ezic

ezic is a native erlang library for working with timezones. It parses the Olson timezone database files, allowing native erlang timezone lookup and zone conversions without the use of shell commands or a UNIX system.

See the tz database page for more information about the Olson database.

Purpose

Erlang/OTP didn't have a native timezone library, so I wrote ezic to fill that void.

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 about it

ezic doesn't have these problems. ezic is, however, a young project with who-knows-how-many problems of its own.

API

• ezic:localtime(TimeZone) -> datetime()
• ezic:utc_to_local(universal_datetime(), TimeZone) -> local_datetime()
• ezic:local_to_utc(local_datetime(), TimeZone) -> universal_datetime()

Example Setup

# setup your local environment
mkdir -p priv/tzdata

# download the timezone data files
wget 'ftp://ftp.iana.org/tz/tzdata-latest.tar.gz'
tar -xvzf tzdata-latest.tar.gz -C priv/tzdata

# remove a few troublesome files
cd priv/tzdata
rm *.sh *.gz *.tab factory Makefile

# build and run ezic
cd -
make all run
1> application:start(ezic).
2> ezic:localtime("Australia/Adelaide").

Static Analysis (Prisma .pplt)

Starting with version 0.2.5, the Hex package ships a pre-built Prisma Persistent Lookup Table (ezic_0.2.6.pplt) covering all 479 modules (ezic core modules and generated IANA timezone modules).

When ezic is used as a dependency in a project checked with rebar3 prisma or mix prisma, Prisma automatically loads the shipped .pplt file from the package root instead of re-analyzing all 479 BEAM modules from scratch.

To rebuild the .pplt file locally after modifying ezic:

rebar3 prisma build

See the ezic case study & benchmark for more details.

License

This project is in 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.

Acknowledgements

A big thanks to ezic's contributors:

• lsowen
• jrgdiz
• arkdro
• amasyura
• manuel-rubio
• danielribes

The decision to release this into the public domain was inspired by the (anti-) license of the SQLite project.