This is a Kotlin Multiplatform line-by-line transliteration port of smol-rs/async-io.

Original Project: This port is based on smol-rs/async-io. All design credit and project intent belong to the upstream authors; this repository is a faithful port to Kotlin Multiplatform with no behavioural changes intended.

This is an in-progress port. The goal is feature parity with the upstream Rust crate while providing a native Kotlin Multiplatform API. Every Kotlin file carries a // port-lint: source <path> header naming its upstream Rust counterpart so the AST-distance tool can track provenance.

The text below is reproduced and lightly edited from https://github.com/smol-rs/async-io. It is the upstream project's own description and remains under the upstream authors' authorship; links have been rewritten to absolute upstream URLs so they continue to resolve from this repository.

Async I/O and timers.

This crate provides two tools:

• Async, an adapter for standard networking types (and many other types) to use in async programs.
• Timer, a future that expires at a point in time.

For concrete async networking types built on top of this crate, see async-net.

The first time Async or Timer is used, a thread named "async-io" will be spawned. The purpose of this thread is to wait for I/O events reported by the operating system, and then wake appropriate futures blocked on I/O or timers when they can be resumed.

To wait for the next I/O event, the "async-io" thread uses epoll on Linux/Android/illumos, kqueue on macOS/iOS/BSD, event ports on illumos/Solaris, and IOCP on Windows. That functionality is provided by the polling crate.

However, note that you can also process I/O events and wake futures on any thread using the block_on() function. The "async-io" thread is therefore just a fallback mechanism processing I/O events in case no other threads are.

Connect to example.com:80, or time out after 10 seconds.

use async_io::{Async, Timer};
use futures_lite::{future::FutureExt, io};

use std::net::{TcpStream, ToSocketAddrs};
use std::time::Duration;

let addr = "example.com:80".to_socket_addrs()?.next().unwrap();

let stream = Async::<TcpStream>::connect(addr).or(async {
    Timer::after(Duration::from_secs(10)).await;
    Err(io::ErrorKind::TimedOut.into())
})
.await?;

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

dependencies {
    implementation("io.github.kotlinmania:async-io-kotlin:0.1.0")
}

./gradlew build
./gradlew test

• macOS arm64
• Linux x64
• Windows mingw-x64
• iOS arm64 / simulator-arm64 (Swift export + XCFramework)
• JS (browser + Node.js)
• Wasm-JS (browser + Node.js)
• Android (API 24+)

See AGENTS.md and CLAUDE.md for translator discipline, port-lint header convention, and Rust → Kotlin idiom mapping.

This Kotlin port is distributed under the same Apache-2.0 license as the upstream smol-rs/async-io. See LICENSE (and any sibling LICENSE-* / NOTICE files mirrored from upstream) for the full text.

Original work copyrighted by the async-io authors.
Kotlin port: Copyright (c) 2026 Sydney Renee and The Solace Project.

Thanks to the smol-rs/async-io maintainers and contributors for the original Rust implementation. This port reproduces their work in Kotlin Multiplatform; bug reports about upstream design or behavior should go to the upstream repository.