dbusconnection.cpp

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// Copyright (C) 2022 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
 
 
#include "dbusconnection_p.h"
 
#include <QtDBus/QDBusMessage>
#include <QtDBus/QDBusServiceWatcher>
#include <qdebug.h>
 
#include <QDBusConnectionInterface>
 
#include <QtGui/qguiapplication.h>
#include <qpa/qplatformnativeinterface.h>
 
QT_BEGIN_NAMESPACE
 
using namespace Qt::StringLiterals;
using namespace QtGuiPrivate; // for D-Bus accessibility wrappers
 
/* note: do not change these to QStringLiteral;
   we are unloaded before QtDBus is done using the strings.
 */
#define A11Y_SERVICE "org.a11y.Bus"_L1
#define A11Y_PATH "/org/a11y/bus"_L1
 
/*!
    \class QAtSpiDBusConnection
    \internal
    \brief Connects to the accessibility dbus.
 
    This is usually a different bus from the session bus.
*/
QAtSpiDBusConnection::QAtSpiDBusConnection(QObject *parent)
    : QObject(parent), m_a11yConnection(QString()), m_enabled(false)
{
    // If the bus is explicitly set via env var it overrides everything else.
    QByteArray addressEnv = qgetenv("AT_SPI_BUS_ADDRESS");
    if (!addressEnv.isEmpty()) {
        m_enabled = true;
        connectA11yBus(QString::fromLocal8Bit(addressEnv));
        return;
    }
 
    // Start monitoring if "org.a11y.Bus" is registered as DBus service.
    QDBusConnection c = QDBusConnection::sessionBus();
    if (!c.isConnected()) {
        return;
    }
 
    m_a11yStatus = new OrgA11yStatusInterface(A11Y_SERVICE, A11Y_PATH, c, this);
    m_dbusProperties = new OrgFreedesktopDBusPropertiesInterface(A11Y_SERVICE, A11Y_PATH, c, this);
 
    dbusWatcher = new QDBusServiceWatcher(A11Y_SERVICE, c, QDBusServiceWatcher::WatchForRegistration, this);
    connect(dbusWatcher, &QDBusServiceWatcher::serviceRegistered,
            this, &QAtSpiDBusConnection::checkEnabledState);
 
    // If it is registered already, setup a11y right away
    if (c.interface()->isServiceRegistered(A11Y_SERVICE))
        checkEnabledState();
 
    // Subscribe to updates about a11y enabled state.
    connect(m_dbusProperties, &OrgFreedesktopDBusPropertiesInterface::PropertiesChanged,
            this, [this](const QString &interface_name) {
        if (interface_name == QLatin1StringView(OrgA11yStatusInterface::staticInterfaceName()))
            checkEnabledState();
    });
 
    if (QGuiApplication::platformName().startsWith("xcb"_L1)) {
        // 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 QAtSpiDBusConnection::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();
}
 
void QAtSpiDBusConnection::checkEnabledState()
{
    //The variable was introduced because on some embedded platforms there are custom accessibility
    //clients which don't set Status.ScreenReaderEnabled to true. The variable is also useful for
    //debugging.
    static const bool a11yAlwaysOn = qEnvironmentVariableIsSet("QT_LINUX_ACCESSIBILITY_ALWAYS_ON");
 
    bool enabled = a11yAlwaysOn || m_a11yStatus->screenReaderEnabled() || m_a11yStatus->isEnabled();
 
    if (enabled != m_enabled) {
        m_enabled = enabled;
        if (m_a11yConnection.isConnected()) {
            emit enabledChanged(m_enabled);
        } else {
            QDBusConnection c = QDBusConnection::sessionBus();
            QDBusMessage m = QDBusMessage::createMethodCall(A11Y_SERVICE, A11Y_PATH, A11Y_SERVICE,
                                                            "GetAddress"_L1);
            c.callWithCallback(m, this, SLOT(connectA11yBus(QString)), SLOT(dbusError(QDBusError)));
        }
    }
}
 
void QAtSpiDBusConnection::serviceUnregistered()
{
    emit enabledChanged(false);
}
 
void QAtSpiDBusConnection::connectA11yBus(const QString &address)
{
    if (address.isEmpty()) {
        qWarning("Could not find Accessibility DBus address.");
        return;
    }
    m_a11yConnection = QDBusConnection(QDBusConnection::connectToBus(address, "a11y"_L1));
 
    if (m_enabled)
        emit enabledChanged(true);
}
 
void QAtSpiDBusConnection::dbusError(const QDBusError &error)
{
    qWarning() << "Accessibility encountered a DBus error:" << error;
}
 
/*!
  Returns the DBus connection that got established.
  Or an invalid connection if not yet connected.
*/
QDBusConnection QAtSpiDBusConnection::connection() const
{
    return m_a11yConnection;
}
 
QT_END_NAMESPACE
 
#include "moc_dbusconnection_p.cpp"