Subj : Closing tcp socket connections
To   : comp.programming
From : Martin Hierholzer
Date : Fri Aug 12 2005 02:25 pm

Hi!

I have a problem closing tcp network server sockets. I have written a
(single threaded) server which is running on Linux (2.6.12-gentoo-r6) and a
client which should run on Linux and Windows.
The protocol between client and server is very simple, for every data packet
sent by the client a new connection will be opened, the client will send
its data and the server sends a reply and should close the connection. For
testing stability, I send these small packets as fast as I can, so many
packets arrive per second.
To close the connection, the server makes calls to shutdown and close on the
appropriate socket:

    i = send(ihConn, &iReply, sizeof(iReply), 0);
    if(i != sizeof(iReply)) {
      // do some error handling
    }
    i = shutdown(ihConn, SHUT_RDWR);
    if(i != 0) {
      // do some error handling
    }
    i = close(ihConn);
    if(i != 0) {
      // do some error handling
    }

But the connections seem to stay open even after these calls. Running
netstat even immediately after cancelling the test client shows a lot of
connections to my server, with state TIME_WAIT. I would expect only one
connection at most, because the client makes only on connection at a time.
After a while, the connections are gone. Of course, restarting the server
while these connections are still there is not possible, because the server
port cannot be opened.
Sometimes the client stops with an error message, I think this is when the
maximum number of ports is reached. Unfortunally these errors are very rare
and I cannot reproduce them now, so I cannot tell you the exact messages
(they are different on linux and windows!).

What have I made wrong? How do I close the connections really?

Greetings and thanks for your help!

.