From: Jan Harkes <jaharkes@cs.cmu.edu>
Date: Sun, 24 Apr 2005 03:04:16 GMT
Subject: Re: Date handling.
Message-ID: <20050424030416.GE16751@delft.aura.cs.cmu.edu>
In-Reply-To: <1113500316.27227.8.camel@hades.cambridge.redhat.com>

On Thu, Apr 14, 2005 at 06:38:36PM +0100, David Woodhouse wrote:
> +/* Gr. strptime is crap for this; it doesn't have a way to require RFC2822
> +   (i.e. English) day/month names, and it doesn't work correctly with %z. */
> +static void parse_rfc2822_date(char *date, char *result, int maxlen)
> +{
...
> +	then = mktime(&tm); /* mktime appears to ignore the GMT offset, stupidly */

I noticed that some commit timestamps seemed to be off, looking into it
a bit more it seems like mktime is influenced by the setting of the
local TZ environment. However in parse_rfc2822_date we are trying to
interpret a time in the timezone of the original author not in the
timezone of the committer.

Here is a short test program that I believe shows the problem.

The question is, do we want to just calculate the time_t offset
ourselves without using mktime, or force the TZ environment to UTC.

Jan


/* cc -o mktime mktime.c ; ./mktime
 *
 * I get the following output,
 *   current 18000
 *   TZ=EST 18000
 *   TZ=UTC 0
 *   TZ=CET -3600
 */

#include <time.h>
#include <stdlib.h>
#include <stdio.h>

int main(int argc, char **argv)
{
    struct tm tm = { 0, };
    time_t zero;

    /* 1970-01-01 00:00:00 UTC, should map to 'time_t 0' */
    tm.tm_mday = 1;
    tm.tm_year = 70;
			    zero = mktime(&tm); printf("current %d\n", zero);
    setenv("TZ", "EST", 1); zero = mktime(&tm); printf("TZ=EST %d\n", zero);
    setenv("TZ", "UTC", 1); zero = mktime(&tm); printf("TZ=UTC %d\n", zero);
    setenv("TZ", "CET", 1); zero = mktime(&tm); printf("TZ=CET %d\n", zero);
}