Expose configuration of packet fragmentation in server options. (#1769)

.github/workflows/ReleaseNotes.md

 * [Client] Fixed _PlatformNotSupportedException_ when using Blazor (#1755, thanks to @Nickztar).
 * [Server] Fixed _NullReferenceException_ in retained messages management (#1762, thanks to @logicaloud).
+* [Server] Exposed new option which allows disabling packet fragmentation (#1753).

Source/MQTTnet/Implementations/MqttTcpServerListener.cs

@@ -231,6 +231,7 @@ namespace MQTTnet.Implementations
                     
                     using (var clientAdapter = new MqttChannelAdapter(tcpChannel, packetFormatterAdapter, _rootLogger))
                     {
+                        clientAdapter.AllowPacketFragmentation = _options.AllowPacketFragmentation;
                         await clientHandler(clientAdapter).ConfigureAwait(false);
                     }
                 }
@@ -255,6 +256,7 @@ namespace MQTTnet.Implementations
             {
                 try
                 {
+                    // ReSharper disable once MethodHasAsyncOverload
                     stream?.Dispose();
                     clientSocket?.Dispose();
                 }

Source/MQTTnet/Server/Options/MqttServerOptionsBuilder.cs

@@ -131,6 +131,18 @@ namespace MQTTnet.Server
             return this;
         }
 
+        /// <summary>
+        ///     Usually the MQTT packets can be send partially to improve memory allocations.
+        ///     This is done by using multiple TCP packets or WebSocket frames etc.
+        ///     Unfortunately not all clients do support this and will close the connection when receiving partial packets.
+        /// </summary>
+        public MqttServerOptionsBuilder WithoutPacketFragmentation()
+        {
+            _options.DefaultEndpointOptions.AllowPacketFragmentation = false;
+            _options.TlsEndpointOptions.AllowPacketFragmentation = false;
+            return this;
+        }
+
         public MqttServerOptionsBuilder WithPersistentSessions(bool value = true)
         {
             _options.EnablePersistentSessions = value;

Source/MQTTnet/Server/Options/MqttServerTcpEndpointBaseOptions.cs

@@ -23,6 +23,14 @@ namespace MQTTnet.Server
         /// </summary>
         public bool? KeepAlive { get; set; }
 
+        /// <summary>
+        ///     Usually the MQTT packets can be send partially. This is done by using multiple TCP packets
+        ///     or WebSocket frames etc. Unfortunately not all clients do support this feature and
+        ///     will close the connection when receiving such packets. If such clients are connecting to this
+        ///     server the flag must be set to _false_.
+        /// </summary>
+        public bool AllowPacketFragmentation { get; set; } = true;
+
         /// <summary>
         ///     Gets or sets the TCP keep alive interval.
         ///     The value _null_ indicates that the OS and framework defaults should be used.