NTPとは何か、時刻プロトコルとアプリケーションにおける同期

// Simplified NTP algorithm schema
struct NTPPacket {
    uint8_t flags;      // LI, VN, Mode
    uint8_t stratum;    // server stratum level
    uint32_t refTimestamp;  // reference timestamp
    uint32_t originTimestamp; // T1
    uint32_t recvTimestamp;   // T2
    uint32_t xmitTimestamp;   // T3
};

// Calculate offset and delay
double offset = ((t2 - t1) + (t3 - t4)) / 2.0;
double delay = (t4 - t1) - (t3 - t2);

// Get NTP time via Apache Commons Net
fun getNtpTime(server: String = "pool.ntp.org"): Date? {
    return try {
        val client = NTPUDPClient()
        client.setDefaultTimeout(5000)
        val info = client.getTime(InetAddress.getByName(server))
        client.close()
        Date(info.getMessage().getTransmitTimeStamp().getTime())
    } catch (e: Exception) {
        null
    }
}