Merge changes from topic "b279054964-flag-api-udc-qpr-dev" into udc-qpr-dev

* changes:
  Allow flags to add metadata directly in code.
  Add permissions to FeatureFlagService and override api.
  Add Local FeatureFlags client to system servier.
  Connect FeatureFlags with FeatureFlagsService.
  Define FeatureFlagsService.
  A new Client-Side FeatureFlags library.

core/java/Android.bp

@@ -33,6 +33,15 @@ filegroup {
     srcs: ["com/android/internal/os/IBinaryTransparencyService.aidl"],
 }
 
+filegroup {
+    name: "feature_flags_aidl",
+    srcs: [
+        "android/flags/IFeatureFlags.aidl",
+        "android/flags/IFeatureFlagsCallback.aidl",
+        "android/flags/SyncableFlag.aidl",
+    ],
+}
+
 filegroup {
     name: "ITracingServiceProxy.aidl",
     srcs: ["android/tracing/ITracingServiceProxy.aidl"],

core/java/android/content/Context.java

@@ -5297,6 +5297,13 @@ public abstract class Context {
     @SystemApi
     public static final String APP_PREDICTION_SERVICE = "app_prediction";
 
+    /**
+     * Used for reading system-wide, overridable flags.
+     *
+     * @hide
+     */
+    public static final String FEATURE_FLAGS_SERVICE = "feature_flags";
+
     /**
      * Official published name of the search ui service.
      *

core/java/android/flags/BooleanFlag.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.annotation.NonNull;
+
+/**
+ * A flag representing a true or false value.
+ *
+ * The value will always be the same during the lifetime of the process it is read in.
+ *
+ * @hide
+ */
+public class BooleanFlag extends BooleanFlagBase {
+    private final boolean mDefault;
+
+    /**
+     * @param namespace A namespace for this flag. See {@link android.provider.DeviceConfig}.
+     * @param name A name for this flag.
+     * @param defaultValue The value of this flag if no other override is present.
+     */
+    BooleanFlag(String namespace, String name, boolean defaultValue) {
+        super(namespace, name);
+        mDefault = defaultValue;
+    }
+
+    @Override
+    @NonNull
+    public Boolean getDefault() {
+        return mDefault;
+    }
+
+    @Override
+    public BooleanFlag defineMetaData(String label, String description, String categoryName) {
+        super.defineMetaData(label, description, categoryName);
+        return this;
+    }
+}

core/java/android/flags/BooleanFlagBase.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.annotation.NonNull;
+
+abstract class BooleanFlagBase implements Flag<Boolean> {
+
+    private final String mNamespace;
+    private final String mName;
+    private String mLabel;
+    private String mDescription;
+    private String mCategoryName;
+
+    /**
+     * @param namespace A namespace for this flag. See {@link android.provider.DeviceConfig}.
+     * @param name A name for this flag.
+     */
+    BooleanFlagBase(String namespace, String name) {
+        mNamespace = namespace;
+        mName = name;
+        mLabel = name;
+    }
+
+    public abstract Boolean getDefault();
+
+    @Override
+    @NonNull
+    public String getNamespace() {
+        return mNamespace;
+    }
+
+    @Override
+    @NonNull
+    public String getName() {
+        return mName;
+    }
+
+    @Override
+    public BooleanFlagBase defineMetaData(String label, String description, String categoryName) {
+        mLabel = label;
+        mDescription = description;
+        mCategoryName = categoryName;
+        return this;
+    }
+
+    @Override
+    @NonNull
+    public String getLabel() {
+        return mLabel;
+    }
+
+    @Override
+    public String getDescription() {
+        return mDescription;
+    }
+
+    @Override
+    public String getCategoryName() {
+        return mCategoryName;
+    }
+
+    @Override
+    @NonNull
+    public String toString() {
+        return getNamespace() + "." + getName() + "[" + getDefault() + "]";
+    }
+}

core/java/android/flags/DynamicBooleanFlag.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+/**
+ * A flag representing a true or false value.
+ *
+ * The value may be different from one read to the next.
+ *
+ * @hide
+ */
+public class DynamicBooleanFlag extends BooleanFlagBase implements DynamicFlag<Boolean> {
+
+    private final boolean mDefault;
+
+    /**
+     * @param namespace A namespace for this flag. See {@link android.provider.DeviceConfig}.
+     * @param name A name for this flag.
+     * @param defaultValue The value of this flag if no other override is present.
+     */
+    DynamicBooleanFlag(String namespace, String name, boolean defaultValue) {
+        super(namespace, name);
+        mDefault = defaultValue;
+    }
+
+    @Override
+    public Boolean getDefault() {
+        return mDefault;
+    }
+
+    @Override
+    public DynamicBooleanFlag defineMetaData(String label, String description, String categoryName) {
+        super.defineMetaData(label, description, categoryName);
+        return this;
+    }
+}

core/java/android/flags/DynamicFlag.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+/**
+ * A flag for which the value may be different from one read to the next.
+ *
+ * @param <T> The type of value that this flag stores. E.g. Boolean or String.
+ *
+ * @hide
+ */
+public interface DynamicFlag<T> extends Flag<T> {
+    @Override
+    default boolean isDynamic() {
+        return true;
+    }
+}

core/java/android/flags/FeatureFlags.java

@@ -0,0 +1,379 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.annotation.NonNull;
+import android.content.Context;
+import android.os.RemoteException;
+import android.os.ServiceManager;
+import android.util.ArraySet;
+import android.util.Log;
+
+import com.android.internal.annotations.VisibleForTesting;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * A class for querying constants from the system - primarily booleans.
+ *
+ * Clients using this class can define their flags and their default values in one place,
+ * can override those values on running devices for debugging and testing purposes, and can control
+ * what flags are available to be used on release builds.
+ *
+ * TODO(b/279054964): A lot. This is skeleton code right now.
+ * @hide
+ */
+public class FeatureFlags {
+    private static final String TAG = "FeatureFlags";
+    private static FeatureFlags sInstance;
+    private static final Object sInstanceLock = new Object();
+
+    private final Set<Flag<?>> mKnownFlags = new ArraySet<>();
+    private final Set<Flag<?>> mDirtyFlags = new ArraySet<>();
+
+    private IFeatureFlags mIFeatureFlags;
+    private final Map<String, Map<String, Boolean>> mBooleanOverrides = new HashMap<>();
+    private final Set<ChangeListener> mListeners = new HashSet<>();
+
+    /**
+     * Obtain a per-process instance of FeatureFlags.
+     * @return A singleton instance of {@link FeatureFlags}.
+     */
+    @NonNull
+    public static FeatureFlags getInstance() {
+        synchronized (sInstanceLock) {
+            if (sInstance == null) {
+                sInstance = new FeatureFlags();
+            }
+        }
+
+        return sInstance;
+    }
+
+    /** See {@link FeatureFlagsFake}. */
+    @VisibleForTesting(visibility = VisibleForTesting.Visibility.PRIVATE)
+    public static void setInstance(FeatureFlags instance) {
+        synchronized (sInstanceLock) {
+            sInstance = instance;
+        }
+    }
+
+    private final IFeatureFlagsCallback mIFeatureFlagsCallback = new IFeatureFlagsCallback.Stub() {
+        @Override
+        public void onFlagChange(SyncableFlag flag) {
+            for (Flag<?> f : mKnownFlags) {
+                if (flagEqualsSyncableFlag(f, flag)) {
+                    if (f instanceof DynamicFlag<?>) {
+                        if (f instanceof DynamicBooleanFlag) {
+                            String value = flag.getValue();
+                            if (value == null) {  // Null means any existing overrides were erased.
+                                value = ((DynamicBooleanFlag) f).getDefault().toString();
+                            }
+                            addBooleanOverride(flag.getNamespace(), flag.getName(), value);
+                        }
+                        FeatureFlags.this.onFlagChange((DynamicFlag<?>) f);
+                    }
+                    break;
+                }
+            }
+        }
+    };
+
+    private FeatureFlags() {
+        this(null);
+    }
+
+    @VisibleForTesting(visibility = VisibleForTesting.Visibility.PRIVATE)
+    public FeatureFlags(IFeatureFlags iFeatureFlags) {
+        mIFeatureFlags = iFeatureFlags;
+
+        if (mIFeatureFlags != null) {
+            try {
+                mIFeatureFlags.registerCallback(mIFeatureFlagsCallback);
+            } catch (RemoteException e) {
+                // Shouldn't happen with things passed into tests.
+                Log.e(TAG, "Could not register callbacks!", e);
+            }
+        }
+    }
+
+    /**
+     * Construct a new {@link BooleanFlag}.
+     *
+     * Use this instead of constructing a {@link BooleanFlag} directly, as it registers the flag
+     * with the internals of the flagging system.
+     */
+    @NonNull
+    public static BooleanFlag booleanFlag(
+            @NonNull String namespace, @NonNull String name, boolean def) {
+        return getInstance().addFlag(new BooleanFlag(namespace, name, def));
+    }
+
+    /**
+     * Construct a new {@link FusedOffFlag}.
+     *
+     * Use this instead of constructing a {@link FusedOffFlag} directly, as it registers the
+     * flag with the internals of the flagging system.
+     */
+    @NonNull
+    public static FusedOffFlag fusedOffFlag(@NonNull String namespace, @NonNull String name) {
+        return getInstance().addFlag(new FusedOffFlag(namespace, name));
+    }
+
+    /**
+     * Construct a new {@link FusedOnFlag}.
+     *
+     * Use this instead of constructing a {@link FusedOnFlag} directly, as it registers the flag
+     * with the internals of the flagging system.
+     */
+    @NonNull
+    public static FusedOnFlag fusedOnFlag(@NonNull String namespace, @NonNull String name) {
+        return getInstance().addFlag(new FusedOnFlag(namespace, name));
+    }
+
+    /**
+     * Construct a new {@link DynamicBooleanFlag}.
+     *
+     * Use this instead of constructing a {@link DynamicBooleanFlag} directly, as it registers
+     * the flag with the internals of the flagging system.
+     */
+    @NonNull
+    public static DynamicBooleanFlag dynamicBooleanFlag(
+            @NonNull String namespace, @NonNull String name, boolean def) {
+        return getInstance().addFlag(new DynamicBooleanFlag(namespace, name, def));
+    }
+
+    /**
+     * Add a listener to be alerted when a {@link DynamicFlag} changes.
+     *
+     * See also {@link #removeChangeListener(ChangeListener)}.
+     *
+     * @param listener The listener to add.
+     */
+    public void addChangeListener(@NonNull ChangeListener listener) {
+        mListeners.add(listener);
+    }
+
+    /**
+     * Remove a listener that was added earlier.
+     *
+     * See also {@link #addChangeListener(ChangeListener)}.
+     *
+     * @param listener The listener to remove.
+     */
+    public void removeChangeListener(@NonNull ChangeListener listener) {
+        mListeners.remove(listener);
+    }
+
+    protected void onFlagChange(@NonNull DynamicFlag<?> flag) {
+        for (ChangeListener l : mListeners) {
+            l.onFlagChanged(flag);
+        }
+    }
+
+    /**
+     * Returns whether the supplied flag is true or not.
+     *
+     * {@link BooleanFlag} should only be used in debug builds. They do not get optimized out.
+     *
+     * The first time a flag is read, its value is cached for the lifetime of the process.
+     */
+    public boolean isEnabled(@NonNull BooleanFlag flag) {
+        return getBooleanInternal(flag);
+    }
+
+    /**
+     * Returns whether the supplied flag is true or not.
+     *
+     * Always returns false.
+     */
+    public boolean isEnabled(@NonNull FusedOffFlag flag) {
+        return false;
+    }
+
+    /**
+     * Returns whether the supplied flag is true or not.
+     *
+     * Always returns true;
+     */
+    public boolean isEnabled(@NonNull FusedOnFlag flag) {
+        return true;
+    }
+
+    /**
+     * Returns whether the supplied flag is true or not.
+     *
+     * Can return a different value for the flag each time it is called if an override comes in.
+     */
+    public boolean isCurrentlyEnabled(@NonNull DynamicBooleanFlag flag) {
+        return getBooleanInternal(flag);
+    }
+
+    private boolean getBooleanInternal(Flag<Boolean> flag) {
+        sync();
+        Map<String, Boolean> ns = mBooleanOverrides.get(flag.getNamespace());
+        Boolean value = null;
+        if (ns != null) {
+            value = ns.get(flag.getName());
+        }
+        if (value == null) {
+            throw new IllegalStateException("Boolean flag being read but was not synced: " + flag);
+        }
+
+        return value;
+    }
+
+    private <T extends Flag<?>> T addFlag(T flag)  {
+        synchronized (FeatureFlags.class) {
+            mDirtyFlags.add(flag);
+            mKnownFlags.add(flag);
+        }
+        return flag;
+    }
+
+    /**
+     * Sync any known flags that have not yet been synced.
+     *
+     * This is called implicitly when any flag is read, and is not generally needed except in
+     * exceptional circumstances.
+     */
+    public void sync() {
+        synchronized (FeatureFlags.class) {
+            if (mDirtyFlags.isEmpty()) {
+                return;
+            }
+            syncInternal(mDirtyFlags);
+            mDirtyFlags.clear();
+        }
+    }
+
+    /**
+     * Called when new flags have been declared. Gives the implementation a chance to act on them.
+     *
+     * Guaranteed to be called from a synchronized, thread-safe context.
+     */
+    protected void syncInternal(Set<Flag<?>> dirtyFlags) {
+        IFeatureFlags iFeatureFlags = bind();
+        List<SyncableFlag> syncableFlags = new ArrayList<>();
+        for (Flag<?> f : dirtyFlags) {
+            syncableFlags.add(flagToSyncableFlag(f));
+        }
+
+        List<SyncableFlag> serverFlags = List.of();  // Need to initialize the list with something.
+        try {
+            // New values come back from the service.
+            serverFlags = iFeatureFlags.syncFlags(syncableFlags);
+        } catch (RemoteException e) {
+            e.rethrowFromSystemServer();
+        }
+
+        for (Flag<?> f : dirtyFlags) {
+            boolean found = false;
+            for (SyncableFlag sf : serverFlags) {
+                if (flagEqualsSyncableFlag(f, sf)) {
+                    if (f instanceof BooleanFlag || f instanceof DynamicBooleanFlag) {
+                        addBooleanOverride(sf.getNamespace(), sf.getName(), sf.getValue());
+                    }
+                    found = true;
+                    break;
+                }
+            }
+            if (!found) {
+                if (f instanceof BooleanFlag) {
+                    addBooleanOverride(
+                            f.getNamespace(),
+                            f.getName(),
+                            ((BooleanFlag) f).getDefault() ? "true" : "false");
+                }
+            }
+        }
+    }
+
+    private void addBooleanOverride(String namespace, String name, String override) {
+        Map<String, Boolean> nsOverrides = mBooleanOverrides.get(namespace);
+        if (nsOverrides == null) {
+            nsOverrides = new HashMap<>();
+            mBooleanOverrides.put(namespace, nsOverrides);
+        }
+        nsOverrides.put(name, parseBoolean(override));
+    }
+
+    private SyncableFlag flagToSyncableFlag(Flag<?> f) {
+        return new SyncableFlag(
+                f.getNamespace(),
+                f.getName(),
+                f.getDefault().toString(),
+                f instanceof DynamicFlag<?>);
+    }
+
+    private IFeatureFlags bind() {
+        if (mIFeatureFlags == null) {
+            mIFeatureFlags = IFeatureFlags.Stub.asInterface(
+                    ServiceManager.getService(Context.FEATURE_FLAGS_SERVICE));
+            try {
+                mIFeatureFlags.registerCallback(mIFeatureFlagsCallback);
+            } catch (RemoteException e) {
+                Log.e(TAG, "Failed to listen for flag changes!");
+            }
+        }
+
+        return mIFeatureFlags;
+    }
+
+    static boolean parseBoolean(String value) {
+        // Check for a truish string.
+        boolean result = value.equalsIgnoreCase("true")
+                || value.equals("1")
+                || value.equalsIgnoreCase("t")
+                || value.equalsIgnoreCase("on");
+        if (!result) {  // Expect a falsish string, else log an error.
+            if (!(value.equalsIgnoreCase("false")
+                    || value.equals("0")
+                    || value.equalsIgnoreCase("f")
+                    || value.equalsIgnoreCase("off"))) {
+                Log.e(TAG,
+                        "Tried parsing " + value + " as boolean but it doesn't look like one. "
+                                + "Value expected to be one of true|false, 1|0, t|f, on|off.");
+            }
+        }
+        return result;
+    }
+
+    private static boolean flagEqualsSyncableFlag(Flag<?> f, SyncableFlag sf) {
+        return f.getName().equals(sf.getName()) && f.getNamespace().equals(sf.getNamespace());
+    }
+
+
+    /**
+     * A simpler listener that is alerted when a {@link DynamicFlag} changes.
+     *
+     * See {@link #addChangeListener(ChangeListener)}
+     */
+    public interface ChangeListener {
+        /**
+         * Called when a {@link DynamicFlag} changes.
+         *
+         * @param flag The flag that has changed.
+         */
+        void onFlagChanged(DynamicFlag<?> flag);
+    }
+}

