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Re: Comments on draft-ietf-http-negotiation-00.txt

From: Roy T. Fielding <fielding@kiwi.ICS.UCI.EDU>
Date: Tue, 18 Feb 1997 01:07:10 -0800
To: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Message-Id: <9702180107.aa17119@paris.ics.uci.edu>
In message <Pine.SUN.3.95.970217175449.6072C-100000@xochi.tezcat.com>,
Klaus Weide writes:
>10.2, in description of the algorithm:
>--- begin excerpt ---
>     3. Check for an origin server configuration error. If the HTTP
>        response message generated in step 2 contains an Alternates
>        header, a Content-Location header, or has the 300 status code,
>                  ^^^^^^^^^^^^^^^^
>        then the best variant resource is not a proper end point in
>        the negotiation process, and a 506 (Variant Also Negotiates)
>        error response message should be generated instead of going to
>        step 4.
>--- end excerpt ---
>
>This seems slightly too restrictive.  Suggestion: change to "[...],
>a non-matching Content-Location header, [...]", and add:
>  "A Content-Location header is non-matching if the location given
>   by its value, after resolution according to the HTTP/1.1 specification
>   in the case of a relative URI, does not match (in the sense of the
>   HTTP/1.1 specification, 3.2.3) the chosen variant's location.
>   Remove any existing Content-Location header."
>
>Reason: RFC 2068 describes several uses of Content-Location outside of
>content negotiation (even with a SHOULD in 14.15).  Use of this header
>should not be discouraged by the negotiation draft if it doesn't
>create any conflict (i.e. if the variant "knows" its own correct
>location, this should be ok).  After all a Vary header *is* allowed 
>here, and Content-Location together with Vary may help caching in some
>cases if there are any non-negotiating proxies between a proxy implementing
>this algorithm and the origin server.

I'll second this.  Further, I'd say that there is no condition under
which a 5xx response is justified.  If the response looks bad for TCN,
then disable TCN for that response and flush your cache.

 ...Roy T. Fielding
    Department of Information & Computer Science    (fielding@ics.uci.edu)
    University of California, Irvine, CA 92697-3425    fax:+1(714)824-4056
    http://www.ics.uci.edu/~fielding/
Received on Tuesday, 18 February 1997 01:18:47 EST

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