Add flag evaluation metrics via OTel counter and OpenFeature Hook

products/feature-flagging/feature-flagging-api/README.md

@@ -0,0 +1,79 @@
+# dd-openfeature
+
+Datadog OpenFeature Provider for Java. Implements the [OpenFeature](https://openfeature.dev/) `FeatureProvider` interface for Datadog's Feature Flags and Experimentation (FFE) product.
+
+Published as `com.datadoghq:dd-openfeature` on Maven Central.
+
+## Setup
+
+```xml
+<dependency>
+    <groupId>com.datadoghq</groupId>
+    <artifactId>dd-openfeature</artifactId>
+    <version>${dd-openfeature.version}</version>
+</dependency>
+```
+
+The OpenFeature SDK (`dev.openfeature:sdk`) is included as a transitive dependency.
+
+### Evaluation metrics (optional)
+
+To enable evaluation metrics (`feature_flag.evaluations` counter), add the OpenTelemetry SDK dependencies:
+
+```xml
+<dependency>
+    <groupId>io.opentelemetry</groupId>
+    <artifactId>opentelemetry-sdk-metrics</artifactId>
+    <version>1.47.0</version>
+</dependency>
+<dependency>
+    <groupId>io.opentelemetry</groupId>
+    <artifactId>opentelemetry-exporter-otlp</artifactId>
+    <version>1.47.0</version>
+</dependency>
+```
+
+Any OpenTelemetry API 1.x version is compatible. If these dependencies are absent, the provider operates normally without metrics.
+
+## Usage
+
+```java
+import datadog.trace.api.openfeature.Provider;
+import dev.openfeature.sdk.OpenFeatureAPI;
+import dev.openfeature.sdk.Client;
+
+OpenFeatureAPI api = OpenFeatureAPI.getInstance();
+api.setProviderAndWait(new Provider());
+Client client = api.getClient();
+
+boolean enabled = client.getBooleanValue("my-feature", false,
+    new MutableContext("user-123"));
+```
+
+## Evaluation metrics
+
+When the OTel SDK dependencies are on the classpath, the provider records a `feature_flag.evaluations` counter via OTLP HTTP/protobuf. Metrics are exported every 10 seconds to the Datadog Agent's OTLP receiver.
+
+### Configuration
+
+| Environment variable | Description | Default |
+|---|---|---|
+| `OTEL_EXPORTER_OTLP_METRICS_ENDPOINT` | Signal-specific OTLP endpoint (used as-is) | — |
+| `OTEL_EXPORTER_OTLP_ENDPOINT` | Generic OTLP endpoint (`/v1/metrics` appended) | — |
+| (none set) | Default endpoint | `http://localhost:4318/v1/metrics` |
+
+### Metric attributes
+
+| Attribute | Description |
+|---|---|
+| `feature_flag.key` | Flag key |
+| `feature_flag.result.variant` | Resolved variant key |
+| `feature_flag.result.reason` | Evaluation reason (lowercased) |
+| `error.type` | Error code (lowercased, only on error) |
+| `feature_flag.result.allocation_key` | Allocation key (when present) |
+
+## Requirements
+
+- Java 11+
+- Datadog Agent with Remote Configuration enabled
+- `DD_EXPERIMENTAL_FLAGGING_PROVIDER_ENABLED=true`

products/feature-flagging/feature-flagging-api/build.gradle.kts

@@ -44,8 +44,15 @@ dependencies {
   api("dev.openfeature:sdk:1.20.1")
 
   compileOnly(project(":products:feature-flagging:feature-flagging-bootstrap"))
+  compileOnly(project(":utils:config-utils"))
+  compileOnly("io.opentelemetry:opentelemetry-api:1.47.0")
+  compileOnly("io.opentelemetry:opentelemetry-sdk-metrics:1.47.0")
+  compileOnly("io.opentelemetry:opentelemetry-exporter-otlp:1.47.0")
 
   testImplementation(project(":products:feature-flagging:feature-flagging-bootstrap"))
+  testImplementation("io.opentelemetry:opentelemetry-api:1.47.0")
+  testImplementation("io.opentelemetry:opentelemetry-sdk-metrics:1.47.0")
+  testImplementation("io.opentelemetry:opentelemetry-exporter-otlp:1.47.0")
   testImplementation(libs.bundles.junit5)
   testImplementation(libs.bundles.mockito)
   testImplementation(libs.moshi)

products/feature-flagging/feature-flagging-api/src/main/java/datadog/trace/api/openfeature/FlagEvalHook.java

