How to only allow one user connection alive at the same time with Nodejs and Expressjs?

Question

I just need to manage the concurrence on my app built with nodejs on the top of the nestjs framework.

As a far as I know, the most simplest way to do that is controlling that online one session user in expressjs is alive.

I am not taking care about security or whatever other issues, just want to know how many users are connected and restricting it to only one user session till its session is expired .

Here is my codebase

var express = require('express');
var session = require('express-session');
var app = express();

var numConnections = 0;


app.use(session({
    cookieName: 'sessionTest',
    secret: 'eg[isfd-8yF9-7w2315df{}+Ijsli;;to8', 
    cookie: {
      secure: false,
      maxAge: 1000 * 10,
      sameSite: true
    }
}));


app.use((req, res, next) => {
    console.log(req.session.store)
    console.log(req.session.ip)
    console.log(req.session.useragent)
    console.log(req.connection.remoteAddress)
    console.log(req.headers['user-agent'])
    if (numConnections === 0 
        // && req.session
        ) {
        req.session.ip = req.connection.remoteAddress;
        req.session.useragent = req.headers['user-agent'];
        req.session.page_views = 1;
        res.send("Welcome to this page for the first time!");
        numConnections++;
        console.log(req.session);
        next();
    }
    else if (numConnections == 1 &&
        req.session.ip === req.connection.remoteAddress
        && req.session.useragent === req.headers['user-agent']
    ) {
        req.session.page_views++;
        res.send("You visited this page " + req.session.page_views + " times");
        console.log('TEST');
        next();
    } else {
        console.log('There is someone using the app!!!');
        return res.sendStatus(401);
    }

})

app.listen(3001);

I really appreciate if someone can help me

Answer 1

You could use the store to retrieve the current amount of open sessions. The doc says stores may implement length and/or all methods. However, it appears that only the default MemoryStore handles these. You can look at all the compatible store implementations at the bottom of the page and pick the one that fits your environment.

It probably (ie not tested) looks like this:

var session = require('express-session');
var memoryStoreThatWillBeChangedBeforeLiveEnvironment = new MemoryStore();
...
app.use(session({
  ...
  store: memoryStoreThatWillBeChangedBeforeLiveEnvironment
}));

app.use((req, res, next) => {
  memoryStoreThatWillBeChangedBeforeLiveEnvironment.length((err, size) => {
    if (err) return res.status(418).send("I'm a teapot");
    var numConnections = size;
    // call your code here
  })
});

(Quite obviously, if an implementation only offers the all method, you can count the returned array of sessions.)