1/*
2 * Copyright (C) 2011 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.util;
18
19import android.content.ContentResolver;
20import android.content.Context;
21import android.content.res.Resources;
22import android.net.ConnectivityManager;
23import android.net.NetworkInfo;
24import android.net.SntpClient;
25import android.os.SystemClock;
26import android.provider.Settings;
27
28/**
29 * {@link TrustedTime} that connects with a remote NTP server as its trusted
30 * time source.
31 *
32 * @hide
33 */
34public class NtpTrustedTime implements TrustedTime {
35    private static final String TAG = "NtpTrustedTime";
36    private static final boolean LOGD = false;
37
38    private static NtpTrustedTime sSingleton;
39    private static Context sContext;
40
41    private final String mServer;
42    private final long mTimeout;
43
44    private ConnectivityManager mCM;
45
46    private boolean mHasCache;
47    private long mCachedNtpTime;
48    private long mCachedNtpElapsedRealtime;
49    private long mCachedNtpCertainty;
50
51    private NtpTrustedTime(String server, long timeout) {
52        if (LOGD) Log.d(TAG, "creating NtpTrustedTime using " + server);
53        mServer = server;
54        mTimeout = timeout;
55    }
56
57    public static synchronized NtpTrustedTime getInstance(Context context) {
58        if (sSingleton == null) {
59            final Resources res = context.getResources();
60            final ContentResolver resolver = context.getContentResolver();
61
62            final String defaultServer = res.getString(
63                    com.android.internal.R.string.config_ntpServer);
64            final long defaultTimeout = res.getInteger(
65                    com.android.internal.R.integer.config_ntpTimeout);
66
67            final String secureServer = Settings.Global.getString(
68                    resolver, Settings.Global.NTP_SERVER);
69            final long timeout = Settings.Global.getLong(
70                    resolver, Settings.Global.NTP_TIMEOUT, defaultTimeout);
71
72            final String server = secureServer != null ? secureServer : defaultServer;
73            sSingleton = new NtpTrustedTime(server, timeout);
74            sContext = context;
75        }
76
77        return sSingleton;
78    }
79
80    @Override
81    public boolean forceRefresh() {
82        if (mServer == null) {
83            // missing server, so no trusted time available
84            return false;
85        }
86
87        // We can't do this at initialization time: ConnectivityService might not be running yet.
88        synchronized (this) {
89            if (mCM == null) {
90                mCM = (ConnectivityManager) sContext.getSystemService(Context.CONNECTIVITY_SERVICE);
91            }
92        }
93
94        final NetworkInfo ni = mCM == null ? null : mCM.getActiveNetworkInfo();
95        if (ni == null || !ni.isConnected()) {
96            if (LOGD) Log.d(TAG, "forceRefresh: no connectivity");
97            return false;
98        }
99
100
101        if (LOGD) Log.d(TAG, "forceRefresh() from cache miss");
102        final SntpClient client = new SntpClient();
103        if (client.requestTime(mServer, (int) mTimeout)) {
104            mHasCache = true;
105            mCachedNtpTime = client.getNtpTime();
106            mCachedNtpElapsedRealtime = client.getNtpTimeReference();
107            mCachedNtpCertainty = client.getRoundTripTime() / 2;
108            return true;
109        } else {
110            return false;
111        }
112    }
113
114    @Override
115    public boolean hasCache() {
116        return mHasCache;
117    }
118
119    @Override
120    public long getCacheAge() {
121        if (mHasCache) {
122            return SystemClock.elapsedRealtime() - mCachedNtpElapsedRealtime;
123        } else {
124            return Long.MAX_VALUE;
125        }
126    }
127
128    @Override
129    public long getCacheCertainty() {
130        if (mHasCache) {
131            return mCachedNtpCertainty;
132        } else {
133            return Long.MAX_VALUE;
134        }
135    }
136
137    @Override
138    public long currentTimeMillis() {
139        if (!mHasCache) {
140            throw new IllegalStateException("Missing authoritative time source");
141        }
142        if (LOGD) Log.d(TAG, "currentTimeMillis() cache hit");
143
144        // current time is age after the last ntp cache; callers who
145        // want fresh values will hit makeAuthoritative() first.
146        return mCachedNtpTime + getCacheAge();
147    }
148
149    public long getCachedNtpTime() {
150        if (LOGD) Log.d(TAG, "getCachedNtpTime() cache hit");
151        return mCachedNtpTime;
152    }
153
154    public long getCachedNtpTimeReference() {
155        return mCachedNtpElapsedRealtime;
156    }
157}
158