feat: emit changed flags in configuration change event (#925)

Signed-off-by: utkarsh <utkarsh.sharma@engati.com>
Signed-off-by: Todd Baert <todd.baert@dynatrace.com>
Co-authored-by: utkarsh <utkarsh.sharma@engati.com>
Co-authored-by: Todd Baert <todd.baert@dynatrace.com>

providers/flagd/lombok.config

@@ -0,0 +1,5 @@
+# This file is needed to avoid errors throw by findbugs when working with lombok.
+lombok.addSuppressWarnings = true
+lombok.addLombokGeneratedAnnotation = true
+config.stopBubbling = true
+lombok.extern.findbugs.addSuppressFBWarnings = true

providers/flagd/src/main/java/dev/openfeature/contrib/providers/flagd/FlagdProvider.java

@@ -6,14 +6,14 @@
 import dev.openfeature.contrib.providers.flagd.resolver.process.InProcessResolver;
 import dev.openfeature.sdk.EvaluationContext;
 import dev.openfeature.sdk.EventProvider;
-import dev.openfeature.sdk.FeatureProvider;
 import dev.openfeature.sdk.Metadata;
 import dev.openfeature.sdk.ProviderEvaluation;
 import dev.openfeature.sdk.ProviderEventDetails;
 import dev.openfeature.sdk.ProviderState;
 import dev.openfeature.sdk.Value;
 import lombok.extern.slf4j.Slf4j;
 
+import java.util.List;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReadWriteLock;
 import java.util.concurrent.locks.ReentrantReadWriteLock;
@@ -23,7 +23,7 @@
  */
 @Slf4j
 @SuppressWarnings({"PMD.TooManyStaticImports", "checkstyle:NoFinalizer"})
-public class FlagdProvider extends EventProvider implements FeatureProvider {
+public class FlagdProvider extends EventProvider {
     private static final String FLAGD_PROVIDER = "flagD Provider";
 
     private final ReadWriteLock lock = new ReentrantReadWriteLock();
@@ -142,7 +142,7 @@ private EvaluationContext mergeContext(final EvaluationContext clientCallCtx) {
         return clientCallCtx;
     }
 
-    private void setState(ProviderState newState) {
+    private void setState(ProviderState newState, List<String> changedFlagsKeys) {
         ProviderState oldState;
         Lock l = this.lock.writeLock();
         try {
@@ -152,17 +152,17 @@ private void setState(ProviderState newState) {
         } finally {
             l.unlock();
         }
-        this.handleStateTransition(oldState, newState);
+        this.handleStateTransition(oldState, newState, changedFlagsKeys);
     }
 
-    private void handleStateTransition(ProviderState oldState, ProviderState newState) {
+    private void handleStateTransition(ProviderState oldState, ProviderState newState, List<String> changedFlagKeys) {
         // we got initialized
         if (ProviderState.NOT_READY.equals(oldState) && ProviderState.READY.equals(newState)) {
             // nothing to do, the SDK emits the events
             log.debug("Init completed");
             return;
         }
-        // we got shutdown, not checking oldState as behavior remains the same for shutdown 
+        // we got shutdown, not checking oldState as behavior remains the same for shutdown
         if (ProviderState.NOT_READY.equals(newState)) {
             // nothing to do
             log.debug("shutdown completed");
@@ -171,7 +171,8 @@ private void handleStateTransition(ProviderState oldState, ProviderState newStat
         // configuration changed
         if (ProviderState.READY.equals(oldState) && ProviderState.READY.equals(newState)) {
             log.debug("Configuration changed");
-            ProviderEventDetails details = ProviderEventDetails.builder().message("configuration changed").build();
+            ProviderEventDetails details = ProviderEventDetails.builder().flagsChanged(changedFlagKeys)
+                    .message("configuration changed").build();
             this.emitProviderConfigurationChanged(details);
             return;
         }

providers/flagd/src/main/java/dev/openfeature/contrib/providers/flagd/resolver/grpc/EventStreamObserver.java

@@ -8,16 +8,19 @@
 import io.grpc.stub.StreamObserver;
 import lombok.extern.slf4j.Slf4j;
 
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 import java.util.Map;
-import java.util.function.Consumer;
+import java.util.function.BiConsumer;
 
