endSessionDialog: Check for PackageKit before considering updates/upgrades

GNOME Shell is spitting out some errors in the journal due to its attempts
to speak to PackageKit, which is not present on Endless OS, so let's add
some runtime checks to make sure that PackageKit is actually available
before assuming so and using its proxy to decide which kind of UI to
show to the user when ending the session.

https://gitlab.gnome.org/GNOME/gnome-shell/issues/369

js/ui/endSessionDialog.js

@@ -231,14 +231,13 @@ class EndSessionDialog extends ModalDialog.ModalDialog {
         this._loginManager = LoginManager.getLoginManager();
         this._userManager = AccountsService.UserManager.get_default();
         this._user = this._userManager.get_user(GLib.get_user_name());
+        this._updatesPermission = null;
 
         this._pkOfflineProxy = new PkOfflineProxy(Gio.DBus.system,
                                                   'org.freedesktop.PackageKit',
                                                   '/org/freedesktop/PackageKit',
-                                                  (proxy, error) => {
+                                                  this._onPkOfflineProxyCreated.bind(this));
-                                                      if (error)
+
-                                                          log(error.message);
-                                                  });
         this._powerProxy = new UPowerProxy(Gio.DBus.system,
                                            'org.freedesktop.UPower',
                                            '/org/freedesktop/UPower',
@@ -333,16 +332,33 @@ class EndSessionDialog extends ModalDialog.ModalDialog {
         this._inhibitorSection.add_actor(this._sessionHeader);
         this._inhibitorSection.add_actor(this._sessionList);
 
-        try {
-            this._updatesPermission = Polkit.Permission.new_sync("org.freedesktop.packagekit.trigger-offline-update", null, null);
-        } catch (e) {
-            log('No permission to trigger offline updates: %s'.format(e.toString()));
-        }
-
         this._dbusImpl = Gio.DBusExportedObject.wrapJSObject(EndSessionDialogIface, this);
         this._dbusImpl.export(Gio.DBus.session, '/org/gnome/SessionManager/EndSessionDialog');
     }
 
+    _onPkOfflineProxyCreated(proxy, error) {
+        if (error) {
+            log(error.message);
+            return;
+        }
+
+        // Creating a D-Bus proxy won't propagate SERVICE_UNKNOWN or NAME_HAS_NO_OWNER
+        // errors if PackageKit is not available, but the GIO implementation will make
+        // sure in that case that the proxy's g-name-owner is set to null, so check that.
+        if (this._pkOfflineProxy.g_name_owner === null) {
+            this._pkOfflineProxy = null;
+            return;
+        }
+
+        // It only makes sense to check for this permission if PackageKit is available.
+        try {
+            this._updatesPermission = Polkit.Permission.new_sync(
+                "org.freedesktop.packagekit.trigger-offline-update", null, null);
+        } catch(e) {
+            log('No permission to trigger offline updates: %s'.format(e.toString()));
+        }
+    }
+
     _onDestroy() {
         this._user.disconnect(this._userLoadedId);
         this._user.disconnect(this._userChangedId);
@@ -387,7 +403,8 @@ class EndSessionDialog extends ModalDialog.ModalDialog {
         }
 
         // Use a different description when we are installing a system upgrade
-        if (dialogContent.upgradeDescription) {
+        // if the PackageKit proxy is available (i.e. PackageKit is available).
+        if (this._pkOfflineProxy && dialogContent.upgradeDescription) {
             let name = this._pkOfflineProxy.PreparedUpgrade['name'].deep_unpack();
             let version = this._pkOfflineProxy.PreparedUpgrade['version'].deep_unpack();
 
@@ -496,6 +513,12 @@ class EndSessionDialog extends ModalDialog.ModalDialog {
     }
 
     _triggerOfflineUpdateReboot(callback) {
+        // Handle this gracefully if PackageKit is not available.
+        if (!this._pkOfflineProxy) {
+            callback();
+            return;
+        }
+
         this._pkOfflineProxy.TriggerRemote('reboot', (result, error) => {
             if (error)
                 log(error.message);
@@ -505,6 +528,12 @@ class EndSessionDialog extends ModalDialog.ModalDialog {
     }
 
     _triggerOfflineUpdateShutdown(callback) {
+        // Handle this gracefully if PackageKit is not available.
+        if (!this._pkOfflineProxy) {
+            callback();
+            return;
+        }
+
         this._pkOfflineProxy.TriggerRemote('power-off', (result, error) => {
             if (error)
                 log(error.message);
@@ -514,6 +543,12 @@ class EndSessionDialog extends ModalDialog.ModalDialog {
     }
 
     _triggerOfflineUpdateCancel(callback) {
+        // Handle this gracefully if PackageKit is not available.
+        if (!this._pkOfflineProxy) {
+            callback();
+            return;
+        }
+
         this._pkOfflineProxy.CancelRemote((result, error) => {
             if (error)
                 log(error.message);
@@ -676,7 +711,8 @@ class EndSessionDialog extends ModalDialog.ModalDialog {
         this._totalSecondsToStayOpen = totalSecondsToStayOpen;
         this._type = type;
 
-        if (this._type == DialogType.RESTART) {
+        // Only consider updates and upgrades if PackageKit is available.
+        if (this._pkOfflineProxy && this._type == DialogType.RESTART) {
             if (this._pkOfflineProxy.UpdateTriggered)
                 this._type = DialogType.UPDATE_RESTART;
             else if (this._pkOfflineProxy.UpgradeTriggered)
@@ -708,8 +744,9 @@ class EndSessionDialog extends ModalDialog.ModalDialog {
         if (dialogContent.showOtherSessions)
             this._loadSessions();
 
-        let updateTriggered = this._pkOfflineProxy.UpdateTriggered;
+        // Only consider updates and upgrades if PackageKit is available.
-        let updatePrepared = this._pkOfflineProxy.UpdatePrepared;
+        let updateTriggered = this._pkOfflineProxy ? this._pkOfflineProxy.UpdateTriggered : false;
+        let updatePrepared = this._pkOfflineProxy ? this._pkOfflineProxy.UpdatePrepared : false;
         let updatesAllowed = this._updatesPermission && this._updatesPermission.allowed;
 
         _setCheckBoxLabel(this._checkBox, dialogContent.checkBoxText || '');