Async tcp client and server. How can I determine that the client or the server is no longer available?

Question

Hello. I would like to write async tcp client and server. I wrote this code but a have a problem, when I call the disconnect method on client or stop method on server. I can't identify that the client or the server is no longer connected.
I thought I will get an exception if the client or the server is not available but this is not happening.
private async void Process()
try
while (true)
var data = await this.Receive();
this.NewMessage.SafeInvoke(Encoding.ASCII.GetString(data));
catch (Exception exception)
How can I determine that the client or the server is no longer available?
Server
public class Server
private readonly Dictionary<IPEndPoint, TcpClient> clients = new Dictionary<IPEndPoint, TcpClient>();
private readonly List<CancellationTokenSource> cancellationTokens = new List<CancellationTokenSource>();
private TcpListener tcpListener;
private bool isStarted;
public event Action<string> NewMessage;
public async Task Start(int port)
this.tcpListener = TcpListener.Create(port);
this.tcpListener.Start();
this.isStarted = true;
while (this.isStarted)
var tcpClient = await this.tcpListener.AcceptTcpClientAsync();
var cts = new CancellationTokenSource();
this.cancellationTokens.Add(cts);
await Task.Factory.StartNew(() => this.Process(cts.Token, tcpClient), cts.Token, TaskCreationOptions.LongRunning, TaskScheduler.Default);
public void Stop()
this.isStarted = false;
foreach (var cancellationTokenSource in this.cancellationTokens)
cancellationTokenSource.Cancel();
foreach (var tcpClient in this.clients.Values)
tcpClient.GetStream().Close();
tcpClient.Close();
this.clients.Clear();
public async Task SendMessage(string message, IPEndPoint endPoint)
try
var tcpClient = this.clients[endPoint];
await this.Send(tcpClient.GetStream(), Encoding.ASCII.GetBytes(message));
catch (Exception exception)
private async Task Process(CancellationToken cancellationToken, TcpClient tcpClient)
try
var stream = tcpClient.GetStream();
this.clients.Add((IPEndPoint)tcpClient.Client.RemoteEndPoint, tcpClient);
while (!cancellationToken.IsCancellationRequested)
var data = await this.Receive(stream);
this.NewMessage.SafeInvoke(Encoding.ASCII.GetString(data));
catch (Exception exception)
private async Task Send(NetworkStream stream, byte[] buf)
await stream.WriteAsync(BitConverter.GetBytes(buf.Length), 0, 4);
await stream.WriteAsync(buf, 0, buf.Length);
private async Task<byte[]> Receive(NetworkStream stream)
var lengthBytes = new byte[4];
await stream.ReadAsync(lengthBytes, 0, 4);
var length = BitConverter.ToInt32(lengthBytes, 0);
var buf = new byte[length];
await stream.ReadAsync(buf, 0, buf.Length);
return buf;
Client
public class Client
private TcpClient tcpClient;
private NetworkStream stream;
public event Action<string> NewMessage;
public async void Connect(string host, int port)
try
this.tcpClient = new TcpClient();
await this.tcpClient.ConnectAsync(host, port);
this.stream = this.tcpClient.GetStream();
this.Process();
catch (Exception exception)
public void Disconnect()
try
this.stream.Close();
this.tcpClient.Close();
catch (Exception exception)
public async void SendMessage(string message)
try
await this.Send(Encoding.ASCII.GetBytes(message));
catch (Exception exception)
private async void Process()
try
while (true)
var data = await this.Receive();
this.NewMessage.SafeInvoke(Encoding.ASCII.GetString(data));
catch (Exception exception)
private async Task Send(byte[] buf)
await this.stream.WriteAsync(BitConverter.GetBytes(buf.Length), 0, 4);
await this.stream.WriteAsync(buf, 0, buf.Length);
private async Task<byte[]> Receive()
var lengthBytes = new byte[4];
await this.stream.ReadAsync(lengthBytes, 0, 4);
var length = BitConverter.ToInt32(lengthBytes, 0);
var buf = new byte[length];
await this.stream.ReadAsync(buf, 0, buf.Length);
return buf;

Answer 1

Hi,
Have you debug these two applications? Does it go into the catch exception block when you close the client or the server?
According to my test, it will throw an exception when the client or the server is closed, just log the exception message in the catch block and then you'll get it:
private async void Process()
try
while (true)
var data = await this.Receive();
this.NewMessage.Invoke(Encoding.ASCII.GetString(data));
catch (Exception exception)
Console.WriteLine(exception.Message);
Unable to read data from the transport connection: An existing   connection was forcibly closed by the remote host.
By the way, I don't know what the SafeInvoke method is, it may be an extension method, right? I used Invoke instead to test it.
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