Add a secure UDP server example

It's a simple DTLS server, implemented with QUdpSocket,
QDtlsClientVerifier and QDtls. The server is configured
to use PSK only (it has no certificate/key).

The server uses a single QUdpSocket socket and
de-multiplexes UDP datagrams internally (thus
it can work with several clients simultaneously).

Future update will probably add more options (like
configuring with certificate/key, etc). For now -
it's as minimalistic and simple as possible.

Task-number: QTBUG-67596
Change-Id: Ic7d18dbab6dbcc9ed44c82e69a2b364df24aa256
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

11 files changed, 1212 insertions, 1 deletions

diff --git a/examples/network/network.pro b/examples/network/network.pro
index d64b16c760..3187c1d43e 100644
--- a/examples/network/network.pro
+++ b/examples/network/network.pro
@@ -29,7 +29,11 @@ qtHaveModule(widgets) {
 
     }
 
-    qtConfig(openssl): SUBDIRS += securesocketclient
+    qtConfig(openssl) {
+        SUBDIRS += \
+                securesocketclient \
+                secureudpserver
+    }
     qtConfig(sctp): SUBDIRS += multistreamserver multistreamclient
 }
 
diff --git a/examples/network/secureudpserver/main.cpp b/examples/network/secureudpserver/main.cpp
new file mode 100644
index 0000000000..1a29d9d7ec
--- /dev/null
+++ b/examples/network/secureudpserver/main.cpp
@@ -0,0 +1,64 @@
+/****************************************************************************
+**
+** 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 <QApplication>
+
+#include "mainwindow.h"
+
+int main(int argc, char *argv[])
+{
+    QT_USE_NAMESPACE
+
+    QApplication a(argc, argv);
+    MainWindow w;
+    w.show();
+
+    return a.exec();
+}
diff --git a/examples/network/secureudpserver/mainwindow.cpp b/examples/network/secureudpserver/mainwindow.cpp
new file mode 100644
index 0000000000..d751ec931d
--- /dev/null
+++ b/examples/network/secureudpserver/mainwindow.cpp
@@ -0,0 +1,136 @@
+/****************************************************************************
+**
+** 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 "mainwindow.h"
+#include "nicselector.h"
+#include "ui_mainwindow.h"
+
+MainWindow::MainWindow()
+    : ui(new Ui::MainWindow)
+{
+    ui->setupUi(this);
+
+    connect(&server, &DtlsServer::errorMessage, this, &MainWindow::addErrorMessage);
+    connect(&server, &DtlsServer::warningMessage, this, &MainWindow::addWarningMessage);
+    connect(&server, &DtlsServer::infoMessage, this, &MainWindow::addInfoMessage);
+    connect(&server, &DtlsServer::datagramReceived, this, &MainWindow::addClientMessage);
+
+    updateUi();
+}
+
+MainWindow::~MainWindow()
+{
+    delete ui;
+}
+
+void MainWindow::on_startButton_clicked()
+{
+    if (!server.isListening()) {
+        NicSelector ipDialog;
+        if (ipDialog.exec() == QDialog::Accepted) {
+            const QHostAddress address = ipDialog.selectedIp();
+            const quint16 port = ipDialog.selectedPort();
+            if (address.isNull()) {
+                addErrorMessage(tr("Failed to start listening, no valid address/port"));
+            } else if (server.listen(address, port)) {
+                addInfoMessage(tr("Server is listening on address %1 and port %2")
+                                 .arg(address.toString())
+                                 .arg(port));
+            }
+        }
+    } else {
+        server.close();
+        addInfoMessage(tr("Server is not accepting new connections"));
+    }
+
+    updateUi();
+}
+
+void MainWindow::on_quitButton_clicked()
+{
+    QCoreApplication::exit(0);
+}
+
+void MainWindow::updateUi()
+{
+    server.isListening() ? ui->startButton->setText(tr("Stop listening"))
+                         : ui->startButton->setText(tr("Start listening"));
+}
+
+const QString colorizer(QStringLiteral("<font color=\"%1\">%2</font><br>"));
+
+void MainWindow::addErrorMessage(const QString &message)
+{
+    ui->serverInfo->insertHtml(colorizer.arg(QStringLiteral("Crimson"), message));
