与基于udp协议的tracker服务器进行交互

通常BT客户端每几分钟就要向tracker发送一次请求.对于一些比较大的BT站点,其tracker的压力是可想而知的.降低tracker的压力首先考虑到的当然是采用更低网络开销的udp协议.于是Bittorrent udp-tracker protocol应运而生.
这个协议很简单.
下面是实现它的封装类:

// UDPTrackerClient.h: interface for the CUDPTrackerClient class.
//
//////////////////////////////////////////////////////////////////////

#if !defined(AFX_UDPTRACKERCLIENT_H__69B6ACC8_8193_4680_81D8_925B1550E92C__INCLUDED_)
#define AFX_UDPTRACKERCLIENT_H__69B6ACC8_8193_4680_81D8_925B1550E92C__INCLUDED_

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000

#include <winsock2.h>
#pragma comment(lib, "ws2_32.lib")

#ifndef _DISABLEWARNING4786_4355
#define _DISABLEWARNING4786_4355
#pragma warning( disable : 4786 )
#pragma warning( disable : 4355 )
#endif
#ifndef _ENABLEUSESTL
#define _ENABLEUSESTL
#include <list>
#include <map>
#include <set>
#include <vector>
#include <queue>
#include <string>
using namespace std;
#endif

class CPeerHostInfo
{
public:
DWORD		IP;//节点IP
WORD		Port;//节点端口
};
class CUDPTrackerClient
{
public:
CUDPTrackerClient();
virtual ~CUDPTrackerClient();
void CancelSocketOperate();
BOOL Connect(const char * szServer,WORD wPort = 0);
DWORD Announcing(BYTE* pInfoHash,BYTE * pPeerID,
__int64 idownloaded,__int64 ileft,__int64 iuploaded,
int		ievent,
DWORD dwIP,WORD  wPort);

BOOL Disconnect();
public:
SOCKET			m_socket;
DWORD			m_dwIP;
WORD			m_wPort;
__int64			m_iConnection_id;
DWORD			m_dwConnectTick;
string			m_strError;		//如果请求失败,此变量保存错误信息
DWORD m_dwDonePeers;	//种子数
DWORD m_dwNumPeers;	//当前下载者个数
DWORD m_dwInterval;	//查询间隔时间
list<CPeerHostInfo> m_listPeers;
};

#endif // !defined(AFX_UDPTRACKERCLIENT_H__69B6ACC8_8193_4680_81D8_925B1550E92C__INCLUDED_)
[code]// UDPTrackerClient.cpp: implementation of the CUDPTrackerClient class.
//
//////////////////////////////////////////////////////////////////////

#include "stdafx.h"
#include "UDPTrackerClient.h"

#include "DataStream.h"
#ifdef _DEBUG
#undef THIS_FILE
static char THIS_FILE[]=__FILE__;
#define new DEBUG_NEW
#endif

//////////////////////////////////////////////////////////////////////
// Construction/Destruction
//////////////////////////////////////////////////////////////////////
#define RECVBUFSIZE 2048

CUDPTrackerClient::CUDPTrackerClient()
{
m_socket = INVALID_SOCKET;
m_iConnection_id = 0;
m_dwConnectTick = 0;
m_dwIP = 0;
m_wPort = 0;
m_dwDonePeers = 0;	//种子数
m_dwNumPeers = 0;	//当前下载者个数
m_dwInterval = 0;	//查询间隔时间
}

CUDPTrackerClient::~CUDPTrackerClient()
{
Disconnect();

}
void CUDPTrackerClient::CancelSocketOperate()
{
if(m_socket != INVALID_SOCKET)
{
LINGER lingerStruct;
// If we're supposed to abort the connection, set the linger value
// on the socket to 0.
lingerStruct.l_onoff = 1;
lingerStruct.l_linger = 0;
setsockopt(m_socket, SOL_SOCKET, SO_LINGER,
(char *)&lingerStruct, sizeof(lingerStruct) );
}
}
BOOL CUDPTrackerClient::Disconnect()
{
m_iConnection_id = 0;
m_dwDonePeers = 0;	//种子数
m_dwNumPeers = 0;	//当前下载者个数
m_dwInterval = 0;	//查询间隔时间
if ( m_socket != INVALID_SOCKET )
{
m_dwIP = 0;
m_wPort = 0;
// Now close the socket handle.  This will do an abortive or
// graceful close, as requested.
shutdown(m_socket,SD_BOTH);
closesocket(m_socket);
m_socket = INVALID_SOCKET;
return TRUE;
}
return FALSE;
}