 /**
  * EventStreamObserver handles events emitted by flagd.
  */
 @Slf4j
 @SuppressFBWarnings(justification = "cache needs to be read and write by multiple objects")
 class EventStreamObserver implements StreamObserver<EventStreamResponse> {
-    private final Consumer<ProviderState> stateConsumer;
+    private final BiConsumer<ProviderState, List<String>> stateConsumer;
     private final Object sync;
     private final Cache cache;
 
@@ -28,11 +31,11 @@ class EventStreamObserver implements StreamObserver<EventStreamResponse> {
     /**
      * Create a gRPC stream that get notified about flag changes.
      *
-     * @param sync                 synchronization object from caller
-     * @param cache                cache to update
-     * @param stateConsumer        lambda to call for setting the state
+     * @param sync          synchronization object from caller
+     * @param cache         cache to update
+     * @param stateConsumer lambda to call for setting the state
      */
-    EventStreamObserver(Object sync, Cache cache, Consumer<ProviderState> stateConsumer) {
+    EventStreamObserver(Object sync, Cache cache, BiConsumer<ProviderState, List<String>> stateConsumer) {
         this.sync = sync;
         this.cache = cache;
         this.stateConsumer = stateConsumer;
@@ -58,7 +61,7 @@ public void onError(Throwable t) {
         if (this.cache.getEnabled()) {
             this.cache.clear();
         }
-        this.stateConsumer.accept(ProviderState.ERROR);
+        this.stateConsumer.accept(ProviderState.ERROR, Collections.emptyList());
 
         // handle last call of this stream
         handleEndOfStream();
@@ -69,32 +72,38 @@ public void onCompleted() {
         if (this.cache.getEnabled()) {
             this.cache.clear();
         }
-        this.stateConsumer.accept(ProviderState.ERROR);
+        this.stateConsumer.accept(ProviderState.ERROR, Collections.emptyList());
 
         // handle last call of this stream
         handleEndOfStream();
     }
 
     private void handleConfigurationChangeEvent(EventStreamResponse value) {
-        this.stateConsumer.accept(ProviderState.READY);
-        if (!this.cache.getEnabled()) {
-            return;
-        }
+        List<String> changedFlags = new ArrayList<>();
+        boolean cachingEnabled = this.cache.getEnabled();
+
         Map<String, Value> data = value.getData().getFieldsMap();
         Value flagsValue = data.get(FLAGS_KEY);
         if (flagsValue == null) {
-            this.cache.clear();
-            return;
+            if (cachingEnabled) {
+                this.cache.clear();
+            }
+        } else {
+            Map<String, Value> flags = flagsValue.getStructValue().getFieldsMap();
+            this.cache.getEnabled();
+            for (String flagKey : flags.keySet()) {
+                changedFlags.add(flagKey);
+                if (cachingEnabled) {
+                    this.cache.remove(flagKey);
+                }
+            }
         }
 
-        Map<String, Value> flags = flagsValue.getStructValue().getFieldsMap();
-        for (String flagKey : flags.keySet()) {
-            this.cache.remove(flagKey);
-        }
+        this.stateConsumer.accept(ProviderState.READY, changedFlags);
     }
 
     private void handleProviderReadyEvent() {
-        this.stateConsumer.accept(ProviderState.READY);
+        this.stateConsumer.accept(ProviderState.READY, Collections.emptyList());
         if (this.cache.getEnabled()) {
             this.cache.clear();
         }

providers/flagd/src/main/java/dev/openfeature/contrib/providers/flagd/resolver/grpc/GrpcConnector.java

@@ -1,10 +1,11 @@
 package dev.openfeature.contrib.providers.flagd.resolver.grpc;
 
+import java.util.Collections;
+import java.util.List;
 import java.util.Random;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
-import java.util.function.Consumer;
-
+import java.util.function.BiConsumer;
 import dev.openfeature.contrib.providers.flagd.FlagdOptions;
 import dev.openfeature.contrib.providers.flagd.resolver.common.ChannelBuilder;
 import dev.openfeature.contrib.providers.flagd.resolver.common.Util;
@@ -37,7 +38,7 @@ public class GrpcConnector {
     private final long deadline;
 
     private final Cache cache;
-    private final Consumer<ProviderState> stateConsumer;
+    private final BiConsumer<ProviderState, List<String>> stateConsumer;
 
