public function getFullPath($path = '/')
    {
        if (mb_substr($path, 0, 1) == '/') {
            $path = mb_substr($path, 1);
        }

        $full_path = $this->getSandboxPath() . $path;

        if (strpos($full_path, '..')) {
            $full_path = realpath($full_path);

            if (mb_substr($full_path, 0, $this->sandbox_path_length) != $this->sandbox_path) {
                throw new InvalidArgumentException('$path is outside of the sanbox path');
            }
        }

        return $full_path;
    }