Fix issues in QoS 2 handling.

Build/MQTTnet.nuspec

@@ -17,6 +17,7 @@
 * [Core] Added support for _MaximumQoS_ transmit when using MQTTv5 (thanks to @nayato).
 * [Core] Aligned the format of some log messages.
 * [Client] Fixed an issue with connection state detection (thanks to @tobiasfrick).
+* [Client] Fixed an issue when receiving partial QoS 2 packets after a reconnect.
 * [ManagedClient] Removed _AutoReconnect_ since this does no longer work (BREAKING CHANGE!).
 * [RpcClient] Moved the RPC topic validation to the topic generation strategy.
 * [RcpClient] Added interface for _MqttRpcClient_.
@@ -68,6 +69,9 @@ Git commit: $gitCommit
     <!-- Images -->
     <file src="..\Images\Logo_128x128.png" target="images\" />
 
+    <!-- .NET 5.0 -->
+    <file src="..\Source\MQTTnet\bin\Release\net5.0\MQTTnet.*" target="lib\net5.0"/>
+
     <!-- .NET Standard 1.3 -->
     <file src="..\Source\MQTTnet\bin\Release\netstandard1.3\MQTTnet.*" target="lib\netstandard1.3\"/>
     

Source/MQTTnet/Client/MqttClient.cs

@@ -17,6 +17,7 @@ using System;
 using System.Diagnostics;
 using System.Threading;
 using System.Threading.Tasks;
+using MQTTnet.Implementations;
 
 namespace MQTTnet.Client
 {
@@ -551,37 +552,25 @@ namespace MQTTnet.Client
                 {
                     EnqueueReceivedPublishPacket(publishPacket);
                 }
+                else if (packet is MqttPubRecPacket pubRecPacket)
+                {
+                    await ProcessReceivedPubRecPacket(pubRecPacket, cancellationToken).ConfigureAwait(false);
+                }
                 else if (packet is MqttPubRelPacket pubRelPacket)
                 {
-                    await SendAsync(new MqttPubCompPacket
+                    await ProcessReceivedPubRelPacket(pubRelPacket, cancellationToken).ConfigureAwait(false);
-                    {
-                        PacketIdentifier = pubRelPacket.PacketIdentifier,
-                        ReasonCode = MqttPubCompReasonCode.Success
-                    }, cancellationToken).ConfigureAwait(false);
                 }
                 else if (packet is MqttPingReqPacket)
                 {
-                    await SendAsync(new MqttPingRespPacket(), cancellationToken).ConfigureAwait(false);
+                    await SendAsync(MqttPingRespPacket.Instance, cancellationToken).ConfigureAwait(false);
                 }
                 else if (packet is MqttDisconnectPacket disconnectPacket)
                 {
-                    _disconnectReason = (MqttClientDisconnectReason)(disconnectPacket.ReasonCode ?? MqttDisconnectReasonCode.NormalDisconnection);
+                    await ProcessReceivedDisconnectPacket(disconnectPacket).ConfigureAwait(false);
-
-                    // Also dispatch disconnect to waiting threads to generate a proper exception.
-                    _packetDispatcher.Dispatch(packet);
-
-                    if (!DisconnectIsPending())
-                    {
-                        await DisconnectInternalAsync(_packetReceiverTask, null, null).ConfigureAwait(false);
-                    }
                 }
                 else if (packet is MqttAuthPacket authPacket)
                 {
-                    var extendedAuthenticationExchangeHandler = Options.ExtendedAuthenticationExchangeHandler;
+                    await ProcessReceivedAuthPacket(authPacket).ConfigureAwait(false);
-                    if (extendedAuthenticationExchangeHandler != null)
-                    {
-                        await extendedAuthenticationExchangeHandler.HandleRequestAsync(new MqttExtendedAuthenticationExchangeContext(authPacket, this)).ConfigureAwait(false);
-                    }
                 }
                 else
                 {
@@ -685,6 +674,57 @@ namespace MQTTnet.Client
             }
         }
 
