Minimal local example of Cap'n Web

client.ts

import { newWebSocketRpcSession } from "capnweb";

import type { MyApi } from "./server.ts";

const api = newWebSocketRpcSession<MyApi>("ws://localhost:8080/api");

const result = await api.hello("World");

console.log(result);

package.json

{
  "name": "@mmyoji/capnweb-test",
  "private": true,
  "version": "1.0.0",
  "main": "server.ts",
  "type": "module",
  "scripts": {
    "start:client": "node --experimental-strip-types client.ts",
    "start:server": "node --experimental-strip-types server.ts"
  },
  "author": "mmyoji",
  "license": "ISC",
  "dependencies": {
    "capnweb": "^0.1.0",
    "ws": "^8.18.3"
  },
  "devDependencies": {
    "@types/node": "^22.18.7",
    "@types/ws": "^8.18.1"
  }
}

server.ts

import http from "node:http";

import {
  RpcTarget,
  newWebSocketRpcSession,
  nodeHttpBatchRpcResponse,
} from "capnweb";
import { WebSocketServer } from "ws";

export interface MyApi {
  hello(name: string): string;
}

class MyApiServer extends RpcTarget implements MyApi {
  hello(name: string) {
    return `Hello, ${name}`;
  }
}

const send = (
  res: http.ServerResponse,
  { status, text }: { status: number; text: string }
) => {
  res.writeHead(status, { "Content-Type": "text/plain" });
  res.end(text);
};

const server = http.createServer(async (req, res) => {
  if (req.headers.upgrade?.toLowerCase() === "websocket") {
    return;
  }

  if (req.url === "/api") {
    try {
      await nodeHttpBatchRpcResponse(req, res, new MyApiServer(), {
        headers: { "Access-Control-Allow-Origin": "*" },
      });
    } catch (err) {
      send(res, { status: 500, text: String(err?.stack || err) });
    }
    return;
  }

  send(res, { status: 404, text: "Not Found" });
});

const wsServer = new WebSocketServer({ server });
wsServer.on("connection", (ws) => {
  newWebSocketRpcSession(ws as any, new MyApiServer());
});

server.listen(8080);