fix: make OTEL evaluation event attribute types compliant to OTEL types

Signed-off-by: Lukas Reining <[email protected]>

Author: lukas-reining

packages/shared/src/telemetry/evaluation-event.ts

@@ -1,8 +1,20 @@
-import { ErrorCode, StandardResolutionReasons, type EvaluationDetails, type FlagValue } from '../evaluation/evaluation';
-import type { HookContext } from '../hooks/hooks';
+import { ErrorCode, StandardResolutionReasons, type EvaluationDetails, type FlagValue } from '../evaluation';
+import type { HookContext } from '../hooks';
 import { TelemetryAttribute } from './attributes';
 import { TelemetryFlagMetadata } from './flag-metadata';
 
+/**
+ * Attribute types for OpenTelemetry.
+ * @see https://github.com/open-telemetry/opentelemetry-js/blob/fbbce6e1c0de86e4c504b5788d876fae4d3bc254/api/src/common/Attributes.ts#L35
+ */
+export declare type AttributeValue =
+  | string
+  | number
+  | boolean
+  | Array<null | undefined | string>
+  | Array<null | undefined | number>
+  | Array<null | undefined | boolean>;
+
 type EvaluationEvent = {
   /**
    * The name of the feature flag evaluation event.
@@ -13,7 +25,7 @@ type EvaluationEvent = {
    * @experimental The attributes are subject to change.
    * @see https://opentelemetry.io/docs/specs/semconv/feature-flags/feature-flags-logs/
    */
-  attributes: Record<string, string | number | boolean | FlagValue>;
+  attributes: Record<string, AttributeValue | undefined>;
 };
 
 const FLAG_EVALUATION_EVENT_NAME = 'feature_flag.evaluation';
@@ -36,12 +48,23 @@ export function createEvaluationEvent(
 
   if (evaluationDetails.variant) {
     attributes[TelemetryAttribute.VARIANT] = evaluationDetails.variant;
-  } else {
-    attributes[TelemetryAttribute.VALUE] = evaluationDetails.value;
+  }
+
+  if (evaluationDetails.value !== null) {
+    if (typeof evaluationDetails.value !== 'object') {
+      attributes[TelemetryAttribute.VALUE] = evaluationDetails.value;
+    } else {
+      try {
+        // Objects are not valid attribute values, so we convert them to a JSON string
+        attributes[TelemetryAttribute.VALUE] = JSON.stringify(evaluationDetails.value);
+      } catch {
+        // We ignore non serializable values
+      }
+    }
   }
 
   const contextId =
-    evaluationDetails.flagMetadata[TelemetryFlagMetadata.CONTEXT_ID] || hookContext.context.targetingKey;
+    evaluationDetails.flagMetadata[TelemetryFlagMetadata.CONTEXT_ID] ?? hookContext.context.targetingKey;
   if (contextId) {
     attributes[TelemetryAttribute.CONTEXT_ID] = contextId;
   }