feat(from): support AbortSignal in from(observable) (#333)

Author: aikoven

spec/asynciterable/from-spec.ts

@@ -2,6 +2,8 @@ import { hasNext, noNext, toObserver } from '../asynciterablehelpers';
 import { setInterval, clearInterval } from 'timers';
 import { PartialObserver } from '../../src/observer';
 import { from } from 'ix/asynciterable';
+import { AbortError } from 'ix/Ix';
+import { withAbort } from 'ix/asynciterable/operators';
 
 test('AsyncIterable#from from promise list', async () => {
   const xs: Iterable<Promise<number>> = [
@@ -246,3 +248,59 @@ test('AsyncIterable#fromObservable with error', async () => {
   const it = ys[Symbol.asyncIterator]();
   await expect(it.next()).rejects.toThrow(err);
 });
+
+test('AsyncIterable#fromObservable with abort while waiting', async () => {
+  let unsubscribed = false;
+
+  const xs = new TestObservable<number>((obs) => {
+    obs.next(0);
+
+    return {
+      unsubscribe() {
+        unsubscribed = true;
+      },
+    };
+  });
+
+  const abortController = new AbortController();
+
+  const ys = from(xs).pipe(withAbort(abortController.signal));
+  const it = ys[Symbol.asyncIterator]();
+
+  await hasNext(it, 0);
+
+  setTimeout(() => {
+    abortController.abort();
+  }, 100);
+
+  await expect(it.next()).rejects.toBeInstanceOf(AbortError);
+  expect(unsubscribed).toBe(true);
+});
+
+test('AsyncIterable#fromObservable with abort while queueing', async () => {
+  let unsubscribed = false;
+
+  const xs = new TestObservable<number>((obs) => {
+    obs.next(0);
+    obs.next(1);
+    obs.next(2);
+
+    return {
+      unsubscribe() {
+        unsubscribed = true;
+      },
+    };
+  });
+
+  const abortController = new AbortController();
+
+  const ys = from(xs).pipe(withAbort(abortController.signal));
+  const it = ys[Symbol.asyncIterator]();
+
+  await hasNext(it, 0);
+
+  abortController.abort();
+
+  await expect(it.next()).rejects.toBeInstanceOf(AbortError);
+  expect(unsubscribed).toBe(true);
+});

src/asynciterable/from.ts

@@ -12,6 +12,7 @@ import {
 import { Observable } from '../observer';
 import { toLength } from '../util/tolength';
 import { AsyncSink } from './asyncsink';
+import { AbortError, throwIfAborted } from '../aborterror';
 
 export let from: <TSource, TResult = TSource>(
   source: AsyncIterableInput<TSource>,
@@ -149,7 +150,9 @@ export function _initialize(Ctor: typeof AsyncIterableX) {
       this._selector = selector;
     }
 
-    async *[Symbol.asyncIterator]() {
+    async *[Symbol.asyncIterator](signal?: AbortSignal) {
+      throwIfAborted(signal);
+
       const sink: AsyncSink<TSource> = new AsyncSink<TSource>();
       const subscription = this._observable.subscribe({
         next(value: TSource) {
@@ -163,12 +166,25 @@ export function _initialize(Ctor: typeof AsyncIterableX) {
         }
       });
 
+      function onAbort() {
+        sink.error(new AbortError());
+      }
+
+      if (signal) {
+        signal.addEventListener('abort', onAbort);
+      }
+
       let i = 0;
       try {
         for (let next; !(next = await sink.next()).done; ) {
+          throwIfAborted(signal);
           yield await this._selector(next.value!, i++);
         }
       } finally {
+        if (signal) {
+          signal.removeEventListener('abort', onAbort);
+        }
+
         subscription.unsubscribe();
       }
     }