A11y: query a11y bus address from X display

Attempt to get the accessibility bus address from the X display, to
match libatspi's behavior. This allows the accessibility bus to be
found when an application is running as root.

[ChangeLog][QtGui] Linux accessibility (using XCB) will now works for
applications launched as root

Done-with: Mike Gorse
Change-Id: I49a263571b328cbd1fd90cb7f5cb40919d2a4951
Task-number: QTBUG-43674
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>

src/platformsupport/linuxaccessibility/dbusconnection.cpp

@@ -42,6 +42,9 @@
 #include <QDBusConnectionInterface>
 #include "bus_interface.h"
 
+#include <QtGui/qguiapplication.h>
+#include <qplatformnativeinterface.h>
+
 QT_BEGIN_NAMESPACE
 
 QString A11Y_SERVICE = QStringLiteral("org.a11y.Bus");
@@ -65,6 +68,29 @@ DBusConnection::DBusConnection(QObject *parent)
     // If it is registered already, setup a11y right away
     if (c.interface()->isServiceRegistered(A11Y_SERVICE))
         serviceRegistered();
+
+    // In addition try if there is an xatom exposing the bus address, this allows applications run as root to work
+    QString address = getAddressFromXCB();
+    if (!address.isEmpty()) {
+        m_enabled = true;
+        connectA11yBus(address);
+    }
+}
+
+QString DBusConnection::getAddressFromXCB()
+{
+    QGuiApplication *app = qobject_cast<QGuiApplication *>(QCoreApplication::instance());
+    if (!app)
+        return QString();
+    QPlatformNativeInterface *platformNativeInterface = app->platformNativeInterface();
+    QByteArray *addressByteArray = reinterpret_cast<QByteArray*>(
+                platformNativeInterface->nativeResourceForIntegration(QByteArrayLiteral("AtspiBus")));
+    if (addressByteArray) {
+        QString address = QString::fromLatin1(*addressByteArray);
+        delete addressByteArray;
+        return address;
+    }
+    return QString();
 }
 
 // We have the a11y registry on the session bus.

src/platformsupport/linuxaccessibility/dbusconnection_p.h

@@ -68,6 +68,7 @@ Q_SIGNALS:
     void enabledChanged(bool enabled);
 
 private Q_SLOTS:
+    QString getAddressFromXCB();
     void serviceRegistered();
     void serviceUnregistered();
     void connectA11yBus(const QString &address);

src/plugins/platforms/xcb/qxcbnativeinterface.cpp

@@ -77,7 +77,8 @@ static int resourceType(const QByteArray &key)
         QByteArrayLiteral("gettimestamp"), QByteArrayLiteral("x11screen"),
         QByteArrayLiteral("rootwindow"),
         QByteArrayLiteral("subpixeltype"), QByteArrayLiteral("antialiasingEnabled"),
-        QByteArrayLiteral("nofonthinting")
+        QByteArrayLiteral("nofonthinting"),
+        QByteArrayLiteral("atspibus")
     };
     const QByteArray *end = names + sizeof(names) / sizeof(names[0]);
     const QByteArray *result = std::find(names, end, key);
@@ -175,6 +176,9 @@ void *QXcbNativeInterface::nativeResourceForIntegration(const QByteArray &resour
     case Display:
         result = display();
         break;
+    case AtspiBus:
+        result = atspiBus();
+        break;
     default:
         break;
     }
@@ -402,6 +406,27 @@ void *QXcbNativeInterface::display()
 #endif
 }
 
+void *QXcbNativeInterface::atspiBus()
+{
+    QXcbIntegration *integration = static_cast<QXcbIntegration *>(QGuiApplicationPrivate::platformIntegration());
+    QXcbConnection *defaultConnection = integration->defaultConnection();
+    if (defaultConnection) {
+        xcb_atom_t atspiBusAtom = defaultConnection->internAtom("AT_SPI_BUS");
+        xcb_get_property_cookie_t cookie = Q_XCB_CALL(xcb_get_property(defaultConnection->xcb_connection(), false,
+                                                            defaultConnection->rootWindow(),
+                                                            atspiBusAtom,
+                                                            XCB_ATOM_STRING, 0, 128));
+        xcb_get_property_reply_t *reply = Q_XCB_CALL(xcb_get_property_reply(defaultConnection->xcb_connection(), cookie, 0));
+        Q_ASSERT(!reply->bytes_after);
+        char *data = (char *)xcb_get_property_value(reply);
+        int length = xcb_get_property_value_length(reply);
+        QByteArray *busAddress = new QByteArray(data, length);
+        free(reply);
+        return busAddress;
+    }
+    return 0;
+}
+
 void QXcbNativeInterface::setAppTime(QScreen* screen, xcb_timestamp_t time)
 {
     static_cast<QXcbScreen *>(screen->handle())->connection()->setTime(time);

src/plugins/platforms/xcb/qxcbnativeinterface.h

@@ -67,7 +67,8 @@ public:
         RootWindow,
         ScreenSubpixelType,
         ScreenAntialiasingEnabled,
-        NoFontHinting
+        NoFontHinting,
+        AtspiBus
     };
 
     QXcbNativeInterface();
@@ -98,6 +99,7 @@ public:
     void *x11Screen();
     void *rootWindow();
     void *display();
+    void *atspiBus();
     static void setStartupId(const char *);
     static void setAppTime(QScreen *screen, xcb_timestamp_t time);
     static void setAppUserTime(QScreen *screen, xcb_timestamp_t time);