ZeroTierOne/zeroidc/vendor/chrono/README.md

Chrono: Date and Time for Rust

It aims to be a feature-complete superset of the time library. In particular,

• Chrono strictly adheres to ISO 8601.
• Chrono is timezone-aware by default, with separate timezone-naive types.
• Chrono is space-optimal and (while not being the primary goal) reasonably efficient.

There were several previous attempts to bring a good date and time library to Rust, which Chrono builds upon and should acknowledge:

• Initial research on the wiki
• Dietrich Epp's datetime-rs
• Luis de Bethencourt's rust-datetime

Any significant changes to Chrono are documented in the CHANGELOG.md file.

Usage

Put this in your Cargo.toml:

[dependencies]
chrono = "0.4"

Features

Chrono supports various runtime environments and operating systems, and has several features that may be enabled or disabled.

Default features:

• alloc: Enable features that depend on allocation (primarily string formatting)
• std: Enables functionality that depends on the standard library. This is a superset of alloc and adds interoperation with standard library types and traits.
• clock: enables reading the system time (now), independent of whether std::time::SystemTime is present, depends on having a libc.

Optional features:

• wasmbind: Enable integration with wasm-bindgen and its js-sys project
• serde: Enable serialization/deserialization via serde.
• unstable-locales: Enable localization. This adds various methods with a _localized suffix. The implementation and API may change or even be removed in a patch release. Feedback welcome.

See the cargo docs for examples of specifying features.

Overview

Duration

Chrono currently uses its own [Duration] type to represent the magnitude of a time span. Since this has the same name as the newer, standard type for duration, the reference will refer this type as OldDuration.

Note that this is an "accurate" duration represented as seconds and nanoseconds and does not represent "nominal" components such as days or months.

When the oldtime feature is enabled, [Duration] is an alias for the time::Duration type from v0.1 of the time crate. time v0.1 is deprecated, so new code should disable the oldtime feature and use the chrono::Duration type instead. The oldtime feature is enabled by default for backwards compatibility, but future versions of Chrono are likely to remove the feature entirely.

Chrono does not yet natively support the standard Duration type, but it will be supported in the future. Meanwhile you can convert between two types with Duration::from_std and Duration::to_std methods.

Date and Time

Chrono provides a DateTime type to represent a date and a time in a timezone.

For more abstract moment-in-time tracking such as internal timekeeping that is unconcerned with timezones, consider time::SystemTime, which tracks your system clock, or time::Instant, which is an opaque but monotonically-increasing representation of a moment in time.

DateTime is timezone-aware and must be constructed from the TimeZone object, which defines how the local date is converted to and back from the UTC date. There are three well-known TimeZone implementations:

• Utc specifies the UTC time zone. It is most efficient.

• Local specifies the system local time zone.

• FixedOffset specifies an arbitrary, fixed time zone such as UTC+09:00 or UTC-10:30. This often results from the parsed textual date and time. Since it stores the most information and does not depend on the system environment, you would want to normalize other TimeZones into this type.

DateTimes with different TimeZone types are distinct and do not mix, but can be converted to each other using the DateTime::with_timezone method.

You can get the current date and time in the UTC time zone (Utc::now()) or in the local time zone (Local::now()).

use chrono::prelude::*;

let utc: DateTime<Utc> = Utc::now();       // e.g. `2014-11-28T12:45:59.324310806Z`
let local: DateTime<Local> = Local::now(); // e.g. `2014-11-28T21:45:59.324310806+09:00`

Alternatively, you can create your own date and time. This is a bit verbose due to Rust's lack of function and method overloading, but in turn we get a rich combination of initialization methods.

