external/ibm-public/postfix/dist/src/global/mail_date.c

   1 /*      $NetBSD$        */
   2
   3 /*++
   4 /* NAME
   5 /*      mail_date 3
   6 /* SUMMARY
   7 /*      return formatted time
   8 /* SYNOPSIS
   9 /*      #include <mail_date.h>
  10 /*
  11 /*      const char *mail_date(when)
  12 /*      time_t  when;
  13 /* DESCRIPTION
  14 /*      mail_date() converts the time specified in \fIwhen\fR to the
  15 /*      form: "Mon, 9 Dec 1996 05:38:26 -0500 (EST)" and returns
  16 /*      a pointer to the result. The result is overwritten upon
  17 /*      each call.
  18 /* DIAGNOSTICS
  19 /*      Panic: the offset from UTC is more than a whole day. Fatal
  20 /*      error: out of memory.
  21 /* LICENSE
  22 /* .ad
  23 /* .fi
  24 /*      The Secure Mailer license must be distributed with this software.
  25 /* AUTHOR(S)
  26 /*      Wietse Venema
  27 /*      IBM T.J. Watson Research
  28 /*      P.O. Box 704
  29 /*      Yorktown Heights, NY 10598, USA
  30 /*--*/
  31
  32 /* System library. */
  33
  34 #include <sys_defs.h>
  35 #include <time.h>
  36 #include <stdlib.h>
  37
  38 /* Utility library. */
  39
  40 #include <msg.h>
  41 #include <vstring.h>
  42
  43 /* Global library. */
  44
  45 #include "mail_date.h"
  46
  47  /*
  48   * Application-specific.
  49   */
  50 #define DAY_MIN         (24 * HOUR_MIN) /* minutes in a day */
  51 #define HOUR_MIN        60              /* minutes in an hour */
  52 #define MIN_SEC         60              /* seconds in a minute */
  53
  54 /* mail_date - return formatted time */
  55
  56 const char *mail_date(time_t when)
  57 {
  58     static VSTRING *vp;
  59     struct tm *lt;
  60     struct tm gmt;
  61     int     gmtoff;
  62
  63     /*
  64      * As if strftime() isn't expensive enough, we're dynamically adjusting
  65      * the size for the result, so we won't be surprised by long names etc.
  66      */
  67     if (vp == 0)
  68         vp = vstring_alloc(100);
  69     else
  70         VSTRING_RESET(vp);
  71
  72     /*
  73      * POSIX does not require that struct tm has a tm_gmtoff field, so we
  74      * must compute the time offset from UTC by hand.
  75      *
  76      * Starting with the difference in hours/minutes between 24-hour clocks,
  77      * adjust for differences in years, in yeardays, and in (leap) seconds.
  78      *
  79      * Assume 0..23 hours in a day, 0..59 minutes in an hour. The library spec
  80      * has changed: we can no longer assume that there are 0..59 seconds in a
  81      * minute.
  82      */
  83     gmt = *gmtime(&when);
  84     lt = localtime(&when);
  85     gmtoff = (lt->tm_hour - gmt.tm_hour) * HOUR_MIN + lt->tm_min - gmt.tm_min;
  86     if (lt->tm_year < gmt.tm_year)
  87         gmtoff -= DAY_MIN;
  88     else if (lt->tm_year > gmt.tm_year)
  89         gmtoff += DAY_MIN;
  90     else if (lt->tm_yday < gmt.tm_yday)
  91         gmtoff -= DAY_MIN;
  92     else if (lt->tm_yday > gmt.tm_yday)
  93         gmtoff += DAY_MIN;
  94     if (lt->tm_sec <= gmt.tm_sec - MIN_SEC)
  95         gmtoff -= 1;
  96     else if (lt->tm_sec >= gmt.tm_sec + MIN_SEC)
  97         gmtoff += 1;
  98
  99     /*
 100      * First, format the date and wall-clock time. XXX The %e format (day of
 101      * month, leading zero replaced by blank) isn't in my POSIX book, but
 102      * many vendors seem to support it.
 103      */
 104 #ifdef MISSING_STRFTIME_E
 105 #define STRFTIME_FMT "%a, %d %b %Y %H:%M:%S "
 106 #else
 107 #define STRFTIME_FMT "%a, %e %b %Y %H:%M:%S "
 108 #endif
 109
 110     while (strftime(vstring_end(vp), vstring_avail(vp), STRFTIME_FMT, lt) == 0)
 111         VSTRING_SPACE(vp, 100);
 112     VSTRING_SKIP(vp);
 113
 114     /*
 115      * Then, add the UTC offset.
 116      */
 117     if (gmtoff < -DAY_MIN || gmtoff > DAY_MIN)
 118         msg_panic("UTC time offset %d is larger than one day", gmtoff);
 119     vstring_sprintf_append(vp, "%+03d%02d", (int) (gmtoff / HOUR_MIN),
 120                            (int) (abs(gmtoff) % HOUR_MIN));
 121
 122     /*
 123      * Finally, add the time zone name.
 124      */
 125     while (strftime(vstring_end(vp), vstring_avail(vp), " (%Z)", lt) == 0)
 126         VSTRING_SPACE(vp, vstring_avail(vp) + 100);
 127     VSTRING_SKIP(vp);
 128
 129     return (vstring_str(vp));
 130 }
 131
 132 #ifdef TEST
 133
 134 #include <vstream.h>
 135
 136 int     main(void)
 137 {
 138     vstream_printf("%s\n", mail_date(time((time_t *) 0)));
 139     vstream_fflush(VSTREAM_OUT);
 140     return (0);
 141 }
 142
 143 #endif