Add InputDeviceBatteryListener to InputManager

System apps can now register an InputDeviceBatteryListener on a
per-device basis to be notified of battery changes.

- InputManager manages registration of the binder callback with
  InputManagerService to ensure that there is only one battery
  listener per process.
- The battery listener is invoked immediately upon registration
  to provide the initial battery state for the device.
- The callbacks are removed automatically when the process dies.
- This CL does not yet identify changes in battery state for monitored
  devices.

DD: go/inputdevice-battery-notifications

Bug: 243005009
Test: atest FrameworkServicesTests
Test: atest FrameworkCoreTests
Change-Id: Idf2b06a099155a6f5cc13b55dcd40852f54aa56c

core/java/android/hardware/input/IInputDeviceBatteryListener.aidl

@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.hardware.input;
+
+/** @hide */
+oneway interface IInputDeviceBatteryListener {
+
+    /**
+     * Called when there is a change in battery state for a monitored device. This will be called
+     * immediately after the listener is successfully registered for a new device via IInputManager.
+     * The parameters are values exposed through {@link android.hardware.BatteryState}.
+     */
+    void onBatteryStateChanged(int deviceId, boolean isBatteryPresent, int status, float capacity,
+            long eventTime);
+}

core/java/android/hardware/input/IInputManager.aidl

@@ -20,6 +20,7 @@ import android.graphics.Rect;
 import android.hardware.input.InputDeviceIdentifier;
 import android.hardware.input.KeyboardLayout;
 import android.hardware.input.IInputDevicesChangedListener;
+import android.hardware.input.IInputDeviceBatteryListener;
 import android.hardware.input.ITabletModeChangedListener;
 import android.hardware.input.TouchCalibration;
 import android.os.CombinedVibration;
@@ -157,4 +158,8 @@ interface IInputManager {
     void closeLightSession(int deviceId, in IBinder token);
 
     void cancelCurrentTouch();
+
+    void registerBatteryListener(int deviceId, IInputDeviceBatteryListener listener);
+
+    void unregisterBatteryListener(int deviceId, IInputDeviceBatteryListener listener);
 }

core/java/android/hardware/input/InputManager.java

@@ -30,6 +30,7 @@ import android.app.ActivityThread;
 import android.compat.annotation.ChangeId;
 import android.compat.annotation.UnsupportedAppUsage;
 import android.content.Context;
+import android.hardware.BatteryState;
 import android.hardware.SensorManager;
 import android.hardware.lights.Light;
 import android.hardware.lights.LightState;
@@ -65,6 +66,7 @@ import android.view.PointerIcon;
 import android.view.VerifiedInputEvent;
 import android.view.WindowManager.LayoutParams;
 
+import com.android.internal.annotations.GuardedBy;
 import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.os.SomeArgs;
 
@@ -72,6 +74,8 @@ import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Objects;
+import java.util.concurrent.Executor;
 
 /**
  * Provides information about input devices and available key layouts.
@@ -103,6 +107,14 @@ public final class InputManager {
     private TabletModeChangedListener mTabletModeChangedListener;
     private List<OnTabletModeChangedListenerDelegate> mOnTabletModeChangedListeners;
 
+    private final Object mBatteryListenersLock = new Object();
+    // Maps a deviceId whose battery is currently being monitored to an entry containing the
+    // registered listeners for that device.
+    @GuardedBy("mBatteryListenersLock")
+    private SparseArray<RegisteredBatteryListeners> mBatteryListeners;
+    @GuardedBy("mBatteryListenersLock")
+    private IInputDeviceBatteryListener mInputDeviceBatteryListener;
+
     private InputDeviceSensorManager mInputDeviceSensorManager;
     /**
      * Broadcast Action: Query available keyboard layouts.
@@ -1706,6 +1718,129 @@ public final class InputManager {
         }
     }
 
