smol

A small and fast async runtime.

Examples

Connect to an HTTP website, make a GET request, and pipe the response to the standard output:

use async_net::TcpStream;
use smol::{io, prelude::*, Unblock};

fn main() -> io::Result<()> {
    smol::run(async {
        let mut stream = TcpStream::connect("example.com:80").await?;
        let req = b"GET / HTTP/1.1\r\nHost: example.com\r\nConnection: close\r\n\r\n";
        stream.write_all(req).await?;

        let mut stdout = Unblock::new(std::io::stdout());
        io::copy(&stream, &mut stdout).await?;
        Ok(())
    })
}

This example uses async-net for networking, but you can also use the primitive Async type. See the full code.

Look inside the examples directory for more.

Compatibility

All async libraries work with smol out of the box.

However, tokio is generally hostile towards non-tokio libraries, insists on non-standard I/O traits, and deliberately lacks documentation on integration with the larger Rust ecosystem. Fortunately, there are ways around it.

Enable the tokio02 feature flag and smol::run() will create a minimal tokio runtime for its libraries:

[dependencies]
smol = { version = "0.2", features = ["tokio02"] }

TLS certificate

Some code examples are using TLS for authentication. The repository contains a self-signed certificate usable for testing, but it should not be used for real-world scenarios. Browsers and tools like curl will show this certificate as insecure.

In browsers, accept the security prompt or use curl -k on the command line to bypass security warnings.

The certificate file was generated using minica and openssl:

minica --domains localhost -ip-addresses 127.0.0.1 -ca-cert certificate.pem
openssl pkcs12 -export -out identity.pfx -inkey localhost/key.pem -in localhost/cert.pem

License

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.

Contribution

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.