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

This is a Node.js module available through the npm registry. Installation is done using the npm install command:

$ npm install express-session

API

var session = require('express-session')

session(options)

Create a session middleware with the given options.

Note Session data is not saved in the cookie itself, just the session ID. Session data is stored server-side.

Note Since version 1.5.0, the cookie-parser middleware no longer needs to be used for this module to work. This module now directly reads and writes cookies on req/res. Using cookie-parser may result in issues if the secret is not the same between this module and cookie-parser.

Warning The default server-side session storage, MemoryStore, is purposely not designed for a production environment. It will leak memory under most conditions, does not scale past a single process, and is meant for debugging and developing.

For a list of stores, see compatible session stores.

Options

express-session accepts these properties in the options object.

cookie

Settings object for the session ID cookie. The default value is { path: '/', httpOnly: true, secure: false, maxAge: null }.

The following are options that can be set in this object.

cookie.domain

Specifies the value for the Domain Set-Cookie attribute. By default, no domain is set, and most clients will consider the cookie to apply to only the current domain.

cookie.expires

Specifies the Date object to be the value for the Expires Set-Cookie attribute. By default, no expiration is set, and most clients will consider this a "non-persistent cookie" and will delete it on a condition like exiting a web browser application.

Note If both expires and maxAge are set in the options, then the last one defined in the object is what is used.

Note The expires option should not be set directly; instead only use the maxAge option.

cookie.httpOnly

Specifies the boolean value for the HttpOnly Set-Cookie attribute. When truthy, the HttpOnly attribute is set, otherwise it is not. By default, the HttpOnly attribute is set.

Note be careful when setting this to true, as compliant clients will not allow client-side JavaScript to see the cookie in document.cookie.

cookie.maxAge

Specifies the number (in milliseconds) to use when calculating the Expires Set-Cookie attribute. This is done by taking the current server time and adding maxAge milliseconds to the value to calculate an Expires datetime. By default, no maximum age is set.

Note If both expires and maxAge are set in the options, then the last one defined in the object is what is used.

cookie.path

Specifies the value for the Path Set-Cookie. By default, this is set to '/', which is the root path of the domain.

cookie.sameSite

Specifies the boolean or string to be the value for the SameSite Set-Cookie attribute.

• true will set the SameSite attribute to Strict for strict same site enforcement.
• false will not set the SameSite attribute.
• 'lax' will set the SameSite attribute to Lax for lax same site enforcement.
• 'strict' will set the SameSite attribute to Strict for strict same site enforcement.

More information about the different enforcement levels can be found in the specification https://tools.ietf.org/html/draft-west-first-party-cookies-07#section-4.1.1

Note This is an attribute that has not yet been fully standardized, and may change in the future. This also means many clients may ignore this attribute until they understand it.

cookie.secure

Specifies the boolean value for the Secure Set-Cookie attribute. When truthy, the Secure attribute is set, otherwise it is not. By default, the Secure attribute is not set.

Note be careful when setting this to true, as compliant clients will not send the cookie back to the server in the future if the browser does not have an HTTPS connection.

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))

The cookie.secure option can also be set to the special value 'auto' to have this setting automatically match the determined security of the connection. Be careful when using this setting if the site is available both as HTTP and HTTPS, as once the cookie is set on HTTPS, it will no longer be visible over HTTP. This is useful when the Express "trust proxy" setting is properly setup to simplify development vs production configuration.

genid

Function to call to generate a new session ID. 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.

The default value is a function which uses the uid-safe library to generate IDs.

NOTE be careful to 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'
}))

name

The name of the session ID cookie to set in the response (and read from in the request).

The default value is 'connect.sid'.

Note if you have multiple apps running on the same hostname (this is just the name, i.e. localhost or 127.0.0.1; different schemes and ports do not name a different hostname), then you need to separate the session cookies from each other. The simplest method is to simply set different names per app.

proxy

Trust the reverse proxy when setting secure cookies (via the "X-Forwarded-Proto" header).

The default value is undefined.

• true The "X-Forwarded-Proto" header will be used.
• false All headers are ignored and the connection is considered secure only if there is a direct TLS/SSL connection.
• undefined Uses the "trust proxy" setting from express

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 makes 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).

The default value is 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.

How do I know if this is necessary for my store? The best way to know is to check with your store if it implements the touch method. If it does, then you can safely set resave: false. If it does not implement the touch method and your store sets an expiration date on stored sessions, then you likely need resave: true.

rolling

Force a session identifier cookie to be set on every response. The expiration is reset to the original maxAge, resetting the expiration countdown.

The default value is false.

Note When this option is set to true but the saveUninitialized option is set to false, the cookie will not be set on a response with an uninitialized session.

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. Choosing false will also help with race conditions where a client makes multiple parallel requests without a session.

The default value is 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.

Note if you are using Session in conjunction with PassportJS, Passport will add an empty Passport object to the session for use after a user is authenticated, which will be treated as a modification to the session, causing it to be saved. This has been fixed in PassportJS 0.3.0

secret

Required option

This is the secret used to sign the session ID cookie. This can be either a string for a single secret, or an array of multiple secrets. If an array of secrets is provided, only the first element will be used to sign the session ID cookie, while all the elements will be considered when verifying the signature in requests.

store

The session store instance, defaults to a new MemoryStore instance.

unset

Control the result of unsetting req.session (through delete, setting to null, etc.).

The default value is 'keep'.

• 'destroy' The session will be destroyed (deleted) when the response ends.
• 'keep' The session in the store will be kept, but modifications made during the request are ignored and not saved.

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:

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

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

Session.regenerate(callback)

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

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

Session.destroy(callback)

Destroys the session and will unset the req.session property. Once complete, the callback will be invoked.

