网络同步校时客户端代码(RFC868/C++/WIN32/SOCKET)

大量的工业机肯定需要同步校时, 故去察看了RFC868, 我就试编了一个获得网络时间的小程序, 大家可以借鉴到自己的同步校时程序, 只是试验,所以程序结构并不严谨, 过一段时间我会把服务器段的代码贴出,今天先发布客户端:

#pragma warning(disable: 4530)
#pragma warning(disable: 4786)

#include <iostream>
#include <ctime>
#include <cassert>
using namespace std;
#include <winsock2.h>
#include <windows.h>

static char * get_error_msg()
{
 static char msg_buf[1024];
 FormatMessage(
  FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
  NULL,
  GetLastError(),
  MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // Default language
  msg_buf,
  1023,
  NULL
  );
 return msg_buf;
}

void time_internet_to_local(void *recv_buf) //接到的数据转换为本地时间
{
 assert(recv_buf);
 char p[4], *precv = ((char *)recv_buf) + 3;
 for(int i=0; i<4; i++)
  p[i] = *precv--; //网络主机的数据进行转换
 *(long *)p -= 2208988800;//转换为本地时间 time_t

 SYSTEMTIME st;
 tm * ptm = gmtime((time_t *)p);
 st.wYear =  ptm->tm_year + 1900;
 st.wMonth = ptm->tm_mon + 1;
 st.wDay = ptm->tm_mday;
 st.wHour = ptm->tm_hour;
 st.wMinute = ptm->tm_min;
 st.wSecond = ptm->tm_sec;
 st.wMilliseconds = 0;
 SetSystemTime(&st);
}

void print_time(void *recv_buf)//打印接到的数据
{
 assert(recv_buf);
 char p[4], *precv = ((char *)recv_buf) + 3;
 for(int i=0; i<4; i++) //网络主机的数据进行转换
  p[i] = *precv--;
 *(long *)p -= 2208988800;
 char buf[20];
 strftime(buf, 20, "%Y-%m-%d %H:%M:%S", localtime((time_t *)p));
 cout << buf << endl;
}

void tcp(void *ip)//RFC868 PORT 37 TCP协议
{
 struct sockaddr_in server;
 server.sin_family = AF_INET;
 server.sin_port = htons(37);
 server.sin_addr.s_addr = inet_addr((char *)ip) ;

 SOCKET s = socket(AF_INET, SOCK_STREAM, 0);
 if(s == INVALID_SOCKET)
  cout << __LINE__<<"  socket error  : " << WSAGetLastError() << endl;

 int ret = connect(s, (struct sockaddr*)&server, sizeof(server));
 if(ret == SOCKET_ERROR)
  cout << __LINE__ << get_error_msg() << endl;
 else
 {
  char xx[4];
  ret = recv(s, xx, 4, 0);
  if(ret == SOCKET_ERROR) 
   cout << __LINE__ << get_error_msg() << endl;
  else
  {
   print_time(xx);
   //time_internet_to_local(xx);设定本地时间 最好加一个判断网络延时
  }

  if(shutdown(s, SD_RECEIVE) == SOCKET_ERROR)
   cout << __LINE__ << get_error_msg() << endl;
 }
 closesocket(s);
}

void udp(void *ip) //RFC868 PORT 37 UDP
{
 struct sockaddr_in server;
 server.sin_family = AF_INET;
 server.sin_port = htons(37);
 server.sin_addr.s_addr = inet_addr((char *)ip) ;
 
 SOCKET s = socket(AF_INET, SOCK_DGRAM, 0);
 if(s == INVALID_SOCKET)
 {
  cout << __LINE__ << get_error_msg() << endl;
 }

 int ret, c_len = sizeof(server);
 char r_buf[4];
 ret = sendto(s, r_buf, 0, 0, (struct sockaddr *)&server, sizeof(server));//发送空的数据报
 if(ret == SOCKET_ERROR)
  cout << __LINE__ << get_error_msg() << endl;

