tst_QUdpSocket: always use an interface when binding to IPv6

Binding without an interface and expecting the OS to select something is
not supported in all OSes. On FreeBSD, I keep getting EADDRNOTAVAIL. So
modify our test to only join, leave and send to multicast groups with an
interface selection.

With this, all tests either pass or are skipped for me on Linux,
FreeBSD, and macOS. On Windows, this revealed an inconsistency in
behavior, which this commit adds a workaround for.

Change-Id: Ifb5969bf206e4cd7b14efffd14fb6815456494d2
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

4 files changed, 70 insertions, 7 deletions

diff --git a/src/network/socket/qnativesocketengine_win.cpp b/src/network/socket/qnativesocketengine_win.cpp
index 747fdeb967..6a091209be 100644
--- a/src/network/socket/qnativesocketengine_win.cpp
+++ b/src/network/socket/qnativesocketengine_win.cpp
@@ -1319,6 +1319,9 @@ qint64 QNativeSocketEnginePrivate::nativeSendDatagram(const char *data, qint64 l
 
     setPortAndAddress(header.destinationPort, header.destinationAddress, &aa, &msg.namelen);
 
+    uint oldIfIndex = 0;
+    bool mustSetIpv6MulticastIf = false;
+
     if (msg.namelen == sizeof(aa.a6)) {
         // sending IPv6
         if (header.hopLimit != -1) {
@@ -1330,7 +1333,7 @@ qint64 QNativeSocketEnginePrivate::nativeSendDatagram(const char *data, qint64 l
             cmsgptr = reinterpret_cast<WSACMSGHDR *>(reinterpret_cast<char *>(cmsgptr)
                                                      + WSA_CMSG_SPACE(sizeof(int)));
         }
-        if (header.ifindex != 0 || !header.senderAddress.isNull()) {
+        if (!header.senderAddress.isNull()) {
             struct in6_pktinfo *data = reinterpret_cast<in6_pktinfo *>(WSA_CMSG_DATA(cmsgptr));
             memset(data, 0, sizeof(*data));
             msg.Control.len += WSA_CMSG_SPACE(sizeof(*data));
@@ -1343,6 +1346,21 @@ qint64 QNativeSocketEnginePrivate::nativeSendDatagram(const char *data, qint64 l
             memcpy(&data->ipi6_addr, &tmp, sizeof(tmp));
             cmsgptr = reinterpret_cast<WSACMSGHDR *>(reinterpret_cast<char *>(cmsgptr)
                                                      + WSA_CMSG_SPACE(sizeof(*data)));
+        } else if (header.ifindex != 0) {
+            // Unlike other operating systems, setting the interface index in the in6_pktinfo
+            // structure above and leaving the ipi6_addr set to :: will cause the packets to be
+            // sent with source address ::. So we have to use IPV6_MULTICAST_IF, which MSDN is
+            // quite clear that "This option does not change the default interface for receiving
+            // IPv6 multicast traffic."
+            QT_SOCKOPTLEN_T len = sizeof(oldIfIndex);
+            if (::getsockopt(socketDescriptor, IPPROTO_IPV6, IPV6_MULTICAST_IF,
+                             reinterpret_cast<char *>(&oldIfIndex), &len) == -1
+                    || ::setsockopt(socketDescriptor, IPPROTO_IPV6, IPV6_MULTICAST_IF,
+                                    reinterpret_cast<const char *>(&header.ifindex), sizeof(header.ifindex)) == -1) {
+                setError(QAbstractSocket::NetworkError, SendDatagramErrorString);
+                return -1;
+            }
+            mustSetIpv6MulticastIf = true;
         }
     } else {
         // sending IPv4
@@ -1396,6 +1414,12 @@ qint64 QNativeSocketEnginePrivate::nativeSendDatagram(const char *data, qint64 l
         ret = qint64(bytesSent);
     }
 
+    if (mustSetIpv6MulticastIf) {
+        // undo what we did above
+        ::setsockopt(socketDescriptor, IPPROTO_IPV6, IPV6_MULTICAST_IF,
+                     reinterpret_cast<char *>(&oldIfIndex), sizeof(oldIfIndex));
+    }
+
 #if defined (QNATIVESOCKETENGINE_DEBUG)
     qDebug("QNativeSocketEnginePrivate::nativeSendDatagram(%p \"%s\", %lli, \"%s\", %i) == %lli", data,
            qt_prettyDebug(data, qMin<qint64>(len, 16), len).data(), len,
diff --git a/src/network/socket/qudpsocket.cpp b/src/network/socket/qudpsocket.cpp
index 79629a07f2..85c4f4cbfd 100644
--- a/src/network/socket/qudpsocket.cpp
+++ b/src/network/socket/qudpsocket.cpp
@@ -185,6 +185,10 @@ QUdpSocket::~QUdpSocket()
     This function returns \c true if successful; otherwise it returns \c false
     and sets the socket error accordingly.
 
+    \note Joining IPv6 multicast groups without an interface selection is not
+    supported in all operating systems. Consider using the overload where the
+    interface is specified.
+
     \sa leaveMulticastGroup()
 */
 bool QUdpSocket::joinMulticastGroup(const QHostAddress &groupAddress)
@@ -219,6 +223,9 @@ bool QUdpSocket::joinMulticastGroup(const QHostAddress &groupAddress,
    This function returns \c true if successful; otherwise it returns \c false and
    sets the socket error accordingly.
 