core/java/android/flags/FeatureFlagsFake.java

@@ -0,0 +1,115 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.annotation.NonNull;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * An implementation of {@link FeatureFlags} for testing.
+ *
+ * Before you read a flag from using this Fake, you must set that flag using
+ * {@link #setFlagValue(BooleanFlagBase, boolean)}. This ensures that your tests are deterministic.
+ *
+ * If you are relying on {@link FeatureFlags#getInstance()} to access FeatureFlags in your code
+ * under test, (instead of dependency injection), you can pass an instance of this fake to
+ * {@link FeatureFlags#setInstance(FeatureFlags)}. Be sure to call that method again, passing null,
+ * to ensure hermetic testing - you don't want static state persisting between your test methods.
+ *
+ * @hide
+ */
+public class FeatureFlagsFake extends FeatureFlags {
+    private final Map<BooleanFlagBase, Boolean> mFlagValues = new HashMap<>();
+    private final Set<BooleanFlagBase> mReadFlags = new HashSet<>();
+
+    public FeatureFlagsFake(IFeatureFlags iFeatureFlags) {
+        super(iFeatureFlags);
+    }
+
+    @Override
+    public boolean isEnabled(@NonNull BooleanFlag flag) {
+        return requireFlag(flag);
+    }
+
+    @Override
+    public boolean isEnabled(@NonNull FusedOffFlag flag) {
+        return requireFlag(flag);
+    }
+
+    @Override
+    public boolean isEnabled(@NonNull FusedOnFlag flag) {
+        return requireFlag(flag);
+    }
+
+    @Override
+    public boolean isCurrentlyEnabled(@NonNull DynamicBooleanFlag flag) {
+        return requireFlag(flag);
+    }
+
+    @Override
+    protected void syncInternal(Set<Flag<?>> dirtyFlags) {
+    }
+
+    /**
+     * Explicitly set a flag's value for reading in tests.
+     *
+     * You _must_ call this for every flag your code-under-test will read. Otherwise, an
+     * {@link IllegalStateException} will be thrown.
+     *
+     * You are able to set values for {@link FusedOffFlag} and {@link FusedOnFlag}, despite those
+     * flags having a fixed value at compile time, since unit tests should still test the state of
+     * those flags as both true and false. I.e. a flag that is off might be turned on in a future
+     * build or vice versa.
+     *
+     * You can not call this method _after_ a non-dynamic flag has been read. Non-dynamic flags
+     * are held stable in the system, so changing a value after reading would not match
+     * real-implementation behavior.
+     *
+     * Calling this method will trigger any {@link android.flags.FeatureFlags.ChangeListener}s that
+     * are registered for the supplied flag if the flag is a {@link DynamicFlag}.
+     *
+     * @param flag  The BooleanFlag that you want to set a value for.
+     * @param value The value that the flag should return when accessed.
+     */
+    public void setFlagValue(@NonNull BooleanFlagBase flag, boolean value) {
+        if (!(flag instanceof DynamicBooleanFlag) && mReadFlags.contains(flag)) {
+            throw new RuntimeException(
+                    "You can not set the value of a flag after it has been read. Tried to set "
+                            + flag + " to " + value + " but it already " + mFlagValues.get(flag));
+        }
+        mFlagValues.put(flag, value);
+        if (flag instanceof DynamicBooleanFlag) {
+            onFlagChange((DynamicFlag<?>) flag);
+        }
+    }
+
+    private boolean requireFlag(BooleanFlagBase flag) {
+        if (!mFlagValues.containsKey(flag)) {
+            throw new IllegalStateException(
+                    "Tried to access " + flag + " in test but no overrided specified. You must "
+                            + "call #setFlagValue for each flag read in a test.");
+        }
+        mReadFlags.add(flag);
+
+        return mFlagValues.get(flag);
+    }
+
+}

core/java/android/flags/Flag.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.annotation.NonNull;
+
+/**
+ * Base class for constants read via {@link android.flags.FeatureFlags}.
+ *
+ * @param <T> The type of value that this flag stores. E.g. Boolean or String.
+ *
+ * @hide
+ */
+public interface Flag<T> {
+    /** The namespace for a flag. Should combine uniquely with its name. */
+    @NonNull
+    String getNamespace();
+
+    /** The name of the flag. Should combine uniquely with its namespace. */
+    @NonNull
+    String getName();
+
+    /** The value of this flag if no override has been set. Null values are not supported. */
+    @NonNull
+    T getDefault();
+
+    /** Returns true if the value of this flag can change at runtime. */
+    default boolean isDynamic() {
+        return false;
+    }
+
+    /**
+     * Add human-readable details to the flag. Flag client's are not required to set this.
+     *
+     * See {@link #getLabel()}, {@link #getDescription()}, and {@link #getCategoryName()}.
+     *
+     * @return Returns `this`, to make a fluent api.
+     */
+    Flag<T> defineMetaData(String label, String description, String categoryName);
+
+    /**
+     * A human-readable name for the flag. Defaults to {@link #getName()}
+     *
+     * See {@link #defineMetaData(String, String, String)}
+     */
+    @NonNull
+    default String getLabel() {
+        return getName();
+    }
+
+    /**
+     * A human-readable description for the flag. Defaults to null if unset.
+     *
+     * See {@link #defineMetaData(String, String, String)}
+     */
+    default String getDescription() {
+        return null;
+    }
+
+    /**
+     * A human-readable category name for the flag. Defaults to null if unset.
+     *
+     * See {@link #defineMetaData(String, String, String)}
+     */
+    default String getCategoryName() {
+        return null;
+    }
+}

core/java/android/flags/FusedOffFlag.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.annotation.NonNull;
+import android.provider.DeviceConfig;
+
+/**
+ * A flag representing a false value.
+ *
+ * The flag can never be changed or overridden. It is false at compile time.
+ *
+ * @hide
+ */
+public final class FusedOffFlag extends BooleanFlagBase {
+    /**
+     * @param namespace A namespace for this flag. See {@link DeviceConfig}.
+     * @param name      A name for this flag.
+     */
+    FusedOffFlag(String namespace, String name) {
+        super(namespace, name);
+    }
+
+    @Override
+    @NonNull
+    public Boolean getDefault() {
+        return false;
+    }
+
+    @Override
+    public FusedOffFlag defineMetaData(String label, String description, String categoryName) {
+        super.defineMetaData(label, description, categoryName);
+        return this;
+    }
+}

core/java/android/flags/FusedOnFlag.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.annotation.NonNull;
+import android.provider.DeviceConfig;
+
+/**
+ * A flag representing a true value.
+ *
+ * The flag can never be changed or overridden. It is true at compile time.
+ *
+ * @hide
+ */
+public final class FusedOnFlag extends BooleanFlagBase {
+    /**
+     * @param namespace A namespace for this flag. See {@link DeviceConfig}.
+     * @param name      A name for this flag.
+     */
+    FusedOnFlag(String namespace, String name) {
+        super(namespace, name);
+    }
+
+    @Override
+    @NonNull
+    public Boolean getDefault() {
+        return true;
+    }
+
+    @Override
+    public FusedOnFlag defineMetaData(String label, String description, String categoryName) {
+        super.defineMetaData(label, description, categoryName);
+        return this;
+    }
+}

core/java/android/flags/IFeatureFlags.aidl

@@ -0,0 +1,89 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.flags.IFeatureFlagsCallback;
+import android.flags.SyncableFlag;
+
+/**
+ * Binder interface for communicating with {@link com.android.server.flags.FeatureFlagsService}.
+ *
+ * This interface is used by {@link android.flags.FeatureFlags} and developers should use that to
+ * interface with the service. FeatureFlags is the "client" in this documentation.
+ *
+ * The methods allow client apps to communicate what flags they care about, and receive back
+ * current values for those flags. For stable flags, this is the finalized value until the device
+ * restarts. For {@link DynamicFlag}s, this is the last known value, though it may change in the
+ * future. Clients can listen for changes to flag values so that it can react accordingly.
+ * @hide
+ */
+interface IFeatureFlags {
+    /**
+     * Synchronize with the {@link com.android.server.flags.FeatureFlagsService} about flags of
+     * interest.
+     *
+     * The client should pass in a list of flags that it is using as {@link SyncableFlag}s, which
+     * includes what it thinks the default values of the flags are.
+     *
+     * The response will contain a list of matching SyncableFlags, whose values are set to what the
+     * value of the flags actually are. The client should update its internal state flag data to
+     * match.
+     *
+     * Generally speaking, if a flag that is passed in is new to the FeatureFlagsService, the
+     * service will cache the passed-in value, and return it back out. If, however, a different
+     * client has synced that flag with the service previously, FeatureFlagsService will return the
+     * existing cached value, which may or may not be what the current client passed in. This allows
+     * FeatureFlagsService to keep clients in agreement with one another.
+     */
+    List<SyncableFlag> syncFlags(in List<SyncableFlag> flagList);
+
+    /**
+     * Pass in an {@link IFeatureFlagsCallback} that will be called whenever a {@link DymamicFlag}
+     * changes.
+     */
+    void registerCallback(IFeatureFlagsCallback callback);
+
+    /**
+     * Remove a {@link IFeatureFlagsCallback} that was previously registered with
+     * {@link #registerCallback}.
+     */
+    void unregisterCallback(IFeatureFlagsCallback callback);
+
+    /**
+     * Query the {@link com.android.server.flags.FeatureFlagsService} for flags, but don't
+     * cache them. See {@link #syncFlags}.
+     *
+     * You almost certainly don't want this method. This is intended for the Flag Flipper
+     * application that needs to query the state of system but doesn't want to affect it by
+     * doing so. All other clients should use {@link syncFlags}.
+     */
+    List<SyncableFlag> queryFlags(in List<SyncableFlag> flagList);
+
+    /**
+     * Change a flags value in the system.
+     *
+     * This is intended for use by the Flag Flipper application.
+     */
+    void overrideFlag(in SyncableFlag flag);
+
+    /**
+     * Restore a flag to its default value.
+     *
+     * This is intended for use by the Flag Flipper application.
+     */
+    void resetFlag(in SyncableFlag flag);
+}

