Fix client dead lock and protocol version issues.

Build/MQTTnet.AspNetCore.nuspec

@@ -2,7 +2,7 @@
 <package >
   <metadata>
     <id>MQTTnet.AspNetCore</id>
-    <version>2.7.3</version>
+    <version>2.7.4</version>
     <authors>Christian Kratky</authors>
     <owners>Christian Kratky</owners>
     <licenseUrl>https://github.com/chkr1011/MQTTnet/blob/master/LICENSE</licenseUrl>
@@ -10,13 +10,13 @@
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <description>This is a support library to integrate MQTTnet into AspNetCore.</description>
-    <releaseNotes>* Updated to MQTTnet 2.7.3.
+    <releaseNotes>* Updated to MQTTnet 2.7.4.
     </releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2018</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin</tags> 
     <dependencies>
       <group targetFramework="netstandard2.0">
-        <dependency id="MQTTnet" version="2.7.3" />
+        <dependency id="MQTTnet" version="2.7.4" />
       </group>
     </dependencies>
   </metadata>

Build/MQTTnet.nuspec

@@ -10,9 +10,13 @@
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <description>MQTTnet is a high performance .NET library for MQTT based communication. It provides a MQTT client and a MQTT server (broker).</description>
-    <releaseNotes>
+    <releaseNotes> * [Client] Fixed a deadlock while the client disconnects.
+* [Client] Fixed broken support for protocol version 3.1.0.
 * [Server] The _MqttTcpServerAdapter_ is now added to the ASP.NET services.
 * [Server] _MqttServerAdapter_ is renamed to _MqttTcpServerAdapter_ (BREAKING CHANGE!).
+* [Server] The server no longer sends the will message of a client if the disconnect was clean (via _Disconnect_ packet).
+* [Server] The application message interceptor now allows closing the connection.
+* [Server] Added a new flag for the _ClientDisconnected_ event which contains a value indicating whether the disconnect was clean (via _Disconnect_ packet).
     </releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2018</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin</tags> 
@@ -42,12 +46,6 @@
       <group targetFramework="net461">
       </group>
       
-      <group targetFramework="net462">
-      </group>
-      
-      <group targetFramework="net471">
-      </group>
-
     </dependencies>
   </metadata>
 
@@ -65,8 +63,6 @@
     <!-- .NET Framework -->
     <file src="..\Frameworks\MQTTnet.Netstandard\bin\Release\net452\MQTTnet.*" target="lib\net452\"/>
     <file src="..\Frameworks\MQTTnet.Netstandard\bin\Release\net461\MQTTnet.*" target="lib\net461\"/>
-    <file src="..\Frameworks\MQTTnet.Netstandard\bin\Release\net462\MQTTnet.*" target="lib\net462\"/>
-    <file src="..\Frameworks\MQTTnet.Netstandard\bin\Release\net471\MQTTnet.*" target="lib\net471\"/>
     
   </files>
 </package>

Frameworks/MQTTnet.NetStandard/Adapter/MqttChannelAdapter.cs

@@ -36,7 +36,7 @@ namespace MQTTnet.Adapter
         public Task ConnectAsync(TimeSpan timeout)
         {
             ThrowIfDisposed();
-            _logger.Trace<MqttChannelAdapter>("Connecting [Timeout={0}]", timeout);
+            _logger.Verbose<MqttChannelAdapter>("Connecting [Timeout={0}]", timeout);
 
             return ExecuteAndWrapExceptionAsync(() => _channel.ConnectAsync().TimeoutAfter(timeout));
         }
@@ -44,7 +44,7 @@ namespace MQTTnet.Adapter
         public Task DisconnectAsync(TimeSpan timeout)
         {
             ThrowIfDisposed();
-            _logger.Trace<MqttChannelAdapter>("Disconnecting [Timeout={0}]", timeout);
+            _logger.Verbose<MqttChannelAdapter>("Disconnecting [Timeout={0}]", timeout);
 
             return ExecuteAndWrapExceptionAsync(() => _channel.DisconnectAsync().TimeoutAfter(timeout));
         }
@@ -70,7 +70,7 @@ namespace MQTTnet.Adapter
                             continue;
                         }
 
-                        _logger.Trace<MqttChannelAdapter>("TX >>> {0} [Timeout={1}]", packet, timeout);
+                        _logger.Verbose<MqttChannelAdapter>("TX >>> {0} [Timeout={1}]", packet, timeout);
 
                         var chunks = PacketSerializer.Serialize(packet);
                         foreach (var chunk in chunks)
@@ -135,7 +135,7 @@ namespace MQTTnet.Adapter
                         throw new MqttProtocolViolationException("Received malformed packet.");
                     }
 
