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From Raphaël <>
Subject [users@httpd] Re: mod_cache_disk: how to avoid Vary: User-Agent?
Date Tue, 03 Nov 2015 01:04:45 GMT

still related to the previous post, but put simply:
I'd just appreciate to learn how to keep Apache from automatically
adding "User-Agent" to the "Vary" header.

thank you in advance

On Thu, Oct 22, 2015 at 11:51:31PM -0300, Raphaël Droz wrote:
> I recently received a dozens of AH00708: errors in my logs.
> Example:
> > (2)No such file or directory: AH00708: Cannot open data file /var/cache/apache2/mod_cache_disk/Y/Z/CLVvRR_4nNWabdUv_5wA.header.vary/B/z/
> Said file does not exist, only does the corresponding .header file.
> The cache is 455 MB, I don't know what could have happened and I
> activated debug loglevel for mod_cache_disk for next days in order to
> understand why the data file isn't created.
> ... but, looking at the header file I found the following line rather
> strange:
> [...]
> > Content-Encoding: gzip
> > Vary: User-Agent, User-Agent, User-Agent, User-Agent
> > Accept-Ranges: byte
> [...]
> - I've no occurrence of Vary either in /var/www nor in /etc/apache2
> - searching google retrieved a couple of similar results of this Vary: string
> The origin is probably the BrowserMatch directive which, by default are
> enabled in Debian's mods-available/setenvif.conf.
> (and mod_ssl depends upon mod_setenvif)
> This is how I realized that the cache coupled to setenvif in it's
> default configuration was *very* inefficient (disk-space).
> `Vary: User-Agent` is something we would rather avoid given the
> ridiculously huge number of combination for this string nowadays.
> From the last quick grep' I had 325 of them what could reduce my cache's
> size to a dozens of MB and increase proportionally it's efficiency.
> First, not really a question, but a couple of suggestions:
> - BrowserMatch should not blindly add to the Vary header but
>   addifnotexist (it's part of the mod_headers possibility in Apache 2.4
>   series isn't?)
> - mod_cache_disk documentation could state whether this duplication hurts or not
> - the default setenvif.conf may avoid use of "exotic"/"rare" default
>   BrowserMatch directives in case of <IfModule mod_cache.c>
> ... but then, following the objective to avoid a Vary: User-Agent, I
> found that I had two other BrowserMatch in default-ssl.conf.
> The second one about MSIE 7 to 10, in order to set ssl-unclean-shutdown.
> - I didn't find where is documented what this variable does internally
> - I guess this variable only affects mod_ssl behavior but nothing about
>   request header/data
> If the above is right, then is it pertinent with discard^W Vary:
> User-Agent if the content can't change according to the User-Agent.
> Maybe BrowserMatch could be more flexible about that.
> Anyway, I commented these two mod_ssl BrowserMatch directives (in case I
> would not care about broken? MSIE behaviors), but I'm still Vary'ing:
> User-Agent.
> I commented the ultimate SetEnvIfExpr my configuration contained
> (unrelated to browsers anyway) and egrep -ri '(Browser|SetEnvIf)'
> but still... Vary: User-Agent
> didn't brought up another clear source for this.
> Any hint about where this Vary's value could come from?
> thank you

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