マシンの時計ベースのNTPサーバをGoで実装する
マシンの時計がズレていたら知りません
code:main.go
package main
import (
"encoding/binary"
"log"
"net"
"time"
"golang.org/x/net/ipv4"
)
var ntpEpoch = time.Date(1900, 1, 1, 0, 0, 0, 0, time.UTC)
type NtpPacket struct {
Settings uint8
Stratum uint8
Poll uint8
Precision uint8
RootDelay uint32
RootDispersion uint32
ReferenceID uint32
ReferenceTimestamp 8byte
OriginateTimestamp 8byte
ReceiveTimestamp 8byte
TransmitTimestamp 8byte
}
func toNtpTime(t time.Time) (ntpTime 8byte) {
seconds := uint32(t.Sub(ntpEpoch).Seconds())
fraction := uint32((t.Sub(ntpEpoch) % time.Second) * (1 << 32 / time.Second))
binary.BigEndian.PutUint32(ntpTime:4, seconds)
binary.BigEndian.PutUint32(ntpTime4:, fraction)
return ntpTime
}
func NewNtpPacket(receivedPacket NtpPacket, now time.Time) *NtpPacket {
return &NtpPacket{
Settings: 0x24,
Stratum: 1,
Poll: receivedPacket.Poll,
Precision: receivedPacket.Precision,
RootDelay: 0,
RootDispersion: 0,
ReferenceID: 0,
ReferenceTimestamp: toNtpTime(now),
OriginateTimestamp: receivedPacket.TransmitTimestamp,
ReceiveTimestamp: toNtpTime(now),
TransmitTimestamp: toNtpTime(now),
}
}
func handleRequest(conn *net.UDPConn, p *ipv4.PacketConn) {
b := make([]byte, 48)
for {
_, _, remoteAddr, err := p.ReadFrom(b)
if err != nil {
log.Fatalf("読み取りに失敗: %v", err)
}
var ntpPacket *NtpPacket
receivedPacket := NtpPacket{}
receivedPacket.Settings = b0
receivedPacket.Stratum = b1
receivedPacket.Poll = b2
receivedPacket.Precision = b3
receivedPacket.RootDelay = binary.BigEndian.Uint32(b4:8)
receivedPacket.RootDispersion = binary.BigEndian.Uint32(b8:12)
receivedPacket.ReferenceID = binary.BigEndian.Uint32(b12:16)
copy(receivedPacket.ReferenceTimestamp:, b16:24)
copy(receivedPacket.OriginateTimestamp:, b24:32)
copy(receivedPacket.ReceiveTimestamp:, b32:40)
copy(receivedPacket.TransmitTimestamp:, b40:48)
mode := b0 & 0x7
now := time.Now()
switch mode {
case 3:
log.Println("受信 <- " + remoteAddr.String())
log.Printf("%+v", receivedPacket)
ntpPacket = NewNtpPacket(receivedPacket, now)
copy(b32:40, ntpPacket.TransmitTimestamp:)
default:
log.Printf("非対応のモードです: %v", mode)
}
b0 = ntpPacket.Settings
b1 = ntpPacket.Stratum
b2 = ntpPacket.Poll
b3 = ntpPacket.Precision
binary.BigEndian.PutUint32(b4:8, ntpPacket.RootDelay)
binary.BigEndian.PutUint32(b8:12, ntpPacket.RootDispersion)
binary.BigEndian.PutUint32(b12:16, ntpPacket.ReferenceID)
copy(b16:24, ntpPacket.ReferenceTimestamp:)
copy(b24:32, ntpPacket.OriginateTimestamp:)
copy(b32:40, ntpPacket.ReceiveTimestamp:)
copy(b40:48, ntpPacket.TransmitTimestamp:)
log.Println("送信 -> " + remoteAddr.String())
log.Printf("%+v", ntpPacket)
_, err = conn.WriteTo(b, remoteAddr)
if err != nil {
log.Fatalf("書き込みに失敗: %v", err)
}
}
}
func main() {
addr, err := net.ResolveUDPAddr("udp", ":123")
if err != nil {
log.Fatalf("アドレス解決に失敗: %v", err)
}
conn, err := net.ListenUDP("udp", addr)
if err != nil {
log.Fatalf("起動に失敗: %v", err)
}
defer conn.Close()
p := ipv4.NewPacketConn(conn)
defer p.Close()
handleRequest(conn, p)
}
code:sh
sntp -d ::1 # or 127.0.0.1, localhost