-                    _logger.Trace<MqttChannelAdapter>("RX <<< {0}", packet);
+                    _logger.Verbose<MqttChannelAdapter>("RX <<< {0}", packet);
                 }
                 finally
                 {

Frameworks/MQTTnet.NetStandard/Client/IMqttClientAdapterFactory.cs

@@ -5,6 +5,6 @@ namespace MQTTnet.Client
 {
     public interface IMqttClientAdapterFactory
     {
-        IMqttChannelAdapter CreateClientAdapter(IMqttClientChannelOptions options, IMqttNetLogger logger);
+        IMqttChannelAdapter CreateClientAdapter(IMqttClientOptions options, IMqttNetLogger logger);
     }
 }

Frameworks/MQTTnet.NetStandard/Client/IMqttClientOptions.cs

@@ -13,7 +13,7 @@ namespace MQTTnet.Client
         
         TimeSpan CommunicationTimeout { get; }
         TimeSpan KeepAlivePeriod { get; }
-        TimeSpan? KeepAliveSendInterval { get; set; }
+        TimeSpan? KeepAliveSendInterval { get; }
 
         MqttProtocolVersion ProtocolVersion { get; }
 

Frameworks/MQTTnet.NetStandard/Client/MqttClient.cs

@@ -57,16 +57,16 @@ namespace MQTTnet.Client
                 _packetIdentifierProvider.Reset();
                 _packetDispatcher.Reset();
 
-                _adapter = _adapterFactory.CreateClientAdapter(options.ChannelOptions, _logger);
+                _adapter = _adapterFactory.CreateClientAdapter(options, _logger);
 
-                _logger.Trace<MqttClient>("Trying to connect with server.");
+                _logger.Verbose<MqttClient>("Trying to connect with server.");
                 await _adapter.ConnectAsync(_options.CommunicationTimeout).ConfigureAwait(false);
-                _logger.Trace<MqttClient>("Connection with server established.");
+                _logger.Verbose<MqttClient>("Connection with server established.");
 
                 await StartReceivingPacketsAsync().ConfigureAwait(false);
 
                 var connectResponse = await AuthenticateAsync(options.WillMessage).ConfigureAwait(false);
-                _logger.Trace<MqttClient>("MQTT connection with server established.");
+                _logger.Verbose<MqttClient>("MQTT connection with server established.");
 
                 _sendTracker.Restart();
 
@@ -77,12 +77,14 @@ namespace MQTTnet.Client
 
                 IsConnected = true;
                 Connected?.Invoke(this, new MqttClientConnectedEventArgs(connectResponse.IsSessionPresent));
+
+                _logger.Info<MqttClient>("Connected.");
                 return new MqttClientConnectResult(connectResponse.IsSessionPresent);
             }
             catch (Exception exception)
             {
                 _logger.Error<MqttClient>(exception, "Error while connecting with server.");
-                await DisconnectInternalAsync(exception).ConfigureAwait(false);
+                await DisconnectInternalAsync(null, exception).ConfigureAwait(false);
 
                 throw;
             }
@@ -104,7 +106,7 @@ namespace MQTTnet.Client
             }
             finally
             {
-                await DisconnectInternalAsync(null).ConfigureAwait(false);
+                await DisconnectInternalAsync(null, null).ConfigureAwait(false);
             }
         }
 
@@ -159,7 +161,7 @@ namespace MQTTnet.Client
                     case MqttQualityOfServiceLevel.AtMostOnce:
                         {
                             // No packet identifier is used for QoS 0 [3.3.2.2 Packet Identifier]
-                            await SendAsync((MqttPublishPacket[])qosGroup.ToArray()).ConfigureAwait(false);
+                            await SendAsync(qosGroup.Cast<MqttBasePacket>().ToArray()).ConfigureAwait(false);
                             break;
                         }
                     case MqttQualityOfServiceLevel.AtLeastOnce:
@@ -236,33 +238,48 @@ namespace MQTTnet.Client
             if (IsConnected) throw new MqttProtocolViolationException(message);
         }
 
-        private async Task DisconnectInternalAsync(Exception exception)
+        private async Task DisconnectInternalAsync(Task sender, Exception exception)
         {
             await _disconnectLock.WaitAsync();
-            var clientWasConnected = IsConnected;
             try
             {
-                IsConnected = false;
-
                 if (_cancellationTokenSource == null || _cancellationTokenSource.IsCancellationRequested)
                 {
                     return;
                 }
 
