[pve-devel] [PATCH common 1/3] fix #1963: don't do day-time related math on time stamps

[Wolfgang Bumiller]

On Wed, Oct 31, 2018 at 10:54:16AM +0100, Wolfgang Bumiller wrote:
> Since our schedules are usually written in local time, we
> cannot actually perform calculations using time stamps as
> for instance adding 3600 (1 hour) may yield the exact same
> local time as before when translated to the current timezone
> during a DST change, or might skip an hour. Thus, 2:30am + 1
> hour can be all of 2:30am, 3:30am or 4:30am.
> 
> Instead, perform the translation to a "day time" array once,
> then search for the scheduled time, and only at the end
> translate to a time stamp again. This means adding helpers
> to wrap around minutes, hours, days (of month)...
> 
> Previously, the following code looped endlessly in
> compute_next_event under CEST:
>     my $dst_time = timelocal(0, 0, 0, 28, 9, 2018);
>     my $t = PVE::CalendarEvent::parse_calendar_event('mon..fri');
>     my $next = PVE::CalendarEvent::compute_next_event($t, $start);
> Afterwards $next will be '2018-10-29 00:00 CET' as expected.
> 
> Of course, a day in which 3am appears twice with a scheduled
> event for 3am will cause the event to be scheduled twice
> now. Ideally we add the ability to make calendar specs use
> UTC (and actually use the $utc parameter we have in
> compute_next_event()). systemd.time(7) seems to allow simply
> suffixing the spec with the string " UTC" for that purpose,
> so we should follow this.
> 
> Signed-off-by: Wolfgang Bumiller <w.bumiller at proxmox.com>
> ---
>  src/PVE/CalendarEvent.pm | 174 ++++++++++++++++++++++++++++++-----------------
>  1 file changed, 113 insertions(+), 61 deletions(-)
> 
> diff --git a/src/PVE/CalendarEvent.pm b/src/PVE/CalendarEvent.pm
> index 9fdc95a..7192712 100644
> --- a/src/PVE/CalendarEvent.pm
> +++ b/src/PVE/CalendarEvent.pm
> @@ -161,6 +161,71 @@ sub parse_calendar_event {
>      return { h => $h, m => $m, dow => [ sort keys %$dow_hash ]};
>  }
>  
> +sub is_leap_year($) {
> +    return 0 if $_[0] % 4;
> +    return 1 if $_[0] % 100;
> +    return 0 if $_[0] % 400;
> +    return 1;
> +}
> +
> +# mon = 0.. (Jan = 0)
> +sub days_in_month($$) {
> +    my ($mon, $year) = @_;
> +    return 28 + is_leap_year($year) if $mon == 1;
> +    return (31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31)[$mon];
> +}
> +
> +# day = 1..
> +# mon = 0.. (Jan = 0)
> +sub wrap_time($) {
> +    my ($time) = @_;
> +    my ($sec, $min, $hour, $day, $mon, $year, $wday) = @$time;
> +
> +    use integer;
> +    if ($sec >= 60) {
> +	$min += $sec / 60;
> +	$sec %= 60;
> +    }
> +
> +    if ($min >= 60) {
> +	$hour += $min / 60;
> +	$min %= 60;
> +    }
> +
> +    if ($hour >= 24) {
> +	$day  += $hour / 24;
> +	$wday += $hour / 24;
> +	$hour %= 24;
> +    }
> +
> +    # Translate to 0..($days_in_mon-1)
> +    --$day;
> +    while (1) {
> +	my $days_in_mon = days_in_month($mon % 12, $year);
> +	last if $day < $days_in_mon;
> +	# Wrap one month
> +	$day -= $days_in_mon;
> +	++$mon;
> +    }
> +    # Translate back to 1..$days_in_mon
> +    ++$day;
> +
> +    if ($mon >= 12) {
> +	$year += $mon / 12;
> +	$mon %= 12;
> +    }
> +
> +    $wday %= 7;
> +    return [$sec, $min, $hour, $day, $mon, $year, $wday];
> +}
> +
> +# helper as we need to keep weekdays in sync
> +sub time_add_days($$) {
> +    my ($time, $inc) = @_;
> +    my ($sec, $min, $hour, $day, $mon, $year, $wday) = @$time;
> +    return wrap_time([$sec, $min, $hour, $day + $inc, $mon, $year, $wday + $inc]);
> +}
> +
>  sub compute_next_event {
>      my ($calspec, $last, $utc) = @_;
>  
> @@ -170,73 +235,60 @@ sub compute_next_event {
>  
>      $last += 60; # at least one minute later
>  
> -    while (1) {
> -
> -	my ($min, $hour, $mday, $mon, $year, $wday);
> -	my $startofday;
> -
> -	if ($utc) {
> -	    (undef, $min, $hour, $mday, $mon, $year, $wday) = gmtime($last);
> -	    # gmtime and timegm interpret two-digit years differently
> -	    $year += 1900;
> -	    $startofday = timegm(0, 0, 0, $mday, $mon, $year);
> -	} else {
> -	    (undef, $min, $hour, $mday, $mon, $year, $wday) = localtime($last);
> -	    # localtime and timelocal interpret two-digit years differently
> -	    $year += 1900;
> -	    $startofday = timelocal(0, 0, 0, $mday, $mon, $year);
> -	}
> -
> -	$last = $startofday + $hour*3600 + $min*60;
> -
> -	my $check_dow = sub {
> -	    foreach my $d (@$dowspec) {
> -		return $last if $d == $wday;
> -		if ($d > $wday) {
> -		    return $startofday + ($d-$wday)*86400;
> -		}
> +    my $t = [$utc ? gmtime($last) : localtime($last)];
> +    $t->[0] = 0;     # we're not interested in seconds, actually
> +    $t->[5] += 1900; # real years for clarity
> +
> +    outer: for (my $i = 0; $i < 1000; ++$i) {
> +	my $wday = $t->[-1];

