Resize channel buffers

lib/ui/channel_buffers.dart

@@ -112,6 +112,8 @@ class ChannelBuffers {
   /// buffer size that will avoid any overflows.
   static const int kDefaultBufferSize = 1;
 
+  static const String kControlChannelName = 'dev.flutter/channel-buffers';
+
   /// A mapping between a channel name and its associated [_RingBuffer].
   final Map<String, _RingBuffer<_StoredMessage>> _messages =
     <String, _RingBuffer<_StoredMessage>>{};
@@ -162,7 +164,7 @@ class ChannelBuffers {
   ///
   /// This could result in the dropping of messages if newSize is less
   /// than the current length of the queue.
-  void resize(String channel, int newSize) {
+  void _resize(String channel, int newSize) {
     _RingBuffer<_StoredMessage> queue = _messages[channel];
     if (queue == null) {
       queue = _makeRingBuffer(newSize);
@@ -185,6 +187,30 @@ class ChannelBuffers {
       await callback(message.data, message.callback);
     }
   }
+
+  String _getString(ByteData data) {
+    final ByteBuffer buffer = data.buffer;
+    final Uint8List list = buffer.asUint8List(data.offsetInBytes, data.lengthInBytes);
+    return utf8.decode(list);
+  }
+
+  /// Handle a control message.
+  ///
+  /// This is intended to be called by the platform messages dispatcher.
+  ///
+  /// Available messages:
+  /// - Name: resize
+  ///   Arity: 2
+  ///   Format: `resize\r<channel name>\r<new size>`
+  ///   Description: Allows you to set the size of a channel's buffer.
+  void handleMessage(ByteData data) {
+    final List<String> command = _getString(data).split('\r');
+    if (command.length == /*arity=*/2 + 1 && command[0] == 'resize') {
+      _resize(command[1], int.parse(command[2]));
+    } else {
+      throw Exception('Unrecognized command $command sent to $kControlChannelName.');
+    }
+  }
 }
 
 /// [ChannelBuffer]s that allow the storage of messages between the

lib/ui/hooks.dart

@@ -150,7 +150,15 @@ void _updateAccessibilityFeatures(int values) {
 
 @pragma('vm:entry-point')
 void _dispatchPlatformMessage(String name, ByteData data, int responseId) {
-  if (window.onPlatformMessage != null) {
+  if (name == ChannelBuffers.kControlChannelName) {
+    try {
+      channelBuffers.handleMessage(data);
+    } catch (ex) {
+      _printDebug('Message to "$name" caused exception $ex');
+    } finally {
+      window._respondToPlatformMessage(responseId, null);
+    }
+  } else if (window.onPlatformMessage != null) {
     _invoke3<String, ByteData, PlatformMessageResponseCallback>(
       window.onPlatformMessage,
       window._onPlatformMessageZone,

lib/web_ui/lib/src/ui/channel_buffers.dart

@@ -16,8 +16,8 @@ class ChannelBuffers {
     return true;
   }
 
-  /// Noop in web_ui, caches are always size zero.
-  void resize(String channel, int newSize) {}
+  /// A noop since the web_ui implementation doesn't handle any messages.
+  void handleMessage(ByteData data) {}
 
   /// Remove and process all stored messages for a given channel.
   ///

shell/platform/android/io/flutter/plugin/common/BasicMessageChannel.java

@@ -9,6 +9,8 @@
 import android.support.annotation.UiThread;
 import android.util.Log;
 import java.nio.ByteBuffer;
+import java.nio.charset.Charset;
+import java.util.Locale;
 
 import io.flutter.BuildConfig;
 import io.flutter.plugin.common.BinaryMessenger.BinaryReply;
@@ -29,6 +31,8 @@
  */
 public final class BasicMessageChannel<T> {
     private static final String TAG = "BasicMessageChannel#";
+    public static final String CHANNEL_BUFFERS_CHANNEL =
+        "dev.flutter/channel-buffers";
 
     @NonNull
     private final BinaryMessenger messenger;
@@ -102,6 +106,18 @@ public void setMessageHandler(@Nullable final MessageHandler<T> handler) {
             handler == null ? null : new IncomingMessageHandler(handler));
     }
 
+    /**
+     * Adjusts the number of messages that will get buffered when sending messages to
+     * channels that aren't fully setup yet.  For example, the engine isn't running
+     * yet or the channel's message handler isn't setup on the Dart side yet.
+     */
+    public void resizeChannelBuffer(int newSize) {
+        Charset charset = Charset.forName("UTF-8");
+        String messageString = String.format(Locale.US, "resize\r%s\r%d", name, newSize);
+        ByteBuffer message = ByteBuffer.wrap(messageString.getBytes(charset));
+        messenger.send(CHANNEL_BUFFERS_CHANNEL, message);
+    }
+
     /**
      * A handler of incoming messages.
      */

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

@@ -114,6 +114,14 @@ FLUTTER_EXPORT
  * @param handler The message handler.
  */
 - (void)setMessageHandler:(FlutterMessageHandler _Nullable)handler;
+
+/**
+ * Adjusts the number of messages that will get buffered when sending messages to
+ * channels that aren't fully setup yet.  For example, the engine isn't running
+ * yet or the channel's message handler isn't setup on the Dart side yet.
+ */
+- (void)resizeChannelBuffer:(NSInteger)newSize;
+
 @end
 
