Cookie from a http_request_t - howto?

[rovar]

Is there a simple example of how to read a cookie, or some other header value, like "Host"  from an ngx_http_request_t ? 
I see $variables discussed, but I'm not sure how to retrieve them. 

I am guessing it has something to do with ngx_http_script_compile/run, but I don't fully understand the concept. 
Those functions seem to rely on a config file, but what if I'm not interested in configuring the variable, I just wish to
retrieve Host or a specific Cookie from each request. 

Also, at which stage in an upstream module process is the http request filled? 
Are they available in both init_<module>_peer and get_<module>_peer? 

Thanks,

Rick

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,94077,94077#msg-94077