This should be $t->[6]; (Originally I had the result of localtime()
truncated to only the values I use in the time helpers above...)

> +	foreach my $d (@$dowspec) {
> +	    goto this_wday if $d == $wday;
> +	    if ($d > $wday) {
> +		$t->[0] = $t->[1] = $t->[2] = 0; # sec = min = hour = 0
> +		$t = time_add_days($t, $d - $wday);
> +		next outer;
>  	    }
> -	    return $startofday + (7-$wday)*86400; # start of next week
> -	};
> -
> -	if ((my $next = $check_dow->()) != $last) {
> -	    $last = $next;
> -	    next; # repeat
>  	}
> -
> -	my $check_hour = sub {
> -	    return $last if $hspec eq '*';
> -	    foreach my $h (@$hspec) {
> -		return $last if $h == $hour;
> -		if ($h > $hour) {
> -		    return $startofday + $h*3600;
> -		}
> +	# Test next week:
> +	$t->[0] = $t->[1] = $t->[2] = 0; # sec = min = hour = 0
> +	$t = time_add_days($t, 7 - $wday);
> +	next outer;
> +    this_wday:
> +
> +	goto this_hour if $hspec eq '*';
> +	my $hour = $t->[2];
> +	foreach my $h (@$hspec) {
> +	    goto this_hour if $h == $hour;
> +	    if ($h > $hour) {
> +		$t->[0] = $t->[1] = 0; # sec = min = 0
> +		$t->[2] = $h;          # hour = $h
> +		next outer;
>  	    }
> -	    return $startofday + 24*3600; # test next day
> -	};
> -
> -	if ((my $next = $check_hour->()) != $last) {
> -	    $last = $next;
> -	    next; # repeat
>  	}
> -
> -	my $check_minute = sub {
> -	    return $last if $mspec eq '*';
> -	    foreach my $m (@$mspec) {
> -		return $last if $m == $min;
> -		if ($m > $min) {
> -		    return $startofday +$hour*3600 + $m*60;
> -		}
> +	# Test next day:
> +	$t->[0] = $t->[1] = $t->[2] = 0; # sec = min = hour = 0
> +	$t = time_add_days($t, 1);
> +	next outer;
> +    this_hour:
> +
> +	goto this_min if $mspec eq '*';
> +	my $min = $t->[1];
> +	foreach my $m (@$mspec) {
> +	    goto this_min if $m == $min;
> +	    if ($m > $min) {
> +		$t->[0] = 0;  # sec = 0
> +		$t->[1] = $m; # min = $m
> +		next outer;
>  	    }
> -	    return $startofday + ($hour + 1)*3600; # test next hour
> -	};
> -
> -	if ((my $next = $check_minute->()) != $last) {
> -	    $last = $next;
> -	    next; # repeat
> -	} else {
> -	    return $last;
>  	}
> +	# Test next hour:
> +	$t->[0] = $t->[1] = 0; # sec = min = hour = 0
> +	$t->[2]++;
> +	$t = wrap_time($t);
> +	next outer;
> +    this_min:
> +
> +	return $utc ? timegm(@$t) : timelocal(@$t);
>      }
>  
>      die "unable to compute next calendar event\n";
> -- 
> 2.11.0
> 
> 
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