Upstream: cache revalidation with conditional requests.

The following new directives are introduced: proxy_cache_revalidate,
fastcgi_cache_revalidate, scgi_cache_revalidate, uwsgi_cache_revalidate.
Default is off.  When set to on, they enable cache revalidation using
conditional requests with If-Modified-Since for expired cache items.

As of now, no attempts are made to merge headers given in a 304 response
during cache revalidation with headers previously stored in a cache item.
Headers in a 304 response are only used to calculate new validity time
of a cache item.

4 files changed, 52 insertions, 4 deletions

diff --git a/src/http/modules/ngx_http_fastcgi_module.c b/src/http/modules/ngx_http_fastcgi_module.c
index dd79418a2..51672e227 100644
--- a/src/http/modules/ngx_http_fastcgi_module.c
+++ b/src/http/modules/ngx_http_fastcgi_module.c
@@ -405,6 +405,13 @@ static ngx_command_t  ngx_http_fastcgi_commands[] = {
       offsetof(ngx_http_fastcgi_loc_conf_t, upstream.cache_lock_timeout),
       NULL },
 
+    { ngx_string("fastcgi_cache_revalidate"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_FLAG,
+      ngx_conf_set_flag_slot,
+      NGX_HTTP_LOC_CONF_OFFSET,
+      offsetof(ngx_http_fastcgi_loc_conf_t, upstream.cache_revalidate),
+      NULL },
+
 #endif
 
     { ngx_string("fastcgi_temp_path"),
@@ -563,7 +570,8 @@ static ngx_str_t  ngx_http_fastcgi_hide_headers[] = {
 #if (NGX_HTTP_CACHE)
 
 static ngx_keyval_t  ngx_http_fastcgi_cache_headers[] = {
-    { ngx_string("HTTP_IF_MODIFIED_SINCE"), ngx_string("") },
+    { ngx_string("HTTP_IF_MODIFIED_SINCE"),
+      ngx_string("$upstream_cache_last_modified") },
     { ngx_string("HTTP_IF_UNMODIFIED_SINCE"), ngx_string("") },
     { ngx_string("HTTP_IF_NONE_MATCH"), ngx_string("") },
     { ngx_string("HTTP_IF_MATCH"), ngx_string("") },
@@ -2336,6 +2344,7 @@ ngx_http_fastcgi_create_loc_conf(ngx_conf_t *cf)
     conf->upstream.cache_valid = NGX_CONF_UNSET_PTR;
     conf->upstream.cache_lock = NGX_CONF_UNSET;
     conf->upstream.cache_lock_timeout = NGX_CONF_UNSET_MSEC;
+    conf->upstream.cache_revalidate = NGX_CONF_UNSET;
 #endif
 
     conf->upstream.hide_headers = NGX_CONF_UNSET_PTR;
@@ -2582,6 +2591,9 @@ ngx_http_fastcgi_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
     ngx_conf_merge_msec_value(conf->upstream.cache_lock_timeout,
                               prev->upstream.cache_lock_timeout, 5000);
 
+    ngx_conf_merge_value(conf->upstream.cache_revalidate,
+                              prev->upstream.cache_revalidate, 0);
+
 #endif
 
     ngx_conf_merge_value(conf->upstream.pass_request_headers,
diff --git a/src/http/modules/ngx_http_proxy_module.c b/src/http/modules/ngx_http_proxy_module.c
index cf68711cd..404607511 100644
--- a/src/http/modules/ngx_http_proxy_module.c
+++ b/src/http/modules/ngx_http_proxy_module.c
@@ -465,6 +465,13 @@ static ngx_command_t  ngx_http_proxy_commands[] = {
       offsetof(ngx_http_proxy_loc_conf_t, upstream.cache_lock_timeout),
       NULL },
 
+    { ngx_string("proxy_cache_revalidate"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_FLAG,
+      ngx_conf_set_flag_slot,
+      NGX_HTTP_LOC_CONF_OFFSET,
+      offsetof(ngx_http_proxy_loc_conf_t, upstream.cache_revalidate),
+      NULL },
+
 #endif
 
     { ngx_string("proxy_temp_path"),
@@ -622,7 +629,8 @@ static ngx_keyval_t  ngx_http_proxy_cache_headers[] = {
     { ngx_string("Keep-Alive"), ngx_string("") },
     { ngx_string("Expect"), ngx_string("") },
     { ngx_string("Upgrade"), ngx_string("") },
-    { ngx_string("If-Modified-Since"), ngx_string("") },
+    { ngx_string("If-Modified-Since"),
+      ngx_string("$upstream_cache_last_modified") },
     { ngx_string("If-Unmodified-Since"), ngx_string("") },
     { ngx_string("If-None-Match"), ngx_string("") },
     { ngx_string("If-Match"), ngx_string("") },
@@ -2454,6 +2462,7 @@ ngx_http_proxy_create_loc_conf(ngx_conf_t *cf)
     conf->upstream.cache_valid = NGX_CONF_UNSET_PTR;
     conf->upstream.cache_lock = NGX_CONF_UNSET;
     conf->upstream.cache_lock_timeout = NGX_CONF_UNSET_MSEC;
+    conf->upstream.cache_revalidate = NGX_CONF_UNSET;
 #endif
 
     conf->upstream.hide_headers = NGX_CONF_UNSET_PTR;
@@ -2710,6 +2719,9 @@ ngx_http_proxy_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
     ngx_conf_merge_msec_value(conf->upstream.cache_lock_timeout,
                               prev->upstream.cache_lock_timeout, 5000);
 
