feat(datadog): Add DD RUM to flipt-node client

.fernignore

@@ -4,6 +4,7 @@ README.md
 CHANGELOG.md
 .github
 src/constants.ts
+src/metrics.ts
 LICENSE
 .gitignore
 .release-please-manifest.json

README.md

@@ -62,6 +62,51 @@ const response = await client.evaluation.variant({
 console.log("Received response from Flipt!", response);
 ```
 
+### Metrics
+
+There is support for [Datadog RUM](https://docs.datadoghq.com/real_user_monitoring/) through this client. This allows you to track the values of feature flag evaluation and how it relates to active browser sessions.
+
+To start tracking feature flags on Datadog:
+
+```typescript
+import { datadogRum } from '@datadog/browser-rum';
+import { FliptMetrics } from '@flipt-io/flipt/metrics';
+
+datadogRum.init({
+  applicationId: '<APPLICATION_ID>',
+  clientToken: '<CLIENT_TOKEN>',
+  site: 'datadoghq.com',
+  service:'<SERVICE_NAME>',
+  env:'<ENV_NAME>',
+  enableExperimentalFeatures: ["feature_flags"],
+  sessionSampleRate:100,
+  sessionReplaySampleRate: 20,
+  trackUserInteractions: true,
+  trackResources: true,
+  trackLongTasks: true,
+  defaultPrivacyLevel:'mask-user-input'
+});
+
+datadogRum.startSessionReplayRecording();
+
+const metricsClient = new FliptMetrics(new FliptApiClient({
+  environment: "http://localhost:8080",
+  auth: {
+    credentials: {
+      username: "YOUR_USERNAME",
+      password: "YOUR_PASSWORD",
+    },
+  },
+}).evaluation, datadogRum);
+
+const response = await metricsClient.variant({
+  namespaceKey: "default",
+  flagKey: "hello-this",
+  entityId: uuidv4(),
+  context: {},
+});
+```
+
 ## Beta status
 
 This SDK is in beta, and there may be breaking changes between versions without a major version update. Therefore, we recommend pinning the package version to a specific version in your package.json file. This way, you can install the same version each time without breaking changes unless you are intentionally looking for the latest version.

src/metrics.ts

@@ -0,0 +1,30 @@
+import { FliptApi } from "@flipt-io/flipt";
+import { Evaluation } from "api/resources/evaluation/client/Client";
+
+export class FliptMetrics {
+    evaluationClient: Evaluation;
+    datadogRum: any;
+
+    constructor(evaluationClient: Evaluation, datadogRum: any) {
+        this.evaluationClient = evaluationClient;
+        this.datadogRum = datadogRum;
+    }
+
+    public async boolean(
+        request: FliptApi.evaluation.EvaluationRequest
+    ): Promise<FliptApi.evaluation.BooleanEvaluationResponse> {
+        const response = await this.evaluationClient.boolean(request);
+
+        this.datadogRum.addFeatureFlagEvaluation(`${request.namespaceKey}/${request.flagKey}`, response.enabled);
+        return response;
+    }
+
+    public async variant(
+        request: FliptApi.evaluation.EvaluationRequest
+    ): Promise<FliptApi.evaluation.VariantEvaluationResponse> {
+        const response = await this.evaluationClient.variant(request);
+
+        this.datadogRum.addFeatureFlagEvaluation(`${request.namespaceKey}/${request.flagKey}`, response.variantKey);
+        return response;
+    }
+}