http协议：request 和 response包组成

Request = Request-Line;

*((general-header|request-header|entity-header)CRLF);

CRLF

[message-body];

解析：（正则表达式语法结构）

1、request请求包的起始为请求行（Request-Line）

2、接着可以出现0个或者多个的general-header,request-header,entity-header。

顺序无关，但一般都按照以上顺序组成。

3、http的header都是键值对，以CRLF（回车换行）结束

4、三个header的区域以一个空行即CRLF结束

5、接着就是可选的message-body了

example:

GET /index.html HTTP/1.1
Accept:*?*
Accept-Language: zh-cn
User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)
Host:192.168.0.119
Connection: Keep-Alive

Response = Status-Line;

*((general-header|response-header|entity-header)CRLF);

CRLF

[message-body];

解析：同上

以上就是request和response的组成结构了，下面解析其各个元素，

general-header = 
	Cache-Control;
	|Connection;
	|Date;
	|Pragma;
	|Triler;
	|Transfe-Encoding;
	|Upgrade;
	|Via;
	|Warning;
entity-header =
    Allow;
    |Content-Encoding;
    |Content-Language;
    |Content-Lenght;
    |Content-Location;
    |Content-MD5;
    |Content-Range;
    |Content-Type;
    |Expires;
    |Last_Modified;
    |extension-header;
request-header = 
	Accept
	|Accept-Charset
	|Accept-Encoding;
	|Accept-Language;
	|Authorization;
	|Expect;
	|From;
	|Host;
	|If-Match;
	|If-Modified-Since;
    ...
    |User-Agent;
Request-Line = Method SP Request-URI SP HTTP-Version CRLF
response-header = 
	Accept-Ranges;
	|Age;
	|ETag;
	|Location;
	|Roxy-Authenticate;
	|Retry-After;
	|Server;
	|Vary;
	|WWW\Authenticate;
Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF