architecture of a module - processing a response from a subrequest

Mirko Dziadzka mirko.dziadzka at
Thu Jul 29 15:04:17 MSD 2010

Piotr Sikora wrote:
>> 6. intercept the response, do a second subrequest and modify the response
>> - should probably done in a filter?
> What exactly are you trying to achieve? 

Well - think of a kind of generic web-application filter plugin like an
ICAP based virus scanner or a web application firewall where the actuall
scanning is done on a second independent component (another process or
maybe even on another machine)

I want to intercept http-requests, reroute them with some additional
information to this second component, get a response from the second
component, allow, reject or modify the original request and send it to
the original target (may be a local php script or a proxy location)

The same with the response.

> Maybe you could use
> X-Accel-Redirect, eval module or ngx_lua [2] instead?

ngx_lua sounds very promising, but when I checked it out it states that:

"This module is at its very early phase of development and considered
highly experimental."

I'm not sure if this should run on a production website :-|

I will have a look at the X-Accel-Redirect implementation

>> Another question: I want to intercept ALL requests to nginx. Which phase
>> would you recommend for my handler? How can I assure, that I'm the first
>> handler in the chain?
> There is only one active content handler at the time. 

Well, as far as I understand nginx, there is an array of
phases[NGX_HTTP_CONTENT_PHASE].handlers which are asked to provide the
content. If a handler returns NGX_DECLINED, the next handler is asked. I
want to make sure to be the first in this array to see every request
independent from other configuration components.

I'm thinking about registering in the the pre-access phase to make
possible modifications on headers like the http-basic-auth header
visible to other modules.

Thanks for your help


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