Merge branch 'master' of https://github.com/chkr1011/MQTTnet

Feature msbuild conditions

Build/MQTTnet.AspNetCore.nuspec

@@ -10,15 +10,14 @@
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <description>This is a support library to integrate MQTTnet into AspNetCore.</description>
-    <releaseNotes>* For more release notes please check the MQTTnet release notes.
-    </releaseNotes>
+    <releaseNotes>For release notes please go to MQTTnet release notes (https://www.nuget.org/packages/MQTTnet/).</releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2018</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin</tags>
     <dependencies>
-      <dependency id="MQTTnet" version="2.8.4" />
-      <dependency id="Microsoft.AspNetCore.Connections.Abstractions" version="2.1.0" />
-      <dependency id="Microsoft.AspNetCore.WebSockets" version="2.0.1" />
-      <dependency id="Microsoft.Extensions.Hosting.Abstractions" version="2.0.1" />
+      <dependency id="MQTTnet" version="2.8.5" />
+      <dependency id="Microsoft.AspNetCore.Connections.Abstractions" version="2.1.3" />
+      <dependency id="Microsoft.AspNetCore.WebSockets" version="2.1.1" />
+      <dependency id="Microsoft.Extensions.Hosting.Abstractions" version="2.1.1" />
     </dependencies>
   </metadata>
 

Build/MQTTnet.Extensions.ManagedClient.nuspec

@@ -10,12 +10,11 @@
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <description>This is an extension library which provides a managed MQTT client with additional features using MQTTnet.</description>
-    <releaseNotes>* For more release notes please check the MQTTnet release notes.
-    </releaseNotes>
+    <releaseNotes>For release notes please go to MQTTnet release notes (https://www.nuget.org/packages/MQTTnet/).</releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2018</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin</tags> 
     <dependencies>
-      <dependency id="MQTTnet" version="2.8.4" />
+      <dependency id="MQTTnet" version="2.8.5" />
     </dependencies>
   </metadata>
 

Build/MQTTnet.Extensions.Rpc.nuspec

@@ -10,12 +10,11 @@
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <description>This is an extension library which allows executing synchronous device calls including a response using MQTTnet.</description>
-    <releaseNotes>* For more release notes please check the MQTTnet release notes.
-    </releaseNotes>
+    <releaseNotes>For release notes please go to MQTTnet release notes (https://www.nuget.org/packages/MQTTnet/).</releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2018</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin</tags> 
     <dependencies>
-      <dependency id="MQTTnet" version="2.8.4" />
+      <dependency id="MQTTnet" version="2.8.5" />
     </dependencies>
   </metadata>
 

Build/MQTTnet.nuspec

@@ -10,7 +10,19 @@
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <description>MQTTnet is a high performance .NET library for MQTT based communication. It provides a MQTT client and a MQTT server (broker).</description>
-    <releaseNotes>* [Client] Fixed a deadlock when an exception is fired while connecting (thanks to @malibVB).
+    <releaseNotes> * [Core] Updated nuget packages due to security issues.
+* [Client] Fixed wrong behavior of publish method when client is disconnecting (thanks to @PaulFake).
+* [Client] Added readonly property for accessing options.
+* [ManagedClient] Added max pending messages count option.
+* [ManagedClient] Add pending messages overflow strategy option.
+* [ManagedClient] Fixed an issue which deletes the wrong message from the internal queue (thanks to @PaulFake).
+* [ManagedClient] Added readonly property for accessing options.
+* [Server] Added new method which exposes all retained messages.
+* [Server] Removed (wrong) setter from the server options interface.
+* [Server] Fixed cpu spike in case a client disconnects (issue 421).
+* [Server] Fixed concurrent sends with Aspnetcore.Connections.Abstractions based transport.
+* [Server] Fixed wrong retain flag when distributing application messages (thanks to @trev0115).
+* [Server] Fixed issue which closes a connection when reconnecting with the same client ID (thanks to @fogzot).
     </releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2018</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin</tags> 
@@ -19,7 +31,7 @@
         <dependency id="NETStandard.Library" version="1.3.0" />
         <dependency id="System.Net.Security" version="4.3.2" />
         <dependency id="System.Net.WebSockets" version="4.3.0" />
-        <dependency id="System.Net.WebSockets.Client" version="4.3.1" />      
+        <dependency id="System.Net.WebSockets.Client" version="4.3.2" />      
       </group>
       <group targetFramework="netstandard2.0">
         <dependency id="NETStandard.Library" version="2.0.0" />
@@ -28,7 +40,7 @@
         <dependency id="System.Net.WebSockets.Client" version="4.3.2" />
       </group>
       <group targetFramework="uap10.0">
-        <dependency id="Microsoft.NETCore.UniversalWindowsPlatform" version="6.1.4" />
+        <dependency id="Microsoft.NETCore.UniversalWindowsPlatform" version="6.1.9" />
       </group>
       <group targetFramework="net452">
       </group>

MQTTnet.noUWP.sln

@@ -0,0 +1,222 @@
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+EndProject
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+	ProjectSection(SolutionItems) = preProject
+		Build\build.ps1 = Build\build.ps1
+		Build\MQTTnet.AspNetCore.nuspec = Build\MQTTnet.AspNetCore.nuspec
+		Build\MQTTnet.Extensions.ManagedClient.nuspec = Build\MQTTnet.Extensions.ManagedClient.nuspec
+		Build\MQTTnet.Extensions.Rpc.nuspec = Build\MQTTnet.Extensions.Rpc.nuspec
+		Build\MQTTnet.nuspec = Build\MQTTnet.nuspec
+		Build\upload.ps1 = Build\upload.ps1
+	EndProjectSection
+EndProject
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+	ProjectSection(SolutionItems) = preProject
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+		appveyor.yml = appveyor.yml
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+		README.md = README.md
+	EndProjectSection
+EndProject
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+EndProject
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+EndProject
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+EndProject
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+	EndGlobalSection
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+		{998D04DD-7CB0-45F5-A393-E2495C16399E}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{998D04DD-7CB0-45F5-A393-E2495C16399E}.Debug|x86.Build.0 = Debug|Any CPU
+		{998D04DD-7CB0-45F5-A393-E2495C16399E}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{998D04DD-7CB0-45F5-A393-E2495C16399E}.Release|Any CPU.Build.0 = Release|Any CPU
+		{998D04DD-7CB0-45F5-A393-E2495C16399E}.Release|ARM.ActiveCfg = Release|Any CPU
+		{998D04DD-7CB0-45F5-A393-E2495C16399E}.Release|ARM.Build.0 = Release|Any CPU
+		{998D04DD-7CB0-45F5-A393-E2495C16399E}.Release|x64.ActiveCfg = Release|Any CPU
+		{998D04DD-7CB0-45F5-A393-E2495C16399E}.Release|x64.Build.0 = Release|Any CPU
+		{998D04DD-7CB0-45F5-A393-E2495C16399E}.Release|x86.ActiveCfg = Release|Any CPU
+		{998D04DD-7CB0-45F5-A393-E2495C16399E}.Release|x86.Build.0 = Release|Any CPU
+		{C400533A-8EBA-4F0B-BF4D-295C3708604B}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{C400533A-8EBA-4F0B-BF4D-295C3708604B}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{C400533A-8EBA-4F0B-BF4D-295C3708604B}.Debug|ARM.ActiveCfg = Debug|Any CPU
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+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(NestedProjects) = preSolution
+		{A7FF0C91-25DE-4BA6-B39E-F54E8DADF1CC} = {9248C2E1-B9D6-40BF-81EC-86004D7765B4}
+		{3587E506-55A2-4EB3-99C7-DC01E42D25D2} = {32A630A7-2598-41D7-B625-204CD906F5FB}
+		{3D283AAD-AAA8-4339-8394-52F80B6304DB} = {9248C2E1-B9D6-40BF-81EC-86004D7765B4}
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+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {07536672-5CBC-4BE3-ACE0-708A431A7894}
+	EndGlobalSection
+EndGlobal

README.md

@@ -25,7 +25,7 @@ MQTTnet is a high performance .NET library for MQTT based communication. It prov
 * Performance optimized (processing ~70.000 messages / second)*
 * Interfaces included for mocking and testing
 * Access to internal trace messages
-* Unit tested (~90 tests)
+* Unit tested (~100 tests)
 
 \* Tested on local machine (Intel i7 8700K) with MQTTnet client and server running in the same process using the TCP channel. The app for verification is part of this repository and stored in _/Tests/MQTTnet.TestApp.NetCore_.
 
@@ -85,12 +85,13 @@ This project also listed at Open Collective (https://opencollective.com/mqttnet)
 
 This library is used in the following projects:
 
+* Azure Functions MQTT Bindings, [CaseOnline.Azure.WebJobs.Extensions.Mqtt](https://github.com/keesschollaart81/CaseOnline.Azure.WebJobs.Extensions.Mqtt/)
 * HA4IoT (Open Source Home Automation system for .NET, <https://github.com/chkr1011/HA4IoT>)
 * MQTT Client Rx (Wrapper for Reactive Extensions, <https://github.com/1iveowl/MQTTClient.rx>)
 * MQTT Tester (MQTT client test app for [Android](https://play.google.com/store/apps/details?id=com.liveowl.mqtttester) and [iOS](https://itunes.apple.com/us/app/mqtt-tester/id1278621826?mt=8))
 * Wirehome.Core (Open Source Home Automation system for .NET Core, <https://github.com/chkr1011/Wirehome.Core>)
 
-If you use this library and want to see your project here please let me know.
+If you use this library and want to see your project here please create a pull request.
 
 ## MIT License
 

Source/MQTTnet.AspnetCore/MQTTnet.AspNetCore.csproj

@@ -14,9 +14,9 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.AspNetCore.Connections.Abstractions" Version="2.1.0" />
-    <PackageReference Include="Microsoft.AspNetCore.WebSockets" Version="2.0.1" />
-    <PackageReference Include="Microsoft.Extensions.Hosting.Abstractions" Version="2.0.1" />
+    <PackageReference Include="Microsoft.AspNetCore.Connections.Abstractions" Version="2.1.3" />
+    <PackageReference Include="Microsoft.AspNetCore.WebSockets" Version="2.1.1" />
+    <PackageReference Include="Microsoft.Extensions.Hosting.Abstractions" Version="2.1.1" />
   </ItemGroup>
 
   <ItemGroup>

Source/MQTTnet.AspnetCore/MqttConnectionContext.cs

@@ -1,6 +1,7 @@
 using Microsoft.AspNetCore.Connections;
 using MQTTnet.Adapter;
 using MQTTnet.AspNetCore.Client.Tcp;
+using MQTTnet.Exceptions;
 using MQTTnet.Packets;
 using MQTTnet.Serializer;
 using System;
@@ -26,6 +27,8 @@ namespace MQTTnet.AspNetCore
         public event EventHandler ReadingPacketStarted;
         public event EventHandler ReadingPacketCompleted;
 
+        private readonly SemaphoreSlim _writerSemaphore = new SemaphoreSlim(1, 1);
+
         public Task ConnectAsync(TimeSpan timeout, CancellationToken cancellationToken)
         {
             if (Connection is TcpConnection tcp && !tcp.IsConnected)
@@ -59,7 +62,7 @@ namespace MQTTnet.AspNetCore
                     }
                     else
                     {
-                        readResult = await readTask;
+                        readResult = await readTask.ConfigureAwait(false);
                     }
 
                     var buffer = readResult.Buffer;
@@ -83,7 +86,7 @@ namespace MQTTnet.AspNetCore
                         }
                         else if (readResult.IsCompleted)
                         {
-                            break;
+                            throw new MqttCommunicationException("Connection Aborted");
                         }
                     }
                     finally
@@ -104,10 +107,20 @@ namespace MQTTnet.AspNetCore
             return null;
         }
 
-        public Task SendPacketAsync(MqttBasePacket packet, CancellationToken cancellationToken)
+        public async Task SendPacketAsync(MqttBasePacket packet, CancellationToken cancellationToken)
         {
-            var buffer = PacketSerializer.Serialize(packet);
-            return Connection.Transport.Output.WriteAsync(buffer.AsMemory(), cancellationToken).AsTask();
+            var buffer = PacketSerializer.Serialize(packet).AsMemory();
+            var output = Connection.Transport.Output;
+
+            await _writerSemaphore.WaitAsync(cancellationToken).ConfigureAwait(false);
+            try
+            {
+                await output.WriteAsync(buffer, cancellationToken).ConfigureAwait(false);
+            }
+            finally
+            {
+                _writerSemaphore.Release();
+            }
         }
 
         public void Dispose()

Source/MQTTnet.Extensions.ManagedClient/ApplicationMessageSkippedEventArgs.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace MQTTnet.Extensions.ManagedClient
+{
+    public class ApplicationMessageSkippedEventArgs : EventArgs
+    {
+        public ApplicationMessageSkippedEventArgs(ManagedMqttApplicationMessage applicationMessage)
+        {
+            ApplicationMessage = applicationMessage ?? throw new ArgumentNullException(nameof(applicationMessage));
+        }
+
+        public ManagedMqttApplicationMessage ApplicationMessage { get; }
+    }
+}

Source/MQTTnet.Extensions.ManagedClient/IManagedMqttClient.cs

@@ -10,11 +10,13 @@ namespace MQTTnet.Extensions.ManagedClient
         bool IsStarted { get; }
         bool IsConnected { get; }
         int PendingApplicationMessagesCount { get; }
+        IManagedMqttClientOptions Options { get; }
 
         event EventHandler<MqttClientConnectedEventArgs> Connected;
         event EventHandler<MqttClientDisconnectedEventArgs> Disconnected;
 
         event EventHandler<ApplicationMessageProcessedEventArgs> ApplicationMessageProcessed;
+        event EventHandler<ApplicationMessageSkippedEventArgs> ApplicationMessageSkipped;
 
         event EventHandler<MqttManagedProcessFailedEventArgs> ConnectingFailed;
         event EventHandler<MqttManagedProcessFailedEventArgs> SynchronizingSubscriptionsFailed;

Source/MQTTnet.Extensions.ManagedClient/IManagedMqttClientOptions.cs

@@ -1,5 +1,6 @@
 using System;
 using MQTTnet.Client;
+using MQTTnet.Server;
 
 namespace MQTTnet.Extensions.ManagedClient
 {
@@ -12,5 +13,9 @@ namespace MQTTnet.Extensions.ManagedClient
         TimeSpan ConnectionCheckInterval { get; }
 
