QNetworkInfo[NetworkManager]: Mark invalid if unconnected

On some configs (e.g. using Snap) the NetworkManager service is not
available without some manifest or similar. In this case, the
_interface_ we have is still valid but we can't connect to the
service. So we need to mark the interface as invalid in this case, so
that we can avoid trying to use this plugin.

Pick-to: 6.6 6.5
Fixes: QTBUG-117490
Change-Id: I3c5ebb492f9ca4dfdf4353d77705ba993279eb69
Reviewed-by: Ilya Fedin <fedin-ilja2010@ya.ru>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/plugins/networkinformation/networkmanager/qnetworkmanagernetworkinformationbackend.cpp

@@ -167,6 +167,8 @@ private:
 
 QNetworkManagerNetworkInformationBackend::QNetworkManagerNetworkInformationBackend()
 {
+    if (!iface.isValid())
+        return;
     auto updateReachability = [this](QNetworkManagerInterface::NMState newState) {
         setReachability(reachabilityFromNMState(newState));
     };

src/plugins/networkinformation/networkmanager/qnetworkmanagerservice.cpp

@@ -41,7 +41,7 @@ bool QNetworkManagerInterfaceBase::networkManagerAvailable()
 QNetworkManagerInterface::QNetworkManagerInterface(QObject *parent)
     : QNetworkManagerInterfaceBase(parent)
 {
-    if (!isValid())
+    if (!QDBusAbstractInterface::isValid())
         return;
 
     PropertiesDBusInterface managerPropertiesInterface(
@@ -51,13 +51,15 @@ QNetworkManagerInterface::QNetworkManagerInterface(QObject *parent)
     argumentList << NM_DBUS_SERVICE;
     QDBusPendingReply<QVariantMap> propsReply = managerPropertiesInterface.callWithArgumentList(
             QDBus::Block, "GetAll"_L1, argumentList);
-    if (!propsReply.isError()) {
-        propertyMap = propsReply.value();
-    } else {
-        qWarning() << "propsReply" << propsReply.error().message();
+    if (propsReply.isError()) {
+        validDBusConnection = false;
+        if (auto error = propsReply.error(); error.type() != QDBusError::AccessDenied)
+            qWarning() << "Failed to query NetworkManager properties:" << error.message();
+        return;
     }
+    propertyMap = propsReply.value();
 
-    QDBusConnection::systemBus().connect(NM_DBUS_SERVICE, NM_DBUS_PATH,
+    validDBusConnection = QDBusConnection::systemBus().connect(NM_DBUS_SERVICE, NM_DBUS_PATH,
             DBUS_PROPERTIES_INTERFACE, "PropertiesChanged"_L1, this,
             SLOT(setProperties(QString,QMap<QString,QVariant>,QList<QString>)));
 }

src/plugins/networkinformation/networkmanager/qnetworkmanagerservice.h

@@ -136,6 +136,8 @@ public:
     NMDeviceType deviceType() const;
     NMMetered meteredState() const;
 
+    bool isValid() const { return QDBusAbstractInterface::isValid() && validDBusConnection; }
+
 Q_SIGNALS:
     void stateChanged(NMState);
     void connectivityChanged(NMConnectivityState);
@@ -155,6 +157,7 @@ private:
     std::optional<QDBusObjectPath> primaryConnectionDevicePath() const;
 
     QVariantMap propertyMap;
+    bool validDBusConnection = true;
 };
 
 class PropertiesDBusInterface : public QDBusAbstractInterface