/* gettime.c - Wrapper for time functions

 * Copyright (C) 1998, 2002, 2007, 2011 Free Software Foundation, Inc.

 *

 * This file is part of GnuPG.

 *

 * This file is free software; you can redistribute it and/or modify

 * it under the terms of either

 *

 *   - the GNU Lesser General Public License as published by the Free

 *     Software Foundation; either version 3 of the License, or (at

 *     your option) any later version.

 *

 * or

 *

 *   - the GNU General Public License as published by the Free

 *     Software Foundation; either version 2 of the License, or (at

 *     your option) any later version.

 *

 * or both in parallel, as here.

 *

 * This file is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, see <https://www.gnu.org/licenses/>.

 */

#include <config.h>

#include <stdlib.h>

#include <time.h>

#include <ctype.h>

#ifdef HAVE_LOCALE_H

#include <locale.h>

#endif

#ifdef HAVE_LANGINFO_H

#include <langinfo.h>

#endif

#ifdef HAVE_W32_SYSTEM

# define WIN32_LEAN_AND_MEAN

# include <windows.h>

#endif /*!HAVE_W32_SYSTEM*/

#include <stdint.h>    /* We use uint64_t.  */

#include "util.h"

#include "i18n.h"

#include "gettime.h"

#ifdef HAVE_W32_SYSTEM

#include <windows.h>

#endif

#ifdef HAVE_UNSIGNED_TIME_T

# define IS_INVALID_TIME_T(a) ((a) == (time_t)(-1))

#else

  /* Error or 32 bit time_t and value after 2038-01-19.  */

# define IS_INVALID_TIME_T(a) ((a) < 0)

#endif

static unsigned long timewarp;

static enum { NORMAL = 0, FROZEN, FUTURE, PAST } timemode;

/* Correction used to map to real Julian days. */

#define JD_DIFF 1721060L

/*

  timegm() is a GNU function that might not be available everywhere.

  It's basically the inverse of gmtime() - you give it a struct tm,

  and get back a time_t.  It differs from mktime() in that it handles

  the case where the struct tm is UTC and the local environment isn't.

  Note, that this replacement implementation might not be thread-safe!

  Some BSDs don't handle the putenv("foo") case properly, so we use

  unsetenv if the platform has it to remove environment variables.

*/

#ifndef HAVE_TIMEGM

time_t

timegm (struct tm *tm)

{

#ifdef HAVE_W32_SYSTEM

  uint64_t val = timegm_u64 (tm);

  if (val == (uint64_t)(-1))

    return (time_t)(-1);

  return (time_t)val;

#else /* (Non thread safe implementation!) */

  time_t answer;

  char *zone;

  zone=getenv("TZ");

  putenv("TZ=UTC");

  tzset();

  answer=mktime(tm);

  if(zone)

    {

      static char *old_zone;

      if (!old_zone)

        {

          old_zone = malloc(3+strlen(zone)+1);

          if (old_zone)

            {

              strcpy(old_zone,"TZ=");

              strcat(old_zone,zone);

            }

  }

      if (old_zone)

        putenv (old_zone);

    }

  else

    gnupg_unsetenv("TZ");

  tzset();

  return answer;

#endif

}

#endif /*!HAVE_TIMEGM*/

/* Version of the GNU timegm which returns an unsigned 64 bit integer

 * instead of the usually signed time_t.  On error (uint64_t)(-1) is

 * returned.  This function is mostly here because on 32 bit Windows

 * we have an internal API to get the system time even after

 * 2023-01-19.  For 32 bit Unix we need to suffer from the too short

 * time_t and no system function to construct the time from a tm.  */

uint64_t

timegm_u64 (struct tm *tm)

{

#ifdef HAVE_W32_SYSTEM

  /* This one is thread safe.  */

  SYSTEMTIME st;

  FILETIME ft;

  unsigned long long cnsecs;

  st.wYear   = tm->tm_year + 1900;

  st.wMonth  = tm->tm_mon  + 1;

  st.wDay    = tm->tm_mday;

  st.wHour   = tm->tm_hour;

  st.wMinute = tm->tm_min;

  st.wSecond = tm->tm_sec;

  st.wMilliseconds = 0; /* Not available.  */

  st.wDayOfWeek = 0;    /* Ignored.  */

  /* System time is UTC thus the conversion is pretty easy.  */

  if (!SystemTimeToFileTime (&st, &ft))