+}
+
+void MainWindow::addWarningMessage(const QString &message)
+{
+    ui->serverInfo->insertHtml(colorizer.arg(QStringLiteral("DarkOrange"), message));
+}
+
+void MainWindow::addInfoMessage(const QString &message)
+{
+    ui->serverInfo->insertHtml(colorizer.arg(QStringLiteral("DarkBlue"), message));
+}
+
+void MainWindow::addClientMessage(const QString &peerInfo, const QByteArray &datagram,
+                                  const QByteArray &plainText)
+{
+    static const QString messageColor = QStringLiteral("DarkMagenta");
+    static const QString formatter = QStringLiteral("<br>---------------"
+                                                    "<br>A message from %1"
+                                                    "<br>DTLS datagram:<br> %2"
+                                                    "<br>As plain text:<br> %3");
+
+    const QString html = formatter.arg(peerInfo, QString::fromUtf8(datagram.toHex(' ')),
+                                       QString::fromUtf8(plainText));
+    ui->messages->insertHtml(colorizer.arg(messageColor, html));
+}
diff --git a/examples/network/secureudpserver/mainwindow.h b/examples/network/secureudpserver/mainwindow.h
new file mode 100644
index 0000000000..0c914f5021
--- /dev/null
+++ b/examples/network/secureudpserver/mainwindow.h
@@ -0,0 +1,95 @@
+/****************************************************************************
+**
+** 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."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+#ifndef MAINWINDOW_H
+#define MAINWINDOW_H
+
+#include "server.h"
+
+#include <QMainWindow>
+
+QT_BEGIN_NAMESPACE
+
+namespace Ui {
+class MainWindow;
+}
+
+QT_END_NAMESPACE
+
+QT_USE_NAMESPACE
+
+class MainWindow : public QMainWindow
+{
+    Q_OBJECT
+
+public:
+
+    MainWindow();
+    ~MainWindow();
+
+private slots:
+
+    void addErrorMessage(const QString &message);
+    void addWarningMessage(const QString &message);
+    void addInfoMessage(const QString &message);
+    void addClientMessage(const QString &peerInfo, const QByteArray &datagram,
+                          const QByteArray &plainText);
+
+    void on_startButton_clicked();
+    void on_quitButton_clicked();
+
+private:
+
+    void updateUi();
+
+    Ui::MainWindow *ui = nullptr;
+    DtlsServer server;
+};
+
+#endif // MAINWINDOW_H
diff --git a/examples/network/secureudpserver/mainwindow.ui b/examples/network/secureudpserver/mainwindow.ui
new file mode 100644
index 0000000000..e25e19921b
--- /dev/null
+++ b/examples/network/secureudpserver/mainwindow.ui
@@ -0,0 +1,207 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ui version="4.0">
+ <class>MainWindow</class>
+ <widget class="QMainWindow" name="MainWindow">
+  <property name="geometry">
+   <rect>
+    <x>0</x>
+    <y>0</y>
+    <width>1090</width>
+    <height>670</height>
+   </rect>
+  </property>
+  <property name="minimumSize">
+   <size>
+    <width>1090</width>
+    <height>670</height>
+   </size>
+  </property>
+  <property name="maximumSize">
+   <size>
+    <width>1090</width>
+    <height>670</height>
+   </size>
+  </property>
+  <property name="windowTitle">
+   <string>DTLS server</string>
+  </property>
+  <widget class="QWidget" name="centralWidget">
+   <widget class="QWidget" name="layoutWidget">
+    <property name="geometry">
+     <rect>
+      <x>20</x>
+      <y>20</y>
+      <width>1050</width>
+      <height>576</height>
+     </rect>
+    </property>
+    <layout class="QVBoxLayout" name="verticalLayout">
+     <item>
+      <layout class="QHBoxLayout" name="horizontalLayout">
+       <item>
+        <widget class="QGroupBox" name="infoBox">
+         <property name="minimumSize">
+          <size>
+           <width>520</width>
+           <height>540</height>
+          </size>
+         </property>
+         <property name="maximumSize">
+          <size>
+           <width>520</width>
+           <height>540</height>
+          </size>
+         </property>
+         <property name="title">
