http介绍
参考资料
http://www.360doc.com/content/10/0930/17/3668821_57590979.shtml 理解http协议
http://www.cnblogs.com/TankXiao/archive/2012/10/10/2711777.html#introduction wireshark的使用介绍
http://www.cnblogs.com/renyuan/archive/2013/01/19/2867720.html tcp和http的区别
http://www.cnblogs.com/EricaMIN1987_IT/p/3837436.html http协议详解
http是什么？
HTTP协议（HyperText Transfer Protocol，超文本传输协议)：
从web服务器端传输超文本到本地客户端浏览器的传送协议
是一个基于请求与响应模式的、无状态的、应用层的协议
1.格式
HTTP协议
URI:Uniform Resource Indentifier 统一资源标识符
URL：Uniform Resource location 统一资源定位符
网页访问格式URL
protocol：//Host：port/path/to/file
获取资源
HTTP方法：GET PUT POST DELETE
GET:通过浏览器查看web服务器上的网页数据
PUT:从web服务器上将数据下载到本地
POST:提交数据到服务器
DELETE:删除服务器文件
MIME：Multipurpose Internet Mail Extension
多用途互联网邮件扩展
2.在协议栈中的位置
3.请求响应模型
由客户端（浏览器）向服务端（web服务器）发起请求，服务端响应请求的过程（单向）
4.CS工作流程（简单宏观理解，页面较大时，第三、四步会进行多次）
1）客户端向服务端建立连接（单击超级链接或手动输入网址） 三次握手
2）客户端发送请求数据（格式：URL、协议版本号、MIME信息） 请求获取网页内容信息
3）服务端接收请求并给予响应信息（状态行，信息有协议版本号、成功或失败的错误代码、MIME信息） 发送网页内容信息
4）客户端将接收的信息以浏览器显示，然后断开与服务器的连接 浏览器显示网页内容
5.抓包查看数据
这里以访问百度主页为例
下面的是抓包的内容
一次完整的百度主页web访问
1，2，3条表示TCP的三次握手，即建立连接请求
4.客户端开始向web服务器发送http报文以请求需要获取的数据（网页请求，以便服务器端的web软件可以识别请求内容并进行解析和处理），通过tcp传输HTTP报文请求信息
5.服务器发送一个TCP响应报文（对HTTP请求报文进行响应，这个回传不需要发送HTTP报文，因为响应信息tcp就可以完成），表示收到请求，正在处理中。。。
6.处理完请求，将客户端需要的请求数据（即网页文件以及MIME可以识别的图片、视频等），通过http协议报文进行封装（添加头部信息、版本号等内容）
7，8，9，10表示通过TCP协议将载有http报文的实体数据传输给客户端的过程（这里的数据通过两次传输才完毕）
11，12，13，14表示断开TCP会话的过程
下面就针对抓包进行较为详细的解答
第一次TCP握手：请求连接tcp连接（第一步）
Transmission Control Protocol, Src Port: 58168 (58168), Dst Port: 80 (80), Seq: 0, Len: 0 Source Port: 58168 Destination Port: 80 [Stream index: 0] [TCP Segment Len: 0] Sequence number: 0 (relative sequence number) Acknowledgment number: 0 Header Length: 32 bytes Flags: 0x002 (SYN) Window size value: 8192 [Calculated window size: 8192] Checksum: 0xda42 [validation disabled] Urgent pointer: 0 Options: (12 bytes), Maximum segment size, No-Operation (NOP), Window scale, No-Operation (NOP), No-Operation (NOP), SACK permitted Maximum segment size: 1460 bytes No-Operation (NOP) Window scale: 8 (multiply by 256) No-Operation (NOP) No-Operation (NOP) TCP SACK Permitted Option: True
第二次握手：同意并响应建立tcp连接（第二步）
Transmission Control Protocol, Src Port: 80 (80), Dst Port: 58168 (58168), Seq: 0, Ack: 1, Len: 0 Source Port: 80 Destination Port: 58168 [Stream index: 0] [TCP Segment Len: 0] Sequence number: 0 (relative sequence number) Acknowledgment number: 1 (relative ack number) Header Length: 32 bytes Flags: 0x012 (SYN, ACK) Window size value: 8192 [Calculated window size: 8192] Checksum: 0xe135 [validation disabled] Urgent pointer: 0 Options: (12 bytes), Maximum segment size, No-Operation (NOP), Window scale, No-Operation (NOP), No-Operation (NOP), SACK permitted Maximum segment size: 1440 bytes No-Operation (NOP) Window scale: 7 (multiply by 128) No-Operation (NOP) No-Operation (NOP) TCP SACK Permitted Option: True [SEQ/ACK analysis] [This is an ACK to the segment in frame: 22] [The RTT to ACK the segment was: 0.014527000 seconds] [iRTT: 0.014704000 seconds]
第三次TCP握手：确实收到同意，双方建立tcp连接（第三步）
Transmission Control Protocol, Src Port: 58168 (58168), Dst Port: 80 (80), Seq: 1, Ack: 1, Len: 0 Source Port: 58168 Destination Port: 80 [Stream index: 0] [TCP Segment Len: 0] Sequence number: 1 (relative sequence number) Acknowledgment number: 1 (relative ack number) Header Length: 20 bytes Flags: 0x010 (ACK) Window size value: 258 [Calculated window size: 66048] [Window size scaling factor: 256] Checksum: 0x40f2 [validation disabled] Urgent pointer: 0 [SEQ/ACK analysis] [This is an ACK to the segment in frame: 25] [The RTT to ACK the segment was: 0.000177000 seconds] [iRTT: 0.014704000 seconds]
客户端发送http请求（第四步）