                 _cancellationTokenSource.Cancel(false);
+            }
+            catch (Exception adapterException)
+            {
+                _logger.Warning<MqttClient>(adapterException, "Error while disconnecting from adapter.");
+            }
+            finally
+            {
+                _disconnectLock.Release();
+            }
+
+            var clientWasConnected = IsConnected;
+            IsConnected = false;
 
-                if (_packetReceiverTask != null)
+            try
+            {
+                if (_packetReceiverTask != null && _packetReceiverTask != sender)
                 {
-                    Task.WaitAll(_packetReceiverTask);
+                    _packetReceiverTask.Wait();
                 }
 
-                if (_keepAliveMessageSenderTask != null)
+                if (_keepAliveMessageSenderTask != null && _keepAliveMessageSenderTask != sender)
                 {
-                    Task.WaitAll(_keepAliveMessageSenderTask);
+                    _keepAliveMessageSenderTask.Wait();
                 }
 
-                await _adapter.DisconnectAsync(_options.CommunicationTimeout).ConfigureAwait(false);
-                _logger.Trace<MqttClient>("Disconnected from adapter.");
+                if (_adapter != null)
+                {
+                    await _adapter.DisconnectAsync(_options.CommunicationTimeout).ConfigureAwait(false);
+                }
+                
+                _logger.Verbose<MqttClient>("Disconnected from adapter.");
             }
             catch (Exception adapterException)
             {
@@ -272,12 +289,9 @@ namespace MQTTnet.Client
             {
                 _adapter?.Dispose();
                 _adapter = null;
-
                 _cancellationTokenSource?.Dispose();
                 _cancellationTokenSource = null;
 
-                _disconnectLock.Release();
-                
                 _logger.Info<MqttClient>("Disconnected.");
                 Disconnected?.Invoke(this, new MqttClientDisconnectedEventArgs(clientWasConnected, exception));
             }
@@ -287,8 +301,6 @@ namespace MQTTnet.Client
         {
             try
             {
-                _logger.Info<MqttClient>("Received <<< {0}", packet);
-
                 if (packet is MqttPublishPacket publishPacket)
                 {
                     await ProcessReceivedPublishPacketAsync(publishPacket).ConfigureAwait(false);
@@ -395,7 +407,7 @@ namespace MQTTnet.Client
 
         private async Task SendKeepAliveMessagesAsync()
         {
-            _logger.Info<MqttClient>("Start sending keep alive packets.");
+            _logger.Verbose<MqttClient>("Start sending keep alive packets.");
 
             try
             {
@@ -415,37 +427,31 @@ namespace MQTTnet.Client
                     await Task.Delay(keepAliveSendInterval, _cancellationTokenSource.Token).ConfigureAwait(false);
                 }
             }
-            catch (OperationCanceledException)
-            {
-            }
             catch (Exception exception)
             {
-                if (_cancellationTokenSource.Token.IsCancellationRequested)
+                if (exception is OperationCanceledException)
                 {
-                    return;
                 }
-
-                if (exception is MqttCommunicationException)
+                else if (exception is MqttCommunicationException)
                 {
                     _logger.Warning<MqttClient>(exception, "MQTT communication exception while sending/receiving keep alive packets.");
                 }
                 else
                 {
-                    _logger.Warning<MqttClient>(exception, "Unhandled exception while sending/receiving keep alive packets.");
-
+                    _logger.Error<MqttClient>(exception, "Unhandled exception while sending/receiving keep alive packets.");
                 }
-
-                await DisconnectInternalAsync(exception).ConfigureAwait(false);
+                
+                await DisconnectInternalAsync(_keepAliveMessageSenderTask, exception).ConfigureAwait(false);
             }
             finally
             {
-                _logger.Info<MqttClient>("Stopped sending keep alive packets.");
+                _logger.Verbose<MqttClient>("Stopped sending keep alive packets.");
             }
         }
 
         private async Task ReceivePacketsAsync()
         {
-            _logger.Info<MqttClient>("Start receiving packets.");
+            _logger.Verbose<MqttClient>("Start receiving packets.");
 
             try
             {
@@ -463,31 +469,25 @@ namespace MQTTnet.Client
                     StartProcessReceivedPacket(packet);
                 }
             }
-            catch (OperationCanceledException)
-            {
-            }
             catch (Exception exception)
             {
-                if (_cancellationTokenSource.IsCancellationRequested)
+                if (exception is OperationCanceledException)
                 {
-                    return;
                 }
-
-                if (exception is MqttCommunicationException)
+                else if (exception is MqttCommunicationException)
                 {
                     _logger.Warning<MqttClient>(exception, "MQTT communication exception while receiving packets.");
                 }
                 else
                 {
                     _logger.Error<MqttClient>(exception, "Unhandled exception while receiving packets.");
-
                 }
 
