rusm — the TypeScript guest API

The guest API for RUSM TypeScript components: the Process actor API, the spawn typed-client, the websocket() serving helper, and the types. The Rust twin is the rusm-rs crate — they share one JSON wire and interoperate.

bun add rusm-ts

import { Process, spawn } from "rusm-ts";
import type { Calc } from "../calc";       // type-only: the service's published contract

const calc = spawn<Calc>("calc");          // spawn a service by name, typed client
const sum = await calc.add(2, 3);          // a call
for await (const n of calc.countTo(3)) {}  // a stream
await calc.work((pct) => updateBar(pct));  // a callback (stays in the caller)

The js-runner injects Process/spawn as globals and polyfills the Web APIs (URL, TextEncoder, Headers, ReadableStream, AbortController, crypto, console, and a capability-gated streaming fetch); this package re-exports Process/spawn/supervise as a normal module and ships the types. receive/Stream.read are async (await); pids are bigint.

Serving

A component is served by declaring it in rusm.toml; you just write the handler. HTTP/SSE are zero-dependency web-standard handlers:

export default function handle(request: Request): Response {
  return new Response("hello\n", { headers: { "content-type": "text/plain" } });
}

WebSockets use the websocket() helper — one instance serves every connection, reply with socket.send(…):

import { websocket } from "rusm-ts";

export default websocket({
  open(socket) {
    socket.send("welcome\n");
  },
  message(socket, data) {
    socket.send(data); // echo this connection's frame
  },
  close(socket) {
    // disconnect — clean or dropped (optional)
  },
});

Building

rusm build bundles each components/<name>/index.ts with Bun → wasm/<name>.js (precompiled to QuickJS bytecode), run on the shared rquickjs runner. Add the standard DOM lib to your tsconfig.json ("lib": ["ES2022", "DOM"]) so the polyfilled Web APIs are typed. See the RUSM docs and rusm new to scaffold an app.