fix: adding .metrics property and circuit breaker metrics

README.md

@@ -156,6 +156,15 @@ For a complete list of options, consult the [undici documentation](https://undic
 
 Closes the client and it's connections.
 
+## Metrics
+
+The expose metrics on the circuit breaking behaviour.
+
+| name                         | type    | description                                                                               |
+|------------------------------|---------|-------------------------------------------------------------------------------------------|
+| `http_client_breaker_events` | counter | Counters on events exposed by the circuit breaker library,<br/>see  [opossum] for details |
+
+
 [@metrics/metric]: https://github.com/metrics-js/metric '@metrics/metric'
 [abslog]: https://github.com/trygve-lie/abslog 'abslog'
 [undici]: https://undici.nodejs.org/

lib/http-client.js

@@ -2,6 +2,7 @@ import { Agent, request, interceptors } from 'undici';
 import createError from 'http-errors';
 import Opossum from 'opossum';
 import abslog from 'abslog';
+import Metrics from '@metrics/client';
 
 /**
  * @typedef HttpClientOptions
@@ -22,10 +23,12 @@ export default class HttpClient {
     #abortController;
     #agent;
     #breaker;
+    #breakerCounter;
     #followRedirects;
     // eslint-disable-next-line no-unused-private-class-members
     #hasFallback = false;
     #logger;
+    #metrics = new Metrics();
     #throwOn400;
     #throwOn500;
 
@@ -66,6 +69,27 @@ export default class HttpClient {
             timeout,
         });
 
+        this.#breakerCounter = this.#metrics.counter({
+            name: 'http_client_breaker_events',
+            description: 'Metrics on breaker events',
+        });
+        for (const eventName of this.#breaker.eventNames()) {
+            //@ts-ignore
+            const event = eventName;
+            //@ts-ignore
+            this.#breaker.on(event, (e) => {
+                let obj = Array.isArray(e) ? e[0] : e;
+                this.#breakerCounter.inc({
+                    labels: {
+                        //@ts-ignore
+                        name: event,
+                        ...(obj && obj.path && { path: obj.path }),
+                        ...(obj && obj.origin && { origin: obj.origin }),
+                    },
+                });
+            });
+        }
+
         this.#agent = new Agent({
             keepAliveMaxTimeout,
             keepAliveTimeout,
@@ -84,6 +108,14 @@ export default class HttpClient {
         }
     }
 
+    /**
+     *
+     * @returns {import('@metrics/client')}
+     */
+    get metrics() {
+        return this.#metrics;
+    }
+
     async #request(options = {}) {
         if (this.#followRedirects || options.redirectable) {
             const { redirect } = interceptors;

tests/http-client.test.js

@@ -250,7 +250,71 @@ await test('http-client - circuit breaker behaviour', async (t) => {
         assert.strictEqual(response.statusCode, 200);
         await afterEach(client);
     });
-    // await t.test('has a .metrics property', async () => {
-    //     const client = new HttpClient({ threshold: 50, reset: breakerReset });
-    // });
+});
+
+await test('http-client: metrics', async (t) => {
+    await t.test('has a .metrics property', () => {
+        const client = new HttpClient();
+        assert.notEqual(client.metrics, undefined);
+    });
+    await t.test('metric on open breakers', async () => {
+        beforeEach();
+        const url = 'http://lochalost:3003';
+        const client = new HttpClient({
+            threshold: 1,
+            reset: 10,
+            throwOn400: false,
+            throwOn500: false,
+        });
+        const metrics = [];
+        //@ts-expect-error
+        client.metrics.on('data', (metric) => {
+            metrics.push(metric);
+        });
+        //@ts-expect-error
+        client.metrics.on('end', () => {
+            assert.strictEqual(metrics.length, 6);
+            assert.strictEqual(metrics[0].name, 'http_client_breaker_events');
+            assert.strictEqual(metrics[0].type, 2);
+            assert.strictEqual(metrics[0].labels[0].value, 'fire');
+            assert.strictEqual(metrics[0].labels[1].value, '/not-found');
+
+            assert.strictEqual(metrics[1].name, 'http_client_breaker_events');
+            assert.strictEqual(metrics[1].type, 2);
+            assert.strictEqual(metrics[1].labels[0].value, 'failure');
+
+            assert.strictEqual(metrics[2].name, 'http_client_breaker_events');
+            assert.strictEqual(metrics[2].type, 2);
+            assert.strictEqual(metrics[2].labels[0].value, 'open');
+
+            assert.strictEqual(metrics[3].name, 'http_client_breaker_events');
+            assert.strictEqual(metrics[3].type, 2);
+            assert.strictEqual(metrics[3].labels[0].value, 'fire');
+
+            assert.strictEqual(metrics[4].name, 'http_client_breaker_events');
+            assert.strictEqual(metrics[4].type, 2);
+            assert.strictEqual(metrics[4].labels[0].value, 'close');
+        });
+        try {
+            // Make the circuit open
+            await client.request({
+                path: '/not-found',
+                origin: url,
+                method: 'GET',
+            });
+            // eslint-disable-next-line no-unused-vars
+        } catch (_) {
+            //
+        }
+        await wait(11);
+        // Wait for circuit to reset, before using the client again.
+        await client.request({
+            path: '/',
+            origin: 'http://localhost:3003',
+            method: 'GET',
+        });
+        //@ts-expect-error
+        client.metrics.push(null);
+        await afterEach(client);
+    });
 });