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Re: PROPOSAL: Weak Validator definition [i101]

From: Henrik Nordstrom <henrik@henriknordstrom.net>
Date: Tue, 18 Mar 2008 15:50:41 +0100
To: Robert Siemer <Robert.Siemer-httpwg@backsla.sh>
Cc: Werner Baumann <werner.baumann@onlinehome.de>, ietf-http-wg@w3.org
Message-Id: <1205851841.18425.85.camel@HenrikLaptop>

On Mon, 2008-03-17 at 03:44 +0100, Robert Siemer wrote:

> Current practice is to deliver weak etags that never match later on. 
> These are based on "weak last-modified" dates. I hope that this 
> useless practice ("we always generate ETags") never makes it into the 
> spec!

It's imho not a bad practice. Returning a reasonable weak ETag is better
than just Last-Modified. In Apache even the weak ETag is very likely to
change on subsecond modification (change in size or inode). The weak
ETag stays unchanged on modification only if the object is overwritten
in-place with no change in size. (assuming the default configuration for
ETag generation, administrators may relax this to just "no change in
modification time or size")

You should not read much more into a weak etag than that it's a weak
validator, in which category "modification time" is included. Both means
'is likely "good enough" to be equivalent'. Not 'is "good enough" to be
equivalent'. A weak validator signals "likely to be considered equal by
the recipient". A weak etag probably (but not guaranteed to) signals
this stronger than just last-modified, but still is just "likely to be
considered equal".

Received on Tuesday, 18 March 2008 14:52:32 UTC

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