XCB: Do not create instance of QPlatformIntegration for invalid displays

Extract a static factory for QXcbConnection objects and pass
potential connection errors to qxcbmain.cpp, which will then return 0.

Task-number: QTBUG-68859
Change-Id: I9c0faf82462a78a576360c19bef251ad1d034d84
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>

src/plugins/platforms/xcb/qxcbconnection.cpp

@@ -544,31 +544,59 @@ void QXcbConnection::initializeScreens()
     }
 }
 
-QXcbConnection::QXcbConnection(QXcbNativeInterface *nativeInterface, bool canGrabServer, xcb_visualid_t defaultVisualId, const char *displayName)
+QXcbConnection *QXcbConnection::create(QXcbNativeInterface *nativeInterface, bool canGrabServer,
-    : m_canGrabServer(canGrabServer)
+                                       xcb_visualid_t defaultVisualId,
-    , m_defaultVisualId(defaultVisualId)
+                                       const char *displayNameIn)
-    , m_displayName(displayName ? QByteArray(displayName) : qgetenv("DISPLAY"))
-    , m_nativeInterface(nativeInterface)
 {
+    const QByteArray displayName = displayNameIn ? QByteArray(displayNameIn) : qgetenv("DISPLAY");
+    int primaryScreenNumber = 0;
+    void *xlibDisplay = nullptr;
+    xcb_connection_t *connection = nullptr;
 #if QT_CONFIG(xcb_xlib)
-    Display *dpy = XOpenDisplay(m_displayName.constData());
+    Display *dpy = XOpenDisplay(displayName.constData());
     if (dpy) {
-        m_primaryScreenNumber = DefaultScreen(dpy);
+        primaryScreenNumber = DefaultScreen(dpy);
-        m_connection = XGetXCBConnection(dpy);
+        connection = XGetXCBConnection(dpy);
         XSetEventQueueOwner(dpy, XCBOwnsEventQueue);
         XSetErrorHandler(nullErrorHandler);
         XSetIOErrorHandler(ioErrorHandler);
-        m_xlib_display = dpy;
+        xlibDisplay = dpy;
     }
 #else
-    m_connection = xcb_connect(m_displayName.constData(), &m_primaryScreenNumber);
+    connection = xcb_connect(displayName.constData(), &primaryScreenNumber);
 #endif // QT_CONFIG(xcb_xlib)
-
+    if (Q_UNLIKELY(connection == nullptr)) {
-    if (Q_UNLIKELY(!m_connection || xcb_connection_has_error(m_connection))) {
+        qWarning("QXcbConnection: Could not connect to display \"%s\"", displayName.constData());
-        qCWarning(lcQpaScreen, "QXcbConnection: Could not connect to display %s", m_displayName.constData());
+        return nullptr;
-        return;
+    }
+    if (Q_UNLIKELY(xcb_connection_has_error(connection))) {
+#if QT_CONFIG(xcb_xlib)
+        XCloseDisplay(static_cast<Display *>(xlibDisplay));
+#else
+        xcb_disconnect(connection);
+#endif
+        qWarning("QXcbConnection: Errors occurred connecting to display \"%s\"", displayName.constData());
+        return nullptr;
+    }
+    return new QXcbConnection(connection, primaryScreenNumber, nativeInterface,
+                              canGrabServer, defaultVisualId, displayName, xlibDisplay);
 }
 
+
+QXcbConnection::QXcbConnection(xcb_connection_t *c, int primaryScreenNumber,
+                               QXcbNativeInterface *nativeInterface, bool canGrabServer,
+                               xcb_visualid_t defaultVisualId, const QByteArray &displayName,
+                               void *xlibDisplay)
+    : m_connection(c)
+    , m_canGrabServer(canGrabServer)
+    , m_defaultVisualId(defaultVisualId)
+    , m_primaryScreenNumber(primaryScreenNumber)
+    , m_displayName(displayName)
+    , m_nativeInterface(nativeInterface)
+#if QT_CONFIG(xcb_xlib)
+    , m_xlib_display(xlibDisplay)
+#endif
+{
     m_reader = new QXcbEventReader(this);
     m_reader->start();
 

src/plugins/platforms/xcb/qxcbconnection.h

@@ -377,9 +377,16 @@ class Q_XCB_EXPORT QXcbConnection : public QObject
 {
     Q_OBJECT
 public:
-    QXcbConnection(QXcbNativeInterface *nativeInterface, bool canGrabServer, xcb_visualid_t defaultVisualId, const char *displayName = 0);
+    explicit QXcbConnection(xcb_connection_t *c, int primaryScreenNumber,
+                            QXcbNativeInterface *nativeInterface, bool canGrabServer,
+                            xcb_visualid_t defaultVisualId, const QByteArray &displayName,
+                            void *xlibDisplay = nullptr);
+
     ~QXcbConnection();
 
