Android Open Source - google-authenticator-android Totp Clock

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License

The source code is released under:

Apache License

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Java Source Code

/*
 * Copyright 2012 Google Inc. All Rights Reserved.
 */*from  ww  w  . j a v  a 2 s .  com*/
 * 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 com.google.android.apps.authenticator;

import android.content.Context;
import android.content.SharedPreferences;
import android.preference.PreferenceManager;

/**
 * Clock input for the time-based OTPs (TOTP). The input is based on the current system time
 * and is adjusted by a persistently stored correction value (offset in minutes).
 *
 * @author klyubin@google.com (Alex Klyubin)
 */
public class TotpClock {

  // @VisibleForTesting
  static final String PREFERENCE_KEY_OFFSET_MINUTES = "timeCorrectionMinutes";

  private final SharedPreferences mPreferences;

  private final Object mLock = new Object();

  /**
   * Cached value of time correction (in minutes) or {@code null} if not cached. The value is cached
   * because it's read very frequently (once every 100ms) and is modified very infrequently.
   *
   * @GuardedBy {@link #mLock}
   */
  private Integer mCachedCorrectionMinutes;

  public TotpClock(Context context) {
    mPreferences = PreferenceManager.getDefaultSharedPreferences(context);
  }

  /**
   * Gets the number of milliseconds since epoch.
   */
  public long currentTimeMillis() {
    return System.currentTimeMillis() + getTimeCorrectionMinutes() * Utilities.MINUTE_IN_MILLIS;
  }

  /**
   * Gets the currently used time correction value.
   *
   * @return number of minutes by which this device is behind the correct time.
   */
  public int getTimeCorrectionMinutes() {
    synchronized (mLock) {
      if (mCachedCorrectionMinutes == null) {
        mCachedCorrectionMinutes = mPreferences.getInt(PREFERENCE_KEY_OFFSET_MINUTES, 0);
      }
      return mCachedCorrectionMinutes;
    }
  }

  /**
   * Sets the currently used time correction value.
   *
   * @param minutes number of minutes by which this device is behind the correct time.
   */
  public void setTimeCorrectionMinutes(int minutes) {
    synchronized (mLock) {
      mPreferences.edit().putInt(PREFERENCE_KEY_OFFSET_MINUTES, minutes).commit();
      // Invalidate the cache to force reading actual settings from time to time
      mCachedCorrectionMinutes = null;
    }
  }
}

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