code: func (r *responseWriter) Write(b []byte) (int, error) {
  	if r.buf == nil {
  		return 0, ErrReqNotSupp
  	}
  	if len(b) > r.buf.Cap()-r.buf.Len() {
  		return 0, io.ErrShortWrite
  	}
  
  	return r.buf.Write(b)
  }
docs: // Write writes data to return as the characteristic value.
  // Cap returns 0 with error set to ErrReqNotSupp if it is a dummy write response for WriteCommand.