    {

      gpg_err_set_errno (EINVAL);

      return (uint64_t)(-1);

    }

  cnsecs = (((unsigned long long)ft.dwHighDateTime << 32)

            | ft.dwLowDateTime);

  cnsecs -= 116444736000000000ULL; /* The filetime epoch is 1601-01-01.  */

  return (uint64_t)(cnsecs / 10000000ULL);

#else /*Unix*/

  time_t t = timegm (tm);

  if (t == (time_t)(-1))

    return (uint64_t)(-1);

  if ((int64_t)t < 0)

    return (uint64_t)(-1);

  return (uint64_t)t;

#endif /*Unix*/

}

/* Wrapper for the time(3).  We use this here so we can fake the time

   for tests */

time_t

gnupg_get_time (void)

{

  time_t current = time (NULL);

  if (current == (time_t)(-1))

    log_fatal ("time() failed\n");

  if (timemode == NORMAL)

    return current;

  else if (timemode == FROZEN)

    return timewarp;

  else if (timemode == FUTURE)

    return current + timewarp;

  else

    return current - timewarp;

}

/* Wrapper around gmtime_r.

   On systems without gmtime_r this implementation works within gnupg

   because we use only one thread a time.  FIXME: An independent

   library may use gmtime in one of its own thread (or via

   npth_enter/npth_leave) - in this case we run into a problem.  The

   solution would be to use a mutex here.  */

struct tm *

gnupg_gmtime (const time_t *timep, struct tm *result)

{

#ifdef HAVE_GMTIME_R

  return gmtime_r (timep, result);

#else

  struct tm *tp;

  tp = gmtime (timep);

  if (tp)

    memcpy (result, tp, sizeof *result);

  return tp;

#endif

}

/* Return the current time (possibly faked) in ISO format. */

void

gnupg_get_isotime (gnupg_isotime_t timebuf)

{

  time_t atime = gnupg_get_time ();

  struct tm *tp;

  struct tm tmbuf;

  tp = gnupg_gmtime (&atime, &tmbuf);

  if (!tp)

    *timebuf = 0;

  else

    snprintf (timebuf, 16, "%04d%02d%02dT%02d%02d%02d",

              1900 + tp->tm_year, tp->tm_mon+1, tp->tm_mday,

              tp->tm_hour, tp->tm_min, tp->tm_sec);

}

/* Set the time to NEWTIME so that gnupg_get_time returns a time

   starting with this one.  With FREEZE set to 1 the returned time

   will never change.  Just for completeness, a value of (time_t)-1

   for NEWTIME gets you back to reality.  Note that this is obviously

   not thread-safe but this is not required. */

void

gnupg_set_time (time_t newtime, int freeze)

{

  time_t current = time (NULL);

  if ( newtime == (time_t)-1 || current == newtime)

    {

      timemode = NORMAL;

      timewarp = 0;

    }

  else if (freeze)

    {

      timemode = FROZEN;

      timewarp = newtime == (time_t)-1 ? current : newtime;

    }

  else if (newtime > current)

    {

      timemode = FUTURE;

      timewarp = newtime - current;

    }

  else

    {

      timemode = PAST;

      timewarp = current - newtime;

    }

}

/* Returns true when we are in timewarp mode */

int

gnupg_faked_time_p (void)

{

  return timemode;

}

/* This function is used by gpg because OpenPGP defines the timestamp

   as an unsigned 32 bit value. */

u32

make_timestamp (void)

{

  time_t t = gnupg_get_time ();

  return (u32)t;

}

/* Specialized version of atoi which returns an u32 instead of an int

 * and caps the result at 2^32-2.  Leading white space is skipped,

 * scanning stops at at the first non-convertable byte.  Note that we

 * do not cap at 2^32-1 because that value is often used as error

 * return. */

u32

scan_secondsstr (const char *string)

{

  uint64_t value = 0;

  while (*string == ' ' || *string == '\t')

    string++;

  for (; *string >= '0' && *string <= '9'; string++)

    {

      value *= 10;

      value += atoi_1 (string);

      if (value >= (u32)(-1))

        return (u32)(-1) - 1;

    }

  return (u32)value;

}

/****************

 * Scan a date string and return a timestamp.

 * The only supported format is "yyyy-mm-dd"

 * Returns 0 for an invalid date.