+    /**
+     * Adds a battery listener to be notified about {@link BatteryState} changes for an input
+     * device. The same listener can be registered for multiple input devices.
+     * The listener will be notified of the initial battery state of the device after it is
+     * successfully registered.
+     * @param deviceId the input device that should be monitored
+     * @param executor an executor on which the callback will be called
+     * @param listener the {@link InputDeviceBatteryListener}
+     * @see #removeInputDeviceBatteryListener(int, InputDeviceBatteryListener)
+     * @hide
+     */
+    public void addInputDeviceBatteryListener(int deviceId, @NonNull Executor executor,
+            @NonNull InputDeviceBatteryListener listener) {
+        Objects.requireNonNull(executor, "executor should not be null");
+        Objects.requireNonNull(listener, "listener should not be null");
+
+        synchronized (mBatteryListenersLock) {
+            if (mBatteryListeners == null) {
+                mBatteryListeners = new SparseArray<>();
+                mInputDeviceBatteryListener = new LocalInputDeviceBatteryListener();
+            }
+            RegisteredBatteryListeners listenersForDevice = mBatteryListeners.get(deviceId);
+            if (listenersForDevice == null) {
+                // The deviceId is currently not being monitored for battery changes.
+                // Start monitoring the device.
+                listenersForDevice = new RegisteredBatteryListeners();
+                mBatteryListeners.put(deviceId, listenersForDevice);
+                try {
+                    mIm.registerBatteryListener(deviceId, mInputDeviceBatteryListener);
+                } catch (RemoteException e) {
+                    throw e.rethrowFromSystemServer();
+                }
+            } else {
+                // The deviceId is already being monitored for battery changes.
+                // Ensure that the listener is not already registered.
+                for (InputDeviceBatteryListenerDelegate delegate : listenersForDevice.mDelegates) {
+                    if (Objects.equals(listener, delegate.mListener)) {
+                        throw new IllegalArgumentException(
+                                "Attempting to register an InputDeviceBatteryListener that has "
+                                        + "already been registered for deviceId: "
+                                        + deviceId);
+                    }
+                }
+            }
+            final InputDeviceBatteryListenerDelegate delegate =
+                    new InputDeviceBatteryListenerDelegate(listener, executor);
+            listenersForDevice.mDelegates.add(delegate);
+
+            // Notify the listener immediately if we already have the latest battery state.
+            if (listenersForDevice.mLatestBatteryState != null) {
+                delegate.notifyBatteryStateChanged(listenersForDevice.mLatestBatteryState);
+            }
+        }
+    }
+
+    /**
+     * Removes a previously registered battery listener for an input device.
+     * @see #addInputDeviceBatteryListener(int, Executor, InputDeviceBatteryListener)
+     * @hide
+     */
+    public void removeInputDeviceBatteryListener(int deviceId,
+            @NonNull InputDeviceBatteryListener listener) {
+        Objects.requireNonNull(listener, "listener should not be null");
+
+        synchronized (mBatteryListenersLock) {
+            if (mBatteryListeners == null) {
+                return;
+            }
+            RegisteredBatteryListeners listenersForDevice = mBatteryListeners.get(deviceId);
+            if (listenersForDevice == null) {
+                // The deviceId is not currently being monitored.
+                return;
+            }
+            final List<InputDeviceBatteryListenerDelegate> delegates =
+                    listenersForDevice.mDelegates;
+            for (int i = 0; i < delegates.size();) {
+                if (Objects.equals(listener, delegates.get(i).mListener)) {
+                    delegates.remove(i);
+                    continue;
+                }
+                i++;
+            }
+            if (!delegates.isEmpty()) {
+                return;
+            }
+
+            // There are no more battery listeners for this deviceId. Stop monitoring this device.
+            mBatteryListeners.remove(deviceId);
+            try {
+                mIm.unregisterBatteryListener(deviceId, mInputDeviceBatteryListener);
+            } catch (RemoteException e) {
+                throw e.rethrowFromSystemServer();
+            }
+            if (mBatteryListeners.size() == 0) {
+                // There are no more devices being monitored, so the registered
+                // IInputDeviceBatteryListener will be automatically dropped by the server.
+                mBatteryListeners = null;
+                mInputDeviceBatteryListener = null;
+            }
+        }
+    }
+
+    /**
+     * A callback used to be notified about battery state changes for an input device. The
+     * {@link #onBatteryStateChanged(int, long, BatteryState)} method will be called once after the
+     * listener is successfully registered to provide the initial battery state of the device.
+     * @see InputDevice#getBatteryState()
+     * @see #addInputDeviceBatteryListener(int, Executor, InputDeviceBatteryListener)
+     * @see #removeInputDeviceBatteryListener(int, InputDeviceBatteryListener)
+     * @hide
+     */
+    public interface InputDeviceBatteryListener {
+        /**
+         * Called when the battery state of an input device changes.
+         * @param deviceId the input device for which the battery changed.
+         * @param eventTimeMillis the time (in ms) when the battery change took place.
+         *        This timestamp is in the {@link SystemClock#uptimeMillis()} time base.
+         * @param batteryState the new battery state, never null.
+         */
+        void onBatteryStateChanged(
+                int deviceId, long eventTimeMillis, @NonNull BatteryState batteryState);
+    }
+
     /**
      * Listens for changes in input devices.
      */
@@ -1816,4 +1951,76 @@ public final class InputManager {
             }
         }
     }
+
+    private static final class LocalBatteryState extends BatteryState {
+        final int mDeviceId;
+        final boolean mIsPresent;
+        final int mStatus;
+        final float mCapacity;
+        final long mEventTime;
+
+        LocalBatteryState(int deviceId, boolean isPresent, int status, float capacity,
+                long eventTime) {
+            mDeviceId = deviceId;
+            mIsPresent = isPresent;
+            mStatus = status;
+            mCapacity = capacity;
+            mEventTime = eventTime;
+        }
+
+        @Override
+        public boolean isPresent() {
+            return mIsPresent;
+        }
+
+        @Override
+        public int getStatus() {
+            return mStatus;
+        }
+
+        @Override
+        public float getCapacity() {
+            return mCapacity;
+        }
+    }
+
+    private static final class RegisteredBatteryListeners {
+        final List<InputDeviceBatteryListenerDelegate> mDelegates = new ArrayList<>();
+        LocalBatteryState mLatestBatteryState;
+    }
+
+    private static final class InputDeviceBatteryListenerDelegate {
+        final InputDeviceBatteryListener mListener;
+        final Executor mExecutor;
+
+        InputDeviceBatteryListenerDelegate(InputDeviceBatteryListener listener, Executor executor) {
+            mListener = listener;
+            mExecutor = executor;
+        }
+
+        void notifyBatteryStateChanged(LocalBatteryState batteryState) {
+            mExecutor.execute(() ->
+                    mListener.onBatteryStateChanged(batteryState.mDeviceId, batteryState.mEventTime,
+                            batteryState));
+        }
+    }
+
+    private class LocalInputDeviceBatteryListener extends IInputDeviceBatteryListener.Stub {
+        @Override
+        public void onBatteryStateChanged(int deviceId, boolean isBatteryPresent, int status,
+                float capacity, long eventTime) {
+            synchronized (mBatteryListenersLock) {
+                if (mBatteryListeners == null) return;
+                final RegisteredBatteryListeners entry = mBatteryListeners.get(deviceId);
+                if (entry == null) return;
+
+                entry.mLatestBatteryState =
+                        new LocalBatteryState(
+                                deviceId, isBatteryPresent, status, capacity, eventTime);
+                for (InputDeviceBatteryListenerDelegate delegate : entry.mDelegates) {
+                    delegate.notifyBatteryStateChanged(entry.mLatestBatteryState);
+                }
+            }
+        }
+    }
 }