core/java/android/flags/IFeatureFlagsCallback.aidl

@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.flags.SyncableFlag;
+
+/**
+ * Callback for {@link IFeatureFlags#registerCallback} to get alerts when a {@link DynamicFlag}
+ * changes.
+ *
+ * DynamicFlags can change at run time. Stable flags will never result in a call to this method.
+ *
+ * @hide
+ */
+oneway interface IFeatureFlagsCallback {
+    void onFlagChange(in SyncableFlag flag);
+}

core/java/android/flags/OWNERS

@@ -0,0 +1,7 @@
+# Bug component: 1306523
+
+mankoff@google.com
+pixel@google.com
+
+dsandler@android.com
+

core/java/android/flags/SyncableFlag.aidl

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+/**
+ * A parcelable data class for serializing {@link Flag} across a Binder.
+ */
+parcelable SyncableFlag;

core/java/android/flags/SyncableFlag.java

@@ -0,0 +1,112 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.annotation.NonNull;
+import android.os.Parcel;
+import android.os.Parcelable;
+
+/**
+ * @hide
+ */
+public final class SyncableFlag implements Parcelable {
+    private final String mNamespace;
+    private final String mName;
+    private final String mValue;
+    private final boolean mDynamic;
+    private final boolean mOverridden;
+
+    public SyncableFlag(
+            @NonNull String namespace,
+            @NonNull String name,
+            @NonNull String value,
+            boolean dynamic) {
+        this(namespace, name, value, dynamic, false);
+    }
+
+    public SyncableFlag(
+            @NonNull String namespace,
+            @NonNull String name,
+            @NonNull String value,
+            boolean dynamic,
+            boolean overridden
+    ) {
+        mNamespace = namespace;
+        mName = name;
+        mValue = value;
+        mDynamic = dynamic;
+        mOverridden = overridden;
+    }
+
+    @NonNull
+    public String getNamespace() {
+        return mNamespace;
+    }
+
+    @NonNull
+    public String getName() {
+        return mName;
+    }
+
+    @NonNull
+    public String getValue() {
+        return mValue;
+    }
+
+    public boolean isDynamic() {
+        return mDynamic;
+    }
+
+    public boolean isOverridden() {
+        return mOverridden;
+    }
+
+    @NonNull
+    public static final Parcelable.Creator<SyncableFlag> CREATOR = new Parcelable.Creator<>() {
+        public SyncableFlag createFromParcel(Parcel in) {
+            return new SyncableFlag(
+                    in.readString(),
+                    in.readString(),
+                    in.readString(),
+                    in.readBoolean(),
+                    in.readBoolean());
+        }
+
+        public SyncableFlag[] newArray(int size) {
+            return new SyncableFlag[size];
+        }
+    };
+
+    @Override
+    public int describeContents() {
+        return 0;
+    }
+
+    @Override
+    public void writeToParcel(@NonNull Parcel dest, int flags) {
+        dest.writeString(mNamespace);
+        dest.writeString(mName);
+        dest.writeString(mValue);
+        dest.writeBoolean(mDynamic);
+        dest.writeBoolean(mOverridden);
+    }
+
+    @Override
+    public String toString() {
+        return getNamespace() + "." + getName() + "[" + getValue() + "]";
+    }
+}

core/java/com/android/internal/flags/CoreFlags.java

@@ -0,0 +1,93 @@
+/*
+ * Copyright (C) 2023 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.internal.flags;
+
+import android.flags.BooleanFlag;
+import android.flags.DynamicBooleanFlag;
+import android.flags.FeatureFlags;
+import android.flags.FusedOffFlag;
+import android.flags.FusedOnFlag;
+import android.flags.SyncableFlag;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Flags defined here are can be read by code in core.
+ *
+ * Flags not defined here will throw a security exception if third-party processes attempts to read
+ * them.
+ *
+ * DO NOT define a flag here unless you explicitly intend for that flag to be readable by code that
+ * runs inside a third party process.
+ */
+public abstract class CoreFlags {
+    private static final List<SyncableFlag> sKnownFlags = new ArrayList<>();
+
+    public static BooleanFlag BOOL_FLAG = booleanFlag("core", "bool_flag", false);
+    public static FusedOffFlag OFF_FLAG = fusedOffFlag("core", "off_flag");
+    public static FusedOnFlag ON_FLAG = fusedOnFlag("core", "on_flag");
+    public static DynamicBooleanFlag DYN_FLAG = dynamicBooleanFlag("core", "dyn_flag", true);
+
+    /** Returns true if the passed in flag matches a flag in this class. */
+    public static boolean isCoreFlag(SyncableFlag flag) {
+        for (SyncableFlag knownFlag : sKnownFlags) {
+            if (knownFlag.getName().equals(flag.getName())
+                    && knownFlag.getNamespace().equals(flag.getNamespace())) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    public static List<SyncableFlag> getCoreFlags() {
+        return sKnownFlags;
+    }
+
+    private static BooleanFlag booleanFlag(String namespace, String name, boolean defaultValue) {
+        BooleanFlag f = FeatureFlags.booleanFlag(namespace, name, defaultValue);
+
+        sKnownFlags.add(new SyncableFlag(namespace, name, Boolean.toString(defaultValue), false));
+
+        return f;
+    }
+
+    private static FusedOffFlag fusedOffFlag(String namespace, String name) {
+        FusedOffFlag f = FeatureFlags.fusedOffFlag(namespace, name);
+
+        sKnownFlags.add(new SyncableFlag(namespace, name, "false", false));
+
+        return f;
+    }
+
+    private static FusedOnFlag fusedOnFlag(String namespace, String name) {
+        FusedOnFlag f = FeatureFlags.fusedOnFlag(namespace, name);
+
+        sKnownFlags.add(new SyncableFlag(namespace, name, "true", false));
+
+        return f;
+    }
+
+    private static DynamicBooleanFlag dynamicBooleanFlag(
+            String namespace, String name, boolean defaultValue) {
+        DynamicBooleanFlag f = FeatureFlags.dynamicBooleanFlag(namespace, name, defaultValue);
+
+        sKnownFlags.add(new SyncableFlag(namespace, name, Boolean.toString(defaultValue), true));
+
+        return f;
+    }
+}

core/res/AndroidManifest.xml

@@ -7655,6 +7655,24 @@
     <permission android:name="android.permission.GET_ANY_PROVIDER_TYPE"
                 android:protectionLevel="signature" />
 
+
+    <!-- @hide Allows internal applications to read and synchronize non-core flags.
+         Apps without this permission can only read a subset of flags specifically intended
+         for use in "core", (i.e. third party apps). Apps with this permission can define their
+         own flags, and federate those values with other system-level apps.
+         <p>Not for use by third-party applications.
+         <p>Protection level: signature
+    -->
+    <permission android:name="android.permission.SYNC_FLAGS"
+        android:protectionLevel="signature" />
+
+    <!-- @hide Allows internal applications to override flags in the FeatureFlags service.
+         <p>Not for use by third-party applications.
+         <p>Protection level: signature
+    -->
+    <permission android:name="android.permission.WRITE_FLAGS"
+        android:protectionLevel="signature" />
+
     <!-- Attribution for Geofencing service. -->
     <attribution android:tag="GeofencingService" android:label="@string/geofencing_service"/>
     <!-- Attribution for Country Detector. -->

core/tests/coretests/src/android/flags/FeatureFlagsTest.java

@@ -0,0 +1,155 @@
+/*
+ * Copyright (C) 2020 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.flags;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import android.platform.test.annotations.Presubmit;
+
+import androidx.test.filters.SmallTest;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.List;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+
+@SmallTest
+@Presubmit
+public class FeatureFlagsTest {
+
+    IFeatureFlagsFake mIFeatureFlagsFake = new IFeatureFlagsFake();
+    FeatureFlags mFeatureFlags = new FeatureFlags(mIFeatureFlagsFake);
+
+    @Before
+    public void setup() {
+        FeatureFlags.setInstance(mFeatureFlags);
+    }
+
+    @Test
+    public void testFusedOff_Disabled() {
+        FusedOffFlag flag = FeatureFlags.fusedOffFlag("test", "a");
+        assertThat(mFeatureFlags.isEnabled(flag)).isFalse();
+    }
+
+    @Test
+    public void testFusedOn_Enabled() {
+        FusedOnFlag flag = FeatureFlags.fusedOnFlag("test", "a");
+        assertThat(mFeatureFlags.isEnabled(flag)).isTrue();
+    }
+
+    @Test
+    public void testBooleanFlag_DefaultDisabled() {
+        BooleanFlag flag = FeatureFlags.booleanFlag("test", "a", false);
+        assertThat(mFeatureFlags.isEnabled(flag)).isFalse();
+    }
+
+    @Test
+    public void testBooleanFlag_DefaultEnabled() {
+        BooleanFlag flag = FeatureFlags.booleanFlag("test", "a", true);
+        assertThat(mFeatureFlags.isEnabled(flag)).isTrue();
+    }
+
+    @Test
+    public void testDynamicBooleanFlag_DefaultDisabled() {
+        DynamicBooleanFlag flag = FeatureFlags.dynamicBooleanFlag("test", "a", false);
+        assertThat(mFeatureFlags.isCurrentlyEnabled(flag)).isFalse();
+    }
+
+    @Test
+    public void testDynamicBooleanFlag_DefaultEnabled() {
+        DynamicBooleanFlag flag = FeatureFlags.dynamicBooleanFlag("test", "a", true);
+        assertThat(mFeatureFlags.isCurrentlyEnabled(flag)).isTrue();
+    }
+
+    @Test
+    public void testBooleanFlag_OverrideBeforeRead() {
+        BooleanFlag flag = FeatureFlags.booleanFlag("test", "a", false);
+        SyncableFlag syncableFlag = new SyncableFlag(
+                flag.getNamespace(), flag.getName(), "true", false);
+
+        mIFeatureFlagsFake.setFlagOverrides(List.of(syncableFlag));
+
+        assertThat(mFeatureFlags.isEnabled(flag)).isTrue();
+    }
+
+    @Test
+    public void testFusedOffFlag_OverrideHasNoEffect() {
+        FusedOffFlag flag = FeatureFlags.fusedOffFlag("test", "a");
+        SyncableFlag syncableFlag = new SyncableFlag(
+                flag.getNamespace(), flag.getName(), "true", false);
+
+        mIFeatureFlagsFake.setFlagOverrides(List.of(syncableFlag));
+
+        assertThat(mFeatureFlags.isEnabled(flag)).isFalse();
+    }
+
+    @Test
+    public void testFusedOnFlag_OverrideHasNoEffect() {
+        FusedOnFlag flag = FeatureFlags.fusedOnFlag("test", "a");
+        SyncableFlag syncableFlag = new SyncableFlag(
+                flag.getNamespace(), flag.getName(), "false", false);
+
+        mIFeatureFlagsFake.setFlagOverrides(List.of(syncableFlag));
+
+        assertThat(mFeatureFlags.isEnabled(flag)).isTrue();
+    }
+
+    @Test
+    public void testDynamicFlag_OverrideBeforeRead() {
+        DynamicBooleanFlag flag = FeatureFlags.dynamicBooleanFlag("test", "a", false);
+        SyncableFlag syncableFlag = new SyncableFlag(
+                flag.getNamespace(), flag.getName(), "true", true);
+
+        mIFeatureFlagsFake.setFlagOverrides(List.of(syncableFlag));
+
+        // Changes to true
+        assertThat(mFeatureFlags.isCurrentlyEnabled(flag)).isTrue();
+    }
+
+    @Test
+    public void testDynamicFlag_OverrideAfterRead() {
+        DynamicBooleanFlag flag = FeatureFlags.dynamicBooleanFlag("test", "a", false);
+        SyncableFlag syncableFlag = new SyncableFlag(
+                flag.getNamespace(), flag.getName(), "true", true);
+
+        // Starts false
+        assertThat(mFeatureFlags.isCurrentlyEnabled(flag)).isFalse();
+
+        mIFeatureFlagsFake.setFlagOverrides(List.of(syncableFlag));
+
+        // Changes to true
+        assertThat(mFeatureFlags.isCurrentlyEnabled(flag)).isTrue();
+    }
+
+    @Test
+    public void testDynamicFlag_FiresListener() {
+        DynamicBooleanFlag flag = FeatureFlags.dynamicBooleanFlag("test", "a", false);
+        AtomicBoolean called = new AtomicBoolean(false);
+        FeatureFlags.ChangeListener listener = flag1 -> called.set(true);
+
+        mFeatureFlags.addChangeListener(listener);
+
+        SyncableFlag syncableFlag = new SyncableFlag(
+                flag.getNamespace(), flag.getName(), flag.getDefault().toString(), true);
+
+        mIFeatureFlagsFake.setFlagOverrides(List.of(syncableFlag));
+
+        // Fires listener.
+        assertThat(called.get()).isTrue();
+    }
+}

