unparsed_uri setting in ngx_http_subrequest?

[Brian Pane]

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
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?

Thanks,
-Brian