Refactor deferred ACK of publish packets.

Build/MQTTnet.nuspec

@@ -16,6 +16,7 @@
 * [Client] Changed exception types so that proper exceptions are thrown when connecting (#1082).
 * [Client] Exposed Dup flag in application messages.
 * [Client] Improved keep alive message sending.
+* [Client] Added support for deferred message approval (#1075, thanks to @tkurucsai). 
 * [RpcClient] Fixed an issue when using a custom application message reveived handler (#1093).
 * [RpcClient] Fixed a race condition when using timeout and cancellation token at the same time (BREAKING CHANGE!).
 * [Server] Improved keep alive message sending.

Source/MQTTnet/Client/MqttClient.cs

@@ -230,21 +230,21 @@ namespace MQTTnet.Client
             switch (applicationMessage.QualityOfServiceLevel)
             {
                 case MqttQualityOfServiceLevel.AtMostOnce:
-                    {
-                        return PublishAtMostOnce(publishPacket, cancellationToken);
-                    }
+                {
+                    return PublishAtMostOnce(publishPacket, cancellationToken);
+                }
                 case MqttQualityOfServiceLevel.AtLeastOnce:
-                    {
-                        return PublishAtLeastOnceAsync(publishPacket, cancellationToken);
-                    }
+                {
+                    return PublishAtLeastOnceAsync(publishPacket, cancellationToken);
+                }
                 case MqttQualityOfServiceLevel.ExactlyOnce:
-                    {
-                        return PublishExactlyOnceAsync(publishPacket, cancellationToken);
-                    }
+                {
+                    return PublishExactlyOnceAsync(publishPacket, cancellationToken);
+                }
                 default:
-                    {
-                        throw new NotSupportedException();
-                    }
+                {
+                    throw new NotSupportedException();
+                }
             }
         }
 
@@ -365,7 +365,8 @@ namespace MQTTnet.Client
                 {
                     // This handler must be executed in a new thread because otherwise a dead lock may happen
                     // when trying to reconnect in that handler etc.
-                    Task.Run(() => disconnectedHandler.HandleDisconnectedAsync(new MqttClientDisconnectedEventArgs(clientWasConnected, exception, authenticateResult, _disconnectReason))).RunInBackground(_logger);
+                    Task.Run(() => disconnectedHandler.HandleDisconnectedAsync(new MqttClientDisconnectedEventArgs(clientWasConnected, exception, authenticateResult, _disconnectReason)))
+                        .RunInBackground(_logger);
                 }
             }
         }
@@ -585,9 +586,9 @@ namespace MQTTnet.Client
                     if (!_packetDispatcher.TryDispatch(packet))
                     {
                         throw new MqttProtocolViolationException($"Received packet '{packet}' at an unexpected time.");
+                    }
                 }
             }
-            }
             catch (Exception exception)
             {
                 if (_cleanDisconnectInitiated)
@@ -641,13 +642,12 @@ namespace MQTTnet.Client
                     }
 
                     var publishPacket = publishPacketDequeueResult.Item;
-                    var eventArgs = await HandleReceivedApplicationMessageAsync(publishPacket, cancellationToken);
+                    var eventArgs = await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false);
 
-                    if (eventArgs.AutoAcknowledge) 
+                    if (eventArgs.AutoAcknowledge)
                     {
-                        await eventArgs.Acknowledge();
+                        await eventArgs.AcknowledgeAsync(cancellationToken).ConfigureAwait(false);
                     }
-                    
                 }
                 catch (OperationCanceledException)
                 {
@@ -659,7 +659,7 @@ namespace MQTTnet.Client
             }
         }
 
