var buffer = require('buffer');
var bufferpack = require('bufferpack');    
var fmt;
var pack = function(data) {
    var header = '000000000000000000xxxxxxxxxxxxxx';
    var packlen = data.length;
    var packarr = [header, packlen, data];
    var fmtStr = 'sis';     //字符串长整型字符串
    var fmtStrRes = [];
    var idx = 0;
    for (k in fmtStr) {
        v = fmtStr[k];
        if(v=='i') {    //signed long
            fmtStrRes.push('i');
        }else if(v=='b'){   //signed char
            fmtStrRes.push('b');
        }else if(v=='s'){   //char[]
            var _strLength = packarr[idx].length;
            fmtStrRes.push(_strLength.toString()+'s');
        }
        idx += 1;
    }
    fmt = '<'+fmtStrRes.join('');
    console.log('packarr='+packarr);
    console.log('fmt='+fmt);
    res = bufferpack.pack(fmt, packarr);
    console.log('pack=', res);
}

var packed = pack('xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx');

var unpacked = bufferpack.unpack(fmt, packed, 0);

为什么 unpack的时候报错了，求解，应该是没有问题才对啊