2.1 How can I tell when a socket is closed on the other end?
>From Andrew Gierth ( andrewg@microlise.co.uk):
AFAIK:
If the peer calls close() or exits, without having messed with SO_LINGER, then
our calls to read() should return 0. It is less clear
what happens to write() calls in this case; I would expect EPIPE, not on the
next call, but the one after.
If the peer reboots, or sets l_onoff = 1, l_linger = 0 and then closes, then
we should get ECONNRESET (eventually) from
read(), or EPIPE from write().
I should also point out that when write() returns EPIPE, it also raises the
SIGPIPE signal - you never see the EPIPE error unless
you handle or ignore the signal.
If the peer remains unreachable, we should get some other error.
I don't think that write() can legitimately return 0. read() should return 0
on receipt of a FIN from the peer, and on all following
calls.
So yes, you must expect read() to return 0.
As an example, suppose you are receiving a file down a TCP link; you might
handle the return from read() like this:
rc = read(sock,buf,sizeof(buf));
if (rc > 0)
{
write(file,buf,rc);
/* error checking on file omitted */
}
else if (rc == 0)
{
close(file);
close(sock);
/* file received successfully */
}
else /* rc < 0 */
{
/* close file and delete it, since data is not complete
report error, or whatever */
}
Hope this helps
Radovan
Rajpaul Bagga wrote:
>
> Hello all.
> I'm trying to develop a network server/client setup where the server
> periodically checks for messages from the client. The socket is set for
> non-blockin i/o so that when it tries to receive a message if nothing is
> there it can go on to do other things.
>
> The problem occurs when the client drops the connection. I need to assume
> that it will not always send a nice message requesting to drop the
> connection. After the client has dropped a connection, if I issues a
> socket->Recv() command, I get a SIGSEGV signal. Is there someway to
> detect whether the client has dropped the connection before trying to
> receive a message?
>
> Thanks,
> -Rajpaul
>
> ------------------------------------------------------------------
> Rajpaul Bagga email: rajpaul@hp866a.lanl.gov
> P-25, M.S. H846 phone: (505) 665-8568
> Los Alamos National Laboratory
> Los Alamos, NM 87545
--
Radovan Chytracek
LHCb experiment at CERN
Radovan.Chytracek@cern.ch
http://wwwinfo.cern.ch/~chytrace