Fixing ngx_http_slice_module use with named locations

[Roman Arutyunyan]

Hello Mindaugas,

On Wed, May 04, 2016 at 02:20:30PM +0100, Mindaugas Rasiukevicius wrote:
> Hi,
> 
> There is a problem with ngx_http_slice_module when it is used together
> with an internal redirection to a named location.  It results in Nginx
> workers caching incorrect content and spinning in an infinite loop.
> Consider the following fragment:
> 
>     location /foo {
>         error_page 550 = @bar;
>         return 550;
>     }
>     location @bar {
>         slice ...;
>         proxy_pass ...;
>         proxy_cache ...;
>         ...
>     }
> 
> In ngx_http_slice_body_filter(), the slice context is associated with
> the subrequest:
> 
>     ngx_http_set_ctx(sr, ctx, ngx_http_slice_filter_module);
> 
> However, the location re-match is triggered for the subrequests trying
> to fetch each slice.  In the ngx_http_named_location() function:
> 
>             /* clear the modules contexts */
>             ngx_memzero(r->ctx, sizeof(void *) * ngx_http_max_module);
> 
> So, the slice context gets lost.  There are several ways to fix this.
> Unless you want an API to preserve the context, one simple fix would be
> to get the context via r->parent (if ctx == NULL && r != r->main).
> 
> What would be the preferred way to fix this?

We have fixed the issue in http://hg.nginx.org/nginx/rev/d16ba0ea3434

Thanks for reporting this.

-- 
Roman Arutyunyan