core/java/android/view/InputDevice.java

@@ -1039,6 +1039,15 @@ public final class InputDevice implements Parcelable {
         InputManager.getInstance().setCustomPointerIcon(icon);
     }
 
+    /**
+     * Reports whether the device has a battery.
+     * @return true if the device has a battery, false otherwise.
+     * @hide
+     */
+    public boolean hasBattery() {
+        return mHasBattery;
+    }
+
     /**
      * Provides information about the range of values for a particular {@link MotionEvent} axis.
      *

core/tests/coretests/src/android/hardware/input/InputDeviceBatteryListenerTest.kt

@@ -0,0 +1,227 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package android.hardware.input
+
+import android.hardware.BatteryState
+import android.os.Handler
+import android.os.HandlerExecutor
+import android.os.test.TestLooper
+import android.platform.test.annotations.Presubmit
+import com.android.server.testutils.any
+import java.util.concurrent.Executor
+import kotlin.test.assertEquals
+import kotlin.test.assertNotNull
+import kotlin.test.assertTrue
+import kotlin.test.fail
+import org.junit.After
+import org.junit.Before
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.Mock
+import org.mockito.Mockito.anyInt
+import org.mockito.Mockito.doAnswer
+import org.mockito.junit.MockitoJUnit
+import org.mockito.junit.MockitoJUnitRunner
+
+/**
+ * Tests for [InputManager.InputDeviceBatteryListener].
+ *
+ * Build/Install/Run:
+ * atest FrameworksCoreTests:InputDeviceBatteryListenerTest
+ */
+@Presubmit
+@RunWith(MockitoJUnitRunner::class)
+class InputDeviceBatteryListenerTest {
+    @get:Rule
+    val rule = MockitoJUnit.rule()!!
+
+    private lateinit var testLooper: TestLooper
+    private var registeredListener: IInputDeviceBatteryListener? = null
+    private val monitoredDevices = mutableListOf<Int>()
+    private lateinit var executor: Executor
+    private lateinit var inputManager: InputManager
+
+    @Mock
+    private lateinit var iInputManagerMock: IInputManager
+
+    @Before
+    fun setUp() {
+        testLooper = TestLooper()
+        executor = HandlerExecutor(Handler(testLooper.looper))
+        registeredListener = null
+        monitoredDevices.clear()
+        inputManager = InputManager.resetInstance(iInputManagerMock)
+
+        // Handle battery listener registration.
+        doAnswer {
+            val deviceId = it.getArgument(0) as Int
+            val listener = it.getArgument(1) as IInputDeviceBatteryListener
+            if (registeredListener != null &&
+                    registeredListener!!.asBinder() != listener.asBinder()) {
+                // There can only be one registered battery listener per process.
+                fail("Trying to register a new listener when one already exists")
+            }
+            if (monitoredDevices.contains(deviceId)) {
+                fail("Trying to start monitoring a device that was already being monitored")
+            }
+            monitoredDevices.add(deviceId)
+            registeredListener = listener
+            null
+        }.`when`(iInputManagerMock).registerBatteryListener(anyInt(), any())
+
+        // Handle battery listener being unregistered.
+        doAnswer {
+            val deviceId = it.getArgument(0) as Int
+            val listener = it.getArgument(1) as IInputDeviceBatteryListener
+            if (registeredListener == null ||
+                    registeredListener!!.asBinder() != listener.asBinder()) {
+                fail("Trying to unregister a listener that is not registered")
+            }
+            if (!monitoredDevices.remove(deviceId)) {
+                fail("Trying to stop monitoring a device that is not being monitored")
+            }
+            if (monitoredDevices.isEmpty()) {
+                registeredListener = null
+            }
+        }.`when`(iInputManagerMock).unregisterBatteryListener(anyInt(), any())
+    }
+
+    @After
+    fun tearDown() {
+        InputManager.clearInstance()
+    }
+
+    private fun notifyBatteryStateChanged(
+        deviceId: Int,
+        isPresent: Boolean = true,
+        status: Int = BatteryState.STATUS_FULL,
+        capacity: Float = 1.0f,
+        eventTime: Long = 12345L
+    ) {
+        registeredListener!!.onBatteryStateChanged(deviceId, isPresent, status, capacity, eventTime)
+    }
+
+    @Test
+    fun testListenerIsNotifiedCorrectly() {
+        var callbackCount = 0
+
+        // Add a battery listener to monitor battery changes.
+        inputManager.addInputDeviceBatteryListener(1 /*deviceId*/, executor) {
+                deviceId: Int, eventTime: Long, batteryState: BatteryState ->