+    static QXcbConnection *create(QXcbNativeInterface *nativeInterface, bool canGrabServer,
+                                  xcb_visualid_t defaultVisualId, const char *displayName = nullptr);
+
     QXcbConnection *connection() const { return const_cast<QXcbConnection *>(this); }
     bool isConnected() const;
 
@@ -639,21 +646,21 @@ private:
     static bool xi2GetValuatorValueIfSet(const void *event, int valuatorNum, double *value);
 #endif
 
-    xcb_connection_t *m_connection = nullptr;
+    xcb_connection_t *const m_connection;
     const xcb_setup_t *m_setup = nullptr;
     const bool m_canGrabServer;
     const xcb_visualid_t m_defaultVisualId;
 
     QList<QXcbVirtualDesktop *> m_virtualDesktops;
     QList<QXcbScreen *> m_screens;
-    int m_primaryScreenNumber = 0;
+    const int m_primaryScreenNumber;
 
     xcb_atom_t m_allAtoms[QXcbAtom::NAtoms];
 
     xcb_timestamp_t m_time = XCB_CURRENT_TIME;
     xcb_timestamp_t m_netWmUserTime = XCB_CURRENT_TIME;
 
-    QByteArray m_displayName;
+    const QByteArray m_displayName;
 
     QXcbKeyboard *m_keyboard = nullptr;
 #ifndef QT_NO_CLIPBOARD
@@ -666,7 +673,7 @@ private:
     QXcbNativeInterface *m_nativeInterface = nullptr;
 
 #if QT_CONFIG(xcb_xlib)
-    void *m_xlib_display = nullptr;
+    void *const m_xlib_display;
 #endif
     QXcbEventReader *m_reader = nullptr;
 

src/plugins/platforms/xcb/qxcbintegration.cpp

@@ -192,25 +192,15 @@ QXcbIntegration::QXcbIntegration(const QStringList &parameters, int &argc, char
 
     const int numParameters = parameters.size();
     m_connections.reserve(1 + numParameters / 2);
-    auto conn = new QXcbConnection(m_nativeInterface.data(), m_canGrab, m_defaultVisualId, displayName);
-    if (conn->isConnected())
-        m_connections << conn;
-    else
-        delete conn;
 
+    if (QXcbConnection *defaultConnection = QXcbConnection::create(m_nativeInterface.data(), m_canGrab, m_defaultVisualId, displayName)) {
+        m_connections.append(defaultConnection);
         for (int i = 0; i < numParameters - 1; i += 2) {
             qCDebug(lcQpaScreen) << "connecting to additional display: " << parameters.at(i) << parameters.at(i+1);
             QString display = parameters.at(i) + QLatin1Char(':') + parameters.at(i+1);
-        conn = new QXcbConnection(m_nativeInterface.data(), m_canGrab, m_defaultVisualId, display.toLatin1().constData());
+            if (QXcbConnection *connection = QXcbConnection::create(m_nativeInterface.data(), m_canGrab, m_defaultVisualId, display.toLatin1().constData()))
-        if (conn->isConnected())
+                m_connections.append(connection);
-            m_connections << conn;
-        else
-            delete conn;
         }
-
-    if (m_connections.isEmpty()) {
-        qCritical("Could not connect to any X display.");
-        exit(1);
     }
 
     m_fontDatabase.reset(new QGenericUnixFontDatabase());

src/plugins/platforms/xcb/qxcbintegration.h

@@ -103,6 +103,7 @@ public:
     QPlatformTheme *createPlatformTheme(const QString &name) const override;
     QVariant styleHint(StyleHint hint) const override;
 
+    bool hasDefaultConnection() const { return !m_connections.isEmpty(); }
     QXcbConnection *defaultConnection() const { return m_connections.first(); }
 
     QByteArray wmClass() const;

src/plugins/platforms/xcb/qxcbmain.cpp

@@ -52,10 +52,16 @@ public:
 
 QPlatformIntegration* QXcbIntegrationPlugin::create(const QString& system, const QStringList& parameters, int &argc, char **argv)
 {
-    if (!system.compare(QLatin1String("xcb"), Qt::CaseInsensitive))
+    if (!system.compare(QLatin1String("xcb"), Qt::CaseInsensitive)) {
-        return new QXcbIntegration(parameters, argc, argv);
+        QXcbIntegration *xcbIntegration = new QXcbIntegration(parameters, argc, argv);
+        if (!xcbIntegration->hasDefaultConnection()) {
+            delete xcbIntegration;
+            return nullptr;
+        }
+        return xcbIntegration;
+    }
 
-    return 0;
+    return nullptr;
 }
 
 QT_END_NAMESPACE