Differences between socket.io and websockets

2012-04-12 node.js google-chrome firebug websocket socket.io

What are the differences between socket.io and websockets in node.js?
Are they both server push technologies? The only differences I felt was,

  1. socket.io allowed me to send/emit messages by specifying an event name.

  2. In the case of socket.io a message from server will reach on all clients, but for the same in websockets I was forced to keep an array of all connections and loop through it to send messages to all clients.

Also, I wonder why web inspectors (like Chrome/firebug/fiddler) are unable to catch these messages (from socket.io/websocket) from server?

Please clarify this.

Answers

Its advantages are that it simplifies the usage of WebSockets as you described in #2, and probably more importantly it provides fail-overs to other protocols in the event that WebSockets are not supported on the browser or server. I would avoid using WebSockets directly unless you are very familiar with what environments they don't work and you are capable of working around those limitations.

This is a good read on both WebSockets and Socket.IO.

http://davidwalsh.name/websocket

Im going to provide an argument against using socket.io.

I think using socket.io solely because it has fallbacks isnt a good idea. Let IE8 RIP.

In the past there have been many cases where new versions of NodeJS has broken socket.io. You can check these lists for examples... https://github.com/socketio/socket.io/issues?q=install+error

If you go to develop an Android app or something that needs to work with your existing app, you would probably be okay working with WS right away, socket.io might give you some trouble there...

Plus the WS module for Node.JS is amazingly simple to use.

Misconceptions

There are few common misconceptions regarding WebSocket and Socket.IO:

  1. The first misconception is that using Socket.IO is significantly easier than using WebSocket which doesn't seem to be the case. See examples below.

  2. The second misconception is that WebSocket is not widely supported in the browsers. See below for more info.

  3. The third misconception is that Socket.IO downgrades the connection as a fallback on older browsers. It actually assumes that the browser is old and starts an AJAX connection to the server, that gets later upgraded on browsers supporting WebSocket, after some traffic is exchanged. See below for details.

My experiment

I wrote an npm module to demonstrate the difference between WebSocket and Socket.IO:

It is a simple example of server-side and client-side code - the client connects to the server using either WebSocket or Socket.IO and the server sends three messages in 1s intervals, which are added to the DOM by the client.

Server-side

Compare the server-side example of using WebSocket and Socket.IO to do the same in an Express.js app:

WebSocket Server

WebSocket server example using Express.js:

var path = require('path');
var app = require('express')();
var ws = require('express-ws')(app);
app.get('/', (req, res) => {
  console.error('express connection');
  res.sendFile(path.join(__dirname, 'ws.html'));
});
app.ws('/', (s, req) => {
  console.error('websocket connection');
  for (var t = 0; t < 3; t++)
    setTimeout(() => s.send('message from server', ()=>{}), 1000*t);
});
app.listen(3001, () => console.error('listening on http://localhost:3001/'));
console.error('websocket example');

Source: https://github.com/rsp/node-websocket-vs-socket.io/blob/master/ws.js

Socket.IO Server

Socket.IO server example using Express.js:

var path = require('path');
var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);
app.get('/', (req, res) => {
  console.error('express connection');
  res.sendFile(path.join(__dirname, 'si.html'));
});
io.on('connection', s => {
  console.error('socket.io connection');
  for (var t = 0; t < 3; t++)
    setTimeout(() => s.emit('message', 'message from server'), 1000*t);
});
http.listen(3002, () => console.error('listening on http://localhost:3002/'));
console.error('socket.io example');

Source: https://github.com/rsp/node-websocket-vs-socket.io/blob/master/si.js

Client-side

Compare the client-side example of using WebSocket and Socket.IO to do the same in the browser:

WebSocket Client

WebSocket client example using vanilla JavaScript:

var l = document.getElementById('l');
var log = function (m) {
    var i = document.createElement('li');
    i.innerText = new Date().toISOString()+' '+m;
    l.appendChild(i);
}
log('opening websocket connection');
var s = new WebSocket('ws://'+window.location.host+'/');
s.addEventListener('error', function (m) { log("error"); });
s.addEventListener('open', function (m) { log("websocket connection open"); });
s.addEventListener('message', function (m) { log(m.data); });

