1/*
2 * Copyright (C) 2006 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
17package android.os;
18
19import android.util.Log;
20import android.util.MutableInt;
21
22import com.android.internal.annotations.GuardedBy;
23
24import java.util.ArrayList;
25import java.util.HashMap;
26
27
28/**
29 * Gives access to the system properties store.  The system properties
30 * store contains a list of string key-value pairs.
31 *
32 * {@hide}
33 */
34public class SystemProperties {
35    private static final String TAG = "SystemProperties";
36    private static final boolean TRACK_KEY_ACCESS = false;
37
38    /**
39     * Android O removed the property name length limit, but com.amazon.kindle 7.8.1.5
40     * uses reflection to read this whenever text is selected (http://b/36095274).
41     */
42    public static final int PROP_NAME_MAX = Integer.MAX_VALUE;
43
44    public static final int PROP_VALUE_MAX = 91;
45
46    private static final ArrayList<Runnable> sChangeCallbacks = new ArrayList<Runnable>();
47
48    @GuardedBy("sRoReads")
49    private static final HashMap<String, MutableInt> sRoReads;
50    static {
51        if (TRACK_KEY_ACCESS) {
52            sRoReads = new HashMap<>();
53        } else {
54            sRoReads = null;
55        }
56    }
57
58    private static void onKeyAccess(String key) {
59        if (!TRACK_KEY_ACCESS) return;
60
61        if (key != null && key.startsWith("ro.")) {
62            synchronized (sRoReads) {
63                MutableInt numReads = sRoReads.getOrDefault(key, null);
64                if (numReads == null) {
65                    numReads = new MutableInt(0);
66                    sRoReads.put(key, numReads);
67                }
68                numReads.value++;
69                if (numReads.value > 3) {
70                    Log.d(TAG, "Repeated read (count=" + numReads.value
71                            + ") of a read-only system property '" + key + "'",
72                            new Exception());
73                }
74            }
75        }
76    }
77
78    private static native String native_get(String key);
79    private static native String native_get(String key, String def);
80    private static native int native_get_int(String key, int def);
81    private static native long native_get_long(String key, long def);
82    private static native boolean native_get_boolean(String key, boolean def);
83    private static native void native_set(String key, String def);
84    private static native void native_add_change_callback();
85    private static native void native_report_sysprop_change();
86
87    /**
88     * Get the value for the given key.
89     * @return an empty string if the key isn't found
90     */
91    public static String get(String key) {
92        if (TRACK_KEY_ACCESS) onKeyAccess(key);
93        return native_get(key);
94    }
95
96    /**
97     * Get the value for the given key.
98     * @return if the key isn't found, return def if it isn't null, or an empty string otherwise
99     */
100    public static String get(String key, String def) {
101        if (TRACK_KEY_ACCESS) onKeyAccess(key);
102        return native_get(key, def);
103    }
104
105    /**
106     * Get the value for the given key, and return as an integer.
107     * @param key the key to lookup
108     * @param def a default value to return
109     * @return the key parsed as an integer, or def if the key isn't found or
110     *         cannot be parsed
111     */
112    public static int getInt(String key, int def) {
113        if (TRACK_KEY_ACCESS) onKeyAccess(key);
114        return native_get_int(key, def);
115    }
116
117    /**
118     * Get the value for the given key, and return as a long.
119     * @param key the key to lookup
120     * @param def a default value to return
121     * @return the key parsed as a long, or def if the key isn't found or
122     *         cannot be parsed
123     */
124    public static long getLong(String key, long def) {
125        if (TRACK_KEY_ACCESS) onKeyAccess(key);
126        return native_get_long(key, def);
127    }
128
129    /**
130     * Get the value for the given key, returned as a boolean.
131     * Values 'n', 'no', '0', 'false' or 'off' are considered false.
132     * Values 'y', 'yes', '1', 'true' or 'on' are considered true.
133     * (case sensitive).
134     * If the key does not exist, or has any other value, then the default
135     * result is returned.
136     * @param key the key to lookup
137     * @param def a default value to return
138     * @return the key parsed as a boolean, or def if the key isn't found or is
139     *         not able to be parsed as a boolean.
140     */
141    public static boolean getBoolean(String key, boolean def) {
142        if (TRACK_KEY_ACCESS) onKeyAccess(key);
143        return native_get_boolean(key, def);
144    }
145
146    /**
147     * Set the value for the given key.
148     * @throws IllegalArgumentException if the value exceeds 92 characters
149     */
150    public static void set(String key, String val) {
151        if (val != null && val.length() > PROP_VALUE_MAX) {
152            throw newValueTooLargeException(key, val);
153        }
154        if (TRACK_KEY_ACCESS) onKeyAccess(key);
155        native_set(key, val);
156    }
157
158    public static void addChangeCallback(Runnable callback) {
159        synchronized (sChangeCallbacks) {
160            if (sChangeCallbacks.size() == 0) {
161                native_add_change_callback();
162            }
163            sChangeCallbacks.add(callback);
164        }
165    }
166
167    static void callChangeCallbacks() {
168        synchronized (sChangeCallbacks) {
169            //Log.i("foo", "Calling " + sChangeCallbacks.size() + " change callbacks!");
170            if (sChangeCallbacks.size() == 0) {
171                return;
172            }
173            ArrayList<Runnable> callbacks = new ArrayList<Runnable>(sChangeCallbacks);
174            for (int i=0; i<callbacks.size(); i++) {
175                callbacks.get(i).run();
176            }
177        }
178    }
179
180    private static IllegalArgumentException newValueTooLargeException(String key, String value) {
181        return new IllegalArgumentException("value of system property '" + key + "' is longer than "
182                + PROP_VALUE_MAX + " characters: " + value);
183    }
184
185    /*
186     * Notifies listeners that a system property has changed
187     */
188    public static void reportSyspropChanged() {
189        native_report_sysprop_change();
190    }
191}
192