task.Run(() => ReceivePacketsLoop(backgroundCancellationToken), backgroundCancellationToken);
+                }
+
+                return connectResult;
+            }
+        }
+
+        async Task DisconnectCore(Task sender, Exception exception, MqttClientConnectResult connectResult, bool clientWasConnected)
         {
             TryInitiateDisconnect();
 
@@ -445,11 +555,11 @@ namespace MQTTnet.Client
 
             try
             {
-                _packetDispatcher.Dispose(new MqttClientDisconnectedException(exception));
-                
-                var receiverTask = WaitForTaskAsync(_packetReceiverTask, sender);
-                var publishPacketReceiverTask = WaitForTaskAsync(_publishPacketReceiverTask, sender);
-                var keepAliveTask = WaitForTaskAsync(_keepAlivePacketsSenderTask, sender);
+                _packetDispatcher?.Dispose(new MqttClientDisconnectedException(exception));
+
+                var receiverTask = _packetReceiverTask.WaitAsync(sender, _logger);
+                var publishPacketReceiverTask = _publishPacketReceiverTask.WaitAsync(sender, _logger);
+                var keepAliveTask = _keepAlivePacketsSenderTask.WaitAsync(sender, _logger);
 
                 await Task.WhenAll(receiverTask, publishPacketReceiverTask, keepAliveTask).ConfigureAwait(false);
             }
@@ -465,28 +575,27 @@ namespace MQTTnet.Client
 
                 _logger.Info("Disconnected.");
 
-                var eventArgs = new MqttClientDisconnectedEventArgs
-                {
-                    ClientWasConnected = clientWasConnected,
-                    Exception = exception,
-                    ConnectResult = connectResult,
-                    Reason = _disconnectReason,
-                    ReasonString = _disconnectReasonString
-                };
+                var eventArgs = new MqttClientDisconnectedEventArgs(
+                    clientWasConnected,
+                    connectResult,
+                    (MqttClientDisconnectReason)_disconnectReason,
+                    _disconnectReasonString,
+                    _disconnectUserProperties,
+                    exception);
 
                 // This handler must be executed in a new thread because otherwise a dead lock may happen
                 // when trying to reconnect in that handler etc.
-                Task.Run(() => _disconnectedEvent.InvokeAsync(eventArgs)).RunInBackground(_logger);
+                Task.Run(() => _events.DisconnectedEvent.InvokeAsync(eventArgs)).RunInBackground(_logger);
             }
         }
 
-        Task DisconnectInternalAsync(Task sender, Exception exception, MqttClientConnectResult connectResult)
+        Task DisconnectInternal(Task sender, Exception exception, MqttClientConnectResult connectResult)
         {
             var clientWasConnected = IsConnected;
 
             if (!DisconnectIsPendingOrFinished())
             {
-                return DisconnectCoreAsync(sender, exception, connectResult, clientWasConnected);
+                return DisconnectCore(sender, exception, connectResult, clientWasConnected);
             }
 
             return CompletedTask.Instance;
@@ -531,16 +640,26 @@ namespace MQTTnet.Client
             }
         }
 
-        async Task<MqttApplicationMessageReceivedEventArgs> HandleReceivedApplicationMessageAsync(MqttPublishPacket publishPacket)
+        async Task<MqttApplicationMessageReceivedEventArgs> HandleReceivedApplicationMessage(MqttPublishPacket publishPacket)
         {
             var applicationMessage = MqttApplicationMessageFactory.Create(publishPacket);
             var eventArgs = new MqttApplicationMessageReceivedEventArgs(Options.ClientId, applicationMessage, publishPacket, AcknowledgeReceivedPublishPacket);
-
-            await _applicationMessageReceivedEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
+            await _events.ApplicationMessageReceivedEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
 
             return eventArgs;
         }
 
+        Task OnConnected(MqttClientConnectResult connectResult)
+        {
+            if (_events.ConnectedEvent.HasHandlers)
+            {
+                var eventArgs = new MqttClientConnectedEventArgs(connectResult);
+                return _events.ConnectedEvent.InvokeAsync(eventArgs);
+            }
+
+            return CompletedTask.Instance;
+        }
+
         Task ProcessReceivedAuthPacket(MqttAuthPacket authPacket)
         {
             var extendedAuthenticationExchangeHandler = Options.ExtendedAuthenticationExchangeHandler;
@@ -554,13 +673,14 @@ namespace MQTTnet.Client
 
         Task ProcessReceivedDisconnectPacket(MqttDisconnectPacket disconnectPacket)
         {
-            _disconnectReason = (MqttClientDisconnectReason)disconnectPacket.ReasonCode;
+            _disconnectReason = (int)disconnectPacket.ReasonCode;
             _disconnectReasonString = disconnectPacket.ReasonString;
+            _disconnectUserProperties = disconnectPacket.UserProperties;
 
             // Also dispatch disconnect to waiting threads to generate a proper exception.
             _packetDispatcher.Dispose(new MqttClientUnexpectedDisconnectReceivedException(disconnectPacket));
 
