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

    public static function getTrustedHeaderName($key)
    {
        if (!array_key_exists($key, self::$trustedHeaders)) {
            throw new \InvalidArgumentException(sprintf('Unable to get the trusted header name for key "%s".', $key));
        }

        return self::$trustedHeaders[$key];
    }

 /**
  * @param string $uri
  * @param Request $request
  * @return Request
  */
 protected function createSubRequest($uri, Request $request)
 {
     $cookies = $request->cookies->all();
     $server = $request->server->all();
     // Override the arguments to emulate a sub-request.
     // Sub-request object will point to localhost as client ip and real client ip
     // will be included into trusted header for client ip
     try {
         if ($trustedHeaderName = Request::getTrustedHeaderName(Request::HEADER_CLIENT_IP)) {
             $currentXForwardedFor = $request->headers->get($trustedHeaderName, '');
             $server['HTTP_' . $trustedHeaderName] = ($currentXForwardedFor ? $currentXForwardedFor . ', ' : '') . $request->getClientIp();
         }
     } catch (\InvalidArgumentException $e) {
         // Do nothing
     }
     $server['REMOTE_ADDR'] = '127.0.0.1';
     $subRequest = TheliaRequest::create($uri, 'get', array(), $cookies, array(), $server);
     if ($request->headers->has('Surrogate-Capability')) {
         $subRequest->headers->set('Surrogate-Capability', $request->headers->get('Surrogate-Capability'));
     }
     if ($session = $request->getSession()) {
         $subRequest->setSession($session);
     }
     return $subRequest;
 }