Merge branch 'develop'

Build/MQTTnet.nuspec

@@ -11,8 +11,15 @@
     <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) and supports v3.1.0, v3.1.1 and v5.0.0 of the MQTT protocol.</description>
     <releaseNotes>
+* [ManagedClient] Added builder class for MqttClientUnsubscribeOptions (thanks to @dominikviererbe).
 * [ManagedClient] Added support for persisted sessions (thansk to @PMExtra).
+* [Client] Improve connection stability (thanks to @jltjohanlindqvist).
+* [ManagedClient] Fixed a memory leak (thanks to @zawodskoj).
+* [ManagedClient] Improved internal subscription management (#569, thanks to @cstichlberger).
+* [ManagedClient] Refactored log messages (thanks to @cstichlberger).
 * [Server] Added support for assigned client IDs (MQTTv5 only) (thanks to @bcrosnier).
+* [Server] Added interceptor for unsubscriptions.
+* [MQTTnet.Server] Added interceptor for unsubscriptions.
     </releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2019</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> 

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClient.cs

@@ -16,15 +16,25 @@ using MQTTnet.Server;
 
 namespace MQTTnet.Extensions.ManagedClient
 {
-    public class ManagedMqttClient : IManagedMqttClient
+    public class ManagedMqttClient : Disposable, IManagedMqttClient
     {
         private readonly BlockingQueue<ManagedMqttApplicationMessage> _messageQueue = new BlockingQueue<ManagedMqttApplicationMessage>();
+
+        /// <summary>
+        /// The subscriptions are managed in 2 separate buckets:
+        /// <see cref="_subscriptions"/> and <see cref="_unsubscriptions"/> are processed during normal operation
+        /// and are moved to the <see cref="_reconnectSubscriptions"/> when they get processed. They can be accessed by
+        /// any thread and are therefore mutex'ed. <see cref="_reconnectSubscriptions"/> get sent to the broker
+        ///  at reconnect and are solely owned by <see cref="MaintainConnectionAsync"/>.
+        /// </summary>
+        private readonly Dictionary<string, MqttQualityOfServiceLevel> _reconnectSubscriptions = new Dictionary<string, MqttQualityOfServiceLevel>();
         private readonly Dictionary<string, MqttQualityOfServiceLevel> _subscriptions = new Dictionary<string, MqttQualityOfServiceLevel>();
         private readonly HashSet<string> _unsubscriptions = new HashSet<string>();
+        private readonly SemaphoreSlim _subscriptionsQueuedSignal = new SemaphoreSlim(0);
 
         private readonly IMqttClient _mqttClient;
         private readonly IMqttNetChildLogger _logger;
-        
+
         private readonly AsyncLock _messageQueueLock = new AsyncLock();
 
         private CancellationTokenSource _connectionCancellationToken;
@@ -32,10 +42,7 @@ namespace MQTTnet.Extensions.ManagedClient
         private Task _maintainConnectionTask;
 
         private ManagedMqttClientStorageManager _storageManager;
-
-        private bool _disposed;
-        private bool _subscriptionsNotPushed;
-
+        
         public ManagedMqttClient(IMqttClient mqttClient, IMqttNetChildLogger logger)
         {
             _mqttClient = mqttClient ?? throw new ArgumentNullException(nameof(mqttClient));
@@ -82,10 +89,6 @@ namespace MQTTnet.Extensions.ManagedClient
             if (options == null) throw new ArgumentNullException(nameof(options));
             if (options.ClientOptions == null) throw new ArgumentException("The client options are not set.", nameof(options));
 
-            if (!options.ClientOptions.CleanSession)
-            {
-                throw new NotSupportedException("The managed client does not support existing sessions.");
-            }
 
             if (!_maintainConnectionTask?.IsCompleted ?? false) throw new InvalidOperationException("The managed client is already started.");
 
@@ -141,6 +144,7 @@ namespace MQTTnet.Extensions.ManagedClient
             ThrowIfDisposed();
 
             if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
+            if (Options == null) throw new InvalidOperationException("call StartAsync before publishing messages");
 
             MqttTopicValidator.ThrowIfInvalid(applicationMessage.ApplicationMessage.Topic);
 
@@ -169,7 +173,7 @@ namespace MQTTnet.Extensions.ManagedClient
                     }
 
                     _messageQueue.Enqueue(applicationMessage);
-                    
+
                     if (_storageManager != null)
                     {
                         if (removedMessage != null)
@@ -206,9 +210,10 @@ namespace MQTTnet.Extensions.ManagedClient
                 foreach (var topicFilter in topicFilters)
                 {
                     _subscriptions[topicFilter.Topic] = topicFilter.QualityOfServiceLevel;
-                    _subscriptionsNotPushed = true;
+                    _unsubscriptions.Remove(topicFilter.Topic);
                 }
             }
+            _subscriptionsQueuedSignal.Release();
 
             return Task.FromResult(0);
         }
@@ -223,45 +228,34 @@ namespace MQTTnet.Extensions.ManagedClient
             {
                 foreach (var topic in topics)
                 {
-                    if (_subscriptions.Remove(topic))
-                    {
-                        _unsubscriptions.Add(topic);
-                        _subscriptionsNotPushed = true;
-                    }
+                    _subscriptions.Remove(topic);
+                    _unsubscriptions.Add(topic);
                 }
             }
+            _subscriptionsQueuedSignal.Release();
 
             return Task.FromResult(0);
         }
 
-        public void Dispose()
+        protected override void Dispose(bool disposing)
         {
-            if (_disposed)
-            {
-                return;
-            }
-
-            _disposed = true;
-
-            StopPublishing();
-            StopMaintainingConnection();
-
-            if (_maintainConnectionTask != null)
+            if (disposing)
             {
-                Task.WaitAny(_maintainConnectionTask);
-                _maintainConnectionTask = null;
-            }
+                StopPublishing();
+                StopMaintainingConnection();
 
-            _messageQueueLock.Dispose();
-            _mqttClient.Dispose();
-        }
+                if (_maintainConnectionTask != null)
+                {
+                    _maintainConnectionTask.GetAwaiter().GetResult();
+                    _maintainConnectionTask = null;
+                }
 
-        private void ThrowIfDisposed()
-        {
-            if (_disposed)
-            {
-                throw new ObjectDisposedException(nameof(ManagedMqttClient));
+                _messageQueue.Dispose();
+                _messageQueueLock.Dispose();
+                _mqttClient.Dispose();
+                _subscriptionsQueuedSignal.Dispose();
             }
+            base.Dispose(disposing);
         }
 
         private async Task MaintainConnectionAsync(CancellationToken cancellationToken)
@@ -278,11 +272,11 @@ namespace MQTTnet.Extensions.ManagedClient
             }
             catch (Exception exception)
             {
-                _logger.Error(exception, "Unhandled exception while maintaining connection.");
+                _logger.Error(exception, "Error exception while maintaining connection.");
             }
             finally
             {
-                if (!_disposed)
+                if (!IsDisposed)
                 {
                     try
                     {
@@ -295,6 +289,12 @@ namespace MQTTnet.Extensions.ManagedClient
 
                     _logger.Info("Stopped");
                 }
+                _reconnectSubscriptions.Clear();
+                lock (_subscriptions)
+                {
+                    _subscriptions.Clear();
+                    _unsubscriptions.Clear();
+                }
             }
         }
 
@@ -310,16 +310,22 @@ namespace MQTTnet.Extensions.ManagedClient
                     return;
                 }
 
-                if (connectionState == ReconnectionResult.Reconnected || _subscriptionsNotPushed)
+                if (connectionState == ReconnectionResult.Reconnected)
+                {
+                    await PublishReconnectSubscriptionsAsync().ConfigureAwait(false);
+                    StartPublishing();
+                    return;
+                }
+
+                if (connectionState == ReconnectionResult.Recovered)
                 {
-                    await SynchronizeSubscriptionsAsync().ConfigureAwait(false);
                     StartPublishing();
                     return;
                 }
 
                 if (connectionState == ReconnectionResult.StillConnected)
                 {
-                    await Task.Delay(Options.ConnectionCheckInterval, cancellationToken).ConfigureAwait(false);
+                    await PublishSubscriptionsAsync(Options.ConnectionCheckInterval, cancellationToken).ConfigureAwait(false);
                 }
             }
             catch (OperationCanceledException)
@@ -327,11 +333,11 @@ namespace MQTTnet.Extensions.ManagedClient
             }
             catch (MqttCommunicationException exception)
             {
-                _logger.Warning(exception, "Communication exception while maintaining connection.");
+                _logger.Warning(exception, "Communication error while maintaining connection.");
             }
             catch (Exception exception)
             {
-                _logger.Error(exception, "Unhandled exception while maintaining connection.");
+                _logger.Error(exception, "Error exception while maintaining connection.");
             }
         }
 
@@ -349,7 +355,7 @@ namespace MQTTnet.Extensions.ManagedClient
                     // 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();
+                    var message = _messageQueue.PeekAndWait(cancellationToken);
                     if (message == null)
                     {
                         continue;
@@ -389,7 +395,7 @@ namespace MQTTnet.Extensions.ManagedClient
                     // 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));
-                    
+
                     if (_storageManager != null)
                     {
                         await _storageManager.RemoveAsync(message).ConfigureAwait(false);
@@ -414,7 +420,7 @@ namespace MQTTnet.Extensions.ManagedClient
                     using (await _messageQueueLock.WaitAsync(CancellationToken.None).ConfigureAwait(false)) //lock to avoid conflict with this.PublishAsync
                     {
                         _messageQueue.RemoveFirst(i => i.Id.Equals(message.Id));
-                        
+
                         if (_storageManager != null)
                         {
                             await _storageManager.RemoveAsync(message).ConfigureAwait(false);
@@ -438,50 +444,84 @@ namespace MQTTnet.Extensions.ManagedClient
             }
         }
 
-        private async Task SynchronizeSubscriptionsAsync()
+        private async Task PublishSubscriptionsAsync(TimeSpan timeout, CancellationToken cancellationToken)
         {
-            _logger.Info("Synchronizing subscriptions");
+            var endTime = DateTime.UtcNow + timeout;
+            while (await _subscriptionsQueuedSignal.WaitAsync(GetRemainingTime(endTime), cancellationToken).ConfigureAwait(false))
+            {
+                List<TopicFilter> subscriptions;
+                HashSet<string> unsubscriptions;
 
-            List<TopicFilter> subscriptions;
-            HashSet<string> unsubscriptions;
+                lock (_subscriptions)
+                {
+                    subscriptions = _subscriptions.Select(i => new TopicFilter { Topic = i.Key, QualityOfServiceLevel = i.Value }).ToList();
+                    _subscriptions.Clear();
+                    unsubscriptions = new HashSet<string>(_unsubscriptions);
+                    _unsubscriptions.Clear();
+                }
 
-            lock (_subscriptions)
-            {
-                subscriptions = _subscriptions.Select(i => new TopicFilter { Topic = i.Key, QualityOfServiceLevel = i.Value }).ToList();
+                if (!subscriptions.Any() && !unsubscriptions.Any())
+                {
+                    continue;
+                }
 
-                unsubscriptions = new HashSet<string>(_unsubscriptions);
-                _unsubscriptions.Clear();
+                _logger.Verbose($"Publishing subscriptions ({subscriptions.Count} subscriptions and {unsubscriptions.Count} unsubscriptions)");
 
-                _subscriptionsNotPushed = false;
-            }
+                foreach (var unsubscription in unsubscriptions)
+                {
+                    _reconnectSubscriptions.Remove(unsubscription);
+                }
 
-            if (!subscriptions.Any() && !unsubscriptions.Any())
-            {
-                return;
-            }
+                foreach (var subscription in subscriptions)
+                {
+                    _reconnectSubscriptions[subscription.Topic] = subscription.QualityOfServiceLevel;
+                }
 
-            try
-            {
-                if (unsubscriptions.Any())
+                try
+                {
+                    if (unsubscriptions.Any())
+                    {
+                        await _mqttClient.UnsubscribeAsync(unsubscriptions.ToArray()).ConfigureAwait(false);
+                    }
+
+                    if (subscriptions.Any())
+                    {
+                        await _mqttClient.SubscribeAsync(subscriptions.ToArray()).ConfigureAwait(false);
+                    }
+                }
+                catch (Exception exception)
                 {
-                    await _mqttClient.UnsubscribeAsync(unsubscriptions.ToArray()).ConfigureAwait(false);
+                    await HandleSubscriptionExceptionAsync(exception).ConfigureAwait(false);
                 }
+            }
+        }
+
+        private async Task PublishReconnectSubscriptionsAsync()
+        {
+            _logger.Info("Publishing subscriptions at reconnect");
 
-                if (subscriptions.Any())
+            try
+            {
+                if (_reconnectSubscriptions.Any())
                 {
+                    var subscriptions = _reconnectSubscriptions.Select(i => new TopicFilter { Topic = i.Key, QualityOfServiceLevel = i.Value });
                     await _mqttClient.SubscribeAsync(subscriptions.ToArray()).ConfigureAwait(false);
                 }
             }
             catch (Exception exception)
             {
-                _logger.Warning(exception, "Synchronizing subscriptions failed.");
-                _subscriptionsNotPushed = true;
+                await HandleSubscriptionExceptionAsync(exception).ConfigureAwait(false);
+            }
+        }
 
-                var synchronizingSubscriptionsFailedHandler = SynchronizingSubscriptionsFailedHandler;
-                if (SynchronizingSubscriptionsFailedHandler != null)
-                {
-                    await synchronizingSubscriptionsFailedHandler.HandleSynchronizingSubscriptionsFailedAsync(new ManagedProcessFailedEventArgs(exception)).ConfigureAwait(false);
-                }
+        private async Task HandleSubscriptionExceptionAsync(Exception exception)
+        {
+            _logger.Warning(exception, "Synchronizing subscriptions failed.");
+
+            var synchronizingSubscriptionsFailedHandler = SynchronizingSubscriptionsFailedHandler;
+            if (SynchronizingSubscriptionsFailedHandler != null)
+            {
+                await synchronizingSubscriptionsFailedHandler.HandleSynchronizingSubscriptionsFailedAsync(new ManagedProcessFailedEventArgs(exception)).ConfigureAwait(false);
             }
         }
 
@@ -494,8 +534,8 @@ namespace MQTTnet.Extensions.ManagedClient
 
             try
             {
-                await _mqttClient.ConnectAsync(Options.ClientOptions).ConfigureAwait(false);
-                return ReconnectionResult.Reconnected;
+                var result = await _mqttClient.ConnectAsync(Options.ClientOptions).ConfigureAwait(false);
+                return result.IsSessionPresent ? ReconnectionResult.Recovered : ReconnectionResult.Reconnected;
             }
             catch (Exception exception)
             {
@@ -508,7 +548,7 @@ namespace MQTTnet.Extensions.ManagedClient
                 return ReconnectionResult.NotConnected;
             }
         }
-        
+
         private void StartPublishing()
         {
             if (_publishingCancellationToken != null)
@@ -535,5 +575,11 @@ namespace MQTTnet.Extensions.ManagedClient
             _connectionCancellationToken?.Dispose();
             _connectionCancellationToken = null;
         }
+
+        private TimeSpan GetRemainingTime(DateTime endTime)
+        {
+            var remainingTime = endTime - DateTime.UtcNow;
+            return remainingTime < TimeSpan.Zero ? TimeSpan.Zero : remainingTime;
+        }
     }
 }

Source/MQTTnet.Extensions.ManagedClient/ReconnectionResult.cs

@@ -4,6 +4,7 @@
     {
         StillConnected,
         Reconnected,
+        Recovered,
         NotConnected
     }
 }

Source/MQTTnet.Extensions.WebSocket4Net/WebSocket4NetMqttChannel.cs

@@ -85,7 +85,12 @@ namespace MQTTnet.Extensions.WebSocket4Net
             {
                 foreach (var certificate in _webSocketOptions.TlsOptions.Certificates)
                 {
+#if WINDOWS_UWP
                     certificates.Add(new X509Certificate(certificate));
+#else
+                    certificates.Add(certificate);
+#endif
+                    
                 }
             }
 

Source/MQTTnet.Server/Mqtt/MqttServerService.cs

@@ -33,6 +33,7 @@ namespace MQTTnet.Server.Mqtt
         private readonly MqttServerConnectionValidator _mqttConnectionValidator;
         private readonly IMqttServer _mqttServer;
         private readonly MqttSubscriptionInterceptor _mqttSubscriptionInterceptor;
+        private readonly MqttUnsubscriptionInterceptor _mqttUnsubscriptionInterceptor;
         private readonly PythonScriptHostService _pythonScriptHostService;
         private readonly MqttWebSocketServerAdapter _webSocketServerAdapter;
 
@@ -45,6 +46,7 @@ namespace MQTTnet.Server.Mqtt
             MqttClientUnsubscribedTopicHandler mqttClientUnsubscribedTopicHandler,
             MqttServerConnectionValidator mqttConnectionValidator,
             MqttSubscriptionInterceptor mqttSubscriptionInterceptor,
+            MqttUnsubscriptionInterceptor mqttUnsubscriptionInterceptor,
             MqttApplicationMessageInterceptor mqttApplicationMessageInterceptor,
             MqttServerStorage mqttServerStorage,
             PythonScriptHostService pythonScriptHostService,
@@ -57,6 +59,7 @@ namespace MQTTnet.Server.Mqtt
             _mqttClientUnsubscribedTopicHandler = mqttClientUnsubscribedTopicHandler ?? throw new ArgumentNullException(nameof(mqttClientUnsubscribedTopicHandler));
             _mqttConnectionValidator = mqttConnectionValidator ?? throw new ArgumentNullException(nameof(mqttConnectionValidator));
             _mqttSubscriptionInterceptor = mqttSubscriptionInterceptor ?? throw new ArgumentNullException(nameof(mqttSubscriptionInterceptor));
+            _mqttUnsubscriptionInterceptor = mqttUnsubscriptionInterceptor ?? throw new ArgumentNullException(nameof(mqttUnsubscriptionInterceptor));
             _mqttApplicationMessageInterceptor = mqttApplicationMessageInterceptor ?? throw new ArgumentNullException(nameof(mqttApplicationMessageInterceptor));
             _mqttServerStorage = mqttServerStorage ?? throw new ArgumentNullException(nameof(mqttServerStorage));
             _pythonScriptHostService = pythonScriptHostService ?? throw new ArgumentNullException(nameof(pythonScriptHostService));
@@ -178,6 +181,7 @@ namespace MQTTnet.Server.Mqtt
                 .WithConnectionValidator(_mqttConnectionValidator)
                 .WithApplicationMessageInterceptor(_mqttApplicationMessageInterceptor)
                 .WithSubscriptionInterceptor(_mqttSubscriptionInterceptor)
+                .WithUnsubscriptionInterceptor(_mqttUnsubscriptionInterceptor)
                 .WithStorage(_mqttServerStorage);
 
