Dispose socket when TCP connect failed.

Build/MQTTnet.nuspec

@@ -17,6 +17,7 @@
 * [Client] Added method to trigger PING/PONG manually (connection check etc.).
 * [Client] Added support for certificate validation callback when using Web Sockets (requires netstandard2.1+).
 * [Client] Fixed a memory leak when web socket based connections trying to reconnect with an offline server.
+* [Client] Fixed a memory leak when TCP based connections trying to reconnect with an offline server.
 * [Client] Fixed an issue when connecting to an invalid host (format).
 * [ManagedClient] Added method to trigger PING/PONG manually (connection check etc.).
 * [MQTTnet.AspNetCore] improved compatibility with AspNetCore 3.1.

Source/MQTTnet/Implementations/CrossPlatformSocket.cs

@@ -143,7 +143,7 @@ namespace MQTTnet.Implementations
             {
                 _networkStream?.Dispose();
 
-                // Workaround for: workaround for https://github.com/dotnet/corefx/issues/24430
+                // Workaround for: https://github.com/dotnet/corefx/issues/24430
                 using (cancellationToken.Register(() => _socket.Dispose()))
                 {
                     cancellationToken.ThrowIfCancellationRequested();

Source/MQTTnet/Implementations/MqttTcpChannel.cs

@@ -46,56 +46,63 @@ namespace MQTTnet.Implementations
 
         public async Task ConnectAsync(CancellationToken cancellationToken)
         {
-            CrossPlatformSocket socket;
+            CrossPlatformSocket socket = null;
-
+            try
-            if (_options.AddressFamily == AddressFamily.Unspecified)
             {
-                socket = new CrossPlatformSocket();
+                if (_options.AddressFamily == AddressFamily.Unspecified)
-            }
-            else
-            {
-                socket = new CrossPlatformSocket(_options.AddressFamily);
-            }
-
-            socket.ReceiveBufferSize = _options.BufferSize;
-            socket.SendBufferSize = _options.BufferSize;
-            socket.NoDelay = _options.NoDelay;
-
-            if (_options.DualMode.HasValue)
-            {
-                // It is important to avoid setting the flag if no specific value is set by the user
-                // because on IPv4 only networks the setter will always throw an exception. Regardless
-                // of the actual value.
-                socket.DualMode = _options.DualMode.Value;
-            }
-
-            await socket.ConnectAsync(_options.Server, _options.GetPort(), cancellationToken).ConfigureAwait(false);
-
-            cancellationToken.ThrowIfCancellationRequested();
-
-            var networkStream = socket.GetStream();
-
-            if (_options.TlsOptions?.UseTls == true)
-            {
-                var sslStream = new SslStream(networkStream, false, InternalUserCertificateValidationCallback);
-                try
                 {
-                    await sslStream.AuthenticateAsClientAsync(_options.Server, LoadCertificates(), _options.TlsOptions.SslProtocol, !_options.TlsOptions.IgnoreCertificateRevocationErrors).ConfigureAwait(false);
+                    socket = new CrossPlatformSocket();
                 }
-                catch
+                else
                 {
-                    sslStream.Dispose();
+                    socket = new CrossPlatformSocket(_options.AddressFamily);
-                    throw;
                 }
 
-                _stream = sslStream;
+                socket.ReceiveBufferSize = _options.BufferSize;
-            }
+                socket.SendBufferSize = _options.BufferSize;
-            else
+                socket.NoDelay = _options.NoDelay;
-            {
-                _stream = networkStream;
-            }
 
-            Endpoint = socket.RemoteEndPoint?.ToString();
+                if (_options.DualMode.HasValue)
+                {
+                    // It is important to avoid setting the flag if no specific value is set by the user
+                    // because on IPv4 only networks the setter will always throw an exception. Regardless
+                    // of the actual value.
+                    socket.DualMode = _options.DualMode.Value;
+                }
+
+                await socket.ConnectAsync(_options.Server, _options.GetPort(), cancellationToken).ConfigureAwait(false);
+
+                cancellationToken.ThrowIfCancellationRequested();
+
+                var networkStream = socket.GetStream();
+
+                if (_options.TlsOptions?.UseTls == true)
+                {
+                    var sslStream = new SslStream(networkStream, false, InternalUserCertificateValidationCallback);
+                    try
+                    {
+                        await sslStream.AuthenticateAsClientAsync(_options.Server, LoadCertificates(), _options.TlsOptions.SslProtocol, !_options.TlsOptions.IgnoreCertificateRevocationErrors).ConfigureAwait(false);
+                    }
+                    catch
+                    {
+                        sslStream.Dispose();
+                        throw;
+                    }
+
+                    _stream = sslStream;
+                }
+                else
+                {
+                    _stream = networkStream;
+                }
+
+                Endpoint = socket.RemoteEndPoint?.ToString();
+            }
+            catch (Exception)
+            {
+                socket?.Dispose();
+                throw;
+            }
         }
 
         public Task DisconnectAsync(CancellationToken cancellationToken)