[Interest] Simple device discovery using UDP

Jason H jhihn at gmx.com
Tue Oct 2 15:43:39 CEST 2018

I have an app (Desktop) that I want it to know about other running instances on the local network. I figured UDP broadcast was a natural choice. I tried it, but I never saw anything but my own (local) packets. There's quite a few stackoverflow questions, but none used Qt. I'm wondering if it's a wifi/router thing?

The hosts are on the same WiFi SSID and address space: host1 host2

Both are on my desk. 
HostInfoService::HostInfoService(...) {
	udpSocket4.bind(QHostAddress::Any, 13999, QUdpSocket::ShareAddress);
	connect(&udpSocket4, SIGNAL(readyRead()), this, SLOT(readPendingDatagrams()));

void HostInfoService::readPendingDatagrams()
	for (auto udpSocket: {&udpSocket4 } ) { //, &udpSocket6}) {
		while (udpSocket->hasPendingDatagrams()) {
			QNetworkDatagram datagram = udpSocket->receiveDatagram();
			QString host = QString(datagram.data().constData());
			messages[host] = datagram.senderAddress();
			qDebug() << Q_FUNC_INFO << host << datagram.senderAddress().toString();

I also tried on an IPv6 socket, no joy.

Has anyone else done something like this?

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