 */

u32

scan_isodatestr( const char *string )

{

    int year, month, day;

    struct tm tmbuf;

    time_t stamp;

    int i;

    if( strlen(string) != 10 || string[4] != '-' || string[7] != '-' )

  return 0;

    for( i=0; i < 4; i++ )

  if( !digitp (string+i) )

      return 0;

    if( !digitp (string+5) || !digitp(string+6) )

  return 0;

    if( !digitp(string+8) || !digitp(string+9) )

  return 0;

    year = atoi(string);

    month = atoi(string+5);

    day = atoi(string+8);

    /* some basic checks */

    if( year < 1970 || month < 1 || month > 12 || day < 1 || day > 31 )

  return 0;

    memset( &tmbuf, 0, sizeof tmbuf );

    tmbuf.tm_mday = day;

    tmbuf.tm_mon = month-1;

    tmbuf.tm_year = year - 1900;

    tmbuf.tm_isdst = -1;

    stamp = mktime( &tmbuf );

    if( stamp == (time_t)-1 )

      {

        /* mktime did not work.  Construct an ISO timestring for noon

         * of the given day instead.  We keep the use of mktime for 64

         * bit system to limit the risk of regressions. */

        gnupg_isotime_t isobuf;

        uint64_t tmp64;

        snprintf (isobuf, 16, "%04d%02d%02dT120000", year, month, day);

        tmp64 = isotime2epoch_u64 (isobuf);

        if (tmp64 == (uint64_t)(-1))

          return 0;  /* Error.  */

        if (tmp64 >= (u32)(-1))

          return 0;   /* Error.  */

        return (u32)tmp64;

      }

    return stamp;

}

int

isotime_p (const char *string)

{

  const char *s;

  int i;

  if (!*string)

    return 0;

  for (s=string, i=0; i < 8; i++, s++)

    if (!digitp (s))

      return 0;

  if (*s != 'T')

      return 0;

  for (s++, i=9; i < 15; i++, s++)

    if (!digitp (s))

      return 0;

  if (*s == 'Z')

    s++;

  if ( !(!*s || (isascii (*s) && isspace(*s)) || *s == ':' || *s == ','))

    return 0;  /* Wrong delimiter.  */

  return 1;

}

/* Scan a string and return true if the string represents the human

   readable format of an ISO time.  This format is:

      yyyy-mm-dd[ hh[:mm[:ss]]]

   Scanning stops at the second space or at a comma.  If DATE_ONLY is

   true the time part is not expected and the scanning stops at the

   first space or at a comma. */

int

isotime_human_p (const char *string, int date_only)

{

  const char *s;

  int i;

  if (!*string)

    return 0;

  for (s=string, i=0; i < 4; i++, s++)

    if (!digitp (s))

      return 0;

  if (*s != '-')

    return 0;

  s++;

  if (!digitp (s) || !digitp (s+1) || s[2] != '-')

    return 0;

  i = atoi_2 (s);

  if (i < 1 || i > 12)

    return 0;

  s += 3;

  if (!digitp (s) || !digitp (s+1))

    return 0;

  i = atoi_2 (s);

  if (i < 1 || i > 31)

    return 0;

  s += 2;

  if (!*s || *s == ',')

    return 1; /* Okay; only date given.  */

  if (!spacep (s))

    return 0;

  if (date_only)

    return 1; /* Okay; only date was requested.  */

  s++;

  if (spacep (s))

    return 1; /* Okay, second space stops scanning.  */

  if (!digitp (s) || !digitp (s+1))

    return 0;

  i = atoi_2 (s);

  if (i < 0 || i > 23)

    return 0;

  s += 2;

  if (!*s || *s == ',')

    return 1; /* Okay; only date and hour given.  */

  if (*s != ':')

    return 0;

  s++;

  if (!digitp (s) || !digitp (s+1))

    return 0;

  i = atoi_2 (s);

  if (i < 0 || i > 59)

    return 0;

  s += 2;

  if (!*s || *s == ',')

    return 1; /* Okay; only date, hour and minute given.  */

  if (*s != ':')

    return 0;

  s++;

  if (!digitp (s) || !digitp (s+1))

    return 0;

  i = atoi_2 (s);

  if (i < 0 || i > 60)

    return 0;

  s += 2;

  if (!*s || *s == ',' || spacep (s))

    return 1; /* Okay; date, hour and minute and second given.  */

  return 0; /* Unexpected delimiter.  */

}

/* Convert a standard isotime or a human readable variant into an

   isotime structure.  The allowed formats are those described by

   isotime_p and isotime_human_p.  The function returns 0 on failure

   or the length of the scanned string on success.  */

size_t

string2isotime (gnupg_isotime_t atime, const char *string)