         IManagedMqttClientStorage Storage { get; }
+
+        int MaxPendingMessages { get; }
+
+        MqttPendingMessagesOverflowStrategy PendingMessagesOverflowStrategy { get; }
     }
 }

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

@@ -1,7 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard1.3;netstandard2.0;net452;net461</TargetFrameworks>
+    <TargetFrameworks>netstandard1.3;netstandard2.0</TargetFrameworks>
+    <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461</TargetFrameworks>
     <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' AND '$(MSBuildRuntimeType)' != 'Core'">$(TargetFrameworks);uap10.0</TargetFrameworks>
     <Product />
     <Company />

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClient.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
@@ -7,13 +6,17 @@ using System.Threading.Tasks;
 using MQTTnet.Client;
 using MQTTnet.Diagnostics;
 using MQTTnet.Exceptions;
+using MQTTnet.Internal;
 using MQTTnet.Protocol;
+using MQTTnet.Server;
+using MqttClientConnectedEventArgs = MQTTnet.Client.MqttClientConnectedEventArgs;
+using MqttClientDisconnectedEventArgs = MQTTnet.Client.MqttClientDisconnectedEventArgs;
 
 namespace MQTTnet.Extensions.ManagedClient
 {
     public class ManagedMqttClient : IManagedMqttClient
     {
-        private readonly BlockingCollection<ManagedMqttApplicationMessage> _messageQueue = new BlockingCollection<ManagedMqttApplicationMessage>();
+        private readonly BlockingQueue<ManagedMqttApplicationMessage> _messageQueue = new BlockingQueue<ManagedMqttApplicationMessage>();
         private readonly Dictionary<string, MqttQualityOfServiceLevel> _subscriptions = new Dictionary<string, MqttQualityOfServiceLevel>();
         private readonly HashSet<string> _unsubscriptions = new HashSet<string>();
 
@@ -24,8 +27,7 @@ namespace MQTTnet.Extensions.ManagedClient
         private CancellationTokenSource _publishingCancellationToken;
 
         private ManagedMqttClientStorageManager _storageManager;
-        private IManagedMqttClientOptions _options;
-
+        
         private bool _subscriptionsNotPushed;
 
         public ManagedMqttClient(IMqttClient mqttClient, IMqttNetChildLogger logger)
@@ -44,12 +46,14 @@ namespace MQTTnet.Extensions.ManagedClient
         public bool IsConnected => _mqttClient.IsConnected;
         public bool IsStarted => _connectionCancellationToken != null;
         public int PendingApplicationMessagesCount => _messageQueue.Count;
+        public IManagedMqttClientOptions Options { get; private set; }
 
         public event EventHandler<MqttClientConnectedEventArgs> Connected;
         public event EventHandler<MqttClientDisconnectedEventArgs> Disconnected;
 
         public event EventHandler<MqttApplicationMessageReceivedEventArgs> ApplicationMessageReceived;
         public event EventHandler<ApplicationMessageProcessedEventArgs> ApplicationMessageProcessed;
+        public event EventHandler<ApplicationMessageSkippedEventArgs> ApplicationMessageSkipped;
 
         public event EventHandler<MqttManagedProcessFailedEventArgs> ConnectingFailed;
         public event EventHandler<MqttManagedProcessFailedEventArgs> SynchronizingSubscriptionsFailed;
@@ -66,16 +70,16 @@ namespace MQTTnet.Extensions.ManagedClient
 
             if (_connectionCancellationToken != null) throw new InvalidOperationException("The managed client is already started.");
 
-            _options = options;
+            Options = options;
 
-            if (_options.Storage != null)
+            if (Options.Storage != null)
             {
-                _storageManager = new ManagedMqttClientStorageManager(_options.Storage);
+                _storageManager = new ManagedMqttClientStorageManager(Options.Storage);
                 var messages = await _storageManager.LoadQueuedMessagesAsync().ConfigureAwait(false);
 
                 foreach (var message in messages)
                 {
-                    _messageQueue.Add(message);
+                    _messageQueue.Enqueue(message);
                 }
             }
 
@@ -93,10 +97,7 @@ namespace MQTTnet.Extensions.ManagedClient
             StopPublishing();
             StopMaintainingConnection();
 
-            while (_messageQueue.Any())
-            {
-                _messageQueue.Take();
-            }
+            _messageQueue.Clear();
 
             return Task.FromResult(0);
         }
@@ -112,12 +113,38 @@ namespace MQTTnet.Extensions.ManagedClient
         {
             if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
 
-            if (_storageManager != null)
+            ManagedMqttApplicationMessage removedMessage = null;
+            lock (_messageQueue)
             {
-                await _storageManager.AddAsync(applicationMessage).ConfigureAwait(false);
+                if (_messageQueue.Count >= Options.MaxPendingMessages)
+                {
+                    if (Options.PendingMessagesOverflowStrategy == MqttPendingMessagesOverflowStrategy.DropNewMessage)
+                    {
+                        _logger.Verbose("Skipping publish of new application message because internal queue is full.");
+                        ApplicationMessageSkipped?.Invoke(this, new ApplicationMessageSkippedEventArgs(applicationMessage));
+                        return;
+                    }
+
+                    if (Options.PendingMessagesOverflowStrategy == MqttPendingMessagesOverflowStrategy.DropOldestQueuedMessage)
+                    {
+                        removedMessage = _messageQueue.RemoveFirst();
+                        _logger.Verbose("Removed oldest application message from internal queue because it is full.");
+                        ApplicationMessageSkipped?.Invoke(this, new ApplicationMessageSkippedEventArgs(removedMessage));
+                    }
+                }
+
+                _messageQueue.Enqueue(applicationMessage);
             }
 
-            _messageQueue.Add(applicationMessage);
+            if (_storageManager != null)
+            {
+                if (removedMessage != null)
+                {
+                    await _storageManager.RemoveAsync(removedMessage).ConfigureAwait(false);
+                }
+
+                await _storageManager.AddAsync(applicationMessage).ConfigureAwait(false);
+            }
         }
 
         public Task SubscribeAsync(IEnumerable<TopicFilter> topicFilters)
@@ -157,7 +184,6 @@ namespace MQTTnet.Extensions.ManagedClient
 
         public void Dispose()
         {
-            _messageQueue?.Dispose();
             _connectionCancellationToken?.Dispose();
             _publishingCancellationToken?.Dispose();
         }
@@ -193,7 +219,7 @@ namespace MQTTnet.Extensions.ManagedClient
                 if (connectionState == ReconnectionResult.NotConnected)
                 {
                     StopPublishing();
-                    await Task.Delay(_options.AutoReconnectDelay, cancellationToken).ConfigureAwait(false);
+                    await Task.Delay(Options.AutoReconnectDelay, cancellationToken).ConfigureAwait(false);
                     return;
                 }
 
@@ -206,7 +232,7 @@ namespace MQTTnet.Extensions.ManagedClient
 
                 if (connectionState == ReconnectionResult.StillConnected)
                 {
-                    await Task.Delay(_options.ConnectionCheckInterval, cancellationToken).ConfigureAwait(false);
+                    await Task.Delay(Options.ConnectionCheckInterval, cancellationToken).ConfigureAwait(false);
                 }
             }
             catch (OperationCanceledException)
@@ -228,7 +254,15 @@ namespace MQTTnet.Extensions.ManagedClient
             {
                 while (!cancellationToken.IsCancellationRequested && _mqttClient.IsConnected)
                 {
-                    var message = _messageQueue.Take(cancellationToken);
+                    //Peek at the message without dequeueing in order to prevent the
+                    //possibility of the queue growing beyond the configured cap.
+                    //Previously, messages could be re-enqueued if there was an
+                    //exception, and this re-enqueueing did not honor the cap.
+                    //Furthermore, because re-enqueueing would shuffle the order
+                    //of the messages, the DropOldestQueuedMessage strategy would
+                    //be unable to know which message is actually the oldest and would
+                    //instead drop the first item in the queue.
+                    var message = _messageQueue.PeekAndWait();
                     if (message == null)
                     {
                         continue;
@@ -258,6 +292,16 @@ namespace MQTTnet.Extensions.ManagedClient
             try
             {
                 _mqttClient.PublishAsync(message.ApplicationMessage).GetAwaiter().GetResult();
+                lock (_messageQueue) //lock to avoid conflict with this.PublishAsync
+                {
+                    //While publishing this message, this.PublishAsync could have booted this
+                    //message off the queue to make room for another (when using a cap
+                    //with the DropOldestQueuedMessage strategy).  If the first item
+                    //in the queue is equal to this message, then it's safe to remove
+                    //it from the queue.  If not, that means this.PublishAsync has already
+                    //removed it, in which case we don't want to do anything.
+                    _messageQueue.RemoveFirst(i => i.Id.Equals(message.Id));
+                }
                 _storageManager?.RemoveAsync(message).GetAwaiter().GetResult();
             }
             catch (MqttCommunicationException exception)
@@ -266,9 +310,19 @@ namespace MQTTnet.Extensions.ManagedClient
 
                 _logger.Warning(exception, $"Publishing application ({message.Id}) message failed.");
 
-                if (message.ApplicationMessage.QualityOfServiceLevel > MqttQualityOfServiceLevel.AtMostOnce)
+                if (message.ApplicationMessage.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
                 {
-                    _messageQueue.Add(message);
+                    //If QoS 0, we don't want this message to stay on the queue.
+                    //If QoS 1 or 2, it's possible that, when using a cap, this message
+                    //has been booted off the queue by this.PublishAsync, in which case this
+                    //thread will not continue to try to publish it. While this does
+                    //contradict the expected behavior of QoS 1 and 2, that's also true
+                    //for the usage of a message queue cap, so it's still consistent
+                    //with prior behavior in that way.
+                    lock (_messageQueue) //lock to avoid conflict with this.PublishAsync
+                    {
+                        _messageQueue.RemoveFirst(i => i.Id.Equals(message.Id));
+                    }
                 }
             }
             catch (Exception exception)
@@ -334,7 +388,7 @@ namespace MQTTnet.Extensions.ManagedClient
 
             try
             {
-                await _mqttClient.ConnectAsync(_options.ClientOptions).ConfigureAwait(false);
+                await _mqttClient.ConnectAsync(Options.ClientOptions).ConfigureAwait(false);
                 return ReconnectionResult.Reconnected;
             }
             catch (Exception exception)

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClientOptions.cs

@@ -1,5 +1,6 @@
 using System;
 using MQTTnet.Client;
+using MQTTnet.Server;
 
 namespace MQTTnet.Extensions.ManagedClient
 {
@@ -12,5 +13,9 @@ namespace MQTTnet.Extensions.ManagedClient
         public TimeSpan ConnectionCheckInterval { get; set; } = TimeSpan.FromSeconds(1);
 
         public IManagedMqttClientStorage Storage { get; set; }
+
+        public int MaxPendingMessages { get; set; } = int.MaxValue;
+
+        public MqttPendingMessagesOverflowStrategy PendingMessagesOverflowStrategy { get; set; } = MqttPendingMessagesOverflowStrategy.DropNewMessage;
     }
 }

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClientOptionsBuilder.cs

@@ -1,5 +1,6 @@
 using System;
 using MQTTnet.Client;
+using MQTTnet.Server;
 
 namespace MQTTnet.Extensions.ManagedClient
 {
@@ -8,6 +9,18 @@ namespace MQTTnet.Extensions.ManagedClient
         private readonly ManagedMqttClientOptions _options = new ManagedMqttClientOptions();
         private MqttClientOptionsBuilder _clientOptionsBuilder;
 
+        public ManagedMqttClientOptionsBuilder WithMaxPendingMessages(int value)
+        {
+            _options.MaxPendingMessages = value;
+            return this;
+        }
+
+        public ManagedMqttClientOptionsBuilder WithPendingMessagesOverflowStrategy(MqttPendingMessagesOverflowStrategy value)
+        {
+            _options.PendingMessagesOverflowStrategy = value;
+            return this;
+        }
+
         public ManagedMqttClientOptionsBuilder WithAutoReconnectDelay(TimeSpan value)
         {
             _options.AutoReconnectDelay = value;

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClientStorageManager.cs

@@ -28,6 +28,8 @@ namespace MQTTnet.Extensions.ManagedClient
 
         public async Task AddAsync(ManagedMqttApplicationMessage applicationMessage)
         {
+            if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
+
             using (await _messagesLock.LockAsync(CancellationToken.None).ConfigureAwait(false))
             {
                 _messages.Add(applicationMessage);
@@ -37,6 +39,8 @@ namespace MQTTnet.Extensions.ManagedClient
 
         public async Task RemoveAsync(ManagedMqttApplicationMessage applicationMessage)
         {
+            if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
+
             using (await _messagesLock.LockAsync(CancellationToken.None).ConfigureAwait(false))
             {
                 var index = _messages.IndexOf(applicationMessage);

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

@@ -1,7 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard1.3;netstandard2.0;net452;net461</TargetFrameworks>
+    <TargetFrameworks>netstandard1.3;netstandard2.0</TargetFrameworks>
+    <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461</TargetFrameworks>
     <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' AND '$(MSBuildRuntimeType)' != 'Core'">$(TargetFrameworks);uap10.0</TargetFrameworks>
     <Product />
     <Company />

Source/MQTTnet/Client/IMqttClient.cs

@@ -7,6 +7,7 @@ namespace MQTTnet.Client
     public interface IMqttClient : IApplicationMessageReceiver, IApplicationMessagePublisher, IDisposable
     {
         bool IsConnected { get; }
+        IMqttClientOptions Options { get; }
 
         event EventHandler<MqttClientConnectedEventArgs> Connected;
         event EventHandler<MqttClientDisconnectedEventArgs> Disconnected;

Source/MQTTnet/Client/MqttClient.cs

@@ -23,13 +23,12 @@ namespace MQTTnet.Client
         private readonly IMqttClientAdapterFactory _adapterFactory;
         private readonly IMqttNetChildLogger _logger;
 
-        private IMqttClientOptions _options;
         private CancellationTokenSource _cancellationTokenSource;
         internal Task _packetReceiverTask;
         internal Task _keepAliveMessageSenderTask;
         private IMqttChannelAdapter _adapter;
         private bool _cleanDisconnectInitiated;
-        private int _disconnectGate;
+        private long _disconnectGate;
 
         public MqttClient(IMqttClientAdapterFactory channelFactory, IMqttNetLogger logger)
         {
@@ -44,6 +43,7 @@ namespace MQTTnet.Client
         public event EventHandler<MqttApplicationMessageReceivedEventArgs> ApplicationMessageReceived;
 
         public bool IsConnected { get; private set; }
+        public IMqttClientOptions Options { get; private set; }
 
         public async Task<MqttClientConnectResult> ConnectAsync(IMqttClientOptions options)
         {
@@ -54,7 +54,8 @@ namespace MQTTnet.Client
 
             try
             {
-                _options = options;
+                Options = options;
+
                 _packetIdentifierProvider.Reset();
                 _packetDispatcher.Reset();
 