 /**

shell/platform/darwin/common/framework/Source/FlutterChannels.mm

@@ -6,6 +6,8 @@
 
 #pragma mark - Basic message channel
 
+static NSString* const FlutterChannelBuffersChannel = @"dev.flutter/channel-buffers";
+
 @implementation FlutterBasicMessageChannel {
   NSObject<FlutterBinaryMessenger>* _messenger;
   NSString* _name;
@@ -70,6 +72,13 @@ - (void)setMessageHandler:(FlutterMessageHandler)handler {
   };
   [_messenger setMessageHandlerOnChannel:_name binaryMessageHandler:messageHandler];
 }
+
+- (void)resizeChannelBuffer:(NSInteger)newSize {
+  NSString* messageString = [NSString stringWithFormat:@"resize\r%@\r%@", _name, @(newSize)];
+  NSData* message = [messageString dataUsingEncoding:NSUTF8StringEncoding];
+  [_messenger sendOnChannel:FlutterChannelBuffersChannel message:message];
+}
+
 @end
 
 #pragma mark - Method channel

shell/platform/darwin/common/framework/Source/FlutterChannelsTest.m

@@ -139,4 +139,22 @@ - (void)testCallMethodHandler {
   [self waitForExpectationsWithTimeout:1.0 handler:nil];
 }
 
+- (void)testResize {
+  NSString* channelName = @"foo";
+  id binaryMessenger = OCMStrictProtocolMock(@protocol(FlutterBinaryMessenger));
+  id codec = OCMProtocolMock(@protocol(FlutterMethodCodec));
+  FlutterBasicMessageChannel* channel =
+      [[FlutterBasicMessageChannel alloc] initWithName:channelName
+                                       binaryMessenger:binaryMessenger
+                                                 codec:codec];
+  XCTAssertNotNil(channel);
+
+  NSString* expectedMessageString =
+      [NSString stringWithFormat:@"resize\r%@\r%@", channelName, @100];
+  NSData* expectedMessage = [expectedMessageString dataUsingEncoding:NSUTF8StringEncoding];
+  OCMExpect([binaryMessenger sendOnChannel:@"dev.flutter/channel-buffers" message:expectedMessage]);
+  [channel resizeChannelBuffer:100];
+  OCMVerifyAll(binaryMessenger);
+}
+
 @end

testing/dart/channel_buffers_test.dart

@@ -18,6 +18,10 @@ void main() {
     return utf8.decode(list);
   }
 
+  void _resize(ui.ChannelBuffers buffers, String name, int newSize) {
+    buffers.handleMessage(_makeByteData("resize\r$name\r$newSize"));
+  }
+
   test('push drain', () async {
     String channel = "foo";
     ByteData data = _makeByteData('bar');
@@ -35,7 +39,7 @@ void main() {
     ByteData data = _makeByteData('bar');
     ui.ChannelBuffers buffers = ui.ChannelBuffers();
     ui.PlatformMessageResponseCallback callback = (ByteData responseData) {};
-    buffers.resize(channel, 0);
+    _resize(buffers, channel, 0);
     buffers.push(channel, data, callback);
     bool didCall = false;
     await buffers.drain(channel, (ByteData drainedData, ui.PlatformMessageResponseCallback drainedCallback) {
@@ -64,7 +68,7 @@ void main() {
     ByteData four = _makeByteData('four');
     ui.ChannelBuffers buffers = ui.ChannelBuffers();
     ui.PlatformMessageResponseCallback callback = (ByteData responseData) {};
-    buffers.resize(channel, 3);
+    _resize(buffers, 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));
@@ -84,11 +88,11 @@ void main() {
     ByteData one = _makeByteData('one');
     ByteData two = _makeByteData('two');
     ui.ChannelBuffers buffers = ui.ChannelBuffers();
-    buffers.resize(channel, 100);
+    _resize(buffers, channel, 100);
     ui.PlatformMessageResponseCallback callback = (ByteData responseData) {};
     expect(buffers.push(channel, one, callback), equals(false));
     expect(buffers.push(channel, two, callback), equals(false));
-    buffers.resize(channel, 1);
+    _resize(buffers, channel, 1);
     int counter = 0;
     await buffers.drain(channel, (ByteData drainedData, ui.PlatformMessageResponseCallback drainedCallback) {
       if (counter++ == 0) {
@@ -109,10 +113,10 @@ void main() {
       didCallCallback = true;
     };
     ui.PlatformMessageResponseCallback twoCallback = (ByteData responseData) {};
-    buffers.resize(channel, 100);
+    _resize(buffers, channel, 100);
     expect(buffers.push(channel, one, oneCallback), equals(false));
     expect(buffers.push(channel, two, twoCallback), equals(false));
-    buffers.resize(channel, 1);
+    _resize(buffers, channel, 1);
     expect(didCallCallback, equals(true));
   });
 
@@ -126,9 +130,21 @@ void main() {
       didCallCallback = true;
     };
     ui.PlatformMessageResponseCallback twoCallback = (ByteData responseData) {};
-    buffers.resize(channel, 1);
+    _resize(buffers, channel, 1);
     expect(buffers.push(channel, one, oneCallback), equals(false));
     expect(buffers.push(channel, two, twoCallback), equals(true));
     expect(didCallCallback, equals(true));
   });
+
+  test('handle garbage', () async {
+    ui.ChannelBuffers buffers = ui.ChannelBuffers();
+    expect(() => buffers.handleMessage(_makeByteData("asdfasdf")),
+           throwsException);
+  });
+
+  test('handle resize garbage', () async {
+    ui.ChannelBuffers buffers = ui.ChannelBuffers();
+    expect(() => buffers.handleMessage(_makeByteData("resize\rfoo\rbar")),
+           throwsException);
+  });
 }