node/test/parallel/test-net-server-max-connections-close-makes-more-available.js

'use strict';
require('../common');
const assert = require('assert');

const net = require('net');

// Sets the server's maxConnections property to 1.
// Open 2 connections (connection 0 and connection 1).
// Connection 0  should be accepted.
// Connection 1 should be rejected.
// Closes connection 0.
// Open 2 more connections (connection 2 and 3).
// Connection 2 should be accepted.
// Connection 3 should be rejected.

const connections = [];
const received = [];
const sent = [];

function createConnection(index) {
  console.error('creating connection ' + index);

  return new Promise(function(resolve, reject) {
    const connection = net.createConnection(server.address().port, function() {
      const msg = '' + index;
      console.error('sending message: ' + msg);
      this.write(msg);
      sent.push(msg);
    });

    connection.on('error', function(err) {
      assert.strictEqual(err.code, 'ECONNRESET');
      resolve();
    });

    connection.on('data', function(e) {
      console.error('connection ' + index + ' received response');
      resolve();
    });

    connection.on('end', function() {
      console.error('ending ' + index);
      resolve();
    });

    connections[index] = connection;
  });
}

function closeConnection(index) {
  console.error('closing connection ' + index);
  return new Promise(function(resolve, reject) {
    connections[index].on('end', function() {
      resolve();
    });
    connections[index].end();
  });
}

const server = net.createServer(function(socket) {
  socket.on('data', function(data) {
    console.error('received message: ' + data);
    received.push('' + data);
    socket.write('acknowledged');
  });
});

server.maxConnections = 1;

server.listen(0, function() {
  createConnection(0)
    .then(createConnection.bind(null, 1))
    .then(closeConnection.bind(null, 0))
    .then(createConnection.bind(null, 2))
    .then(createConnection.bind(null, 3))
    .then(server.close.bind(server))
    .then(closeConnection.bind(null, 2));
});

process.on('exit', function() {
  // Confirm that all connections tried to send data...
  assert.deepStrictEqual(sent, ['0', '1', '2', '3']);
  // ...but that only connections 0 and 2 were successful.
  assert.deepStrictEqual(received, ['0', '2']);
});

process.on('unhandledRejection', function() {
  console.error('promise rejected');
  assert.fail('A promise in the chain rejected');
});