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.
diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 47f98cc..dda4046 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -2473,7 +2473,7 @@
#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;
