bump version to 8.0.1

Bumps [body-parser](https://github.com/expressjs/body-parser) to 1.20.3 and updates ancestor dependency [express](https://github.com/expressjs/express). These dependencies need to be updated together.


Updates `body-parser` from 1.20.2 to 1.20.3
- [Release notes](https://github.com/expressjs/body-parser/releases)
- [Changelog](https://github.com/expressjs/body-parser/blob/master/HISTORY.md)
- [Commits](https://github.com/expressjs/body-parser/compare/1.20.2...1.20.3)

Updates `express` from 4.19.2 to 4.21.1
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/4.21.1/History.md)
- [Commits](https://github.com/expressjs/express/compare/4.19.2...4.21.1)

---
updated-dependencies:
- dependency-name: body-parser
  dependency-type: indirect
- dependency-name: express
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

.eslintrc

@@ -17,6 +17,7 @@
   "extends": "eslint:recommended",
 
   "rules": {
+    "indent": [1, 2],
     "array-bracket-spacing": [2, "never"],
     "block-scoped-var": 2,
     "brace-style": [2, "1tbs"],

.gitignore

@@ -2,4 +2,4 @@
 node_modules
 coverage
 /.vscode
-
+.env

.travis.yml

@@ -1,9 +1,11 @@
 language: node_js
 node_js:
-    - "6"
-    - "8"
-    - "10"
+    - "18"
 notifications:
     email: false
 before_install:
     - npm install prom-client
+script:
+    - npm run lint
+    - npm test
+    - npm run test-types

Makefile

@@ -1,9 +1,10 @@
 .PHONY: coverage
 
 test:
-	./node_modules/jasme/run.js
+	npm test
 lint:
-	node_modules/eslint/bin/eslint.js src
+	npx eslint src
+	npm run dtslint-next
 coverage:
 	node_modules/istanbul/lib/cli.js cover \
 		-i 'src/*' \

README.md

@@ -4,7 +4,9 @@
 
 Express middleware with popular prometheus metrics in one bundle. It's also compatible with koa v1 and v2 (see below).
 
-Since version 5 it uses **prom-client** as a peer dependency. See: https://github.com/siimon/prom-client
+This library uses **prom-client v15+** as a peer dependency. See: https://github.com/siimon/prom-client
+
+If you need a support for older versions of prom-client (v12-v14), downgrade to express-prom-bundle v6.6.0
 
 Included metrics:
 
@@ -46,12 +48,14 @@ Which labels to include in `http_request_duration_seconds` metric:
 
 * **includeStatusCode**: HTTP status code (200, 400, 404 etc.), default: **true**
 * **includeMethod**: HTTP method (GET, PUT, ...), default: **false**
-* **includePath**: URL path (see importent details below), default: **false**
+* **includePath**: URL path (see important details below), default: **false**
 * **customLabels**: an object containing extra labels, e.g. ```{project_name: 'hello_world'}```.
   Most useful together with **transformLabels** callback, otherwise it's better to use native Prometheus relabeling.
 * **includeUp**: include an auxiliary "up"-metric which always returns 1, default: **true**
 * **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
+* **httpDurationMetricName**: Allows you change the name of HTTP duration metric, default: **`http_request_duration_seconds`**.
+* **upMetricName**: Allows you change the name of up metric, default: **`up`**.
 
 ### metricType option ###
 
@@ -66,6 +70,7 @@ Additional options for **summary**:
 * **percentiles**: percentiles used for `http_request_duration_seconds` summary
 * **ageBuckets**: ageBuckets configures how many buckets we have in our sliding window for the summary
 * **maxAgeSeconds**: the maxAgeSeconds will tell how old a bucket can be before it is reset
+* **pruneAgedBuckets**: When enabled, timed out buckets will be removed entirely. By default, buckets are reset to 0.
 
