* [PATCH] Call timegm and timelocal with 4-digit year
@ 2018-02-23 17:20 Bernhard M. Wiedemann
2018-02-23 22:28 ` Junio C Hamano
2018-02-24 22:28 ` Ævar Arnfjörð Bjarmason
0 siblings, 2 replies; 4+ messages in thread
From: Bernhard M. Wiedemann @ 2018-02-23 17:20 UTC (permalink / raw)
To: git; +Cc: Ben Walton, Matthias Urlichs, Ryuichi Kokubo,
Bernhard M. Wiedemann
amazingly timegm(gmtime(0)) is only 0 before 2020
because perl's timegm deviates from GNU timegm(3) in how it handles years.
man Time::Local says
Whenever possible, use an absolute four digit year instead.
with a detailed explanation about ambiguity of 2-digit years above that.
Even though this ambiguity is error-prone with >50% of users getting it
wrong, it has been like this for 20+ years, so we just use 4-digit years
everywhere to be on the safe side.
We add some extra logic to cvsimport because it allows 2-digit year
input and interpreting an 18 as 1918 can be avoided easily and safely.
Signed-off-by: Bernhard M. Wiedemann <bwiedemann@suse.de>
---
contrib/examples/git-svnimport.perl | 2 +-
git-cvsimport.perl | 4 +++-
perl/Git.pm | 4 +++-
perl/Git/SVN.pm | 2 +-
4 files changed, 8 insertions(+), 4 deletions(-)
diff --git a/contrib/examples/git-svnimport.perl b/contrib/examples/git-svnimport.perl
index c414f0d9c..75a43e23b 100755
--- a/contrib/examples/git-svnimport.perl
+++ b/contrib/examples/git-svnimport.perl
@@ -238,7 +238,7 @@ sub pdate($) {
my($d) = @_;
$d =~ m#(\d\d\d\d)-(\d\d)-(\d\d)T(\d\d):(\d\d):(\d\d)#
or die "Unparseable date: $d\n";
- my $y=$1; $y-=1900 if $y>1900;
+ my $y=$1; $y+=1900 if $y<1000;
return timegm($6||0,$5,$4,$3,$2-1,$y);
}
diff --git a/git-cvsimport.perl b/git-cvsimport.perl
index 2d8df8317..b31613cb8 100755
--- a/git-cvsimport.perl
+++ b/git-cvsimport.perl
@@ -601,7 +601,9 @@ sub pdate($) {
my ($d) = @_;
m#(\d{2,4})/(\d\d)/(\d\d)\s(\d\d):(\d\d)(?::(\d\d))?#
or die "Unparseable date: $d\n";
- my $y=$1; $y-=1900 if $y>1900;
+ my $y=$1;
+ $y+=100 if $y<70;
+ $y+=1900 if $y<1000;
return timegm($6||0,$5,$4,$3,$2-1,$y);
}
diff --git a/perl/Git.pm b/perl/Git.pm
index ffa09ace9..df62518c7 100644
--- a/perl/Git.pm
+++ b/perl/Git.pm
@@ -534,7 +534,9 @@ If TIME is not supplied, the current local time is used.
sub get_tz_offset {
# some systems don't handle or mishandle %z, so be creative.
my $t = shift || time;
- my $gm = timegm(localtime($t));
+ my @t = localtime($t);
+ $t[5] += 1900;
+ my $gm = timegm(@t);
my $sign = qw( + + - )[ $gm <=> $t ];
return sprintf("%s%02d%02d", $sign, (gmtime(abs($t - $gm)))[2,1]);
}
diff --git a/perl/Git/SVN.pm b/perl/Git/SVN.pm
index bc4eed3d7..991a5885e 100644
--- a/perl/Git/SVN.pm
+++ b/perl/Git/SVN.pm
@@ -1405,7 +1405,7 @@ sub parse_svn_date {
$ENV{TZ} = 'UTC';
my $epoch_in_UTC =
- Time::Local::timelocal($S, $M, $H, $d, $m - 1, $Y - 1900);
+ Time::Local::timelocal($S, $M, $H, $d, $m - 1, $Y);
# Determine our local timezone (including DST) at the
# time of $epoch_in_UTC. $Git::SVN::Log::TZ stored the
--
2.13.6
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] Call timegm and timelocal with 4-digit year
2018-02-23 17:20 [PATCH] Call timegm and timelocal with 4-digit year Bernhard M. Wiedemann
@ 2018-02-23 22:28 ` Junio C Hamano
2018-02-24 22:28 ` Ævar Arnfjörð Bjarmason
1 sibling, 0 replies; 4+ messages in thread
From: Junio C Hamano @ 2018-02-23 22:28 UTC (permalink / raw)
To: Bernhard M. Wiedemann; +Cc: git, Ben Walton, Matthias Urlichs, Ryuichi Kokubo
"Bernhard M. Wiedemann" <bwiedemann@suse.de> writes:
> amazingly timegm(gmtime(0)) is only 0 before 2020
> because perl's timegm deviates from GNU timegm(3) in how it handles years.