@@ -62,8 +63,8 @@ namespace MQTTnet.Client
                 _disconnectGate = 0;
                 _adapter = _adapterFactory.CreateClientAdapter(options, _logger);
 
-                _logger.Verbose($"Trying to connect with server ({_options.ChannelOptions}).");
-                await _adapter.ConnectAsync(_options.CommunicationTimeout, _cancellationTokenSource.Token).ConfigureAwait(false);
+                _logger.Verbose($"Trying to connect with server ({Options.ChannelOptions}).");
+                await _adapter.ConnectAsync(Options.CommunicationTimeout, _cancellationTokenSource.Token).ConfigureAwait(false);
                 _logger.Verbose("Connection with server established.");
 
                 StartReceivingPackets(_cancellationTokenSource.Token);
@@ -73,7 +74,7 @@ namespace MQTTnet.Client
 
                 _sendTracker.Restart();
 
-                if (_options.KeepAlivePeriod != TimeSpan.Zero)
+                if (Options.KeepAlivePeriod != TimeSpan.Zero)
                 {
                     StartSendingKeepAliveMessages(_cancellationTokenSource.Token);
                 }
@@ -139,7 +140,7 @@ namespace MQTTnet.Client
             return subscribePacket.TopicFilters.Select((t, i) => new MqttSubscribeResult(t, response.SubscribeReturnCodes[i])).ToList();
         }
 
-        public async Task UnsubscribeAsync(IEnumerable<string> topicFilters)
+        public Task UnsubscribeAsync(IEnumerable<string> topicFilters)
         {
             if (topicFilters == null) throw new ArgumentNullException(nameof(topicFilters));
 
@@ -151,7 +152,7 @@ namespace MQTTnet.Client
                 TopicFilters = topicFilters.ToList()
             };
 
-            await SendAndReceiveAsync<MqttUnsubAckPacket>(unsubscribePacket, _cancellationTokenSource.Token).ConfigureAwait(false);
+            return SendAndReceiveAsync<MqttUnsubAckPacket>(unsubscribePacket, _cancellationTokenSource.Token);
         }
 
         public Task PublishAsync(MqttApplicationMessage applicationMessage)
@@ -197,11 +198,11 @@ namespace MQTTnet.Client
         {
             var connectPacket = new MqttConnectPacket
             {
-                ClientId = _options.ClientId,
-                Username = _options.Credentials?.Username,
-                Password = _options.Credentials?.Password,
-                CleanSession = _options.CleanSession,
-                KeepAlivePeriod = (ushort)_options.KeepAlivePeriod.TotalSeconds,
+                ClientId = Options.ClientId,
+                Username = Options.Credentials?.Username,
+                Password = Options.Credentials?.Password,
+                CleanSession = Options.CleanSession,
+                KeepAlivePeriod = (ushort)Options.KeepAlivePeriod.TotalSeconds,
                 WillMessage = willApplicationMessage
             };
 
@@ -216,7 +217,7 @@ namespace MQTTnet.Client
 
         private void ThrowIfNotConnected()
         {
-            if (!IsConnected) throw new MqttCommunicationException("The client is not connected.");
+            if (!IsConnected || Interlocked.Read(ref _disconnectGate) == 1) throw new MqttCommunicationException("The client is not connected.");
         }
 
         private void ThrowIfConnected(string message)
@@ -234,14 +235,14 @@ namespace MQTTnet.Client
 
             try
             {
-                await WaitForTaskAsync(_packetReceiverTask, sender).ConfigureAwait(false);
-                await WaitForTaskAsync(_keepAliveMessageSenderTask, sender).ConfigureAwait(false);
-
                 if (_adapter != null)
                 {
-                    await _adapter.DisconnectAsync(_options.CommunicationTimeout, CancellationToken.None).ConfigureAwait(false);
+                    await _adapter.DisconnectAsync(Options.CommunicationTimeout, CancellationToken.None).ConfigureAwait(false);
                 }
 
+                await WaitForTaskAsync(_packetReceiverTask, sender).ConfigureAwait(false);
+                await WaitForTaskAsync(_keepAliveMessageSenderTask, sender).ConfigureAwait(false);
+                
                 _logger.Verbose("Disconnected from adapter.");
             }
             catch (Exception adapterException)
@@ -303,7 +304,7 @@ namespace MQTTnet.Client
             try
             {
                 await _adapter.SendPacketAsync(requestPacket, cancellationToken).ConfigureAwait(false);
-                var respone = await Internal.TaskExtensions.TimeoutAfterAsync(ct => packetAwaiter.Task, _options.CommunicationTimeout, cancellationToken).ConfigureAwait(false);
+                var respone = await Internal.TaskExtensions.TimeoutAfterAsync(ct => packetAwaiter.Task, Options.CommunicationTimeout, cancellationToken).ConfigureAwait(false);
 
                 return (TResponsePacket)respone;
             }
@@ -320,16 +321,16 @@ namespace MQTTnet.Client
 
         private async Task SendKeepAliveMessagesAsync(CancellationToken cancellationToken)
         {
-            _logger.Verbose("Start sending keep alive packets.");
-
             try
             {
+                _logger.Verbose("Start sending keep alive packets.");
+
                 while (!cancellationToken.IsCancellationRequested)
                 {
-                    var keepAliveSendInterval = TimeSpan.FromSeconds(_options.KeepAlivePeriod.TotalSeconds * 0.75);
-                    if (_options.KeepAliveSendInterval.HasValue)
+                    var keepAliveSendInterval = TimeSpan.FromSeconds(Options.KeepAlivePeriod.TotalSeconds * 0.75);
+                    if (Options.KeepAliveSendInterval.HasValue)
                     {
-                        keepAliveSendInterval = _options.KeepAliveSendInterval.Value;
+                        keepAliveSendInterval = Options.KeepAliveSendInterval.Value;
                     }
 
                     var waitTime = keepAliveSendInterval - _sendTracker.Elapsed;
@@ -374,10 +375,10 @@ namespace MQTTnet.Client
 
         private async Task ReceivePacketsAsync(CancellationToken cancellationToken)
         {
-            _logger.Verbose("Start receiving packets.");
-
             try
             {
+                _logger.Verbose("Start receiving packets.");
+
                 while (!cancellationToken.IsCancellationRequested)
                 {
                     var packet = await _adapter.ReceivePacketAsync(TimeSpan.Zero, cancellationToken)
@@ -500,7 +501,7 @@ namespace MQTTnet.Client
                 () => ReceivePacketsAsync(cancellationToken),
                 cancellationToken,
                 TaskCreationOptions.LongRunning, 
-                TaskScheduler.Default);
+                TaskScheduler.Default).Unwrap();
         }
 
         private void StartSendingKeepAliveMessages(CancellationToken cancellationToken)
@@ -509,7 +510,7 @@ namespace MQTTnet.Client
                 () => SendKeepAliveMessagesAsync(cancellationToken),
                 cancellationToken,
                 TaskCreationOptions.LongRunning,
-                TaskScheduler.Default);
+                TaskScheduler.Default).Unwrap();
         }
 
         private void FireApplicationMessageReceivedEvent(MqttPublishPacket publishPacket)
@@ -517,7 +518,7 @@ namespace MQTTnet.Client
             try
             {
                 var applicationMessage = publishPacket.ToApplicationMessage();
-                ApplicationMessageReceived?.Invoke(this, new MqttApplicationMessageReceivedEventArgs(_options.ClientId, applicationMessage));
+                ApplicationMessageReceived?.Invoke(this, new MqttApplicationMessageReceivedEventArgs(Options.ClientId, applicationMessage));
             }
             catch (Exception exception)
             {
@@ -551,4 +552,4 @@ namespace MQTTnet.Client
             return Interlocked.CompareExchange(ref _disconnectGate, 1, 0) != 0;
         }
     }
-}
+}

Source/MQTTnet/Implementations/MqttTcpChannel.cs

@@ -2,7 +2,6 @@
 using System;
 using System.Net.Security;
 using System.Net.Sockets;
-using System.Security.Authentication;
 using System.Security.Cryptography.X509Certificates;
 using System.Threading.Tasks;
 using System.IO;
@@ -17,7 +16,7 @@ namespace MQTTnet.Implementations
     {
         private readonly IMqttClientOptions _clientOptions;
         private readonly MqttClientTcpOptions _options;
-        
+
         private Socket _socket;
         private Stream _stream;
 
@@ -87,8 +86,9 @@ namespace MQTTnet.Implementations
 
         public void Dispose()
         {
-            Cleanup(ref _stream, (s) => s.Dispose());
-            Cleanup(ref _socket, (s) => {
+            Cleanup(ref _stream, s => s.Dispose());
+            Cleanup(ref _socket, s =>
+            {
                 if (s.Connected)
                 {
                     s.Shutdown(SocketShutdown.Both);
@@ -102,7 +102,7 @@ namespace MQTTnet.Implementations
             // Try the instance callback.
             if (_options.TlsOptions.CertificateValidationCallback != null)
             {
-                return _options.TlsOptions.CertificateValidationCallback(x509Certificate, chain, sslPolicyErrors,_clientOptions);
+                return _options.TlsOptions.CertificateValidationCallback(x509Certificate, chain, sslPolicyErrors, _clientOptions);
             }
 
             // Try static callback.

Source/MQTTnet/Implementations/MqttTcpServerListener.cs

@@ -20,8 +20,8 @@ namespace MQTTnet.Implementations
         private readonly CancellationToken _cancellationToken;
         private readonly AddressFamily _addressFamily;
         private readonly MqttServerTcpEndpointBaseOptions _options;
+        private readonly MqttServerTlsTcpEndpointOptions _tlsOptions;
         private readonly X509Certificate2 _tlsCertificate;
-
         private Socket _socket;
 
         public MqttTcpServerListener(
@@ -36,6 +36,11 @@ namespace MQTTnet.Implementations
             _tlsCertificate = tlsCertificate;
             _cancellationToken = cancellationToken;
             _logger = logger.CreateChildLogger(nameof(MqttTcpServerListener));
+            
+            if (_options is MqttServerTlsTcpEndpointOptions tlsOptions)
+            {
+                _tlsOptions = tlsOptions;
+            }
         }
 
         public event EventHandler<MqttServerAdapterClientAcceptedEventArgs> ClientAccepted;
@@ -75,7 +80,7 @@ namespace MQTTnet.Implementations
                     if (_tlsCertificate != null)
                     {
                         sslStream = new SslStream(new NetworkStream(clientSocket), false);
-                        await sslStream.AuthenticateAsServerAsync(_tlsCertificate, false, SslProtocols.Tls12, false).ConfigureAwait(false);
+                        await sslStream.AuthenticateAsServerAsync(_tlsCertificate, false, _tlsOptions.SslProtocol, false).ConfigureAwait(false);
                     }
 
                     _logger.Verbose("Client '{0}' accepted by TCP listener '{1}, {2}'.",

Source/MQTTnet/Internal/BlockingQueue.cs

@@ -0,0 +1,112 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+
+namespace MQTTnet.Internal
+{
+    public class BlockingQueue<TItem>
+    {
+        private readonly object _syncRoot = new object();
+        private readonly LinkedList<TItem> _items = new LinkedList<TItem>();
+        private readonly ManualResetEvent _gate = new ManualResetEvent(false);
+
+        public int Count
+        {
+            get
+            {
+                lock (_syncRoot)
+                {
+                    return _items.Count;
+                }
+            }
+        }
+
+        public void Enqueue(TItem item)
+        {
+            if (item == null) throw new ArgumentNullException(nameof(item));
+
+            lock (_syncRoot)
+            {
+                _items.AddLast(item);
+                _gate.Set();
+            }
+        }
+
+        public TItem Dequeue()
+        {
+            while (true)
+            {
+                lock (_syncRoot)
+                {
+                    if (_items.Count > 0)
+                    {
+                        var item = _items.First.Value;
+                        _items.RemoveFirst();
+
+                        return item;
+                    }
+
+                    if (_items.Count == 0)
+                    {
+                        _gate.Reset();
+                    }
+                }
+
+                _gate.WaitOne();
+            }
+        }
+        
+        public TItem PeekAndWait()
+        {
+            while (true)
+            {
+                lock (_syncRoot)
+                {
+                    if (_items.Count > 0)
+                    {
+                        return _items.First.Value;
+                    }
+
+                    if (_items.Count == 0)
+                    {
+                        _gate.Reset();
+                    }
+                }
+
+                _gate.WaitOne();
+            }
+        }
+
+        public void RemoveFirst(Predicate<TItem> match)
+        {
+            if (match == null) throw new ArgumentNullException(nameof(match));
+
+            lock (_syncRoot)
+            {
+                if (_items.Count > 0 && match(_items.First.Value))
+                {
+                    _items.RemoveFirst();
+                }
+            }
+        }
+
+        public TItem RemoveFirst()
+        {
+            lock (_syncRoot)
+            {
+                var item = _items.First;
+                _items.RemoveFirst();
+
+                return item.Value;
+            }
+        }
+
+        public void Clear()
+        {
+            lock (_syncRoot)
+            {
+                _items.Clear();
+            }
+        }
+    }
+}

Source/MQTTnet/MQTTnet.csproj

@@ -54,7 +54,7 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)'=='uap10.0'">
-    <PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform" Version="6.1.5" />
+    <PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform" Version="6.1.9" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)'=='net452'">

Source/MQTTnet/Server/IMqttServer.cs

@@ -16,14 +16,18 @@ namespace MQTTnet.Server
         
         IMqttServerOptions Options { get; }
 
+        [Obsolete("This method is no longer async. Use the not async method.")]
         Task<IList<IMqttClientSessionStatus>> GetClientSessionsStatusAsync();
 
+        IList<IMqttClientSessionStatus> GetClientSessionsStatus();
+
+        IList<MqttApplicationMessage> GetRetainedMessages();
+        Task ClearRetainedMessagesAsync();
+
         Task SubscribeAsync(string clientId, IList<TopicFilter> topicFilters);
         Task UnsubscribeAsync(string clientId, IList<string> topicFilters);
 