-            return DisconnectInternalAsync(_packetReceiverTask, null, null);
+            return DisconnectInternal(_packetReceiverTask, null, null);
         }
 
         async Task ProcessReceivedPublishPackets(CancellationToken cancellationToken)
@@ -576,7 +696,7 @@ namespace MQTTnet.Client
                     }
 
                     var publishPacket = publishPacketDequeueResult.Item;
-                    var eventArgs = await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false);
+                    var eventArgs = await HandleReceivedApplicationMessage(publishPacket).ConfigureAwait(false);
 
                     if (eventArgs.AutoAcknowledge)
                     {
@@ -600,7 +720,7 @@ namespace MQTTnet.Client
                 // The packet is unknown. Probably due to a restart of the client.
                 // So wen send this to the server to trigger a full resend of the message.
                 var pubRelPacket = MqttPacketFactories.PubRel.Create(pubRecPacket, MqttApplicationMessageReceivedReasonCode.PacketIdentifierNotFound);
-                return SendAsync(pubRelPacket, cancellationToken);
+                return Send(pubRelPacket, cancellationToken);
             }
 
             return CompletedTask.Instance;
@@ -609,40 +729,115 @@ namespace MQTTnet.Client
         Task ProcessReceivedPubRelPacket(MqttPubRelPacket pubRelPacket, CancellationToken cancellationToken)
         {
             var pubCompPacket = MqttPacketFactories.PubComp.Create(pubRelPacket, MqttApplicationMessageReceivedReasonCode.Success);
-            return SendAsync(pubCompPacket, cancellationToken);
+            return Send(pubCompPacket, cancellationToken);
         }
 
-        async Task<MqttClientPublishResult> PublishAtLeastOnceAsync(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
+        async Task<MqttClientPublishResult> PublishAtLeastOnce(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
         {
             publishPacket.PacketIdentifier = _packetIdentifierProvider.GetNextPacketIdentifier();
 
-            var pubAckPacket = await SendAndReceiveAsync<MqttPubAckPacket>(publishPacket, cancellationToken).ConfigureAwait(false);
-
-            return _clientPublishResultFactory.Create(pubAckPacket);
+            var pubAckPacket = await Request<MqttPubAckPacket>(publishPacket, cancellationToken).ConfigureAwait(false);
+            return MqttClientResultFactory.PublishResult.Create(pubAckPacket);
         }
 
         async Task<MqttClientPublishResult> PublishAtMostOnce(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
         {
             // No packet identifier is used for QoS 0 [3.3.2.2 Packet Identifier]
-            await SendAsync(publishPacket, cancellationToken).ConfigureAwait(false);
+            await Send(publishPacket, cancellationToken).ConfigureAwait(false);
 
-            return _clientPublishResultFactory.Create(null);
+            return MqttClientResultFactory.PublishResult.Create(null);
         }
 
-        async Task<MqttClientPublishResult> PublishExactlyOnceAsync(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
+        async Task<MqttClientPublishResult> PublishExactlyOnce(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
         {
             publishPacket.PacketIdentifier = _packetIdentifierProvider.GetNextPacketIdentifier();
 
-            var pubRecPacket = await SendAndReceiveAsync<MqttPubRecPacket>(publishPacket, cancellationToken).ConfigureAwait(false);
+            var pubRecPacket = await Request<MqttPubRecPacket>(publishPacket, cancellationToken).ConfigureAwait(false);
 
             var pubRelPacket = MqttPacketFactories.PubRel.Create(pubRecPacket, MqttApplicationMessageReceivedReasonCode.Success);
 
-            var pubCompPacket = await SendAndReceiveAsync<MqttPubCompPacket>(pubRelPacket, cancellationToken).ConfigureAwait(false);
+            var pubCompPacket = await Request<MqttPubCompPacket>(pubRelPacket, cancellationToken).ConfigureAwait(false);
 
-            return _clientPublishResultFactory.Create(pubRecPacket, pubCompPacket);
+            return MqttClientResultFactory.PublishResult.Create(pubRecPacket, pubCompPacket);
         }
 
-        async Task<TResponsePacket> SendAndReceiveAsync<TResponsePacket>(MqttPacket requestPacket, CancellationToken cancellationToken) where TResponsePacket : MqttPacket
+        async Task<MqttPacket> Receive(CancellationToken cancellationToken)
+        {
+            var packetTask = _adapter.ReceivePacketAsync(cancellationToken);
+
+            MqttPacket packet;
+            if (packetTask.IsCompleted)
+            {
+                packet = packetTask.Result;
+            }
+            else
+            {
+                packet = await packetTask.ConfigureAwait(false);
+            }
+
+            return packet;
+        }
+
+        async Task ReceivePacketsLoop(CancellationToken cancellationToken)
+        {
+            try
+            {
+                _logger.Verbose("Start receiving packets.");
+
+                while (!cancellationToken.IsCancellationRequested)
+                {
+                    var packet = await Receive(cancellationToken).ConfigureAwait(false);
+
+                    if (cancellationToken.IsCancellationRequested)
+                    {
+                        return;
+                    }
+
+                    if (packet == null)
+                    {
+                        await DisconnectInternal(_packetReceiverTask, null, null).ConfigureAwait(false);
+
+                        return;
+                    }
+
+                    await TryProcessReceivedPacket(packet, cancellationToken).ConfigureAwait(false);
+                }
+            }
+            catch (Exception exception)
+            {
+                if (_cleanDisconnectInitiated)
+                {
+                    return;
+                }
+
+                if (exception is AggregateException aggregateException)
+                {
+                    exception = aggregateException.GetBaseException();
+                }
+
+                if (exception is OperationCanceledException)
+                {
+                }
+                else if (exception is MqttCommunicationException)
+                {
+                    _logger.Warning(exception, "Communication error while receiving packets.");
+                }
+                else
+                {
+                    _logger.Error(exception, "Error while receiving packets.");
+                }
+
+                _packetDispatcher.FailAll(exception);
+
+                await DisconnectInternal(_packetReceiverTask, exception, null).ConfigureAwait(false);
+            }
+            finally
+            {
+                _logger.Verbose("Stopped receiving packets.");
+            }
+        }
+
+        async Task<TResponsePacket> Request<TResponsePacket>(MqttPacket requestPacket, CancellationToken cancellationToken) where TResponsePacket : MqttPacket
         {
             cancellationToken.ThrowIfCancellationRequested();
 
