[Android] Return the keyboard pressed state (flutter/engine#42758)

## Description

This PR updates the Android engine in order to answer to keyboard pressed state queries from the framework (as implemented in https://github.com/flutter/flutter/pull/122885).

This is a rework of https://github.com/flutter/engine/pull/41695 which was reverted in https://github.com/flutter/engine/pull/42346.

This issue with https://github.com/flutter/engine/pull/41695 was that the framework side did not get an answer when the channel was setup in the engine without registering a handler (on the engine side) to handle framework requests. The issue was reproducible when the engine initialization was managed by the app (see https://github.com/flutter/flutter/issues/122441#issuecomment-1582052616 for a repro).

This PR fixes this issue by changing `flutter/keyboard` lifecycle: the engine now creates the channel and registers a handler just after the channel creation.
In order to avoid regression, this PR also updates the channel implemenation (see `KeyboardChannel`) to return an empty `HashMap` when there is no handler registered.

## Related Issue

Android engine implementation for https://github.com/flutter/flutter/issues/87391
(see https://github.com/flutter/engine/pull/42346 for Linux implementation)
Fixes https://github.com/flutter/flutter/issues/122441

## Tests

Adds 3 tests.

engine/src/flutter/ci/licenses_golden/licenses_flutter

@@ -2384,6 +2384,7 @@ ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/rend
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/renderer/SurfaceTextureWrapper.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/DeferredComponentChannel.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/KeyEventChannel.java + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/KeyboardChannel.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/LifecycleChannel.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/LocalizationChannel.java + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/MouseCursorChannel.java + ../../../flutter/LICENSE
@@ -5067,6 +5068,7 @@ FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/render
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/AccessibilityChannel.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/DeferredComponentChannel.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/KeyEventChannel.java
+FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/KeyboardChannel.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/LifecycleChannel.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/LocalizationChannel.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/MouseCursorChannel.java

engine/src/flutter/shell/platform/android/BUILD.gn

@@ -252,6 +252,7 @@ android_java_sources = [
   "io/flutter/embedding/engine/systemchannels/AccessibilityChannel.java",
   "io/flutter/embedding/engine/systemchannels/DeferredComponentChannel.java",
   "io/flutter/embedding/engine/systemchannels/KeyEventChannel.java",
+  "io/flutter/embedding/engine/systemchannels/KeyboardChannel.java",
   "io/flutter/embedding/engine/systemchannels/LifecycleChannel.java",
   "io/flutter/embedding/engine/systemchannels/LocalizationChannel.java",
   "io/flutter/embedding/engine/systemchannels/MouseCursorChannel.java",

engine/src/flutter/shell/platform/android/io/flutter/embedding/android/KeyEmbedderResponder.java

@@ -11,7 +11,9 @@ import io.flutter.embedding.android.KeyboardMap.PressingGoal;
 import io.flutter.embedding.android.KeyboardMap.TogglingGoal;
 import io.flutter.plugin.common.BinaryMessenger;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashMap;
+import java.util.Map;
 
 /**
  * A {@link KeyboardManager.Responder} of {@link KeyboardManager} that handles events by sending
@@ -405,4 +407,14 @@ public class KeyEmbedderResponder implements KeyboardManager.Responder {
       onKeyEventHandledCallback.onKeyEventHandled(true);
     }
   }
+
+  /**
+   * Returns an unmodifiable view of the pressed state.
+   *
+   * @return A map whose keys are physical keyboard key IDs and values are the corresponding logical
+   *     keyboard key IDs.
+   */
+  public Map<Long, Long> getPressedState() {
+    return Collections.unmodifiableMap(pressingRecords);
+  }
 }

engine/src/flutter/shell/platform/android/io/flutter/embedding/android/KeyboardManager.java

@@ -9,10 +9,12 @@ import android.view.KeyEvent;
 import androidx.annotation.NonNull;
 import io.flutter.Log;
 import io.flutter.embedding.engine.systemchannels.KeyEventChannel;
+import io.flutter.embedding.engine.systemchannels.KeyboardChannel;
 import io.flutter.plugin.common.BinaryMessenger;
 import io.flutter.plugin.editing.InputConnectionAdaptor;
 import io.flutter.plugin.editing.TextInputPlugin;
 import java.util.HashSet;
+import java.util.Map;
 
 /**
  * Processes keyboard events and cooperate with {@link TextInputPlugin}.
@@ -40,7 +42,8 @@ import java.util.HashSet;
  *       encounter.
  * </ul>
  */
-public class KeyboardManager implements InputConnectionAdaptor.KeyboardDelegate {
+public class KeyboardManager
+    implements InputConnectionAdaptor.KeyboardDelegate, KeyboardChannel.KeyboardMethodHandler {
   private static final String TAG = "KeyboardManager";
 
