bittorrent 學習(三) MSG

時間 2019-11-12

標籤 bittorrent 學習 msg 简体版

原文原文鏈接

msg.c中html

int轉化 char[4] char[4]轉化int的函數以下(有多種方案)linux

 1 int int_to_char(int i, unsigned char c[4])
 2 {
 3     c[3] = i % 256;
 4     c[2] = (i - c[3]) / 256 % 256;
 5     c[1] = (i - c[3] - c[2] * 256) / 256 / 256 % 256;
 6     c[0] = (i - c[3] - c[2] * 256 - c[1] * 256 * 256) / 256 / 256 / 256 % 256;
 7 
 8     return 0;
 9 }
10 
11 int IntToChar(int j, unsigned char c[4]) {
12     int i = 0;
13     for (i = 0; i < 4; i++) {
14         c[i] = (j >> (4 - i - 1) * 8) & 0xff;
15     }
16     return 0;
17 }
18 
19 int CharToInt1(unsigned char c[4]) {
20     int i = 0;
21 
22     unsigned char* p = (unsigned char*)&i;
23     for (int j = 3; j > 0 ; j--) {
24         memcpy(p, &c[j], sizeof(c[j]));
25         p++;
26     }
27     memcpy(p, &c[0], sizeof(c[0]));
28 
29     return i;
30 }
31 
32 int CharToInt(unsigned char c[4]) {
33     int i = 0;
34     for (int j = 0; j < 3; j++) {
35         i += c[j];
36         i <<= 8;
37     }
38     i += c[3];
39 
40     return i;
41 }
42 
43 int char_to_int(unsigned char c[4])
44 {
45     int i;
46 
47     i = c[0] * 256 * 256 * 256 + c[1] * 256 * 256 + c[2] * 256 + c[3];
48 
49     return i;
50 }

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建立握手信息的函數 create_handshake_msg()編程

握手消息數組

客戶端與一個peer創建TCP鏈接後，首先向peer發送握手消息，peer收到握手消息後迴應一個握手消息。握手消息是一個長度固定爲68字節的消息，格式以下：
<pstrlen><pstr><reserved><info_hash><peer_id>socket

握手消息參數
參數含義
pstrlen pstr的長度，固定爲19
pstr BitTorrent協議的關鍵字，即」BitTorrent protocol」
reserved 佔8字節，用於擴展BT協議。可忽略
info_hash 與發往Tracker的GET請求中的info_hash爲同一個值，固定爲20字節
peer_id 與發往Tracker的GET請求中的peer_id爲同一個值，固定爲20字節ide

info_hash就是種子文件中 4:info 後的種子信息計算的哈希值函數

 1 int create_handshake_msg(char *info_hash,char *peer_id,Peer *peer)
 2 {
 3     int            i;
 4     unsigned char  keyword[20] = "BitTorrent protocol", c = 0x00;
 5     unsigned char  *buffer = peer->out_msg + peer->msg_len;
 6     int            len = MSG_SIZE - peer->msg_len;
 7 
 8     if(len < 68)  return -1;  // 68爲握手消息的固定長度
 9 
10     buffer[0] = 19;
11     for(i = 0; i < 19; i++)  buffer[i+1]  = keyword[i];
12     for(i = 0; i < 8;  i++)  buffer[i+20] = c;
13     for(i = 0; i < 20; i++)  buffer[i+28] = info_hash[i];
14     for(i = 0; i < 20; i++)  buffer[i+48] = peer_id[i];
15 
16     peer->msg_len += 68;
17     return 0;
18 }

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心跳函數代表I本身在線 create_chock_interested_msg()spa

發送4個0.net

 1 int create_keep_alive_msg(Peer *peer)
 2 {
 3     unsigned char  *buffer = peer->out_msg + peer->msg_len;
 4     int            len = MSG_SIZE - peer->msg_len;
 5 
 6     if(len < 4)  return -1;  // 4爲keep_alive消息的固定長度
 7 
 8     memset(buffer,0,4);
 9     peer->msg_len += 4;
10     return 0;
11 }

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chock 函數 create_chock_interested_msg() 代表對方因爲某種緣由阻塞好比貢獻度不夠？或者是否感興趣 3d

結構都是一致的 5字節第四個爲1 第五個表示消息類型(choke、unchoke、interested、uninterested)

 1 int create_chock_interested_msg(int type,Peer *peer)
 2 {
 3     unsigned char  *buffer = peer->out_msg + peer->msg_len;
 4     int            len = MSG_SIZE - peer->msg_len;
 5 
 6     // 5爲choke、unchoke、interested、uninterested消息的固定長度
 7     if(len < 5)  return -1;
 8 
 9     memset(buffer,0,5);
10     buffer[3] = 1;
11     buffer[4] = type;
12 
13     peer->msg_len += 5;
14     return 0;
15 }

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表示是否擁有該index的piece函數 create_have_msg()

9個字節最後4個字節是index的int to char 計算的結果。第4 5個字節填寫 5 4 。這個彷佛在協議說明裏沒看到

 1 int create_have_msg(int index,Peer *peer)
 2 {
 3     unsigned char  *buffer = peer->out_msg + peer->msg_len;
 4     int            len = MSG_SIZE - peer->msg_len;
 5     unsigned char  c[4];
 6 
 7     if(len < 9)  return -1;  // 9爲have消息的固定長度
 8     
 9     memset(buffer,0,9);    
10     buffer[3] = 5;
11     buffer[4] = 4;
12     
13     int_to_char(index,c);
14     buffer[5] = c[0];
15     buffer[6] = c[1];
16     buffer[7] = c[2];
17     buffer[8] = c[3];
18     
19     peer->msg_len += 9;
20     return 0;
21 }

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建立位圖消息 create_bitfield_msg() 傳遞本地位圖文件消息

長度不定位圖長度+5 前4位是位圖長度 int to char 的數組第五位標記爲5 後面是位圖

 1 int create_bitfield_msg(char *bitfield,int bitfield_len,Peer *peer)
 2 {
 3     int            i;
 4     unsigned char  c[4];
 5     unsigned char  *buffer = peer->out_msg + peer->msg_len;
 6     int            len = MSG_SIZE - peer->msg_len;
 7 
 8     if( len < bitfield_len+5 )  {  // bitfield消息的長度爲bitfield_len+5
 9         printf("%s:%d buffer too small\n",__FILE__,__LINE__); 
10         return -1;
11     }
12 
13     int_to_char(bitfield_len+1,c);
14     for(i = 0; i < 4; i++)  buffer[i] = c[i];
15     buffer[4] = 5;
16     for(i = 0; i < bitfield_len; i++) buffer[i+5] = bitfield[i];
17 
18     peer->msg_len += bitfield_len+5;  
19     return 0;
20 }

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請求文件的內容函數 create_request_msg()

前5字節固定第4 5字節填寫13 6.後面每4個字節分別填寫 index begin end的int to char。

由於peer之間交換數據時以slice（長度爲16KB的塊）爲單位的，所以request消息中length的值通常爲16K。最大不超過128K

 1 int create_request_msg(int index,int begin,int length,Peer *peer)
 2 {
 3     int            i;
 4     unsigned char  c[4];
 5     unsigned char  *buffer = peer->out_msg + peer->msg_len;
 6     int            len = MSG_SIZE - peer->msg_len;
 7 
 8     if(len < 17)  return -1;  // 17爲request消息的固定長度
 9 
10     memset(buffer,0,17);
11     buffer[3] = 13;
12     buffer[4] = 6;
13     int_to_char(index,c);
14     for(i = 0; i < 4; i++)  buffer[i+5]  = c[i];
15     int_to_char(begin,c);
16     for(i = 0; i < 4; i++)  buffer[i+9]  = c[i];
17     int_to_char(length,c);
18     for(i = 0; i < 4; i++)  buffer[i+13] = c[i];
19 
20     peer->msg_len += 17;
21     return 0;
22 }

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建立piece信息 create_piece_msg()

長度爲piece長度加13。

頭4個字節是總長度 piece_length+13通過 int to char轉化。接下來是一個標記7的字節。而後是index begin兩個長度int to char.接下來是傳輸piece

 1 int create_piece_msg(int index,int begin,char *block,int b_len,Peer *peer)
 2 {
 3     int            i;
 4     unsigned char  c[4];
 5     unsigned char  *buffer = peer->out_msg + peer->msg_len;
 6     int            len = MSG_SIZE - peer->msg_len;
 7 
 8     if( len < b_len+13 ) {  // piece消息的長度爲b_len+13
 9         printf("IP:%s len:%d\n",peer->ip,len);
10         printf("%s:%d buffer too small\n",__FILE__,__LINE__); 
11         return -1;
12     }
13     
14     int_to_char(b_len+9,c);
15     for(i = 0; i < 4; i++)      buffer[i]    = c[i];
16     buffer[4] = 7;
17     int_to_char(index,c);
18     for(i = 0; i < 4; i++)      buffer[i+5]  = c[i];
19     int_to_char(begin,c);
20     for(i = 0; i < 4; i++)      buffer[i+9]  = c[i];
21     for(i = 0; i < b_len; i++)  buffer[i+13] = block[i];
22 
23     peer->msg_len += b_len+13;  
24     return 0;
25 }