@@ -656,7 +851,7 @@ namespace MQTTnet.Client
             {
                 try
                 {
-                    await SendAsync(requestPacket, cancellationToken).ConfigureAwait(false);
+                    await Send(requestPacket, cancellationToken).ConfigureAwait(false);
                 }
                 catch (Exception exception)
                 {
@@ -680,7 +875,7 @@ namespace MQTTnet.Client
             }
         }
 
-        Task SendAsync(MqttPacket packet, CancellationToken cancellationToken)
+        Task Send(MqttPacket packet, CancellationToken cancellationToken)
         {
             cancellationToken.ThrowIfCancellationRequested();
 
@@ -693,7 +888,7 @@ namespace MQTTnet.Client
         {
             if (IsConnected)
             {
-                throw new MqttProtocolViolationException(message);
+                throw new InvalidOperationException(message);
             }
         }
 
@@ -701,17 +896,40 @@ namespace MQTTnet.Client
         {
             if (!IsConnected)
             {
-                throw new MqttCommunicationException("The client is not connected.");
+                ThrowNotConnected();
             }
         }
 
+        static void ThrowIfOptionsInvalid(MqttClientOptions options)
+        {
+            if (options == null)
+            {
+                throw new ArgumentNullException(nameof(options));
+            }
+
+            if (options.ChannelOptions == null)
+            {
+                throw new ArgumentException("ChannelOptions are not set.");
+            }
+
+            if (options.ValidateFeatures)
+            {
+                MqttClientOptionsValidator.ThrowIfNotSupported(options);
+            }
+        }
+
+        static void ThrowNotConnected()
+        {
+            throw new MqttCommunicationException("The client is not connected.");
+        }
+
         void TryInitiateDisconnect()
         {
             lock (_disconnectLock)
             {
                 try
                 {
-                    _backgroundCancellationTokenSource?.Cancel(false);
+                    _mqttClientAlive?.Cancel(false);
                 }
                 catch (Exception exception)
                 {
@@ -720,7 +938,7 @@ namespace MQTTnet.Client
             }
         }
 
-        async Task TryProcessReceivedPacketAsync(MqttPacket packet, CancellationToken cancellationToken)
+        async Task TryProcessReceivedPacket(MqttPacket packet, CancellationToken cancellationToken)
         {
             try
             {
@@ -781,80 +999,11 @@ namespace MQTTnet.Client
 
                 _packetDispatcher.FailAll(exception);
 
-                await DisconnectInternalAsync(_packetReceiverTask, exception, null).ConfigureAwait(false);
+                await DisconnectInternal(_packetReceiverTask, exception, null).ConfigureAwait(false);
             }
         }
 
-        async Task TryReceivePacketsAsync(CancellationToken cancellationToken)
-        {
-            try
-            {
-                _logger.Verbose("Start receiving packets.");
-
-                while (!cancellationToken.IsCancellationRequested)
-                {
-                    MqttPacket packet;
-                    var packetTask = _adapter.ReceivePacketAsync(cancellationToken);
-
-                    if (packetTask.IsCompleted)
-                    {
-                        packet = packetTask.Result;
-                    }
-                    else
-                    {
-                        packet = await packetTask.ConfigureAwait(false);
-                    }
-
-                    if (cancellationToken.IsCancellationRequested)
-                    {
-                        return;
-                    }
-
-                    if (packet == null)
-                    {
-                        await DisconnectInternalAsync(_packetReceiverTask, null, null).ConfigureAwait(false);
-
-                        return;
-                    }
-
-                    await TryProcessReceivedPacketAsync(packet, cancellationToken).ConfigureAwait(false);
-                }
-            }
-            catch (Exception exception)
-            {
-                if (_cleanDisconnectInitiated)
-                {
-                    return;
-                }
-
-                if (exception is AggregateException aggregateException)
-                {
-                    exception = aggregateException.GetBaseException();
-                }
-                
-                if (exception is OperationCanceledException)
-                {
-                }
-                else if (exception is MqttCommunicationException)
-                {
-                    _logger.Warning(exception, "Communication error while receiving packets.");
-                }
-                else
-                {
-                    _logger.Error(exception, "Error while receiving packets.");
-                }
-
-                _packetDispatcher.FailAll(exception);
-
-                await DisconnectInternalAsync(_packetReceiverTask, exception, null).ConfigureAwait(false);
-            }
-            finally
-            {
-                _logger.Verbose("Stopped receiving packets.");
-            }
-        }
-
-        async Task TrySendKeepAliveMessagesAsync(CancellationToken cancellationToken)
+        async Task TrySendKeepAliveMessages(CancellationToken cancellationToken)
         {
             try
             {
@@ -903,43 +1052,12 @@ namespace MQTTnet.Client
                     _logger.Error(exception, "Error exception while sending/receiving keep alive packets.");
                 }
 
