手动创建 HTTP 响应时,如何获取Server
和ETag
* HTTP/1.1 200 OK
* Date: Mon, 23 Apr 2012 23:44:52 GMT
* Server: Apache/2.2.3 (Red Hat) <-----
* Last-Modified: Fri, 16 Sep 2005 18:08:50 GMT
* ETag: "421142-2f-400e77c517080" <-----
* Accept-Ranges: bytes
* Content-Length: 47
* Content-Type: text/plain
* Connection: close