reliakit-timeout

Clock-agnostic deadlines and timeouts for Rust.

reliakit-timeout answers one question: has my time budget run out, and how much is left? It does not read the clock, sleep, or spawn anything — you capture a start instant and a budget, then pass now to the query methods. That keeps it usable from synchronous code, any async runtime, and no_std / embedded targets, with deterministic tests.

Time is a plain u64 in any monotonic unit you choose (milliseconds is typical), matching reliakit-circuit and reliakit-ratelimit. All arithmetic saturates, so no method panics — not on overflow, and not on a clock that moves backwards.

The crate has no dependencies, is #![no_std], and forbids unsafe code.

What This Crate Does

• Timeout — a reusable budget that is not yet pinned to a timeline. Configure it once, then call Timeout::start(now) per operation to get a Deadline.
• Deadline — a budget pinned to a start instant; it expires at start + budget. Query it with:
  • remaining(now) / elapsed(now) — saturating time left / time used.
  • is_expired(now) — whether now >= expiry.
  • check(now) — Some(remaining) while live, None once expired.
  • allows(now, duration) — whether an operation of that length still fits.
  • clamp(now, duration) — duration capped to the time left in the budget.

What This Crate Does Not Do

It does not sleep, cancel futures, or enforce the timeout for you. It tracks a budget against a clock you own; you decide what to do when it expires. Pair it with your runtime's timer or select! to actually abort work.

Installation

[dependencies]
reliakit-timeout = "0.1"

This crate is no_std and has no feature flags; it depends only on core.

Example

use reliakit_timeout::{Deadline, Timeout};

// A 30s budget (here in milliseconds), pinned to the start of the operation.
let policy = Timeout::new(30_000);
let deadline = policy.start(1_000); // started at t = 1_000

assert_eq!(deadline.remaining(21_000), 10_000);
assert_eq!(deadline.check(21_000), Some(10_000));
assert_eq!(deadline.check(40_000), None); // expired

Bound a retry delay by the time left in the budget:

use reliakit_timeout::Deadline;

let deadline = Deadline::new(0, 1_000);
let proposed_backoff = 800;

let now = 500;
if !deadline.is_expired(now) {
    let wait = deadline.clamp(now, proposed_backoff); // min(800, 500 left) = 500
    assert_eq!(wait, 500);
    // sleep(wait); try_again();
}

Behavior

Safety

This crate is #![forbid(unsafe_code)] and #![no_std]. Every method is a const fn over saturating integer arithmetic, so there is no input — including a backwards clock or an overflowing start + budget — that panics.

Minimum Supported Rust Version

Rust 1.85 and newer. No nightly features are used.

License

Licensed under the MIT License. See LICENSE.