-                await DisconnectInternalAsync(_keepAlivePacketsSenderTask, exception, null).ConfigureAwait(false);
+                await DisconnectInternal(_keepAlivePacketsSenderTask, exception, null).ConfigureAwait(false);
             }
             finally
             {
                 _logger.Verbose("Stopped sending keep alive packets.");
             }
         }
-
-        async Task WaitForTaskAsync(Task task, Task sender)
-        {
-            if (task == null)
-            {
-                return;
-            }
-
-            if (task == sender)
-            {
-                // Return here to avoid deadlocks, but first any eventual exception in the task
-                // must be handled to avoid not getting an unhandled task exception
-                if (!task.IsFaulted)
-                {
-                    return;
-                }
-
-                // By accessing the Exception property the exception is considered handled and will
-                // not result in an unhandled task exception later by the finalizer
-                _logger.Warning(task.Exception, "Error while waiting for background task.");
-                return;
-            }
-
-            try
-            {
-                await task.ConfigureAwait(false);
-            }
-            catch (OperationCanceledException)
-            {
-            }
-        }
     }
-}
+}

Source/MQTTnet/Client/MqttClientExtensions.cs

@@ -14,20 +14,28 @@ namespace MQTTnet.Client
 {
     public static class MqttClientExtensions
     {
-        public static Task DisconnectAsync(this IMqttClient client, MqttClientDisconnectReason reason = MqttClientDisconnectReason.NormalDisconnection, string reasonString = null)
+        public static Task DisconnectAsync(
+            this IMqttClient client,
+            MqttClientDisconnectOptionsReason reason = MqttClientDisconnectOptionsReason.NormalDisconnection,
+            string reasonString = null,
+            uint sessionExpiryInterval = 0,
+            List<MqttUserProperty> userProperties = null,
+            CancellationToken cancellationToken = default)
         {
             if (client == null)
             {
                 throw new ArgumentNullException(nameof(client));
             }
 
-            return client.DisconnectAsync(
-                new MqttClientDisconnectOptions
-                {
-                    Reason = reason,
-                    ReasonString = reasonString
-                },
-                CancellationToken.None);
+            var disconnectOptions = new MqttClientDisconnectOptions
+            {
+                Reason = reason,
+                ReasonString = reasonString,
+                SessionExpiryInterval = sessionExpiryInterval,
+                UserProperties = userProperties
+            };
+
+            return client.DisconnectAsync(disconnectOptions, cancellationToken);
         }
 
         public static Task<MqttClientPublishResult> PublishBinaryAsync(
@@ -128,6 +136,29 @@ namespace MQTTnet.Client
             return mqttClient.SubscribeAsync(subscribeOptions, cancellationToken);
         }
 
+        public static async Task<bool> TryDisconnectAsync(
+            this IMqttClient client,
+            MqttClientDisconnectOptionsReason reason = MqttClientDisconnectOptionsReason.NormalDisconnection,
+            string reasonString = null)
+        {
+            if (client == null)
+            {
+                throw new ArgumentNullException(nameof(client));
+            }
+
+            try
+            {
+                await client.DisconnectAsync(reason, reasonString).ConfigureAwait(false);
+                return true;
+            }
+            catch
+            {
+                // Ignore all errors.
+            }
+
+            return false;
+        }
+
         public static async Task<bool> TryPingAsync(this IMqttClient client, CancellationToken cancellationToken = default)
         {
             if (client == null)

Source/MQTTnet/Client/Options/DefaultMqttCertificatesProvider.cs

@@ -0,0 +1,36 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Generic;
+using System.Security.Cryptography.X509Certificates;
+
+namespace MQTTnet.Client
+{
+    public sealed class DefaultMqttCertificatesProvider : IMqttClientCertificatesProvider
+    {
+        readonly X509Certificate2Collection _certificates;
+
+        public DefaultMqttCertificatesProvider(X509Certificate2Collection certificates)
+        {
+            _certificates = certificates;
+        }
+
+        public DefaultMqttCertificatesProvider(IEnumerable<X509Certificate> certificates)
+        {
+            if (certificates != null)
+            {
+                _certificates = new X509Certificate2Collection();
+                foreach (var certificate in certificates)
+                {
+                    _certificates.Add(certificate);
+                }
+            }
+        }
+
+        public X509CertificateCollection GetCertificates()
+        {
+            return _certificates;
+        }
+    }
+}

Source/MQTTnet/Client/Options/IMqttClientCertificatesProvider.cs

@@ -0,0 +1,11 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace MQTTnet.Client
+{
+    public interface IMqttClientCertificatesProvider
+    {
+        System.Security.Cryptography.X509Certificates.X509CertificateCollection GetCertificates();
+    }
+}

Source/MQTTnet/Client/Options/MqttClientCertificateValidationEventArgs.cs

@@ -14,8 +14,14 @@ namespace MQTTnet.Client
 
         public X509Chain Chain { get; set; }
 
-        public SslPolicyErrors SslPolicyErrors { get; set; }
-
         public IMqttClientChannelOptions ClientOptions { get; set; }
+#if NET452 || NET461 || NET48
+        /// <summary>
+        ///     Can be a host string name or an object derived from WebRequest.
+        /// </summary>
+        public object Sender { get; set; }
+#endif
+
+        public SslPolicyErrors SslPolicyErrors { get; set; }
     }
-}
+}

Source/MQTTnet/Client/Options/MqttClientOptions.cs

@@ -12,15 +12,23 @@ namespace MQTTnet.Client
 {
     public sealed class MqttClientOptions
     {
+        /// <summary>
+        ///     Usually the MQTT packets can be send partially. This is done by using multiple TCP packets
+        ///     or WebSocket frames etc. Unfortunately not all brokers (like Amazon Web Services (AWS)) do support this feature and
+        ///     will close the connection when receiving such packets. If such a service is used this flag must
+        ///     be set to _false_.
+        /// </summary>
+        public bool AllowPacketFragmentation { get; set; } = true;
+
         /// <summary>
         ///     Gets or sets the authentication data.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public byte[] AuthenticationData { get; set; }
 