core/tests/coretests/src/android/flags/IFeatureFlagsFake.java

@@ -0,0 +1,113 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.os.IBinder;
+import android.os.RemoteException;
+
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+class IFeatureFlagsFake implements IFeatureFlags {
+
+    private final Set<IFeatureFlagsCallback> mCallbacks = new HashSet<>();
+
+    List<SyncableFlag> mOverrides;
+
+    @Override
+    public IBinder asBinder() {
+        return null;
+    }
+
+    @Override
+    public List<SyncableFlag> syncFlags(List<SyncableFlag> flagList) {
+        return mOverrides == null ? flagList : mOverrides;
+    }
+
+    @Override
+    public List<SyncableFlag> queryFlags(List<SyncableFlag> flagList) {
+        return mOverrides == null ? flagList : mOverrides;    }
+
+    @Override
+    public void overrideFlag(SyncableFlag syncableFlag) {
+        SyncableFlag match = findFlag(syncableFlag);
+        if (match != null) {
+            mOverrides.remove(match);
+        }
+
+        mOverrides.add(syncableFlag);
+
+        for (IFeatureFlagsCallback cb : mCallbacks) {
+            try {
+                cb.onFlagChange(syncableFlag);
+            } catch (RemoteException e) {
+                // does not happen in fakes.
+            }
+        }
+    }
+
+    @Override
+    public void resetFlag(SyncableFlag syncableFlag) {
+        SyncableFlag match = findFlag(syncableFlag);
+        if (match != null) {
+            mOverrides.remove(match);
+        }
+
+        for (IFeatureFlagsCallback cb : mCallbacks) {
+            try {
+                cb.onFlagChange(syncableFlag);
+            } catch (RemoteException e) {
+                // does not happen in fakes.
+            }
+        }
+    }
+
+    private SyncableFlag findFlag(SyncableFlag syncableFlag) {
+        SyncableFlag match = null;
+        for (SyncableFlag sf : mOverrides) {
+            if (sf.getName().equals(syncableFlag.getName())
+                    && sf.getNamespace().equals(syncableFlag.getNamespace())) {
+                match = sf;
+                break;
+            }
+        }
+
+        return match;
+    }
+    @Override
+    public void registerCallback(IFeatureFlagsCallback callback) {
+        mCallbacks.add(callback);
+    }
+
+    @Override
+    public void unregisterCallback(IFeatureFlagsCallback callback) {
+        mCallbacks.remove(callback);
+    }
+
+    public void setFlagOverrides(List<SyncableFlag> flagList) {
+        mOverrides = flagList;
+        for (SyncableFlag sf : flagList) {
+            for (IFeatureFlagsCallback cb : mCallbacks) {
+                try {
+                    cb.onFlagChange(sf);
+                } catch (RemoteException e) {
+                    // does not happen in fakes.
+                }
+            }
+        }
+    }
+}

services/Android.bp

@@ -159,6 +159,7 @@ java_library {
         "services.coverage",
         "services.credentials",
         "services.devicepolicy",
+        "services.flags",
         "services.midi",
         "services.musicsearch",
         "services.net",

services/flags/Android.bp

@@ -0,0 +1,18 @@
+package {
+    // See: http://go/android-license-faq
+    // A large-scale-change added 'default_applicable_licenses' to import
+    // all of the 'license_kinds' from "frameworks_base_license"
+    // to get the below license kinds:
+    //   SPDX-license-identifier-Apache-2.0
+    default_applicable_licenses: ["frameworks_base_license"],
+}
+
+java_library_static {
+    name: "services.flags",
+    defaults: ["platform_service_defaults"],
+    srcs: [
+        "java/**/*.java",
+        ":feature_flags_aidl",
+    ],
+    libs: ["services.core"],
+}

services/flags/OWNERS

@@ -0,0 +1,6 @@
+# Bug component: 1306523
+
+mankoff@google.com
+
+pixel@google.com
+dsandler@android.com

services/flags/java/com/android/server/flags/DynamicFlagBinderDelegate.java

@@ -0,0 +1,280 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.annotation.NonNull;
+import android.flags.IFeatureFlagsCallback;
+import android.flags.SyncableFlag;
+import android.os.Build;
+import android.os.IBinder;
+import android.os.RemoteException;
+import android.provider.DeviceConfig;
+import android.util.Slog;
+
+import com.android.internal.os.BackgroundThread;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Function;
+
+/**
+ * Handles DynamicFlags for {@link FeatureFlagsBinder}.
+ *
+ * Dynamic flags are simultaneously simpler and more complicated than process stable flags. We can
+ * return whatever value is last known for a flag is, without too much worry about the flags
+ * changing (they are dynamic after all). However, we have to alert all the relevant clients
+ * about those flag changes, and need to be able to restore to a default value if the flag gets
+ * reset/erased during runtime.
+ */
+class DynamicFlagBinderDelegate {
+
+    private final FlagOverrideStore mFlagStore;
+    private final FlagCache<DynamicFlagData> mDynamicFlags = new FlagCache<>();
+    private final Map<Integer, Set<IFeatureFlagsCallback>> mCallbacks = new HashMap<>();
+    private static final Function<Integer, Set<IFeatureFlagsCallback>> NEW_CALLBACK_SET =
+            k -> new HashSet<>();
+
+    private final DeviceConfig.OnPropertiesChangedListener mDeviceConfigListener =
+            new DeviceConfig.OnPropertiesChangedListener() {
+                @Override
+                public void onPropertiesChanged(@NonNull DeviceConfig.Properties properties) {
+                    String ns = properties.getNamespace();
+                    for (String name : properties.getKeyset()) {
+                        // Don't alert for flags we don't care about.
+                        // Don't alert for flags that have been overridden locally.
+                        if (!mDynamicFlags.contains(ns, name) || mFlagStore.contains(ns, name)) {
+                            continue;
+                        }
+                        mFlagChangeCallback.onFlagChanged(
+                                ns, name, properties.getString(name, null));
+                    }
+                }
+            };
+
+    private final FlagOverrideStore.FlagChangeCallback mFlagChangeCallback =
+            (namespace, name, value) -> {
+                // Don't bother with callbacks for non-dynamic flags.
+                if (!mDynamicFlags.contains(namespace, name)) {
+                    return;
+                }
+
+                // Don't bother with callbacks if nothing changed.
+                // Handling erasure (null) is special, as we may be restoring back to a value
+                // we were already at.
+                DynamicFlagData data = mDynamicFlags.getOrNull(namespace, name);
+                if (data == null) {
+                    return;  // shouldn't happen, but better safe than sorry.
+                }
+                if (value == null) {
+                    if (data.getValue().equals(data.getDefaultValue())) {
+                        return;
+                    }
+                    value = data.getDefaultValue();
+                } else if (data.getValue().equals(value)) {
+                    return;
+                }
+                data.setValue(value);
+
+                final Set<IFeatureFlagsCallback> cbCopy;
+                synchronized (mCallbacks) {
+                    cbCopy = new HashSet<>();
+
+                    for (Integer pid : mCallbacks.keySet()) {
+                        if (data.containsPid(pid)) {
+                            cbCopy.addAll(mCallbacks.get(pid));
+                        }
+                    }
+                }
+                SyncableFlag sFlag = new SyncableFlag(namespace, name, value, true);
+                cbCopy.forEach(cb -> {
+                    try {
+                        cb.onFlagChange(sFlag);
+                    } catch (RemoteException e) {
+                        Slog.w(
+                                FeatureFlagsService.TAG,
+                                "Failed to communicate flag change to client.");
+                    }
+                });
+            };
+
+    DynamicFlagBinderDelegate(FlagOverrideStore flagStore) {
+        mFlagStore = flagStore;
+        mFlagStore.setChangeCallback(mFlagChangeCallback);
+    }
+
+    SyncableFlag syncDynamicFlag(int pid, SyncableFlag sf) {
+        if (!sf.isDynamic()) {
+            return sf;
+        }
+
+        String ns = sf.getNamespace();
+        String name = sf.getName();
+
+        // Dynamic flags don't need any special threading or synchronization considerations.
+        // We simply give them whatever the current value is.
+        // However, we do need to keep track of dynamic flags, so that we can alert
+        // about changes coming in from adb, DeviceConfig, or other sources.
+        // And also so that we can keep flags relatively consistent across processes.
+
+        DynamicFlagData data = mDynamicFlags.getOrNull(ns, name);
+        String value = getFlagValue(ns, name, sf.getValue());
+        // DeviceConfig listeners are per-namespace.
+        if (!mDynamicFlags.containsNamespace(ns)) {
+            DeviceConfig.addOnPropertiesChangedListener(
+                    ns, BackgroundThread.getExecutor(), mDeviceConfigListener);
+        }
+        data.addClientPid(pid);
+        data.setValue(value);
+        // Store the default value so that if an override gets erased, we can restore
+        // to something.
+        data.setDefaultValue(sf.getValue());
+
+        return new SyncableFlag(sf.getNamespace(), sf.getName(), value, true);
+    }
+
+
+    void registerCallback(int pid, IFeatureFlagsCallback callback) {
+        // Always add callback so that we don't end up with a possible race/leak.
+        // We remove the callback directly if we fail to call #linkToDeath.
+        // If we tried to add the callback after we linked, then we could end up in a
+        // scenario where we link, then the binder dies, firing our BinderGriever which tries
+        // to remove the callback (which has not yet been added), then finally we add the
+        // callback, creating a leak.
+        Set<IFeatureFlagsCallback> callbacks;
+        synchronized (mCallbacks) {
+            callbacks = mCallbacks.computeIfAbsent(pid, NEW_CALLBACK_SET);
+            callbacks.add(callback);
+        }
+        try {
+            callback.asBinder().linkToDeath(new BinderGriever(pid), 0);
+        } catch (RemoteException e) {
+            Slog.e(
+                    FeatureFlagsService.TAG,
+                    "Failed to link to binder death. Callback not registered.");
+            synchronized (mCallbacks) {
+                callbacks.remove(callback);
+            }
+        }
+    }
+
+    void unregisterCallback(int pid, IFeatureFlagsCallback callback) {
+        // No need to unlink, since the BinderGriever will essentially be a no-op.
+        // We would have to track our BinderGriever's in a map otherwise.
+        synchronized (mCallbacks) {
+            Set<IFeatureFlagsCallback> callbacks =
+                    mCallbacks.computeIfAbsent(pid, NEW_CALLBACK_SET);
+            callbacks.remove(callback);
+        }
+    }
+
+    String getFlagValue(String namespace, String name, String defaultValue) {
+        // If we already have a value cached, just use that.
+        String value = null;
+        DynamicFlagData data = mDynamicFlags.getOrNull(namespace, name);
+        if (data != null) {
+            value = data.getValue();
+        } else {
+            // Put the value in the cache for future reference.
+            data = new DynamicFlagData(namespace, name);
+            mDynamicFlags.setIfChanged(namespace, name, data);
+        }
+        // If we're not in a release build, flags can be overridden locally on device.
+        if (!Build.IS_USER && value == null) {
+            value = mFlagStore.get(namespace, name);
+        }
+        // If we still don't have a value, maybe DeviceConfig does?
+        // Fallback to sf.getValue() here as well.
+        if (value == null) {
+            value = DeviceConfig.getString(namespace, name, defaultValue);
+        }
+
+        return value;
+    }
+
+    private static class DynamicFlagData {
+        private final String mNamespace;
+        private final String mName;
+        private final Set<Integer> mPids = new HashSet<>();
+        private String mValue;
+        private String mDefaultValue;
+
+        private DynamicFlagData(String namespace, String name) {
+            mNamespace = namespace;
+            mName = name;
+        }
+
+        String getValue() {
+            return mValue;
+        }
+
+        void setValue(String value) {
+            mValue = value;
+        }
+
+        String getDefaultValue() {
+            return mDefaultValue;
+        }
+
+        void setDefaultValue(String value) {
+            mDefaultValue = value;
+        }
+
+        void addClientPid(int pid) {
+            mPids.add(pid);
+        }
+
+        boolean containsPid(int pid) {
+            return mPids.contains(pid);
+        }
+
+        @Override
+        public boolean equals(Object other) {
+            if (other == null || !(other instanceof DynamicFlagData)) {
+                return false;
+            }
+
+            DynamicFlagData o = (DynamicFlagData) other;
+
+            return mName.equals(o.mName) && mNamespace.equals(o.mNamespace)
+                    && mValue.equals(o.mValue) && mDefaultValue.equals(o.mDefaultValue);
+        }
+
+        @Override
+        public int hashCode() {
+            return mName.hashCode() + mNamespace.hashCode()
+              + mValue.hashCode() + mDefaultValue.hashCode();
+        }
+    }
+
+
+    private class BinderGriever implements IBinder.DeathRecipient {
+        private final int mPid;
+
+        private BinderGriever(int pid) {
+            mPid = pid;
+        }
+
+        @Override
+        public void binderDied() {
+            synchronized (mCallbacks) {
+                mCallbacks.remove(mPid);
+            }
+        }
+    }
+}