+          <string>Dtls server info:</string>
+         </property>
+         <property name="flat">
+          <bool>true</bool>
+         </property>
+         <widget class="QTextEdit" name="serverInfo">
+          <property name="geometry">
+           <rect>
+            <x>10</x>
+            <y>30</y>
+            <width>500</width>
+            <height>500</height>
+           </rect>
+          </property>
+          <property name="minimumSize">
+           <size>
+            <width>500</width>
+            <height>500</height>
+           </size>
+          </property>
+          <property name="maximumSize">
+           <size>
+            <width>500</width>
+            <height>500</height>
+           </size>
+          </property>
+          <property name="readOnly">
+           <bool>true</bool>
+          </property>
+         </widget>
+        </widget>
+       </item>
+       <item>
+        <widget class="QGroupBox" name="groupBox">
+         <property name="minimumSize">
+          <size>
+           <width>520</width>
+           <height>540</height>
+          </size>
+         </property>
+         <property name="maximumSize">
+          <size>
+           <width>520</width>
+           <height>540</height>
+          </size>
+         </property>
+         <property name="title">
+          <string>Received messages:</string>
+         </property>
+         <property name="flat">
+          <bool>true</bool>
+         </property>
+         <widget class="QTextEdit" name="messages">
+          <property name="geometry">
+           <rect>
+            <x>10</x>
+            <y>30</y>
+            <width>500</width>
+            <height>500</height>
+           </rect>
+          </property>
+          <property name="minimumSize">
+           <size>
+            <width>500</width>
+            <height>500</height>
+           </size>
+          </property>
+          <property name="maximumSize">
+           <size>
+            <width>500</width>
+            <height>500</height>
+           </size>
+          </property>
+          <property name="readOnly">
+           <bool>true</bool>
+          </property>
+         </widget>
+        </widget>
+       </item>
+      </layout>
+     </item>
+     <item>
+      <layout class="QHBoxLayout" name="horizontalLayout_2">
+       <item>
+        <spacer name="horizontalSpacer">
+         <property name="orientation">
+          <enum>Qt::Horizontal</enum>
+         </property>
+         <property name="sizeHint" stdset="0">
+          <size>
+           <width>40</width>
+           <height>20</height>
+          </size>
+         </property>
+        </spacer>
+       </item>
+       <item>
+        <widget class="QPushButton" name="startButton">
+         <property name="text">
+          <string>Start listening</string>
+         </property>
+        </widget>
+       </item>
+       <item>
+        <widget class="QPushButton" name="quitButton">
+         <property name="text">
+          <string>Quit</string>
+         </property>
+        </widget>
+       </item>
+       <item>
+        <spacer name="horizontalSpacer_2">
+         <property name="orientation">
+          <enum>Qt::Horizontal</enum>
+         </property>
+         <property name="sizeHint" stdset="0">
+          <size>
+           <width>40</width>
+           <height>20</height>
+          </size>
+         </property>
+        </spacer>
+       </item>
+      </layout>
+     </item>
+    </layout>
+   </widget>
+  </widget>
+  <widget class="QMenuBar" name="menuBar">
+   <property name="geometry">
+    <rect>
+     <x>0</x>
+     <y>0</y>
+     <width>1090</width>
+     <height>22</height>
+    </rect>
+   </property>
+  </widget>
+  <widget class="QToolBar" name="mainToolBar">
+   <attribute name="toolBarArea">
+    <enum>TopToolBarArea</enum>
+   </attribute>
+   <attribute name="toolBarBreak">
+    <bool>false</bool>
+   </attribute>
+  </widget>
+  <widget class="QStatusBar" name="statusBar"/>
