将 socket.io 升级到 v3 后出现快速会话问题

Question

I'm working on a Node/Express backend that uses the socket.io library to send events to the frontend. We've decided to upgrade it (both in the backend and frontend) to version 3 and we're having an issue that we can't solve so far. I'll try to explain it:

• Whenever a client authenticates with the backend, it opens a socket connection between them
• We use the express-session library to save the new socket ID into the session with the following code:

this._socketIO.on('connection', socket => {
    // Add the socket id to the session
    socket.request.session.socketId = socket.id;
    socket.request.session.save();

    logger().info(`WebSocket: User connected (ID: ${socket.id})`);
    
    socket.on('disconnect', () => {
        logger().info(`WebSocket: User disconnected (ID: ${socket.id})`);
    });
});

• After updating the socket library to v3.0.4, the session doesn't have the socketId field anymore.
• I've realized that if I restart the backend server, while there's a logged client in the UI (and, so, there's an existing session file), it works fine. If I log out from the UI and log in again (so it creates a new session file), it doesn't work again.

I've been checking the migration documentation from the official page ( https://socket.io/docs/v3/migrating-from-2-x-to-3-0 ) but I couldn't find an answer for this problem.

Any clues? Thanks in advance,

Answer 1

We've found out that the problem is because we've registered 2 session middlewares, one for the regular requests and another one for the socket requests (to save the associated socket ID) and sometimes it fails due to a race condition. Depending on which requests is managed first, the session is saved with the socket id or not.

We've delayed the socket connection after all the needed login requests are done and now it's working fine.

Cheers,