From fd5ff1cfe0ac522c669cd8af92cf009d500d6caf Mon Sep 17 00:00:00 2001
From: Timm Stelzer <timmstelzer@gmail.com>
Date: Sat, 6 Jan 2024 11:31:26 +0100
Subject: [PATCH] feat: respect pruneAgedBuckets, update README

---
 README.md          |  1 +
 spec/index.spec.js | 40 +++++++++++++++++++++++++++++++++++++++-
 src/index.js       |  3 ++-
 types/index.d.ts   | 29 ++++++++++++++++++-----------
 4 files changed, 60 insertions(+), 13 deletions(-)

diff --git a/README.md b/README.md
index a491d0d..24226f4 100644
--- a/README.md
+++ b/README.md
@@ -69,6 +69,7 @@ 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 ###
 
diff --git a/spec/index.spec.js b/spec/index.spec.js
index 193e4b9..429e709 100644
--- a/spec/index.spec.js
+++ b/spec/index.spec.js
@@ -20,6 +20,10 @@ function extractBucket (instance, key) {
   }
 }
 
+function getMetricCount (s) {
+  return s.replace(/^#.*$\n|^$\n/gm, '').trim().split('\n').length;
+}
+
 describe('index', () => {
   beforeEach(() => {
     promClient.register.clear();
@@ -342,7 +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';
@@ -366,6 +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({
diff --git a/src/index.js b/src/index.js
index 187de0d..5cf81d0 100644
--- a/src/index.js
+++ b/src/index.js
@@ -112,7 +112,8 @@ function main(opts) {
         percentiles: opts.percentiles || [0.5, 0.75, 0.95, 0.98, 0.99, 0.999],
         maxAgeSeconds:  opts.maxAgeSeconds,
         ageBuckets: opts.ageBuckets,
-        registers: [opts.promRegistry]
+        registers: [opts.promRegistry],
+        pruneAgedBuckets: opts.pruneAgedBuckets
       });
     } else if (opts.metricType === 'histogram' || !opts.metricType) {
       return new promClient.Histogram({
diff --git a/types/index.d.ts b/types/index.d.ts
index 1ab68bc..af88a47 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -17,7 +17,7 @@ declare namespace express_prom_bundle {
   type NormalizeStatusCodeFn = (res: Response) => number | string;
   type TransformLabelsFn = (labels: Labels, req: Request, res: Response) => void;
 
-  interface Opts {
+  interface BaseOptions {
     autoregister?: boolean;
 
     customLabels?: { [key: string]: any };
@@ -36,16 +36,6 @@ declare namespace express_prom_bundle {
 
     excludeRoutes?: Array<string | RegExp>;
 
-    metricType?: 'summary' | 'histogram';
-
-    // https://github.com/siimon/prom-client#histogram
-    buckets?: number[];
-
-    // https://github.com/siimon/prom-client#summary
-    percentiles?: number[];
-    maxAgeSeconds?: number;
-    ageBuckets?: number;
-
     metricsPath?: string;
     httpDurationMetricName?: string;
     promClient?: { collectDefaultMetrics?: DefaultMetricsCollectorConfiguration<RegistryContentType> };
@@ -65,6 +55,23 @@ declare namespace express_prom_bundle {
     };
   }
 
+  /** @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;
   }