Timeout on TCP Server on Wiznet

Question

Hello All. So I want to run a TCP server on W5100 or W5550. My question is can I detect from the server that the connection is no longer established with a client (cable disconnected, etc) without collaboration from the client? The examples I have seen are based on sending a message to the client and interpreting the lack of a reply as a signal that the connection is no longer established. I have no control of code from the client side (PC running Windows or Linux) so I would like to have a solution that runs on the server only. Thank You

Eugeny · Answer

The TCP protocol assumes client sending FIN to server if it has nothing more to say, and server receiving this flag says something final if it needs to and frees the socket. But you may expect developers to omit this and close socket at their side without sending FIN flag. Then, as is, you will not know that client is done unless try sending something to old socket and receiving RST back. In client-server communication server usually knows how much data it must send to serve client’s request, sends FIN at the end and closes its socket. If you open TCP connection and expect variable data exchange, then you may need to develop your own protocol (or use any other which has remote node test as one of its features).

Ironic · Answer

Thank you. So can I send a control signal or similar to test if the socket is open? Ideally, something that would not be received as a message by the client.