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RE: IE vs vary header

From: Alex Rousskov <rousskov@measurement-factory.com>
Date: Wed, 19 Jun 2002 10:03:20 -0600 (MDT)
To: Julian Reschke <julian.reschke@gmx.de>
cc: ietf-http-wg@w3.org
Message-ID: <Pine.BSF.4.10.10206190930490.3187-100000@measurement-factory.com>

On Wed, 19 Jun 2002, Julian Reschke wrote:

> Of course you are right -- if and only if "user-agent" is added to
> the Vary header. I'd like to avoid that, because that adds yet
> another dimension. 

Oh, I see. In this context, you cannot negotiate depending on user
agent without adding User-Agent to the Vary header and you have to
negotiate based on user agent if you want to work around user agent
bugs.

> And even if I do that, the second scenario still can happen,
> right?

The second scenario should not happen if you mark Vary-less responses
as uncachable. You have to mark them as uncachable for the
Apache-suggested work-around to make sense in your case (IMO).

> What are these other, more robust mechanisms?

There are probably several such mechanisms. The simplest is to mark
all negotiated content as uncachable and return no Vary headers, but
there may be more elegant solutions. For example, would it be possible
to change the URL (using an HTTP redirect response) based on the
request headers or based on whatever you are using to negotiate? You
could redirect all IE clients to their own URL "space" that does not
use Vary while using default URLs for other clients.  Changing URLs
solves all solvable problems caused by broken caches. The redirection
and its side-effects must be handled transparently to the user and
content author, of course.

Alex.
Received on Wednesday, 19 June 2002 12:03:23 GMT

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