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+/* 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
+
+#include "util.h"
+#include "i18n.h"
+#include "gettime.h"
+
+#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
+
+
+/* Wrapper for the time(3). We use this here so we can fake the time
+ for tests */
+time_t
+gnupg_get_time ()
+{
+ 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;
+}
+
+
+
+/****************
+ * 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 )
+ return 0;
+ 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;
+}
+
+
+/* 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)
+{
+ int year, month, day, hour, minu, sec;
+ struct tm tmbuf;
+
+ if (!isotime_p (string))
+ return (time_t)(-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 (time_t)(-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 timegm (&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;
+}
+
+
+/* This function is a copy of gpgme/src/conversion.c:_gpgme_timegm.
+ If you change it, then update the other one too. */
+#ifdef HAVE_W32_SYSTEM
+static time_t
+_win32_timegm (struct tm *tm)
+{
+ /* 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 (time_t)(-1);
+ }
+
+ cnsecs = (((unsigned long long)ft.dwHighDateTime << 32)
+ | ft.dwLowDateTime);
+ cnsecs -= 116444736000000000ULL; /* The filetime epoch is 1601-01-01. */
+ return (time_t)(cnsecs / 10000000ULL);
+}
+#endif
+
+
+/* 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. */
+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);
+
+#ifdef HAVE_W32_SYSTEM
+ return _win32_timegm (&buf);
+#else
+#ifdef HAVE_TIMEGM
+ return timegm (&buf);
+#else
+ {
+ time_t tim;
+
+ putenv ("TZ=UTC");
+ tim = mktime (&buf);
+#ifdef __GNUC__
+#warning fixme: we must somehow reset TZ here. It is not threadsafe anyway.
+#endif
+ return tim;
+ }
+#endif /* !HAVE_TIMEGM */
+#endif /* !HAVE_W32_SYSTEM */
+ }
+ 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;
+}
+
+
+/* Windows version of strftime returning the string as utf-8. */
+#ifdef HAVE_W32_SYSTEM
+
+#define strftime(a,b,c,d) w32_strftime ((a),(b),(c),(d))
+
+static size_t
+w32_strftime (char *s, size_t max, const char *format, const struct tm *tm)
+{
+ wchar_t *wformatbuf = NULL;
+ const wchar_t *wformat = L"%c %Z";
+ wchar_t wbuf[200];
+ size_t n;
+ char *buf;
+
+ if (strcmp (format, "%c %Z"))
+ {
+ log_debug (" comverted\n");
+ wformatbuf = utf8_to_wchar (format);
+ if (wformatbuf)
+ wformat = wformatbuf;
+ }
+
+ n = wcsftime (wbuf, sizeof wbuf, wformat, tm);
+ xfree (wformatbuf);
+ if (!n)
+ {
+ /* Most likely the buffer is too short - try ISO format instead. */
+ n = wcsftime (wbuf, sizeof wbuf, L"%Y-%m-%d %H:%M:%S", tm);
+ if (!n)
+ wcscpy (wbuf, L"[????" "-??" "-??]");
+ }
+ buf = wchar_to_utf8 (wbuf);
+ mem2str (s, buf? buf : "[????" "-??" "-??]", max);
+ xfree (buf);
+ return strlen (s) + 1;
+}
+#endif /*HAVE_W32_SYSTEM*/
+
+
+
+/****************
+ * 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);
+# elif defined(HAVE_W32CE_SYSTEM)
+ /* tzset is not available but %Z nevertheless prints a default
+ nonsense timezone ("WILDABBR"). Thus we don't print the time
+ zone at all. */
+ strftime (buffer, DIM(buffer)-1, "%c", 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, "");
+ 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)
+{
+ int s;
+
+ switch(m)
+ {
+ case 1: case 3: case 5: case 7: case 8: case 10: case 12:
+ return 31 ;
+ case 2:
+ s = !(y % 4);
+ if (!(y % 100))
+ if ((y % 400))
+ s = 0;
+ return s? 29 : 28 ;
+ case 4: case 6: case 9: case 11:
+ return 30;
+ }
+ BUG();
+}
+
+
+/* Convert YEAR, MONTH and DAY into the Julian date. We assume that
+ it is already noon. We do not support dates before 1582-10-15. */
+static unsigned long
+date2jd (int year, int month, int day)
+{
+ unsigned long jd;
+
+ jd = 365L * year + 31 * (month-1) + day + JD_DIFF;
+ if (month < 3)
+ year-- ;
+ else
+ jd -= (4 * month + 23) / 10;
+
+ jd += year / 4 - ((year / 100 + 1) *3) / 4;
+
+ return jd ;
+}
+
+/* Convert a Julian date back to YEAR, MONTH and DAY. Return day of
