Advanced - Socket.io Join Room in external file on HTTP request - node.js

Question

I am getting confused with this Node.js, Angular 13 and Socket IO scenario.
First of all let's asume we are already saving all required info in a Database, like roomId, roomOwner, username etc.
So, let's say we want to create an Online Quizz game using sockets to sync all players, 6 max for this scenario. HOWEVER, this is the problem...
On the Angular code there is this Service which is connecting Client
with Back-End
SocketService.ts
export class SocketService {
socket: any;
readonly url: string = "ws://localhost:3000";
constructor() {
this.socket = io(this.url)
}
}
On the Server side index.js inits webSocket
index.js
const app = express();
const io = require('./sockets/websocket')(app);
Inside webSocket.js we create the instance of socketIO to be exported and used across the whole back-end controllers as needed
webSocket.js
module.exports = function(app){
this.server = require('http').createServer(app);
this.socket = require('socket.io');
this.io = socket(server, {
cors: {
origin: "https://localhost:4200",
credentials: true
}
});
this.server.listen(3000, () => {
console.log("Socket IO is lestineng on port 3000");
});
io.on("connection", function (socket) {
console.log("A user connected");
});
this.registerSocketToRoom = function(roomId){
try{
console.log('[socket]','join room :',roomId)
io.join(roomId);
io.sockets.to(roomId).emit('user joined', socket.id);
}catch(e){
console.log('[error]','join room :',e);
io.emit('error','couldnt perform requested action');
}
} }
This is an example controller. We import the exported instance of SocketIO exported from webSocket.js file. Let's say we want to join a room if Client makes an http request to join a room HOWEVER, WE DID NOT joined the room "on socket connection" so we have to do it now. We try to use the exported method {registerSocketToRoom}.
GameRoomManagerController.js
require('../../sockets/websocket');
... // Some code here
exports.joinGameRoom = function(req, res){
const roomId = req.params.roomId;
console.log(roomId);
registerSocketToRoom(roomId);
return res.send({status: "success", msg: `joined Room: ${roomId}` });
}
When executing the process of creating a room -> saving the info to the DB -> Join Room the following error occurs.
TypeError: io.sockets.join is not a function
In theory this sound right to me, but I think I am misunderstanding the difference between io and socket.
Can someone explain to me what's going on here? Is it even possible
to export the same instance of io to be used in any place of the
back-end?
Is it even possible to join a room AFTER the connection was
created?
What's the difference between io and socket?

Answer 1

Before starting the topic, it is better to get acquainted with some terms from the socket.io library
io
In fact, it refers to all sockets connected to the server. You can
send messages individually, in groups, or to all sockets.
Your idea of ​​the socket that is written in this way
io.on('connection', socket => {
socket.on('message', data => {
});
});
In this section, you can only read the information related to this
event or you can transfer this information between sockets
Well, now we are going to solve this problem. The reason for this error is not following this hierarchy in your coding. I suggest you refer to the socket.io document next time and strengthen your foundation.
And finally, I will provide you with a simple example of the correct implementation method
let app = require('express')(),
http = require('http').Server(app),
io = require('socket.io')(http);
let listOfRoom = [];
io.on('connection', socket => {
let joinUserInRoom = (roomId) => {
if (socket.adapter.rooms.has(roomId) === false) {
listOfRoom.push(roomId);
socket.join(roomId);
}
},
leaveUserInRoom = (roomId) => {
if (listOfRoom.includes(roomId)) {
listOfRoom.splice(listOfRoom.indexOf(roomId), 1);
socket.leave(roomId);
}
};
socket.on('joinRoom', data => {
joinUserInRoom(data.roomId);
})
socket.on('disconnect', data => {
leaveUserInRoom(data.roomId);
});
socket.on('messageRoom', data => {
io.to(data.roomId).emit('eventMessageRoom', data); // send data in special room
});
});