Fix hang caused by no Notifications service registered in DBus (#4357)

Issue #4353

Add a check when looking up the `org.freedesktop.Notifications` service
to see if the it actually exists before trying to fetch it

Add a check on QDBus service lookup in screengrabber freedesktop

Author: samwcoulter

src/utils/screengrabber.cpp

@@ -61,8 +61,18 @@ void ScreenGrabber::freeDesktopPortal(bool& ok, QPixmap& res)
 {
 
 #if !(defined(Q_OS_MACOS) || defined(Q_OS_WIN))
+    auto* connectionInterface = QDBusConnection::sessionBus().interface();
+    auto service = QStringLiteral("org.freedesktop.portal.Desktop");
+
+    if (!connectionInterface->isServiceRegistered(service)) {
+        ok = false;
+        AbstractLogger::error() << tr(
+          "Could not locate the `org.freedesktop.portal.Desktop` service");
+        return;
+    }
+
     QDBusInterface screenshotInterface(
-      QStringLiteral("org.freedesktop.portal.Desktop"),
+      service,
       QStringLiteral("/org/freedesktop/portal/desktop"),
       QStringLiteral("org.freedesktop.portal.Screenshot"));
 
@@ -72,7 +82,7 @@ void ScreenGrabber::freeDesktopPortal(bool& ok, QPixmap& res)
 
     // premake interface
     auto* request = new OrgFreedesktopPortalRequestInterface(
-      QStringLiteral("org.freedesktop.portal.Desktop"),
+      service,
       "/org/freedesktop/portal/desktop/request/" +
         QDBusConnection::sessionBus().baseService().remove(':').replace('.',
                                                                         '_') +

src/utils/systemnotification.cpp

@@ -1,11 +1,13 @@
 #include "systemnotification.h"
 #include "src/core/flameshot.h"
+#include "src/utils/abstractlogger.h"
 #include "src/utils/confighandler.h"
 #include <QApplication>
 #include <QUrl>
 
 #if !(defined(Q_OS_MACOS) || defined(Q_OS_WIN))
 #include <QDBusConnection>
+#include <QDBusConnectionInterface>
 #include <QDBusInterface>
 #include <QDBusMessage>
 #else
@@ -27,12 +29,20 @@ SystemNotification::SystemNotification(QObject* parent)
     if (!ConfigHandler().showDesktopNotification()) {
         return;
     }
-    m_interface =
-      new QDBusInterface(QStringLiteral("org.freedesktop.Notifications"),
-                         QStringLiteral("/org/freedesktop/Notifications"),
-                         QStringLiteral("org.freedesktop.Notifications"),
-                         QDBusConnection::sessionBus(),
-                         this);
+    auto bus = QDBusConnection::sessionBus();
+    auto* connectionInterface = bus.interface();
+
+    auto service = QStringLiteral("org.freedesktop.Notifications");
+    auto path = QStringLiteral("/org/freedesktop/Notifications");
+    auto interface = QStringLiteral("org.freedesktop.Notifications");
+
+    if (connectionInterface->isServiceRegistered(service)) {
+        m_interface = new QDBusInterface(service, path, interface, bus, this);
+    } else {
+        AbstractLogger::warning(AbstractLogger::Stderr |
+                                AbstractLogger::LogFile)
+          << tr("No DBus System Notification service found");
+    }
 #endif
 }
 
@@ -63,24 +73,26 @@ void SystemNotification::sendMessage(const QString& text,
       },
       Qt::QueuedConnection);
 #else
-    QList<QVariant> args;
-    QVariantMap hintsMap;
-    if (!savePath.isEmpty()) {
-        QUrl fullPath = QUrl::fromLocalFile(savePath);
-        // allows the notification to be dragged and dropped
-        hintsMap[QStringLiteral("x-kde-urls")] =
-          QStringList({ fullPath.toString() });
-    }
+    if (nullptr != m_interface && m_interface->isValid()) {
+        QList<QVariant> args;
+        QVariantMap hintsMap;
+        if (!savePath.isEmpty()) {
+            QUrl fullPath = QUrl::fromLocalFile(savePath);
+            // allows the notification to be dragged and dropped
+            hintsMap[QStringLiteral("x-kde-urls")] =
+              QStringList({ fullPath.toString() });
+        }
 
-    args << (qAppName())                 // appname
-         << static_cast<unsigned int>(0) // id
-         << FLAMESHOT_ICON               // icon
-         << title                        // summary
-         << text                         // body
-         << QStringList()                // actions
-         << hintsMap                     // hints
-         << timeout;                     // timeout
-    m_interface->callWithArgumentList(
-      QDBus::AutoDetect, QStringLiteral("Notify"), args);
+        args << (qAppName())                 // appname
+             << static_cast<unsigned int>(0) // id
+             << FLAMESHOT_ICON               // icon
+             << title                        // summary
+             << text                         // body
+             << QStringList()                // actions
+             << hintsMap                     // hints
+             << timeout;                     // timeout
+        m_interface->callWithArgumentList(
+          QDBus::AutoDetect, QStringLiteral("Notify"), args);
+    }
 #endif
 }