 ### Transformation callbacks ###
 
@@ -78,13 +83,29 @@ Additional options for **summary**:
   See the [docs](https://github.com/disjunction/url-value-parser) of url-value-parser module for details.
 * **formatStatusCode**: `function(res)` producing final status code from express `res` object, e.g. you can combine `200`, `201` and `204` to just `2xx`.
 * **transformLabels**: `function(labels, req, res)` transforms the **labels** object, e.g. setting dynamic values to **customLabels**
+* **urlPathReplacement**: replacement string for the values (default: "#val")
 
 ### Other options ###
 
-* **autoregister**: if `/metrics` endpoint should be registered. (Default: **true**)
+* **autoregister**: if `/metrics` endpoint should be registered (default: **true**)
 * **promClient**: options for promClient startup, e.g. **collectDefaultMetrics**. This option was added
   to keep `express-prom-bundle` runnable using confit (e.g. with kraken.js) without writing any JS code,
   see [advanced example](https://github.com/jochen-schweizer/express-prom-bundle/blob/master/advanced-example.js)
+* **promRegistry**: Optional `promClient.Registry` instance to attach metrics to. Defaults to global `promClient.register`.
+* **metricsApp**: Allows you to attach the metrics endpoint to a different express app. You probably want to use it in combination with `autoregister: false`.
+* **bypass**: An object that takes onRequest and onFinish callbacks that determines whether the given request should be excluded in the metrics. Default:
+
+  ```js
+  {
+    onRequest: (req) => false,
+    onFinish: (req, res) => false
+  }
+  ```
+
+  `onRequest` is run directly in the middleware chain, before the request is processed. `onFinish` is run after the request has been processed, and has access to the express response object in addition to the request object. Both callbacks are optional, and if one or both returns true the request is excluded.
+
+  As a shorthand, just the onRequest callback can be used instead of the object.
+
 
 ### More details on includePath option
 
@@ -142,6 +163,17 @@ For more details:
  * [normalizePath.js](https://github.com/jochen-schweizer/express-prom-bundle/blob/master/src/normalizePath.js) - source code for path processing
 
 
+#### Example 3 (return express route definition):
+
+```javascript
+app.use(promBundle(/* options? */));
+
+promBundle.normalizePath = (req, opts) => {
+  // Return the path of the express route (i.e. /v1/user/:id or /v1/timer/automated/:userid/:timerid")
+  return req.route?.path ?? "NULL";
+};
+```
+
 ## express example
 