   /**
@@ -119,6 +122,8 @@ public class KeyboardManager implements InputConnectionAdaptor.KeyboardDelegate
           new KeyEmbedderResponder(viewDelegate.getBinaryMessenger()),
           new KeyChannelResponder(new KeyEventChannel(viewDelegate.getBinaryMessenger())),
         };
+    final KeyboardChannel keyboardChannel = new KeyboardChannel(viewDelegate.getBinaryMessenger());
+    keyboardChannel.setKeyboardMethodHandler(this);
   }
 
   /**
@@ -252,4 +257,15 @@ public class KeyboardManager implements InputConnectionAdaptor.KeyboardDelegate
       Log.w(TAG, "A redispatched key event was consumed before reaching KeyboardManager");
     }
   }
+
+  /**
+   * Returns an unmodifiable view of the pressed state.
+   *
+   * @return A map whose keys are physical keyboard key IDs and values are the corresponding logical
+   *     keyboard key IDs.
+   */
+  public Map<Long, Long> getKeyboardState() {
+    KeyEmbedderResponder embedderResponder = (KeyEmbedderResponder) responders[0];
+    return embedderResponder.getPressedState();
+  }
 }

engine/src/flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/KeyboardChannel.java

@@ -0,0 +1,75 @@
+// 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.
+
+package io.flutter.embedding.engine.systemchannels;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import io.flutter.plugin.common.BinaryMessenger;
+import io.flutter.plugin.common.MethodCall;
+import io.flutter.plugin.common.MethodChannel;
+import io.flutter.plugin.common.StandardMethodCodec;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Event message channel for keyboard events to/from the Flutter framework.
+ *
+ * <p>Receives asynchronous messages from the framework to query the engine known pressed state.
+ */
+public class KeyboardChannel {
+  public final MethodChannel channel;
+  private KeyboardMethodHandler keyboardMethodHandler;
+
+  @NonNull
+  public final MethodChannel.MethodCallHandler parsingMethodHandler =
+      new MethodChannel.MethodCallHandler() {
+        Map<Long, Long> pressedState = new HashMap<>();
+
+        @Override
+        public void onMethodCall(@NonNull MethodCall call, @NonNull MethodChannel.Result result) {
+          if (keyboardMethodHandler == null) {
+            // Returns an empty pressed state when the engine did not get a chance to register
+            // a method handler for this channel.
+            result.success(pressedState);
+          } else {
+            switch (call.method) {
+              case "getKeyboardState":
+                try {
+                  pressedState = keyboardMethodHandler.getKeyboardState();
+                } catch (IllegalStateException exception) {
+                  result.error("error", exception.getMessage(), null);
+                }
+                result.success(pressedState);
+                break;
+              default:
+                result.notImplemented();
+                break;
+            }
+          }
+        }
+      };
+
+  public KeyboardChannel(@NonNull BinaryMessenger messenger) {
+    channel = new MethodChannel(messenger, "flutter/keyboard", StandardMethodCodec.INSTANCE);
+    channel.setMethodCallHandler(parsingMethodHandler);
+  }
+
+  /**
+   * Sets the {@link KeyboardMethodHandler} which receives all requests to query the keyboard state.
+   */
+  public void setKeyboardMethodHandler(@Nullable KeyboardMethodHandler keyboardMethodHandler) {
+    this.keyboardMethodHandler = keyboardMethodHandler;
+  }
+
+  public interface KeyboardMethodHandler {
+    /**
+     * Returns the keyboard pressed states.
+     *
+     * @return A map whose keys are physical keyboard key IDs and values are the corresponding
+     *     logical keyboard key IDs.
+     */
+    Map<Long, Long> getKeyboardState();
+  }
+}

engine/src/flutter/shell/platform/android/test/io/flutter/embedding/android/KeyboardManagerTest.java

