fix(platform-express) respect existing parser middlewares when using Express 5

Express 5 made the router public API again and renamed the field from app._router to app.router.
This broke the detection mechanism whether a middleware named "jsonParser" or "urlencodedParser"
is already registered or not.
Unfortunately, #14574 only fixed the issue partially.
This commit now uses app.router everywhere.
To avoid future regressions a test was added to verify the expected behavior.

Author: luddwichr

packages/platform-express/adapters/express-adapter.ts

@@ -470,7 +470,7 @@ export class ExpressAdapter extends AbstractHttpAdapter<
   private isMiddlewareApplied(name: string): boolean {
     const app = this.getInstance();
     return (
-      !!app._router &&
+      !!app.router &&
       !!app.router.stack &&
       isFunction(app.router.stack.filter) &&
       app.router.stack.some(

packages/platform-express/test/adapters/express-adapter.spec.ts

@@ -0,0 +1,46 @@
+import { ExpressAdapter } from '@nestjs/platform-express';
+import { expect } from 'chai';
+import * as express from 'express';
+import * as sinon from 'sinon';
+
+afterEach(() => sinon.restore());
+
+describe.only('ExpressAdapter', () => {
+  describe('registerParserMiddleware', () => {
+    it('should register the express built-in parsers for json and urlencoded payloads', () => {
+      const expressInstance = express();
+      const jsonParserInstance = express.json();
+      const urlencodedInstance = express.urlencoded();
+      const jsonParserSpy = sinon
+        .stub(express, 'json')
+        .returns(jsonParserInstance);
+      const urlencodedParserSpy = sinon
+        .stub(express, 'urlencoded')
+        .returns(urlencodedInstance);
+      const useSpy = sinon.spy(expressInstance, 'use');
+      const expressAdapter = new ExpressAdapter(expressInstance);
+
+      expressAdapter.registerParserMiddleware();
+
+      expect(useSpy.calledTwice).to.be.true;
+      expect(useSpy.calledWith(sinon.match.same(jsonParserInstance))).to.be
+        .true;
+      expect(useSpy.calledWith(sinon.match.same(urlencodedInstance))).to.be
+        .true;
+      expect(jsonParserSpy.calledOnceWith({})).to.be.true;
+      expect(urlencodedParserSpy.calledOnceWith({ extended: true })).to.be.true;
+    });
+
+    it('should not register default parsers if custom parsers have already been registered', () => {
+      const expressInstance = express();
+      expressInstance.use(function jsonParser() {});
+      expressInstance.use(function urlencodedParser() {});
+      const useSpy = sinon.spy(expressInstance, 'use');
+      const expressAdapter = new ExpressAdapter(expressInstance);
+
+      expressAdapter.registerParserMiddleware();
+
+      expect(useSpy.called).to.be.false;
+    });
+  });
+});