chore: remove response time metrics fix (#6779)

## About the changes
The feature `responseTimeMetricsFix` has been enabled for a while. Since
it's released in 5.11 this prepares the removal for the next major
version.


![image](https://github.com/Unleash/unleash/assets/455064/cc49ba3f-f775-45b2-998c-ef7a02c537b4)

src/lib/middleware/response-time-metrics.test.ts

@@ -33,11 +33,6 @@ const flagResolver = {
     getVariant: jest.fn(),
 };
 
-const flagResolverWithResponseTimeMetricsFix = {
-    ...flagResolver,
-    isEnabled: (name: string) => name === 'responseTimeMetricsFix',
-};
-
 // Make sure it's always cleaned up
 let res: any;
 beforeEach(() => {
@@ -47,180 +42,6 @@ beforeEach(() => {
     };
 });
 
-describe('responseTimeMetrics old behavior', () => {
-    const instanceStatsService = {
-        getAppCountSnapshot: jest.fn(),
-    };
-    const eventBus = new EventEmitter();
-    afterEach(() => {
-        eventBus.removeAllListeners();
-    });
-
-    test('uses baseUrl and route path to report metrics', async () => {
-        let timeInfo: any;
-        // register a listener
-        eventBus.on(REQUEST_TIME, (data) => {
-            timeInfo = data;
-        });
-        const middleware = responseTimeMetrics(
-            eventBus,
-            flagResolver,
-            instanceStatsService,
-        );
-        const req = {
-            baseUrl: '/api/admin',
-            route: {
-                path: '/features',
-            },
-            method: 'GET',
-            path: 'should-not-be-used',
-        };
-
-        // @ts-expect-error req and res doesn't have all properties
-        middleware(req, res);
-
-        await isDefined(timeInfo);
-        expect(timeInfo).toMatchObject({
-            path: '/api/admin/features',
-            method: 'GET',
-            statusCode: 200,
-            time: 100,
-            appName: undefined,
-        });
-    });
-
-    test('uses baseUrl and route path to report metrics even with the new flag enabled', async () => {
-        let timeInfo: any;
-        // register a listener
-        eventBus.on(REQUEST_TIME, (data) => {
-            timeInfo = data;
-        });
-        const middleware = responseTimeMetrics(
-            eventBus,
-            flagResolverWithResponseTimeMetricsFix,
-            instanceStatsService,
-        );
-        const req = {
-            baseUrl: '/api/admin',
-            route: {
-                path: '/features',
-            },
-            method: 'GET',
-            path: 'should-not-be-used',
-        };
-
-        // @ts-expect-error req and res doesn't have all properties
-        middleware(req, res);
-
-        await isDefined(timeInfo);
-        expect(timeInfo).toMatchObject({
-            path: '/api/admin/features',
-        });
-    });
-
-    test('uses baseUrl and route path to report metrics even with res.locals.route but flag disabled', async () => {
-        let timeInfo: any;
-        // register a listener
-        eventBus.on(REQUEST_TIME, (data) => {
-            timeInfo = data;
-        });
-        const middleware = responseTimeMetrics(
-            eventBus,
-            flagResolver,
-            instanceStatsService,
-        );
-        const req = {
-            baseUrl: '/api/admin',
-            route: {
-                path: '/features',
-            },
-            method: 'GET',
-            path: 'should-not-be-used',
-        };
-
-        // @ts-expect-error req and res doesn't have all properties
-        middleware(req, {
-            statusCode: 200,
-            locals: { route: '/should-not-be-used-eiter' },
-        });
-
-        await isDefined(timeInfo);
-        expect(timeInfo).toMatchObject({
-            path: '/api/admin/features',
-        });
-    });
-
-    test('reports (hidden) when route is not present', async () => {
-        let timeInfo: any;
-        // register a listener
-        eventBus.on(REQUEST_TIME, (data) => {
-            timeInfo = data;
-        });
-        const middleware = responseTimeMetrics(
-            eventBus,
-            flagResolver,
-            instanceStatsService,
-        );
-        const req = {
-            baseUrl: '/api/admin',
-            method: 'GET',
-            path: 'should-not-be-used',
-        };
-
-        // @ts-expect-error req and res doesn't have all properties
-        middleware(req, res);
