Tzdata

Tzdata. The timezone database in Elixir.

Extracted from the Calendar library.

As of version 1.1.1 the tz release 2021e is included in the package.

When a new release is out, it will be automatically downloaded at runtime.

The tz release version in use can be verified with the following function:

iex> Tzdata.tzdata_version
"2021e"

Getting started

To use the Tzdata library with Elixir 1.8+, add it to the dependencies in your mix file:

defp deps do
  [  {:tzdata, "~> 1.1"},  ]
end

In your application you can choose to globally configure Elixir to use Tzdata. This can be done by putting the following line in the config file of your application:

config :elixir, :time_zone_database, Tzdata.TimeZoneDatabase

That's it!

That allows you to use the Elixir standard library to use Tzdata to do time zone calculations. One example is getting the current time in a certain time zone:

iex> DateTime.now("Europe/Copenhagen")
{:ok, #DateTime<2018-11-30 20:51:59.076524+01:00 CET Europe/Copenhagen>}

If you do not want Elixir to have a time zone database globally defined you can instead pass the module name Tzdata.TimeZoneDatabase directly to the functions that need a time zone database:

DateTime.now("Europe/Copenhagen", Tzdata.TimeZoneDatabase)

Data directory and releases

The library uses a file directory to store data. By default this directory is priv. In some cases you might want to use a different directory. For instance when using releases this is recommended. If so, create the directory and make sure Elixir can read and write to it. Then use elixir config files like this to tell Tzdata to use that directory:

config :tzdata, :data_dir, "/etc/elixir_tzdata_data"

Add the release_ets directory from priv to that directory containing the 20xxx.ets file that ships with this library.

For instance with this config: config :tzdata, :data_dir, "/etc/elixir_tzdata_data" an .ets file such as /etc/elixir_tzdata_data/release_ets/2017b.ets should be present.

Automatic data updates

By default Tzdata will poll for timezone database updates every day. In case new data is available, Tzdata will download it and use it.

This feature can be disabled with the following configuration:

config :tzdata, :autoupdate, :disabled

If the autoupdate setting is set to disabled, one has to manually put updated .ets files in the release_ets sub-dir of the "data_dir" (see the "Data directory and releases" section above). When IANA releases new versions of the time zone data, this Tzdata library can be used to generate a new .ets file containing the new data.

Changes from 0.1.x to 0.5.x

The 0.5.1+ versions uses ETS tables and automatically polls the IANA servers for updated data. When a new version of the timezone database is available, it is automatically downloaded and used.

For use with Calendar you can still specify tzdata ~> 0.1.7 in your mix.exs file in case you experience problems using version ~> 0.5.20

Hackney dependency and security

Tzdata depends on Hackney in order to do HTTPS requests to get new updates. This is done because Erlang's built in HTTP client httpc does not verify SSL certificates when doing HTTPS requests. Hackney verifies the certificate of IANA when getting new tzdata releases from IANA.