secret-backend: Check if portal is available

Before decising to use the file backend, check if the necessary portal
interface is available on the D-Bus.

Suggested by Patrick Griffis.

libsecret/secret-backend.c

@@ -155,7 +155,8 @@ backend_get_impl_type (void)
 #endif
 
 #ifdef WITH_GCRYPT
-	if (g_file_test ("/.flatpak-info", G_FILE_TEST_EXISTS))
+	if (g_file_test ("/.flatpak-info", G_FILE_TEST_EXISTS) &&
+	    _secret_file_backend_check_portal_version ())
 		extension_name = "file";
 	else
 #endif

libsecret/secret-file-backend.c

@@ -33,6 +33,7 @@ EGG_SECURE_DECLARE (secret_file_backend);
 #define PORTAL_OBJECT_PATH "/org/freedesktop/portal/desktop"
 #define PORTAL_REQUEST_INTERFACE "org.freedesktop.portal.Request"
 #define PORTAL_SECRET_INTERFACE "org.freedesktop.portal.Secret"
+#define PORTAL_SECRET_VERSION 1
 
 static void secret_file_backend_async_initable_iface (GAsyncInitableIface *iface);
 static void secret_file_backend_backend_iface (SecretBackendInterface *iface);
@@ -776,3 +777,50 @@ secret_file_backend_backend_iface (SecretBackendInterface *iface)
 	iface->search = secret_file_backend_real_search;
 	iface->search_finish = secret_file_backend_real_search_finish;
 }
+
+gboolean
+_secret_file_backend_check_portal_version (void)
+{
+	GDBusConnection *connection;
+	GVariant *ret;
+	GVariant *value;
+	guint32 version;
+	GError *error = NULL;
+
+	connection = g_bus_get_sync (G_BUS_TYPE_SESSION, NULL, &error);
+	if (!connection) {
+		g_warning ("couldn't get session bus: %s", error->message);
+		g_error_free (error);
+		return FALSE;
+	}
+
+	ret = g_dbus_connection_call_sync (connection,
+					   PORTAL_BUS_NAME,
+					   PORTAL_OBJECT_PATH,
+					   "org.freedesktop.DBus.Properties",
+					   "Get",
+					   g_variant_new ("(ss)",
+							  PORTAL_SECRET_INTERFACE,
+							  "version"),
+					   G_VARIANT_TYPE ("(v)"),
+					   0, -1, NULL, &error);
+	g_object_unref (connection);
+	if (!ret) {
+		g_message ("secret portal is not available: %s",
+			   error->message);
+		g_error_free (error);
+		return FALSE;
+	}
+
+	g_variant_get (ret, "(v)", &value);
+	g_variant_unref (ret);
+	version = g_variant_get_uint32 (value);
+	g_variant_unref (value);
+	if (version != PORTAL_SECRET_VERSION) {
+		g_message ("secret portal version mismatch: %u != %u",
+			   version, PORTAL_SECRET_VERSION);
+		return FALSE;
+	}
+
+	return TRUE;
+}

libsecret/secret-file-backend.h

@@ -26,6 +26,8 @@ G_BEGIN_DECLS
 #define SECRET_TYPE_FILE_BACKEND (secret_file_backend_get_type ())
 G_DECLARE_FINAL_TYPE (SecretFileBackend, secret_file_backend, SECRET, FILE_BACKEND, GObject)
 
+gboolean _secret_file_backend_check_portal_version (void);
+
 G_END_DECLS
 
 #endif /* __SECRET_FILE_BACKEND_H__ */