Hypertext Transfer Protocol GET / HTTP/1.1\r\n Host: www.baidu.com\r\n Connection: keep-alive\r\n Accept: text/html,application/xhtml+xml,application/xml;q=0.9,p_w_picpath/webp,*/*;q=0.8\r\n Upgrade-Insecure-Requests: 1\r\n User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.102 Safari/537.36\r\n Accept-Encoding: gzip, deflate, sdch\r\n Accept-Language: zh-CN,zh;q=0.8\r\n Cookie: BIDUPSID=9C25713BD075F319DD1BA478B66C18FE; BAIDUID=950E984CFBDACBF12090E5A9AE1DF0A9:FG=1; PSTM=1463842646; BD_UPN=12314753; H_PS_645EC=d0bekcm7B5sCDsTHM76XdCjTAv1euIq5%2Fx411Qxuo3%2BVgno2jmKFo41jdS4\r\n \r\n [Full request URI: http://www.baidu.com/] [HTTP request 1/1] [Response in frame: 75]
服务器响应http请求（第五步）
Transmission Control Protocol, Src Port: 80 (80), Dst Port: 58168 (58168), Seq: 1, Ack: 581, Len: 0 Source Port: 80 Destination Port: 58168 [Stream index: 0] [TCP Segment Len: 0] Sequence number: 1 (relative sequence number) Acknowledgment number: 581 (relative ack number) Header Length: 20 bytes Flags: 0x010 (ACK) Window size value: 203 [Calculated window size: 25984] [Window size scaling factor: 128] Checksum: 0x3ee5 [validation disabled] Urgent pointer: 0 [SEQ/ACK analysis] [This is an ACK to the segment in frame: 71] [The RTT to ACK the segment was: 0.027141000 seconds] [iRTT: 0.014704000 seconds]
服务器封装http响应数据（第六步）
Hypertext Transfer Protocol HTTP/1.1 302 Moved Temporarily\r\n [Expert Info (Chat/Sequence): HTTP/1.1 302 Moved Temporarily\r\n] [HTTP/1.1 302 Moved Temporarily\r\n] [Severity level: Chat] [Group: Sequence] Request Version: HTTP/1.1 Status Code: 302 Response Phrase: Moved Temporarily Date: Sun, 22 May 2016 14:41:21 GMT\r\n Content-Type: text/html\r\n Content-Length: 215\r\n [Content length: 215] Connection: Keep-Alive\r\n Location: https://www.baidu.com/\r\n Server: BWS/1.1\r\n X-UA-Compatible: IE=Edge,chrome=1\r\n Set-Cookie: BD_LAST_QID=16901673809965183666; path=/; Max-Age=1\r\n \r\n [HTTP response 1/1] [Time since request: 0.032063000 seconds] [Request in frame: 71]
服务器传输数据（第七步）
Transmission Control Protocol, Src Port: 80 (80), Dst Port: 58168 (58168), Seq: 293, Ack: 581, Len: 215 Source Port: 80 Destination Port: 58168 [Stream index: 0] [TCP Segment Len: 215] Sequence number: 293 (relative sequence number) [Next sequence number: 508 (relative sequence number)] Acknowledgment number: 581 (relative ack number) Header Length: 20 bytes Flags: 0x018 (PSH, ACK) Window size value: 203 [Calculated window size: 25984] [Window size scaling factor: 128] Checksum: 0x3130 [validation disabled] Urgent pointer: 0 [SEQ/ACK analysis] [iRTT: 0.014704000 seconds] [Bytes in flight: 507]
客户端确认收到数据请求（第八步）
Transmission Control Protocol, Src Port: 58168 (58168), Dst Port: 80 (80), Seq: 581, Ack: 508, Len: 0 Source Port: 58168 Destination Port: 80 [Stream index: 0] [TCP Segment Len: 0] Sequence number: 581 (relative sequence number) Acknowledgment number: 508 (relative ack number) Header Length: 20 bytes Flags: 0x010 (ACK) Window size value: 256 [Calculated window size: 65536] [Window size scaling factor: 256] Checksum: 0x3cb5 [validation disabled] Urgent pointer: 0 [SEQ/ACK analysis] [This is an ACK to the segment in frame: 83] [The RTT to ACK the segment was: 0.000121000 seconds] [iRTT: 0.014704000 seconds]
服务器继续发送数据（第九步）
Transmission Control Protocol, Src Port: 80 (80), Dst Port: 58168 (58168), Seq: 293, Ack: 581, Len: 215 Source Port: 80 Destination Port: 58168 [Stream index: 0] [TCP Segment Len: 215] Sequence number: 293 (relative sequence number) [Next sequence number: 508 (relative sequence number)] Acknowledgment number: 581 (relative ack number) Header Length: 20 bytes Flags: 0x018 (PSH, ACK) Window size value: 203 [Calculated window size: 25984] [Window size scaling factor: 128] Checksum: 0x3130 [validation disabled] Urgent pointer: 0 [SEQ/ACK analysis] [iRTT: 0.014704000 seconds] [Bytes in flight: 215] [TCP Analysis Flags] [Expert Info (Note/Sequence): This frame is a (suspected) retransmission] [This frame is a (suspected) retransmission] [Severity level: Note] [Group: Sequence] [The RTO for this segment was: 0.002339000 seconds] [RTO based on delta from frame: 83] Retransmitted TCP segment data (215 bytes)
