[Android] Expose channel buffer resize and overflow calls (flutter/engine#44434)

## Description

This PR updates the Android engine in order to provide a more efficient implementation for `BasicMessageChannel.resizeChannelBuffer` (helper to call the `resize` control command).
It also adds a new helper called`BasicMessageChannel.allowChannelBufferOverflow` to call the `overflow` control command.

## Related Issue

Fixes https://github.com/flutter/flutter/issues/132048
Android implementation for https://github.com/flutter/flutter/issues/132386

## Tests

Adds 2 tests.

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

@@ -12,8 +12,7 @@ import io.flutter.Log;
 import io.flutter.plugin.common.BinaryMessenger.BinaryMessageHandler;
 import io.flutter.plugin.common.BinaryMessenger.BinaryReply;
 import java.nio.ByteBuffer;
-import java.nio.charset.Charset;
-import java.util.Locale;
+import java.util.Arrays;
 
 /**
  * A named channel for communicating with the Flutter application using basic, asynchronous message
@@ -143,13 +142,56 @@ public final class BasicMessageChannel<T> {
     resizeChannelBuffer(messenger, name, newSize);
   }
 
-  static void resizeChannelBuffer(
-      @NonNull BinaryMessenger messenger, @NonNull String channel, int newSize) {
-    Charset charset = Charset.forName("UTF-8");
-    String messageString = String.format(Locale.US, "resize\r%s\r%d", channel, newSize);
-    final byte[] bytes = messageString.getBytes(charset);
+  /**
+   * Toggles whether the channel should show warning messages when discarding messages due to
+   * overflow. When 'allowed' is true the channel is expected to overflow and warning messages will
+   * not be shown.
+   */
+  public void allowChannelBufferOverflow(boolean allowed) {
+    allowChannelBufferOverflow(messenger, name, allowed);
+  }
+
+  private static ByteBuffer packetFromEncodedMessage(ByteBuffer message) {
+    // Create a bytes array using the buffer content (messages.array() can not be used here).
+    message.flip();
+    final byte[] bytes = new byte[message.remaining()];
+    message.get(bytes);
+
+    // The current Android Java/JNI platform message implementation assumes
+    // that all buffers passed to native are direct buffers.
     ByteBuffer packet = ByteBuffer.allocateDirect(bytes.length);
     packet.put(bytes);
+
+    return packet;
+  }
+
+  /**
+   * 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.
+   */
+  public static void resizeChannelBuffer(
+      @NonNull BinaryMessenger messenger, @NonNull String channel, int newSize) {
+    final StandardMethodCodec codec = StandardMethodCodec.INSTANCE;
+    Object[] arguments = {channel, newSize};
+    MethodCall methodCall = new MethodCall("resize", Arrays.asList(arguments));
+    ByteBuffer message = codec.encodeMethodCall(methodCall);
+    ByteBuffer packet = packetFromEncodedMessage(message);
+    messenger.send(BasicMessageChannel.CHANNEL_BUFFERS_CHANNEL, packet);
+  }
+
+  /**
+   * Toggles whether the channel should show warning messages when discarding messages due to
+   * overflow. When 'allowed' is true the channel is expected to overflow and warning messages will
+   * not be shown.
+   */
+  public static void allowChannelBufferOverflow(
+      @NonNull BinaryMessenger messenger, @NonNull String channel, boolean allowed) {
+    final StandardMethodCodec codec = StandardMethodCodec.INSTANCE;
+    Object[] arguments = {channel, allowed};
+    MethodCall methodCall = new MethodCall("overflow", Arrays.asList(arguments));
+    ByteBuffer message = codec.encodeMethodCall(methodCall);
+    ByteBuffer packet = packetFromEncodedMessage(message);
     messenger.send(BasicMessageChannel.CHANNEL_BUFFERS_CHANNEL, packet);
   }
 

engine/src/flutter/shell/platform/android/io/flutter/plugin/common/MethodChannel.java

@@ -157,6 +157,15 @@ public class MethodChannel {
     BasicMessageChannel.resizeChannelBuffer(messenger, name, newSize);
   }
 
+  /**
+   * Toggles whether the channel should show warning messages when discarding messages due to
+   * overflow. When 'allowed' is true the channel is expected to overflow and warning messages will
+   * not be shown.
+   */
+  public void allowChannelBufferOverflow(boolean allowed) {
+    BasicMessageChannel.allowChannelBufferOverflow(messenger, name, allowed);
+  }
+
   /** A handler of incoming method calls. */
   public interface MethodCallHandler {
     /**

engine/src/flutter/shell/platform/android/test/io/flutter/plugin/common/MethodChannelTest.java