//szServer连接的主机,可以是下列形式的字符串:
//easeso.com:1000
//easeso.com
//如果wPort不为0,则szServer不应该包含端口信息
BOOL CUDPTrackerClient::Connect(const char * szServer,WORD wPort)
{
m_strError = "";
BOOL bRes = FALSE;
if ( m_socket == INVALID_SOCKET )
{
//用UDP初始化套接字
BOOL optval = TRUE;
m_socket =socket(AF_INET,SOCK_DGRAM,0);
if(m_socket == INVALID_SOCKET)
return FALSE;
//设置超时时间
int TimeOut=10000;
int err = setsockopt (m_socket, SOL_SOCKET,SO_RCVTIMEO,(CHAR *) &TimeOut,sizeof (TimeOut));
}
if(m_dwIP == 0)
{
CString strServer = szServer;
CString strHost;
if(wPort == 0)
{
int iNext = strServer.Find(':');
if(iNext>0)
{
strHost = strServer.Mid(0,iNext);
CString strPort = strServer.Mid(iNext+1);
m_wPort = (WORD)atoi(strPort);
}
else
strHost = strServer;
}
else
{
strHost = strServer;
m_wPort = wPort;
}
if(m_wPort == 0)
m_wPort = 80;

//Check if address is an IP or a Domain Name
int a = strHost[0];
if (a > 47 && a < 58)
m_dwIP = inet_addr(strHost);
else
{
struct hostent *pHost;
pHost = gethostbyname(strHost);
if(pHost != NULL)
m_dwIP = *((ULONG*)pHost->h_addr);
else
m_dwIP = 0;
}
}
if((GetTickCount()-m_dwConnectTick)>30000)
{
m_dwConnectTick = 0;
m_iConnection_id = 0;
}
if(m_socket != INVALID_SOCKET && m_dwIP && m_wPort && m_iConnection_id ==0)
{
DWORD dwTransaction_id = GetTickCount();
SOCKADDR_IN		from;
int fromlength=sizeof(SOCKADDR);

char buf[RECVBUFSIZE];
from.sin_family=AF_INET;
from.sin_addr.s_addr=m_dwIP;
from.sin_port=htons(m_wPort);
CDataStream sendstream(buf,2047);
sendstream.clear();
__int64 iCID = 0x41727101980;
sendstream.writeint64(CNetworkByteOrder::convert(iCID));
sendstream.writedword(CNetworkByteOrder::convert((int)0));
sendstream.writedword(dwTransaction_id);

int iRes = 0;
int iTimes = 6;
while(iTimes>0&&m_dwIP)
{
sendto(m_socket,sendstream.getbuffer(),sendstream.size(),0,(struct sockaddr FAR *)&from,sizeof(from));
iRes = recvfrom(m_socket,buf,RECVBUFSIZE-1,0,(struct sockaddr FAR *)&from,(int FAR *)&fromlength);
if(iRes >=0)
break;
iTimes--;
}
if(iRes>=16)
{
CDataStream recvstream(buf,RECVBUFSIZE-1);
DWORD dwAction = (DWORD)CNetworkByteOrder::convert((int)recvstream.readdword());
DWORD dwTIDResp= recvstream.readdword();
if(dwTIDResp == dwTransaction_id)
{
if(dwAction == 0)
{
m_iConnection_id = recvstream.readint64();
//BitComet将回复0x16字节数据,最后6字节是服务器查看到的本地IP和UDP端口
}
else if(dwAction == 3)//得到一个错误信息包
{
buf[iRes]=0;
m_strError = recvstream.readstring();
}
}
}
}
if(m_iConnection_id)
bRes = TRUE;
return bRes;
}
//提交请求
//pInfoHash 20字节的数据缓冲区指针
//pPeerID	20字节的数据缓冲区指针
//ievent参数值:
//none = 0
//completed = 1
//started = 2
//stopped = 3

