node/test/parallel/test-cluster-bind-twice.js

'use strict';
// This test starts two clustered HTTP servers on the same port. It expects the
// first cluster to succeed and the second cluster to fail with EADDRINUSE.
//
// The test may seem complex but most of it is plumbing that routes messages
// from the child processes back to the supervisor. As a tree it looks something
// like this:
//
//          <supervisor>
//         /            \
//    <master 1>     <master 2>
//       /                \
//  <worker 1>         <worker 2>
//
// The first worker starts a server on a fixed port and fires a ready message
// that is routed to the second worker. When it tries to bind, it expects to
// see an EADDRINUSE error.
//
// See https://github.com/joyent/node/issues/2721 for more details.

const common = require('../common');
const assert = require('assert');
const cluster = require('cluster');
const fork = require('child_process').fork;
const http = require('http');

const id = process.argv[2];

if (!id) {
  const a = fork(__filename, ['one']);
  const b = fork(__filename, ['two']);

  a.on('exit', common.mustCall((c) => {
    if (c) {
      b.send('QUIT');
      throw new Error('A exited with ' + c);
    }
  }));

  b.on('exit', common.mustCall((c) => {
    if (c) {
      a.send('QUIT');
      throw new Error('B exited with ' + c);
    }
  }));


  a.on('message', common.mustCall((m) => {
    if (typeof m === 'object') return;
    assert.strictEqual(m, 'READY');
    b.send('START');
  }));

  b.on('message', common.mustCall((m) => {
    assert.strictEqual(m, 'EADDRINUSE');
    a.send('QUIT');
    b.send('QUIT');
  }));

} else if (id === 'one') {
  if (cluster.isMaster) return startWorker();

  http.createServer(common.fail).listen(common.PORT, common.mustCall(() => {
    process.send('READY');
  }));

  process.on('message', common.mustCall((m) => {
    if (m === 'QUIT') process.exit();
  }));
} else if (id === 'two') {
  if (cluster.isMaster) return startWorker();

  const server = http.createServer(common.fail);
  process.on('message', common.mustCall((m) => {
    if (m === 'QUIT') process.exit();
    assert.strictEqual(m, 'START');
    server.listen(common.PORT, common.fail);
    server.on('error', common.mustCall((e) => {
      assert.strictEqual(e.code, 'EADDRINUSE');
      process.send(e.code);
    }));
  }, 2));
} else {
  assert(0); // bad command line argument
}

function startWorker() {
  const worker = cluster.fork();
  worker.on('exit', process.exit);
  worker.on('message', process.send.bind(process));
  process.on('message', worker.send.bind(worker));
}