WebSocket : Simple client and Server

25 Aug 2015

When I was looking for samples of WebSocket Server in NodeJS most results where using socket.io. But since I was learning I needed some more basic one. First I thought of using simple net.Socket, later I came to know that its just a TCP socket and WebSocket won’t works with it unless you use websockify to bridge in between.

Then I found ws, a basic WebSocket implementation. So I build a simple websocket server using ws.

// server.js
var Server = require('ws').Server;
var port = process.env.PORT || 9030;
var ws = new Server({port: port});

ws.on('connection', function(w){
  
  w.on('message', function(msg){
    console.log('message from client');
  });
  
  w.on('close', function() {
    console.log('closing connection');
  });

});

Now this server can accept connection.
Next we need a client.

var connection = new WebSocket('ws://localhost:9030');

connection.onopen = function () {
  
};

// Log errors
connection.onerror = function (error) {
  console.error('WebSocket Error ' + error);
};

// Log messages from the server
connection.onmessage = function (e) {

};

Now we can send message via WebSocket from server to client and back.

    w.on('message', function(msg){
      console.log('message from client :: ', msg);
    });

    w.send('message to client');

And I in client I received it message in onmessage event and from client I can send the message using send method.

// Log messages from the server
connection.onmessage = function (e) {
    console.log('message from server', e.data);
};

connection.send('hello from client');

Now when I need to send some message to individual client, I want to keep some reference/indetifier to each client. So I used sec-websocket-key in header. when each client gets connected I keep the object of connection in an array.

var Server = require('ws').Server;
var port = process.env.PORT || 9030;
var ws = new Server({port: port});

var sockets = [];
ws.on('connection', function(w){
  
  var id = w.upgradeReq.headers['sec-websocket-key'];
  console.log('New Connection id :: ', id);
  w.send(id);
  w.on('message', function(msg){
    var id = w.upgradeReq.headers['sec-websocket-key'];
    var message = JSON.parse(msg);
    
    sockets[message.to].send(message.message);

    console.log('Message on :: ', id);
    console.log('On message :: ', msg);
  });
  
  w.on('close', function() {
    var id = w.upgradeReq.headers['sec-websocket-key'];
    console.log('Closing :: ', id);
  });

  sockets[id] = w;
});

And for client I just I send a JSON with info whome this message should be delivered like

var data = {
    to: "sec-websocket-identifier",
    message: 'hello from client 1'
};
connection.send(JSON.stringify(data));

I think this is the base of 1-1 chat application.

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