Uploaded image for project: 'Qt'
  1. Qt
  2. QTBUG-27641

Multicast joining fails on multiple interfaces

XMLWordPrintable

    • Icon: Bug Bug
    • Resolution: Done
    • Icon: P3: Somewhat important P3: Somewhat important
    • 5.9.0 Beta 2
    • 4.8.x, 5.7.0
    • Network: Sockets
    • None
    • Windows, Linux
    • 4c367833b4c1776f01eff3d51472a9889c85e1c5

      When trying to use QUdpSocket::joinMulticastGroup with multiple interfaces it often fails under certain conditions.

      After looking into the source code of qnativesocketengine_*.cpp I found the following code that is actually incorrect:

                  QList<QNetworkAddressEntry> addressEntries = iface.addressEntries();
            if (!addressEntries.isEmpty()) {
                QHostAddress firstIP = addressEntries.first().ip();
                mreq4.imr_interface.s_addr = htonl(firstIP.toIPv4Address());
            } else {
                d->setError(QAbstractSocket::NetworkError,
                            QNativeSocketEnginePrivate::NetworkUnreachableErrorString);
                return false;
            }

      This code takes the first address from the list and assumes it is an IPv4 address (which might not be true).
      The proper approach would be to iterate through the list and check for IPv4 protocol:

      	QList<QNetworkAddressEntry> addressEntries = iface.addressEntries();
		for (int i = 0; i < addressEntries.length(); i++) {
			if (addressEntries[i].ip().protocol() == QAbstractSocket::IPv4Protocol) {
				...
				break;

        1. qtbug-27641.patch
          3 kB
        No reviews matched the request. Check your Options in the drop-down menu of this sections header.

            Eddy Edward Welbourne
            dremon Dmitry Pankratov
            Votes:
            5 Vote for this issue
            Watchers:
            11 Start watching this issue

              Created:
              Updated:
              Resolved:

                There are no open Gerrit changes