bittorrent 学习(四) tracker peer通讯

看看 tracker.c文件

http_encode() 为http发送进行编码转换

 int http_encode(unsigned char *in,int len1,char *out,int len2)
 {
     int  i, j;
     char hex_table[] = "0123456789abcdef"; 

     if( (len1 != ) || (len2 <= ) )  return -;
     for(i = , j = ; i < ; i++, j++) {
         if( isalpha(in[i]) || isdigit(in[i]) )
             out[j] = in[i];
         else {
             out[j] = '%';
             j++;
             out[j] = hex_table[in[i] >> ];
             j++;
             out[j] = hex_table[in[i] & 0xf];
         }
     }
     out[j] = '\0';

 #ifdef DEBUG
     //printf("http encoded:%s\n",out);
 #endif

     return ;
 }

get_tracker_name() 通过截取关键字符 获取网址的名称部分

 int get_tracker_name(Announce_list *node,char *name,int len)
 {
     int i = , j = ;

     if( (len < ) || (node == NULL) )  return -;
     if( memcmp(node->announce,"http://",) ==  )
         i = i + ;
     while( (node->announce[i] != '/') && (node->announce[i] != ':') ) {
         name[j] = node->announce[i];
         i++;
         j++;
         if( i == strlen(node->announce) )  break;
     }
     name[j] = '\0';

 #ifdef DEBUG
     printf("%s\n",node->announce);
     printf("tracker name:%s\n",name);
 #endif

     return ;
 }

get_tracker_port() 通过截取关键字符 获取端口部分

 int get_tracker_port(Announce_list *node,unsigned short *port)
 {
     int i = ;

     if( (node == NULL) || (port == NULL) )  return -;
     if( memcmp(node->announce,"http://",) ==  )  i = i + ;
     *port = ;
     while( i < strlen(node->announce) ) {
         if( node->announce[i] != ':')   { i++; continue; }

         i++;  // skip ':'
         while( isdigit(node->announce[i]) ) {
             *port =  *port *  + (node->announce[i] - '');
             i++;
         }
         break;
     }
     if(*port == )  *port = ;

 #ifdef DEBUG
     printf("tracker port:%d\n",*port);
 #endif

     return ;
 }

create_request()创建一个http的请求

 int create_request(char *request,int len,Announce_list *node,
                    unsigned short port,long long down,long long up,
                    long long left,int numwant)
 {
     char           encoded_info_hash[];
     char           encoded_peer_id[];
     int            key;
     char           tracker_name[];
     unsigned short tracker_port;

     http_encode(info_hash,,encoded_info_hash,);
     http_encode(peer_id,,encoded_peer_id,);

     srand(time(NULL));
     key = rand() / ;

     get_tracker_name(node,tracker_name,);
     get_tracker_port(node,&tracker_port);

     sprintf(request,
     "GET /announce?info_hash=%s&peer_id=%s&port=%u"
     "&uploaded=%lld&downloaded=%lld&left=%lld"
     "&event=started&key=%d&compact=1&numwant=%d HTTP/1.0\r\n"
     "Host: %s\r\nUser-Agent: Bittorrent\r\nAccept: */*\r\n"
     "Accept-Encoding: gzip\r\nConnection: closed\r\n\r\n",
     encoded_info_hash,encoded_peer_id,port,up,down,left,
     key,numwant,tracker_name);

 #ifdef DEBUG
     printf("request:%s\n",request);
 #endif

     return ;
 }

get_response_type() 分析返回的内容 确认返回内容的类型

 int get_response_type(char *buffer,int len,int *total_length)
 {
     int i, content_length = ;

     for(i = ; i < len-; i++) {
         if(memcmp(&buffer[i],"5:peers",) == ) {
             i = i+;
             break;
         }
     }
     if(i == len-)        return -;  // 返回的消息不含"5:peers"关键字
     if(buffer[i] != 'l')  return ;   // 返回的消息的类型为第一种

     *total_length = ;
     for(i = ; i < len-; i++) {
         if(memcmp(&buffer[i],"Content-Length: ",) == ) {
             i = i+;
             break;
         }
     }
     if(i != len-) {
         while(isdigit(buffer[i])) {
             content_length = content_length *  + (buffer[i] - '');
             i++;
         }
         for(i = ; i < len-; i++) {
             if(memcmp(&buffer[i],"\r\n\r\n",) == )  { i = i+; break; }
         }
         if(i != len-)  *total_length = content_length + i;
     }

     if(*total_length == )  return -;
     else return ;
 }

代码都比较清晰易懂 划分明确

以上所有都是为了peer之间的通讯做准备 peer间的通讯流程如下

参考

《linux C编程实战》