PHPSocketIO源码问题

    /**
     * Decodes a packet encoded in a base64 string.
     *
     * @param {String} base64 encoded message
     * @return {Object} with `type` and `data` (if any)
     */

    public static function decodeBase64Packet($msg, $binaryType) 
    {
        $type = self::$packetsList[$msg[0]];
        $data = base64_decode(substr($data, 1));
        return array('type'=> $type, 'data'=> $data);
    }