+ </widget>
+ <layoutdefault spacing="6" margin="11"/>
+ <resources/>
+ <connections/>
+</ui>
diff --git a/examples/network/secureudpserver/nicselector.cpp b/examples/network/secureudpserver/nicselector.cpp
new file mode 100644
index 0000000000..ea26439d74
--- /dev/null
+++ b/examples/network/secureudpserver/nicselector.cpp
@@ -0,0 +1,95 @@
+/****************************************************************************
+**
+** 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 <limits>
+
+#include <QtCore>
+#include <QtNetwork>
+
+#include "nicselector.h"
+#include "ui_nicselector.h"
+
+NicSelector::NicSelector(QWidget *parent) :
+    QDialog(parent),
+    ui(new Ui::NicSelector)
+{
+    ui->setupUi(this);
+    auto portValidator = new QIntValidator(0, int(std::numeric_limits<quint16>::max()),
+                                           ui->portSelector);
+    ui->portSelector->setValidator(portValidator);
+    ui->portSelector->setText(QStringLiteral("22334"));
+
+    const QList<QHostAddress> ipAddressesList = QNetworkInterface::allAddresses();
+    availableAddresses.reserve(ipAddressesList.size());
+    for (const QHostAddress &ip : ipAddressesList) {
+        if (ip != QHostAddress::LocalHost && ip.toIPv4Address()) {
+            availableAddresses.push_back(ip);
+            ui->ipSelector->addItem(ip.toString());
+        }
+    }
+}
+
+NicSelector::~NicSelector()
+{
+    delete ui;
+}
+
+QHostAddress NicSelector::selectedIp() const
+{
+    if (!availableAddresses.size())
+        return {};
+
+    return availableAddresses[ui->ipSelector->currentIndex()];
+}
+
+quint16 NicSelector::selectedPort() const
+{
+    return quint16(ui->portSelector->text().toUInt());
+}
diff --git a/examples/network/secureudpserver/nicselector.h b/examples/network/secureudpserver/nicselector.h
new file mode 100644
index 0000000000..7962a78318
--- /dev/null
+++ b/examples/network/secureudpserver/nicselector.h
@@ -0,0 +1,84 @@
+/****************************************************************************
+**
+** 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."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef NICSELECTOR_H
+#define NICSELECTOR_H
+
+#include <QDialog>
+#include <QHostAddress>
+#include <QVector>
+
+QT_BEGIN_NAMESPACE
+
+namespace Ui {
+class NicSelector;
+}
+
+QT_END_NAMESPACE
+
+QT_USE_NAMESPACE
+
+class NicSelector : public QDialog
+{
+    Q_OBJECT
+
+public:
+    explicit NicSelector(QWidget *parent = nullptr);
+    ~NicSelector();
+
+    QHostAddress selectedIp() const;
+    quint16 selectedPort() const;
+
+private:
+    Ui::NicSelector *ui = nullptr;
+    QVector<QHostAddress> availableAddresses;
+};
+
+#endif // NICSELECTOR_H
diff --git a/examples/network/secureudpserver/nicselector.ui b/examples/network/secureudpserver/nicselector.ui
new file mode 100644
index 0000000000..b0ba376b66
--- /dev/null
+++ b/examples/network/secureudpserver/nicselector.ui
@@ -0,0 +1,144 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ui version="4.0">
+ <class>NicSelector</class>
+ <widget class="QDialog" name="NicSelector">
+  <property name="geometry">
+   <rect>
+    <x>0</x>
+    <y>0</y>
+    <width>373</width>
+    <height>213</height>
+   </rect>
+  </property>
+  <property name="windowTitle">
+   <string>IP and port</string>
+  </property>
+  <layout class="QVBoxLayout" name="verticalLayout_3">
+   <item>
+    <layout class="QVBoxLayout" name="verticalLayout">
+     <property name="sizeConstraint">
+      <enum>QLayout::SetFixedSize</enum>
+     </property>
+     <item>
+      <widget class="QLabel" name="label">
+       <property name="text">
+        <string>Listen on address:</string>
+       </property>
+      </widget>
+     </item>
+     <item>
+      <widget class="QComboBox" name="ipSelector">
+       <property name="minimumSize">
+        <size>
+         <width>250</width>
+         <height>0</height>
+        </size>
+       </property>
+      </widget>
+     </item>
+     <item>
+      <spacer name="verticalSpacer">
