ros2 service server callback interface

edit

Why do service serverss in rclcpp have a callback interface in which the request is not const?

From https://github.com/ros2/rclcpp/blob/8...:

  using CallbackType = std::function<
    void (
      const std::shared_ptr<typename ServiceT::Request>,
      std::shared_ptr<typename ServiceT::Response>)>;

instead of

  using CallbackType = std::function<
    void (
      const std::shared_ptr<const typename ServiceT::Request>,
      std::shared_ptr<typename ServiceT::Response>)>;