>
> man Time::Local says
>
> Whenever possible, use an absolute four digit year instead.
>
> with a detailed explanation about ambiguity of 2-digit years above that.
That's amusing. Will queue; thanks.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Call timegm and timelocal with 4-digit year
2018-02-23 17:20 [PATCH] Call timegm and timelocal with 4-digit year Bernhard M. Wiedemann
2018-02-23 22:28 ` Junio C Hamano
@ 2018-02-24 22:28 ` Ævar Arnfjörð Bjarmason
2018-02-26 10:59 ` Bernhard M. Wiedemann
1 sibling, 1 reply; 4+ messages in thread
From: Ævar Arnfjörð Bjarmason @ 2018-02-24 22:28 UTC (permalink / raw)
To: Bernhard M. Wiedemann
Cc: git, Ben Walton, Matthias Urlichs, Ryuichi Kokubo, Junio C Hamano
On Fri, Feb 23 2018, Bernhard M. Wiedemann jotted:
> amazingly timegm(gmtime(0)) is only 0 before 2020
> because perl's timegm deviates from GNU timegm(3) in how it handles years.
>
> man Time::Local says
>
> Whenever possible, use an absolute four digit year instead.
>
> with a detailed explanation about ambiguity of 2-digit years above that.
>
> Even though this ambiguity is error-prone with >50% of users getting it
> wrong, it has been like this for 20+ years, so we just use 4-digit years
> everywhere to be on the safe side.
>
> We add some extra logic to cvsimport because it allows 2-digit year
> input and interpreting an 18 as 1918 can be avoided easily and safely.
>
> Signed-off-by: Bernhard M. Wiedemann <bwiedemann@suse.de>
> ---
> contrib/examples/git-svnimport.perl | 2 +-
> git-cvsimport.perl | 4 +++-
> perl/Git.pm | 4 +++-
> perl/Git/SVN.pm | 2 +-
> 4 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/contrib/examples/git-svnimport.perl b/contrib/examples/git-svnimport.perl
> index c414f0d9c..75a43e23b 100755
> --- a/contrib/examples/git-svnimport.perl
> +++ b/contrib/examples/git-svnimport.perl
> @@ -238,7 +238,7 @@ sub pdate($) {
> my($d) = @_;
> $d =~ m#(\d\d\d\d)-(\d\d)-(\d\d)T(\d\d):(\d\d):(\d\d)#
> or die "Unparseable date: $d\n";
> - my $y=$1; $y-=1900 if $y>1900;
> + my $y=$1; $y+=1900 if $y<1000;
> return timegm($6||0,$5,$4,$3,$2-1,$y);
I wonder if this whole thing was just cargo-culted to begin with. We
need to match (\d\d\d\d) here, so did SVN's format ever have years like
"0098" (just "98" wouldn't match), so I suspect the whole munging could
be dropped, but this change seems harmless. Just something that jumped
out at me reviewing this.
> diff --git a/git-cvsimport.perl b/git-cvsimport.perl
> index 2d8df8317..b31613cb8 100755
> --- a/git-cvsimport.perl
> +++ b/git-cvsimport.perl
> @@ -601,7 +601,9 @@ sub pdate($) {
> my ($d) = @_;
> m#(\d{2,4})/(\d\d)/(\d\d)\s(\d\d):(\d\d)(?::(\d\d))?#
> or die "Unparseable date: $d\n";
> - my $y=$1; $y-=1900 if $y>1900;
> + my $y=$1;
> + $y+=100 if $y<70;
> + $y+=1900 if $y<1000;
> return timegm($6||0,$5,$4,$3,$2-1,$y);
> }
My Time::Local 1.2300 on perl 5.024001 currently interprets "69" here as
1969, but after this it'll be 2069.