             // Configure unencrypted connections

Source/MQTTnet.Server/Mqtt/MqttUnsubscriptionInterceptor.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Threading.Tasks;
+using IronPython.Runtime;
+using Microsoft.Extensions.Logging;
+using MQTTnet.Server.Scripting;
+
+namespace MQTTnet.Server.Mqtt
+{
+    public class MqttUnsubscriptionInterceptor : IMqttServerUnsubscriptionInterceptor
+    {
+        private readonly PythonScriptHostService _pythonScriptHostService;
+        private readonly ILogger _logger;
+
+        public MqttUnsubscriptionInterceptor(PythonScriptHostService pythonScriptHostService, ILogger<MqttUnsubscriptionInterceptor> logger)
+        {
+            _pythonScriptHostService = pythonScriptHostService ?? throw new ArgumentNullException(nameof(pythonScriptHostService));
+            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+        }
+
+        public Task InterceptUnsubscriptionAsync(MqttUnsubscriptionInterceptorContext context)
+        {
+            try
+            {
+                var sessionItems = (PythonDictionary)context.SessionItems[MqttServerConnectionValidator.WrappedSessionItemsKey];
+
+                var pythonContext = new PythonDictionary
+                {
+                    { "client_id", context.ClientId },
+                    { "session_items", sessionItems },
+                    { "topic", context.Topic },
+                    { "accept_unsubscription", context.AcceptUnsubscription },
+                    { "close_connection", context.CloseConnection }
+                };
+
+                _pythonScriptHostService.InvokeOptionalFunction("on_intercept_unsubscription", pythonContext);
+
+                context.AcceptUnsubscription = (bool)pythonContext["accept_unsubscription"];
+                context.CloseConnection = (bool)pythonContext["close_connection"];
+            }
+            catch (Exception exception)
+            {
+                _logger.LogError(exception, "Error while intercepting unsubscription.");
+            }
+
+            return Task.CompletedTask;
+        }
+    }
+}

Source/MQTTnet/Adapter/MqttChannelAdapter.cs

@@ -14,7 +14,7 @@ using MQTTnet.Packets;
 
 namespace MQTTnet.Adapter
 {
-    public class MqttChannelAdapter : IMqttChannelAdapter
+    public class MqttChannelAdapter : Disposable, IMqttChannelAdapter
     {
         private const uint ErrorOperationAborted = 0x800703E3;
         private const int ReadBufferSize = 4096;  // TODO: Move buffer size to config
@@ -26,9 +26,7 @@ namespace MQTTnet.Adapter
         private readonly MqttPacketReader _packetReader;
 
         private readonly byte[] _fixedHeaderBuffer = new byte[2];
-
-        private bool _isDisposed;
-
+        
         private long _bytesReceived;
         private long _bytesSent;
 
@@ -269,19 +267,13 @@ namespace MQTTnet.Adapter
             }
         }
 
-        public void Dispose()
-        {
-            _isDisposed = true;
-
-            _channel?.Dispose();
-        }
-
-        private void ThrowIfDisposed()
+        protected override void Dispose(bool disposing)
         {
-            if (_isDisposed)
+            if (disposing)
             {
-                throw new ObjectDisposedException(nameof(MqttChannelAdapter));
+                _channel?.Dispose();
             }
+            base.Dispose(disposing);
         }
 
         private static bool IsWrappedException(Exception exception)

Source/MQTTnet/Adapter/MqttConnectingFailedException.cs

@@ -5,12 +5,13 @@ namespace MQTTnet.Adapter
 {
     public class MqttConnectingFailedException : MqttCommunicationException
     {
-        public MqttConnectingFailedException(MqttClientConnectResultCode resultCode)
-            : base($"Connecting with MQTT server failed ({resultCode.ToString()}).")
+        public MqttConnectingFailedException(MqttClientAuthenticateResult result)
+            : base($"Connecting with MQTT server failed ({result.ResultCode.ToString()}).")
         {
-            ResultCode = resultCode;
+            Result = result;
         }
 
-        public MqttClientConnectResultCode ResultCode { get; }
+        public MqttClientAuthenticateResult Result { get; }
+        public MqttClientConnectResultCode ResultCode => Result.ResultCode;
     }
 }

Source/MQTTnet/Client/MqttClient.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Diagnostics;
 using System.Threading;
 using System.Threading.Tasks;
@@ -20,11 +20,12 @@ using MQTTnet.Protocol;
 
 namespace MQTTnet.Client
 {
-    public class MqttClient : IMqttClient
+    public class MqttClient : Disposable, IMqttClient
     {
         private readonly MqttPacketIdentifierProvider _packetIdentifierProvider = new MqttPacketIdentifierProvider();
         private readonly MqttPacketDispatcher _packetDispatcher = new MqttPacketDispatcher();
         private readonly Stopwatch _sendTracker = new Stopwatch();
+        private readonly Stopwatch _receiveTracker = new Stopwatch();
         private readonly object _disconnectLock = new object();
 
         private readonly IMqttClientAdapterFactory _adapterFactory;
@@ -63,6 +64,8 @@ namespace MQTTnet.Client
 
             ThrowIfConnected("It is not allowed to connect with a server after the connection is established.");
 
+            ThrowIfDisposed();
+
             MqttClientAuthenticateResult authenticateResult = null;
 
             try
@@ -79,15 +82,19 @@ namespace MQTTnet.Client
                 var adapter = _adapterFactory.CreateClientAdapter(options, _logger);
                 _adapter = adapter;
 
-                _logger.Verbose($"Trying to connect with server '{options.ChannelOptions}' (Timeout={options.CommunicationTimeout}).");
-                await _adapter.ConnectAsync(options.CommunicationTimeout, cancellationToken).ConfigureAwait(false);
-                _logger.Verbose("Connection with server established.");
+                using (var combined = CancellationTokenSource.CreateLinkedTokenSource(backgroundCancellationToken, cancellationToken))
+                {
+                    _logger.Verbose($"Trying to connect with server '{options.ChannelOptions}' (Timeout={options.CommunicationTimeout}).");
+                    await _adapter.ConnectAsync(options.CommunicationTimeout, combined.Token).ConfigureAwait(false);
+                    _logger.Verbose("Connection with server established.");
 
-                _packetReceiverTask = Task.Run(() => TryReceivePacketsAsync(backgroundCancellationToken), backgroundCancellationToken);
+                    _packetReceiverTask = Task.Run(() => TryReceivePacketsAsync(backgroundCancellationToken), backgroundCancellationToken);
 
-                authenticateResult = await AuthenticateAsync(adapter, options.WillMessage, cancellationToken).ConfigureAwait(false);
+                    authenticateResult = await AuthenticateAsync(adapter, options.WillMessage, combined.Token).ConfigureAwait(false);
+                }
 
                 _sendTracker.Restart();
+                _receiveTracker.Restart();
 
                 if (Options.KeepAlivePeriod != TimeSpan.Zero)
                 {
@@ -149,7 +156,7 @@ namespace MQTTnet.Client
                 Properties = new MqttAuthPacketProperties
                 {
                     // This must always be equal to the value from the CONNECT packet. So we use it here to ensure that.
-                    AuthenticationMethod = Options.AuthenticationMethod, 
+                    AuthenticationMethod = Options.AuthenticationMethod,
                     AuthenticationData = data.AuthenticationData,
                     ReasonString = data.ReasonString,
                     UserProperties = data.UserProperties
@@ -161,6 +168,7 @@ namespace MQTTnet.Client
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
+            ThrowIfDisposed();
             ThrowIfNotConnected();
 
             var subscribePacket = _adapter.PacketFormatterAdapter.DataConverter.CreateSubscribePacket(options);
@@ -174,6 +182,7 @@ namespace MQTTnet.Client
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
+            ThrowIfDisposed();
             ThrowIfNotConnected();
 
             var unsubscribePacket = _adapter.PacketFormatterAdapter.DataConverter.CreateUnsubscribePacket(options);
@@ -189,6 +198,7 @@ namespace MQTTnet.Client
 
             MqttTopicValidator.ThrowIfInvalid(applicationMessage.Topic);
 
+            ThrowIfDisposed();
             ThrowIfNotConnected();
 
             var publishPacket = _adapter.PacketFormatterAdapter.DataConverter.CreatePublishPacket(applicationMessage);
@@ -214,7 +224,7 @@ namespace MQTTnet.Client
             }
         }
 
-        public void Dispose()
+        private void Cleanup()
         {
             _backgroundCancellationTokenSource?.Cancel(false);
             _backgroundCancellationTokenSource?.Dispose();
@@ -224,6 +234,18 @@ namespace MQTTnet.Client
             _adapter = null;
         }
 
+
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                Cleanup();
+
+                DisconnectedHandler = null;
+            }
+            base.Dispose(disposing);
+        }
+
         private async Task<MqttClientAuthenticateResult> AuthenticateAsync(IMqttChannelAdapter channelAdapter, MqttApplicationMessage willApplicationMessage, CancellationToken cancellationToken)
         {
             var connectPacket = channelAdapter.PacketFormatterAdapter.DataConverter.CreateConnectPacket(
@@ -235,7 +257,7 @@ namespace MQTTnet.Client
 
             if (result.ResultCode != MqttClientConnectResultCode.Success)
             {
-                throw new MqttConnectingFailedException(result.ResultCode);
+                throw new MqttConnectingFailedException(result);
             }
 
             _logger.Verbose("Authenticated MQTT connection with server established.");
@@ -258,29 +280,37 @@ namespace MQTTnet.Client
             var clientWasConnected = IsConnected;
 
             TryInitiateDisconnect();
+            IsConnected = false;
 
             try
             {
-                IsConnected = false;
-
                 if (_adapter != null)
                 {
                     _logger.Verbose("Disconnecting [Timeout={0}]", Options.CommunicationTimeout);
                     await _adapter.DisconnectAsync(Options.CommunicationTimeout, CancellationToken.None).ConfigureAwait(false);
                 }
 
-                await WaitForTaskAsync(_packetReceiverTask, sender).ConfigureAwait(false);
-                await WaitForTaskAsync(_keepAlivePacketsSenderTask, sender).ConfigureAwait(false);
-
                 _logger.Verbose("Disconnected from adapter.");
             }
             catch (Exception adapterException)
             {
                 _logger.Warning(adapterException, "Error while disconnecting from adapter.");
             }
+
+            try
+            {
+                var receiverTask = WaitForTaskAsync(_packetReceiverTask, sender);
+                var keepAliveTask = WaitForTaskAsync(_keepAlivePacketsSenderTask, sender);
+
+                await Task.WhenAll(receiverTask, keepAliveTask).ConfigureAwait(false);
+            }
+            catch (Exception e)
+            {
+                _logger.Warning(e, "Error while waiting for internal tasks.");
+            }
             finally
             {
-                Dispose();
+                Cleanup();
                 _cleanDisconnectInitiated = false;
 
                 _logger.Info("Disconnected.");
@@ -344,11 +374,26 @@ namespace MQTTnet.Client
                 try
                 {
                     await _adapter.SendPacketAsync(requestPacket, Options.CommunicationTimeout, cancellationToken).ConfigureAwait(false);
-                    return await packetAwaiter.WaitOneAsync(Options.CommunicationTimeout).ConfigureAwait(false);
                 }
-                catch (MqttCommunicationTimedOutException)
+                catch (Exception e)
+                {
+                    _logger.Warning(e, "Error when sending packet of type '{0}'.", typeof(TResponsePacket).Name);
+                    packetAwaiter.Cancel();
+                }
+
+                try
                 {
-                    _logger.Warning(null, "Timeout while waiting for packet of type '{0}'.", typeof(TResponsePacket).Name);
+                    var response = await packetAwaiter.WaitOneAsync(Options.CommunicationTimeout).ConfigureAwait(false);
+                    _receiveTracker.Restart();
+                    return response;
+                }
+                catch (Exception exception)
+                {
+                    if (exception is MqttCommunicationTimedOutException)
+                    {
+                        _logger.Warning(null, "Timeout while waiting for packet of type '{0}'.", typeof(TResponsePacket).Name);
+                    }
+
                     throw;
                 }
             }
@@ -369,14 +414,14 @@ namespace MQTTnet.Client
                         keepAliveSendInterval = Options.KeepAliveSendInterval.Value;
                     }
 
-                    var waitTime = keepAliveSendInterval - _sendTracker.Elapsed;
-                    if (waitTime <= TimeSpan.Zero)
+                    var waitTimeSend = keepAliveSendInterval - _sendTracker.Elapsed;
+                    var waitTimeReceive = keepAliveSendInterval - _receiveTracker.Elapsed;
+                    if (waitTimeSend <= TimeSpan.Zero || waitTimeReceive <= TimeSpan.Zero)
                     {
                         await SendAndReceiveAsync<MqttPingRespPacket>(new MqttPingReqPacket(), cancellationToken).ConfigureAwait(false);
-                        waitTime = keepAliveSendInterval;
                     }
 
-                    await Task.Delay(waitTime, cancellationToken).ConfigureAwait(false);
+                    await Task.Delay(keepAliveSendInterval, cancellationToken).ConfigureAwait(false);
                 }
             }
             catch (Exception exception)
@@ -391,11 +436,11 @@ namespace MQTTnet.Client
                 }
                 else if (exception is MqttCommunicationException)
                 {
-                    _logger.Warning(exception, "MQTT communication exception while sending/receiving keep alive packets.");
+                    _logger.Warning(exception, "Communication error while sending/receiving keep alive packets.");
                 }
                 else
                 {
-                    _logger.Error(exception, "Unhandled exception while sending/receiving keep alive packets.");
+                    _logger.Error(exception, "Error exception while sending/receiving keep alive packets.");
                 }
 
                 if (!DisconnectIsPending())
@@ -449,11 +494,11 @@ namespace MQTTnet.Client
                 }
                 else if (exception is MqttCommunicationException)
                 {
-                    _logger.Warning(exception, "MQTT communication exception while receiving packets.");
+                    _logger.Warning(exception, "Communication error while receiving packets.");
                 }
                 else
                 {
-                    _logger.Error(exception, "Unhandled exception while receiving packets.");
+                    _logger.Error(exception, "Error while receiving packets.");
                 }
 
                 _packetDispatcher.Dispatch(exception);
@@ -473,6 +518,8 @@ namespace MQTTnet.Client
         {
             try
             {
+                _receiveTracker.Restart();
+
                 if (packet is MqttPublishPacket publishPacket)
                 {
                     await TryProcessReceivedPublishPacketAsync(publishPacket, cancellationToken).ConfigureAwait(false);
@@ -521,11 +568,11 @@ namespace MQTTnet.Client
                 }
                 else if (exception is MqttCommunicationException)
                 {
-                    _logger.Warning(exception, "MQTT communication exception while receiving packets.");
+                    _logger.Warning(exception, "Communication error while receiving packets.");
                 }
                 else
                 {
-                    _logger.Error(exception, "Unhandled exception while receiving packets.");
+                    _logger.Error(exception, "Error while receiving packets.");
                 }
 
                 _packetDispatcher.Dispatch(exception);
@@ -567,7 +614,7 @@ namespace MQTTnet.Client
                         };
 
                         await SendAsync(pubRecPacket, cancellationToken).ConfigureAwait(false);
-                    }                    
+                    }
                 }
                 else
                 {
@@ -576,7 +623,7 @@ namespace MQTTnet.Client
             }
             catch (Exception exception)
             {
-                _logger.Error(exception, "Unhandled exception while handling application message.");
+                _logger.Error(exception, "Error while handling application message.");
             }
         }
 
@@ -626,15 +673,25 @@ namespace MQTTnet.Client
             return true;
         }
 
-        private static async Task WaitForTaskAsync(Task task, Task sender)
+        private async Task WaitForTaskAsync(Task task, Task sender)
         {
-            if (task == sender || task == null)
+            if (task == null)
             {
                 return;
             }
 
-            if (task.IsCanceled || task.IsCompleted || task.IsFaulted)
+            if (task == sender)
             {
+                // Return here to avoid deadlocks, but first any eventual exception in the task
+                // must be handled to avoid not getting an unhandled task exception
+                if (!task.IsFaulted)
+                {
+                    return;
+                }
+
+                // By accessing the Exception property the exception is considered handled and will
+                // not result in an unhandled task exception later by the finalizer
+                _logger.Warning(task.Exception, "Error while waiting for background task.");
                 return;
             }
 
@@ -652,4 +709,4 @@ namespace MQTTnet.Client
             return Interlocked.CompareExchange(ref _disconnectGate, 1, 0) != 0;
         }
     }
-}
+}

Source/MQTTnet/Client/Options/MqttClientOptionsBuilder.cs

@@ -256,7 +256,11 @@ namespace MQTTnet.Client.Options
                         UseTls = true,
                         SslProtocol = _tlsParameters.SslProtocol,
                         AllowUntrustedCertificates = _tlsParameters.AllowUntrustedCertificates,
+#if WINDOWS_UWP
                         Certificates = _tlsParameters.Certificates?.Select(c => c.ToArray()).ToList(),
+#else
+                        Certificates = _tlsParameters.Certificates?.ToList(),
+#endif
                         CertificateValidationCallback = _tlsParameters.CertificateValidationCallback,
                         IgnoreCertificateChainErrors = _tlsParameters.IgnoreCertificateChainErrors,
                         IgnoreCertificateRevocationErrors = _tlsParameters.IgnoreCertificateRevocationErrors

Source/MQTTnet/Client/Options/MqttClientOptionsBuilderTlsParameters.cs

@@ -18,7 +18,12 @@ namespace MQTTnet.Client.Options
 
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12;
 
+#if WINDOWS_UWP
         public IEnumerable<IEnumerable<byte>> Certificates { get; set; }
+#else
+        public IEnumerable<X509Certificate> Certificates { get; set; }
+#endif
+        
 
         public bool AllowUntrustedCertificates { get; set; }
 

Source/MQTTnet/Client/Options/MqttClientTlsOptions.cs

@@ -15,8 +15,11 @@ namespace MQTTnet.Client.Options
         public bool IgnoreCertificateChainErrors { get; set; }
 
         public bool AllowUntrustedCertificates { get; set; }
-
+#if WINDOWS_UWP
         public List<byte[]> Certificates { get; set; }
+#else
+        public List<X509Certificate> Certificates { get; set; }
+#endif
 
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12;
 

Source/MQTTnet/Client/Unsubscribing/MqttClientUnsubscribeOptionsBuilder.cs

@@ -0,0 +1,60 @@
+using MQTTnet.Packets;
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace MQTTnet.Client.Unsubscribing
+{
+    public class MqttClientUnsubscribeOptionsBuilder
+    {
+        private readonly MqttClientUnsubscribeOptions _unsubscribeOptions = new MqttClientUnsubscribeOptions();
+
+        public MqttClientUnsubscribeOptionsBuilder WithUserProperty(string name, string value)
+        {
+            if (name is null) throw new ArgumentNullException(nameof(name));
+            if (value is null) throw new ArgumentNullException(nameof(value));
+
+            return WithUserProperty(new MqttUserProperty(name, value));
+        }
+
+        public MqttClientUnsubscribeOptionsBuilder WithUserProperty(MqttUserProperty userProperty)
+        {
+            if (userProperty is null) throw new ArgumentNullException(nameof(userProperty));
+
+            if (_unsubscribeOptions.UserProperties is null)
+            {
+                _unsubscribeOptions.UserProperties = new List<MqttUserProperty>();
+            }
+
+            _unsubscribeOptions.UserProperties.Add(userProperty);
+
+            return this;
+        }
+
+        public MqttClientUnsubscribeOptionsBuilder WithTopicFilter(string topic)
+        {
+            if (topic is null) throw new ArgumentNullException(nameof(topic));
+
+            if (_unsubscribeOptions.TopicFilters is null)
+            {
+                _unsubscribeOptions.TopicFilters = new List<string>();
+            }
+
+            _unsubscribeOptions.TopicFilters.Add(topic);
+
+            return this;
+        }
+        
+        public MqttClientUnsubscribeOptionsBuilder WithTopicFilter(TopicFilter topicFilter)
+        {
+            if (topicFilter is null) throw new ArgumentNullException(nameof(topicFilter));
+
+            return WithTopic(topicFilter.Topic);
+        }
+
+        public MqttClientUnsubscribeOptions Build()
+        {
+            return _unsubscribeOptions;
+        }
+    }
+}

