Bug #79698 [Opn]: timelib mishandles future timestamps (triggered by 'zic -b slim')

From: Date: Sat, 13 Jun 2020 20:03:03 +0000
Subject: Bug #79698 [Opn]: timelib mishandles future timestamps (triggered by 'zic -b slim')
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Edit report at https://bugs.php.net/bug.php?id=79698&edit=1

 ID:                 79698
 Updated by:         nikic@php.net
 Reported by:        eggert at cs dot ucla dot edu
 Summary:            timelib mishandles future timestamps (triggered by
                     'zic -b slim')
 Status:             Open
 Type:               Bug
 Package:            Date/time related
 Operating System:   any
 PHP Version:        7.4.7
 Block user comment: N
 Private report:     N

 New Comment:

Can you please report this issue upstream at https://github.com/derickr/timelib/issues?


Previous Comments:
------------------------------------------------------------------------
[2020-06-13 20:00:27] eggert at cs dot ucla dot edu

Description:
------------
Since tzdb 2019b, the 'zic' command has had a '-b slim' option that generates
smaller-but-equivalent TZif files, intended to save memory/cache/whatever. These files conform to
the TZif format specified in Internet RFC 8536 and are supported by tzcode, glibc, etc. and '-b
slim' is intended to be the default in future tzdb releases. However, some current PHP timelib
test cases fail with slim TZif files.

This mishandling seems to occur because timelib gets confused about timestamps after the last
explicit transition in a TZif file. For example, 'zic -b slim' generates a TZif file
Europe/Amsterdam where the last explicit transition is on 1996-03-31 and transitions thereafter are
deduced from the "CET-1CEST,M3.5.0,M10.5.0/3" string embedded at the end of the TZif file.
The test case decoding 2008-03-30 01:00:00 fails, I expect because this timestamp is after the last
explicit transition.

If my guess is right, timelib also mishandles timestamps past the last explicit transition even in
traditional "fat" TZif files. For example, since the last transition in a traditional
Europe/Amsterdam file is 2037-10-25 I would expect timelib to mishandle some timestamps after that.

As the '-b slim' option becomes more popular this problem will affect PHP even for past
and current timestamps, so the bug needs to be fixed sooner than 2038.

Test script:
---------------
#!/bin/sh
# This assumes a typical GNU/Linux host.

wget https://data.iana.org/time-zones/releases/tzdb-2020a.tar.lz
tar xf tzdb-2020a.tar.lz
cd tzdb-2020a
make
make ZFLAGS='-b slim' posix_only  # This needs root privileges!
cd ..

git clone https://github.com/derickr/timelib.git
cd timelib
make test

Expected result:
----------------
I expect all tests in 'make test' to succeed.

Actual result:
--------------
Most tests succeed, but I see the following failures:

transition.render
FAIL | 2008-03-30 02:00:00 CEST Europe/Amsterdam | 1206835200 (Europe/Amsterdam) 
EXP  = 2008-03-30 01:00:00 CET Europe/Amsterdam
FAIL | 2008-03-30 02:59:59 CEST Europe/Amsterdam | 1206838799 (Europe/Amsterdam) 
EXP  = 2008-03-30 01:59:59 CET Europe/Amsterdam
...

render.render
...
FAIL | 2005-10-30 03:00:00 CEST Europe/Oslo | 1130634000 (Europe/Oslo) 
EXP  = 2005-10-30 02:00:00 CET Europe/Oslo
...
FAIL | 2005-10-30 03:00:00 CEST Europe/Amsterdam | 1130634000 (Europe/Amsterdam) 
EXP  = 2005-10-30 02:00:00 CET Europe/Amsterdam
FAIL | 2005-10-30 04:00:00 CEST Europe/Amsterdam | 1130637600 (Europe/Amsterdam) 
EXP  = 2005-10-30 03:00:00 CET Europe/Amsterdam
FAIL | 2005-10-30 05:00:00 CEST Europe/Amsterdam | 1130641200 (Europe/Amsterdam) 
EXP  = 2005-10-30 04:00:00 CET Europe/Amsterdam



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