使用C++编写模拟ntp校时服务器

#include "stdafx.h"

#include <Winsock2.h>

#pragma comment(lib, "Ws2_32.lib")

#include <time.h> /* for time() and ctime() */

#define UTC_NTP 2208988800U /* 1970 - 1900 */

int gettimeofday(struct timeval *tp, void *tzp)

{

time_t clock;

struct tm tm;

SYSTEMTIME wtm;

GetLocalTime(&wtm);

tm.tm_year   = wtm.wYear - 1900;

tm.tm_mon   = wtm.wMonth - 1;

tm.tm_mday   = wtm.wDay;

tm.tm_hour   = wtm.wHour;

tm.tm_min   = wtm.wMinute;

tm.tm_sec   = wtm.wSecond;

tm. tm_isdst  = -1;

clock = mktime(&tm);

tp->tv_sec = clock;

tp->tv_usec = wtm.wMilliseconds * 1000;

return (0);

}

/* get Timestamp for NTP in LOCAL ENDIAN */

void gettime64(unsigned int ts[])

{

struct timeval tv;

gettimeofday(&tv, NULL);

ts[0] = tv.tv_sec + UTC_NTP;

ts[1] = (4294*(tv.tv_usec)) + ((1981*(tv.tv_usec))>>11);

}

int die(const char *msg)

{

if (msg)

{

fputs(msg, stderr);

}

exit(-1);

}

void log_request_arrive(unsigned int *ntp_time)

{

time_t t; 

if (ntp_time) {

t = *ntp_time - UTC_NTP;

} else {

t = time(NULL);

}

printf("A request comes at: %s", ctime(&t));

}

void log_ntp_event(char *msg)

{

puts(msg);

}

int ntp_reply(int socket_fd, struct sockaddr *saddr_p, unsigned int saddrlen, unsigned char recv_buf[], unsigned int recv_time[])

{

/* Assume that recv_time is in local endian ! */

unsigned char send_buf[48];

unsigned int *u32p;

  /* do not use 0xC7 because the LI can be `unsynchronized` */

if ((recv_buf[0] & 0x07/*0xC7*/) != 0x3)

{

/* LI VN Mode stimmt nicht */

log_ntp_event("Invalid request: found error at the first byte");

return 1;

}

/* füllt LI VN Mode aus

    LI   = 0

VN   = Version Nummer aus dem Client

Mode = 4

*/

send_buf[0] = (recv_buf[0] & 0x38) + 4;

/* Stratum = 1 (primary reference)

   Reference ID = 'LOCL"

       (falscher) Bezug auf der lokalen Uhr.

*/

/* Stratum */

send_buf[1] = 0x01;

/* Reference ID = "LOCL" */

*(unsigned int*)&send_buf[12] = htonl(0x4C4F434C);

/* Copy Poll */

send_buf[2] = recv_buf[2];

/* Precision in Microsecond ( from API gettimeofday() ) */

send_buf[3] = (signed char)(-6);  /* 2^(-6) sec */

/* danach sind alle Werte DWORD aligned  */

u32p = (unsigned int *)&send_buf[4];

/* zur Vereinfachung , Root Delay = 0, Root Dispersion = 0 */

*u32p++ = 0;

*u32p++ = 0;

/* Reference ID ist vorher eingetragen */

u32p++;

/* falscher Reference TimeStamp,

* wird immer vor eine minute synchronisiert,

* damit die Überprüfung in Client zu belügen */

gettime64(u32p);

*u32p = htonl(*u32p - 60);   /* -1 Min.*/

u32p++;

*u32p = htonl(*u32p);   /* -1 Min.*/

u32p++;

/* Originate Time = Transmit Time @ Client */

*u32p++ = *(unsigned int *)&recv_buf[40];

*u32p++ = *(unsigned int *)&recv_buf[44];

/* Receive Time @ Server */

*u32p++ = htonl(recv_time[0]);

*u32p++ = htonl(recv_time[1]);

/* zum Schluss: Transmit Time*/

gettime64(u32p);

*u32p = htonl(*u32p);   /* -1 Min.*/

u32p++;

*u32p = htonl(*u32p);   /* -1 Min.*/

if (sendto(socket_fd, (const char*)send_buf, sizeof(send_buf), 0, saddr_p, saddrlen) < 48)

{

perror("sendto error");

return 1;

}

return 0;

}

void request_process_loop(int fd)

{

struct sockaddr src_addr;

int src_addrlen = sizeof(src_addr);

unsigned char buf[48];

unsigned int recv_time[2];

while (1)

{

DWORD kk = 0;

int klen = 0;

do

{

klen = recvfrom(fd, (char*)buf, 48, 0, &src_addr, &src_addrlen);

DWORD kk = GetLastError();

}while (klen < 48 );  /* invalid request */

gettime64(recv_time);

/* recv_time in local endian */

log_request_arrive(recv_time);

ntp_reply(fd, &src_addr , src_addrlen, buf, recv_time);

}

}

void ntp_server()

{

struct sockaddr_in sinaddr;

int s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);

if (s == -1)

{

perror("Can not create socket.");

die(NULL);

}

memset(&sinaddr, 0, sizeof(sinaddr));

sinaddr.sin_family = AF_INET;

sinaddr.sin_port = htons(123);

sinaddr.sin_addr.s_addr = INADDR_ANY;

if (0 != bind(s, (struct sockaddr *)&sinaddr, sizeof(sinaddr)))

{

perror("Bind error");

die(NULL);

}

log_ntp_event( "\n========================================\n"

"= Server started, waiting for requests =\n"

"========================================\n");

request_process_loop(s);

closesocket(s);

}

int main(int argc, char *argv[], char **env)

{

WSADATA wsaData;

WORD wVersionRequested = MAKEWORD(2, 2);

int err = WSAStartup(wVersionRequested, &wsaData);

if (err != 0)

return -1;

ntp_server();

return 0;

}