[PATCH] Upstream: avoid closing client connection in edge case

[Maxim Dounin]

Hello!

On Tue, Mar 08, 2016 at 10:40:12PM -0500, Justin Li wrote:

> # HG changeset patch
> # User Justin Li <jli.justinli at gmail.com>
> # Date 1457494315 18000
> #      Tue Mar 08 22:31:55 2016 -0500
> # Node ID 80d1d2148e4bd82eb27e50fba91fa36fed039871
> # Parent  c5f81dcf97a79576138917501c9a6cc6f53ee930
> Upstream: avoid closing client connection in edge case.
> 
> If proxy_cache is enabled, and proxy_no_cache tests true, it was previously
> possible for the client connection to be closed after a 304. The fix is to
> recheck r->header_only after the final cacheability is determined, and end the
> request if no longer cacheable.
> 
> Example configuration:
> 
> proxy_cache foo;
> proxy_cache_bypass 1;
> proxy_no_cache 1;
> 
> If a client sends If-None-Match, and the upstream server returns 200 with a
> matching ETag, no body should be returned to the client. At the start of
> ngx_http_upstream_send_response proxy_no_cache is not yet tested, thus cacheable
> is still 1 and downstream_error is set.
> 
> However, by the time the downstream_error check is done in process_request,
> proxy_no_cache has been tested and cacheable is set to 0. The client connection
> is then closed, regardless of keepalive.
> 
> diff -r c5f81dcf97a7 -r 80d1d2148e4b src/http/ngx_http_upstream.c
> --- a/src/http/ngx_http_upstream.c	Thu Mar 03 21:14:19 2016 +0300
> +++ b/src/http/ngx_http_upstream.c	Tue Mar 08 22:31:55 2016 -0500
> @@ -2861,6 +2861,11 @@ ngx_http_upstream_send_response(ngx_http
>          ngx_http_file_cache_free(r->cache, u->pipe->temp_file);
>      }
>  
> +    if (r->header_only && !u->cacheable && !u->store) {
> +        ngx_http_upstream_finalize_request(r, u, 0);
> +        return;
> +    }
> +
>  #endif
>  
>      p = u->pipe;

Committed, thanks.

-- 
Maxim Dounin
http://nginx.org/