[Discussion] Cache instances of MqttClientPublishResult

Source/MQTTnet/Client/Publishing/MqttClientPublishResult.cs

@@ -1,11 +1,15 @@
-
+
+using System;
 using System.Collections.Generic;
 using MQTTnet.Packets;
 
 namespace MQTTnet.Client.Publishing
 {
-    public class MqttClientPublishResult
+    public sealed class MqttClientPublishResult : IDisposable
     {
+        [ThreadStatic]
+        private static MqttClientPublishResult t_cache;
+
         public ushort? PacketIdentifier { get; set; }
 
         /// <summary>
@@ -28,5 +32,20 @@ public class MqttClientPublishResult
         /// Hint: MQTT 5 feature only.
         /// </summary>
         public List<MqttUserProperty> UserProperties { get; set; }
+
+        void IDisposable.Dispose()
+        {
+            PacketIdentifier = null;
+            ReasonCode = default;
+            ReasonString = null;
+            UserProperties = null;
+
+            t_cache = this;
+        }
+
+        internal static MqttClientPublishResult GetInstance()
+        {
+            return t_cache ?? new MqttClientPublishResult();
+        }
     }
 }

Source/MQTTnet/Formatter/V3/MqttV310DataConverter.cs

@@ -1,4 +1,4 @@
-using MQTTnet.Client.Connecting;
+using MQTTnet.Client.Connecting;
 using MQTTnet.Client.Disconnecting;
 using MQTTnet.Client.Options;
 using MQTTnet.Client.Publishing;
@@ -251,28 +251,28 @@ public MqttDisconnectPacket CreateDisconnectPacket(MqttClientDisconnectOptions o
 
         public MqttClientPublishResult CreateClientPublishResult(MqttPubAckPacket pubAckPacket)
         {
-            return new MqttClientPublishResult
-            {
-                PacketIdentifier = pubAckPacket?.PacketIdentifier,
-                ReasonCode = MqttClientPublishReasonCode.Success
-            };
+            var mqttClientPublishResult = MqttClientPublishResult.GetInstance();
+            mqttClientPublishResult.PacketIdentifier = pubAckPacket?.PacketIdentifier;
+            mqttClientPublishResult.ReasonCode = MqttClientPublishReasonCode.Success;
+
+            return mqttClientPublishResult;
         }
 
         public MqttClientPublishResult CreateClientPublishResult(MqttPubRecPacket pubRecPacket, MqttPubCompPacket pubCompPacket)
         {
+            var mqttClientPublishResult = MqttClientPublishResult.GetInstance();
+
             if (pubRecPacket == null || pubCompPacket == null)
             {
-                return new MqttClientPublishResult
-                {
-                    ReasonCode = MqttClientPublishReasonCode.UnspecifiedError
-                };
+                mqttClientPublishResult.ReasonCode = MqttClientPublishReasonCode.UnspecifiedError;
             }
-
-            return new MqttClientPublishResult
+            else
             {
-                PacketIdentifier = pubCompPacket.PacketIdentifier,
-                ReasonCode = MqttClientPublishReasonCode.Success
-            };
+                mqttClientPublishResult.PacketIdentifier = pubCompPacket.PacketIdentifier;
+                mqttClientPublishResult.ReasonCode = MqttClientPublishReasonCode.Success;
+            }
+
+            return mqttClientPublishResult;
         }
     }
 }

Source/MQTTnet/Formatter/V5/MqttV500DataConverter.cs

@@ -1,4 +1,4 @@
-using MQTTnet.Client.Connecting;
+using MQTTnet.Client.Connecting;
 using MQTTnet.Client.Disconnecting;
 using MQTTnet.Client.Options;
 using MQTTnet.Client.Publishing;
@@ -308,12 +308,10 @@ public MqttDisconnectPacket CreateDisconnectPacket(MqttClientDisconnectOptions o
 
