Doesn't post_action do what you need?
http://wiki.nginx.org/HttpCoreModule#post_action

On Thu, Nov 3, 2011 at 09:06, forum_id <nginx-forum@nginx.us> wrote:

> I have a requirement for HTTP request filter. Whenever I receive a HTTP
> request this filter module should read the request and does some
> internal statistical work, it doesn't manipulate the request page nor
> creates response page. It just need to peep into request that's it.
> After this filter module, nginx HTTP server should continue to process
> the request and serve the response to user. Can we do it without a proxy
> handler, because nginx serves the responses directly here.
>
> Please help me.
>
> Posted at Nginx Forum:
> http://forum.nginx.org/read.php?2,217739,217739#msg-217739
>
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