--- weblib.php.without-conditional-get	2007-08-21 14:10:15.000000000 +0200
+++ weblib.php	2007-08-21 17:40:15.000000000 +0200
@@ -2792,14 +2792,7 @@
 
     global $CFG, $THEME;
 
-    // Fix for IE6 caching - we don't want the filemtime('styles.php'), instead use now.
-    $lastmodified = time();
-
-    header('Last-Modified: ' . gmdate("D, d M Y H:i:s", $lastmodified) . ' GMT');
-    header('Expires: ' . gmdate("D, d M Y H:i:s", time() + $lifetime) . ' GMT');
-    header('Cache-Control: max-age='. $lifetime);
-    header('Pragma: ');
-    header('Content-type: text/css');  // Correct MIME type
+    ob_start();
 
     $DEFAULT_SHEET_LIST = array('styles_layout', 'styles_fonts', 'styles_color');
 
@@ -2850,6 +2843,24 @@
         }
     }
 
+/// Respond only with a 304 if the stylesheets have not been modified
+/// since they last were fetched
+    $modifiedtext = gmdate('D, d M Y H:i:s', $lastmodified) . ' GMT';
+    $etagtext = "\"$lastmodified\"";
+
+    if ($_SERVER['HTTP_IF_MODIFIED_SINCE'] == $modifiedtext && $_SERVER['HTTP_IF_NONE_MATCH'] == $etagtext) {
+        ob_end_clean();
+        header('HTTP/1.1 304 Not Modified');
+        header('Expires: ' . gmdate('D, d M Y H:i:s', time() + $lifetime) . ' GMT');
+        exit();
+    }
+    else {
+        header('Last-Modified: ' . $modifiedtext);
+        header('Expires: ' . gmdate('D, d M Y H:i:s', time() + $lifetime) . ' GMT');
+        header('Cache-Control: max-age='. $lifetime);
+        header('ETag: ' . $etagtext);
+        header('Content-type: text/css');  // Correct MIME type
+    }
 
 /// Get a list of all the files we want to include
     $files = array();
@@ -2941,6 +2952,8 @@
         }
     }
 
+    ob_end_flush();
+
     return $CFG->themewww.'/'.$themename;   // Only to help old themes (1.4 and earlier)
 }