WASI

You can also browse this source code online and clone the wasmtime repository to run the example locally.

This example shows off how to instantiate a wasm module using WASI imports.

Wasm Source code

fn main() {
    println!("Hello, world!");
}

wasi.rs

//! Example of instantiating of instantiating a wasm module which uses WASI
//! imports.

// You can execute this example with `cargo run --example wasi`

use anyhow::Result;
use wasi_cap_std_sync::WasiCtxBuilder;
use wasmtime::*;
use wasmtime_wasi::Wasi;

fn main() -> Result<()> {
    tracing_subscriber::FmtSubscriber::builder()
        .with_env_filter(tracing_subscriber::EnvFilter::from_default_env())
        .with_ansi(true)
        .init();

    let store = Store::default();
    let mut linker = Linker::new(&store);

    // Create an instance of `Wasi` which contains a `WasiCtx`. Note that
    // `WasiCtx` provides a number of ways to configure what the target program
    // will have access to.
    let wasi = Wasi::new(
        &store,
        WasiCtxBuilder::new()
            .inherit_stdio()
            .inherit_args()?
            .build()?,
    );
    wasi.add_to_linker(&mut linker)?;

    // Instantiate our module with the imports we've created, and run it.
    let module = Module::from_file(store.engine(), "target/wasm32-wasi/debug/wasi.wasm")?;
    linker.module("", &module)?;
    linker.get_default("")?.get0::<()>()?()?;

    Ok(())
}