         public MqttClientPublishResult CreateClientPublishResult(MqttPubAckPacket pubAckPacket)
         {
-            var result = new MqttClientPublishResult
-            {
-                ReasonCode = MqttClientPublishReasonCode.Success,
-                ReasonString = pubAckPacket?.Properties?.ReasonString,
-                UserProperties = pubAckPacket?.Properties?.UserProperties
-            };
+            var result = MqttClientPublishResult.GetInstance();
+            result.ReasonCode = MqttClientPublishReasonCode.Success;
+            result.ReasonString = pubAckPacket?.Properties?.ReasonString;
+            result.UserProperties = pubAckPacket?.Properties?.UserProperties;
 
             if (pubAckPacket != null)
             {
@@ -329,33 +327,29 @@ public MqttClientPublishResult CreateClientPublishResult(MqttPubAckPacket pubAck
 
         public MqttClientPublishResult CreateClientPublishResult(MqttPubRecPacket pubRecPacket, MqttPubCompPacket pubCompPacket)
         {
+            var result = MqttClientPublishResult.GetInstance();
+
             if (pubRecPacket == null || pubCompPacket == null)
             {
-                return new MqttClientPublishResult
-                {
-                    ReasonCode = MqttClientPublishReasonCode.UnspecifiedError
-                };
+                result.ReasonCode = MqttClientPublishReasonCode.UnspecifiedError;
+                return result;
             }
 
             // The PUBCOMP is the last packet in QoS 2. So we use the results from that instead of PUBREC.
             if (pubCompPacket.ReasonCode == MqttPubCompReasonCode.PacketIdentifierNotFound)
             {
-                return new MqttClientPublishResult
-                {
-                    PacketIdentifier = pubCompPacket.PacketIdentifier,
-                    ReasonCode = MqttClientPublishReasonCode.UnspecifiedError,
-                    ReasonString = pubCompPacket.Properties?.ReasonString,
-                    UserProperties = pubCompPacket.Properties?.UserProperties
-                };
+                result.PacketIdentifier = pubCompPacket.PacketIdentifier;
+                result.ReasonCode = MqttClientPublishReasonCode.UnspecifiedError;
+                result.ReasonString = pubCompPacket.Properties?.ReasonString;
+                result.UserProperties = pubCompPacket.Properties?.UserProperties;
+
+                return result;
             }
 
-            var result = new MqttClientPublishResult
-            {
-                PacketIdentifier = pubCompPacket.PacketIdentifier,
-                ReasonCode = MqttClientPublishReasonCode.Success,
-                ReasonString = pubCompPacket.Properties?.ReasonString,
-                UserProperties = pubCompPacket.Properties?.UserProperties
-            };
+            result.PacketIdentifier = pubCompPacket.PacketIdentifier;
+            result.ReasonCode = MqttClientPublishReasonCode.Success;
+            result.ReasonString = pubCompPacket.Properties?.ReasonString;
+            result.UserProperties = pubCompPacket.Properties?.UserProperties;
 
             if (pubRecPacket.ReasonCode.HasValue)
             {

Source/MQTTnet/Server/MqttServer.cs

@@ -1,4 +1,4 @@
-using MQTTnet.Adapter;
+using MQTTnet.Adapter;
 using MQTTnet.Client.Publishing;
 using MQTTnet.Client.Receiving;
 using MQTTnet.Diagnostics;
@@ -19,6 +19,8 @@ namespace MQTTnet.Server
 {
     public class MqttServer : Disposable, IMqttServer
     {
+        static readonly Task<MqttClientPublishResult> s_completedClientPublishResult = Task.FromResult(new MqttClientPublishResult());
+
         readonly MqttServerEventDispatcher _eventDispatcher;
         readonly ICollection<IMqttServerAdapter> _adapters;
         readonly IMqttNetLogger _rootLogger;
@@ -150,7 +152,7 @@ public Task<MqttClientPublishResult> PublishAsync(MqttApplicationMessage applica
 
             _clientSessionsManager.DispatchApplicationMessage(applicationMessage, null);
 
-            return Task.FromResult(new MqttClientPublishResult());
+            return s_completedClientPublishResult;
         }
 
         public async Task StartAsync(IMqttServerOptions options)