 setup std. metrics but exclude `up`-metric:
@@ -195,7 +227,8 @@ which returns an aggregate of all metrics from all the workers.
 
 ``` javascript
 const cluster = require('cluster');
-const promBundle = require('./src/index');
+const promBundle = require('express-prom-bundle');
+const promClient = require('prom-client');
 const numCPUs = Math.max(2, require('os').cpus().length);
 const express = require('express');
 
@@ -211,6 +244,7 @@ if (cluster.isMaster) {
     console.log('cluster metrics listening on 9999');
     console.log('call localhost:9999/metrics for aggregated metrics');
 } else {
+    new promClient.AggregatorRegistry();
     const app = express();
     app.use(promBundle({
         autoregister: false, // disable /metrics for single workers
@@ -243,7 +277,6 @@ while replacing all HEX values starting from 5 characters and all IP addresses i
             "buckets": [0.1, 1, 5],
             "promClient": {
               "collectDefaultMetrics": {
-                "timeout": 2000
               }
             },
             "urlValueParser": {

advanced-example.js

@@ -3,6 +3,8 @@
 const express = require('express');
 const app = express();
 const promClient = require('prom-client');
+
+// replace this with require('.') when running from library code
 const promBundle = require('express-prom-bundle');
 
 const bundle = promBundle({
@@ -14,13 +16,13 @@ const bundle = promBundle({
   metricsPath: '/prometheus',
   promClient: {
     collectDefaultMetrics: {
-      timeout: 1000
     }
   },
   urlValueParser: {
     minHexLength: 5,
     extraMasks: [
-      "^[0-9]+\\.[0-9]+\\.[0-9]+$" // replace dot-separated dates with #val
+      "^[0-9]+\\.[0-9]+\\.[0-9]+$", // replace dot-separated dates with #val, (regex as string)
+      /^[0-9]+\-[0-9]+\-[0-9]+$/ // replace dash-separated dates with #val (actual regex)
     ]
   },
   normalizePath: [

index.d.ts

@@ -1,45 +0,0 @@
-import * as express from "express";
-import { DefaultMetricsCollectorConfiguration } from "prom-client";
-
-type NormalizePathRegexs = [string, string];
-
-interface Labels {
-  [key: string]: string | number;
-}
-
-interface Opts {
-  autoregister?: boolean;
-  buckets?: [number];
-
-  includeStatusCode?: boolean;
-  includeMethod?: boolean;
-  includePath?: boolean;
-  includeUp?: boolean;
-
-  metricType?: "summary" | "histogram";
-  metricsPath?: string;
-  promClient?: DefaultMetricsCollectorConfiguration;
-  normalizePath?: NormalizePathRegexs;
-  formatStatusCode?: (res: express.Response) => number | string;
-
-  transformLabels: (
-    labels: Labels,
-    req: express.Request,
-    res: express.Response
-  ) => Labels;
-
-  // https://github.com/disjunction/url-value-parser#options
-  urlValueParser?: {
-    minHexLength?: number;
-    minBase64Length?: number;
-    replaceMasks?: string[];
-    extraMasks?: string[];
-  };
-}
-
-export function normalizePath(
-  req: express.Request,
-  opts?: { normalizePath?: NormalizePathRegexs }
-);
-
-export default function(opts: Opts): express.RequestHandler;

package.json

@@ -1,6 +1,6 @@
 {
   "name": "express-prom-bundle",
-  "version": "5.1.1",
+  "version": "8.0.1",
   "description": "express middleware with popular prometheus metrics in one bundle",
   "main": "src/index.js",
   "keywords": [
@@ -12,37 +12,44 @@
   ],
   "files": [
     "src",
-    "index.d.ts"
+    "types/index.d.ts"
   ],
+  "types": "types/index.d.ts",
   "scripts": {
-    "test": "node_modules/jasme/run.js",
-    "coverage": "make coverage"
+    "test": "NODE_ENV=test node_modules/jasme/run.js",
+    "lint": "eslint src",
+    "coverage": "make coverage",
+    "test-types": "tsd"
   },
   "author": "Konstantin Pogorelov <or@pluseq.com>",
   "license": "MIT",
   "dependencies": {
+    "@types/express": "^5.0.0",
     "on-finished": "^2.3.0",
     "url-value-parser": "^2.0.0"
   },
   "devDependencies": {
-    "coveralls": "^3.0.2",
+    "dts": "^0.1.1",
     "eslint": "^5.11.0",
-    "express": "^4.16.4",
+    "express": "^5.0.1",
     "istanbul": "^0.4.5",
     "jasme": "^6.0.0",
     "koa": "^2.6.2",
     "koa-connect": "^2.0.1",
+    "prom-client": "^15.0.0",
     "supertest": "^3.3.0",
-    "supertest-koa-agent": "^0.3.0"
+    "supertest-koa-agent": "^0.3.0",
+    "tsd": "^0.30.3",
+    "typescript": "^3.4.5"
   },
   "peerDependencies": {
