address code review comments

Signed-off-by: Brian Fletcher <brian@roadie.io>

.changeset/tall-meals-dress.md

@@ -2,4 +2,6 @@
 '@backstage/plugin-events-backend': patch
 ---
 
-Export `InMemoryEventBroker` to allow decoupling of the catalog and events backends in the `example-backend`.
+Export `DefaultEventBroker` to allow decoupling of the catalog and events backends in the `example-backend`.
+
+Please look at `plugins/events-backend/README.md` for the currently advised was to set up the event backend and catalog providers.

packages/backend/src/index.ts

@@ -67,7 +67,7 @@ import linguist from './plugins/linguist';
 import { PluginEnvironment } from './types';
 import { ServerPermissionClient } from '@backstage/plugin-permission-node';
 import { DefaultIdentityClient } from '@backstage/plugin-auth-node';
-import { InMemoryEventBroker } from '@backstage/plugin-events-backend';
+import { DefaultEventBroker } from '@backstage/plugin-events-backend';
 
 function makeCreateEnv(config: Config) {
   const root = getRootLogger();
@@ -85,7 +85,7 @@ function makeCreateEnv(config: Config) {
     discovery,
   });
 
-  const eventBroker = new InMemoryEventBroker(root.child({ type: 'plugin' }));
+  const eventBroker = new DefaultEventBroker(root.child({ type: 'plugin' }));
 
   root.info(`Created UrlReader ${reader}`);
 

packages/backend/src/plugins/DemoEventBasedEntityProvider.ts

@@ -18,16 +18,29 @@ import {
   EntityProvider,
   EntityProviderConnection,
 } from '@backstage/plugin-catalog-node';
-import { EventParams, EventSubscriber } from '@backstage/plugin-events-node';
+import {
+  EventBroker,
+  EventParams,
+  EventSubscriber,
+} from '@backstage/plugin-events-node';
 import { Logger } from 'winston';
 
 export class DemoEventBasedEntityProvider
   implements EntityProvider, EventSubscriber
 {
-  constructor(
-    private readonly logger: Logger,
-    private readonly topics: string[],
-  ) {}
+  private readonly logger: Logger;
+  private readonly topics: string[];
+
+  constructor(opts: {
+    eventBroker: EventBroker;
+    logger: Logger;
+    topics: string[];
+  }) {
+    const { eventBroker, logger, topics } = opts;
+    eventBroker.subscribe(this);
+    this.logger = logger;
+    this.topics = topics;
+  }
 
   async onEvent(params: EventParams): Promise<void> {
     this.logger.info(

packages/backend/src/plugins/catalog.ts

@@ -23,13 +23,14 @@ import { DemoEventBasedEntityProvider } from './DemoEventBasedEntityProvider';
 export default async function createPlugin(
   env: PluginEnvironment,
 ): Promise<Router> {
-  const { eventBroker, logger } = env;
-
   const builder = await CatalogBuilder.create(env);
   builder.addProcessor(new ScaffolderEntitiesProcessor());
 
-  const demoProvider = new DemoEventBasedEntityProvider(logger, ['example']);
-  eventBroker.subscribe(demoProvider);
+  const demoProvider = new DemoEventBasedEntityProvider({
+    logger: env.logger,
+    topics: ['example'],
+    eventBroker: env.eventBroker,
+  });
   builder.addEntityProvider(demoProvider);
 
   const { processingEngine, router } = await builder.build();

plugins/events-backend/README.md

@@ -28,7 +28,7 @@ You will need to add the following to the backend configuration `#makeCreateEnv`
 
 ```diff
 // packages/backend/src/index.ts
-+   const eventBroker = new InMemoryEventBroker(root.child({ type: 'plugin' }));
++   const eventBroker = new DefaultEventBroker(root.child({ type: 'plugin' }));
 ```
 
 Then update plugin environment to include the event broker.

plugins/events-backend/api-report.md

@@ -12,6 +12,17 @@ import express from 'express';
 import { HttpPostIngressOptions } from '@backstage/plugin-events-node';
 import { Logger } from 'winston';
 