{

  gnupg_isotime_t dummyatime;

  if (!atime)

    atime = dummyatime;

  atime[0] = 0;

  if (isotime_p (string))

    {

      memcpy (atime, string, 15);

      atime[15] = 0;

      return 15;

    }

  if (!isotime_human_p (string, 0))

    return 0;

  atime[0] = string[0];

  atime[1] = string[1];

  atime[2] = string[2];

  atime[3] = string[3];

  atime[4] = string[5];

  atime[5] = string[6];

  atime[6] = string[8];

  atime[7] = string[9];

  atime[8] = 'T';

  memset (atime+9, '0', 6);

  atime[15] = 0;

  if (!spacep (string+10))

    return 10;

  if (spacep (string+11))

    return 11; /* As per def, second space stops scanning.  */

  atime[9] = string[11];

  atime[10] = string[12];

  if (string[13] != ':')

    return 13;

  atime[11] = string[14];

  atime[12] = string[15];

  if (string[16] != ':')

    return 16;

  atime[13] = string[17];

  atime[14] = string[18];

  return 19;

}

/* Helper for isotime2epoch.  Returns 0 on success. */

static int

isotime_make_tm (const char *string, struct tm *tmbuf)

{

  int year, month, day, hour, minu, sec;

  if (!isotime_p (string))

    return -1;

  year  = atoi_4 (string);

  month = atoi_2 (string + 4);

  day   = atoi_2 (string + 6);

  hour  = atoi_2 (string + 9);

  minu  = atoi_2 (string + 11);

  sec   = atoi_2 (string + 13);

  /* Basic checks.  */

  if (year < 1970 || month < 1 || month > 12 || day < 1 || day > 31

      || hour > 23 || minu > 59 || sec > 61 )

    return -1;

  memset (tmbuf, 0, sizeof *tmbuf);

  tmbuf->tm_sec  = sec;

  tmbuf->tm_min  = minu;

  tmbuf->tm_hour = hour;

  tmbuf->tm_mday = day;

  tmbuf->tm_mon  = month-1;

  tmbuf->tm_year = year - 1900;

  tmbuf->tm_isdst = -1;

  return 0;

}

/* Scan an ISO timestamp and return an Epoch based timestamp.  The

   only supported format is "yyyymmddThhmmss[Z]" delimited by white

   space, nul, a colon or a comma.  Returns (time_t)(-1) for an

   invalid string.  */

time_t

isotime2epoch (const char *string)

{

  struct tm tmbuf;

  if (isotime_make_tm (string, &tmbuf))

    return (time_t)(-1);

  return timegm (&tmbuf);

}

uint64_t

isotime2epoch_u64 (const char *string)

{

  struct tm tmbuf;

  if (isotime_make_tm (string, &tmbuf))

    return (uint64_t)(-1);

  return timegm_u64 (&tmbuf);

}

/* Convert an Epoch time to an iso time stamp. */

void

epoch2isotime (gnupg_isotime_t timebuf, time_t atime)

{

  if (atime == (time_t)(-1))

    *timebuf = 0;

  else

    {

      struct tm *tp;

#ifdef HAVE_GMTIME_R

      struct tm tmbuf;

      tp = gmtime_r (&atime, &tmbuf);

#else

      tp = gmtime (&atime);

#endif

      snprintf (timebuf, 16, "%04d%02d%02dT%02d%02d%02d",

                1900 + tp->tm_year, tp->tm_mon+1, tp->tm_mday,

                tp->tm_hour, tp->tm_min, tp->tm_sec);

    }

}

/* Parse a short ISO date string (YYYY-MM-DD) into a TM structure.

   Returns 0 on success.  */

int

isodate_human_to_tm (const char *string, struct tm *t)

{

  int year, month, day;

  if (!isotime_human_p (string, 1))

    return -1;

  year  = atoi_4 (string);

  month = atoi_2 (string + 5);

  day   = atoi_2 (string + 8);

  /* Basic checks.  */

  if (year < 1970 || month < 1 || month > 12 || day < 1 || day > 31)

    return -1;

  memset (t, 0, sizeof *t);

  t->tm_sec  = 0;

  t->tm_min  = 0;

  t->tm_hour = 0;

  t->tm_mday = day;

  t->tm_mon  = month-1;

  t->tm_year = year - 1900;

  t->tm_isdst = -1;

  return 0;

}

/* Parse the string TIMESTAMP into a time_t.  The string may either be

   seconds since Epoch or in the ISO 8601 format like

   "20390815T143012".  Returns 0 for an empty string or seconds since

   Epoch. Leading spaces are skipped. If ENDP is not NULL, it will

   point to the next non-parsed character in TIMESTRING.