-    "prom-client": "^11.1.2"
+    "prom-client": ">=15.0.0"
   },
   "repository": {
     "type": "git",
     "url": "https://github.com/jochen-schweizer/express-prom-bundle.git"
   },
   "engines": {
-    "node": ">=6.0.0"
+    "node": ">=18"
   }
 }

spec/index.spec.js

@@ -10,6 +10,20 @@ const supertestKoa = require('supertest-koa-agent');
 const promClient = require('prom-client');
 const cluster = require('cluster');
 
+// for some reason in prom-client 15 the hashmap has a trailing comma
+function extractBucket (instance, key) {
+  const hashmap = instance.metrics.http_request_duration_seconds.hashMap;
+  if (hashmap[key]) {
+    return hashmap[key];
+  } else {
+    return hashmap[key + ','];
+  }
+}
+
+function getMetricCount (s) {
+  return s.replace(/^#.*$\n|^$\n/gm, '').trim().split('\n').length;
+}
+
 describe('index', () => {
   beforeEach(() => {
     promClient.register.clear();
@@ -158,10 +172,9 @@ describe('index', () => {
     agent
       .get('/test')
       .end(() => {
-        const metricHashMap = instance.metrics.http_request_duration_seconds.hashMap;
-        expect(metricHashMap['status_code:200']).toBeDefined();
-        const labeled = metricHashMap['status_code:200'];
-        expect(labeled.count).toBe(1);
+        const bucket = extractBucket(instance, 'status_code:200');
+        expect(bucket).toBeDefined();
+        expect(bucket.count).toBe(1);
 
         agent
           .get('/metrics')
@@ -200,6 +213,84 @@ describe('index', () => {
       });
   });
 
+  it('bypass requests', done => {
+    const app = express();
+    const instance = bundle({
+      bypass: (req)=> {
+        // metrics added here to attempt skipping /metrics
+        // this should fail though, because serving /metrics preceeds bypassing
+        return !!req.url.match(/test|bad.word|metrics/);
+      }
+    });
+    app.use(instance);
+    app.use('/test', (req, res) => res.send('it worked'));
+    app.use('/some/bad-word', (req, res) => res.send('it worked too'));
+    app.use('/good-word', (req, res) => res.send('this will be counted'));
+    const agent = supertest(app);
+    agent
+      .get('/test')
+      .end(() => {
+        agent
+          .get('/some/bad-word')
+          .end(() => {
+            agent
+              .get('/good-word')
+              .end(() => {
+                const bucket = extractBucket(instance, 'status_code:200');
+                expect(bucket).toBeDefined();
+
+                // only /good-word should be counted
+                expect(bucket.count).toBe(1);
+
+                agent
+                  .get('/metrics')
+                  .end((err, res) => {
+                    expect(res.status).toBe(200);
+                    done();
+                  });
+              });
+          });
+      });
+  });
+
+  it('bypass requests, checking res', done => {
+    const app = express();
+    const instance = bundle({
+      bypass: {
+        onFinish: (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(() => {
+        // only /200 and /500 should be counted
+        expect(extractBucket(instance, 'status_code:200').count).toBe(1);
+        expect(extractBucket(instance, 'status_code:404')).not.toBeDefined();
+        expect(extractBucket(instance, 'status_code:500').count).toBe(1);
+
+        return agent
+          .get('/metrics')
+          .expect(200);
+      })
+      .then(done);
+  });
+
   it('complains about deprecated options', () => {
     expect(() => bundle({prefix: 'hello'})).toThrow();
   });
@@ -255,7 +346,7 @@ describe('index', () => {
 
   describe('usage of normalizePath()', () => {
 
-    it('normalizePath can be replaced gloablly', done => {
+    it('normalizePath can be replaced globally', done => {
       const app = express();
       const original = bundle.normalizePath;
       bundle.normalizePath = () => 'dummy';
@@ -279,6 +370,40 @@ describe('index', () => {
         });
     });
 
+    it('respects pruneAgedBuckets', done => {
+      const app = express();
+      const metricsApp = express();
+      const bundled = bundle({
+        metricsApp,
+        metricType: 'summary',
+        includePath: true,
+        maxAgeSeconds: 1,
+        percentiles: [0.5],
+        ageBuckets: 1,
+        pruneAgedBuckets: true,
+      });
+
+      app.use(bundled);
+
+      const agent = supertest(app);