+    ngx_conf_merge_value(conf->upstream.cache_revalidate,
+                              prev->upstream.cache_revalidate, 0);
+
 #endif
 
     ngx_conf_merge_str_value(conf->method, prev->method, "");
diff --git a/src/http/modules/ngx_http_scgi_module.c b/src/http/modules/ngx_http_scgi_module.c
index f9c0d1427..9163c6b3c 100644
--- a/src/http/modules/ngx_http_scgi_module.c
+++ b/src/http/modules/ngx_http_scgi_module.c
@@ -262,6 +262,13 @@ static ngx_command_t ngx_http_scgi_commands[] = {
       offsetof(ngx_http_scgi_loc_conf_t, upstream.cache_lock_timeout),
       NULL },
 
+    { ngx_string("scgi_cache_revalidate"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_FLAG,
+      ngx_conf_set_flag_slot,
+      NGX_HTTP_LOC_CONF_OFFSET,
+      offsetof(ngx_http_scgi_loc_conf_t, upstream.cache_revalidate),
+      NULL },
+
 #endif
 
     { ngx_string("scgi_temp_path"),
@@ -369,7 +376,8 @@ static ngx_str_t ngx_http_scgi_hide_headers[] = {
 #if (NGX_HTTP_CACHE)
 
 static ngx_keyval_t  ngx_http_scgi_cache_headers[] = {
-    { ngx_string("HTTP_IF_MODIFIED_SINCE"), ngx_string("") },
+    { ngx_string("HTTP_IF_MODIFIED_SINCE"),
+      ngx_string("$upstream_cache_last_modified") },
     { ngx_string("HTTP_IF_UNMODIFIED_SINCE"), ngx_string("") },
     { ngx_string("HTTP_IF_NONE_MATCH"), ngx_string("") },
     { ngx_string("HTTP_IF_MATCH"), ngx_string("") },
@@ -1093,6 +1101,7 @@ ngx_http_scgi_create_loc_conf(ngx_conf_t *cf)
     conf->upstream.cache_valid = NGX_CONF_UNSET_PTR;
     conf->upstream.cache_lock = NGX_CONF_UNSET;
     conf->upstream.cache_lock_timeout = NGX_CONF_UNSET_MSEC;
+    conf->upstream.cache_revalidate = NGX_CONF_UNSET;
 #endif
 
     conf->upstream.hide_headers = NGX_CONF_UNSET_PTR;
@@ -1333,6 +1342,9 @@ ngx_http_scgi_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
     ngx_conf_merge_msec_value(conf->upstream.cache_lock_timeout,
                               prev->upstream.cache_lock_timeout, 5000);
 
+    ngx_conf_merge_value(conf->upstream.cache_revalidate,
+                              prev->upstream.cache_revalidate, 0);
+
 #endif
 
     ngx_conf_merge_value(conf->upstream.pass_request_headers,
diff --git a/src/http/modules/ngx_http_uwsgi_module.c b/src/http/modules/ngx_http_uwsgi_module.c
index 0635299e8..9c5d76213 100644
--- a/src/http/modules/ngx_http_uwsgi_module.c
+++ b/src/http/modules/ngx_http_uwsgi_module.c
@@ -289,6 +289,13 @@ static ngx_command_t ngx_http_uwsgi_commands[] = {
       offsetof(ngx_http_uwsgi_loc_conf_t, upstream.cache_lock_timeout),
       NULL },
 
+    { ngx_string("uwsgi_cache_revalidate"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_FLAG,
+      ngx_conf_set_flag_slot,
+      NGX_HTTP_LOC_CONF_OFFSET,
+      offsetof(ngx_http_uwsgi_loc_conf_t, upstream.cache_revalidate),
+      NULL },
+
 #endif
 
     { ngx_string("uwsgi_temp_path"),
@@ -402,7 +409,8 @@ static ngx_str_t ngx_http_uwsgi_hide_headers[] = {
 #if (NGX_HTTP_CACHE)
 
 static ngx_keyval_t  ngx_http_uwsgi_cache_headers[] = {
-    { ngx_string("HTTP_IF_MODIFIED_SINCE"), ngx_string("") },
+    { ngx_string("HTTP_IF_MODIFIED_SINCE"),
+      ngx_string("$upstream_cache_last_modified") },
     { ngx_string("HTTP_IF_UNMODIFIED_SINCE"), ngx_string("") },
     { ngx_string("HTTP_IF_NONE_MATCH"), ngx_string("") },
     { ngx_string("HTTP_IF_MATCH"), ngx_string("") },
@@ -1130,6 +1138,7 @@ ngx_http_uwsgi_create_loc_conf(ngx_conf_t *cf)
     conf->upstream.cache_valid = NGX_CONF_UNSET_PTR;
     conf->upstream.cache_lock = NGX_CONF_UNSET;
     conf->upstream.cache_lock_timeout = NGX_CONF_UNSET_MSEC;
+    conf->upstream.cache_revalidate = NGX_CONF_UNSET;
 #endif
 
     conf->upstream.hide_headers = NGX_CONF_UNSET_PTR;
@@ -1370,6 +1379,9 @@ ngx_http_uwsgi_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
     ngx_conf_merge_msec_value(conf->upstream.cache_lock_timeout,
                               prev->upstream.cache_lock_timeout, 5000);
 
+    ngx_conf_merge_value(conf->upstream.cache_revalidate,
+                              prev->upstream.cache_revalidate, 0);
+
 #endif
 
     ngx_conf_merge_value(conf->upstream.pass_request_headers,