   This function is a copy of

   gpgme/src/conversion.c:_gpgme_parse_timestamp.  If you change it,

   then update the other one too.

   FIXME: Replace users of this function by one of the more modern

          functions or change the return type to u64.

*/

time_t

parse_timestamp (const char *timestamp, char **endp)

{

  /* Need to skip leading spaces, because that is what strtoul does

     but not our ISO 8601 checking code. */

  while (*timestamp && *timestamp== ' ')

    timestamp++;

  if (!*timestamp)

    return 0;

  if (strlen (timestamp) >= 15 && timestamp[8] == 'T')

    {

      struct tm buf;

      int year;

      year = atoi_4 (timestamp);

      if (year < 1900)

        return (time_t)(-1);

      if (endp)

        *endp = (char*)(timestamp + 15);

      /* Fixme: We would better use a configure test to see whether

         mktime can handle dates beyond 2038. */

      if (sizeof (time_t) <= 4 && year >= 2038)

        return (time_t)2145914603; /* 2037-12-31 23:23:23 */

      memset (&buf, 0, sizeof buf);

      buf.tm_year = year - 1900;

      buf.tm_mon = atoi_2 (timestamp+4) - 1;

      buf.tm_mday = atoi_2 (timestamp+6);

      buf.tm_hour = atoi_2 (timestamp+9);

      buf.tm_min = atoi_2 (timestamp+11);

      buf.tm_sec = atoi_2 (timestamp+13);

      return timegm (&buf);

    }

  else

    return (time_t)strtoul (timestamp, endp, 10);

}

u32

add_days_to_timestamp( u32 stamp, u16 days )

{

    return stamp + days*86400L;

}

/****************

 * Return a string with a time value in the form: x Y, n D, n H

 */

const char *

strtimevalue( u32 value )

{

    static char buffer[30];

    unsigned int years, days, hours, minutes;

    value /= 60;

    minutes = value % 60;

    value /= 60;

    hours = value % 24;

    value /= 24;

    days = value % 365;

    value /= 365;

    years = value;

    sprintf(buffer,"%uy%ud%uh%um", years, days, hours, minutes );

    if( years )

  return buffer;

    if( days )

  return strchr( buffer, 'y' ) + 1;

    return strchr( buffer, 'd' ) + 1;

}

/* Return a malloced string with the time elapsed between NOW and

   SINCE.  May return NULL on error. */

char *

elapsed_time_string (time_t since, time_t now)

{

  char *result;

  double diff;

  unsigned long value;

  unsigned int days, hours, minutes, seconds;

  if (!now)

    now = gnupg_get_time ();

  diff = difftime (now, since);

  if (diff < 0)

    return xtrystrdup ("time-warp");

  seconds = (unsigned long)diff % 60;

  value = (unsigned long)(diff / 60);

  minutes = value % 60;

  value /= 60;

  hours = value % 24;

  value /= 24;

  days = value % 365;

  if (days)

    result = xtryasprintf ("%ud%uh%um%us", days, hours, minutes, seconds);

  else if (hours)

    result = xtryasprintf ("%uh%um%us", hours, minutes, seconds);

  else if (minutes)

    result = xtryasprintf ("%um%us", minutes, seconds);

  else

    result = xtryasprintf ("%us", seconds);

  return result;

}

/*

 * Note: this function returns GMT

 */

const char *

strtimestamp (u32 stamp)

{

  static char buffer[11+5];

  struct tm *tp;

  time_t atime = stamp;

  if (IS_INVALID_TIME_T (atime))

    {

      strcpy (buffer, "????" "-??" "-??");

    }

  else

    {

      tp = gmtime( &atime );

      snprintf (buffer, sizeof buffer, "%04d-%02d-%02d",

                1900+tp->tm_year, tp->tm_mon+1, tp->tm_mday );

    }

  return buffer;

}

/*

 * Note: this function returns GMT

 */

const char *

isotimestamp (u32 stamp)

