simple-ntp-client.go

package main

import (
	"encoding/binary"
	"fmt"
	"net"
	"time"
)

type Packet struct {
	Flags      uint8
	_          [39]uint8
	TxTimeSec  uint32
	TxTimeFrac uint32
}

func main() {
	conn, _ := net.Dial("udp", "time.nist.gov:123")
	defer conn.Close()
	buf := &Packet{Flags: 0b1110011}
	_ = binary.Write(conn, binary.BigEndian, buf)
	_ = binary.Read(conn, binary.BigEndian, buf)
	sec := float64(buf.TxTimeSec) - 2208988800
	nsec := (int64(buf.TxTimeFrac) * 1e9) >> 32
	fmt.Println(time.Unix(int64(sec), nsec))
}