test(core): add a sse failed test to reproduce nestjs#11601

packages/core/test/router/router-response-controller.spec.ts

@@ -7,6 +7,7 @@ import { PassThrough, Writable } from 'stream';
 import { HttpStatus, RequestMethod } from '../../../common';
 import { RouterResponseController } from '../../router/router-response-controller';
 import { NoopHttpAdapter } from '../utils/noop-adapter.spec';
+import { SseStream } from '../../router/sse-stream';
 
 describe('RouterResponseController', () => {
   let adapter: NoopHttpAdapter;
@@ -374,6 +375,73 @@ data: test
       done();
     });
 
+    describe('when writing data too densely', () => {
+      const DEFAULT_MAX_LISTENERS = SseStream.defaultMaxListeners;
+      const MAX_LISTENERS = 1;
+      const sandbox = sinon.createSandbox();
+
+      beforeEach(() => {
+        // Can't access to the internal sseStream,
+        // as a workround, set `defaultMaxListeners` of `SseStream` and reset the max listeners of `process`
+        const PROCESS_MAX_LISTENERS = process.getMaxListeners();
+        SseStream.defaultMaxListeners = MAX_LISTENERS;
+        process.setMaxListeners(PROCESS_MAX_LISTENERS);
+
+        const sseStream = sinon.createStubInstance(SseStream);
+        const originalWrite = SseStream.prototype.write;
+        // Make `.write()` always return false, so as to listen `drain` event
+        sseStream.write.callsFake(function (...args: any[]) {
+          originalWrite.apply(this, args);
+          return false;
+        });
+        sandbox.replace(SseStream.prototype, 'write', sseStream.write);
+      });
+
+      afterEach(() => {
+        sandbox.restore();
+        SseStream.defaultMaxListeners = DEFAULT_MAX_LISTENERS;
+      });
+
+      it('should not cause memory leak', async () => {
+        let maxDrainListenersExceededWarning = null;
+        process.on('warning', (warning: any) => {
+          if (
+            warning.name === 'MaxListenersExceededWarning' &&
+            warning.emitter instanceof SseStream &&
+            warning.type === 'drain' &&
+            warning.count === MAX_LISTENERS + 1
+          ) {
+            maxDrainListenersExceededWarning = warning;
+          }
+        });
+
+        const result = new Subject();
+
+        const response = new Writable();
+        response._write = () => {};
+
+        const request = new Writable();
+        request._write = () => {};
+
+        routerResponseController.sse(
+          result,
+          response as unknown as ServerResponse,
+          request as unknown as IncomingMessage,
+        );
+
+        // Send multiple messages simultaneously
+        Array.from({ length: MAX_LISTENERS + 1 }).forEach((_, i) =>
+          result.next(String(i)),
+        );
+
+        await new Promise(resolve => process.nextTick(resolve));
+
+        expect(() => {
+          expect(maxDrainListenersExceededWarning).to.equal(null);
+        }, 'it will fail as there is an issue here to be addressed').to.throw();
+      });
+    });
+
     describe('when there is an error', () => {
       it('should close the request', done => {
         const result = new Subject();