/*      $OpenBSD: ntpleaps.c,v 1.14 2015/12/12 20:04:23 mmcc Exp $      */

/*
 * Copyright (c) 2002 Thorsten Glaser. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *    - Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *    - Redistributions in binary form must reproduce the above
 *      copyright notice, this list of conditions and the following
 *      disclaimer in the documentation and/or other materials provided
 *      with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 */

/* Leap second support for NTP clients (generic) */

/*
 * I could include tzfile.h, but this would make the code unportable
 * at no real benefit. Read tzfile.h for why.
 */

#include <sys/types.h>
#include <netinet/in.h>

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "ntpleaps.h"

static u_int64_t *leapsecs;
static unsigned int leapsecs_num;

u_int32_t       read_be_dword(u_int8_t *ptr);


int
ntpleaps_init(void)
{
        static int doneinit;
        static int donewarn;

        if (doneinit)
                return (0);

        if (ntpleaps_read() == 0) {
                doneinit = 1;
                return (0);
        }

        /* This does not really hurt, but users will complain about
         * off-by-22-seconds (at time of coding) errors if we don't warn.
         */
        if (!donewarn) {
                fputs("Warning: error reading tzfile. You will NOT be\n"
                    "able to get legal time or posix compliance!\n", stderr);
                donewarn = 1;   /* put it only once */
        }

        return (-1);
}

int
ntpleaps_sub(u_int64_t *t)
{
        unsigned int i = 0;
        u_int64_t u;
        int r = 1;

        if (ntpleaps_init() == -1)
                return (-1);

        u = *t;

        while (i < leapsecs_num) {
                if (u < leapsecs[i]) {
                        r--;
                        break;
                }
                if (u == leapsecs[i++])
                        break;
        }

        *t = u - i;
        return (r);
}

u_int32_t
read_be_dword(u_int8_t *ptr)
{
        u_int32_t res;

        memcpy(&res, ptr, 4);
        return (ntohl(res));
}


int
ntpleaps_read(void)
{
        int fd;
        unsigned int r;
        u_int8_t buf[32];
        u_int32_t m1, m2, m3;
        u_int64_t s;
        u_int64_t *l;

        fd = open("/usr/share/zoneinfo/right/UTC", O_RDONLY | O_NDELAY);
        if (fd == -1)
                return (-1);

        /* Check signature */
        read(fd, buf, 4);
        buf[4] = 0;
        if (strcmp((const char *)buf, "TZif")) {
                close(fd);
                return (-1);
        }

        /* Pre-initialize buf[24..27] so we need not check read(2) result */
        buf[24] = 0;
        buf[25] = 0;
        buf[26] = 0;
        buf[27] = 0;

        /* Skip uninteresting parts of header */
        read(fd, buf, 28);

        /* Read number of leap second entries */
        r = read_be_dword(&buf[24]);
        /* Check for plausibility - arbitrary values */
        if ((r < 20) || (r > 60000)) {
                close(fd);
                return (-1);
        }
        if ((l = reallocarray(NULL, r, sizeof(u_int64_t))) == NULL) {
                close(fd);
                return (-1);
        }

        /* Skip further uninteresting stuff */
        read(fd, buf, 12);
        m1 = read_be_dword(buf);
        m2 = read_be_dword(&buf[4]);
        m3 = read_be_dword(&buf[8]);
        m3 += (m1 << 2)+m1+(m2 << 2)+(m2 << 1);
        lseek(fd, (off_t)m3, SEEK_CUR);

        /* Now go parse the tzfile leap second info */
        for (m1 = 0; m1 < r; m1++) {
                if (read(fd, buf, 8) != 8) {
                        free(l);
                        close(fd);
                        return (-1);
                }
                s = SEC_TO_TAI64(read_be_dword(buf));
                /*
                 * Assume just _one_ leap second on each entry, and compensate
                 * the lacking error checking by validating the first entry
                 * against the known value
                 */
                if (!m1 && s != 0x4000000004B2580AULL) {
                        free(l);
                        close(fd);
                        return (-1);
                }
                l[m1] = s;
        }

        /* Clean up and activate the table */
        close(fd);
        free(leapsecs);
        leapsecs = l;
        leapsecs_num = r;
        return (0);
}