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

    private function getUrlencodedPrefix($string, $prefix)
    {
        if (0 !== strpos(rawurldecode($string), $prefix)) {
            return false;
        }

        $len = strlen($prefix);

        if (preg_match(sprintf('#^(%%[[:xdigit:]]{2}|.){%d}#', $len), $string, $match)) {
            return $match[0];
        }

        return false;
    }