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From "Paul Fee" <>
Subject Header compression (or lack of) in mod_proxy
Date Tue, 07 Nov 2006 09:35:26 GMT
Hello all,

I'm using Apache as a HTTP proxy.  Regarding the request and
response headers, I've done some tests and noticed different
behaviour in the request and response direction.

The request headers are compressed (i.e. headers with same name are
merged into one header and comma separated). e.g.

hdr: value1
hdr: value2

hdr: value1, value2

This due to ap_get_mime_headers_core() calling
apr_table_compress().  It occurs in protocol.c before Apache even
detects that the incoming request is a proxy request.

The response headers on the other hand are read by mod_proxy in
ap_proxy_read_headers() which calls apr_table_add() but not

RFC 2616 states that header compression MUST be allowed, i.e. it's optional, therefore Apache's
behaviour is compliant.

However if a proxy is between a non-compliant client and/or server
then it may be best to leave the headers in their original form.
If a direct connection works and a proxied connection fails then
the proxy will be perceived as the problem.

Could someone point out a reason for the different behaviour in the
request and response path?

How about making the behaviour configurable so that it's consistent
in both directions and if necessary the headers can be left in
their original uncompressed form?

By the way, my tests were on httpd 2.0.59, however reading the
source for 2.2.3 suggests it has same behaviour.

Thanks for your time,

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