Channel buffers

lib/ui/channel_buffers.dart

@@ -0,0 +1,110 @@
+// 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.
+
+part of dart.ui;
+
+/// A saved platform message for a channel with its callback.
+class StoredMessage {
+  final ByteData _data;
+  final PlatformMessageResponseCallback _callback;
+
+  StoredMessage(this._data, this._callback);
+  ByteData get data => _data;
+  PlatformMessageResponseCallback get callback => _callback;
+}
+
+/// A fixed-size circular queue.
+class _RingBuffer<T> {
+  final collection.ListQueue<T> _queue;
+  int _capacity;
+
+  _RingBuffer(this._capacity)
+    : _queue = collection.ListQueue<T>(_capacity);
+
+  int get length => _queue.length;
+
+  int get capacity => _capacity;
+
+  bool get isEmpty => _queue.isEmpty;
+
+  /// Returns true on overflow.
+  bool push(T val) {
+    bool overflow = false;
+    while (_queue.length >= _capacity) {
+      _queue.removeFirst();
+      overflow = true;
+    }
+    _queue.addLast(val);
+    return overflow;
+  }
+
+  /// Returns null when empty.
+  T pop() {
+    return _queue.isEmpty ? null : _queue.removeFirst();
+  }
+
+  /// Returns the number of discarded items resulting from resize.
+  int resize(int newSize) {
+    int result = 0;
+
+    while (length > newSize) {
+      result += 1;
+      _queue.removeFirst();
+    }
+
+    _capacity = newSize;
+
+    return result;
+  }
+}
+
+/// Storage of channel messages until the channels are completely routed.
+class ChannelBuffers {
+  /// A somewhat arbitrary size that tries to balance handling typical
+  /// cases and not wasting memory.
+  static const int kDefaultBufferSize = 100;
+
+  final Map<String, _RingBuffer<StoredMessage>> _messages = {};
+
+  /// Returns true on overflow.
+  bool push(String channel, ByteData data, PlatformMessageResponseCallback callback) {
+    _RingBuffer<StoredMessage> queue = _messages[channel];
+    if (queue == null) {
+      queue = _RingBuffer<StoredMessage>(kDefaultBufferSize);
+      _messages[channel] = queue;
+    }
+    final bool result = queue.push(StoredMessage(data, callback));
+    if (result) {
+      _Logger._printString('Overflow on channel:' + channel);
+    }
+    return result;
+  }
+
+  /// Returns null on underflow.
+  StoredMessage pop(String channel) {
+    final _RingBuffer<StoredMessage> queue = _messages[channel];
+    final StoredMessage result = queue?.pop();
+    if (result == null) {
+      _Logger._printString('Underflow on channel:' + channel);
+    }
+    return result;
+  }
+
+  bool isEmpty(String channel) {
+    final _RingBuffer<StoredMessage> queue = _messages[channel];
+    return queue?.isEmpty ?? true;
+  }
+
+  void resize(String channel, int newSize) {
+    _RingBuffer<StoredMessage> queue = _messages[channel];
+    if (queue == null) {
+      queue = _RingBuffer<StoredMessage>(newSize);
+      _messages[channel] = queue;
+    } else {
+      queue.resize(newSize);
+    }
+  }
+}
+
+final ChannelBuffers channelBuffers = ChannelBuffers();

lib/ui/dart_ui.gni

@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 dart_ui_files = [
+  "$flutter_root/lib/ui/channel_buffers.dart",
   "$flutter_root/lib/ui/compositing.dart",
   "$flutter_root/lib/ui/geometry.dart",
   "$flutter_root/lib/ui/hash_codes.dart",

lib/ui/hooks.dart

@@ -161,7 +161,9 @@ void _dispatchPlatformMessage(String name, ByteData data, int responseId) {
       },
     );
   } else {
-    window._respondToPlatformMessage(responseId, null);
+    channelBuffers.push(name, data, (ByteData responseData) {
+      window._respondToPlatformMessage(responseId, responseData);
+    });
   }
 }
 

lib/ui/ui.dart

@@ -22,6 +22,7 @@ import 'dart:math' as math;
 import 'dart:nativewrappers';
 import 'dart:typed_data';
 
+part 'channel_buffers.dart';
 part 'compositing.dart';
 part 'geometry.dart';
 part 'hash_codes.dart';

testing/dart/channel_buffers_test.dart

@@ -0,0 +1,62 @@
+import 'dart:ui' as ui;
+import 'dart:typed_data';
+import 'dart:convert';
+
+import 'package:test/test.dart';
+
+void main() {
+
+  ByteData _makeByteData(String str) {
+    var list = utf8.encode(str);
+    var buffer = list is Uint8List ? list.buffer : new Uint8List.fromList(list).buffer;
+    return ByteData.view(buffer);
+  }
+
+  String _getString(ByteData data) {
+    final buffer = data.buffer;
+    var list = buffer.asUint8List(data.offsetInBytes, data.lengthInBytes);
+    return utf8.decode(list);
+  }
+
+  test('push pop', () async {
+    String channel = "foo";
+    ByteData data = _makeByteData('bar');
+    ui.ChannelBuffers buffers = ui.ChannelBuffers();
+    ui.PlatformMessageResponseCallback callback = (ByteData responseData) {};
+    buffers.push(channel, data, callback);
+    ui.StoredMessage storedMessage = buffers.pop(channel);
+    expect(storedMessage.data, equals(data));
+    expect(storedMessage.callback, equals(callback));
+  });
+
+  test('empty', () async {
+    String channel = "foo";
+    ByteData data = _makeByteData('bar');
+    ui.ChannelBuffers buffers = ui.ChannelBuffers();
+    ui.PlatformMessageResponseCallback callback = (ByteData responseData) {};
+    expect(buffers.isEmpty(channel), equals(true));
+    buffers.push(channel, data, callback);
+    expect(buffers.isEmpty(channel), equals(false));
+  });
+
+  test('pop', () async {
+    ui.ChannelBuffers buffers = ui.ChannelBuffers();
+    expect(buffers.pop("channel"), equals(null));
+  });
+
+  test('overflow', () async {
+    String channel = "foo";
+    ByteData one = _makeByteData('one');
+    ByteData two = _makeByteData('two');
+    ByteData three = _makeByteData('three');
+    ByteData four = _makeByteData('four');
+    ui.ChannelBuffers buffers = ui.ChannelBuffers();
+    ui.PlatformMessageResponseCallback callback = (ByteData responseData) {};
+    buffers.resize(channel, 3);
+    expect(buffers.push(channel, one, callback), equals(false));
+    expect(buffers.push(channel, two, callback), equals(false));
+    expect(buffers.push(channel, three, callback), equals(false));
+    expect(buffers.push(channel, four, callback), equals(true));
+    expect(_getString(buffers.pop(channel).data), equals('two'));
+  });
+}

testing/dart/window_hooks_integration_test.dart

@@ -18,6 +18,7 @@ import 'dart:typed_data';
 import 'package:test/test.dart';
 
 // HACK: these parts are to get access to private functions tested here.
+part '../../lib/ui/channel_buffers.dart';
 part '../../lib/ui/compositing.dart';
 part '../../lib/ui/geometry.dart';
 part '../../lib/ui/hash_codes.dart';