+   \note This function should be called with the same arguments as were passed
+   to joinMulticastGroup().
+
    \sa joinMulticastGroup()
 */
 bool QUdpSocket::leaveMulticastGroup(const QHostAddress &groupAddress)
@@ -233,6 +240,9 @@ bool QUdpSocket::leaveMulticastGroup(const QHostAddress &groupAddress)
     Leaves the multicast group specified by \a groupAddress on the interface \a
     iface.
 
+    \note This function should be called with the same arguments as were passed
+    to joinMulticastGroup().
+
     \sa joinMulticastGroup()
 */
 bool QUdpSocket::leaveMulticastGroup(const QHostAddress &groupAddress,
diff --git a/tests/auto/network/socket/qudpsocket/BLACKLIST b/tests/auto/network/socket/qudpsocket/BLACKLIST
index dcb5f87628..5b8d4f1e34 100644
--- a/tests/auto/network/socket/qudpsocket/BLACKLIST
+++ b/tests/auto/network/socket/qudpsocket/BLACKLIST
@@ -1,5 +1,3 @@
-[multicast]
-osx
 [writeDatagramToNonExistingPeer]
 windows
 osx
diff --git a/tests/auto/network/socket/qudpsocket/tst_qudpsocket.cpp b/tests/auto/network/socket/qudpsocket/tst_qudpsocket.cpp
index 69d549d738..5fdf014fc6 100644
--- a/tests/auto/network/socket/qudpsocket/tst_qudpsocket.cpp
+++ b/tests/auto/network/socket/qudpsocket/tst_qudpsocket.cpp
@@ -122,6 +122,7 @@ private:
 #ifdef SHOULD_CHECK_SYSCALL_SUPPORT
     bool ipv6SetsockoptionMissing(int level, int optname);
 #endif
+    QNetworkInterface interfaceForGroup(const QHostAddress &multicastGroup);
 
     bool m_skipUnsupportedIPv6Tests;
     QList<QHostAddress> allAddresses;
@@ -167,6 +168,33 @@ bool tst_QUdpSocket::shouldSkipIpv6TestsForBrokenSetsockopt()
     return false;
 }
 
+QNetworkInterface tst_QUdpSocket::interfaceForGroup(const QHostAddress &multicastGroup)
+{
+    if (multicastGroup.protocol() == QAbstractSocket::IPv4Protocol)
+        return QNetworkInterface();
+
+    static QNetworkInterface ipv6if = [=]() {
+        // find any link local address in the allAddress list
+        for (const QHostAddress &addr: qAsConst(allAddresses)) {
+            if (addr.isLoopback())
+                continue;
+
+            QString scope = addr.scopeId();
+            if (!scope.isEmpty()) {
+                QNetworkInterface iface = QNetworkInterface::interfaceFromName(scope);
+                qDebug() << "Will bind IPv6 sockets to" << iface;
+                return iface;
+            }
+        }
+
+        qWarning("interfaceForGroup(%s) could not find any link-local IPv6 address! "
+                 "Make sure this test is behind a check of QtNetworkSettings::hasIPv6().",
+                 qUtf8Printable(multicastGroup.toString()));
+        return QNetworkInterface();
+    }();
+    return ipv6if;
+}
+
 static QHostAddress makeNonAny(const QHostAddress &address, QHostAddress::SpecialAddress preferForAny = QHostAddress::LocalHost)
 {
     if (address == QHostAddress::Any)
@@ -1299,7 +1327,7 @@ void tst_QUdpSocket::multicastLeaveAfterClose()
         bindAddress = QHostAddress::AnyIPv6;
     QVERIFY2(udpSocket.bind(bindAddress, 0),
              qPrintable(udpSocket.errorString()));
-    QVERIFY2(udpSocket.joinMulticastGroup(groupAddress),
+    QVERIFY2(udpSocket.joinMulticastGroup(groupAddress, interfaceForGroup(groupAddress)),
              qPrintable(udpSocket.errorString()));
     udpSocket.close();
     QTest::ignoreMessage(QtWarningMsg, "QUdpSocket::leaveMulticastGroup() called on a QUdpSocket when not in QUdpSocket::BoundState");
@@ -1413,7 +1441,7 @@ void tst_QUdpSocket::multicast()
                              "QAbstractSocket: cannot bind to QHostAddress::Any (or an IPv6 address) and join an IPv4 multicast group;"
                              " bind to QHostAddress::AnyIPv4 instead if you want to do this");
     }
-    QVERIFY2(receiver.joinMulticastGroup(groupAddress) == joinResult,
+    QVERIFY2(receiver.joinMulticastGroup(groupAddress, interfaceForGroup(groupAddress)) == joinResult,
              qPrintable(receiver.errorString()));
     if (!joinResult)
         return;
@@ -1427,7 +1455,9 @@ void tst_QUdpSocket::multicast()
     QUdpSocket sender;
     sender.bind();
     foreach (const QByteArray &datagram, datagrams) {
-        QCOMPARE(int(sender.writeDatagram(datagram, groupAddress, receiver.localPort())),
+        QNetworkDatagram dgram(datagram, groupAddress, receiver.localPort());
+        dgram.setInterfaceIndex(interfaceForGroup(groupAddress).index());
+        QCOMPARE(int(sender.writeDatagram(dgram)),
                  int(datagram.size()));
     }
 
@@ -1452,7 +1482,8 @@ void tst_QUdpSocket::multicast()
     }
     QCOMPARE(receivedDatagrams, datagrams);
 
-    QVERIFY2(receiver.leaveMulticastGroup(groupAddress), qPrintable(receiver.errorString()));
+    QVERIFY2(receiver.leaveMulticastGroup(groupAddress, interfaceForGroup(groupAddress)),
+             qPrintable(receiver.errorString()));
 }
 
 void tst_QUdpSocket::echo_data()