/*      $OpenBSD: asctime.c,v 1.24 2019/07/03 03:24:04 deraadt Exp $ */
/*
** This file is in the public domain, so clarified as of
** 1996-06-05 by Arthur David Olson.
*/

/*
** Avoid the temptation to punt entirely to strftime;
** the output of strftime is supposed to be locale specific
** whereas the output of asctime is supposed to be constant.
*/

#include <errno.h>
#include <stdio.h>
#include <string.h>
#include "private.h"
#include "tzfile.h"
#include "thread_private.h"

/*
** Some systems only handle "%.2d"; others only handle "%02d";
** "%02.2d" makes (most) everybody happy.
** At least some versions of gcc warn about the %02.2d;
** we conditionalize below to avoid the warning.
*/
/*
** All years associated with 32-bit time_t values are exactly four digits long;
** some years associated with 64-bit time_t values are not.
** Vintage programs are coded for years that are always four digits long
** and may assume that the newline always lands in the same place.
** For years that are less than four digits, we pad the output with
** leading zeroes to get the newline in the traditional place.
** The -4 ensures that we get four characters of output even if
** we call a strftime variant that produces fewer characters for some years.
** The ISO C 1999 and POSIX 1003.1-2004 standards prohibit padding the year,
** but many implementations pad anyway; most likely the standards are buggy.
*/
#define ASCTIME_FMT     "%.3s %.3s%3d %2.2d:%2.2d:%2.2d %-4s\n"

/*
** For years that are more than four digits we put extra spaces before the year
** so that code trying to overwrite the newline won't end up overwriting
** a digit within a year and truncating the year (operating on the assumption
** that no output is better than wrong output).
*/
#define ASCTIME_FMT_B   "%.3s %.3s%3d %2.2d:%2.2d:%2.2d     %s\n"

#define STD_ASCTIME_BUF_SIZE    26
/*
** Big enough for something such as
** ??? ???-2147483648 -2147483648:-2147483648:-2147483648     -2147483648\n
** (two three-character abbreviations, five strings denoting integers,
** seven explicit spaces, two explicit colons, a newline,
** and a trailing ASCII nul).
** The values above are for systems where an int is 32 bits and are provided
** as an example; the define below calculates the maximum for the system at
** hand.
*/
#define MAX_ASCTIME_BUF_SIZE    (2*3+5*INT_STRLEN_MAXIMUM(int)+7+2+1+1)

static char *
asctime3(const struct tm *timeptr, char *buf, int bufsize)
{
        static const char       wday_name[][4] = {
                "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
        };
        static const char       mon_name[][4] = {
                "Jan", "Feb", "Mar", "Apr", "May", "Jun",
                "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
        };
        const char *    wn;
        const char *    mn;
        char            year[INT_STRLEN_MAXIMUM(int) + 2];
        int             len;

        if (timeptr == NULL) {
                errno = EINVAL;
                strlcpy(buf, "??? ??? ?? ??:??:?? ????\n", bufsize);
                return buf;
        }
        if (timeptr->tm_wday < 0 || timeptr->tm_wday >= DAYSPERWEEK)
                wn = "???";
        else
                wn = wday_name[timeptr->tm_wday];
        if (timeptr->tm_mon < 0 || timeptr->tm_mon >= MONSPERYEAR)
                mn = "???";
        else
                mn = mon_name[timeptr->tm_mon];
        /*
        ** Use strftime's %Y to generate the year, to avoid overflow problems
        ** when computing timeptr->tm_year + TM_YEAR_BASE.
        ** Assume that strftime is unaffected by other out-of-range members
        ** (e.g., timeptr->tm_mday) when processing "%Y".
        */
        (void) strftime(year, sizeof year, "%Y", timeptr);
        len = snprintf(buf, bufsize,
            ((strlen(year) <= 4) ? ASCTIME_FMT : ASCTIME_FMT_B),
            wn, mn,
            timeptr->tm_mday, timeptr->tm_hour,
            timeptr->tm_min, timeptr->tm_sec,
            year);
        if (len >= 0 && len < bufsize) {
                return buf;
        } else {
                errno = EOVERFLOW;
                return NULL;
        }
}

/*
** A la ISO/IEC 9945-1, ANSI/IEEE Std 1003.1, 2004 Edition.
*/

char *
asctime_r(const struct tm *timeptr, char *buf)
{
        /*
        ** P1003 8.3.5.2 says that asctime_r() can only assume at most
        ** a 26 byte buffer.
        */
        return asctime3(timeptr, buf, STD_ASCTIME_BUF_SIZE);
}
DEF_WEAK(asctime_r);

/*
** A la ISO/IEC 9945-1, ANSI/IEEE Std 1003.1, 2004 Edition.
*/

char *
asctime(const struct tm *timeptr)
{
        static char result[MAX_ASCTIME_BUF_SIZE];
        _THREAD_PRIVATE_KEY(asctime);
        char *resultp = (char *)_THREAD_PRIVATE(asctime, result, NULL);

        if (resultp == NULL)
                return NULL;
        else
                return asctime3(timeptr, resultp, sizeof(result));
}
DEF_STRONG(asctime);