Jiff

Jiff is a datetime library for Rust that encourages you to jump into the pit of success. The focus of this library is providing high level datetime primitives that are difficult to misuse and have reasonable performance. Jiff supports automatic and seamless integration with the Time Zone Database, DST aware arithmetic and rounding, formatting and parsing zone aware datetimes losslessly, opt-in Serde support and a whole lot more.

Jiff takes enormous inspiration from Temporal, which is a TC39 proposal to improve datetime handling in JavaScript.

Dual-licensed under MIT or the UNLICENSE.

Documentation

• API documentation on docs.rs
• Comparison with chrono, time, hifitime and icu
• The API design rationale for Jiff
• Platform support
• CHANGELOG

Example

Here is a quick example that shows how to parse a typical RFC 3339 instant, convert it to a zone aware datetime, add a span of time and losslessly print it:

use jiff::{Timestamp, ToSpan};

fn main() -> Result<(), jiff::Error> {
    let time: Timestamp = "2024-07-11T01:14:00Z".parse()?;
    let zoned = time.in_tz("America/New_York")?.checked_add(1.month().hours(2))?;
    assert_eq!(zoned.to_string(), "2024-08-10T23:14:00-04:00[America/New_York]");
    // Or, if you want an RFC3339 formatted string:
    assert_eq!(zoned.timestamp().to_string(), "2024-08-11T03:14:00Z");
    Ok(())
}

There are many more examples in the documentation.

Usage

Jiff is on crates.io and can be used by adding jiff to your dependencies in your project's Cargo.toml. Or more simply, just run cargo add jiff.

Here is a complete example that creates a new Rust project, adds a dependency on jiff, creates the source code for a simple datetime program and then runs it.

First, create the project in a new directory:

$ cargo new jiff-example
$ cd jiff-example

Second, add a dependency on jiff:

$ cargo add jiff

Third, edit src/main.rs. Delete what's there and replace it with this:

use jiff::{Unit, Zoned};

fn main() -> Result<(), jiff::Error> {
    let now = Zoned::now().round(Unit::Second)?;
    println!("{now}");
    Ok(())
}

Fourth, run it with cargo run:

$ cargo run
   Compiling jiff v0.2.0 (/home/andrew/rust/jiff)
   Compiling jiff-play v0.2.0 (/home/andrew/tmp/scratch/rust/jiff-play)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.37s
     Running `target/debug/jiff-play`
2024-07-10T19:54:20-04:00[America/New_York]

The first time you run the program will show more output like above. But subsequent runs shouldn't have to re-compile the dependencies.

Crate features

Jiff has several crate features for customizing support for Rust's standard library, serde support and whether to embed a copy of the Time Zone Database into your binary.

The "crate features" section of the documentation lists the full set of supported features.

Future plans

With jiff 0.2 out about 6 months after the jiff 0.1 initial release, my plan remains roughly the same as it started. That is, I'd still like to get a jiff 1.0 release out this summer 2025 (in about 6 months) and then commit to it indefinitely. This plan may change if something critically wrong is found with the current API.

The purpose of this plan is to get Jiff to a 1.0 stable state as quickly as possible. The reason is so that others feel comfortable relying on Jiff as a public dependency that won't cause ecosystem churn.

Performance

The most important design goal of Jiff is to be a high level datetime library that makes it hard to do the wrong thing. Second to that is performance. Jiff should have reasonable performance, but there are likely areas in which it could improve. See the bench directory for benchmarks.

Note that performance is still an important goal. Some aspects of Jiff have had optimization attention paid to them, but many still have not. It is a goal to improve where we can, but performance will generally come second to API comprehension and correctness.

Platform support

The question of platform support in the context of datetime libraries comes up primarily in relation to time zone support. Specifically:

• How should Jiff determine the time zone transitions for an IANA time zone identifier like Antarctica/Troll?
• How should Jiff determine the default time zone for the current system?

Both of these require some level of platform interaction.

For discovering time zone transition data, Jiff relies on the IANA Time Zone Database. On Unix systems, this is usually found at /usr/share/zoneinfo, although it can be configured via the TZDIR environment variable (which Jiff respects). On Windows, Jiff will automatically embed a copy of the time zone database into the compiled library.

For discovering the system time zone, Jiff reads /etc/localtime on Unix. On Windows, Jiff reads the Windows-specific time zone identifier via GetDynamicTimeZoneInformation and then maps it to an IANA time zone identifier via Unicode's CLDR XML data.

I expect Jiff to grow more support for other platforms over time. Please file issues, although I will likely be reliant on contributor pull requests for more obscure platforms that aren't easy for me to test.

For more on platform support, see PLATFORM.md.

Dependencies

At time of writing, it is no accident that Jiff has zero dependencies on Unix. In general, my philosophy on adding new dependencies in an ecosystem crate like Jiff is very conservative. I consider there to be two primary use cases for adding new dependencies:

1. When a dependency is practically required in order to interact with a platform. For example, windows-sys for discovering the system time zone on Windows.
2. When a dependency is necessary for inter-operability. For example, serde. But even here, I expect to be conservative, where I'm generally only willing to depend on things that have fewer breaking change releases than Jiff.

A secondary use case for new dependencies is if Jiff gets split into multiple crates. I did a similar thing for the regex crate for very compelling reasons. It is possible that will happen with Jiff as well, although there are no plans for that. And in general, I expect the number of crates to stay small, if only to make keep maintenance lightweight. (Managing lots of semver API boundaries has a lot of overhead in my experience.)

Minimum Rust version policy

This crate's minimum supported rustc version is 1.70.0.

The policy is that the minimum Rust version required to use this crate can be increased in minor version updates. For example, if jiff 1.0 requires Rust 1.20.0, then jiff 1.0.z for all values of z will also require Rust 1.20.0 or newer. However, jiff 1.y for y > 0 may require a newer minimum version of Rust.