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RE: i107

From: Brian Smith <brian@briansmith.org>
Date: Thu, 13 Mar 2008 21:09:43 -0700
To: "'HTTP Working Group'" <ietf-http-wg@w3.org>
Cc: "'Henrik Nordstrom'" <henrik@henriknordstrom.net>
Message-ID: <001b01c88589$3c600a80$4001a8c0@T60>

Henrik Nordstrom wrote:
> If-None-Match is pretty clearly defined to apply to "the 
> selected representation" only.
>    If any of the entity tags match the entity tag of the entity that
>    would have been returned in the response to a similar GET request
>    (without the If-None-Match header) on that resource, or if 
>    "*" is [...]

The specification also says: "A client that has one or more entities
previously obtained from the resource can verify that none of those
entities is current by including a list of their associated entity tags
in the If-None-Match header field."

If the purpose is to allow the client to verify that none of the
entities it has are current (conversely, at least one of its
currently-held entities are current), then the server must consider all
entities for the resource, not just the ones that would bet returned by
a similar GET.

Also, the name itself, If-*None*-Match, indicates that it isn't supposed
to be matched against multiple entities, not just against a singular
"selected representation".

>    The meaning of "If-None-Match: *" is that the method MUST NOT be
>    performed if the representation selected by the origin 
>    server (or by a cache, possibly using the Vary mechanism,
>    see section 14.44)

The specification also says: "As a special case, the value '*' matches
any current entity of the resource." and "...if '*' is given and any
current entity exists for that resource...".

Consider a resource /foo that has a single text/plain representation,
and the following request:

   PUT /foo HTTP/1.1
   If-None-Match: *
   Accept: text/html

If the server would respond with 406 Not Acceptable to a GET with the
same headers, then should it process the PUT? No, because If-None-Match:
* matches any current entity, not just one that would have been returned
by a similar GET request.

Received on Friday, 14 March 2008 04:10:17 UTC

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