Source/MQTTnet/Exceptions/MqttConfigurationException.cs

@@ -0,0 +1,21 @@
+using System;
+
+namespace MQTTnet.Exceptions
+{
+    public class MqttConfigurationException : Exception
+    {
+        protected MqttConfigurationException()
+        {
+        }
+
+        public MqttConfigurationException(Exception innerException)
+            : base(innerException.Message, innerException)
+        {
+        }
+
+        public MqttConfigurationException(string message)
+            : base(message)
+        {
+        }
+    }
+}

Source/MQTTnet/Formatter/V5/MqttV500DataConverter.cs

@@ -139,7 +139,7 @@ namespace MQTTnet.Formatter.V5
                 ReasonCode = connectionValidatorContext.ReasonCode,
                 Properties = new MqttConnAckPacketProperties
                 {
-                    UserProperties = connectionValidatorContext.UserProperties,
+                    UserProperties = connectionValidatorContext.ResponseUserProperties,
                     AuthenticationMethod = connectionValidatorContext.AuthenticationMethod,
                     AuthenticationData = connectionValidatorContext.ResponseAuthenticationData,
                     AssignedClientIdentifier = connectionValidatorContext.AssignedClientIdentifier,

Source/MQTTnet/Implementations/MqttTcpChannel.cs

@@ -10,10 +10,11 @@ using System.Runtime.ExceptionServices;
 using System.Threading;
 using MQTTnet.Channel;
 using MQTTnet.Client.Options;
+using MQTTnet.Internal;
 
 namespace MQTTnet.Implementations
 {
-    public class MqttTcpChannel : IMqttChannel
+    public class MqttTcpChannel : Disposable, IMqttChannel
     {
         private readonly IMqttClientOptions _clientOptions;
         private readonly MqttClientTcpOptions _options;
@@ -72,11 +73,7 @@ namespace MQTTnet.Implementations
             // Workaround for: workaround for https://github.com/dotnet/corefx/issues/24430
             using (cancellationToken.Register(() => socket.Dispose()))
             {
-#if NET452 || NET461
-                await Task.Factory.FromAsync(socket.BeginConnect, socket.EndConnect, _options.Server, _options.GetPort(), null).ConfigureAwait(false);
-#else
-                await socket.ConnectAsync(_options.Server, _options.GetPort()).ConfigureAwait(false);
-#endif
+                await PlatformAbstractionLayer.ConnectAsync(socket, _options.Server, _options.GetPort()).ConfigureAwait(false);
             }
 
             var networkStream = new NetworkStream(socket, true);
@@ -98,7 +95,7 @@ namespace MQTTnet.Implementations
 
         public Task DisconnectAsync(CancellationToken cancellationToken)
         {
-            Dispose();
+            Cleanup();
             return Task.FromResult(0);
         }
 
@@ -117,6 +114,10 @@ namespace MQTTnet.Implementations
                     return await _stream.ReadAsync(buffer, offset, count, cancellationToken).ConfigureAwait(false);
                 }
             }
+            catch (ObjectDisposedException)
+            {
+                return 0;
+            }
             catch (IOException exception)
             {
                 if (exception.InnerException is SocketException socketException)
@@ -143,6 +144,10 @@ namespace MQTTnet.Implementations
                     await _stream.WriteAsync(buffer, offset, count, cancellationToken).ConfigureAwait(false);
                 }
             }
+            catch (ObjectDisposedException)
+            {
+                return;
+            }
             catch (IOException exception)
             {
                 if (exception.InnerException is SocketException socketException)
@@ -154,7 +159,7 @@ namespace MQTTnet.Implementations
             }
         }
 
-        public void Dispose()
+        private void Cleanup()
         {
             // When the stream is disposed it will also close the socket and this will also dispose it.
             // So there is no need to dispose the socket again.
@@ -173,6 +178,15 @@ namespace MQTTnet.Implementations
             _stream = null;
         }
 
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                Cleanup();
+            }
+            base.Dispose(disposing);
+        }
+
         private bool InternalUserCertificateValidationCallback(object sender, X509Certificate x509Certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
         {
             if (_options.TlsOptions.CertificateValidationCallback != null)
@@ -214,7 +228,7 @@ namespace MQTTnet.Implementations
 
             foreach (var certificate in _options.TlsOptions.Certificates)
             {
-                certificates.Add(new X509Certificate2(certificate));
+                certificates.Add(certificate);
             }
 
             return certificates;

Source/MQTTnet/Implementations/MqttTcpServerAdapter.cs

@@ -8,11 +8,12 @@ using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Adapter;
 using MQTTnet.Diagnostics;
+using MQTTnet.Internal;
 using MQTTnet.Server;
 
 namespace MQTTnet.Implementations
 {
-    public class MqttTcpServerAdapter : IMqttServerAdapter
+    public class MqttTcpServerAdapter : Disposable, IMqttServerAdapter
     {
         private readonly List<MqttTcpServerListener> _listeners = new List<MqttTcpServerListener>();
         private readonly IMqttNetChildLogger _logger;
@@ -72,11 +73,11 @@ namespace MQTTnet.Implementations
 
         public Task StopAsync()
         {
-            Dispose();
+            Cleanup();
             return Task.FromResult(0);
         }
 
-        public void Dispose()
+        private void Cleanup()
         {
             _cancellationTokenSource?.Cancel(false);
             _cancellationTokenSource?.Dispose();
@@ -90,6 +91,15 @@ namespace MQTTnet.Implementations
             _listeners.Clear();
         }
 
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                Cleanup();
+            }
+            base.Dispose(disposing);
+        }
+
         private void RegisterListeners(MqttServerTcpEndpointBaseOptions options, X509Certificate2 tlsCertificate, CancellationToken cancellationToken)
         {
             if (!options.BoundInterNetworkAddress.Equals(IPAddress.None))

Source/MQTTnet/Implementations/MqttTcpServerListener.cs

@@ -107,12 +107,7 @@ namespace MQTTnet.Implementations
             {
                 try
                 {
-#if NET452 || NET461
-                    var clientSocket = await Task.Factory.FromAsync(_socket.BeginAccept, _socket.EndAccept, null).ConfigureAwait(false);
-#else
-                    var clientSocket = await _socket.AcceptAsync().ConfigureAwait(false);
-#endif
-
+                    var clientSocket = await PlatformAbstractionLayer.AcceptAsync(_socket).ConfigureAwait(false);
                     if (clientSocket == null)
                     {
                         continue;

Source/MQTTnet/Implementations/MqttWebSocketChannel.cs

@@ -6,10 +6,11 @@ using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Channel;
 using MQTTnet.Client.Options;
+using MQTTnet.Internal;
 
 namespace MQTTnet.Implementations
 {
-    public class MqttWebSocketChannel : IMqttChannel
+    public class MqttWebSocketChannel : Disposable, IMqttChannel
     {
         private readonly MqttClientWebSocketOptions _options;
 
@@ -84,7 +85,12 @@ namespace MQTTnet.Implementations
                 clientWebSocket.Options.ClientCertificates = new X509CertificateCollection();
                 foreach (var certificate in _options.TlsOptions.Certificates)
                 {
+#if WINDOWS_UWP
                     clientWebSocket.Options.ClientCertificates.Add(new X509Certificate(certificate));
+#else
+                    clientWebSocket.Options.ClientCertificates.Add(certificate);
+#endif
+                    
                 }
             }
 
@@ -106,7 +112,7 @@ namespace MQTTnet.Implementations
                 await _webSocket.CloseAsync(WebSocketCloseStatus.NormalClosure, string.Empty, cancellationToken).ConfigureAwait(false);
             }
 
-            Dispose();
+            Cleanup();
         }
 
         public async Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
@@ -136,7 +142,16 @@ namespace MQTTnet.Implementations
             }
         }
 
-        public void Dispose()
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                Cleanup();
+            }
+            base.Dispose(disposing);
+        }
+
+        private void Cleanup()
         {
             _sendLock?.Dispose();
             _sendLock = null;

Source/MQTTnet/Implementations/PlatformAbstractionLayer.cs

@@ -0,0 +1,104 @@
+using System;
+using System.Net;
+using System.Net.Sockets;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Implementations
+{
+    public static class PlatformAbstractionLayer
+    {
+        public static async Task<Socket> AcceptAsync(Socket socket)
+        {
+#if NET452 || NET461
+            try
+            {
+                return await Task.Factory.FromAsync(socket.BeginAccept, socket.EndAccept, null).ConfigureAwait(false);
+            }
+            catch (ObjectDisposedException)
+            {
+                return null;
+            }
+#else
+            return await socket.AcceptAsync().ConfigureAwait(false);
+#endif
+        }
+
+
+        public static Task ConnectAsync(Socket socket, IPAddress ip, int port)
+        {
+#if NET452 || NET461
+            return Task.Factory.FromAsync(socket.BeginConnect, socket.EndConnect, ip, port, null);
+#else
+            return socket.ConnectAsync(ip, port);
+#endif
+        }
+
+        public static Task ConnectAsync(Socket socket, string host, int port)
+        {
+#if NET452 || NET461
+            return Task.Factory.FromAsync(socket.BeginConnect, socket.EndConnect, host, port, null);
+#else
+            return socket.ConnectAsync(host, port);
+#endif
+        }
+
+#if NET452 || NET461
+        public class SocketWrapper 
+        {
+            private readonly Socket _socket;
+            private readonly ArraySegment<byte> _buffer;
+            private readonly SocketFlags _socketFlags;
+
+            public SocketWrapper(Socket socket, ArraySegment<byte> buffer, SocketFlags socketFlags)
+            {
+                _socket = socket;
+                _buffer = buffer;
+                _socketFlags = socketFlags;
+            }
+
+            public static IAsyncResult BeginSend(AsyncCallback callback, object state)
+            {
+                var real = (SocketWrapper)state;
+                return real._socket.BeginSend(real._buffer.Array, real._buffer.Offset, real._buffer.Count, real._socketFlags, callback, state);
+            }
+
+            public static IAsyncResult BeginReceive(AsyncCallback callback, object state)
+            {
+                var real = (SocketWrapper)state;
+                return real._socket.BeginReceive(real._buffer.Array, real._buffer.Offset, real._buffer.Count, real._socketFlags, callback, state);
+            }
+        }
+#endif
+
+        public static Task SendAsync(Socket socket, ArraySegment<byte> buffer, SocketFlags socketFlags)
+        {
+#if NET452 || NET461            
+            return Task.Factory.FromAsync(SocketWrapper.BeginSend, socket.EndSend, new SocketWrapper(socket, buffer, socketFlags));
+#else
+            return socket.SendAsync(buffer, socketFlags);
+#endif
+        }
+
+        public static Task<int> ReceiveAsync(Socket socket, ArraySegment<byte> buffer, SocketFlags socketFlags)
+        {
+#if NET452 || NET461
+            return Task.Factory.FromAsync(SocketWrapper.BeginReceive, socket.EndReceive, new SocketWrapper(socket, buffer, socketFlags));
+#else
+            return socket.ReceiveAsync(buffer, socketFlags);
+#endif
+        }
+
+        public static Task CompletedTask
+        {
+            get 
+            {
+#if NET452 
+                return Task.FromResult(0);
+#else
+                return Task.CompletedTask;
+#endif
+            }
+        }
+
+    }
+}

Source/MQTTnet/Internal/AsyncAutoResetEvent.cs

@@ -1,131 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Threading;
-using System.Threading.Tasks;
-
-namespace MQTTnet.Internal
-{
-    // Inspired from Stephen Toub (https://blogs.msdn.microsoft.com/pfxteam/2012/02/11/building-async-coordination-primitives-part-2-asyncautoresetevent/) and Chris Gillum (https://stackoverflow.com/a/43012490)
-    public class AsyncAutoResetEvent
-    {
-        private readonly LinkedList<TaskCompletionSource<bool>> _waiters = new LinkedList<TaskCompletionSource<bool>>();
-
-        private bool _isSignaled;
-
-        public AsyncAutoResetEvent()
-            : this(false)
-        {
-        }
-
-        public AsyncAutoResetEvent(bool signaled)
-        {
-            _isSignaled = signaled;
-        }
-
-        public int WaitersCount
-        {
-            get
-            {
-                lock (_waiters)
-                {
-                    return _waiters.Count;
-                }
-            }
-        }
-
-        public Task<bool> WaitOneAsync()
-        {
-            return WaitOneAsync(CancellationToken.None);
-        }
-
-        public Task<bool> WaitOneAsync(TimeSpan timeout)
-        {
-            return WaitOneAsync(timeout, CancellationToken.None);
-        }
-
-        public Task<bool> WaitOneAsync(CancellationToken cancellationToken)
-        {
-            return WaitOneAsync(Timeout.InfiniteTimeSpan, cancellationToken);
-        }
-
-        public async Task<bool> WaitOneAsync(TimeSpan timeout, CancellationToken cancellationToken)
-        {
-            cancellationToken.ThrowIfCancellationRequested();
-
-            TaskCompletionSource<bool> tcs;
-
-            lock (_waiters)
-            {
-                if (_isSignaled)
-                {
-                    _isSignaled = false;
-                    return true;
-                }
-
-                if (timeout == TimeSpan.Zero)
-                {
-                    return _isSignaled;
-                }
-
-                tcs = new TaskCompletionSource<bool>();
-                _waiters.AddLast(tcs);
-            }
-
-            Task winner;
-            if (timeout == Timeout.InfiniteTimeSpan)
-            {
-                using (cancellationToken.Register(() => { tcs.TrySetCanceled(); }))
-                {
-                    await tcs.Task.ConfigureAwait(false);
-                    winner = tcs.Task;
-                }               
-            }
-            else
-            {
-                winner = await Task.WhenAny(tcs.Task, Task.Delay(timeout, cancellationToken)).ConfigureAwait(false);
-            }
-            
-            var taskWasSignaled = winner == tcs.Task;
-            if (taskWasSignaled)
-            {
-                return true;
-            }
-
-            // We timed-out; remove our reference to the task.
-            // This is an O(n) operation since waiters is a LinkedList<T>.
-            lock (_waiters)
-            {
-                _waiters.Remove(tcs);
-
-                if (winner.Status == TaskStatus.Canceled)
-                {
-                    throw new OperationCanceledException(cancellationToken);
-                }
-
-                throw new TimeoutException();
-            }
-        }
-
-        public void Set()
-        {
-            TaskCompletionSource<bool> toRelease = null;
-
-            lock (_waiters)
-            {
-                if (_waiters.Count > 0)
-                {
-                    // Signal the first task in the waiters list.
-                    toRelease = _waiters.First.Value;
-                    _waiters.RemoveFirst();
-                }
-                else if (!_isSignaled)
-                {
-                    // No tasks are pending
-                    _isSignaled = true;
-                }
-            }
-
-            toRelease?.TrySetResult(true);
-        }
-    }
-}

Source/MQTTnet/Internal/BlockingQueue.cs

@@ -4,11 +4,11 @@ using System.Threading;
 
 namespace MQTTnet.Internal
 {
-    public class BlockingQueue<TItem>
+    public class BlockingQueue<TItem> : Disposable
     {
         private readonly object _syncRoot = new object();
         private readonly LinkedList<TItem> _items = new LinkedList<TItem>();
-        private readonly ManualResetEvent _gate = new ManualResetEvent(false);
+        private readonly ManualResetEventSlim _gate = new ManualResetEventSlim(false);
 
         public int Count
         {
@@ -32,7 +32,7 @@ namespace MQTTnet.Internal
             }
         }
 
-        public TItem Dequeue()
+        public TItem Dequeue(CancellationToken cancellationToken = default(CancellationToken))
         {
             while (true)
             {
@@ -52,11 +52,11 @@ namespace MQTTnet.Internal
                     }
                 }
 
-                _gate.WaitOne();
+                _gate.Wait(cancellationToken);
             }
         }
         
-        public TItem PeekAndWait()
+        public TItem PeekAndWait(CancellationToken cancellationToken = default(CancellationToken))
         {
             while (true)
             {
@@ -73,7 +73,7 @@ namespace MQTTnet.Internal
                     }
                 }
 
-                _gate.WaitOne();
+                _gate.Wait(cancellationToken);
             }
         }
 
@@ -108,5 +108,14 @@ namespace MQTTnet.Internal
                 _items.Clear();
             }
         }
+
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                _gate.Dispose();
+            }
+            base.Dispose(disposing);
+        }
     }
 }

Source/MQTTnet/Internal/Disposable.cs

@@ -0,0 +1,57 @@
+using System;
+
+namespace MQTTnet.Internal
+{
+    public class Disposable : IDisposable
+    {
+        protected bool IsDisposed => _isDisposed;
+
+        protected void ThrowIfDisposed()
+        {
+            if (_isDisposed)
+            {
+                throw new ObjectDisposedException(GetType().Name);
+            }
+        }
+
+
+        #region IDisposable Support
+       
+        private bool _isDisposed = false; // To detect redundant calls
+
+        protected virtual void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                // TODO: dispose managed state (managed objects).
+            }
+
+            // TODO: free unmanaged resources (unmanaged objects) and override a finalizer below.
+            // TODO: set large fields to null.
+        }
+
+        // TODO: override a finalizer only if Dispose(bool disposing) above has code to free unmanaged resources.
+        // ~Disposable()
+        // {
+        //   // Do not change this code. Put cleanup code in Dispose(bool disposing) above.
+        //   Dispose(false);
+        // }
+
+        // This code added to correctly implement the disposable pattern.
+        public void Dispose()
+        {
+            if (_isDisposed)
+            {
+                return;
+            }
+
+            _isDisposed = true;
+
+            // Do not change this code. Put cleanup code in Dispose(bool disposing) above.
+            Dispose(true);
+            // TODO: uncomment the following line if the finalizer is overridden above.
+            // GC.SuppressFinalize(this);
+        }
+        #endregion
+    }
+}

Source/MQTTnet/MQTTnet.csproj

@@ -62,5 +62,9 @@
 
   <ItemGroup Condition="'$(TargetFramework)'=='net461'">
   </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform" Version="6.2.9" />
+  </ItemGroup>
   
 </Project>

Source/MQTTnet/PacketDispatcher/MqttPacketAwaiter.cs

@@ -2,13 +2,14 @@
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Exceptions;
+using MQTTnet.Internal;
 using MQTTnet.Packets;
 
 namespace MQTTnet.PacketDispatcher
 {
-    public sealed class MqttPacketAwaiter<TPacket> : IMqttPacketAwaiter where TPacket : MqttBasePacket
+    public sealed class MqttPacketAwaiter<TPacket> : Disposable, IMqttPacketAwaiter where TPacket : MqttBasePacket
     {
-        private readonly TaskCompletionSource<MqttBasePacket> _taskCompletionSource = new TaskCompletionSource<MqttBasePacket>();
+        private readonly TaskCompletionSource<MqttBasePacket> _taskCompletionSource;
         private readonly ushort? _packetIdentifier;
         private readonly MqttPacketDispatcher _owningPacketDispatcher;
         
