Process messages async

This commit fixes issues which were caused by processing messages synchronously in the packet receiver loop. This blocked KeepAlive and Ack packets from being processed while a message was processed.

Fixes #648
Fixes #587
Fixes #829

Build/MQTTnet.nuspec

@@ -17,6 +17,8 @@
 * [LowLevelMqttClient] Added low level MQTT client in order to provide more flexibility when using the MQTT protocol. This client requires detailed knowledge about the MQTT protocol.
 * [Client] Improve connection stability (thanks to @jltjohanlindqvist).
 * [Client] Support WithConnectionUri to configure client (thanks to @PMExtra).
+* [Client] Support PublishAsync with QoS 1 and QoS 2 from within an ApplicationMessageReceivedHandler (#648, #587, thanks to @PSanetra).
+* [Client] Fixed MqttCommunicationTimedOutExceptions, caused by a long running ApplicationMessageReceivedHandler, which blocked MQTT packets from being processed (#829, thanks to @PSanetra).
 * [ManagedClient] Added builder class for MqttClientUnsubscribeOptions (thanks to @dominikviererbe).
 * [ManagedClient] Added support for persisted sessions (thansk to @PMExtra).
 * [ManagedClient] Fixed a memory leak (thanks to @zawodskoj).

Source/MQTTnet/Client/MqttClient.cs

@@ -34,6 +34,9 @@ namespace MQTTnet.Client
         private CancellationTokenSource _backgroundCancellationTokenSource;
         private Task _packetReceiverTask;
         private Task _keepAlivePacketsSenderTask;
+        private Task _publishPacketReceiverTask;
+
+        private AsyncQueue<MqttPublishPacket> _publishPacketReceiverQueue;
 
         private IMqttChannelAdapter _adapter;
         private bool _cleanDisconnectInitiated;
@@ -88,6 +91,9 @@ namespace MQTTnet.Client
                     await _adapter.ConnectAsync(options.CommunicationTimeout, combined.Token).ConfigureAwait(false);
                     _logger.Verbose("Connection with server established.");
 
+                    _publishPacketReceiverQueue = new AsyncQueue<MqttPublishPacket>();
+                    _publishPacketReceiverTask = Task.Run(() => ProcessReceivedPublishPackets(backgroundCancellationToken), backgroundCancellationToken);
+
                     _packetReceiverTask = Task.Run(() => TryReceivePacketsAsync(backgroundCancellationToken), backgroundCancellationToken);
 
                     authenticateResult = await AuthenticateAsync(adapter, options.WillMessage, combined.Token).ConfigureAwait(false);
@@ -230,6 +236,9 @@ namespace MQTTnet.Client
             _backgroundCancellationTokenSource?.Dispose();
             _backgroundCancellationTokenSource = null;
 
+            _publishPacketReceiverQueue?.Dispose();
+            _publishPacketReceiverQueue = null;
+
             _adapter?.Dispose();
             _adapter = null;
         }
@@ -300,9 +309,12 @@ namespace MQTTnet.Client
             try
             {
                 var receiverTask = WaitForTaskAsync(_packetReceiverTask, sender);
+                var publishPacketReceiverTask = WaitForTaskAsync(_publishPacketReceiverTask, sender);
                 var keepAliveTask = WaitForTaskAsync(_keepAlivePacketsSenderTask, sender);
 
-                await Task.WhenAll(receiverTask, keepAliveTask).ConfigureAwait(false);
+                await Task.WhenAll(receiverTask, publishPacketReceiverTask, keepAliveTask).ConfigureAwait(false);
+
+                _publishPacketReceiverQueue.Dispose();
             }
             catch (Exception e)
             {
@@ -522,7 +534,7 @@ namespace MQTTnet.Client
 
                 if (packet is MqttPublishPacket publishPacket)
                 {
-                    await TryProcessReceivedPublishPacketAsync(publishPacket, cancellationToken).ConfigureAwait(false);
+                    EnqueueReceivedPublishPacket(publishPacket);
                 }
                 else if (packet is MqttPubRelPacket pubRelPacket)
                 {
@@ -584,47 +596,71 @@ namespace MQTTnet.Client
             }
         }
 
