Ensure background listeners are called even if a foreground listener throws

README.md

@@ -17,6 +17,10 @@ It consists of the following submodules:
 * `@message-queue-toolkit/sqs` - SQS (AWS Simple Queue Service)
 * `@message-queue-toolkit/sns` - SNS (AWS Simple Notification Service)
 
+## Setup
+
+In order to be able to run tests, you first need to run `npm run build`.
+
 ## Basic Usage
 
 ### Publishers

packages/core/lib/events/DomainEventEmitter.spec.ts

@@ -431,6 +431,24 @@ describe('AutopilotEventEmitter', () => {
         false,
       )
     })
+
+    it('emits event to background even if foreground listener throws', async () => {
+      // Given
+      const fakeSyncListener = new FakeListener()
+      vi.spyOn(fakeSyncListener, 'handleEvent').mockRejectedValue(new Error('Test error'))
+      eventEmitter.on('entity.created', fakeSyncListener)
+
+      const fakeAsyncListener = new FakeListener()
+      eventEmitter.on('entity.created', fakeAsyncListener, true)
+
+      // When
+      const emittedEventPromise = eventEmitter.emit(TestEvents.created, createdEventPayload)
+
+      // Then
+      expect(emittedEventPromise).rejects.toThrow('Test error')
+      await eventEmitter.handlerSpy.waitForMessage({ type: 'entity.created' }, 'consumed')
+      expect(fakeAsyncListener.receivedEvents).toHaveLength(1)
+    })
   })
 
   describe('dispose', () => {

packages/core/lib/events/DomainEventEmitter.ts

@@ -167,25 +167,27 @@ export class DomainEventEmitter<SupportedEvents extends CommonEventDefinition[]>
     const eventHandlers = this.eventHandlerMap.get(event.type)
     if (!eventHandlers) return
 
-    for (const handler of eventHandlers.foreground) {
-      await this.executeEventHandler(event, handler, false)
+    try {
+      for (const handler of eventHandlers.foreground) {
+        await this.executeEventHandler(event, handler, false)
+      }
+    } finally {
+      const bgPromise = Promise.all(
+        eventHandlers.background.map((handler) => this.executeEventHandler(event, handler, true)),
+      ).then(() => {
+        this.inProgressBackgroundHandlerByEventId.delete(event.id)
+        if (!this._handlerSpy) return
+        this._handlerSpy.addProcessedMessage(
+          {
+            // @ts-ignore
+            message: event,
+            processingResult: 'consumed',
+          },
+          event.id,
+        )
+      })
+      this.inProgressBackgroundHandlerByEventId.set(event.id, bgPromise)
     }
-
-    const bgPromise = Promise.all(
-      eventHandlers.background.map((handler) => this.executeEventHandler(event, handler, true)),
-    ).then(() => {
-      this.inProgressBackgroundHandlerByEventId.delete(event.id)
-      if (!this._handlerSpy) return
-      this._handlerSpy.addProcessedMessage(
-        {
-          // @ts-ignore
-          message: event,
-          processingResult: 'consumed',
-        },
-        event.id,
-      )
-    })
-    this.inProgressBackgroundHandlerByEventId.set(event.id, bgPromise)
   }
 
   private async executeEventHandler<SupportedEvent extends SupportedEvents[number]>(