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

Session.reload(callback)

Reloads the session data from the store and re-populates the req.session object. Once complete, the callback will be invoked.

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

Session.save(callback)

Save the session back to the store, replacing the contents on the store with the contents in memory (though a store may do something else--consult the store's documentation for exact behavior).

This method is automatically called at the end of the HTTP response if the session data has been altered (though this behavior can be altered with various options in the middleware constructor). Because of this, typically this method does not need to be called.

There are some cases where it is useful to call this method, for example, redirects, long-lived requests or in WebSockets.

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.id

Each session has a unique ID associated with it. This property is an alias of req.sessionID and cannot be modified. It has been added to make the session ID accessible from the session object.

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

req.sessionID

To get the ID of the loaded session, access the request property req.sessionID. This is simply a read-only value set when a session is loaded/created.

Session Store Implementation

Every session store must be an EventEmitter and implement specific methods. The following methods are the list of required, recommended, and optional.

• Required methods are ones that this module will always call on the store.
• Recommended methods are ones that this module will call on the store if available.
• Optional methods are ones this module does not call at all, but helps present uniform stores to users.

For an example implementation view the connect-redis repo.

store.all(callback)

Optional

This optional method is used to get all sessions in the store as an array. The callback should be called as callback(error, sessions).

store.destroy(sid, callback)

Required

This required method is used to destroy/delete a session from the store given a session ID (sid). The callback should be called as callback(error) once the session is destroyed.

store.clear(callback)

Optional

This optional method is used to delete all sessions from the store. The callback should be called as callback(error) once the store is cleared.

store.length(callback)

Optional

This optional method is used to get the count of all sessions in the store. The callback should be called as callback(error, len).

store.get(sid, callback)

Required

This required method is used to get a session from the store given a session ID (sid). The callback should be called as callback(error, session).

The session argument should be a session if found, otherwise null or undefined if the session was not found (and there was no error). A special case is made when error.code === 'ENOENT' to act like callback(null, null).

store.set(sid, session, callback)

Required

This required method is used to upsert a session into the store given a session ID (sid) and session (session) object. The callback should be called as callback(error) once the session has been set in the store.

store.touch(sid, session, callback)

Recommended

This recommended method is used to "touch" a given session given a session ID (sid) and session (session) object. The callback should be called as callback(error) once the session has been touched.

This is primarily used when the store will automatically delete idle sessions and this method is used to signal to the store the given session is active, potentially resetting the idle timer.

Compatible Session Stores

The following modules implement a session store that is compatible with this module. Please make a PR to add additional modules :)

aerospike-session-store A session store using Aerospike.

cassandra-store An Apache Cassandra-based session store.

cluster-store A wrapper for using in-process / embedded stores - such as SQLite (via knex), leveldb, files, or memory - with node cluster (desirable for Raspberry Pi 2 and other multi-core embedded devices).

connect-azuretables An Azure Table Storage-based session store.

connect-cloudant-store An IBM Cloudant-based session store.

connect-couchbase A couchbase-based session store.

connect-datacache An IBM Bluemix Data Cache-based session store.

connect-db2 An IBM DB2-based session store built using ibm_db module.

connect-dynamodb A DynamoDB-based session store.

connect-loki A Loki.js-based session store.

connect-ml A MarkLogic Server-based session store.

connect-mssql A SQL Server-based session store.

connect-monetdb A MonetDB-based session store.

connect-mongo A MongoDB-based session store.

connect-mongodb-session Lightweight MongoDB-based session store built and maintained by MongoDB.

connect-pg-simple A PostgreSQL-based session store.

connect-redis A Redis-based session store.

connect-memcached A memcached-based session store.

connect-memjs A memcached-based session store using memjs as the memcached client.

connect-session-knex A session store using Knex.js, which is a SQL query builder for PostgreSQL, MySQL, MariaDB, SQLite3, and Oracle.

connect-session-sequelize A session store using Sequelize.js, which is a Node.js / io.js ORM for PostgreSQL, MySQL, SQLite and MSSQL.

dynamodb-store A DynamoDB-based session store.

express-mysql-session A session store using native MySQL via the node-mysql module.

express-oracle-session A session store using native oracle via the node-oracledb module.

express-sessions: A session store supporting both MongoDB and Redis.

connect-sqlite3 A SQLite3 session store modeled after the TJ's connect-redis store.

documentdb-session A session store for Microsoft Azure's DocumentDB NoSQL database service.

express-nedb-session A NeDB-based session store.

express-session-cache-manager A store that implements cache-manager, which supports a variety of storage types.

express-session-level A LevelDB based session store.

express-etcd An etcd based session store.

fortune-session A Fortune.js based session store. Supports all backends supported by Fortune (MongoDB, Redis, Postgres, NeDB).

hazelcast-store A Hazelcast-based session store built on the Hazelcast Node Client.

level-session-store A LevelDB-based session store.

medea-session-store A Medea-based session store.

memorystore A memory session store made for production.

mssql-session-store A SQL Server-based session store.

nedb-session-store An alternate NeDB-based (either in-memory or file-persisted) session store.

sequelstore-connect A session store using Sequelize.js.

session-file-store A file system-based session store.

session-rethinkdb A RethinkDB-based session store.

Example

A simple example using express-session to store page views for a user.

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

var app = express()

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

app.use(function (req, res, next) {
  if (!req.session.views) {
    req.session.views = {}
  }

  // get the url pathname
  var pathname = parseurl(req).pathname

  // count the views
  req.session.views[pathname] = (req.session.views[pathname] || 0) + 1

  next()
})

app.get('/foo', function (req, res, next) {
  res.send('you viewed this page ' + req.session.views['/foo'] + ' times')
})

app.get('/bar', function (req, res, next) {
  res.send('you viewed this page ' + req.session.views['/bar'] + ' times')
})

License

MIT