Firestore Real Time updates connection in NodeJS - node.js

Question

I'm developing a NodeJS web app to receive Real Time updates from Firestore DB through Admin SDK.
This is the init code for the Firestore object. It's executed just once, when the app is deployed (on AWS Elastic Beanstalk):
const admin = require('firebase-admin');
var serviceAccount = require('./../key.json');
admin.initializeApp({
credential: admin.credential.cert(serviceAccount)
});
var db = admin.firestore();
FUNC.firestore = db;
Then I use this firestore object in a websocket comunication to send realtime updates to browser. The idea is to use the server as a proxy between browser and Firestore.
socket.on('open', function (client) {
var query = FUNC.firestore.collection("notifications").doc(client.user.id.toString()).collection("global");
query.onSnapshot(querySnapshot => {
querySnapshot.docChanges().forEach(change => {
client.send({ id: change.doc.id, body: change.doc.data(), type: change.type });
});
}, err => {
console.log(`Encountered error: ${err}`);
});
});
socket.on('close', function (client) {
var unsub = FUNC.firestore.collection("notifications").doc(client.user.id.toString()).collection("global").onSnapshot(() => {
});
unsub();
});
It works well for a while, but after few hours the client stop receiving onSnapshot() updates, and after a while the server log the error: Encountered error: Error: 10 ABORTED: The operation was aborted.
What's wrong? Should I initialized firestore on each connection? Is there some lifecycle mistake?
Thank you
EDIT (A very bad solution)
I've tried to create a single firebase-admin app instance for each logged user and changed my code in this way
const admin = require('firebase-admin');
var serviceAccount = require('./../key.json');
admin.initializeApp({
credential: admin.credential.cert(serviceAccount)
});
FUNC.getFirestore = function (user) {
try {
user.firebase = admin.app(user.id.toString());
return user.firebase.firestore();
} catch(e) {
//ignore
}
var app = admin.initializeApp({
credential: admin.credential.cert(serviceAccount)
}, user.id.toString());
user.firebase = app;
return user.firebase.firestore();
}
FUNC.removeFirebase = function (user) {
if (user.firebase) {
user.firebase.delete();
}
}
And then socket listeners:
self.on('open', function (client) {
var query = FUNC.getFirestore(client.user).collection("notifications").doc(client.user.id.toString()).collection("global");
query.onSnapshot(querySnapshot => {
querySnapshot.docChanges().reverse();
querySnapshot.docChanges().forEach(change => {
client.send({ id: change.doc.id, body: change.doc.data(), type: change.type });
});
}, err => {
console.log(`Encountered error: ${err}`);
});
});
self.on('close', function (client) {
var unsub = FUNC.getFirestore(client.user).collection("notifications").doc(client.user.id.toString()).collection("global").onSnapshot(() => {
});
unsub();
FUNC.removeFirebase(client.user);
});
So when a client disconnect for a reason the server removes its firebase app, it works, but I've noticed a huge memory leak on server, I need some help

Answer 1

UPDATED ANSWER
After many reaserch I've understand that this kind of approach is wrong. Of course, the old answer could be a workaround but is not the real solution of the problem, because Firestore was not designed to do something like: Firestore <--(Admin SDK)--> Server <--(WebSocket)--> Client.
In order to create the best comunication I have understand and applied Firestore Security Rules (https://firebase.google.com/docs/firestore/security/get-started) together with Custom token generation (https://firebase.google.com/docs/auth/admin/create-custom-tokens). So the correct flow is:
Client login request --> Server + Admin SDK generate custom auth token and return to client
Then, the real time comunication will be only between Client and Firestore itself, so: Client + Custom Auth Token <--(Firebase JS SDK)--> Firestore DB
As you can see, the server is not involved anymore in real-time comunication, but client receive updates directly from Firestore.
OLD ANSWER
Finally I can answer from myself. First of all the second solution I've tried is a very bad one, because each new app created through Admin SDK is stored in RAM, with 20/30 users the app reaches more then 1GB of RAM, absolutely unacceptable.
So the first implementation was the better solution, anyway I've wrong the register/unregister onSnapshot listener lifecycle. Each onSnapshot() call returns a different function, even if called on the same reference. So, instead of close the listener when socket close, I opened another one. This is how should be:
socket.on('open', function (client) {
var query = FUNC.firestore.collection("notifications").doc(client.user.id.toString()).collection("global");
client.user.firestoreUnsub = query.onSnapshot(querySnapshot => {
querySnapshot.docChanges().forEach(change => {
client.send({ id: change.doc.id, body: change.doc.data(), type: change.type });
});
}, err => {
console.log(`Encountered error: ${err}`);
});
});
socket.on('close', function (client) {
client.user.firestoreUnsub();
});
After almost 48h, listeners still works without problems and no memory leaks occurs.