Symfony\Component\HttpFoundation\Request::getTrustedHosts PHP Method

    public static function getTrustedHosts()
    {
        return self::$trustedHostPatterns;
    }

 /**
  * Determine if an url is external
  *
  * @param string $url
  *
  * @return bool
  */
 public function isExternalUrl($url)
 {
     $trustedHostPatterns = $this->request->getTrustedHosts();
     if (count($trustedHostPatterns) > 0) {
         $parse = parse_url($url);
         foreach ($trustedHostPatterns as $pattern) {
             if (preg_match($pattern, $parse['host'])) {
                 return false;
             }
         }
     }
     return true;
 }