[macOS,iOS] Expose channel buffers 'resize' and 'overflow' control co… (#44848)

## Description

This PR update the helper function that invokes the control channel 'resize' command (previous implementation relied on a deprecated format). It also adds a similar helper function for the 'overflow' commands exposed by the control channel.

See:

https://github.com/flutter/engine/blob/93e8901490e78c7ba7e319cce4470d9c6478c6dc/lib/ui/channel_buffers.dart#L302-L309

## Related Issue

iOS and macOS implementation for flutter/flutter#132386

Similar implementations:
- Android: #44434
- Linux: #44636

## Tests

Adds two tests.

Author: bleroux

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

@@ -143,9 +143,46 @@ FLUTTER_DARWIN_EXPORT
  * Adjusts the number of messages that will get buffered when sending messages to
  * channels that aren't fully set up yet.  For example, the engine isn't running
  * yet or the channel's message handler isn't set up on the Dart side yet.
+ *
+ * @param name The channel name.
+ * @param messenger The binary messenger.
+ * @param newSize The number of messages that will get buffered.
+ */
++ (void)resizeChannelWithName:(NSString*)name
+              binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger
+                         size:(NSInteger)newSize;
+
+/**
+ * Adjusts the number of messages that will get buffered when sending messages to
+ * channels that aren't fully set up yet.  For example, the engine isn't running
+ * yet or the channel's message handler isn't set up on the Dart side yet.
+ *
+ * @param newSize The number of messages that will get buffered.
  */
 - (void)resizeChannelBuffer:(NSInteger)newSize;
 
+/**
+ * Defines whether the channel should show warning messages when discarding messages
+ * due to overflow.
+ *
+ * @param warns When false, the channel is expected to overflow and warning messages
+ *              will not be shown.
+ * @param name The channel name.
+ * @param messenger The binary messenger.
+ */
++ (void)setWarnsOnOverflow:(BOOL)warns
+        forChannelWithName:(NSString*)name
+           binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger;
+
+/**
+ * Defines whether the channel should show warning messages when discarding messages
+ * due to overflow.
+ *
+ * @param warns When false, the channel is expected to overflow and warning messages
+ *              will not be shown.
+ */
+- (void)setWarnsOnOverflow:(BOOL)warns;
+
 @end
 
 /**

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

@@ -9,12 +9,41 @@
 #pragma mark - Basic message channel
 
 static NSString* const kFlutterChannelBuffersChannel = @"dev.flutter/channel-buffers";
+static NSString* const kResizeMethod = @"resize";
+static NSString* const kOverflowMethod = @"overflow";
 
 static void ResizeChannelBuffer(NSObject<FlutterBinaryMessenger>* binaryMessenger,
                                 NSString* channel,
                                 NSInteger newSize) {
-  NSString* messageString = [NSString stringWithFormat:@"resize\r%@\r%@", channel, @(newSize)];
-  NSData* message = [messageString dataUsingEncoding:NSUTF8StringEncoding];
+  NSCAssert(newSize >= 0, @"Channel buffer size must be non-negative");
+  // Cast newSize to int because the deserialization logic handles only 32 bits values,
+  // see
+  // https://github.com/flutter/engine/blob/93e8901490e78c7ba7e319cce4470d9c6478c6dc/lib/ui/channel_buffers.dart#L495.
+  NSArray* args = @[ channel, @(static_cast<int>(newSize)) ];
+  FlutterMethodCall* resizeMethodCall = [FlutterMethodCall methodCallWithMethodName:kResizeMethod
+                                                                          arguments:args];
+  NSObject<FlutterMethodCodec>* codec = [FlutterStandardMethodCodec sharedInstance];
+  NSData* message = [codec encodeMethodCall:resizeMethodCall];
+  [binaryMessenger sendOnChannel:kFlutterChannelBuffersChannel message:message];
+}
+
+/**
+ * Defines whether a channel should show warning messages when discarding messages
+ * due to overflow.
+ *
+ * @param binaryMessenger The binary messenger.
+ * @param channel The channel name.
+ * @param warns When false, the channel is expected to overflow and warning messages
+ *              will not be shown.
+ */
+static void SetWarnsOnOverflow(NSObject<FlutterBinaryMessenger>* binaryMessenger,
+                               NSString* channel,
+                               BOOL warns) {
+  FlutterMethodCall* overflowMethodCall =
+      [FlutterMethodCall methodCallWithMethodName:kOverflowMethod
+                                        arguments:@[ channel, @(!warns) ]];
+  NSObject<FlutterMethodCodec>* codec = [FlutterStandardMethodCodec sharedInstance];
+  NSData* message = [codec encodeMethodCall:overflowMethodCall];
   [binaryMessenger sendOnChannel:kFlutterChannelBuffersChannel message:message];
 }
 
