What is the best Socket.IO design for my application? - sockets

Question

Realising this is gonna be a very general question but I am gonna try to be as specific as possible:
What is the best way to design/structure an Socket.IO app?
I have a NodeJS backend with React frontend, with authentication (user must log in). I have several REST endpoints, for example /foo, /bar, /baz.
I know you can use rooms and namespaces, and I know you can add authentication to the connect as middleware, but I have no idea what the best solution is to glue this all together. I will be using this socket for multiple purposes. For each purpose I am curious what the best way to go is (flow).
General CRUD messages: When someone posts a "foo" on the server side, it needs to also send this to that particular user. WHen someone deletes a "foo", it also needs to send something to this user. So this CRUD messaging should only be for one specific user (based on logged in user ID). How would structure those messages? Namespace for "foo"? Multiple event listeners: on "foo create", on "foo delete", on "foo update?" How to make sure you only send to this user?
I have multiple pages on the client side, for the respective CRUD endpoint. So when I am on the "foo" page, I need to get updates on the "foo" backend object. How can I accomplish this?
General server side messages: I will be running long-running scripts on the server side, started by a user (or by a time trigger). If I go to that page in react and if there are long running scripts active that belong to me, I need to see those logging. (but again, they are personal so those messages are only for me).
Thanks in advance if you need more clarification just ask me and I will add this to my question.
EDIT:
I think the CRUD part can better be created as having only an "listener for updates" (like the firebase onSnapshot). So on page foo, I will listen to updates in the foo database, but the updates or creations are dont through normal REST API. Is that indeed the better way?

Answer 1

You can authenticate socket.io connection in 'connection' event or using middleware - doc.
Also you can use some package from npm, for example this
After authentication store user data in socket object or as separate object in 'connection' event scope.
io.on('connection', (socket) => {
const handshake = socket.handshake;
const user = // fetch user obj according data in handshake, for example, from jwt token in header
});
So after you can use user object in other events for this connection.
Private messages according to your task I implemented in my project using rooms. Here abstract example:
// this is just a helper to get room name according to userId
getUserRoomName(userId) {
return `user_${userId}`;
}
// function to send data to user
sendToUser(userId, event, data) {
io.to(getUserRoomName(userId)).emit(event, data);
}
// in 'connection' event add join to user room
io.on('connection', (socket) => {
const handshake = socket.handshake;
const user = // fetch user obj according data in handshake, for example, from jwt token in header
// join to private room
socket.join(getUserRoomName(user.userId), () => {
// some logic
});
});
So, when the user connected to socket.io we join his connection to private user room. And every connection of same user will be joined to same room, so we can isolate data sending messages to this room.
Using sendToUser method you can send any type of data to all user connections from any part of your application:
sendToUser(userId, 'foo_create', data);
OR
sendToUser(userId, 'foo', {
action: 'create',
// some other data
});