fix: propagate abort reason in derived signals

Fixes #101

src/common/Event.ts

@@ -79,18 +79,18 @@ export namespace Event {
 }
 
 /** Creates an Event that fires when the signal is aborted. */
-export const onAbort = (signal: AbortSignal): { event: Event<void> } & IDisposable => {
-  const evt = new OneShotEvent<void>();
+export const onAbort = (signal: AbortSignal): { event: Event<unknown> } & IDisposable => {
+  const evt = new OneShotEvent<unknown>();
   if (signal.aborted) {
-    evt.emit();
+    evt.emit(signal.reason);
     return { event: evt.addListener, dispose: () => {} };
   }
 
   const dispose = () => (signal as any).removeEventListener('abort', l);
 
   // @types/node is currently missing the event types on AbortSignal
   const l = () => {
-    evt.emit();
+    evt.emit(signal.reason);
     dispose();
   };
 

src/common/abort.test.ts

@@ -0,0 +1,21 @@
+import { expect } from 'chai';
+import { deriveAbortController } from './abort';
+
+describe('deriveAbortController', () => {
+  it('should return an aborted AbortController when the provided signal is already aborted', () => {
+    const parentCtrl = new AbortController();
+    parentCtrl.abort(new Error('asdf'));
+    const { ctrl } = deriveAbortController(parentCtrl.signal);
+    expect(ctrl.signal.aborted).to.be.true;
+    expect(ctrl.signal.reason).to.equal(parentCtrl.signal.reason);
+  });
+
+  it('should abort the new AbortController when the provided signal aborts', () => {
+    const parentCtrl = new AbortController();
+    const { ctrl } = deriveAbortController(parentCtrl.signal);
+    expect(ctrl.signal.aborted).to.be.false;
+    parentCtrl.abort(new Error('asdf'));
+    expect(ctrl.signal.aborted).to.be.true;
+    expect(ctrl.signal.reason).to.equal(parentCtrl.signal.reason);
+  });
+});

src/common/abort.ts

@@ -22,10 +22,10 @@ export const deriveAbortController = (
   }
 
   if (signal.aborted) {
-    ctrl.abort();
+    ctrl.abort(signal.reason);
   } else {
     const abortEvt = onAbort(signal);
-    abortEvt.event(() => ctrl.abort());
+    abortEvt.event(reason => ctrl.abort(reason));
     dispose = abortEvt.dispose;
   }