Source: https://github.com/rsp/node-websocket-vs-socket.io/blob/master/ws.html

Socket.IO Client

Socket.IO client example using vanilla JavaScript:

var l = document.getElementById('l');
var log = function (m) {
    var i = document.createElement('li');
    i.innerText = new Date().toISOString()+' '+m;
    l.appendChild(i);
}
log('opening socket.io connection');
var s = io();
s.on('connect_error', function (m) { log("error"); });
s.on('connect', function (m) { log("socket.io connection open"); });
s.on('message', function (m) { log(m); });

Source: https://github.com/rsp/node-websocket-vs-socket.io/blob/master/si.html

Network traffic

To see the difference in network traffic you can run my test. Here are the results that I got:

WebSocket Results

2 requests, 1.50 KB, 0.05 s

From those 2 requests:

  1. HTML page itself
  2. connection upgrade to WebSocket

(The connection upgrade request is visible on the developer tools with a 101 Switching Protocols response.)

Socket.IO Results

6 requests, 181.56 KB, 0.25 s

From those 6 requests:

  1. the HTML page itself
  2. Socket.IO's JavaScript (180 kilobytes)
  3. first long polling AJAX request
  4. second long polling AJAX request
  5. third long polling AJAX request
  6. connection upgrade to WebSocket

Screenshots

WebSocket results that I got on localhost:

WebSocket results - websocket-vs-socket.io module

Socket.IO results that I got on localhost:

Socket.IO results - websocket-vs-socket.io module

Test yourself

Quick start:

# Install:
npm i -g websocket-vs-socket.io
# Run the server:
websocket-vs-socket.io

Open http://localhost:3001/ in your browser, open developer tools with Shift+Ctrl+I, open the Network tab and reload the page with Ctrl+R to see the network traffic for the WebSocket version.

Open http://localhost:3002/ in your browser, open developer tools with Shift+Ctrl+I, open the Network tab and reload the page with Ctrl+R to see the network traffic for the Socket.IO version.

To uninstall:

# Uninstall:
npm rm -g websocket-vs-socket.io

Browser compatibility

As of June 2016 WebSocket works on everything except Opera Mini, including IE higher than 9.

This is the browser compatibility of WebSocket on Can I Use as of June 2016:

enter image description here

See http://caniuse.com/websockets for up-to-date info.

Using Socket.IO is basically like using jQuery - you want to support older browsers, you need to write less code and the library will provide with fallbacks. Socket.io uses the websockets technology if available, and if not, checks the best communication type available and uses it.

Socket.IO uses WebSocket and when WebSocket is not available uses fallback algo to make real time connections.

Even if modern browsers support WebSockets now, I think there is no need to throw SocketIO away and it still has its place in any nowadays project. It's easy to understand, and personally, I learned how WebSockets work thanks to SocketIO.

As said in this topic, there's a plenty of integration libraries for Angular, React, etc. and definition types for TypeScript and other programming languages.

The other point I would add to the differences between Socket.io and WebSockets is that clustering with Socket.io is not a big deal. Socket.io offers Adapters that can be used to link it with Redis to enhance scalability. You have ioredis and socket.io-redis for example.

Yes I know, SocketCluster exists, but that's off-topic.

https://socket.io/docs/#What-Socket-IO-is-not (with my emphasis)

What Socket.IO is not

Socket.IO is NOT a WebSocket implementation. Although Socket.IO indeed uses WebSocket as a transport when possible, it adds some metadata to each packet: the packet type, the namespace and the packet id when a message acknowledgement is needed. That is why a WebSocket client will not be able to successfully connect to a Socket.IO server, and a Socket.IO client will not be able to connect to a WebSocket server either. Please see the protocol specification here.

// WARNING: the client will NOT be able to connect!
const client = io('ws://echo.websocket.org');

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