Re: [ECOS] How to find out if socket closed?

[Nick Garnett <nickg at ecoscentric dot com>]

Grant Edwards <grante@visi.com> writes:

> I've been browsing around the old network stack code for a
> couple hours now trying to figure out a way to determine if a
> TCP connection has been closed by the other end.
> 
> I can't read data from it because I've got nowhere to put it,
> but I need to know if it's closed.  I can't write any data to
> the socket either.  Is there any way to query a socket to find
> out if the other end has been closed?

Off the top of my head: How about trying a zero sized read? If the
socket is closed then maybe that will be detected before it notices
that you are not reading anything. There may be an ioctl() you can try
which will either give you some status, or generate a detectable
error.

> 
> Under Unix, I think I'd get a SIGPIPE when the other end does a
> close(), right?
> 

Even with a SIGPIPE, this only tells you that one of your connections
has gone, not which one. So there must be some mechanism for polling
them to find our which. Maybe something with select() will work?

I'm just casting about in the dark here. I'm sure the solution is
something trivial and stupid, and we're both too smart to think of it :-)

-- 
Nick Garnett                    eCos Kernel Architect
http://www.ecoscentric.com/     The eCos and RedBoot experts


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