+      const metricsAgent = supertest(metricsApp);
+      agent.get('/foo')
+        .then(() => metricsAgent.get('/metrics'))
+        .then(response => {
+          expect(response.status).toBe(200);
+          // up + bucket, sum, count
+          expect(getMetricCount(response.text)).toBe(4);
+        })
+        .then(() => new Promise(r => setTimeout(r, 1010)))
+        .then(() => metricsAgent.get('/metrics'))
+        .then(response => {
+          expect(response.status).toBe(200);
+          // only up
+          expect(getMetricCount(response.text)).toBe(1);
+        })
+        .finally(done);
+    });
+
     it('normalizePath function can be overridden', done => {
       const app = express();
       const instance = bundle({
@@ -369,6 +494,27 @@ describe('index', () => {
       });
   });
 
+  it('handles errors in collectors', done => {
+    const app = express();
+    const instance = bundle({});
+    app.use(instance);
+
+    new promClient.Gauge({
+      name: 'kaboom',
+      help: 'this metric explodes',
+      collect() {
+        throw new Error('kaboom!');
+      }
+    });
+
+    // the error will NOT be displayed if NODE_ENV=test (as defined in package.json)
+
+    supertest(app)
+      .get('/metrics')
+      .expect(500)
+      .end((err) => done(err));
+  });
+
   it('customLabels={foo: "bar"} adds foo="bar" label to metrics', done => {
     const app = express();
     const instance = bundle({
@@ -438,32 +584,53 @@ describe('index', () => {
     });
   });
 
-  it('calls promClient.collectDefaultMetrics', () => {
-    const spy = spyOn(promClient, 'collectDefaultMetrics');
-    bundle({
-      promClient: {
-        collectDefaultMetrics: {
-          timeout: 3000
+  describe('option collectDefaultMetrics', () => {
+    it('it gets called', () => {
+      const spy = spyOn(promClient, 'collectDefaultMetrics');
+      bundle({
+        promClient: {
+          collectDefaultMetrics: {
+          }
         }
-      }
+      });
+      expect(spy).toHaveBeenCalledWith({});
+    });
+
+    it('prefix is used for up metric', (done) => {
+      const instance = bundle({
+        promClient: {
+          collectDefaultMetrics: {
+            prefix: 'hello_'
+          }
+        }
+      });
+      const app = express();
+      app.use(instance);
+      const agent = supertest(app);
+      agent
+        .get('/metrics')
+        .end((err, res) => {
+          expect(res.status).toBe(200);
+          expect(res.text).toMatch(/^hello_up\s1/m);
+          done();
+        });
     });
-    expect(spy).toHaveBeenCalledWith({timeout: 3000});
   });
 
   describe('usage of clusterMetrics()', () => {
     it('clusterMetrics returns 200 even without a cluster', (done) => {
-        const app = express();
+      const app = express();
 
-        cluster.workers = [];
+      cluster.workers = [];
 
-        app.use('/cluster_metrics', bundle.clusterMetrics());
-        const agent = supertest(app);
-        agent
-          .get('/cluster_metrics')
-          .end((err, res) => {
-            expect(res.status).toBe(200);
-            done();
-          });
+      app.use('/cluster_metrics', bundle.clusterMetrics());
+      const agent = supertest(app);
+      agent
+        .get('/cluster_metrics')
+        .end((err, res) => {
+          expect(res.status).toBe(200);
+          done();
+        });
     });
 
     it('clusterMetrics returns 500 in case of an error', (done) => {
@@ -530,5 +697,23 @@ describe('index', () => {
           });
       });
     });
+
+    it('additional metricsApp can be used', done => {
+      const app = express();
+      const metricsApp = express();
+      const bundled = bundle({metricsApp});
+
+      app.use(bundled);
+
+      const agent = supertest(app);
+      const metricsAgent = supertest(metricsApp);
+      agent.get('/').end(() => {
+        metricsAgent.get('/metrics').end((err, res) => {
+          expect(res.status).toBe(200);
+          expect(res.text).toMatch(/status_code="404"/);
+          done();
+        });
+      });
+    });
   });
 });

spec/normalizePath.spec.js

@@ -28,4 +28,9 @@ describe('normalizePath', () => {
     });
     expect(subject).toThrow();
   });
+
+  it('uses urlPathReplacement when passed to transform the path', () => {
+    expect(normalizePath({url: '/a/12345'}, {urlPathReplacement: ':id'}))
