? 147310-94.patch
? 147310-95.patch
? 147310-96.patch
? 147310-97.patch
? sites/all/modules
? sites/default/files
? sites/default/settings.php
Index: includes/bootstrap.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/bootstrap.inc,v
retrieving revision 1.263
diff -u -p -r1.263 bootstrap.inc
--- includes/bootstrap.inc	4 Jan 2009 16:15:54 -0000	1.263
+++ includes/bootstrap.inc	7 Jan 2009 05:31:33 -0000
@@ -720,10 +720,24 @@ function drupal_load($type, $name) {
  * @see page_set_cache()
  */
 function drupal_page_header() {
-  header("Expires: Sun, 19 Nov 1978 05:00:00 GMT");
-  header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
-  header("Cache-Control: store, no-cache, must-revalidate");
-  header("Cache-Control: post-check=0, pre-check=0", FALSE);
+  // Check if module_implements exists to avoid problems during installation.
+  $send_uncacheable_headers = TRUE;
+  if(function_exists('module_implements') && module_implements('expires')) {
+    // Pass FALSE to hook_expires because the page isn't coming from cache.
+    $lifetime = min(module_invoke_all('expires', FALSE));
+    if($lifetime > 0) {
+      $send_uncacheable_headers = FALSE;
+      header("Expires: " . gmdate(DATE_RFC1123, REQUEST_TIME + $lifetime));
+      header('Cache-Control: public, max-age=' . $lifetime);
+    }
+  }
+
+  if($send_uncacheable_headers) {
+    header("Expires: Sun, 19 Nov 1978 05:00:00 GMT");
+    header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
+    header("Cache-Control: store, no-cache, must-revalidate");
+    header("Cache-Control: post-check=0, pre-check=0", FALSE);
+  }
 }
 
 /**
@@ -756,9 +770,23 @@ function drupal_page_cache_header($cache
   header("Last-Modified: " . gmdate(DATE_RFC1123, $cache->created));
   header("ETag: $etag");
 
-  // The following headers force validation of cache:
-  header("Expires: Sun, 19 Nov 1978 05:00:00 GMT");
-  header("Cache-Control: must-revalidate");
+  // The following allows modules to specify their own cache expiration time.
+  $send_uncacheable_headers = TRUE;
+  if(count(module_implements('expires')) > 0) {
+    $lifetime = min(module_invoke_all('expires', TRUE));
+    $age = abs(REQUEST_TIME - $cache->created);
+    if($lifetime - $age > 0) {
+      $send_uncacheable_headers = FALSE;
+      header("Expires: " . gmdate(DATE_RFC1123, $cache->created + $lifetime));
+      header('Cache-Control: public, max-age=' . max(0, $lifetime - $age)); 
+    }
+  }
+
+  if($send_uncacheable_headers) {
+    // Use the old header which does not get cached.
+    header("Expires: Sun, 19 Nov 1978 05:00:00 GMT");
+    header("Cache-Control: must-revalidate");
+  }
 
   if (variable_get('page_compression', TRUE)) {
     // Determine if the browser accepts gzipped data.
Index: modules/system/system.api.php
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.api.php,v
retrieving revision 1.9
diff -u -p -r1.9 system.api.php
--- modules/system/system.api.php	4 Jan 2009 19:56:51 -0000	1.9
+++ modules/system/system.api.php	7 Jan 2009 05:31:33 -0000
@@ -144,6 +144,24 @@ function hook_exit($destination = NULL) 
   db_query('UPDATE {counter} SET hits = hits + 1 WHERE type = 1');
 }
 
+/** 
+ * Suggest an expiration time to send to the client as the expires HTTP header.
+ *
+ * Only use this hook if you need your pages to be cacheable by reverse proxies
+ * or CDNs. If multiple modules return a value for this function, the earliest
+ * timestamp is honored. The simplest implementation of this function would
+ * return the number of seconds to cache all pages. More advanced implementations
+ * could return a different value depending on the current page.
+ *
+ * @param $page_is_cached
+ *   Whether the response is from cache
+ * @return
+ *   Number of seconds before the current page expires.
+ */
+function hook_expires($page_is_cached) {
+  return 0;
+}
+
 /**
  * Insert closing HTML.
  *