http介紹
參考資料
http://www.360doc.com/content/10/0930/17/3668821_57590979.shtml 理解http協議
http://www.cnblogs.com/TankXiao/archive/2012/10/10/2711777.html#introduction wireshark的使用介紹
http://www.cnblogs.com/renyuan/archive/2013/01/19/2867720.html tcp和http的區別
http://www.cnblogs.com/EricaMIN1987_IT/p/3837436.html http協議詳解
http是什麼？
HTTP協議（HyperText Transfer Protocol，超文本傳輸協議)：
從web服務器端傳輸超文本到本地客戶端瀏覽器的傳送協議
是一個基於請求與響應模式的、無狀態的、應用層的協議
1.格式
HTTP協議
URI:Uniform Resource Indentifier 統一資源標識符
URL：Uniform Resource location 統一資源定位符
網頁訪問格式URL
protocol：//Host：port/path/to/file
獲取資源
HTTP方法：GET PUT POST DELETE
GET:通過瀏覽器查看web服務器上的網頁數據
PUT:從web服務器上將數據下載到本地
POST:提交數據到服務器
DELETE:刪除服務器文件
MIME：Multipurpose Internet Mail Extension
多用途互聯網郵件擴展
2.在協議棧中的位置
3.請求響應模型
由客戶端（瀏覽器）向服務端（web服務器）發起請求，服務端響應請求的過程（單向）
4.CS工作流程（簡單宏觀理解，頁面較大時，第三、四步會進行多次）
1）客戶端向服務端建立連接（單擊超級鏈接或手動輸入網址） 三次握手
2）客戶端發送請求數據（格式：URL、協議版本號、MIME信息） 請求獲取網頁內容信息
3）服務端接收請求並給予響應信息（狀態行，信息有協議版本號、成功或失敗的錯誤代碼、MIME信息） 發送網頁內容信息
4）客戶端將接收的信息以瀏覽器顯示，然後斷開與服務器的連接 瀏覽器顯示網頁內容
5.抓包查看數據
這裏以訪問百度主頁爲例
下面的是抓包的內容
一次完整的百度主頁web訪問
1，2，3條表示TCP的三次握手，即建立連接請求
4.客戶端開始向web服務器發送http報文以請求需要獲取的數據（網頁請求，以便服務器端的web軟件可以識別請求內容並進行解析和處理），通過tcp傳輸HTTP報文請求信息
5.服務器發送一個TCP響應報文（對HTTP請求報文進行響應，這個回傳不需要發送HTTP報文，因爲響應信息tcp就可以完成），表示收到請求，正在處理中。。。
6.處理完請求，將客戶端需要的請求數據（即網頁文件以及MIME可以識別的圖片、視頻等），通過http協議報文進行封裝（添加頭部信息、版本號等內容）
7，8，9，10表示通過TCP協議將載有http報文的實體數據傳輸給客戶端的過程（這裏的數據通過兩次傳輸才完畢）
11，12，13，14表示斷開TCP會話的過程
下面就針對抓包進行較爲詳細的解答
第一次TCP握手：請求連接tcp連接（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：同意並響應建立tcp連接（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：確實收到同意，雙方建立tcp連接（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]
客戶端發送http請求（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]
服務器響應http請求（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]
服務器封裝http響應數據（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]
服務器傳輸數據（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]
客戶端確認收到數據請求（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]
服務器繼續發送數據（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)
客戶端繼續確認收到請求（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]
第一次揮手：服務端發送一個FIN，用來關閉服務端到客戶端的數據傳送（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
第二次揮手：客戶端收到FIN，發回一個ACK，進行確認（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]
第三次揮手：客戶端關閉服務端的連接，發送一個FIN給服務端（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
第四次揮手：服務端發回ACK報文確認，雙方斷開TCP會話（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]