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From Ben Noordhuis <>
Subject Re: Vary:User-Agent, best practices, and making the web faster.
Date Sun, 05 Jun 2011 18:54:58 GMT
On Sun, Jun 5, 2011 at 13:42, Joshua Marantz <> wrote:
> This is a case where the content varies based on user-agent.  The
> recommendation on the mod_deflate doc page is add vary:user-agent for any
> non-image.  Can you think of a case where the absence of a vary:user-agent
> header causes broken behavior when the content doesn't vary?
> I'm not objecting to setting vary:user-agent when content varies: that's
> what it's for.  I'm objecting to setting vary:user-agent when content does
> *not* vary.  The mod_deflate documentation unambiguously recommends setting
> vary:user-agent, and my feeling is that this is to work around a bug that
> exists only in IE5 or pre-2007 patch of IE6.

Sorry, Joshua, we're conflating things. You raised two issues in your
original post:

1. Updating the mod_deflate documentation. Seems reasonable. The Vary:
UA recommendation was added in 2002 during a general clean-up of the
mod_deflate documentation and the commit log doesn't tell why. You
could open a bugzilla issue or raise it on the httpd-dev mailing list
(the former is the proper channel but the bugzilla is something of a

2. mod_pagespeed second-guessing the user's intent. That still seems
like an unambiguously bad idea. To touch on Magento again, its
documentation links (or linked) directly to that section of the
mod_deflate docs and people are using that. If your module scans for
and neutralizes that Header directive, you will break someone's site.

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