Creating Socket.IO Server using Express Generator

Last Updated : 12 Jun, 2020

Socket.IO is a library for real-time communication between the server and the client. In Socket.IO, the headers are shared only once and it also works on the top of the TCP layer. Web Sockets are the base of the Socket.IO library. It is easier to implement the Socket.IO in the express applications that are not formed with express-generator.

Socket.IO mainly works on events based communication. Here the server or the client emits an event and it is being caught by another one.

Installation of modules:

Install the Express Generator:
```
npm install -g express-generator
```
Create the express application:
```
npm express applicaion_name
```
For example you can create “npm express socketIOTest”
We can also set the view engine while making the express application as:

Setting the view Engine (Optional)
```
npm express socketIOTest --view=jade
```

Install the socket IO:

npm install socket.io --save
npm install

Steps to create the socket server:

Go to the App.js file and Import Socket.IO and http module as:

var http=require("http");
var socketio=require("socket.io");

Create a socket IO server:

var createError = require('http-errors'); 
var express = require('express'); 
var path = require('path'); 
var cookieParser = require('cookie-parser'); 
var logger = require('morgan'); 
var http = require("http"); 
var socketio = require("socket.io"); 
var app = express(); 
  
var indexRouter = require('./routes/index'); 
var usersRouter = require('./routes/users'); 
  
// Create the http server 
const server = require('http').createServer(app); 
  
// Create the Socket IO server on  
// the top of http server 
const io = socketio(server); 
  
// View engine setup 
app.set('views', path.join(__dirname, 'views')); 
app.set('view engine', 'hbs'); 
  
app.use(logger('dev')); 
app.use(express.json()); 
app.use(express.urlencoded({ extended: false })); 
app.use(cookieParser()); 
app.use(express.static(path.join(__dirname, 'public'))); 
  
app.use('/', indexRouter); 
app.use('/users', usersRouter); 
  
// Catch 404 and forward to error handler 
app.use(function (req, res, next) { 
    next(createError(404)); 
}); 
  
// Error handler 
app.use(function (err, req, res, next) { 
  
    // Set locals, only providing error 
    // in development 
    res.locals.message = err.message; 
    res.locals.error = req.app.get('env')  
            === 'development' ? err : {}; 
  
    // render the error page 
    res.status(err.status || 500); 
    res.render('error'); 
}); 
  
module.exports = { app: app, server: server }; 

Now go to the www file inside the BIN folder and replace the code with the following code:

#!/usr/bin/env node 
  
// Module dependencies 
var app = require('../app').app; 
var debug = require('debug')('socketiotest:server'); 
var http = require('http'); 
  
// Get port from environment and store in Express 
var port = normalizePort(process.env.PORT || '3000'); 
app.set('port', port); 
  
// Create HTTP server 
var server = require("../app").server; 
  
// Listen on provided port, on all 
// network interfaces. 
  
server.listen(port); 
server.on('error', onError); 
server.on('listening', onListening); 
  
// Normalize a port into a number, 
// string, or false. 
function normalizePort(val) { 
    var port = parseInt(val, 10); 
  
    if (isNaN(port)) { 
  
        // Named pipe 
        return val; 
    } 
  
    if (port >= 0) { 
  
        // Port number 
        return port; 
    } 
  
    return false; 
} 
  
// Event listener for HTTP server "error" event 
function onError(error) { 
    if (error.syscall !== 'listen') { 
        throw error; 
    } 
  
    var bind = typeof port === 'string'
        ? 'Pipe ' + port 
        : 'Port ' + port; 
  
    // Handle specific listen errors with 
    // friendly messages 
    switch (error.code) { 
        case 'EACCES': 
            console.error(bind  
                + ' requires elevated privileges'); 
            process.exit(1); 
            break; 
        case 'EADDRINUSE': 
            console.error(bind + ' is already in use'); 
            process.exit(1); 
            break; 
        default: 
            throw error; 
    } 
} 
  
// Event listener for HTTP server "listening" event. 
function onListening() { 
    var addr = server.address(); 
    var bind = typeof addr === 'string'
        ? 'pipe ' + addr 
        : 'port ' + addr.port; 
    debug('Listening on ' + bind); 
} 

This is how you can link the Socket.IO with the express server.

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