services/flags/java/com/android/server/flags/FeatureFlagsBinder.java

@@ -0,0 +1,168 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.annotation.NonNull;
+import android.annotation.SystemApi;
+import android.flags.IFeatureFlags;
+import android.flags.IFeatureFlagsCallback;
+import android.flags.SyncableFlag;
+import android.os.Build;
+import android.os.ParcelFileDescriptor;
+
+import com.android.internal.flags.CoreFlags;
+import com.android.server.flags.FeatureFlagsService.PermissionsChecker;
+
+import java.io.FileOutputStream;
+import java.util.ArrayList;
+import java.util.List;
+
+class FeatureFlagsBinder extends IFeatureFlags.Stub {
+    private final FlagOverrideStore mFlagStore;
+    private final FlagsShellCommand mShellCommand;
+    private final FlagCache<String> mFlagCache = new FlagCache<>();
+    private final DynamicFlagBinderDelegate mDynamicFlagDelegate;
+    private final PermissionsChecker mPermissionsChecker;
+
+    FeatureFlagsBinder(
+            FlagOverrideStore flagStore,
+            FlagsShellCommand shellCommand,
+            PermissionsChecker permissionsChecker) {
+        mFlagStore = flagStore;
+        mShellCommand = shellCommand;
+        mDynamicFlagDelegate = new DynamicFlagBinderDelegate(flagStore);
+        mPermissionsChecker = permissionsChecker;
+    }
+
+    @Override
+    public void registerCallback(IFeatureFlagsCallback callback) {
+        mDynamicFlagDelegate.registerCallback(getCallingPid(), callback);
+    }
+
+    @Override
+    public void unregisterCallback(IFeatureFlagsCallback callback) {
+        mDynamicFlagDelegate.unregisterCallback(getCallingPid(), callback);
+    }
+
+    // Note: The internals of this method should be kept in sync with queryFlags
+    // as they both should return identical results. The difference is that this method
+    // caches any values it receives and/or reads, whereas queryFlags does not.
+
+    @Override
+    public List<SyncableFlag> syncFlags(List<SyncableFlag> incomingFlags) {
+        int pid = getCallingPid();
+        List<SyncableFlag> outputFlags = new ArrayList<>();
+
+        boolean hasFullSyncPrivileges = false;
+        SecurityException permissionFailureException = null;
+        try {
+            assertSyncPermission();
+            hasFullSyncPrivileges = true;
+        } catch (SecurityException e) {
+            permissionFailureException = e;
+        }
+
+        for (SyncableFlag sf : incomingFlags) {
+            if (!hasFullSyncPrivileges && !CoreFlags.isCoreFlag(sf)) {
+                throw permissionFailureException;
+            }
+
+            String ns = sf.getNamespace();
+            String name = sf.getName();
+            SyncableFlag outFlag;
+            if (sf.isDynamic()) {
+                outFlag = mDynamicFlagDelegate.syncDynamicFlag(pid, sf);
+            } else {
+                synchronized (mFlagCache) {
+                    String value = mFlagCache.getOrNull(ns, name);
+                    if (value == null) {
+                        String overrideValue = Build.IS_USER ? null : mFlagStore.get(ns, name);
+                        value = overrideValue != null ? overrideValue : sf.getValue();
+                        mFlagCache.setIfChanged(ns, name, value);
+                    }
+                    outFlag = new SyncableFlag(sf.getNamespace(), sf.getName(), value, false);
+                }
+            }
+            outputFlags.add(outFlag);
+        }
+        return outputFlags;
+    }
+
+    @Override
+    public void overrideFlag(SyncableFlag flag) {
+        assertWritePermission();
+        mFlagStore.set(flag.getNamespace(), flag.getName(), flag.getValue());
+    }
+
+    @Override
+    public void resetFlag(SyncableFlag flag) {
+        assertWritePermission();
+        mFlagStore.erase(flag.getNamespace(), flag.getName());
+    }
+
+    @Override
+    public List<SyncableFlag> queryFlags(List<SyncableFlag> incomingFlags) {
+        assertSyncPermission();
+        List<SyncableFlag> outputFlags = new ArrayList<>();
+        for (SyncableFlag sf : incomingFlags) {
+            String ns = sf.getNamespace();
+            String name = sf.getName();
+            String value;
+            String storeValue = mFlagStore.get(ns, name);
+            boolean overridden  = storeValue != null;
+
+            if (sf.isDynamic()) {
+                value = mDynamicFlagDelegate.getFlagValue(ns, name, sf.getValue());
+            } else {
+                value = mFlagCache.getOrNull(ns, name);
+                if (value == null) {
+                    value = Build.IS_USER ? null : storeValue;
+                    if (value == null) {
+                        value = sf.getValue();
+                    }
+                }
+            }
+            outputFlags.add(new SyncableFlag(
+                    sf.getNamespace(), sf.getName(), value, sf.isDynamic(), overridden));
+        }
+
+        return outputFlags;
+    }
+
+    private void assertSyncPermission() {
+        mPermissionsChecker.assertSyncPermission();
+        clearCallingIdentity();
+    }
+
+    private void assertWritePermission() {
+        mPermissionsChecker.assertWritePermission();
+        clearCallingIdentity();
+    }
+
+
+    @SystemApi
+    public int handleShellCommand(
+            @NonNull ParcelFileDescriptor in,
+            @NonNull ParcelFileDescriptor out,
+            @NonNull ParcelFileDescriptor err,
+            @NonNull String[] args) {
+        FileOutputStream fout = new FileOutputStream(out.getFileDescriptor());
+        FileOutputStream ferr = new FileOutputStream(err.getFileDescriptor());
+
+        return mShellCommand.process(args, fout, ferr);
+    }
+}

services/flags/java/com/android/server/flags/FeatureFlagsService.java

@@ -0,0 +1,113 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import static android.Manifest.permission.SYNC_FLAGS;
+import static android.Manifest.permission.WRITE_FLAGS;
+
+import android.content.Context;
+import android.content.pm.PackageManager;
+import android.flags.FeatureFlags;
+import android.util.Slog;
+
+import com.android.internal.annotations.VisibleForTesting;
+import com.android.server.SystemService;
+
+/**
+ * A service that manages syncing {@link android.flags.FeatureFlags} across processes.
+ *
+ * This service holds flags stable for at least the lifetime of a process, meaning that if
+ * a process comes online with a flag set to true, any other process that connects here and
+ * tries to read the same flag will also receive the flag as true. The flag will remain stable
+ * until either all of the interested processes have died, or the device restarts.
+ *
+ * TODO(279054964): Add to dumpsys
+ * @hide
+ */
+public class FeatureFlagsService extends SystemService {
+
+    static final String TAG = "FeatureFlagsService";
+    private final FlagOverrideStore mFlagStore;
+    private final FlagsShellCommand mShellCommand;
+
+    /**
+     * Initializes the system service.
+     *
+     * @param context The system server context.
+     */
+    public FeatureFlagsService(Context context) {
+        super(context);
+        mFlagStore = new FlagOverrideStore(
+                new GlobalSettingsProxy(context.getContentResolver()));
+        mShellCommand = new FlagsShellCommand(mFlagStore);
+    }
+
+    @Override
+    public void onStart() {
+        Slog.d(TAG, "Started Feature Flag Service");
+        FeatureFlagsBinder service = new FeatureFlagsBinder(
+                mFlagStore, mShellCommand, new PermissionsChecker(getContext()));
+        publishBinderService(
+                Context.FEATURE_FLAGS_SERVICE, service);
+        publishLocalService(FeatureFlags.class, new FeatureFlags(service));
+    }
+
+    @Override
+    public void onBootPhase(int phase) {
+        super.onBootPhase(phase);
+
+        if (phase == PHASE_SYSTEM_SERVICES_READY) {
+            // Immediately sync our core flags so that they get locked in. We don't want third-party
+            // apps to override them, and syncing immediately is the easiest way to prevent that.
+            FeatureFlags.getInstance().sync();
+        }
+    }
+
+    /**
+     * Delegate for checking flag permissions.
+     */
+    @VisibleForTesting
+    public static class PermissionsChecker {
+        private final Context mContext;
+
+        @VisibleForTesting(visibility = VisibleForTesting.Visibility.PACKAGE)
+        public PermissionsChecker(Context context) {
+            mContext = context;
+        }
+
+        /**
+         * Ensures that the caller has {@link SYNC_FLAGS} permission.
+         */
+        @VisibleForTesting(visibility = VisibleForTesting.Visibility.PACKAGE)
+        public void assertSyncPermission() {
+            if (mContext.checkCallingOrSelfPermission(SYNC_FLAGS)
+                    != PackageManager.PERMISSION_GRANTED) {
+                throw new SecurityException(
+                        "Non-core flag queried. Requires SYNC_FLAGS permission!");
+            }
+        }
+
+        /**
+         * Ensures that the caller has {@link WRITE_FLAGS} permission.
+         */
+        @VisibleForTesting(visibility = VisibleForTesting.Visibility.PACKAGE)
+        public void assertWritePermission() {
+            if (mContext.checkCallingPermission(WRITE_FLAGS) != PackageManager.PERMISSION_GRANTED) {
+                throw new SecurityException("Requires WRITE_FLAGS permission!");
+            }
+        }
+    }
+}

services/flags/java/com/android/server/flags/FlagCache.java

@@ -0,0 +1,103 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.function.Function;
+
+/**
+ * Threadsafe cache of values that stores the supplied default on cache miss.
+ *
+ * @param <V> The type of value to store.
+ */
+public class FlagCache<V> {
+    private final Function<String, HashMap<String, V>> mNewHashMap = k -> new HashMap<>();
+
+    // Cache is organized first by namespace, then by name. All values are stored as strings.
+    final Map<String, Map<String, V>> mCache = new HashMap<>();
+
+    FlagCache() {
+    }
+
+    /**
+     * Returns true if the namespace exists in the cache already.
+     */
+    boolean containsNamespace(String namespace) {
+        synchronized (mCache) {
+            return mCache.containsKey(namespace);
+        }
+    }
+
+    /**
+     * Returns true if the value is stored in the cache.
+     */
+    boolean contains(String namespace, String name) {
+        synchronized (mCache) {
+            Map<String, V> nsCache = mCache.get(namespace);
+            return nsCache != null && nsCache.containsKey(name);
+        }
+    }
+
+    /**
+     * Sets the value if it is different from what is currently stored.
+     *
+     * If the value is not set, or the current value is null, it will store the value and
+     * return true.
+     *
+     * @return True if the value was set. False if the value is the same.
+     */
+    boolean setIfChanged(String namespace, String name, V value) {
+        synchronized (mCache) {
+            Map<String, V> nsCache = mCache.computeIfAbsent(namespace, mNewHashMap);
+            V curValue = nsCache.get(name);
+            if (curValue == null || !curValue.equals(value)) {
+                nsCache.put(name, value);
+                return true;
+            }
+            return false;
+        }
+    }
+
+    /**
+     * Gets the current value from the cache, setting it if it is currently absent.
+     *
+     * @return The value that is now in the cache after the call to the method.
+     */
+    V getOrSet(String namespace, String name, V defaultValue) {
+        synchronized (mCache) {
+            Map<String, V> nsCache = mCache.computeIfAbsent(namespace, mNewHashMap);
+            V value = nsCache.putIfAbsent(name, defaultValue);
+            return value == null ? defaultValue : value;
+        }
+    }
+
+    /**
+     * Gets the current value from the cache, returning null if not present.
+     *
+     * @return The value that is now in the cache if there is one.
+     */
+    V getOrNull(String namespace, String name) {
+        synchronized (mCache) {
+            Map<String, V> nsCache = mCache.get(namespace);
+            if (nsCache == null) {
+                return null;
+            }
+            return nsCache.get(name);
+        }
+    }
+}

services/flags/java/com/android/server/flags/FlagOverrideStore.java

@@ -0,0 +1,122 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.database.Cursor;
+import android.provider.Settings;
+
+import com.android.internal.annotations.VisibleForTesting;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Persistent storage for the {@link FeatureFlagsService}.
+ *
+ * The implementation stores data in Settings.<store> (generally {@link Settings.Global}
+ * is expected).
+ */
+@VisibleForTesting(visibility = VisibleForTesting.Visibility.PACKAGE)
+public class FlagOverrideStore {
+    private static final String KEYNAME_PREFIX = "flag|";
+    private static final String NAMESPACE_NAME_SEPARATOR = ".";
+
+    private final SettingsProxy mSettingsProxy;
+
+    private FlagChangeCallback mCallback;
+
+    FlagOverrideStore(SettingsProxy settingsProxy) {
+        mSettingsProxy = settingsProxy;
+    }
+
+    void setChangeCallback(FlagChangeCallback callback) {
+        mCallback = callback;
+    }
+
+    /** Returns true if a non-null value is in the store. */
+    boolean contains(String namespace, String name) {
+        return get(namespace, name) != null;
+    }
+
+    /** Put a value in the store. */
+    @VisibleForTesting
+    public void set(String namespace, String name, String value) {
+        mSettingsProxy.putString(getPropName(namespace, name), value);
+        mCallback.onFlagChanged(namespace, name, value);
+    }
+
+    /** Read a value out of the store. */
+    @VisibleForTesting
+    public String get(String namespace, String name) {
+        return mSettingsProxy.getString(getPropName(namespace, name));
+    }
+
+    /** Erase a value from the store. */
+    @VisibleForTesting
+    public void erase(String namespace, String name) {
+        set(namespace, name, null);
+    }
+
+    Map<String, Map<String, String>> getFlags() {
+        return getFlagsForNamespace(null);
+    }
+
+    Map<String, Map<String, String>> getFlagsForNamespace(String namespace) {
+        Cursor c = mSettingsProxy.getContentResolver().query(
+                Settings.Global.CONTENT_URI,
+                new String[]{Settings.NameValueTable.NAME, Settings.NameValueTable.VALUE},
+                null, // Doesn't support a "LIKE" query
+                null,
+                null
+        );
+
+        if (c == null) {
+            return Map.of();
+        }
+        int keynamePrefixLength = KEYNAME_PREFIX.length();
+        Map<String, Map<String, String>> results = new HashMap<>();
+        while (c.moveToNext()) {
+            String key = c.getString(0);
+            if (!key.startsWith(KEYNAME_PREFIX)
+                    || key.indexOf(NAMESPACE_NAME_SEPARATOR, keynamePrefixLength) < 0) {
+                continue;
+            }
+            String value = c.getString(1);
+            if (value == null || value.isEmpty()) {
+                continue;
+            }
+            String ns = key.substring(keynamePrefixLength, key.indexOf(NAMESPACE_NAME_SEPARATOR));
+            if (namespace != null && !namespace.equals(ns)) {
+                continue;
+            }
+            String name = key.substring(key.indexOf(NAMESPACE_NAME_SEPARATOR) + 1);
+            results.putIfAbsent(ns, new HashMap<>());
+            results.get(ns).put(name, value);
+        }
+        c.close();
+        return results;
+    }
+
+    @VisibleForTesting(visibility = VisibleForTesting.Visibility.PRIVATE)
+    static String getPropName(String namespace, String name) {
+        return KEYNAME_PREFIX + namespace + NAMESPACE_NAME_SEPARATOR + name;
+    }
+
+    interface FlagChangeCallback {
+        void onFlagChanged(String namespace, String name, String value);
+    }
+}

