基于NTP协议网络校时

た入场券 2022-08-13 17:57 226阅读 0赞

先来个NTP协议介绍  
[http://blog.163.com/yzc\_5001/blog/static/2061963420121283050787/][http_blog.163.com_yzc_5001_blog_static_2061963420121283050787]  
  
关于时间戳的换算工具  
[http://tool.chinaz.com/Tools/unixtime.aspx\#][http_tool.chinaz.com_Tools_unixtime.aspx]

下面是代码，C-Free + MinGW 编译，须在工程连接参数里添加 -lwsock32

#include <stdio.h>
    #include <time.h>
    #include <winsock2.h>
    
    #define JAN_1970 0x83AA7E80      /* 2208988800    1970-1900 in seconds*/
    
    typedef union
    {
        int  time;
        char time_array[4];
    } Timestamp;
    
    typedef struct 
    {
        char message_hdr[16];//报文头部 
        char RefTimestamp[8];
        Timestamp T1;
        char T1_decimal[4]; //T1的小数部分 
        Timestamp T2;
        char T2_decimal[4]; //T2的小数部分 
        Timestamp T3;
        char T3_decimal[4]; //T3的小数部分 
    } NTP_MESSAGE;
    
    int main()
    {
        WORD socketVersion = MAKEWORD(2,2);
        WSADATA wsaData; 
        if(WSAStartup(socketVersion, &wsaData) != 0)
        {
            return 0;
        }
        SOCKET sclient = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
        
        SOCKADDR_IN sin;
        sin.sin_family = AF_INET;
        sin.sin_port = htons(123);
        sin.sin_addr.S_un.S_addr = inet_addr("198.123.30.132");
        int len = sizeof(sin);
        
        char sendData[] = { //构造报文
        0x1B, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xD0, 0xAF, 0x5F, 0xF5, 0x23, 0xD7, 0x08, 0x00
        };
        
        printf("Connect to NTP Server...\n");
        
        time_t T1=time(NULL);
        
        sendto(sclient, sendData, sizeof(sendData), 0, (SOCKADDR *)&sin, len);
    
        char recvData[48]={0};
        int ret = recvfrom(sclient, recvData, 48, 0, (SOCKADDR *)&sin, &len);
        if(ret > 0)
        {
            time_t T4=time(NULL);
            
            printf("Connect success!\n\n");
            printf("Now the local time is %s",ctime(&T4));
            
            NTP_MESSAGE *ntp_time=(NTP_MESSAGE *)recvData;
            
            /* 大小端变换 由于NTP以1900为始，需变换 */
            ntp_time->T2.time=ntohl(ntp_time->T2.time)-JAN_1970;//T2
            ntp_time->T3.time=ntohl(ntp_time->T3.time)-JAN_1970;//T3
            
            /* NTP报文的网络延时=（T4-T1）-（T3-T2） */
            time_t net_delay=(T4-T1)-(ntp_time->T3.time-ntp_time->T2.time);
            printf("Net delay is %ld second(s).\n",net_delay);
            
            /* 误差补偿秒数=（（T2-T1）+（T3-T4））/2 */
            time_t Deviation=(((time_t)ntp_time->T2.time-T1)+((time_t)ntp_time->T3.time-T4))/2;
            printf("\nThe deviation is %d second(s).\n",Deviation);
            
            if(Deviation != 0)
            {
                printf("Reset the local time...\n");
                
                time_t now=time(NULL)+Deviation;
                struct tm *ptr;
                ptr=localtime(&now);
                char buffer[20]={0};
                
                sprintf(buffer,"date %d-%d-%d",ptr->tm_year+1900,ptr->tm_mon+1,ptr->tm_mday);
                system(buffer);
                
                sprintf(buffer,"time %d:%d:%d",ptr->tm_hour,ptr->tm_min,ptr->tm_sec);
                system(buffer);
                now=time(NULL);
                printf("Now the local time is %s",ctime(&now));
            }
            else //没有误差，无需校时 
            {
                printf("Here is no need to set local time.\n");
            }
        }
    
        closesocket(sclient);
        WSACleanup();
        system("pause");
        return 0;
    }

由于使用API 设置时间在 win7 下需要特殊的权限，故采用系统命令 date 和 time 设置，算是  不是办法的办法。  
关于NTP协议，最开始给出的链接有具体的说明，在程序中，只需48个字节的必须内容即可，其它内容属可选项。  
  
时间的小数部分抛弃不用，对于一般校时而言足够了。  
  
下面给个截图

![SouthEast][]

[http_blog.163.com_yzc_5001_blog_static_2061963420121283050787]: http://blog.163.com/yzc_5001/blog/static/2061963420121283050787/
[http_tool.chinaz.com_Tools_unixtime.aspx]: http://tool.chinaz.com/Tools/unixtime.aspx#
[SouthEast]: /images/20220810/f4290ece896446b38f6a49608f39e0f5.png