向web服务器发送请求包后，可以返回一些web服务器的信息
put /index.htm
几个回车后就会有信息，如
HTTP/1.0 400 Bad Request
Server: Squid/2.4.STABLE7
Mime-Version: 1.0
Date: Fri, 17 Oct 2003 00:45:09 GMT
Content-Type: text/html
Content-Length: 843
Expires: Fri, 17 Oct 2003 00:45:09 GMT
X-Squid-Error: ERR_INVALID_REQ 0
X-Cache: MISS from squid2.sohu.com
Proxy-Connection: close
<HTML><HEAD>
<TITLE>ERROR: The requested URL could not be retrieved</TITLE>
</HEAD
><BODY>
<H1>ERROR</H1>
<H2>The requested URL could not be retrieved</H2>
<HR>
<P>。。。
