protected function readBinaryData($length)
    {
        if ($length == 0) {
            $buff = "";
        } else {
            $buff = substr($this->content, $this->pos, $length);
            if (strlen($buff) != $length) {
                throw IOException::readError("");
            }
            $this->pos += $length;
        }

        return new CFData($buff, false);
    }