some renaming

Source/MQTTnet.Server/Internal/MqttRetainedMessagesManager.cs

@@ -110,7 +110,7 @@ public async Task UpdateMessage(string clientId, MqttApplicationMessage applicat
                     }
                 }
 
-                applicationMessage.DisposePayload();
+                applicationMessage.Dispose();
             }
             catch (Exception exception)
             {

Source/MQTTnet.TestApp/PublicBrokerTest.cs

@@ -144,8 +144,7 @@ static async Task ExecuteTestAsync(string name, MqttClientOptions options)
                     MqttApplicationMessage receivedMessage = null;
                     client.ApplicationMessageReceivedAsync += e =>
                     {
-                        e.TransferPayload(true);
-                        receivedMessage = e.ApplicationMessage;
+                        receivedMessage = e.TransferApplicationMessageOwnership(true);
                         return CompletedTask.Instance;
                     };
 

Source/MQTTnet.Tests/Clients/MqttClient/MqttClient_Tests.cs

@@ -870,8 +870,7 @@ public async Task Subscribe_In_Callback_Events()
                 {
                     lock (receivedMessages)
                     {
-                        e.TransferPayload(true);
-                        receivedMessages.Add(e.ApplicationMessage);
+                        receivedMessages.Add(e.TransferApplicationMessageOwnership(true));
                     }
 
                     return CompletedTask.Instance;

Source/MQTTnet.Tests/MQTTv5/Client_Tests.cs

@@ -244,8 +244,7 @@ public async Task Publish_And_Receive_New_Properties()
                 MqttApplicationMessage receivedMessage = null;
                 receiver.ApplicationMessageReceivedAsync += e =>
                 {
-                    e.TransferPayload(false);
-                    receivedMessage = e.ApplicationMessage;
+                    receivedMessage = e.TransferApplicationMessageOwnership(true);
                     return CompletedTask.Instance;
                 };
 
@@ -282,7 +281,7 @@ public async Task Publish_And_Receive_New_Properties()
                 }
                 finally
                 {
-                    receivedMessage?.DisposePayload();
+                    receivedMessage?.Dispose();
                 }
             }
         }

Source/MQTTnet.Tests/Mockups/TestApplicationMessageReceivedHandler.cs

@@ -21,7 +21,7 @@ public void Dispose()
         {
             foreach (var eventArgs in _receivedEventArgs)
             {
-                eventArgs.ApplicationMessage?.DisposePayload();
+                eventArgs.ApplicationMessage?.Dispose();
             }
         }
 
@@ -84,8 +84,8 @@ Task OnApplicationMessageReceivedAsync(MqttApplicationMessageReceivedEventArgs e
         {
             lock (_receivedEventArgs)
             {
-                // take ownership of message payload to avoid cloning
-                eventArgs.TransferPayload(false);
+                // take ownership of application message to avoid cloning
+                eventArgs.TransferApplicationMessageOwnership(false);
                 _receivedEventArgs.Add(eventArgs);
             }
 

Source/MQTTnet/Buffers/MqttPayloadOwner.cs

@@ -72,6 +72,18 @@ public void Dispose()
             _owner = null;
         }
 
+        /// <summary>
+        /// Returns a new <see cref="MqttPayloadOwner{T}"/> with the same
+        /// <see cref="ReadOnlySequence{T}"/> and transfers the ownership
+        /// to the caller.
+        /// </summary>
+        public MqttPayloadOwner<T> TransferOwnership()
+        {
+            var payload = new MqttPayloadOwner<T>(_sequence, _owner);
+            _owner = null;
+            return payload;
+        }
+
         public static implicit operator MqttPayloadOwner<T>(ArrayPoolMemoryOwner<T> memoryOwner) => new MqttPayloadOwner<T>(memoryOwner.Memory, memoryOwner);
         public static implicit operator MqttPayloadOwner<T>(ReadOnlySequence<T> sequence) => new MqttPayloadOwner<T>(sequence);
         public static implicit operator MqttPayloadOwner<T>(ReadOnlyMemory<T> memory) => new MqttPayloadOwner<T>(memory);

