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I am new to nestJs, Now I need to implement the sse in nestJs, In nestJs they have the special decorator called @Sse to establising the sse connection between the clients and server.
If I use this @Sse decorator, I need to return observables. observables are like a events, Whenever the new event is emitted observar will receive the new emitted data.
notification.controller.ts
import { Public } from 'src/decorators';
import { Observable } from 'rxjs';
import { FastifyReply } from 'fastify';
import { NotificationService } from './notification.service';
import { Sse, Controller, Res } from '@nestjs/common';
@Public()
@Controller()
export class NotificationController {
constructor(private notificationService: NotificationService) {}
@Sse('notifications')
async sendNotification(@Res() reply: FastifyReply): Promise<Observable<any>> {
return await this.notificationService.handleConnection();
notification.service.ts
import { Injectable } from '@nestjs/common';
import { Subject } from 'rxjs';
@Injectable()
export class NotificationService {
notificationEvent: Subject<any> = new Subject();
async handleConnection() {
setInterval(() => {
this.notificationEvent.next({ data: { message: 'Hello World' } });
}, 1000);
return this.notificationEvent.asObservable();
I want to demonstrate this problem with an example, Let's consider use A and B, let's consider User A first connect with the sse connection. So then the setInterval method will be triggered from the service file, So every 1-second user A will receive message { message: 'Hello World' } from the server. Now consider user B connect to sse.
Now what happens is, it also triggers the setInterval method, so observable emits the event, this event is received by both user A and B. I consider it as a problem for me.
What my requirement is, user needs to connect to sse, But I want to send the message from server based on the role and some kind of things, I want to send some messages for specific users, and some messages for other some users, this is what my requirement is. If I want to implement this, What do I need to implement?
Is this possible with observable? or I need to find any other approach. If you know the answer, kindly share your answer whatever it is.
To my knowledge, this isn't really what Server Sent Events are for. However, if it's what you really want to do, you could make a map of clients to their events. Essentially using something like
@Sse('notifications/:id')
sendNotification(@Param() { id }: record<string, string>): Observable<any> {
// no need to make this async or return a Promise. Observables are handled just fine as they are
return this.notificationService.handleConnection(id);
And have your NotificationService take in the id to maintain the map of values
import { Injectable } from '@nestjs/common';
import { Subject } from 'rxjs';
@Injectable()
export class NotificationService {
notificationEvents: Record<string, Subject<any>> = {}
async handleConnection(id: string) {
if (!this.notificationEvetnts[id]) {
this.notificationEvents[id] = new Subject();
setInterval(() => {
this.notificationEvents[id].next({ data: { message: 'Hello World' } });
}, 1000);
return this.notificationEvent[id].asObservable();
This way you'll maintain which notifications are for which users based on the id passed to the SSE endpoint.
Otherwise to maintain events per user, sockets are probably a better use case
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