Question

I have a server-client program that use TCP connection to communicate. More than one client can connect to the server at the same time. I want to implement the tcp hole punching on this system.

On the client side, It calls to the public server to look up the public ip,port of my server. Then connect to it.

But on the server side it has to open a port to connect to the public server, and it also has to accept the client connection request on this same port.

What I’m going to do is opening a socket and bind to port X, then connect to the public server, then change this socket to listening state to accept the incoming connection for some period, then start connection to the public server again, over and over.

Is this the right approach ?

EDIT: I have another idea. It is to open a new port and connect to the public server. The main server port is left listening for incoming connection as usual. When the client want to connect, the public server will tell my server via the new port. It will stop the main port from listen the incoming connection, instead, It will connect to the client to do the hole punching. Then It connect to the public server, which will forward the server public ip address to the client, and goes back to listen for incoming connection as usual. The client will then use this address to connect to the server which TCP hole already opened.

Answer 1

Better have two socket and maintain separate the conection between server and client.

1. m_nServerTCPSocket- used to connect and listner socket with server

2. m_nPeerPrivateTCPSocket- to connect with peer (public address)

3. m_nPeerPublicTCPSocket- to connect with peer (private address if other peer is in the same network)

4. m_nListeningTCPSocket – used to listener socket for peer here u need to accept connection from peer.

5. m_nConnectedPeerTCPSocket-> you get this socket once you connected with other peer.

   while(end_client)    
   {
   
      FD_ZERO(&fdRead);
      FD_ZERO(&fdWrite);
      FD_ZERO(&fdExcept);    
   
      if (pControlMgr->GetConnectionMgr()->GetListeningTCPSocket()>0)
   
      {
   
           FD_SET (pControlMgr->GetConnectionMgr()->GetListeningTCPSocket(),&fdRead);      
           FD_SET (pControlMgr->GetConnectionMgr()->GetListeningTCPSocket(),&fdExcept);
       }
   
       if (pControlMgr->GetConnectionMgr()->GetServerTCPSocket()>0)
       {
   
           FD_SET (pControlMgr->GetConnectionMgr()->GetServerTCPSocket(),&fdRead); 
           FD_SET (pControlMgr->GetConnectionMgr()->GetServerTCPSocket(),&fdExcept);
   }
       if (pControlMgr->GetConnectionMgr()->GetConnectedTCPSocket()>0)
   {
       FD_SET (pControlMgr->GetConnectionMgr()->GetConnectedTCPSocket(),&fdRead);      
       FD_SET (pControlMgr->GetConnectionMgr()->GetConnectedTCPSocket(),&fdExcept);        
   }
   
   timeval tv;
   tv.tv_sec = 2;
   tv.tv_usec = 0;
   
   nSelectRetVal =  select(NULL,&fdRead,NULL,&fdExcept,&tv);
   
   
   if (nSelectRetVal>0)
   {
       int nRecvRetVal = 0;
       /* TCP Server Socket handling */
       if ( FD_ISSET(pControlMgr->GetConnectionMgr()->GetServerTCPSocket(), &fdRead ))
       {           
           try
           {
               pRecvBuffer =  new char[TCP_RECV_SIZE];
               nRecvRetVal = recv(pControlMgr->GetConnectionMgr()->GetServerTCPSocket(),
                   pRecvBuffer,TCP_RECV_SIZE,
                   0);
               int n = WSAGetLastError();
               if (nRecvRetVal>0)
               {
                   int nPeerNameRetVal = getpeername(pControlMgr->GetConnectionMgr()->GetServerTCPSocket(),(sockaddr*)&addrRemotePeer,&nSockAddrLen);
                   if ( pControlMgr->HandlePacket(pRecvBuffer,addrRemotePeer)== -1 )                       
                   {
                       if ( NULL != pRecvBuffer)
                       {
                           delete [] pRecvBuffer;
                           pRecvBuffer = NULL;
                           return 0 ;
                       }
                   }
               }                           
           }           
           catch (...)
           {
               if ( NULL != pRecvBuffer )
               {
                   delete [] pRecvBuffer;
                   pRecvBuffer = NULL;
               }
           }
   
           if ( NULL != pRecvBuffer)
           {
               delete [] pRecvBuffer;
               pRecvBuffer = NULL;
           }       
       } /* TCP Server Socket handling */      
   