@@ -114,10 +143,26 @@ - (void)setMessageHandler:(FlutterMessageHandler)handler {
   _connection = SetMessageHandler(_messenger, _name, messageHandler, _taskQueue);
 }
 
++ (void)resizeChannelWithName:(NSString*)name
+              binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger
+                         size:(NSInteger)newSize {
+  ResizeChannelBuffer(messenger, name, newSize);
+}
+
 - (void)resizeChannelBuffer:(NSInteger)newSize {
   ResizeChannelBuffer(_messenger, _name, newSize);
 }
 
++ (void)setWarnsOnOverflow:(BOOL)warns
+        forChannelWithName:(NSString*)name
+           binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger {
+  SetWarnsOnOverflow(messenger, name, warns);
+}
+
+- (void)setWarnsOnOverflow:(BOOL)warns {
+  SetWarnsOnOverflow(_messenger, _name, warns);
+}
+
 @end
 
 #pragma mark - Method channel

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

@@ -147,7 +147,31 @@ - (void)testCallMethodHandler {
 }
 
 - (void)testResize {
-  NSString* channelName = @"foo";
+  NSString* channelName = @"flutter/test";
+  id binaryMessenger = OCMStrictProtocolMock(@protocol(FlutterBinaryMessenger));
+  id codec = OCMProtocolMock(@protocol(FlutterMethodCodec));
+  FlutterBasicMessageChannel* channel =
+      [[FlutterBasicMessageChannel alloc] initWithName:channelName
+                                       binaryMessenger:binaryMessenger
+                                                 codec:codec];
+  XCTAssertNotNil(channel);
+
+  // The expected content was created from the following Dart code:
+  //   MethodCall call = MethodCall('resize', ['flutter/test',3]);
+  //   StandardMethodCodec().encodeMethodCall(call).buffer.asUint8List();
+  const unsigned char bytes[] = {7,   6,   114, 101, 115, 105, 122, 101, 12,  2,
+                                 7,   12,  102, 108, 117, 116, 116, 101, 114, 47,
+                                 116, 101, 115, 116, 3,   3,   0,   0,   0};
+  NSData* expectedMessage = [NSData dataWithBytes:bytes length:sizeof(bytes)];
+
+  OCMExpect([binaryMessenger sendOnChannel:@"dev.flutter/channel-buffers" message:expectedMessage]);
+  [channel resizeChannelBuffer:3];
+  OCMVerifyAll(binaryMessenger);
+  [binaryMessenger stopMocking];
+}
+
+- (bool)testSetWarnsOnOverflow {
+  NSString* channelName = @"flutter/test";
   id binaryMessenger = OCMStrictProtocolMock(@protocol(FlutterBinaryMessenger));
   id codec = OCMProtocolMock(@protocol(FlutterMethodCodec));
   FlutterBasicMessageChannel* channel =
@@ -156,11 +180,15 @@ - (void)testResize {
                                                  codec:codec];
   XCTAssertNotNil(channel);
 
-  NSString* expectedMessageString =
-      [NSString stringWithFormat:@"resize\r%@\r%@", channelName, @100];
-  NSData* expectedMessage = [expectedMessageString dataUsingEncoding:NSUTF8StringEncoding];
+  // The expected content was created from the following Dart code:
+  //   MethodCall call = MethodCall('overflow',['flutter/test', true]);
+  //   StandardMethodCodec().encodeMethodCall(call).buffer.asUint8List();
+  const unsigned char bytes[] = {7,   8,   111, 118, 101, 114, 102, 108, 111, 119, 12,  2,   7, 12,
+                                 102, 108, 117, 116, 116, 101, 114, 47,  116, 101, 115, 116, 1};
+  NSData* expectedMessage = [NSData dataWithBytes:bytes length:sizeof(bytes)];
+
   OCMExpect([binaryMessenger sendOnChannel:@"dev.flutter/channel-buffers" message:expectedMessage]);
-  [channel resizeChannelBuffer:100];
+  [channel setWarnsOnOverflow:NO];
   OCMVerifyAll(binaryMessenger);
   [binaryMessenger stopMocking];
 }