+// @public
+export class DefaultEventBroker implements EventBroker {
+  constructor(logger: Logger);
+  // (undocumented)
+  publish(params: EventParams): Promise<void>;
+  // (undocumented)
+  subscribe(
+    ...subscribers: Array<EventSubscriber | Array<EventSubscriber>>
+  ): void;
+}
+
 // @public
 export class EventsBackend {
   constructor(logger: Logger);
@@ -43,15 +54,4 @@ export class HttpPostIngressEventPublisher implements EventPublisher {
   // (undocumented)
   setEventBroker(eventBroker: EventBroker): Promise<void>;
 }
-
-// @public
-export class InMemoryEventBroker implements EventBroker {
-  constructor(logger: Logger);
-  // (undocumented)
-  publish(params: EventParams): Promise<void>;
-  // (undocumented)
-  subscribe(
-    ...subscribers: Array<EventSubscriber | Array<EventSubscriber>>
-  ): void;
-}
 ```

plugins/events-backend/src/index.ts

@@ -22,4 +22,4 @@
 
 export { EventsBackend } from './service/EventsBackend';
 export { HttpPostIngressEventPublisher } from './service/http';
-export { InMemoryEventBroker } from './service/InMemoryEventBroker';
+export { DefaultEventBroker } from './service/DefaultEventBroker';

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

@@ -17,15 +17,15 @@
 import { getVoidLogger } from '@backstage/backend-common';
 import { TestEventSubscriber } from '@backstage/plugin-events-backend-test-utils';
 import { EventParams, EventSubscriber } from '@backstage/plugin-events-node';
-import { InMemoryEventBroker } from './InMemoryEventBroker';
+import { DefaultEventBroker } from './DefaultEventBroker';
 
 const logger = getVoidLogger();
 
-describe('InMemoryEventBroker', () => {
+describe('DefaultEventBroker', () => {
   it('passes events to interested subscribers', () => {
     const subscriber1 = new TestEventSubscriber('test1', ['topicA', 'topicB']);
     const subscriber2 = new TestEventSubscriber('test2', ['topicB', 'topicC']);
-    const eventBroker = new InMemoryEventBroker(logger);
+    const eventBroker = new DefaultEventBroker(logger);
 
     eventBroker.subscribe(subscriber1);
     eventBroker.subscribe(subscriber2);
@@ -86,7 +86,7 @@ describe('InMemoryEventBroker', () => {
     })();
 
     const errorSpy = jest.spyOn(logger, 'error');
-    const eventBroker = new InMemoryEventBroker(logger);
+    const eventBroker = new DefaultEventBroker(logger);
 
     eventBroker.subscribe(subscriber1);
     await eventBroker.publish({ topic, eventPayload: '1' });

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

@@ -22,14 +22,14 @@ import {
 import { Logger } from 'winston';
 
 /**
- * In-memory event broker which will pass the event to all registered subscribers
+ * In process event broker which will pass the event to all registered subscribers
  * interested in it.
  * Events will not be persisted in any form.
  *
  * @public
  */
 // TODO(pjungermann): add prom metrics? (see plugins/catalog-backend/src/util/metrics.ts, etc.)
-export class InMemoryEventBroker implements EventBroker {
+export class DefaultEventBroker implements EventBroker {
   constructor(private readonly logger: Logger) {}
 
   private readonly subscribers: {

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

@@ -20,7 +20,7 @@ import {
   EventSubscriber,
 } from '@backstage/plugin-events-node';
 import { Logger } from 'winston';
-import { InMemoryEventBroker } from './InMemoryEventBroker';
+import { DefaultEventBroker } from './DefaultEventBroker';
 
 /**
  * A builder that helps wire up all component parts of the event management.
@@ -33,7 +33,7 @@ export class EventsBackend {
   private subscribers: EventSubscriber[] = [];
 
   constructor(logger: Logger) {
-    this.eventBroker = new InMemoryEventBroker(logger);
+    this.eventBroker = new DefaultEventBroker(logger);
   }
 
   setEventBroker(eventBroker: EventBroker): EventsBackend {

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

@@ -29,7 +29,7 @@ import {
   EventSubscriber,
   HttpPostIngressOptions,
 } from '@backstage/plugin-events-node';
-import { InMemoryEventBroker } from './InMemoryEventBroker';
+import { DefaultEventBroker } from './DefaultEventBroker';
 import Router from 'express-promise-router';
 import { HttpPostIngressEventPublisher } from './http';
 
@@ -113,7 +113,7 @@ export const eventsPlugin = createBackendPlugin({
         router.use(eventsRouter);
 
         const eventBroker =
-          extensionPoint.eventBroker ?? new InMemoryEventBroker(winstonLogger);
+          extensionPoint.eventBroker ?? new DefaultEventBroker(winstonLogger);
 
         eventBroker.subscribe(extensionPoint.subscribers);
         [extensionPoint.publishers, http]