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RE: Expires header vs Vary header

From: Joris Dobbelsteen <joris.dobbelsteen@mail.com>
Date: Tue, 9 Dec 2003 19:43:24 +0100
To: "'Julian Reschke'" <julian.reschke@gmx.de>
Cc: "WWW WG" <ietf-http-wg@w3.org>
Message-Id: <20031209184130.9FEC41377B@dr-nick.w3.org>

Indeed the 200 works fine, but this doesn't automatically mean that 304
works fine too.

Better discuss this with the Mozilla developers first.

-Joris

> -----Original Message-----
> From: ietf-http-wg-request@w3.org 
> [mailto:ietf-http-wg-request@w3.org] On Behalf Of Julian Reschke
> Sent: Monday, 8 December 2003 22:50
> To: Jeffrey Mogul
> Cc: Alex Rousskov; ietf-http-wg@w3.org
> Subject: Re: Expires header vs Vary header
> 
> 
> Jeffrey Mogul wrote:
> 
> >     Yes, of course, but Julian says everything works fine 
> without the
> >     Vary. I find it strange that a Vary header would 
> prevent required
> >     updates.  But it is still possible, of course. Sorry 
> for not being
> >     clear.
> >     
> > Sorry, I guess I didn't make my own point clear.
> > 
> > Since RFC 2616 says "the cache MUST update the entry", without any 
> > language about "but this changes if Vary is used", then what Julian 
> > complained about seems to be an implementation bug, if your 
> > interpretation ("Mozilla does not update Expires header 
> when receiving 
> > a 304 response") was correct.
> > 
> > If so, I don't think we really need to discuss it on the 
> HTTP-WG list.  
> > This should go through Mozilla's bug-reporting process.
> 
> Seems so. I just wanted to find out first whether what I am 
> doing is supposed to work.
> 
> > On the other hand, Mozilla could simply have decided to disable 
> > caching for any response that carries a Vary header.  This is 
> > perfectly legal, and is a simple but effective way of ensuring that 
> > the Vary specification is observed.
> 
> Yes, but this is not the case. If the Vary header is present, 
> the Expires header on the first 200 response works as 
> expected, and furthermore the presence of the ETag causes 
> Mozilla to issue a conditional GET. This seems to indicate 
> that caching is supposed to work in presence of Vary.
> 
> > The problem is that we can only infer whether Mozilla is correctly 
> > updating its cache entry, so without some other information 
> (results 
> > of other tests, or reading the source code) we can't tell 
> whether this 
> > is a case of "Vary prevents required updates"
> > or "Vary disables caching".
> > 
> > I'm sure this has nothing at all to do with Schroedinger's cat.
> 
> :-)
> 
> --
> <green/>bytes GmbH -- http://www.greenbytes.de -- tel:+492512807760
> 
> 
Received on Tuesday, 9 December 2003 13:41:53 GMT

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