Re: [bug #21455] date --date "" "+test" fails ONLY WITHIN CERTAIN TIME PERIOD #$%^%

[Philip Rowlands]

On Mon, 29 Oct 2007, Mischa Molhoek wrote:

> ok, here is the text version, because the image is remove by accident 
> :)

It's simpler to debug problems reported by text, not pictures.

> [titan: mischa] ~> date --version
> date (GNU coreutils) 5.97
> Copyright (C) 2006 Free Software Foundation, Inc.
> This is free software.  You may redistribute copies of it under the terms of
> the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
> There is NO WARRANTY, to the extent permitted by law.
>
> Written by David MacKenzie.
> [titan: mischa] ~> date --date "" "+test"
> test
>
> [titan: mischa] ~> sudo date -s "Sun Oct 28 22:00:53 CET 2007"
> Sun Oct 28 22:00:53 CET 2007
>
> [titan: mischa] ~> date --date "" "+test"
> date: invalid date `'

You don't need the "+test", it's invalid by itself :)

> [titan: mischa] ~> sudo rdate -s ntp.xs4all.nl
>
> [titan: mischa] ~> date
> Mon Oct 29 12:08:41 CET 2007

> [titan: mischa] ~> date --date "" "+test"
> test

You don't give your timezone explicitly, so I'm going to guess you're in 
a region which follows Central European Time / Central European Summer 
Time.

I hacked up the following to avoid resetting my system clock all over 
the place:

--------- clock_gettime.c -----------
#include <stdlib.h>
#include <time.h>
#include <errno.h>

int clock_gettime(clockid_t clk_id, struct timespec *tp) {
        if (clk_id != CLOCK_REALTIME) {
                errno = EINVAL;
                return -1;
        }
        char *faketime = getenv("FAKETIME");
        if (! faketime ) {
                errno = EINVAL;
                return -1;
        }
        if (tp) {
                tp->tv_nsec = 0;
                tp->tv_sec = atol(faketime);
        }
        return 0;
}
-------------------------------------

gcc -c -fPIC clock_gettime.c -D_GNU_SOURCE
gcc -shared -fPIC -o clock_gettime.so clock_gettime.o
for anyone following at home.

Firstly, let's see what date -d "" does?

$ date -d ""
Mon Oct 29 00:00:00 GMT 2007

This has shown my current time wound back to the previous midnight. (I 
can't find the documentation which describes this, but let's continue 
regardless.)

$ export TZ=Europe/Paris
$ export FAKETIME=1193605253; LD_PRELOAD=./clock_gettime.so date -d ""
date: invalid date `'

Smells like a DST issue, are we in a DST change?

$ zdump -v Europe/Paris
Europe/Paris  Sun Oct 28 00:59:59 2007 UTC = Sun Oct 28 02:59:59 2007 CEST 
isdst=1 gmtoff=7200
Europe/Paris  Sun Oct 28 01:00:00 2007 UTC = Sun Oct 28 02:00:00 2007 CET 
isdst=0 gmtoff=3600

In Europe/Paris, the boundaries of "invalid" times are 1193533200 -> 
1193612399 inclusive, or
Sun Oct 28 02:00:00 CET 2007 -> Sun Oct 28 23:59:59 CET 2007

If I try the same thing in Europe/Dublin, invalid times become
1193533200 - 1193615999 inclusive, or
Sun Oct 28 01:00:00 GMT 2007 -> Sun Oct 28 23:59:59 GMT 2007

This corresponds to the first second of winter time "isdst=0" and 
persists for the rest of the logical day. I'm wary about diving around 
in unfamiliar code - perhaps someone more familiar with date parsing 
knows how date -d "" is supposed to be treated, and what the problem is 
here?


Cheers,
Phil