services/flags/java/com/android/server/flags/FlagsShellCommand.java

@@ -0,0 +1,214 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import com.android.internal.annotations.VisibleForTesting;
+import com.android.internal.util.FastPrintWriter;
+
+import java.io.OutputStream;
+import java.io.PrintWriter;
+import java.util.Locale;
+import java.util.Map;
+
+/**
+ * Process command line input for the flags service.
+ */
+@VisibleForTesting(visibility = VisibleForTesting.Visibility.PACKAGE)
+public class FlagsShellCommand {
+    private final FlagOverrideStore mFlagStore;
+
+    FlagsShellCommand(FlagOverrideStore flagStore) {
+        mFlagStore = flagStore;
+    }
+
+    /**
+     * Interpret the command supplied in the constructor.
+     *
+     * @return Zero on success or non-zero on error.
+     */
+    public int process(
+            String[] args,
+            OutputStream out,
+            OutputStream err) {
+        PrintWriter outPw = new FastPrintWriter(out);
+        PrintWriter errPw = new FastPrintWriter(err);
+
+        if (args.length == 0) {
+            return printHelp(outPw);
+        }
+        switch (args[0].toLowerCase(Locale.ROOT)) {
+            case "help":
+                return printHelp(outPw);
+            case "list":
+                return listCmd(args, outPw, errPw);
+            case "set":
+                return setCmd(args, outPw, errPw);
+            case "get":
+                return getCmd(args, outPw, errPw);
+            case "erase":
+                return eraseCmd(args, outPw, errPw);
+            default:
+                return unknownCmd(outPw);
+        }
+    }
+
+    private int printHelp(PrintWriter outPw) {
+        outPw.println("Feature Flags command, allowing listing, setting, getting, and erasing of");
+        outPw.println("local flag overrides on a device.");
+        outPw.println();
+        outPw.println("Commands:");
+        outPw.println("  list [namespace]");
+        outPw.println("    List all flag overrides. Namespace is optional.");
+        outPw.println();
+        outPw.println("  get <namespace> <name>");
+        outPw.println("    Return the string value of a specific flag, or <unset>");
+        outPw.println();
+        outPw.println("  set <namespace> <name> <value>");
+        outPw.println("    Set a specific flag");
+        outPw.println();
+        outPw.println("  erase <namespace> <name>");
+        outPw.println("    Unset a specific flag");
+        outPw.flush();
+        return 0;
+    }
+
+    private int listCmd(String[] args, PrintWriter outPw, PrintWriter errPw) {
+        if (!validateNumArguments(args, 0, 1, args[0], errPw)) {
+            errPw.println("Expected `" + args[0] + " [namespace]`");
+            errPw.flush();
+            return -1;
+        }
+        Map<String, Map<String, String>> overrides;
+        if (args.length == 2) {
+            overrides = mFlagStore.getFlagsForNamespace(args[1]);
+        } else {
+            overrides = mFlagStore.getFlags();
+        }
+        if (overrides.isEmpty()) {
+            outPw.println("No overrides set");
+        } else {
+            int longestNamespaceLen = "namespace".length();
+            int longestFlagLen = "flag".length();
+            int longestValLen = "value".length();
+            for (Map.Entry<String, Map<String, String>> namespace : overrides.entrySet()) {
+                longestNamespaceLen = Math.max(longestNamespaceLen, namespace.getKey().length());
+                for (Map.Entry<String, String> flag : namespace.getValue().entrySet()) {
+                    longestFlagLen = Math.max(longestFlagLen, flag.getKey().length());
+                    longestValLen = Math.max(longestValLen, flag.getValue().length());
+                }
+            }
+            outPw.print(String.format("%-" + longestNamespaceLen + "s", "namespace"));
+            outPw.print(' ');
+            outPw.print(String.format("%-" + longestFlagLen + "s", "flag"));
+            outPw.print(' ');
+            outPw.println("value");
+            for (int i = 0; i < longestNamespaceLen; i++) {
+                outPw.print('=');
+            }
+            outPw.print(' ');
+            for (int i = 0; i < longestFlagLen; i++) {
+                outPw.print('=');
+            }
+            outPw.print(' ');
+            for (int i = 0; i < longestValLen; i++) {
+                outPw.print('=');
+            }
+            outPw.println();
+            for (Map.Entry<String, Map<String, String>> namespace : overrides.entrySet()) {
+                for (Map.Entry<String, String> flag : namespace.getValue().entrySet()) {
+                    outPw.print(
+                            String.format("%-" + longestNamespaceLen + "s", namespace.getKey()));
+                    outPw.print(' ');
+                    outPw.print(String.format("%-" + longestFlagLen + "s", flag.getKey()));
+                    outPw.print(' ');
+                    outPw.println(flag.getValue());
+                }
+            }
+        }
+        outPw.flush();
+        return 0;
+    }
+
+    private int setCmd(String[] args, PrintWriter outPw, PrintWriter errPw) {
+        if (!validateNumArguments(args, 3, args[0], errPw)) {
+            errPw.println("Expected `" + args[0] + " <namespace> <name> <value>`");
+            errPw.flush();
+            return -1;
+        }
+        mFlagStore.set(args[1], args[2], args[3]);
+        outPw.println("Flag " + args[1] + "." + args[2] + " is now " + args[3]);
+        outPw.flush();
+        return 0;
+    }
+
+    private int getCmd(String[] args, PrintWriter outPw, PrintWriter errPw) {
+        if (!validateNumArguments(args, 2, args[0], errPw)) {
+            errPw.println("Expected `" + args[0] + " <namespace> <name>`");
+            errPw.flush();
+            return -1;
+        }
+
+        String value = mFlagStore.get(args[1], args[2]);
+        outPw.print(args[1] + "." + args[2] + " is ");
+        if (value == null || value.isEmpty()) {
+            outPw.println("<unset>");
+        } else {
+            outPw.println("\"" + value.translateEscapes() + "\"");
+        }
+        outPw.flush();
+        return 0;
+    }
+
+    private int eraseCmd(String[] args, PrintWriter outPw, PrintWriter errPw) {
+        if (!validateNumArguments(args, 2, args[0], errPw)) {
+            errPw.println("Expected `" + args[0] + " <namespace> <name>`");
+            errPw.flush();
+            return -1;
+        }
+        mFlagStore.erase(args[1], args[2]);
+        outPw.println("Erased " + args[1] + "." + args[2]);
+        return 0;
+    }
+
+    private int unknownCmd(PrintWriter outPw) {
+        outPw.println("This command is unknown.");
+        printHelp(outPw);
+        outPw.flush();
+        return -1;
+    }
+
+    private boolean validateNumArguments(
+            String[] args, int exactly, String cmdName, PrintWriter errPw) {
+        return validateNumArguments(args, exactly, exactly, cmdName, errPw);
+    }
+
+    private boolean validateNumArguments(
+            String[] args, int min, int max, String cmdName, PrintWriter errPw) {
+        int len = args.length - 1; // Discount the command itself.
+        if (len < min) {
+            errPw.println(
+                    "Less than " + min + " arguments provided for \"" + cmdName + "\" command.");
+            return false;
+        } else if (len > max) {
+            errPw.println(
+                    "More than " + max + " arguments provided for \"" + cmdName + "\" command.");
+            return false;
+        }
+
+        return true;
+    }
+}

services/flags/java/com/android/server/flags/GlobalSettingsProxy.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.content.ContentResolver;
+import android.net.Uri;
+import android.provider.Settings;
+
+class GlobalSettingsProxy implements SettingsProxy {
+    private final ContentResolver mContentResolver;
+
+    GlobalSettingsProxy(ContentResolver contentResolver) {
+        mContentResolver = contentResolver;
+    }
+
+    @Override
+    public ContentResolver getContentResolver() {
+        return mContentResolver;
+    }
+
+    @Override
+    public Uri getUriFor(String name) {
+        return Settings.Global.getUriFor(name);
+    }
+
+    @Override
+    public String getStringForUser(String name, int userHandle) {
+        return Settings.Global.getStringForUser(mContentResolver, name, userHandle);
+    }
+
+    @Override
+    public boolean putString(String name, String value, boolean overrideableByRestore) {
+        throw new UnsupportedOperationException(
+                "This method only exists publicly for Settings.System and Settings.Secure");
+    }
+
+    @Override
+    public boolean putStringForUser(String name, String value, int userHandle) {
+        return Settings.Global.putStringForUser(mContentResolver, name, value, userHandle);
+    }
+
+    @Override
+    public boolean putStringForUser(String name, String value, String tag, boolean makeDefault,
+            int userHandle, boolean overrideableByRestore) {
+        return Settings.Global.putStringForUser(
+                mContentResolver, name, value, tag, makeDefault, userHandle,
+                overrideableByRestore);
+    }
+
+    @Override
+    public boolean putString(String name, String value, String tag, boolean makeDefault) {
+        return Settings.Global.putString(mContentResolver, name, value, tag, makeDefault);
+    }
+}

