# Tokio

A runtime for writing reliable, asynchronous, and slim applications with
the Rust programming language. It is:

* **Fast**: Tokio's zero-cost abstractions give you bare-metal
  performance.

* **Reliable**: Tokio leverages Rust's ownership, type system, and
  concurrency model to reduce bugs and ensure thread safety.

* **Scalable**: Tokio has a minimal footprint, and handles backpressure
  and cancellation naturally.

[![Crates.io][crates-badge]][crates-url]
[![MIT licensed][mit-badge]][mit-url]
[![Build Status][actions-badge]][actions-url]
[![Discord chat][discord-badge]][discord-url]

[crates-badge]: https://img.shields.io/crates/v/tokio.svg
[crates-url]: https://crates.io/crates/tokio
[mit-badge]: https://img.shields.io/badge/license-MIT-blue.svg
[mit-url]: https://github.com/tokio-rs/tokio/blob/master/LICENSE
[actions-badge]: https://github.com/tokio-rs/tokio/workflows/CI/badge.svg
[actions-url]: https://github.com/tokio-rs/tokio/actions?query=workflow%3ACI+branch%3Amaster
[discord-badge]: https://img.shields.io/discord/500028886025895936.svg?logo=discord&style=flat-square
[discord-url]: https://discord.gg/tokio

[Website](https://tokio.rs) |
[Guides](https://tokio.rs/tokio/tutorial) |
[API Docs](https://docs.rs/tokio/latest/tokio) |
[Chat](https://discord.gg/tokio)

## Overview

Tokio is an event-driven, non-blocking I/O platform for writing
asynchronous applications with the Rust programming language. At a high
level, it provides a few major components:

* A multithreaded, work-stealing based task [scheduler].
* A reactor backed by the operating system's event queue (epoll, kqueue,
  IOCP, etc...).
* Asynchronous [TCP and UDP][net] sockets.

These components provide the runtime components necessary for building
an asynchronous application.

[net]: https://docs.rs/tokio/latest/tokio/net/index.html
[scheduler]: https://docs.rs/tokio/latest/tokio/runtime/index.html

## Example

A basic TCP echo server with Tokio.

Make sure you activated the full features of the tokio crate on Cargo.toml:

```toml
[dependencies]
tokio = { version = "1.16.1", features = ["full"] }
```
Then, on your main.rs:

```rust,no_run
use tokio::net::TcpListener;
use tokio::io::{AsyncReadExt, AsyncWriteExt};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let listener = TcpListener::bind("127.0.0.1:8080").await?;

    loop {
        let (mut socket, _) = listener.accept().await?;

        tokio::spawn(async move {
            let mut buf = [0; 1024];

            // In a loop, read data from the socket and write the data back.
            loop {
                let n = match socket.read(&mut buf).await {
                    // socket closed
                    Ok(n) if n == 0 => return,
                    Ok(n) => n,
                    Err(e) => {
                        eprintln!("failed to read from socket; err = {:?}", e);
                        return;
                    }
                };

                // Write the data back
                if let Err(e) = socket.write_all(&buf[0..n]).await {
                    eprintln!("failed to write to socket; err = {:?}", e);
                    return;
                }
            }
        });
    }
}
```

More examples can be found [here][examples]. For a larger "real world" example, see the
[mini-redis] repository.

[examples]: https://github.com/tokio-rs/tokio/tree/master/examples
[mini-redis]: https://github.com/tokio-rs/mini-redis/

To see a list of the available features flags that can be enabled, check our
[docs][feature-flag-docs].

## Getting Help

First, see if the answer to your question can be found in the [Guides] or the
[API documentation]. If the answer is not there, there is an active community in
the [Tokio Discord server][chat]. We would be happy to try to answer your
question. You can also ask your question on [the discussions page][discussions].

[Guides]: https://tokio.rs/tokio/tutorial
[API documentation]: https://docs.rs/tokio/latest/tokio
[chat]: https://discord.gg/tokio
[discussions]: https://github.com/tokio-rs/tokio/discussions
[feature-flag-docs]: https://docs.rs/tokio/#feature-flags

## Contributing

:balloon: Thanks for your help improving the project! We are so happy to have
you! We have a [contributing guide][guide] to help you get involved in the Tokio
project.

[guide]: https://github.com/tokio-rs/tokio/blob/master/CONTRIBUTING.md

## Related Projects

In addition to the crates in this repository, the Tokio project also maintains
several other libraries, including:

* [`hyper`]: A fast and correct HTTP/1.1 and HTTP/2 implementation for Rust.

* [`tonic`]: A gRPC over HTTP/2 implementation focused on high performance, interoperability, and flexibility.

* [`warp`]: A super-easy, composable, web server framework for warp speeds.

* [`tower`]: A library of modular and reusable components for building robust networking clients and servers.

* [`tracing`] (formerly `tokio-trace`): A framework for application-level tracing and async-aware diagnostics.

* [`rdbc`]: A Rust database connectivity library for MySQL, Postgres and SQLite.

* [`mio`]: A low-level, cross-platform abstraction over OS I/O APIs that powers
  `tokio`.

* [`bytes`]: Utilities for working with bytes, including efficient byte buffers.

* [`loom`]: A testing tool for concurrent Rust code

[`warp`]: https://github.com/seanmonstar/warp
[`hyper`]: https://github.com/hyperium/hyper
[`tonic`]: https://github.com/hyperium/tonic
[`tower`]: https://github.com/tower-rs/tower
[`loom`]: https://github.com/tokio-rs/loom
[`rdbc`]: https://github.com/tokio-rs/rdbc
[`tracing`]: https://github.com/tokio-rs/tracing
[`mio`]: https://github.com/tokio-rs/mio
[`bytes`]: https://github.com/tokio-rs/bytes

## Supported Rust Versions

Tokio is built against the latest stable release. The minimum supported version
is 1.46.  The current Tokio version is not guaranteed to build on Rust versions
earlier than the minimum supported version.

## Release schedule

Tokio doesn't follow a fixed release schedule, but we typically make one to two
new minor releases each month. We make patch releases for bugfixes as necessary.

## Bug patching policy

For the purposes of making patch releases with bugfixes, we have designated
certain minor releases as LTS (long term support) releases. Whenever a bug
warrants a patch release with a fix for the bug, it will be backported and
released as a new patch release for each LTS minor version. Our current LTS
releases are:

 * `1.8.x` - LTS release until February 2022.
 * `1.14.x` - LTS release until June 2022.

Each LTS release will continue to receive backported fixes for at least half a
year. If you wish to use a fixed minor release in your project, we recommend
that you use an LTS release.

To use a fixed minor version, you can specify the version with a tilde. For
example, to specify that you wish to use the newest `1.8.x` patch release, you
can use the following dependency specification:
```text
tokio = { version = "~1.8", features = [...] }
```

## License

This project is licensed under the [MIT license].

[MIT license]: https://github.com/tokio-rs/tokio/blob/master/LICENSE

### Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in Tokio by you, shall be licensed as MIT, without any additional
terms or conditions.
