Refactor package object model.

Source/MQTTnet/Implementations/MqttTcpChannel.cs

@@ -10,6 +10,7 @@ using System.Runtime.ExceptionServices;
 using System.Security.Cryptography.X509Certificates;
 using System.Threading;
 using System.Threading.Tasks;
+using MQTTnet.Exceptions;
 
 namespace MQTTnet.Implementations
 {
@@ -75,7 +76,7 @@ namespace MQTTnet.Implementations
                 cancellationToken.ThrowIfCancellationRequested();
 
                 var networkStream = socket.GetStream();
-
+                
                 if (_options.TlsOptions?.UseTls == true)
                 {
                     var sslStream = new SslStream(networkStream, false, InternalUserCertificateValidationCallback);
@@ -144,7 +145,7 @@ namespace MQTTnet.Implementations
 
                     if (stream == null)
                     {
-                        throw new ObjectDisposedException(nameof(stream));
+                        return 0;
                     }
 
                     return await stream.ReadAsync(buffer, offset, count, cancellationToken).ConfigureAwait(false);
@@ -185,6 +186,10 @@ namespace MQTTnet.Implementations
                     }
 
                     await stream.WriteAsync(buffer, offset, count, cancellationToken).ConfigureAwait(false);
+
+                    // This subsequent call is required to check whether the socket is still connected. 
+                    // Without this call a broken connection is only recognized at the next call.
+                    await stream.WriteAsync(PlatformAbstractionLayer.EmptyByteArray, 0, 0, cancellationToken);
                 }
             }
             catch (ObjectDisposedException)

Source/MQTTnet/Implementations/MqttTcpServerAdapter.cs

@@ -47,7 +47,7 @@ namespace MQTTnet.Implementations
                 {
                     throw new ArgumentException("TLS certificate is not set.");
                 }
-                
+
                 var tlsCertificate = options.TlsEndpointOptions.CertificateProvider.GetCertificate();
                 if (!tlsCertificate.HasPrivateKey)
                 {
@@ -73,16 +73,22 @@ namespace MQTTnet.Implementations
 
         void Cleanup()
         {
-            _cancellationTokenSource?.Cancel(false);
-            _cancellationTokenSource?.Dispose();
-            _cancellationTokenSource = null;
-
-            foreach (var listener in _listeners)
+            try
             {
-                listener.Dispose();
+                _cancellationTokenSource?.Cancel(false);
             }
+            finally
+            {
+                _cancellationTokenSource?.Dispose();
+                _cancellationTokenSource = null;
 
-            _listeners.Clear();
+                foreach (var listener in _listeners)
+                {
+                    listener.Dispose();
+                }
+
+                _listeners.Clear();
+            }
         }
 
         void RegisterListeners(MqttServerTcpEndpointBaseOptions options, X509Certificate2 tlsCertificate, CancellationToken cancellationToken)

Source/MQTTnet/Implementations/MqttTcpServerListener.cs

@@ -77,7 +77,7 @@ namespace MQTTnet.Implementations
 
                 _socket.Bind(_localEndPoint);
                 _socket.Listen(_options.ConnectionBacklog);
-
+                
                 Task.Run(() => AcceptClientConnectionsAsync(cancellationToken), cancellationToken).Forget(_logger);
 
                 return true;
@@ -152,9 +152,7 @@ namespace MQTTnet.Implementations
                     _addressFamily == AddressFamily.InterNetwork ? "ipv4" : "ipv6");
 
                 clientSocket.NoDelay = _options.NoDelay;
-
                 stream = clientSocket.GetStream();
-
                 X509Certificate2 clientCertificate = null;
 
                 if (_tlsCertificate != null)
@@ -208,17 +206,17 @@ namespace MQTTnet.Implementations
                 {
                     stream?.Dispose();
                     clientSocket?.Dispose();
-
-                    _logger.Verbose("Client '{0}' disconnected at TCP listener '{1}, {2}'.",
-                        remoteEndPoint,
-                        _localEndPoint,
-                        _addressFamily == AddressFamily.InterNetwork ? "ipv4" : "ipv6");
                 }
                 catch (Exception disposeException)
                 {
                     _logger.Error(disposeException, "Error while cleaning up client connection");
                 }
             }
+
+            _logger.Verbose("Client '{0}' disconnected at TCP listener '{1}, {2}'.",
+                remoteEndPoint,
+                _localEndPoint,
+                _addressFamily == AddressFamily.InterNetwork ? "ipv4" : "ipv6");
         }
     }
 }

Source/MQTTnet/Implementations/PlatformAbstractionLayer.cs

@@ -1,20 +1,25 @@
-using System.Threading.Tasks;
+using System;
+using System.Threading.Tasks;
 
 namespace MQTTnet.Implementations
 {
     public static class PlatformAbstractionLayer
     {
-        public static Task CompletedTask
-        {
-            get
-            {
-#if NET452 
-                return Task.FromResult(0);
-#else
-                return Task.CompletedTask;
-#endif
-            }
-        }
+        public static readonly byte[] EmptyByteArray = new byte[0];
 
+#if NET452
+        public static Task CompletedTask => Task.FromResult(0);
+#else
+        public static Task CompletedTask => Task.CompletedTask;
+#endif
+
+        public static void Sleep(TimeSpan timeout)
+        {
+#if NET452 || NETSTANDARD2_0 || NETSTANDARD2_1 || NETCOREAPP3_1
+            System.Threading.Thread.Sleep(timeout);
+#else
+            Task.Delay(timeout).Wait();
+#endif
+        }
     }
 }