Errors when using uWebsockets while clients are connected and server restarts

Describe the bug
Hi,

at my company we are in the middle of switching from express to uWebSockets.

We use

• Nestjs
• Ultimate-Express
• socket.io with attachApp
• engine.use(sessionMiddleware) <- thats the problem... or maybe not? (express-session)

While everything works really good, there is one thing we get errors.

1. Server starts deployment, after that clients can connect and everything works
2. Server goes down, restarts, etc. the client browser stays open!!
3. When Server is up again, the reconnecting begins (sessionMiddleware is called)
4. Various errors are showing up:

5. Ok so I first thought hmm my sessionMiddleware does some bad things
6. But after some debugging, I could fix it quite easy in uServer -> handleUpgrade

1. I had to cork the response write and upgrade
2. I saved the header before entering the async callback

I'm sry that I cannot really give a code example for this problem.

But does this seems to be a bug or just a problem in my project?

Nice to know, I absolutely don't have any error or problems after changing these few lines.

(Re-)Connecting with engine.use and express-session middleware works like a charm.

Platform:

• OS: [e.g. Linux, Windows, Mac]

Thanks in advance!

Start by inspecting the uServer handleUpgrade path and the engine.use(sessionMiddleware) integration described in the report. Reproduce a server restart while browser clients remain connected, then trace reconnect handling and response writes; done means the reported errors no longer occur with this setup.