Reland: iOS Background Platform Channels (flutter#29665) (flutter#30697)

* iOS Background Platform Channels (flutter#29665)

* added test that passes before this change, and fails after it

* started supporting backwards compatible usage of setting handlers

ci/licenses_golden/licenses_flutter

@@ -1177,8 +1177,6 @@ FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/connection_col
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/connection_collection_test.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/platform_message_response_darwin.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/platform_message_response_darwin.mm
-FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/platform_message_router.h
-FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/platform_message_router.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/profiler_metrics_ios.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/profiler_metrics_ios.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/vsync_waiter_ios.h
@@ -1210,6 +1208,9 @@ FILE: ../../../flutter/shell/platform/darwin/ios/ios_surface_software.h
 FILE: ../../../flutter/shell/platform/darwin/ios/ios_surface_software.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/ios_switchable_gl_context.h
 FILE: ../../../flutter/shell/platform/darwin/ios/ios_switchable_gl_context.mm
+FILE: ../../../flutter/shell/platform/darwin/ios/platform_message_handler_ios.h
+FILE: ../../../flutter/shell/platform/darwin/ios/platform_message_handler_ios.mm
+FILE: ../../../flutter/shell/platform/darwin/ios/platform_message_handler_ios_test.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/platform_view_ios.h
 FILE: ../../../flutter/shell/platform/darwin/ios/platform_view_ios.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/rendering_api_selection.h

shell/common/shell.cc

@@ -632,6 +632,13 @@ bool Shell::Setup(std::unique_ptr<PlatformView> platform_view,
 
   platform_view_ = std::move(platform_view);
   platform_message_handler_ = platform_view_->GetPlatformMessageHandler();
+  route_messages_through_platform_thread_.store(true);
+  task_runners_.GetPlatformTaskRunner()->PostTask(
+      [self = weak_factory_.GetWeakPtr()] {
+        if (self) {
+          self->route_messages_through_platform_thread_.store(false);
+        }
+      });
   engine_ = std::move(engine);
   rasterizer_ = std::move(rasterizer);
   io_manager_ = io_manager;
@@ -1183,7 +1190,30 @@ void Shell::OnEngineHandlePlatformMessage(
   }
 
   if (platform_message_handler_) {
-    platform_message_handler_->HandlePlatformMessage(std::move(message));
+    if (route_messages_through_platform_thread_) {
+      // We route messages through the platform thread temporarily when the
+      // shell is being initialized to be backwards compatible with setting
+      // message handlers in the same event as starting the isolate, but after
+      // it is started.
+      auto ui_task_runner = task_runners_.GetUITaskRunner();
+      task_runners_.GetPlatformTaskRunner()->PostTask(fml::MakeCopyable(
+          [weak_platform_message_handler =
+               std::weak_ptr<PlatformMessageHandler>(platform_message_handler_),
+           message = std::move(message), ui_task_runner]() mutable {
+            ui_task_runner->PostTask(fml::MakeCopyable(
+                [weak_platform_message_handler, message = std::move(message),
+                 ui_task_runner]() mutable {
+                  auto platform_message_handler =
+                      weak_platform_message_handler.lock();
+                  if (platform_message_handler) {
+                    platform_message_handler->HandlePlatformMessage(
+                        std::move(message));
+                  }
+                }));
+          }));
+    } else {
+      platform_message_handler_->HandlePlatformMessage(std::move(message));
+    }
   } else {
     task_runners_.GetPlatformTaskRunner()->PostTask(
         fml::MakeCopyable([view = platform_view_->GetWeakPtr(),

shell/common/shell.h

@@ -421,6 +421,7 @@ class Shell final : public PlatformView::Delegate,
   std::shared_ptr<fml::SyncSwitch> is_gpu_disabled_sync_switch_;
   std::shared_ptr<VolatilePathTracker> volatile_path_tracker_;
   std::shared_ptr<PlatformMessageHandler> platform_message_handler_;
+  std::atomic<bool> route_messages_through_platform_thread_ = false;
 
   fml::WeakPtr<Engine> weak_engine_;  // to be shared across threads
   fml::TaskRunnerAffineWeakPtr<Rasterizer>

shell/platform/darwin/common/framework/Headers/FlutterBinaryMessenger.h

@@ -31,6 +31,8 @@ typedef void (^FlutterBinaryMessageHandler)(NSData* _Nullable message, FlutterBi
 
 typedef int64_t FlutterBinaryMessengerConnection;
 
+@protocol FlutterTaskQueue;
+
 /**
  * A facility for communicating with the Flutter side using asynchronous message
  * passing with binary messages.
@@ -44,6 +46,16 @@ typedef int64_t FlutterBinaryMessengerConnection;
  */
 FLUTTER_DARWIN_EXPORT
 @protocol FlutterBinaryMessenger <NSObject>
+/// TODO(gaaclarke): Remove optional when macos supports Background Platform Channels.
+@optional
+- (NSObject<FlutterTaskQueue>*)makeBackgroundTaskQueue;
+
+- (FlutterBinaryMessengerConnection)
+    setMessageHandlerOnChannel:(NSString*)channel
+          binaryMessageHandler:(FlutterBinaryMessageHandler _Nullable)handler
+                     taskQueue:(NSObject<FlutterTaskQueue>* _Nullable)taskQueue;
+
+@required
 /**
  * Sends a binary message to the Flutter side on the specified channel, expecting
  * no reply.

