date,touch: allow timezone offsets in dates

Allow ISO 8601 style dates to include a timezone offset.  Like
the '@' format these dates aren't relative to the user's current
timezone and shouldn't be subject to DST adjustment.

- The implementation uses the strptime() '%z' format specifier.
  This an extension which may not be available so the use of
  timezones is a configuration option.

- The 'touch' applet has been updated to respect whether DST
  adjustment is required, matching 'date'.

function                                             old     new   delta
parse_datestr                                        624     730    +106
static.fmt_str                                       106     136     +30
touch_main                                           388     392      +4
date_main                                            818     819      +1
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 4/0 up/down: 141/0)             Total: 141 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/coreutils/touch.c b/coreutils/touch.c
index 78100ba1d..7e13a27be 100644
--- a/coreutils/touch.c
+++ b/coreutils/touch.c
@@ -140,15 +140,17 @@ int touch_main(int argc UNUSED_PARAM, char **argv)
         if (opts & (OPT_d|OPT_t)) {
                 struct tm tm_time;
                 time_t t;
+                int check_dst;
 
                 //memset(&tm_time, 0, sizeof(tm_time));
                 /* Better than memset: makes "HH:MM" dates meaningful */
                 time(&t);
                 localtime_r(&t, &tm_time);
-                parse_datestr(date_str, &tm_time);
+                check_dst = parse_datestr(date_str, &tm_time);
 
                 /* Correct any day of week and day of year etc. fields */
-                tm_time.tm_isdst = -1;  /* Be sure to recheck dst */
+                if (check_dst)
+                        tm_time.tm_isdst = -1;  /* recheck dst unless date is UTC */
                 t = validate_tm_time(date_str, &tm_time);
 
                 timebuf[1].tv_sec = timebuf[0].tv_sec = t;