Remove unnecessary check in ngx_http_stub_status_handler()

[Maxim Dounin]

Hello!

On Tue, Jan 05, 2021 at 01:24:04PM +0000, Chris Newton wrote:

> I was desk checking return codes generated in handlers following calls to
> ngx_http_send_header(), and noticed what appears to be an unnecessary test
> in ngx_http_stub_status_handler() -- or rather, I think the test should
> always evaluate as true, and if somehow it isn't odd things could occur -
> at least an additional ALERT message would be logged, as well as some
> unnecessary work performed.
> 
> As such, I'd like to propose the following change:
> 
> *--- a/src/http/modules/ngx_http_stub_status_module.c*
> *+++ b/src/http/modules/ngx_http_stub_status_module.c*
> @@ -106,11 +106,7 @@ ngx_http_stub_status_handler(ngx_http_request_t *r)
>      if (r->method == NGX_HTTP_HEAD) {
>          r->headers_out.status = NGX_HTTP_OK;
> 
> -        rc = ngx_http_send_header(r);
> -
> -        if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) {
> -            return rc;
> -        }
> +        return ngx_http_send_header(r);
>      }
> 
>      size = sizeof("Active connections:  \n") + NGX_ATOMIC_T_LEN
> 
> 
> On a successful call to ngx_http_send_header() I believe that
> r->header_only will be set true and otherwise I'd expect one of those error
> checks to evaluate true, so unconditionally returning the value from
> ngx_http_send_header() seems 'cleaner'.
> 
> If the test were to somehow fail, then processing would fall through and
> try the ngx_http_send_header() call again (resulting in the ALERT message),
> as well as performing other additional work that should be unnecessary when
> making a HEAD request
> 
> That test seems to be SOP after calling ngx_http_send_header(), but it
> seems inappropriate when that function is called within an "r->method ==
> NGX_HTTP_HEAD" block.

After looking at this I tend to think that this optimization is 
simply wrong, and, for example, image_filter or xslt filter make 
this obvious.  I've committed a patch which completely removes this 
optimization from the stub_status, as well as similar optimization 
in ngx_http_send_response() (used by "return" and "empty_gif"):

https://hg.nginx.org/nginx/rev/43a0a9e988be

Thanks for reporting this.

-- 
Maxim Dounin
http://mdounin.ru/