有个爬虫项目，获取下载的报表：
await Runtime.evaluate({expression:
"__doPostBack('btnSearch','')"
});
页面的doPostBack触发查询，返回
HTTP/1.1 200 OK
Date: Thu, 11 Jan 2018 13:45:53 GMT
Server: Microsoft-IIS/6.0
X-UA-Compatible: IE=EmulateIE7
X-Powered-By: ASP.NET
X-AspNet-Version: 2.0.50727
Content-Disposition: attachment;filename=V1030105620180111214553346.xls
Content-Length: 19456
Cache-Control: private
Content-Type: application/octet-stream
要如何把获取response中的stream，并保存成本地文件