@@ -25,6 +25,7 @@ import io.flutter.util.FakeKeyEvent;
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Map;
 import java.util.function.BiConsumer;
 import java.util.function.Consumer;
 import java.util.stream.Collectors;
@@ -1564,4 +1565,22 @@ public class KeyboardManagerTest {
         calls.get(0).keyData, Type.kUp, PHYSICAL_CAPS_LOCK, LOGICAL_CAPS_LOCK, null, false);
     calls.clear();
   }
+
+  @Test
+  public void getKeyboardState() {
+    final KeyboardTester tester = new KeyboardTester();
+
+    tester.respondToTextInputWith(true); // Suppress redispatching.
+
+    // Initial pressed state is empty.
+    assertEquals(tester.keyboardManager.getKeyboardState(), Map.of());
+
+    tester.keyboardManager.handleEvent(
+        new FakeKeyEvent(ACTION_DOWN, SCAN_KEY_A, KEYCODE_A, 1, 'a', 0));
+    assertEquals(tester.keyboardManager.getKeyboardState(), Map.of(PHYSICAL_KEY_A, LOGICAL_KEY_A));
+
+    tester.keyboardManager.handleEvent(
+        new FakeKeyEvent(ACTION_UP, SCAN_KEY_A, KEYCODE_A, 0, 'a', 0));
+    assertEquals(tester.keyboardManager.getKeyboardState(), Map.of());
+  }
 }

engine/src/flutter/shell/platform/android/test/io/flutter/embedding/engine/systemchannels/KeyboardChannelTest.java

@@ -0,0 +1,67 @@
+package io.flutter.embedding.android;
+
+import static org.mockito.Mockito.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+import io.flutter.embedding.engine.dart.DartExecutor;
+import io.flutter.embedding.engine.systemchannels.KeyboardChannel;
+import io.flutter.plugin.common.BinaryMessenger;
+import io.flutter.plugin.common.MethodCall;
+import io.flutter.plugin.common.MethodChannel;
+import io.flutter.plugin.common.StandardMethodCodec;
+import java.nio.ByteBuffer;
+import java.util.HashMap;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.ArgumentCaptor;
+import org.robolectric.annotation.Config;
+
+@Config(manifest = Config.NONE)
+@RunWith(AndroidJUnit4.class)
+public class KeyboardChannelTest {
+
+  private static BinaryMessenger.BinaryReply sendToBinaryMessageHandler(
+      BinaryMessenger.BinaryMessageHandler binaryMessageHandler, String method, Object args) {
+    MethodCall methodCall = new MethodCall(method, args);
+    ByteBuffer encodedMethodCall = StandardMethodCodec.INSTANCE.encodeMethodCall(methodCall);
+    BinaryMessenger.BinaryReply reply = mock(BinaryMessenger.BinaryReply.class);
+    binaryMessageHandler.onMessage((ByteBuffer) encodedMethodCall.flip(), reply);
+    return reply;
+  }
+
+  @Test
+  public void respondsToGetKeyboardStateChannelMessage() {
+    ArgumentCaptor<BinaryMessenger.BinaryMessageHandler> binaryMessageHandlerCaptor =
+        ArgumentCaptor.forClass(BinaryMessenger.BinaryMessageHandler.class);
+    DartExecutor mockBinaryMessenger = mock(DartExecutor.class);
+    KeyboardChannel.KeyboardMethodHandler mockHandler =
+        mock(KeyboardChannel.KeyboardMethodHandler.class);
+    KeyboardChannel keyboardChannel = new KeyboardChannel(mockBinaryMessenger);
+
+    verify(mockBinaryMessenger, times(1))
+        .setMessageHandler(any(String.class), binaryMessageHandlerCaptor.capture());
+
+    BinaryMessenger.BinaryMessageHandler binaryMessageHandler =
+        binaryMessageHandlerCaptor.getValue();
+
+    keyboardChannel.setKeyboardMethodHandler(mockHandler);
+    sendToBinaryMessageHandler(binaryMessageHandler, "getKeyboardState", null);
+
+    verify(mockHandler, times(1)).getKeyboardState();
+  }
+
+  @Test
+  public void repliesWhenNoKeyboardChannelHandler() {
+    // Regression test for https://github.com/flutter/flutter/issues/122441#issuecomment-1582052616.
+
+    KeyboardChannel keyboardChannel = new KeyboardChannel(mock(DartExecutor.class));
+    MethodCall methodCall = new MethodCall("getKeyboardState", null);
+    MethodChannel.Result result = mock(MethodChannel.Result.class);
+    keyboardChannel.parsingMethodHandler.onMethodCall(methodCall, result);
+
+    verify(result).success(new HashMap());
+  }
+}

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

@@ -1501,6 +1501,7 @@ public class PlatformViewsControllerTest {
     when(engine.getPlatformViewsController()).thenReturn(platformViewsController);
     when(engine.getLocalizationPlugin()).thenReturn(mock(LocalizationPlugin.class));
     when(engine.getAccessibilityChannel()).thenReturn(mock(AccessibilityChannel.class));
+    when(engine.getDartExecutor()).thenReturn(executor);
 
     flutterView.attachToFlutterEngine(engine);
     platformViewsController.attachToView(flutterView);