Initial implementation of the OpenFeature SDK

Author: manuel-alvarez-alvarez

.github/CODEOWNERS

@@ -139,3 +139,10 @@ dd-trace-core/src/test/groovy/datadog/trace/llmobs/  @DataDog/ml-observability
 /internal-api/src/test/groovy/datadog/trace/api/rum/ @DataDog/rum
 /telemetry/src/main/java/datadog/telemetry/rum/      @DataDog/rum
 /telemetry/src/test/groovy/datadog/telemetry/rum/    @DataDog/rum
+
+# @DataDog/feature-flagging-and-experimentation-sdk
+/dd-java-agent/agent-featureflag/                           @DataDog/feature-flagging-and-experimentation-sdk
+/dd-smoke-tests/featureflag/                                @DataDog/feature-flagging-and-experimentation-sdk
+/internal-api/src/main/java/datadog/trace/api/featureflag   @DataDog/feature-flagging-and-experimentation-sdk
+/internal-api/src/test/groovy/datadog/trace/api/featureflag @DataDog/feature-flagging-and-experimentation-sdk
+/products/openfeature/                                      @DataDog/feature-flagging-and-experimentation-sdk

dd-java-agent/agent-bootstrap/src/main/java/datadog/trace/bootstrap/Agent.java

@@ -32,6 +32,7 @@
 import datadog.trace.api.config.CrashTrackingConfig;
 import datadog.trace.api.config.CwsConfig;
 import datadog.trace.api.config.DebuggerConfig;
+import datadog.trace.api.config.FeatureFlagConfig;
 import datadog.trace.api.config.GeneralConfig;
 import datadog.trace.api.config.IastConfig;
 import datadog.trace.api.config.JmxFetchConfig;
@@ -125,7 +126,8 @@ private enum AgentFeature {
     DATA_JOBS(GeneralConfig.DATA_JOBS_ENABLED, false),
     AGENTLESS_LOG_SUBMISSION(GeneralConfig.AGENTLESS_LOG_SUBMISSION_ENABLED, false),
     LLMOBS(LlmObsConfig.LLMOBS_ENABLED, false),
-    LLMOBS_AGENTLESS(LlmObsConfig.LLMOBS_AGENTLESS_ENABLED, false);
+    LLMOBS_AGENTLESS(LlmObsConfig.LLMOBS_AGENTLESS_ENABLED, false),
+    FEATURE_FLAG(FeatureFlagConfig.FLAGGING_PROVIDER_ENABLED, false);
 
     private final String configKey;
     private final String systemProp;
@@ -184,6 +186,7 @@ public boolean isEnabledByDefault() {
   private static boolean codeOriginEnabled = false;
   private static boolean distributedDebuggerEnabled = false;
   private static boolean agentlessLogSubmissionEnabled = false;
+  private static boolean featureFlagEnabled = false;
 
   private static void safelySetContextClassLoader(ClassLoader classLoader) {
     try {
@@ -268,6 +271,7 @@ public static void start(
     codeOriginEnabled = isFeatureEnabled(AgentFeature.CODE_ORIGIN);
     agentlessLogSubmissionEnabled = isFeatureEnabled(AgentFeature.AGENTLESS_LOG_SUBMISSION);
     llmObsEnabled = isFeatureEnabled(AgentFeature.LLMOBS);
+    featureFlagEnabled = isFeatureEnabled(AgentFeature.FEATURE_FLAG);
 
     // setup writers when llmobs is enabled to accomodate apm and llmobs
     if (llmObsEnabled) {
@@ -662,6 +666,7 @@ public void execute() {
       maybeStartDebugger(instrumentation, scoClass, sco);
       maybeStartRemoteConfig(scoClass, sco);
       maybeStartAiGuard();
+      maybeStartFeatureFlag(scoClass, sco);
 
       if (telemetryEnabled) {
         startTelemetry(instrumentation, scoClass, sco);
@@ -1083,6 +1088,23 @@ private static void maybeStartLLMObs(Instrumentation inst, Class<?> scoClass, Ob
     }
   }
 
