monitor_internet_connection.js

/**
 * Copyright 2018 Google Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * @author ebidel@ (Eric Bidelman)
 */

/**
 * Uses Puppeteer and the browser's online/offline events to monitor internet
 * connection status.
 */

const util = require('util');
const dns = require('dns');
const puppeteer = require('puppeteer');

async function isConnected() {
  try {
    const lookupService = util.promisify(dns.lookupService);
    const result = await lookupService('8.8.8.8', 53);
    return true;
  } catch (err) {
    return false;
  }
}

puppeteer.launch().then(async browser => {
  const page = await browser.newPage();

  page.on('online', () => console.info('Online!'));
  page.on('offline', () => console.info('Offline!'));

  // Adds window.connectionChange in page.
  await page.exposeFunction('connectionChange', async online => {
    // Since online/offline events aren't 100% reliable, do an
    // actual dns lookup to verify connectivity.
    const isReallyConnected = await isConnected();
    page.emit(isReallyConnected ? 'online' : 'offline');
  });

  // Monitor browser online/offline events in the page.
  await page.evaluateOnNewDocument(() => {
    window.addEventListener('online', e => window.connectionChange(navigator.onLine));
    window.addEventListener('offline', e => window.connectionChange(navigator.onLine));
  });

  // Kick off a navigation so evaluateOnNewDocument runs.
  await page.goto('data:text/html,hi');


  // ... do other stuff ...

  // await browser.close(); // Don't close the browser so we can monitor!
});