使用Go语言编写一个简单的NTP服务器

NTP服务介绍

NTP服务器【Network Time Protocol（NTP）】是用来使计算机时间同步化的一种协议。

应用场景说明
为了确保封闭局域网内多个服务器的时间同步，我们计划部署一个网络时间同步服务器（NTP服务器）。这一角色将由一台个人笔记本电脑承担，该笔记本将连接到局域网中，并以其当前时间为基准。我们将利用这台笔记本电脑作为NTP服务器，对局域网内的多个运行CentOS 8的服务器进行时间校准，以保证系统时间的一致性和准确性。

NTP协议

NTP通信协议的传输层协议是UDP
NTP通信协议的应用层协议是NTP

NTP报文说明

NTP的报文是48字节

第1个字节可以理解为简易的报文头，这8个bit包含Leap Indicator、NTP Version、Mode
a> LI 占用2个bit
b> VN 占用3个bit，笔者编写的服务器设置为版本v4.0
c> Mode 占用3个bit，ntp server时为4，ntp client时为3
第2个字节为 Peer Clock Stratum
第3个字节为 Peer Polling Interval
第4个字节为 Peer Clock Precision
第5 - 8字节为 Root Delay
第9 - 12字节为 Root Dispersion
第13- 16字节为 Reference Identifier
第17 - 24字节为 Reference Timestamp 参考时间戳
第25 - 32字节为 Originate Timestamp 起始时间戳
第33 - 40字节为 Receive Timestamp 接收时间戳
第 41 - 48字节 Transmit Timestamp 传输时间戳

根据NTP报文编码实现Go语言的结构体

go 复制代码

type NtpPacket struct {
	/*
		LI: 2bit      00   Leap Indicator(0)
		VN: 3bit      100  NTP Version(4)
		Mode: 3bit    100  Mode: server(4), client(3)
	*/
	Header    uint8 // 报文头: 包含LI、VN、Mode
	Stratum   uint8 // Peer Clock Stratum: primary reference (1)
	Poll      uint8 // Peer Polling Interval: invalid (0)
	Precision uint8 // Peer Clock Precision: 0.000000 seconds

	RootDelay uint32 // Root Delay
	RootDisp  uint32 // Root Dispersion
	RefID     uint32 // Reference Identifier

	RefTS   uint64 // Reference Timestamp 参考时间戳
	OrigTS  uint64 // Originate Timestamp 起始时间戳
	RecvTS  uint64 // Receive Timestamp   接收时间戳
	TransTS uint64 // Transmit Timestamp  传输时间戳
}

NTP服务器的源码

ntpsrv.go

go 复制代码

package main

import (
	hldlog "NTPServer/log4go"
	"encoding/binary"
	"fmt"
	"log"
	"net"
	"sync"
	"time"
)

const (
	STANDARD_PACKET_SIZE = 48 // 标准NTP的报文大小
)

type NTPServer struct {
	srvAddress string

	conn *net.UDPConn
	wait sync.WaitGroup

	ntpPack      NtpPacket // NTP协议报文
	requestCount uint64    // 请求计数
}

type NtpPacket struct {
	/*
		LI: 2bit      00   Leap Indicator(0)
		VN: 3bit      100  NTP Version(4)
		Mode: 3bit    100  Mode: server(4), client(3)
	*/
	Header    uint8 // 报文头: 包含LI、VN、Mode
	Stratum   uint8 // Peer Clock Stratum: primary reference (1)
	Poll      uint8 // Peer Polling Interval: invalid (0)
	Precision uint8 // Peer Clock Precision: 0.000000 seconds

	RootDelay uint32 // Root Delay
	RootDisp  uint32 // Root Dispersion
	RefID     uint32 // Reference Identifier

	RefTS   uint64 // Reference Timestamp 参考时间戳
	OrigTS  uint64 // Originate Timestamp 起始时间戳
	RecvTS  uint64 // Receive Timestamp   接收时间戳
	TransTS uint64 // Transmit Timestamp  传输时间戳
}

func (srv *NTPServer) NewNtpPacket() *NtpPacket {
	// 初始化Header字段
	header := uint8(0)
	header |= (0 << 6) // LI: 2bit 00
	header |= (4 << 3) // VN: 3bit 100
	header |= (4 << 0) // Mode: 3bit 100

	// 创建新的NtpPacket实例
	packet := &NtpPacket{
		Header:    header,
		Stratum:   0x01,
		Poll:      0x00,
		Precision: 0x00,
		RootDelay: 0,
		RootDisp:  0,
		RefID:     0,
		RefTS:     0,
		OrigTS:    0,
		RecvTS:    0,
		TransTS:   0,
	}

	return packet
}

func (pack *NtpPacket) SetTimestamp(timestamp time.Time, field string) {
	ntpTime := ToNTPTime(timestamp)
	switch field {
	case "RefTS":
		pack.RefTS = ntpTime
	case "OrigTS":
		pack.OrigTS = ntpTime
	case "RecvTS":
		pack.RecvTS = ntpTime
	case "TransTS":
		pack.TransTS = ntpTime
	}
}

