private function encodeByteSequence(array $bytes, int &$size): string
    {
        $ret = '';
        $size = 0;
        foreach ($bytes as $b) {
            if (isset($this->safeMap[$b])) {
                $ret .= $this->safeMap[$b];
                ++$size;
            } else {
                $ret .= self::$qpMap[$b];
                $size += 3;
            }
        }

        return $ret;
    }