DWORD CUDPTrackerClient::Announcing(BYTE* pInfoHash,BYTE * pPeerID,
__int64 idownloaded,__int64 ileft,__int64 iuploaded,
int		ievent,
DWORD dwIP,WORD  wPort)
{
m_listPeers.clear();
m_dwNumPeers = 0;
m_dwDonePeers = 0;
m_strError = "";
DWORD dwReturnCode = 0;
if(m_iConnection_id && m_socket != INVALID_SOCKET && m_dwIP & m_wPort)
{
DWORD dwTransaction_id = GetTickCount();
//srand(dwTransaction_id);
//DWORD dwKey = rand();
DWORD dwKey = 0x3753;
SOCKADDR_IN		from;
int fromlength=sizeof(SOCKADDR);
char buf[RECVBUFSIZE];
from.sin_family=AF_INET;
from.sin_addr.s_addr=m_dwIP;
from.sin_port=htons(m_wPort);
CDataStream sendstream(buf,RECVBUFSIZE-1);
sendstream.clear();
sendstream.writeint64(m_iConnection_id);
sendstream.writedword(CNetworkByteOrder::convert((int)1));
sendstream.writedword(dwTransaction_id);
sendstream.writedata(pInfoHash,20);
sendstream.writedata(pPeerID,20);
sendstream.writeint64(CNetworkByteOrder::convert(idownloaded));
sendstream.writeint64(CNetworkByteOrder::convert(ileft));
sendstream.writeint64(CNetworkByteOrder::convert(iuploaded));
sendstream.writedword(CNetworkByteOrder::convert(ievent));
sendstream.writedword(dwIP);
sendstream.writedword(CNetworkByteOrder::convert((int)dwKey));
sendstream.writedword(CNetworkByteOrder::convert((int)200));
sendstream.writedword(CNetworkByteOrder::convert(wPort));

int iRes = 0;
int iTimes = 2;
while(iTimes>0&&m_dwIP)
{
sendto(m_socket,sendstream.getbuffer(),sendstream.size(),0,(struct sockaddr FAR *)&from,sizeof(from));
iRes = recvfrom(m_socket,buf,RECVBUFSIZE-1,0,(struct sockaddr FAR *)&from,(int FAR *)&fromlength);
if(iRes >=0)
break;
iTimes--;
}
if(iRes>=20)
{
CDataStream recvstream(buf,RECVBUFSIZE-1);
DWORD dwAction = (DWORD)CNetworkByteOrder::convert((int)recvstream.readdword());
DWORD dwTIDResp= recvstream.readdword();
if(dwTIDResp == dwTransaction_id)
{
if(dwAction == 1)
{
m_dwInterval = (DWORD)CNetworkByteOrder::convert((int)recvstream.readdword());
m_dwNumPeers = (DWORD)CNetworkByteOrder::convert((int)recvstream.readdword());
m_dwDonePeers = (DWORD)CNetworkByteOrder::convert((int)recvstream.readdword());
CPeerHostInfo hi;
for(int iCurPos = 20;iCurPos+6<=iRes;iCurPos+=6)
{
hi.IP= recvstream.readdword();
hi.Port = (WORD)CNetworkByteOrder::convert((unsigned short)recvstream.readword());
m_listPeers.push_back(hi);
}
if(m_dwNumPeers>m_listPeers.size())
{
iRes = 0;
iTimes = 6;
while(iTimes>0&&m_dwIP)
{
iRes = recvfrom(m_socket,buf,RECVBUFSIZE-1,0,(struct sockaddr FAR *)&from,(int FAR *)&fromlength);
if(iRes >=0)
break;
iTimes--;
}
if(iRes>=6)
{
for(iCurPos = 0;iCurPos+6<=iRes;iCurPos+=6)
{
hi.IP= recvstream.readdword();
hi.Port = (DWORD)CNetworkByteOrder::convert((int)recvstream.readword());
m_listPeers.push_back(hi);
}
}
}
m_dwNumPeers = m_listPeers.size();
dwReturnCode = 200;
}
else if(dwAction == 3)//得到一个错误信息包
{
buf[iRes]=0;
m_strError = recvstream.readstring();
dwReturnCode = 400;
}
}
}
}
//每次都要求重新连接
m_iConnection_id = 0;
return dwReturnCode;
}

// DataStream.h: interface for the CDataStream class.
//
//////////////////////////////////////////////////////////////////////

#if !defined(AFX_DATASTREAM_H__D90A2534_EA73_4BEA_8B7E_87E59A3D1D26__INCLUDED_)
#define AFX_DATASTREAM_H__D90A2534_EA73_4BEA_8B7E_87E59A3D1D26__INCLUDED_