-                await DisconnectInternalAsync(exception).ConfigureAwait(false);
+                await DisconnectInternalAsync(_packetReceiverTask, exception).ConfigureAwait(false);
             }
             finally
             {
-                _logger.Info<MqttClient>("Stopped receiving packets.");
+                _logger.Verbose<MqttClient>("Stopped receiving packets.");
             }
         }
 

Frameworks/MQTTnet.NetStandard/Diagnostics/IMqttNetLogger.cs

@@ -6,7 +6,7 @@ namespace MQTTnet.Diagnostics
     {
         event EventHandler<MqttNetLogMessagePublishedEventArgs> LogMessagePublished;
 
-        void Trace<TSource>(string message, params object[] parameters);
+        void Verbose<TSource>(string message, params object[] parameters);
 
         void Info<TSource>(string message, params object[] parameters);
 

Frameworks/MQTTnet.NetStandard/Diagnostics/MqttNetLogger.cs

@@ -13,7 +13,7 @@ namespace MQTTnet.Diagnostics
 
         public event EventHandler<MqttNetLogMessagePublishedEventArgs> LogMessagePublished;
 
-        public void Trace<TSource>(string message, params object[] parameters)
+        public void Verbose<TSource>(string message, params object[] parameters)
         {
             Publish<TSource>(MqttNetLogLevel.Verbose, null, message, parameters);
         }

Frameworks/MQTTnet.NetStandard/Implementations/MqttClientAdapterFactory.cs

@@ -8,18 +8,28 @@ namespace MQTTnet.Implementations
 {
     public class MqttClientAdapterFactory : IMqttClientAdapterFactory
     {
-        public IMqttChannelAdapter CreateClientAdapter(IMqttClientChannelOptions options, IMqttNetLogger logger)
+        public IMqttChannelAdapter CreateClientAdapter(IMqttClientOptions options, IMqttNetLogger logger)
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
-            switch (options)
+            var serializer = new MqttPacketSerializer { ProtocolVersion = options.ProtocolVersion };
+
+            switch (options.ChannelOptions)
             {
                 case MqttClientTcpOptions tcpOptions:
-                    return new MqttChannelAdapter(new MqttTcpChannel(tcpOptions), new MqttPacketSerializer(), logger);
+                    {
+                        return new MqttChannelAdapter(new MqttTcpChannel(tcpOptions), serializer, logger);
+                    }
+
                 case MqttClientWebSocketOptions webSocketOptions:
-                    return new MqttChannelAdapter(new MqttWebSocketChannel(webSocketOptions), new MqttPacketSerializer(), logger);
+                    {
+                        return new MqttChannelAdapter(new MqttWebSocketChannel(webSocketOptions), serializer, logger);
+                    }
+
                 default:
-                    throw new NotSupportedException();
+                    {
+                        throw new NotSupportedException();
+                    }
             }
         }
     }

Frameworks/MQTTnet.NetStandard/Implementations/MqttWebSocketChannel.cs

@@ -9,7 +9,7 @@ using MQTTnet.Client;
 
 namespace MQTTnet.Implementations
 {
-    public sealed class MqttWebSocketChannel : IMqttChannel, IDisposable
+    public sealed class MqttWebSocketChannel : IMqttChannel
     {
         // ReSharper disable once MemberCanBePrivate.Global
         // ReSharper disable once AutoPropertyCanBeMadeGetOnly.Global

Frameworks/MQTTnet.NetStandard/ManagedClient/ManagedMqttClient.cs

@@ -244,7 +244,7 @@ namespace MQTTnet.ManagedClient
             }
             finally
             {
-                _logger.Trace<ManagedMqttClient>("Stopped publishing messages.");
+                _logger.Verbose<ManagedMqttClient>("Stopped publishing messages.");
             }
         }
 

Frameworks/MQTTnet.NetStandard/Server/MqttApplicationMessageInterceptorContext.cs

@@ -11,5 +11,9 @@
         public string ClientId { get; }
 
         public MqttApplicationMessage ApplicationMessage { get; set; }
+
+        public bool AcceptPublish { get; set; } = true;
+
+        public bool CloseConnection { get; set; }
     }
 }

