handle NGX_AGAIN properly

Julien Zefi jzefip at gmail.com
Thu Jul 18 04:37:59 UTC 2013

Hi all,

thanks for the help but after more changes and taking in count your
suggestions i am still stuck with the problem (it cannot be in Lua, must be
done in C as i am streaming binary data).

If anyone of you is interested, i will put a budget of 100USD for who is
interested into fix the test case as required, for more details send me a
private email to discuss the requirements and what is expected as result.


On Sun, Jul 14, 2013 at 10:57 PM, Yichun Zhang (agentzh)
<agentzh at gmail.com>wrote:

> Hello!
> On Sun, Jul 14, 2013 at 8:43 PM, Julien Zefi wrote:
> >
> > Sorry by bother you again but i still cannot figure out how some
> internals
> > are not working as i expect. I have take in count your suggestions and
> wrote
> > a new test case (file attached).
> >
> 1. You should simply call  ngx_http_output_filter(r, NULL); in your
> r->write_event_handler, but you set r->write_event_handler to
> ngx_http_test_stream_handler which always emits brand new data. I'm
> guessing you don't really understand how the ngx_http_writer and
> ngx_http_set_write_handler functions are implemented in the Nginx
> core. Look harder.
> 2. You should not set r->header_only = 1 in your case because you're
> actually sending out the response body. Ensure that you know how a
> flag works before you start using it.
> 3. Another obvious mistake is that you incorrectly perform
>     r->main->count++;
> without decrementing it by calling ngx_http_finalize_request, which
> will certainly lead to request hang. Ensure that you understand this
> flag before using it.
> > The test case writes 12.3KB of data every 1ms, at some point it will
> raise
> > NGX_AGAIN but from there is not recovering, it keeps in the same state
> > forever, do you see any specific problem when handling the exception ?
> >
> This is trivial to implement by writing some Lua code using ngx_lua module:
>     location /t {
>         content_by_lua '
>            local message = "..."
>            for i = 1, 100 do
>                ngx.print(message)
>                ngx.flush(true)
>                ngx.sleep(0.001)
>            end
>         ';
>     }
> Maybe you can just use ngx_lua for your purposes without all the pain
> of understanding the nginx internals (you seem to lack a lot of
> knowledge here). If you insist in writing your own nginx C module,
> then just check out how ngx_lua implements all the APIs demonstrated
> in the example above. You can also check out the official
> documentation of ngx_lua:
>   http://wiki.nginx.org/HttpLuaModule
> Best regards,
> -agentzh
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