#calendar #ical #rrule

bin+lib rrule

A pure Rust implementation of recurrence rules as defined in the iCalendar RFC

34 releases

Uses new Rust 2021

0.8.0 Jun 21, 2022
0.7.2 Apr 16, 2022
0.7.1 Mar 7, 2022
0.6.0 Sep 23, 2021
0.3.4 Nov 13, 2020

#5 in Date and time

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A pure and efficient Rust implementation of recurrence rules as defined in the iCalendar RFC.


This crate follows the iCalendar (RFC-5545) specification for the "Recurrence Rule". The Recurrence Rule spec corresponds to the RRule object in this crate. In addition, it allows for adding the "DTSTART" property separated by a newline.

The crate allows for a "BYEASTER" filter. But this is opt-in with the feature flag "by-easter".


RRuleSet allows for a combination for RRules and some other properties.

  • List of RRules: Allows multiple RRules to be combined. (Union, A ∪ B)
  • List of RDates: A list of datetime combinations to always include. (Union, A ∪ B)
  • List of ExRule (see note below): Allows of RRules that are removed from the results. (Complement A \ B or A - B)
  • List of ExDate: A list of datetime combinations to always exclude. (Complement A \ B or A - B)

Note: "EXRULE" was originally part of RFC 2445, RFC 5545 supersedes this specification. But "EXRULE" works exactly the same als "RRULE" excepts it excludes dates.

If you notice that the implementation differs from the specifications above, please open an issue.

Library Usage

use rrule::RRule;

// RRule that starts 2012.02.01 and occurs daily for 3 days.
let rrule: RRule = "DTSTART:20120201T093000Z\nRRULE:FREQ=DAILY;COUNT=3".parse().unwrap();

// Set hard limit in case of infinitely recurring rules.
let limit = 100;
// Get all recurrences of the rrule
let recurrences = rrule.all(limit).unwrap();
assert_eq!(recurrences.len(), 3);

See more examples at docs.rs

Command Line Tool Usage

Install the command line tool with:

cargo install rrule --features="cli-tool"

Then run it with:

rrule "DTSTART:20120201T093000Z\nRRULE:FREQ=DAILY;COUNT=3"

Safety and Security

We try to make the crate safe for use by arbitrary users/public APIs, but we can not guaranty the security of it at this point.

The 3 problems we are currently mostly worried about are:

Denial of Service (DoS) by panic

If the user is able to trigger a case where is it able to panic the code it could crash an application or servers. This can limit this by using catch_unwind. Make sure to read the documentation! This does not work if the panic = "abort" setting is set to abort. It is not advices to reuse RRule, RRuleSet or iterators after it has panicked.

Disabling overflow checks using compiler flags might result in unexpected results and crashes. So this is strongly discouraged.

When the validation limits are disabled this problem will be much more prevalent. Numbers might overflow in some cases.

Denial of Service (DoS) by CPU exhaustion

The spec allows of infinitely recurring events or by searching of a datetime that meets the requirements but does not exist. There are various protections for this build into the crate. But in order to hit these limits it might take a few seconds/minutes depending on the CPU speed.

This problem can be mitigating by spawning the process in a separate thread and stopping the thread if it hits the timeout. On decent CPUs this might not be a big issue.

Note that by disabling the validation limits this problem will be made MUCH more significant.

Denial of Service (DoS) by memory exhaustion

The spec allows of infinitely recurring events. Thus, the iterator might be practically infinite. So when not setting a limit over the iterator it might create a list of events that practically never ends. And thus will continue until is crashes or hangs the system.

This problem can be easily mitigated by limiting the amount of events expected. This is also the reason why rrule.all(limit) function takes a limit.

Limitation and limits

All dates are limited to the range or years +/-262_000[^1] because of Chrono limits. See Chrono's limits for more info.

Supported timezones are limited to by the timezones that Chrono-Tz supports. This is equivalent to the IANA database. See Chrono-Tz's limits for more info.

Validation Limits

Because the specifications does give a lot of flexibility this can be abused very easily. In order to prevent most of the abuse we have imposed arbitrary limitation on the crate.

These limitations are reasonable in most use cases, but we do allow other developers to opt-out if needed.


Description Arbitrary Limit Crate Limit
Year range -10_000..=10_000 -262_000..=262_000 (Chrono)
Max interval with freq Yearly 10_000 (10000 years) 65_535 (u16::MAX)
Max interval with freq Monthly 1_000 (~83 years) 65_535 (u16::MAX)
Max interval with freq Weekly 1_000 (~19 years) 65_535 (u16::MAX)
Max interval with freq Daily 10_000 (~27 years) 65_535 (u16::MAX)
Max interval with freq Hourly 10_000 (~416 days) 65_535 (u16::MAX)
Max interval with freq Minutely 10_000 (~7 days) 65_535 (u16::MAX)
Max interval with freq Secondly 50_000 (~13 hours) 65_535 (u16::MAX)
Formula loop limit 10_000 65_535 (u16::MAX)
Iteration limit 100_000 4_294_967_295 (u32::MAX)

By default, the "Arbitrary Limit" are used. If you instead want to use the "Crate Limit". Make sure you understand the risks that come with this.

Yes, I understand the risks, but I want to disable the arbitrary limits.

Make sure you actually need this before enabling it.

To disable all arbitrary limits you can enable the "no-validation-limits" feature flag.

Inspired by


The code in this project is licensed under the MIT or Apache 2.0 license.

All contributions to this project will be similarly licensed.

[^1]: See validation limits sections more info.


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