code: func (cln *Client) ReadRSSI() int {
  	rsp := cln.conn.sendReq(44, xpc.Dict{"kCBMsgArgDeviceUUID": cln.id})
  	if rsp.err() != nil {
  		return 0
  	}
  	return rsp.rssi()
  }
docs: // ReadRSSI retrieves the current RSSI value of remote peripheral. [Vol 2, Part E, 7.5.4]