       int n;
       /* TCP Exception Server Socket handling */
       if ( FD_ISSET(pControlMgr->GetConnectionMgr()->GetServerTCPSocket(), &fdExcept ))
       {
           /*FD_CLR(pControlMgr->GetConnectionMgr().GetServerTCPSocket (),&fdRead);
           FD_CLR(pControlMgr->GetConnectionMgr().GetServerTCPSocket (),&fdExcept);*/
           n = WSAGetLastError();
           //return 0;
       }   
          if (FD_ISSET(pControlMgr->GetConnectionMgr()->GetListeningTCPSocket(),&fdRead))
       {
           sockaddr_in addrConnectedPeer;
           int nAddrLen =sizeof(addrConnectedPeer) ;
           int nConnectedSock = accept( pControlMgr->GetConnectionMgr()->GetListeningTCPSocket(),
               (sockaddr*)&addrConnectedPeer,
               &nAddrLen);
           int n1 = WSAGetLastError();
           if (nConnectedSock>0)
           {
               pControlMgr->GetConnectionMgr()->SetConnectedTCPSocket(nConnectedSock);
               int n = pControlMgr->GetConnectionMgr()->GetConnectedTCPSocket();
               continue;
           }
       }
       /* TCP Exception Listening Socket handling */
       if ( FD_ISSET(pControlMgr->GetConnectionMgr()->GetListeningTCPSocket(), &fdExcept ))
       {
           FD_CLR(pControlMgr->GetConnectionMgr()->GetListeningTCPSocket (),&fdRead);
           FD_CLR(pControlMgr->GetConnectionMgr()->GetListeningTCPSocket (),&fdExcept);
           //return 0;
       }   /* TCP Exception Listening Socket handling */   
   
       /* Connected Peer TCP Read Socket handling */
       if ( FD_ISSET(pControlMgr->GetConnectionMgr()->GetConnectedTCPSocket(), &fdRead ))
       {           
           try
           {
               pRecvBuffer =  new char[TCP_RECV_SIZE];
               nRecvRetVal = recv (pControlMgr->GetConnectionMgr()->GetConnectedTCPSocket(),
                   pRecvBuffer,TCP_RECV_SIZE,
                   0);
               if (nRecvRetVal>0)
               {
                   int nPeerNameRetVal = getpeername(pControlMgr->GetConnectionMgr()->GetConnectedTCPSocket(),(sockaddr*)&addrRemotePeer,&nSockAddrLen);
                   if ( pControlMgr->HandlePacket(pRecvBuffer,addrRemotePeer)== -1 )                       
                   {
                       if ( NULL != pRecvBuffer)
                       {
                           delete [] pRecvBuffer;
                           pRecvBuffer = NULL;
                           return 0 ;
                       }
                   }
               }                           
           }           
           catch (...)
           {
               if ( NULL != pRecvBuffer )
               {
                   delete [] pRecvBuffer;
                   pRecvBuffer = NULL;
               }
           }
           //FD_CLR(pControlMgr->GetConnectionMgr().GetConnectedTCPSocket(),&fdRead);  
           if ( NULL != pRecvBuffer)
           {
               delete [] pRecvBuffer;
               pRecvBuffer = NULL;
           }       
       } /* Peer TCP Read Socket handling */   
       /* TCP Exception Connected Socket handling */
       if ( FD_ISSET(pControlMgr->GetConnectionMgr()->GetConnectedTCPSocket(), &fdExcept ))
       {
           /*FD_CLR(pControlMgr->GetConnectionMgr()->GetConnectedTCPSocket (),&fdRead);
           FD_CLR(pControlMgr->GetConnectionMgr()->GetConnectedTCPSocket (),&fdExcept);
           return 0;*/
           n = WSAGetLastError();
       }
   

logic to create sockets

      int CConnectionMgr::CreateSocket(const int nSockType)
      {
       //TODO: Add code here    
           if (InitWinSock() == -1) 
       {
        return -1;      
       }
       SetLocalIPAddress(); 

       m_nListeningTCPSocket = socket(AF_INET, SOCK_STREAM ,nSockType );                    
       if ( GetListeningTCPSocket() <0 )
        return -1;  
       if (BindSocket(GetListeningTCPSocket())<0)
        return -1;
       int nListenRet = listen(GetListeningTCPSocket(),SOMAXCONN);

        if (nListenRet!=0)
        {
        return -1;
         }      
         m_nPeerPrivateTCPSocket = socket(AF_INET, SOCK_STREAM ,nSockType );
         if (GetPeerPrivateTCPSocket()<0)
         return -1; 
        if (BindSocket(GetPeerPrivateTCPSocket())<0)
         return -1;

         m_nPeerPublicTCPSocket = socket(AF_INET, SOCK_STREAM ,nSockType );
         if ( GetPeerPublicTCPSocket()<0)
           return -1;
          if (BindSocket(GetPeerPublicTCPSocket())<0)
           return -1;

          m_nServerTCPSocket = socket(AF_INET, SOCK_STREAM ,nSockType );
          if (GetServerTCPSocket()<0)
           return -1;
          if (BindSocket(GetServerTCPSocket())<0)
           return -1;
        return 1;
         }