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Re: Clarification on cacheability

From: Koen Holtman <koen@win.tue.nl>
Date: Thu, 23 Dec 1999 13:44:12 +0100 (MET)
Message-Id: <199912231244.NAA00813@wsooti28.win.tue.nl>
To: joshco@Exchange.Microsoft.com (Josh Cohen (Exchange))
Cc: fielding@kiwi.ics.uci.edu, joshco@Exchange.Microsoft.com, http-wg@hplb.hpl.hp.com
Josh Cohen:
>
[...]
>I guess if there is any chance that the response could be different,
>based on client auth, client type, or whatever, then it is not safe to
>cache. 

It _is_ safe to make the response cacheable as long as you use Vary
correctly, this is what Vary was invented for.

>(especially since caches dont filter based on accept before
>returning responses)

As Roy said, most (all?) 1.1 caches don't actually implement the
refined filtering made possible by Vary.  They implement the Vary
requirements in 1.1 by treating 'Vary: anything' as equivalent to
'no-cache'.

But you can still use Vary if you want to help possible future caches:
I would consider this to be good protocol design.  You can find some
examples of the use of Vary+Expires in RFC2295.


Koen.
Received on Thursday, 23 December 1999 12:48:14 EST

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