+        Task ProcessReceivedPubRecPacket(MqttPubRecPacket pubRecPacket, CancellationToken cancellationToken)
+        {
+            if (!_packetDispatcher.TryDispatch(pubRecPacket))
+            {
+                // The packet is unknown. Probably due to a restart of the client. 
+                // So wen send this to the server to trigger a full resend of the message.
+                return SendAsync(new MqttPubRelPacket
+                {
+                    PacketIdentifier = pubRecPacket.PacketIdentifier,
+                    ReasonCode = MqttPubRelReasonCode.PacketIdentifierNotFound
+                }, cancellationToken);
+            }
+
+            return PlatformAbstractionLayer.CompletedTask;
+        }
+
+        Task ProcessReceivedPubRelPacket(MqttPubRelPacket pubRelPacket, CancellationToken cancellationToken)
+        {
+            return SendAsync(new MqttPubCompPacket
+            {
+                PacketIdentifier = pubRelPacket.PacketIdentifier,
+                ReasonCode = MqttPubCompReasonCode.Success
+            }, cancellationToken);
+        }
+
+        Task ProcessReceivedDisconnectPacket(MqttDisconnectPacket disconnectPacket)
+        {
+            _disconnectReason = (MqttClientDisconnectReason)(disconnectPacket.ReasonCode ?? MqttDisconnectReasonCode.NormalDisconnection);
+
+            // Also dispatch disconnect to waiting threads to generate a proper exception.
+            _packetDispatcher.Dispatch(disconnectPacket);
+
+            if (!DisconnectIsPending())
+            {
+                return DisconnectInternalAsync(_packetReceiverTask, null, null);
+            }
+
+            return PlatformAbstractionLayer.CompletedTask;
+        }
+
+        Task ProcessReceivedAuthPacket(MqttAuthPacket authPacket)
+        {
+            var extendedAuthenticationExchangeHandler = Options.ExtendedAuthenticationExchangeHandler;
+            if (extendedAuthenticationExchangeHandler != null)
+            {
+                return extendedAuthenticationExchangeHandler.HandleRequestAsync(new MqttExtendedAuthenticationExchangeContext(authPacket, this));
+            }
+
+            return PlatformAbstractionLayer.CompletedTask;
+        }
+
         async Task<MqttClientPublishResult> PublishAtMostOnce(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
         {
             // No packet identifier is used for QoS 0 [3.3.2.2 Packet Identifier]

Source/MQTTnet/PacketDispatcher/MqttPacketDispatcher.cs

@@ -19,7 +19,7 @@ namespace MQTTnet.PacketDispatcher
             _awaiters.Clear();
         }
 
-        public void Dispatch(MqttBasePacket packet)
+        public bool TryDispatch(MqttBasePacket packet)
         {
             if (packet == null) throw new ArgumentNullException(nameof(packet));
 
@@ -30,7 +30,7 @@ namespace MQTTnet.PacketDispatcher
                     packetAwaiter.Value.Fail(new MqttUnexpectedDisconnectReceivedException(disconnectPacket));
                 }
 
-                return;
+                return true;
             }
 
             ushort identifier = 0;
@@ -45,10 +45,20 @@ namespace MQTTnet.PacketDispatcher
             if (_awaiters.TryRemove(key, out var awaiter))
             {
                 awaiter.Complete(packet);
-                return;
+                return true;
             }
 
-            throw new MqttProtocolViolationException($"Received packet '{packet}' at an unexpected time.");
+            return false;
+        }
+
+        public void Dispatch(MqttBasePacket packet)
+        {
+            if (packet == null) throw new ArgumentNullException(nameof(packet));
+
+            if (!TryDispatch(packet))
+            {
+                throw new MqttProtocolViolationException($"Received packet '{packet}' at an unexpected time.");
+            }
         }
 
         public void Cancel()