feat(app): tag User-Agent with concrete receiver class name

The App constructor now emits a second `addAppMetadata` entry whose name
includes the receiver's class name (e.g. `@slack/bolt-HTTPReceiver`).
Having the receiver type in outbound WebClient User-Agent strings lets
the Slack team see which receivers are actually deployed in the wild
and prioritize missing features accordingly.

Closes #1150

Author: tmchow

src/App.ts

@@ -366,6 +366,21 @@ export default class App<AppCustomContext extends StringIndexed = StringIndexed>
       // Since v3.4, WebClient starts sharing logger with App
       this.clientOptions.logger = this.logger;
     }
+
+    // Tag the User-Agent with the concrete receiver class before any
+    // WebClient is constructed. WebClient snapshots `getUserAgent()` into
+    // its axios headers at construction time, so this must run before
+    // `new WebClient(...)` below (see #1150).
+    const receiverTypeName = receiver
+      ? receiver.constructor.name
+      : this.socketMode
+        ? 'SocketModeReceiver'
+        : 'HTTPReceiver';
+    addAppMetadata({
+      name: `${packageJson.name}-${receiverTypeName}`,
+      version: packageJson.version,
+    });
+
     // The public WebClient instance (app.client)
     // Since v3.4, it can have the passed token in the case of single workspace installation.
     this.client = new WebClient(token, this.clientOptions);

test/unit/App/basic.spec.ts

@@ -346,6 +346,23 @@ describe('App basic features', () => {
     // TODO: tests for providing endpoints option
   });
 
+  describe('receiver-type app metadata', () => {
+    it('should tag the user-agent metadata with the concrete receiver class name', () => {
+      const addAppMetadata = sinon.fake();
+      const customOverrides = mergeOverrides(
+        { '@slack/web-api': { addAppMetadata } },
+        withSuccessfulBotUserFetchingWebClient(fakeBotId, fakeBotUserId),
+      );
+      const MockApp = importApp(customOverrides);
+      new MockApp({ receiver: new FakeReceiver(), authorize: noop });
+      const names: string[] = addAppMetadata.getCalls().map((call) => call.args[0].name);
+      assert.isTrue(
+        names.some((name) => name.endsWith('-FakeReceiver')),
+        `expected an addAppMetadata call ending in "-FakeReceiver", got ${JSON.stringify(names)}`,
+      );
+    });
+  });
+
   describe('#start', () => {
     it('should pass calls through to receiver', async () => {
       // Arrange