         /// <summary>
         ///     Gets or sets the authentication method.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public string AuthenticationMethod { get; set; }
 
@@ -58,6 +66,10 @@ namespace MQTTnet.Client
         /// </summary>
         public TimeSpan KeepAlivePeriod { get; set; } = TimeSpan.FromSeconds(15);
 
+        /// <summary>
+        ///     Gets or sets the maximum packet size.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
+        /// </summary>
         public uint MaximumPacketSize { get; set; }
 
         public MqttProtocolVersion ProtocolVersion { get; set; } = MqttProtocolVersion.V311;
@@ -65,27 +77,34 @@ namespace MQTTnet.Client
         /// <summary>
         ///     Gets or sets the receive maximum.
         ///     This gives the maximum length of the receive messages.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public ushort ReceiveMaximum { get; set; }
 
         /// <summary>
         ///     Gets or sets the request problem information.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public bool RequestProblemInformation { get; set; } = true;
 
         /// <summary>
         ///     Gets or sets the request response information.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public bool RequestResponseInformation { get; set; }
 
         /// <summary>
         ///     Gets or sets the session expiry interval.
         ///     The time after a session expires when it's not actively used.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public uint SessionExpiryInterval { get; set; }
 
+        /// <summary>
+        ///     Gets or sets whether an exception should be thrown when the server has sent a non success ACK packet.
+        /// </summary>
+        public bool ThrowOnNonSuccessfulConnectResponse { get; set; } = true;
+
         /// <summary>
         ///     Gets or sets the timeout which will be applied at socket level and internal operations.
         ///     The default value is the same as for sockets in .NET in general.
@@ -95,6 +114,7 @@ namespace MQTTnet.Client
         /// <summary>
         ///     Gets or sets the topic alias maximum.
         ///     This gives the maximum length of the topic alias.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public ushort TopicAliasMaximum { get; set; }
 
@@ -103,8 +123,10 @@ namespace MQTTnet.Client
         ///     client.
         ///     If successful, this means that loop detection will be more effective and that retained messages will be propagated
         ///     correctly.
-        ///     Not all brokers support this feature so it may be necessary to set it to false if your bridge does not connect
-        ///     properly.
+        ///     <remarks>
+        ///         Not all brokers support this feature so it may be necessary to set it to false if your bridge does not
+        ///         connect properly.
+        ///     </remarks>
         /// </summary>
         public bool TryPrivate { get; set; } = true;
 
@@ -115,28 +137,41 @@ namespace MQTTnet.Client
         ///     As long as you don’t exceed the maximum message size, you can use an unlimited number of user properties to add
         ///     metadata to MQTT messages and pass information between publisher, broker, and subscriber.
         ///     The feature is very similar to the HTTP header concept.
-        ///     Hint: MQTT 5 feature only.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public List<MqttUserProperty> UserProperties { get; set; }
 
+        /// <summary>
+        ///     When this feature is enabled the client will check if used properties are supported in the selected protocol
+        ///     version.
+        ///     This feature can be validated if an application message is generated one time but sent via different protocol
+        ///     versions.
+        ///     Default values are applied if the validation is off and features are not supported.
+        /// </summary>
+        public bool ValidateFeatures { get; set; } = true;
+
         /// <summary>
         ///     Gets or sets the content type of the will message.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public string WillContentType { get; set; }
 
         /// <summary>
         ///     Gets or sets the correlation data of the will message.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public byte[] WillCorrelationData { get; set; }
 
         /// <summary>
         ///     Gets or sets the will delay interval.
         ///     This is the time between the client disconnect and the time the will message will be sent.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public uint WillDelayInterval { get; set; }
 
         /// <summary>
         ///     Gets or sets the message expiry interval of the will message.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public uint WillMessageExpiryInterval { get; set; }
 
@@ -147,8 +182,9 @@ namespace MQTTnet.Client
 
         /// <summary>
         ///     Gets or sets the payload format indicator of the will message.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
-        public MqttPayloadFormatIndicator WillPayloadFormatIndicator { get; set; }
+        public MqttPayloadFormatIndicator WillPayloadFormatIndicator { get; set; } = MqttPayloadFormatIndicator.Unspecified;
 
         /// <summary>
         ///     Gets or sets the QoS level of the will message.
@@ -157,6 +193,7 @@ namespace MQTTnet.Client
 
         /// <summary>
         ///     Gets or sets the response topic of the will message.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public string WillResponseTopic { get; set; }
 
@@ -172,6 +209,7 @@ namespace MQTTnet.Client
 
         /// <summary>
         ///     Gets or sets the user properties of the will message.
+        ///     <remarks>MQTT 5.0.0+ feature.</remarks>
         /// </summary>
         public List<MqttUserProperty> WillUserProperties { get; set; }
 

Source/MQTTnet/Client/Options/MqttClientOptionsBuilder.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
@@ -15,10 +15,14 @@ namespace MQTTnet.Client
     public sealed class MqttClientOptionsBuilder
     {
         readonly MqttClientOptions _options = new MqttClientOptions();
-        MqttClientWebSocketProxyOptions _proxyOptions;
+
+        [Obsolete] MqttClientWebSocketProxyOptions _proxyOptions;
 
         MqttClientTcpOptions _tcpOptions;
-        MqttClientOptionsBuilderTlsParameters _tlsParameters;
+        MqttClientTlsOptions _tlsOptions;
+
+        [Obsolete] MqttClientOptionsBuilderTlsParameters _tlsParameters;
+
         MqttClientWebSocketOptions _webSocketOptions;
 
         public MqttClientOptions Build()
@@ -28,11 +32,12 @@ namespace MQTTnet.Client
                 throw new InvalidOperationException("A channel must be set.");
             }
 
