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/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.util;
import android.content.ContentResolver;
import android.content.Context;
import android.content.res.Resources;
import android.net.SntpClient;
import android.os.SystemClock;
import android.provider.Settings;
/**
* {@link TrustedTime} that connects with a remote NTP server as its trusted
* time source.
*
* @hide
*/
public class NtpTrustedTime implements TrustedTime {
private static final String TAG = "NtpTrustedTime";
private static final boolean LOGD = false;
private static NtpTrustedTime sSingleton;
private final String mServer;
private final long mTimeout;
private boolean mHasCache;
private long mCachedNtpTime;
private long mCachedNtpElapsedRealtime;
private long mCachedNtpCertainty;
private NtpTrustedTime(String server, long timeout) {
if (LOGD) Log.d(TAG, "creating NtpTrustedTime using " + server);
mServer = server;
mTimeout = timeout;
}
public static synchronized NtpTrustedTime getInstance(Context context) {
if (sSingleton == null) {
final Resources res = context.getResources();
final ContentResolver resolver = context.getContentResolver();
final String defaultServer = res.getString(
com.android.internal.R.string.config_ntpServer);
final long defaultTimeout = res.getInteger(
com.android.internal.R.integer.config_ntpTimeout);
final String secureServer = Settings.Secure.getString(
resolver, Settings.Secure.NTP_SERVER);
final long timeout = Settings.Secure.getLong(
resolver, Settings.Secure.NTP_TIMEOUT, defaultTimeout);
final String server = secureServer != null ? secureServer : defaultServer;
sSingleton = new NtpTrustedTime(server, timeout);
}
return sSingleton;
}
/** {@inheritDoc} */
public boolean forceRefresh() {
if (mServer == null) {
// missing server, so no trusted time available
return false;
}
if (LOGD) Log.d(TAG, "forceRefresh() from cache miss");
final SntpClient client = new SntpClient();
if (client.requestTime(mServer, (int) mTimeout)) {
mHasCache = true;
mCachedNtpTime = client.getNtpTime();
mCachedNtpElapsedRealtime = client.getNtpTimeReference();
mCachedNtpCertainty = client.getRoundTripTime() / 2;
return true;
} else {
return false;
}
}
/** {@inheritDoc} */
public boolean hasCache() {
return mHasCache;
}
/** {@inheritDoc} */
public long getCacheAge() {
if (mHasCache) {
return SystemClock.elapsedRealtime() - mCachedNtpElapsedRealtime;
} else {
return Long.MAX_VALUE;
}
}
/** {@inheritDoc} */
public long getCacheCertainty() {
if (mHasCache) {
return mCachedNtpCertainty;
} else {
return Long.MAX_VALUE;
}
}
/** {@inheritDoc} */
public long currentTimeMillis() {
if (!mHasCache) {
throw new IllegalStateException("Missing authoritative time source");
}
if (LOGD) Log.d(TAG, "currentTimeMillis() cache hit");
// current time is age after the last ntp cache; callers who
// want fresh values will hit makeAuthoritative() first.
return mCachedNtpTime + getCacheAge();
}
public long getCachedNtpTime() {
if (LOGD) Log.d(TAG, "getCachedNtpTime() cache hit");
return mCachedNtpTime;
}
public long getCachedNtpTimeReference() {
return mCachedNtpElapsedRealtime;
}
}
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