Source/MQTTnet/Client/MqttClient.cs

@@ -720,9 +720,9 @@ async Task ProcessReceivedPublishPackets(CancellationToken cancellationToken)
             }
             finally
             {
-                if (eventArgs?.TransferredPayload == false)
+                if (eventArgs?.DisposeApplicationMessage == true)
                 {
-                    eventArgs.ApplicationMessage?.DisposePayload();
+                    eventArgs.ApplicationMessage?.Dispose();
                 }
             }
         }

Source/MQTTnet/Client/Receiving/MqttApplicationMessageReceivedEventArgs.cs

@@ -29,26 +29,29 @@ public MqttApplicationMessageReceivedEventArgs(
     }
 
     /// <summary>
-    ///     The invoked message receiver can take ownership of the payload to avoid cloning.
-    ///     If not cloned, it is the obligation of the new owner to dispose the payload by
-    ///     calling <see cref="MqttApplicationMessage.DisposePayload()"/>.
+    ///     The invoked message receiver can take ownership of the application
+    ///     message with payload to avoid cloning.
+    ///     It is then the obligation of the new owner to dispose the obtained
+    ///     application message.
     /// </summary>
     /// <param name="clonePayload">
-    ///     If set to true, clones the applicationMessage and copies the payload.
-    ///     The new instance does not need to be disposed.
+    ///     If set to true, clones the ApplicationMessage and copies the payload.
     /// </param>
-    public void TransferPayload(bool clonePayload)
+    public MqttApplicationMessage TransferApplicationMessageOwnership(bool clonePayload)
     {
-        TransferredPayload = true;
+        DisposeApplicationMessage = false;
         if (clonePayload)
         {
             var applicationMessage = ApplicationMessage;
-            if (applicationMessage != null)
+            // replace application message with a clone
+            // if the payload is owner managed
+            if (applicationMessage?.Payload.Owner != null)
             {
                 ApplicationMessage = applicationMessage.Clone();
-                applicationMessage.DisposePayload();
+                applicationMessage.Dispose();
             }
         }
+        return ApplicationMessage;
     }
 
     public MqttApplicationMessage ApplicationMessage { get; private set; }
@@ -68,10 +71,10 @@ public void TransferPayload(bool clonePayload)
     ///     Gets or sets whether the ownership of the message payload 
     ///     was handed over to the invoked code. This value determines
     ///     if the payload can be disposed after the callback returns.
-    ///     If transferred, the new owner is responsible
+    ///     If transferred, the new owner of the message is responsible
     ///     to dispose the payload after processing.
     /// </summary>
-    public bool TransferredPayload { get; private set; } = false;
+    public bool DisposeApplicationMessage { get; private set; } = true;
 
     /// <summary>
     ///     Gets or sets whether this message was handled.

Source/MQTTnet/MQTTnet.csproj

@@ -44,10 +44,11 @@
         <NuGetAuditMode>all</NuGetAuditMode>
         <NuGetAudit>true</NuGetAudit>
         <AnalysisLevel>latest-Recommended</AnalysisLevel>
+        <LangVersion>latest</LangVersion>
     </PropertyGroup>
 
     <PropertyGroup Condition="'$(Configuration)'=='Debug'">
-        <DebugType>Full</DebugType>
+        <DebugType>portable</DebugType>
     </PropertyGroup>
 
     <PropertyGroup Condition=" '$(Configuration)' == 'Release' ">

Source/MQTTnet/MqttApplicationMessage.cs

@@ -11,11 +11,11 @@
 
 namespace MQTTnet
 {
-    public sealed class MqttApplicationMessage 
+    public sealed class MqttApplicationMessage : IDisposable
     {
         /// <summary>
-        /// Create a clone of the <see cref="MqttApplicationMessage"/>
-        /// with a deep copy of the Payload which is cleaned up by the GC.
+        /// Create a clone of the <see cref="MqttApplicationMessage"/>.
+        /// with a deep copy of the Payload allocated from the heap.
         /// </summary>
         public MqttApplicationMessage Clone()
         {
@@ -40,7 +40,7 @@ public MqttApplicationMessage Clone()
         /// <summary>
         ///    Disposes the payload used by the current instance of the <see cref="MqttApplicationMessage" /> class.
         /// </summary>
-        public void DisposePayload()
+        public void Dispose()
         {
             Payload.Dispose();
         }