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取消信息用於取消對某個piece的請求 create_cancel_msg()

固定長度17

第4 5個字節賦值 13 8. 後面12個字節分別是 index begin length的int to char 數組

 1 int create_cancel_msg(int index,int begin,int length,Peer *peer)
 2 {
 3     int            i;
 4     unsigned char  c[4];
 5     unsigned char  *buffer = peer->out_msg + peer->msg_len;
 6     int            len = MSG_SIZE - peer->msg_len;
 7     
 8     if(len < 17)  return -1;  // 17爲cancel消息的固定長度
 9     
10     memset(buffer,0,17);
11     buffer[3] = 13;
12     buffer[4] = 8;
13     int_to_char(index,c);
14     for(i = 0; i < 4; i++)  buffer[i+5]  = c[i];
15     int_to_char(begin,c);
16     for(i = 0; i < 4; i++)  buffer[i+9]  = c[i];
17     int_to_char(length,c);
18     for(i = 0; i < 4; i++)  buffer[i+13] = c[i];
19 
20     peer->msg_len += 17;    
21     return 0;
22 }

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傳遞端口信息固定7個字節第四五字節爲3 9 第六七個字節爲端口 int to char的後兩個字節

 1 int create_port_msg(int port,Peer *peer)
 2 {
 3     unsigned char  c[4];
 4     unsigned char  *buffer = peer->out_msg + peer->msg_len;
 5     int            len = MSG_SIZE - peer->msg_len;
 6 
 7     if( len < 7)  return 0;  // 7爲port消息的固定長度
 8 
 9     memset(buffer,0,7);
10     buffer[3] = 3;
11     buffer[4] = 9;
12     int_to_char(port,c);
13     buffer[5] = c[2];
14     buffer[6] = c[3];
15 
16     peer->msg_len += 7;
17     return 0;
18 }

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print_msg_buffer() 打印buffer內容

 1 // 以十六進制的形式打印消息的內容,用於調試
 2 int print_msg_buffer(unsigned char *buffer, int len)
 3 {
 4     int i;
 5 
 6     for(i = 0; i < len; i++) {
 7         printf("%.2x ",buffer[i]);
 8         if( (i+1) % 16 == 0 )  printf("\n");
 9     }
10     printf("\n");
11 
12     return 0;
13 }

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is_complete_message()檢測是否一條完整信息存放在BUF中

首先比對固定頭信息的集中類型好比握手 choke interested have request cancel port 而後檢測 bitfield 和piece不定長協議。最後根據頭文件信息指定的長度是否吻合判斷是否接收到未知定義仍是未結束的消息

