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A small and fast async runtime.

This crate simply re-exports other smaller async crates (see the source).

To use tokio-based libraries with smol, apply the async-compat adapter to futures and I/O types.


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

use smol::{io, net, prelude::*, Unblock};

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

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

There's a lot more in the examples directory.


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 -ca-cert certificate.pem
openssl pkcs12 -export -out identity.pfx -inkey localhost/key.pem -in localhost/cert.pem

Another useful tool for making certificates is mkcert.

MSRV Policy

The Minimum Supported Rust Version (MSRV) of this crate is 1.63. As a tentative policy, the MSRV will not advance past the current Rust version provided by Debian Stable. At the time of writing, this version of Rust is 1.63. However, the MSRV may be advanced further in the event of a major ecosystem shift or a security vulnerability.


Licensed under either of

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.