Hello!
On Wed, Dec 22, 2010 at 02:26:56PM -0500, Sirsiwal, Umesh wrote:
> I am trying to write a module which uses a number of subrequests
> to talk to backend servers. Combines the responses and sends
> them back to the client. The communication with the backend
> server is using HTTP and I am using proxy_pass for that.
>
> The peculiarity in our setup is that on failure-retry I need to
> use a different URI than the original request. Current, proxy
> reinit request does not regenerate request hence cannot be used
> for the purpose. I tried using the error_page in the subrequest
> location to point to a different location. But, it seems that
> the error_page is not evaluated on subrequest. The only option I
> can think of is for my module to detect error and issue a new
> subrequest.
Fallback via error_page should work ok for subrequests. It may be
disabled from post_subrequest handler though: if you use it and
return something like NGX_OK from there (i.e. not NGX_HTTP_...
error), error_page handling won't be executed assuming you've
handled problem yourself.
Take a look at ngx_http_finalize_request(), it's more or less
clear how it works. Relevant parts are:
if (r != r->main && r->post_subrequest) {
rc = r->post_subrequest->handler(r, r->post_subrequest->data, rc);
}
...
if (rc >= NGX_HTTP_SPECIAL_RESPONSE
|| rc == NGX_HTTP_CREATED
|| rc == NGX_HTTP_NO_CONTENT)
{
...
ngx_http_finalize_request(r, ngx_http_special_response_handler(r, rc));
return;
}
(ngx_http_special_response_handler() is where actual error_page handling
happens).
Maxim Dounin
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