 1 int is_complete_message(unsigned char *buff,unsigned int len,int *ok_len)
 2 {
 3     unsigned int   i;
 4     char           btkeyword[20];
 5 
 6     unsigned char  keep_alive[4]   = { 0x0, 0x0, 0x0, 0x0 };
 7     unsigned char  chocke[5]       = { 0x0, 0x0, 0x0, 0x1, 0x0};
 8     unsigned char  unchocke[5]     = { 0x0, 0x0, 0x0, 0x1, 0x1};
 9     unsigned char  interested[5]   = { 0x0, 0x0, 0x0, 0x1, 0x2};
10     unsigned char  uninterested[5] = { 0x0, 0x0, 0x0, 0x1, 0x3};
11     unsigned char  have[5]         = { 0x0, 0x0, 0x0, 0x5, 0x4};
12     unsigned char  request[5]      = { 0x0, 0x0, 0x0, 0xd, 0x6};
13     unsigned char  cancel[5]       = { 0x0, 0x0, 0x0, 0xd, 0x8};
14     unsigned char  port[5]         = { 0x0, 0x0, 0x0, 0x3, 0x9};
15     
16     if(buff==NULL || len<=0 || ok_len==NULL)  return -1;
17     *ok_len = 0;
18     
19     btkeyword[0] = 19;
20     memcpy(&btkeyword[1],"BitTorrent protocol",19);  // BitTorrent協議關鍵字
21 
22     unsigned char  c[4];
23     unsigned int   length;
24     
25     for(i = 0; i < len; ) {
26         // 握手、chocke、have等消息的長度是固定的
27         if( i+68<=len && memcmp(&buff[i],btkeyword,20)==0 )         i += 68;
28         else if( i+4 <=len && memcmp(&buff[i],keep_alive,4)==0 )    i += 4;
29         else if( i+5 <=len && memcmp(&buff[i],chocke,5)==0 )        i += 5;
30         else if( i+5 <=len && memcmp(&buff[i],unchocke,5)==0 )      i += 5;
31         else if( i+5 <=len && memcmp(&buff[i],interested,5)==0 )    i += 5;
32         else if( i+5 <=len && memcmp(&buff[i],uninterested,5)==0 )  i += 5;
33         else if( i+9 <=len && memcmp(&buff[i],have,5)==0 )          i += 9;
34         else if( i+17<=len && memcmp(&buff[i],request,5)==0 )       i += 17;
35         else if( i+17<=len && memcmp(&buff[i],cancel,5)==0 )        i += 17;
36         else if( i+7 <=len && memcmp(&buff[i],port,5)==0 )          i += 7;
37         // bitfield消息的長度是變化的
38         else if( i+5 <=len && buff[i+4]==5 )  {
39             c[0] = buff[i];   c[1] = buff[i+1];
40             c[2] = buff[i+2]; c[3] = buff[i+3];
41             length = char_to_int(c);    
42             // 消息長度佔4字節,消息自己佔length個字節
43             if( i+4+length <= len )  i += 4+length;
44             else { *ok_len = i; return -1; }
45         }
46         // piece消息的長度也是變化的
47         else if( i+5 <=len && buff[i+4]==7 )  {
48             c[0] = buff[i];   c[1] = buff[i+1];
49             c[2] = buff[i+2]; c[3] = buff[i+3];
50             length = char_to_int(c);
51             // 消息長度佔4字節,消息自己佔length個字節
52             if( i+4+length <= len )  i += 4+length;
53             else { *ok_len = i; return -1; }
54         }
55         else {
56             // 處理未知類型的消息
57             if(i+4 <= len) {
58                 c[0] = buff[i];   c[1] = buff[i+1];
59                 c[2] = buff[i+2]; c[3] = buff[i+3];
60                 length = char_to_int(c);
61                 // 消息長度佔4字節,消息自己佔length個字節
62                 if(i+4+length <= len)  { i += 4+length; continue; }
63                 else { *ok_len = i; return -1; }
64             }
65             // 若是也不是未知消息類型,則認爲目前接收的數據還不是一個完整的消息
66             *ok_len = i;
67             return -1;
68         }
69     }
70     
71     *ok_len = i;
72     return 1;
73 }

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process_handshake_msg()處理握手信息

比對info_hash 判斷是否須要處理仍是丟棄而後從initial進入到 handshaked狀態

 1 int process_handshake_msg(Peer *peer,unsigned char *buff,int len)
 2 {
 3     if(peer==NULL || buff==NULL)  return -1;
 4 
 5     if(memcmp(info_hash,buff+28,20) != 0) { 
 6         peer->state = CLOSING;
 7         // 丟棄發送緩衝區中的數據
 8         discard_send_buffer(peer);
 9         clear_btcache_before_peer_close(peer);
10         close(peer->socket);
11         return -1;
12     }
13     
14     memcpy(peer->id,buff+48,20);
15     (peer->id)[20] = '\0';
16     
17     if(peer->state == INITIAL) {
18         peer->state = HANDSHAKED;
19         create_handshake_msg(info_hash,peer_id,peer);
20     }
21     if(peer->state == HALFSHAKED)  peer->state = HANDSHAKED;
22 
23     peer->start_timestamp = time(NULL);
24     return 0;
25 }

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process_keep_alive_msg() 心跳處理更新下peer的時間不作其餘處理

1 int process_keep_alive_msg(Peer *peer,unsigned char *buff,int len)
2 {
3     if(peer==NULL || buff==NULL)  return -1;
4 
5     peer->start_timestamp = time(NULL);
6     return 0;
7 }

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process_choke_msg處理函數若是peer未關閉且處於未堵塞狀態更改成堵塞時間從新計數

 1 int process_choke_msg(Peer *peer,unsigned char *buff,int len)
 2 {
 3     if(peer==NULL || buff==NULL)  return -1;
 4 
 5     if( peer->state!=CLOSING && peer->peer_choking==0 ) {
 6         peer->peer_choking = 1;
 7         peer->last_down_timestamp = 0;
 8         peer->down_count          = 0;
 9         peer->down_rate           = 0;
10     }
11 
12     peer->start_timestamp = time(NULL);
13     return 0;
14 }

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process_unchoke_msg 解開堵塞狀態建立interested的pieces

