feat:slack block extension

Signed-off-by: Kai Dubauskas <kai.dubauskas@doordash.com>

plugins/notifications-backend-module-slack/src/extensions.ts

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2025 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.
+ */
+import { createExtensionPoint } from '@backstage/backend-plugin-api';
+import { NotificationPayload } from '@backstage/plugin-notifications-common';
+import { KnownBlock } from '@slack/web-api';
+
+/**
+ * @public
+ */
+export type SlackBlockKitRenderer = (
+  payload: NotificationPayload,
+) => KnownBlock[];
+
+/**
+ * @public
+ */
+export interface NotificationsSlackBlockKitExtensionPoint {
+  setBlockKitRenderer(renderer: SlackBlockKitRenderer): void;
+}
+
+/**
+ * @public
+ */
+export const notificationsSlackBlockKitExtensionPoint =
+  createExtensionPoint<NotificationsSlackBlockKitExtensionPoint>({
+    id: 'notifications.slack.blockkit',
+  });

plugins/notifications-backend-module-slack/src/index.ts

@@ -22,3 +22,4 @@
 
 export { ANNOTATION_SLACK_BOT_NOTIFY } from './lib';
 export { notificationsModuleSlack as default } from './module';
+export * from './extensions';

plugins/notifications-backend-module-slack/src/lib/SlackNotificationProcessor.test.ts

@@ -209,6 +209,43 @@ describe('SlackNotificationProcessor', () => {
     });
   });
 
+  it('should use a custom block kit renderer when provided', async () => {
+    const slack = new WebClient();
+    const customBlocks = [
+      {
+        type: 'section',
+        text: { type: 'mrkdwn', text: 'Custom block' },
+      },
+    ];
+
+    const processor = SlackNotificationProcessor.fromConfig(config, {
+      auth,
+      logger,
+      catalog: catalogServiceMock({
+        entities: DEFAULT_ENTITIES_RESPONSE.items,
+      }),
+      slack,
+      blockKitRenderer: () => customBlocks,
+    })[0];
+
+    await processor.processOptions({
+      recipients: { type: 'entity', entityRef: 'group:default/mock' },
+      payload: { title: 'notification' },
+    });
+
+    expect(slack.chat.postMessage).toHaveBeenCalledWith({
+      channel: 'C12345678',
+      text: 'notification',
+      attachments: [
+        {
+          color: '#00A699',
+          blocks: customBlocks,
+          fallback: 'notification',
+        },
+      ],
+    });
+  });
+
   describe('when a user notification is sent directly', () => {
     it('should send a notification to a user', async () => {
       const slack = new WebClient();

plugins/notifications-backend-module-slack/src/lib/SlackNotificationProcessor.ts

@@ -37,6 +37,7 @@ import { ANNOTATION_SLACK_BOT_NOTIFY } from './constants';
 import { BroadcastRoute } from './types';
 import { ExpiryMap, toChatPostMessageArgs } from './util';
 import { CatalogService } from '@backstage/plugin-catalog-node';
+import { SlackBlockKitRenderer } from '../extensions';
 
 export class SlackNotificationProcessor implements NotificationProcessor {
   private readonly logger: LoggerService;
@@ -54,6 +55,7 @@ export class SlackNotificationProcessor implements NotificationProcessor {
   private readonly username?: string;
   private readonly concurrencyLimit: number;
   private readonly throttleInterval: number;
+  private readonly blockKitRenderer?: SlackBlockKitRenderer;
 
