packSync have same error

[fananchong]

(function () {
    'use strict';

    var _ = require('c-struct');

    module.exports = ClientVertifyReq;

    var CMD = NetMsgMsgId.ClientVertifyReqMsgID;
    var structName = 'ClientVertifyReq';
    function ClientVertifyReq() {
        this.size = 0;
        this.flag = 0;
        this.cmd = 0;
        this.Source = 0;
        this.UID = 0;
        this.Token = "";
    }

    var _ClientVertifyReq = new _.Schema({
        size: _.type.uint24,
        flag: _.type.uint8,
        cmd: _.type.uint16,
        Source: _.type.uint8,
        UID: _.type.uint64,
        Token: _.type.string(32)
    });

    _.register(structName, _ClientVertifyReq);

    var proto = ClientVertifyReq.prototype;

    proto.encode = function () {
        var self = this;
        self.size = 2 + 1 + 8 + 32;
        self.cmd = CMD;
        var buf = _.packSync(structName, {
            size: self.size,
            flag: self.flag,
            cmd: self.cmd,
            Source: self.Source,
            UID: self.UID,
            Token: self.Token
        });
        console.log('buf.length:', buf.length);
        return buf;
    };
})();

packSync have same error! console print the buf.length is 39. right value is 47.