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Re: ETags vs Variants, was: Revising RFC2616 - what's happening

From: Julian Reschke <julian.reschke@gmx.de>
Date: Fri, 20 Oct 2006 20:46:55 +0200
Message-ID: <4539199F.7020006@gmx.de>
To: "Roy T. Fielding" <fielding@gbiv.com>
CC: Henrik Nordstrom <henrik@henriknordstrom.net>, Jamie Lokier <jamie@shareable.org>, HTTP Working Group <ietf-http-wg@w3.org>

Roy T. Fielding schrieb:
> 
> On Oct 20, 2006, at 11:27 AM, Julian Reschke wrote:
>> Well, that's clearer, but not my interpretation of what it should say. 
>> Don't we want a missing header to be treated the same way as an empty 
>> header?
> 
> Nope.  They usually don't mean the same thing (see Accept).
> 
>> That is, if the cache has a cached response from a previous request 
>> with "Accept-Language: de", and the server replied with "Vary: 
>> Accept-Language", can a subsequent request without "Accept-Language" 
>> header be served with the cached reply? I wouldn't have thought so....
> 
> No, we have no idea what the language pref algorithm is on the server.

Right. So we don't want the cache to serve the cached response in 
absence of the request header, right?

But if we say (as you suggested):

"When the cache receives a subsequent request whose Request-URI 
specifies one or more cache entries including a Vary header field, the 
cache MUST NOT use such a cache entry to construct a response to the new 
request unless the set of selecting request-headers present in the new 
request match the corresponding set of stored request-headers in the 
original request."

In this case, the cache would have an entry where the set of stored 
request headers is "Accept-Language", which isn't present in the new 
request. Thus, the cache would be allowed to use the cached entry, right 
(because the set of selecting response headers *present* in the request 
is empty).

Best regards, Julian
Received on Friday, 20 October 2006 18:47:12 GMT

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