+            callbackCount++
+            assertEquals(1, deviceId)
+            assertEquals(true, batteryState.isPresent)
+            assertEquals(BatteryState.STATUS_DISCHARGING, batteryState.status)
+            assertEquals(0.5f, batteryState.capacity)
+            assertEquals(8675309L, eventTime)
+        }
+
+        // Adding the listener should register the callback with InputManagerService.
+        assertNotNull(registeredListener)
+        assertTrue(monitoredDevices.contains(1))
+
+        // Notifying battery change for a different device should not trigger the listener.
+        notifyBatteryStateChanged(deviceId = 2)
+        testLooper.dispatchAll()
+        assertEquals(0, callbackCount)
+
+        // Notifying battery change for the registered device will notify the listener.
+        notifyBatteryStateChanged(1 /*deviceId*/, true /*isPresent*/,
+            BatteryState.STATUS_DISCHARGING, 0.5f /*capacity*/, 8675309L /*eventTime*/)
+        testLooper.dispatchNext()
+        assertEquals(1, callbackCount)
+    }
+
+    @Test
+    fun testMultipleListeners() {
+        // Set up two callbacks.
+        var callbackCount1 = 0
+        var callbackCount2 = 0
+        val callback1 = InputManager.InputDeviceBatteryListener { _, _, _ -> callbackCount1++ }
+        val callback2 = InputManager.InputDeviceBatteryListener { _, _, _ -> callbackCount2++ }
+
+        // Monitor battery changes for three devices. The first callback monitors devices 1 and 3,
+        // while the second callback monitors devices 2 and 3.
+        inputManager.addInputDeviceBatteryListener(1 /*deviceId*/, executor, callback1)
+        assertEquals(1, monitoredDevices.size)
+        inputManager.addInputDeviceBatteryListener(2 /*deviceId*/, executor, callback2)
+        assertEquals(2, monitoredDevices.size)
+        inputManager.addInputDeviceBatteryListener(3 /*deviceId*/, executor, callback1)
+        assertEquals(3, monitoredDevices.size)
+        inputManager.addInputDeviceBatteryListener(3 /*deviceId*/, executor, callback2)
+        assertEquals(3, monitoredDevices.size)
+
+        // Notifying battery change for each of the devices should trigger the registered callbacks.
+        notifyBatteryStateChanged(deviceId = 1)
+        testLooper.dispatchNext()
+        assertEquals(1, callbackCount1)
+        assertEquals(0, callbackCount2)
+
+        notifyBatteryStateChanged(deviceId = 2)
+        testLooper.dispatchNext()
+        assertEquals(1, callbackCount1)
+        assertEquals(1, callbackCount2)
+
+        notifyBatteryStateChanged(deviceId = 3)
+        testLooper.dispatchNext()
+        testLooper.dispatchNext()
+        assertEquals(2, callbackCount1)
+        assertEquals(2, callbackCount2)
+
+        // Stop monitoring devices 1 and 2.
+        inputManager.removeInputDeviceBatteryListener(1 /*deviceId*/, callback1)
+        assertEquals(2, monitoredDevices.size)
+        inputManager.removeInputDeviceBatteryListener(2 /*deviceId*/, callback2)
+        assertEquals(1, monitoredDevices.size)
+
+        // Ensure device 3 continues to be monitored.
+        notifyBatteryStateChanged(deviceId = 3)
+        testLooper.dispatchNext()
+        testLooper.dispatchNext()
+        assertEquals(3, callbackCount1)
+        assertEquals(3, callbackCount2)
+
+        // Stop monitoring all devices.
+        inputManager.removeInputDeviceBatteryListener(3 /*deviceId*/, callback1)
+        assertEquals(1, monitoredDevices.size)
+        inputManager.removeInputDeviceBatteryListener(3 /*deviceId*/, callback2)
+        assertEquals(0, monitoredDevices.size)
+    }
+
+    @Test
+    fun testAdditionalListenersNotifiedImmediately() {
+        var callbackCount1 = 0
+        var callbackCount2 = 0
+        val callback1 = InputManager.InputDeviceBatteryListener { _, _, _ -> callbackCount1++ }
+        val callback2 = InputManager.InputDeviceBatteryListener { _, _, _ -> callbackCount2++ }
+
+        // Add a battery listener and send the latest battery state.
+        inputManager.addInputDeviceBatteryListener(1 /*deviceId*/, executor, callback1)
+        assertEquals(1, monitoredDevices.size)
+        notifyBatteryStateChanged(deviceId = 1)
+        testLooper.dispatchNext()
+        assertEquals(1, callbackCount1)
+
+        // Add a second listener for the same device that already has the latest battery state.
+        inputManager.addInputDeviceBatteryListener(1 /*deviceId*/, executor, callback2)
+        assertEquals(1, monitoredDevices.size)
+
+        // Ensure that this listener is notified immediately.
+        testLooper.dispatchNext()
+        assertEquals(1, callbackCount2)
+    }
+}

