putting input module before mod_proxy

Hello,
I want to write a module that will process incoming content, modify it, and
this content will be send further by mod_proxy. I found some
guides about writing input filter modules, also few examples of such modules.
I tried module described in
http://www.onlamp.com/pub/a/apache/2001/09/20/apache_2.html,
also I created input module based on mod_ext_filter. These modules work
if I mod_proxy is turned off. If I turn it on child crashes. Last
log entry is:

proxy: start body send

May be some of you tried to do something similar, or may be you know
some resources that could help me. I used google, but there's not much
about writing input filters.

Now I'm sitting and reading sources in the hope I will find any clues
but it's hard because I'm fresh to apache internals.
May be I'll try to debug running process and see what's going on.

I will appreciate any clues.

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**Pawel Niewiadomski**, new()foo-baz.com, http://new.foo-baz.com/
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