[Interest] Simple UDP listener question

[Thiago Macieira]

Em seg 23 jun 2014, às 13:03:03, Robert Wood escreveu:
> Folks,
> 
> I've managed to get a simple program going that sends out a UDP packet
> to a broadcast address (an Artnet Poll packet) and my embedded software
> is receiving this and sending out a Poll reply. Wireshark confirms that
> my embedded device is sending out the correct response, however, my Qt
> program is not picking up any reply at all. I should say, this is the
> first time I've used Qt for networking and it's my first embedded
> netowrking project, so I may be missing some very basic point.
> 
> I am doing this in MainWindow initialisation:
> 
>      udpSocSend = new QUdpSocket(this);
>      udpSocRec = new QUdpSocket(this);
>      udpSocSend->bind(QHostAddress("192.168.0.18"),6454);
>      udpSocRec->bind(6454, QUdpSocket::ShareAddress);

Pass the ShareAddress to all instances. Setting it on the second after the 
first has bound without the flag will probably result in EADDRINUSE.

>      connect(udpSocRec, SIGNAL(readyRead()),this,
> SLOT(processPendingDatagrams()));
> 
> void MainWindow::processPendingDatagrams()
> {
> 
>      while (udpSocRec->hasPendingDatagrams())
>          {
>          QByteArray datagram;
>          datagram.resize(udpSocRec->pendingDatagramSize());
>          udpSocRec->readDatagram(datagram.data(), datagram.size());
>          ui->textEdit->setText(tr("Received datagram:
> \"%1\"").arg(datagram.data()));
> 
>          }
> }
> 
> My udpSocSend is working to send data out (an Artnet Poll), my STM32
> (embedded micro) is sending packets back according to Wireshark, but
> processPendingDatagrams() flatly refuses to be called!

Probably because it failed to bind to the port. See above.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center