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Re: WGLC p6 4.2.1

From: Adrien W. de Croy <adrien@qbik.com>
Date: Mon, 18 Mar 2013 12:19:17 +0000
To: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
Cc: "Amos Jeffries" <squid3@treenet.co.nz>, "ietf-http-wg@w3.org" <ietf-http-wg@w3.org>
Message-Id: <em2c99bf04-f567-48b2-b6c9-34d6777aad66@bombed>


------ Original Message ------
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
To: "Adrien W. de Croy" <adrien@qbik.com>
Cc: "Amos Jeffries" <squid3@treenet.co.nz>; "ietf-http-wg@w3.org" 
<ietf-http-wg@w3.org>
Sent: 19/03/2013 1:05:11 a.m.
Subject: Re: WGLC p6 4.2.1
>In message <em94119d23-43b0-4de4-a3e3-8c30e8a40bfc@bombed>, "Adrien W. 
>de Croy" writes:
>
>>>>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,=20
>>>>and
>>>>discard its own copy.
>>>
>>>Uhm, so you're saying I can clean the entire cache with bogos IMS
>>>requests ?
>>
>>that's not the point.
>
>It very much is: A cache would have to be stupid to make that
>assumption, and we should not be protecting stupid mistakes with
>the specification, we should make things work.
it was just one example.  There are potentially limitless ones.

fundamentally, we're changing the semantics.

Do we even know what that may break?

I don't recall seeing a discussion about it on list, but maybe it was 
discussed in a meeting.

>
>No matter what you write in the specification, you will have IMS
>headers with non-server-supplied timestamps, because it is possible
>and there are legitimate use-cases.
I agree it's possible, I'm not sure about the use-cases. at least not 
the one you mentioned before.

Sending If-Modified-Since currently indicates you have a copy.  So we're 
looking to break that too?

A cache needs to know which version is being re-validated, whether its 
own or the clients.  It's probably not a train wreck, but it's 
convoluted enough trying to figure out what on earth is going on when 
you get a 304 back and you were checking multiple items, some with ETag 
some with IMS.

I never got a straight answer on my query about whether it's valid to 
send a 304 back to a request that contained If-None-Match with a 
different ETag.  Personally I consider that a server bug as well.

>
>We can discuss if the text expresses this optimally, but there is
>no way the text can put this particular genie back in his bottle.
I think we will need to make further changes, to refer to these changes 
elsewhere in the spec, e.g. where it's discussed that to make a 
conditional request one adds If-Modified-Since using the content of a 
previous Last-Modified response header.


>
>--
>Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
>phk@FreeBSD.ORG | TCP/IP since RFC 956
>FreeBSD committer | BSD since 4.3-tahoe
>Never attribute to malice what can adequately be explained by 
>incompetence.
>
Received on Monday, 18 March 2013 12:19:41 GMT

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