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From Nick Kew <>
Subject Re: [users@httpd] Disabling the "Vary" header / Potential repercussions
Date Fri, 04 May 2007 05:28:50 GMT

On 4 May 2007, at 03:49, Fred Tyler wrote:

> [chop]

This is OTTOMH.

> 1. Add "Header unset Vary" to httpd.conf. The problem with this is
> that it just doesn't work. I don't know why, but I've stuck it in
> about 100 different places and it doesn't make any difference. That
> "Vary" header never goes away.

That'll be order of execution.

> 2. Add "SetEnv force-no-vary" to httpd.conf. The problem with this is
> that it also degrades the connection to HTTP/1.0, which presumably has
> the side effect of killing HTTP pipelining. On a heavily trafficked
> site with a lot of small files requested on each page view, this is
> not a good trade-off.

I don't think so.  HTTP/1.0 defaults to keepalive off, but still allows
keepalive.  Pipelining beyond that isn't AFAIK well-supported in today's
browsers, so isn't really an issue.  But I haven't looked at force-no- 
which presumably has a specific purpose.

> 1. Modify src/main/http_protocol.c so that "force-no-vary" does not
> also trigger "force-no-response".

Both of those are hacks.  I'd say go ahead if and only if you can trace
and understand the exact purpose of them, and how that'll affect them.

> 2. Modify src/modules/standard/mod_negotiation.c by commenting out the
> entire section that sets the Vary and TCN headers in the first place.

It might be as simple as reordering mod_negotiation's adding the headers
and mod_headers hacking them.  But I'd need to look.

Nick Kew

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