ntp — получает время / дату с сервера с помощью sntp (windows c ++)

Это то, что я использую. Это не очень элегантно, но этого должно быть достаточно, чтобы донести идею. Основная идея состоит в том, чтобы иметь структуру, которая соответствует тому, что сеть отправляет и получает. Обратный порядок байтов был изначально неочевиден. Здесь стоит упомянуть, что это в значительной степени не помогает при возникновении ошибок. Вы бы хотели это исправить. 🙂

#define ReverseEndianInt(x) ((x) = \
((x)&0xff000000) >> 24 |\
((x)&0x00ff0000) >> 8 |\
((x)&0x0000ff00) << 8 |\
((x)&0x000000ff) << 24)

/**
* NTP Fixed-Point Timestamp Format.
* From [RFC 5905](http://tools.ietf.org/html/rfc5905).
*/
struct Timestamp
{
unsigned int seconds; /**< Seconds since Jan 1, 1900. */
unsigned int fraction; /**< Fractional part of seconds. Integer number of 2^-32 seconds. */

/**
* Reverses the Endianness of the timestamp.
* Network byte order is big endian, so it needs to be switched before
* sending or reading.
*/
void ReverseEndian() {
ReverseEndianInt(seconds);
ReverseEndianInt(fraction);
}

/**
* Convert to time_t.
* Returns the integer part of the timestamp in unix time_t format,
* which is seconds since Jan 1, 1970.
*/
time_t to_time_t()
{
return (seconds - ((70 * 365 + 17) * 86400))&0x7fffffff;
}
};

/**
* A Network Time Protocol Message.
* From [RFC 5905](http://tools.ietf.org/html/rfc5905).
*/
struct NTPMessage
{
unsigned int mode :3; /**< Mode of the message sender. 3 = Client, 4 = Server */
unsigned int version :2; /**< Protocol version. Should be set to 3. */
unsigned int leap :2; /**< Leap seconds warning. See the [RFC](http://tools.ietf.org/html/rfc5905#section-7.3) */
unsigned char stratum; /**< Servers between client and physical timekeeper. 1 = Server is Connected to Physical Source. 0 = Unknown. */
unsigned char poll; /**< Max Poll Rate. In log2 seconds. */
unsigned char precision; /**< Precision of the clock. In log2 seconds. */
unsigned int sync_distance; /**< Round-trip to reference clock. NTP Short Format. */
unsigned int drift_rate; /**< Dispersion to reference clock. NTP Short Format. */
unsigned char ref_clock_id[4]; /**< Reference ID. For Stratum 1 devices, a 4-byte string. For other devices, 4-byte IP address. */
Timestamp ref; /**< Reference Timestamp. The time when the system clock was last updated. */
Timestamp orig; /**< Origin Timestamp. Send time of the request. Copied from the request. */
Timestamp rx; /**< Recieve Timestamp. Reciept time of the request. */
Timestamp tx; /**< Transmit Timestamp. Send time of the response. If only a single time is needed, use this one. *//**
* Reverses the Endianness of all the timestamps.
* Network byte order is big endian, so they need to be switched before
* sending and after reading.
*
* Maintaining them in little endian makes them easier to work with
* locally, though.
*/
void ReverseEndian() {
ref.ReverseEndian();
orig.ReverseEndian();
rx.ReverseEndian();
tx.ReverseEndian();
}

/**
* Recieve an NTPMessage.
* Overwrites this object with values from the recieved packet.
*/
int recv(int sock)
{
int ret = ::recv(sock, (char*)this, sizeof(*this), 0);
ReverseEndian();
return ret;
}

/**
* Send an NTPMessage.
*/
int sendto(int sock, struct sockaddr_in* srv_addr)
{
ReverseEndian();
int ret = ::sendto(sock, (const char*)this, sizeof(*this), 0, (sockaddr*)srv_addr, sizeof(*srv_addr));
ReverseEndian();
return ret;
}

/**
* Zero all the values.
*/
void clear()
{
memset(this, 0, sizeof(*this));
}
};

Вы бы использовали это так, возможно, в main(),

WSADATA wsaData;
DWORD ret = WSAStartup(MAKEWORD(2,0), &wsaData);

char *host = "pool.ntp.org"; /* Don't distribute stuff pointing here, it's not polite. */
//char *host = "time.nist.gov"; /* This one's probably ok, but can get grumpy about request rates during debugging. */

NTPMessage msg;
/* Important, if you don't set the version/mode, the server will ignore you. */
msg.clear();
msg.version = 3;
msg.mode = 3 /* client */;

NTPMessage response;
response.clear();

int sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
sockaddr_in srv_addr;
memset(&srv_addr, 0, sizeof(srv_addr));
dns_lookup(host, &srv_addr); /* Helper function defined below. */

msg.sendto(sock, &srv_addr);
response.recv(sock);

time_t t = response.tx.to_time_t();
char *s = ctime(&t);
printf("The time is %s.", s);

WSACleanup();

Есть много способов получить ip и порт, но getaddrinfo отлично работает на Windows:

int dns_lookup(const char *host, sockaddr_in *out)
{
struct addrinfo *result;
int ret = getaddrinfo(host, "ntp", NULL, &result);
for (struct addrinfo *p = result; p; p = p->ai_next)
{
if (p->ai_family != AF_INET)
continue;

memcpy(out, p->ai_addr, sizeof(*out));
}
freeaddrinfo(result);
}

Естественно, это решение примерно такое же портативное, как и китовый берег, но оно работает для меня ™.