Re: [PATCH 5/5] log: do not segfault on gmtime errors

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On Sat, Mar 22, 2014 at 10:32:37AM +0100, René Scharfe wrote:

> >This test is of questionable portability, since we are depending on
> >gmtime's arbitrary point to decide that our input is crazy and return
> >NULL. The value is sufficiently large that I'd expect most to do so,
> >though, so it may be safe.
> 
> Just came around to testing on FreeBSD 10 amd64; the new test in t4212 fails
> there:

Thanks for the report. I don't think the problem is in the test here,
but rather that we should do a more thorough job of detecting gmtime's
"I don't know what to do with this" response.

> >@@ -184,8 +184,10 @@ const char *show_date(unsigned long time, int tz, enum date_mode mode)
> >  		tz = local_tzoffset(time);
> >
> >  	tm = time_to_tm(time, tz);
> >-	if (!tm)
> >-		return NULL;
> >+	if (!tm) {
> 
> Would it make sense to work around the FreeBSD issue by adding a check like
> this?
> 
> 	if (!tm || tm->tm_year < 70) {

That feels like a bit of a maintenance headache.  Right now we do not
internally represent times prior to the epoch, since we mostly use
"unsigned long" through the code. So anything < 70 has to be an error.
But it would be nice one day to consistently use a 64-bit signed time_t
throughout git, and represent even ancient timestamps (e.g., for people
doing historical projects, like importing laws into git). This would set
quite a trap for people working later on the code.

If the result is all-zeroes, can we check for that case instead? I
suppose that will eventually create a "trap" at midnight on January 1st
of the year 0 (though I am not sure such a date is even meaningful,
given the history of our calendars).

-Peff
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