         Task StartAsync(IMqttServerOptions options);
         Task StopAsync();
-
-        Task ClearRetainedMessagesAsync();
     }
 }

Source/MQTTnet/Server/IMqttServerOptions.cs

@@ -14,7 +14,7 @@ namespace MQTTnet.Server
         Action<MqttConnectionValidatorContext> ConnectionValidator { get; }
         Action<MqttSubscriptionInterceptorContext> SubscriptionInterceptor { get; }
         Action<MqttApplicationMessageInterceptorContext> ApplicationMessageInterceptor { get; }
-        Action<MqttClientMessageQueueInterceptorContext> ClientMessageQueueInterceptor { get; set; }
+        Action<MqttClientMessageQueueInterceptorContext> ClientMessageQueueInterceptor { get; }
 
         MqttServerTcpEndpointOptions DefaultEndpointOptions { get; }
         MqttServerTlsTcpEndpointOptions TlsEndpointOptions { get; }

Source/MQTTnet/Server/MqttClientKeepAliveMonitor.cs

@@ -36,8 +36,8 @@ namespace MQTTnet.Server
             {
                 return;
             }
-
-            Task.Run(() => RunAsync(keepAlivePeriod, cancellationToken), cancellationToken);
+            
+            Task.Run(() => RunAsync(keepAlivePeriod, cancellationToken), cancellationToken).ConfigureAwait(false);
         }
 
         public void Pause()
@@ -50,6 +50,12 @@ namespace MQTTnet.Server
             _isPaused = false;
         }
 
+        public void Reset()
+        {
+            _lastPacketReceivedTracker.Restart();
+            _lastNonKeepAlivePacketReceivedTracker.Restart();
+        }
+
         public void PacketReceived(MqttBasePacket packet)
         {
             _lastPacketReceivedTracker.Restart();

Source/MQTTnet/Server/MqttClientSession.cs

@@ -9,6 +9,7 @@ using MQTTnet.Exceptions;
 using MQTTnet.Internal;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
+using MQTTnet.Serializer;
 
 namespace MQTTnet.Server
 {
@@ -17,6 +18,7 @@ namespace MQTTnet.Server
         private readonly MqttPacketIdentifierProvider _packetIdentifierProvider = new MqttPacketIdentifierProvider();
 
         private readonly MqttRetainedMessagesManager _retainedMessagesManager;
+        private readonly MqttServerEventDispatcher _eventDispatcher;
         private readonly MqttClientKeepAliveMonitor _keepAliveMonitor;
         private readonly MqttClientPendingPacketsQueue _pendingPacketsQueue;
         private readonly MqttClientSubscriptionsManager _subscriptionsManager;
@@ -28,29 +30,33 @@ namespace MQTTnet.Server
         private CancellationTokenSource _cancellationTokenSource;
         private MqttApplicationMessage _willMessage;
         private bool _wasCleanDisconnect;
-        private IMqttChannelAdapter _adapter;
         private Task _workerTask;
         private IDisposable _cleanupHandle;
 
+        private string _adapterEndpoint;
+        private MqttProtocolVersion? _adapterProtocolVersion;
+        
         public MqttClientSession(
             string clientId,
             IMqttServerOptions options,
             MqttClientSessionsManager sessionsManager,
             MqttRetainedMessagesManager retainedMessagesManager,
+            MqttServerEventDispatcher eventDispatcher,
             IMqttNetChildLogger logger)
         {
             if (logger == null) throw new ArgumentNullException(nameof(logger));
 
             _options = options ?? throw new ArgumentNullException(nameof(options));
-            _sessionsManager = sessionsManager;
+            _sessionsManager = sessionsManager ?? throw new ArgumentNullException(nameof(sessionsManager));
             _retainedMessagesManager = retainedMessagesManager ?? throw new ArgumentNullException(nameof(retainedMessagesManager));
+            _eventDispatcher = eventDispatcher ?? throw new ArgumentNullException(nameof(eventDispatcher));
 
             ClientId = clientId;
 
             _logger = logger.CreateChildLogger(nameof(MqttClientSession));
 
             _keepAliveMonitor = new MqttClientKeepAliveMonitor(this, _logger);
-            _subscriptionsManager = new MqttClientSubscriptionsManager(clientId, _options, sessionsManager.Server);
+            _subscriptionsManager = new MqttClientSubscriptionsManager(clientId, _options, eventDispatcher);
             _pendingPacketsQueue = new MqttClientPendingPacketsQueue(_options, this, _logger);
         }
 
@@ -59,9 +65,9 @@ namespace MQTTnet.Server
         public void FillStatus(MqttClientSessionStatus status)
         {
             status.ClientId = ClientId;
-            status.IsConnected = _adapter != null;
-            status.Endpoint = _adapter?.Endpoint;
-            status.ProtocolVersion = _adapter?.PacketSerializer?.ProtocolVersion;
+            status.IsConnected = _cancellationTokenSource != null;
+            status.Endpoint = _adapterEndpoint;
+            status.ProtocolVersion = _adapterProtocolVersion;
             status.PendingApplicationMessagesCount = _pendingPacketsQueue.Count;
             status.LastPacketReceived = _keepAliveMonitor.LastPacketReceived;
             status.LastNonKeepAlivePacketReceived = _keepAliveMonitor.LastNonKeepAlivePacketReceived;
@@ -73,145 +79,11 @@ namespace MQTTnet.Server
             return _workerTask;
         }
 
-        private async Task RunInternalAsync(MqttConnectPacket connectPacket, IMqttChannelAdapter adapter)
-        {
-            if (connectPacket == null) throw new ArgumentNullException(nameof(connectPacket));
-            if (adapter == null) throw new ArgumentNullException(nameof(adapter));
-
-            try
-            {
-                _adapter = adapter;
-
-                adapter.ReadingPacketStarted += OnAdapterReadingPacketStarted;
-                adapter.ReadingPacketCompleted += OnAdapterReadingPacketCompleted;
-
-                _cancellationTokenSource = new CancellationTokenSource();
-
-                //woraround for https://github.com/dotnet/corefx/issues/24430
-#pragma warning disable 4014
-                _cleanupHandle = _cancellationTokenSource.Token.Register(() => CleanupAsync());
-#pragma warning restore 4014
-                //endworkaround
-
-                _wasCleanDisconnect = false;
-                _willMessage = connectPacket.WillMessage;
-
-                _pendingPacketsQueue.Start(adapter, _cancellationTokenSource.Token);
-                _keepAliveMonitor.Start(connectPacket.KeepAlivePeriod, _cancellationTokenSource.Token);
-
-                while (!_cancellationTokenSource.IsCancellationRequested)
-                {
-                    var packet = await adapter.ReceivePacketAsync(TimeSpan.Zero, _cancellationTokenSource.Token).ConfigureAwait(false);
-                    if (packet != null)
-                    {
-                        _keepAliveMonitor.PacketReceived(packet);
-                        ProcessReceivedPacket(adapter, packet, _cancellationTokenSource.Token);
-                    }
-                }
-            }
-            catch (OperationCanceledException)
-            {
-            }
-            catch (Exception exception)
-            {
-                if (exception is MqttCommunicationException)
-                {
-                    if (exception is MqttCommunicationClosedGracefullyException)
-                    {
-                        _logger.Verbose("Client '{0}': Connection closed gracefully.", ClientId);
-                    }
-                    else
-                    {
-                        _logger.Warning(exception, "Client '{0}': Communication exception while receiving client packets.", ClientId);
-                    }
-                }
-                else
-                {
-                    _logger.Error(exception, "Client '{0}': Unhandled exception while receiving client packets.", ClientId);
-                }
-
-                Stop(MqttClientDisconnectType.NotClean, true);
-            }
-            finally
-            {
-                await CleanupAsync().ConfigureAwait(false);
-
-                _cleanupHandle?.Dispose();
-                _cleanupHandle = null;
-                
-                _adapter = null;
-                _cancellationTokenSource?.Cancel(false);
-                _cancellationTokenSource?.Dispose();
-                _cancellationTokenSource = null;
-            }
-        }
-
-        private async Task CleanupAsync()
-        {
-            var adapter = _adapter;
-            try
-            {
-                if (adapter == null)
-                {
-                    return;
-                }
-
-                _adapter = null;
-
-                adapter.ReadingPacketStarted -= OnAdapterReadingPacketStarted;
-                adapter.ReadingPacketCompleted -= OnAdapterReadingPacketCompleted;
-
-                await adapter.DisconnectAsync(_options.DefaultCommunicationTimeout, CancellationToken.None).ConfigureAwait(false);
-            }
-            catch (Exception exception)
-            {
-                _logger.Error(exception, exception.Message);
-            }
-            finally
-            {
-                adapter?.Dispose();
-            }
-        }
-
         public void Stop(MqttClientDisconnectType type)
         {
             Stop(type, false);
         }
 
-        private void Stop(MqttClientDisconnectType type, bool isInsideSession)
-        {
-            try
-            {
-                var cts = _cancellationTokenSource;
-                if (cts == null || cts.IsCancellationRequested)
-                {
-                    return;
-                }
-
-                _wasCleanDisconnect = type == MqttClientDisconnectType.Clean;
-
-                _cancellationTokenSource?.Cancel(false);
-
-                if (_willMessage != null && !_wasCleanDisconnect)
-                {
-                    _sessionsManager.EnqueueApplicationMessage(this, _willMessage.ToPublishPacket());
-                }
-
-                _willMessage = null;
-
-                if (!isInsideSession)
-                {
-                    _workerTask?.GetAwaiter().GetResult();
-                }
-            }
-            finally
-            {
-                _logger.Info("Client '{0}': Session stopped.", ClientId);
-
-                _sessionsManager.Server.OnClientDisconnected(ClientId, _wasCleanDisconnect);
-            }
-        }
-
         public void EnqueueApplicationMessage(MqttClientSession senderClientSession, MqttPublishPacket publishPacket)
         {
             if (publishPacket == null) throw new ArgumentNullException(nameof(publishPacket));
@@ -227,7 +99,7 @@ namespace MQTTnet.Server
                 Topic = publishPacket.Topic,
                 Payload = publishPacket.Payload,
                 QualityOfServiceLevel = checkSubscriptionsResult.QualityOfServiceLevel,
-                Retain = false,
+                Retain = publishPacket.Retain,
                 Dup = false
             };
 
@@ -297,6 +169,163 @@ namespace MQTTnet.Server
             _cancellationTokenSource = null;
         }
 
+        private void Stop(MqttClientDisconnectType type, bool isInsideSession)
+        {
+            try
+            {
+                var cts = _cancellationTokenSource;
+                if (cts == null || cts.IsCancellationRequested)
+                {
+                    return;
+                }
+
+                _cancellationTokenSource?.Cancel(false);
+
+                _wasCleanDisconnect = type == MqttClientDisconnectType.Clean;
+
+                if (_willMessage != null && !_wasCleanDisconnect)
+                {
+                    _sessionsManager.EnqueueApplicationMessage(this, _willMessage.ToPublishPacket());
+                }
+
+                _willMessage = null;
+
+                if (!isInsideSession)
+                {
+                    _workerTask?.GetAwaiter().GetResult();
+                }
+            }
+            finally
+            {
+                _logger.Info("Client '{0}': Disconnected (clean={1}).", ClientId, _wasCleanDisconnect);
+                _eventDispatcher.OnClientDisconnected(ClientId, _wasCleanDisconnect);
+            }
+        }
+
+        private async Task RunInternalAsync(MqttConnectPacket connectPacket, IMqttChannelAdapter adapter)
+        {
+            if (connectPacket == null) throw new ArgumentNullException(nameof(connectPacket));
+            if (adapter == null) throw new ArgumentNullException(nameof(adapter));
+
+            try
+            {
+                if (_cancellationTokenSource != null)
+                {
+                    Stop(MqttClientDisconnectType.Clean, true);
+                }
+
+                adapter.ReadingPacketStarted += OnAdapterReadingPacketStarted;
+                adapter.ReadingPacketCompleted += OnAdapterReadingPacketCompleted;
+
+                _cancellationTokenSource = new CancellationTokenSource();
+
+                //workaround for https://github.com/dotnet/corefx/issues/24430
+#pragma warning disable 4014
+                _cleanupHandle = _cancellationTokenSource.Token.Register(async () =>
+                {
+                    await TryDisconnectAdapterAsync(adapter).ConfigureAwait(false);
+                    TryDisposeAdapter(adapter);
+                });
+#pragma warning restore 4014
+                //end workaround
+
+                _wasCleanDisconnect = false;
+                _willMessage = connectPacket.WillMessage;
+
+                _pendingPacketsQueue.Start(adapter, _cancellationTokenSource.Token);
+                _keepAliveMonitor.Start(connectPacket.KeepAlivePeriod, _cancellationTokenSource.Token);
+
+                _adapterEndpoint = adapter.Endpoint;
+                _adapterProtocolVersion = adapter.PacketSerializer.ProtocolVersion;
+
+                while (!_cancellationTokenSource.IsCancellationRequested)
+                {
+                    var packet = await adapter.ReceivePacketAsync(TimeSpan.Zero, _cancellationTokenSource.Token).ConfigureAwait(false);
+                    if (packet != null)
+                    {
+                        _keepAliveMonitor.PacketReceived(packet);
+                        ProcessReceivedPacket(adapter, packet, _cancellationTokenSource.Token);
+                    }
+                }
+            }
+            catch (OperationCanceledException)
+            {
+            }
+            catch (Exception exception)
+            {
+                if (exception is MqttCommunicationException)
+                {
+                    if (exception is MqttCommunicationClosedGracefullyException)
+                    {
+                        _logger.Verbose("Client '{0}': Connection closed gracefully.", ClientId);
+                    }
+                    else
+                    {
+                        _logger.Warning(exception, "Client '{0}': Communication exception while receiving client packets.", ClientId);
+                    }
+                }
+                else
+                {
+                    _logger.Error(exception, "Client '{0}': Unhandled exception while receiving client packets.", ClientId);
+                }
+
+                Stop(MqttClientDisconnectType.NotClean, true);
+            }
+            finally
+            {
+                _adapterEndpoint = null;
+                _adapterProtocolVersion = null;
+
+                // Uncomment as soon as the workaround above is no longer needed.
+                //await TryDisconnectAdapterAsync(adapter).ConfigureAwait(false);
+                //TryDisposeAdapter(adapter);
+
+                _cleanupHandle?.Dispose();
+                _cleanupHandle = null;
+                
+                _cancellationTokenSource?.Cancel(false);
+                _cancellationTokenSource?.Dispose();
+                _cancellationTokenSource = null;
+            }
+        }
+
+        private void TryDisposeAdapter(IMqttChannelAdapter adapter)
+        {
+            if (adapter == null)
+            {
+                return;
+            }
+
+            try
+            {
+                adapter.ReadingPacketStarted -= OnAdapterReadingPacketStarted;
+                adapter.ReadingPacketCompleted -= OnAdapterReadingPacketCompleted;
+
+                adapter.Dispose();
+            }
+            catch (Exception exception)
+            {
+                _logger.Error(exception, "Error while disposing channel adapter.");
+            }
+        }
+
+        private async Task TryDisconnectAdapterAsync(IMqttChannelAdapter adapter)
+        {
+            if (adapter == null)
+            {
+                return;
+            }
+
+            try
+            {
+                await adapter.DisconnectAsync(_options.DefaultCommunicationTimeout, CancellationToken.None).ConfigureAwait(false);
+            }
+            catch (Exception exception)
+            {
+                _logger.Error(exception, "Error while disconnecting channel adapter.");
+            }
+        }
+
         private void ProcessReceivedPacket(IMqttChannelAdapter adapter, MqttBasePacket packet, CancellationToken cancellationToken)
         {
             if (packet is MqttPublishPacket publishPacket)
@@ -371,7 +400,12 @@ namespace MQTTnet.Server
             var retainedMessages = _retainedMessagesManager.GetSubscribedMessages(topicFilters);
             foreach (var applicationMessage in retainedMessages)
             {
-                EnqueueApplicationMessage(null, applicationMessage.ToPublishPacket());
+                var publishPacket = applicationMessage.ToPublishPacket();
+
+                // Set the retain flag to true according to [MQTT-3.3.1-8].
+                publishPacket.Retain = true;
+
+                EnqueueApplicationMessage(null, publishPacket);
             }
         }
 

