W3C home > Mailing lists > Public > ietf-http-wg-old@w3.org > September to December 1995

Re: two-phase send concerns

From: David W. Morris <dwm@shell.portal.com>
Date: Thu, 7 Dec 1995 22:19:35 -0800 (PST)
To: http working group <http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com>
Message-Id: <Pine.SUN.3.90.951207213331.15574A-100000@jobe.shell.portal.com>

On Thu, 7 Dec 1995, Jeffrey Mogul wrote:

> One answer would be "it doesn't matter" (more precisely, "it's
> up to the server implementer").  Take your first example: if the
> client wants to PUT a zillion bytes to a location that requires
> authentication, then does it really matter why it fails?  Either
> way, it can't be done.

Well there is the interesting situation where the server requires
authentication for a PUT AND also can't accept 1meg of data.
The way WWW/HTTP authentication works, the client may not know that
authentication is required until attempting the PUT and getting the
401 unauthorized response.  HENCE, we have a situation where the
client could be presented two possible errors, one which it can possibly
correct and one which it can't ever correct. In normal transaction flow
authentication would be verified and the semantics of the request would
be verified.  YET, what is the point of a server issuing an unauthorized
response when it could/should/might know it's is never going to process
the transaction anyway.  As an end user, I'd be mightly annoyed if I
did what I believed was valid, was delayed for the password prompt in
response to the 401 UNAUTHORIZED and possibly some substantial delay
because of the bytes in the pipe the first time only to be then told that
the size of the data to PUT was too big.

rom a protocol perspective it needs to be valid to issue the failures
in either order because the size failure may be detected only when a
processing 'CGI' program responds while the server detects the unauthorized
situation. It would be good however to encourage presentation of fatal
(can't be overcome) errors before correctable failures, when possib

To backup .... as I understand the discussion, the purpose of the 2 phase
send was to increase the probablility that the client has a chance to
receive the response. The impression was that some/many TCP implementations
may close a connection in such a way that the response is flushed and
never seen from the client.  The second lesser concern was that by
using a short delay, there was less waste of bandwidth in the failure case.

I like your (Jeffrey Mogul) suggestion for requiring the explict two phase
request from the client in the quiet close case.  I would further
extend your suggestion to get rid of the timeout or make it quite large
and only allow the client to continue when the response arrives.

Dave Morris
Received on Thursday, 7 December 1995 22:24:29 EST

This archive was generated by hypermail pre-2.1.9 : Wednesday, 24 September 2003 06:31:36 EDT