Instantly detect client disconnection from server socket

Question

How can I detect that a client has disconnected from my server?

I have the following code in my AcceptCallBack method

static Socket handler = null;
public static void AcceptCallback(IAsyncResult ar)
{
  //Accept incoming connection
  Socket listener = (Socket)ar.AsyncState;
  handler = listener.EndAccept(ar);
}

I need to find a way to discover as soon as possible that the client has disconnected from the handler Socket.

I've tried:

1. handler.Available;
2. handler.Send(new byte[1], 0, SocketFlags.None);
3. handler.Receive(new byte[1], 0, SocketFlags.None);

The above approaches work when you are connecting to a server and want to detect when the server disconnects but they do not work when you are the server and want to detect client disconnection.

Any help will be appreciated.

Answer 1

Since there are no events available to signal when the socket is disconnected, you will have to poll it at a frequency that is acceptable to you.

Using this extension method, you can have a reliable method to detect if a socket is disconnected.

static class SocketExtensions
{
  public static bool IsConnected(this Socket socket)
  {
    try
    {
      return !(socket.Poll(1, SelectMode.SelectRead) && socket.Available == 0);
    }
    catch (SocketException) { return false; }
  }
}