Solvedangular HttpClient doesn't throw on observable if Chrome cancels a request

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[x] Bug report  
[ ] Feature request
[ ] Documentation issue or request

Current behavior

If Google Chrome cancels a request the HttpClient.get() observable never finishes. This happens for example when you put your computer to sleep (or in our concrete use-case close a laptop).

Expected behavior

The observable should throw just like any other network related request error would.

Minimal reproduction of the problem with instructions

To cancel a request in chrome you have to put your windows into sleep mode (E.g. close laptop). I don't know enough about the pipeline to simulate a request cancelation by hand, so I created a stackblitz where you can simulate a request which takes at least 5s so you have time to put your computer to sleep. You can also provoke a cancelation by simply pressing ctrl+s.
https://stackblitz.com/edit/angular-request-cancelation?file=app/app.component.ts

What is the motivation / use case for changing the behavior?

We have a request which rerstarts itself once it finishes. As a user might close his laptop (put it to sleep) and keep the site open, this request is never restarted. The only feasible workaround for this would be to either detect a browser sleep (unrealiable) or add a timeout to the request (delayed reaction).

Miscellaneous

  • The same sleep-problem doesn't seem to exist in other browsers (tested IE11 & FF58) as they don't cancel the request like Chrome does.
  • I couldn't find an existing issue talking about this concrete problem, but it might also be related to:
    • The sleep of windows (7)
    • Google Chrome handling of cancelation
    • RxJS
  • I also tried these steps to fix this issue, sadly without any success:
    • Use new RxJS pipe() instead of the "old-school" methods (E.g. finally() => finalize())
    • Specify observe: 'response'
  • Using my provided stackblitz I got the following warning from Chrome itself: The FetchEvent for "..." resulted in a network error response: an object that was not a Response was passed to respondWith(). Maybe it's a Chrome issue?

Environment

Angular version: 4.4.6 & 5.2.5 & 6.0.2 tested


Browser:
- [x] Chrome (desktop) version 66
- [ ] Chrome (Android) version XX
- [ ] Chrome (iOS) version XX
- [ ] Firefox version 58
- [ ] Safari (desktop) version XX
- [ ] Safari (iOS) version XX
- [ ] IE version 11
- [ ] Edge version XX
 
For Tooling issues:
- Node version: 8.9.4
- Platform:  Windows

Others:

Windows 7
25 Answers

✔️Accepted Answer

I understand your specific use-case, but I don't think a cancelled HTTP request should throw an error.

Remember that HTTP in-flight requests are cancelled automatically if a new one is launched or if you manually unsubscribe from the stream, which in essence is the desired behavior.

I think we're better of if a new HttpEvent is implemented, which can be later accessed via the observe option.

this._http.get(endpoint, {
  params,
  observe: 'events',
})
  .pipe(
    tap(ev => {
      if (ev.type === HttpEventType.Cancel) {
        // do something
      }
    })
  );

This check can also be easily added within a HttpInterceptor allowing configuration at an application wide level.

Regarding the abort event, I agree that the observer should be completed if the browser cancels the event.

xhr.addEventListener('abort', () => observer.complete());

Other Answers:

This is a huge problem, I am surprised it hasn't been fixed yet.

I noticed an additional (and devastating) behavior in the latest chrome: You can cancel a request using the ctrl+s shortcut (which opens a save dialog). This makes it stupidly easy to break an angular website which relies on the completion of an observable to show / hide loading messages. This can for example also break the angular.io website by simply hitting ctrl+s while switching to a new page (simulating a slow network makes the timing easier). I know that most users don't spam ctrl+s, but I still think this issue should be investigated / prioritized.

Seems like we figured out where is the problem.

We fallowed the same steps @PascalHonegger provided: make a pending request and put laptop into sleep mode.

We tested it by creating two requests: one through simple XMLHttpRequest and another one through Angular HttpClint. We subscribed on HttpClint and all XMLHttpRequest events. As was discovered cancelation of request triggers abort event on XMLHttpRequest. We dived deeper and found that HttpClient listens to only three events: progress, load and error.

That is why Observable never ends. XMLHttpClient returns an abort but Angular doesn't react on it.

We made a small fix on our side just adding an HTTP_INTERCEPTOR which cancels a request if it doesn't respond after 1 min. But we also made a PR to Angular to support this event (#28338).

So is there a workaround or not right now?

@vladjerca Is this something I can implement in my code or is it just a demonstration of what Angular can do to fix this problem?

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