No network interfaces have flag "CanMulticast" in Windows UWP app

Ivan B

I printed the flags for network interfaces and they show that no interface has CanMulticast flag set.
So I believe that is the reason, why socket fails to join multicast group.
The same code runs just fine on Windows (non-UWP), Ubuntu, Android, iOS.
I run this sample on Windows under Virtualbox. But I also tested in real Windows machine and Windows tablet.

Here is the code:

    if (m_multicastSocket->state() != QAbstractSocket::BoundState) {
        if (!m_multicastSocket->bind(QHostAddress::AnyIPv4, MULTICAST_HELLO_PORT, QAbstractSocket::ShareAddress | QAbstractSocket::ReuseAddressHint)) {
            LOGW << "Error: Failed to bind multicast socket!";
            return;
        }
        else
            LOGD << "Successfully bound to multicast HELLO port:" << MULTICAST_HELLO_PORT;

        const QString& ifName = ClientNetworkManager::instance().desiredInterfaceName();
        if (!ifName.isEmpty())
            m_multicastSocket->setMulticastInterface(QNetworkInterface::interfaceFromName(ifName));

        for (const auto& i : QNetworkInterface::allInterfaces()) {
            LOGW << "Interface:" << i.name() << "loopback:" << bool(i.flags() & QNetworkInterface::IsLoopBack)
                 << "\nrunning:" << bool(i.flags() & QNetworkInterface::IsRunning)
                 << "\nmulticast:" <<bool(i.flags() & QNetworkInterface::CanMulticast)
                 << "\naddress is empty:" << i.addressEntries().isEmpty();

            if (!(i.flags() & QNetworkInterface::IsLoopBack)
                    && (i.flags() & QNetworkInterface::IsRunning)
                    && (i.flags() & QNetworkInterface::CanMulticast)
                    && (!i.addressEntries().isEmpty()))
            {
                if (!m_multicastSocket->joinMulticastGroup(QHostAddress(MULTICAST_HELLO_GROUP), i)) {
                    LOGW << "Error: Joining multicast group failed on interface" << i.name() << i.humanReadableName() << i.hardwareAddress() << "with error:" << m_multicastSocket->errorString();
                }
                else
                    LOGW << "Successfully joined multicast group on interface" << i.name() << i.humanReadableName() << i.hardwareAddress();
            }
        }
    }

The log output is:

Successfully bound to multicast HELLO port: 55555

Interface: "{76FCD10B-5F45-4155-9C42-31960A66A6E2}" loopback: false 
running: true 
multicast: false 
address is empty: false

Interface: "{76FCD10B-5F45-4155-9C42-31960A66A6E2}" loopback: false 
running: true 
multicast: false 
address is empty: true

The log for the same app rebuilt as normal Windows app:

Successfully bound to multicast HELLO port: 55555

Interface: "ethernet_32771" loopback: false
running: true
multicast: true
address is empty: false
Successfully joined multicast group on interface "ethernet_32771" "vEthernet (Default Switch) 2" "50:15:5D:D0:DB:77"

Interface: "ethernet_32774" loopback: false
running: true
multicast: true
address is empty: false
Successfully joined multicast group on interface "ethernet_32774" "Ethernet 2" "08:00:27:DC:00:5D"

Interface: "loopback_0" loopback: true
running: true
multicast: true
address is empty: false

Interface: "ethernet_32780" loopback: false
running: true
multicast: true
address is empty: false
Successfully joined multicast group on interface "ethernet_32780" "vEthernet (nat) 2" "00:15:5D:C8:5C:2A"

QT multicastreceiver example produces the same results.

Do you have any hints?