[PATCH] Upstream: Cache stale responses if they may be revalidated.

[Maxim Dounin]

Hello!

On Wed, Dec 16, 2015 at 03:37:27PM +0100, Thorvaldur Thorvaldsson wrote:

> # HG changeset patch
> # User Thorvaldur Thorvaldsson <thorvaldur.thorvaldsson at gmail.com>
> # Date 1450190015 -3600
> #      Tue Dec 15 15:33:35 2015 +0100
> # Node ID 2c1f00c7f857c12587f0ac47323f04c6a881843a
> # Parent  def9c9c9ae05cfa7467b0ec96e76afa180c23dfb
> Upstream: Cache stale responses if they may be revalidated.
> 
> Previously, the proxy cache would never store stale responses, e.g.,
> when the "Cache-Control" header contained "max-age=0", even if the
> "proxy_cache_revalidate" directive was "on" and the response included
> both an "ETag" and a "Last-Modified" header. This came as a surprise.
> 
> Now, a header like "Cache-Control: max-age=0, must-revalidate" can be
> used along with an ETag/Last-Modified header to make nginx cache
> responses that always require revalidation, e.g., when authorization is
> required (and cheap).

[...]

> diff -r def9c9c9ae05 -r 2c1f00c7f857 src/http/ngx_http_upstream.c
> --- a/src/http/ngx_http_upstream.c Sat Dec 12 10:32:58 2015 +0300
> +++ b/src/http/ngx_http_upstream.c Tue Dec 15 15:33:35 2015 +0100
> @@ -2815,11 +2815,16 @@
>              valid = ngx_http_file_cache_valid(u->conf->cache_valid,
>                                                u->headers_in.status_n);
>              if (valid) {
> -                r->cache->valid_sec = now + valid;
> +                valid += now;
> +                r->cache->valid_sec = valid;
>              }
>          }
> 
> -        if (valid) {
> +        if (valid > now
> +            || (r->upstream->conf->cache_revalidate
> +                && (u->headers_in.etag
> +                    || u->headers_in.last_modified_time != -1)))
> +        {
>              r->cache->date = now;
>              r->cache->body_start = (u_short) (u->buffer.pos - u->buffer.start);

As far as I see, this still allows caching of all
responses, even ones without Cache-Control/Expires/X-Accel-Expires
and proxy_cache_valid configured.  This is not something that 
should happen because of revalidation enabled.

You may want to rethink how the patch is expected to work.

[...]

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