Issue with sending SSE from express - node.js

Question

We are using microservices architecture for our project. Our project is similar to a blog. There is an activities service, which logs all the activities done by the user, like, adding post, comment, replying to a comment and so on.
Now for each activity, we need to send an SSE notification to the involved users. For this, we are using another service called notifications. So whenever an activity occurs, an HTTP request will be sent to notifications service which handles sending various SSE events.
However, we are facing some issues in sending SSE. The two major issue we are facing are memory leak and an error Error: write after end
Route
router
.route("/")
.get(controller.eventStream)
.post(controller.sendNotification);
Controller
import axios from "axios";
import eventEmitter from '../services';
const controller = {
eventStream: (req, res, next) => {
console.log("Inside event stream");
res.writeHead(200, {
"Content-Type": "text/event-stream",
"Cache-Control": "no-cache",
"Connection": "keep-alive"
});
eventEmitter.on("sse", (event, data) => {
console.log('Event Triggered');
res.write(`event: ${event}\ndata: ${JSON.stringify(data)} \n\n`);
});
req.on("close", () => {
console.log("Inside Close");
res.end();
});
},
sendNotification: (req, res, next) => {
try {
const {
userId,
action,
type,
item_id,
} = req.body;
// First check the type of activity that has been performed
switch (type) {
case "topic":
// Then check the type of action that has been done
switch (action) {
case "edit":
console.log("Topic edited");
const data= 'John Doe has edited a topic';
eventEmitter.emit("sse", `edit-topic`, data);
break;
}
break;
}
res.send('sse successfully send');
} catch (error) {
res.status(500).json({error: 'SSE failed'});
}
}
};
export default controller;
Service
export default new events.EventEmitter();
Initally client side will send a GET request which executes the eventStream controller.
Now for each activity, an SSE needs to be sent through this stream
I believe Error: write after end is because the event is triggered after sending a respose. This can be fixed by removing res.send('sse successfully send'); However, node will throw the timeout error.
I am not sure how to send an SSE from sendNotification controller. Moreover, I am not sure whether this is the right approach. Any guidence would be much appreciated.