1 /*
2  * Copyright (C) 2020 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 android.media.permission;
18 
19 import android.annotation.NonNull;
20 import android.os.Binder;
21 
22 /**
23  * An RAII-style object, used to establish a scope in which the binder calling identity is cleared.
24  *
25  * <p>
26  * Intended usage:
27  * <pre>
28  * void caller() {
29  *   try (SafeCloseable ignored = ClearCallingIdentityContext.create()) {
30  *       // Within this scope the binder calling identity is cleared.
31  *       ...
32  *   }
33  *   // Outside the scope the calling identity is restored to its prior state.
34  * </pre>
35  *
36  * @hide
37  */
38 public class ClearCallingIdentityContext implements SafeCloseable {
39     private final long mRestoreKey;
40 
41     /**
42      * Creates a new instance.
43      * @return A {@link SafeCloseable}, intended to be used in a try-with-resource block.
44      */
45     public static @NonNull
create()46     SafeCloseable create() {
47         return new ClearCallingIdentityContext();
48     }
49 
50     @SuppressWarnings("ResultOfClearIdentityCallNotStoredInVariable")
ClearCallingIdentityContext()51     private ClearCallingIdentityContext() {
52         mRestoreKey = Binder.clearCallingIdentity();
53     }
54 
55     @Override
close()56     public void close() {
57         Binder.restoreCallingIdentity(mRestoreKey);
58     }
59 }
60