When r != r->connection->data

[Yichun Zhang (agentzh)]

Hello!

On Sun, Mar 15, 2015 at 5:05 PM, Marat Dakota wrote:
> In a few modules I've found a trick:
>
> if (r != r->connection->data)
>     r->connection->data = r;
>

Careful. This is a common hack to cheat nginx's
ngx_http_postpone_filter_module when the in-stock subrequest model
cannot serve us well.

When the currently serving (sub)request is not the request doing
output, r is not equal to r->connection->data. The latter means the
currently *active* request. This is needed for the postpone filter
module mentioned above. You need to carefully study the filter module
(and ngx_http_finalize_request) before doing any serious subrequest
programming. And nginx subrequests are really a mess for nontrivial
things IMHO (no offense to the official designer) and better avoid
them :)

Regards,
-agentzh