Send AND receive a broadcast message



  • Hello,

    following code does not work:

    udpSocketSend = new QUdpSocket(this);
    udpSocketSend->connectToHost(QHostAddress("192.168.3.255"), 8090);
    QHostAddress *host = new QHostAddress("192.168.3.2");
    udpSocketGet = new QUdpSocket(this);
    udpSocketGet->bind(*host, udpSocketSend->localPort());
    connect(udpSocketGet, SIGNAL(readyRead()), this, SLOT(readPendingDatagrams()));
    connect(startButton, SIGNAL(clicked()), this, SLOT(startBroadcasting()));
    connect(quitButton, SIGNAL(clicked()), this, SLOT(close()));
    connect(timer, SIGNAL(timeout()), this, SLOT(broadcastDatagram()));
    
    void Sender::readPendingDatagrams()
    {
        while (udpSocketGet->hasPendingDatagrams()) {
            QByteArray datagram;
            datagram.resize(udpSocketGet->pendingDatagramSize());
            udpSocketGet->readDatagram(datagram.data(), datagram.size());
            statusLabel->setText(tr("Received datagram: \"%1\"")
                                 .arg(datagram.data()));
        }
    }
    
    
    void Sender::broadcastDatagram()
    {
        statusLabel->setText(tr("Now broadcasting datagram %1").arg(messageNo));
        QByteArray datagram = "<deviceInformationRequest/>";
        udpSocketSend->write(datagram.data(), datagram.size());
        ++messageNo;
    }
    

    In Wireshark log I can see that the write with datagram '<deviceInformationRequest/>' is performed successfully. Furthermore the devices in the network which process the datagram were responding correctly with a special response message.

    The problem is now that it seems that 'readPendingDatagrams()' is never fired. Therefore I am not able to parse request message.

    What is the problem? This is an extended example from given QT "Sender" Broadcast example http://doc.qt.io/qt-5/qtnetwork-broadcastsender-example.html


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