@@ -0,0 +1,41 @@
+package datadog.trace.api.openfeature;
+
+import dev.openfeature.sdk.ErrorCode;
+import dev.openfeature.sdk.FlagEvaluationDetails;
+import dev.openfeature.sdk.Hook;
+import dev.openfeature.sdk.HookContext;
+import dev.openfeature.sdk.ImmutableMetadata;
+import java.util.Map;
+
+class FlagEvalHook implements Hook<Object> {
+
+  private final FlagEvalMetrics metrics;
+
+  FlagEvalHook(FlagEvalMetrics metrics) {
+    this.metrics = metrics;
+  }
+
+  @Override
+  public void finallyAfter(
+      HookContext<Object> ctx, FlagEvaluationDetails<Object> details, Map<String, Object> hints) {
+    if (metrics == null || details == null) {
+      return;
+    }
+    try {
+      String flagKey = details.getFlagKey();
+      String variant = details.getVariant();
+      String reason = details.getReason();
+      ErrorCode errorCode = details.getErrorCode();
+
+      String allocationKey = null;
+      ImmutableMetadata metadata = details.getFlagMetadata();
+      if (metadata != null) {
+        allocationKey = metadata.getString("allocationKey");
+      }
+
+      metrics.record(flagKey, variant, reason, errorCode, allocationKey);
+    } catch (Exception e) {
+      // Never let metrics recording break flag evaluation
+    }
+  }
+}

products/feature-flagging/feature-flagging-api/src/main/java/datadog/trace/api/openfeature/FlagEvalMetrics.java

@@ -0,0 +1,131 @@
+package datadog.trace.api.openfeature;
+
+import datadog.trace.config.inversion.ConfigHelper;
+import dev.openfeature.sdk.ErrorCode;
+import io.opentelemetry.api.common.AttributeKey;
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.api.common.AttributesBuilder;
+import io.opentelemetry.api.metrics.LongCounter;
+import io.opentelemetry.api.metrics.Meter;
+import io.opentelemetry.exporter.otlp.http.metrics.OtlpHttpMetricExporter;
+import io.opentelemetry.sdk.metrics.SdkMeterProvider;
+import io.opentelemetry.sdk.metrics.export.PeriodicMetricReader;
+import java.io.Closeable;
+import java.time.Duration;
+
+class FlagEvalMetrics implements Closeable {
+
+  private static final String METER_NAME = "ddtrace.openfeature";
+  private static final String METRIC_NAME = "feature_flag.evaluations";
+  private static final String METRIC_UNIT = "{evaluation}";
+  private static final String METRIC_DESC = "Number of feature flag evaluations";
+  private static final Duration EXPORT_INTERVAL = Duration.ofSeconds(10);
+
+  private static final String DEFAULT_ENDPOINT = "http://localhost:4318/v1/metrics";
+  // Signal-specific env var (used as-is, must include /v1/metrics path)
+  private static final String ENDPOINT_ENV = "OTEL_EXPORTER_OTLP_METRICS_ENDPOINT";
+  // Generic env var fallback (base URL, /v1/metrics is appended)
+  private static final String ENDPOINT_GENERIC_ENV = "OTEL_EXPORTER_OTLP_ENDPOINT";
+
+  private static final AttributeKey<String> ATTR_FLAG_KEY =
+      AttributeKey.stringKey("feature_flag.key");
+  private static final AttributeKey<String> ATTR_VARIANT =
+      AttributeKey.stringKey("feature_flag.result.variant");
+  private static final AttributeKey<String> ATTR_REASON =
+      AttributeKey.stringKey("feature_flag.result.reason");
+  private static final AttributeKey<String> ATTR_ERROR_TYPE = AttributeKey.stringKey("error.type");
+  private static final AttributeKey<String> ATTR_ALLOCATION_KEY =
+      AttributeKey.stringKey("feature_flag.result.allocation_key");
+
+  private volatile LongCounter counter;
+  // Typed as Closeable to avoid loading SdkMeterProvider at class-load time
+  // when the OTel SDK is absent from the classpath
+  private volatile java.io.Closeable meterProvider;
+
+  FlagEvalMetrics() {
+    try {
+      String endpoint = ConfigHelper.env(ENDPOINT_ENV);
+      if (endpoint == null || endpoint.isEmpty()) {
+        String base = ConfigHelper.env(ENDPOINT_GENERIC_ENV);
+        if (base != null && !base.isEmpty()) {
+          endpoint = base.endsWith("/") ? base + "v1/metrics" : base + "/v1/metrics";
+        } else {
+          endpoint = DEFAULT_ENDPOINT;
+        }
+      }
+
+      OtlpHttpMetricExporter exporter =
+          OtlpHttpMetricExporter.builder().setEndpoint(endpoint).build();
+
+      PeriodicMetricReader reader =
+          PeriodicMetricReader.builder(exporter).setInterval(EXPORT_INTERVAL).build();
+
+      SdkMeterProvider sdkMeterProvider =
+          SdkMeterProvider.builder().registerMetricReader(reader).build();
+      meterProvider = sdkMeterProvider;
+
+      Meter meter = sdkMeterProvider.meterBuilder(METER_NAME).build();
+      counter =
+          meter
+              .counterBuilder(METRIC_NAME)
+              .setUnit(METRIC_UNIT)
+              .setDescription(METRIC_DESC)
+              .build();
+    } catch (NoClassDefFoundError | Exception e) {
+      // OTel SDK not on classpath or initialization failed — counter stays null (no-op)
+      counter = null;
+      meterProvider = null;
+    }
+  }
+
+  /** Package-private constructor for testing with a mock counter. */
+  FlagEvalMetrics(LongCounter counter) {
+    this.counter = counter;
+    this.meterProvider = null;
+  }
+
+  void record(
+      String flagKey, String variant, String reason, ErrorCode errorCode, String allocationKey) {
+    LongCounter c = counter;
+    if (c == null) {
+      return;
+    }
+    try {
+      AttributesBuilder builder =
+          Attributes.builder()
+              .put(ATTR_FLAG_KEY, flagKey)
+              .put(ATTR_VARIANT, variant != null ? variant : "")
+              .put(ATTR_REASON, reason != null ? reason.toLowerCase() : "unknown");
+
+      if (errorCode != null) {
+        builder.put(ATTR_ERROR_TYPE, errorCode.name().toLowerCase());
+      }
+
+      if (allocationKey != null && !allocationKey.isEmpty()) {
+        builder.put(ATTR_ALLOCATION_KEY, allocationKey);
+      }
+
+      c.add(1, builder.build());
+    } catch (Exception e) {
+      // Never let metrics recording break flag evaluation
+    }
+  }
+
+  @Override
+  public void close() {
+    shutdown();
+  }
+
+  void shutdown() {
+    counter = null;
+    java.io.Closeable mp = meterProvider;
+    if (mp != null) {
+      meterProvider = null;
+      try {
+        mp.close();
+      } catch (Exception e) {
+        // Ignore shutdown errors
+      }
+    }
+  }
+}

