code: func (cln *Client) WriteCharacteristic(c *ble.Characteristic, b []byte, noRsp bool) error {
  	args := xpc.Dict{
  		"kCBMsgArgDeviceUUID":                cln.id,
  		"kCBMsgArgCharacteristicHandle":      c.Handle,
  		"kCBMsgArgCharacteristicValueHandle": c.ValueHandle,
  		"kCBMsgArgData":                      b,
  		"kCBMsgArgType":                      map[bool]int{false: 0, true: 1}[noRsp],
  	}
  	if noRsp {
  		cln.conn.sendCmd(66, args)
  		return nil
  	}
  	return cln.conn.sendReq(66, args).err()
  }
docs: // WriteCharacteristic writes a characteristic value to a server. [Vol 3, Part G, 4.9.3]