Hi all, I would like to contribute a patch to provide the cached file
age as a variable $proxy_cache_age , which can then be used together
with add_header Age $proxy_cache_age.

The age calculation is not RFC2616 compliant (13.2.3) as it doesn't take
into consideration the cached origin Age header and Date. Is it feasible
to extract this from the cached headers?

--
regards,
wK

Index: http/modules/ngx_http_proxy_module.c
===================================================================
--- http/modules/ngx_http_proxy_module.c (revision 405)
+++ http/modules/ngx_http_proxy_module.c (working copy)
@@ -117,6 +117,9 @@
static ngx_int_t
ngx_http_proxy_internal_body_length_variable(ngx_http_request_t *r,
ngx_http_variable_value_t *v, uintptr_t data);
+static ngx_int_t
+ ngx_http_proxy_cache_age_variable(ngx_http_request_t *r,
+ ngx_http_variable_value_t *v, uintptr_t data);
static ngx_int_t ngx_http_proxy_rewrite_redirect(ngx_http_request_t *r,
ngx_table_elt_t *h, size_t prefix);

@@ -580,6 +583,11 @@
{ ngx_string("proxy_internal_body_length"), NULL,
ngx_http_proxy_internal_body_length_variable, 0, NGX_HTTP_VAR_NOHASH, 0 },

+#if (NGX_HTTP_CACHE)
+ { ngx_string("proxy_cache_age"), NULL,
+ ngx_http_proxy_cache_age_variable, 0, NGX_HTTP_VAR_NOHASH, 0 },
+#endif
+
{ ngx_null_string, NULL, NULL, 0, 0, 0 }
};

@@ -3052,3 +3060,33 @@

v->uri = u->uri;
}
+
+#if (NGX_HTTP_CACHE)
+static ngx_int_t
+ngx_http_proxy_cache_age_variable(ngx_http_request_t *r,
+ ngx_http_variable_value_t *v, uintptr_t data)
+{
+ ngx_int_t age;
+
+ if (r->cache == NULL || r->cache->date == 0) {
+ v->not_found = 1;
+ return NGX_OK;
+ }
+
+ v->valid = 1;
+ v->no_cacheable = 0;
+ v->not_found = 0;
+
+ v->data = ngx_pnalloc(r->connection->pool, NGX_TIME_T_LEN);
+
+ if (v->data == NULL) {
+ return NGX_ERROR;
+ }
+
+ age = r->start_sec - r->cache->date;
+ v->len = ngx_sprintf(v->data, "%T", age) - v->data;
+
+ return NGX_OK;
+}
+
+#endif
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