Examples: Update multicast sender and receiver examples for IPv6

It's the right thing to do, as we're in 2017, not 1997. Also, this takes
care to indicate that QAbstractSocket::MulticastTtlOption makes sense
mostly for IPv4, even though it's implemented for both families. In
IPv4, it's used to indicatae the scope, whereas in IPv6 it's stored in
bits 12-15 of the address.

Task-number: QTBUG-46046
Change-Id: I9741f017961b410c910dfffd14ffaabe0a2024d8
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

2 files changed, 22 insertions, 7 deletions

diff --git a/examples/network/multicastsender/sender.cpp b/examples/network/multicastsender/sender.cpp
index cb4bf45672..a542a2528f 100644
--- a/examples/network/multicastsender/sender.cpp
+++ b/examples/network/multicastsender/sender.cpp
@@ -52,11 +52,21 @@
 
 Sender::Sender(QWidget *parent)
     : QDialog(parent),
-      groupAddress(QStringLiteral("239.255.43.21"))
+      groupAddress4(QStringLiteral("239.255.43.21")),
+      groupAddress6(QStringLiteral("ff12::2115"))
 {
-    statusLabel = new QLabel(tr("Ready to multicast datagrams to group %1 on port 45454").arg(groupAddress.toString()));
+    // force binding to their respective families
+    udpSocket4.bind(QHostAddress(QHostAddress::AnyIPv4), 0);
+    udpSocket6.bind(QHostAddress(QHostAddress::AnyIPv6), udpSocket4.localPort());
 
-    auto ttlLabel = new QLabel(tr("TTL for multicast datagrams:"));
+    QString msg = tr("Ready to multicast datagrams to groups %1 and [%2] on port 45454").arg(groupAddress4.toString());
+    if (udpSocket6.state() != QAbstractSocket::BoundState)
+        msg = tr("IPv6 failed. Ready to multicast datagrams to group %1 on port 45454").arg(groupAddress4.toString());
+    else
+        msg = msg.arg(groupAddress6.toString());
+    statusLabel = new QLabel(msg);
+
+    auto ttlLabel = new QLabel(tr("TTL for IPv4 multicast datagrams:"));
     auto ttlSpinBox = new QSpinBox;
     ttlSpinBox->setRange(0, 255);
 
@@ -88,7 +98,8 @@ Sender::Sender(QWidget *parent)
 
 void Sender::ttlChanged(int newTtl)
 {
-    udpSocket.setSocketOption(QAbstractSocket::MulticastTtlOption, newTtl);
+    // we only set the TTL on the IPv4 socket, as that changes the multicast scope
+    udpSocket4.setSocketOption(QAbstractSocket::MulticastTtlOption, newTtl);
 }
 
 void Sender::startSending()
@@ -101,6 +112,8 @@ void Sender::sendDatagram()
 {
     statusLabel->setText(tr("Now sending datagram %1").arg(messageNo));
     QByteArray datagram = "Multicast message " + QByteArray::number(messageNo);
-    udpSocket.writeDatagram(datagram, groupAddress, 45454);
+    udpSocket4.writeDatagram(datagram, groupAddress4, 45454);
+    if (udpSocket6.state() == QAbstractSocket::BoundState)
+        udpSocket6.writeDatagram(datagram, groupAddress6, 45454);
     ++messageNo;
 }
diff --git a/examples/network/multicastsender/sender.h b/examples/network/multicastsender/sender.h
index 5d8769790e..0af6f9aaec 100644
--- a/examples/network/multicastsender/sender.h
+++ b/examples/network/multicastsender/sender.h
@@ -70,9 +70,11 @@ private slots:
 private:
     QLabel *statusLabel = nullptr;
     QPushButton *startButton = nullptr;
-    QUdpSocket udpSocket;
+    QUdpSocket udpSocket4;
+    QUdpSocket udpSocket6;
     QTimer timer;
-    QHostAddress groupAddress;
+    QHostAddress groupAddress4;
+    QHostAddress groupAddress6;
     int messageNo = 1;
 };