@@ -16,13 +17,18 @@ namespace MQTTnet.PacketDispatcher
         {
             _packetIdentifier = packetIdentifier;
             _owningPacketDispatcher = owningPacketDispatcher ?? throw new ArgumentNullException(nameof(owningPacketDispatcher));
+#if NET452
+            _taskCompletionSource = new TaskCompletionSource<MqttBasePacket>();
+#else
+            _taskCompletionSource = new TaskCompletionSource<MqttBasePacket>(TaskCreationOptions.RunContinuationsAsynchronously);
+#endif
         }
 
         public async Task<TPacket> WaitOneAsync(TimeSpan timeout)
         {
             using (var timeoutToken = new CancellationTokenSource(timeout))
             {
-                timeoutToken.Token.Register(() => _taskCompletionSource.TrySetException(new MqttCommunicationTimedOutException()));
+                timeoutToken.Token.Register(() => Fail(new MqttCommunicationTimedOutException()));
 
                 var packet = await _taskCompletionSource.Task.ConfigureAwait(false);
                 return (TPacket)packet;
@@ -32,29 +38,56 @@ namespace MQTTnet.PacketDispatcher
         public void Complete(MqttBasePacket packet)
         {
             if (packet == null) throw new ArgumentNullException(nameof(packet));
-            
+
+
+#if NET452
             // To prevent deadlocks it is required to call the _TrySetResult_ method
             // from a new thread because the awaiting code will not(!) be executed in
             // a new thread automatically (due to await). Furthermore _this_ thread will
             // do it. But _this_ thread is also reading incoming packets -> deadlock.
+            // NET452 does not support RunContinuationsAsynchronously
             Task.Run(() => _taskCompletionSource.TrySetResult(packet));
+#else
+            _taskCompletionSource.TrySetResult(packet);
+#endif
         }
 
         public void Fail(Exception exception)
         {
             if (exception == null) throw new ArgumentNullException(nameof(exception));
-
+#if NET452
+            // To prevent deadlocks it is required to call the _TrySetResult_ method
+            // from a new thread because the awaiting code will not(!) be executed in
+            // a new thread automatically (due to await). Furthermore _this_ thread will
+            // do it. But _this_ thread is also reading incoming packets -> deadlock.
+            // NET452 does not support RunContinuationsAsynchronously
             Task.Run(() => _taskCompletionSource.TrySetException(exception));
+#else
+            _taskCompletionSource.TrySetException(exception);
+#endif
         }
 
         public void Cancel()
         {
+#if NET452
+            // To prevent deadlocks it is required to call the _TrySetResult_ method
+            // from a new thread because the awaiting code will not(!) be executed in
+            // a new thread automatically (due to await). Furthermore _this_ thread will
+            // do it. But _this_ thread is also reading incoming packets -> deadlock.
+            // NET452 does not support RunContinuationsAsynchronously
             Task.Run(() => _taskCompletionSource.TrySetCanceled());
+#else
+            _taskCompletionSource.TrySetCanceled();
+#endif
         }
 
-        public void Dispose()
+        protected override void Dispose(bool disposing)
         {
-            _owningPacketDispatcher.RemovePacketAwaiter<TPacket>(_packetIdentifier);
+            if (disposing)
+            {
+                _owningPacketDispatcher.RemovePacketAwaiter<TPacket>(_packetIdentifier);
+            }
+            base.Dispose(disposing);
         }
     }
 }

Source/MQTTnet/Server/IMqttRetainedMessagesManager.cs

@@ -0,0 +1,21 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using MQTTnet.Diagnostics;
+
+namespace MQTTnet.Server
+{
+    public interface IMqttRetainedMessagesManager
+    {
+        Task Start(IMqttServerOptions options, IMqttNetChildLogger logger);
+
+        Task LoadMessagesAsync();
+
+        Task ClearMessagesAsync();
+
+        Task HandleMessageAsync(string clientId, MqttApplicationMessage applicationMessage);
+
+        Task<IList<MqttApplicationMessage>> GetMessagesAsync();
+
+        Task<IList<MqttApplicationMessage>> GetSubscribedMessagesAsync(ICollection<TopicFilter> topicFilters);
+    }
+}

Source/MQTTnet/Server/IMqttServerOptions.cs

@@ -15,14 +15,15 @@ namespace MQTTnet.Server
 
         IMqttServerConnectionValidator ConnectionValidator { get; }
         IMqttServerSubscriptionInterceptor SubscriptionInterceptor { get; }
+        IMqttServerUnsubscriptionInterceptor UnsubscriptionInterceptor { get; }
         IMqttServerApplicationMessageInterceptor ApplicationMessageInterceptor { get; }
         IMqttServerClientMessageQueueInterceptor ClientMessageQueueInterceptor { get; }
 
         MqttServerTcpEndpointOptions DefaultEndpointOptions { get; }
         MqttServerTlsTcpEndpointOptions TlsEndpointOptions { get; }
 
-        IMqttServerStorage Storage { get; }       
-        
+        IMqttServerStorage Storage { get; }
 
+        IMqttRetainedMessagesManager RetainedMessagesManager { get; }
     }
 }

Source/MQTTnet/Server/IMqttServerUnsubscriptionInterceptor.cs

@@ -0,0 +1,9 @@
+using System.Threading.Tasks;
+
+namespace MQTTnet.Server
+{
+    public interface IMqttServerUnsubscriptionInterceptor
+    {
+        Task InterceptUnsubscriptionAsync(MqttUnsubscriptionInterceptorContext context);
+    }
+}

Source/MQTTnet/Server/MqttClientConnection.cs

@@ -21,7 +21,7 @@ namespace MQTTnet.Server
         private readonly MqttPacketDispatcher _packetDispatcher = new MqttPacketDispatcher();
         private readonly CancellationTokenSource _cancellationToken = new CancellationTokenSource();
 
-        private readonly MqttRetainedMessagesManager _retainedMessagesManager;
+        private readonly IMqttRetainedMessagesManager _retainedMessagesManager;
         private readonly MqttClientKeepAliveMonitor _keepAliveMonitor;
         private readonly MqttClientSessionsManager _sessionsManager;
 
@@ -36,7 +36,7 @@ namespace MQTTnet.Server
         private Task<MqttClientDisconnectType> _packageReceiverTask;
         private DateTime _lastPacketReceivedTimestamp;
         private DateTime _lastNonKeepAlivePacketReceivedTimestamp;
-        
+
         private long _receivedPacketsCount;
         private long _sentPacketsCount = 1; // Start with 1 because the CONNECT packet is not counted anywhere.
         private long _receivedApplicationMessagesCount;
@@ -48,14 +48,14 @@ namespace MQTTnet.Server
             MqttClientSession session,
             IMqttServerOptions serverOptions,
             MqttClientSessionsManager sessionsManager,
-            MqttRetainedMessagesManager retainedMessagesManager,
+            IMqttRetainedMessagesManager retainedMessagesManager,
             IMqttNetChildLogger logger)
         {
             Session = session ?? throw new ArgumentNullException(nameof(session));
             _serverOptions = serverOptions ?? throw new ArgumentNullException(nameof(serverOptions));
             _sessionsManager = sessionsManager ?? throw new ArgumentNullException(nameof(sessionsManager));
             _retainedMessagesManager = retainedMessagesManager ?? throw new ArgumentNullException(nameof(retainedMessagesManager));
-            
+
             _channelAdapter = channelAdapter ?? throw new ArgumentNullException(nameof(channelAdapter));
             _dataConverter = _channelAdapter.PacketFormatterAdapter.DataConverter;
             _endpoint = _channelAdapter.Endpoint;
@@ -76,7 +76,7 @@ namespace MQTTnet.Server
         public string ClientId => ConnectPacket.ClientId;
 
         public MqttClientSession Session { get; }
-        
+
         public async Task StopAsync()
         {
             StopInternal();
@@ -112,25 +112,25 @@ namespace MQTTnet.Server
             status.BytesSent = _channelAdapter.BytesSent;
             status.BytesReceived = _channelAdapter.BytesReceived;
         }
-        
+
         public void Dispose()
         {
             _cancellationToken.Dispose();
         }
 
-        public Task<MqttClientDisconnectType> RunAsync()
+        public Task<MqttClientDisconnectType> RunAsync(MqttConnectionValidatorContext connectionValidatorContext)
         {
-            _packageReceiverTask = RunInternalAsync();
+            _packageReceiverTask = RunInternalAsync(connectionValidatorContext);
             return _packageReceiverTask;
         }
 
-        private async Task<MqttClientDisconnectType> RunInternalAsync()
+        private async Task<MqttClientDisconnectType> RunInternalAsync(MqttConnectionValidatorContext connectionValidatorContext)
         {
             var disconnectType = MqttClientDisconnectType.NotClean;
             try
             {
                 _logger.Info("Client '{0}': Session started.", ClientId);
-                
+
                 _channelAdapter.ReadingPacketStartedCallback = OnAdapterReadingPacketStarted;
                 _channelAdapter.ReadingPacketCompletedCallback = OnAdapterReadingPacketCompleted;
 
@@ -142,12 +142,8 @@ namespace MQTTnet.Server
                 _keepAliveMonitor.Start(ConnectPacket.KeepAlivePeriod, _cancellationToken.Token);
 
                 await SendAsync(
-                    new MqttConnAckPacket
-                    {
-                        ReturnCode = MqttConnectReturnCode.ConnectionAccepted,
-                        ReasonCode = MqttConnectReasonCode.Success,
-                        IsSessionPresent = !Session.IsCleanSession
-                    }).ConfigureAwait(false);
+                    _channelAdapter.PacketFormatterAdapter.DataConverter.CreateConnAckPacket(connectionValidatorContext)
+                    ).ConfigureAwait(false);
 
                 Session.IsCleanSession = false;
 
@@ -248,7 +244,7 @@ namespace MQTTnet.Server
                 _channelAdapter.ReadingPacketCompletedCallback = null;
 
                 _logger.Info("Client '{0}': Session stopped.", ClientId);
-                
+
                 _packageReceiverTask = null;
             }
 

Source/MQTTnet/Server/MqttClientSession.cs

@@ -52,7 +52,7 @@ namespace MQTTnet.Server
             ApplicationMessagesQueue.Enqueue(applicationMessage, senderClientId, checkSubscriptionsResult.QualityOfServiceLevel, isRetainedApplicationMessage);
         }
 
-        public async Task SubscribeAsync(ICollection<TopicFilter> topicFilters, MqttRetainedMessagesManager retainedMessagesManager)
+        public async Task SubscribeAsync(ICollection<TopicFilter> topicFilters, IMqttRetainedMessagesManager retainedMessagesManager)
         {
             await SubscriptionsManager.SubscribeAsync(topicFilters).ConfigureAwait(false);
 

Source/MQTTnet/Server/MqttClientSessionApplicationMessagesQueue.cs

@@ -6,7 +6,7 @@ using System.Threading.Tasks;
 
 namespace MQTTnet.Server
 {
-    public class MqttClientSessionApplicationMessagesQueue : IDisposable
+    public class MqttClientSessionApplicationMessagesQueue : Disposable
     {
         private readonly AsyncQueue<MqttQueuedApplicationMessage> _messageQueue = new AsyncQueue<MqttQueuedApplicationMessage>();
         
@@ -71,9 +71,14 @@ namespace MQTTnet.Server
             }
         }
 
-        public void Dispose()
+        protected override void Dispose(bool disposing)
         {
-            _messageQueue.Dispose();
+            if (disposing)
+            {
+                _messageQueue.Dispose();
+            }
+
+            base.Dispose(disposing);
         }
     }
 }

Source/MQTTnet/Server/MqttClientSessionsManager.cs

@@ -13,7 +13,7 @@ using MQTTnet.Server.Status;
 
 namespace MQTTnet.Server
 {
-    public class MqttClientSessionsManager : IDisposable
+    public class MqttClientSessionsManager : Disposable
     {
         private readonly AsyncQueue<MqttEnqueuedApplicationMessage> _messageQueue = new AsyncQueue<MqttEnqueuedApplicationMessage>();
 
@@ -25,13 +25,13 @@ namespace MQTTnet.Server
         private readonly CancellationToken _cancellationToken;
         private readonly MqttServerEventDispatcher _eventDispatcher;
 
-        private readonly MqttRetainedMessagesManager _retainedMessagesManager;
+        private readonly IMqttRetainedMessagesManager _retainedMessagesManager;
         private readonly IMqttServerOptions _options;
         private readonly IMqttNetChildLogger _logger;
 
         public MqttClientSessionsManager(
             IMqttServerOptions options,
-            MqttRetainedMessagesManager retainedMessagesManager,
+            IMqttRetainedMessagesManager retainedMessagesManager,
             CancellationToken cancellationToken,
             MqttServerEventDispatcher eventDispatcher,
             IMqttNetChildLogger logger)
@@ -72,7 +72,7 @@ namespace MQTTnet.Server
             {
                 var clientStatus = new MqttClientStatus(connection);
                 connection.FillStatus(clientStatus);
-                
+
                 var sessionStatus = new MqttSessionStatus(connection.Session, this);
                 connection.Session.FillStatus(sessionStatus);
                 clientStatus.Session = sessionStatus;
@@ -91,7 +91,7 @@ namespace MQTTnet.Server
             {
                 var sessionStatus = new MqttSessionStatus(session, this);
                 session.FillStatus(sessionStatus);
-    
+
                 result.Add(sessionStatus);
             }
 
@@ -145,9 +145,13 @@ namespace MQTTnet.Server
             _logger.Verbose("Session for client '{0}' deleted.", clientId);
         }
 
-        public void Dispose()
+        protected override void Dispose(bool disposing)
         {
-            _messageQueue?.Dispose();
+            if (disposing)
+            {
+                _messageQueue?.Dispose();
+            }
+            base.Dispose(disposing);
         }
 
         private async Task TryProcessQueuedApplicationMessagesAsync(CancellationToken cancellationToken)
@@ -230,6 +234,7 @@ namespace MQTTnet.Server
         {
             var disconnectType = MqttClientDisconnectType.NotClean;
             string clientId = null;
+            var clientWasConnected = true;
 
             try
             {
@@ -240,12 +245,13 @@ namespace MQTTnet.Server
                     return;
                 }
 
-                clientId = connectPacket.ClientId;
-
                 var connectionValidatorContext = await ValidateConnectionAsync(connectPacket, channelAdapter).ConfigureAwait(false);
 
+                clientId = connectPacket.ClientId;
+
                 if (connectionValidatorContext.ReasonCode != MqttConnectReasonCode.Success)
                 {
+                    clientWasConnected = false;
                     // Send failure response here without preparing a session. The result for a successful connect
                     // will be sent from the session itself.
                     var connAckPacket = channelAdapter.PacketFormatterAdapter.DataConverter.CreateConnAckPacket(connectionValidatorContext);
@@ -257,8 +263,8 @@ namespace MQTTnet.Server
                 var connection = await CreateConnectionAsync(connectPacket, connectionValidatorContext, channelAdapter).ConfigureAwait(false);
 
                 await _eventDispatcher.HandleClientConnectedAsync(clientId).ConfigureAwait(false);
-                
-                disconnectType = await connection.RunAsync().ConfigureAwait(false);
+
+                disconnectType = await connection.RunAsync(connectionValidatorContext).ConfigureAwait(false);
             }
             catch (OperationCanceledException)
             {
@@ -269,21 +275,24 @@ namespace MQTTnet.Server
             }
             finally
             {
-                if (clientId != null)
+                if (clientWasConnected)
                 {
-                    _connections.TryRemove(clientId, out _);
-
-                    if (!_options.EnablePersistentSessions)
+                    if (clientId != null)
                     {
-                        await DeleteSessionAsync(clientId).ConfigureAwait(false);
+                        _connections.TryRemove(clientId, out _);
+
+                        if (!_options.EnablePersistentSessions)
+                        {
+                            await DeleteSessionAsync(clientId).ConfigureAwait(false);
+                        }
                     }
-                }
 
-                await TryCleanupChannelAsync(channelAdapter).ConfigureAwait(false);
+                    await TryCleanupChannelAsync(channelAdapter).ConfigureAwait(false);
 
-                if (clientId != null)
-                {
-                    await _eventDispatcher.TryHandleClientDisconnectedAsync(clientId, disconnectType).ConfigureAwait(false);
+                    if (clientId != null)
+                    {
+                        await _eventDispatcher.TryHandleClientDisconnectedAsync(clientId, disconnectType).ConfigureAwait(false);
+                    }
                 }
             }
         }
@@ -328,13 +337,13 @@ namespace MQTTnet.Server
                 {
                     await existingConnection.StopAsync().ConfigureAwait(false);
                 }
-                
+
                 if (isSessionPresent)
                 {
                     if (connectPacket.CleanSession)
                     {
                         session = null;
-                        
+
                         _logger.Verbose("Deleting existing session of client '{0}'.", connectPacket.ClientId);
                     }
                     else

Source/MQTTnet/Server/MqttClientSubscriptionsManager.cs

@@ -107,9 +107,16 @@ namespace MQTTnet.Server
                 PacketIdentifier = unsubscribePacket.PacketIdentifier
             };
 
-            lock (_subscriptions)
+            foreach (var topicFilter in unsubscribePacket.TopicFilters)
             {
-                foreach (var topicFilter in unsubscribePacket.TopicFilters)
+                var interceptorContext = await InterceptUnsubscribeAsync(topicFilter).ConfigureAwait(false);
+                if (!interceptorContext.AcceptUnsubscription)
+                {
+                    unsubAckPacket.ReasonCodes.Add(MqttUnsubscribeReasonCode.ImplementationSpecificError);
+                    continue;
+                }
+
+                lock (_subscriptions)
                 {
                     if (_subscriptions.Remove(topicFilter))
                     {
@@ -130,19 +137,23 @@ namespace MQTTnet.Server
             return unsubAckPacket;
         }
 
-        public Task UnsubscribeAsync(IEnumerable<string> topicFilters)
+        public async Task UnsubscribeAsync(IEnumerable<string> topicFilters)
         {
             if (topicFilters == null) throw new ArgumentNullException(nameof(topicFilters));
 
-            lock (_subscriptions)
+            foreach (var topicFilter in topicFilters)
             {
-                foreach (var topicFilter in topicFilters)
+                var interceptorContext = await InterceptUnsubscribeAsync(topicFilter).ConfigureAwait(false);
+                if (!interceptorContext.AcceptUnsubscription)
                 {
-                    _subscriptions.Remove(topicFilter);
+                    continue;
                 }
-            }
 
-            return Task.FromResult(0);
+                lock (_subscriptions)
+                {
+                    _subscriptions.Remove(topicFilter);
+                }    
+            }
         }
 
         public CheckSubscriptionsResult CheckSubscriptions(string topic, MqttQualityOfServiceLevel qosLevel)
@@ -206,6 +217,17 @@ namespace MQTTnet.Server
             return context;
         }
 
