unparsed_uri setting in ngx_http_subrequest?

[Maxim Dounin]

Hello!

On Sat, Feb 27, 2010 at 10:34:15AM -0800, Brian Pane wrote:

> On Sat, Feb 27, 2010 at 10:17 AM, Maxim Dounin <mdounin at mdounin.ru> wrote:
> > Hello!
> >
> > On Sat, Feb 27, 2010 at 09:39:56AM -0800, Brian Pane wrote:
> >
> >> I think I've found a separate bug in ngx_http_subrequest:
> >>
> >> ngx_http_core_module.c, line 2080 (in 0.8.33):
> >>     sr->headers_in = r->headers_in;
> >>
> >> This results in a bitwise copy of headers_in from the parent request
> >> to the subrequest.  Inside headers_in is a list:
> >> typedef struct {
> >>     ngx_list_t                        headers;
> >>     // ...
> >> } ngx_http_headers_in_t;
> >>
> >> When you do a bitwise copy of an ngx_list_t, you end up with a broken
> >> list.  Specifically, sr->headers_in->list->last in the subrequest
> >> points to the last node in the r->headers_in.list.part chain in the
> >> parent request.  It should instead point to the last node in the
> >> subrequest's sr->headers_in.list.part chain.
> >>
> >> Thus if any module attempts to add more headers to the subrequest's
> >> sr->headers_in, they actually will be added to the parent request's
> >> r->headers_in instead.
> >>
> >> I ran into this problem in a module that needs to add extra request
> >> headers to a proxied subrequest.
> >
> > It is expected that r->headers_in represent headers got from
> > client (i.e. inbound headers).  It is not expected to be modified
> > by anything but nginx core when it reads headers from client (and
> > some modules which sets special variables there, like
> > r->headers_in.user).
> >
> > To add headers to proxied [sub]request you have to use means
> > provided by proxy module, specifically proxy_set_header
> > configuration directive.
> 
> I don't think proxy_set_header will work for what I'm doing,
> though, because I need to decide which headers to send
> to the upstream based on information that isn't known at

It is possible unless set of headers is infinite (i.e. set of 
header names, not values).  E.g. 

    proxy_set_header X-Something-1 $some_value_1;
    proxy_set_header X-Something-2 $some_value_2;
    proxy_set_header X-Something-3 $some_value_3;

Headers which values evaluate to empty string aren't sent.

Note well: proxy module itself uses this to provide ability to 
pass X-Forwarded-For header with client's address added (see 
$proxy_add_x_forwarded_for variable).

> configuration time.  Is there a recommended programmatic
> way for another module to submit additional request headers
> to the proxy module on a per-request basis?

There is no one.

Maxim Dounin