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Re: 13.1.2 Warnings

From: Ari Luotonen <luotonen@netscape.com>
Date: Thu, 17 Oct 1996 13:17:15 -0700 (PDT)
Message-Id: <199610172017.NAA04848@step.mcom.com>
To: ben@algroup.co.uk
Cc: dan@spyglass.com, luotonen@netscape.com, masinter@parc.xerox.com, http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
X-Mailing-List: <http-wg@cuckoo.hpl.hp.com> archive/latest/1793

> > What part is not right?   "never weaken the transparency" is right.  A
> Perhaps we have different ideas of what "transparency" means, but it seems to
> me that receiving an entity with an erroneous header is not transparent. It
> could certainly lead to undesirable behaviour on the part of downstream 1.1
> caches, such as periodically trying to refetch the "stale" entity (and, of
> course, getting another stale one).

Agree with Ben.  I think it's undesirable if I get a Warning header
when there it's not suppose to be there.

Say I hav document X, last-modified at Y.  The document is cached in
HTTP/1.1 cache A.  An HTTP/1.0 cache B requests for this document X
from the cache A.  Cache A returns it directly from its cache without
an up-to-date check, and attaches the Warning header of that fact.
Cache B caches the Warning header.

Later cache B receives another request for the document X and
determines it's time to do an up-to-date check.  Cache A has also
reached the time to do an up-to-date check.  So an up-to-date check is
made, and the remote server reponds that X has not been modified since
date Y, and is hence still up-to-date.

Now, cache A responds to B saying B's copy is up-to-date.
Unfortunately, the Warning header will (erroneously) remain in the
cache of B and will be passed to the user, forever giving the
perception that the returned copy may be stale, even though in this
case it was guaranteed to be up-to-date.

Ari Luotonen	* * * Opinions my own, not Netscape's * * *
Netscape Communications Corp.		ari@netscape.com
501 East Middlefield Road		http://home.netscape.com/people/ari/
Mountain View, CA 94043, USA		Netscape Proxy Server Development
Received on Thursday, 17 October 1996 13:24:13 UTC

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