Croner

Croner is a fully-featured, lightweight, and efficient Rust library designed for parsing and evaluating cron patterns.

This is the Rust flavor of the popular JavaScript/TypeScript cron parser croner.

Features

• Parse and evaluate cron expressions to calculate upcoming execution times.
• Follows POSIX/Vixie-cron standards, while extending it with additional specifiers such as L for the last day and weekday of the month, # for the nth weekday of the month, W for closest weekday to a day of month.
• Evaluate cron expressions across different time zones.
• Supports optional second granularity .with_seconds_optional or .with_seconds_required
• Supports optional alternative weekday mode to use Quartz-style weekdays instead of POSIX using with_alternative_weekdays
• Allows for flexible combination of DOM and DOW conditions, enabling patterns to match specific days of the week in specific weeks of the month or the closest weekday to a specific day.
• Compatible with chrono and (optionally) chrono-tz.
• Robust error handling.

Why croner instead of cron or saffron?

Croner combines the features of cron and saffron, while following the POSIX/Vixie "standards" for the relevant parts. See this table:

Feature	Croner	Cron	Saffron
Time Zones	X	X
Ranges (15-25)	X	X	X
Ranges with stepping (15-25/2)	X	X	X
L - Last day of month	X		X
5#L - Last occurrence of weekday	X	X
5L - Last occurrence of weekday	X	?	X
# - Nth occurrence of weekday	X		X
W - Closest weekday	X		X
"Standards"-compliant weekdays (1 is monday)	X
Five part patterns (minute granularity)	X		X
Six part patterns (second granularity)	X	X
Weekday/Month text representations	X	X	X
Aliases (@hourly etc.)	X	X
chrono DateTime compatibility	X	X	X
DOM-and-DOW option	X

Note Tests carried out at 2023-12-02 using cron@0.12.0 and saffron@.0.1.0

Getting Started

Prerequisites

Ensure you have Rust installed on your machine. If not, you can get it from the official Rust website.

Installation

Add croner to your Cargo.toml dependencies:

[dependencies]
croner = "2.0.6" # Adjust the version as necessary

Usage

Here's a quick example to get you started with matching current time, and finding the next occurrence. is_time_matching takes a chrono DateTime:

use croner::Cron;
use chrono::Local;

fn main() {

    // Parse cron expression
    let cron_all = Cron::new("18 * * * 5")
      .parse()
      .expect("Couldn't parse cron string");

    // Compare cron pattern with current local time
    let time = Local::now();
    let matches_all = cron_all.is_time_matching(&time).unwrap();

    // Get next match
    let next = cron_all.find_next_occurrence(&time, false).unwrap();

    // Output results
    println!("Time is: {}", time);
    println!("Pattern \"{}\" does {} time {}", cron_all.pattern.to_string(), if matches_all { "match" } else { "not match" }, time );
    println!("Pattern \"{}\" will match next time at {}", cron_all.pattern.to_string(), next);

}

To match against a non local timezone, croner supports zoned chrono DateTime's DateTime<Tz>. To use a named time zone, you can utilize the chrono-tz crate.

use croner::Cron;
use chrono::Local;
use chrono_tz::Tz;

fn main() {
    // Parse cron expression
    let cron = Cron::new("18 * * * 5")
      .parse()
      .expect("Couldn't parse cron string");

    // Choose a different time zone, for example America/New_York
    let est_timezone: Tz = "America/New_York".parse().expect("Invalid timezone");

    // Find the next occurrence in EST
    let time_est = Local::now().with_timezone(&est_timezone);
    let next_est = cron.find_next_occurrence(&time_est, false).unwrap();

    // Output results for EST
    println!("EST time is: {}", time_est);
    println!(
        "Pattern \"{}\" will match next time at (EST): {}",
        cron.pattern.to_string(),
        next_est
    );
}

This example demonstrates how to calculate the next 5 occurrences of New Year's Eve that fall on a Friday. We'll use a cron expression to match every Friday (FRI) in December (12) and use the with_dom_and_dow method to ensure both day of month and day of week conditions are met.

use croner::Cron;
use chrono::Local;

fn main() {
    // Parse cron expression for Fridays in December
    let cron = Cron::new("0 0 0 31 12 FRI")
      // Include seconds in pattern
      .with_seconds_optional()
      // Ensure both day of month and day of week conditions are met
      .with_dom_and_dow()
      .parse()
      .expect("Couldn't parse cron string");

    let time = Local::now();

    println!("Finding the next 5 New Year's Eves on a Friday:");
    for time in cron.iter_from(time).take(5) {
        println!("{}", time);
    }
}

Pattern

The expressions used by Croner are very similar to those of Vixie Cron, but with a few additions and changes as outlined below:

// ┌──────────────── (optional) second (0 - 59)
// │ ┌────────────── minute (0 - 59)
// │ │ ┌──────────── hour (0 - 23)
// │ │ │ ┌────────── day of month (1 - 31)
// │ │ │ │ ┌──────── month (1 - 12, JAN-DEC)
// │ │ │ │ │ ┌────── day of week (0 - 6, SUN-Mon)
// │ │ │ │ │ │       (0 to 6 are Sunday to Saturday; 7 is Sunday, the same as 0)
// │ │ │ │ │ │
// * * * * * *