+      .toBe('/a/:id');
+  });
 });

spec/normalizeStatusCode.spec.js

@@ -6,7 +6,11 @@ const normalizeStatusCode = require('../src/normalizeStatusCode');
 describe('normalizeStatusCode', () => {
   it('returns run callback if configured', () => {
     expect(
-      normalizeStatusCode({status_code: 500})
+      normalizeStatusCode({status_code: 500, headersSent: true})
     ).toBe(500);
   });
+
+  it('returns 499 if headers are not sent', () => {
+    expect(normalizeStatusCode({statusCode: 200, headersSent: false})).toBe(499);
+  });
 });

src/index.js

@@ -17,20 +17,37 @@ function matchVsRegExps(element, regexps) {
 }
 
 function clusterMetrics() {
-    const aggregatorRegistry = new promClient.AggregatorRegistry();
+  const aggregatorRegistry = new promClient.AggregatorRegistry();
 
-    const metricsMiddleware = function(req, res) {
-      aggregatorRegistry.clusterMetrics((err, clusterMetrics) => {
-        if (err) {
-            console.error(err);
-            return res.sendStatus(500);
-        }
-        res.set('Content-Type', aggregatorRegistry.contentType);
-        res.send(clusterMetrics);
-      });
-    };
+  const metricsMiddleware = function(req, res) {
+    function sendClusterMetrics(clusterMetrics) {
+      res.set('Content-Type', aggregatorRegistry.contentType);
+      res.send(clusterMetrics);
+    }
 
-    return metricsMiddleware;
+    function sendClusterMetricsError(err) {
+      console.error(err);
+      return res.sendStatus(500);
+    }
+
+    // since prom-client@13 clusterMetrics() method doesn't take cb param,
+    // but we provide it anyway, as at this stage it's unknown which version of prom-client is used
+    const response = aggregatorRegistry.clusterMetrics((err, clusterMetrics) => {
+      if (err) {
+        return sendClusterMetricsError(err);
+      }
+      sendClusterMetrics(clusterMetrics);
+    });
+
+    // if we find out that it was a promise and our cb was useless...
+    if (response && response.then) {
+      response
+        .then(result => sendClusterMetrics(result))
+        .catch(err => sendClusterMetricsError(err));
+    }
+  };
+
+  return metricsMiddleware;
 }
 
 function main(opts) {
@@ -50,7 +67,9 @@ function main(opts) {
       normalizePath: main.normalizePath,
       formatStatusCode: main.normalizeStatusCode,
       metricType: 'histogram',
-      promClient: {}
+      promClient: {},
+      promRegistry: promClient.register,
+      metricsApp: null,
     }, opts
   );
 
@@ -72,6 +91,7 @@ function main(opts) {
   }
 
   const httpMetricName = opts.httpDurationMetricName || 'http_request_duration_seconds';
+  const upMetricName = opts.upMetricName || 'up';
 
   function makeHttpMetric() {
     const labels = ['status_code'];
@@ -92,14 +112,17 @@ function main(opts) {
         labelNames: labels,
         percentiles: opts.percentiles || [0.5, 0.75, 0.95, 0.98, 0.99, 0.999],
         maxAgeSeconds:  opts.maxAgeSeconds,
-        ageBuckets: opts.ageBuckets
+        ageBuckets: opts.ageBuckets,
+        registers: [opts.promRegistry],
+        pruneAgedBuckets: opts.pruneAgedBuckets
       });
     } else if (opts.metricType === 'histogram' || !opts.metricType) {
       return new promClient.Histogram({
         name: httpMetricName,
         help: 'duration histogram of http responses labeled with: ' + labels.join(', '),
         labelNames: labels,
-        buckets: opts.buckets || [0.003, 0.03, 0.1, 0.3, 1.5, 10]
+        buckets: opts.buckets || [0.003, 0.03, 0.1, 0.3, 1.5, 10],
+        registers: [opts.promRegistry]
       });
     } else {
       throw new Error('metricType option must be histogram or summary');
@@ -111,26 +134,58 @@ function main(opts) {
   };
 
   if (opts.includeUp !== false) {
+    let prefix = '';
+    if (opts.promClient && opts.promClient.collectDefaultMetrics) {
+      prefix = opts.promClient.collectDefaultMetrics.prefix || '';
+    }
     metrics.up = new promClient.Gauge({
-      name: 'up',
-      help: '1 = up, 0 = not up'
+      name: prefix + upMetricName,
+      help: '1 = up, 0 = not up',
+      registers: [opts.promRegistry]
     });
     metrics.up.set(1);
   }
 
-  const metricsMiddleware = function(req, res) {
-    res.writeHead(200, {'Content-Type': 'text/plain'});
-    res.end(promClient.register.metrics());