shell/platform/darwin/common/framework/Headers/FlutterChannels.h

@@ -8,6 +8,8 @@
 #import "FlutterBinaryMessenger.h"
 #import "FlutterCodecs.h"
 
+@protocol FlutterTaskQueue;
+
 NS_ASSUME_NONNULL_BEGIN
 /**
  * A message reply callback.
@@ -24,7 +26,8 @@ typedef void (^FlutterReply)(id _Nullable reply);
  * asynchronous replies back to Flutter.
  *
  * @param message The message.
- * @param callback A callback for submitting a reply to the sender.
+ * @param callback A callback for submitting a reply to the sender which can be invoked from any
+ * thread.
  */
 typedef void (^FlutterMessageHandler)(id _Nullable message, FlutterReply callback);
 
@@ -88,6 +91,27 @@ FLUTTER_DARWIN_EXPORT
              binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger
                        codec:(NSObject<FlutterMessageCodec>*)codec;
 
+/**
+ * Initializes a `FlutterBasicMessageChannel` with the specified name, binary
+ * messenger, and message codec.
+ *
+ * The channel name logically identifies the channel; identically named channels
+ * interfere with each other's communication.
+ *
+ * The binary messenger is a facility for sending raw, binary messages to the
+ * Flutter side. This protocol is implemented by `FlutterEngine` and `FlutterViewController`.
+ *
+ * @param name The channel name.
+ * @param messenger The binary messenger.
+ * @param codec The message codec.
+ * @param taskQueue The FlutterTaskQueue that executes the handler (see
+                    -[FlutterBinaryMessenger makeBackgroundTaskQueue]).
+ */
+- (instancetype)initWithName:(NSString*)name
+             binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger
+                       codec:(NSObject<FlutterMessageCodec>*)codec
+                   taskQueue:(NSObject<FlutterTaskQueue>* _Nullable)taskQueue;
+
 /**
  * Sends the specified message to the Flutter side, ignoring any reply.
  *
@@ -142,7 +166,7 @@ typedef void (^FlutterResult)(id _Nullable result);
  *     Invoke the callback with a `FlutterError` to indicate that the call failed.
  *     Invoke the callback with `FlutterMethodNotImplemented` to indicate that the
  *     method was unknown. Any other values, including `nil`, are interpreted as
- *     successful results.
+ *     successful results.  This can be invoked from any thread.
  */
 typedef void (^FlutterMethodCallHandler)(FlutterMethodCall* call, FlutterResult result);
 
@@ -213,6 +237,27 @@ FLUTTER_DARWIN_EXPORT
              binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger
                        codec:(NSObject<FlutterMethodCodec>*)codec;
 
+/**
+ * Initializes a `FlutterMethodChannel` with the specified name, binary messenger,
+ * method codec, and task queue.
+ *
+ * The channel name logically identifies the channel; identically named channels
+ * interfere with each other's communication.
+ *
+ * The binary messenger is a facility for sending raw, binary messages to the
+ * Flutter side. This protocol is implemented by `FlutterEngine` and `FlutterViewController`.
+ *
+ * @param name The channel name.
+ * @param messenger The binary messenger.
+ * @param codec The method codec.
+ * @param taskQueue The FlutterTaskQueue that executes the handler (see
+                    -[FlutterBinaryMessenger makeBackgroundTaskQueue]).
+ */
+- (instancetype)initWithName:(NSString*)name
+             binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger
+                       codec:(NSObject<FlutterMethodCodec>*)codec
+                   taskQueue:(NSObject<FlutterTaskQueue>* _Nullable)taskQueue;
+
 // clang-format off
 /**
  * Invokes the specified Flutter method with the specified arguments, expecting
@@ -371,6 +416,27 @@ FLUTTER_DARWIN_EXPORT
 - (instancetype)initWithName:(NSString*)name
              binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger
                        codec:(NSObject<FlutterMethodCodec>*)codec;
+
+/**
+ * Initializes a `FlutterEventChannel` with the specified name, binary messenger,
+ * method codec and task queue.
+ *
+ * The channel name logically identifies the channel; identically named channels
+ * interfere with each other's communication.
+ *
+ * The binary messenger is a facility for sending raw, binary messages to the
+ * Flutter side. This protocol is implemented by `FlutterEngine` and `FlutterViewController`.
+ *
+ * @param name The channel name.
+ * @param messenger The binary messenger.
+ * @param codec The method codec.
+ * @param taskQueue The FlutterTaskQueue that executes the handler (see
+                    -[FlutterBinaryMessenger makeBackgroundTaskQueue]).
+ */
+- (instancetype)initWithName:(NSString*)name
+             binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger
+                       codec:(NSObject<FlutterMethodCodec>*)codec
+                   taskQueue:(NSObject<FlutterTaskQueue>* _Nullable)taskQueue;
 /**
  * Registers a handler for stream setup requests from the Flutter side.
  *