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Re: Identifying the Resource Associated with a Representation?

From: Mike Kelly <mike@mykanjo.co.uk>
Date: Sun, 7 Nov 2010 16:33:54 +0000
Message-ID: <AANLkTimfHD+8xjzaS1KVSzqoMtb7YD-9LbmipsDkF3-Y@mail.gmail.com>
To: Julian Reschke <julian.reschke@gmx.de>
Cc: nathan@webr3.org, HTTP Working Group <ietf-http-wg@w3.org>
On Sun, Nov 7, 2010 at 4:05 PM, Julian Reschke <julian.reschke@gmx.de> wrote:
> On 06.11.2010 04:40, Nathan wrote:
>>
>> Hi,
>>
>>  From an HTTP response I need to be able to work out an identifier for a
>> resource, from the Content-Location, in order to:
>>
>> (a) which URI to send PUT and DELETE requests to
>> (b) which URI to store a cached representation against.
>>
>
> (b) Not entirely sure what you mean here.

I think I do; and as it stands the spec says:

http://tools.ietf.org/html/draft-ietf-httpbis-p3-payload-12#section-6.7

"A cache cannot assume that a representation with a Content-Location
   different from the URI used to retrieve it can be used to respond to
   later requests on that Content-Location URI."

Which implies that any cache controls apply only to the effective
Request URI. Understandable, because the conditions for variance could
differ between the URIs.

Initially I felt this was bit odd given this bit on 'Request Methods
that Invalidate':

http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-12#section-2.5

The following HTTP methods MUST cause a cache to invalidate the
   effective Request URI (Section 4.3 of [Part1]) as well as the URI(s)
   in the Location and Content-Location header fields (if present)

but on reflection this does actually make sense since invalidation is
about general resource state, whereas cache controls and vary are
representation specific. It would also require a statement only
allowing same-origin URIs to ensure the mechanism was secure.

Out of interest; has anyone explored the possibility of a specific
cache-control directive that could indicate that the cache conditions
apply to the Content-Location URI?

 Cheers,
Mike
Received on Sunday, 7 November 2010 16:34:30 GMT

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