   static fromConfig(
     config: Config,
@@ -63,6 +65,7 @@ export class SlackNotificationProcessor implements NotificationProcessor {
       catalog: CatalogService;
       slack?: WebClient;
       broadcastChannels?: string[];
+      blockKitRenderer?: SlackBlockKitRenderer;
     },
   ): SlackNotificationProcessor[] {
     const slackConfig =
@@ -104,6 +107,7 @@ export class SlackNotificationProcessor implements NotificationProcessor {
     username?: string;
     concurrencyLimit?: number;
     throttleInterval?: number;
+    blockKitRenderer?: SlackBlockKitRenderer;
   }) {
     const {
       auth,
@@ -115,6 +119,7 @@ export class SlackNotificationProcessor implements NotificationProcessor {
       username,
       concurrencyLimit,
       throttleInterval,
+      blockKitRenderer,
     } = options;
     this.logger = logger;
     this.catalog = catalog;
@@ -126,6 +131,7 @@ export class SlackNotificationProcessor implements NotificationProcessor {
     this.concurrencyLimit = concurrencyLimit ?? 10;
     this.throttleInterval =
       throttleInterval ?? durationToMilliseconds({ minutes: 1 });
+    this.blockKitRenderer = blockKitRenderer;
 
     this.entityLoader = new DataLoader<string, Entity | undefined>(
       async entityRefs => {
@@ -246,6 +252,7 @@ export class SlackNotificationProcessor implements NotificationProcessor {
           channel,
           payload: options.payload,
           username: this.username,
+          blockKitRenderer: this.blockKitRenderer,
         });
 
         this.logger.debug(
@@ -306,6 +313,7 @@ export class SlackNotificationProcessor implements NotificationProcessor {
         channel,
         payload: formattedPayload,
         username: this.username,
+        blockKitRenderer: this.blockKitRenderer,
       }),
     );
 

plugins/notifications-backend-module-slack/src/lib/util.ts

@@ -19,13 +19,16 @@ import {
   NotificationSeverity,
 } from '@backstage/plugin-notifications-common';
 import { ChatPostMessageArguments, KnownBlock } from '@slack/web-api';
+import { SlackBlockKitRenderer } from '../extensions';
 
 export function toChatPostMessageArgs(options: {
   channel: string;
   payload: NotificationPayload;
   username?: string;
+  blockKitRenderer?: SlackBlockKitRenderer;
 }): ChatPostMessageArguments {
-  const { channel, payload, username } = options;
+  const { channel, payload, username, blockKitRenderer } = options;
+  const blocks = (blockKitRenderer ?? toSlackBlockKit)(payload);
 
   const args: ChatPostMessageArguments = {
     channel,
@@ -34,7 +37,7 @@ export function toChatPostMessageArgs(options: {
     attachments: [
       {
         color: getColor(payload.severity),
-        blocks: toSlackBlockKit(payload),
+        blocks,
         fallback: payload.title,
       },
     ],

plugins/notifications-backend-module-slack/src/module.ts

@@ -20,6 +20,10 @@ import {
 import { notificationsProcessingExtensionPoint } from '@backstage/plugin-notifications-node';
 import { SlackNotificationProcessor } from './lib/SlackNotificationProcessor';
 import { catalogServiceRef } from '@backstage/plugin-catalog-node';
+import {
+  notificationsSlackBlockKitExtensionPoint,
+  SlackBlockKitRenderer,
+} from './extensions';
 
 /**
  * The Slack notification processor for use with the notifications plugin.
@@ -31,6 +35,16 @@ export const notificationsModuleSlack = createBackendModule({
   pluginId: 'notifications',
   moduleId: 'slack',
   register(reg) {
+    let blockKitRenderer: SlackBlockKitRenderer | undefined;
+    reg.registerExtensionPoint(notificationsSlackBlockKitExtensionPoint, {
+      setBlockKitRenderer(renderer) {
+        if (blockKitRenderer) {
+          throw new Error(`Slack block kit renderer was already registered`);
+        }
+        blockKitRenderer = renderer;
+      },
+    });
+
     reg.registerInit({
       deps: {
         auth: coreServices.auth,
@@ -45,6 +59,7 @@ export const notificationsModuleSlack = createBackendModule({
             auth,
             logger,
             catalog,
+            blockKitRenderer,
           }),
         );
       },