+        private async Task<MqttUnsubscriptionInterceptorContext> InterceptUnsubscribeAsync(string topicFilter)
+        {
+            var context = new MqttUnsubscriptionInterceptorContext(_clientSession.ClientId, topicFilter, _clientSession.Items);
+            if (_serverOptions.UnsubscriptionInterceptor != null)
+            {
+                await _serverOptions.UnsubscriptionInterceptor.InterceptUnsubscriptionAsync(context).ConfigureAwait(false);
+            }
+
+            return context;
+        }
+
         private static CheckSubscriptionsResult CreateSubscriptionResult(MqttQualityOfServiceLevel qosLevel, HashSet<MqttQualityOfServiceLevel> subscribedQoSLevels)
         {
             MqttQualityOfServiceLevel effectiveQoS;

Source/MQTTnet/Server/MqttRetainedMessagesManager.cs

@@ -3,24 +3,26 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
 using MQTTnet.Diagnostics;
+using MQTTnet.Implementations;
 using MQTTnet.Internal;
 
 namespace MQTTnet.Server
 {
-    public class MqttRetainedMessagesManager
+    public class MqttRetainedMessagesManager : IMqttRetainedMessagesManager
     {
         private readonly byte[] _emptyArray = new byte[0];
         private readonly AsyncLock _messagesLock = new AsyncLock();
         private readonly Dictionary<string, MqttApplicationMessage> _messages = new Dictionary<string, MqttApplicationMessage>();
 
-        private readonly IMqttNetChildLogger _logger;
-        private readonly IMqttServerOptions _options;
+        private IMqttNetChildLogger _logger;
+        private IMqttServerOptions _options;
 
-        public MqttRetainedMessagesManager(IMqttServerOptions options, IMqttNetChildLogger logger)
+        public Task Start(IMqttServerOptions options, IMqttNetChildLogger logger)
         {
             if (logger == null) throw new ArgumentNullException(nameof(logger));
             _logger = logger.CreateChildLogger(nameof(MqttRetainedMessagesManager));
             _options = options ?? throw new ArgumentNullException(nameof(options));
+            return PlatformAbstractionLayer.CompletedTask;
         }
 
         public async Task LoadMessagesAsync()
@@ -103,7 +105,7 @@ namespace MQTTnet.Server
             }
         }
 
-        public async Task<List<MqttApplicationMessage>> GetSubscribedMessagesAsync(ICollection<TopicFilter> topicFilters)
+        public async Task<IList<MqttApplicationMessage>> GetSubscribedMessagesAsync(ICollection<TopicFilter> topicFilters)
         {
             if (topicFilters == null) throw new ArgumentNullException(nameof(topicFilters));
 
@@ -128,7 +130,7 @@ namespace MQTTnet.Server
                     break;
                 }
             }
-            
+
             return matchingRetainedMessages;
         }
 

Source/MQTTnet/Server/MqttServer.cs

@@ -7,6 +7,7 @@ using MQTTnet.Adapter;
 using MQTTnet.Client.Publishing;
 using MQTTnet.Client.Receiving;
 using MQTTnet.Diagnostics;
+using MQTTnet.Exceptions;
 using MQTTnet.Protocol;
 using MQTTnet.Server.Status;
 
@@ -19,7 +20,7 @@ namespace MQTTnet.Server
         private readonly IMqttNetChildLogger _logger;
 
         private MqttClientSessionsManager _clientSessionsManager;
-        private MqttRetainedMessagesManager _retainedMessagesManager;
+        private IMqttRetainedMessagesManager _retainedMessagesManager;
         private CancellationTokenSource _cancellationTokenSource;
 
         public MqttServer(IEnumerable<IMqttServerAdapter> adapters, IMqttNetChildLogger logger)
@@ -48,7 +49,7 @@ namespace MQTTnet.Server
             get => _eventDispatcher.ClientDisconnectedHandler;
             set => _eventDispatcher.ClientDisconnectedHandler = value;
         }
-        
+
         public IMqttServerClientSubscribedTopicHandler ClientSubscribedTopicHandler
         {
             get => _eventDispatcher.ClientSubscribedTopicHandler;
@@ -60,7 +61,7 @@ namespace MQTTnet.Server
             get => _eventDispatcher.ClientUnsubscribedTopicHandler;
             set => _eventDispatcher.ClientUnsubscribedTopicHandler = value;
         }
-        
+
         public IMqttApplicationMessageReceivedHandler ApplicationMessageReceivedHandler
         {
             get => _eventDispatcher.ApplicationMessageReceivedHandler;
@@ -117,11 +118,14 @@ namespace MQTTnet.Server
         {
             Options = options ?? throw new ArgumentNullException(nameof(options));
 
+            if (Options.RetainedMessagesManager == null) throw new MqttConfigurationException("options.RetainedMessagesManager should not be null.");
+
             if (_cancellationTokenSource != null) throw new InvalidOperationException("The server is already started.");
 
             _cancellationTokenSource = new CancellationTokenSource();
 
-            _retainedMessagesManager = new MqttRetainedMessagesManager(Options, _logger);
+            _retainedMessagesManager = Options.RetainedMessagesManager;
+            await _retainedMessagesManager.Start(Options, _logger);
             await _retainedMessagesManager.LoadMessagesAsync().ConfigureAwait(false);
 
             _clientSessionsManager = new MqttClientSessionsManager(Options, _retainedMessagesManager, _cancellationTokenSource.Token, _eventDispatcher, _logger);
@@ -150,9 +154,9 @@ namespace MQTTnet.Server
                 {
                     return;
                 }
-                
+
                 await _clientSessionsManager.StopAsync().ConfigureAwait(false);
-                
+
                 _cancellationTokenSource.Cancel(false);
 
                 foreach (var adapter in _adapters)

Source/MQTTnet/Server/MqttServerOptions.cs

@@ -21,11 +21,15 @@ namespace MQTTnet.Server
         public IMqttServerConnectionValidator ConnectionValidator { get; set; }
 
         public IMqttServerApplicationMessageInterceptor ApplicationMessageInterceptor { get; set; }
-        
+
         public IMqttServerClientMessageQueueInterceptor ClientMessageQueueInterceptor { get; set; }
 
         public IMqttServerSubscriptionInterceptor SubscriptionInterceptor { get; set; }
 
+        public IMqttServerUnsubscriptionInterceptor UnsubscriptionInterceptor { get; set; }
+
         public IMqttServerStorage Storage { get; set; }
+
+        public IMqttRetainedMessagesManager RetainedMessagesManager { get; set; } = new MqttRetainedMessagesManager();
     }
 }

Source/MQTTnet/Server/MqttServerOptionsBuilder.cs

@@ -57,7 +57,7 @@ namespace MQTTnet.Server
             _options.DefaultEndpointOptions.IsEnabled = false;
             return this;
         }
-        
+
         public MqttServerOptionsBuilder WithEncryptedEndpoint()
         {
             _options.TlsEndpointOptions.IsEnabled = true;
@@ -118,13 +118,19 @@ namespace MQTTnet.Server
             return this;
         }
 #endif
-        
+
         public MqttServerOptionsBuilder WithStorage(IMqttServerStorage value)
         {
             _options.Storage = value;
             return this;
         }
 
+        public MqttServerOptionsBuilder WithRetainedMessagesManager(IMqttRetainedMessagesManager value)
+        {
+            _options.RetainedMessagesManager = value;
+            return this;
+        }
+
         public MqttServerOptionsBuilder WithConnectionValidator(IMqttServerConnectionValidator value)
         {
             _options.ConnectionValidator = value;
@@ -155,6 +161,12 @@ namespace MQTTnet.Server
             return this;
         }
 
+        public MqttServerOptionsBuilder WithUnsubscriptionInterceptor(IMqttServerUnsubscriptionInterceptor value)
+        {
+            _options.UnsubscriptionInterceptor = value;
+            return this;
+        }
+
         public MqttServerOptionsBuilder WithSubscriptionInterceptor(Action<MqttSubscriptionInterceptorContext> value)
         {
             _options.SubscriptionInterceptor = new MqttServerSubscriptionInterceptorDelegate(value);

Source/MQTTnet/Server/MqttUnsubscriptionInterceptorContext.cs

@@ -0,0 +1,27 @@
+using System.Collections.Generic;
+
+namespace MQTTnet.Server
+{
+    public class MqttUnsubscriptionInterceptorContext
+    {
+        public MqttUnsubscriptionInterceptorContext(string clientId, string topic, IDictionary<object, object> sessionItems)
+        {
+            ClientId = clientId;
+            Topic = topic;
+            SessionItems = sessionItems;
+        }
+
+        public string ClientId { get; }
+
+        public string Topic { get; set; }
+
+        /// <summary>
+        /// Gets or sets a key/value collection that can be used to share data within the scope of this session.
+        /// </summary>
+        public IDictionary<object, object> SessionItems { get; }
+
+        public bool AcceptUnsubscription { get; set; } = true;
+
+        public bool CloseConnection { get; set; }
+    }
+}

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

@@ -6,9 +6,9 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.2.0" />
-    <PackageReference Include="MSTest.TestAdapter" Version="1.4.0" />
-    <PackageReference Include="MSTest.TestFramework" Version="1.4.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.4.0" />
+    <PackageReference Include="MSTest.TestAdapter" Version="2.0.0" />
+    <PackageReference Include="MSTest.TestFramework" Version="2.0.0" />
   </ItemGroup>
 
   <ItemGroup>

Tests/MQTTnet.Benchmarks/Configurations/RuntimeCompareConfig.cs

@@ -9,8 +9,8 @@ namespace MQTTnet.Benchmarks.Configurations
     {
         public RuntimeCompareConfig()
         {
-            Add(Job.Default.With(Runtime.Clr));
-            Add(Job.Default.With(Runtime.Core).With(CsProjCoreToolchain.NetCoreApp21));
+            Add(Job.Default.With(ClrRuntime.Net472));
+            Add(Job.Default.With(CoreRuntime.Core22).With(CsProjCoreToolchain.NetCoreApp22));
         }
 
     }

Tests/MQTTnet.Benchmarks/LoggerBenchmark.cs

@@ -1,9 +1,10 @@
 using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Jobs;
 using MQTTnet.Diagnostics;
 
 namespace MQTTnet.Benchmarks
 {
-    [ClrJob]
+    [SimpleJob(RuntimeMoniker.Net461)]
     [RPlotExporter]
     [MemoryDiagnoser]
     public class LoggerBenchmark

Tests/MQTTnet.Benchmarks/MQTTnet.Benchmarks.csproj

@@ -9,7 +9,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="BenchmarkDotNet" Version="0.11.5" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.12.0" />
     <PackageReference Include="System.IO.Pipelines" Version="4.5.2" />
     <PackageReference Include="Microsoft.AspNetCore" Version="2.1.6" />
   </ItemGroup>

Tests/MQTTnet.Benchmarks/MessageProcessingBenchmark.cs

@@ -1,11 +1,12 @@
 using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Jobs;
 using MQTTnet.Client;
 using MQTTnet.Client.Options;
 using MQTTnet.Server;
 
 namespace MQTTnet.Benchmarks
 {
-    [ClrJob]
+    [SimpleJob(RuntimeMoniker.Net461)]
     [RPlotExporter, RankColumn]
     [MemoryDiagnoser]
     public class MessageProcessingBenchmark

Tests/MQTTnet.Benchmarks/SerializerBenchmark.cs

@@ -8,10 +8,11 @@ using MQTTnet.Adapter;
 using MQTTnet.Channel;
 using MQTTnet.Formatter;
 using MQTTnet.Formatter.V3;
+using BenchmarkDotNet.Jobs;
 
 namespace MQTTnet.Benchmarks
 {
-    [ClrJob]
+    [SimpleJob(RuntimeMoniker.Net461)]
     [RPlotExporter]
     [MemoryDiagnoser]
     public class SerializerBenchmark

Tests/MQTTnet.Benchmarks/TopicFilterComparerBenchmark.cs

@@ -1,10 +1,11 @@
 using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Jobs;
 using MQTTnet.Server;
 using System;
 
 namespace MQTTnet.Benchmarks
 {
-    [ClrJob]
+    [SimpleJob(RuntimeMoniker.Net461)]
     [RPlotExporter]
     [MemoryDiagnoser]
     public class TopicFilterComparerBenchmark

Tests/MQTTnet.Core.Tests/AsyncAutoResentEvent_Tests.cs

@@ -1,237 +0,0 @@
-using System;
-using System.Threading;
-using System.Threading.Tasks;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MQTTnet.Internal;
-
-namespace MQTTnet.Tests
-{
-    [TestClass]
-    // Inspired from the vs-threading tests (https://github.com/Microsoft/vs-threading/blob/master/src/Microsoft.VisualStudio.Threading.Tests/AsyncAutoResetEventTests.cs)
-    public class AsyncAutoResetEvent_Tests
-    {
-        private readonly AsyncAutoResetEvent _aare;
-
-        public AsyncAutoResetEvent_Tests()
-        {
-            _aare = new AsyncAutoResetEvent();
-        }
-
-        [TestMethod]
-        public async Task Cleanup_Waiters()
-        {
-            var @lock = new AsyncAutoResetEvent();
-            
-            var waitOnePassed = false;
-
-#pragma warning disable 4014
-            Task.Run(async () =>
-#pragma warning restore 4014
-            {
-                await @lock.WaitOneAsync(TimeSpan.FromSeconds(2));
-                waitOnePassed = true;
-            });
-
-            await Task.Delay(500);
-
-            Assert.AreEqual(1, @lock.WaitersCount);
-
-            @lock.Set();
-
-            await Task.Delay(1000);
-
-            Assert.IsTrue(waitOnePassed);
-            Assert.AreEqual(0, @lock.WaitersCount);
-        }
-
-        [TestMethod]
-        public async Task SingleThreadedPulse()
-        {
-            for (int i = 0; i < 5; i++)
-            {
-                var t = _aare.WaitOneAsync();
-                Assert.IsFalse(t.IsCompleted);
-                _aare.Set();
-                await t;
-                Assert.IsTrue(t.IsCompleted);
-            }
-        }
-
-        [TestMethod]
-        public async Task MultipleSetOnlySignalsOnce()
-        {
-            _aare.Set();
-            _aare.Set();
-            await _aare.WaitOneAsync();
-            var t = _aare.WaitOneAsync();
-            Assert.IsFalse(t.IsCompleted);
-            await Task.Delay(500);
-            Assert.IsFalse(t.IsCompleted);
-            _aare.Set();
-            await t;
-            Assert.IsTrue(t.IsCompleted);
-        }
-
-        [TestMethod]
-        public async Task OrderPreservingQueue()
-        {
-            var waiters = new Task[5];
-            for (int i = 0; i < waiters.Length; i++)
-            {
-                waiters[i] = _aare.WaitOneAsync();
-            }
-
-            for (int i = 0; i < waiters.Length; i++)
-            {
-                _aare.Set();
-                await waiters[i].ConfigureAwait(false);
-            }
-        }
-
-        // This test does not work in appveyor but on local machine it does!?
-        /////// <summary>
-        /////// Verifies that inlining continuations do not have to complete execution before Set() returns.
-        /////// </summary>
-        ////[TestMethod]
-        ////public async Task SetReturnsBeforeInlinedContinuations()
-        ////{
-        ////    var setReturned = new ManualResetEventSlim();
-        ////    var inlinedContinuation = _aare.WaitOneAsync()
-        ////        .ContinueWith(delegate
-        ////        {
-        ////            // Arrange to synchronously block the continuation until Set() has returned,
-        ////            // which would deadlock if Set does not return until inlined continuations complete.
-        ////            Assert.IsTrue(setReturned.Wait(500));
-        ////        });
-        ////    await Task.Delay(100);
-        ////    _aare.Set();
-        ////    setReturned.Set();
-        ////    Assert.IsTrue(inlinedContinuation.Wait(500));
-        ////}
-
-        [TestMethod]
-        public void WaitAsync_WithCancellationToken()
-        {
-            var cts = new CancellationTokenSource();
-            Task waitTask = _aare.WaitOneAsync(cts.Token);
-            Assert.IsFalse(waitTask.IsCompleted);
-
-            // Cancel the request and ensure that it propagates to the task.
-            cts.Cancel();
-            try
-            {
-                waitTask.GetAwaiter().GetResult();
-                Assert.IsTrue(false, "Task was expected to transition to a canceled state.");
-            }
-            catch (OperationCanceledException)
-            {
-            }
-
-            // Now set the event and verify that a future waiter gets the signal immediately.
-            _aare.Set();
-            waitTask = _aare.WaitOneAsync();
-            Assert.AreEqual(TaskStatus.WaitingForActivation, waitTask.Status);
-        }
-
-        [TestMethod]
-        public void WaitAsync_WithCancellationToken_Precanceled()
-        {
-            // We construct our own pre-canceled token so that we can do
-            // a meaningful identity check later.
-            var tokenSource = new CancellationTokenSource();
-            tokenSource.Cancel();
-            var token = tokenSource.Token;
-
-            // Verify that a pre-set signal is not reset by a canceled wait request.
-            _aare.Set();
-            try
-            {
-                _aare.WaitOneAsync(token).GetAwaiter().GetResult();
-                Assert.IsTrue(false, "Task was expected to transition to a canceled state.");
-            }
-            catch (OperationCanceledException ex)
-            {
-                Assert.AreEqual(token, ex.CancellationToken);
-            }
-
-            // Verify that the signal was not acquired.
-            Task waitTask = _aare.WaitOneAsync();
-            Assert.AreEqual(TaskStatus.RanToCompletion, waitTask.Status);
-        }
-
-        [TestMethod]
-        public async Task WaitAsync_WithTimeout()
-        {
-            Task waitTask = _aare.WaitOneAsync(TimeSpan.FromMilliseconds(500));
-            Assert.IsFalse(waitTask.IsCompleted);
-
-            // Cancel the request and ensure that it propagates to the task.
-            await Task.Delay(1000).ConfigureAwait(false);
-            try
-            {
-                waitTask.GetAwaiter().GetResult();
-                Assert.IsTrue(false, "Task was expected to transition to a timeout state.");
-            }
-            catch (TimeoutException)
-            {
-                Assert.IsTrue(true);
-            }
-
-            // Now set the event and verify that a future waiter gets the signal immediately.
-            _aare.Set();
-            waitTask = _aare.WaitOneAsync(TimeSpan.FromMilliseconds(500));
-            Assert.AreEqual(TaskStatus.RanToCompletion, waitTask.Status);
-        }
-
-        [TestMethod]
-        public void WaitAsync_Canceled_DoesNotInlineContinuations()
-        {
-            var cts = new CancellationTokenSource();
-            var task = _aare.WaitOneAsync(cts.Token);
-
-            var completingActionFinished = new ManualResetEventSlim();
-            var continuation = task.ContinueWith(
-                _ => Assert.IsTrue(completingActionFinished.Wait(500)),
-                CancellationToken.None,
-                TaskContinuationOptions.None,
-                TaskScheduler.Default);
-
-            cts.Cancel();
-            completingActionFinished.Set();
-
-            // Rethrow the exception if it turned out it deadlocked.
-            continuation.GetAwaiter().GetResult();
-        }
-
-        [TestMethod]
-        public async Task AsyncAutoResetEvent()
-        {
-            var aare = new AsyncAutoResetEvent();
-
-            var globalI = 0;
-#pragma warning disable 4014
-            Task.Run(async () =>
-#pragma warning restore 4014
-            {
-                await aare.WaitOneAsync(CancellationToken.None);
-                globalI += 1;
-            });
-
-#pragma warning disable 4014
-            Task.Run(async () =>
-#pragma warning restore 4014
-            {
-                await aare.WaitOneAsync(CancellationToken.None);
-                globalI += 2;
-            });
-
-            await Task.Delay(500);
-            aare.Set();
-            await Task.Delay(500);
-            aare.Set();
-            await Task.Delay(100);
-
-            Assert.AreEqual(3, globalI);
-        }
-    }
-}