Frameworks/MQTTnet.NetStandard/Server/MqttClientDisconnectedEventArgs.cs

@@ -4,11 +4,14 @@ namespace MQTTnet.Server
 {
     public class MqttClientDisconnectedEventArgs : EventArgs
     {
-        public MqttClientDisconnectedEventArgs(ConnectedMqttClient client)
+        public MqttClientDisconnectedEventArgs(ConnectedMqttClient client, bool wasCleanDisconnect)
         {
             Client = client ?? throw new ArgumentNullException(nameof(client));
+            WasCleanDisconnect = wasCleanDisconnect;
         }
         
         public ConnectedMqttClient Client { get; }
+
+        public bool WasCleanDisconnect { get; }
     }
 }

Frameworks/MQTTnet.NetStandard/Server/MqttClientKeepAliveMonitor.cs

@@ -81,7 +81,7 @@ namespace MQTTnet.Server
             }
             finally
             {
-                _logger.Trace<MqttClientSession>("Client {0}: Stopped checking keep alive timeout.", _clientId);
+                _logger.Verbose<MqttClientSession>("Client {0}: Stopped checking keep alive timeout.", _clientId);
             }
         }
 

Frameworks/MQTTnet.NetStandard/Server/MqttClientPendingMessagesQueue.cs

@@ -57,7 +57,7 @@ namespace MQTTnet.Server
             _queue.Enqueue(packet);
             _queueWaitSemaphore.Release();
 
-            _logger.Trace<MqttClientPendingMessagesQueue>("Enqueued packet (ClientId: {0}).", _clientSession.ClientId);
+            _logger.Verbose<MqttClientPendingMessagesQueue>("Enqueued packet (ClientId: {0}).", _clientSession.ClientId);
         }
 
         private async Task SendQueuedPacketsAsync(IMqttChannelAdapter adapter, CancellationToken cancellationToken)
@@ -96,7 +96,7 @@ namespace MQTTnet.Server
 
                 await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new[] { packet }).ConfigureAwait(false);
 
-                _logger.Trace<MqttClientPendingMessagesQueue>("Enqueued packet sent (ClientId: {0}).", _clientSession.ClientId);
+                _logger.Verbose<MqttClientPendingMessagesQueue>("Enqueued packet sent (ClientId: {0}).", _clientSession.ClientId);
             }
             catch (Exception exception)
             {

Frameworks/MQTTnet.NetStandard/Server/MqttClientSession.cs

@@ -23,6 +23,7 @@ namespace MQTTnet.Server
         private IMqttChannelAdapter _adapter;
         private CancellationTokenSource _cancellationTokenSource;
         private MqttApplicationMessage _willMessage;
+        private bool _wasCleanDisconnect;
 
         public MqttClientSession(
             string clientId,
@@ -55,7 +56,7 @@ namespace MQTTnet.Server
 
         public bool IsConnected => _adapter != null;
 
-        public async Task RunAsync(MqttConnectPacket connectPacket, IMqttChannelAdapter adapter)
+        public async Task<bool> RunAsync(MqttConnectPacket connectPacket, IMqttChannelAdapter adapter)
         {
             if (connectPacket == null) throw new ArgumentNullException(nameof(connectPacket));
             if (adapter == null) throw new ArgumentNullException(nameof(adapter));
@@ -64,6 +65,7 @@ namespace MQTTnet.Server
             {
                 var cancellationTokenSource = new CancellationTokenSource();
 
+                _wasCleanDisconnect = false;
                 _willMessage = connectPacket.WillMessage;
                 _adapter = adapter;
                 _cancellationTokenSource = cancellationTokenSource;
@@ -84,9 +86,11 @@ namespace MQTTnet.Server
             {
                 _logger.Error<MqttClientSession>(exception, "Client '{0}': Unhandled exception while processing client packets.", ClientId);
             }
+
+            return _wasCleanDisconnect;
         }
 
-        public async Task StopAsync()
+        public async Task StopAsync(bool wasCleanDisconnect = false)
         {
             try
             {
@@ -95,6 +99,8 @@ namespace MQTTnet.Server
                     return;
                 }
 
+                _wasCleanDisconnect = wasCleanDisconnect;
+
                 _cancellationTokenSource?.Cancel(false);
 
                 PendingMessagesQueue.WaitForCompletion();
@@ -110,9 +116,10 @@ namespace MQTTnet.Server
             finally
             {
                 var willMessage = _willMessage;
-                if (willMessage != null)
+                _willMessage = null; // clear willmessage so it is send just once
+
+                if (willMessage != null && !wasCleanDisconnect)
                 {
-                    _willMessage = null; // clear willmessage so it is send just once
                     await ApplicationMessageReceivedCallback(this, willMessage).ConfigureAwait(false);
                 }
             }
@@ -246,7 +253,12 @@ namespace MQTTnet.Server
                 return HandleIncomingUnsubscribePacketAsync(adapter, unsubscribePacket, cancellationToken);
             }
 