-        internal Task AcknowledgeReceivedPublishPacket(MqttApplicationMessageReceivedEventArgs eventArgs)
+        internal Task AcknowledgeReceivedPublishPacket(MqttApplicationMessageReceivedEventArgs eventArgs, CancellationToken cancellationToken)
         {
             if (eventArgs.PublishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
             {
@@ -670,7 +670,7 @@ namespace MQTTnet.Client
                 if (!eventArgs.ProcessingFailed)
                 {
                     var pubAckPacket = _adapter.PacketFormatterAdapter.DataConverter.CreatePubAckPacket(eventArgs.PublishPacket, eventArgs.ReasonCode);
-                    return SendAsync(pubAckPacket, eventArgs.CancellationToken);
+                    return SendAsync(pubAckPacket, cancellationToken);
                 }
             }
             else if (eventArgs.PublishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
@@ -678,7 +678,7 @@ namespace MQTTnet.Client
                 if (!eventArgs.ProcessingFailed)
                 {
                     var pubRecPacket = _adapter.PacketFormatterAdapter.DataConverter.CreatePubRecPacket(eventArgs.PublishPacket, eventArgs.ReasonCode);
-                    return SendAsync(pubRecPacket, eventArgs.CancellationToken);
+                    return SendAsync(pubRecPacket, cancellationToken);
                 }
             }
             else
@@ -710,7 +710,7 @@ namespace MQTTnet.Client
 
         Task ProcessReceivedDisconnectPacket(MqttDisconnectPacket disconnectPacket)
         {
-            _disconnectReason = (MqttClientDisconnectReason)(disconnectPacket.ReasonCode ?? MqttDisconnectReasonCode.NormalDisconnection);
+            _disconnectReason = (MqttClientDisconnectReason) (disconnectPacket.ReasonCode ?? MqttDisconnectReasonCode.NormalDisconnection);
 
             // Also dispatch disconnect to waiting threads to generate a proper exception.
             _packetDispatcher.FailAll(new MqttUnexpectedDisconnectReceivedException(disconnectPacket));
@@ -755,16 +755,16 @@ namespace MQTTnet.Client
             var pubRecPacket = await SendAndReceiveAsync<MqttPubRecPacket>(publishPacket, cancellationToken).ConfigureAwait(false);
 
             var pubRelPacket = _adapter.PacketFormatterAdapter.DataConverter.CreatePubRelPacket(pubRecPacket, MqttApplicationMessageReceivedReasonCode.Success);
-            
+
             var pubCompPacket = await SendAndReceiveAsync<MqttPubCompPacket>(pubRelPacket, cancellationToken).ConfigureAwait(false);
 
             return _adapter.PacketFormatterAdapter.DataConverter.CreateClientPublishResult(pubRecPacket, pubCompPacket);
         }
 
-        async Task<MqttApplicationMessageReceivedEventArgs> HandleReceivedApplicationMessageAsync(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
+        async Task<MqttApplicationMessageReceivedEventArgs> HandleReceivedApplicationMessageAsync(MqttPublishPacket publishPacket)
         {
             var applicationMessage = _adapter.PacketFormatterAdapter.DataConverter.CreateApplicationMessage(publishPacket);
-            var eventArgs = new MqttApplicationMessageReceivedEventArgs(this, publishPacket, cancellationToken, Options.ClientId, applicationMessage);
+            var eventArgs = new MqttApplicationMessageReceivedEventArgs(Options.ClientId, applicationMessage, publishPacket, AcknowledgeReceivedPublishPacket);
 
             var handler = ApplicationMessageReceivedHandler;
             if (handler != null)
@@ -813,4 +813,4 @@ namespace MQTTnet.Client
             return Interlocked.CompareExchange(ref _isDisconnectPending, 1, 0) != 0;
         }
     }
-}
+}

Source/MQTTnet/MqttApplicationMessageReceivedEventArgs.cs

@@ -1,41 +1,30 @@
-using MQTTnet.Client;
-using MQTTnet.Implementations;
-using MQTTnet.Packets;
 using System;
 using System.Threading;
 using System.Threading.Tasks;
+using MQTTnet.Packets;
 