+ the year or 0 on error. This function uses some more or less
+ arbitrary limits, most important is that days before 1582 are not
+ supported. */
+static int
+jd2date (unsigned long jd, int *year, int *month, int *day)
+{
+ int y, m, d;
+ long delta;
+
+ if (!jd)
+ return 0 ;
+ if (jd < 1721425 || jd > 2843085)
+ return 0;
+
+ y = (jd - JD_DIFF) / 366;
+ d = m = 1;
+
+ while ((delta = jd - date2jd (y, m, d)) > days_per_year (y))
+ y++;
+
+ m = (delta / 31) + 1;
+ while( (delta = jd - date2jd (y, m, d)) > days_per_month (y,m))
+ if (++m > 12)
+ {
+ m = 1;
+ y++;
+ }
+
+ d = delta + 1 ;
+ if (d > days_per_month (y, m))
+ {
+ d = 1;
+ m++;
+ }
+ if (m > 12)
+ {
+ m = 1;
+ y++;
+ }
+
+ if (year)
+ *year = y;
+ if (month)
+ *month = m;
+ if (day)
+ *day = d ;
+
+ return (jd - date2jd (y, 1, 1)) + 1;
+}
+
+
+/* Check that the 15 bytes in ATIME represent a valid ISO time. Note
+ that this function does not expect a string but a plain 15 byte
+ isotime buffer. */
+gpg_error_t
+check_isotime (const gnupg_isotime_t atime)
+{
+ int i;
+ const char *s;
+
+ if (!*atime)
+ return gpg_error (GPG_ERR_NO_VALUE);
+
+ for (s=atime, i=0; i < 8; i++, s++)
+ if (!digitp (s))
+ return gpg_error (GPG_ERR_INV_TIME);
+ if (*s != 'T')
+ return gpg_error (GPG_ERR_INV_TIME);
+ for (s++, i=9; i < 15; i++, s++)
+ if (!digitp (s))
+ return gpg_error (GPG_ERR_INV_TIME);
+ return 0;
+}
+
+
+/* Dump the ISO time T to the log stream without a LF. */
+void
+dump_isotime (const gnupg_isotime_t t)
+{
+ if (!t || !*t)
+ log_printf ("%s", _("[none]"));
+ else
+ log_printf ("%.4s-%.2s-%.2s %.2s:%.2s:%s",
+ t, t+4, t+6, t+9, t+11, t+13);
+}
+
+
+/* Copy one ISO date to another, this is inline so that we can do a
+ minimal sanity check. A null date (empty string) is allowed. */
+void
+gnupg_copy_time (gnupg_isotime_t d, const gnupg_isotime_t s)
+{
+ if (*s)
+ {
+ if ((strlen (s) != 15 || s[8] != 'T'))
+ BUG();
+ memcpy (d, s, 15);
+ d[15] = 0;
+ }
+ else
+ *d = 0;
+}
+
+
+/* Add SECONDS to ATIME. SECONDS may not be negative and is limited
+ to about the equivalent of 62 years which should be more then
+ enough for our purposes. */
+gpg_error_t
+add_seconds_to_isotime (gnupg_isotime_t atime, int nseconds)
+{
+ gpg_error_t err;
+ int year, month, day, hour, minute, sec, ndays;
+ unsigned long jd;
+
+ err = check_isotime (atime);
+ if (err)
+ return err;
+
+ if (nseconds < 0 || nseconds >= (0x7fffffff - 61) )
+ return gpg_error (GPG_ERR_INV_VALUE);
+
+ year = atoi_4 (atime+0);
+ month = atoi_2 (atime+4);
+ day = atoi_2 (atime+6);
+ hour = atoi_2 (atime+9);
+ minute= atoi_2 (atime+11);
+ sec = atoi_2 (atime+13);
+
+ if (year <= 1582) /* The julian date functions don't support this. */
+ return gpg_error (GPG_ERR_INV_VALUE);
+
+ sec += nseconds;
+ minute += sec/60;
+ sec %= 60;
+ hour += minute/60;
+ minute %= 60;
+ ndays = hour/24;
+ hour %= 24;
+
+ jd = date2jd (year, month, day) + ndays;
+ jd2date (jd, &year, &month, &day);
+
+ if (year > 9999 || month > 12 || day > 31
+ || year < 0 || month < 1 || day < 1)
+ return gpg_error (GPG_ERR_INV_VALUE);
+
+ snprintf (atime, 16, "%04d%02d%02dT%02d%02d%02d",
+ year, month, day, hour, minute, sec);
+ return 0;
+}
+
+
+gpg_error_t
+add_days_to_isotime (gnupg_isotime_t atime, int ndays)
+{
+ gpg_error_t err;
+ int year, month, day, hour, minute, sec;
+ unsigned long jd;
+
+ err = check_isotime (atime);
+ if (err)
+ return err;
+
+ if (ndays < 0 || ndays >= 9999*366 )
+ return gpg_error (GPG_ERR_INV_VALUE);
+
+ year = atoi_4 (atime+0);
+ month = atoi_2 (atime+4);
+ day = atoi_2 (atime+6);
+ hour = atoi_2 (atime+9);
+ minute= atoi_2 (atime+11);
+ sec = atoi_2 (atime+13);
+
+ if (year <= 1582) /* The julian date functions don't support this. */
+ return gpg_error (GPG_ERR_INV_VALUE);
+
+ jd = date2jd (year, month, day) + ndays;
+ jd2date (jd, &year, &month, &day);
+
+ if (year > 9999 || month > 12 || day > 31
+ || year < 0 || month < 1 || day < 1)
+ return gpg_error (GPG_ERR_INV_VALUE);
+
+ snprintf (atime, 16, "%04d%02d%02dT%02d%02d%02d",
+ year, month, day, hour, minute, sec);
+ return 0;
+}