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Date:	Wed, 30 Mar 2005 18:54:07 +0200
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: recv and errno during a connection reset/closed by peer
Message-ID:	<20050330165407.GA7144@cygbert.vinschen.de>
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On Mar 30 10:18, Brian Ford wrote:
> On Tue, 29 Mar 2005, Peter A. Castro wrote:
> 
> > On Tue, 29 Mar 2005, Brian Ford wrote:
> >
> > > If you are doing a normal blocking recv without MSG_PEEK, any return of 0
> > > should mean a closed connection AFAIK.
> >
> > Unfortunately that's not true for all implementation.  It's legal for a
> > zero length data object to be sent.  The network simply sends a header
> > with no payload in it, but it's passed through the network anyways and is
> > presented to the receiver.  The receiver, which might be blocking at the
> > time, will return from the call and get zero length data, but the
> > connection is still valid at this point.  I've seen AS/400's do just this
> > sending zero length data to an AIX box.  If the sender closes the
> > connection normally, then subsequent calls to recv return zero with no
> > indication that the connection is closed.  Call it a bug if you want, but
> > that's how it works.
> 
> I agree that zero length data can be sent, but only for UDP or datagram
> based sockets, not for TCP or stream based ones (nothing denotes a message
> here).  Even then, they are only sent by application choice, not just
> randomly by the OS.  Whether a connection is open or closed in this case
> has little meaning.

What Cygwin returns is what Cygwin gets from WinSock.  If Cygwin gets 0,
how should Cygwin suspect that something's wrong with the answer?  I'm
wondering how the OP has made sure that the connection has been closed
non-gracefully.  Has the process on the other side of the connection
been killed forcefully?  Or was the network cable plugged off?  Otherwise
there's a good chance that the process has closed the connection gracefully
and the 0 return is perfectly fine.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          mailto:cygwin AT cygwin DOT com
Red Hat, Inc.

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