 FD_SET read_set;
 timeval tv = {3, 0}; //tv.tv_sec = 0, tv.tv_usec = 100000; 0.1s
 FD_ZERO(&read_set);
 FD_SET(s, &read_set);
 ret = select(0, &read_set, NULL, NULL, &tv);
 if(ret == SOCKET_ERROR)
 {
  cout << __LINE__ << get_error_msg() << endl;
 }
 else
  if(FD_ISSET(s, &read_set))
  {
   ret = recvfrom(s, r_buf, 4, 0, (struct sockaddr *)&server, &c_len);
   
   if(ret == SOCKET_ERROR)
    cout << __LINE__ << get_error_msg() << endl;
   else
   {
    print_time(r_buf);
   }
  }
 closesocket(s);
}

int main(int argc, char *argv[])
{
 WORD wVersionRequested;
 WSADATA wsaData;
 wVersionRequested = MAKEWORD(2, 2);
 WSAStartup(wVersionRequested, &wsaData);

 char *ipcn = "159.226.154.16";//国家授时中心
 char *iphk = "210.0.235.14";//香港天文台授时中心

 time_t now;
 char buf[20] = {0};

 now = time(NULL);
 strftime(buf, 20, "%Y-%m-%d %H:%M:%S", localtime(&now));
 cout << "TCP 连接国家授时中心 " << endl << "本地时间 " << buf << endl << "远程时间 ";
 tcp(ipcn);

 now = time(NULL);
 strftime(buf, 20, "%Y-%m-%d %H:%M:%S", localtime(&now));
 cout << "UDP 连接香港天文台授时中心 " << endl << "本地时间 " << buf << endl << "远程时间 ";
 udp(iphk);

 WSACleanup();
 return 0;
}

RFC 868   

Network Working Group                                    J. Postel - ISI
Request for Comments: 868                           K. Harrenstien - SRI
                                                                May 1983

                             Time Protocol

This RFC specifies a standard for the ARPA Internet community.  Hosts on
the ARPA Internet that choose to implement a Time Protocol are expected
to adopt and implement this standard.

This protocol provides a site-independent, machine readable date and
time.  The Time service sends back to the originating source the time in
seconds since midnight on January first 1900.

One motivation arises from the fact that not all systems have a
date/time clock, and all are subject to occasional human or machine
error.  The use of time-servers makes it possible to quickly confirm or
correct a system's idea of the time, by making a brief poll of several
independent sites on the network.

This protocol may be used either above the Transmission Control Protocol
(TCP) or above the User Datagram Protocol (UDP).

When used via TCP the time service works as follows:

   S: Listen on port 37 (45 octal).

   U: Connect to port 37.

   S: Send the time as a 32 bit binary number.

   U: Receive the time.

   U: Close the connection.

   S: Close the connection.

   The server listens for a connection on port 37.  When the connection
   is established, the server returns a 32-bit time value and closes the
   connection.  If the server is unable to determine the time at its
   site, it should either refuse the connection or close it without
   sending anything.

RFC 868                                                         May 1983
Time Protocol                                                          

When used via UDP the time service works as follows:

   S: Listen on port 37 (45 octal).

   U: Send an empty datagram to port 37.

   S: Receive the empty datagram.

   S: Send a datagram containing the time as a 32 bit binary number.

   U: Receive the time datagram.

   The server listens for a datagram on port 37.  When a datagram
   arrives, the server returns a datagram containing the 32-bit time
   value.  If the server is unable to determine the time at its site, it
   should discard the arriving datagram and make no reply.

The Time

The time is the number of seconds since 00:00 (midnight) 1 January 1900
GMT, such that the time 1 is 12:00:01 am on 1 January 1900 GMT; this
base will serve until the year 2036.

For example:

   the time  2,208,988,800 corresponds to 00:00  1 Jan 1970 GMT,

             2,398,291,200 corresponds to 00:00  1 Jan 1976 GMT,

             2,524,521,600 corresponds to 00:00  1 Jan 1980 GMT,

             2,629,584,000 corresponds to 00:00  1 May 1983 GMT,

        and -1,297,728,000 corresponds to 00:00 17 Nov 1858 GMT.