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

@@ -1,14 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp3.1</TargetFramework>
+    <TargetFramework>netcoreapp3.1;net461</TargetFramework>
     <IsPackable>false</IsPackable>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="MSTest.TestAdapter" Version="1.4.0" />
-    <PackageReference Include="MSTest.TestFramework" Version="1.4.0" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.2.0" />
+    <PackageReference Include="MSTest.TestAdapter" Version="2.0.0" />
+    <PackageReference Include="MSTest.TestFramework" Version="2.0.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.4.0" />
   </ItemGroup>
 
   <ItemGroup>

Tests/MQTTnet.Core.Tests/MQTTv5/Client_Tests.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
@@ -17,10 +18,12 @@ namespace MQTTnet.Tests.MQTTv5
     [TestClass]
     public class Client_Tests
     {
+        public TestContext TestContext { get; set; }
+
         [TestMethod]
         public async Task Connect_With_New_Mqtt_Features()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -57,6 +60,65 @@ namespace MQTTnet.Tests.MQTTv5
                 Assert.AreEqual(2, receivedMessage.UserProperties.Count);
             }
         }
+        [TestMethod]
+        public async Task Connect_With_AssignedClientId()
+        {
+            using (var testEnvironment = new TestEnvironment(TestContext))
+            {
+                string serverConnectedClientId = null;
+                string serverDisconnectedClientId = null;
+                string clientAssignedClientId = null;
+
+                // Arrange server
+                var disconnectedMre = new ManualResetEventSlim();
+                var serverOptions = new MqttServerOptionsBuilder()
+                    .WithConnectionValidator((context) =>
+                    {
+                        if (string.IsNullOrEmpty(context.ClientId))
+                        {
+                            context.AssignedClientIdentifier = "test123";
+                            context.ReasonCode = MqttConnectReasonCode.Success;
+                        }
+                    });
+                await testEnvironment.StartServerAsync(serverOptions);
+                testEnvironment.Server.UseClientConnectedHandler((args) =>
+                {
+                    serverConnectedClientId = args.ClientId;
+                });
+                testEnvironment.Server.UseClientDisconnectedHandler((args) =>
+                {
+                    serverDisconnectedClientId = args.ClientId;
+                    disconnectedMre.Set();
+                });
+
+                // Arrange client
+                var client = testEnvironment.CreateClient();
+                client.UseConnectedHandler((args) =>
+                {
+                    clientAssignedClientId = args.AuthenticateResult.AssignedClientIdentifier;
+                });
+
+                // Act
+                await client.ConnectAsync(new MqttClientOptionsBuilder()
+                    .WithTcpServer("127.0.0.1", testEnvironment.ServerPort)
+                    .WithProtocolVersion(MqttProtocolVersion.V500)
+                    .WithClientId(null)
+                    .Build());
+                await client.DisconnectAsync();
+
+                // Wait for ClientDisconnectedHandler to trigger
+                disconnectedMre.Wait(500);
+
+                // Assert
+                Assert.IsNotNull(serverConnectedClientId);
+                Assert.IsNotNull(serverDisconnectedClientId);
+                Assert.IsNotNull(clientAssignedClientId);
+                Assert.AreEqual("test123", serverConnectedClientId);
+                Assert.AreEqual("test123", serverDisconnectedClientId);
+                Assert.AreEqual("test123", clientAssignedClientId);
+
+            }
+        }
 
         [TestMethod]
         public async Task Connect()
@@ -297,7 +359,7 @@ namespace MQTTnet.Tests.MQTTv5
         [TestMethod]
         public async Task Publish_And_Receive_New_Properties()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 

Tests/MQTTnet.Core.Tests/MQTTv5/Feature_Tests.cs

@@ -13,10 +13,12 @@ namespace MQTTnet.Tests.MQTTv5
     [TestClass]
     public class Feature_Tests
     {
+        public TestContext TestContext { get; set; }
+
         [TestMethod]
         public async Task Use_User_Properties()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 

Tests/MQTTnet.Core.Tests/MQTTv5/Server_Tests.cs

@@ -11,10 +11,12 @@ namespace MQTTnet.Tests.MQTTv5
     [TestClass]
     public class Server_Tests
     {
+        public TestContext TestContext { get; set; }
+
         [TestMethod]
         public async Task Will_Message_Send()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var receivedMessagesCount = 0;
 

Tests/MQTTnet.Core.Tests/ManagedMqttClient_Tests.cs

@@ -1,10 +1,13 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
+using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
 using MQTTnet.Client.Connecting;
 using MQTTnet.Client.Options;
+using MQTTnet.Client.Receiving;
 using MQTTnet.Diagnostics;
 using MQTTnet.Extensions.ManagedClient;
 using MQTTnet.Server;
@@ -15,6 +18,8 @@ namespace MQTTnet.Tests
     [TestClass]
     public class ManagedMqttClient_Tests
     {
+        public TestContext TestContext { get; set; }
+
         [TestMethod]
         public async Task Drop_New_Messages_On_Full_Queue()
         {
@@ -51,7 +56,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task ManagedClients_Will_Message_Send()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var receivedMessagesCount = 0;
 
@@ -85,7 +90,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Start_Stop()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var factory = new MqttFactory();
 
@@ -95,25 +100,24 @@ namespace MQTTnet.Tests
                 var clientOptions = new MqttClientOptionsBuilder()
                     .WithTcpServer("localhost", testEnvironment.ServerPort);
 
-                TaskCompletionSource<bool> connected = new TaskCompletionSource<bool>();
-                managedClient.ConnectedHandler = new MqttClientConnectedHandlerDelegate(e => { connected.SetResult(true);});
+                var connected = GetConnectedTask(managedClient);
 
                 await managedClient.StartAsync(new ManagedMqttClientOptionsBuilder()
                     .WithClientOptions(clientOptions)
                     .Build());
 
-                await connected.Task;
+                await connected;
 
                 await managedClient.StopAsync();
 
                 Assert.AreEqual(0, (await server.GetClientStatusAsync()).Count);
             }
         }
-        
+
         [TestMethod]
         public async Task Storage_Queue_Drains()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 testEnvironment.IgnoreClientLogErrors = true;
                 testEnvironment.IgnoreServerLogErrors = true;
@@ -127,12 +131,7 @@ namespace MQTTnet.Tests
                     .WithTcpServer("localhost", testEnvironment.ServerPort);
                 var storage = new ManagedMqttClientTestStorage();
 
-                TaskCompletionSource<bool> connected = new TaskCompletionSource<bool>();
-                managedClient.ConnectedHandler = new MqttClientConnectedHandlerDelegate(e =>
-                {
-                    managedClient.ConnectedHandler = null;
-                    connected.SetResult(true);
-                });
+                var connected = GetConnectedTask(managedClient);
 
                 await managedClient.StartAsync(new ManagedMqttClientOptionsBuilder()
                     .WithClientOptions(clientOptions)
@@ -140,7 +139,7 @@ namespace MQTTnet.Tests
                     .WithAutoReconnectDelay(System.TimeSpan.FromSeconds(5))
                     .Build());
 
-                await connected.Task;
+                await connected;
 
                 await testEnvironment.Server.StopAsync();
 
@@ -151,17 +150,12 @@ namespace MQTTnet.Tests
                 //in storage at this point (i.e. no waiting).
                 Assert.AreEqual(1, storage.GetMessageCount());
 
-                connected = new TaskCompletionSource<bool>();
-                managedClient.ConnectedHandler = new MqttClientConnectedHandlerDelegate(e =>
-                {
-                    managedClient.ConnectedHandler = null;
-                    connected.SetResult(true);
-                });
+                connected = GetConnectedTask(managedClient);
 
                 await testEnvironment.Server.StartAsync(new MqttServerOptionsBuilder()
                     .WithDefaultEndpointPort(testEnvironment.ServerPort).Build());
 
-                await connected.Task;
+                await connected;
 
                 //Wait 500ms here so the client has time to publish the queued message
                 await Task.Delay(500);
@@ -171,8 +165,235 @@ namespace MQTTnet.Tests
                 await managedClient.StopAsync();
             }
         }
+
+        [TestMethod]
+        public async Task Subscriptions_And_Unsubscriptions_Are_Made_And_Reestablished_At_Reconnect()
+        {
+            using (var testEnvironment = new TestEnvironment(TestContext))
+            {
+                var unmanagedClient = testEnvironment.CreateClient();
+                var managedClient = await CreateManagedClientAsync(testEnvironment, unmanagedClient);
+
+                var received = SetupReceivingOfMessages(managedClient, 2);
+
+                // Perform some opposing subscriptions and unsubscriptions to verify
+                // that these conflicting subscriptions are handled correctly
+                await managedClient.SubscribeAsync("keptSubscribed");
+                await managedClient.SubscribeAsync("subscribedThenUnsubscribed");
+
+                await managedClient.UnsubscribeAsync("subscribedThenUnsubscribed");
+                await managedClient.UnsubscribeAsync("unsubscribedThenSubscribed");
+
+                await managedClient.SubscribeAsync("unsubscribedThenSubscribed");
+
+                //wait a bit for the subscriptions to become established before the messages are published
+                await Task.Delay(500);
+
+                var sendingClient = await testEnvironment.ConnectClientAsync();
+
+                async Task PublishMessages()
+                {
+                    await sendingClient.PublishAsync("keptSubscribed", new byte[] { 1 });
+                    await sendingClient.PublishAsync("subscribedThenUnsubscribed", new byte[] { 1 });
+                    await sendingClient.PublishAsync("unsubscribedThenSubscribed", new byte[] { 1 });
+                }
+
+                await PublishMessages();
+
+                async Task AssertMessagesReceived()
+                {
+                    var messages = await received;
+                    Assert.AreEqual("keptSubscribed", messages[0].Topic);
+                    Assert.AreEqual("unsubscribedThenSubscribed", messages[1].Topic);
+                }
+
+                await AssertMessagesReceived();
+
+                var connected = GetConnectedTask(managedClient);
+
+                await unmanagedClient.DisconnectAsync();
+
+                // the managed client has to reconnect by itself
+                await connected;
+
+                // wait a bit so that the managed client can reestablish the subscriptions
+                await Task.Delay(500);
+
+                received = SetupReceivingOfMessages(managedClient, 2);
+
+                await PublishMessages();
+
+                // and then the same subscriptions need to exist again
+                await AssertMessagesReceived();
+            }
+        }
+
+        // This case also serves as a regression test for the previous behavior which re-published
+        // each and every existing subscriptions with every new subscription that was made
+        // (causing performance problems and having the visible symptom of retained messages being received again)
+        [TestMethod]
+        public async Task Subscriptions_Subscribe_Only_New_Subscriptions()
+        {
+            using (var testEnvironment = new TestEnvironment(TestContext))
+            {
+                var managedClient = await CreateManagedClientAsync(testEnvironment);
+
+                var sendingClient = await testEnvironment.ConnectClientAsync();
+
+                await managedClient.SubscribeAsync("topic");
+
+                //wait a bit for the subscription to become established
+                await Task.Delay(500);
+
+                await sendingClient.PublishAsync(new MqttApplicationMessage { Topic = "topic", Payload = new byte[] { 1 }, Retain = true });
+
+                var messages = await SetupReceivingOfMessages(managedClient, 1);
+
+                Assert.AreEqual(1, messages.Count);
+                Assert.AreEqual("topic", messages.Single().Topic);
+
+                await managedClient.SubscribeAsync("anotherTopic");
+
+                await Task.Delay(500);
+
+                // The subscription of the other topic must not trigger a re-subscription of the existing topic
+                // (and thus renewed receiving of the retained message)
+                Assert.AreEqual(1, messages.Count);
+            }
+        }
+
+        // This case also serves as a regression test for the previous behavior
+        // that subscriptions were only published at the ConnectionCheckInterval
+        [TestMethod]
+        public async Task Subscriptions_Are_Published_Immediately()
+        {
+            using (var testEnvironment = new TestEnvironment(TestContext))
+            {
+                // Use a long connection check interval to verify that the subscriptions
+                // do not depend on the connection check interval anymore
+                var connectionCheckInterval = TimeSpan.FromSeconds(10);
+                var managedClient = await CreateManagedClientAsync(testEnvironment, null, connectionCheckInterval);
+                var sendingClient = await testEnvironment.ConnectClientAsync();
+                await sendingClient.PublishAsync(new MqttApplicationMessage { Topic = "topic", Payload = new byte[] { 1 }, Retain = true });
+
+                await managedClient.SubscribeAsync("topic");
+
+                var subscribeTime = DateTime.UtcNow;
+
+                var messages = await SetupReceivingOfMessages(managedClient, 1);
+
+                var elapsed = DateTime.UtcNow - subscribeTime;
+                Assert.IsTrue(elapsed < TimeSpan.FromSeconds(1), $"Subscriptions must be activated immediately, this one took {elapsed}");
+                Assert.AreEqual(messages.Single().Topic, "topic");
+            }
+        }
+
+        [TestMethod]
+        public async Task Subscriptions_Are_Cleared_At_Logout()
+        {
+            using (var testEnvironment = new TestEnvironment(TestContext))
+            {
+                var managedClient = await CreateManagedClientAsync(testEnvironment);
+
+                var sendingClient = await testEnvironment.ConnectClientAsync();
+                await sendingClient.PublishAsync(new MqttApplicationMessage
+                { Topic = "topic", Payload = new byte[] { 1 }, Retain = true });
+
+                // Wait a bit for the retained message to be available
+                await Task.Delay(500);
+
+                await managedClient.SubscribeAsync("topic");
+
+                await SetupReceivingOfMessages(managedClient, 1);
+
+                await managedClient.StopAsync();
+
+                var clientOptions = new MqttClientOptionsBuilder()
+                  .WithTcpServer("localhost", testEnvironment.ServerPort);
+                await managedClient.StartAsync(new ManagedMqttClientOptionsBuilder()
+                  .WithClientOptions(clientOptions)
+                  .WithAutoReconnectDelay(TimeSpan.FromSeconds(1))
+                  .Build());
+
+                var messages = new List<MqttApplicationMessage>();
+                managedClient.ApplicationMessageReceivedHandler = new MqttApplicationMessageReceivedHandlerDelegate(r =>
+                {
+                    messages.Add(r.ApplicationMessage);
+                });
+
+                await Task.Delay(500);
+
+                // After reconnect and then some delay, the retained message must not be received,
+                // showing that the subscriptions were cleared
+                Assert.AreEqual(0, messages.Count);
+            }
+        }
+
+        private async Task<ManagedMqttClient> CreateManagedClientAsync(
+          TestEnvironment testEnvironment,
+          IMqttClient underlyingClient = null,
+          TimeSpan? connectionCheckInterval = null)
+        {
+            await testEnvironment.StartServerAsync();
+
+            var clientOptions = new MqttClientOptionsBuilder()
+              .WithTcpServer("localhost", testEnvironment.ServerPort);
+
+            var managedOptions = new ManagedMqttClientOptionsBuilder()
+              .WithClientOptions(clientOptions)
+              .Build();
+
+            // Use a short connection check interval so that subscription operations are performed quickly
+            // in order to verify against a previous implementation that performed subscriptions only
+            // at connection check intervals
+            managedOptions.ConnectionCheckInterval = connectionCheckInterval ?? TimeSpan.FromSeconds(0.1);
+
+            var managedClient =
+              new ManagedMqttClient(underlyingClient ?? testEnvironment.CreateClient(), new MqttNetLogger().CreateChildLogger());
+
+            var connected = GetConnectedTask(managedClient);
+
+            await managedClient.StartAsync(managedOptions);
+
+            await connected;
+
+            return managedClient;
+        }
+
+        /// <summary>
+        /// Returns a task that will finish when the <paramref name="managedClient"/> has connected
+        /// </summary>
+        private Task GetConnectedTask(ManagedMqttClient managedClient)
+        {
+            TaskCompletionSource<bool> connected = new TaskCompletionSource<bool>();
+            managedClient.ConnectedHandler = new MqttClientConnectedHandlerDelegate(e =>
+            {
+                managedClient.ConnectedHandler = null;
+                connected.SetResult(true);
+            });
+            return connected.Task;
+        }
+
+        /// <summary>
+        /// Returns a task that will return the messages received on <paramref name="managedClient"/>
+        /// when <paramref name="expectedNumberOfMessages"/> have been received
+        /// </summary>
+        private Task<List<MqttApplicationMessage>> SetupReceivingOfMessages(ManagedMqttClient managedClient, int expectedNumberOfMessages)
+        {
+            var receivedMessages = new List<MqttApplicationMessage>();
+            var allReceived = new TaskCompletionSource<List<MqttApplicationMessage>>();
+            managedClient.ApplicationMessageReceivedHandler = new MqttApplicationMessageReceivedHandlerDelegate(r =>
+            {
+                receivedMessages.Add(r.ApplicationMessage);
+                if (receivedMessages.Count == expectedNumberOfMessages)
+                {
+                    allReceived.SetResult(receivedMessages);
+                }
+            });
+            return allReceived.Task;
+        }
     }
-    
+
     public class ManagedMqttClientTestStorage : IManagedMqttClientStorage
     {
         private IList<ManagedMqttApplicationMessage> _messages = null;

