code: func (d *Descriptor) HandleRead(h ReadHandler) {
  	if d.Value != nil {
  		panic("descriptor has been configured with a static value")
  	}
  	d.Property |= CharRead
  	d.ReadHandler = h
  }
docs: // HandleRead makes the descriptor support read requests, and routes read requests to h.
  // HandleRead must be called before the containing service is added to a server.
  // HandleRead panics if the descriptor has been configured with a static value.