+       <property name="orientation">
+        <enum>Qt::Vertical</enum>
+       </property>
+       <property name="sizeType">
+        <enum>QSizePolicy::Fixed</enum>
+       </property>
+       <property name="sizeHint" stdset="0">
+        <size>
+         <width>20</width>
+         <height>20</height>
+        </size>
+       </property>
+      </spacer>
+     </item>
+    </layout>
+   </item>
+   <item>
+    <layout class="QVBoxLayout" name="verticalLayout_2">
+     <property name="sizeConstraint">
+      <enum>QLayout::SetFixedSize</enum>
+     </property>
+     <item>
+      <widget class="QLabel" name="label_2">
+       <property name="text">
+        <string>Port:</string>
+       </property>
+      </widget>
+     </item>
+     <item>
+      <widget class="QLineEdit" name="portSelector">
+       <property name="sizePolicy">
+        <sizepolicy hsizetype="Fixed" vsizetype="Fixed">
+         <horstretch>0</horstretch>
+         <verstretch>0</verstretch>
+        </sizepolicy>
+       </property>
+      </widget>
+     </item>
+     <item>
+      <spacer name="verticalSpacer_2">
+       <property name="orientation">
+        <enum>Qt::Vertical</enum>
+       </property>
+       <property name="sizeType">
+        <enum>QSizePolicy::Fixed</enum>
+       </property>
+       <property name="sizeHint" stdset="0">
+        <size>
+         <width>20</width>
+         <height>20</height>
+        </size>
+       </property>
+      </spacer>
+     </item>
+    </layout>
+   </item>
+   <item>
+    <widget class="QDialogButtonBox" name="buttonBox">
+     <property name="orientation">
+      <enum>Qt::Horizontal</enum>
+     </property>
+     <property name="standardButtons">
+      <set>QDialogButtonBox::Cancel|QDialogButtonBox::Ok</set>
+     </property>
+    </widget>
+   </item>
+  </layout>
+ </widget>
+ <resources/>
+ <connections>
+  <connection>
+   <sender>buttonBox</sender>
+   <signal>accepted()</signal>
+   <receiver>NicSelector</receiver>
+   <slot>accept()</slot>
+   <hints>
+    <hint type="sourcelabel">
+     <x>248</x>
+     <y>254</y>
+    </hint>
+    <hint type="destinationlabel">
+     <x>157</x>
+     <y>274</y>
+    </hint>
+   </hints>
+  </connection>
+  <connection>
+   <sender>buttonBox</sender>
+   <signal>rejected()</signal>
+   <receiver>NicSelector</receiver>
+   <slot>reject()</slot>
+   <hints>
+    <hint type="sourcelabel">
+     <x>316</x>
+     <y>260</y>
+    </hint>
+    <hint type="destinationlabel">
+     <x>286</x>
+     <y>274</y>
+    </hint>
+   </hints>
+  </connection>
+ </connections>
+</ui>
diff --git a/examples/network/secureudpserver/secureudpserver.pro b/examples/network/secureudpserver/secureudpserver.pro
new file mode 100644
index 0000000000..910655aae4
--- /dev/null
+++ b/examples/network/secureudpserver/secureudpserver.pro
@@ -0,0 +1,21 @@
+QT += widgets network
+
+TARGET = secureudpserver
+TEMPLATE = app
+
+SOURCES += \
+        main.cpp \
+        mainwindow.cpp \
+        server.cpp \
+    nicselector.cpp
+
+HEADERS += \
+        mainwindow.h \
+        server.h \
+    nicselector.h
+
+FORMS = mainwindow.ui \
+    nicselector.ui
+
+target.path = $$[QT_INSTALL_EXAMPLES]/network/secureudpserver
+INSTALLS += target
diff --git a/examples/network/secureudpserver/server.cpp b/examples/network/secureudpserver/server.cpp
new file mode 100644
index 0000000000..918307013c
--- /dev/null
+++ b/examples/network/secureudpserver/server.cpp
@@ -0,0 +1,252 @@
+/****************************************************************************
+**
+** 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 "server.h"
+
+#include <algorithm>
+
+QT_BEGIN_NAMESPACE
+
+namespace {
+
+QString peer_info(const QHostAddress &address, quint16 port)
+{
+    const static QString info = QStringLiteral("(%1:%2)");
+    return info.arg(address.toString()).arg(port);
+}
+
+QString connection_info(QSharedPointer<QDtls> connection)
+{
+    QString info(DtlsServer::tr("Session cipher: "));
