Error: Can't set headers after they are sent.

[hongbo-miao]

I put the error log here, since it is a little bit long
http://pastie.org/10945816

The reproduce codes app is here
https://github.com/Hongbo-Miao/zonejs-bug

It uses universal-starter, just added socket.io, see in second commit.

To see the error, npm start and open page http://localhost:3000/.

The app works with zone.js 0.6.21, and it shows the error starts from 0.6.22 and also shows in latest 0.6.26

[JiaLiPassion]

I made a pull request to fix this issue, for now you can change your package.json to make zone.js reference to https://github.com/JiaLiPassion/zone.js.git to see the result.

[NgxDev]

So, after more than a year, this is still around in 0.8.20.

My scenario, I have an SSR Response Service:

import { Injectable, Inject } from '@angular/core';

import { Response } from 'express';
import { RESPONSE } from '@nguniversal/express-engine';

@Injectable()
export class SsrResponseService {
  constructor(@Inject(RESPONSE) private response: Response) {}

  redirect(url: string, code?: number) {
    if (!!code) {
      return this.response.redirect(code, url);
    } else {
      return this.response.redirect(url);
    }
  }
}

Then, in a component, based on some logic, I might need to redirect the user:

this.responseService.redirect('/some-other-url', 301);

The redirect works, but the server logs:

Unhandled Promise rejection: Can't set headers after they are sent. ; 
Zone: <root> ; Task: Promise.then ; Value: Error: Can't set headers after they are sent.

Full stack trace here

Any ETA on this fix?

[mike-suggitt]

Bump - same here

[JiaLiPassion]

@mike-suggitt , @MrCroft , I don't think the Can't set headers after they are sent is zone.js error, it is just express http response error.

[NgxDev]

@JiaLiPassion I believe so. But my issue (or question, rather) is: how could we set appropriate headers/response codes?
Keeping in mind that those are conditioned by what information we only have in the Angular code, at runtime, and nowhere else.
Example: I want to access /post/100/some-slug (by directly entering the URL in the address bar - or a search engine might crawl that, from a bad link) but that post doesn't exist. The fact that it doesn't exist is only known after making the API call. So, how do I set a 404 response code at this point? Because, when the app is rendered server-side, we need to send not found header.

[JiaLiPassion]

@MrCroft , sorry I am not familiar with SSR, you can ask at stackoverflow.

[NgxDev]

@JiaLiPassion actually, I remember that the response headers were in fact being set (at least in my case). And the app worked fine. But I was just seeing that error in the log and it mentioned zone.js. Weird... Haven't been doing SSR recently.

[JiaLiPassion]

@MrCroft, yeah, almost all the errors in angular will mention zone.js, so really very little error is really zone.js error.