fix(socket-mode): handle events_api payloads without an inner event

.changeset/socket-mode-app-rate-limited.md

@@ -0,0 +1,5 @@
+---
+"@slack/socket-mode": patch
+---
+
+Fix a crash on `events_api` messages without an inner event ([#2167](https://github.com/slackapi/node-slack-sdk/issues/2167)). Slack sends `app_rate_limited` notifications this way, and the client threw `Cannot read properties of undefined (reading 'type')`. These messages are now emitted under their payload type, e.g. `app_rate_limited`.

packages/socket-mode/src/SocketModeClient.test.ts

@@ -259,6 +259,20 @@ describe('SocketModeClient', () => {
         retry_attempt: 2,
         retry_reason: 'timeout',
       });
+      const appRateLimited = JSON.stringify({
+        envelope_id: envelopeId,
+        payload: {
+          token: 'verification-token',
+          api_app_id: 'A111',
+          minute_rate_limited: 1792487520,
+          type: 'app_rate_limited',
+          team_id: 'T111',
+        },
+        type: 'events_api',
+        accepts_response_payload: false,
+        retry_attempt: 1,
+        retry_reason: 'timeout',
+      });
 
       it('should be sent to the specific and generic event listeners, and should not trip an unrelated event listener', async () => {
         const client = new SocketModeClient({ appToken: 'xapp-' });
@@ -316,6 +330,30 @@ describe('SocketModeClient', () => {
         client.emit('ws_message', message, false /* isBinary */);
         sinon.assert.callCount(spy, 1);
       });
+      it('should send payloads without an inner event to the payload type and slack_event listeners', async () => {
+        const client = new SocketModeClient({ appToken: 'xapp-' });
+        const rateLimitedSpy = sinon.spy();
+        const slackEventSpy = sinon.spy();
+        client.on('app_rate_limited', rateLimitedSpy);
+        client.on('slack_event', slackEventSpy);
+        client.emit('ws_message', appRateLimited, false /* isBinary */);
+        await sleep(30);
+        sinon.assert.calledOnce(rateLimitedSpy);
+        sinon.assert.calledOnce(slackEventSpy);
+      });
+      it('should pass all the properties to listeners of payloads without an inner event', async () => {
+        const client = new SocketModeClient({ appToken: 'xapp-' });
+        const spy = sinon.spy();
+        client.on('app_rate_limited', spy);
+        client.emit('ws_message', appRateLimited, false /* isBinary */);
+        await sleep(30);
+        const args = spy.firstCall.args[0];
+        assert.strictEqual(args.envelope_id, envelopeId);
+        assert.strictEqual(args.body.minute_rate_limited, 1792487520);
+        assert.strictEqual(args.retry_num, 1);
+        assert.strictEqual(args.retry_reason, 'timeout');
+        assert.strictEqual('event' in args, false);
+      });
     });
 
     describe('interactivity messages', () => {

packages/socket-mode/src/SocketModeClient.ts

@@ -362,7 +362,7 @@ export class SocketModeClient extends EventEmitter {
     };
 
     // For events_api messages, expose the type of the event
-    if (event.type === 'events_api') {
+    if (event.type === 'events_api' && event.payload?.event?.type) {
       this.emit(event.payload.event.type, {
         ack,
         envelope_id: event.envelope_id,
@@ -372,6 +372,20 @@ export class SocketModeClient extends EventEmitter {
         retry_reason: event.retry_reason,
         accepts_response_payload: event.accepts_response_payload,
       });
+    } else if (event.type === 'events_api') {
+      // Some events_api payloads carry no inner event, e.g. app_rate_limited
+      if (event.payload?.type) {
+        this.emit(event.payload.type, {
+          ack,
+          envelope_id: event.envelope_id,
+          body: event.payload,
+          retry_num: event.retry_attempt,
+          retry_reason: event.retry_reason,
+          accepts_response_payload: event.accepts_response_payload,
+        });
+      } else {
+        this.logger.debug(`events_api message has no event or payload type: ${event.envelope_id}`);
+      }
     } else {
       // Emit just ack and body for all other types of messages
       this.emit(event.type, {