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How to set SO_REUSEPORT option for QUdpSocket?

  • Hello. How to set SO_REUSEPORT option for QUdpSocket?

  • Qt Champions 2017

    use BindMode and BindFlag in bind(..) method

  • I could not get this to work using the QUdpSocket::bind() functions and the BindFlag as dheerendra suggested. There doesn't seem to be a BindFlag for reusing ports, at least not in in Qt4 (what I use). I did look quickly at the Qt5 documentation and didn't see any appropriate BindFlag, either.

    So I did it using Berkeley sockets. I'm using Linux, the same code might work with WinSock, if not something trivially similar will. The following code creates a QUdpSocket, provides it with a low-level socket descriptor that has been set for SO_REUSEPORT, then binds it to port 34567:

    QUdpSocket *sock = new QUdpSocket;
    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    int optval = 1;
    setsockopt(sockfd, SOL_SOCKET, SO_REUSEPORT, 
                  (void *) &optval, sizeof(optval));
    sock->setSocketDescriptor(sockfd, QUdpSocket::UnconnectedState);
    sock->bind(34567, QUdpSocket::ShareAddress | QUdpSocket::ReuseAddressHint);

  • @Xando

    https://stackoverflow.com/questions/47268023/how-to-set-so-reuseaddr-on-the-socket-used-by-qtcpserver takes the same approach as you do if required to access flags not available from Qt.

    FYI though, have a careful read of https://bugreports.qt.io/browse/QTBUG-33419. At one point I see:

       case QNativeSocketEngine::AddressReusable:
    #if defined(SO_REUSEPORT)
            // on OS X, SO_REUSEADDR isn't sufficient to allow multiple binds to the
            // same port (which is useful for multicast UDP). SO_REUSEPORT is, but
            // we most definitely do not want to use this for TCP. See QTBUG-6305.
            if (socketType == QAbstractSocket::UdpSocket)
                n = SO_REUSEPORT;
                n = SO_REUSEADDR;
            n = SO_REUSEADDR;

    implying that code for QNativeSocketEngine::AddressReusable will use SO_REUSEPORT for QAbstractSocket::UdpSocket , provided available at compilation?

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