From 6efb0a540546bd78d0ea582e949beb3c77be3288 Mon Sep 17 00:00:00 2001
From: Ivan Santos <pragmaticivan@gmail.com>
Date: Sat, 25 Sep 2021 22:29:52 -0500
Subject: [PATCH] feat: add defaultLabels support

---
 .../opentelemetry-options.interface.ts        |  5 ++-
 src/middleware/api-metrics.middleware.ts      | 12 +++++--
 .../middleware/api-metrics.middleware.spec.ts | 35 +++++++++++++++++++
 3 files changed, 46 insertions(+), 6 deletions(-)

diff --git a/src/interfaces/opentelemetry-options.interface.ts b/src/interfaces/opentelemetry-options.interface.ts
index 4e024d8..5eef432 100644
--- a/src/interfaces/opentelemetry-options.interface.ts
+++ b/src/interfaces/opentelemetry-options.interface.ts
@@ -1,4 +1,5 @@
 import { ModuleMetadata, Type, Abstract } from '@nestjs/common';
+import { Labels } from '@opentelemetry/api-metrics';
 
 export type OpenTelemetryModuleOptions = {
   /**
@@ -50,8 +51,6 @@ export type OpenTelemetryMetrics = {
     timeBuckets?: number[],
     requestSizeBuckets?: number[],
     responseSizeBuckets?: number[],
-  },
-  defaultLabels?: {
-    [key: string]: string | number
+    defaultLabels?: Labels,
   },
 };
diff --git a/src/middleware/api-metrics.middleware.ts b/src/middleware/api-metrics.middleware.ts
index 3560584..7acbd18 100644
--- a/src/middleware/api-metrics.middleware.ts
+++ b/src/middleware/api-metrics.middleware.ts
@@ -1,7 +1,7 @@
 import { Inject, Injectable, NestMiddleware } from '@nestjs/common';
 import * as responseTime from 'response-time';
 import * as urlParser from 'url';
-import { Counter, ValueRecorder } from '@opentelemetry/api-metrics';
+import { Counter, Labels, ValueRecorder } from '@opentelemetry/api-metrics';
 import { OpenTelemetryModuleOptions } from '../interfaces';
 import { MetricService } from '../metrics/metric.service';
 import { OPENTELEMETRY_MODULE_OPTIONS } from '../opentelemetry.constants';
@@ -43,6 +43,8 @@ export class ApiMetricsMiddleware implements NestMiddleware {
 
   private responseSizeValueRecorder: ValueRecorder;
 
+  private defaultLabels: Labels;
+
   constructor(
     @Inject(OPENTELEMETRY_MODULE_OPTIONS) private readonly options: OpenTelemetryModuleOptions = {},
     @Inject(MetricService) private readonly metricService: MetricService,
@@ -76,9 +78,11 @@ export class ApiMetricsMiddleware implements NestMiddleware {
     });
 
     const {
-      timeBuckets = [], requestSizeBuckets = [], responseSizeBuckets = [],
+      timeBuckets = [], requestSizeBuckets = [], responseSizeBuckets = [], defaultLabels = {},
     } = options?.metrics?.apiMetrics;
 
+    this.defaultLabels = defaultLabels;
+
     this.requestDuration = this.metricService.getValueRecorder('http_request_duration_seconds', {
       boundaries: timeBuckets.length > 0 ? timeBuckets : this.defaultLongRunningRequestBuckets,
       description: 'HTTP latency value recorder in seconds',
@@ -125,7 +129,9 @@ export class ApiMetricsMiddleware implements NestMiddleware {
       const responseLength: number = parseInt(res.get('Content-Length'), 10) || 0;
 
       const status = res.statusCode || 500;
-      const labels = { method, status, path };
+      const labels: Labels = {
+        method, status, path, ...this.defaultLabels,
+      };
 
       this.requestSizeValueRecorder.bind(labels).record(requestLength);
       this.responseSizeValueRecorder.bind(labels).record(responseLength);
diff --git a/tests/e2e/middleware/api-metrics.middleware.spec.ts b/tests/e2e/middleware/api-metrics.middleware.spec.ts
index 68b5177..3e4ce57 100644
--- a/tests/e2e/middleware/api-metrics.middleware.spec.ts
+++ b/tests/e2e/middleware/api-metrics.middleware.spec.ts
@@ -235,6 +235,41 @@ describe('Api Metrics Middleware', () => {
     expect(/http_server_error_total 1/.test(text)).toBeTruthy();
   });
 
+  it('registers requests with custom labels', async () => {
+    const testingModule = await Test.createTestingModule({
+      imports: [OpenTelemetryModule.forRoot({
+        metrics: {
+          apiMetrics: {
+            enable: true,
+            defaultLabels: {
+              custom: 'label',
+            },
+          },
+        },
+      })],
+      controllers: [AppController],
+    }).compile();
+    testingModule.useLogger(new EmptyLogger());
+
+    app = testingModule.createNestApplication();
+    await app.init();
+
+    const agent = request(app.getHttpServer());
+    await agent.get('/example/internal-error');
+
+    // Workaround for delay of metrics going to prometheus
+    await new Promise(resolve => setTimeout(resolve, 200));
+
+    // TODO: OpenTelemetry exporter does not expose server in a public function.
+    // @ts-ignore
+    // eslint-disable-next-line no-underscore-dangle
+    const { text } = await request(exporter._server)
+      .get('/metrics')
+      .expect(200);
+
+    expect(/custom/.test(text)).toBeTruthy();
+  });
+
   afterEach(async () => {
     metrics.disable();
     if (exporter) {