Phly\Http\Server::listen PHP Method

    public function listen(callable $finalHandler = null)
    {
        $callback = $this->callback;
        ob_start();
        $bufferLevel = ob_get_level();
        $response = $callback($this->request, $this->response, $finalHandler);
        if (!$response instanceof ResponseInterface) {
            $response = $this->response;
        }
        $this->getEmitter()->emit($response, $bufferLevel);
    }