152 lines
3.6 KiB
C
152 lines
3.6 KiB
C
#include <getopt.h>
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#include <netdb.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <time.h>
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#include <unistd.h>
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#include <netinet/in.h>
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#include <sys/types.h>
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#include <sys/socket.h>
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#define EPOCH 2208988800ull
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// assumes either little or big endian. pdp-endian, youre out of luck
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#define NLITTLE 0x41424344UL
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#define NENDIAN ('ABCD')
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typedef struct {
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#if NENDIAN == NLITTLE
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unsigned int mode: 3;
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unsigned int vn: 3;
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unsigned int li: 2;
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#else
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unsigned int li: 2;
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unsigned int vn: 3;
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unsigned int mode: 3;
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#endif
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uint8_t stratum;
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uint8_t poll;
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uint8_t prec;
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uint32_t delay;
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uint32_t dispersion;
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uint32_t refid;
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uint32_t rtms;
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uint32_t rtmf;
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uint32_t otms;
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uint32_t otmf;
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uint32_t rctms;
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uint32_t rctmf;
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uint32_t ttms;
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uint32_t ttmf;
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} ntp;
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typedef struct {
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const char* host;
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int port;
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const char* format;
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} ntp_info;
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ntp_info NDEFAULT = {.host="europe.pool.ntp.org", .port = 123, .format = NULL};
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char* nstrftime(const char* fmt, const struct tm* t) {
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int size = 40;
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char* res = malloc(size);
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int n;
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do {
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n = strftime(res, size-1, fmt, t);
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size *= 2;
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} while (!n);
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return res;
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}
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void err(const char* msg) {
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fprintf(stderr, "Error %s.\n", msg);
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exit(1);
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}
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void usage(const char* program, int code) {
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fprintf(stderr, "Usage: %s [options]\n", program);
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fputs("Options:\n", stderr);
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fputs(" -h HOST, --host=HOST NTP server to use\n", stderr);
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fputs(" defaults to 'europe.pool.ntp.org'\n", stderr);
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fputs(" -p PORT, --port=PORT NTP server port to use (must be numerical)\n", stderr);
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fputs(" defaults to '123'\n", stderr);
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fputs(" -f FORMAT, --format=FORMAT Date format string (passed to strftime)\n", stderr);
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fputs(" defaults to standard of ctime\n", stderr);
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fputs(" --help Display this message and exit\n", stderr);
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exit(code);
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}
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ntp_info args(int argc, char** argv) {
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char c;
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ntp_info res = NDEFAULT;
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static struct option long_options[] = {
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{"host", required_argument, 0, 'h'},
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{"port", required_argument, 0, 'p'},
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{"format", required_argument, 0, 'f'},
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{"help", no_argument, 0, 'u'},
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{NULL, 0, NULL, 0}
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};
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while ((c = getopt_long(argc, argv, "t:a:f:", long_options, 0)) != -1) {
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switch (c) {
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case 'h': res.host = optarg; break;
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case 'f': res.format = optarg; break;
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case 'p': {
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char* end;
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res.port = strtol(optarg, &end, 10);
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if (end[0] != 0) {
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fputs("Port is not numerical.\n", stderr);
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usage(argv[0], 1);
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}
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break;
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}
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case 'u': usage(argv[0], 0);
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default: usage(argv[0], 1);
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}
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}
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return res;
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}
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int main(int argc, char** argv) {
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int sock;
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ntp n;
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struct sockaddr_in a;
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struct hostent* s;
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ntp_info i = args(argc, argv);
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memset(&n, 0, sizeof(ntp));
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n.vn = 3;
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n.mode = 3;
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sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
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if (sock < 0) err("opening socket");
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s = gethostbyname(i.host);
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if (!s) err("resolving host");
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bzero(&a, sizeof(a));
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a.sin_family = AF_INET;
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a.sin_port = htons(i.port);
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bcopy(s->h_addr, &a.sin_addr.s_addr, s->h_length);
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if (connect(sock, (struct sockaddr *) &a, sizeof(a)) < 0) err("connecting");
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if (write(sock, &n, sizeof(ntp)) < 0) err("writing to network");
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if (read(sock, &n, sizeof(ntp)) < 0) err("reading from network");
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n.ttms = ntohl(n.ttms);
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time_t tm = n.ttms - EPOCH;
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if (!i.format) {
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fputs(ctime(&tm), stdout);
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} else {
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char* fmt = nstrftime(i.format, localtime(&tm));
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puts(fmt);
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free(fmt);
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}
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return 0;
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}
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