Now I doubt anyone's going to be importing CVS history of projects a
little over 20 years before CVS was created in 1990 (although I suppose
old imports...), but just wanted to note it since it seems odd for code
that's auto-interpreting double digit years for the purposes of
importing existing data to end up in an edge case where it returns dates
more than 50 years in the future.
> diff --git a/perl/Git.pm b/perl/Git.pm
> index ffa09ace9..df62518c7 100644
> --- a/perl/Git.pm
> +++ b/perl/Git.pm
> @@ -534,7 +534,9 @@ If TIME is not supplied, the current local time is used.
> sub get_tz_offset {
> # some systems don't handle or mishandle %z, so be creative.
> my $t = shift || time;
> - my $gm = timegm(localtime($t));
> + my @t = localtime($t);
> + $t[5] += 1900;
> + my $gm = timegm(@t);
>
Nice. Just using the 4-digit date is always more correct and won't ever
be buggy.
> my $sign = qw( + + - )[ $gm <=> $t ];
> return sprintf("%s%02d%02d", $sign, (gmtime(abs($t - $gm)))[2,1]);
> }
> diff --git a/perl/Git/SVN.pm b/perl/Git/SVN.pm
> index bc4eed3d7..991a5885e 100644
> --- a/perl/Git/SVN.pm
> +++ b/perl/Git/SVN.pm
> @@ -1405,7 +1405,7 @@ sub parse_svn_date {
> $ENV{TZ} = 'UTC';
>
> my $epoch_in_UTC =
> - Time::Local::timelocal($S, $M, $H, $d, $m - 1, $Y - 1900);
> + Time::Local::timelocal($S, $M, $H, $d, $m - 1, $Y);
Ditto. Nicely caught.
>
> # Determine our local timezone (including DST) at the
> # time of $epoch_in_UTC. $Git::SVN::Log::TZ stored the
Anyway, this all looks good to me as-is. That CVS edge case is obscure
and not worth focusing on, and the SVN one could be fixed up in another
commit if anyone cared.
I just spent a bit more time than I should have wondering what this
timegm() edge case was about and whether it might impact other
(unrelated to git) code I had.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Call timegm and timelocal with 4-digit year
2018-02-24 22:28 ` Ævar Arnfjörð Bjarmason
@ 2018-02-26 10:59 ` Bernhard M. Wiedemann
0 siblings, 0 replies; 4+ messages in thread
From: Bernhard M. Wiedemann @ 2018-02-26 10:59 UTC (permalink / raw)
To: Ævar Arnfjörð Bjarmason
Cc: git, Ben Walton, Matthias Urlichs, Ryuichi Kokubo, Junio C Hamano
On 2018-02-24 23:28, Ævar Arnfjörð Bjarmason wrote:
> My Time::Local 1.2300 on perl 5.024001 currently interprets "69" here as
> 1969, but after this it'll be 2069.
on one hand, there is already
perl -e 'use Time::Local;
print scalar gmtime(Time::Local::timegm(0,0,0,1,0,68))'
Sun Jan 1 00:00:00 2068
The problem here is the 'currently', because in 11 months from now, 69
will be interpreted as 2069 by Time::Local, too.
faketime 2019-01-01 perl -e 'use Time::Local;
print scalar gmtime(Time::Local::timegm(0,0,0,1,0,69))'
Tue Jan 1 00:00:00 2069
We could compromize for
$y+=100 if $y<69;
to freeze the behaviour to what Time::Local does in 2018, but then there
might not be actual repos with such 2-digit year timestamps.
There are definitely CVS repos from before 1999 and without this change,
those might be misinterpreted in 2049 (or before, depending on age)
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2018-02-26 11:00 UTC | newest]
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2018-02-23 17:20 [PATCH] Call timegm and timelocal with 4-digit year Bernhard M. Wiedemann
2018-02-23 22:28 ` Junio C Hamano
2018-02-24 22:28 ` Ævar Arnfjörð Bjarmason
2018-02-26 10:59 ` Bernhard M. Wiedemann
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