screenshot: Move HAVE_RECORDER check into screencast service

Some gstreamer plugins require a connection to the display server,
so if we end up initializing gstreamer before we are ourselves
fully initialized, we may end up with a locked compositor.

Avoid this by moving the runtime recorder check into the screencast
D-Bus service, so that all gstreamer calls happen out of process.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5710

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2519>

data/dbus-interfaces/org.gnome.Shell.Screencast.xml

@@ -10,6 +10,7 @@
       The interface used to record screen contents.
   -->
   <interface name="org.gnome.Shell.Screencast">
+    <property name="ScreencastSupported" type="b" access="read"/>
 
     <!--
         Screencast:

js/dbusServices/screencast/main.js

@@ -1,13 +1,12 @@
 /* exported main */
 
-const Config = imports.misc.config;
 const {DBusService} = imports.dbusService;
 
 function main() {
-    if (!Config.HAVE_RECORDER)
+    const {ScreencastService} = imports.screencastService;
+    if (!ScreencastService.canScreencast())
         return;
 
-    const { ScreencastService } = imports.screencastService;
     const service = new DBusService(
         'org.gnome.Shell.Screencast',
         new ScreencastService());

js/dbusServices/screencast/screencastService.js

@@ -258,9 +258,17 @@ var Recorder = class {
 };
 
 var ScreencastService = class extends ServiceImplementation {
+    static canScreencast() {
+        return Gst.init_check(null) &&
+            Gst.ElementFactory.find('pipewiresrc') &&
+            Gst.ElementFactory.find('filesink');
+    }
+
     constructor() {
         super(ScreencastIface, '/org/gnome/Shell/Screencast');
 
+        this._canScreencast = ScreencastService.canScreencast();
+
         Gst.init(null);
         Gtk.init();
 
@@ -280,6 +288,10 @@ var ScreencastService = class extends ServiceImplementation {
             '/org/gnome/Shell/Introspect');
     }
 
+    get ScreencastSupported() {
+        return this._canScreencast;
+    }
+
     _removeRecorder(sender) {
         this._recorders.delete(sender);
         if (this._recorders.size === 0)

js/misc/config.js.in

@@ -21,8 +21,3 @@ var LIBMUTTER_API_VERSION = '@LIBMUTTER_API_VERSION@'
 
 var HAVE_BLUETOOTH = pkg.checkSymbol('GnomeBluetooth', '3.0',
     'Client.default_adapter_state')
-var HAVE_RECORDER =
-    pkg.checkSymbol('Gst', '1.0') &&
-    imports.gi.Gst.init_check(null) &&
-    imports.gi.Gst.ElementFactory.find('pipewiresrc') &&
-    imports.gi.Gst.ElementFactory.find('filesink');

js/ui/screenshot.js

@@ -3,7 +3,6 @@
 
 const { Clutter, Cogl, Gio, GObject, GLib, Graphene, Gtk, Meta, Shell, St } = imports.gi;
 
-const Config = imports.misc.config;
 const GrabHelper = imports.ui.grabHelper;
 const Layout = imports.ui.layout;
 const Lightbox = imports.ui.lightbox;
@@ -1019,6 +1018,19 @@ var ScreenshotUI = GObject.registerClass({
 
         this._screencastInProgress = false;
 
+        this._screencastProxy = new ScreencastProxy(
+            Gio.DBus.session,
+            'org.gnome.Shell.Screencast',
+            '/org/gnome/Shell/Screencast',
+            (object, error) => {
+                if (error !== null) {
+                    log('Error connecting to the screencast service');
+                    return;
+                }
+
+                this._castButton.visible = this._screencastProxy.ScreencastSupported;
+            });
+
         this._lockdownSettings = new Gio.Settings({ schema_id: 'org.gnome.desktop.lockdown' });
 
         // The full-screen screenshot has a separate container so that we can
@@ -1212,7 +1224,7 @@ var ScreenshotUI = GObject.registerClass({
             style_class: 'screenshot-ui-shot-cast-button',
             icon_name: 'camera-web-symbolic',
             toggle_mode: true,
-            visible: Config.HAVE_RECORDER,
+            visible: false,
         });
         this._castButton.connect('notify::checked',
             this._onCastButtonToggled.bind(this));
@@ -1438,7 +1450,7 @@ var ScreenshotUI = GObject.registerClass({
         if (this._screencastInProgress)
             return;
 
-        if (mode === UIMode.SCREENCAST && !Config.HAVE_RECORDER)
+        if (mode === UIMode.SCREENCAST && !this._screencastProxy.ScreencastSupported)
             return;
 
         this._castButton.checked = mode === UIMode.SCREENCAST;
@@ -1809,7 +1821,7 @@ var ScreenshotUI = GObject.registerClass({
         }
     }
 
-    _startScreencast() {
+    async _startScreencast() {
         if (this._windowButton.checked)
             return; // TODO
 
@@ -1833,7 +1845,6 @@ var ScreenshotUI = GObject.registerClass({
         this.close(true);
 
         // This is a bit awkward because creating a proxy synchronously hangs Shell.
-        const doStartScreencast = async () => {
         let method =
             this._screencastProxy.ScreencastAsync.bind(this._screencastProxy);
         if (w !== -1) {
@@ -1841,6 +1852,10 @@ var ScreenshotUI = GObject.registerClass({
                 this._screencastProxy, x, y, w, h);
         }
 
+        // Set this before calling the method as the screen recording indicator
+        // will check it before the success callback fires.
+        this._setScreencastInProgress(true);
+
         try {
             const [success, path] = await method(
                 GLib.build_filenamev([
@@ -1865,30 +1880,6 @@ var ScreenshotUI = GObject.registerClass({
             else
                 log('Error starting screencast');
         }
-        };
-
-        // Set this before calling the method as the screen recording indicator
-        // will check it before the success callback fires.
-        this._setScreencastInProgress(true);
-
-        if (this._screencastProxy) {
-            doStartScreencast();
-        } else {
-            new ScreencastProxy(
-                Gio.DBus.session,
-                'org.gnome.Shell.Screencast',
-                '/org/gnome/Shell/Screencast',
-                (object, error) => {
-                    if (error !== null) {
-                        log('Error connecting to the screencast service');
-                        return;
-                    }
-
-                    this._screencastProxy = object;
-                    doStartScreencast();
-                }
-            );
-        }
     }
 
     async stopScreencast() {