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000
#include <stdio.h>
//数据流操作函数
class CDataStream
{
public :
CDataStream(char * szBuf,int isize)
{
m_isize = isize;
buffer = szBuf;
current = buffer;
}
~CDataStream()
{
}
void clear()
{
current = buffer;
current[0]=0;
}
//此函数不动态增加内存,一次打印的数据长度不应该超过缓冲区的三分之一,否则可能导致失败
bool printf(const char * format,...)
{
if(current)
{
if(current - buffer > (m_isize*2)/3)
return false;
va_list argPtr ;
va_start( argPtr, format ) ;
int count = vsprintf( current, format, argPtr ) ;
va_end( argPtr );
current += count ;
return true;
}
return false;
}
//此函数拷贝字符串
bool strcpy(const char * szStr)
{
if(current&&szStr)
{
int ilen = lstrlen(szStr);
if((m_isize-(current - buffer)) < (ilen +2))
return false;
memcpy(current,szStr,ilen+1);
current += ilen;
return true;
}
return false;
}
char * getcurrentpos()
{
return current;
}
void move(int ilen)//当前指针向后移动ilen
{
current += ilen;
}
void reset()
{
current = buffer;
}
BYTE readbyte()
{
current ++;
return *(current-1);
}
void writebyte(BYTE btValue)
{
*current = btValue;
current ++;
}
WORD readword()
{
current +=2;
return *((WORD*)(current-2));
}
void writeword(WORD wValue)
{
*((WORD*)current) = wValue;
current +=2;
}
DWORD readdword()
{
current +=4;
return *((DWORD*)(current-4));
}
void writedword(DWORD dwValue)
{
*((DWORD*)current) = dwValue;
current +=4;
}
__int64 readint64()
{
current +=8;
return *((__int64*)(current-8));
}
void writeint64(__int64 iValue)
{
*((__int64*)current) = iValue;
current +=8;
}
BYTE * readdata(DWORD dwLen)
{
current +=dwLen;
return (BYTE*)(current-dwLen);
}
void writedata(BYTE * pData,DWORD dwLen)
{
memcpy(current,pData,dwLen);
current +=dwLen;
}
char * readstring()
{
char * szRes = current;
int ilen = lstrlen(current);
current +=(ilen+1);
return szRes;
}
int size()
{
return (int)(current-buffer);
}
const char * getbuffer(){return buffer;}
private :
char* buffer;
char* current;
int m_isize;
};
class CNetworkByteOrder
{
public:
static unsigned short int convert(unsigned short int iValue)
{
unsigned short int iData;
((BYTE*)&iData)[0] = ((BYTE*)&iValue)[1];
((BYTE*)&iData)[1] = ((BYTE*)&iValue)[0];
return iData;
}
static int convert(int iValue)
{
int iData;
((BYTE*)&iData)[0] = ((BYTE*)&iValue)[3];
((BYTE*)&iData)[1] = ((BYTE*)&iValue)[2];
((BYTE*)&iData)[2] = ((BYTE*)&iValue)[1];
((BYTE*)&iData)[3] = ((BYTE*)&iValue)[0];
return iData;
}
static __int64 convert(__int64 iValue)
{
__int64 iData;
((BYTE*)&iData)[0] = ((BYTE*)&iValue)[7];
((BYTE*)&iData)[1] = ((BYTE*)&iValue)[6];
((BYTE*)&iData)[2] = ((BYTE*)&iValue)[5];
((BYTE*)&iData)[3] = ((BYTE*)&iValue)[4];
((BYTE*)&iData)[4] = ((BYTE*)&iValue)[3];
((BYTE*)&iData)[5] = ((BYTE*)&iValue)[2];
((BYTE*)&iData)[6] = ((BYTE*)&iValue)[1];
((BYTE*)&iData)[7] = ((BYTE*)&iValue)[0];
return iData;
}

};
#endif // !defined(AFX_DATASTREAM_H__D90A2534_EA73_4BEA_8B7E_87E59A3D1D26__INCLUDED_)
在逸搜(EaseSo)论坛可以下载到支持udp tracker的测试程序BTTrackerTest.

到此,第一阶段工作完成,下面要做的就是peer之间的交互了.