feat(events): add new events service

Signed-off-by: Patrick Jungermann <Patrick.Jungermann@gmail.com>

plugins/events-backend/api-report.md

@@ -7,14 +7,17 @@ import { Config } from '@backstage/config';
 import { EventBroker } from '@backstage/plugin-events-node';
 import { EventParams } from '@backstage/plugin-events-node';
 import { EventPublisher } from '@backstage/plugin-events-node';
+import { EventsService } from '@backstage/plugin-events-node';
 import { EventSubscriber } from '@backstage/plugin-events-node';
 import express from 'express';
 import { HttpPostIngressOptions } from '@backstage/plugin-events-node';
 import { Logger } from 'winston';
+import { LoggerService } from '@backstage/backend-plugin-api';
 
-// @public
+// @public @deprecated
 export class DefaultEventBroker implements EventBroker {
-  constructor(logger: Logger);
+  // @deprecated
+  constructor(logger: LoggerService, events?: EventsService);
   // (undocumented)
   publish(params: EventParams): Promise<void>;
   // (undocumented)
@@ -23,7 +26,7 @@ export class DefaultEventBroker implements EventBroker {
   ): void;
 }
 
-// @public
+// @public @deprecated
 export class EventsBackend {
   constructor(logger: Logger);
   // (undocumented)

plugins/events-backend/src/deprecated.ts

@@ -0,0 +1,18 @@
+/*
+ * Copyright 2024 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export { EventsBackend } from './service/EventsBackend';
+export { DefaultEventBroker } from './service/DefaultEventBroker';

plugins/events-backend/src/index.ts

@@ -20,6 +20,5 @@
  * @packageDocumentation
  */
 
-export { EventsBackend } from './service/EventsBackend';
+export * from './deprecated';
 export { HttpPostIngressEventPublisher } from './service/http';
-export { DefaultEventBroker } from './service/DefaultEventBroker';

plugins/events-backend/src/service/DefaultEventBroker.test.ts

@@ -85,15 +85,15 @@ describe('DefaultEventBroker', () => {
       }
     })();
 
-    const errorSpy = jest.spyOn(logger, 'error');
+    const warnSpy = jest.spyOn(logger, 'warn');
     const eventBroker = new DefaultEventBroker(logger);
 
     eventBroker.subscribe(subscriber1);
     await eventBroker.publish({ topic, eventPayload: '1' });
 
-    expect(errorSpy).toHaveBeenCalledTimes(1);
-    expect(errorSpy).toHaveBeenCalledWith(
-      'Subscriber "Subscriber1" failed to process event',
+    expect(warnSpy).toHaveBeenCalledTimes(1);
+    expect(warnSpy).toHaveBeenCalledWith(
+      'Subscriber "Subscriber1" failed to process event for topic "testTopic"',
       new Error('NOPE 1'),
     );
 
@@ -101,13 +101,13 @@ describe('DefaultEventBroker', () => {
     await eventBroker.publish({ topic, eventPayload: '2' });
 
     // With two subscribers we should not halt on the first error but call all subscribers
-    expect(errorSpy).toHaveBeenCalledTimes(3);
-    expect(errorSpy).toHaveBeenCalledWith(
-      'Subscriber "Subscriber1" failed to process event',
+    expect(warnSpy).toHaveBeenCalledTimes(3);
+    expect(warnSpy).toHaveBeenCalledWith(
+      'Subscriber "Subscriber1" failed to process event for topic "testTopic"',
       new Error('NOPE 2'),
     );
-    expect(errorSpy).toHaveBeenCalledWith(
-      'Subscriber "Subscriber2" failed to process event',
+    expect(warnSpy).toHaveBeenCalledWith(
+      'Subscriber "Subscriber2" failed to process event for topic "testTopic"',
       new Error('NOPE 2'),
     );
   });

plugins/events-backend/src/service/DefaultEventBroker.ts

@@ -14,12 +14,14 @@
  * limitations under the License.
  */
 
+import { LoggerService } from '@backstage/backend-plugin-api';
 import {
+  DefaultEventsService,
   EventBroker,
   EventParams,
+  EventsService,
   EventSubscriber,
 } from '@backstage/plugin-events-node';
-import { Logger } from 'winston';
 
 /**
  * In process event broker which will pass the event to all registered subscribers
@@ -27,44 +29,34 @@ import { Logger } from 'winston';
  * Events will not be persisted in any form.
  *
  * @public
+ * @deprecated use `DefaultEventsService` from `@backstage/plugin-events-node` instead
  */
-// TODO(pjungermann): add prom metrics? (see plugins/catalog-backend/src/util/metrics.ts, etc.)
 export class DefaultEventBroker implements EventBroker {
-  constructor(private readonly logger: Logger) {}
+  private readonly events: EventsService;
 
-  private readonly subscribers: {
-    [topic: string]: EventSubscriber[];
-  } = {};
+  /**
+   *
+   * @param logger - logger
+   * @param events - replacement that gets wrapped to support not yet migrated implementations.
+   * An instance can be passed (required for a mixed mode), otherwise a new instance gets created internally.
+   * @deprecated use `DefaultEventsService` directly instead
+   */
+  constructor(logger: LoggerService, events?: EventsService) {
+    this.events = events ?? DefaultEventsService.create({ logger });
+  }
 
   async publish(params: EventParams): Promise<void> {
-    this.logger.debug(
-      `Event received: topic=${params.topic}, metadata=${JSON.stringify(
-        params.metadata,
-      )}, payload=${JSON.stringify(params.eventPayload)}`,
-    );
-
-    const subscribed = this.subscribers[params.topic] ?? [];
-    await Promise.all(
-      subscribed.map(async subscriber => {
-        try {
-          await subscriber.onEvent(params);
-        } catch (error) {
-          this.logger.error(
-            `Subscriber "${subscriber.constructor.name}" failed to process event`,
-            error,
-          );
-        }
-      }),
-    );
+    return this.events.publish(params);
   }
 
   subscribe(
     ...subscribers: Array<EventSubscriber | Array<EventSubscriber>>
   ): void {
-    subscribers.flat().forEach(subscriber => {
-      subscriber.supportsEventTopics().forEach(topic => {
-        this.subscribers[topic] = this.subscribers[topic] ?? [];
-        this.subscribers[topic].push(subscriber);
+    subscribers.flat().forEach(async subscriber => {
+      await this.events.subscribe({
+        id: subscriber.constructor.name,
+        topics: subscriber.supportsEventTopics(),
+        onEvent: subscriber.onEvent.bind(subscriber),
       });
     });
   }

plugins/events-backend/src/service/EventsBackend.ts

@@ -26,6 +26,7 @@ import { DefaultEventBroker } from './DefaultEventBroker';
  * A builder that helps wire up all component parts of the event management.
  *
  * @public
+ * @deprecated `EventBroker`, `EventPublisher`, and `EventSubscriber` got replaced by `EventsService` and its methods.
  */
 export class EventsBackend {
   private eventBroker: EventBroker;