remote-desktop/eis: Add support for ConnectToEIS.

Remote desktop version 2 added a new method ConnectToEIS .

ConnectToEIS allows clients to requests a file descriptor from the
compositor which can then be used directly from libei.

Once established, the communication between compositor and application
is direct, without the need to go through the portal process(es).

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2628>

data/dbus-interfaces/org.gnome.Mutter.RemoteDesktop.xml

@@ -348,6 +348,17 @@
     <property name="CapsLockState" type="b" access="read" />
     <property name="NumLockState" type="b" access="read" />
 
+    <!--
+        ConnectToEIS:
+
+        Request a connection to an EIS implementation.
+    -->
+    <method name="ConnectToEIS">
+      <arg type="a{sv}" name="options" direction="in"/>
+      <annotation name="org.gtk.GDBus.C.UnixFD" value="true"/>
+      <arg type="h" name="fd" direction="out"/>
+    </method>
+
   </interface>
 
 </node>

src/backends/meta-remote-desktop-session.c

@@ -1630,6 +1630,46 @@ handle_selection_read (MetaDBusRemoteDesktopSession *skeleton,
   return TRUE;
 }
 
+static gboolean
+handle_connect_to_eis (MetaDBusRemoteDesktopSession *skeleton,
+                       GDBusMethodInvocation        *invocation,
+                       GUnixFDList                  *fd_list_in,
+                       GVariant                     *arg_options)
+{
+  MetaRemoteDesktopSession *session = META_REMOTE_DESKTOP_SESSION (skeleton);
+  MetaBackend *backend =
+    meta_dbus_session_manager_get_backend (session->session_manager);
+  g_autoptr (GUnixFDList) fd_list = NULL;
+  int fd_idx;
+  GVariant *fd_variant;
+  int fd;
+  MetaEis *meis;
+
+  meis = meta_backend_get_eis (backend);
+
+  fd = meta_eis_add_client_get_fd (meis);
+  if (fd < 0)
+    {
+      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
+                                             G_DBUS_ERROR_FAILED,
+                                             "Failed to create socket: %s",
+                                             g_strerror (-fd));
+      return G_DBUS_METHOD_INVOCATION_HANDLED;
+    }
+
+  fd_list = g_unix_fd_list_new ();
+  fd_idx = g_unix_fd_list_append (fd_list, fd, NULL);
+  close (fd);
+  fd_variant = g_variant_new_handle (fd_idx);
+
+  meta_dbus_remote_desktop_session_complete_connect_to_eis (skeleton,
+                                                            invocation,
+                                                            fd_list,
+                                                            fd_variant);
+
+  return G_DBUS_METHOD_INVOCATION_HANDLED;
+}
+
 static gboolean
 meta_remote_desktop_session_initable_init (GInitable     *initable,
                                            GCancellable  *cancellable,
@@ -1691,6 +1731,7 @@ meta_remote_desktop_session_init_iface (MetaDBusRemoteDesktopSessionIface *iface
   iface->handle_selection_write = handle_selection_write;
   iface->handle_selection_write_done = handle_selection_write_done;
   iface->handle_selection_read = handle_selection_read;
+  iface->handle_connect_to_eis = handle_connect_to_eis;
 }
 
 static void