products/feature-flagging/feature-flagging-api/src/main/java/datadog/trace/api/openfeature/Provider.java

@@ -5,6 +5,7 @@
 import de.thetaphi.forbiddenapis.SuppressForbidden;
 import dev.openfeature.sdk.EvaluationContext;
 import dev.openfeature.sdk.EventProvider;
+import dev.openfeature.sdk.Hook;
 import dev.openfeature.sdk.Metadata;
 import dev.openfeature.sdk.ProviderEvaluation;
 import dev.openfeature.sdk.ProviderEvent;
@@ -14,6 +15,8 @@
 import dev.openfeature.sdk.exceptions.OpenFeatureError;
 import dev.openfeature.sdk.exceptions.ProviderNotReadyError;
 import java.lang.reflect.Constructor;
+import java.util.Collections;
+import java.util.List;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 
@@ -25,6 +28,8 @@ public class Provider extends EventProvider implements Metadata {
   private volatile Evaluator evaluator;
   private final Options options;
   private final AtomicBoolean initialized = new AtomicBoolean(false);
+  private final FlagEvalMetrics flagEvalMetrics;
+  private final FlagEvalHook flagEvalHook;
 
   public Provider() {
     this(DEFAULT_OPTIONS, null);
@@ -37,6 +42,16 @@ public Provider(final Options options) {
   Provider(final Options options, final Evaluator evaluator) {
     this.options = options;
     this.evaluator = evaluator;
+    FlagEvalMetrics metrics = null;
+    FlagEvalHook hook = null;
+    try {
+      metrics = new FlagEvalMetrics();
+      hook = new FlagEvalHook(metrics);
+    } catch (NoClassDefFoundError | Exception e) {
+      // OTel classes not on classpath — metrics disabled
+    }
+    this.flagEvalMetrics = metrics;
+    this.flagEvalHook = hook;
   }
 
   @Override
@@ -77,8 +92,19 @@ private Evaluator buildEvaluator() throws Exception {
     return (Evaluator) ctor.newInstance((Runnable) this::onConfigurationChange);
   }
 
+  @Override
+  public List<Hook> getProviderHooks() {
+    if (flagEvalHook == null) {
+      return Collections.emptyList();
+    }
+    return Collections.singletonList(flagEvalHook);
+  }
+
   @Override
   public void shutdown() {
+    if (flagEvalMetrics != null) {
+      flagEvalMetrics.shutdown();
+    }
     if (evaluator != null) {
       evaluator.shutdown();
     }