express-session loses session when app runs into error about session

[joewagner]

Unless specifically done in your application's code, session saving is done by proxy of req.end.
What is happening is that your call to Session#regenerate is destroying the session in redis. Then the error occurs before the newly generated session is initially saved –since req.end isn't called–. Two solutions might be:

1. save the session immediately in the regenerate callback
2. Don't regenerate the session on each request, particularly since this creates a race condition if a user makes two concurrent requests from the same client.

I don't think this is an express-session issue, feel free to reopen this if you disagree.