 1 int process_unchoke_msg(Peer *peer,unsigned char *buff,int len)
 2 {
 3     if(peer==NULL || buff==NULL)  return -1;
 4 
 5     if( peer->state!=CLOSING && peer->peer_choking==1 ) {
 6         peer->peer_choking = 0;
 7         if(peer->am_interested == 1)  create_req_slice_msg(peer);
 8         else {
 9             peer->am_interested = is_interested(&(peer->bitmap), bitmap);
10             if(peer->am_interested == 1) create_req_slice_msg(peer);
11             else printf("Received unchoke but Not interested to IP:%s \n",peer->ip);
12         }
13 
14         peer->last_down_timestamp = 0;
15         peer->down_count          = 0;
16         peer->down_rate           = 0;
17     }
18 
19     peer->start_timestamp = time(NULL);
20     return 0;
21 }

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process_interested_msg更新時間根據位圖更新感興趣的狀態

 1 int process_interested_msg(Peer *peer,unsigned char *buff,int len)
 2 {
 3     if(peer==NULL || buff==NULL)  return -1;
 4 
 5     if( peer->state!=CLOSING && peer->state==DATA ) {
 6         peer->peer_interested = is_interested(bitmap, &(peer->bitmap));
 7         if(peer->peer_interested == 0)  return -1;
 8         if(peer->am_choking == 0) create_chock_interested_msg(1,peer);
 9     }
10 
11     peer->start_timestamp = time(NULL);
12     return 0;
13 }

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process_uninterested_msg 更新時間從要求名單中刪除peer相關的數據

 1 int process_uninterested_msg(Peer *peer,unsigned char *buff,int len)
 2 {
 3     if(peer==NULL || buff==NULL)  return -1;
 4 
 5     if( peer->state!=CLOSING && peer->state==DATA ) {
 6         peer->peer_interested = 0;
 7         cancel_requested_list(peer);
 8     }
 9 
10     peer->start_timestamp = time(NULL);
11     return 0;
12 }

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process_have_msg 收到其餘peer的have信息更新該peermap 再次檢測是否感興趣。無興趣的點也有1/3的機率進行回覆

 1 int process_have_msg(Peer *peer,unsigned char *buff,int len)
 2 {
 3     int           rand_num;
 4     unsigned char c[4];
 5 
 6     if(peer==NULL || buff==NULL)  return -1;
 7 
 8     srand(time(NULL));
 9     rand_num = rand() % 3;
10 
11     if( peer->state!=CLOSING && peer->state==DATA ) {
12         c[0] = buff[5]; c[1] = buff[6];
13         c[2] = buff[7]; c[3] = buff[8];        
14         if(peer->bitmap.bitfield != NULL)
15             set_bit_value(&(peer->bitmap),char_to_int(c),1);
16 
17         if(peer->am_interested == 0) {
18             peer->am_interested = is_interested(&(peer->bitmap), bitmap);
19             // 由原來的對peer不感興趣變爲感興趣時,發interested消息
20             if(peer->am_interested == 1) create_chock_interested_msg(2,peer);    
21         } else {  // 收到三個have則發一個interested消息
22             if(rand_num == 0) create_chock_interested_msg(2,peer);
23         }
24     }
25 
26     peer->start_timestamp = time(NULL);
27     return 0;
28 }

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process_cancel_msg 放棄請求的處理

遍歷記錄鏈表刪除

 1 int process_cancel_msg(Peer *peer,unsigned char *buff,int len)
 2 {
 3     unsigned char c[4];
 4     int           index, begin, length;
 5 
 6     if(peer==NULL || buff==NULL)  return -1;
 7     
 8     c[0] = buff[5];  c[1] = buff[6];
 9     c[2] = buff[7];  c[3] = buff[8];
10     index = char_to_int(c);
11     c[0] = buff[9];  c[1] = buff[10];
12     c[2] = buff[11]; c[3] = buff[12];
13     begin = char_to_int(c);
14     c[0] = buff[13]; c[1] = buff[14];
15     c[2] = buff[15]; c[3] = buff[16];
16     length = char_to_int(c);
17     
18     Request_piece *p, *q;
19     p = q = peer->Requested_piece_head;
20     while(p != NULL) { 
21         if( p->index==index && p->begin==begin && p->length==length ) {
22             if(p == peer->Requested_piece_head) 
23                 peer->Requested_piece_head = p->next;
24             else
25                 q->next = p->next;
26             free(p);
27             break;
28         }
29         q = p;
30         p = p->next;
31     }    
32 
33     peer->start_timestamp = time(NULL);
34     return 0;
35 }