content handler priority

[Jeff Kaufman]

Can a module add a content handler that runs before any other content handler?

For example, if someone has:

   location / {
      proxy_pass ...;
   }

or:

   location ~ \.(js|css|png|jpg|gif|swf|ico|pdf|mov|fla|zip|rar)$ {
        try_files $uri =404;
    }

then the content handler I set with:

    ngx_http_handler_pt* h = static_cast<ngx_http_handler_pt*>(
        ngx_array_push(&cmcf->phases[NGX_HTTP_CONTENT_PHASE].handlers));
    if (h == NULL) {
      return NGX_ERROR;
    }
    *h = my_content_handler;

won't run.  I can work around this by adding location blocks like:

    location ~ "\.pagespeed\.[a-z]{2}\.[^.]{10}\.[^.]+" {
       # let ngx_pagespeed's content handler run
    }
    location ~ "^/ngx_pagespeed_static/" {
       # let ngx_pagespeed's content handler run
    }

but is this something I can make the ngx_pagespeed module do by
default, without configuration?

Is it safe for me to modify
cmcf->phases[NGX_HTTP_CONTENT_PHASE].handlers by inserting my handler
at the beginning instead of appending it?  Will that make it run
first?

Motivation: ngx_pagespeed (a mod_pagespeed port) has two cases where
it needs to be sure it's controlling the handler.  One is where the
request is for anything in the top level ngx_pagespeed_static
directory, like
"http://example.com/ngx_pagespeed_static/js_defer.0.js" and the other
is for any path like
"http://example.com/foo/bar/Puzzle.jpg.pagespeed.ce.91_WewrLtP.jpg".
These are dynamically generated, and any other handler won't know how
to produce them.  My content handler already knows how to return
NGX_DECLINED for unrelated requests but it doesn't get invoked if
something else claims the content handling first.

Jeff