Node session is not saved correctly

Question

I see something very strange with node sessions. I use express-session and connect-mongo to save the session.

My session setup is as follows (all requests exceed https):

var session = require('express-session'); var MongoStore = require('connect-mongo/es5')(session); var sess = {}; app.use(session({ secret: 'xxxx', saveUninitialized: false, store: new MongoStore({ mongooseConnection: mongoose.connection, ttl: 60 * 30 // haf hour }), cookie: { secure: true } })); 

I have a route that creates an image with a node canvas:

 app.get('/api/canvas', function(req, res) { sess = req.session; console.log('in canvas and sess is ', sess); // create image stuff }); 

Elsewhere in the application, you can set things like background colors. Then I have a route to clear them:

 app.get('/api/clear', function(req, res) { sess = req.session; if (sess.colors) { delete sess.colors; } sess.save(function(err) { console.log('saved sess is now ', sess); // session saved helper.sendJsonResponse(req, res, 200, {}); }) }); 

helper.sendJsonResponse() just responds with a 200 HTTP code and an empty body.

You can see that I am using the callback for session.save() , as I only want to respond to the request when I KNOW that the session has been edited and saved.

However, this does not always work. If I set the colors in the session, then clear them (calling the api / clear route), then call the route to create the image (by calling the api / canvas route), the session on the api / canvas. The route session sometimes still has set colors.

This is similar to the case if I do it quickly. If I wait a few seconds, the colors will be cleared for the api / canvas route.

Note. I do not allow calls to these routes at the same time - I use promises and have a counter in the user interface that covers the entire screen until the requests are completely completed.

When this happens, the logs look like this:

 saved sess is now { cookie: { path: '/', _expires: null, originalMaxAge: null, httpOnly: true }, canvasHeight: 500, canvasWidth: 591 } 

And when I make an api / canvas request:

 in canvas and sess is { cookie: { path: '/', _expires: null, originalMaxAge: null, httpOnly: true }, canvasHeight: 500, canvasWidth: 591, colors: { color1: 'red', color2: 'green' } } 

so you can see, the colors property is still set. This occurs in approximately 50% of cases. The rest of the time, on the second request, the colors property was removed.

What could be wrong? I don’t understand how sessions work?

EDIT

This is getting weirder. If I link the calls in the user interface called the api / clear route, and then in the Promise then () method, call the api / canvas route, it ALWAYS works. If I call to make requests individually, the results are completely random - sometimes the session will be updated, sometimes it will not.

I checked req.sessionID and it is always the same for different requests.

EDIT Using the regeneration method works correctly, but not perfect, since I am losing everything in the session.

Answer 1

The delete operator deletes only the link, not the object itself. If he deleted the object itself, the other remaining links would be dangling, for example, C ++ delete. (And access to one of them will fail. In order for all of them to communicate with zero, this would mean that there is additional work when deleting or additional memory for each object.)

Since Javascript is garbage collection, you do not need to delete objects yourself - they will be deleted when there are no more links to them.

It may be useful to remove object references if you are done with them, because this gives the garbage collector additional information about what can be returned. If links remain on a large object, this may lead to its failure to be restored - even if the rest of your program does not actually use this object.

Link: http://jennifermann.ghost.io/deleting-objects-in-javascript/

Hope this helps.