@fungi.computer/capnweb

Cap'n Web is a JavaScript-native, object-capability RPC system: no schemas, no code generation, human-readable (JSON-based) wire format, and support for bidirectional calling, passing functions/objects by reference, and promise pipelining (chaining dependent calls into a single network round trip). It works over HTTP, WebSocket, and postMessage(), in browsers, Cloudflare Workers, Node.js, Bun, and Deno.

Fungi fork

This package is a Fungi fork of cloudflare/capnweb at the 0.12.0 release (commit 7702075). It carries two fixes:

• In src/types.ts, UnstubifyInner spreads a tuple tail through UnstubifyAll<Tail> instead of Unstubify<Tail>. Unstubify<Tail> is a union that includes Promise, so the upstream declarations fail with TS2574 ("A rest element type must be an array type") under skipLibCheck: false and lose tuple parameter types.
• In src/streams.ts and src/rpc.ts, exported stubs report breakage through the existing onBroken callback and broken-reference reject message. Native writable-stream hooks now report writer failure through that machinery. Writable proxies observe that callback, so cancelling a received readable interrupts an idle sender's pipe without waiting for another chunk. This does not expose writer properties or add wire messages, peer negotiation or a fallback. Upstream 0.12.0 and Fungi's 0.6.0-era peers keep streaming normally with their previous cancellation latency; immediate idle cancellation requires the fix at both ends. Import entries release their callback registrations when disposed, including normally completed pipes; session abort notifies a snapshot of live observers so one observer's cleanup cannot suppress the others.

Drop this fork when upstream Cap'n Web includes both fixes. Agent and inbox transport cancellation is exercised through actual MessagePort RPC and native HTTP in packages/agar/src/agents-rpc.test.ts. pnpm test exercises mixed-peer streaming against maintained upstream [email protected], a test-only dependency, and resource release in a live session plus complete observer delivery on abort. Its resource law uses Node's maintained V8 object counter rather than private RPC tables.

Install

npm install @fungi.computer/capnweb

Example

A client:

import { newWebSocketRpcSession } from "@fungi.computer/capnweb";

// One-line setup.
let api = newWebSocketRpcSession("wss://example.com/api");

// Call a method on the server!
let result = await api.hello("World");

console.log(result);

A server:

import { RpcTarget, newWorkersRpcResponse } from "@fungi.computer/capnweb";

// This is the server implementation.
class MyApiServer extends RpcTarget {
  hello(name) {
    return `Hello, ${name}!`;
  }
}

// Standard Cloudflare Workers HTTP handler.
//
// (Node, Deno, Bun and other runtimes are supported too.)
export default {
  fetch(request, env, ctx) {
    let url = new URL(request.url);

    if (url.pathname === "/api") {
      return newWorkersRpcResponse(request, new MyApiServer());
    }

    return new Response("Not found", { status: 404 });
  },
};

Three dependent calls, one round trip:

using api = newHttpBatchRpcSession<Api>("https://example.com/api");

// No awaits, so no round trips yet.
using authed = api.authenticate(apiToken);
let friendIds = authed.getFriendIds();

// One await. One round trip. Everything above travelled together.
let friends = await friendIds.map((id) => api.getUserProfile(id));

For the full API, transports, and server-runtime guides, see the upstream documentation site and the upstream README.

Where it's used

Oyster, the Hub and App SDK use this fork for browser/frame RPC and Agent/inbox Request and Response bodies. The Computer client and Cordyceps's bundled computerd also use it for WebSocket and HTTP-batch RPC, including file/Blob and execution-event streams. App Releases, hosts, CLI bundles and Computer images can be built independently; normal streaming must remain valid with their upstream 0.12.0-era peers.

License

MIT. This package carries the upstream Cloudflare copyright and license unchanged — see LICENSE.txt and NOTICE.