When updating from Qt 5.9.2 to 5.9.3 today, our UDP based network protocol stopped working on Windows 8.1!

The reason is that QUdpSocket::readDatagram() does not assign the sender address any more.

Here is some example code that fails with 5.9.3:

QHostAddress sender;
QByteArray datagram;
datagram.resize( m_requestSocket->pendingDatagramSize());
m_requestSocket->readDatagram( datagram.data(), datagram.size(), &sender);
qDebug() << "sender:" << sender.isNull() << sender;
processHeartbeat( datagram, sender);

// output: 
sender: true QHostAddress("")

So sender.isNull() returns true, which should not be possible!

The same code is still working on Linux and Android.

Fortunately using QUdpSocket::receiveDatagram() instead seems to be working.