ws 8.21.3: Run a WebSocket server and client round trip with ws

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        "ws": "8.21.3"
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      "license": "MIT",
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      "peerDependencies": {
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{
  "name": "csx-sample-ws-echo-roundtrip",
  "version": "1.0.0",
  "private": true,
  "type": "module",
  "license": "MIT-0",
  "dependencies": {
    "ws": "8.21.3"
  }
}

import { WebSocketServer, WebSocket } from 'ws';

// ws is CommonJS but ships named exports that ESM can import directly.
// Messages arrive as Buffer by default, so compare with String(data) rather
// than === on the raw value.
export function startEchoServer() {
  const server = new WebSocketServer({ port: 0, host: '127.0.0.1' });
  server.on('connection', (socket) => {
    socket.on('message', (data) => socket.send(`echo:${String(data)}`));
  });
  return new Promise((resolve) => server.on('listening', () => resolve(server)));
}

export function askEcho(port, message) {
  return new Promise((resolve, reject) => {
    const client = new WebSocket(`ws://127.0.0.1:${port}`);
    client.on('open', () => client.send(message));
    client.on('message', (data) => {
      client.close();
      resolve(String(data));
    });
    client.on('error', reject);
  });
}

import { strict as assert } from 'node:assert';
import { startEchoServer, askEcho } from '../src/index.mjs';

const server = await startEchoServer();
const { port } = server.address();

const reply = await askEcho(port, 'hello');
assert.equal(reply, 'echo:hello');

await new Promise((r) => server.close(r));
console.log('CONTRACT PASS: ws server and client completed an echo round trip');