Detecting a broken TCP connection, which was not closed

[seulater]

Once I make a TCP connection to another board and lets say the remote end either looses power or unplugs the Ethernet cable, I need to be able to detect that the connection is gone and not just sit there in the do while loop of
do
{
n = ReadWithTimeout( tcp_fd[LINE1], RC_Buffer, RC_BUFSIZE, 5);

}while(n >=0);

Because when the connection is dropped in the manner described this ReadWithTimeout does not produce the -1 like I would expect if connection terminated.

[rnixon]

TCP does not have the inherent capability to detect when the other side has gone away if no data is being sent. If you think about it, it makes sense; how could one side possibly tell if something it is not talking to is gone? Some people refer to this as a "half open socket". If it happens when data is being transferred, then an error will occur because the ack is not received. So one way to do it is to send a heartbeat every so many seconds that the other side responds to. If you don't have control over that, another way is to have a timeout counter and if data has not been received in x amount of time, the socket is closed or can be over ridden by a new connection. I think a standard way for larger servers to handle it is the timeout.

[seulater]

Thanks, that is exactly what i did.