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From: dls@mentor.cc.purdue.edu (David L Stevens)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Questions on TCP shutdown and RFC-793
Message-ID: <2527@mentor.cc.purdue.edu>
Date: 10 Dec 90 20:29:43 GMT
References: <36540017@hpindwa.cup.hp.com> <2452@mentor.cc.purdue.edu> <1990Dec10.131116.19393@jarvis.csri.toronto.edu>
Organization: PUCC UNIX Group
Lines: 36

In article <1990Dec10.131116.19393@jarvis.csri.toronto.edu>, thomson@hub.toronto.edu (Brian Thomson) writes:
> 
> I think the original question was about the TCP shutdown procedure, not the
> BSD shutdown() system call, but this answer caught my attention because it
> seems to contradict everything I thought I knew about the BSD routine.
> My understanding is as follows:
> 	shutdown(s, 0)	- flushes data queued for receive, and shrinks
> 			  my receive window to zero.  Succeeding reads will
> 			  fail.
> 	shutdown(s, 1)	- data already queued will be delivered, followed
> 			  by a FIN.  Succeeding writes will fail.
> 	shutdown(s, 2)	- equivalent to { shutdown(s, 0); shutdown(s, 1); }
> ...
> 
> And, to top it off, my manual pages (Sun) say nothing about loss of
> buffered data pending.

	Sorry, I had forgotten where I saw it. It isn't in the man page, and
I originally came across it in the code, but I knew there was a documentation
reference as well. The "IPC Primer" (section 2.6) says:

	"....Applying shutdown to a socket causes any data queued to be
immediately discarded."

Also, from the "Advanced 4.3BSD IPC Tutorial" (PS1:8-8):

	"Once a socket is no longer of interest, it may be discarded by
applying close to the descriptor, close(s);
	If data is associated with a socket which promises reliable delivery
(e.g., a stream socket) when a close takes place, the system will continue
to attempt to transfer the data. However, after a fairly long period of time,
if the data is still undelivered, it will be discarded. Should a user have no
use for a any pending data, it may perform a shutdown on the socket prior to
closing it."
-- 
					+-DLS  (dls@mentor.cc.purdue.edu)