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Re: Improving If-Modified-Since

From: Roy Fielding <fielding@beach.w3.org>
Date: Tue, 15 Aug 1995 16:43:21 -0400
Message-Id: <199508152043.QAA32177@beach.w3.org>
To: Lou Montulli <montulli@mozilla.com>
Cc: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
>> >In addition to supporting size=SIZE I encourage other server authors to
>> >do an _equals_ comparison rather than a greater than or equal comparison
>> >of the two dates.
>> 
>> Absolutely not -- that would be a violation of both the spec and the
>> intentions of IMS.  In addition to being a cache mechanism, it allows
>> a client to request a document "only if it has been changed in the last
>> fifteen minutes".  In this case, it may not know what the server's
>> Last-Modified date is prior to the request.
>
>If it is a violation of the spec then you really ought to make the spec
>clearer on this point.  All the major servers that I know of do a
>greater than or equal comparison.  The spec needs to be changed to
>specifically say that 304 should only be returned when the If-modified-since
>date matches the current modification date of the file.

No, the spec is correct as it currently stands.  Your interpretation
(that it should do date matching and not >= comparison) is incorrect
as defined by the original IMS design and testing.


 ....Roy T. Fielding  Department of ICS, University of California, Irvine USA
                      Visiting Scholar, MIT/LCS + World-Wide Web Consortium
                      (fielding@w3.org)                (fielding@ics.uci.edu)
Received on Tuesday, 15 August 1995 13:49:29 EDT

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