This crate contains bindings for WASIp2 APIs for the worlds:

• wasi:cli/command
• wasi:http/proxy

This crate is procedurally generated from WIT files using wit-bindgen.

Usage

Depending on this crate can be done by adding it to your dependencies:

$ cargo add wasip2

Next you can use the APIs in the root of the module like so:

fn main() {
    let stdout = wasip2::cli::stdout::get_stdout();
    stdout.blocking_write_and_flush(b"Hello, world!\n").unwrap();
}

This crate can currently be used in three main ways.

• One is to use it and compile for the wasm32-wasip2 target in Rust 1.82 and later. this is the simplest approach, as all the tools needed are included in the Rust tooling, however it doesn't yet support some of the features of the other approaches.

• Another is to use it and compile using cargo component. This is essentially the same as the next option, except that cargo component handles most of the steps for you. cargo component also has a number of additional features for working with dependencies and custom WIT interfaces.

• And the third is to compile for the wasm32-wasip1 target, and then adapt the resulting modules into component using wasm-tools component new; see the next section here for details.

Building with wasm32-wasip1 and cargo component new.

The wasm32-wasip2 target works with a simple cargo build --target wasm32-wasip2 and doesn't need a lot of documentation here, and cargo component has its own documentation, so here we have some documentation for the wasm32-wasip1 way.

$ cargo build --target wasm32-wasip1

Next you'll want an "adapter" to convert the Rust standard library's usage of wasi_snapshot_preview1 to the component model. An example adapter can be found from Wasmtime's release page.

$ curl -LO https://github.com/bytecodealliance/wasmtime/releases/download/v17.0.0/wasi_snapshot_preview1.command.wasm

Next to create a component you'll use the wasm-tools CLI to create a component:

$ cargo install wasm-tools
$ wasm-tools component new target/wasm32-wasip1/debug/foo.wasm \
    --adapt ./wasi_snapshot_preview1.command.wasm \
    -o component.wasm

And finally the component can be run by a runtime that has Component Model support, such as Wasmtime:

$ wasmtime run component.wasm
Hello, world!

Development

The bulk of the wasip2 crate is generated by the wit-bindgen tool. The src/bindings.rs file can be regenerated with:

$ ./ci/regenerate.sh

WASI definitions are located in the wit directory of this repository. Currently they're copied from upstream repositories but are hoped to be better managed in the future.