Express JS Controllers with Socket IO Issue - node.js

Question

I am trying to setup Socket IO to work well in different controllers in my Express application.
Here is how I have Socket IO initialized in my server.js
//Run When Connection Received
io.on('connection', (socket) => {
socket.emit('message', 'This is a test message from the server.')
})
Here is what one of my controllers looks like:
const getComments = asyncHandler(async (request, response) => {
const { liveID, token: accessToken } = request.body
var source = new EventSource(
`https://streaming-graph.facebook.com/${liveID}/live_comments?access_token=${accessToken}&comment_rate=one_per_two_seconds&fields=from{name,id},message`
)
source.onmessage = function (event) {
// Do something with event.message for example
console.log(event)
// THIS IS WHERE I NEED TO EMIT A SOCKET IO EVENT.
// THE DATA IN 'event' NEEDS TO BE SENT BACK TO THE CLIENT VIA THE SOCKET
}
source.onerror = function (error) {
console.log('Error!')
console.log(error)
}
source.onopen = function (event) {
console.log(event)
}
})
I have been trying to follow this documentation from Socket IO but for the life in me I can not seem to figure out how to make this work with my above example I have tried so many different things and I just seem to be missing something.
https://socket.io/docs/v4/server-application-structure/
Any help here would be greatly appreciated!

Answer 1

What you can do to have access to io in controller is to attach it to request object like so:
app.use((req, res, next) => {
req.io = io;
next();
});
When a socket connects add an user id to the socket
io.on('connection', (socket) => {
// assuming you send user id in a header for example
socket.userId = socket.client.request.headers.userId;
})
Then in a controller:
const getComments = asyncHandler(async (request, response) => {
var io = request.io;
// https://socket.io/docs/v4/server-api/#serverfetchsockets
// return all Socket instances
const sockets = await io.fetchSockets();
// assuming there's a loggedin user object attached to request
const socket = sockets.find(s => s.userId === request.user.id);
const { liveID, token: accessToken } = request.body
var source = new EventSource(
`https://streaming-graph.facebook.com/${liveID}/live_comments?access_token=${accessToken}&comment_rate=one_per_two_seconds&fields=from{name,id},message`
)
source.onmessage = function (event) {
// Do something with event.message for example
console.log(event)
socket.emit(....);
}
source.onerror = function (error) {
console.log('Error!')
console.log(error)
}
source.onopen = function (event) {
console.log(event)
}
})