     private int eventStreamAttempt = 1;
     private int eventStreamRetryBackoff;
@@ -52,7 +53,8 @@ public class GrpcConnector {
      * @param cache         cache to use.
      * @param stateConsumer lambda to call for setting the state.
      */
-    public GrpcConnector(final FlagdOptions options, final Cache cache, Consumer<ProviderState> stateConsumer) {
+    public GrpcConnector(final FlagdOptions options, final Cache cache,
+            BiConsumer<ProviderState, List<String>> stateConsumer) {
         this.channel = ChannelBuilder.nettyChannel(options);
         this.serviceStub = ServiceGrpc.newStub(channel);
         this.serviceBlockingStub = ServiceGrpc.newBlockingStub(channel);
@@ -80,7 +82,8 @@ public void initialize() throws Exception {
     /**
      * Shuts down all gRPC resources.
      *
-     * @throws Exception is something goes wrong while terminating the communication.
+     * @throws Exception is something goes wrong while terminating the
+     *                   communication.
      */
     public void shutdown() throws Exception {
         // first shutdown the event listener
@@ -100,7 +103,7 @@ public void shutdown() throws Exception {
                 this.channel.awaitTermination(this.deadline, TimeUnit.MILLISECONDS);
                 log.warn(String.format("Unable to shut down channel by %d deadline", this.deadline));
             }
-            this.stateConsumer.accept(ProviderState.NOT_READY);
+            this.stateConsumer.accept(ProviderState.NOT_READY, Collections.emptyList());
         }
     }
 
@@ -114,21 +117,24 @@ public ServiceGrpc.ServiceBlockingStub getResolver() {
     }
 
     /**
-     * Event stream observer logic. This contains blocking mechanisms, hence must be run in a dedicated thread.
+     * Event stream observer logic. This contains blocking mechanisms, hence must be
+     * run in a dedicated thread.
      */
     private void observeEventStream() {
         while (this.eventStreamAttempt <= this.maxEventStreamRetries) {
-            final StreamObserver<EventStreamResponse> responseObserver =
-                    new EventStreamObserver(sync, this.cache, this::grpcStateConsumer);
+            final StreamObserver<EventStreamResponse> responseObserver = new EventStreamObserver(sync, this.cache,
+                    this::grpcStateConsumer);
             this.serviceStub.eventStream(EventStreamRequest.getDefaultInstance(), responseObserver);
 
             try {
                 synchronized (sync) {
                     sync.wait();
                 }
             } catch (InterruptedException e) {
-                // Interruptions are considered end calls for this observer, hence log and return
-                // Note - this is the most common interruption when shutdown, hence the log level debug
+                // Interruptions are considered end calls for this observer, hence log and
+                // return
+                // Note - this is the most common interruption when shutdown, hence the log
+                // level debug
                 log.debug("interruption while waiting for condition", e);
                 Thread.currentThread().interrupt();
             }
@@ -140,17 +146,18 @@ private void observeEventStream() {
             try {
                 Thread.sleep(this.eventStreamRetryBackoff);
             } catch (InterruptedException e) {
-                // Interruptions are considered end calls for this observer, hence log and return
+                // Interruptions are considered end calls for this observer, hence log and
+                // return
                 log.warn("interrupted while restarting gRPC Event Stream");
                 Thread.currentThread().interrupt();
             }
         }
 
         log.error("failed to connect to event stream, exhausted retries");
-        this.grpcStateConsumer(ProviderState.ERROR);
+        this.grpcStateConsumer(ProviderState.ERROR, null);
     }
 
-    private void grpcStateConsumer(final ProviderState state) {
+    private void grpcStateConsumer(final ProviderState state, final List<String> changedFlags) {
         // check for readiness
         if (ProviderState.READY.equals(state)) {
             this.eventStreamAttempt = 1;
@@ -162,6 +169,6 @@ private void grpcStateConsumer(final ProviderState state) {
         }
 
         // chain to initiator
-        this.stateConsumer.accept(state);
+        this.stateConsumer.accept(state, changedFlags);
     }
 }

providers/flagd/src/main/java/dev/openfeature/contrib/providers/flagd/resolver/grpc/GrpcResolver.java

@@ -5,7 +5,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.function.Consumer;
+import java.util.function.BiConsumer;
 import java.util.function.Function;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
@@ -62,7 +62,7 @@ public final class GrpcResolver implements Resolver {
      * @param stateConsumer lambda to communicate back the state.
      */
     public GrpcResolver(final FlagdOptions options, final Cache cache, final Supplier<ProviderState> stateSupplier,
-            final Consumer<ProviderState> stateConsumer) {
+            final BiConsumer<ProviderState,List<String>> stateConsumer) {
         this.cache = cache;
         this.stateSupplier = stateSupplier;