code: func (h *handler) unsubscribe(ctx context.Context, id ID) (bool, error) {
  	h.subLock.Lock()
  	defer h.subLock.Unlock()
  
  	s := h.serverSubs[id]
  	if s == nil {
  		return false, ErrSubscriptionNotFound
  	}
  	close(s.err)
  	delete(h.serverSubs, id)
  	return true, nil
  }
docs: // unsubscribe is the callback function for all *_unsubscribe calls.