A pure javascript shim for WASI

Implementation status: A subset of wasi_snapshot_preview1 is implemented. The rest either throws an exception, returns an error or is incorrectly implemented.

Usage

npm install @bjorn3/browser_wasi_shim --save

import { WASI, File, OpenFile, ConsoleStdout, PreopenDirectory } from "@bjorn3/browser_wasi_shim";

let args = ["bin", "arg1", "arg2"];
let env = ["FOO=bar"];
let fds = [
    new OpenFile(new File([])), // stdin
    ConsoleStdout.lineBuffered(msg => console.log(`[WASI stdout] ${msg}`)),
    ConsoleStdout.lineBuffered(msg => console.warn(`[WASI stderr] ${msg}`)),
    new PreopenDirectory(".", [
        ["example.c", new File(new TextEncoder("utf-8").encode(`#include "a"`))],
        ["hello.rs", new File(new TextEncoder("utf-8").encode(`fn main() { println!("Hello World!"); }`))],
    ]),
];
let wasi = new WASI(args, env, fds);

let wasm = await WebAssembly.compileStreaming(fetch("bin.wasm"));
let inst = await WebAssembly.instantiate(wasm, {
    "wasi_snapshot_preview1": wasi.wasiImport,
});
wasi.start(inst);

Building

$ npm install
$ npm run build

Running the demo

The demo requires the wasm rustc artifacts and the xterm js package. To get them run:

$ git submodule update --init
$ cd examples && npm install

Run the demo with a static web server from the root of this project:

$ npx http-server

And visit http://127.0.0.1:8080/examples/rustc.html in your browser.

A more complete demo by @LyonSyonII which runs miri inside the browser can be found at https://garriga.dev/rubri/. (source at https://github.com/LyonSyonII/rubri)

Testing

$ python3 -m pip install -r ./test/wasi-testsuite/test-runner/requirements.txt
$ npm test

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 shall be dual licensed as above, without any additional terms or conditions.