+            var tlsOptions = _tlsOptions;
             if (_tlsParameters != null)
             {
                 if (_tlsParameters?.UseTls == true)
                 {
-                    var tlsOptions = new MqttClientTlsOptions
+                    tlsOptions = new MqttClientTlsOptions
                     {
                         UseTls = true,
                         SslProtocol = _tlsParameters.SslProtocol,
@@ -40,28 +45,23 @@ namespace MQTTnet.Client
                         CertificateValidationHandler = _tlsParameters.CertificateValidationHandler,
                         IgnoreCertificateChainErrors = _tlsParameters.IgnoreCertificateChainErrors,
                         IgnoreCertificateRevocationErrors = _tlsParameters.IgnoreCertificateRevocationErrors,
-#if WINDOWS_UWP
-                        Certificates = _tlsParameters.Certificates?.Select(c => c.ToArray()).ToList(),
-#else
-                        Certificates = _tlsParameters.Certificates?.ToList(),
-#endif
-
-#if NETCOREAPP3_1 || NET5_0_OR_GREATER
+                        ClientCertificatesProvider = _tlsParameters.CertificatesProvider,
+#if NETCOREAPP3_1_OR_GREATER
                         ApplicationProtocols = _tlsParameters.ApplicationProtocols,
 #endif
                     };
-
-                    if (_tcpOptions != null)
-                    {
-                        _tcpOptions.TlsOptions = tlsOptions;
-                    }
-                    else if (_webSocketOptions != null)
-                    {
-                        _webSocketOptions.TlsOptions = tlsOptions;
-                    }
                 }
             }
 
+            if (_tcpOptions != null)
+            {
+                _tcpOptions.TlsOptions = tlsOptions;
+            }
+            else if (_webSocketOptions != null)
+            {
+                _webSocketOptions.TlsOptions = tlsOptions;
+            }
+
             if (_proxyOptions != null)
             {
                 if (_webSocketOptions == null)
@@ -74,6 +74,8 @@ namespace MQTTnet.Client
 
             _options.ChannelOptions = (IMqttClientChannelOptions)_tcpOptions ?? _webSocketOptions;
 
+            MqttClientOptionsValidator.ThrowIfNotSupported(_options);
+
             return _options;
         }
 
@@ -84,18 +86,31 @@ 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;
             return this;
         }
 
+        [Obsolete("Use WithTcpServer(... configure) or WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithConnectionUri(Uri uri)
         {
             if (uri == null)
@@ -112,12 +127,16 @@ namespace MQTTnet.Client
                     break;
 
                 case "mqtts":
-                    WithTcpServer(uri.Host, port).WithTls();
+                    WithTcpServer(uri.Host, port)
+                        .WithTlsOptions(
+                            o =>
+                            {
+                            });
                     break;
 
                 case "ws":
                 case "wss":
-                    WithWebSocketServer(uri.ToString());
+                    WithWebSocketServer(o => o.WithUri(uri.ToString()));
                     break;
 
                 default:
@@ -135,6 +154,7 @@ namespace MQTTnet.Client
             return this;
         }
 
+        [Obsolete("Use WithTcpServer(... configure) or WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithConnectionUri(string uri)
         {
             return WithConnectionUri(new Uri(uri, UriKind.Absolute));
@@ -186,6 +206,28 @@ 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;
+        }
+
+        /// <summary>
+        ///     The client will not throw an exception when the MQTT server responses with a non success ACK packet.
+        ///     This will become the default behavior in future versions of the library.
+        /// </summary>
+        public MqttClientOptionsBuilder WithoutThrowOnNonSuccessfulConnectResponse()
+        {
+            _options.ThrowOnNonSuccessfulConnectResponse = false;
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithProtocolVersion(MqttProtocolVersion value)
         {
             if (value == MqttProtocolVersion.Unknown)
@@ -197,6 +239,7 @@ namespace MQTTnet.Client
             return this;
         }
 
+        [Obsolete("Use WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithProxy(
             string address,
             string username = null,
@@ -218,6 +261,7 @@ namespace MQTTnet.Client
             return this;
         }
 
+        [Obsolete("Use WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithProxy(Action<MqttClientWebSocketProxyOptions> optionsBuilder)
         {
             if (optionsBuilder == null)
@@ -264,7 +308,7 @@ namespace MQTTnet.Client
 
             return this;
         }
-        
+
         public MqttClientOptionsBuilder WithTcpServer(Action<MqttClientTcpOptions> optionsBuilder)
         {
             if (optionsBuilder == null)
@@ -288,17 +332,20 @@ namespace MQTTnet.Client
             return this;
         }
 
+        [Obsolete("Use WithTlsOptions(... configure) instead.")]
         public MqttClientOptionsBuilder WithTls(MqttClientOptionsBuilderTlsParameters parameters)
         {
             _tlsParameters = parameters;
             return this;
         }
 
+        [Obsolete("Use WithTlsOptions(... configure) instead.")]
         public MqttClientOptionsBuilder WithTls()
         {
             return WithTls(new MqttClientOptionsBuilderTlsParameters { UseTls = true });
         }
 
+        [Obsolete("Use WithTlsOptions(... configure) instead.")]
         public MqttClientOptionsBuilder WithTls(Action<MqttClientOptionsBuilderTlsParameters> optionsBuilder)
         {
             if (optionsBuilder == null)
@@ -315,6 +362,26 @@ namespace MQTTnet.Client
             return this;
         }
 
