Possible memory leak when using server side events

[ggagosh]

Is there an existing issue for this?

• I have searched the existing issues

Current behavior

I use Server-Sent Events for one of my routes and then push db changes for subscribed users. The functionality works fine, but as soon as the event count is 10k for example, the error appears:

(node:43243) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 101 drain listeners added to [SseStream]. Use emitter.setMaxListeners() to increase limit

Minimum reproduction code

https://gist.github.com/ggagosh/0850fd0100f17e2bc040095a917c0342

Steps to reproduce

No response

Expected behavior

I suppose should work without any warning

Package

• I don't know. Or some 3rd-party package
• @nestjs/common
• @nestjs/core
• @nestjs/microservices
• @nestjs/platform-express
• @nestjs/platform-fastify
• @nestjs/platform-socket.io
• @nestjs/platform-ws
• @nestjs/testing
• @nestjs/websockets
• Other (see below)

Other package

No response

NestJS version

^9.0.0

Packages versions

"@nestjs/common": "^9.0.0",
"@nestjs/config": "2.3.1",
"@nestjs/core": "^9.0.0",
"@nestjs/event-emitter": "^1.4.1",
"@nestjs/graphql": "^11.0.5",
"@nestjs/jwt": "10.0.3",
"@nestjs/mongoose": "^9.2.2",
"@nestjs/passport": "9.0.3",
"@nestjs/platform-express": "^9.0.0",
"@nestjs/swagger": "6.3.0",
"@nestjs/terminus": "^9.2.2",

Node.js version

18.16.0

In which operating systems have you tested?

• macOS
• Windows
• Linux

Other

No response

[micalevisk]

What if you remove that setTimeout call?

[ggagosh]

What if you remove that setTimeout call?

It's do nothing actually, just for show purposes. When subscribing to the route, start pushing values after 1 sec, nothing more.

[micalevisk]

then I don't think that that code is enough to reproduce your issue, right? Please share the full code along with the steps to reproduce.

why reproductions are required

[ggagosh]

then I don't think that that code is enough to reproduce your issue, right? Please share the full code along with the steps to reproduce.

why reproductions are required

example nest application you can use to reproduce this behavior. after running the application, use Postman or any other similar application and enter localhost:3000/sse, then check the console where the warning appears.

[jmcdo29]

Seems like some sort of issue with usd adding this.once('drain') here. Interestingly it doesn't happen when using rxjs directly via interval

Stack Trace

(node:1588817) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 drain listeners added to [SseStream]. Use emitter.setMaxListeners() to increase limit
    at _addListener (node:events:587:17)
    at SseStream.addListener (node:events:605:10)
    at SseStream.Readable.on (node:internal/streams/readable:875:35)
    at SseStream.once (node:events:649:8)
    at SseStream.writeMessage (/home/jay/Documents/code/help/sse/node_modules/.pnpm/@nestjs+core@9.0.0_@nestjs+common@9.0.0_@nestjs+platform-express@9.0.0_reflect-metadata@0.1.13_rxjs@7.2.0/node_modules/@nestjs/core/router/sse-stream.js:70:18)
    at /home/jay/Documents/code/help/sse/node_modules/.pnpm/@nestjs+core@9.0.0_@nestjs+common@9.0.0_@nestjs+platform-express@9.0.0_reflect-metadata@0.1.13_rxjs@7.2.0/node_modules/@nestjs/core/router/router-response-controller.js:65:80
    at new Promise (<anonymous>)
    at /home/jay/Documents/code/help/sse/node_modules/.pnpm/@nestjs+core@9.0.0_@nestjs+common@9.0.0_@nestjs+platform-express@9.0.0_reflect-metadata@0.1.13_rxjs@7.2.0/node_modules/@nestjs/core/router/router-response-controller.js:65:50
    at /home/jay/Documents/code/help/sse/node_modules/.pnpm/rxjs@7.2.0/node_modules/rxjs/src/internal/operators/debounce.ts:101:21

[ggagosh]

As I continue debugging, find out this comment and think it's related to this.

I don't know why it does not appear when you use interval directly, maybe because of debounse?

[kamilmysliwiec]

cc @soyuka would you like to take a look?

[azhaochen]

I have the same issue:
(node:167175) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 drain listeners added to [SseStream]. Use emitter.setMaxListeners() to increase limit

[Furmanov19]

@ggagosh could you please provide an example with interval?

[ggagosh]

@ggagosh could you please provide an example with interval?

Hey, this is the example branch

I take the interval example from NestJS documentation, I just change the interval time to 0, because first I think the warning was caused by the amount of data I try to return.

[MatheusWoeffel]

I have the same issue: (node:167175) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 drain listeners added to [SseStream]. Use emitter.setMaxListeners() to increase limit

I have the same issue, has anyone found some workaround/solution to this problem? In my case, I can reproduce the issue by sending HTTP requests and immediately cancelling them, after a couple of cancelled requests the warning pops up.

[dgastudio]

same here

[lxmfly123]

I have the same issue: (node:167175) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 drain listeners added to [SseStream]. Use emitter.setMaxListeners() to increase limit

I have the same issue, has anyone found some workaround/solution to this problem? In my case, I can reproduce the issue by sending HTTP requests and immediately cancelling them, after a couple of cancelled requests the warning pops up.

I figured out a solution: Add a listener for disconnect event, which stops the streaming.

@Sse('stream`)
sse(@Req() req: Request) {
    const stream = /* start your stream */
    req.on('close', ()=>{ stream.destroy() })
}

or something like that.