Index: includes/bootstrap.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/bootstrap.inc,v
retrieving revision 1.220
diff -u -F^f -r1.220 bootstrap.inc
--- includes/bootstrap.inc	21 Aug 2008 19:36:36 -0000	1.220
+++ includes/bootstrap.inc	5 Sep 2008 20:23:13 -0000
@@ -634,6 +634,8 @@ function drupal_page_header() {
  *
  */
 function drupal_page_cache_header($cache) {
+  global $user;
+
   // Set default values:
   $last_modified = gmdate('D, d M Y H:i:s', $cache->created) . ' GMT';
   $etag = '"' . md5($last_modified) . '"';
@@ -655,9 +657,28 @@ function drupal_page_cache_header($cache
   header("Last-Modified: $last_modified");
   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");
+  if (variable_get('reverse_proxy', 0)) {
+    $cache_lifetime = variable_get('cache_lifetime', 0);
+    if (!$cache_lifetime) {
+      // If cache_lifetime is not set, then assume 15 minutes
+      $cache_lifetime = 900;
+    }
+
+    // Set a cookie that indicates whether a user is logged in or not, this is used
+    // by the caching proxies
+    $logged_in = ($user->uid) ? 1 : 0;
+    setcookie('DRUPAL_LOGGED_IN', $logged_in, time() + $cache_lifetime, '/');
+
+    // The following headers makes for better caching for anonymous users when using
+    // reverse proxies such as Squid or Varnish
+    header("Expires: ". gmdate("D, d M Y H:i:s", time() + $cache_lifetime) ." GMT");
+    header("Cache-Control: public, max-age=". $cache_lifetime);
+  }
+  else {
+    // Use the old header which do 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: sites/default/default.settings.php
===================================================================
RCS file: /cvs/drupal/drupal/sites/default/default.settings.php,v
retrieving revision 1.14
diff -u -F^f -r1.14 default.settings.php
--- sites/default/default.settings.php	21 Aug 2008 19:36:39 -0000	1.14
+++ sites/default/default.settings.php	5 Sep 2008 20:23:13 -0000
@@ -268,6 +268,18 @@
  * logging, statistics and access management systems; if you are unsure
  * about this setting, do not have a reverse proxy, or Drupal operates in
  * a shared hosting environment, this setting should remain commented out.
+ *
+ * Configuration for Squid
+ *   acl cookie_logged_in     req_header Set-Cookie DRUPAL_LOGGED_IN=1
+ *   cache deny cookie_logged_in
+ *   acl cookie_logged_in_set req_header     Cookie DRUPAL_LOGGED_IN=1
+ *   cache deny cookie_logged_in_set
+ *   
+ * Configuration for Varnish
+ *  if (req.http.Cookie && req.http.Cookie ~ "DRUPAL_LOGGED_IN=1") {
+ *    pass;
+ *  }
+ *
  */
 #   'reverse_proxy' => TRUE, // Leave the comma here.
 /**