+        public MqttClientOptionsBuilder WithTlsOptions(MqttClientTlsOptions tlsOptions)
+        {
+            _tlsOptions = tlsOptions;
+            return this;
+        }
+
+        public MqttClientOptionsBuilder WithTlsOptions(Action<MqttClientTlsOptionsBuilder> configure)
+        {
+            if (configure == null)
+            {
+                throw new ArgumentNullException(nameof(configure));
+            }
+
+            var builder = new MqttClientTlsOptionsBuilder();
+            configure.Invoke(builder);
+
+            _tlsOptions = builder.Build();
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithTopicAliasMaximum(ushort topicAliasMaximum)
         {
             _options.TopicAliasMaximum = topicAliasMaximum;
@@ -337,16 +404,6 @@ namespace MQTTnet.Client
 
         public MqttClientOptionsBuilder WithUserProperty(string name, string value)
         {
-            if (name is null)
-            {
-                throw new ArgumentNullException(nameof(name));
-            }
-
-            if (value is null)
-            {
-                throw new ArgumentNullException(nameof(value));
-            }
-
             if (_options.UserProperties == null)
             {
                 _options.UserProperties = new List<MqttUserProperty>();
@@ -356,6 +413,7 @@ namespace MQTTnet.Client
             return this;
         }
 
+        [Obsolete("Use WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithWebSocketServer(string uri, MqttClientOptionsBuilderWebSocketParameters parameters = null)
         {
             _webSocketOptions = new MqttClientWebSocketOptions
@@ -368,6 +426,21 @@ namespace MQTTnet.Client
             return this;
         }
 
+        public MqttClientOptionsBuilder WithWebSocketServer(Action<MqttClientWebSocketOptionsBuilder> configure)
+        {
+            if (configure == null)
+            {
+                throw new ArgumentNullException(nameof(configure));
+            }
+
+            var webSocketOptionsBuilder = new MqttClientWebSocketOptionsBuilder();
+            configure.Invoke(webSocketOptionsBuilder);
+
+            _webSocketOptions = webSocketOptionsBuilder.Build();
+            return this;
+        }
+
+        [Obsolete("Use WithWebSocketServer(... configure) instead.")]
         public MqttClientOptionsBuilder WithWebSocketServer(Action<MqttClientWebSocketOptions> optionsBuilder)
         {
             if (optionsBuilder == null)
@@ -381,38 +454,74 @@ 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;
             return this;
         }
 
+        public MqttClientOptionsBuilder WithWillMessageExpiryInterval(uint willMessageExpiryInterval)
+        {
+            _options.WillMessageExpiryInterval = willMessageExpiryInterval;
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithWillPayload(byte[] willPayload)
         {
             _options.WillPayload = willPayload;
             return this;
         }
-        
+
+        public MqttClientOptionsBuilder WithWillPayload(ArraySegment<byte> willPayload)
+        {
+            if (willPayload.Count == 0)
+            {
+                _options.WillPayload = null;
+                return this;
+            }
+
+            _options.WillPayload = willPayload.ToArray();
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithWillPayload(string willPayload)
         {
             if (string.IsNullOrEmpty(willPayload))
             {
                 return WithWillPayload((byte[])null);
             }
-            
+
             _options.WillPayload = Encoding.UTF8.GetBytes(willPayload);
             return this;
         }
 
+        public MqttClientOptionsBuilder WithWillPayloadFormatIndicator(MqttPayloadFormatIndicator willPayloadFormatIndicator)
+        {
+            _options.WillPayloadFormatIndicator = willPayloadFormatIndicator;
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithWillQualityOfServiceLevel(MqttQualityOfServiceLevel willQualityOfServiceLevel)
         {
             _options.WillQualityOfServiceLevel = willQualityOfServiceLevel;
             return this;
         }
 
-        public MqttClientOptionsBuilder WithWillTopic(string willTopic)
+        public MqttClientOptionsBuilder WithWillResponseTopic(string willResponseTopic)
         {
-            _options.WillTopic = willTopic;
+            _options.WillResponseTopic = willResponseTopic;
             return this;
         }
 
@@ -421,38 +530,20 @@ namespace MQTTnet.Client
             _options.WillRetain = willRetain;
             return this;
         }
-        
-        public MqttClientOptionsBuilder WithWillContentType(string willContentType)
+
+        public MqttClientOptionsBuilder WithWillTopic(string willTopic)
         {
-            _options.WillContentType = willContentType;
+            _options.WillTopic = willTopic;
             return this;
         }
-        
-        public MqttClientOptionsBuilder WithWillCorrelationData(byte[] willCorrelationData)
-        {
-            _options.WillCorrelationData = willCorrelationData;
-            return this;
-        }
-        
-        public MqttClientOptionsBuilder WithWillResponseTopic(string willResponseTopic)
-        {
-            _options.WillResponseTopic = willResponseTopic;
-            return this;
-        }
-        
-        public MqttClientOptionsBuilder WithWillPayloadFormatIndicator(MqttPayloadFormatIndicator willPayloadFormatIndicator)
-        {
-            _options.WillPayloadFormatIndicator = willPayloadFormatIndicator;
-            return this;
-        }
-        
+
         public MqttClientOptionsBuilder WithWillUserProperty(string name, string value)
         {
             if (_options.WillUserProperties == null)
             {
                 _options.WillUserProperties = new List<MqttUserProperty>();
             }
-            
+
             _options.WillUserProperties.Add(new MqttUserProperty(name, value));
             return this;
         }