services/flags/java/com/android/server/flags/SettingsProxy.java

@@ -0,0 +1,381 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+import android.annotation.UserIdInt;
+import android.content.ContentResolver;
+import android.database.ContentObserver;
+import android.net.Uri;
+import android.provider.Settings;
+
+/**
+ * Wrapper class meant to enable hermetic testing of {@link Settings}.
+ *
+ * Implementations of this class are expected to be constructed with a {@link ContentResolver} or,
+ * otherwise have access to an implicit one. All the proxy methods in this class exclude
+ * {@link ContentResolver} from their signature and rely on an internally defined one instead.
+ *
+ * Most methods in the {@link Settings} classes have default implementations defined.
+ * Implementations of this interfac need only concern themselves with getting and putting Strings.
+ * They should also override any methods for a class they are proxying that _are not_ defined, and
+ * throw an appropriate {@link UnsupportedOperationException}. For instance, {@link Settings.Global}
+ * does not define {@link #putString(String, String, boolean)}, so an implementation of this
+ * interface that proxies through to it should throw an exception when that method is called.
+ *
+ * This class adds in the following helpers as well:
+ *  - {@link #getBool(String)}
+ *  - {@link #putBool(String, boolean)}
+ *  - {@link #registerContentObserver(Uri, ContentObserver)}
+ *
+ * ... and similar variations for all of those.
+ */
+public interface SettingsProxy {
+
+    /**
+     * Returns the {@link ContentResolver} this instance uses.
+     */
+    ContentResolver getContentResolver();
+
+    /**
+     * Construct the content URI for a particular name/value pair,
+     * useful for monitoring changes with a ContentObserver.
+     * @param name to look up in the table
+     * @return the corresponding content URI, or null if not present
+     */
+    Uri getUriFor(String name);
+
+    /**See {@link Settings.Secure#getString(ContentResolver, String)} */
+    String getStringForUser(String name, int userHandle);
+
+    /**See {@link Settings.Secure#putString(ContentResolver, String, String, boolean)} */
+    boolean putString(String name, String value, boolean overrideableByRestore);
+
+    /** See {@link Settings.Secure#putStringForUser(ContentResolver, String, String, int)} */
+    boolean putStringForUser(String name, String value, int userHandle);
+
+    /**
+     * See {@link Settings.Secure#putStringForUser(ContentResolver, String, String, String, boolean,
+     * int, boolean)}
+     */
+    boolean putStringForUser(@NonNull String name, @Nullable String value, @Nullable String tag,
+            boolean makeDefault, @UserIdInt int userHandle, boolean overrideableByRestore);
+
+    /** See {@link Settings.Secure#putString(ContentResolver, String, String, String, boolean)} */
+    boolean putString(@NonNull String name, @Nullable String value, @Nullable String tag,
+            boolean makeDefault);
+
+    /**
+     * Returns the user id for the associated {@link ContentResolver}.
+     */
+    default int getUserId() {
+        return getContentResolver().getUserId();
+    }
+
+    /** See {@link Settings.Secure#getString(ContentResolver, String)} */
+    default String getString(String name) {
+        return getStringForUser(name, getUserId());
+    }
+
+    /** See {@link Settings.Secure#putString(ContentResolver, String, String)} */
+    default boolean putString(String name, String value) {
+        return putStringForUser(name, value, getUserId());
+    }
+    /** See {@link Settings.Secure#getIntForUser(ContentResolver, String, int, int)} */
+    default int getIntForUser(String name, int def, int userHandle) {
+        String v = getStringForUser(name, userHandle);
+        try {
+            return v != null ? Integer.parseInt(v) : def;
+        } catch (NumberFormatException e) {
+            return def;
+        }
+    }
+
+    /** See {@link Settings.Secure#getInt(ContentResolver, String)}  */
+    default int getInt(String name) throws Settings.SettingNotFoundException {
+        return getIntForUser(name, getUserId());
+    }
+
+    /** See {@link Settings.Secure#getIntForUser(ContentResolver, String, int)} */
+    default int getIntForUser(String name, int userHandle)
+            throws Settings.SettingNotFoundException {
+        String v = getStringForUser(name, userHandle);
+        try {
+            return Integer.parseInt(v);
+        } catch (NumberFormatException e) {
+            throw new Settings.SettingNotFoundException(name);
+        }
+    }
+
+    /** See {@link Settings.Secure#putInt(ContentResolver, String, int)} */
+    default boolean putInt(String name, int value) {
+        return putIntForUser(name, value, getUserId());
+    }
+
+    /** See {@link Settings.Secure#putIntForUser(ContentResolver, String, int, int)} */
+    default boolean putIntForUser(String name, int value, int userHandle) {
+        return putStringForUser(name, Integer.toString(value), userHandle);
+    }
+
+    /**
+     * Convenience function for retrieving a single settings value
+     * as a boolean.  Note that internally setting values are always
+     * stored as strings; this function converts the string to a boolean
+     * for you. The default value will be returned if the setting is
+     * not defined or not a boolean.
+     *
+     * @param name The name of the setting to retrieve.
+     * @param def Value to return if the setting is not defined.
+     *
+     * @return The setting's current value, or 'def' if it is not defined
+     * or not a valid boolean.
+     */
+    default boolean getBool(String name, boolean def) {
+        return getBoolForUser(name, def, getUserId());
+    }
+
+    /** See {@link #getBool(String, boolean)}. */
+    default boolean getBoolForUser(String name, boolean def, int userHandle) {
+        return getIntForUser(name, def ? 1 : 0, userHandle) != 0;
+    }
+
+    /**
+     * Convenience function for retrieving a single settings value
+     * as a boolean.  Note that internally setting values are always
+     * stored as strings; this function converts the string to a boolean
+     * for you.
+     * <p>
+     * This version does not take a default value.  If the setting has not
+     * been set, or the string value is not a number,
+     * it throws {@link Settings.SettingNotFoundException}.
+     *
+     * @param name The name of the setting to retrieve.
+     *
+     * @throws Settings.SettingNotFoundException Thrown if a setting by the given
+     * name can't be found or the setting value is not a boolean.
+     *
+     * @return The setting's current value.
+     */
+    default boolean getBool(String name) throws Settings.SettingNotFoundException {
+        return getBoolForUser(name, getUserId());
+    }
+
+    /** See {@link #getBool(String)}. */
+    default boolean getBoolForUser(String name, int userHandle)
+            throws Settings.SettingNotFoundException {
+        return getIntForUser(name, userHandle) != 0;
+    }
+
+    /**
+     * Convenience function for updating a single settings value as a
+     * boolean. This will either create a new entry in the table if the
+     * given name does not exist, or modify the value of the existing row
+     * with that name.  Note that internally setting values are always
+     * stored as strings, so this function converts the given value to a
+     * string before storing it.
+     *
+     * @param name The name of the setting to modify.
+     * @param value The new value for the setting.
+     * @return true if the value was set, false on database errors
+     */
+    default boolean putBool(String name, boolean value) {
+        return putBoolForUser(name, value, getUserId());
+    }
+
+    /** See {@link #putBool(String, boolean)}. */
+    default boolean putBoolForUser(String name, boolean value, int userHandle) {
+        return putIntForUser(name, value ? 1 : 0, userHandle);
+    }
+
+    /** See {@link Settings.Secure#getLong(ContentResolver, String, long)}  */
+    default long getLong(String name, long def) {
+        return getLongForUser(name, def, getUserId());
+    }
+
+    /** See {@link Settings.Secure#getLongForUser(ContentResolver, String, long, int)}  */
+    default long getLongForUser(String name, long def, int userHandle) {
+        String valString = getStringForUser(name, userHandle);
+        long value;
+        try {
+            value = valString != null ? Long.parseLong(valString) : def;
+        } catch (NumberFormatException e) {
+            value = def;
+        }
+        return value;
+    }
+
+    /** See {@link Settings.Secure#getLong(ContentResolver, String)}  */
+    default long getLong(String name) throws Settings.SettingNotFoundException {
+        return getLongForUser(name, getUserId());
+    }
+
+    /** See {@link Settings.Secure#getLongForUser(ContentResolver, String, int)}  */
+    default long getLongForUser(String name, int userHandle)
+            throws Settings.SettingNotFoundException {
+        String valString = getStringForUser(name, userHandle);
+        try {
+            return Long.parseLong(valString);
+        } catch (NumberFormatException e) {
+            throw new Settings.SettingNotFoundException(name);
+        }
+    }
+
+    /** See {@link Settings.Secure#putLong(ContentResolver, String, long)} */
+    default boolean putLong(String name, long value) {
+        return putLongForUser(name, value, getUserId());
+    }
+
+    /** See {@link Settings.Secure#putLongForUser(ContentResolver, String, long, int)}  */
+    default boolean putLongForUser(String name, long value, int userHandle) {
+        return putStringForUser(name, Long.toString(value), userHandle);
+    }
+
+    /** See {@link Settings.Secure#getFloat(ContentResolver, String, float)} */
+    default float getFloat(String name, float def) {
+        return getFloatForUser(name, def, getUserId());
+    }
+
+    /** See {@link Settings.Secure#getFloatForUser(ContentResolver, String, int)} */
+    default float getFloatForUser(String name, float def, int userHandle) {
+        String v = getStringForUser(name, userHandle);
+        try {
+            return v != null ? Float.parseFloat(v) : def;
+        } catch (NumberFormatException e) {
+            return def;
+        }
+    }
+
+
+    /** See {@link Settings.Secure#getFloat(ContentResolver, String)}  */
+    default float getFloat(String name) throws Settings.SettingNotFoundException {
+        return getFloatForUser(name, getUserId());
+    }
+
+    /** See {@link Settings.Secure#getFloatForUser(ContentResolver, String, int)}   */
+    default float getFloatForUser(String name, int userHandle)
+            throws Settings.SettingNotFoundException {
+        String v = getStringForUser(name, userHandle);
+        if (v == null) {
+            throw new Settings.SettingNotFoundException(name);
+        }
+        try {
+            return Float.parseFloat(v);
+        } catch (NumberFormatException e) {
+            throw new Settings.SettingNotFoundException(name);
+        }
+    }
+
+    /** See {@link Settings.Secure#putFloat(ContentResolver, String, float)} */
+    default boolean putFloat(String name, float value) {
+        return putFloatForUser(name, value, getUserId());
+    }
+
+    /** See {@link Settings.Secure#putFloatForUser(ContentResolver, String, float, int)} */
+    default boolean putFloatForUser(String name, float value, int userHandle) {
+        return putStringForUser(name, Float.toString(value), userHandle);
+    }
+
+    /**
+     * Convenience wrapper around
+     * {@link ContentResolver#registerContentObserver(Uri, boolean, ContentObserver)}.'
+     *
+     * Implicitly calls {@link #getUriFor(String)} on the passed in name.
+     */
+    default void registerContentObserver(String name, ContentObserver settingsObserver) {
+        registerContentObserver(getUriFor(name), settingsObserver);
+    }
+
+    /**
+     * Convenience wrapper around
+     * {@link ContentResolver#registerContentObserver(Uri, boolean, ContentObserver)}.'
+     */
+    default void registerContentObserver(Uri uri, ContentObserver settingsObserver) {
+        registerContentObserverForUser(uri, settingsObserver, getUserId());
+    }
+
+    /**
+     * Convenience wrapper around
+     * {@link ContentResolver#registerContentObserver(Uri, boolean, ContentObserver)}.
+     *
+     * Implicitly calls {@link #getUriFor(String)} on the passed in name.
+     */
+    default void registerContentObserver(String name, boolean notifyForDescendants,
+            ContentObserver settingsObserver) {
+        registerContentObserver(getUriFor(name), notifyForDescendants, settingsObserver);
+    }
+
+    /**
+     * Convenience wrapper around
+     * {@link ContentResolver#registerContentObserver(Uri, boolean, ContentObserver)}.'
+     */
+    default void registerContentObserver(Uri uri, boolean notifyForDescendants,
+            ContentObserver settingsObserver) {
+        registerContentObserverForUser(uri, notifyForDescendants, settingsObserver, getUserId());
+    }
+
+    /**
+     * Convenience wrapper around
+     * {@link ContentResolver#registerContentObserver(Uri, boolean, ContentObserver, int)}
+     *
+     * Implicitly calls {@link #getUriFor(String)} on the passed in name.
+     */
+    default void registerContentObserverForUser(
+            String name, ContentObserver settingsObserver, int userHandle) {
+        registerContentObserverForUser(
+                getUriFor(name), settingsObserver, userHandle);
+    }
+
+    /**
+     * Convenience wrapper around
+     * {@link ContentResolver#registerContentObserver(Uri, boolean, ContentObserver, int)}
+     */
+    default void registerContentObserverForUser(
+            Uri uri, ContentObserver settingsObserver, int userHandle) {
+        registerContentObserverForUser(
+                uri, false, settingsObserver, userHandle);
+    }
+
+    /**
+     * Convenience wrapper around
+     * {@link ContentResolver#registerContentObserver(Uri, boolean, ContentObserver, int)}
+     *
+     * Implicitly calls {@link #getUriFor(String)} on the passed in name.
+     */
+    default void registerContentObserverForUser(
+            String name, boolean notifyForDescendants, ContentObserver settingsObserver,
+            int userHandle) {
+        registerContentObserverForUser(
+                getUriFor(name), notifyForDescendants, settingsObserver, userHandle);
+    }
+
+    /**
+     * Convenience wrapper around
+     * {@link ContentResolver#registerContentObserver(Uri, boolean, ContentObserver, int)}
+     */
+    default void registerContentObserverForUser(
+            Uri uri, boolean notifyForDescendants, ContentObserver settingsObserver,
+            int userHandle) {
+        getContentResolver().registerContentObserver(
+                uri, notifyForDescendants, settingsObserver, userHandle);
+    }
+
+    /** See {@link ContentResolver#unregisterContentObserver(ContentObserver)}. */
+    default void unregisterContentObserver(ContentObserver settingsObserver) {
+        getContentResolver().unregisterContentObserver(settingsObserver);
+    }
+}

services/java/com/android/server/SystemServer.java

@@ -132,6 +132,7 @@ import com.android.server.display.DisplayManagerService;
 import com.android.server.display.color.ColorDisplayService;
 import com.android.server.dreams.DreamManagerService;
 import com.android.server.emergency.EmergencyAffordanceService;
+import com.android.server.flags.FeatureFlagsService;
 import com.android.server.gpu.GpuService;
 import com.android.server.grammaticalinflection.GrammaticalInflectionService;
 import com.android.server.graphics.fonts.FontManagerService;
@@ -1111,6 +1112,12 @@ public final class SystemServer implements Dumpable {
         mSystemServiceManager.startService(DeviceIdentifiersPolicyService.class);
         t.traceEnd();
 
+        // Starts a service for reading runtime flag overrides, and keeping processes
+        // in sync with one another.
+        t.traceBegin("StartFeatureFlagsService");
+        mSystemServiceManager.startService(FeatureFlagsService.class);
+        t.traceEnd();
+
         // Uri Grants Manager.
         t.traceBegin("UriGrantsManagerService");
         mSystemServiceManager.startService(UriGrantsManagerService.Lifecycle.class);

services/tests/servicestests/Android.bp

@@ -34,6 +34,7 @@ android_test {
         "services.core",
         "services.credentials",
         "services.devicepolicy",
+        "services.flags",
         "services.net",
         "services.people",
         "services.usage",

services/tests/servicestests/src/com/android/server/flags/FeatureFlagsServiceTest.java

