Using Express.js, sessions are dead simple. I'm curious how they actually work though.
Does it store some cookie on the client? If so, where can I find that cookie? If required, how do I decode it?
I basically want to be able to see if a user is logged in, even when the user is not actually on the site at the time (like how facebook knows you're logged in when you're on other sites). But I suppose to understand that I should first understand how sessions work.
Here, since sess is global, the session won't work for multiple users as the server will create the same session for all the users. This can be solved by using what is called a session store. We have to store every session in the store so that each one will belong to only a single user.
With express-session in particular, it has a built-in "not-meant-for-production" memory store (so session data is kept in memory and would not survive a server restart).
Express.js uses a cookie to store a session id (with an encryption signature) in the user's browser and then, on subsequent requests, uses the value of that cookie to retrieve session information stored on the server. This server side storage can be a memory store (default) or any other store which implements the required methods (like connect-redis).
Express.js/Connect creates a 24-character Base64 string using utils.uid(24)
and stores it in req.sessionID
. This string is then used as the value in a cookie.
Signed cookies are always used for sessions, so the cookie value will have the following format.
[sid].[signature]
Where [sid] is the sessionID and [signature] is generated by signing [sid] using the secret key provided when initializing the session middleware. The signing step is done to prevent tampering. It should be computationally infeasable to modify [sid] and then recreate [signature] without knowledge of the secret key used. The session cookie is still vulnerable to theft and reuse, if no modification of [sid] is required.
The name for this cookie is
connect.sid
If a handler occurs after the cookieParser
and session
middleware it will have access to the variable req.cookies
. This contains a JSON object whose keys are the cookie keys and values are the cookie values. This will contain a key named connect.sid
and its value will be the signed session identifier.
Here's an example of how to set up a route that will check for the existence of the session cookie on every request and print its value to the console.
app.get("/*", function(req, res, next) { if(typeof req.cookies['connect.sid'] !== 'undefined') { console.log(req.cookies['connect.sid']); } next(); // Call the next middleware });
You'll also need to make sure the router (app.use(app.router)
) is included after cookieParser
and session
in your configure section.
The following is an example of the data stored internally by Express.js/Connect.
{ "lastAccess": 1343846924959, "cookie": { "originalMaxAge": 172800000, "expires": "2012-08-03T18:48:45.144Z", "httpOnly": true, "path": "/" }, "user": { "name":"waylon", "status":"pro" } }
The user
field is custom. Everything else is part of session management.
The example is from Express 2.5.
I have never used Express.js, although according to their documentation on the subject it sounds like:
Cookies are stored on the client, with a key (which the server will use to retrieve the session data) and a hash (which the server will use to make sure the cookie data hasn't been tampered with, so if you try and change a value the cookie will be invalid)
The session data, as opposed to some frameworks (e.g. Play Framework!) is held on the server, so the cookie is more like a placeholder for the session than a holder of actual session data.
From here, it looks like this session data on the server is by default held in memory, although that could be altered to whatever storage form implements the appropriate API.
So if you want to check things without a specific req
request object, like you said, you need to just access that same storage. On the bottom of the first documentation page, it details required methods the storage needs to implement, so if you're familiar with your storage API, maybe you could execute a .getAll()
if something like that exists, and loop through the session data and read whatever values you want.
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With