Tests/MQTTnet.Core.Tests/Mockups/TestClientWrapper.cs

@@ -0,0 +1,94 @@
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Client;
+using MQTTnet.Client.Connecting;
+using MQTTnet.Client.Disconnecting;
+using MQTTnet.Client.ExtendedAuthenticationExchange;
+using MQTTnet.Client.Options;
+using MQTTnet.Client.Publishing;
+using MQTTnet.Client.Receiving;
+using MQTTnet.Client.Subscribing;
+using MQTTnet.Client.Unsubscribing;
+
+namespace MQTTnet.Tests.Mockups
+{
+    public class TestClientWrapper : IMqttClient
+    {
+        public TestClientWrapper(IMqttClient implementation, TestContext testContext)
+        {
+            Implementation = implementation;
+            TestContext = testContext;
+        }
+
+        public IMqttClient Implementation { get; }
+        public TestContext TestContext { get; }
+
+        public bool IsConnected => Implementation.IsConnected;
+
+        public IMqttClientOptions Options => Implementation.Options;
+
+        public IMqttClientConnectedHandler ConnectedHandler { get => Implementation.ConnectedHandler; set => Implementation.ConnectedHandler = value; }
+        public IMqttClientDisconnectedHandler DisconnectedHandler { get => Implementation.DisconnectedHandler; set => Implementation.DisconnectedHandler = value; }
+        public IMqttApplicationMessageReceivedHandler ApplicationMessageReceivedHandler { get => Implementation.ApplicationMessageReceivedHandler; set => Implementation.ApplicationMessageReceivedHandler = value; }
+
+        public Task<MqttClientAuthenticateResult> ConnectAsync(IMqttClientOptions options, CancellationToken cancellationToken)
+        {
+            switch (options)
+            {
+                case MqttClientOptionsBuilder builder:
+                    {
+                        var existingClientId = builder.Build().ClientId;
+                        if (existingClientId != null && !existingClientId.StartsWith(TestContext.TestName))
+                        {
+                            builder.WithClientId(TestContext.TestName + existingClientId);
+                        }
+                    }
+                    break;
+                case MqttClientOptions op:
+                    {
+                        var existingClientId = op.ClientId;
+                        if (existingClientId != null && !existingClientId.StartsWith(TestContext.TestName))
+                        {
+                            op.ClientId = TestContext.TestName + existingClientId;
+                        }
+                    }
+                    break;
+                default:
+                    break;
+            }
+
+            return Implementation.ConnectAsync(options, cancellationToken);
+        }
+
+        public Task DisconnectAsync(MqttClientDisconnectOptions options, CancellationToken cancellationToken)
+        {
+            return Implementation.DisconnectAsync(options, cancellationToken);
+        }
+
+        public void Dispose()
+        {
+            Implementation.Dispose();
+        }
+
+        public Task<MqttClientPublishResult> PublishAsync(MqttApplicationMessage applicationMessage, CancellationToken cancellationToken)
+        {
+            return Implementation.PublishAsync(applicationMessage, cancellationToken);
+        }
+
+        public Task SendExtendedAuthenticationExchangeDataAsync(MqttExtendedAuthenticationExchangeData data, CancellationToken cancellationToken)
+        {
+            return Implementation.SendExtendedAuthenticationExchangeDataAsync(data, cancellationToken);
+        }
+
+        public Task<Client.Subscribing.MqttClientSubscribeResult> SubscribeAsync(MqttClientSubscribeOptions options, CancellationToken cancellationToken)
+        {
+            return Implementation.SubscribeAsync(options, cancellationToken);
+        }
+
+        public Task<MqttClientUnsubscribeResult> UnsubscribeAsync(MqttClientUnsubscribeOptions options, CancellationToken cancellationToken)
+        {
+            return Implementation.UnsubscribeAsync(options, cancellationToken);
+        }
+    }
+}

Tests/MQTTnet.Core.Tests/Mockups/TestEnvironment.cs

@@ -2,14 +2,16 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
 using MQTTnet.Client.Options;
 using MQTTnet.Diagnostics;
+using MQTTnet.Internal;
 using MQTTnet.Server;
 
 namespace MQTTnet.Tests.Mockups
 {
-    public class TestEnvironment : IDisposable
+    public class TestEnvironment : Disposable
     {
         private readonly MqttFactory _mqttFactory = new MqttFactory();
         private readonly List<IMqttClient> _clients = new List<IMqttClient>();
@@ -33,7 +35,9 @@ namespace MQTTnet.Tests.Mockups
 
         public IMqttNetLogger ClientLogger => _clientLogger;
 
-        public TestEnvironment()
+        public TestContext TestContext { get; }
+
+        public TestEnvironment(TestContext testContext)
         {
             _serverLogger.LogMessagePublished += (s, e) =>
             {
@@ -56,13 +60,14 @@ namespace MQTTnet.Tests.Mockups
                     }
                 }
             };
+            TestContext = testContext;
         }
 
         public IMqttClient CreateClient()
         {
             var client = _mqttFactory.CreateMqttClient(_clientLogger);
             _clients.Add(client);
-            return client;
+            return new TestClientWrapper(client, TestContext);
         }
 
         public Task<IMqttServer> StartServerAsync()
@@ -77,7 +82,7 @@ namespace MQTTnet.Tests.Mockups
                 throw new InvalidOperationException("Server already started.");
             }
 
-            Server = _mqttFactory.CreateMqttServer(_serverLogger);
+            Server = new TestServerWrapper(_mqttFactory.CreateMqttServer(_serverLogger), TestContext, this);
             await Server.StartAsync(options.WithDefaultEndpointPort(ServerPort).Build());
 
             return Server;
@@ -85,7 +90,7 @@ namespace MQTTnet.Tests.Mockups
 
         public Task<IMqttClient> ConnectClientAsync()
         {
-            return ConnectClientAsync(new MqttClientOptionsBuilder());
+            return ConnectClientAsync(new MqttClientOptionsBuilder() );
         }
 
         public async Task<IMqttClient> ConnectClientAsync(MqttClientOptionsBuilder options)
@@ -127,21 +132,25 @@ namespace MQTTnet.Tests.Mockups
             }
         }
 
-        public void Dispose()
+        protected override void Dispose(bool disposing)
         {
-            foreach (var mqttClient in _clients)
+            if (disposing)
             {
-                mqttClient?.Dispose();
-            }
+                foreach (var mqttClient in _clients)
+                {
+                    mqttClient?.Dispose();
+                }
 
-            Server?.StopAsync().GetAwaiter().GetResult();
+                Server?.StopAsync().GetAwaiter().GetResult();
 
-            ThrowIfLogErrors();
+                ThrowIfLogErrors();
 
-            if (_exceptions.Any())
-            {
-                throw new Exception($"{_exceptions.Count} exceptions tracked.\r\n" + string.Join(Environment.NewLine, _exceptions));
+                if (_exceptions.Any())
+                {
+                    throw new Exception($"{_exceptions.Count} exceptions tracked.\r\n" + string.Join(Environment.NewLine, _exceptions));
+                }
             }
+            base.Dispose(disposing);
         }
 
         public void TrackException(Exception exception)

Tests/MQTTnet.Core.Tests/Mockups/TestServerWrapper.cs

@@ -0,0 +1,108 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Client.Publishing;
+using MQTTnet.Client.Receiving;
+using MQTTnet.Server;
+using MQTTnet.Server.Status;
+
+namespace MQTTnet.Tests.Mockups
+{
+    public class TestServerWrapper : IMqttServer
+    {
+        public TestServerWrapper(IMqttServer implementation, TestContext testContext, TestEnvironment testEnvironment)
+        {
+            Implementation = implementation;
+            TestContext = testContext;
+            TestEnvironment = testEnvironment;
+        }
+
+        public IMqttServer Implementation { get; }
+        public TestContext TestContext { get; }
+        public TestEnvironment TestEnvironment { get; }
+        public IMqttServerStartedHandler StartedHandler { get => Implementation.StartedHandler; set => Implementation.StartedHandler = value; }
+        public IMqttServerStoppedHandler StoppedHandler { get => Implementation.StoppedHandler; set => Implementation.StoppedHandler = value; }
+        public IMqttServerClientConnectedHandler ClientConnectedHandler { get => Implementation.ClientConnectedHandler; set => Implementation.ClientConnectedHandler = value; }
+        public IMqttServerClientDisconnectedHandler ClientDisconnectedHandler { get => Implementation.ClientDisconnectedHandler; set => Implementation.ClientDisconnectedHandler = value; }
+        public IMqttServerClientSubscribedTopicHandler ClientSubscribedTopicHandler { get => Implementation.ClientSubscribedTopicHandler; set => Implementation.ClientSubscribedTopicHandler = value; }
+        public IMqttServerClientUnsubscribedTopicHandler ClientUnsubscribedTopicHandler { get => Implementation.ClientUnsubscribedTopicHandler; set => Implementation.ClientUnsubscribedTopicHandler = value; }
+
+        public IMqttServerOptions Options => Implementation.Options;
+
+        public IMqttApplicationMessageReceivedHandler ApplicationMessageReceivedHandler { get => Implementation.ApplicationMessageReceivedHandler; set => Implementation.ApplicationMessageReceivedHandler = value; }
+
+        public Task ClearRetainedApplicationMessagesAsync()
+        {
+            return Implementation.ClearRetainedApplicationMessagesAsync();
+        }
+
+        public Task<IList<IMqttClientStatus>> GetClientStatusAsync()
+        {
+            return Implementation.GetClientStatusAsync();
+        }
+
+        public Task<IList<MqttApplicationMessage>> GetRetainedApplicationMessagesAsync()
+        {
+            return Implementation.GetRetainedApplicationMessagesAsync();
+        }
+
+        public Task<IList<IMqttSessionStatus>> GetSessionStatusAsync()
+        {
+            return Implementation.GetSessionStatusAsync();
+        }
+
+        public Task<MqttClientPublishResult> PublishAsync(MqttApplicationMessage applicationMessage, CancellationToken cancellationToken)
+        {
+            return Implementation.PublishAsync(applicationMessage, cancellationToken);
+        }
+
+        public Task StartAsync(IMqttServerOptions options)
+        {
+            switch (options)
+            {
+                case MqttServerOptionsBuilder builder:
+                    if (builder.Build().ConnectionValidator == null)
+                    {
+                        builder.WithConnectionValidator(ConnectionValidator);
+                    }
+                    break;
+                case MqttServerOptions op:
+                    if (op.ConnectionValidator == null)
+                    {
+                        op.ConnectionValidator = new MqttServerConnectionValidatorDelegate(ConnectionValidator);
+                    }
+                    break;
+                default:
+                    break;
+            }
+
+            return Implementation.StartAsync(options);
+        }
+
+        public void ConnectionValidator(MqttConnectionValidatorContext ctx)
+        {
+            if (!ctx.ClientId.StartsWith(TestContext.TestName))
+            {
+                TestEnvironment.TrackException(new InvalidOperationException($"invalid client connected '{ctx.ClientId}'"));
+                ctx.ReasonCode = Protocol.MqttConnectReasonCode.ClientIdentifierNotValid;
+            }
+        }
+
+        public Task StopAsync()
+        {
+            return Implementation.StopAsync();
+        }
+
+        public Task SubscribeAsync(string clientId, ICollection<TopicFilter> topicFilters)
+        {
+            return Implementation.SubscribeAsync(clientId, topicFilters);
+        }
+
+        public Task UnsubscribeAsync(string clientId, ICollection<string> topicFilters)
+        {
+            return Implementation.UnsubscribeAsync(clientId, topicFilters);
+        }
+    }
+}

Tests/MQTTnet.Core.Tests/MqttClient_Tests.cs

@@ -20,10 +20,12 @@ namespace MQTTnet.Tests
     [TestClass]
     public class Client_Tests
     {
+        public TestContext TestContext { get; set; }
+
         [TestMethod]
         public async Task Send_Reply_In_Message_Handler_For_Same_Client()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
                 var client = await testEnvironment.ConnectClientAsync();
@@ -57,7 +59,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Send_Reply_In_Message_Handler()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
                 var client1 = await testEnvironment.ConnectClientAsync();
@@ -89,7 +91,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Reconnect()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync();
                 var client = await testEnvironment.ConnectClientAsync();
@@ -112,7 +114,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Reconnect_While_Server_Offline()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 testEnvironment.IgnoreClientLogErrors = true;
 
@@ -149,7 +151,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Reconnect_From_Disconnected_Event()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 testEnvironment.IgnoreClientLogErrors = true;
 
@@ -189,7 +191,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task PacketIdentifier_In_Publish_Result()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
                 var client = await testEnvironment.ConnectClientAsync();
@@ -235,10 +237,40 @@ namespace MQTTnet.Tests
             }
         }
 
+        [TestMethod]
+        public async Task ConnectTimeout_Throws_Exception()
+        {
+            var factory = new MqttFactory();
+            using (var client = factory.CreateMqttClient())
+            {
+                bool disconnectHandlerCalled = false;
+                try
+                {
+                    client.DisconnectedHandler = new MqttClientDisconnectedHandlerDelegate(args =>
+                    {
+                        disconnectHandlerCalled = true;
+                    });
+
+                    await client.ConnectAsync(new MqttClientOptionsBuilder().WithTcpServer("1.2.3.4").Build());
+
+                    Assert.Fail("Must fail!");
+                }
+                catch (Exception exception)
+                {
+                    Assert.IsNotNull(exception);
+                    Assert.IsInstanceOfType(exception, typeof(MqttCommunicationException));
+                    //Assert.IsInstanceOfType(exception.InnerException, typeof(SocketException));
+                }
+
+                await Task.Delay(100); // disconnected handler is called async
+                Assert.IsTrue(disconnectHandlerCalled);
+            }
+        }
+
         [TestMethod]
         public async Task Fire_Disconnected_Event_On_Server_Shutdown()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync();
                 var client = await testEnvironment.ConnectClientAsync();
@@ -290,7 +322,7 @@ namespace MQTTnet.Tests
             // is an issue).
             const int MessagesCount = 50;
 
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -330,7 +362,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Send_Reply_For_Any_Received_Message()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -374,7 +406,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Publish_With_Correct_Retain_Flag()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -405,7 +437,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Subscribe_In_Callback_Events()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -444,7 +476,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Message_Send_Retry()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 testEnvironment.IgnoreClientLogErrors = true;
                 testEnvironment.IgnoreServerLogErrors = true;
@@ -488,7 +520,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task NoConnectedHandler_Connect_DoesNotThrowException()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -501,7 +533,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task NoDisconnectedHandler_Disconnect_DoesNotThrowException()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
                 var client = await testEnvironment.ConnectClientAsync();
@@ -516,7 +548,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Frequent_Connects()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -560,7 +592,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task No_Payload()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 

Tests/MQTTnet.Core.Tests/MqttFactory_Tests.cs

@@ -18,7 +18,7 @@ namespace MQTTnet.Tests
             //This test compares
             //1. correct logID
             string logId = "logId";
-            bool invalidLogIdOccured = false;
+            string invalidLogId = null;
 
             //2. if the total log calls are the same for global and local
             int globalLogCount = 0;
@@ -31,7 +31,7 @@ namespace MQTTnet.Tests
             {
                 if (logId != e.TraceMessage.LogId)
                 {
-                    invalidLogIdOccured = true;
+                    invalidLogId = e.TraceMessage.LogId;
                 }
                 Interlocked.Increment(ref globalLogCount);
             });
@@ -42,7 +42,7 @@ namespace MQTTnet.Tests
             {
                 if (logId != e.TraceMessage.LogId)
                 {
-                    invalidLogIdOccured = true;
+                    invalidLogId = e.TraceMessage.LogId;
                 }
                 Interlocked.Increment(ref localLogCount);
             };
@@ -69,7 +69,7 @@ namespace MQTTnet.Tests
                 MqttNetGlobalLogger.LogMessagePublished -= globalLog;
             }
 
-            Assert.IsFalse(invalidLogIdOccured);
+            Assert.IsNull(invalidLogId);
             Assert.AreNotEqual(0, globalLogCount);
             Assert.AreEqual(globalLogCount, localLogCount);
         }

Tests/MQTTnet.Core.Tests/MqttTcpChannel_Tests.cs

@@ -28,14 +28,14 @@ namespace MQTTnet.Tests
                 {
                     while (!ct.IsCancellationRequested)
                     {
-                        var client = await serverSocket.AcceptAsync();
+                        var client = await PlatformAbstractionLayer.AcceptAsync(serverSocket);
                         var data = new byte[] { 128 };
-                        await client.SendAsync(new ArraySegment<byte>(data), SocketFlags.None);
+                        await PlatformAbstractionLayer.SendAsync(client, new ArraySegment<byte>(data), SocketFlags.None);
                     }
                 }, ct.Token);
 
                 var clientSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
-                await clientSocket.ConnectAsync(IPAddress.Loopback, 50001);
+                await PlatformAbstractionLayer.ConnectAsync(clientSocket, IPAddress.Loopback, 50001);
 
                 await Task.Delay(100, ct.Token);
 

Tests/MQTTnet.Core.Tests/RPC_Tests.cs

@@ -18,6 +18,8 @@ namespace MQTTnet.Tests
     [TestClass]
     public class RPC_Tests
     {
+        public TestContext TestContext { get; set; }
+
         [TestMethod]
         public Task Execute_Success_With_QoS_0()
         {
@@ -58,7 +60,7 @@ namespace MQTTnet.Tests
         [ExpectedException(typeof(MqttCommunicationTimedOutException))]
         public async Task Execute_Timeout()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
                 
@@ -73,7 +75,7 @@ namespace MQTTnet.Tests
         [ExpectedException(typeof(MqttCommunicationTimedOutException))]
         public async Task Execute_With_Custom_Topic_Names()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -86,7 +88,7 @@ namespace MQTTnet.Tests
 
         private async Task Execute_Success(MqttQualityOfServiceLevel qosLevel, MqttProtocolVersion protocolVersion)
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
                 var responseSender = await testEnvironment.ConnectClientAsync(new MqttClientOptionsBuilder().WithProtocolVersion(protocolVersion));

Tests/MQTTnet.Core.Tests/RoundtripTime_Tests.cs

@@ -11,10 +11,12 @@ namespace MQTTnet.Tests
     [TestClass]
     public class RoundtripTime_Tests
     {
+        public TestContext TestContext { get; set; }
+
         [TestMethod]
         public async Task Round_Trip_Time()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
                 var receiverClient = await testEnvironment.ConnectClientAsync();

Tests/MQTTnet.Core.Tests/Server_Status_Tests.cs

@@ -6,16 +6,19 @@ using MQTTnet.Tests.Mockups;
 using MQTTnet.Client;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
+using System.Threading;
 
 namespace MQTTnet.Tests
 {
     [TestClass]
     public class Server_Status_Tests
     {
+        public TestContext TestContext { get; set; }
+
         [TestMethod]
         public async Task Show_Client_And_Session_Statistics()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync();
 
@@ -30,8 +33,8 @@ namespace MQTTnet.Tests
                 Assert.AreEqual(2, clientStatus.Count);
                 Assert.AreEqual(2, sessionStatus.Count);
 
-                Assert.IsTrue(clientStatus.Any(s => s.ClientId == "client1"));
-                Assert.IsTrue(clientStatus.Any(s => s.ClientId == "client2"));
+                Assert.IsTrue(clientStatus.Any(s => s.ClientId == c1.Options.ClientId));
+                Assert.IsTrue(clientStatus.Any(s => s.ClientId == c2.Options.ClientId));
 
                 await c1.DisconnectAsync();
                 await c2.DisconnectAsync();
@@ -49,19 +52,19 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Disconnect_Client()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync();
 
                 var c1 = await testEnvironment.ConnectClientAsync(new MqttClientOptionsBuilder().WithClientId("client1"));
                 
-                await Task.Delay(500);
+                await Task.Delay(1000);
 
                 var clientStatus = await server.GetClientStatusAsync();
-                
+
                 Assert.AreEqual(1, clientStatus.Count);
                 
-                Assert.IsTrue(clientStatus.Any(s => s.ClientId == "client1"));
+                Assert.IsTrue(clientStatus.Any(s => s.ClientId == c1.Options.ClientId));
 
                 await clientStatus.First().DisconnectAsync();
 
@@ -78,7 +81,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Keep_Persistent_Session()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync(new MqttServerOptionsBuilder().WithPersistentSessions());
 
@@ -110,7 +113,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Track_Sent_Application_Messages()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync(new MqttServerOptionsBuilder().WithPersistentSessions());
 
@@ -131,7 +134,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Track_Sent_Packets()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync(new MqttServerOptionsBuilder().WithPersistentSessions());
 

