Add new option bypassOnFinish, for when response is required in bypass callback

README.md

@@ -53,6 +53,7 @@ Which labels to include in `http_request_duration_seconds` metric:
 * **metricsPath**: replace the `/metrics` route with a **regex** or exact **string**. Note: it is highly recommended to just stick to the default
 * **metricType**: histogram/summary selection. See more details below
 * **bypass**: function taking express request as an argument and determines whether the given request should be excluded in the metrics, default: **() => false**
+* **bypassOnFinish**: function taking express request and response as arguments and determines whether the given request should be excluded in the metrics, default: **() => false**. Prefer using **bypass** if you don't need the response object.
 * **httpDurationMetricName**: Allows you change the name of HTTP duration metric, default: **`http_request_duration_seconds`**.
 
 ### metricType option ###

spec/index.spec.js

@@ -240,6 +240,44 @@ describe('index', () => {
       });
   });
 
+  it('bypass requests, checking res', done => {
+    const app = express();
+    const instance = bundle({
+      bypassOnFinish: (req, res) => res.statusCode === 404,
+    });
+    app.use(instance);
+    app.use('/200', (req, res) => res.send(''));
+    app.use('/404', (req, res) => res.status(404).send(''));
+    app.use('/500', (req, res) => res.status(500).send(''));
+
+    const agent = supertest(app);
+    agent.get('/200')
+      .expect(200)
+      .then(() => {
+        return agent
+          .get('/404')
+          .expect(404);
+      })
+      .then(() => {
+        return agent
+          .get('/500')
+          .expect(500);
+      })
+      .then(() => {
+        const metricHashMap = instance.metrics.http_request_duration_seconds.hashMap;
+
+        // only /200 and /500 should be counted
+        expect(metricHashMap['status_code:200'].count).toBe(1);
+        expect(metricHashMap['status_code:404']).not.toBeDefined();
+        expect(metricHashMap['status_code:500'].count).toBe(1);
+
+        return agent
+          .get('/metrics')
+          .expect(200);
+      })
+      .then(done);
+  });
+
   it('complains about deprecated options', () => {
     expect(() => bundle({prefix: 'hello'})).toThrow();
   });

src/index.js

@@ -182,6 +182,10 @@ function main(opts) {
     const timer = metrics[httpMetricName].startTimer(labels);
 
     onFinished(res, () => {
+      if (opts.bypassOnFinish && opts.bypassOnFinish(req, res)) {
+        return;
+      }
+
       if (opts.includeStatusCode) {
         labels.status_code = opts.formatStatusCode(res, opts);
       }

types/index.d.ts

@@ -28,6 +28,7 @@ declare namespace express_prom_bundle {
     includeUp?: boolean;
 
     bypass?: (req: Request) => boolean;
+    bypassOnFinish?: (req: Request, res: Response) => boolean;
 
     excludeRoutes?: Array<string | RegExp>;