Fix wrong exceptions during a clean disconnect.

Frameworks/MQTTnet.NetStandard/Client/MqttClient.cs

@@ -28,6 +28,7 @@ namespace MQTTnet.Client
         private Task _packetReceiverTask;
         private Task _keepAliveMessageSenderTask;
         private IMqttChannelAdapter _adapter;
+        private bool _cleanDisconnectInitiated;
 
         public MqttClient(IMqttClientAdapterFactory channelFactory, IMqttNetLogger logger)
         {
@@ -59,7 +60,7 @@ namespace MQTTnet.Client
 
                 _adapter = _adapterFactory.CreateClientAdapter(options, _logger);
 
-                _logger.Verbose("Trying to connect with server.");
+                _logger.Verbose($"Trying to connect with server ({_options.ChannelOptions}).");
                 await _adapter.ConnectAsync(_options.CommunicationTimeout, _cancellationTokenSource.Token).ConfigureAwait(false);
                 _logger.Verbose("Connection with server established.");
 
@@ -94,6 +95,8 @@ namespace MQTTnet.Client
         {
             try
             {
+                _cleanDisconnectInitiated = true;
+
                 if (IsConnected && !_cancellationTokenSource.IsCancellationRequested)
                 {
                     await SendAsync(new MqttDisconnectPacket(), _cancellationTokenSource.Token).ConfigureAwait(false);
@@ -235,24 +238,7 @@ namespace MQTTnet.Client
 
         private async Task DisconnectInternalAsync(Task sender, Exception exception)
         {
-            await _disconnectLock.WaitAsync().ConfigureAwait(false);
-            try
-            {
-                if (_cancellationTokenSource == null || _cancellationTokenSource.IsCancellationRequested)
-                {
-                    return;
-                }
-
-                _cancellationTokenSource.Cancel(false);
-            }
-            catch (Exception adapterException)
-            {
-                _logger.Warning(adapterException, "Error while disconnecting from adapter.");
-            }
-            finally
-            {
-                _disconnectLock.Release();
-            }
+            await InitiateDisconnectAsync().ConfigureAwait(false);
 
             var clientWasConnected = IsConnected;
             IsConnected = false;
@@ -279,12 +265,35 @@ namespace MQTTnet.Client
                 _adapter = null;
                 _cancellationTokenSource?.Dispose();
                 _cancellationTokenSource = null;
+                _cleanDisconnectInitiated = false;
 
                 _logger.Info("Disconnected.");
                 Disconnected?.Invoke(this, new MqttClientDisconnectedEventArgs(clientWasConnected, exception));
             }
         }
 
+        private async Task InitiateDisconnectAsync()
+        {
+            await _disconnectLock.WaitAsync().ConfigureAwait(false);
+            try
+            {
+                if (_cancellationTokenSource == null || _cancellationTokenSource.IsCancellationRequested)
+                {
+                    return;
+                }
+
+                _cancellationTokenSource.Cancel(false);
+            }
+            catch (Exception adapterException)
+            {
+                _logger.Warning(adapterException, "Error while initiating disconnect.");
+            }
+            finally
+            {
+                _disconnectLock.Release();
+            }
+        }
+
         private Task SendAsync(MqttBasePacket packet, CancellationToken cancellationToken)
         {
             return SendAsync(new[] { packet }, cancellationToken);
@@ -361,6 +370,11 @@ namespace MQTTnet.Client
             }
             catch (Exception exception)
             {
+                if (_cleanDisconnectInitiated)
+                {
+                    return;
+                }
+
                 if (exception is OperationCanceledException)
                 {
                 }
@@ -390,11 +404,19 @@ namespace MQTTnet.Client
                 while (!cancellationToken.IsCancellationRequested)
                 {
                     var packet = await _adapter.ReceivePacketAsync(TimeSpan.Zero, cancellationToken).ConfigureAwait(false);
-                    await ProcessReceivedPacketAsync(packet, cancellationToken).ConfigureAwait(false);
+                    if (packet != null)
+                    {
+                        await ProcessReceivedPacketAsync(packet, cancellationToken).ConfigureAwait(false);
+                    }
                 }
             }
             catch (Exception exception)
             {
+                if (_cleanDisconnectInitiated)
+                {
+                    return;
+                }
+
                 if (exception is OperationCanceledException)
                 {
                 }
@@ -407,8 +429,8 @@ namespace MQTTnet.Client
                     _logger.Error(exception, "Unhandled exception while receiving packets.");
                 }
 
-                await DisconnectInternalAsync(_packetReceiverTask, exception).ConfigureAwait(false);
                 _packetDispatcher.Dispatch(exception);
+                await DisconnectInternalAsync(_packetReceiverTask, exception).ConfigureAwait(false);
             }
             finally
             {
@@ -458,7 +480,7 @@ namespace MQTTnet.Client
 
             if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
             {
-                // QoS 2 is implement as method "B" [4.3.3 QoS 2: Exactly once delivery]
+                // QoS 2 is implement as method "B" (4.3.3 QoS 2: Exactly once delivery)
                 FireApplicationMessageReceivedEvent(publishPacket);
                 return SendAsync(new MqttPubRecPacket { PacketIdentifier = publishPacket.PacketIdentifier }, cancellationToken);
             }