Index: includes/bootstrap.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/bootstrap.inc,v
retrieving revision 1.145.2.12
diff -u -p -r1.145.2.12 bootstrap.inc
--- includes/bootstrap.inc	10 Dec 2008 18:16:03 -0000	1.145.2.12
+++ includes/bootstrap.inc	14 Jan 2009 17:01:57 -0000
@@ -240,6 +240,9 @@ function drupal_unset_globals() {
  *  TRUE if only containing valid characters, or FALSE otherwise.
  */
 function drupal_valid_http_host() {
+  if ($_SERVER['HTTP_HOST'] == '') {
+    return TRUE;
+  }
   $_SERVER['HTTP_HOST'] = strtolower($_SERVER['HTTP_HOST']);
   return preg_match('/^\[?(?:[a-z0-9-:\]_]+\.?)+$/', $_SERVER['HTTP_HOST']);
 }
@@ -255,6 +258,12 @@ function conf_init() {
   global $db_url, $db_prefix, $cookie_domain, $conf, $installed_profile;
   $conf = array();
 
+  // Some pre-HTTP/1.1 clients will not send a Host header. Ensure the key is
+  // defined for E_ALL compliance.
+  if (!isset($_SERVER['HTTP_HOST'])) {
+    $_SERVER['HTTP_HOST'] = '';
+  }
+
   if (!drupal_valid_http_host()) {
     // HTTP_HOST is invalid, e.g. if containing slashes it may be an attack.
     header('HTTP/1.1 400 Bad Request');