static int on_begin_frame_callback(nghttp2_session *session,
                                   const nghttp2_frame_hd *hd,
                                   void *user_data) {
  my_user_data *ud = (my_user_data *)user_data;
  (void)session;
  (void)hd;

  ++ud->begin_frame_cb_called;
  return 0;
}
static int on_begin_frame_callback(nghttp2_session *session,
                                   const nghttp2_frame_hd *hd,
                                   void *user_data) {
  my_user_data *ud = (my_user_data *)user_data;
  (void)session;
  (void)hd;

  ++ud->begin_frame_cb_called;
  return 0;
}