.NET UdpClient and Winsock Interoperability Issue

Question

I have an application written in C++ that uses Winsock for a UDP client. I am trying to send data to another UDP client that is written in C++/CLI, that uses the .Net UdpClient class. The messages are successfully sent, but never received. That is, never come out of the listener->Receive(endPoint); call on the .NET side.

I replaced the .Net UDPClient code with Winsock in the C++/CLI code, and there is no problem.

Both machines are running Windows 7 (so, .NET 4, and whatever version of WSA under Windows 7)

Here is the C++ Winsock code:

    SOCKET jsDataSocket;
    WSADATA WSAData;
    string dottedInetAddress = "192.168.2.100"
    int port = 5601;

bool JoystickDataPublisher::socketSetup()
{
    int iError;

    // Call "WSAStartup" and display description text
    if (iError = WSAStartup (MAKEWORD(2,2), &WSAData))
    {
        OutputDebugString(L"JoystickDataPublisher - Unable to start WinSock");
        return false;
    }
    else
        return socketSetup();

    int status;

    // create UDP socket for receiving
    jsDataSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (jsDataSocket == SOCKET_ERROR)
    {
        OutputDebugString(L"JoystickDataPublisher - Server socket creation error\n");
        return false;
    }

bool JoystickDataPublisher::sendData(const char * buf, int size)
{

    struct sockaddr_in srv_addr;
    int status;

    if (jsDataSocket == 0)
    {
        OutputDebugString(L"No socket exists yet!");
        return false;
    }

    // this is where we fill in the specific server address 
    // and port, and use our generic client socket to send
    // a message
    srv_addr.sin_family = AF_INET;
    srv_addr.sin_addr.s_addr = inet_addr (dottedInetAddress.c_str()) ;
    srv_addr.sin_port = port;

    status = sendto(jsDataSocket, (const char *)buf, size, 0, 
        (struct sockaddr*)&srv_addr, sizeof(srv_addr));

    if (status != size)
    {
        OutputDebugString(L"Message not sent Perhaps your friend is not listening");
        return false;
    }

    return true;
}

Here is the .NET Side:

    // this code exists in a System::Threading::Thread

    private: UdpClient ^ listener;

private: void UpdateFunction()

    listener = gcnew UdpClient(5601);
    IPEndPoint ^ endPoint = gcnew IPEndPoint(IPAddress::Any,5601);
             array<byte> ^ receiveData = gcnew array<byte>(1024);
             JoystickData jsData;

    while(1)
    {
     endPoint->Address = IPAddress::Any;
     endPoint->Port = 5601;
     try
     {
                     **// never unblock from following call**
         receiveData = listener->Receive(endPoint);
     }
     catch (SocketException ^ e)
     {
         // got here because either the Receive failed, or more
         // or more likely the socket was destroyed by 
         // exiting from the JoystickPositionWindow form
        Console::WriteLine(e->ToString());
        return;
     }
         Marshal::Copy(receiveData,0,(IntPtr)&jsData,sizeof(jsData));

                     currentXRelPosition = jsData.xRelPosition;
                     currentYRelPosition = jsData.yRelPosition;

     Invalidate();
         }
      }

user1298237 user1298237 · Accepted Answer · 2012-04-10T14:53:14

The issue came down to the byte order of the port. On the Winsock side, when setting up the port, I needed to use htons(port), as follows:

srv_addr.sin_port = htons(port);

.NET UdpClient and Winsock Interoperability Issue

1 Answers