-            if (packet is MqttDisconnectPacket || packet is MqttConnectPacket)
+            if (packet is MqttDisconnectPacket)
+            {
+                return StopAsync(true);
+            }
+
+            if (packet is MqttConnectPacket)
             {
                 return StopAsync();
             }
@@ -262,7 +274,6 @@ namespace MQTTnet.Server
 
             if (subscribeResult.CloseConnection)
             {
-                await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new[] { new MqttDisconnectPacket() }).ConfigureAwait(false);
                 await StopAsync().ConfigureAwait(false);
             }
 

Frameworks/MQTTnet.NetStandard/Server/MqttClientSessionsManager.cs

@@ -29,7 +29,7 @@ namespace MQTTnet.Server
         }
 
         public Action<ConnectedMqttClient> ClientConnectedCallback { get; set; }
-        public Action<ConnectedMqttClient> ClientDisconnectedCallback { get; set; }
+        public Action<ConnectedMqttClient, bool> ClientDisconnectedCallback { get; set; }
         public Action<string, TopicFilter> ClientSubscribedTopicCallback { get; set; }
         public Action<string, string> ClientUnsubscribedTopicCallback { get; set; }
         public Action<string, MqttApplicationMessage> ApplicationMessageReceivedCallback { get; set; }
@@ -37,7 +37,9 @@ namespace MQTTnet.Server
         public async Task RunSessionAsync(IMqttChannelAdapter clientAdapter, CancellationToken cancellationToken)
         {
             var clientId = string.Empty;
+            var wasCleanDisconnect = false;
             MqttClientSession clientSession = null;
+            
             try
             {
                 if (!(await clientAdapter.ReceivePacketAsync(_options.DefaultCommunicationTimeout, cancellationToken)
@@ -84,7 +86,7 @@ namespace MQTTnet.Server
                     ProtocolVersion = clientAdapter.PacketSerializer.ProtocolVersion
                 });
 
-                await clientSession.RunAsync(connectPacket, clientAdapter).ConfigureAwait(false);
+                wasCleanDisconnect = await clientSession.RunAsync(connectPacket, clientAdapter).ConfigureAwait(false);
             }
             catch (OperationCanceledException)
             {
@@ -110,7 +112,8 @@ namespace MQTTnet.Server
                     ClientId = clientId,
                     ProtocolVersion = clientAdapter.PacketSerializer.ProtocolVersion,
                     PendingApplicationMessages = clientSession?.PendingMessagesQueue.Count ?? 0
-                });
+                },
+                wasCleanDisconnect);
             }
         }
 
@@ -156,8 +159,13 @@ namespace MQTTnet.Server
         {
             try
             {
-                applicationMessage = InterceptApplicationMessage(senderClientSession, applicationMessage);
-                if (applicationMessage == null)
+                var interceptorContext = InterceptApplicationMessage(senderClientSession, applicationMessage);
+                if (interceptorContext.CloseConnection)
+                {
+                    await senderClientSession.StopAsync().ConfigureAwait(false);
+                }
+
+                if (interceptorContext.ApplicationMessage == null || !interceptorContext.AcceptPublish)
                 {
                     return;
                 }
@@ -230,20 +238,20 @@ namespace MQTTnet.Server
             }
         }
 
-        private MqttApplicationMessage InterceptApplicationMessage(MqttClientSession senderClientSession, MqttApplicationMessage applicationMessage)
+        private MqttApplicationMessageInterceptorContext InterceptApplicationMessage(MqttClientSession senderClientSession, MqttApplicationMessage applicationMessage)
         {
-            var interceptor = _options.ApplicationMessageInterceptor;
-            if (interceptor == null)
-            {
-                return applicationMessage;
-            }
-
             var interceptorContext = new MqttApplicationMessageInterceptorContext(
                 senderClientSession?.ClientId,
                 applicationMessage);
 
+            var interceptor = _options.ApplicationMessageInterceptor;
+            if (interceptor == null)
+            {
+                return interceptorContext;
+            }
+            
             interceptor(interceptorContext);
-            return interceptorContext.ApplicationMessage;
+            return interceptorContext;
         }
 
         private MqttConnectReturnCode ValidateConnection(MqttConnectPacket connectPacket)
@@ -279,11 +287,11 @@ namespace MQTTnet.Server
                         clientSession.Dispose();
                         clientSession = null;
 
