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Re: WGLC p6 4.2.1

From: Adrien W. de Croy <adrien@qbik.com>
Date: Mon, 18 Mar 2013 08:59:02 +0000
To: "Amos Jeffries" <squid3@treenet.co.nz>, "ietf-http-wg@w3.org" <ietf-http-wg@w3.org>
Message-Id: <ema8b6f777-7b08-4723-b705-f55ab8fa61af@bombed>

there are some interactions with caches.

for instance a cache receiving a request with If-Modified-Since later 
than its own Last-Modified, may presume the client has a later copy, and 
discard its own copy.

I think really if we're to introduce this sort of allowed behaviour, we 
need to do a bit more work on the spec, if only to cover the other parts 
where IMS is covered etc.

And set some rules.

Adrien



------ Original Message ------
From: "Amos Jeffries" <squid3@treenet.co.nz>
To: "ietf-http-wg@w3.org" <ietf-http-wg@w3.org>
Sent: 18/03/2013 9:17:26 p.m.
Subject: Re: WGLC p6 4.2.1
>On 18/03/2013 7:58 p.m., Poul-Henning Kamp wrote:
>>  In message <em2a931273-ea65-4c5c-83d3-2d9698e19de0@bombed>, "Adrien 
>>W. de Croy" writes:
>>
>>>  I see there were some changes made to the 3rd bullet point in 4.2.1
>>>  about selection of representations to update with a 304.
>>>
>>>  The new text hints that dates other than those received in a 
>>>previous
>>>  Last-Modified can be used to generate a conditional request with
>>>  If-Modified-Since.
>>  There are several uses I know of, where IMS is used by clients
>>  without having an older object, as a way to say "Is a recent version
>>  of this object available ?".
>>
>>  One such usage is "Are there any severe weather warnings published
>>  in the last 24 hours ?" which avoids pulling the "no warnings"
>>  boilerplate most of the year.
>>
>>  I will fully agree, that using only values originally received from
>>  the server is a lot more water-tight, and is to be strongly 
>>recommended
>>  (at the SHOULD level), but trying to outlaw other values is a waste
>>  of everybodys time, given that such a ban cannot be sensibly enforced
>>  by us.
>>
>>  If the server for some reason insists on not receiving arbitrary
>>  timestamps in IMS, it can use E-tags, which by definition are
>>  impossible to synthesize anywhere else.
>
>+1 on what PHK said.
>
>A client with out-of-band information about the server state should not
>be hindered by HTTP as to the conditionals it makes a request with.
>As long as the server response is correct in relation to those
>conditionals it cannot cause problematic side effects elsewhere than 
>the
>client itself, since all intermediaries will be considering that
>request+reply in isolation.
>
>Amos
>
Received on Monday, 18 March 2013 08:59:30 GMT

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