Source/MQTTnet/Server/MqttClientSessionsManager.cs

@@ -23,25 +23,29 @@ namespace MQTTnet.Server
         private readonly Dictionary<string, MqttClientSession> _sessions = new Dictionary<string, MqttClientSession>();
 
         private readonly CancellationToken _cancellationToken;
+        private readonly MqttServerEventDispatcher _eventDispatcher;
 
         private readonly MqttRetainedMessagesManager _retainedMessagesManager;
         private readonly IMqttServerOptions _options;
         private readonly IMqttNetChildLogger _logger;
 
-        public MqttClientSessionsManager(IMqttServerOptions options, MqttServer server, MqttRetainedMessagesManager retainedMessagesManager, CancellationToken cancellationToken, IMqttNetChildLogger logger)
+        public MqttClientSessionsManager(
+            IMqttServerOptions options, 
+            MqttRetainedMessagesManager retainedMessagesManager, 
+            CancellationToken cancellationToken,
+            MqttServerEventDispatcher eventDispatcher,
+            IMqttNetChildLogger logger)
         {
-            if (logger == null) throw new ArgumentNullException(nameof(logger));
+            _cancellationToken = cancellationToken;
 
+            if (logger == null) throw new ArgumentNullException(nameof(logger));
             _logger = logger.CreateChildLogger(nameof(MqttClientSessionsManager));
 
-            _cancellationToken = cancellationToken;
+            _eventDispatcher = eventDispatcher ?? throw new ArgumentNullException(nameof(eventDispatcher));
             _options = options ?? throw new ArgumentNullException(nameof(options));
-            Server = server ?? throw new ArgumentNullException(nameof(server));
             _retainedMessagesManager = retainedMessagesManager ?? throw new ArgumentNullException(nameof(retainedMessagesManager));
         }
 
-        public MqttServer Server { get; }
-
         public void Start()
         {
             Task.Factory.StartNew(() => TryProcessQueuedApplicationMessages(_cancellationToken), _cancellationToken, TaskCreationOptions.LongRunning, TaskScheduler.Default);
@@ -62,10 +66,10 @@ namespace MQTTnet.Server
 
         public Task StartSession(IMqttChannelAdapter clientAdapter)
         {
-            return Task.Run(() => RunSession(clientAdapter, _cancellationToken), _cancellationToken);
+            return Task.Run(() => RunSessionAsync(clientAdapter, _cancellationToken), _cancellationToken);
         }
 
-        public Task<IList<IMqttClientSessionStatus>> GetClientStatusAsync()
+        public IList<IMqttClientSessionStatus> GetClientStatus()
         {
             var result = new List<IMqttClientSessionStatus>();
 
@@ -77,7 +81,7 @@ namespace MQTTnet.Server
                 result.Add(status);
             }
 
-            return Task.FromResult((IList<IMqttClientSessionStatus>)result);
+            return result;
         }
 
         public void EnqueueApplicationMessage(MqttClientSession senderClientSession, MqttPublishPacket publishPacket)
@@ -176,7 +180,7 @@ namespace MQTTnet.Server
                     applicationMessage = interceptorContext.ApplicationMessage;
                 }
 
-                Server.OnApplicationMessageReceived(sender?.ClientId, applicationMessage);
+                _eventDispatcher.OnApplicationMessageReceived(sender?.ClientId, applicationMessage);
 
                 if (applicationMessage.Retain)
                 {
@@ -185,7 +189,12 @@ namespace MQTTnet.Server
 
                 foreach (var clientSession in GetSessions())
                 {
-                    clientSession.EnqueueApplicationMessage(enqueuedApplicationMessage.Sender, applicationMessage.ToPublishPacket());
+                    var publishPacket = applicationMessage.ToPublishPacket();
+
+                    // Set the retain flag to true according to [MQTT-3.3.1-9].
+                    publishPacket.Retain = false;
+
+                    clientSession.EnqueueApplicationMessage(enqueuedApplicationMessage.Sender, publishPacket);
                 }
             }
             catch (OperationCanceledException)
@@ -205,7 +214,7 @@ namespace MQTTnet.Server
             }
         }
 
-        private async Task RunSession(IMqttChannelAdapter clientAdapter, CancellationToken cancellationToken)
+        private async Task RunSessionAsync(IMqttChannelAdapter clientAdapter, CancellationToken cancellationToken)
         {
             var clientId = string.Empty;
             
@@ -241,7 +250,6 @@ namespace MQTTnet.Server
                 }
 
                 var result = PrepareClientSession(connectPacket);
-                var clientSession = result.Session;
 
                 await clientAdapter.SendPacketAsync(
                     new MqttConnAckPacket
@@ -251,9 +259,10 @@ namespace MQTTnet.Server
                     },
                     cancellationToken).ConfigureAwait(false);
 
-                Server.OnClientConnected(clientId);
+                _logger.Info("Client '{0}': Connected.", clientId);
+                _eventDispatcher.OnClientConnected(clientId);
 
-                await clientSession.RunAsync(connectPacket, clientAdapter).ConfigureAwait(false);
+                await result.Session.RunAsync(connectPacket, clientAdapter).ConfigureAwait(false);
             }
             catch (OperationCanceledException)
             {
@@ -317,7 +326,7 @@ namespace MQTTnet.Server
                 {
                     isExistingSession = false;
 
-                    clientSession = new MqttClientSession(connectPacket.ClientId, _options, this, _retainedMessagesManager, _logger);
+                    clientSession = new MqttClientSession(connectPacket.ClientId, _options, this, _retainedMessagesManager, _eventDispatcher, _logger);
                     _sessions[connectPacket.ClientId] = clientSession;
 
                     _logger.Verbose("Created a new session for client '{0}'.", connectPacket.ClientId);

Source/MQTTnet/Server/MqttClientSubscriptionsManager.cs

@@ -10,14 +10,14 @@ namespace MQTTnet.Server
     {
         private readonly Dictionary<string, MqttQualityOfServiceLevel> _subscriptions = new Dictionary<string, MqttQualityOfServiceLevel>();
         private readonly IMqttServerOptions _options;
-        private readonly MqttServer _server;
+        private readonly MqttServerEventDispatcher _eventDispatcher;
         private readonly string _clientId;
 
-        public MqttClientSubscriptionsManager(string clientId, IMqttServerOptions options, MqttServer server)
+        public MqttClientSubscriptionsManager(string clientId, IMqttServerOptions options, MqttServerEventDispatcher eventDispatcher)
         {
             _clientId = clientId ?? throw new ArgumentNullException(nameof(clientId));
             _options = options ?? throw new ArgumentNullException(nameof(options));
-            _server = server;
+            _eventDispatcher = eventDispatcher ?? throw new ArgumentNullException(nameof(eventDispatcher));
         }
 
         public MqttClientSubscribeResult Subscribe(MqttSubscribePacket subscribePacket)
@@ -58,7 +58,7 @@ namespace MQTTnet.Server
                         _subscriptions[topicFilter.Topic] = topicFilter.QualityOfServiceLevel;
                     }
 
-                    _server.OnClientSubscribedTopic(_clientId, topicFilter);
+                    _eventDispatcher.OnClientSubscribedTopic(_clientId, topicFilter);
                 }
             }
 
@@ -75,7 +75,7 @@ namespace MQTTnet.Server
                 {
                     _subscriptions.Remove(topicFilter);
 
-                    _server.OnClientUnsubscribedTopic(_clientId, topicFilter);
+                    _eventDispatcher.OnClientUnsubscribedTopic(_clientId, topicFilter);
                 }
             }
 

Source/MQTTnet/Server/MqttRetainedMessagesManager.cs

@@ -52,7 +52,51 @@ namespace MQTTnet.Server
 
             try
             {
-                await HandleMessageInternalAsync(clientId, applicationMessage).ConfigureAwait(false);
+                List<MqttApplicationMessage> messagesForSave = null;
+                lock (_messages)
+                {
+                    var saveIsRequired = false;
+
+                    if (applicationMessage.Payload?.Length == 0)
+                    {
+                        saveIsRequired = _messages.Remove(applicationMessage.Topic);
+                        _logger.Verbose("Client '{0}' cleared retained message for topic '{1}'.", clientId, applicationMessage.Topic);
+                    }
+                    else
+                    {
+                        if (!_messages.TryGetValue(applicationMessage.Topic, out var existingMessage))
+                        {
+                            _messages[applicationMessage.Topic] = applicationMessage;
+                            saveIsRequired = true;
+                        }
+                        else
+                        {
+                            if (existingMessage.QualityOfServiceLevel != applicationMessage.QualityOfServiceLevel || !existingMessage.Payload.SequenceEqual(applicationMessage.Payload ?? new byte[0]))
+                            {
+                                _messages[applicationMessage.Topic] = applicationMessage;
+                                saveIsRequired = true;
+                            }
+                        }
+
+                        _logger.Verbose("Client '{0}' set retained message for topic '{1}'.", clientId, applicationMessage.Topic);
+                    }
+
+                    if (saveIsRequired)
+                    {
+                        messagesForSave = new List<MqttApplicationMessage>(_messages.Values);
+                    }
+                }
+
+                if (messagesForSave == null)
+                {
+                    _logger.Verbose("Skipped saving retained messages because no changes were detected.");
+                    return;
+                }
+
+                if (_options.Storage != null)
+                {
+                    await _options.Storage.SaveRetainedMessagesAsync(messagesForSave).ConfigureAwait(false);
+                }
             }
             catch (Exception exception)
             {
@@ -84,6 +128,14 @@ namespace MQTTnet.Server
             return retainedMessages;
         }
 
+        public IList<MqttApplicationMessage> GetMessages()
+        {
+            lock (_messages)
+            {
+                return _messages.Values.ToList();
+            }
+        }
+
         public Task ClearMessagesAsync()
         {
             lock (_messages)
@@ -91,55 +143,12 @@ namespace MQTTnet.Server
                 _messages.Clear();
             }
 
-            return _options.Storage.SaveRetainedMessagesAsync(new List<MqttApplicationMessage>());
-        }
-
-        private async Task HandleMessageInternalAsync(string clientId, MqttApplicationMessage applicationMessage)
-        {
-            var saveIsRequired = false;
-
-            lock (_messages)
+            if (_options.Storage != null)
             {
-                if (applicationMessage.Payload?.Length == 0)
-                {
-                    saveIsRequired = _messages.Remove(applicationMessage.Topic);
-                    _logger.Verbose("Client '{0}' cleared retained message for topic '{1}'.", clientId, applicationMessage.Topic);
-                }
-                else
-                {
-                    if (!_messages.TryGetValue(applicationMessage.Topic, out var existingMessage))
-                    {
-                        _messages[applicationMessage.Topic] = applicationMessage;
-                        saveIsRequired = true;
-                    }
-                    else
-                    {
-                        if (existingMessage.QualityOfServiceLevel != applicationMessage.QualityOfServiceLevel || !existingMessage.Payload.SequenceEqual(applicationMessage.Payload ?? new byte[0]))
-                        {
-                            _messages[applicationMessage.Topic] = applicationMessage;
-                            saveIsRequired = true;
-                        }
-                    }
-
-                    _logger.Verbose("Client '{0}' set retained message for topic '{1}'.", clientId, applicationMessage.Topic);
-                }
+                return _options.Storage.SaveRetainedMessagesAsync(new List<MqttApplicationMessage>());
             }
 
-            if (!saveIsRequired)
-            {
-                _logger.Verbose("Skipped saving retained messages because no changes were detected.");
-            }
-
-            if (saveIsRequired && _options.Storage != null)
-            {
-                List<MqttApplicationMessage> messages;
-                lock (_messages)
-                {
-                    messages = _messages.Values.ToList();
-                }
-
-                await _options.Storage.SaveRetainedMessagesAsync(messages).ConfigureAwait(false);
-            }
+            return Task.FromResult((object)null);
         }
     }
 }

Source/MQTTnet/Server/MqttServer.cs

@@ -11,6 +11,7 @@ namespace MQTTnet.Server
 {
     public class MqttServer : IMqttServer
     {
+        private readonly MqttServerEventDispatcher _eventDispatcher = new MqttServerEventDispatcher();
         private readonly ICollection<IMqttServerAdapter> _adapters;
         private readonly IMqttNetChildLogger _logger;
 
@@ -21,10 +22,16 @@ namespace MQTTnet.Server
         public MqttServer(IEnumerable<IMqttServerAdapter> adapters, IMqttNetChildLogger logger)
         {
             if (adapters == null) throw new ArgumentNullException(nameof(adapters));
+            _adapters = adapters.ToList();
+
             if (logger == null) throw new ArgumentNullException(nameof(logger));
             _logger = logger.CreateChildLogger(nameof(MqttServer));
 
