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From Martin Kraemer <Martin.Krae...@Fujitsu-Siemens.com>
Subject Re: Expires: header prevents caching
Date Wed, 23 Jan 2002 09:06:55 GMT
On Tue, Jan 22, 2002 at 01:50:58PM -0600, William A. Rowe, Jr. wrote:
> > I'm no protcol expert, but that doesn't make sense to me.  mod_negotiation
> > should be adding "Accept-Language" to the Vary: header (yep, it's doing
> > that), but it shouldn't be setting Expires, should it?  Proxies should be
> > free to cache the page, conditional on the Accept-Language.
> 
> Which proxies?
> 
> HTTP/1.1 proxies, yes, should be able to serve based on Vary: recognition.
> 
> HTTP/1.0 proxies, no, cannot do that.  We should add [if it's not already
> present] the appropriate conditions in that reset.

But you wouldn't defeat everything HTTP/1.1 has brought us, cache-wise,
only for being backwards compatible until 1992?

It has always been like that: a caching proxy which ignores both
Content-Location and Vary: WILL be caching the first copy it gets, and
will ignore client's Accept-Language headers on subsequent requests.

That's life, and it makes no sense to become a cache-pig for that.
(That does not mean BTW that every HTTP/1.0 cache behaves so badly.
Many honor these headers, even if they say they speak HTTP/1.0 only).

Worse: even if a site decides it wants to become a cache-pig, then
it's the site's decision.
But Apache, as reference inplementation for HTTP/1.1, should *NEVER*
hard-code such a stupidity into the server. That's just plain wrong.

Yes, mod_negotiate should supply the Vary: and Content-*: headers for
the page, and if it is a truly dynamic page (which a negotiated set
of static documents isn't), only then should it omit the Last-Modified
header (or set it to now?). But setting Expires: is a configurative
decision of the pages' author, it must not be a decision of the server.

Just my $ .02

   Martin
-- 
<Martin.Kraemer@Fujitsu-Siemens.com>         |     Fujitsu Siemens
Fon: +49-89-636-46021, FAX: +49-89-636-47655 | 81730  Munich,  Germany

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