1 /*
2  * Copyright (C) 2023 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package com.android.adservices.service.common;
18 
19 import android.os.Binder;
20 
21 import androidx.annotation.NonNull;
22 
23 import java.util.Objects;
24 import java.util.function.Supplier;
25 
26 /**
27  * Utility class for reading {@link android.provider.DeviceConfig} flags from the Binder thread.
28  *
29  * <p>The caller in the {@link Binder} thread does not have the {@link
30  * android.Manifest.permission#READ_DEVICE_CONFIG} permission, so the calling identity needs to be
31  * temporarily cleared in order to read with the local process's permissions.
32  */
33 public class BinderFlagReader {
34     /**
35      * Reads and returns the given flag from the {@link Binder} thread.
36      *
37      * <p>The {@link Binder} thread does not have the {@link
38      * android.Manifest.permission#READ_DEVICE_CONFIG} permission, so the calling identity needs to
39      * be temporarily cleared in order to read with the local process's permissions.
40      *
41      * @param <T> type returned by the {@code flagSupplier}
42      */
readFlag(@onNull Supplier<T> flagSupplier)43     public static <T> T readFlag(@NonNull Supplier<T> flagSupplier) {
44         Objects.requireNonNull(flagSupplier);
45         final long token = Binder.clearCallingIdentity();
46         try {
47             return flagSupplier.get();
48         } finally {
49             Binder.restoreCallingIdentity(token);
50         }
51     }
52 }
53