ntp服务器udp协议,golang实现NTP协议获取服务器时间[通俗易懂]

// file project main.go

package main

import (

“encoding/binary”

“fmt”

“net”

“os”

“os/signal”

“sync”

“time”

)

const (

NTP_SERVER_IP = “time.windows.com” /*NTP IP*/

NTP_PORT_STR  = “123”              /*NTP专用端口号字 符串*/

NTP_PCK_LEN   = 48

LI            = 0

VN            = 3

MODE          = 3

STRATUM       = 0

POLL          = 4

PREC          = -6

JAN_1970      = 0x83aa7e80 /* 1900年～1970年之间的时间秒数 */

)

func NTPFRAC(x int64) int64 {

return (4294*(x) + ((1981 * (x)) >> 11))

}

func USEC(x int64) int64 {

return (((x) >> 12) – 759*((((x)>>10)+32768)>>16))

}

type ntp_time struct {

coarse uint32

fine   uint32

}

type ntp_packet struct {

leap_ver_mode        byte

startum              byte

poll                 byte

precision            byte

root_delay           int

root_dispersion      int

reference_identifier int

reference_timestamp  ntp_time

originage_timestamp  ntp_time

receive_timestamp    ntp_time

transmit_timestamp   ntp_time

}

var protocol []byte

func construct_packet() ([]byte, int) {

reqData := make([]byte, NTP_PCK_LEN)

//设置16字节的包头

head := (LI << 30) | (VN << 27) | (MODE << 24) | (STRATUM << 16) | (POLL << 8) | (PREC & 0xff)

binary.BigEndian.PutUint32(reqData[0:4], uint32(head))

//设置Root Delay、Root Dispersion和Reference Indentifier

binary.BigEndian.PutUint32(reqData[4:8], uint32(1<<16))

binary.BigEndian.PutUint32(reqData[8:12], uint32(1<<16))

binary.BigEndian.PutUint32(reqData[12:16], uint32(1<<16))

//设置Timestamp部分

timeOri := JAN_1970 + time.Now().Unix()

//设置Transmit Timestamp coarse

binary.BigEndian.PutUint32(reqData[40:44], uint32(timeOri))

//设置Transmit Timestamp fine

binary.BigEndian.PutUint32(reqData[44:48], uint32(NTPFRAC(timeOri)))

return reqData, NTP_PCK_LEN

}

func main() {

protocol = make([]byte, 32)

// Resolve address

fmt.Println(“ntp begin NTC…..”)

udpAddr, errData := net.ResolveUDPAddr(“udp”, NTP_SERVER_IP+”:”+NTP_PORT_STR)

if nil != errData {

fmt.Printf(“ntp connect err: %v\n”, errData)

return

}

fmt.Println(“ntp after ResolveTCPAddr…..: “, udpAddr)

conn, err := net.DialUDP(“udp”, nil, udpAddr)

if nil != err {

fmt.Printf(“ntp net connect error: %v\n”, err)

return

}

fmt.Println(“ntp after DialUDP…..”)

data, packet_len := construct_packet()

if packet_len == 0 {

fmt.Println(“ntp packet len is 0”)

return

}

fmt.Println(“ntp begin send: %v, data: %v”, packet_len, data)

conn.SetWriteDeadline(time.Now().Add(time.Second))

size, err := conn.Write(data)

if nil != err {

fmt.Printf(“ntp write data error: %v\n”, err)

return

} else {

fmt.Printf(“ntp write len: %v\n”, size)

}

fmt.Println(“after send”)

recvBody := make([]byte, 4096)

wait := &sync.WaitGroup{}

wait.Add(1)

go func() {

defer wait.Done()

for {

fmt.Println(“ntp begin read”)

conn.SetReadDeadline(time.Now().Add(time.Second))

size, remoteAddr, err := conn.ReadFromUDP(recvBody)

if nil != err {

fmt.Printf(“ntp read data error: %v\n”, err)

} else {

fmt.Printf(“ntp read len: %v\n”, size)

}

fmt.Println(“ntp after read, remoteAddr: %v\n”, remoteAddr.String(), recvBody[:size])

break

}

}()

wait.Wait()

var dataStru ntp_packet

dataStru.transmit_timestamp.coarse = binary.BigEndian.Uint32(recvBody[40:44]) – JAN_1970

dataStru.transmit_timestamp.fine = uint32(USEC(int64(binary.BigEndian.Uint32(recvBody[44:48]))))

fmt.Println(dataStru)

//等待退出

c := make(chan os.Signal, 1)

signal.Notify(c, os.Interrupt, os.Kill)

fmt.Println(“ntp Receive ctrl-c”)

}