services/core/java/com/android/server/input/BatteryController.java

@@ -0,0 +1,235 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.server.input;
+
+import android.annotation.BinderThread;
+import android.annotation.NonNull;
+import android.content.Context;
+import android.hardware.input.IInputDeviceBatteryListener;
+import android.hardware.input.InputManager;
+import android.os.IBinder;
+import android.os.RemoteException;
+import android.os.SystemClock;
+import android.util.ArrayMap;
+import android.util.ArraySet;
+import android.util.Log;
+import android.util.Slog;
+import android.view.InputDevice;
+
+import com.android.internal.annotations.GuardedBy;
+
+import java.io.PrintWriter;
+import java.util.Arrays;
+import java.util.Objects;
+import java.util.Set;
+
+/**
+ * A thread-safe component of {@link InputManagerService} responsible for managing the battery state
+ * of input devices.
+ */
+final class BatteryController {
+    private static final String TAG = BatteryController.class.getSimpleName();
+
+    // To enable these logs, run:
+    // 'adb shell setprop log.tag.BatteryController DEBUG' (requires restart)
+    private static final boolean DEBUG = Log.isLoggable(TAG, Log.DEBUG);
+
+    private final Object mLock = new Object();
+    private final Context mContext;
+    private final NativeInputManagerService mNative;
+
+    // Maps a pid to the registered listener record for that process. There can only be one battery
+    // listener per process.
+    @GuardedBy("mLock")
+    private final ArrayMap<Integer, ListenerRecord> mListenerRecords = new ArrayMap<>();
+
+    BatteryController(Context context, NativeInputManagerService nativeService) {
+        mContext = context;
+        mNative = nativeService;
+    }
+
+    /**
+     * Register the battery listener for the given input device and start monitoring its battery
+     * state.
+     */
+    @BinderThread
+    void registerBatteryListener(int deviceId, @NonNull IInputDeviceBatteryListener listener,
+            int pid) {
+        synchronized (mLock) {
+            ListenerRecord listenerRecord = mListenerRecords.get(pid);
+
+            if (listenerRecord == null) {
+                listenerRecord = new ListenerRecord(pid, listener);
+                try {
+                    listener.asBinder().linkToDeath(listenerRecord.mDeathRecipient, 0);
+                } catch (RemoteException e) {
+                    Slog.i(TAG, "Client died before battery listener could be registered.");
+                    return;
+                }
+                mListenerRecords.put(pid, listenerRecord);
+                if (DEBUG) Slog.d(TAG, "Battery listener added for pid " + pid);
+            }
+
+            if (listenerRecord.mListener.asBinder() != listener.asBinder()) {
+                throw new SecurityException(
+                        "Cannot register a new battery listener when there is already another "
+                                + "registered listener for pid "
+                                + pid);
+            }
+            if (!listenerRecord.mMonitoredDevices.add(deviceId)) {
+                throw new IllegalArgumentException(
+                        "The battery listener for pid " + pid
+                                + " is already monitoring deviceId " + deviceId);
+            }
+
+            if (DEBUG) {
+                Slog.d(TAG, "Battery listener for pid " + pid
+                        + " is monitoring deviceId " + deviceId);
+            }
+
+            notifyBatteryListener(deviceId, listenerRecord);
+        }
+    }
+
+    private void notifyBatteryListener(int deviceId, ListenerRecord record) {
+        final long eventTime = SystemClock.uptimeMillis();
+        try {
+            record.mListener.onBatteryStateChanged(
+                    deviceId,
+                    hasBattery(deviceId),
+                    mNative.getBatteryStatus(deviceId),
+                    mNative.getBatteryCapacity(deviceId) / 100.f,
+                    eventTime);
+        } catch (RemoteException e) {
+            Slog.e(TAG, "Failed to notify listener", e);
+        }
+    }
+
+    private boolean hasBattery(int deviceId) {
+        final InputDevice device =
+                Objects.requireNonNull(mContext.getSystemService(InputManager.class))
+                        .getInputDevice(deviceId);
+        return device != null && device.hasBattery();
+    }
+
+    /**
+     * Unregister the battery listener for the given input device and stop monitoring its battery
+     * state. If there are no other input devices that this listener is monitoring, the listener is
+     * removed.
+     */
+    @BinderThread