use chrono::prelude::*;
use chrono::offset::LocalResult;

let dt = Utc.ymd(2014, 7, 8).and_hms(9, 10, 11); // `2014-07-08T09:10:11Z`
// July 8 is 188th day of the year 2014 (`o` for "ordinal")
assert_eq!(dt, Utc.yo(2014, 189).and_hms(9, 10, 11));
// July 8 is Tuesday in ISO week 28 of the year 2014.
assert_eq!(dt, Utc.isoywd(2014, 28, Weekday::Tue).and_hms(9, 10, 11));

let dt = Utc.ymd(2014, 7, 8).and_hms_milli(9, 10, 11, 12); // `2014-07-08T09:10:11.012Z`
assert_eq!(dt, Utc.ymd(2014, 7, 8).and_hms_micro(9, 10, 11, 12_000));
assert_eq!(dt, Utc.ymd(2014, 7, 8).and_hms_nano(9, 10, 11, 12_000_000));

// dynamic verification
assert_eq!(Utc.ymd_opt(2014, 7, 8).and_hms_opt(21, 15, 33),
           LocalResult::Single(Utc.ymd(2014, 7, 8).and_hms(21, 15, 33)));
assert_eq!(Utc.ymd_opt(2014, 7, 8).and_hms_opt(80, 15, 33), LocalResult::None);
assert_eq!(Utc.ymd_opt(2014, 7, 38).and_hms_opt(21, 15, 33), LocalResult::None);

// other time zone objects can be used to construct a local datetime.
// obviously, `local_dt` is normally different from `dt`, but `fixed_dt` should be identical.
let local_dt = Local.ymd(2014, 7, 8).and_hms_milli(9, 10, 11, 12);
let fixed_dt = FixedOffset::east(9 * 3600).ymd(2014, 7, 8).and_hms_milli(18, 10, 11, 12);
assert_eq!(dt, fixed_dt);

Various properties are available to the date and time, and can be altered individually. Most of them are defined in the traits Datelike and Timelike which you should use before. Addition and subtraction is also supported. The following illustrates most supported operations to the date and time:

use chrono::prelude::*;
use chrono::Duration;

// assume this returned `2014-11-28T21:45:59.324310806+09:00`:
let dt = FixedOffset::east(9*3600).ymd(2014, 11, 28).and_hms_nano(21, 45, 59, 324310806);

// property accessors
assert_eq!((dt.year(), dt.month(), dt.day()), (2014, 11, 28));
assert_eq!((dt.month0(), dt.day0()), (10, 27)); // for unfortunate souls
assert_eq!((dt.hour(), dt.minute(), dt.second()), (21, 45, 59));
assert_eq!(dt.weekday(), Weekday::Fri);
assert_eq!(dt.weekday().number_from_monday(), 5); // Mon=1, ..., Sun=7
assert_eq!(dt.ordinal(), 332); // the day of year
assert_eq!(dt.num_days_from_ce(), 735565); // the number of days from and including Jan 1, 1

// time zone accessor and manipulation
assert_eq!(dt.offset().fix().local_minus_utc(), 9 * 3600);
assert_eq!(dt.timezone(), FixedOffset::east(9 * 3600));
assert_eq!(dt.with_timezone(&Utc), Utc.ymd(2014, 11, 28).and_hms_nano(12, 45, 59, 324310806));

// a sample of property manipulations (validates dynamically)
assert_eq!(dt.with_day(29).unwrap().weekday(), Weekday::Sat); // 2014-11-29 is Saturday
assert_eq!(dt.with_day(32), None);
assert_eq!(dt.with_year(-300).unwrap().num_days_from_ce(), -109606); // November 29, 301 BCE

// arithmetic operations
let dt1 = Utc.ymd(2014, 11, 14).and_hms(8, 9, 10);
let dt2 = Utc.ymd(2014, 11, 14).and_hms(10, 9, 8);
assert_eq!(dt1.signed_duration_since(dt2), Duration::seconds(-2 * 3600 + 2));
assert_eq!(dt2.signed_duration_since(dt1), Duration::seconds(2 * 3600 - 2));
assert_eq!(Utc.ymd(1970, 1, 1).and_hms(0, 0, 0) + Duration::seconds(1_000_000_000),
           Utc.ymd(2001, 9, 9).and_hms(1, 46, 40));
assert_eq!(Utc.ymd(1970, 1, 1).and_hms(0, 0, 0) - Duration::seconds(1_000_000_000),
           Utc.ymd(1938, 4, 24).and_hms(22, 13, 20));

Formatting and Parsing

Formatting is done via the format method, which format is equivalent to the familiar strftime format.

