net-watcher.js

/***
 * Excerpted from "Node.js the Right Way",
 * published by The Pragmatic Bookshelf.
 * Copyrights apply to this code. It may not be used to create training material, 
 * courses, books, articles, and the like. Contact us if you are in doubt.
 * We make no guarantees that this code is fit for any purpose. 
 * Visit http://www.pragmaticprogrammer.com/titles/jwnode for more book information.
***/
'use strict';
const

  fs = require('fs'),
  net = require('net'),

  filename = process.argv[2],

  server = net.createServer(function (connection) {

      // reporting
      console.log('Subscriber connected.');
      connection.write(JSON.stringify({
          type: 'watching',
          file: filename
      }) + '\n');

      // watcher setup
      let watcher = fs.watch(filename, function () {
          connection.write(JSON.stringify({
              type: 'changed',
              file: filename,
              timestamp: Date.now()
          }) + '\n');
      });

      // cleanup
      connection.on('close', function () {
          console.log('Subscriber disconnected.');
          watcher.close();
      });
  });

if (!filename) {
    throw Error('No target filename was specified.');
}

server.listen(5432, function () {
    console.log('Listening for subscribers...');
});