[nginx] Upstream: using the "Age" header when caching responses.

[Maxim Dounin]

details:   http://freenginx.org/hg/nginx/rev/8cdab3d89c44
branches:  
changeset: 9305:8cdab3d89c44
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Thu Jul 18 19:39:39 2024 +0300
description:
Upstream: using the "Age" header when caching responses.

As long as the "Age" header is present and not ignored, it is now
respected when caching responses per "Cache-Control: max-age", reducing
cache validity time.

diffstat:

 src/http/ngx_http_upstream.c |  69 ++++++++++++++++++++++++++++++++++++++++++-
 src/http/ngx_http_upstream.h |   4 ++
 2 files changed, 71 insertions(+), 2 deletions(-)

diffs (155 lines):

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -136,6 +136,8 @@ static ngx_int_t
     ngx_table_elt_t *h, ngx_uint_t offset);
 static ngx_int_t ngx_http_upstream_process_vary(ngx_http_request_t *r,
     ngx_table_elt_t *h, ngx_uint_t offset);
+static ngx_int_t ngx_http_upstream_process_age(ngx_http_request_t *r,
+    ngx_table_elt_t *h, ngx_uint_t offset);
 static ngx_int_t ngx_http_upstream_copy_header_line(ngx_http_request_t *r,
     ngx_table_elt_t *h, ngx_uint_t offset);
 static ngx_int_t
@@ -293,6 +295,10 @@ static ngx_http_upstream_header_t  ngx_h
                  ngx_http_upstream_copy_multi_header_lines,
                  offsetof(ngx_http_headers_out_t, link), 0 },
 
+    { ngx_string("Age"),
+                 ngx_http_upstream_process_age, 0,
+                 ngx_http_upstream_copy_header_line, 0, 0 },
+
     { ngx_string("X-Accel-Expires"),
                  ngx_http_upstream_process_accel_expires, 0,
                  ngx_http_upstream_copy_header_line, 0, 0 },
@@ -475,6 +481,7 @@ ngx_conf_bitmask_t  ngx_http_upstream_ig
     { ngx_string("Cache-Control"), NGX_HTTP_UPSTREAM_IGN_CACHE_CONTROL },
     { ngx_string("Set-Cookie"), NGX_HTTP_UPSTREAM_IGN_SET_COOKIE },
     { ngx_string("Vary"), NGX_HTTP_UPSTREAM_IGN_VARY },
+    { ngx_string("Age"), NGX_HTTP_UPSTREAM_IGN_AGE },
     { ngx_null_string, 0 }
 };
 
@@ -4939,13 +4946,14 @@ ngx_http_upstream_process_cache_control(
             return NGX_OK;
         }
 
-        if (n == 0) {
+        if (n <= u->headers_in.age_n) {
             u->headers_in.no_cache = 1;
             return NGX_OK;
         }
 
-        r->cache->valid_sec = ngx_time() + n;
+        r->cache->valid_sec = ngx_time() + n - u->headers_in.age_n;
         u->headers_in.expired = 0;
+        u->headers_in.max_age = 1;
     }
 
 extensions:
@@ -5109,6 +5117,7 @@ ngx_http_upstream_process_accel_expires(
             r->cache->valid_sec = ngx_time() + n;
             u->headers_in.no_cache = 0;
             u->headers_in.expired = 0;
+            u->headers_in.max_age = 0;
             return NGX_OK;
         }
     }
@@ -5122,6 +5131,7 @@ ngx_http_upstream_process_accel_expires(
         r->cache->valid_sec = n;
         u->headers_in.no_cache = 0;
         u->headers_in.expired = 0;
+        u->headers_in.max_age = 0;
     }
     }
 #endif
@@ -5373,6 +5383,61 @@ ngx_http_upstream_process_vary(ngx_http_
 
 
 static ngx_int_t
+ngx_http_upstream_process_age(ngx_http_request_t *r,
+    ngx_table_elt_t *h, ngx_uint_t offset)
+{
+    ngx_http_upstream_t  *u;
+
+    u = r->upstream;
+
+    if (u->headers_in.age) {
+        ngx_log_error(NGX_LOG_WARN, r->connection->log, 0,
+                      "upstream sent duplicate header line: \"%V: %V\", "
+                      "previous value: \"%V: %V\", ignored",
+                      &h->key, &h->value,
+                      &u->headers_in.age->key,
+                      &u->headers_in.age->value);
+        h->hash = 0;
+        return NGX_OK;
+    }
+
+    u->headers_in.age = h;
+    h->next = NULL;
+
+#if (NGX_HTTP_CACHE)
+    {
+    ngx_int_t  n;
+
+    if (u->conf->ignore_headers & NGX_HTTP_UPSTREAM_IGN_AGE) {
+        return NGX_OK;
+    }
+
+    if (r->cache == NULL || !u->cacheable) {
+        return NGX_OK;
+    }
+
+    n = ngx_atoi(h->value.data, h->value.len);
+
+    if (n != NGX_ERROR) {
+        u->headers_in.age_n = n;
+
+        if (u->headers_in.max_age) {
+            if (n >= r->cache->valid_sec - ngx_time()) {
+                u->headers_in.no_cache = 1;
+                return NGX_OK;
+            }
+
+            r->cache->valid_sec -= n;
+        }
+    }
+    }
+#endif
+
+    return NGX_OK;
+}
+
+
+static ngx_int_t
 ngx_http_upstream_copy_header_line(ngx_http_request_t *r, ngx_table_elt_t *h,
     ngx_uint_t offset)
 {
diff --git a/src/http/ngx_http_upstream.h b/src/http/ngx_http_upstream.h
--- a/src/http/ngx_http_upstream.h
+++ b/src/http/ngx_http_upstream.h
@@ -54,6 +54,7 @@
 #define NGX_HTTP_UPSTREAM_IGN_XA_BUFFERING   0x00000080
 #define NGX_HTTP_UPSTREAM_IGN_XA_CHARSET     0x00000100
 #define NGX_HTTP_UPSTREAM_IGN_VARY           0x00000200
+#define NGX_HTTP_UPSTREAM_IGN_AGE            0x00000400
 
 
 typedef struct {
@@ -287,14 +288,17 @@ typedef struct {
 
     ngx_table_elt_t                 *cache_control;
     ngx_table_elt_t                 *set_cookie;
+    ngx_table_elt_t                 *age;
 
     off_t                            content_length_n;
     time_t                           last_modified_time;
+    time_t                           age_n;
 
     unsigned                         connection_close:1;
     unsigned                         chunked:1;
     unsigned                         no_cache:1;
     unsigned                         expired:1;
+    unsigned                         max_age:1;
 } ngx_http_upstream_headers_in_t;