Add a secure UDP client example

A simple application that establishes DTLS connection(s) and
sends/receives datagrams. Class DtlsAssociation is
essentially a QUdpSocket|QDtls pair: it initiates a handshake,
handles timeouts and errors. After establishing an encrypted
connection it sends messages to the server and processes responses.

Task-number: QTBUG-67596
Change-Id: I92d481b7dfd2459e6a93c754b338a2e897a7feaf
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

1 files changed, 158 insertions, 0 deletions

diff --git a/examples/network/secureudpclient/association.cpp b/examples/network/secureudpclient/association.cpp
new file mode 100644
index 0000000000..11f52ba96c
--- /dev/null
+++ b/examples/network/secureudpclient/association.cpp
@@ -0,0 +1,158 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "association.h"
+
+QT_BEGIN_NAMESPACE
+
+DtlsAssociation::DtlsAssociation(const QHostAddress &address, quint16 port,
+                                 const QString &connectionName)
+    : name(connectionName),
+      crypto(QSslSocket::SslClientMode)
+{
+    auto configuration = QSslConfiguration::defaultDtlsConfiguration();
+    configuration.setPeerVerifyMode(QSslSocket::VerifyNone);
+    crypto.setRemote(address, port);
+    crypto.setDtlsConfiguration(configuration);
+
+    connect(&crypto, &QDtls::handshakeTimeout, this, &DtlsAssociation::handshakeTimeout);
+    connect(&crypto, &QDtls::pskRequired, this, &DtlsAssociation::pskRequired);
+
+    connect(&socket, &QUdpSocket::readyRead, this, &DtlsAssociation::readyRead);
+
+    pingTimer.setInterval(5000);
+    connect(&pingTimer, &QTimer::timeout, this, &DtlsAssociation::pingTimeout);
+}
+
+DtlsAssociation::~DtlsAssociation()
+{
+    if (crypto.connectionEncrypted())
+        crypto.sendShutdownAlert(&socket);
+}
+
+void DtlsAssociation::startHandshake()
+{
+    if (!crypto.doHandshake(&socket, {}))
+        emit errorMessage(name + tr(": failed to start a handshake - ") + crypto.dtlsErrorString());
+    else
+        emit infoMessage(name + tr(": starting a handshake"));
+}
+
+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?"));
+        return;
+    }
+
+    dgram.resize(bytesRead);
+    if (crypto.connectionEncrypted()) {
+        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"));
+            socket.close();
+            pingTimer.stop();
+            return;
+        }
+
+        emit warningMessage(name + tr(": zero-length datagram received?"));
+    } else {
+        if (!crypto.doHandshake(&socket, dgram)) {
+            emit errorMessage(name + tr(": handshake error - ") + crypto.dtlsErrorString());
+            return;
+        }
+        if (crypto.connectionEncrypted()) {
+            emit infoMessage(name + tr(": encrypted connection established!"));
+            pingTimer.start();
+            pingTimeout();
+        } else {
+            emit infoMessage(name + tr(": continuing with handshake ..."));
+        }
+    }
+}
+
+void DtlsAssociation::handshakeTimeout()
+{
+    emit warningMessage(name + tr(": handshake timeout, trying to re-transmit"));
+    if (!crypto.handleTimeout(&socket))
+        emit errorMessage(name + tr(": failed to re-transmit - ") + crypto.dtlsErrorString());
+}
+
+void DtlsAssociation::pskRequired(QSslPreSharedKeyAuthenticator *auth)
+{
+    Q_ASSERT(auth);
+
+    emit infoMessage(name + tr(": providing pre-shared key ..."));
+    auth->setIdentity(name.toLatin1());
+    auth->setPreSharedKey(QByteArrayLiteral("\x1a\x2b\x3c\x4d\x5e\x6f"));
+}
+
+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());
+        pingTimer.stop();
+        return;
+    }
+
+    ++ping;
+}
+
+QT_END_NAMESPACE