-            _adapters = adapters.ToList();
+            _eventDispatcher.ClientConnected += (s, e) => ClientConnected?.Invoke(s, e);
+            _eventDispatcher.ClientDisconnected += (s, e) => ClientDisconnected?.Invoke(s, e);
+            _eventDispatcher.ClientSubscribedTopic += (s, e) => ClientSubscribedTopic?.Invoke(s, e);
+            _eventDispatcher.ClientUnsubscribedTopic += (s, e) => ClientUnsubscribedTopic?.Invoke(s, e);
+            _eventDispatcher.ApplicationMessageReceived += (s, e) => ApplicationMessageReceived?.Invoke(s, e);
         }
 
         public event EventHandler Started;
@@ -41,7 +48,17 @@ namespace MQTTnet.Server
 
         public Task<IList<IMqttClientSessionStatus>> GetClientSessionsStatusAsync()
         {
-            return _clientSessionsManager.GetClientStatusAsync();
+            return Task.FromResult(_clientSessionsManager.GetClientStatus());
+        }
+
+        public IList<IMqttClientSessionStatus> GetClientSessionsStatus()
+        {
+            return _clientSessionsManager.GetClientStatus();
+        }
+
+        public IList<MqttApplicationMessage> GetRetainedMessages()
+        {
+            return _retainedMessagesManager.GetMessages();
         }
 
         public Task SubscribeAsync(string clientId, IList<TopicFilter> topicFilters)
@@ -82,7 +99,7 @@ namespace MQTTnet.Server
             _retainedMessagesManager = new MqttRetainedMessagesManager(Options, _logger);
             await _retainedMessagesManager.LoadMessagesAsync().ConfigureAwait(false);
 
-            _clientSessionsManager = new MqttClientSessionsManager(Options, this, _retainedMessagesManager, _cancellationTokenSource.Token, _logger);
+            _clientSessionsManager = new MqttClientSessionsManager(Options, _retainedMessagesManager, _cancellationTokenSource.Token, _eventDispatcher, _logger);
             _clientSessionsManager.Start();
 
             foreach (var adapter in _adapters)
@@ -134,33 +151,6 @@ namespace MQTTnet.Server
             return _retainedMessagesManager?.ClearMessagesAsync();
         }
 
-        internal void OnClientConnected(string clientId)
-        {
-            _logger.Info("Client '{0}': Connected.", clientId);
-            ClientConnected?.Invoke(this, new MqttClientConnectedEventArgs(clientId));
-        }
-
-        internal void OnClientDisconnected(string clientId, bool wasCleanDisconnect)
-        {
-            _logger.Info("Client '{0}': Disconnected (clean={1}).", clientId, wasCleanDisconnect);
-            ClientDisconnected?.Invoke(this, new MqttClientDisconnectedEventArgs(clientId, wasCleanDisconnect));
-        }
-
-        internal void OnClientSubscribedTopic(string clientId, TopicFilter topicFilter)
-        {
-            ClientSubscribedTopic?.Invoke(this, new MqttClientSubscribedTopicEventArgs(clientId, topicFilter));
-        }
-
-        internal void OnClientUnsubscribedTopic(string clientId, string topicFilter)
-        {
-            ClientUnsubscribedTopic?.Invoke(this, new MqttClientUnsubscribedTopicEventArgs(clientId, topicFilter));
-        }
-
-        internal void OnApplicationMessageReceived(string clientId, MqttApplicationMessage applicationMessage)
-        {
-            ApplicationMessageReceived?.Invoke(this, new MqttApplicationMessageReceivedEventArgs(clientId, applicationMessage));
-        }
-
         private void OnClientAccepted(object sender, MqttServerAdapterClientAcceptedEventArgs eventArgs)
         {
             eventArgs.SessionTask = _clientSessionsManager.StartSession(eventArgs.Client);

Source/MQTTnet/Server/MqttServerEventDispatcher.cs

@@ -0,0 +1,42 @@
+using System;
+
+namespace MQTTnet.Server
+{
+    public class MqttServerEventDispatcher
+    {
+        public event EventHandler<MqttClientSubscribedTopicEventArgs> ClientSubscribedTopic;
+
+        public event EventHandler<MqttClientUnsubscribedTopicEventArgs> ClientUnsubscribedTopic;
+
+        public event EventHandler<MqttClientConnectedEventArgs> ClientConnected;
+
+        public event EventHandler<MqttClientDisconnectedEventArgs> ClientDisconnected;
+
+        public event EventHandler<MqttApplicationMessageReceivedEventArgs> ApplicationMessageReceived;
+
+        public void OnClientSubscribedTopic(string clientId, TopicFilter topicFilter)
+        {
+            ClientSubscribedTopic?.Invoke(this, new MqttClientSubscribedTopicEventArgs(clientId, topicFilter));
+        }
+
+        public void OnClientUnsubscribedTopic(string clientId, string topicFilter)
+        {
+            ClientUnsubscribedTopic?.Invoke(this, new MqttClientUnsubscribedTopicEventArgs(clientId, topicFilter));
+        }
+
+        public void OnClientDisconnected(string clientId, bool wasCleanDisconnect)
+        {
+            ClientDisconnected?.Invoke(this, new MqttClientDisconnectedEventArgs(clientId, wasCleanDisconnect));
+        }
+
+        public void OnApplicationMessageReceived(string senderClientId, MqttApplicationMessage applicationMessage)
+        {
+            ApplicationMessageReceived?.Invoke(this, new MqttApplicationMessageReceivedEventArgs(senderClientId, applicationMessage));
+        }
+
+        public void OnClientConnected(string clientId)
+        {
+            ClientConnected?.Invoke(this, new MqttClientConnectedEventArgs(clientId));
+        }
+    }
+}

Source/MQTTnet/Server/MqttServerOptionsBuilder.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Net;
+using System.Security.Authentication;
 
 namespace MQTTnet.Server
 {
@@ -80,6 +81,12 @@ namespace MQTTnet.Server
             return this;
         }
 
+        public MqttServerOptionsBuilder WithEncryptionSslProtocol(SslProtocols value)
+        {
+            _options.TlsEndpointOptions.SslProtocol = value;
+            return this;
+        }
+
         public MqttServerOptionsBuilder WithoutEncryptedEndpoint()
         {
             _options.TlsEndpointOptions.IsEnabled = false;

Source/MQTTnet/Server/MqttServerTlsTcpEndpointOptions.cs

@@ -1,4 +1,6 @@
-namespace MQTTnet.Server
+using System.Security.Authentication;
+
+namespace MQTTnet.Server
 {
     public class MqttServerTlsTcpEndpointOptions : MqttServerTcpEndpointBaseOptions
     {
@@ -8,5 +10,8 @@
         }
 
         public byte[] Certificate { get; set; }
+
+
+        public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12;
     }
 }

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

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFramework>netcoreapp2.1</TargetFramework>
@@ -7,9 +7,9 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.7.0" />
-    <PackageReference Include="MSTest.TestAdapter" Version="1.2.1" />
-    <PackageReference Include="MSTest.TestFramework" Version="1.2.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.9.0" />
+    <PackageReference Include="MSTest.TestAdapter" Version="1.3.2" />
+    <PackageReference Include="MSTest.TestFramework" Version="1.3.2" />
   </ItemGroup>
 
   <ItemGroup>

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

@@ -0,0 +1,22 @@
+using System.Collections.Generic;
+using System.IO.Pipelines;
+using Microsoft.AspNetCore.Connections;
+using Microsoft.AspNetCore.Http.Features;
+
+namespace MQTTnet.AspNetCore.Tests.Mockups
+{
+    public class ConnectionContextMockup : ConnectionContext
+    {
+        public override string ConnectionId { get; set; }
+
+        public override IFeatureCollection Features { get; }
+
+        public override IDictionary<object, object> Items { get; set; }
+        public override IDuplexPipe Transport { get; set; }
+
+        public ConnectionContextMockup()
+        {
+            //Transport = new DefaultConnectionContext
+        }
+    }
+}

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

@@ -0,0 +1,16 @@
+using System.IO.Pipelines;
+
+namespace MQTTnet.AspNetCore.Tests.Mockups
+{
+    public class DuplexPipeMockup : IDuplexPipe
+    {
+        PipeReader IDuplexPipe.Input => Receive.Reader;
+
+        PipeWriter IDuplexPipe.Output => Send.Writer;
+
+
+        public Pipe Receive { get; set; } = new Pipe();
+
+        public Pipe Send { get; set; } = new Pipe();
+    }
+}

Tests/MQTTnet.AspNetCore.Tests/MqttConnectionContextTest.cs

@@ -0,0 +1,51 @@
+using Microsoft.AspNetCore.Connections;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.AspNetCore.Tests.Mockups;
+using MQTTnet.Exceptions;
+using MQTTnet.Packets;
+using MQTTnet.Serializer;
+using System;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace MQTTnet.AspNetCore.Tests
+{
+    [TestClass]
+    public class MqttConnectionContextTest
+    {
+        [TestMethod]
+        public async Task TestReceivePacketAsyncThrowsWhenReaderCompleted()
+        {
+            var serializer = new MqttPacketSerializer {};
+            var pipe = new DuplexPipeMockup();
+            var connection = new DefaultConnectionContext();
+            connection.Transport = pipe;
+            var ctx = new MqttConnectionContext(serializer, connection);
+
+            pipe.Receive.Writer.Complete();
+
+            await Assert.ThrowsExceptionAsync<MqttCommunicationException>(() => ctx.ReceivePacketAsync(TimeSpan.FromSeconds(1), CancellationToken.None));
+        }
+        
+        [TestMethod]
+        public async Task TestParallelWrites()
+        {
+            var serializer = new MqttPacketSerializer { };
+            var pipe = new DuplexPipeMockup();
+            var connection = new DefaultConnectionContext();
+            connection.Transport = pipe;
+            var ctx = new MqttConnectionContext(serializer, connection);
+
+            var tasks = Enumerable.Range(1, 10).Select(_ => Task.Run(async () => 
+            {
+                for (int i = 0; i < 100; i++)
+                {
+                    await ctx.SendPacketAsync(new MqttPublishPacket(), CancellationToken.None).ConfigureAwait(false);
+                }
+            }));
+
+            await Task.WhenAll(tasks).ConfigureAwait(false);
+        }
+    }
+}

Tests/MQTTnet.Benchmarks/LoggerBenchmark.cs

@@ -1,6 +1,4 @@
 using BenchmarkDotNet.Attributes;
-using BenchmarkDotNet.Attributes.Exporters;
-using BenchmarkDotNet.Attributes.Jobs;
 using MQTTnet.Diagnostics;
 
 namespace MQTTnet.Benchmarks

Tests/MQTTnet.Benchmarks/MQTTnet.Benchmarks.csproj

@@ -3,14 +3,15 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <DebugType>Full</DebugType>
-    <TargetFramework>net461</TargetFramework>
-      <LangVersion>7.2</LangVersion>
+    <TargetFramework Condition=" '$(OS)' == 'Windows_NT' ">net461</TargetFramework>
+    <TargetFramework Condition=" '$(OS)' != 'Windows_NT' ">netcoreapp2.1</TargetFramework>
+    <LangVersion>7.2</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="BenchmarkDotNet" Version="0.10.14" />
-    <PackageReference Include="System.IO.Pipelines" Version="4.5.0" />
-    <PackageReference Include="Microsoft.AspNetCore" Version="2.1.0" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.11.1" />
+    <PackageReference Include="System.IO.Pipelines" Version="4.5.2" />
+    <PackageReference Include="Microsoft.AspNetCore" Version="2.1.4" />
   </ItemGroup>
 
   <ItemGroup>

Tests/MQTTnet.Benchmarks/MessageProcessingBenchmark.cs

@@ -1,7 +1,4 @@
 using BenchmarkDotNet.Attributes;
-using BenchmarkDotNet.Attributes.Columns;
-using BenchmarkDotNet.Attributes.Exporters;
-using BenchmarkDotNet.Attributes.Jobs;
 using MQTTnet.Client;
 using MQTTnet.Server;
 

Tests/MQTTnet.Benchmarks/SerializerBenchmark.cs

@@ -2,8 +2,6 @@
 using MQTTnet.Packets;
 using MQTTnet.Serializer;
 using MQTTnet.Internal;
-using BenchmarkDotNet.Attributes.Jobs;
-using BenchmarkDotNet.Attributes.Exporters;
 using System;
 using System.Threading;
 using System.Threading.Tasks;

Tests/MQTTnet.Benchmarks/TopicFilterComparerBenchmark.cs

@@ -1,6 +1,4 @@
 using BenchmarkDotNet.Attributes;
-using BenchmarkDotNet.Attributes.Exporters;
-using BenchmarkDotNet.Attributes.Jobs;
 using MQTTnet.Server;
 using System;
 

Tests/MQTTnet.Core.Tests/BlockingQueueTests.cs

@@ -0,0 +1,108 @@
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Internal;
+
+namespace MQTTnet.Core.Tests
+{
+    [TestClass]
+    public class BlockingQueueTests
+    {
+        [TestMethod]
+        public void Preserve_Order()
+        {
+            var queue = new BlockingQueue<string>();
+            queue.Enqueue("a");
+            queue.Enqueue("b");
+            queue.Enqueue("c");
+
+            Assert.AreEqual(3, queue.Count);
+
+            Assert.AreEqual("a", queue.Dequeue());
+            Assert.AreEqual("b", queue.Dequeue());
+            Assert.AreEqual("c", queue.Dequeue());
+        }
+
+        [TestMethod]
+        public void Remove_First_Items()
+        {
+            var queue = new BlockingQueue<string>();
+            queue.Enqueue("a");
+            queue.Enqueue("b");
+            queue.Enqueue("c");
+
+            Assert.AreEqual("a", queue.RemoveFirst());
+            Assert.AreEqual("b", queue.RemoveFirst());
+            
+            Assert.AreEqual(1, queue.Count);
+
+            Assert.AreEqual("c", queue.Dequeue());
+        }
+
+        [TestMethod]
+        public void Clear_Items()
+        {
+            var queue = new BlockingQueue<string>();
+            queue.Enqueue("a");
+            queue.Enqueue("b");
+            queue.Enqueue("c");
+
+            Assert.AreEqual(3, queue.Count);
+
+            queue.Clear();
+
+            Assert.AreEqual(0, queue.Count);
+        }
+
+        [TestMethod]
+        public async Task Wait_For_Item()
+        {
+            var queue = new BlockingQueue<string>();
+
+            string item = null;
+#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+            Task.Run(() =>
+            {
+                item = queue.Dequeue();
+            });
+#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+
+            await Task.Delay(100);
+
+            Assert.AreEqual(0, queue.Count);
+            Assert.AreEqual(null, item);
+
+            queue.Enqueue("x");
+
+            await Task.Delay(100);
+
+            Assert.AreEqual("x", item);
+            Assert.AreEqual(0, queue.Count);
+        }
+
+        [TestMethod]
+        public void Wait_For_Times()
+        {
+            var number = 0;
+
+            var queue = new BlockingQueue<int>();
+
+#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+            Task.Run(async () =>
+            {
+                while (true)
+                {
+                    queue.Enqueue(1);
+                    await Task.Delay(100);
+                }
+            });
+#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+
+            while (number < 50)
+            {
+                queue.Dequeue();
+                Interlocked.Increment(ref number);
+            }
+        }
+    }
+}

