express.js 4 and sockets with express router - express

Question

I'm trying to create a really simple node API using express.js 4 but I need a few 'realtime' events for which I added socket.io. I'm fairly new to both so I'm likely missing something basic but I can't find good docs/tuts on this.
In the express app (created with the express generator) I have something like this based on simple examples and project docs that I read. This works OK and from client apps, I can send/receive the socket events:
var express = require('express');
var path = require('path');
var logger = require('morgan');
var api = require('./routes/api');
var app = express();
var io = require('socket.io').listen(app.listen(3000));
app.use(logger('dev'));
app.use(express.static(path.join(__dirname, 'public')));
app.use('/api', api);
io.sockets.on('connection', function (socket) {
console.log('client connect');
socket.on('echo', function (data) {
io.sockets.emit('message', data);
});
});
// error handlers omitted
module.exports = app;
but I want to use the sockets from my API routes (in the ./routes/api.js file that I 'require' above). For example, someone might use the API to PUT/POST a resource and I want that broadcast to connected socket.io clients.
I cannot see how to use the 'io' variable or organise the code currently in the io.sockets.on('connection' ... function inside express routes. Here's the ./routes/api.js file:
var express = require('express');
var router = express.Router();
var io = ???;
router.put('/foo', function(req, res) {
/*
do stuff to update the foo resource
...
*/
// now broadcast the updated foo..
io.sockets.emit('update', foo); // how?
});
module.exports = router;

Answer 1

One option is to pass it in to req object.
app.js:
var express = require('express');
var path = require('path');
var logger = require('morgan');
var api = require('./routes/api');
var app = express();
var io = require('socket.io').listen(app.listen(3000));
app.use(logger('dev'));
app.use(express.static(path.join(__dirname, 'public')));
io.sockets.on('connection', function (socket) {
console.log('client connect');
socket.on('echo', function (data) {
io.sockets.emit('message', data);
});
});
// Make io accessible to our router
app.use(function(req,res,next){
req.io = io;
next();
});
app.use('/api', api);
// error handlers omitted
module.exports = app;
./routes/api.js:
var express = require('express');
var router = express.Router();
router.put('/foo', function(req, res) {
/*
do stuff to update the foo resource
...
*/
// now broadcast the updated foo..
req.io.sockets.emit('update', foo);
});
module.exports = router;

Answer 2

I've modified your files a little bit, may you check if it works?
You can pass the io you've defined to your routes like below;
require('./routes/api')(app,io);
I didn't test the Socket.IO parts but there is no syntax error and routes also working.
server.js file:
var express = require('express');
var app = express();
var path = require('path');
var logger = require('morgan');
var io = require('socket.io').listen(app.listen(3000));
app.use(logger('dev'));
app.use(express.static(path.join(__dirname, 'public')));
io.sockets.on('connection', function (socket) {
console.log('client connect');
socket.on('echo', function (data) {
io.sockets.emit('message', data);
});
});
require('./routes/api')(app,io);
console.log("Server listening at port 3000");
api.js:
module.exports = function(app,io) {
app.put('/foo', function(req, res) {
/*
do stuff to update the foo resource
...
*/
// now broadcast the updated foo..
console.log("PUT OK!");
io.sockets.emit('update'); // how?
res.json({result: "update sent over IO"});
});
}

Answer 3

Supposing you want to access the SocketIO from anywhere in your application, not just in the router, you could create a singleton for it. This is what works for me:
//socket-singletion.js
var socket = require('socket.io');
var SocketSingleton = (function() {
this.io = null;
this.configure = function(server) {
this.io = socket(server);
}
return this;
})();
module.exports = SocketSingleton;
Then, you need to configure it using your server:
//server config file
var SocketSingleton = require('./socket-singleton');
var http = require('http');
var server = http.createServer(app);
SocketSingleton.configure(server); // <--here
server.listen('3000');
Finally, use it wherever you want:
//router/index.js
var express = require('express');
var router = express.Router();
var SocketSingleton = require('../socket-singleton');
/* GET home page. */
router.get('/', function(req, res, next) {
setTimeout(function(){
SocketSingleton.io.emit('news', {msg: 'success!'});
}, 3000);
res.render('index', { title: 'Express' });
});
module.exports = router;

Answer 4

One more option is to use req.app.
app.js
const express = require('express');
const path = require('path');
const logger = require('morgan');
const api = require('./routes/api');
const app = express();
const io = require('socket.io').listen(app.listen(3000));
// Keep the io instance
app.io = io;
app.use(logger('dev'));
app.use(express.static(path.join(__dirname, 'public')));
// ...
app.use('/api', api);
module.exports = app;
routes/api.js
const express = require('express');
const router = express.Router();
router.put('/foo', function(req, res) {
/*
* API
*/
// Broadcast the updated foo..
req.app.io.sockets.emit('update', foo);
});
module.exports = router;

Answer 5

Refactored Edudjr's answer.
Change the singleton to create a new instance of socket.io server
const { Server } = require('socket.io');
const singleton = (() => {
this.configure = (server) => this.io = new Server(server)
return this
})();
module.exports = singleton
Initialise your express app, the server and the singleton.
// initialise app
const app = express();
const server = require('http').createServer(app);
// configure socket.io
socket.configure(server)
Then in your router
const socket = require('/utils/socket-singleton');
socket.io.emit('event', {message: 'your message here'})

Answer 6

I think best way is to set io as a property of req, like below:
app.use(function(req,res,next){
req.io = io;
next();
});
app.use('/your-sub-link', your-router);