+    info += connection->sessionCipher().name();
+
+    info += DtlsServer::tr("; session protocol: ");
+    switch (connection->sessionProtocol()) {
+    case QSsl::DtlsV1_0:
+        info += DtlsServer::tr("DTLS 1.0.");
+        break;
+    case QSsl::DtlsV1_2:
+        info += DtlsServer::tr("DTLS 1.2.");
+        break;
+    case QSsl::DtlsV1_2OrLater:
+        info += DtlsServer::tr("DTLS 1.2 or later.");
+        break;
+    default:
+        info += DtlsServer::tr("Unknown protocol.");
+    }
+
+    return info;
+}
+
+} // unnamed namespace
+
+DtlsServer::DtlsServer()
+{
+    connect(&serverSocket, &QAbstractSocket::readyRead, this, &DtlsServer::readyRead);
+
+    serverConfiguration.setPreSharedKeyIdentityHint("Qt DTLS example server");
+    serverConfiguration.setPeerVerifyMode(QSslSocket::VerifyNone);
+}
+
+DtlsServer::~DtlsServer()
+{
+    shutdown();
+}
+
+bool DtlsServer::listen(const QHostAddress &address, quint16 port)
+{
+    if (address != serverSocket.localAddress() || port != serverSocket.localPort()) {
+        shutdown();
+        listening = serverSocket.bind(address, port);
+        if (!listening)
+            emit errorMessage(serverSocket.errorString());
+    } else {
+        listening = true;
+    }
+
+    return listening;
+}
+
+bool DtlsServer::isListening() const
+{
+    return listening;
+}
+
+void DtlsServer::close()
+{
+    listening = false;
+}
+
+void DtlsServer::readyRead()
+{
+    const qint64 bytesToRead = serverSocket.pendingDatagramSize();
+    if (bytesToRead <= 0) {
+        emit warningMessage(tr("A spurious read notification"));
+        return;
+    }
+
+    QByteArray dgram(bytesToRead, Qt::Uninitialized);
+    QHostAddress peerAddress;
+    quint16 peerPort = 0;
+    const qint64 bytesRead = serverSocket.readDatagram(dgram.data(), dgram.size(),
+                                                       &peerAddress, &peerPort);
+    if (bytesRead <= 0) {
+        emit warningMessage(tr("Failed to read a datagram: ") + serverSocket.errorString());
+        return;
+    }
+
+    dgram.resize(bytesRead);
+
+    if (peerAddress.isNull() || !peerPort) {
+        emit warningMessage(tr("Failed to extract peer info (address, port)"));
+        return;
+    }
+
+    const auto client = std::find_if(knownClients.begin(), knownClients.end(),
+                                     [&](const DtlsConnection &connection){
+        return connection->remoteAddress() == peerAddress
+               && connection->remotePort() == peerPort;
+    });
+
+    if (client == knownClients.end())
+        return handleNewConnection(peerAddress, peerPort, dgram);
+
+    if ((*client)->connectionEncrypted()) {
+        decryptDatagram(*client, dgram);
+        if ((*client)->dtlsError() == QDtlsError::RemoteClosedConnectionError)
+            knownClients.erase(client);
+        return;
+    }
+
+    doHandshake(*client, dgram);
+}
+
+void DtlsServer::pskRequired(QSslPreSharedKeyAuthenticator *auth)
+{
+    Q_ASSERT(auth);
+
+    emit infoMessage(tr("PSK callback, received a client's identity: '%1'")
+                     .arg(QString::fromLatin1(auth->identity())));
+    auth->setPreSharedKey(QByteArrayLiteral("\x1a\x2b\x3c\x4d\x5e\x6f"));
+}
+
+void DtlsServer::handleNewConnection(const QHostAddress &peerAddress,
+                                     quint16 peerPort, const QByteArray &clientHello)
+{
+    if (!listening)
+        return;
+
+    const QString peerInfo = peer_info(peerAddress, peerPort);
+    if (cookieSender.verifyClient(&serverSocket, clientHello, peerAddress, peerPort)) {
+        emit infoMessage(peerInfo + tr(": verified, starting a handshake"));
+
+        DtlsConnection newConnection(new QDtls(QSslSocket::SslServerMode));
+        newConnection->setDtlsConfiguration(serverConfiguration);
+        newConnection->setRemote(peerAddress, peerPort);
+        newConnection->connect(newConnection.data(), &QDtls::pskRequired,
+                               this, &DtlsServer::pskRequired);
+        knownClients.push_back(newConnection);
