Forum OpenACS Q&A: How to use ns_register_filter to establish a route to be served by NaviServer

We are currently using the reverse proxy with great success. It handles what we want it to quite nicely. We have come up with a case that we are wondering about though. Is there a way to specify a route that will fall through and be served by NaviServer?

Here is an example:

# I have a route /some-site-loc/* that gets forwarded to a target but, I want two of the sub-routes to be handled else where.
# I want a separate target to handle requests to the sub-route /some-site-loc/names/*; this filter works as expected
# I want NaviServer to handle the sub-route /some-site-loc/ns-special/*; can this be done?

ns_register_filter postauth * /some-site-loc/names/* ::revproxy::upstream -target $target_1_url -url_rewrite_callback my::rewrite_url
ns_register_filter postauth * /some-site-loc/ns-special/* some_call ; # this route I want NaviServer to serve.
ns_register_filter postauth * /some-site-loc/* ::revproxy::upstream -target $target_2_url -url_rewrite_callback my::rewrite_url

The requests to target_1_url and target_2_url work well and as expected. Is there something that I can put in the place of some_call, in the second filter above, that will cause a request to /some-site-loc/ns_special/* to be served by NaviServer itself?

Thanks,

-Tony Kirkham

I have been unable to find what to use in place of "some_call" in

ns_register_filter postauth /some-site-loc/ns-special/* some_call

to obtain the desired behavior. Owing to the fact that I do not really understand how the filters work, I tried to copy other ns_register_filter calls I could find in other places and, trying to follow your suggestions, I attempted to write a proc that called things like rp_filter and then returned filter_break which I placed in the place of "some_call" above. It did prevent the calling of any later filter but, it did not render the requested page.

I continued reading through the documentation that you referenced and found the call ns_shortcut_filter that only takes when method urlPattern as arguments. If I replace the middle call in my original post with

ns_shortcut_filter postauth * /some-site-loc/ns-special/*

It works exactly how I want!

Is this the call I should use for this purpose, or is there something better and are there any negative side effects of making this call? Like I mentioned, I do not really understand how the filters work. I have read through the request processor documentation but, have not found anything specifically related to the filters and how they work. Is there documentation somewhere that would help me get a better understanding?

Thank you very much for all of your help. I am a bit slow at times with my responses but, I really appreciate and value your help.

-Tony

Here is a diagram to visualize the differences between procs in the filter chain (filter procs) and the usual request content handlers ((pre-) registered procs stored on disk or in handlers).

Note that the filters are less efficient, since for every incoming request, all filters procs of a filter chain are sequentially matched and are potentially executed, unless a filter proc terminates the chain explicitly. This happens for every filter chain. Under certain uncaught error conditions, some of the steps are skipped.