原 golang实现NTP协议获取服务器时间

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// 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)