+        doHandshake(newConnection, clientHello);
+    } else if (cookieSender.dtlsError() != QDtlsError::NoError) {
+        emit errorMessage(tr("DTLS error: ") + cookieSender.dtlsErrorString());
+    } else {
+        emit infoMessage(peerInfo + tr(": not verified yet"));
+    }
+}
+
+void DtlsServer::doHandshake(DtlsConnection newConnection, const QByteArray &clientHello)
+{
+    const bool result = newConnection->doHandshake(&serverSocket, clientHello);
+    if (!result) {
+        emit errorMessage(newConnection->dtlsErrorString());
+        return;
+    }
+
+    const QString peerInfo = peer_info(newConnection->remoteAddress(),
+                                       newConnection->remotePort());
+    switch (newConnection->handshakeState()) {
+    case QDtls::HandshakeInProgress:
+        emit infoMessage(peerInfo + tr(": handshake is in progress ..."));
+        break;
+    case QDtls::HandshakeComplete:
+        emit infoMessage(tr("Connection with %1 encrypted. %2")
+                         .arg(peerInfo, connection_info(newConnection)));
+        break;
+    default:
+        Q_UNREACHABLE();
+    }
+}
+
+void DtlsServer::decryptDatagram(DtlsConnection connection, const QByteArray &clientMessage)
+{
+    Q_ASSERT(connection->connectionEncrypted());
+
+    const QString peerInfo = peer_info(connection->remoteAddress(), connection->remotePort());
+    const QByteArray dgram = connection->decryptDatagram(&serverSocket, clientMessage);
+    if (dgram.size()) {
+        emit datagramReceived(peerInfo, clientMessage, dgram);
+        connection->writeDatagramEncrypted(&serverSocket, tr("to %1: ACK").arg(peerInfo).toLatin1());
+    } else if (connection->dtlsError() == QDtlsError::NoError) {
+        emit warningMessage(peerInfo + ": " + tr("0 byte dgram, could be a re-connect attempt?"));
+    } else {
+        emit errorMessage(peerInfo + ": " + connection->dtlsErrorString());
+    }
+}
+
+void DtlsServer::shutdown()
+{
+    for (DtlsConnection &connection : knownClients)
+        connection->sendShutdownAlert(&serverSocket);
+
+    knownClients.clear();
+    serverSocket.close();
+}
+
+QT_END_NAMESPACE
diff --git a/examples/network/secureudpserver/server.h b/examples/network/secureudpserver/server.h
new file mode 100644
index 0000000000..33444f7407
--- /dev/null
+++ b/examples/network/secureudpserver/server.h
@@ -0,0 +1,109 @@
+/****************************************************************************
+**
+** 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."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+#ifndef SERVER_H
+#define SERVER_H
+
+#include <QtCore>
+#include <QtNetwork>
+
+#include <vector>
+
+QT_BEGIN_NAMESPACE
+
+class DtlsServer : public QObject
+{
+    Q_OBJECT
+
+public:
+
+    DtlsServer();
+    ~DtlsServer();
+
+    bool listen(const QHostAddress &address, quint16 port);
+    bool isListening() const;
+    void close();
+
+signals:
+
+    void errorMessage(const QString &message);
+    void warningMessage(const QString &message);
+    void infoMessage(const QString &message);
+
+    void datagramReceived(const QString &peerInfo, const QByteArray &cipherText,
+                          const QByteArray &plainText);
+
+private slots:
+
+    void readyRead();
+    void pskRequired(QSslPreSharedKeyAuthenticator *auth);
+
+private:
+
+    void handleNewConnection(const QHostAddress &peerAddress, quint16 peerPort,
+                             const QByteArray &clientHello);
+
+    using DtlsConnection = QSharedPointer<QDtls>;
+    void doHandshake(DtlsConnection newConnection, const QByteArray &clientHello);
+    void decryptDatagram(DtlsConnection connection, const QByteArray &clientMessage);
+    void shutdown();
+
+    bool listening = false;
+    QUdpSocket serverSocket;
+
+    QSslConfiguration serverConfiguration;
+    QDtlsClientVerifier cookieSender;
+    QVector<DtlsConnection> knownClients;
+
+    Q_DISABLE_COPY(DtlsServer)
+};
+
+QT_END_NAMESPACE
+
+#endif // SERVER_H