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I'm writing an event-driven publish/subscribe application with NodeJS and Redis. I need an example of how to notify web clients when the data values in Redis change.
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Implementing publish in Node. js file in the publish directory that will contain our code: const redis = require('redis'); const publisher = redis. createClient(); (async () => { const article = { id: '123456', name: 'Using Redis Pub/Sub with Node. js', blog: 'Logrocket Blog', }; await publisher.
Create new session. js file in the root directory with the following content: const express = require('express'); const session = require('express-session'); const redis = require('redis'); const client = redis. createClient(); const redisStore = require('connect-redis')(session); const app = express(); app.
Redis does not provide guaranteed delivery using its Pub/Sub mechanism. Moreover, if a subscriber is not actively listening on a channel, it will not receive messages that would have been published.
uses express, socket.io, node_redis and last but not least the sample code from media fire.
First you should(if you have not done this yet) install node.js+npm in 30 seconds (the right way because you should NOT run npm as root):
echo 'export PATH=$HOME/local/bin:$PATH' >> ~/.bashrc . ~/.bashrc mkdir ~/local mkdir ~/node-latest-install cd ~/node-latest-install curl http://nodejs.org/dist/node-latest.tar.gz | tar xz --strip-components=1 ./configure --prefix=~/local make install # ok, fine, this step probably takes more than 30 seconds... curl http://npmjs.org/install.sh | sh After you installed node+npm you should install dependencies by issuing:
npm install express npm install socket.io npm install hiredis redis # hiredis to use c binding for redis => FAST :) You can download complete sample from mediafire.
unzip pbsb.zip # can also do via graphical interface if you prefer. ./app.js
const PORT = 3000; const HOST = 'localhost'; var express = require('express'); var app = module.exports = express.createServer(); app.use(express.staticProvider(__dirname + '/public')); const redis = require('redis'); const client = redis.createClient(); const io = require('socket.io'); if (!module.parent) { app.listen(PORT, HOST); console.log("Express server listening on port %d", app.address().port) const socket = io.listen(app); socket.on('connection', function(client) { const subscribe = redis.createClient(); subscribe.subscribe('pubsub'); // listen to messages from channel pubsub subscribe.on("message", function(channel, message) { client.send(message); }); client.on('message', function(msg) { }); client.on('disconnect', function() { subscribe.quit(); }); }); } ./public/index.html
<html> <head> <title>PubSub</title> <script src="/socket.io/socket.io.js"></script> <script src="/javascripts/jquery-1.4.3.min.js"></script> </head> <body> <div id="content"></div> <script> $(document).ready(function() { var socket = new io.Socket('localhost', {port: 3000, rememberTransport: false/*, transports: ['xhr-polling']*/}); var content = $('#content'); socket.on('connect', function() { }); socket.on('message', function(message){ content.prepend(message + '<br />'); }) ; socket.on('disconnect', function() { console.log('disconnected'); content.html("<b>Disconnected!</b>"); }); socket.connect(); }); </script> </body> </html> cd pbsb node app.js Best if you start google chrome(because of websockets support, but not necessary). Visit http://localhost:3000 to see sample(in the beginning you don't see anything but PubSub as title).
But on publish to channel pubsub you should see a message. Below we publish "Hello world!" to the browser.
publish pubsub "Hello world!" here's a simplified example without as many dependencies. You do still need to npm install hiredis redis
The node JavaScript:
var redis = require("redis"), client = redis.createClient(); client.subscribe("pubsub"); client.on("message", function(channel, message){ console.log(channel + ": " + message); }); ...put that in a pubsub.js file and run node pubsub.js
in redis-cli:
redis> publish pubsub "Hello Wonky!" (integer) 1 which should display: pubsub: Hello Wonky! in the terminal running node! Congrats!
Additional 4/23/2013: I also want to make note that when a client subscribes to a pub/sub channel it goes into subscriber mode and is limited to subscriber commands. You'll just need to create additional instances of redis clients. client1 = redis.createClient(), client2 = redis.createClient() so one can be in subscriber mode and the other can issue regular DB commands.
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