329f699e51
Time comparisons are patently wrong. They do not consider s/w/u/g/z time modifiers, so the comparisons can be off by hours. At least 24 hours within any time or zone change, ezic will give unreliable results. I think a solution can involve "flattening" the data, starting from the earliest time possible for each zone/rule, going forward. There exist ambiguous local times for zones and rules. For example, on Nov 7th, in Los Angeles, the times from 1:00:00am to 1:59:59am were repeated, once for PDT and once for PST. Given a local time in that zone between those times, we cannot determine what UTC time is unambiguously. Similar for Zone transitions where fall-back occurs.
2.6 KiB
ezic
ezic is a set of erlang utilities for the Olsen timezone database files. See the tz database page for more information.
Status
2010.11.07
- The time comparisons don't consider time relativity, so they're plain wrong. Within at least 24 hours of timechange or zone change, the results cannot be trusted.
2010.11.04
- ezic is "apparently functional". It has been tested very lightly, a bit by unit tests, but mostly by inspection. It's probably not fit for production use.
License
I have dedicated this work to the public domain. Anyone is free to copy, modify, publish, use, compile, sell, or distribute the original code, either in source code form or as a compiled binary, for any purpose, commercial or non-commercial, and by any means.
Contributed Code
To maintain ezic's status as a public domain work, all contributions must also be dedicated to the public domain.
API
ezic:localtime(TimeZone) -> datetime()ezic:utc_to_time(universal_datetime(), TimeZone) -> local_datetime()ezic:utc_from_time(local_datetime(), TimeZone) -> universal_datetime()ezic:zone_convert(from_datetime(), TimeZoneFrom, TimeZoneTo) -> to_datetime()
Admin API
ezic:load("/path/to/tzdata") -> ok
Setup
# download the timezone data files
wget 'ftp://elsie.nci.nih.gov/pub/tzdata*.tar.gz'
tar -xvzf tzdata*.tar.gz -C /path/to/tzdata
# remove a few troublesome files
cd /path/to/tzdata
rm *.sh *.tab factory
# build and run ezic
make all run
1> ezic:load("/path/to/tzdata").
2> ezic:localtime("Australia/Adelaide").
Purpose
Erlang/OTP doesn't have a timezone library, so I decided to write one.
The recommended way of handling timezones in erlang involves setting the system environment variable TZ to the desired timezone, then calling erlang time functions. As far as I can tell, this technique has a few key issues:
- it only works on *nix systems,
- it depends on your system's timezone data (preventing custom timezone hackery), and
- you can create race conditions if you aren't careful
ezic doesn't have these problems. ezic is, however, a young project with who-knows-how-many problems of its own ;)
Acknowledgements
I was inspired by the (anti-) license of the SQLite project in my decision to release this into the public domain.