AbortSignal.timeout inconsistently leads to TimeoutError or AbortError

[cancan101]

Bug Description

If fetch is passed a AbortSignal.timeout(timeout) as the signal and the timeout occurs, a TimeoutError is raised in certain cases whereas in other cases a AbortError is raised. The TimeoutError occurs when the fetch itself times out whereas the AbortError is raised if the timeout occurs while streaming the response.

Reproducible By

export async function fetchWithTimeout(
  resource: RequestInfo,
  options: RequestInit & { timeout?: number } = {}
) {
  const { timeout = 8000 } = options;

  const response = await fetch(resource, {
    ...options,
    signal: AbortSignal.timeout(timeout),
  });
  return response;
}

async function main() {
  const response = await fetchWithTimeout("https://google.com/", {
    timeout: 1000,
  });

  if (!response.body) {
    return null;
  }

  const saver = new WritableStream<string>({
    async write(data, controller) {
      await new Promise((r) => setTimeout(r, 1000));
    },
  });

  return await response.body.pipeThrough(new TextDecoderStream()).pipeTo(saver);
}

main().catch((x) => console.error(x));

Expected Behavior

An error of the format:

DOMException [TimeoutError]: The operation was aborted due to timeout
    at Object.fetch (node:internal/deps/undici/undici:11457:11)
...

Logs & Screenshots

Instead we get:

DOMException [AbortError]: The operation was aborted.
    at new DOMException (node:internal/per_context/domexception:53:5)
    at Fetch.abort (node:internal/deps/undici/undici:10586:19)
    at EventTarget.requestObject.signal.addEventListener.once (node:internal/deps/undici/undici:10620:22)
    at EventTarget.[nodejs.internal.kHybridDispatch] (node:internal/event_target:761:20)
    at EventTarget.dispatchEvent (node:internal/event_target:703:26)
    at abortSignal (node:internal/abort_controller:314:10)
    at AbortController.abort (node:internal/abort_controller:332:5)
    at EventTarget.abort (node:internal/deps/undici/undici:7174:18)
    at EventTarget.[nodejs.internal.kHybridDispatch] (node:internal/event_target:761:20)
    at EventTarget.dispatchEvent (node:internal/event_target:703:26)

Environment

MacOS: 12.6
Node: v19.9.0

Additional context

[ronag]

I'm not sure I see a problem here? The current behavior makes sense to me.

[cancan101]

I would expect to get a TimeoutError in both cases, ie whether the delay occurs in the actual fetching vs the processing of the stream since the abort is coming from the same AbortSignal.timeout.

You can see the alternative error by shortening the timeout on the AbortSignal:

  const response = await fetchWithTimeout("https://google.com/", {
    timeout: 10,
  });

which will then cause a TimeoutError rather than the AbortError.

[ronag]

I'm pretty sure this is spec compliant. AbortSignal.timeout is supposed to cause an abort error. Do you see a different behavior in e.g. Chrome?

[ronag]

Ah, you might be right https://dom.spec.whatwg.org/#ref-for-dom-abortsignal-timeout%E2%91%A0. @KhafraDev

[KhafraDev]

fetch is expected to only throw an AbortError (previous discussion about this starts here).

[cancan101]

That is definitely not the case right now. As mentioned above fetch will throw TimeoutError in certain circumstances. I think this was a new feature as of node 19. Prior versions did throw just AbortError. That being said, I don't follow why you would not want to have a differentiated TimeoutError for timeouts, consistent with the linked spec above.

[cancan101]

Also the linked comment refers to user supplied reasons which isn't the issue that I have here.

[cancan101]

this seems to indicate the functionality was added to the spec: https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal/timeout_static

and running this on FIrefox (on Google):

fetch("https://www.google.com/", {signal: AbortSignal.timeout(100)}).catch(e => console.log(e.name)) 

yields TimeoutError

[KhafraDev]

I'm inclined to think that is a bug in Firefox, the spec doesn't mention TimeoutError at all. It mentions AbortError for timeouts.

[cancan101]

The DOM spec does mention it, however:

[cancan101]

and the fetch spec seems to indicate that AbortError is used as the fallbackError:

[ronag]

I'm inclined to think that is a bug in Firefox, the spec doesn't mention TimeoutError at all. It mentions AbortError for timeouts.

I'm leaning towards that you might be wrong here...

[KhafraDev]

Yeah I was, we weren't forwarding the reason. Will have a PR up soon.

[Dzieni]

Great to see that it's fixed. Can't wait to have it oficially released. Is there any release schedule?