+  const metricsMiddleware = function(req, res, next) {
+    const sendSuccesss = (output) => {
+      res.writeHead(200, {'Content-Type': 'text/plain'});
+      res.end(output);
+    };
+
+    const metricsResponse = opts.promRegistry.metrics();
+    // starting from prom-client@13 .metrics() returns a Promise
+    if (metricsResponse.then) {
+      metricsResponse
+        .then(output => sendSuccesss(output))
+        .catch(err => next(err));
+    } else {
+      // compatibility fallback for previous versions of prom-client@<=12
+      sendSuccesss(metricsResponse);
+    }
   };
 
   const metricsMatch = opts.metricsPath instanceof RegExp ? opts.metricsPath
     : new RegExp('^' + (opts.metricsPath || '/metrics') + '/?$');
 
+  if (typeof opts.bypass === 'function') {
+    opts.bypass = {
+      onRequest: opts.bypass
+    };
+  } else if (!opts.bypass) {
+    opts.bypass = {};
+  }
+
   const middleware = function (req, res, next) {
     const path = req.originalUrl || req.url; // originalUrl gets lost in koa-connect?
 
     if (opts.autoregister && path.match(metricsMatch)) {
-        return metricsMiddleware(req, res);
+      return metricsMiddleware(req, res, next);
+    }
+
+    // bypass() is checked only after /metrics was processed
+    // if you wish to disable /metrics use autoregister:false instead
+    if (opts.bypass.onRequest && opts.bypass.onRequest(req)) {
+      return next();
     }
 
     if (opts.excludeRoutes && matchVsRegExps(path, opts.excludeRoutes)) {
@@ -141,6 +196,10 @@ function main(opts) {
     const timer = metrics[httpMetricName].startTimer(labels);
 
     onFinished(res, () => {
+      if (opts.bypass.onFinish && opts.bypass.onFinish(req, res)) {
+        return;
+      }
+
       if (opts.includeStatusCode) {
         labels.status_code = opts.formatStatusCode(res, opts);
       }
@@ -164,6 +223,14 @@ function main(opts) {
     next();
   };
 
+  if (opts.metricsApp) {
+    opts.metricsApp.get(opts.metricsPath || '/metrics', (req, res) => {
+      res.set('Content-Type', opts.promRegistry.contentType);
+      opts.promRegistry.metrics()
+        .then(metrics => res.end(metrics));
+    });
+  }
+
   middleware.metrics = metrics;
   middleware.promClient = promClient;
   middleware.metricsMiddleware = metricsMiddleware;

src/normalizePath.js

@@ -11,6 +11,7 @@ module.exports = function(req, opts) {
   // by middlewares such as 'router'. Note: this function is called onFinish
   /// i.e. always in the tail of the middleware chain
   let path = url.parse(req.originalUrl || req.url).pathname;
+  const urlPathReplacement = opts ? opts.urlPathReplacement : '#val';
 
   const normalizePath = opts && opts.normalizePath;
   if (Array.isArray(normalizePath)) {
@@ -26,5 +27,5 @@ module.exports = function(req, opts) {
   if (!urlValueParser) {
     urlValueParser = new UrlValueParser(opts && opts.urlValueParser);
   }
-  return urlValueParser.replacePathValues(path);
+  return urlValueParser.replacePathValues(path, urlPathReplacement);
 };

src/normalizeStatusCode.js

@@ -1,5 +1,11 @@
 'use strict';
 
+const CLIENT_CLOSED_REQUEST_CODE = 499;
+
 module.exports = function(res) {
-  return res.status_code || res.statusCode;
+  if (res.headersSent) {
+    return res.status_code || res.statusCode;
+  } else {
+    return CLIENT_CLOSED_REQUEST_CODE;
+  }
 };

types/index.d.ts

@@ -0,0 +1,91 @@
+// TypeScript Version: 2.8
+
+import { Request, RequestHandler, Response, Express } from 'express';
+import { DefaultMetricsCollectorConfiguration, Registry, RegistryContentType } from 'prom-client';
+
+export {};
+
+export = express_prom_bundle;
+
+declare namespace express_prom_bundle {
+  interface Labels {
+    [key: string]: string | number;
+  }
+
+  type NormalizePathEntry = [string | RegExp, string];
+  type NormalizePathFn = (req: Request, opts: Opts) => string;
+  type NormalizeStatusCodeFn = (res: Response) => number | string;
+  type TransformLabelsFn = (labels: Labels, req: Request, res: Response) => void;
+
+  interface BaseOptions {
+    autoregister?: boolean;
+
+    customLabels?: { [key: string]: any };
+
+    includeStatusCode?: boolean;
+    includeMethod?: boolean;
+    includePath?: boolean;
+    includeUp?: boolean;
+
+    bypass?:
+      | ((req: Request) => boolean)
+      | {
+          onRequest?: (req: Request) => boolean;
