zoneinfo-parse

Rust library for reading the text files comprising the zoneinfo database, which records time zone changes and offsets across the world from multiple sources.

The zoneinfo database is distributed in one of two formats: a raw text format with one file per continent, and a compiled binary format with one file per time zone. This crate deals with the former; for the latter, see the zoneinfo_compiled crate instead.

The database itself is maintained by IANA. For more information, see IANA’s page on the time zone database. You can also find the text files themselves in the tz repository.

View the Rustdoc

Format

The zoneinfo files contains Zone, Rule, and Link information. Each type of line forms a variant in the line::Line enum.

To get started, here are a few lines representing what time is like in the Europe/Madrid time zone:

# Zone      NAME            GMTOFF  RULES   FORMAT  [UNTIL]
Zone        Europe/Madrid   -0:14:44 -      LMT     1901 Jan  1  0:00s
                             0:00   Spain   WE%sT   1946 Sep 30
                             1:00   Spain   CE%sT   1979
                             1:00   EU      CE%sT

The first line is a comment. The second starts with Zone, so we know

So parsing these five lines would return the five following results:

• A line::Line::Space for the comment, because the line doesn’t contain any information (but isn’t strictly invalid either).
• A line::Line::Zone for the first Zone entry. This contains a Zone struct that holds the name of the zone. All the other fields are stored in the ZoneInfo struct.
• A line::Line::Continuation for the next entry. This is different from the line above as it doesn’t contain a name field; it only has the information in a ZoneInfo struct.
• The fourth line contains the same types of data as the third.
• As does the fifth.

Lines with rule definitions look like this:

# Rule      NAME    FROM    TO      TYPE    IN      ON      AT      SAVE    LETTER/S
Rule        Spain   1917    only    -       May      5      23:00s  1:00    S
Rule        Spain   1917    1919    -       Oct      6      23:00s  0       -
Rule        Spain   1918    only    -       Apr     15      23:00s  1:00    S
Rule        Spain   1919    only    -       Apr      5      23:00s  1:00    S

All these lines follow the same pattern: A line::Line::Rule that contains a Rule struct, which has a field for each column of data.

Finally, there are lines that link one zone to another’s name:

Link   Europe/Prague   Europe/Bratislava

The Link struct simply contains the names of both the existing and new time zones.

Interpretation

Once the input lines have been parsed, they must be interpreted to form a table of time zone data.

The easiest way to do this is with a TableBuilder. You can add various lines to the builder, and it will throw an error as soon as it detects that something’s wrong, such as a duplicate or a missing entry. When all the lines have been fed to the builder, you can use the build method to produce a Table containing fields for the rule, zone, and link lines.

Example program

This crate is used to produce the data for the zoneinfo-data crate. For an example of its use, see the bundled data crate builder.