This is the mail archive of the cygwin mailing list for the Cygwin project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

RE: recv and errno during a connection reset/closed by peer


On Wed, 30 Mar 2005, 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.

Nope, sorry, the example I cited above was using TCP, and wasn't really the applications choice (as I wrote both the server and client apps on both ends in this example, I can tell you the server app did not send zero byte data, but the client got a zero byte return after a previous non-zero byte return). The network stack on the AS/400 is rather awful and does send empty segments at odd times. It's a real life example. Unfortunately it's neither Cygwin nor Linux, and so likely not relevent for the OP.

--
Brian Ford

-- Peter A. Castro <doctor@fruitbat.org> or <Peter.Castro@oracle.com> "Cats are just autistic Dogs" -- Dr. Tony Attwood

--
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
Problem reports:       http://cygwin.com/problems.html
Documentation:         http://cygwin.com/docs.html
FAQ:                   http://cygwin.com/faq/


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]