• Croner expressions have the following additional modifiers:
  • ?: In the Rust version of croner, a questionmark behaves just as *, to allow for legacy cron patterns to be used.
  • L: The letter 'L' can be used in the day of the month field to indicate the last day of the month. When used in the day of the week field in conjunction with the # character, it denotes the last specific weekday of the month. For example, 5#L represents the last Friday of the month.
  • #: The # character specifies the "nth" occurrence of a particular day within a month. For example, supplying 5#2 in the day of week field signifies the second Friday of the month. This can be combined with ranges and supports day names. For instance, MON-FRI#2 would match the Monday through Friday of the second week of the month.
  • W: The character 'W' is used to specify the closest weekday to a given day in the day of the month field. For example, 15W will match the closest weekday to the 15th of the month. If the specified day falls on a weekend (Saturday or Sunday), the pattern will match the closest weekday before or after that date. For instance, if the 15th is a Saturday, 15W will match the 14th (Friday), and if the 15th is a Sunday, it will match the 16th (Monday).

Field	Required	Allowed values	Allowed special characters	Remarks
Seconds	Optional	0-59	* , - / ?
Minutes	Yes	0-59	* , - / ?
Hours	Yes	0-23	* , - / ?
Day of Month	Yes	1-31	* , - / ? L W
Month	Yes	1-12 or JAN-DEC	* , - / ?
Day of Week	Yes	0-7 or SUN-MON	* , - / ? # L	0 to 6 are Sunday to Saturday 7 is Sunday, the same as 0 # is used to specify nth occurrence of a weekday

Note Weekday and month names are case-insensitive. Both MON and mon work. When using L in the Day of Week field, it affects all specified weekdays. For example, 5-6#L means the last Friday and Saturday in the month." The # character can be used to specify the "nth" weekday of the month. For example, 5#2 represents the second Friday of the month.

It is also possible to use the following "nicknames" as pattern.

Nickname	Description
@yearly	Run once a year, ie. "0 0 1 1 *".
@annually	Run once a year, ie. "0 0 1 1 *".
@monthly	Run once a month, ie. "0 0 1 * *".
@weekly	Run once a week, ie. "0 0 * * 0".
@daily	Run once a day, ie. "0 0 * * *".
@hourly	Run once an hour, ie. "0 * * * *".

Configuration

Croner offers several configuration methods to change how patterns are interpreted:

1. with_seconds_optional()

This method enables the inclusion of seconds in the cron pattern, but it's not mandatory. By using this method, you can create cron patterns that either include or omit the seconds field. This offers greater flexibility, allowing for more precise scheduling without imposing the strict requirement of defining seconds in every pattern.

Example Usage:

let cron = Cron::new("*/10 * * * * *") // Every 10 seconds
    .with_seconds_optional()
    .parse()
    .expect("Invalid cron pattern");

2. with_seconds_required()

In contrast to with_seconds_optional(), the with_seconds_required() method requires the seconds field in every cron pattern. This enforces a high level of precision in task scheduling, ensuring that every pattern explicitly specifies the second at which the task should run.

Example Usage:

let cron = Cron::new("5 */2 * * * *") // At 5 seconds past every 2 minutes
    .with_seconds_required()
    .parse()
    .expect("Invalid cron pattern");

3. with_dom_and_dow()

This method enables the combination of Day of Month (DOM) and Day of Week (DOW) conditions in your cron expressions. It's particularly useful for creating schedules that require specificity in terms of both the day of the month and the day of the week, such as running a task when the first of the month is a Monday, or christmas day is on a friday.

Example Usage:

let cron = Cron::new("0 0 25 * FRI") // When christmas day is on a friday
    .with_dom_and_dow()
    .parse()
    .expect("Invalid cron pattern");

4. with_alternative_weekdays() (Quartz mode)

This configuration method switches the weekday mode from the POSIX standard to the Quartz-style, commonly used in Java-based scheduling systems. It's useful for those who are accustomed to Quartz's way of specifying weekdays or for ensuring compatibility with existing Quartz-based schedules.

Example Usage:

let cron = Cron::new("0 0 12 * * 6") // Every Friday (denoted with 6 in Quartz mode) at noon
    .with_alternative_weekdays()
    .parse()
    .expect("Invalid cron pattern");

Documentation

For detailed usage and API documentation, visit Croner on docs.rs.

Development

To start developing in the Croner project:

1. Clone the repository.
2. Navigate into the project directory.
3. Build the project using cargo build.
4. Run tests with cargo test.
5. Run demo with cargo run --example pattern_demo

Contributing

We welcome contributions! Please feel free to submit a pull request or open an issue.

License

This project is licensed under the MIT License - see the LICENSE.md file for details.

Disclaimer

Please note that Croner is currently in its early stages of development. As such, the API is subject to change in future releases, adhering to semantic versioning principles. We recommend keeping this in mind when integrating Croner into your projects.

Contact

If you have any questions or feedback, please open an issue in the repository and we'll get back to you as soon as possible.