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Re: Require UAs and intermediary caches to assume Vary: User-Agent

From: Willy Tarreau <w@1wt.eu>
Date: Thu, 18 Oct 2012 08:11:29 +0200
To: Poul-Henning Kamp <phk@phk.freebsd.dk>
Cc: Simon Pieters <simonp@opera.com>, ietf-http-wg@w3.org
Message-ID: <20121018061129.GG7517@1wt.eu>
On Wed, Oct 17, 2012 at 08:15:51AM +0000, Poul-Henning Kamp wrote:
> --------
> In message <op.wmbam8vtidj3kv@simons-macbook-pro.local>, "Simon Pieters" writes
> :
> 
> >It would be useful if the spec required that UAs and intermediary caches  
> >act as if all responses had Vary: User-Agent specified, since many pages  
> >on the Web serve different content depending on the User-Agent header but  
> >do not bother specifying Vary: User-Agent.
> >
> >I would like this to be filed as a new issue in the issue tracker.
> 
> Fine with me, provided you _first_ reduce the number of distinct
> U-A strings on the web to something reasonable, lets say no more than 25 ?

One of my customers encodes them in logs to reduce log size, so basically
each new UA string gets assigned a 16-bit ID which is reused everytime the
same string is encountered. Last time we checked, we saw something like
30k different strings in one day worth of logs ! Some browsers emit all
the combinations of their plugins and versions, making the UA currently
useless.

Another benefit of getting much less different UAs is that their
identification string could significantly shrink then.

Willy
Received on Thursday, 18 October 2012 06:12:16 GMT

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