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

    public function getETags()
    {
        return preg_split('/\s*,\s*/', $this->headers->get('if_none_match'), null, PREG_SPLIT_NO_EMPTY);
    }

 public function createContexts(Request $request)
 {
     $map = array('request_method' => $request->getMethod(), 'request_uri' => $request->getRequestUri(), 'request_route' => $request->attributes->get('_route'), 'request_host' => $request->getHost(), 'request_port' => $request->getPort(), 'request_scheme' => $request->getScheme(), 'request_client_ip' => $request->getClientIp(), 'request_content_type' => $request->getContentType(), 'request_acceptable_content_types' => $request->getAcceptableContentTypes(), 'request_etags' => $request->getETags(), 'request_charsets' => $request->getCharsets(), 'request_languages' => $request->getLanguages(), 'request_locale' => $request->getLocale(), 'request_auth_user' => $request->getUser(), 'request_auth_has_password' => !is_null($request->getPassword()));
     // Attributes from newer versions.
     if (method_exists($request, 'getEncodings')) {
         $map['request_encodings'] = $request->getEncodings();
     }
     if (method_exists($request, 'getClientIps')) {
         $map['request_client_ips'] = $request->getClientIps();
     }
     return $map;
 }