feat: onConfigurationChange

README.md

@@ -9,7 +9,7 @@
 
 ```groovy
 dependencies {
-  implementation 'cloud.eppo:eppo-server-sdk:5.0.0'
+  implementation 'cloud.eppo:eppo-server-sdk:5.1.0'
 }
 ```
 

build.gradle

@@ -11,7 +11,7 @@ java {
 }
 
 group = 'cloud.eppo'
-version = '5.0.1-SNAPSHOT'
+version = '5.1.0'
 ext.isReleaseVersion = !version.endsWith("SNAPSHOT")
 
 import org.apache.tools.ant.filters.ReplaceTokens
@@ -30,7 +30,7 @@ repositories {
 }
 
 dependencies {
-  api 'cloud.eppo:sdk-common-jvm:3.8.0'
+  api 'cloud.eppo:sdk-common-jvm:3.9.0'
 
   implementation 'com.github.zafarkhaja:java-semver:0.10.2'
   implementation 'com.fasterxml.jackson.core:jackson-databind:2.18.2'

src/main/java/cloud/eppo/EppoClient.java

@@ -1,11 +1,13 @@
 package cloud.eppo;
 
+import cloud.eppo.api.Configuration;
 import cloud.eppo.api.IAssignmentCache;
 import cloud.eppo.cache.ExpiringInMemoryAssignmentCache;
 import cloud.eppo.cache.LRUInMemoryAssignmentCache;
 import cloud.eppo.logging.AssignmentLogger;
 import cloud.eppo.logging.BanditLogger;
 import java.util.concurrent.TimeUnit;
+import java.util.function.Consumer;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.slf4j.Logger;
@@ -79,6 +81,7 @@ public static class Builder {
     private boolean forceReinitialize = DEFAULT_FORCE_REINITIALIZE;
     private long pollingIntervalMs = DEFAULT_POLLING_INTERVAL_MS;
     private String apiBaseUrl = null;
+    @Nullable private Consumer<Configuration> configChangeCallback;
 
     // Assignment and bandit caching on by default. To disable, call
     // `builder.assignmentCache(null).banditAssignmentCache(null);`
@@ -156,6 +159,14 @@ public Builder banditAssignmentCache(IAssignmentCache banditAssignmentCache) {
       return this;
     }
 
+    /**
+     * Registers a callback for when a new configuration is applied to the `EppoClient` instance.
+     */
+    public Builder onConfigurationChange(Consumer<Configuration> configChangeCallback) {
+      this.configChangeCallback = configChangeCallback;
+      return this;
+    }
+
     public EppoClient buildAndInit() {
       AppDetails appDetails = AppDetails.getInstance();
       String sdkName = appDetails.getName();
@@ -186,6 +197,10 @@ public EppoClient buildAndInit() {
               assignmentCache,
               banditAssignmentCache);
 
+      if (configChangeCallback != null) {
+        instance.onConfigurationChange(configChangeCallback);
+      }
+
       // Fetch first configuration
       instance.loadConfiguration();
 

src/test/java/cloud/eppo/EppoClientTest.java

@@ -25,7 +25,10 @@
 import com.github.tomakehurst.wiremock.junit5.WireMockExtension;
 import java.io.File;
 import java.lang.reflect.Field;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
 import java.util.stream.Stream;
 import org.apache.commons.io.FileUtils;
 import org.junit.jupiter.api.AfterAll;
@@ -51,6 +54,8 @@ public class EppoClientTest {
   private AssignmentLogger mockAssignmentLogger;
   private BanditLogger mockBanditLogger;
 
+  private static final byte[] EMPTY_CONFIG = "{\"flags\":{}}".getBytes();
+
   @BeforeAll
   public static void initMockServer() {
     mockServer = new WireMockServer(TEST_PORT);
@@ -271,6 +276,47 @@ public void testGetConfiguration() {
     assertEquals(VariationType.NUMERIC, configuration.getFlagType("numeric_flag"));
   }
 
+  @Test
+  public void testConfigurationChangeListener() throws ExecutionException, InterruptedException {
+    List<Configuration> received = new ArrayList<>();
+
+    // Set up a changing response from the "server"
+    EppoHttpClient mockHttpClient = mock(EppoHttpClient.class);
+
+    // Mock sync get to return empty
+    when(mockHttpClient.get(anyString())).thenReturn(EMPTY_CONFIG);
+
+    // Mock async get to return empty
+    when(mockHttpClient.get(anyString())).thenReturn(EMPTY_CONFIG);
+
+    setBaseClientHttpClientOverrideField(mockHttpClient);
+
+    EppoClient.Builder clientBuilder =
+        EppoClient.builder(DUMMY_FLAG_API_KEY)
+            .forceReinitialize(true)
+            .onConfigurationChange(received::add)
+            .isGracefulMode(false);
+
+    // Initialize and no exception should be thrown.
+    EppoClient eppoClient = clientBuilder.buildAndInit();
+
+    verify(mockHttpClient, times(1)).get(anyString());
+    assertEquals(1, received.size());
+
+    // Now, return the boolean flag config so that the config has changed.
+    when(mockHttpClient.get(anyString())).thenReturn(BOOL_FLAG_CONFIG);
+
+    // Trigger a reload of the client
+    eppoClient.loadConfiguration();
+
+    assertEquals(2, received.size());
+
+    // Reload the client again; the config hasn't changed, but Java doesn't check eTag (yet)
+    eppoClient.loadConfiguration();
+
+    assertEquals(3, received.size());
+  }
+
   public static void mockHttpError() {
     // Create a mock instance of EppoHttpClient
     EppoHttpClient mockHttpClient = mock(EppoHttpClient.class);
@@ -353,4 +399,40 @@ public static void setBaseClientHttpClientOverrideField(EppoHttpClient httpClien
       throw new RuntimeException(e);
     }
   }
+
+  private static final byte[] BOOL_FLAG_CONFIG =
+      ("{\n"
+              + "  \"createdAt\": \"2024-04-17T19:40:53.716Z\",\n"
+              + "  \"format\": \"SERVER\",\n"
+              + "  \"environment\": {\n"
+              + "    \"name\": \"Test\"\n"
+              + "  },\n"
+              + "  \"flags\": {\n"
+              + "    \"9a2025738dde19ff44cd30b9d2967000\": {\n"
+              + "      \"key\": \"9a2025738dde19ff44cd30b9d2967000\",\n"
+              + "      \"enabled\": true,\n"
+              + "      \"variationType\": \"BOOLEAN\",\n"
+              + "      \"variations\": {\n"
+              + "        \"b24=\": {\n"
+              + "          \"key\": \"b24=\",\n"
+              + "          \"value\": \"dHJ1ZQ==\"\n"
+              + "        }\n"
+              + "      },\n"
+              + "      \"allocations\": [\n"
+              + "        {\n"
+              + "          \"key\": \"b24=\",\n"
+              + "          \"doLog\": true,\n"
+              + "          \"splits\": [\n"
+              + "            {\n"
+              + "              \"variationKey\": \"b24=\",\n"
+              + "              \"shards\": []\n"
+              + "            }\n"
+              + "          ]\n"
+              + "        }\n"
+              + "      ],\n"
+              + "      \"totalShards\": 10000\n"
+              + "    }\n"
+              + "  }\n"
+              + "}")
+          .getBytes();
 }