[PATCH v3] Upstream: prioritise X-Accel-Expire over Cache-Control and Expire

[Vadim Fedorenko]

# HG changeset patch
# User Vadim Fedorenko <vadim.fedorenko at cdnnow.ru>
# Date 1650406016 -10800
#      Wed Apr 20 01:06:56 2022 +0300
# Node ID e04dac22328020cf8d8abcc4863b982b513b0c80
# Parent  a736a7a613ea6e182ff86fbadcb98bb0f8891c0b
Upstream: prioritise X-Accel-Expire over Cache-Control and Expire

RFC7234 explicitly says that cache recipient MUST ignore Expires
header if response includes Cache-Control header with max-age or
s-maxage directives. Previously Cache-Control was ignored if it
was after Expires in reply headers.

At the same time documentation states that there is special header
X-Accel-Expires that controls the behavior of nginx and should be
prioritized over other cache-specific headers and this patch
implements this priority.

More informantion could be found in ticket #964.
---
 src/http/ngx_http_upstream.c | 62 +++++++++++++++++++++++++-----------
 src/http/ngx_http_upstream.h |  6 ++++
 2 files changed, 50 insertions(+), 18 deletions(-)

diff -r a736a7a613ea -r e04dac223280 src/http/ngx_http_upstream.c
--- a/src/http/ngx_http_upstream.c	Tue Feb 08 17:35:27 2022 +0300
+++ b/src/http/ngx_http_upstream.c	Wed Apr 20 01:06:56 2022 +0300
@@ -2350,6 +2350,32 @@
 
 
 static void
+ngx_http_upstream_validate_cache_headers(ngx_http_request_t *r, ngx_http_upstream_t *u)
+{
+    ngx_http_upstream_headers_in_t *uh = &u->headers_in;
+    if (uh->x_accel_expires != NULL  &&
+        !(u->conf->ignore_headers & NGX_HTTP_UPSTREAM_IGN_XA_EXPIRES)) {
+        u->cacheable = uh->x_accel_expires_c;
+        r->cache->valid_sec = uh->x_accel_expires_n;
+        return;
+    }
+
+    if (uh->cache_control.elts != NULL &&
+        !(u->conf->ignore_headers & NGX_HTTP_UPSTREAM_IGN_CACHE_CONTROL)) {
+        u->cacheable = uh->cache_control_c;
+        r->cache->valid_sec = uh->cache_control_n;
+        return;
+    }
+
+    if (uh->expires != NULL  &&
+        !(u->conf->ignore_headers & NGX_HTTP_UPSTREAM_IGN_EXPIRES)) {
+        u->cacheable = uh->expires_c;
+        r->cache->valid_sec = uh->expires_n;
+    }
+}
+
+
+static void
 ngx_http_upstream_process_header(ngx_http_request_t *r, ngx_http_upstream_t *u)
 {
     ssize_t            n;
@@ -2468,6 +2494,11 @@
 
             continue;
         }
+#if (NGX_HTTP_CACHE)
+        if (u->cacheable) {
+            ngx_http_upstream_validate_cache_headers(r, u);
+        }
+#endif
 
         break;
     }
@@ -4735,10 +4766,6 @@
         return NGX_OK;
     }
 
-    if (r->cache->valid_sec != 0 && u->headers_in.x_accel_expires != NULL) {
-        return NGX_OK;
-    }
-
     start = h->value.data;
     last = start + h->value.len;
 
@@ -4746,7 +4773,7 @@
         || ngx_strlcasestrn(start, last, (u_char *) "no-store", 8 - 1) != NULL
         || ngx_strlcasestrn(start, last, (u_char *) "private", 7 - 1) != NULL)
     {
-        u->cacheable = 0;
+        u->headers_in.cache_control_c = 0;
         return NGX_OK;
     }
 
@@ -4771,16 +4798,15 @@
                 continue;
             }
 
-            u->cacheable = 0;
             return NGX_OK;
         }
 
         if (n == 0) {
-            u->cacheable = 0;
             return NGX_OK;
         }
 
-        r->cache->valid_sec = ngx_time() + n;
+        u->headers_in.cache_control_c = 1;
+        u->headers_in.cache_control_n = ngx_time() + n;
     }
 
     p = ngx_strlcasestrn(start, last, (u_char *) "stale-while-revalidate=",
@@ -4856,18 +4882,18 @@
         return NGX_OK;
     }
 
-    if (r->cache->valid_sec != 0) {
+    expires = ngx_parse_http_time(h->value.data, h->value.len);
+
+    if (expires == NGX_ERROR || expires < ngx_time()) {
         return NGX_OK;
     }
 
-    expires = ngx_parse_http_time(h->value.data, h->value.len);
-
-    if (expires == NGX_ERROR || expires < ngx_time()) {
-        u->cacheable = 0;
-        return NGX_OK;
-    }
-
-    r->cache->valid_sec = expires;
+    if (u->headers_in.expires_c) {
+        expires = ngx_min(expires, u->headers_in.expires_n);
+    }
+    u->headers_in.expires_n = expires;
+    u->headers_in.expires_c = 1;
+
     }
 #endif
 
@@ -4906,14 +4932,12 @@
 
         switch (n) {
         case 0:
-            u->cacheable = 0;
-            /* fall through */
-
         case NGX_ERROR:
             return NGX_OK;
 
         default:
-            r->cache->valid_sec = ngx_time() + n;
+            u->headers_in.x_accel_expires_c = 1;
+            u->headers_in.x_accel_expires_n = ngx_time() + n;
             return NGX_OK;
         }
     }
@@ -4924,7 +4948,8 @@
     n = ngx_atoi(p, len);
 
     if (n != NGX_ERROR) {
-        r->cache->valid_sec = n;
+            u->headers_in.x_accel_expires_c = 1;
+            u->headers_in.x_accel_expires_n = ngx_time() + n;
     }
     }
 #endif
diff -r a736a7a613ea -r e04dac223280 src/http/ngx_http_upstream.h
--- a/src/http/ngx_http_upstream.h	Tue Feb 08 17:35:27 2022 +0300
+++ b/src/http/ngx_http_upstream.h	Wed Apr 20 01:06:56 2022 +0300
@@ -294,9 +294,15 @@
 
     off_t                            content_length_n;
     time_t                           last_modified_time;
+    ngx_int_t                        cache_control_n;
+    ngx_int_t                        expires_n;
+    ngx_int_t                        x_accel_expires_n;
 
     unsigned                         connection_close:1;
     unsigned                         chunked:1;
+    unsigned                         cache_control_c;
+    unsigned                         expires_c;
+    unsigned                         x_accel_expires_c;
 } ngx_http_upstream_headers_in_t;