huttj · October 10, 2015 00:48
diff --git a/index.html b/index.html
 <!DOCTYPE html>
 <html lang="en">
 <head>
    <meta charset="UTF-8">
    <title>Redis pubsub</title>
 </head>
 <body>

    <button id="add">Add 1</button>
    <p><span id="count">?</span> click(s)</p>

 <script src="/socket.io/socket.io.js"></script>
 <script>

    var CLIENT_INCREMENT = 'add';
    var CLIENT_COUNT     = 'count';

    var socket = io('http://localhost:{port}');

    var add   = document.getElementById('add');
    var count = document.getElementById('count');

    add.addEventListener('click', function () {
        socket.emit(CLIENT_INCREMENT);
    });

    socket.on(CLIENT_COUNT, function (n) {
        count.textContent = n;
    });

 </script>
 </body>
 </html>
diff --git a/index.js b/index.js
 // Make it easy to spin up the server on different ports
 var PORT = process.argv[2] || 3000;

 // Just some constants to make it easier to modify. Of note is
 // that the redis and socket.io event/message names are independent
 var CLIENT_INCREMENT = 'add';
 var REDIS_INCREMENT  = 'increment';
 var CLIENT_COUNT     = 'count';
 var REDIS_COUNT      = 'count';

 // You need two redis connections, because using `subscribe`
 // makes the connection unable to publish messages
 var redis = require('redis').createClient();
 var sub   = require('redis').createClient();

 // Standard socket.io fare
 var app   = require('http').createServer(handler);
 var io    = require('socket.io')(app);
 var fs    = require('fs');

 var count = 0; // Keep track of the current count, for new connections
 var indexHtml; // Cache to avoid reading from disk each time

 // Get current count after connecting
 redis.get(REDIS_COUNT, function(err, reply) {
    log('redis got count', reply);

    // If we're the first one, set the count to 0
    if (reply == null) {
        count = 0;
        redis.set(REDIS_COUNT, 0);
    } else {
        count = Number(reply);
    }
 });

 // Subscribe to messages on the 'incremented' channel
 sub.subscribe(REDIS_INCREMENT, noop);

 // Get notified when a message is published
 sub.on('message', function(channel, message) {

    // Ignore messages not on 'incremented' channel
    if (channel !== REDIS_INCREMENT) return;

    // Update local cache
    count++;

    // Send count to all connected clients
    io.emit(CLIENT_COUNT, count);
 });

 // Start the server
 app.listen(PORT, function(){
    log('Running on port:', PORT);
 });

 io.on('connection', function (socket) {
    log('connection', socket.handshake.address);

    // Send the current count to the client
    socket.emit(CLIENT_COUNT, count);

    // When the client generates an 'increment' event,
    // increment the global count and notify everyone
    socket.on(CLIENT_INCREMENT, function() {
        redis.incr(REDIS_COUNT);
        redis.publish(REDIS_INCREMENT, count);
    });
 });

 // console.log shorthand
 function log() {
    console.log.apply(console, arguments);
 }

 // Serve the index.html to new clients
 function handler (req, res) {
    if (indexHtml) {
        res.writeHead(200);
        return res.end(indexHtml);
    }

    fs.readFile(__dirname + '/index.html', function (err, data) {
        if (err) {
            res.writeHead(500);
            return res.end('Error loading index.html');
        }

        indexHtml = data.toString().replace(/\{port\}/, PORT);
        res.writeHead(200);
        res.end(indexHtml);
    });
 }

 function noop(){}
diff --git a/package.json b/package.json
 {
  "name": "Redis pubsub",
  "version": "0.0.1",
  "description": "Just a short demo of how to use redis to sync across servers.",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Joshua Hutt <[email protected]>",
  "license": "MIT",
  "dependencies": {
    "redis": "^2.1.0",
    "socket.io": "^1.3.7"
  }
 }
	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8">
	<title>Redis pubsub</title>
	</head>
	<body>

	<button id="add">Add 1</button>
	<p><span id="count">?</span> click(s)</p>

	<script src="/socket.io/socket.io.js"></script>
	<script>

	var CLIENT_INCREMENT = 'add';
	var CLIENT_COUNT = 'count';

	var socket = io('http://localhost:{port}');

	var add = document.getElementById('add');
	var count = document.getElementById('count');

	add.addEventListener('click', function () {
	socket.emit(CLIENT_INCREMENT);
	});

	socket.on(CLIENT_COUNT, function (n) {
	count.textContent = n;
	});

	</script>
	</body>
	</html>
	// Make it easy to spin up the server on different ports
	var PORT = process.argv[2] \|\| 3000;

	// Just some constants to make it easier to modify. Of note is
	// that the redis and socket.io event/message names are independent
	var CLIENT_INCREMENT = 'add';
	var REDIS_INCREMENT = 'increment';
	var CLIENT_COUNT = 'count';
	var REDIS_COUNT = 'count';

	// You need two redis connections, because using `subscribe`
	// makes the connection unable to publish messages
	var redis = require('redis').createClient();
	var sub = require('redis').createClient();

	// Standard socket.io fare
	var app = require('http').createServer(handler);
	var io = require('socket.io')(app);
	var fs = require('fs');

	var count = 0; // Keep track of the current count, for new connections
	var indexHtml; // Cache to avoid reading from disk each time

	// Get current count after connecting
	redis.get(REDIS_COUNT, function(err, reply) {
	log('redis got count', reply);

	// If we're the first one, set the count to 0
	if (reply == null) {
	count = 0;
	redis.set(REDIS_COUNT, 0);
	} else {
	count = Number(reply);
	}
	});

	// Subscribe to messages on the 'incremented' channel
	sub.subscribe(REDIS_INCREMENT, noop);

	// Get notified when a message is published
	sub.on('message', function(channel, message) {

	// Ignore messages not on 'incremented' channel
	if (channel !== REDIS_INCREMENT) return;

	// Update local cache
	count++;

	// Send count to all connected clients
	io.emit(CLIENT_COUNT, count);
	});

	// Start the server
	app.listen(PORT, function(){
	log('Running on port:', PORT);
	});

	io.on('connection', function (socket) {
	log('connection', socket.handshake.address);

	// Send the current count to the client
	socket.emit(CLIENT_COUNT, count);

	// When the client generates an 'increment' event,
	// increment the global count and notify everyone
	socket.on(CLIENT_INCREMENT, function() {
	redis.incr(REDIS_COUNT);
	redis.publish(REDIS_INCREMENT, count);
	});
	});

	// console.log shorthand
	function log() {
	console.log.apply(console, arguments);
	}

	// Serve the index.html to new clients
	function handler (req, res) {
	if (indexHtml) {
	res.writeHead(200);
	return res.end(indexHtml);
	}

	fs.readFile(__dirname + '/index.html', function (err, data) {
	if (err) {
	res.writeHead(500);
	return res.end('Error loading index.html');
	}

	indexHtml = data.toString().replace(/\{port\}/, PORT);
	res.writeHead(200);
	res.end(indexHtml);
	});
	}

	function noop(){}
	{
	"name": "Redis pubsub",
	"version": "0.0.1",
	"description": "Just a short demo of how to use redis to sync across servers.",
	"main": "index.js",
	"scripts": {
	"test": "echo \"Error: no test specified\" && exit 1"
	},
	"author": "Joshua Hutt <[email protected]>",
	"license": "MIT",
	"dependencies": {
	"redis": "^2.1.0",
	"socket.io": "^1.3.7"
	}
	}