Tests/MQTTnet.Core.Tests/MQTTnet.Core.Tests.csproj

@@ -3,16 +3,17 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <DebugType>Full</DebugType>
-    <TargetFramework>netcoreapp2.0</TargetFramework>
+    <TargetFramework>netcoreapp2.1</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
     <PackageReference Include="MSTest.TestAdapter" Version="1.3.2" />
     <PackageReference Include="MSTest.TestFramework" Version="1.3.2" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.7.2" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.9.0" />
   </ItemGroup>
 
   <ItemGroup>
+    <ProjectReference Include="..\..\Source\MQTTnet.Extensions.ManagedClient\MQTTnet.Extensions.ManagedClient.csproj" />
     <ProjectReference Include="..\..\Source\MQTTnet\MQTTnet.csproj" />
   </ItemGroup>
 

Tests/MQTTnet.Core.Tests/ManagedMqttClientTests.cs

@@ -0,0 +1,38 @@
+using MQTTnet.Extensions.ManagedClient;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Server;
+
+namespace MQTTnet.Core.Tests
+{
+    [TestClass]
+    public class ManagedMqttClientTests
+    {
+        [TestMethod]
+        public async Task Drop_New_Messages_On_Full_Queue()
+        {
+            var factory = new MqttFactory();
+            var managedClient = factory.CreateManagedMqttClient();
+
+            var clientOptions = new ManagedMqttClientOptionsBuilder()
+                .WithMaxPendingMessages(5)
+                .WithPendingMessagesOverflowStrategy(MqttPendingMessagesOverflowStrategy.DropNewMessage);
+
+            clientOptions.WithClientOptions(o => o.WithTcpServer("localhost"));
+
+            await managedClient.StartAsync(clientOptions.Build());
+
+            await managedClient.PublishAsync(new MqttApplicationMessage { Topic = "1" });
+            await managedClient.PublishAsync(new MqttApplicationMessage { Topic = "2" });
+            await managedClient.PublishAsync(new MqttApplicationMessage { Topic = "3" });
+            await managedClient.PublishAsync(new MqttApplicationMessage { Topic = "4" });
+            await managedClient.PublishAsync(new MqttApplicationMessage { Topic = "5" });
+
+            await managedClient.PublishAsync(new MqttApplicationMessage { Topic = "6" });
+            await managedClient.PublishAsync(new MqttApplicationMessage { Topic = "7" });
+            await managedClient.PublishAsync(new MqttApplicationMessage { Topic = "8" });
+
+            Assert.AreEqual(5, managedClient.PendingApplicationMessagesCount);
+        }
+    }
+}

Tests/MQTTnet.Core.Tests/MqttClientTests.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Collections.Generic;
+using System.Linq;
 using System.Net.Sockets;
 using System.Threading;
 using System.Threading.Tasks;
@@ -8,6 +10,7 @@ using MQTTnet.Client;
 using MQTTnet.Diagnostics;
 using MQTTnet.Exceptions;
 using MQTTnet.Packets;
+using MQTTnet.Server;
 
 namespace MQTTnet.Core.Tests
 {
@@ -15,7 +18,7 @@ namespace MQTTnet.Core.Tests
     public class MqttClientTests
     {
         [TestMethod]
-        public async Task ClientDisconnectException()
+        public async Task Client_Disconnect_Exception()
         {
             var factory = new MqttFactory();
             var client = factory.CreateMqttClient();
@@ -39,9 +42,95 @@ namespace MQTTnet.Core.Tests
             Assert.IsInstanceOfType(ex.InnerException, typeof(SocketException));
         }
 
+        [TestMethod]
+        public async Task Client_Publish()
+        {
+            var server = new MqttFactory().CreateMqttServer();
+            
+            try
+            {
+                var receivedMessages = new List<MqttApplicationMessage>();
+
+                await server.StartAsync(new MqttServerOptions());
+
+                var client1 = new MqttFactory().CreateMqttClient();
+                client1.ApplicationMessageReceived += (_, e) =>
+                {
+                    lock (receivedMessages)
+                    {
+                        receivedMessages.Add(e.ApplicationMessage);
+                    }
+                };
+
+                await client1.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1").Build());
+                await client1.SubscribeAsync("a");
+
+                var client2 = new MqttFactory().CreateMqttClient();
+                await client2.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1").Build());
+                var message = new MqttApplicationMessageBuilder().WithTopic("a").WithRetainFlag().Build();
+                await client2.PublishAsync(message);
+
+                await Task.Delay(500);
+
+                Assert.AreEqual(1, receivedMessages.Count);
+                Assert.IsFalse(receivedMessages.First().Retain); // Must be false even if set above!
+            }
+            finally
+            {
+                await server.StopAsync();
+            }
+        }
+
+        [TestMethod]
+        public async Task Publish_Special_Content()
+        {
+            var factory = new MqttFactory();
+            var server = factory.CreateMqttServer();
+            var serverOptions = new MqttServerOptionsBuilder().Build();
+
+            var receivedMessages = new List<MqttApplicationMessage>();
+
+            var client = factory.CreateMqttClient();
+
+            try
+            {
+                await server.StartAsync(serverOptions);
+
+                client.Connected += async (s, e) =>
+                {
+                    await client.SubscribeAsync("RCU/P1/H0001/R0003");
+
+                    var msg = new MqttApplicationMessageBuilder()
+                        .WithPayload("DA|18RS00SC00XI0000RV00R100R200R300R400L100L200L300L400Y100Y200AC0102031800BELK0000BM0000|")
+                        .WithTopic("RCU/P1/H0001/R0003");
+
+                    await client.PublishAsync(msg.Build());
+                };
+
+                client.ApplicationMessageReceived += (s, e) =>
+                {
+                    lock (receivedMessages)
+                    {
+                        receivedMessages.Add(e.ApplicationMessage);
+                    }
+                };
+
+                await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost").Build());
+
+                await Task.Delay(500);
+
+                Assert.AreEqual(1, receivedMessages.Count);
+                Assert.AreEqual("DA|18RS00SC00XI0000RV00R100R200R300R400L100L200L300L400Y100Y200AC0102031800BELK0000BM0000|", receivedMessages.First().ConvertPayloadToString());
+            }
+            finally
+            {
+                await server.StopAsync();
+            }
+        }
+
 #if DEBUG
         [TestMethod]
-        public async Task ClientCleanupOnAuthentificationFails()
+        public async Task Client_Cleanup_On_Authentification_Fails()
         {
             var channel = new TestMqttCommunicationAdapter();
             var channel2 = new TestMqttCommunicationAdapter();
@@ -50,11 +139,12 @@ namespace MQTTnet.Core.Tests
 
             Task.Run(async () => {
                 var connect = await channel2.ReceivePacketAsync(TimeSpan.Zero, CancellationToken.None);
-                await channel2.SendPacketAsync(new MqttConnAckPacket() { ConnectReturnCode = Protocol.MqttConnectReturnCode.ConnectionRefusedNotAuthorized }, CancellationToken.None);
+                await channel2.SendPacketAsync(new MqttConnAckPacket
+                {
+                    ConnectReturnCode = Protocol.MqttConnectReturnCode.ConnectionRefusedNotAuthorized
+                }, CancellationToken.None);
             });
-
-
-
+            
             var fake = new TestMqttCommunicationAdapterFactory(channel);
 
             var client = new MqttClient(fake, new MqttNetLogger());

Tests/MQTTnet.Core.Tests/MqttServerTests.cs

@@ -4,7 +4,9 @@ using MQTTnet.Diagnostics;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
+using System.Linq;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
@@ -98,11 +100,11 @@ namespace MQTTnet.Core.Tests
                 c1.ApplicationMessageReceived += (_, __) => receivedMessagesCount++;
 
                 var message = new MqttApplicationMessageBuilder().WithTopic("a").WithAtLeastOnceQoS().Build();
-                
+
                 await c2.PublishAsync(message);
                 await Task.Delay(1000);
                 Assert.AreEqual(0, receivedMessagesCount);
-                
+
                 var subscribeEventCalled = false;
                 s.ClientSubscribedTopic += (_, e) =>
                     {
@@ -116,7 +118,7 @@ namespace MQTTnet.Core.Tests
                 await c2.PublishAsync(message);
                 await Task.Delay(500);
                 Assert.AreEqual(1, receivedMessagesCount);
-                
+
                 var unsubscribeEventCalled = false;
                 s.ClientUnsubscribedTopic += (_, e) =>
                 {
@@ -226,6 +228,39 @@ namespace MQTTnet.Core.Tests
 
             Assert.AreEqual(2000, receivedMessagesCount);
         }
+        
+        [TestMethod]
+        public async Task MqttServer_SessionTakeover()
+        {
+            var server = new MqttFactory().CreateMqttServer();
+            try
+            {
+                await server.StartAsync(new MqttServerOptions());
+
+                var client1 = new MqttFactory().CreateMqttClient();
+                var client2 = new MqttFactory().CreateMqttClient();
+
+                var options = new MqttClientOptionsBuilder()
+                    .WithTcpServer("localhost")
+                    .WithCleanSession(false)
+                    .WithClientId("a").Build();
+
+                await client1.ConnectAsync(options);
+
+                await Task.Delay(500);
+
+                await client2.ConnectAsync(options);
+
+                await Task.Delay(500);
+
+                Assert.IsFalse(client1.IsConnected);
+                Assert.IsTrue(client2.IsConnected);
+            }
+            finally
+            {
+                await server.StopAsync();
+            }
+        }
 
         private static async Task Publish(IMqttClient c1, MqttApplicationMessage message)
         {
@@ -234,7 +269,7 @@ namespace MQTTnet.Core.Tests
                 await c1.PublishAsync(message);
             }
         }
-        
+
         [TestMethod]
         public async Task MqttServer_ShutdownDisconnectsClientsGracefully()
         {
@@ -266,11 +301,6 @@ namespace MQTTnet.Core.Tests
         [TestMethod]
         public async Task MqttServer_HandleCleanDisconnect()
         {
-            MqttNetGlobalLogger.LogMessagePublished += (_, e) =>
-            {
-                System.Diagnostics.Debug.WriteLine($"[{e.TraceMessage.Timestamp:s}] {e.TraceMessage.Source} {e.TraceMessage.Message}");
-            };
-
             var serverAdapter = new MqttTcpServerAdapter(new MqttNetLogger().CreateChildLogger());
             var s = new MqttFactory().CreateMqttServer(new[] { serverAdapter }, new MqttNetLogger());
 
@@ -303,6 +333,104 @@ namespace MQTTnet.Core.Tests
             Assert.AreEqual(clientConnectedCalled, clientDisconnectedCalled);
         }
 
+        [TestMethod]
+        public async Task MqttServer_Client_Disconnect_Without_Errors()
+        {
+            var errors = 0;
+
+            MqttNetGlobalLogger.LogMessagePublished += (_, e) =>
+            {
+                System.Diagnostics.Debug.WriteLine($"[{e.TraceMessage.Timestamp:s}] {e.TraceMessage.Source} {e.TraceMessage.Message}");
+
+                if (e.TraceMessage.Level == MqttNetLogLevel.Error)
+                {
+                    errors++;
+                }
+            };
+
+            bool clientWasConnected;
+
+            var server = new MqttFactory().CreateMqttServer();
+            try
+            {
+                var options = new MqttServerOptionsBuilder().Build();
+                await server.StartAsync(options);
+
+                var client = new MqttFactory().CreateMqttClient();
+                var clientOptions = new MqttClientOptionsBuilder()
+                    .WithTcpServer("localhost")
+                    .Build();
+
+                await client.ConnectAsync(clientOptions);
+
+                clientWasConnected = true;
+
+                await client.DisconnectAsync();
+
+                await Task.Delay(500);
+            }
+            finally
+            {
+                await server.StopAsync();
+            }
+            
+            Assert.IsTrue(clientWasConnected);
+            Assert.AreEqual(0, errors);
+        }
+
+        [TestMethod]
+        public async Task MqttServer_LotsOfRetainedMessages()
+        {
+            const int ClientCount = 100;
+
+            var server = new MqttFactory().CreateMqttServer();
+            try
+            {
+                await server.StartAsync(new MqttServerOptionsBuilder().Build());
+
+                Parallel.For(
+                    0,
+                    ClientCount,
+                    new ParallelOptions { MaxDegreeOfParallelism = 10 },
+                    i =>
+                {
+                    using (var client = new MqttFactory().CreateMqttClient())
+                    {
+                        client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost").Build())
+                            .GetAwaiter().GetResult();
+
+                        for (var j = 0; j < 10; j++)
+                        {
+                            // Clear retained message.
+                            client.PublishAsync(new MqttApplicationMessageBuilder().WithTopic("r" + i)
+                                .WithPayload(new byte[0]).WithRetainFlag().Build()).GetAwaiter().GetResult();
+
+                            // Set retained message.
+                            client.PublishAsync(new MqttApplicationMessageBuilder().WithTopic("r" + i)
+                                .WithPayload("value" + j).WithRetainFlag().Build()).GetAwaiter().GetResult();
+                        }
+
+                        client.DisconnectAsync().GetAwaiter().GetResult();
+                    }
+                });
+
+                await Task.Delay(100);
+
+                var retainedMessages = server.GetRetainedMessages();
+
+                Assert.AreEqual(ClientCount, retainedMessages.Count);
+
+                for (var i = 0; i < ClientCount; i++)
+                {
+                    Assert.IsTrue(retainedMessages.Any(m => m.Topic == "r" + i));
+                }
+            }
+            finally
+            {
+                await server.StopAsync();
+            }
+        }
+
         [TestMethod]
         public async Task MqttServer_RetainedMessagesFlow()
         {
@@ -335,6 +463,8 @@ namespace MQTTnet.Core.Tests
             }
 
             await c2.DisconnectAsync();
+
+            await s.StopAsync();
         }
 
         [TestMethod]
@@ -373,7 +503,7 @@ namespace MQTTnet.Core.Tests
             var serverAdapter = new TestMqttServerAdapter();
             var s = new MqttFactory().CreateMqttServer(new[] { serverAdapter }, new MqttNetLogger());
 
