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