-
-        await isDefined(timeInfo);
-        expect(timeInfo).toMatchObject({
-            path: '(hidden)',
-        });
-    });
-
-    test.each([
-        ['/api/admin/features', '(hidden)'],
-        ['/api/admin/features/my-feature', '(hidden)'],
-        ['/api/frontend/client/metrics', '(hidden)'],
-        ['/api/client/metrics', '(hidden)'],
-        ['/edge/validate', '(hidden)'],
-        ['/whatever', '(hidden)'],
-        ['/healthz', '(hidden)'],
-        ['/internal-backstage/prometheus', '(hidden)'],
-    ])(
-        'when path is %s and route is undefined, reports %s',
-        async (path: string, expected: string) => {
-            let timeInfo: any;
-            // register a listener
-            eventBus.on(REQUEST_TIME, (data) => {
-                timeInfo = data;
-            });
-            const middleware = responseTimeMetrics(
-                eventBus,
-                flagResolver,
-                instanceStatsService,
-            );
-            const req = {
-                baseUrl: '/api/admin',
-                method: 'GET',
-                path: 'should-not-be-used',
-            };
-            const reqWithoutRoute = {
-                method: 'GET',
-                path,
-            };
-
-            // @ts-expect-error req and res doesn't have all properties
-            storeRequestedRoute(req, res, () => {});
-            // @ts-expect-error req and res doesn't have all properties
-            middleware(reqWithoutRoute, res);
-
-            await isDefined(timeInfo);
-            expect(timeInfo).toMatchObject({
-                path: expected,
-            });
-        },
-    );
-});
-
 describe('responseTimeMetrics new behavior', () => {
     const instanceStatsService = {
         getAppCountSnapshot: jest.fn(),
@@ -235,7 +56,7 @@ describe('responseTimeMetrics new behavior', () => {
         });
         const middleware = responseTimeMetrics(
             eventBus,
-            flagResolverWithResponseTimeMetricsFix,
+            flagResolver,
             instanceStatsService,
         );
         const req = {
@@ -264,7 +85,7 @@ describe('responseTimeMetrics new behavior', () => {
         });
         const middleware = responseTimeMetrics(
             eventBus,
-            flagResolverWithResponseTimeMetricsFix,
+            flagResolver,
             instanceStatsService,
         );
         const req = {
@@ -298,7 +119,7 @@ describe('responseTimeMetrics new behavior', () => {
         });
         const middleware = responseTimeMetrics(
             eventBus,
-            flagResolverWithResponseTimeMetricsFix,
+            flagResolver,
             instanceStatsService,
         );
         const req = {
@@ -334,7 +155,7 @@ describe('responseTimeMetrics new behavior', () => {
             });
             const middleware = responseTimeMetrics(
                 eventBus,
-                flagResolverWithResponseTimeMetricsFix,
+                flagResolver,
                 instanceStatsService,
             );
             const req = {
@@ -378,7 +199,7 @@ describe('responseTimeMetrics new behavior', () => {
             });
             const middleware = responseTimeMetrics(
                 eventBus,
-                flagResolverWithResponseTimeMetricsFix,
+                flagResolver,
                 instanceStatsService,
             );
             const req = {

src/lib/middleware/response-time-metrics.ts

@@ -46,19 +46,14 @@ export function responseTimeMetrics(
 ): RequestHandler {
     return _responseTime((req, res, time) => {
         const { statusCode } = res;
-        const responseTimeMetricsFix = flagResolver.isEnabled(
-            'responseTimeMetricsFix',
-        );
         let pathname: string | undefined = undefined;
-        if (responseTimeMetricsFix && res.locals.route) {
+        if (res.locals.route) {
             pathname = res.locals.route;
         } else if (req.route) {
             pathname = req.baseUrl + req.route.path;
         }
         // when pathname is undefined use a fallback
-        pathname =
+        pathname = pathname ?? collapse(req.path);
-            pathname ??
-            (responseTimeMetricsFix ? collapse(req.path) : '(hidden)');
         let appName: string | undefined;
         if (
             !flagResolver.isEnabled('responseTimeWithAppNameKillSwitch') &&