nodejs 为什么我下载的图片是空的呢？

var http = require('http'); var querystring = require('querystring'); var fs = require('fs'); var data = '{"uid":"502acbd07fc640768ac3621bfaa55be4","pageSize":10,"pageIndex":0}'; var moment = require('moment'); var shijian = moment().format('YYYYMMDD') console.log(shijian); var optiOns= { hostname: '016888.net', port: 80, //端口号 https 默认端口 443，http 默认的端口号是 80 path: '/personProduct/getPersonProductByType.action', method: 'POST', headers: {'Connection': 'keep-alive','User-Agent': 'Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.86 Safari/537.36', 'Content-Type': 'application/json;charset=', 'Accept': 'application/json, text/Javascript', 'Content-Length': 70} }; var req=http.request(options,function(res){ res.setEncoding('utf-8'); var respOnseString= ''; res.on('data', function(data) { responseString += data; }); res.on('end', function() { var resultObject = JSON.parse(responseString); for(var i=0;i < resultObject.data.rows.length;i++){ var r=resultObject.data.rows[i]; for (var b = 0; b < r.pics.picList.length; b++) { console.log(r.pics.picList[b]+'保存完成'); fs.writeFile('./imgs/'+shijian+'_'+r.code+'_'+b+'.jpg',r.pics.picList[b],'binary', function (err) { if (err) throw err; }); } } }); req.on('error', function(e) { console.log('-----error-------',e); }); }); req.write(data); req.end();