[Winpcap-users] capture tcp packets directly

[Yale Zhang]

Hi. I'm trying to build a port forwarding program that lets two computers
that are behind NATs (mutually invisible to each other) communicate via a
computer they both can connect to (bridge). To do this, I need to be able to
capture TCP packets directly and send them. Is there a way to capture TCP
packets (either without or with headers) without being superuser on UNIX
like systems or Administrator on Windows?

I tried the following program, but the socket cannot be bound. I suppose
that this is because there is no mechanism receiving TCP packets in the
network stack - only stream communication?

byte buffer[2048];
int main(int argc, char **argv)
{
   WSADATA wsa_data;
   if (WSAStartup(MAKEWORD(2, 0), &wsa_data) != 0)
    {
        cout << "WSAStartup() failed\n";
        return 0;
    }
  socket = socket(AF_INET, SOCK_DGRAM, IPPROTO_TCP);
  sockaddr_in addrLocal;
  addrLocal.sin_family = AF_INET;
  addrLocal.sin_addr.s_addr = inet_addr("127.0.0.1");
  addrLocal.sin_port = htons(3390);

  if (bind(socket, (sockaddr *)&addrLocal, sizeof(sockaddr_in)) ==
SOCKET_ERROR)
    cout << "error bind" << endl;

  listen(socket, 10);
  while (true)
  {
      sockaddr_in addr;
      int address_length = sizeof(addr), connection;
      while ((connection = accept(g_socket, (sockaddr *)&addr,
&address_length)) < 0);
      cout << "connected";
      while (true)
      {
      int length = recvfrom(connection, (char *)buffer, 2048, 0, (sockaddr
*)&addr, &address_length);
    //      int length = recv(connection, (char *)buffer, 2048, 0);
      cout << length << endl;
      }
  }
  return 0;
}

Any ideas about how to do what I want or alternatives? Thanks for any help.
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