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Re: i37 - Vary and non-existant headers

From: Henrik Nordstrom <henrik@henriknordstrom.net>
Date: Thu, 15 Nov 2007 03:04:50 +0100
To: Jamie Lokier <jamie@shareable.org>
Cc: Adrien de Croy <adrien@qbik.com>, "'HTTP Working Group'" <ietf-http-wg@w3.org>
Message-Id: <1195092290.30372.80.camel@henriknordstrom.net>
On ons, 2007-11-14 at 19:06 +0000, Jamie Lokier wrote:

> As there's no harm in occasional mis-matches, and I think there is
> some harm in preventing code like the example from working in a simple
> automatic dynamic caching system, I propose that empty headers be
> treated as distinct from present headers with any value, and that the
> rules are the same for all headers, unless particularly good reasons
> why that's a problem for a particular header can be shown.

It's in fact what the specs says. The problem is the language which
doesn't fire the right associations in many peoples mind. It's meant to
fire thoughts about headers as data sets, but for many people just
leaves a questionmark.

Vary is a selector on what to compare between two request. Think of it
as a grep selecting the interesting data of the requests before compare.

If you read "13.6 Caching Negotiated Responses" it's spelled out quite
in detail. Reading this section is mandatory before discussing ETag or
Vary. If you know this section then most (all?) questionmarks regarding
ETag or Vary in other sections kind of disappears.


Received on Thursday, 15 November 2007 02:05:04 UTC

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