Pagekit\Installer\Controller\UpdateController::updateAction PHP Method

    public function updateAction()
    {
        if (!($file = App::session()->get('system.update'))) {
            App::abort(400, __('You may not call this step directly.'));
        }
        App::session()->remove('system.update');
        return App::response()->stream(function () use($file) {
            $output = new StreamOutput(fopen('php://output', 'w'));
            try {
                if (!file_exists($file) || !is_file($file)) {
                    throw new \RuntimeException('File does not exist.');
                }
                $updater = new SelfUpdater($output);
                $updater->update($file);
            } catch (\Exception $e) {
                $output->writeln(sprintf("\n<error>%s</error>", $e->getMessage()));
                $output->write("status=error");
            }
        });
    }