Tests/MQTTnet.Core.Tests/Server_Tests.cs

@@ -13,6 +13,7 @@ using MQTTnet.Client.Disconnecting;
 using MQTTnet.Client.Options;
 using MQTTnet.Client.Receiving;
 using MQTTnet.Client.Subscribing;
+using MQTTnet.Implementations;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
 using MQTTnet.Tests.Mockups;
@@ -22,10 +23,12 @@ namespace MQTTnet.Tests
     [TestClass]
     public class Server_Tests
     {
+        public TestContext TestContext { get; set; }
+
         [TestMethod]
         public async Task Use_Empty_Client_ID()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -51,7 +54,8 @@ namespace MQTTnet.Tests
                 MqttQualityOfServiceLevel.AtMostOnce,
                 "A/B/C",
                 MqttQualityOfServiceLevel.AtMostOnce,
-                1);
+                1, 
+                TestContext);
         }
 
         [TestMethod]
@@ -62,7 +66,8 @@ namespace MQTTnet.Tests
                 MqttQualityOfServiceLevel.AtLeastOnce,
                 "A/B/C",
                 MqttQualityOfServiceLevel.AtLeastOnce,
-                1);
+                1,
+                TestContext);
         }
 
         [TestMethod]
@@ -73,13 +78,14 @@ namespace MQTTnet.Tests
                 MqttQualityOfServiceLevel.ExactlyOnce,
                 "A/B/C",
                 MqttQualityOfServiceLevel.ExactlyOnce,
-                1);
+                1,
+                TestContext);
         }
 
         [TestMethod]
         public async Task Use_Clean_Session()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -93,7 +99,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Will_Message_Do_Not_Send()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var receivedMessagesCount = 0;
 
@@ -119,7 +125,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Will_Message_Send()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var receivedMessagesCount = 0;
 
@@ -145,7 +151,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Intercept_Subscription()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync(new MqttServerOptionsBuilder().WithSubscriptionInterceptor(
                     c =>
@@ -184,7 +190,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Subscribe_Unsubscribe()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var receivedMessagesCount = 0;
 
@@ -204,7 +210,7 @@ namespace MQTTnet.Tests
                 var subscribeEventCalled = false;
                 server.ClientSubscribedTopicHandler = new MqttServerClientSubscribedHandlerDelegate(e =>
                 {
-                    subscribeEventCalled = e.TopicFilter.Topic == "a" && e.ClientId == "c1";
+                    subscribeEventCalled = e.TopicFilter.Topic == "a" && e.ClientId == c1.Options.ClientId;
                 });
 
                 await c1.SubscribeAsync(new TopicFilter { Topic = "a", QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce });
@@ -218,7 +224,7 @@ namespace MQTTnet.Tests
                 var unsubscribeEventCalled = false;
                 server.ClientUnsubscribedTopicHandler = new MqttServerClientUnsubscribedTopicHandlerDelegate(e =>
                 {
-                    unsubscribeEventCalled = e.TopicFilter == "a" && e.ClientId == "c1";
+                    unsubscribeEventCalled = e.TopicFilter == "a" && e.ClientId == c1.Options.ClientId;
                 });
 
                 await c1.UnsubscribeAsync("a");
@@ -238,7 +244,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Subscribe_Multiple_In_Single_Request()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var receivedMessagesCount = 0;
 
@@ -271,7 +277,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Subscribe_Multiple_In_Multiple_Request()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var receivedMessagesCount = 0;
 
@@ -310,7 +316,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Publish_From_Server()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync();
 
@@ -336,7 +342,7 @@ namespace MQTTnet.Tests
             var receivedMessagesCount = 0;
             var locked = new object();
 
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -378,7 +384,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Session_Takeover()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -400,7 +406,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task No_Messages_If_No_Subscription()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -433,7 +439,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Set_Subscription_At_Server()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync();
                 server.ClientConnectedHandler = new MqttServerClientConnectedHandlerDelegate(e => server.SubscribeAsync(e.ClientId, "topic1"));
@@ -464,7 +470,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Shutdown_Disconnects_Clients_Gracefully()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync(new MqttServerOptionsBuilder());
 
@@ -486,7 +492,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Handle_Clean_Disconnect()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync(new MqttServerOptionsBuilder());
 
@@ -515,7 +521,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Client_Disconnect_Without_Errors()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 bool clientWasConnected;
 
@@ -546,7 +552,7 @@ namespace MQTTnet.Tests
         {
             const int ClientCount = 50;
 
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync();
 
@@ -598,7 +604,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Retained_Messages_Flow()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var retainedMessage = new MqttApplicationMessageBuilder().WithTopic("r").WithPayload("r").WithRetainFlag().Build();
 
@@ -635,7 +641,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Receive_No_Retained_Message_After_Subscribe()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -658,7 +664,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Receive_Retained_Message_After_Subscribe()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -689,7 +695,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Clear_Retained_Message_With_Empty_Payload()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var receivedMessagesCount = 0;
 
@@ -717,7 +723,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Clear_Retained_Message_With_Null_Payload()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var receivedMessagesCount = 0;
 
@@ -745,7 +751,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Intercept_Application_Message()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync(
                     new MqttServerOptionsBuilder().WithApplicationMessageInterceptor(
@@ -768,7 +774,7 @@ namespace MQTTnet.Tests
         {
             var serverStorage = new TestServerStorage();
 
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync(new MqttServerOptionsBuilder().WithStorage(serverStorage));
 
@@ -785,7 +791,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Publish_After_Client_Connects()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync();
                 server.UseClientConnectedHandler(async e =>
@@ -818,7 +824,7 @@ namespace MQTTnet.Tests
                 context.ApplicationMessage.Payload = Encoding.ASCII.GetBytes("extended");
             }
 
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync(new MqttServerOptionsBuilder().WithApplicationMessageInterceptor(Interceptor));
 
@@ -844,7 +850,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Send_Long_Body()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 const int PayloadSizeInMB = 30;
                 const int CharCount = PayloadSizeInMB * 1024 * 1024;
@@ -889,38 +895,128 @@ namespace MQTTnet.Tests
         {
             var serverOptions = new MqttServerOptionsBuilder().WithConnectionValidator(context =>
             {
-                context.ReturnCode = MqttConnectReturnCode.ConnectionRefusedNotAuthorized;
+                context.ReasonCode = MqttConnectReasonCode.NotAuthorized;
             });
 
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 testEnvironment.IgnoreClientLogErrors = true;
 
                 await testEnvironment.StartServerAsync(serverOptions);
 
-                try
+
+                var connectingFailedException = await Assert.ThrowsExceptionAsync<MqttConnectingFailedException>(() => testEnvironment.ConnectClientAsync());
+                Assert.AreEqual(MqttClientConnectResultCode.NotAuthorized, connectingFailedException.ResultCode);
+            }
+        }
+
+
+        private Dictionary<string, bool> _connected;
+        private void ConnectionValidationHandler(MqttConnectionValidatorContext eventArgs)
+        {
+            if (_connected.ContainsKey(eventArgs.ClientId))
+            {
+                eventArgs.ReasonCode = MqttConnectReasonCode.BadUserNameOrPassword;
+                return;
+            }
+            _connected[eventArgs.ClientId] = true;
+            eventArgs.ReasonCode = MqttConnectReasonCode.Success;
+            return;
+        }
+
+        [TestMethod]
+        public async Task Same_Client_Id_Refuse_Connection()
+        {
+            using (var testEnvironment = new TestEnvironment(TestContext))
+            {
+                testEnvironment.IgnoreClientLogErrors = true;
+
+                _connected = new Dictionary<string, bool>();
+                var options = new MqttServerOptionsBuilder();
+                options.WithConnectionValidator(e => ConnectionValidationHandler(e));
+                var server = await testEnvironment.StartServerAsync(options);
+
+                var events = new List<string>();
+
+                server.ClientConnectedHandler = new MqttServerClientConnectedHandlerDelegate(_ =>
                 {
-                    await testEnvironment.ConnectClientAsync();
-                    Assert.Fail("An exception should be raised.");
-                }
-                catch (Exception exception)
+                    lock (events)
+                    {
+                        events.Add("c");
+                    }
+                });
+
+                server.ClientDisconnectedHandler = new MqttServerClientDisconnectedHandlerDelegate(_ =>
+                {
+                    lock (events)
+                    {
+                        events.Add("d");
+                    }
+                });
+
+                var clientOptions = new MqttClientOptionsBuilder()
+                    .WithClientId("same_id");
+
+                // c
+                var c1 = await testEnvironment.ConnectClientAsync(clientOptions);
+
+                c1.UseDisconnectedHandler(_ =>
                 {
-                    if (exception is MqttConnectingFailedException connectingFailedException)
+                    lock (events)
                     {
-                        Assert.AreEqual(MqttClientConnectResultCode.NotAuthorized, connectingFailedException.ResultCode);
+                        events.Add("x");
                     }
-                    else
+                });
+
+
+                c1.UseApplicationMessageReceivedHandler(_ =>
+                {
+                    lock (events)
                     {
-                        Assert.Fail("Wrong exception.");
+                        events.Add("r");
                     }
+
+                });
+
+                c1.SubscribeAsync("topic").Wait();
+
+                await Task.Delay(500);
+
+                c1.PublishAsync("topic").Wait();
+
+                await Task.Delay(500);
+
+                var flow = string.Join(string.Empty, events);
+                Assert.AreEqual("cr", flow);
+
+                try
+                {
+                    await testEnvironment.ConnectClientAsync(clientOptions);
+                    Assert.Fail("same id connection is expected to fail");
+                }
+                catch
+                {
+                    //same id connection is expected to fail
                 }
+
+                await Task.Delay(500);
+
+                flow = string.Join(string.Empty, events);
+                Assert.AreEqual("cr", flow);
+
+                c1.PublishAsync("topic").Wait();
+
+                await Task.Delay(500);
+
+                flow = string.Join(string.Empty, events);
+                Assert.AreEqual("crr", flow);
             }
         }
 
         [TestMethod]
         public async Task Same_Client_Id_Connect_Disconnect_Event_Order()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync(new MqttServerOptionsBuilder());
 
@@ -956,17 +1052,40 @@ namespace MQTTnet.Tests
                 // dc
                 var c2 = await testEnvironment.ConnectClientAsync(clientOptions);
 
+                c2.UseApplicationMessageReceivedHandler(_ =>
+                {
+                    lock (events)
+                    {
+                        events.Add("r");
+                    }
+
+                });
+                c2.SubscribeAsync("topic").Wait();
+
                 await Task.Delay(500);
 
                 flow = string.Join(string.Empty, events);
                 Assert.AreEqual("cdc", flow);
 
+                // r
+                c2.PublishAsync("topic").Wait();
+
+                await Task.Delay(500);
+
+                flow = string.Join(string.Empty, events);
+                Assert.AreEqual("cdcr", flow);
+
+
                 // nothing
+
+                Assert.AreEqual(false, c1.IsConnected);
                 await c1.DisconnectAsync();
+                Assert.AreEqual (false, c1.IsConnected);
 
                 await Task.Delay(500);
 
                 // d
+                Assert.AreEqual(true, c2.IsConnected);
                 await c2.DisconnectAsync();
 
                 await Task.Delay(500);
@@ -974,14 +1093,14 @@ namespace MQTTnet.Tests
                 await server.StopAsync();
 
                 flow = string.Join(string.Empty, events);
-                Assert.AreEqual("cdcd", flow);
+                Assert.AreEqual("cdcrd", flow);
             }
         }
 
         [TestMethod]
         public async Task Remove_Session()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync(new MqttServerOptionsBuilder());
 
@@ -1000,7 +1119,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Stop_And_Restart()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 testEnvironment.IgnoreClientLogErrors = true;
 
@@ -1022,23 +1141,23 @@ namespace MQTTnet.Tests
                 await testEnvironment.ConnectClientAsync();
             }
         }
-
+        
         [TestMethod]
         public async Task Close_Idle_Connection()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync(new MqttServerOptionsBuilder().WithDefaultCommunicationTimeout(TimeSpan.FromSeconds(1)));
 
                 var client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
-                await client.ConnectAsync("localhost", testEnvironment.ServerPort);
+                await PlatformAbstractionLayer.ConnectAsync(client, "localhost", testEnvironment.ServerPort);
 
                 // Don't send anything. The server should close the connection.
                 await Task.Delay(TimeSpan.FromSeconds(3));
 
                 try
                 {
-                    var receivedBytes = await client.ReceiveAsync(new ArraySegment<byte>(new byte[10]), SocketFlags.Partial);
+                    var receivedBytes = await PlatformAbstractionLayer.ReceiveAsync(client, new ArraySegment<byte>(new byte[10]), SocketFlags.Partial);
                     if (receivedBytes == 0)
                     {
                         return;
@@ -1055,14 +1174,14 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Send_Garbage()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync(new MqttServerOptionsBuilder().WithDefaultCommunicationTimeout(TimeSpan.FromSeconds(1)));
 
                 // Send an invalid packet and ensure that the server will close the connection and stay in a waiting state
                 // forever. This is security related.
                 var client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
-                await client.ConnectAsync("localhost", testEnvironment.ServerPort);
+                await PlatformAbstractionLayer.ConnectAsync(client, "localhost", testEnvironment.ServerPort);
                                 
                 var buffer = Encoding.UTF8.GetBytes("Garbage");
                 client.Send(buffer, buffer.Length, SocketFlags.None);
@@ -1071,7 +1190,7 @@ namespace MQTTnet.Tests
 
                 try
                 {
-                    var receivedBytes = await client.ReceiveAsync(new ArraySegment<byte>(new byte[10]), SocketFlags.Partial);
+                    var receivedBytes = await PlatformAbstractionLayer.ReceiveAsync(client, new ArraySegment<byte>(new byte[10]), SocketFlags.Partial);
                     if (receivedBytes == 0)
                     {
                         return;
@@ -1088,7 +1207,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Do_Not_Send_Retained_Messages_For_Denied_Subscription()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync(new MqttServerOptionsBuilder().WithSubscriptionInterceptor(c =>
                 {
@@ -1132,7 +1251,7 @@ namespace MQTTnet.Tests
         [TestMethod]
         public async Task Collect_Messages_In_Disconnected_Session()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var server = await testEnvironment.StartServerAsync(new MqttServerOptionsBuilder().WithPersistentSessions());
 
@@ -1159,7 +1278,7 @@ namespace MQTTnet.Tests
                 Assert.AreEqual(0, clientStatus.Count);
                 Assert.AreEqual(2, sessionStatus.Count);
 
-                Assert.AreEqual(3, sessionStatus.First(s => s.ClientId == "a").PendingApplicationMessagesCount);
+                Assert.AreEqual(3, sessionStatus.First(s => s.ClientId == client1.Options.ClientId).PendingApplicationMessagesCount);
             }
         }
 
@@ -1168,9 +1287,10 @@ namespace MQTTnet.Tests
             MqttQualityOfServiceLevel qualityOfServiceLevel,
             string topicFilter,
             MqttQualityOfServiceLevel filterQualityOfServiceLevel,
-            int expectedReceivedMessagesCount)
+            int expectedReceivedMessagesCount,
+            TestContext testContext)
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(testContext))
             {
                 var receivedMessagesCount = 0;
 

Tests/MQTTnet.Core.Tests/Session_Tests.cs

@@ -11,10 +11,12 @@ namespace MQTTnet.Tests
     [TestClass]
     public class Session_Tests
     {
+        public TestContext TestContext { get; set; }
+
         [TestMethod]
         public async Task Set_Session_Item()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 var serverOptions = new MqttServerOptionsBuilder()
                     .WithConnectionValidator(delegate (MqttConnectionValidatorContext context)

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

@@ -11,14 +11,11 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNetCore" Version="2.1.6" />
-    <PackageReference Include="Microsoft.AspNetCore.App" Version="2.1.6" />
-    <PackageReference Include="Microsoft.AspNetCore.Connections.Abstractions" Version="2.1.3" />
-    <PackageReference Include="Microsoft.AspNetCore.Http.Abstractions" Version="2.1.1" />
+    <PackageReference Include="Microsoft.AspNetCore.StaticFiles" Version="2.1.1" />
   </ItemGroup>
 
   <ItemGroup>
     <ProjectReference Include="..\..\Source\MQTTnet.AspnetCore\MQTTnet.AspNetCore.csproj" />
-    <ProjectReference Include="..\..\Source\MQTTnet\MQTTnet.csproj" />
   </ItemGroup>
 
   <ItemGroup>

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

@@ -12,7 +12,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Newtonsoft.Json" Version="12.0.2" />
+    <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
   </ItemGroup>
 
   <ItemGroup>

Tests/MQTTnet.TestApp.NetCore/ManagedClientTest.cs

@@ -40,11 +40,11 @@ namespace MQTTnet.TestApp.NetCore
                     Console.WriteLine(">> RECEIVED: " + e.ApplicationMessage.Topic);
                 });
 
-                await managedClient.PublishAsync(builder => builder.WithTopic("Step").WithPayload("1"));
-                await managedClient.PublishAsync(builder => builder.WithTopic("Step").WithPayload("2").WithAtLeastOnceQoS());
-
                 await managedClient.StartAsync(options);
 
+                await managedClient.PublishAsync(builder => builder.WithTopic("Step").WithPayload("1"));
+                await managedClient.PublishAsync(builder => builder.WithTopic("Step").WithPayload("2").WithAtLeastOnceQoS());
+                
                 await managedClient.SubscribeAsync(new TopicFilter { Topic = "xyz", QualityOfServiceLevel = MqttQualityOfServiceLevel.AtMostOnce });
                 await managedClient.SubscribeAsync(new TopicFilter { Topic = "abc", QualityOfServiceLevel = MqttQualityOfServiceLevel.AtMostOnce });
 

Tests/MQTTnet.TestApp.NetCore/ServerTest.cs

@@ -30,7 +30,7 @@ namespace MQTTnet.TestApp.NetCore
                         {
                             if (p.Username != "USER" || p.Password != "PASS")
                             {
-                                p.ReturnCode = MqttConnectReturnCode.ConnectionRefusedBadUsernameOrPassword;
+                                p.ReasonCode = MqttConnectReasonCode.BadUserNameOrPassword;
                             }
                         }
                     }),

appveyor.yml

@@ -14,5 +14,5 @@ build:
   verbosity: minimal
 
 test_script:
-- cmd: dotnet vstest "%APPVEYOR_BUILD_FOLDER%\Tests\MQTTnet.Core.Tests\bin\Release\netcoreapp2.1\MQTTnet.Tests.dll"
-- cmd: dotnet vstest "%APPVEYOR_BUILD_FOLDER%\Tests\MQTTnet.AspNetCore.Tests\bin\Release\netcoreapp2.1\MQTTnet.AspNetCore.Tests.dll"
+- cmd: dotnet vstest "%APPVEYOR_BUILD_FOLDER%\Tests\MQTTnet.Core.Tests\bin\Release\netcoreapp2.2\MQTTnet.Tests.dll"
+- cmd: dotnet vstest "%APPVEYOR_BUILD_FOLDER%\Tests\MQTTnet.AspNetCore.Tests\bin\Release\netcoreapp2.2\MQTTnet.AspNetCore.Tests.dll"