+    void unregisterBatteryListener(int deviceId, @NonNull IInputDeviceBatteryListener listener,
+            int pid) {
+        synchronized (mLock) {
+            final ListenerRecord listenerRecord = mListenerRecords.get(pid);
+            if (listenerRecord == null) {
+                throw new IllegalArgumentException(
+                        "Cannot unregister battery callback: No listener registered for pid "
+                                + pid);
+            }
+
+            if (listenerRecord.mListener.asBinder() != listener.asBinder()) {
+                throw new IllegalArgumentException(
+                        "Cannot unregister battery callback: The listener is not the one that "
+                                + "is registered for pid "
+                                + pid);
+            }
+
+            if (!listenerRecord.mMonitoredDevices.contains(deviceId)) {
+                throw new IllegalArgumentException(
+                        "Cannot unregister battery callback: The device is not being "
+                                + "monitored for deviceId " + deviceId);
+            }
+
+            unregisterRecordLocked(listenerRecord, deviceId);
+        }
+    }
+
+    @GuardedBy("mLock")
+    private void unregisterRecordLocked(ListenerRecord listenerRecord, int deviceId) {
+        final int pid = listenerRecord.mPid;
+
+        if (!listenerRecord.mMonitoredDevices.remove(deviceId)) {
+            throw new IllegalStateException("Cannot unregister battery callback: The deviceId "
+                    + deviceId
+                    + " is not being monitored by pid "
+                    + pid);
+        }
+
+        if (listenerRecord.mMonitoredDevices.isEmpty()) {
+            // There are no more devices being monitored by this listener.
+            listenerRecord.mListener.asBinder().unlinkToDeath(listenerRecord.mDeathRecipient, 0);
+            mListenerRecords.remove(pid);
+            if (DEBUG) Slog.d(TAG, "Battery listener removed for pid " + pid);
+        }
+    }
+
+    private void handleListeningProcessDied(int pid) {
+        synchronized (mLock) {
+            final ListenerRecord listenerRecord = mListenerRecords.get(pid);
+            if (listenerRecord == null) {
+                return;
+            }
+            if (DEBUG) {
+                Slog.d(TAG,
+                        "Removing battery listener for pid " + pid + " because the process died");
+            }
+            for (final int deviceId : listenerRecord.mMonitoredDevices) {
+                unregisterRecordLocked(listenerRecord, deviceId);
+            }
+        }
+    }
+
+    void dump(PrintWriter pw, String prefix) {
+        synchronized (mLock) {
+            pw.println(prefix + TAG + ": " + mListenerRecords.size()
+                    + " battery listeners");
+            for (int i = 0; i < mListenerRecords.size(); i++) {
+                pw.println(prefix + "  " + i + ": " + mListenerRecords.valueAt(i));
+            }
+        }
+    }
+
+    @SuppressWarnings("all")
+    void monitor() {
+        synchronized (mLock) {
+            return;
+        }
+    }
+
+    // A record of a registered battery listener from one process.
+    private class ListenerRecord {
+        final int mPid;
+        final IInputDeviceBatteryListener mListener;
+        final IBinder.DeathRecipient mDeathRecipient;
+        // The set of deviceIds that are currently being monitored by this listener.
+        final Set<Integer> mMonitoredDevices;
+
+        ListenerRecord(int pid, IInputDeviceBatteryListener listener) {
+            mPid = pid;
+            mListener = listener;
+            mMonitoredDevices = new ArraySet<>();
+            mDeathRecipient = () -> handleListeningProcessDied(pid);
+        }
+
+        @Override
+        public String toString() {
+            return "pid=" + mPid
+                    + ", monitored devices=" + Arrays.toString(mMonitoredDevices.toArray());
+        }
+    }
+}

services/core/java/com/android/server/input/InputManagerService.java

@@ -48,6 +48,7 @@ import android.hardware.SensorPrivacyManager.Sensors;
 import android.hardware.SensorPrivacyManagerInternal;
 import android.hardware.display.DisplayManager;
 import android.hardware.display.DisplayViewport;
+import android.hardware.input.IInputDeviceBatteryListener;
 import android.hardware.input.IInputDevicesChangedListener;
 import android.hardware.input.IInputManager;
 import android.hardware.input.IInputSensorEventListener;
@@ -308,6 +309,9 @@ public class InputManagerService extends IInputManager.Stub
     @GuardedBy("mInputMonitors")
     final Map<IBinder, GestureMonitorSpyWindow> mInputMonitors = new HashMap<>();
 
