@angular/ssr - node drain breaks serverless

[dklmuc]

Command

other

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

19.1.3

Description

When updating to angular 19.2.2 we see a regression while running SSR inside an AWS lambda. Local tests with a 3rd party lib lambda-local shows that response was created by angularNodeAppEngine, but writeResponseToNodeResponse does not seem to resolve anymore as before and lambda process will result in a timeout.

Minimal Reproduction

Reverting locally the changes of #29491 made it work again.

Further debugging:
f (!canContinue) { console.log('destination.write()', canContinue); await new Promise((resolve) => destination.once('drain', resolve)); }
strangely shows canContinue as undefined.

If needed a repro could be provided.

Exception or Error

Your Environment

Angular CLI: 19.2.1
Node: 22.14.0
Package Manager: npm 10.9.2
OS: linux x64

Angular: 19.2.1
... cli, common, compiler, compiler-cli, core, forms
... platform-browser, platform-browser-dynamic, platform-server
... router, ssr

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1902.1
@angular-devkit/build-angular   19.2.1
@angular-devkit/core            19.2.1
@angular-devkit/schematics      19.2.1
@schematics/angular             19.2.1
rxjs                            7.8.2
typescript                      5.7.3
zone.js                         0.15.0

Anything else relevant?

No response

[alan-agius4]

Hi @dklmuc, it would be great to have a reproduction. However, OutgoingMessage .write should never return undefined.

[dklmuc]

@alan-agius4 yes, this is also what is confusing me after reading the node docs for .write

I've added a small repro: https://github.com/dklmuc/angular-srr-lambda

• npm ci
• npm run build
• lambda-local -l lambda.js -e event_origin_request.json

This will output the angular response to console and then it runs into the default timeout of 3 seconds.

Sidenodes:
I've added also a console log when writeResponseToNodeResponse resolves which is not coming, so this is why I think somehow the added promise in the pull request is now stuck due to the undefined and maybe that drain event is not fired.

I can't rule out if it is an error in the used serverless package translating the lambda event into a request object, but like I've said removing that change from the pull request locally is solving this problem.

[alan-agius4]

Indeed, it does seem like a bug in the mentioned package. In fact there has been a long standing issue CodeGenieApp/serverless-express#683

For the time being we could potentially do a workaround.

[dklmuc]

@alan-agius4 thanks a lot for the quick help.