fix: wait saveConfiguration futures (#46)

wait for saveConfig futures, include empty config static string.

Author: typotter

build.gradle

@@ -6,7 +6,7 @@ plugins {
 }
 
 group = 'cloud.eppo'
-version = '3.3.0-SNAPSHOT'
+version = '3.3.1-SNAPSHOT'
 ext.isReleaseVersion = !version.endsWith("SNAPSHOT")
 
 java {

src/main/java/cloud/eppo/ConfigurationRequestor.java

@@ -2,7 +2,6 @@
 
 import cloud.eppo.api.Configuration;
 import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.CompletionException;
 import java.util.concurrent.ExecutionException;
 import org.jetbrains.annotations.NotNull;
 import org.slf4j.Logger;
@@ -39,12 +38,8 @@ public void setInitialConfiguration(@NotNull Configuration configuration) {
       throw new IllegalStateException("Initial configuration has already been set");
     }
 
-    try {
-      configurationStore.saveConfiguration(configuration).join();
-      initialConfigSet = true;
-    } catch (CompletionException e) {
-      log.error("Error setting initial configuration", e);
-    }
+    initialConfigSet =
+        configurationStore.saveConfiguration(configuration).thenApply(v -> true).join();
   }
 
   // Asynchronously sets the initial configuration.
@@ -54,23 +49,32 @@ public CompletableFuture<Void> setInitialConfiguration(
       throw new IllegalStateException("Configuration future has already been set");
     }
     this.configurationFuture =
-        configurationFuture.thenAccept(
-            (config) -> {
-              synchronized (configurationStore) {
-                if (config == null) {
-                  log.debug("Initial configuration future returned null");
-                } else if (remoteFetchFuture != null
-                    && remoteFetchFuture.isDone()
-                    && !remoteFetchFuture.isCompletedExceptionally()) {
-                  // Don't clobber a successful fetch.
-                  log.debug("Fetch successfully beat the initial config; not clobbering");
-                } else {
-                  log.debug("saving initial configuration");
-                  configurationStore.saveConfiguration(config);
-                  initialConfigSet = true;
-                }
-              }
-            });
+        configurationFuture
+            .thenAccept(
+                (config) -> {
+                  synchronized (configurationStore) {
+                    if (config == null || config.isEmpty()) {
+                      log.debug("Initial configuration future returned empty/null");
+                    } else if (remoteFetchFuture != null
+                        && remoteFetchFuture.isDone()
+                        && !remoteFetchFuture.isCompletedExceptionally()) {
+                      // Don't clobber a successful fetch.
+                      log.debug("Fetch has completed; ignoring initial config load.");
+                    } else {
+                      log.debug("saving initial configuration");
+                      initialConfigSet =
+                          configurationStore
+                              .saveConfiguration(config)
+                              .thenApply((s) -> true)
+                              .join();
+                    }
+                  }
+                })
+            .exceptionally(
+                (e) -> {
+                  log.error("Error setting initial config", e);
+                  return null;
+                });
     return this.configurationFuture;
   }
 
@@ -91,7 +95,7 @@ void fetchAndSaveFromRemote() {
       configBuilder.banditParameters(banditParametersJsonBytes);
     }
 
-    configurationStore.saveConfiguration(configBuilder.build());
+    configurationStore.saveConfiguration(configBuilder.build()).join();
   }
 
   /** Loads configuration asynchronously from the API server, off-thread. */
@@ -128,15 +132,9 @@ CompletableFuture<Void> fetchAndSaveFromRemoteAsync() {
                         configBuilder.banditParameters(banditParametersJsonBytes);
                       }
                     }
-                    return configBuilder.build();
-                  }
-                })
-            .thenApply(
-                configuration -> {
-                  synchronized (configurationStore) {
-                    configurationStore.saveConfiguration(configuration);
+
+                    return configurationStore.saveConfiguration(configBuilder.build()).join();
                   }
-                  return null;
                 });
     return remoteFetchFuture;
   }

src/main/java/cloud/eppo/api/Configuration.java

@@ -52,6 +52,9 @@ public class Configuration {
   private static final ObjectMapper mapper =
       new ObjectMapper().registerModule(EppoModule.eppoModule());
 
+  private static final byte[] emptyFlagsBytes =
+      "{ \"flags\": {}, \"format\": \"SERVER\" }".getBytes();
+
   private static final Logger log = LoggerFactory.getLogger(Configuration.class);
   private final Map<String, BanditReference> banditReferences;
   private final Map<String, FlagConfig> flags;
@@ -95,7 +98,12 @@ private Configuration(
 
   public static Configuration emptyConfig() {
     return new Configuration(
-        Collections.emptyMap(), Collections.emptyMap(), Collections.emptyMap(), false, null, null);
+        Collections.emptyMap(),
+        Collections.emptyMap(),
+        Collections.emptyMap(),
+        false,
+        emptyFlagsBytes,
+        null);
   }
 
   public FlagConfig getFlag(String flagKey) {