Source/MQTTnet/Client/Options/MqttClientOptionsBuilderTlsParameters.cs

@@ -4,19 +4,20 @@
 
 using System;
 using System.Collections.Generic;
-using System.Net.Security;
 using System.Security.Authentication;
-using System.Security.Cryptography.X509Certificates;
 
 namespace MQTTnet.Client
 {
+    [Obsolete("Use methods from MqttClientOptionsBuilder instead.")]
     public sealed class MqttClientOptionsBuilderTlsParameters
     {
+        IEnumerable<System.Security.Cryptography.X509Certificates.X509Certificate> _obsoleteCertificates;
+
         public bool UseTls { get; set; }
-        
+
         public Func<MqttClientCertificateValidationEventArgs, bool> CertificateValidationHandler { get; set; }
 
-#if NET48 || NETCOREAPP3_1 || NET5 || NET6
+#if NET48 || NETCOREAPP3_1_OR_GREATER
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12 | SslProtocols.Tls13;
 #else
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12 | (SslProtocols)0x00003000 /*Tls13*/;
@@ -25,17 +26,36 @@ namespace MQTTnet.Client
 #if WINDOWS_UWP
         public IEnumerable<IEnumerable<byte>> Certificates { get; set; }
 #else
-        public IEnumerable<X509Certificate> Certificates { get; set; }
+        [Obsolete("Use CertificatesProvider instead.")]
+        public IEnumerable<System.Security.Cryptography.X509Certificates.X509Certificate> Certificates
+        {
+            get => _obsoleteCertificates;
+            set
+            {
+                _obsoleteCertificates = value;
+
+                if (value == null)
+                {
+                    CertificatesProvider = null;
+                }
+                else
+                {
+                    CertificatesProvider = new DefaultMqttCertificatesProvider(value);
+                }
+            }
+        }
 #endif
 
-#if NETCOREAPP3_1 || NET5_0_OR_GREATER
-        public List<SslApplicationProtocol> ApplicationProtocols { get;set; }
+#if NETCOREAPP3_1_OR_GREATER
+        public List<System.Net.Security.SslApplicationProtocol> ApplicationProtocols { get; set; }
 #endif
 
-	    public bool AllowUntrustedCertificates { get; set; }
+        public bool AllowUntrustedCertificates { get; set; }
 
         public bool IgnoreCertificateChainErrors { get; set; }
 
         public bool IgnoreCertificateRevocationErrors { get; set; }
+
+        public IMqttClientCertificatesProvider CertificatesProvider { get; set; }
     }
-}
+}

Source/MQTTnet/Client/Options/MqttClientOptionsBuilderWebSocketParameters.cs

@@ -2,11 +2,13 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
 using System.Net;
 
 namespace MQTTnet.Client
 {
+    [Obsolete("Use dedicated methods in MqttClientOptionsBuilder.")]
     public class MqttClientOptionsBuilderWebSocketParameters
     {
         public IDictionary<string, string> RequestHeaders { get; set; }

Source/MQTTnet/Client/Options/MqttClientOptionsValidator.cs

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

Source/MQTTnet/Client/Options/MqttClientTcpOptionsExtensions.cs

@@ -17,7 +17,7 @@ namespace MQTTnet.Client
                 return options.Port.Value;
             }
 
-            return !options.TlsOptions.UseTls ? 1883 : 8883;
+            return !(options.TlsOptions?.UseTls ?? false) ? 1883 : 8883;
         }
     }
 }

Source/MQTTnet/Client/Options/MqttClientTlsOptions.cs

@@ -4,6 +4,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Net.Security;
 using System.Security.Authentication;
 using System.Security.Cryptography.X509Certificates;
 
@@ -23,19 +24,31 @@ namespace MQTTnet.Client
 
         public X509RevocationMode RevocationMode { get; set; } = X509RevocationMode.Online;
 
-#if WINDOWS_UWP
-        public List<byte[]> Certificates { get; set; }
-#else
-        public List<X509Certificate> Certificates { get; set; }
+        /// <summary>
+        ///     Gets or sets the provider for certificates.
+        ///     This provider gets called whenever the client wants to connect
+        ///     with the server and requires certificates for authentication.
+        ///     The implementation may return different certificates each time.
+        /// </summary>
+        public IMqttClientCertificatesProvider ClientCertificatesProvider { get; set; }
+
+#if NETCOREAPP3_1_OR_GREATER
+        public List<SslApplicationProtocol> ApplicationProtocols { get; set; }
+
+        public CipherSuitesPolicy CipherSuitesPolicy { get; set; }
+
+        public EncryptionPolicy EncryptionPolicy { get; set; } = EncryptionPolicy.RequireEncryption;
+
+        public bool AllowRenegotiation { get; set; } = true;
 #endif
 
-#if NETCOREAPP3_1 || NET5_0_OR_GREATER
-        public List<System.Net.Security.SslApplicationProtocol> ApplicationProtocols { get; set; }
-        
-        public System.Net.Security.CipherSuitesPolicy CipherSuitesPolicy { get; set; }
-#endif
+        /// <summary>
+        ///     Gets or sets the target host.
+        ///     If the value is null or empty the same host as the TCP socket host will be used.
+        /// </summary>
+        public string TargetHost { get; set; }
 
-#if NET48 || NETCOREAPP3_1 || NET5 || NET6
+#if NET48 || NETCOREAPP3_1_OR_GREATER
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12 | SslProtocols.Tls13;
 #else
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12 | (SslProtocols)0x00003000 /*Tls13*/;