express-session

What is express-session?

The express-session npm package is a middleware for Express applications that enables server-side session management. It allows you to store and access user data as they interact with your web application. The package creates a session ID for each client and uses it to store data across multiple HTTP requests.

What are express-session's main functionalities?

Session Initialization

This code initializes the express-session middleware with a secret to sign the session ID cookie, and configuration options such as 'resave', 'saveUninitialized', and 'cookie' settings.

const express = require('express');
const session = require('express-session');

const app = express();

app.use(session({
  secret: 'keyboard cat',
  resave: false,
  saveUninitialized: true,
  cookie: { secure: true }
}));

Storing Session Data

This code demonstrates how to store data in the session object. The value 'This is saved in session' is stored under the key 'myValue' in the session.

app.use(session({ /* ... */ }));

app.get('/save', function(req, res) {
  // Save a value to the session
  req.session.myValue = 'This is saved in session';
  res.send('Session value stored.');
});

Retrieving Session Data

This code shows how to retrieve data from the session. It accesses the value stored under the key 'myValue' and sends it in the HTTP response.

app.get('/retrieve', function(req, res) {
  // Retrieve a value from the session
  const myValue = req.session.myValue;
  res.send(`Session value: ${myValue}`);
});

Destroying a Session

This code provides an example of how to destroy a session, effectively logging out the user. It handles any errors that might occur during the destruction process.

app.get('/logout', function(req, res) {
  // Destroy the session
  req.session.destroy(function(err) {
    if(err) {
      return res.send('Error destroying session');
    }
    res.send('Session destroyed');
  });
});

Other packages similar to express-session

cookie-session

The cookie-session package is similar to express-session but stores the session data directly in a cookie on the client-side, rather than on the server. This can be simpler and more scalable for some applications, but it is less secure and has limitations on the amount of data you can store.

connect-redis

Connect-redis is a Redis session store for the express-session package. It requires express-session to be installed and configured, but it uses Redis to store session data, which can be more performant and scalable for applications with a high number of sessions.

connect-mongo

Connect-mongo is a MongoDB session store for the express-session package. Similar to connect-redis, it leverages MongoDB to store session data, providing a scalable and performant solution for managing sessions in Express applications.

README

express-session

Installation

$ npm install express-session

API

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

var app = express()

app.use(session({
  secret: 'keyboard cat',
  resave: false,
  saveUninitialized: true
}))

session(options)

Setup session store with the given options.

Session data is not saved in the cookie itself, just the session ID.

Options

• name - cookie name (formerly known as key). (default: 'connect.sid')
• store - session store instance.
• secret - session cookie is signed with this secret to prevent tampering.
• cookie - session cookie settings.
  • (default: { path: '/', httpOnly: true, secure: false, maxAge: null })
• genid - function to call to generate a new session ID. (default: uses uid2 library)
• rolling - forces a cookie set on every response. This resets the expiration date. (default: false)
• resave - forces session to be saved even when unmodified. (default: true, but using the default has been deprecated, as the default will change in the future. Please research into this setting and choose what is appropriate to your use-case. Typically, you'll want false)
• proxy - trust the reverse proxy when setting secure cookies (via "x-forwarded-proto" header). When set to true, the "x-forwarded-proto" header will be used. When set to false, all headers are ignored. When left unset, will use the "trust proxy" setting from express. (default: undefined)
• saveUninitialized - forces a session that is "uninitialized" to be saved to the store. A session is uninitialized when it is new but not modified. (default: true, but using the default has been deprecated, as the default will change in the future. Please research into this setting and choose what is appropriate to your use-case)
• unset - controls result of unsetting req.session (through delete, setting to null, etc.). This can be "keep" to keep the session in the store but ignore modifications or "destroy" to destroy the stored session. (default: 'keep')

options.genid

Generate a custom session ID for new sessions. Provide a function that returns a string that will be used as a session ID. The function is given req as the first argument if you want to use some value attached to req when generating the ID.

