Question

I am currently developing a chat system using Node.js. My question is, how do I handle multiple chat sessions with Node.js. That’s a bit vague so I’ll explain…

So for example two people might engage in a chat session. Node.js checks every couple of seconds for new messages. This is simple enough as I can get this to work fine using my code below.

My issue is when another two people at the same time are in another chat session.

At present I am sending two query strings called “chat_id” and “check_date” so it can check for new chat messages after a certain date and time.

Problem is, the “chat_id” and “check_date” are overwritten every time a new chat is started because the server is being used by both chat rooms.

Am I making sense?

My code below:

var chat_id, check_date;

var sys = require("sys"),  
    http = require("http"),  
    url = require("url"),  
    path = require("path"),  
    fs = require("fs"),  
    events = require("events");  

// Conntect to database
var Client = require('mysql').Client;
var client = new Client();
client.host = 'localhost';
client.port = 3306;
client.database = '****';
client.user = '****';
client.password = '****';
client.connect(function(error, results) {
  if(error) {
    console.log('Connection Error: ' + error.message);
    return;
  }
  console.log('Connected to MySQL');
});

// Check for chat updates
function getChatUpdates() {  

    if (typeof(check_date) == 'undefined')
        return;

    client.query('SELECT name, message FROM chat WHERE chat_id = "' + chat_id + '" AND date_entered > "' + check_date + '"', 
    function selectCb(error, results, fields) {
        if (error) {
            console.log('GetData Error: ' + error.message);
            client.end();
            return;
        }

        if (results.length > 0) {
            for(var i = 0;i<results.length;i++) {
                console.log('Name: ' + results[i]['name']);
                console.log('Message: ' + results[i]['message']);
            }
        }

  });

}  

// Set interval to check for chat updates every 2 seconds
setInterval(getChatUpdates, 2000);  

http.createServer(function(request, response) {  

    // Get the query strings
    var uri = url.parse(request.url, true);  
    chat_id = uri.query.chat_id;
    check_date = uri.query.check_date;
    console.log('Chat ID: ' + chat_id);
    console.log('Last Check: ' + check_date);

    // we'll do something here later.

}).listen(8080);  

sys.puts("Server running at http://localhost:8080/");

Answer 1

It seems like you are having a PHP background and when programming in node.js you should have a completely different mindset. You should not poll(setInterval(getChatUpdates, 2000);
) for messages, but push(callbacks/events) messages to users on event. I advice you to have a look at socket.io and use a in-memory database like redis(instead of mysql) to store your messages. When you code like this your site will perform much better and is going to be real-time(more). Also I would advice you to use express as your framework to develop websites instead of using raw http module. I don’t know if you already know about npm, but you should use that to manage your dependencies.