FIX: Accept Returns FALSE but GetLastError Returns 0

RESOLUTION

If your class is derived directly from CAsyncSocket, then replace the Accept function and modify it so that the error code is not lost.

This can be done by first borrowing the function from the CAsyncSocket::Accept function found in the MFC source code in the file SOCKCORE.CPP. Change the function to be implemented as follows:

   #if _MFC_VER >= 0x0410 && _MFC_VER <= 0x0420

   BOOL CMySocket::Accept(CAsyncSocket& rConnectedSocket,
                          SOCKADDR* lpSockAddr, int* lpSockAddrLen)
   {
     ASSERT(rConnectedSocket.m_hSocket == INVALID_SOCKET);
     ASSERT(CAsyncSocket::FromHandle(INVALID_SOCKET) == NULL);

     CAsyncSocket::AttachHandle(INVALID_SOCKET, &rConnectedSocket);

     SOCKET hTemp = accept(m_hSocket, lpSockAddr, lpSockAddrLen);

     if (hTemp == INVALID_SOCKET)
     {
   // <===== STORE THE ERROR CODE RECEIVED FROM THE accept CALL
       int nError = WSAGetLastError();

       CAsyncSocket::DetachHandle(rConnectedSocket.m_hSocket, FALSE);

   // <===== RE-SET THE ERROR CODE THAT WAS SET IN THE accept CALL
       WSASetLastError(nError);

       rConnectedSocket.m_hSocket = INVALID_SOCKET;
     }
     else if (CAsyncSocket::FromHandle(INVALID_SOCKET) != NULL)
     {
       rConnectedSocket.m_hSocket = hTemp;
       CAsyncSocket::DetachHandle(INVALID_SOCKET, FALSE);
       CAsyncSocket::AttachHandle(hTemp, &rConnectedSocket);
     }

     return (hTemp != INVALID_SOCKET);
   }

   #endif  // _MFC_VER
				

If your class is derived from CSocket, then you will have to replace CAsyncSocket::Accept as well as CSocket::Accept. This is necessary because CSocket::Accept directly calls CAsyncSocket::Accept. This can be accomplished by providing your own Accept function, called AcceptFix. It would be implemented just as the Accept function shown above. For example:

   #if _MFC_VER >= 0x0410 && _MFC_VER <= 0x0420

   BOOL CMySocket::AcceptFix(CAsyncSocket& rConnectedSocket,
                             SOCKADDR* lpSockAddr, int* lpSockAddrLen)
   {
      ...
      // IMPLEMENTATION IS THE SAME AS THE ONE SHOWN ABOVE
      ...
      return (hTemp != INVALID_SOCKET);
   }

   #endif // _MFC_VER
				

Then provide a replacement for CSocket::Accept and modify it to call AcceptFix instead of CAsyncSocket::Accept. You can borrow the CSocket::Accept function from SOCKCORE.CPP and modify it as follows:

   #if _MFC_VER >= 0x0410 && _MFC_VER <= 0x0420

   BOOL CMySocket::Accept(CAsyncSocket& rConnectedSocket,
                          SOCKADDR* lpSockAddr, int* lpSockAddrLen)
   {
     if (m_pbBlocking != NULL)
     {
       WSASetLastError(WSAEINPROGRESS);
       return FALSE;
     }

     // <===============  REPLACE THE FOLLOWING LINE
     // while (!CAsyncSocket::Accept(rConnectedSocket, lpSockAddr,...
     // <===============  WITH THIS:

     while (!AcceptFix(rConnectedSocket, lpSockAddr, lpSockAddrLen))
     {
       if (GetLastError() == WSAEWOULDBLOCK)
       {
         if (!PumpMessages(FD_ACCEPT))
           return FALSE;
       }
       else
         return FALSE;
     }
     return TRUE;
   }

   #endif // _MFC_VER