Chrono-TZ

Chrono-TZ is a library that provides implementors of the [TimeZone] trait for chrono. The impls are generated by a build script using the IANA database and [parse-zoneinfo].

Documentation

Documentation is hosted on docs.rs

Examples

Create a time in one timezone and convert it to UTC

use chrono::{TimeZone, Utc};
use chrono_tz::US::Pacific;

let pacific_time = Pacific.ymd(1990, 5, 6).and_hms(12, 30, 45);
let utc_time = pacific_time.with_timezone(&Utc);
assert_eq!(utc_time, Utc.ymd(1990, 5, 6).and_hms(19, 30, 45));

Create a naive datetime and convert it to a timezone-aware datetime

use chrono::{TimeZone, NaiveDate};
use chrono_tz::Africa::Johannesburg;

let naive_dt = NaiveDate::from_ymd(2038, 1, 19).and_hms(3, 14, 08);
let tz_aware = Johannesburg.from_local_datetime(&naive_dt).unwrap();
assert_eq!(tz_aware.to_string(), "2038-01-19 03:14:08 SAST");

London and New York change their clocks on different days in March so only have a 4-hour difference on certain days.

use chrono::TimeZone;
use chrono_tz::Europe::London;
use chrono_tz::America::New_York;

let london_time = London.ymd(2016, 3, 18).and_hms(3, 0, 0);
let ny_time = london_time.with_timezone(&New_York);
assert_eq!(ny_time, New_York.ymd(2016, 3, 17).and_hms(23, 0, 0));

You can get the raw offsets as well if you want to see the standard UTC offset as well as any special offsets in effect (such as DST) at a given time. Note that you need to import the OffsetComponents trait.

use chrono::{Duration, TimeZone};
use chrono_tz::Europe::London;
use chrono_tz::OffsetComponents;

let london_time = London.ymd(2016, 5, 10).and_hms(12, 0, 0);

// London typically has zero offset from UTC, but has a 1h adjustment forward
// when summer time is in effect.
assert_eq!(london_time.offset().base_utc_offset(), Duration::hours(0));
assert_eq!(london_time.offset().dst_offset(), Duration::hours(1));

Adding 24 hours across a daylight savings change causes a change in local time

use chrono::{TimeZone, Duration};
use chrono_tz::Europe::London;

let dt = London.ymd(2016, 10, 29).and_hms(12, 0, 0);
let later = dt + Duration::hours(24);
assert_eq!(later, London.ymd(2016, 10, 30).and_hms(11, 0, 0));

And of course you can always convert a local time to a unix timestamp

use chrono::TimeZone;
use chrono_tz::Asia::Kolkata;

let dt = Kolkata.ymd(2000, 1, 1).and_hms(0, 0, 0);
let timestamp = dt.timestamp();
assert_eq!(timestamp, 946665000);

Pretty-printing a string will use the correct abbreviation for the timezone

use chrono::TimeZone;
use chrono_tz::Europe::London;

let dt = London.ymd(2016, 5, 10).and_hms(12, 0, 0);
assert_eq!(dt.to_string(), "2016-05-10 12:00:00 BST");
assert_eq!(dt.to_rfc3339(), "2016-05-10T12:00:00+01:00");

You can convert a timezone string to a timezone using the FromStr trait

use chrono::TimeZone;
use chrono_tz::Tz;
use chrono_tz::UTC;

let tz: Tz = "Antarctica/South_Pole".parse().unwrap();
let dt = tz.ymd(2016, 10, 22).and_hms(12, 0, 0);
let utc = dt.with_timezone(&UTC);
assert_eq!(utc.to_string(), "2016-10-21 23:00:00 UTC");

no_std Support

To use this library without depending on the Rust standard library, put this in your Cargo.toml:

[dependencies]
chrono = { version = "0.4", default-features = false }
chrono-tz = { version = "0.5", default-features = false }

If you are using this library in an environment with limited program space, such as a microcontroller, take note that you will also likely need to enable optimizations and Link Time Optimization:

[profile.dev]
opt-level = 2
lto = true

[profile.release]
lto = true

Otherwise, the additional binary size added by this library may overflow available program space and trigger a linker error.

Limiting the Timezone Table to Zones of Interest

Chrono-tz by default generates timezones for all entries in the IANA database. If you are interested in only a few timezones you can use enable the filter-by-regex feature and set an environment variable to select them. The environment variable is called CHRONO_TZ_TIMEZONE_FILTER and is a regular expression. It should be specified in your top-level build:

CHRONO_TZ_TIMEZONE_FILTER="(Europe/London|US/.*)" cargo build

This can significantly reduce the size of the generated database, depending on how many timezones you are interested in. Wikipedia has an article listing the timezone names.

The filtering applied is liberal; if you use a pattern such as "US/.*" then chrono-tz will include all the zones that are linked, such as "America/Denver", not just "US/Mountain".

Developing

chrono-tz uses git submodules, so in order to build locally you will need to run git submodule init and git submodule update.

Future Improvements

• Handle leap seconds
• Handle Julian to Gregorian calendar transitions
• Load tzdata always from latest version
• Dynamic tzdata loading