NOTE be careful you generate unique IDs so your sessions do not conflict.

app.use(session({
  genid: function(req) {
    return genuuid(); // use UUIDs for session IDs
  },
  secret: 'keyboard cat'
}))

options.resave

Forces the session to be saved back to the session store, even if the session was never modified during the request. Depending on your store this may be necessary, but it can also create race conditions where a client has two parallel requests to your server and changes made to the session in one request may get overwritten when the other request ends, even if it made no changes (this behavior also depends on what store you're using).

options.saveUninitialized

Forces a session that is "uninitialized" to be saved to the store. A session is uninitialized when it is new but not modified. Choosing false is useful for implementing login sessions, reducing server storage usage, or complying with laws that require permission before setting a cookie. Choose false will also help with race conditions where a client makes multiple parallel requests without a session.

Cookie options

Please note that secure: true is a recommended option. However, it requires an https-enabled website, i.e., HTTPS is necessary for secure cookies. If secure is set, and you access your site over HTTP, the cookie will not be set. If you have your node.js behind a proxy and are using secure: true, you need to set "trust proxy" in express:

var app = express()
app.set('trust proxy', 1) // trust first proxy
app.use(session({
  secret: 'keyboard cat',
  resave: false,
  saveUninitialized: true,
  cookie: { secure: true }
}))

For using secure cookies in production, but allowing for testing in development, the following is an example of enabling this setup based on NODE_ENV in express:

var app = express()
var sess = {
  secret: 'keyboard cat',
  cookie: {}
}

if (app.get('env') === 'production') {
  app.set('trust proxy', 1) // trust first proxy
  sess.cookie.secure = true // serve secure cookies
}

app.use(session(sess))

By default cookie.maxAge is null, meaning no "expires" parameter is set so the cookie becomes a browser-session cookie. When the user closes the browser the cookie (and session) will be removed.

req.session

To store or access session data, simply use the request property req.session, which is (generally) serialized as JSON by the store, so nested objects are typically fine. For example below is a user-specific view counter:

app.use(session({ secret: 'keyboard cat', cookie: { maxAge: 60000 }}))

app.use(function(req, res, next) {
  var sess = req.session
  if (sess.views) {
    sess.views++
    res.setHeader('Content-Type', 'text/html')
    res.write('<p>views: ' + sess.views + '</p>')
    res.write('<p>expires in: ' + (sess.cookie.maxAge / 1000) + 's</p>')
    res.end()
  } else {
    sess.views = 1
    res.end('welcome to the session demo. refresh!')
  }
})

Session.regenerate()

To regenerate the session simply invoke the method, once complete a new SID and Session instance will be initialized at req.session.

req.session.regenerate(function(err) {
  // will have a new session here
})

Session.destroy()

Destroys the session, removing req.session, will be re-generated next request.

req.session.destroy(function(err) {
  // cannot access session here
})

Session.reload()

Reloads the session data.

req.session.reload(function(err) {
  // session updated
})

Session.save()

req.session.save(function(err) {
  // session saved
})

Session.touch()

Updates the .maxAge property. Typically this is not necessary to call, as the session middleware does this for you.

req.session.cookie

Each session has a unique cookie object accompany it. This allows you to alter the session cookie per visitor. For example we can set req.session.cookie.expires to false to enable the cookie to remain for only the duration of the user-agent.

Cookie.maxAge

Alternatively req.session.cookie.maxAge will return the time remaining in milliseconds, which we may also re-assign a new value to adjust the .expires property appropriately. The following are essentially equivalent

var hour = 3600000
req.session.cookie.expires = new Date(Date.now() + hour)
req.session.cookie.maxAge = hour

For example when maxAge is set to 60000 (one minute), and 30 seconds has elapsed it will return 30000 until the current request has completed, at which time req.session.touch() is called to reset req.session.maxAge to its original value.

req.session.cookie.maxAge // => 30000

Session Store Implementation

Every session store must be an EventEmitter and implement the following methods:

• .get(sid, callback)
• .set(sid, session, callback)
• .destroy(sid, callback)

Recommended methods include, but are not limited to:

• .touch(sid, session, callback)
• .length(callback)
• .clear(callback)

For an example implementation view the connect-redis repo.

License

MIT