[nginx] Cache: ignore stale-if-error for 4xx and 5xx codes.

[Roman Arutyunyan]

details:   https://hg.nginx.org/nginx/rev/7015f26aef90
branches:  
changeset: 7702:7015f26aef90
user:      Roman Arutyunyan <arut at nginx.com>
date:      Wed Jul 29 13:28:04 2020 +0300
description:
Cache: ignore stale-if-error for 4xx and 5xx codes.

Previously the stale-if-error extension of the Cache-Control upstream header
triggered the return of a stale response for all error conditions that can be
specified in the proxy_cache_use_stale directive.  The list of these errors
includes both network/timeout/format errors, as well as some HTTP codes like
503, 504, 403, 429 etc.  The latter prevented a cache entry from being updated
by a response with any of these HTTP codes during the stale-if-error period.

Now stale-if-error only works for network/timeout/format errors and ignores
the upstream HTTP code.  The return of a stale response for certain HTTP codes
is still possible using the proxy_cache_use_stale directive.

This change also applies to the stale-while-revalidate extension of the
Cache-Control header, which triggers stale-if-error if it is missing.

Reported at
http://mailman.nginx.org/pipermail/nginx/2020-July/059723.html.

diffstat:

 src/http/ngx_http_upstream.c |  2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diffs (12 lines):

diff -r 8ca47f094d5b -r 7015f26aef90 src/http/ngx_http_upstream.c
--- a/src/http/ngx_http_upstream.c	Fri Aug 14 12:45:52 2020 +0300
+++ b/src/http/ngx_http_upstream.c	Wed Jul 29 13:28:04 2020 +0300
@@ -2473,7 +2473,7 @@ ngx_http_upstream_test_next(ngx_http_req
 #if (NGX_HTTP_CACHE)
 
         if (u->cache_status == NGX_HTTP_CACHE_EXPIRED
-            && ((u->conf->cache_use_stale & un->mask) || r->cache->stale_error))
+            && (u->conf->cache_use_stale & un->mask))
         {
             ngx_int_t  rc;