1 /*
2  * Copyright (C) 2016 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.internal.util;
18 
19 import android.os.Message;
20 import android.util.Log;
21 import android.util.SparseArray;
22 
23 import java.lang.reflect.Field;
24 import java.lang.reflect.Modifier;
25 
26 /**
27  * Static utility class for dealing with {@link Message} objects.
28  */
29 public class MessageUtils {
30 
31     private static final String TAG = MessageUtils.class.getSimpleName();
32     private static final boolean DBG = false;
33 
34     /** Thrown when two different constants have the same value. */
35     public static class DuplicateConstantError extends Error {
DuplicateConstantError()36         private DuplicateConstantError() {}
DuplicateConstantError(String name1, String name2, int value)37         public DuplicateConstantError(String name1, String name2, int value) {
38             super(String.format("Duplicate constant value: both %s and %s = %d",
39                 name1, name2, value));
40         }
41     }
42 
43     /**
44      * Finds the names of integer constants. Searches the specified {@code classes}, looking for
45      * accessible static integer fields whose names begin with one of the specified {@prefixes}.
46      *
47      * @param classes the classes to examine.
48      * @prefixes only consider fields names starting with one of these prefixes.
49      * @return a {@link SparseArray} mapping integer constants to their names.
50      */
findMessageNames(Class[] classes, String[] prefixes)51     public static SparseArray<String> findMessageNames(Class[] classes, String[] prefixes) {
52         SparseArray<String> messageNames = new SparseArray<>();
53         for (Class c : classes) {
54             String className = c.getName();
55             if (DBG) Log.d(TAG, "Examining class " + className);
56 
57             Field[] fields;
58             try {
59                 fields = c.getDeclaredFields();
60             } catch (SecurityException e) {
61                 Log.e(TAG, "Can't list fields of class " + className);
62                 continue;
63             }
64 
65             for (Field field : fields) {
66                 int modifiers = field.getModifiers();
67                 if (!Modifier.isStatic(modifiers) | !Modifier.isFinal(modifiers)) {
68                     continue;
69                 }
70 
71                 String name = field.getName();
72                 for (String prefix : prefixes) {
73                     // Does this look like a constant?
74                     if (!name.startsWith(prefix)) {
75                         continue;
76                     }
77 
78                     try {
79                         // TODO: can we have the caller try to access the field instead, so we don't
80                         // expose constants it does not have access to?
81                         field.setAccessible(true);
82 
83                         // Fetch the constant's value.
84                         int value;
85                         try {
86                             value = field.getInt(null);
87                         } catch (IllegalArgumentException | ExceptionInInitializerError e) {
88                             // The field is not an integer (or short or byte), or c's static
89                             // initializer failed and we have no idea what its value is.
90                             // Either way, give up on this field.
91                             break;
92                         }
93 
94                         // Check for duplicate values.
95                         String previousName = messageNames.get(value);
96                         if (previousName != null && !previousName.equals(name)) {
97                             throw new DuplicateConstantError(name, previousName, value);
98                         }
99 
100                         messageNames.put(value, name);
101                         if (DBG) {
102                             Log.d(TAG, String.format("Found constant: %s.%s = %d",
103                                     className, name, value));
104                         }
105                     } catch (SecurityException | IllegalAccessException e) {
106                         // Not allowed to make the field accessible, or no access. Ignore.
107                         continue;
108                     }
109                 }
110             }
111         }
112         return messageNames;
113     }
114 
115     /**
116      * Default prefixes for constants.
117      */
118     public static final String[] DEFAULT_PREFIXES = {"CMD_", "EVENT_"};
119 
120     /**
121      * Finds the names of integer constants. Searches the specified {@code classes}, looking for
122      * accessible static integer values whose names begin with {@link #DEFAULT_PREFIXES}.
123      *
124      * @param classNames the classes to examine.
125      * @prefixes only consider fields names starting with one of these prefixes.
126      * @return a {@link SparseArray} mapping integer constants to their names.
127      */
findMessageNames(Class[] classNames)128     public static SparseArray<String> findMessageNames(Class[] classNames) {
129         return findMessageNames(classNames, DEFAULT_PREFIXES);
130     }
131 }
132 
133