See format::strftime documentation for full syntax and list of specifiers.

The default to_string method and {:?} specifier also give a reasonable representation. Chrono also provides to_rfc2822 and to_rfc3339 methods for well-known formats.

Chrono now also provides date formatting in almost any language without the help of an additional C library. This functionality is under the feature unstable-locales:

chrono { version = "0.4", features = ["unstable-locales"]

The unstable-locales feature requires and implies at least the alloc feature.

use chrono::prelude::*;

let dt = Utc.ymd(2014, 11, 28).and_hms(12, 0, 9);
assert_eq!(dt.format("%Y-%m-%d %H:%M:%S").to_string(), "2014-11-28 12:00:09");
assert_eq!(dt.format("%a %b %e %T %Y").to_string(), "Fri Nov 28 12:00:09 2014");
assert_eq!(dt.format_localized("%A %e %B %Y, %T", Locale::fr_BE).to_string(), "vendredi 28 novembre 2014, 12:00:09");
assert_eq!(dt.format("%a %b %e %T %Y").to_string(), dt.format("%c").to_string());

assert_eq!(dt.to_string(), "2014-11-28 12:00:09 UTC");
assert_eq!(dt.to_rfc2822(), "Fri, 28 Nov 2014 12:00:09 +0000");
assert_eq!(dt.to_rfc3339(), "2014-11-28T12:00:09+00:00");
assert_eq!(format!("{:?}", dt), "2014-11-28T12:00:09Z");

// Note that milli/nanoseconds are only printed if they are non-zero
let dt_nano = Utc.ymd(2014, 11, 28).and_hms_nano(12, 0, 9, 1);
assert_eq!(format!("{:?}", dt_nano), "2014-11-28T12:00:09.000000001Z");

Parsing can be done with three methods:

1. The standard FromStr trait (and parse method on a string) can be used for parsing DateTime<FixedOffset>, DateTime<Utc> and DateTime<Local> values. This parses what the {:?} (std::fmt::Debug) format specifier prints, and requires the offset to be present.

2. DateTime::parse_from_str parses a date and time with offsets and returns DateTime<FixedOffset>. This should be used when the offset is a part of input and the caller cannot guess that. It cannot be used when the offset can be missing. DateTime::parse_from_rfc2822 and DateTime::parse_from_rfc3339 are similar but for well-known formats.

3. Offset::datetime_from_str is similar but returns DateTime of given offset. When the explicit offset is missing from the input, it simply uses given offset. It issues an error when the input contains an explicit offset different from the current offset.

More detailed control over the parsing process is available via format module.

use chrono::prelude::*;

let dt = Utc.ymd(2014, 11, 28).and_hms(12, 0, 9);
let fixed_dt = dt.with_timezone(&FixedOffset::east(9*3600));

// method 1
assert_eq!("2014-11-28T12:00:09Z".parse::<DateTime<Utc>>(), Ok(dt.clone()));
assert_eq!("2014-11-28T21:00:09+09:00".parse::<DateTime<Utc>>(), Ok(dt.clone()));
assert_eq!("2014-11-28T21:00:09+09:00".parse::<DateTime<FixedOffset>>(), Ok(fixed_dt.clone()));

// method 2
assert_eq!(DateTime::parse_from_str("2014-11-28 21:00:09 +09:00", "%Y-%m-%d %H:%M:%S %z"),
           Ok(fixed_dt.clone()));
assert_eq!(DateTime::parse_from_rfc2822("Fri, 28 Nov 2014 21:00:09 +0900"),
           Ok(fixed_dt.clone()));
assert_eq!(DateTime::parse_from_rfc3339("2014-11-28T21:00:09+09:00"), Ok(fixed_dt.clone()));