-                        _logger.Trace<MqttClientSessionsManager>("Stopped existing session of client '{0}'.", connectPacket.ClientId);
+                        _logger.Verbose<MqttClientSessionsManager>("Stopped existing session of client '{0}'.", connectPacket.ClientId);
                     }
                     else
                     {
-                        _logger.Trace<MqttClientSessionsManager>("Reusing existing session of client '{0}'.", connectPacket.ClientId);
+                        _logger.Verbose<MqttClientSessionsManager>("Reusing existing session of client '{0}'.", connectPacket.ClientId);
                     }
                 }
 
@@ -302,7 +310,7 @@ namespace MQTTnet.Server
 
                     _sessions[connectPacket.ClientId] = clientSession;
 
-                    _logger.Trace<MqttClientSessionsManager>("Created a new session for client '{0}'.", connectPacket.ClientId);
+                    _logger.Verbose<MqttClientSessionsManager>("Created a new session for client '{0}'.", connectPacket.ClientId);
                 }
 
                 return new GetOrCreateClientSessionResult { IsExistingSession = isExistingSession, Session = clientSession };

Frameworks/MQTTnet.NetStandard/Server/MqttRetainedMessagesManager.cs

@@ -132,7 +132,7 @@ namespace MQTTnet.Server
 
             if (!saveIsRequired)
             {
-                _logger.Trace<MqttRetainedMessagesManager>("Skipped saving retained messages because no changes were detected.");
+                _logger.Verbose<MqttRetainedMessagesManager>("Skipped saving retained messages because no changes were detected.");
             }
 
             if (saveIsRequired && _options.Storage != null)

Frameworks/MQTTnet.NetStandard/Server/MqttServer.cs

@@ -138,10 +138,10 @@ namespace MQTTnet.Server
             ClientConnected?.Invoke(this, new MqttClientConnectedEventArgs(client));
         }
 
-        private void OnClientDisconnected(ConnectedMqttClient client)
+        private void OnClientDisconnected(ConnectedMqttClient client, bool wasCleanDisconnect)
         {
-            _logger.Info<MqttServer>("Client '{0}': Disconnected.", client.ClientId);
-            ClientDisconnected?.Invoke(this, new MqttClientDisconnectedEventArgs(client));
+            _logger.Info<MqttServer>("Client '{0}': Disconnected (clean={1}).", client.ClientId, wasCleanDisconnect);
+            ClientDisconnected?.Invoke(this, new MqttClientDisconnectedEventArgs(client, wasCleanDisconnect));
         }
 
         private void OnClientSubscribedTopic(string clientId, TopicFilter topicFilter)
@@ -162,7 +162,7 @@ namespace MQTTnet.Server
         private void OnClientAccepted(object sender, MqttServerAdapterClientAcceptedEventArgs eventArgs)
         {
             eventArgs.SessionTask = Task.Run(
-                async () => await _clientSessionsManager.RunSessionAsync(eventArgs.Client, _cancellationTokenSource.Token).ConfigureAwait(false),
+                () => _clientSessionsManager.RunSessionAsync(eventArgs.Client, _cancellationTokenSource.Token),
                 _cancellationTokenSource.Token);
         }
     }

Tests/MQTTnet.Core.Tests/TestMqttCommunicationAdapterFactory.cs

@@ -13,7 +13,7 @@ namespace MQTTnet.Core.Tests
             _adapter = adapter;
         }
         
-        public IMqttChannelAdapter CreateClientAdapter(IMqttClientChannelOptions options, IMqttNetLogger logger)
+        public IMqttChannelAdapter CreateClientAdapter(IMqttClientOptions options, IMqttNetLogger logger)
         {
             return _adapter;
         }

Tests/MQTTnet.TestApp.NetCore/ServerTest.cs

@@ -3,7 +3,6 @@ using System.Text;
 using System.Threading.Tasks;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
-using Newtonsoft.Json.Linq;
 
 namespace MQTTnet.TestApp.NetCore
 {
@@ -38,6 +37,12 @@ namespace MQTTnet.TestApp.NetCore
                             // based payload with the timestamp is a suitable use case.
                             context.ApplicationMessage.Payload = Encoding.UTF8.GetBytes(DateTime.Now.ToString("O"));
                         }
+
+                        if (context.ApplicationMessage.Topic == "not_allowed_topic")
+                        {
+                            context.AcceptPublish = false;
+                            context.CloseConnection = true;
+                        }
                     },
                     SubscriptionInterceptor = context =>
                     {
@@ -72,27 +77,27 @@ namespace MQTTnet.TestApp.NetCore
                         ConsoleColor.Magenta);
                 };
 
