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>

examples/network/multicastreceiver/receiver.cpp

@@ -55,9 +55,10 @@
 
 Receiver::Receiver(QWidget *parent)
     : QDialog(parent),
-      groupAddress(QStringLiteral("239.255.43.21"))
+      groupAddress4(QStringLiteral("239.255.43.21")),
+      groupAddress6(QStringLiteral("ff12::2115"))
 {
-    statusLabel = new QLabel(tr("Listening for multicasted messages"));
+    statusLabel = new QLabel(tr("Listening for multicast messages on both IPv4 and IPv6"));
     auto quitButton = new QPushButton(tr("&Quit"));
 
     auto buttonLayout = new QHBoxLayout;
@@ -72,21 +73,37 @@ Receiver::Receiver(QWidget *parent)
 
     setWindowTitle(tr("Multicast Receiver"));
 
-    udpSocket.bind(QHostAddress::AnyIPv4, 45454, QUdpSocket::ShareAddress);
-    udpSocket.joinMulticastGroup(groupAddress);
+    udpSocket4.bind(QHostAddress::AnyIPv4, 45454, QUdpSocket::ShareAddress);
+    udpSocket4.joinMulticastGroup(groupAddress4);
 
-    connect(&udpSocket, SIGNAL(readyRead()),
+    if (!udpSocket6.bind(QHostAddress::AnyIPv6, 45454, QUdpSocket::ShareAddress) ||
+            !udpSocket6.joinMulticastGroup(groupAddress6))
+        statusLabel->setText(tr("Listening for multicast messages on IPv4 only"));
+
+    connect(&udpSocket4, SIGNAL(readyRead()),
             this, SLOT(processPendingDatagrams()));
+    connect(&udpSocket6, &QUdpSocket::readyRead, this, &Receiver::processPendingDatagrams);
     connect(quitButton, SIGNAL(clicked()), this, SLOT(close()));
 }
 
 void Receiver::processPendingDatagrams()
 {
     QByteArray datagram;
-    while (udpSocket.hasPendingDatagrams()) {
-        datagram.resize(int(udpSocket.pendingDatagramSize()));
-        udpSocket.readDatagram(datagram.data(), datagram.size());
-        statusLabel->setText(tr("Received datagram: \"%1\"")
+
+    // using QUdpSocket::readDatagram (API since Qt 4)
+    while (udpSocket4.hasPendingDatagrams()) {
+        datagram.resize(int(udpSocket4.pendingDatagramSize()));
+        udpSocket4.readDatagram(datagram.data(), datagram.size());
+        statusLabel->setText(tr("Received IPv4 datagram: \"%1\"")
                              .arg(datagram.constData()));
     }
+
+    // using QUdpSocket::receiveDatagram (API since Qt 5.8)
+    while (udpSocket6.hasPendingDatagrams()) {
+        QNetworkDatagram dgram = udpSocket6.receiveDatagram();
+        statusLabel->setText(statusLabel->text() +
+                             tr("\nReceived IPv6 datagram from [%2]:%3: \"%1\"")
+                             .arg(dgram.data().constData(), dgram.senderAddress().toString())
+                             .arg(dgram.senderPort()));
+    }
 }

examples/network/multicastreceiver/receiver.h

@@ -71,8 +71,10 @@ private slots:
 
 private:
     QLabel *statusLabel = nullptr;
-    QUdpSocket udpSocket;
-    QHostAddress groupAddress;
+    QUdpSocket udpSocket4;
+    QUdpSocket udpSocket6;
+    QHostAddress groupAddress4;
+    QHostAddress groupAddress6;
 };
 
 #endif

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;
 }

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;
 };