// toNTPTime 将Unix时间转换为NTP时间
func ToNTPTime(t time.Time) uint64 {
	seconds := uint32(t.Unix()) + 2208988800 // NTP时间从1900年开始计算
	fraction := uint32(float64(t.Nanosecond()) * (1 << 32) / 1e9)
	return uint64(seconds)<<32 | uint64(fraction)
}

func NewNTPServer(srvAddr string) *NTPServer {
	return &NTPServer{srvAddress: srvAddr}
}

// 启动NTP服务器
func (srv *NTPServer) Start() error {
	addr, err := net.ResolveUDPAddr("udp", srv.srvAddress)
	if err != nil {
		return err
	}
	hldlog.Info(fmt.Sprintf("<%s:%d>", addr.IP.String(), addr.Port))

	conn, err := net.ListenUDP("udp", addr)
	if err != nil {
		return err
	}

	srv.wait.Add(1)
	srv.conn = conn

	go RecvMsg(srv)

	return nil
}

// 关闭NTP服务器
func (srv *NTPServer) Stop() {
	srv.conn.Close()
	srv.wait.Wait()
}

// 接收数据
func RecvMsg(srv *NTPServer) {
	defer srv.wait.Done()
	buffer := make([]byte, 2*1024)

	for {
		n, remoteAddr, err := srv.conn.ReadFromUDP(buffer[0:])
		if err != nil {
			fmt.Println("ReadFromUDP error:", err)
			return
		}
		hldlog.Info(fmt.Sprintf("[Recv] %d bytes from <%s>", n, remoteAddr.String()))
		if n != STANDARD_PACKET_SIZE {
			continue
		}

		// 接收到NTP客户端消息的时间
		recvMsgTime := time.Now().UTC()

		recvHexString := BytesToHex(buffer[:n])
		hldlog.Info(fmt.Sprintf("[Recv] %s", recvHexString))

		udpPacket, err := ParseUDPPacket(buffer[:n])
		if err != nil {
			log.Printf("Error parsing UDP packet: %v", err)
			continue
		}
		ntpPack := srv.NewNtpPacket()
		ntpPack.SetTimestamp(time.Now().UTC(), "RefTS")
		ntpPack.OrigTS = udpPacket.TransTS
		ntpPack.SetTimestamp(recvMsgTime, "RecvTS")
		ntpPack.SetTimestamp(time.Now().UTC(), "TransTS")

		sendPacket := ntpPack.Serialize()

		sendLen, err := srv.conn.WriteToUDP(sendPacket, remoteAddr)
		if err != nil {
			log.Println(err.Error())
			continue
		}

		if sendLen > 0 {
			hldlog.Info(fmt.Sprintf("[Send] %s", BytesToHex(sendPacket)))
		}

		srv.requestCount++
	}
}

func (pack *NtpPacket) Serialize() []byte {
	packet := make([]byte, 48)

	// binary.BigEndian.PutUint32(packet[0:4], pack.Header)
	packet[0] = pack.Header
	packet[1] = pack.Stratum
	packet[2] = pack.Poll
	packet[3] = pack.Precision
	binary.BigEndian.PutUint32(packet[4:8], pack.RootDelay)
	binary.BigEndian.PutUint32(packet[8:12], pack.RootDisp)
	binary.BigEndian.PutUint32(packet[12:16], pack.RefID)
	binary.BigEndian.PutUint64(packet[16:24], pack.RefTS)
	binary.BigEndian.PutUint64(packet[24:32], pack.OrigTS)
	binary.BigEndian.PutUint64(packet[32:40], pack.RecvTS)
	binary.BigEndian.PutUint64(packet[40:48], pack.TransTS)

	return packet
}

// BytesToHex 将字节数组转换为16进制字符串
func BytesToHex(data []byte) string {
	hexString := make([]byte, 3*len(data)-1)
	for i, b := range data {
		high := "0123456789ABCDEF"[(b >> 4)]
		low := "0123456789ABCDEF"[(b & 0x0F)]
		hexString[i*3] = high
		hexString[i*3+1] = low
		if i < len(data)-1 {
			hexString[i*3+2] = ' ' // 每个16进制数据之间加空格
		}
	}
	return string(hexString)
}

func ParseUDPPacket(buf []byte) (*NtpPacket, error) {
	if len(buf) < STANDARD_PACKET_SIZE { // 最小有效长度为48字节
		return nil, fmt.Errorf("Invalid UDP packet length: %d", len(buf))
	}