+    // Manages battery state for input devices.
+    private final BatteryController mBatteryController;
+
     // Maximum number of milliseconds to wait for input event injection.
     private static final int INJECTION_TIMEOUT_MILLIS = 30 * 1000;
 
@@ -417,6 +421,7 @@ public class InputManagerService extends IInputManager.Stub
         mContext = injector.getContext();
         mHandler = new InputManagerHandler(injector.getLooper());
         mNative = injector.getNativeService(this);
+        mBatteryController = new BatteryController(mContext, mNative);
 
         mUseDevInputEventForAudioJack =
                 mContext.getResources().getBoolean(R.bool.config_useDevInputEventForAudioJack);
@@ -2652,6 +2657,18 @@ public class InputManagerService extends IInputManager.Stub
         mNative.cancelCurrentTouch();
     }
 
+    @Override
+    public void registerBatteryListener(int deviceId, IInputDeviceBatteryListener listener) {
+        Objects.requireNonNull(listener);
+        mBatteryController.registerBatteryListener(deviceId, listener, Binder.getCallingPid());
+    }
+
+    @Override
+    public void unregisterBatteryListener(int deviceId, IInputDeviceBatteryListener listener) {
+        Objects.requireNonNull(listener);
+        mBatteryController.unregisterBatteryListener(deviceId, listener, Binder.getCallingPid());
+    }
+
     @Override
     public void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
         if (!DumpUtils.checkDumpPermission(mContext, TAG, pw)) return;
@@ -2665,7 +2682,8 @@ public class InputManagerService extends IInputManager.Stub
         pw.println("Input Manager Service (Java) State:");
         dumpAssociations(pw, "  " /*prefix*/);
         dumpSpyWindowGestureMonitors(pw, "  " /*prefix*/);
-        dumpDisplayInputPropertiesValues(pw, "  " /* prefix */);
+        dumpDisplayInputPropertiesValues(pw, "  " /*prefix*/);
+        mBatteryController.dump(pw, "  " /*prefix*/);
     }
 
     private void dumpAssociations(PrintWriter pw, String prefix) {
@@ -2776,6 +2794,7 @@ public class InputManagerService extends IInputManager.Stub
         synchronized (mLidSwitchLock) { /* Test if blocked by lid switch lock. */ }
         synchronized (mInputMonitors) { /* Test if blocked by input monitor lock. */ }
         synchronized (mAdditionalDisplayInputPropertiesLock) { /* Test if blocked by props lock */ }
+        mBatteryController.monitor();
         mNative.monitor();
     }
 

services/tests/servicestests/src/com/android/server/input/BatteryControllerTests.kt