// method 3
assert_eq!(Utc.datetime_from_str("2014-11-28 12:00:09", "%Y-%m-%d %H:%M:%S"), Ok(dt.clone()));
assert_eq!(Utc.datetime_from_str("Fri Nov 28 12:00:09 2014", "%a %b %e %T %Y"), Ok(dt.clone()));

// oops, the year is missing!
assert!(Utc.datetime_from_str("Fri Nov 28 12:00:09", "%a %b %e %T %Y").is_err());
// oops, the format string does not include the year at all!
assert!(Utc.datetime_from_str("Fri Nov 28 12:00:09", "%a %b %e %T").is_err());
// oops, the weekday is incorrect!
assert!(Utc.datetime_from_str("Sat Nov 28 12:00:09 2014", "%a %b %e %T %Y").is_err());

Again : See format::strftime documentation for full syntax and list of specifiers.

Conversion from and to EPOCH timestamps

Use Utc.timestamp(seconds, nanoseconds) to construct a DateTime<Utc> from a UNIX timestamp (seconds, nanoseconds that passed since January 1st 1970).

Use DateTime.timestamp to get the timestamp (in seconds) from a DateTime. Additionally, you can use DateTime.timestamp_subsec_nanos to get the number of additional number of nanoseconds.

// We need the trait in scope to use Utc::timestamp().
use chrono::{DateTime, TimeZone, Utc};

// Construct a datetime from epoch:
let dt = Utc.timestamp(1_500_000_000, 0);
assert_eq!(dt.to_rfc2822(), "Fri, 14 Jul 2017 02:40:00 +0000");

// Get epoch value from a datetime:
let dt = DateTime::parse_from_rfc2822("Fri, 14 Jul 2017 02:40:00 +0000").unwrap();
assert_eq!(dt.timestamp(), 1_500_000_000);

Individual date

Chrono also provides an individual date type (Date). It also has time zones attached, and have to be constructed via time zones. Most operations available to DateTime are also available to Date whenever appropriate.

use chrono::prelude::*;
use chrono::offset::LocalResult;

assert_eq!(Utc::today(), Utc::now().date());
assert_eq!(Local::today(), Local::now().date());

assert_eq!(Utc.ymd(2014, 11, 28).weekday(), Weekday::Fri);
assert_eq!(Utc.ymd_opt(2014, 11, 31), LocalResult::None);
assert_eq!(Utc.ymd(2014, 11, 28).and_hms_milli(7, 8, 9, 10).format("%H%M%S").to_string(),
           "070809");

There is no timezone-aware Time due to the lack of usefulness and also the complexity.

DateTime has date method which returns a Date which represents its date component. There is also a time method, which simply returns a naive local time described below.

Naive date and time

Chrono provides naive counterparts to Date, (non-existent) Time and DateTime as NaiveDate, NaiveTime and NaiveDateTime respectively.

They have almost equivalent interfaces as their timezone-aware twins, but are not associated to time zones obviously and can be quite low-level. They are mostly useful for building blocks for higher-level types.

Timezone-aware DateTime and Date types have two methods returning naive versions: naive_local returns a view to the naive local time, and naive_utc returns a view to the naive UTC time.

Limitations

Only proleptic Gregorian calendar (i.e. extended to support older dates) is supported. Be very careful if you really have to deal with pre-20C dates, they can be in Julian or others.

Date types are limited in about +/- 262,000 years from the common epoch. Time types are limited in the nanosecond accuracy.

Leap seconds are supported in the representation but Chrono doesn't try to make use of them. (The main reason is that leap seconds are not really predictable.) Almost every operation over the possible leap seconds will ignore them. Consider using NaiveDateTime with the implicit TAI (International Atomic Time) scale if you want.

Chrono inherently does not support an inaccurate or partial date and time representation. Any operation that can be ambiguous will return None in such cases. For example, "a month later" of 2014-01-30 is not well-defined and consequently Utc.ymd(2014, 1, 30).with_month(2) returns None.

Non ISO week handling is not yet supported. For now you can use the chrono_ext crate (sources).

Advanced time zone handling is not yet supported. For now you can try the Chrono-tz crate instead.