	packet := &NtpPacket{
		// Header:    binary.BigEndian.Uint32(buf[0:4]),
		Header:    buf[0],
		Stratum:   buf[1],
		Poll:      buf[2],
		Precision: buf[3],
		RootDelay: binary.BigEndian.Uint32(buf[4:8]),
		RootDisp:  binary.BigEndian.Uint32(buf[8:12]),
		RefID:     binary.BigEndian.Uint32(buf[12:16]),
		RefTS:     binary.BigEndian.Uint64(buf[16:24]),
		OrigTS:    binary.BigEndian.Uint64(buf[24:32]),
		RecvTS:    binary.BigEndian.Uint64(buf[32:40]),
		TransTS:   binary.BigEndian.Uint64(buf[40:48]),
	}

	return packet, nil
}

main.go

go 复制代码

package main

import (
	hldlog "NTPServer/log4go"
	"fmt"
	"gopkg.in/ini.v1"
	"time"
)

type NetAddr struct {
	IP   string
	Port string
}

var LocalHost = NetAddr{IP: "0.0.0.0", Port: "60123"}

func loadConfig() (NetAddr, error) {
	// 读取INI配置文件
	iniConf, err := ini.Load("./config/config.ini")
	if err != nil {
		hldlog.Error(fmt.Sprintf("Fail to read INI file: %v", err))
		return LocalHost, nil
	}

	iniSection := iniConf.Section("LocalHost")
	return NetAddr{
		IP:   iniSection.Key("ip").String(),
		Port: iniSection.Key("port").String(),
	}, nil
}

// 初始化log4go日志库
func init() {
	hldlog.LoadConfiguration("./config/log.xml", "xml")
}

func main() {
	hldlog.Info("===NTP SERVER Start(48 Bytes)===")

	LocalHost, err := loadConfig()
	if err != nil {
		hldlog.Error(fmt.Sprintf("Failed to load configuration: %v", err))
	}

	ntpSrv := NewNTPServer(fmt.Sprintf("%s:%s", LocalHost.IP, LocalHost.Port))
	ntpSrv.Start()

	for {
		time.Sleep(60 * time.Second)
	}
}

代码细节说明
NTP服务器在回复NTP客户端的消息中其中OrigTS uint64（Originate Timestamp 起始时间戳）必须是NTP客户端发送来的TransTS uint64（Transmit Timestamp 传输时间戳）。

验证GoNTPSrv

上述实现的NTP服务已经过Go语言中开源的NTP Client库 https://github.com/beevik/ntp 验证。

UDP数据包

sh 复制代码

# 客户端发送的数据
23 00 00 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 39 1C 79 9E 83 D3 D5 82

# 服务器返回的数据
24 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 EA D9 CF EE AD 4D DC 2B 39 1C 79 9E 83 D3 D5 82 EA D9 CF EE AD 4D DC 2B EA D9 CF EE AD 4D DC 2B

NTP Client的简单源码

go 复制代码

package main

import (
	hldlog "NTPCli/log4go"
	"fmt"
	"log"
	"os"
	"os/exec"
	"time"

	"github.com/beevik/ntp"
	"gopkg.in/ini.v1"
)

type NetAddr struct {
	IP   string
	Port int
}

var RemoteAddr = NetAddr{IP: "0.0.0.0", Port: 60123}

func init() {
	hldlog.LoadConfiguration("./config/log.xml", "xml")
}

func main() {
	hldlog.Info("===NTP CLIENT Start===")

	currTime := time.Now()
	formattedTime := currTime.Format("2006-01-02 15:04:05.000")
	hldlog.Info(formattedTime)

	// 读取INI配置文件
	iniConf, err := ini.Load("./config/config.ini")
	if err != nil {
		log.Fatalf("Fail to read INI file: %v", err)
	}

	remoteSection := iniConf.Section("NTP_SERVER")
	RemoteAddr.IP = remoteSection.Key("ip").String()
	RemoteAddr.Port, _ = remoteSection.Key("port").Int()
	hldlog.Info(fmt.Sprintf("ntp://%s:%d", RemoteAddr.IP, RemoteAddr.Port))

	// edu.ntp.org.cn
	// resp, err := ntp.Time("edu.ntp.org.cn")
	resp, err := ntp.Time(fmt.Sprintf("%s:%d", RemoteAddr.IP, RemoteAddr.Port))
	if err != nil {
		hldlog.Error(fmt.Sprintf("%v", err))
		os.Exit(-1)
	}
	hldlog.Info(resp.String())

	localTime := resp.Local()
	hldlog.Info(localTime.Format("2006-01-02 15:04:05.000"))

	// setTime(localTime)

	for {
		time.Sleep(60 * time.Second)
	}
}