DTLS client - improve the example

- Remove redundant pingTimer.start() call (timer is not a single
shot timer and already started before this point in code).
- Use connected UDP sockets to show that it can work with QDtls.
- Replace (translated) string concatenations with formatted strings
  and 'arg' where needed.

Change-Id: I8dba54f43464a718062cd897d24f89b75b99f2a4
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

examples/network/secureudpclient/association.cpp

@@ -65,6 +65,7 @@ DtlsAssociation::DtlsAssociation(const QHostAddress &address, quint16 port,
     connect(&crypto, &QDtls::handshakeTimeout, this, &DtlsAssociation::handshakeTimeout);
     connect(&crypto, &QDtls::pskRequired, this, &DtlsAssociation::pskRequired);
 
+    socket.connectToHost(address.toString(), port);
     connect(&socket, &QUdpSocket::readyRead, this, &DtlsAssociation::readyRead);
 
     pingTimer.setInterval(5000);
@@ -79,10 +80,22 @@ DtlsAssociation::~DtlsAssociation()
 
 void DtlsAssociation::startHandshake()
 {
+    if (socket.state() != QAbstractSocket::ConnectedState) {
+        emit infoMessage(tr("%1: connecting UDP socket first ...").arg(name));
+        connect(&socket, &QAbstractSocket::connected, this, &DtlsAssociation::udpSocketConnected);
+        return;
+    }
+
     if (!crypto.doHandshake(&socket, {}))
-        emit errorMessage(name + tr(": failed to start a handshake - ") + crypto.dtlsErrorString());
+        emit errorMessage(tr("%1: failed to start a handshake - %2").arg(name, crypto.dtlsErrorString()));
     else
-        emit infoMessage(name + tr(": starting a handshake"));
+        emit infoMessage(tr("%1: starting a handshake").arg(name));
+}
+
+void DtlsAssociation::udpSocketConnected()
+{
+    emit infoMessage(tr("%1: UDP socket is now in ConnectedState, continue with handshake ...").arg(name));
+    startHandshake();
 }
 
 void DtlsAssociation::readyRead()
@@ -90,7 +103,7 @@ void DtlsAssociation::readyRead()
     QByteArray dgram(socket.pendingDatagramSize(), '\0');
     const qint64 bytesRead = socket.readDatagram(dgram.data(), dgram.size());
     if (bytesRead <= 0) {
-        emit warningMessage(name + tr(": spurious read notification?"));
+        emit warningMessage(tr("%1: spurious read notification?").arg(name));
         return;
     }
 
@@ -99,45 +112,44 @@ void DtlsAssociation::readyRead()
         const QByteArray plainText = crypto.decryptDatagram(&socket, dgram);
         if (plainText.size()) {
             emit serverResponse(name, dgram, plainText);
-            pingTimer.start();
             return;
         }
 
         if (crypto.dtlsError() == QDtlsError::RemoteClosedConnectionError) {
-            emit errorMessage(name + tr(": shutdown alert received"));
+            emit errorMessage(tr("%1: shutdown alert received").arg(name));
             socket.close();
             pingTimer.stop();
             return;
         }
 
-        emit warningMessage(name + tr(": zero-length datagram received?"));
+        emit warningMessage(tr("%1: zero-length datagram received?").arg(name));
     } else {
         if (!crypto.doHandshake(&socket, dgram)) {
-            emit errorMessage(name + tr(": handshake error - ") + crypto.dtlsErrorString());
+            emit errorMessage(tr("%1: handshake error - %2").arg(name, crypto.dtlsErrorString()));
             return;
         }
         if (crypto.connectionEncrypted()) {
-            emit infoMessage(name + tr(": encrypted connection established!"));
+            emit infoMessage(tr("%1: encrypted connection established!").arg(name));
             pingTimer.start();
             pingTimeout();
         } else {
-            emit infoMessage(name + tr(": continuing with handshake ..."));
+            emit infoMessage(tr("%1: continuing with handshake ...").arg(name));
         }
     }
 }
 
 void DtlsAssociation::handshakeTimeout()
 {
-    emit warningMessage(name + tr(": handshake timeout, trying to re-transmit"));
+    emit warningMessage(tr("%1: handshake timeout, trying to re-transmit").arg(name));
     if (!crypto.handleTimeout(&socket))
-        emit errorMessage(name + tr(": failed to re-transmit - ") + crypto.dtlsErrorString());
+        emit errorMessage(tr("%1: failed to re-transmit - %2").arg(name, crypto.dtlsErrorString()));
 }
 
 void DtlsAssociation::pskRequired(QSslPreSharedKeyAuthenticator *auth)
 {
     Q_ASSERT(auth);
 
-    emit infoMessage(name + tr(": providing pre-shared key ..."));
+    emit infoMessage(tr("%1: providing pre-shared key ...").arg(name));
     auth->setIdentity(name.toLatin1());
     auth->setPreSharedKey(QByteArrayLiteral("\x1a\x2b\x3c\x4d\x5e\x6f"));
 }
@@ -147,7 +159,7 @@ void DtlsAssociation::pingTimeout()
     static const QString message = QStringLiteral("I am %1, please, accept our ping %2");
     const qint64 written = crypto.writeDatagramEncrypted(&socket, message.arg(name).arg(ping).toLatin1());
     if (written <= 0) {
-        emit errorMessage(name + tr(": failed to send a ping - ") + crypto.dtlsErrorString());
+        emit errorMessage(tr("%1: failed to send a ping - %2").arg(name, crypto.dtlsErrorString()));
         pingTimer.stop();
         return;
     }

examples/network/secureudpclient/association.h

@@ -76,6 +76,7 @@ signals:
 
 private slots:
 
+    void udpSocketConnected();
     void readyRead();
     void handshakeTimeout();
     void pskRequired(QSslPreSharedKeyAuthenticator *auth);