package main
import (
"encoding/binary"
"flag"
"fmt"
"log"
"net"
"time"
)
const ntpEpochOffset = 2208988800
type packet struct {
Settings uint8
Stratum uint8
Poll int8
Precision int8
RootDelay uint32
RootDispersion uint32
ReferenceID uint32
RefTimeSec uint32
RefTimeFrac uint32
OrigTimeSec uint32
OrigTimeFrac uint32
RxTimeSec uint32
RxTimeFrac uint32
TxTimeSec uint32
TxTimeFrac uint32
}
func main() {
var host string
flag.StringVar(&host, "e", "182.92.12.11:123", "NTP host")
flag.Parse()
conn, err := net.Dial("udp", host)
if err != nil {
log.Fatalf("failed to connect: %v", err)
}
defer conn.Close()
if err := conn.SetDeadline(time.Now().Add(15 * time.Second)); err != nil {
log.Fatalf("failed to set deadline: %v", err)
}
req := &packet{Settings: 0x1B}
if err := binary.Write(conn, binary.BigEndian, req); err != nil {
log.Fatalf("failed to send request: %v", err)
}
rsp := &packet{}
if err := binary.Read(conn, binary.BigEndian, rsp); err != nil {
log.Fatalf("failed to read server response: %v", err)
}
secs := float64(rsp.TxTimeSec) - ntpEpochOffset
nanos := (int64(rsp.TxTimeFrac) * 1e9) >> 32
showtime := time.Unix(int64(secs), nanos)
fmt.Printf("%v\n", showtime)
}
