This is a simplified version of the @runno/wasi runtime.

This package allows you to run WASI binaries on the web with an emulated filesystem. If the binary receives calls to stdin/out/err then you get callbacks you'll need to handle. In future there may be other callbacks to intercept interesting system level events, or hooks into the filesystem.

The quickest way to get started with Runno is by using the WASI.start class method. It will set up everything you need and run the Wasm binary directly.

Be aware that this will run on the main thread, not inside a worker. So you will interrupt any interactive use of the browser until it completes.

<script src="https://unpkg.com/@antonz/runno/dist/runno.js"></script>

const { WASI } = window.Runno;

//...

const result = WASI.start(fetch("/binary.wasm"), {
    args: ["binary-name", "--do-something", "some-file.txt"],
    env: { SOME_KEY: "some value" },
    stdout: (out) => console.log("stdout", out),
    stderr: (err) => console.error("stderr", err),
    stdin: () => prompt("stdin:"),
    fs: {
        "/some-file.txt": {
            path: "/some-file.txt",
            timestamps: {
                access: new Date(),
                change: new Date(),
                modification: new Date(),
            },
            mode: "string",
            content: "Some content for the file.",
        },
    },
});

Note: The args should start with the name of the binary. Like when you run a terminal command, you write cat somefile the name of the binary is cat.

@runno/wasi internally emulates a unix-like filesystem (FS) from a flat structure. All files must start with a / to indicate they are in the root directory. The / directory is preopened by @runno/wasi for your WASI binary to use.

Paths provided to the FS can include directory names /like/this.png. The FS will treat files with the same prefix /like/so.png as if they are in the same folder. Any folders created will contain an empty .runno file /like/.runno as a placeholder.

WASI has a complex permissions system that is entirely ignored. All files you provide can be accessed by the WASI binary, with all permissions.

Currently @runno/wasi supports running only unstable and snapshot-preview1 WASI binaries. The snapshot-preview1 standard is more recent, and preferred. Additionally its likely some details of unstable have been missed. If you spot these, please file a bug.

Other extension standards like WASMEdge, and WASIX are currently not supported, but could be. WASI Modules are also not supported, but I'm interested in learning more about them.

Copyright 2023 Ben Taylor.

The software is available under the MIT license.