Prevent stale configuration data after iOS device restore (#15442)

Author: tusharkhandelwal8

FirebaseRemoteConfig/CHANGELOG.md

@@ -1,3 +1,9 @@
+# Unreleased
+- [fixed] Fixed a bug where Remote Config does not work after a restore
+  of a previous backup of the device. (#14459)
+- [fixed] Fixed a data race condition on the global database status flag
+  by synchronizing all read and write operations. (#14715)
+
 # 12.3.0
 - [fixed] Add missing GoogleUtilities dependency to fix SwiftPM builds when
   building dynamically linked libraries. (#15276)

FirebaseRemoteConfig/Sources/FIRRemoteConfig.m

@@ -160,6 +160,10 @@ - (instancetype)initWithAppName:(NSString *)appName
 
     // Initialize RCConfigContent if not already.
     _configContent = configContent;
+
+    // We must ensure the DBManager's asynchronous setup (which sets gIsNewDatabase)
+    // completes before RCNConfigSettings tries to read that state for the resetUserDefaults logic.
+    [_DBManager waitForDatabaseOperationQueue];
     _settings = [[RCNConfigSettings alloc] initWithDatabaseManager:_DBManager
                                                          namespace:_FIRNamespace
                                                    firebaseAppName:appName

FirebaseRemoteConfig/Sources/RCNConfigDBManager.h

@@ -130,4 +130,8 @@ typedef void (^RCNDBLoadCompletion)(BOOL success,
 
 /// Returns true if this a new install of the Config database.
 - (BOOL)isNewDatabase;
+
+/// Blocks the calling thread until all pending database operations on the internal serial queue are
+/// completed. Used to enforce initialization order.
+- (void)waitForDatabaseOperationQueue;
 @end

FirebaseRemoteConfig/Sources/RCNConfigDBManager.m

@@ -38,6 +38,9 @@
 /// The storage sub-directory that the Remote Config database resides in.
 static NSString *const RCNRemoteConfigStorageSubDirectory = @"Google/RemoteConfig";
 
+/// Introduce a dedicated serial queue for gIsNewDatabase access.
+static dispatch_queue_t gIsNewDatabaseQueue;
+
 /// Remote Config database path for deprecated V0 version.
 static NSString *RemoteConfigPathForOldDatabaseV0(void) {
   NSArray *dirPaths =
@@ -82,7 +85,9 @@ static BOOL RemoteConfigCreateFilePathIfNotExist(NSString *filePath) {
   }
   NSFileManager *fileManager = [NSFileManager defaultManager];
   if (![fileManager fileExistsAtPath:filePath]) {
-    gIsNewDatabase = YES;
+    dispatch_sync(gIsNewDatabaseQueue, ^{
+      gIsNewDatabase = YES;
+    });
     NSError *error;
     [fileManager createDirectoryAtPath:[filePath stringByDeletingLastPathComponent]
            withIntermediateDirectories:YES
@@ -119,6 +124,8 @@ + (instancetype)sharedInstance {
   static dispatch_once_t onceToken;
   static RCNConfigDBManager *sharedInstance;
   dispatch_once(&onceToken, ^{
+    gIsNewDatabaseQueue = dispatch_queue_create("com.google.FirebaseRemoteConfig.gIsNewDatabase",
+                                                DISPATCH_QUEUE_SERIAL);
     sharedInstance = [[RCNConfigDBManager alloc] init];
   });
   return sharedInstance;
@@ -1219,7 +1226,19 @@ - (BOOL)logErrorWithSQL:(const char *)SQL
 }
 
 - (BOOL)isNewDatabase {
-  return gIsNewDatabase;
+  __block BOOL isNew;
+  dispatch_sync(gIsNewDatabaseQueue, ^{
+    isNew = gIsNewDatabase;
+  });
+  return isNew;
+}
+
+- (void)waitForDatabaseOperationQueue {
+  // This dispatch_sync call ensures that all blocks queued before it on _databaseOperationQueue
+  // (including the createOrOpenDatabase setup block) execute and complete before this method
+  // returns.
+  dispatch_sync(_databaseOperationQueue, ^{
+                });
 }
 
 @end