Fetch abort active streaming upload should cancel ReadableStream

[campersau]

Since we have now half duplex streaming uploads should there also be a test where the AbortController gets aborted after the call to fetch? The asserts should still be the same right?

wpt/fetch/api/abort/general.any.js

Lines 503 to 537 in e77818a

	promise_test(async t => {
	const controller = new AbortController();
	const signal = controller.signal;
	controller.abort();
	let cancelReason;
	const body = new ReadableStream({
	pull(controller) {
	controller.enqueue(new Uint8Array([42]));
	},
	cancel(reason) {
	cancelReason = reason;
	}
	});
	const fetchPromise = fetch('../resources/empty.txt', {
	body, signal,
	method: 'POST',
	duplex: 'half',
	headers: {
	'Content-Type': 'text/plain'
	}
	});
	assert_true(!!cancelReason, 'Cancel called sync');
	assert_equals(cancelReason.constructor, DOMException);
	assert_equals(cancelReason.name, 'AbortError');
	await promise_rejects_dom(t, "AbortError", fetchPromise);
	const fetchErr = await fetchPromise.catch(e => e);
	assert_equals(cancelReason, fetchErr, "Fetch rejects with same error instance");
	}, "Readable stream synchronously cancels with AbortError if aborted before reading");

It looks like browsers don't support the current test as they don't cancel the ReadableStream and cancelReason is not set.
I think the don't even touch the ReadableStream in this case as it isn't locked which I kind of get.
But when an active streaming upload gets cancelled the ReadableStream should always be canceled, as it is locked by the browser.

See also https://bugs.chromium.org/p/chromium/issues/detail?id=1480250

[campersau]

In addition to only cancel the ReadableStream on abort it would also be useful if the ReadableStream got cancelled when fetch fails due to network issues, cors, HTTP1, or anything else.