[FSSDK-12503] fix: guard static MethodChannel from multi-engine overwrite (#103)

* fix: guard static MethodChannel from multi-engine overwrite (Android)

When FirebaseMessaging.onBackgroundMessage (or any mechanism that creates
a second FlutterEngine) triggers onAttachedToEngine a second time, the
static channel was unconditionally overwritten. This caused notification
callbacks to route to the wrong engine, silently dropping them.

The fix adds an early return if channel is already set, and nulls the
channel in onDetachedFromEngine so re-attachment works after a real
detach.

Fixes FSSDK-12503

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: guard logger channel from multi-engine overwrite (Android)

Same root cause as the main channel fix — the static logger channel
could be overwritten by a second FlutterEngine. The setChannel guard
allows explicit null (cleanup) but prevents overwrite of an active
channel.

Fixes FSSDK-12503

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: guard static MethodChannel from multi-engine overwrite (iOS)

Same vulnerability as Android — if register(with:) were called twice
(e.g. by a second FlutterEngine), the static channel would be
overwritten. The fix adds an early return if channel is already set.

Fixes FSSDK-12503

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: guard logger channel from multi-engine overwrite (iOS)

Same pattern as the Android logger fix — prevents a second engine
from overwriting the active logger channel.

Fixes FSSDK-12503

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* refactor: split setChannel into setChannel/clearChannel for logger channels

Replace the compound null-guard logic with explicit setChannel (only sets
if no active channel) and clearChannel (always clears). This matches the
main plugin's pattern and makes intent immediately obvious.

Callers updated: onDetachedFromEngine now calls clearChannel() instead
of setChannel(null).

Fixes FSSDK-12503

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: add iOS engine detach cleanup and enforce private channel access

Add detachFromEngine(for:) to iOS plugin so channel is cleaned up when
the engine detaches, matching Android's onDetachedFromEngine behavior.
Make FlutterLogbackAppender.channel private to enforce use of
setChannel/clearChannel accessors.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: muzahidul-opti

android/src/main/java/com/optimizely/optimizely_flutter_sdk/FlutterLogbackAppender.java

@@ -14,11 +14,17 @@
 public class FlutterLogbackAppender extends AppenderBase<ILoggingEvent> {
 
     public static final String CHANNEL_NAME = "optimizely_flutter_sdk_logger";
-    public static MethodChannel channel;
+    private static MethodChannel channel;
     private static final Handler mainThreadHandler = new Handler(Looper.getMainLooper());
 
-    public static void setChannel(MethodChannel channel) {
-        FlutterLogbackAppender.channel = channel;
+    public static void setChannel(MethodChannel newChannel) {
+        if (channel == null) {
+            channel = newChannel;
+        }
+    }
+
+    public static void clearChannel() {
+        channel = null;
     }
 
     @Override

android/src/main/java/com/optimizely/optimizely_flutter_sdk/OptimizelyFlutterSdkPlugin.java

@@ -212,6 +212,9 @@ public void onMethodCall(@NonNull MethodCall call, @NonNull Result result) {
 
   @Override
   public void onAttachedToEngine(@NonNull FlutterPluginBinding binding) {
+    if (channel != null) {
+      return;
+    }
     channel = new MethodChannel(binding.getBinaryMessenger(), "optimizely_flutter_sdk");
     channel.setMethodCallHandler(this);
     context = binding.getApplicationContext();
@@ -232,15 +235,16 @@ public void onAttachedToEngine(@NonNull FlutterPluginBinding binding) {
   @Override
   public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {
     channel.setMethodCallHandler(null);
+    channel = null;
     // Stop and detach the appender
     if (flutterLogbackAppender != null) {
         Logger rootLogger = (Logger) LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME);
         rootLogger.detachAppender(flutterLogbackAppender);
         flutterLogbackAppender.stop();
         flutterLogbackAppender = null;
     }
-    // Clean up the channel
-    FlutterLogbackAppender.setChannel(null);
+    // Clean up the logger channel
+    FlutterLogbackAppender.clearChannel();
   }
 
   @Override

ios/Classes/OptimizelyFlutterLogger.swift

@@ -13,7 +13,13 @@ public class OptimizelyFlutterLogger: NSObject, OPTLogger {
     }
 
     public static func setChannel(_ channel: FlutterMethodChannel) {
-        loggerChannel = channel
+        if loggerChannel == nil {
+            loggerChannel = channel
+        }
+    }
+
+    public static func clearChannel() {
+        loggerChannel = nil
     }
 
     public func log(level: OptimizelyLogLevel, message: String) {

ios/Classes/SwiftOptimizelyFlutterSdkPlugin.swift

@@ -38,6 +38,9 @@ public class SwiftOptimizelyFlutterSdkPlugin: NSObject, FlutterPlugin {
 
     /// Registers optimizely_flutter_sdk channel to communicate with the flutter sdk to receive requests and send responses
     public static func register(with registrar: FlutterPluginRegistrar) {
+        if channel != nil {
+            return
+        }
         channel = FlutterMethodChannel(name: "optimizely_flutter_sdk", binaryMessenger: registrar.messenger())
         let instance = SwiftOptimizelyFlutterSdkPlugin()
         registrar.addMethodCallDelegate(instance, channel: channel)
@@ -50,7 +53,13 @@ public class SwiftOptimizelyFlutterSdkPlugin: NSObject, FlutterPlugin {
                                                 taskQueue: taskQueue)
         OptimizelyFlutterLogger.setChannel(loggerChannel)
     }
-    
+
+    public func detachFromEngine(for registrar: FlutterPluginRegistrar) {
+        Self.channel?.setMethodCallHandler(nil)
+        Self.channel = nil
+        OptimizelyFlutterLogger.clearChannel()
+    }
+
     /// Part of FlutterPlugin protocol to handle communication with flutter sdk.
     /// All method handlers receive a main-thread-safe result callback so that
     /// any handler calling result() from a background thread (e.g. async SDK