Use dedicated type for MattApplicationMessage injection result

Author: Anton Smolkov

Source/MQTTnet.Server/Status/MqttSessionStatus.cs

@@ -46,9 +46,10 @@ public Task DeleteAsync()
     /// </summary>
     /// <param name="applicationMessage">The application message to deliver.</param>
     /// <returns>
-    /// A task that represents the asynchronous operation. The result contains the delivered MQTT publish packet.
+    /// A task that represents the asynchronous operation.
+    /// The result contains the <see cref="InjectMqttApplicationMessageResult"/> that includes the packet identifier of the enqueued message.
     /// </returns>
-    public async Task<MqttPacketWithIdentifier> DeliverApplicationMessageAsync(MqttApplicationMessage applicationMessage)
+    public async Task<InjectMqttApplicationMessageResult> DeliverApplicationMessageAsync(MqttApplicationMessage applicationMessage)
     {
         ArgumentNullException.ThrowIfNull(applicationMessage);
 
@@ -57,35 +58,41 @@ public async Task<MqttPacketWithIdentifier> DeliverApplicationMessageAsync(MqttA
 
         var mqttPacket = await packetBusItem.WaitAsync();
 
-        return (MqttPacketWithIdentifier)mqttPacket;
+        var result = new InjectMqttApplicationMessageResult()
+        {
+            PacketIdentifier = ((MqttPacketWithIdentifier)mqttPacket).PacketIdentifier
+        };
+
+        return result;
     }
 
     /// <summary>
     /// Attempts to enqueue an application message to the session's send buffer.
     /// </summary>
     /// <param name="applicationMessage">The application message to enqueue.</param>
-    /// <param name="publishPacket">The corresponding MQTT publish packed, if the operation was successful.</param>
+    /// <param name="injectResult"><see cref="InjectMqttApplicationMessageResult"/> that includes the packet identifier of the enqueued message.</param>
     /// <returns><c>true</c> if the message was successfully enqueued; otherwise, <c>false</c>.</returns>
     /// <remarks>
     /// When <see cref="MqttServerOptions.PendingMessagesOverflowStrategy"/> is set to <see cref="MqttPendingMessagesOverflowStrategy.DropOldestQueuedMessage"/>,
     /// this method always returns <c>true</c>.
     /// However, an existing message in the queue may be <b>dropped later</b> to make room for the newly enqueued message.
     /// Such dropped messages can be tracked by subscribing to <see cref="MqttServer.QueuedApplicationMessageOverwrittenAsync"/> event.
     /// </remarks>
-    public bool TryEnqueueApplicationMessage(MqttApplicationMessage applicationMessage, out MqttPacketWithIdentifier publishPacket)
+    public bool TryEnqueueApplicationMessage(MqttApplicationMessage applicationMessage, out InjectMqttApplicationMessageResult injectResult)
     {
         ArgumentNullException.ThrowIfNull(applicationMessage);
 
-        publishPacket = MqttPublishPacketFactory.Create(applicationMessage);
+        var publishPacket = MqttPublishPacketFactory.Create(applicationMessage);
         var enqueueDataPacketResult = _session.EnqueueDataPacket(new MqttPacketBusItem(publishPacket));
 
-        if (enqueueDataPacketResult == EnqueueDataPacketResult.Enqueued)
+        if (enqueueDataPacketResult != EnqueueDataPacketResult.Enqueued)
         {
-            return true;
+            injectResult = null;
+            return false;
         }
 
-        publishPacket = null;
-        return false;
+        injectResult = new InjectMqttApplicationMessageResult() { PacketIdentifier = publishPacket.PacketIdentifier };
+        return true;
     }
 
     [Obsolete("This method is obsolete. Use TryEnqueueApplicationMessage instead.")]

Source/MQTTnet.Tests/Server/Injection_Tests.cs

@@ -33,14 +33,14 @@ public async Task Enqueue_Application_Message_At_Session_Level()
                 .WithQualityOfServiceLevel(MqttQualityOfServiceLevel.AtLeastOnce)
                 .WithTopic("InjectedOne").Build();
 
-            var enqueued = clientStatus.TryEnqueueApplicationMessage(message, out var publishPacket);
+            var enqueued = clientStatus.TryEnqueueApplicationMessage(message, out var injectResult);
 
             Assert.IsTrue(enqueued);
 
             await LongTestDelay();
 
             Assert.AreEqual(1, messageReceivedHandler1.ReceivedEventArgs.Count);
-            Assert.AreEqual(publishPacket.PacketIdentifier, messageReceivedHandler1.ReceivedEventArgs[0].PacketIdentifier);
+            Assert.AreEqual(injectResult.PacketIdentifier, messageReceivedHandler1.ReceivedEventArgs[0].PacketIdentifier);
             Assert.AreEqual("InjectedOne", messageReceivedHandler1.ReceivedEventArgs[0].ApplicationMessage.Topic);
 
             // The second receiver should NOT receive the message.
@@ -223,12 +223,12 @@ public async Task Deliver_Application_Message_At_Session_Level()
                 .WithTopic("InjectedOne")
                 .WithQualityOfServiceLevel(MqttQualityOfServiceLevel.AtLeastOnce)
                 .Build();
-            var publishPacket = await clientStatus.DeliverApplicationMessageAsync(mqttApplicationMessage);
+            var injectResult = await clientStatus.DeliverApplicationMessageAsync(mqttApplicationMessage);
 
             await LongTestDelay();
 
             Assert.AreEqual(1, messageReceivedHandler1.ReceivedEventArgs.Count);
-            Assert.AreEqual(publishPacket.PacketIdentifier, messageReceivedHandler1.ReceivedEventArgs[0].PacketIdentifier);
+            Assert.AreEqual(injectResult.PacketIdentifier, messageReceivedHandler1.ReceivedEventArgs[0].PacketIdentifier);
             Assert.AreEqual("InjectedOne", messageReceivedHandler1.ReceivedEventArgs[0].ApplicationMessage.Topic);
 
             // The second receiver should NOT receive the message.

Source/MQTTnet/InjectMqttApplicationMessageResult.cs

@@ -0,0 +1,10 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace MQTTnet;
+
+public class InjectMqttApplicationMessageResult
+{
+    public ushort PacketIdentifier { get; init; }
+}