Read network-data send by Colasoft Packet Player with Qt

Question

I am trying to read the data send by Colasoft Packet Player via Qt.

I use a loopbackadapter with IP 192.168.1.99 and Wireshark shows me something like this:

SourceIP: 192.168.1.1

SourcePort: 40102

DestinationIP: 224.0.1.12

DestinationPort: 49156

But using those IPs and Ports, Qt QUdpSocket does not show any data. When I try to read over all ports and IPs i receive data, so the programm should work, but it seems, I do not get any data send by Colasoft Packet Player.

What do I do wrong?

Thank you!

MyUDPSocket::MyUDPSocket(QObject *parent)
: QObject(parent)
{
    socket = new QUdpSocket(this);


    //socket->bind(QHostAddress("127.0.0.1"), 40102);
    //socket->bind(QHostAddress("127.0.0.1"), 49156);

    //socket->bind(QHostAddress("224.0.1.12"), 40102);
    //socket->bind(QHostAddress("224.0.1.12"), 49156);

    //socket->bind(QHostAddress("192.168.1.1"), 40102);
    //socket->bind(QHostAddress("192.168.1.1"), 49156);

    //socket->bind(QHostAddress("192.168.1.99"), 40102);
    //socket->bind(QHostAddress("192.168.1.99"), 49156);


    //socket->bind(QHostAddress::Any, 40102);
    //socket->bind(QHostAddress::Any, 49156);

    socket->bind(QHostAddress::Any, 49156, QUdpSocket::ShareAddress);   
    socket->joinMulticastGroup(QHostAddress("224.0.1.12"));
    connect(socket, SIGNAL(readyRead()), this, SLOT(readyRead()));
}

void MyUDPSocket::readyRead()
{
        // when data comes in
        QByteArray buffer;
        buffer.resize(socket->pendingDatagramSize());

        QHostAddress sender;
        quint16 senderPort;

        // qint64 QUdpSocket::readDatagram(char * data, qint64 maxSize, 
        //                 QHostAddress * address = 0, quint16 * port = 0)
        // Receives a datagram no larger than maxSize bytes and stores it in data. 
        // The sender's host address and port is stored in *address and *port 
        // (unless the pointers are 0).

        socket->readDatagram(buffer.data(), buffer.size(),
                             &sender, &senderPort);
        qDebug() << "\n+-------------------------------";
        qDebug() << "|Message from:" << sender.toString(); 
        qDebug() << "|Message port:" << senderPort;
        qDebug() << "|Message:" << buffer;
        qDebug() << "+-------------------------------\n";
    }
}

Answer 1

The address 224.0.1.12 corresponds to multicast. So, you want to join multicast stream, see bool QUdpSocket::joinMulticastGroup(const QHostAddress & groupAddress), from that document:

Note that if you are attempting to join an IPv4 group, your socket must not be bound using IPv6 (or in dual mode, using QHostAddress::Any). You must use QHostAddress::AnyIPv4 instead.

There is also Qt Multicast Receiver Example.

---

Update due to original question code changes

I verified that the original code before edit (without joinMulticastGroup()) was able to receive normal unicast UDP packets to port 49156. So, the code worked as a server listening bound port.

Now with joinMulticastGroup() and replacement QHostAddress::Any -> QHostAddress::AnyIPv4 the code is able to receive multicast stream from VLC player.

So, the coding issues are resolved. Other possible issues:

• routing setup
• incorrectly formed packed by Colasoft Packet Player