content: /*
   * Copyright (C) 2008 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 im.actor.runtime.android.time;
  
  import android.os.SystemClock;
  
  import java.net.DatagramPacket;
  import java.net.DatagramSocket;
  import java.net.InetAddress;
  
  /**
   * {@hide}
   * <p/>
   * Simple SNTP client class for retrieving network time.
   * <p/>
   * Sample usage:
   * <pre>SntpClient client = new SntpClient();
   * if (client.requestTime("time.foo.com")) {
   *     long now = client.getNtpTime() + SystemClock.elapsedRealtime() - client.getNtpTimeReference();
   * }
   * </pre>
   */
  public class SntpClient {
      private static final String TAG = "SntpClient";
  
      private static final int REFERENCE_TIME_OFFSET = 16;
      private static final int ORIGINATE_TIME_OFFSET = 24;
      private static final int RECEIVE_TIME_OFFSET = 32;
      private static final int TRANSMIT_TIME_OFFSET = 40;
      private static final int NTP_PACKET_SIZE = 48;
  
      private static final int NTP_PORT = 123;
      private static final int NTP_MODE_CLIENT = 3;
      private static final int NTP_VERSION = 3;
  
      // Number of seconds between Jan 1, 1900 and Jan 1, 1970
      // 70 years plus 17 leap days
      private static final long OFFSET_1900_TO_1970 = ((365L * 70L) + 17L) * 24L * 60L * 60L;
  
      // system time computed from NTP server response
      private long mNtpTime;
  
      // value of SystemClock.elapsedRealtime() corresponding to mNtpTime
      private long mNtpTimeReference;
  
      // round trip time in milliseconds
      private long mRoundTripTime;
  
      private long mClockOffset;
  
      /**
       * Sends an SNTP request to the given host and processes the response.
       *
       * @param host    host name of the server.
       * @param timeout network timeout in milliseconds.
       * @return true if the transaction was successful.
       */
      public boolean requestTime(String host, int timeout) {
          DatagramSocket socket = null;
          try {
              socket = new DatagramSocket();
              socket.setSoTimeout(timeout);
              InetAddress address = InetAddress.getByName(host);
              byte[] buffer = new byte[NTP_PACKET_SIZE];
              DatagramPacket request = new DatagramPacket(buffer, buffer.length, address, NTP_PORT);
  
              // set mode = 3 (client) and version = 3
              // mode is in low 3 bits of first byte
              // version is in bits 3-5 of first byte
              buffer[0] = NTP_MODE_CLIENT | (NTP_VERSION << 3);
  
              // get current time and write it to the request packet
              long requestTime = System.currentTimeMillis();
              long requestTicks = SystemClock.elapsedRealtime();
              writeTimeStamp(buffer, TRANSMIT_TIME_OFFSET, requestTime);
  
              socket.send(request);
  
              // read the response
              DatagramPacket response = new DatagramPacket(buffer, buffer.length);
              socket.receive(response);
              long responseTicks = SystemClock.elapsedRealtime();
              long responseTime = requestTime + (responseTicks - requestTicks);
  
              // extract the results
              long originateTime = readTimeStamp(buffer, ORIGINATE_TIME_OFFSET);
              long receiveTime = readTimeStamp(buffer, RECEIVE_TIME_OFFSET);
              long transmitTime = readTimeStamp(buffer, TRANSMIT_TIME_OFFSET);
              long roundTripTime = responseTicks - requestTicks - (transmitTime - receiveTime);
              // receiveTime = originateTime + transit + skew
              // responseTime = transmitTime + transit - skew
              // clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime))/2
              //             = ((originateTime + transit + skew - originateTime) +
              //                (transmitTime - (transmitTime + transit - skew)))/2
              //             = ((transit + skew) + (transmitTime - transmitTime - transit + skew))/2
              //             = (transit + skew - transit + skew)/2
              //             = (2 * skew)/2 = skew
              mClockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime)) / 2;
              // if (false) Log.d(TAG, "round trip: " + roundTripTime + " ms");
              // if (false) Log.d(TAG, "clock offset: " + clockOffset + " ms");
  
              // save our results - use the times on this side of the network latency
              // (response rather than request time)
              mNtpTime = responseTime + mClockOffset;
              mNtpTimeReference = responseTicks;
              mRoundTripTime = roundTripTime;
          } catch (Exception e) {
              return false;
          } finally {
              if (socket != null) {
                  socket.close();
              }
          }
  
          return true;
      }
  
      /**
       * Returns the time computed from the NTP transaction.
       *
       * @return time value computed from NTP server response.
       */
      public long getNtpTime() {
          return mNtpTime;
      }
  
      /**
       * Returns the reference clock value (value of SystemClock.elapsedRealtime())
       * corresponding to the NTP time.
       *
       * @return reference clock corresponding to the NTP time.
       */
      public long getNtpTimeReference() {
          return mNtpTimeReference;
      }
  
      /**
       * Returns the round trip time of the NTP transaction
       *
       * @return round trip time in milliseconds.
       */
      public long getRoundTripTime() {
          return mRoundTripTime;
      }
  
      public long getClockOffset() {
          return mClockOffset;
      }
  
      /**
       * Reads an unsigned 32 bit big endian number from the given offset in the buffer.
       */
      private long read32(byte[] buffer, int offset) {
          byte b0 = buffer[offset];
          byte b1 = buffer[offset + 1];
          byte b2 = buffer[offset + 2];
          byte b3 = buffer[offset + 3];
  
          // convert signed bytes to unsigned values
          int i0 = ((b0 & 0x80) == 0x80 ? (b0 & 0x7F) + 0x80 : b0);
          int i1 = ((b1 & 0x80) == 0x80 ? (b1 & 0x7F) + 0x80 : b1);
          int i2 = ((b2 & 0x80) == 0x80 ? (b2 & 0x7F) + 0x80 : b2);
          int i3 = ((b3 & 0x80) == 0x80 ? (b3 & 0x7F) + 0x80 : b3);
  
          return ((long) i0 << 24) + ((long) i1 << 16) + ((long) i2 << 8) + (long) i3;
      }
  
      /**
       * Reads the NTP time stamp at the given offset in the buffer and returns
       * it as a system time (milliseconds since January 1, 1970).
       */
      private long readTimeStamp(byte[] buffer, int offset) {
          long seconds = read32(buffer, offset);
          long fraction = read32(buffer, offset + 4);
          return ((seconds - OFFSET_1900_TO_1970) * 1000) + ((fraction * 1000L) / 0x100000000L);
      }
  
      /**
       * Writes system time (milliseconds since January 1, 1970) as an NTP time stamp
       * at the given offset in the buffer.
       */
      private void writeTimeStamp(byte[] buffer, int offset, long time) {
          long seconds = time / 1000L;
          long milliseconds = time - seconds * 1000L;
          seconds += OFFSET_1900_TO_1970;
  
          // write seconds in big endian format
          buffer[offset++] = (byte) (seconds >> 24);
          buffer[offset++] = (byte) (seconds >> 16);
          buffer[offset++] = (byte) (seconds >> 8);
          buffer[offset++] = (byte) (seconds >> 0);
  
          long fraction = milliseconds * 0x100000000L / 1000L;
          // write fraction in big endian format
          buffer[offset++] = (byte) (fraction >> 24);
          buffer[offset++] = (byte) (fraction >> 16);
          buffer[offset++] = (byte) (fraction >> 8);
          // low order bits should be random data
          buffer[offset++] = (byte) (Math.random() * 255.0);
      }
  }