{

  static char buffer[25+5];

  struct tm *tp;

  time_t atime = stamp;

  if (IS_INVALID_TIME_T (atime))

    {

      strcpy (buffer, "????" "-??" "-??" " " "??" ":" "??" ":" "??");

    }

  else

    {

      tp = gmtime ( &atime );

      snprintf (buffer, sizeof buffer, "%04d-%02d-%02d %02d:%02d:%02d",

                1900+tp->tm_year, tp->tm_mon+1, tp->tm_mday,

                tp->tm_hour, tp->tm_min, tp->tm_sec);

    }

  return buffer;

}

/****************

 * Note: this function returns local time

 */

const char *

asctimestamp (u32 stamp)

{

  static char buffer[80];

#if defined (HAVE_STRFTIME) && defined (HAVE_NL_LANGINFO)

  static char fmt[80];

#endif

  struct tm *tp;

  time_t atime = stamp;

  if (IS_INVALID_TIME_T (atime))

    {

      strcpy (buffer, "????" "-??" "-??");

      return buffer;

    }

  tp = localtime( &atime );

#ifdef HAVE_STRFTIME

# if defined(HAVE_NL_LANGINFO)

  mem2str( fmt, nl_langinfo(D_T_FMT), DIM(fmt)-3 );

  if (!strstr( fmt, "%Z" ))

    strcat( fmt, " %Z");

  /* NOTE: gcc -Wformat-noliteral will complain here.  I have found no

     way to suppress this warning.  */

  strftime (buffer, DIM(buffer)-1, fmt, tp);

# else

#  if HAVE_W32_SYSTEM

  {

    static int done;

    if (!done)

      {

        /* The locale names as used by Windows are in the form

         * "German_Germany.1252" or "German_Austria.1252" with

         * alternate names similar to Unix, e.g. "de-DE".  However

         * that is the theory.  On current Windows and Mingw the

         * alternate names do not work.  We would need a table to map

         * them from the short names as provided by gpgrt to the long

         * names and append some code page.  For now we use "" and

         * take the locale from the user's system settings.  Thus the

         * standard Unix envvars don't work for time and may mismatch

         * with the string translations.  The new UCRT available since

         * 2018 has a lot of additional support but that will for sure

         * break other things.  We should move to ISO strings to get

         * rid of such problems.  */

        setlocale (LC_TIME, ".UTF8");

        done = 1;

        /* log_debug ("LC_ALL  now '%s'\n", setlocale (LC_ALL, NULL)); */

        /* log_debug ("LC_TIME now '%s'\n", setlocale (LC_TIME, NULL)); */

      }

  }

#  endif

   /* FIXME: we should check whether the locale appends a " %Z" These

    * locales from glibc don't put the " %Z": fi_FI hr_HR ja_JP lt_LT

    * lv_LV POSIX ru_RU ru_SU sv_FI sv_SE zh_CN.  */

  strftime (buffer, DIM(buffer)-1, "%c %Z", tp);

# endif

  buffer[DIM(buffer)-1] = 0;

#else

  mem2str( buffer, asctime(tp), DIM(buffer) );

#endif

  return buffer;

}

/* Return the timestamp STAMP in RFC-2822 format.  This is always done

 * in the C locale.  We return the gmtime to avoid computing the

 * timezone. The caller must release the returned string.

 *

 * Example: "Mon, 27 Jun 2016 1:42:00 +0000".

 */

char *

rfctimestamp (u32 stamp)

{

  time_t atime = stamp;

  struct tm tmbuf, *tp;

  if (IS_INVALID_TIME_T (atime))

    {

      gpg_err_set_errno (EINVAL);

      return NULL;

    }

  tp = gnupg_gmtime (&atime, &tmbuf);

  if (!tp)

    return NULL;

  return xtryasprintf ("%.3s, %02d %.3s %04d %02d:%02d:%02d +0000",

                       &"SunMonTueWedThuFriSat"[(tp->tm_wday%7)*3],

                       tp->tm_mday,

                       &"JanFebMarAprMayJunJulAugSepOctNovDec"

                       [(tp->tm_mon%12)*3],

                       tp->tm_year + 1900,

                       tp->tm_hour,

                       tp->tm_min,

                       tp->tm_sec);

}

static int

days_per_year (int y)

{

  int s ;

  s = !(y % 4);

  if ( !(y % 100))

    if ((y%400))

      s = 0;

  return s ? 366 : 365;

}

static int

days_per_month (int y, int m)