@@ -1,6 +1,7 @@
 package io.flutter.plugin.common;
 
 import static org.mockito.ArgumentMatchers.anyInt;
+import static org.mockito.ArgumentMatchers.argThat;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.times;
@@ -11,17 +12,16 @@ import androidx.test.ext.junit.runners.AndroidJUnit4;
 import io.flutter.embedding.engine.FlutterJNI;
 import io.flutter.embedding.engine.dart.DartExecutor;
 import java.nio.ByteBuffer;
-import java.nio.charset.Charset;
-import java.util.Locale;
 import org.junit.Test;
 import org.junit.runner.RunWith;
+import org.mockito.ArgumentMatcher;
 import org.robolectric.annotation.Config;
 
 @Config(manifest = Config.NONE)
 @RunWith(AndroidJUnit4.class)
 public class MethodChannelTest {
   @Test
-  public void methodChannel_resizeChannelBuffer() {
+  public void resizeChannelBufferMessageIsWellformed() {
     FlutterJNI mockFlutterJNI = mock(FlutterJNI.class);
     DartExecutor dartExecutor = new DartExecutor(mockFlutterJNI, mock(AssetManager.class));
     String channel = "flutter/test";
@@ -30,15 +30,68 @@ public class MethodChannelTest {
     int newSize = 3;
     rawChannel.resizeChannelBuffer(newSize);
 
-    Charset charset = Charset.forName("UTF-8");
-    String messageString = String.format(Locale.US, "resize\r%s\r%d", channel, newSize);
-    final byte[] bytes = messageString.getBytes(charset);
-    ByteBuffer packet = ByteBuffer.allocateDirect(bytes.length);
-    packet.put(bytes);
+    // Created from the following Dart code:
+    //   MethodCall methodCall = const MethodCall('resize', ['flutter/test', 3]);
+    //   const StandardMethodCodec().encodeMethodCall(methodCall).buffer.asUint8List();
+    final byte[] expected = {
+      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
+    };
 
-    // Verify that DartExecutor sent the correct message to FlutterJNI.
+    // Verify that the correct message was sent to FlutterJNI.
+    ArgumentMatcher<ByteBuffer> packetMatcher =
+        new ByteBufferContentMatcher(ByteBuffer.wrap(expected));
     verify(mockFlutterJNI, times(1))
         .dispatchPlatformMessage(
-            eq(BasicMessageChannel.CHANNEL_BUFFERS_CHANNEL), eq(packet), anyInt(), anyInt());
+            eq(BasicMessageChannel.CHANNEL_BUFFERS_CHANNEL),
+            argThat(packetMatcher),
+            anyInt(),
+            anyInt());
+  }
+
+  @Test
+  public void overflowChannelBufferMessageIsWellformed() {
+    FlutterJNI mockFlutterJNI = mock(FlutterJNI.class);
+    DartExecutor dartExecutor = new DartExecutor(mockFlutterJNI, mock(AssetManager.class));
+    String channel = "flutter/test";
+    MethodChannel rawChannel = new MethodChannel(dartExecutor, channel);
+
+    rawChannel.allowChannelBufferOverflow(true);
+
+    // Created from the following Dart code:
+    //   MethodCall methodCall = const MethodCall('overflow', ['flutter/test', true]);
+    //   const StandardMethodCodec().encodeMethodCall(methodCall).buffer.asUint8List();
+    final byte[] expected = {
+      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
+    };
+
+    // Verify that the correct message was sent to FlutterJNI.
+    ArgumentMatcher<ByteBuffer> packetMatcher =
+        new ByteBufferContentMatcher(ByteBuffer.wrap(expected));
+    verify(mockFlutterJNI, times(1))
+        .dispatchPlatformMessage(
+            eq(BasicMessageChannel.CHANNEL_BUFFERS_CHANNEL),
+            argThat(packetMatcher),
+            anyInt(),
+            anyInt());
+  }
+}
+
+// Custom ByteBuffer matcher which calls rewind on both buffers before calling equals.
+// ByteBuffer.equals might return true when comparing byte buffers with different content if
+// both have no remaining elements.
+class ByteBufferContentMatcher implements ArgumentMatcher<ByteBuffer> {
+  private ByteBuffer expected;
+
+  public ByteBufferContentMatcher(ByteBuffer expected) {
+    this.expected = expected;
+  }
+
+  @Override
+  public boolean matches(ByteBuffer received) {
+    expected.rewind();
+    received.rewind();
+    return received.equals(expected);
   }
 }