Drupal check that url is really external

drupal_check_that_url_is_really_external.php

/**
 * Check url for external property.
 */
function module_url_is_external($path) {
  global $base_url;
  $url_host = parse_url($path);
  if (empty($url_host['host']) && empty($url_host['scheme'])) {
    return FALSE;
  } else {
    if ($url_host['scheme'] . '://' . $url_host['host'] === substr($base_url, 0, strlen($url_host['scheme'] . '://' . $url_host['host']))) {
      return FALSE;
    }
  }
  return TRUE;
}