+  private static void maybeStartFeatureFlag(final Class<?> scoClass, final Object sco) {
+    if (featureFlagEnabled) {
+      StaticEventLogger.begin("Feature Flag");
+
+      try {
+        final Class<?> ffSysClass =
+            AGENT_CLASSLOADER.loadClass("com.datadog.featureflag.FeatureFlagSystem");
+        final Method ffSysMethod = ffSysClass.getMethod("start", scoClass);
+        ffSysMethod.invoke(null, sco);
+      } catch (final Throwable e) {
+        log.warn("Not starting Feature Flag subsystem", e);
+      }
+
+      StaticEventLogger.end("Feature Flag");
+    }
+  }
+
   private static void maybeInstallLogsIntake(Class<?> scoClass, Object sco) {
     if (agentlessLogSubmissionEnabled) {
       StaticEventLogger.begin("Logs Intake");

dd-java-agent/agent-featureflag/build.gradle

@@ -0,0 +1,42 @@
+import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar
+
+plugins {
+  id 'com.gradleup.shadow'
+}
+
+apply from: "$rootDir/gradle/java.gradle"
+apply from: "$rootDir/gradle/version.gradle"
+
+java {
+  sourceCompatibility = JavaVersion.VERSION_1_8
+  targetCompatibility = JavaVersion.VERSION_1_8
+}
+
+excludedClassesCoverage += [
+  // POJOs
+  'com.datadog.featureflag.ExposureCache.Key',
+  'com.datadog.featureflag.ExposureCache.Value'
+]
+
+dependencies {
+  api libs.slf4j
+  implementation libs.moshi
+  implementation libs.jctools
+
+  api project(':dd-trace-api')
+  compileOnly project(':dd-trace-core')
+  implementation project(':internal-api')
+  implementation project(':communication')
+
+  testImplementation project(':utils:test-utils')
+  testImplementation project(':dd-java-agent:testing')
+}
+
+tasks.named("shadowJar", ShadowJar) {
+  dependencies deps.excludeShared
+}
+
+tasks.named("jar", Jar) {
+  archiveClassifier = 'unbundled'
+}
+

dd-java-agent/agent-featureflag/src/main/java/com/datadog/featureflag/ExposureCache.java

@@ -0,0 +1,61 @@
+package com.datadog.featureflag;
+
+import datadog.trace.api.featureflag.exposure.ExposureEvent;
+import java.util.Objects;
+
+public interface ExposureCache {
+
+  boolean add(ExposureEvent event);
+
+  Value get(Key key);
+
+  int size();
+
+  final class Key {
+    public final String flag;
+    public final String subject;
+
+    public Key(final ExposureEvent event) {
+      this.flag = event.flag == null ? null : event.flag.key;
+      this.subject = event.subject == null ? null : event.subject.id;
+    }
+
+    @Override
+    public boolean equals(final Object o) {
+      if (o == null || getClass() != o.getClass()) {
+        return false;
+      }
+      final Key key = (Key) o;
+      return Objects.equals(flag, key.flag) && Objects.equals(subject, key.subject);
+    }
+
+    @Override
+    public int hashCode() {
+      return Objects.hash(flag, subject);
+    }
+  }
+
+  final class Value {
+    public final String variant;
+    public final String allocation;
+
+    public Value(final ExposureEvent event) {
+      this.variant = event.variant == null ? null : event.variant.key;
+      this.allocation = event.allocation == null ? null : event.allocation.key;
+    }
+
+    @Override
+    public boolean equals(final Object o) {
+      if (o == null || getClass() != o.getClass()) {
+        return false;
+      }
+      final Value value = (Value) o;
+      return Objects.equals(variant, value.variant) && Objects.equals(allocation, value.allocation);
+    }
+
+    @Override
+    public int hashCode() {
+      return Objects.hash(variant, allocation);
+    }
+  }
+}

dd-java-agent/agent-featureflag/src/main/java/com/datadog/featureflag/ExposureWriter.java

@@ -0,0 +1,14 @@
+package com.datadog.featureflag;
+
+import datadog.trace.api.featureflag.FeatureFlagGateway;
+
+/**
+ * Defines an exposure writer responsible for sending exposure events to the EVP proxy.
+ * Implementations should use a background thread to perform these operations asynchronously.
+ */
+public interface ExposureWriter extends AutoCloseable, FeatureFlagGateway.ExposureListener {
+
+  void init();
+
+  void close();
+}