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RE: draft-ietf-httpbis-p6-cache-06

From: Brian Smith <brian@briansmith.org>
Date: Tue, 2 Jun 2009 02:04:13 -0500
To: "'Mark Nottingham'" <mnot@mnot.net>
Cc: "'Thomas Broyer'" <t.broyer@gmail.com>, "'HTTP Working Group'" <ietf-http-wg@w3.org>
Message-ID: <000301c9e350$59074fb0$0b15ef10$@org>
Mark Nottingham wrote:
> On 28/05/2009, at 1:31 AM, Brian Smith wrote:
> > Applying Postel's rule, a cache shouldn't return a cached POST
> > response to a GET/HEAD request, and servers shouldn't include Cache-
> > Control/Expires headers in POST responses. That should be explicit
> > in the specification.
> 
> There has been considerable discussion on this, and your conclusion
> wasn't suggested AFAIK, nor was it the direction we've chosen to move
> in. See:
>     http://trac.tools.ietf.org/wg/httpbis/trac/ticket/139
>     http://www.w3.org/mid/08345F97-7D4D-40AD-98E2-
> EF73E93C031F@mnot.net (entire thread)

My concern is that there are many origin servers that assume that a POST
response will not be returned in response to a subsequent GET/HEAD
request--in other words, they assume the method is part of the cache key.
But, I can see that my concern is unjustified, since even if a POST response
is cached, in cannot be returned in a subsequent request until it has been
revalidated (as required by RFC 2616 section 13.10). Since the cache has to
do one (possibly conditional) GET after every POST anyway, there is very
little chance of any problematic behavior.

Still, I expect that almost all caches will continue to avoid caching any
POST responses, just to avoid the issue altogether--especially since caching
POST responses doesn't reduce the number of requests that need to be
forwarded to the origin server at all (because of mandatory revalidation).

- Brian
Received on Tuesday, 2 June 2009 07:04:55 GMT

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