客户端继续确认收到请求（第十步）
Transmission Control Protocol, Src Port: 58168 (58168), Dst Port: 80 (80), Seq: 581, Ack: 508, Len: 0 Source Port: 58168 Destination Port: 80 [Stream index: 0] [TCP Segment Len: 0] Sequence number: 581 (relative sequence number) Acknowledgment number: 508 (relative ack number) Header Length: 32 bytes Flags: 0x010 (ACK) Window size value: 256 [Calculated window size: 65536] [Window size scaling factor: 256] Checksum: 0x115b [validation disabled] Urgent pointer: 0 Options: (12 bytes), No-Operation (NOP), No-Operation (NOP), SACK No-Operation (NOP) No-Operation (NOP) SACK: 293-508 [SEQ/ACK analysis] [This is an ACK to the segment in frame: 86] [The RTT to ACK the segment was: 0.000096000 seconds] [iRTT: 0.014704000 seconds] [TCP Analysis Flags] [This is a TCP duplicate ack] [Duplicate ACK #: 1] [Duplicate to the ACK in frame: 84] [Expert Info (Note/Sequence): Duplicate ACK (#1)] [Duplicate ACK (#1)] [Severity level: Note] [Group: Sequence]
第一次挥手：服务端发送一个FIN，用来关闭服务端到客户端的数据传送（第十一步）
Transmission Control Protocol, Src Port: 80 (80), Dst Port: 58168 (58168), Seq: 508, Ack: 581, Len: 0 Source Port: 80 Destination Port: 58168 [Stream index: 0] [TCP Segment Len: 0] Sequence number: 508 (relative sequence number) Acknowledgment number: 581 (relative ack number) Header Length: 20 bytes Flags: 0x011 (FIN, ACK) Window size value: 203 [Calculated window size: 25984] [Window size scaling factor: 128] Checksum: 0x3ce9 [validation disabled] Urgent pointer: 0
第二次挥手：客户端收到FIN，发回一个ACK，进行确认（第十二步）
Transmission Control Protocol, Src Port: 58168 (58168), Dst Port: 80 (80), Seq: 581, Ack: 509, Len: 0 Source Port: 58168 Destination Port: 80 [Stream index: 0] [TCP Segment Len: 0] Sequence number: 581 (relative sequence number) Acknowledgment number: 509 (relative ack number) Header Length: 20 bytes Flags: 0x010 (ACK) Window size value: 256 [Calculated window size: 65536] [Window size scaling factor: 256] Checksum: 0x3cb4 [validation disabled] Urgent pointer: 0 [SEQ/ACK analysis] [This is an ACK to the segment in frame: 415] [The RTT to ACK the segment was: 0.000283000 seconds] [iRTT: 0.014704000 seconds]
第三次挥手：客户端关闭服务端的连接，发送一个FIN给服务端（第十三步）
Transmission Control Protocol, Src Port: 58168 (58168), Dst Port: 80 (80), Seq: 581, Ack: 509, Len: 0 Source Port: 58168 Destination Port: 80 [Stream index: 0] [TCP Segment Len: 0] Sequence number: 581 (relative sequence number) Acknowledgment number: 509 (relative ack number) Header Length: 20 bytes Flags: 0x011 (FIN, ACK) Window size value: 256 [Calculated window size: 65536] [Window size scaling factor: 256] Checksum: 0x3cb3 [validation disabled] Urgent pointer: 0
第四次挥手：服务端发回ACK报文确认，双方断开TCP会话（第十四步）
Transmission Control Protocol, Src Port: 80 (80), Dst Port: 58168 (58168), Seq: 509, Ack: 582, Len: 0 Source Port: 80 Destination Port: 58168 [Stream index: 0] [TCP Segment Len: 0] Sequence number: 509 (relative sequence number) Acknowledgment number: 582 (relative ack number) Header Length: 20 bytes Flags: 0x010 (ACK) Window size value: 203 [Calculated window size: 25984] [Window size scaling factor: 128] Checksum: 0x3ce8 [validation disabled] Urgent pointer: 0 [SEQ/ACK analysis] [This is an ACK to the segment in frame: 417] [The RTT to ACK the segment was: 0.018501000 seconds] [iRTT: 0.014704000 seconds]