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Re: ETags and concurrency control

From: Robert Siemer <Robert.Siemer-httpwg@backsla.sh>
Date: Mon, 28 Apr 2008 13:44:47 +0200
To: Brian Smith <brian@briansmith.org>
Cc: 'Pablo Castro' <Pablo.Castro@microsoft.com>, atom-protocol@imc.org, 'HTTP Working Group' <ietf-http-wg@w3.org>
Message-ID: <20080428114447.GA5764@polar.elf12.net>

On Sun, Apr 27, 2008 at 10:01:15PM -0700, Brian Smith wrote:

> I can't think of a reason that weak ETag comparison should be forbidden for
> non-safe HTTP requests (PUT or DELETE), as long as people are using matching
> weak ETags only for "semantically equivalent" representations. Strong ETag
> comparison should only be needed for range requests. Try bringing it up on
> the HTTP Working Group mailing list (ietf-http-wg@w3.org) and see what they
> have to say.

That raises three issues:

1) It's not in RFC2616 (weak comparison for non-GET) and so it's not on 
   RFC2616bis charta.

2) Weak ETags don't mean "semantically equivalent" anymore. They mean 
   nothing now (see i101). As of today there is no replacement text 
   proposed for i101, but weak ETags could get degraded to something way 
   weaker than Last-Modified.

   (mail archive and
   http://www3.tools.ietf.org/wg/httpbis/trac/ticket/101
   )

3) the upgrade/downgrade questions will come up again:
   match_weak("xyz", W/"xyz")

   is 'true' or 'false'?


And 2) makes even future considerations for extending the weak etag 
mechanism much harder.

Regards,
Robert
Received on Monday, 28 April 2008 11:43:50 GMT

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