@@ -0,0 +1,170 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.server.input
+
+import android.content.Context
+import android.content.ContextWrapper
+import android.hardware.BatteryState.STATUS_CHARGING
+import android.hardware.BatteryState.STATUS_FULL
+import android.hardware.input.IInputDeviceBatteryListener
+import android.hardware.input.IInputManager
+import android.hardware.input.InputDeviceCountryCode
+import android.hardware.input.InputManager
+import android.os.Binder
+import android.os.IBinder
+import android.platform.test.annotations.Presubmit
+import android.view.InputDevice
+import androidx.test.InstrumentationRegistry
+import org.junit.After
+import org.junit.Assert.fail
+import org.junit.Before
+import org.junit.Rule
+import org.junit.Test
+import org.mockito.ArgumentCaptor
+import org.mockito.ArgumentMatchers.notNull
+import org.mockito.Mock
+import org.mockito.Mockito.anyInt
+import org.mockito.Mockito.anyLong
+import org.mockito.Mockito.eq
+import org.mockito.Mockito.mock
+import org.mockito.Mockito.never
+import org.mockito.Mockito.spy
+import org.mockito.Mockito.times
+import org.mockito.Mockito.verify
+import org.mockito.Mockito.`when`
+import org.mockito.junit.MockitoJUnit
+
+/**
+ * Tests for {@link InputDeviceBatteryController}.
+ *
+ * Build/Install/Run:
+ * atest FrameworksServicesTests:InputDeviceBatteryControllerTests
+ */
+@Presubmit
+class BatteryControllerTests {
+    companion object {
+        const val PID = 42
+        const val DEVICE_ID = 13
+        const val SECOND_DEVICE_ID = 11
+    }
+
+    @get:Rule
+    val rule = MockitoJUnit.rule()!!
+
+    @Mock
+    private lateinit var native: NativeInputManagerService
+    @Mock
+    private lateinit var iInputManager: IInputManager
+
+    private lateinit var batteryController: BatteryController
+    private lateinit var context: Context
+
+    @Before
+    fun setup() {
+        context = spy(ContextWrapper(InstrumentationRegistry.getContext()))
+        val inputManager = InputManager.resetInstance(iInputManager)
+        `when`(context.getSystemService(eq(Context.INPUT_SERVICE))).thenReturn(inputManager)
+        `when`(iInputManager.inputDeviceIds).thenReturn(intArrayOf(DEVICE_ID, SECOND_DEVICE_ID))
+        `when`(iInputManager.getInputDevice(DEVICE_ID)).thenReturn(createInputDevice(DEVICE_ID))
+        `when`(iInputManager.getInputDevice(SECOND_DEVICE_ID))
+            .thenReturn(createInputDevice(SECOND_DEVICE_ID))
+
+        batteryController = BatteryController(context, native)
+    }
+
+    private fun createInputDevice(deviceId: Int): InputDevice =
+        InputDevice(deviceId, 0 /*generation*/, 0 /*controllerNumber*/,
+            "Device $deviceId" /*name*/, 0 /*vendorId*/, 0 /*productId*/, "descriptor$deviceId",
+            true /*isExternal*/, 0 /*sources*/, 0 /*keyboardType*/, null /*keyCharacterMap*/,
+            InputDeviceCountryCode.INVALID, false /*hasVibrator*/, false /*hasMicrophone*/,
+            false /*hasButtonUnderPad*/, false /*hasSensor*/, true /*hasBattery*/)
+
+    @After
+    fun tearDown() {
+        InputManager.clearInstance()
+    }
+
+    private fun createMockListener(): IInputDeviceBatteryListener {
+        val listener = mock(IInputDeviceBatteryListener::class.java)
+        val binder = mock(Binder::class.java)
+        `when`(listener.asBinder()).thenReturn(binder)
+        return listener
+    }
+
+    @Test
+    fun testRegisterAndUnregisterBinderLifecycle() {
+        val listener = createMockListener()
+        // Ensure the binder lifecycle is tracked when registering a listener.
+        batteryController.registerBatteryListener(DEVICE_ID, listener, PID)
+        verify(listener.asBinder()).linkToDeath(notNull(), anyInt())
+        batteryController.registerBatteryListener(SECOND_DEVICE_ID, listener, PID)
+        verify(listener.asBinder(), times(1)).linkToDeath(notNull(), anyInt())
+
+        // Ensure the binder lifecycle stops being tracked when all devices stopped being monitored.
+        batteryController.unregisterBatteryListener(SECOND_DEVICE_ID, listener, PID)
+        verify(listener.asBinder(), never()).unlinkToDeath(notNull(), anyInt())
+        batteryController.unregisterBatteryListener(DEVICE_ID, listener, PID)
+        verify(listener.asBinder()).unlinkToDeath(notNull(), anyInt())
+    }
+
+    @Test
+    fun testOneListenerPerProcess() {
+        val listener1 = createMockListener()
+        batteryController.registerBatteryListener(DEVICE_ID, listener1, PID)
+        verify(listener1.asBinder()).linkToDeath(notNull(), anyInt())
+
+        // If a second listener is added for the same process, a security exception is thrown.
+        val listener2 = createMockListener()
+        try {
+            batteryController.registerBatteryListener(DEVICE_ID, listener2, PID)
+            fail("Expected security exception when registering more than one listener per process")
+        } catch (ignored: SecurityException) {
+        }
+    }
+
+    @Test
+    fun testProcessDeathRemovesListener() {
+        val deathRecipient = ArgumentCaptor.forClass(IBinder.DeathRecipient::class.java)
+        val listener = createMockListener()
+        batteryController.registerBatteryListener(DEVICE_ID, listener, PID)
+        verify(listener.asBinder()).linkToDeath(deathRecipient.capture(), anyInt())
+
+        // When the binder dies, the callback is unregistered.
+        deathRecipient.value!!.binderDied(listener.asBinder())
+        verify(listener.asBinder()).unlinkToDeath(notNull(), anyInt())
+
+        // It is now possible to register the same listener again.
+        batteryController.registerBatteryListener(DEVICE_ID, listener, PID)
+        verify(listener.asBinder(), times(2)).linkToDeath(notNull(), anyInt())
+    }
+
+    @Test
+    fun testRegisteringListenerNotifiesStateImmediately() {
+        `when`(native.getBatteryStatus(DEVICE_ID)).thenReturn(STATUS_FULL)
+        `when`(native.getBatteryCapacity(DEVICE_ID)).thenReturn(100)
+        val listener = createMockListener()
+        batteryController.registerBatteryListener(DEVICE_ID, listener, PID)
+        verify(listener).onBatteryStateChanged(eq(DEVICE_ID), eq(true /*isPresent*/),
+            eq(STATUS_FULL), eq(1f), anyLong())
+
+        `when`(native.getBatteryStatus(SECOND_DEVICE_ID)).thenReturn(STATUS_CHARGING)
+        `when`(native.getBatteryCapacity(SECOND_DEVICE_ID)).thenReturn(78)
+        batteryController.registerBatteryListener(SECOND_DEVICE_ID, listener, PID)
+        verify(listener).onBatteryStateChanged(eq(SECOND_DEVICE_ID), eq(true /*isPresent*/),
+            eq(STATUS_CHARGING), eq(0.78f), anyLong())
+    }
+}