[FIXED] How to check if a socket is connected/disconnected in C#?

Issue

How can you check if a network socket (System.Net.Sockets.Socket) is still connected if the other host doesn't send you a packet when it disconnects (e.g. because it disconnected ungracefully)?

Solution

As Paul Turner answered Socket.Connected cannot be used in this situation. You need to poll connection every time to see if connection is still active. This is code I used:

bool SocketConnected(Socket s)
{
    bool part1 = s.Poll(1000, SelectMode.SelectRead);
    bool part2 = (s.Available == 0);
    if (part1 && part2)
        return false;
    else
        return true;
}

It works like this:

• s.Poll returns true if
  • connection is closed, reset, terminated or pending (meaning no active connection)
  • connection is active and there is data available for reading
• s.Available returns number of bytes available for reading
• if both are true:
  • there is no data available to read so connection is not active

Answered By - zendar

Answer Checked By - Marilyn (PHPFixing Volunteer)