 namespace MQTTnet
 {
     public sealed class MqttApplicationMessageReceivedEventArgs : EventArgs
     {
-        public MqttApplicationMessageReceivedEventArgs(MqttClient client, MqttPublishPacket publishPacket, CancellationToken cancellationToken, string clientId, MqttApplicationMessage applicationMessage)
-        {
-            Client = client ?? throw new ArgumentNullException(nameof(client));
-            PublishPacket = publishPacket ?? throw new ArgumentNullException(nameof(publishPacket));
-            CancellationToken = cancellationToken;
-            acknowledged = 0;
-            ClientId = clientId;
-            ApplicationMessage = applicationMessage ?? throw new ArgumentNullException(nameof(applicationMessage));
-            AutoAcknowledge = true;
-        }
-
-        public MqttApplicationMessageReceivedEventArgs(string clientId, MqttApplicationMessage applicationMessage)
+        readonly Func<MqttApplicationMessageReceivedEventArgs, CancellationToken, Task> _acknowledgeHandler;
+        
+        int _isAcknowledged;
+        
+        public MqttApplicationMessageReceivedEventArgs(
+            string clientId, 
+            MqttApplicationMessage applicationMessage,
+            MqttPublishPacket publishPacket,
+            Func<MqttApplicationMessageReceivedEventArgs, CancellationToken, Task> acknowledgeHandler)
         {
-            acknowledged = 1;
             ClientId = clientId;
             ApplicationMessage = applicationMessage ?? throw new ArgumentNullException(nameof(applicationMessage));
-            AutoAcknowledge = true;
+            PublishPacket = publishPacket;
+            _acknowledgeHandler = acknowledgeHandler;
         }
 
-        internal MqttClient Client { get; }
-
-        internal CancellationToken CancellationToken { get; }
-
         internal MqttPublishPacket PublishPacket { get; }
-
-        int acknowledged;
-
+        
         /// <summary>
         /// Gets the client identifier.
         /// Hint: This identifier needs to be unique over all used clients / devices on the broker to avoid connection issues.
@@ -53,21 +42,27 @@ namespace MQTTnet
         /// This value can be used in user code for custom control flow.
         /// </summary>
         public bool IsHandled { get; set; }
+
+        /// <summary>
+        /// Gets ir sets whether the library should send MQTT ACK packets automatically if required.
+        /// </summary>
+        public bool AutoAcknowledge { get; set; } = true;
         
         public object Tag { get; set; }
-
-        public bool AutoAcknowledge { get; set; }
-
-        public Task Acknowledge() 
-        { 
-            if (Interlocked.CompareExchange(ref acknowledged, 1, 0) == 0)
+        
+        public Task AcknowledgeAsync(CancellationToken cancellationToken) 
+        {
+            if (_acknowledgeHandler == null)
             {
-                return Client.AcknowledgeReceivedPublishPacket(this);
+                throw new NotSupportedException("Deferred acknowledgement of application message is not yet supported in MQTTnet server.");
             }
-            else
+            
+            if (Interlocked.CompareExchange(ref _isAcknowledged, 1, 0) == 0)
             {
-                return PlatformAbstractionLayer.CompletedTask;
+                return _acknowledgeHandler(this, cancellationToken);
             }
+            
+            throw new InvalidOperationException("The application message is already acknowledged.");
         }
     }
 }

Source/MQTTnet/Server/MqttServerEventDispatcher.cs

@@ -108,7 +108,7 @@ namespace MQTTnet.Server
                     return;
                 }
 
-                await handler.HandleApplicationMessageReceivedAsync(new MqttApplicationMessageReceivedEventArgs(senderClientId, applicationMessage)).ConfigureAwait(false);
+                await handler.HandleApplicationMessageReceivedAsync(new MqttApplicationMessageReceivedEventArgs(senderClientId, applicationMessage, null, null)).ConfigureAwait(false);
             }
             catch (Exception exception)
             {

Tests/MQTTnet.Core.Tests/MqttClient_Tests.cs

@@ -466,7 +466,7 @@ namespace MQTTnet.Tests
                 {
                     var value = int.Parse(eventArgs.ApplicationMessage.ConvertPayloadToString());
                     eventArgs.AutoAcknowledge = false;
-                    Task.Delay(value).ContinueWith(x => eventArgs.Acknowledge());
+                    Task.Delay(value).ContinueWith(x => eventArgs.AcknowledgeAsync(CancellationToken.None));
 
                     System.Diagnostics.Debug.WriteLine($"received {value}");
                     lock (receivedValues)