-            var receivedMessagesCount = 0;
+            var receivedMessages = new List<MqttApplicationMessage>();
             try
             {
                 await s.StartAsync(new MqttServerOptions());
@@ -383,7 +513,14 @@ namespace MQTTnet.Core.Tests
                 await c1.DisconnectAsync();
 
                 var c2 = await serverAdapter.ConnectTestClient("c2");
-                c2.ApplicationMessageReceived += (_, __) => receivedMessagesCount++;
+                c2.ApplicationMessageReceived += (_, e) =>
+                {
+                    lock (receivedMessages)
+                    {
+                        receivedMessages.Add(e.ApplicationMessage);
+                    }
+                };
+
                 await c2.SubscribeAsync(new TopicFilterBuilder().WithTopic("retained").Build());
 
                 await Task.Delay(500);
@@ -393,7 +530,8 @@ namespace MQTTnet.Core.Tests
                 await s.StopAsync();
             }
 
-            Assert.AreEqual(1, receivedMessagesCount);
+            Assert.AreEqual(1, receivedMessages.Count);
+            Assert.IsTrue(receivedMessages.First().Retain);
         }
 
         [TestMethod]
@@ -568,7 +706,7 @@ namespace MQTTnet.Core.Tests
 
                 await server.StartAsync(options);
 
-                
+
                 var clientOptions = new MqttClientOptionsBuilder()
                     .WithTcpServer("localhost").Build();
 
@@ -593,7 +731,7 @@ namespace MQTTnet.Core.Tests
             {
                 await client.DisconnectAsync();
                 await server.StopAsync();
-                
+
                 client.Dispose();
             }
         }
@@ -601,26 +739,29 @@ namespace MQTTnet.Core.Tests
         [TestMethod]
         public async Task MqttServer_SameClientIdConnectDisconnectEventOrder()
         {
-            var serverAdapter = new MqttTcpServerAdapter(new MqttNetLogger().CreateChildLogger());
-            var s = new MqttFactory().CreateMqttServer(new[] { serverAdapter }, new MqttNetLogger());
+            var s = new MqttFactory().CreateMqttServer();
 
-            var connectedClient = false;
-            var connecteCalledBeforeConnectedClients = false;
+            var events = new List<string>();
 
             s.ClientConnected += (_, __) =>
             {
-                connecteCalledBeforeConnectedClients |= connectedClient;
-                connectedClient = true;
+                lock (events)
+                {
+                    events.Add("c");
+                }
             };
 
             s.ClientDisconnected += (_, __) =>
             {
-                connectedClient = false;
+                lock (events)
+                {
+                    events.Add("d");
+                }
             };
 
             var clientOptions = new MqttClientOptionsBuilder()
                 .WithTcpServer("localhost")
-                .WithClientId(Guid.NewGuid().ToString())
+                .WithClientId("same_id")
                 .Build();
 
             await s.StartAsync(new MqttServerOptions());
@@ -630,20 +771,53 @@ namespace MQTTnet.Core.Tests
 
             await c1.ConnectAsync(clientOptions);
 
-            await Task.Delay(100);
+            await Task.Delay(250);
 
             await c2.ConnectAsync(clientOptions);
 
-            await Task.Delay(100);
+            await Task.Delay(250);
 
             await c1.DisconnectAsync();
+
+            await Task.Delay(250);
+
             await c2.DisconnectAsync();
 
+            await Task.Delay(250);
+
             await s.StopAsync();
 
-            await Task.Delay(100);
+            var flow = string.Join(string.Empty, events);
+            Assert.AreEqual("cdcd", flow);
+        }
 
-            Assert.IsFalse(connecteCalledBeforeConnectedClients, "ClientConnected was called before ClientDisconnect was called");
+
+        [TestMethod]
+        public async Task MqttServer_StopAndRestart()
+        {
+            var server = new MqttFactory().CreateMqttServer();
+            await server.StartAsync(new MqttServerOptions());
+
+            var client = new MqttFactory().CreateMqttClient();
+            await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost").Build());
+            await server.StopAsync();
+
+            try
+            {
+                var client2 = new MqttFactory().CreateMqttClient();
+                await client2.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost").Build());
+
+                Assert.Fail("Connecting should fail.");
+            }
+            catch (Exception)
+            {
+            }
+
+            await server.StartAsync(new MqttServerOptions());
+            var client3 = new MqttFactory().CreateMqttClient();
+            await client3.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost").Build());
+
+            await server.StopAsync();
         }
 
         private class TestStorage : IMqttServerStorage

Tests/MQTTnet.Core.Tests/MqttSubscriptionsManagerTests.cs

@@ -1,6 +1,4 @@
 using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MQTTnet.Adapter;
-using MQTTnet.Diagnostics;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
@@ -13,7 +11,7 @@ namespace MQTTnet.Core.Tests
         [TestMethod]
         public void MqttSubscriptionsManager_SubscribeSingleSuccess()
         {
-            var sm = new MqttClientSubscriptionsManager("", new MqttServerOptions(), new MqttServer(new IMqttServerAdapter[0], new MqttNetLogger().CreateChildLogger("")));
+            var sm = new MqttClientSubscriptionsManager("", new MqttServerOptions(), new MqttServerEventDispatcher());
 
             var sp = new MqttSubscribePacket();
             sp.TopicFilters.Add(new TopicFilterBuilder().WithTopic("A/B/C").Build());
@@ -28,7 +26,7 @@ namespace MQTTnet.Core.Tests
         [TestMethod]
         public void MqttSubscriptionsManager_SubscribeDifferentQoSSuccess()
         {
-            var sm = new MqttClientSubscriptionsManager("", new MqttServerOptions(), new MqttServer(new IMqttServerAdapter[0], new MqttNetLogger().CreateChildLogger("")));
+            var sm = new MqttClientSubscriptionsManager("", new MqttServerOptions(), new MqttServerEventDispatcher());
 
             var sp = new MqttSubscribePacket();
             sp.TopicFilters.Add(new TopicFilter("A/B/C", MqttQualityOfServiceLevel.AtMostOnce));
@@ -43,7 +41,7 @@ namespace MQTTnet.Core.Tests
         [TestMethod]
         public void MqttSubscriptionsManager_SubscribeTwoTimesSuccess()
         {
-            var sm = new MqttClientSubscriptionsManager("", new MqttServerOptions(), new MqttServer(new IMqttServerAdapter[0], new MqttNetLogger().CreateChildLogger("")));
+            var sm = new MqttClientSubscriptionsManager("", new MqttServerOptions(), new MqttServerEventDispatcher());
 
             var sp = new MqttSubscribePacket();
             sp.TopicFilters.Add(new TopicFilter("#", MqttQualityOfServiceLevel.AtMostOnce));
@@ -59,7 +57,7 @@ namespace MQTTnet.Core.Tests
         [TestMethod]
         public void MqttSubscriptionsManager_SubscribeSingleNoSuccess()
         {
-            var sm = new MqttClientSubscriptionsManager("", new MqttServerOptions(), new MqttServer(new IMqttServerAdapter[0], new MqttNetLogger().CreateChildLogger("")));
+            var sm = new MqttClientSubscriptionsManager("", new MqttServerOptions(), new MqttServerEventDispatcher());
 
             var sp = new MqttSubscribePacket();
             sp.TopicFilters.Add(new TopicFilterBuilder().WithTopic("A/B/C").Build());
@@ -72,7 +70,7 @@ namespace MQTTnet.Core.Tests
         [TestMethod]
         public void MqttSubscriptionsManager_SubscribeAndUnsubscribeSingle()
         {
-            var sm = new MqttClientSubscriptionsManager("", new MqttServerOptions(), new MqttServer(new IMqttServerAdapter[0], new MqttNetLogger().CreateChildLogger("")));
+            var sm = new MqttClientSubscriptionsManager("", new MqttServerOptions(), new MqttServerEventDispatcher());
 
             var sp = new MqttSubscribePacket();
             sp.TopicFilters.Add(new TopicFilterBuilder().WithTopic("A/B/C").Build());

Tests/MQTTnet.Core.Tests/RoundtripTimeTests.cs

@@ -0,0 +1,53 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Client;
+using MQTTnet.Server;
+
+namespace MQTTnet.Core.Tests
+{
+    [TestClass]
+    public class RoundtripTimeTests
+    {
+        [TestMethod]
+        public async Task Round_Trip_Time()
+        {
+            var factory = new MqttFactory();
+            var server = factory.CreateMqttServer();
+            var receiverClient = factory.CreateMqttClient();
+            var senderClient = factory.CreateMqttClient();
+
+            await server.StartAsync(new MqttServerOptionsBuilder().Build());
+
+            await receiverClient.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost").Build());
+            await receiverClient.SubscribeAsync("#");
+
+            await senderClient.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("localhost").Build());
+
+            TaskCompletionSource<string> response = null;
+
+            receiverClient.ApplicationMessageReceived += (sender, args) =>
+            {
+                response?.SetResult(args.ApplicationMessage.ConvertPayloadToString());
+            };
+
+            var times = new List<TimeSpan>();
+            var stopwatch = Stopwatch.StartNew();
+
+            for (var i = 0; i < 100; i++)
+            {
+                response = new TaskCompletionSource<string>();
+                await senderClient.PublishAsync("test", DateTime.UtcNow.Ticks.ToString());
+                response.Task.GetAwaiter().GetResult();
+
+                stopwatch.Stop();
+                times.Add(stopwatch.Elapsed);
+                stopwatch.Restart();
+            }
+
+            await server.StopAsync();
+        }
+    }
+}

Tests/MQTTnet.Core.Tests/TestServerExtensions.cs

@@ -11,19 +11,20 @@ namespace MQTTnet.Core.Tests
         /// publishes a message with a client and waits in the server until a message with the same topic is received
         /// </summary>
         /// <returns></returns>
-        public static async Task PublishAndWaitForAsync(this IMqttClient client, IMqttServer server, MqttApplicationMessage message) 
+        public static async Task PublishAndWaitForAsync(this IMqttClient client, IMqttServer server, MqttApplicationMessage message)
         {
             var tcs = new TaskCompletionSource<object>();
 
-            EventHandler<MqttApplicationMessageReceivedEventArgs> handler = (sender, args) =>
+            void Handler(object sender, MqttApplicationMessageReceivedEventArgs args)
             {
                 if (args.ApplicationMessage.Topic == message.Topic)
                 {
                     tcs.SetResult(true);
                 }
-            };
-            server.ApplicationMessageReceived += handler;
-            
+            }
+
+            server.ApplicationMessageReceived += Handler;
+
             try
             {
                 await client.PublishAsync(message).ConfigureAwait(false);
@@ -31,7 +32,7 @@ namespace MQTTnet.Core.Tests
             }
             finally
             {
-                server.ApplicationMessageReceived -= handler;
+                server.ApplicationMessageReceived -= Handler;
             }
         }
     }

Tests/MQTTnet.TestApp.AspNetCore2/MQTTnet.TestApp.AspNetCore2.csproj

@@ -10,8 +10,10 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.AspNetCore" Version="2.1.0" />
-    <PackageReference Include="Microsoft.AspNetCore.App" Version="2.1.0" />
+    <PackageReference Include="Microsoft.AspNetCore" Version="2.1.4" />
+    <PackageReference Include="Microsoft.AspNetCore.App" Version="2.1.5" />
+    <PackageReference Include="Microsoft.AspNetCore.Connections.Abstractions" Version="2.1.3" />
+    <PackageReference Include="Microsoft.AspNetCore.Http.Abstractions" Version="2.1.1" />
   </ItemGroup>
 
   <ItemGroup>

Tests/MQTTnet.TestApp.NetCore/MQTTnet.TestApp.NetCore.csproj

@@ -3,11 +3,12 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <DebugType>Full</DebugType>
-    <TargetFrameworks>netcoreapp2.0;net452;net461</TargetFrameworks>
+    <TargetFrameworks>netcoreapp2.1</TargetFrameworks>
+    <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">$(TargetFrameworks);net452;net461</TargetFrameworks>
   </PropertyGroup>
 
-  <PropertyGroup Condition="'$(Configuration)|$(TargetFramework)|$(Platform)'=='Release|netcoreapp2.0|AnyCPU'">
-    <DefineConstants>RELEASE;NETCOREAPP2_0</DefineConstants>
+  <PropertyGroup Condition="'$(Configuration)|$(TargetFramework)|$(Platform)'=='Release|netcoreapp2.1|AnyCPU'">
+    <DefineConstants>RELEASE;NETCOREAPP2_1</DefineConstants>
   </PropertyGroup>
 
   <ItemGroup>

Tests/MQTTnet.TestApp.NetCore/ManagedClientTest.cs

@@ -61,13 +61,7 @@ namespace MQTTnet.TestApp.NetCore
 
         public class RandomPassword : IMqttClientCredentials
         {
-            public string Password
-            {
-                get
-                {
-                    return Guid.NewGuid().ToString(); // The random password.
-                }
-            }
+            public string Password => Guid.NewGuid().ToString();
 
             public string Username => "the_static_user";
         }

Tests/MQTTnet.TestApp.UniversalWindows/MQTTnet.TestApp.UniversalWindows.csproj

@@ -142,10 +142,10 @@
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform">
-      <Version>6.1.5</Version>
+      <Version>6.1.9</Version>
     </PackageReference>
     <PackageReference Include="Microsoft.Toolkit.Uwp.UI.Controls">
-      <Version>3.0.0</Version>
+      <Version>4.0.0</Version>
     </PackageReference>
   </ItemGroup>
   <PropertyGroup Condition=" '$(VisualStudioVersion)' == '' or '$(VisualStudioVersion)' &lt; '14.0' ">

appveyor.yml

@@ -3,7 +3,7 @@ image: Visual Studio 2017
 configuration: Release
 before_build:
 - cmd: >-
-    msbuild /t:restore
+    msbuild /t:restore MQTTnet.sln
 
     cd Tests/MQTTnet.TestApp.AspNetCore2/