c++ - 使用 sntp(windows c++) 从服务器获取时间/日期

Question

我正在用 c/c++ 搜索从服务器 (ntp.belnet.be) 获取时间和日期的工作代码。它使用 UDP 并使用端口 123。

有人可以帮忙吗？

//sending pakket
memset(&sntp_msg_header, 0, sizeof sntp_msg_header);
sntp_msg_header.flags = 27;
sntp_msg_header.originate_timestamp_secs = time(NULL);

// Get data in rxmsg
...
...

// print time
timeval = ntohl(rxmsg.transmit_timestamp_secs) - ((70ul * 365ul + 17ul) * 86400ul);
printf("%s", ctime(&timeval));

这就是我目前所拥有的。但我无法从中获取正确的数据。我希望这是更多信息。

如果找到这个:

import socket
import struct
import sys
import time

TIME1970 = 2208988800L      # Thanks to F.Lundh

client = socket.socket( socket.AF_INET, socket.SOCK_DGRAM )
data = '\x1b' + 47 * '\0'
client.sendto( data, ( sys.argv[1], 123 ))
data, address = client.recvfrom( 1024 )
if data:
    print 'Response received from:', address
    t = struct.unpack( '!12I', data )[10]
    t -= TIME1970
    print '\tTime=%s' % time.ctime(t)

但它是在 python 中。有人可以将其更改为 C++ 还是有转换器？？

Answer 1

这是我用的。它不是很优雅，但应该足以传达这个想法。基本思想是拥有一个与网络发送和接收内容相匹配的结构。颠倒的字节顺序最初并不明显。在这里值得一提的是，这对错误条件几乎没有任何用处。你会想要解决这个问题。 :)

#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));
    }
};

您可以像这样使用它，也许在 main() 中。

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();

获取 ip 和端口的方法有很多，但 getaddrinfo 在 Windows 上做得不错:

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);
}

自然地，这个解决方案就像搁浅的鲸鱼一样便携，但它 Works For Me™。