+          onFinish?: (req: Request, res: Response) => boolean;
+        };
+
+    excludeRoutes?: Array<string | RegExp>;
+
+    metricsPath?: string;
+    httpDurationMetricName?: string;
+    upMetricName?: string;
+    promClient?: { collectDefaultMetrics?: DefaultMetricsCollectorConfiguration<RegistryContentType> };
+    promRegistry?: Registry;
+    normalizePath?: NormalizePathEntry[] | NormalizePathFn;
+    formatStatusCode?: NormalizeStatusCodeFn;
+    transformLabels?: TransformLabelsFn;
+    urlPathReplacement?: string;
+    metricsApp?: Express;
+
+    // https://github.com/disjunction/url-value-parser#options
+    urlValueParser?: {
+      minHexLength?: number;
+      minBase64Length?: number;
+      replaceMasks?: Array<RegExp | string>;
+      extraMasks?: Array<RegExp | string>;
+    };
+  }
+
+  /** @see https://github.com/siimon/prom-client#summary */
+  type SummaryOptions = BaseOptions & {
+    metricType?: 'summary';
+    percentiles?: number[];
+    maxAgeSeconds?: number;
+    ageBuckets?: number;
+    pruneAgedBuckets?: boolean;
+  }
+
+  /** @see https://github.com/siimon/prom-client#histogram */
+  type HistogramOptions = BaseOptions & {
+    metricType?: 'histogram';
+    buckets?: number[];
+  }
+
+  type Opts = SummaryOptions | HistogramOptions;
+
+  interface Middleware extends RequestHandler {
+    metricsMiddleware: RequestHandler;
+  }
+
+  const normalizePath: NormalizePathFn;
+  const normalizeStatusCode: NormalizeStatusCodeFn;
+
+  function clusterMetrics(): RequestHandler;
+}
+
+interface express_prom_bundle {
+  normalizePath: express_prom_bundle.NormalizePathFn;
+  normalizeStatusCode: express_prom_bundle.NormalizeStatusCodeFn;
+}
+
+declare function express_prom_bundle(opts: express_prom_bundle.Opts): express_prom_bundle.Middleware;

types/index.test-d.ts

@@ -0,0 +1,91 @@
+import express, { RequestHandler } from 'express';
+import { expectType } from 'tsd'
+import * as promClient from 'prom-client';
+import promBundle, {
+  type Middleware
+} from '..';
+
+const middleware: express.RequestHandler = promBundle({ includeMethod: true });
+
+expectType<string>(middleware.name);
+
+promClient.register.clear();
+
+expectType<Middleware>(promBundle({
+  normalizePath: [
+    // collect paths like "/customer/johnbobson" as just one "/custom/#name"
+    ['^/customer/.*', '/customer/#name'],
+
+    // collect paths like "/bobjohnson/order-list" as just one "/#name/order-list"
+    ['^.*/order-list', '/#name/order-list']
+  ],
+  urlValueParser: {
+    minHexLength: 5,
+    extraMasks: [
+      'ORD[0-9]{5,}' // replace strings like ORD1243423, ORD673562 as #val
+    ]
+  }
+}));
+
+promClient.register.clear();
+
+expectType<Middleware>(promBundle({
+  buckets: [0.1, 0.4, 0.7],
+  includeMethod: true,
+  includePath: true,
+  excludeRoutes: ['/foo', /^\/bar\/?$/],
+  customLabels: { year: null },
+  transformLabels: (labels: promBundle.Labels) => ({
+    ...labels,
+    year: new Date().getFullYear()
+  }),
+  metricType: 'histogram',
+  metricsPath: '/prometheus',
+  promClient: {
+    collectDefaultMetrics: {
+    }
+  },
+  promRegistry: new promClient.Registry(),
+  urlValueParser: {
+    minHexLength: 5,
+    extraMasks: [
+      '^[0-9]+\\.[0-9]+\\.[0-9]+$' // replace dot-separated dates with #val
+    ]
+  },
+  normalizePath: [
+    ['^/foo', '/example'] // replace /foo with /example
+  ],
+  formatStatusCode: (res: express.Response) => res.statusCode + 100,
+  metricsApp: express()
+}));
+
+promClient.register.clear();
+
+promBundle({
+  metricType: 'summary',
+  maxAgeSeconds: 600,
+  ageBuckets: 5
+});
+
+promClient.register.clear();
+
+promBundle({
+  metricType: 'summary',
+  percentiles: [0.01, 0.1, 0.9, 0.99]
+});
+
+// TypeScript workaround to write a readonly field
+type Writable<T> = { -readonly [K in keyof T]: T[K] };
+const wPromBundle: Writable<promBundle> = promBundle;
+
+wPromBundle.normalizePath = (req: express.Request, opts: promBundle.Opts) => {
+  const path = promBundle.normalizePath(req, opts);
+
+  // count all docs as one path, but /docs/login as a separate one
+  return path.match(/^\/docs/) && !path.match(/^\/login/) ? '/docs/*' : path;
+};
+
+wPromBundle.normalizeStatusCode = (res: express.Response) => res.statusCode.toString();
+
+expectType<RequestHandler>(promBundle.clusterMetrics());
+