platform_message_handler_ios.mm

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// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#import "flutter/shell/platform/darwin/ios/platform_message_handler_ios.h"
 
#import "flutter/fml/trace_event.h"
#import "flutter/lib/ui/window/platform_message.h"
#import "flutter/shell/platform/darwin/common/buffer_conversions.h"
#import "flutter/shell/platform/darwin/common/framework/Headers/FlutterBinaryMessenger.h"
 
static uint64_t platform_message_counter = 1;
 
@interface FLTSerialTaskQueue : NSObject <FlutterTaskQueueDispatch>
@property(nonatomic, strong) dispatch_queue_t queue;
@end
 
@implementation FLTSerialTaskQueue
- (instancetype)init {
  self = [super init];
  if (self) {
    _queue = dispatch_queue_create("FLTSerialTaskQueue", DISPATCH_QUEUE_SERIAL);
  }
  return self;
}
 
- (void)dealloc {
  dispatch_release(_queue);
  [super dealloc];
}
 
- (void)dispatch:(dispatch_block_t)block {
  dispatch_async(self.queue, block);
}
@end
 
namespace flutter {
 
NSObject<FlutterTaskQueue>* PlatformMessageHandlerIos::MakeBackgroundTaskQueue() {
  return [[[FLTSerialTaskQueue alloc] init] autorelease];
}
 
PlatformMessageHandlerIos::PlatformMessageHandlerIos(
    fml::RefPtr<fml::TaskRunner> platform_task_runner)
    : platform_task_runner_(std::move(platform_task_runner)) {}
 
void PlatformMessageHandlerIos::HandlePlatformMessage(std::unique_ptr<PlatformMessage> message) {
  // This can be called from any isolate's thread.
  @autoreleasepool {
    fml::RefPtr<flutter::PlatformMessageResponse> completer = message->response();
    HandlerInfo handler_info;
    {
      // TODO(gaaclarke): This mutex is a bottleneck for multiple isolates sending
      // messages at the same time. This could be potentially changed to a
      // read-write lock.
      std::lock_guard lock(message_handlers_mutex_);
      auto it = message_handlers_.find(message->channel());
      if (it != message_handlers_.end()) {
        handler_info = it->second;
      }
    }
    if (handler_info.handler) {
      FlutterBinaryMessageHandler handler = handler_info.handler;
      NSData* data = nil;
      if (message->hasData()) {
        data = ConvertMappingToNSData(message->releaseData());
      }
 
      uint64_t platform_message_id = platform_message_counter++;
      TRACE_EVENT_ASYNC_BEGIN1("flutter", "PlatformChannel ScheduleHandler", platform_message_id,
                               "channel", message->channel().c_str());
      dispatch_block_t run_handler = ^{
        handler(data, ^(NSData* reply) {
          TRACE_EVENT_ASYNC_END0("flutter", "PlatformChannel ScheduleHandler", platform_message_id);
          // Called from any thread.
          if (completer) {
            if (reply) {
              completer->Complete(ConvertNSDataToMappingPtr(reply));
            } else {
              completer->CompleteEmpty();
            }
          }
        });
      };
 
      if (handler_info.task_queue.get()) {
        [handler_info.task_queue.get() dispatch:run_handler];
      } else {
        dispatch_async(dispatch_get_main_queue(), run_handler);
      }
    } else {
      if (completer) {
        completer->CompleteEmpty();
      }
    }
  }
}
 
bool PlatformMessageHandlerIos::DoesHandlePlatformMessageOnPlatformThread() const {
  return false;
}
 
void PlatformMessageHandlerIos::InvokePlatformMessageResponseCallback(
    int response_id,
    std::unique_ptr<fml::Mapping> mapping) {
  // Called from any thread.
  // TODO(gaaclarke): This vestigal from the Android implementation, find a way
  // to migrate this to PlatformMessageHandlerAndroid.
}
 
void PlatformMessageHandlerIos::InvokePlatformMessageEmptyResponseCallback(int response_id) {
  // Called from any thread.
  // TODO(gaaclarke): This vestigal from the Android implementation, find a way
  // to migrate this to PlatformMessageHandlerAndroid.
}
 
void PlatformMessageHandlerIos::SetMessageHandler(const std::string& channel,
                                                  FlutterBinaryMessageHandler handler,
                                                  NSObject<FlutterTaskQueue>* task_queue) {
  FML_CHECK(platform_task_runner_->RunsTasksOnCurrentThread());
  // Use `respondsToSelector` instead of `conformsToProtocol` to accomodate
  // injecting your own `FlutterTaskQueue`. This is not a supported usage but
  // not one worth breaking.
  FML_CHECK(!task_queue || [task_queue respondsToSelector:@selector(dispatch:)]);
  /// TODO(gaaclarke): This should be migrated to a lockfree datastructure.
  std::lock_guard lock(message_handlers_mutex_);
  message_handlers_.erase(channel);
  if (handler) {
    message_handlers_[channel] = {
        .task_queue = fml::scoped_nsprotocol(
            [static_cast<NSObject<FlutterTaskQueueDispatch>*>(task_queue) retain]),
        .handler =
            fml::ScopedBlock<FlutterBinaryMessageHandler>{
                handler, fml::scoped_policy::OwnershipPolicy::kRetain},
    };
  }
}
}  // namespace flutter