@@ -0,0 +1,293 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import static com.google.common.truth.Truth.assertThat;
+import static com.google.common.truth.Truth.assertWithMessage;
+
+import static org.junit.Assert.fail;
+import static org.mockito.Mockito.any;
+import static org.mockito.Mockito.doThrow;
+import static org.mockito.Mockito.eq;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import android.flags.IFeatureFlagsCallback;
+import android.flags.SyncableFlag;
+import android.os.IBinder;
+import android.os.RemoteException;
+import android.platform.test.annotations.Presubmit;
+
+import androidx.test.filters.SmallTest;
+
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.mockito.Mock;
+import org.mockito.junit.MockitoJUnit;
+import org.mockito.junit.MockitoRule;
+
+import java.util.List;
+
+@Presubmit
+@SmallTest
+public class FeatureFlagsServiceTest {
+    private static final String NS = "ns";
+    private static final String NAME = "name";
+    private static final String PROP_NAME = FlagOverrideStore.getPropName(NS, NAME);
+
+    @Rule
+    public final MockitoRule mockito = MockitoJUnit.rule();
+
+    @Mock
+    private FlagOverrideStore mFlagStore;
+    @Mock
+    private FlagsShellCommand mFlagCommand;
+    @Mock
+    private IFeatureFlagsCallback mIFeatureFlagsCallback;
+    @Mock
+    private IBinder mIFeatureFlagsCallbackAsBinder;
+    @Mock
+    private FeatureFlagsService.PermissionsChecker mPermissionsChecker;
+
+    private FeatureFlagsBinder mFeatureFlagsService;
+
+    @Before
+    public void setup() {
+        when(mIFeatureFlagsCallback.asBinder()).thenReturn(mIFeatureFlagsCallbackAsBinder);
+        mFeatureFlagsService = new FeatureFlagsBinder(
+                mFlagStore, mFlagCommand, mPermissionsChecker);
+    }
+
+    @Test
+    public void testRegisterCallback() {
+        mFeatureFlagsService.registerCallback(mIFeatureFlagsCallback);
+        try {
+            verify(mIFeatureFlagsCallbackAsBinder).linkToDeath(any(), eq(0));
+        } catch (RemoteException e) {
+            fail("Our mock threw a Remote Exception?");
+        }
+    }
+
+    @Test
+    public void testOverrideFlag_requiresWritePermission() {
+        SecurityException exc = new SecurityException("not allowed");
+        doThrow(exc).when(mPermissionsChecker).assertWritePermission();
+
+        SyncableFlag f = new SyncableFlag(NS, "a", "false", false);
+
+        try {
+            mFeatureFlagsService.overrideFlag(f);
+            fail("Should have thrown exception");
+        } catch (SecurityException e) {
+            assertThat(exc).isEqualTo(e);
+        } catch (Exception e) {
+            fail("should have thrown a security exception");
+        }
+    }
+
+    @Test
+    public void testResetFlag_requiresWritePermission() {
+        SecurityException exc = new SecurityException("not allowed");
+        doThrow(exc).when(mPermissionsChecker).assertWritePermission();
+
+        SyncableFlag f = new SyncableFlag(NS, "a", "false", false);
+
+        try {
+            mFeatureFlagsService.resetFlag(f);
+            fail("Should have thrown exception");
+        } catch (SecurityException e) {
+            assertThat(exc).isEqualTo(e);
+        } catch (Exception e) {
+            fail("should have thrown a security exception");
+        }
+    }
+
+    @Test
+    public void testSyncFlags_noOverrides() {
+        List<SyncableFlag> inputFlags = List.of(
+                new SyncableFlag(NS, "a", "false", false),
+                new SyncableFlag(NS, "b", "true", false),
+                new SyncableFlag(NS, "c", "false", false)
+        );
+
+        List<SyncableFlag> outputFlags = mFeatureFlagsService.syncFlags(inputFlags);
+
+        assertThat(inputFlags.size()).isEqualTo(outputFlags.size());
+
+        for (SyncableFlag inpF: inputFlags) {
+            boolean found = false;
+            for (SyncableFlag outF : outputFlags) {
+                if (compareSyncableFlagsNames(inpF, outF)) {
+                    found = true;
+                    break;
+                }
+            }
+            assertWithMessage("Failed to find input flag " + inpF + " in the output")
+                    .that(found).isTrue();
+        }
+    }
+
+    @Test
+    public void testSyncFlags_withSomeOverrides() {
+        List<SyncableFlag> inputFlags = List.of(
+                new SyncableFlag(NS, "a", "false", false),
+                new SyncableFlag(NS, "b", "true", false),
+                new SyncableFlag(NS, "c", "false", false)
+        );
+
+        assertThat(mFlagStore).isNotNull();
+        when(mFlagStore.get(NS, "c")).thenReturn("true");
+        List<SyncableFlag> outputFlags = mFeatureFlagsService.syncFlags(inputFlags);
+
+        assertThat(inputFlags.size()).isEqualTo(outputFlags.size());
+
+        for (SyncableFlag inpF: inputFlags) {
+            boolean found = false;
+            for (SyncableFlag outF : outputFlags) {
+                if (compareSyncableFlagsNames(inpF, outF)) {
+                    found = true;
+
+                    // Once we've found "c", do an extra check
+                    if (outF.getName().equals("c")) {
+                        assertWithMessage("Flag " + outF + "was not returned with an override")
+                                .that(outF.getValue()).isEqualTo("true");
+                    }
+                    break;
+                }
+            }
+            assertWithMessage("Failed to find input flag " + inpF + " in the output")
+                    .that(found).isTrue();
+        }
+    }
+
+    @Test
+    public void testSyncFlags_twoCallsWithDifferentDefaults() {
+        List<SyncableFlag> inputFlagsFirst = List.of(
+                new SyncableFlag(NS, "a", "false", false)
+        );
+        List<SyncableFlag> inputFlagsSecond = List.of(
+                new SyncableFlag(NS, "a", "true", false),
+                new SyncableFlag(NS, "b", "false", false)
+        );
+
+        List<SyncableFlag> outputFlagsFirst = mFeatureFlagsService.syncFlags(inputFlagsFirst);
+        List<SyncableFlag> outputFlagsSecond = mFeatureFlagsService.syncFlags(inputFlagsSecond);
+
+        assertThat(inputFlagsFirst.size()).isEqualTo(outputFlagsFirst.size());
+        assertThat(inputFlagsSecond.size()).isEqualTo(outputFlagsSecond.size());
+
+        // This test only cares that the "a" flag passed in the second time came out with the
+        // same value that was passed in the first time.
+
+        boolean found = false;
+        for (SyncableFlag second : outputFlagsSecond) {
+            if (compareSyncableFlagsNames(second, inputFlagsFirst.get(0))) {
+                found = true;
+                assertThat(second.getValue()).isEqualTo(inputFlagsFirst.get(0).getValue());
+                break;
+            }
+        }
+
+        assertWithMessage(
+                "Failed to find flag " + inputFlagsFirst.get(0) + " in the second calls output")
+                .that(found).isTrue();
+    }
+
+    @Test
+    public void testQueryFlags_onlyOnce() {
+        List<SyncableFlag> inputFlags = List.of(
+                new SyncableFlag(NS, "a", "false", false),
+                new SyncableFlag(NS, "b", "true", false),
+                new SyncableFlag(NS, "c", "false", false)
+        );
+
+        List<SyncableFlag> outputFlags = mFeatureFlagsService.queryFlags(inputFlags);
+
+        assertThat(inputFlags.size()).isEqualTo(outputFlags.size());
+
+        for (SyncableFlag inpF: inputFlags) {
+            boolean found = false;
+            for (SyncableFlag outF : outputFlags) {
+                if (compareSyncableFlagsNames(inpF, outF)) {
+                    found = true;
+                    break;
+                }
+            }
+            assertWithMessage("Failed to find input flag " + inpF + " in the output")
+                    .that(found).isTrue();
+        }
+    }
+
+    @Test
+    public void testQueryFlags_twoCallsWithDifferentDefaults() {
+        List<SyncableFlag> inputFlagsFirst = List.of(
+                new SyncableFlag(NS, "a", "false", false)
+        );
+        List<SyncableFlag> inputFlagsSecond = List.of(
+                new SyncableFlag(NS, "a", "true", false),
+                new SyncableFlag(NS, "b", "false", false)
+        );
+
+        List<SyncableFlag> outputFlagsFirst = mFeatureFlagsService.queryFlags(inputFlagsFirst);
+        List<SyncableFlag> outputFlagsSecond = mFeatureFlagsService.queryFlags(inputFlagsSecond);
+
+        assertThat(inputFlagsFirst.size()).isEqualTo(outputFlagsFirst.size());
+        assertThat(inputFlagsSecond.size()).isEqualTo(outputFlagsSecond.size());
+
+        // This test only cares that the "a" flag passed in the second time came out with the
+        // same value that was passed in (i.e. it wasn't cached).
+
+        boolean found = false;
+        for (SyncableFlag second : outputFlagsSecond) {
+            if (compareSyncableFlagsNames(second, inputFlagsSecond.get(0))) {
+                found = true;
+                assertThat(second.getValue()).isEqualTo(inputFlagsSecond.get(0).getValue());
+                break;
+            }
+        }
+
+        assertWithMessage(
+                "Failed to find flag " + inputFlagsSecond.get(0) + " in the second calls output")
+                .that(found).isTrue();
+    }
+
+    @Test
+    public void testOverrideFlag() {
+        SyncableFlag f = new SyncableFlag(NS, "a", "false", false);
+
+        mFeatureFlagsService.overrideFlag(f);
+
+        verify(mFlagStore).set(f.getNamespace(), f.getName(), f.getValue());
+    }
+
+    @Test
+    public void testResetFlag() {
+        SyncableFlag f = new SyncableFlag(NS, "a", "false", false);
+
+        mFeatureFlagsService.resetFlag(f);
+
+        verify(mFlagStore).erase(f.getNamespace(), f.getName());
+    }
+
+
+    private static boolean compareSyncableFlagsNames(SyncableFlag a, SyncableFlag b) {
+        return a.getNamespace().equals(b.getNamespace())
+                && a.getName().equals(b.getName())
+                && a.isDynamic() == b.isDynamic();
+    }
+}

services/tests/servicestests/src/com/android/server/flags/FlagCacheTest.java

@@ -0,0 +1,86 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class FlagCacheTest {
+    private static final String NS = "ns";
+    private static final String NAME = "name";
+
+    FlagCache mFlagCache = new FlagCache();
+
+    @Test
+    public void testGetOrNull_unset() {
+        assertThat(mFlagCache.getOrNull(NS, NAME)).isNull();
+    }
+
+    @Test
+    public void testGetOrSet_unset() {
+        assertThat(mFlagCache.getOrSet(NS, NAME, "value")).isEqualTo("value");
+    }
+
+    @Test
+    public void testGetOrSet_alreadySet() {
+        mFlagCache.setIfChanged(NS, NAME, "value");
+        assertThat(mFlagCache.getOrSet(NS, NAME, "newvalue")).isEqualTo("value");
+    }
+
+    @Test
+    public void testSetIfChanged_unset() {
+        assertThat(mFlagCache.setIfChanged(NS, NAME, "value")).isTrue();
+    }
+
+    @Test
+    public void testSetIfChanged_noChange() {
+        mFlagCache.setIfChanged(NS, NAME, "value");
+        assertThat(mFlagCache.setIfChanged(NS, NAME, "value")).isFalse();
+    }
+
+    @Test
+    public void testSetIfChanged_changing() {
+        mFlagCache.setIfChanged(NS, NAME, "value");
+        assertThat(mFlagCache.setIfChanged(NS, NAME, "newvalue")).isTrue();
+    }
+
+    @Test
+    public void testContainsNamespace_unset() {
+        assertThat(mFlagCache.containsNamespace(NS)).isFalse();
+    }
+
+    @Test
+    public void testContainsNamespace_set() {
+        mFlagCache.setIfChanged(NS, NAME, "value");
+        assertThat(mFlagCache.containsNamespace(NS)).isTrue();
+    }
+
+    @Test
+    public void testContains_unset() {
+        assertThat(mFlagCache.contains(NS, NAME)).isFalse();
+    }
+
+    @Test
+    public void testContains_set() {
+        mFlagCache.setIfChanged(NS, NAME, "value");
+        assertThat(mFlagCache.contains(NS, NAME)).isTrue();
+    }
+}

services/tests/servicestests/src/com/android/server/flags/FlagOverrideStoreTest.java

@@ -0,0 +1,111 @@
+/*
+ * Copyright (C) 2023 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.flags;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import android.platform.test.annotations.Presubmit;
+
+import androidx.test.filters.SmallTest;
+
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.mockito.Mock;
+import org.mockito.junit.MockitoJUnit;
+import org.mockito.junit.MockitoRule;
+
+@Presubmit
+@SmallTest
+public class FlagOverrideStoreTest {
+    private static final String NS = "ns";
+    private static final String NAME = "name";
+    private static final String PROP_NAME = FlagOverrideStore.getPropName(NS, NAME);
+
+    @Rule
+    public final MockitoRule mockito = MockitoJUnit.rule();
+
+    @Mock
+    private SettingsProxy mSettingsProxy;
+    @Mock
+    private FlagOverrideStore.FlagChangeCallback mCallback;
+
+    private FlagOverrideStore mFlagStore;
+
+    @Before
+    public void setup() {
+        mFlagStore = new FlagOverrideStore(mSettingsProxy);
+        mFlagStore.setChangeCallback(mCallback);
+    }
+
+    @Test
+    public void testSet_unset() {
+        mFlagStore.set(NS, NAME, "value");
+        verify(mSettingsProxy).putString(PROP_NAME, "value");
+    }
+
+    @Test
+    public void testSet_setTwice() {
+        mFlagStore.set(NS, NAME, "value");
+        mFlagStore.set(NS, NAME, "newvalue");
+        verify(mSettingsProxy).putString(PROP_NAME, "value");
+        verify(mSettingsProxy).putString(PROP_NAME, "newvalue");
+    }
+
+    @Test
+    public void testGet_unset() {
+        assertThat(mFlagStore.get(NS, NAME)).isNull();
+    }
+
+    @Test
+    public void testGet_set() {
+        when(mSettingsProxy.getString(PROP_NAME)).thenReturn("value");
+        assertThat(mFlagStore.get(NS, NAME)).isEqualTo("value");
+    }
+
+    @Test
+    public void testErase() {
+        mFlagStore.erase(NS, NAME);
+        verify(mSettingsProxy).putString(PROP_NAME, null);
+    }
+
+    @Test
+    public void testContains_unset() {
+        assertThat(mFlagStore.contains(NS, NAME)).isFalse();
+    }
+
+    @Test
+    public void testContains_set() {
+        when(mSettingsProxy.getString(PROP_NAME)).thenReturn("value");
+        assertThat(mFlagStore.contains(NS, NAME)).isTrue();
+    }
+
+    @Test
+    public void testCallback_onSet() {
+        mFlagStore.set(NS, NAME, "value");
+        verify(mCallback).onFlagChanged(NS, NAME, "value");
+    }
+
+    @Test
+    public void testCallback_onErase() {
+        mFlagStore.erase(NS, NAME);
+        verify(mCallback).onFlagChanged(NS, NAME, null);
+    }
+}

services/tests/servicestests/src/com/android/server/flags/OWNERS

@@ -0,0 +1 @@
+include /services/flags/OWNERS