-                options.ApplicationMessageInterceptor = c =>
-                {
-                    if (c.ApplicationMessage.Payload == null || c.ApplicationMessage.Payload.Length == 0)
-                    {
-                        return;
-                    }
-
-                    try
-                    {
-                        var content = JObject.Parse(Encoding.UTF8.GetString(c.ApplicationMessage.Payload));
-                        var timestampProperty = content.Property("timestamp");
-                        if (timestampProperty != null && timestampProperty.Value.Type == JTokenType.Null)
-                        {
-                            timestampProperty.Value = DateTime.Now.ToString("O");
-                            c.ApplicationMessage.Payload = Encoding.UTF8.GetBytes(content.ToString());
-                        }
-                    }
-                    catch (Exception)
-                    {
-                    }
-                };
+                //options.ApplicationMessageInterceptor = c =>
+                //{
+                //    if (c.ApplicationMessage.Payload == null || c.ApplicationMessage.Payload.Length == 0)
+                //    {
+                //        return;
+                //    }
+
+                //    try
+                //    {
+                //        var content = JObject.Parse(Encoding.UTF8.GetString(c.ApplicationMessage.Payload));
+                //        var timestampProperty = content.Property("timestamp");
+                //        if (timestampProperty != null && timestampProperty.Value.Type == JTokenType.Null)
+                //        {
+                //            timestampProperty.Value = DateTime.Now.ToString("O");
+                //            c.ApplicationMessage.Payload = Encoding.UTF8.GetBytes(content.ToString());
+                //        }
+                //    }
+                //    catch (Exception)
+                //    {
+                //    }
+                //};
 
                 mqttServer.ClientDisconnected += (s, e) =>
                 {

Tests/MQTTnet.TestApp.UniversalWindows/MainPage.xaml.cs

@@ -13,6 +13,8 @@ using MQTTnet.Implementations;
 using MQTTnet.ManagedClient;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
+using MqttClientConnectedEventArgs = MQTTnet.Client.MqttClientConnectedEventArgs;
+using MqttClientDisconnectedEventArgs = MQTTnet.Client.MqttClientDisconnectedEventArgs;
 
 namespace MQTTnet.TestApp.UniversalWindows
 {
@@ -33,6 +35,11 @@ namespace MQTTnet.TestApp.UniversalWindows
         private async void OnTraceMessagePublished(object sender, MqttNetLogMessagePublishedEventArgs e)
         {
             _traceMessages.Enqueue(e.TraceMessage);
+            await UpdateLogAsync();
+        }
+
+        private async Task UpdateLogAsync()
+        {
             while (_traceMessages.Count > 100)
             {
                 _traceMessages.TryDequeue(out _);
@@ -113,11 +120,15 @@ namespace MQTTnet.TestApp.UniversalWindows
                 {
                     await _mqttClient.DisconnectAsync();
                     _mqttClient.ApplicationMessageReceived -= OnApplicationMessageReceived;
+                    _mqttClient.Connected -= OnConnected;
+                    _mqttClient.Disconnected -= OnDisconnected;
                 }
 
                 var factory = new MqttFactory();
                 _mqttClient = factory.CreateMqttClient();
                 _mqttClient.ApplicationMessageReceived += OnApplicationMessageReceived;
+                _mqttClient.Connected += OnConnected;
+                _mqttClient.Disconnected += OnDisconnected;
 
                 await _mqttClient.ConnectAsync(options);
             }
@@ -127,6 +138,22 @@ namespace MQTTnet.TestApp.UniversalWindows
             }
         }
 
+        private void OnDisconnected(object sender, MqttClientDisconnectedEventArgs e)
+        {
+            _traceMessages.Enqueue(new MqttNetLogMessage("", DateTime.Now, -1,
+                "", MqttNetLogLevel.Info, "! DISCONNECTED EVENT FIRED", null));
+
+            Task.Run(UpdateLogAsync);
+        }
+
+        private void OnConnected(object sender, MqttClientConnectedEventArgs e)
+        {
+            _traceMessages.Enqueue(new MqttNetLogMessage("", DateTime.Now, -1,
+                "", MqttNetLogLevel.Info, "! CONNECTED EVENT FIRED", null));
+
+            Task.Run(UpdateLogAsync);
+        }
+
         private async void OnApplicationMessageReceived(object sender, MqttApplicationMessageReceivedEventArgs eventArgs)
         {
             var item = $"Timestamp: {DateTime.Now:O} | Topic: {eventArgs.ApplicationMessage.Topic} | Payload: {Encoding.UTF8.GetString(eventArgs.ApplicationMessage.Payload)} | QoS: {eventArgs.ApplicationMessage.QualityOfServiceLevel}";