-        private async Task TryProcessReceivedPublishPacketAsync(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
+        private void EnqueueReceivedPublishPacket(MqttPublishPacket publishPacket)
         {
             try
             {
-                if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
-                {
-                    await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false);
-                }
-                else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtLeastOnce)
+                _publishPacketReceiverQueue.Enqueue(publishPacket);
+            }
+            catch (Exception exception)
+            {
+                _logger.Error(exception, "Error while enqueueing application message.");
+            }
+        }
+
+        private async Task ProcessReceivedPublishPackets(CancellationToken cancellationToken)
+        {
+            while (!cancellationToken.IsCancellationRequested)
+            {
+                try
                 {
-                    if (await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false))
+                    var publishPacketDequeueResult = await _publishPacketReceiverQueue.TryDequeueAsync(cancellationToken);
+
+                    if (!publishPacketDequeueResult.IsSuccess)
+                    {
+                        return;
+                    }
+
+                    var publishPacket = publishPacketDequeueResult.Item;
+
+                    if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
                     {
-                        await SendAsync(new MqttPubAckPacket
+                        await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false);
+                    }
+                    else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtLeastOnce)
+                    {
+                        if (await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false))
                         {
-                            PacketIdentifier = publishPacket.PacketIdentifier,
-                            ReasonCode = MqttPubAckReasonCode.Success
-                        }, cancellationToken).ConfigureAwait(false);
+                            await SendAsync(new MqttPubAckPacket
+                            {
+                                PacketIdentifier = publishPacket.PacketIdentifier,
+                                ReasonCode = MqttPubAckReasonCode.Success
+                            }, cancellationToken).ConfigureAwait(false);
+                        }
                     }
-                }
-                else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
-                {
-                    if (await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false))
+                    else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
                     {
-                        var pubRecPacket = new MqttPubRecPacket
+                        if (await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false))
                         {
-                            PacketIdentifier = publishPacket.PacketIdentifier,
-                            ReasonCode = MqttPubRecReasonCode.Success
-                        };
+                            var pubRecPacket = new MqttPubRecPacket
+                            {
+                                PacketIdentifier = publishPacket.PacketIdentifier,
+                                ReasonCode = MqttPubRecReasonCode.Success
+                            };
 
-                        await SendAsync(pubRecPacket, cancellationToken).ConfigureAwait(false);
+                            await SendAsync(pubRecPacket, cancellationToken).ConfigureAwait(false);
+                        }
+                    }
+                    else
+                    {
+                        throw new MqttProtocolViolationException("Received a not supported QoS level.");
                     }
                 }
-                else
+                catch (Exception exception)
                 {
-                    throw new MqttProtocolViolationException("Received a not supported QoS level.");
+                    _logger.Error(exception, "Error while handling application message.");
                 }
             }
-            catch (Exception exception)
-            {
-                _logger.Error(exception, "Error while handling application message.");
-            }
         }
 
         private async Task<MqttClientPublishResult> PublishAtMostOnce(MqttPublishPacket publishPacket, CancellationToken cancellationToken)

Source/MQTTnet/Internal/AsyncBlockingQueue.cs → Source/MQTTnet/Internal/AsyncQueue.cs

@@ -23,9 +23,15 @@ namespace MQTTnet.Internal
         {
             while (!cancellationToken.IsCancellationRequested)
             {
-                await _semaphore.WaitAsync(cancellationToken).ConfigureAwait(false);
-
-                cancellationToken.ThrowIfCancellationRequested();
+                try
+                {
+                    await _semaphore.WaitAsync(cancellationToken).ConfigureAwait(false);
+                    cancellationToken.ThrowIfCancellationRequested();
+                }
+                catch (OperationCanceledException)
+                {
+                    return new AsyncQueueDequeueResult<TItem>(false, default(TItem));
+                }
 
                 if (_queue.TryDequeue(out var item))
                 {

Tests/MQTTnet.Core.Tests/MqttClient_Tests.cs

@@ -12,6 +12,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Net.Sockets;
+using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -434,6 +435,49 @@ namespace MQTTnet.Tests
             }
         }
 
+        [TestMethod]
+        public async Task Publish_QoS_1_In_ApplicationMessageReceiveHandler()
+        {
+            using (var testEnvironment = new TestEnvironment(TestContext))
+            {
+                await testEnvironment.StartServerAsync();
+
+                const string client1Topic = "client1/topic";
+                const string client2Topic = "client2/topic";
+                const string expectedClient2Message = "hello client2";
+
+                var client1 = await testEnvironment.ConnectClientAsync();
+                client1.UseApplicationMessageReceivedHandler(async c =>
+                {
+                    await client1.PublishAsync(client2Topic, expectedClient2Message, MqttQualityOfServiceLevel.AtLeastOnce);
+                });
+
+                await client1.SubscribeAsync(client1Topic, MqttQualityOfServiceLevel.AtLeastOnce);
+
+                var client2 = await testEnvironment.ConnectClientAsync();
+
+                var client2TopicResults = new List<string>();
+
+                client2.UseApplicationMessageReceivedHandler(c =>
+                {
+                    client2TopicResults.Add(Encoding.UTF8.GetString(c.ApplicationMessage.Payload));
+                });
+
+                await client2.SubscribeAsync(client2Topic);
+
+                var client3 = await testEnvironment.ConnectClientAsync();
+                var message = new MqttApplicationMessageBuilder().WithTopic(client1Topic).Build();
+                await client3.PublishAsync(message);
+                await client3.PublishAsync(message);
+
+                await Task.Delay(500);
+
+                Assert.AreEqual(2, client2TopicResults.Count);
+                Assert.AreEqual(expectedClient2Message, client2TopicResults[0]);
+                Assert.AreEqual(expectedClient2Message, client2TopicResults[1]);
+            }
+        }
+
         [TestMethod]
         public async Task Subscribe_In_Callback_Events()
         {
@@ -565,7 +609,7 @@ namespace MQTTnet.Tests
 
                 for (var i = 0; i < 98; i++)
                 {
-                    Assert.IsFalse(clients[i].IsConnected);
+                    Assert.IsFalse(clients[i].IsConnected, $"clients[{i}] is not connected");
                 }
 
                 Assert.IsTrue(clients[99].IsConnected);