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From Florian Zumbiehl <>
Subject mod_deflate Vary header
Date Thu, 03 Nov 2005 12:08:21 GMT

While configuring and testing my new and shiny Apache 2, I noticed that
mod_deflate sends a Vary: Content-Encoding header whenever a resource
could potentially be compressed, no matter whether it actually is
compressed in that particular response. That certainly should
work, but in situations where the server's bandwidth is the bottleneck,
wouldn't it be a good idea to omit that Vary: header when no compression
actually takes place? After all, any user agent should be able to cope
with uncompressed content - and when that is what is already "behind
the bottleneck", like in some local proxy cache, a Vary: Content-Encoding
header on it would cause a request from a user agent supporting
compression to cause a reload of the compressed version from the slow
server rather than delivering the already locally-available uncompressed

When the bottleneck is at the client's end, it's completely different,
of course--which is why I'd consider a config option a good idea that
would allow the sending of a Vary: Content-Encoding in case of
uncompressed content to be disabled.

Cya, Florian

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