μWASI

This library provides a WASI implementation for Node.js and browsers in a tree-shaking friendly way.
The system calls provided by this library are configurable.

With minimal configuration, it provides WASI system calls which just return WASI_ENOSYS.

Features

- No dependencies
- Tree-shaking friendly
- 3 KB when minimal configuration
- 6 KB when all features enabled
- Almost compatible interface with Node.js WASI implementation
- Well tested, thanks to wasi-test-suite by Casper Beyer

Installation

``bash
npm install uwasi
`

Example

$3

`js
import { WASI, useAll } from "uwasi";
import fs from "node:fs/promises";

async function main() {
const wasi = new WASI({
args: process.argv.slice(2),
features: [useAll()],
});
const bytes = await fs.readFile(process.argv[2]);
const { instance } = await WebAssembly.instantiate(bytes, {
wasi_snapshot_preview1: wasi.wasiImport,
});
const exitCode = wasi.start(instance);
console.log("exit code:", exitCode);

/* With Reactor model
wasi.initialize(instance);
*/
}

main()
`

$3

`js
import { WASI, useAll } from "uwasi";

const wasi = new WASI({
features: [],
});
`

$3

`js
import { WASI, useArgs, useClock } from "uwasi";

const wasi = new WASI({
args: ["./a.out", "hello", "world"],
features: [useEnviron, useArgs, useClock, useProc, useRandom()],
});
`

$3

By default, stdin behaves like /dev/null, stdout and stderr print to the console.

`js
import { WASI, useStdio } from "uwasi";

const wasi = new WASI({
features: [useStdio()],
});
`

You can use custom backends for stdio by passing handlers to useStdio.

`js
import { WASI, useStdio } from "uwasi";

const inputs = ["Y", "N", "Y", "Y"];
const wasi = new WASI({
features: [useStdio({
stdin: () => inputs.shift() || "",
stdout: (str) => document.body.innerHTML += str,
stderr: (str) => document.body.innerHTML += str,
})],
});
`

By default, the stdout and stderr handlers are passed strings. You can pass outputBuffers: true to get Uint8Array buffers instead. Along with that, you can also pass Uint8Array buffers to stdin.

`js
import { WASI, useStdio } from "uwasi";
const wasi = new WASI({
features: [useStdio({
outputBuffers: true,
stdin: () => new Uint8Array([1, 2, 3, 4, 5]),
stdout: (buf) => console.log(buf),
stderr: (buf) => console.error(buf),
})],
});
`

Implementation Status

Some of WASI system calls are not implemented yet. Contributions are welcome!

| Syscall | Status | Notes |
|-------|----------|---------|
| args_XXX | ✅ | |
| clock_XXX | ✅ | Monotonic clock is unavailable due to JS API limitation |
| environ_XXX | ✅ | |
| fd_XXX | 🚧 | stdin/stdout/stderr are supported |
| path_XXX | ❌ | |
| poll_oneoff | ❌ | |
| proc_XXX | ✅ | |
| random_get | ✅ | |
| sched_yield | ❌ | |
| sock_XXX` | ❌ | |