381 lines
15 KiB
Java
381 lines
15 KiB
Java
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/*
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* Copyright (C) 2008 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package android.net;
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import android.annotation.Nullable;
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import android.compat.annotation.UnsupportedAppUsage;
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import android.net.sntp.Duration64;
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import android.net.sntp.Timestamp64;
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import android.os.SystemClock;
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import android.util.Log;
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import android.util.Slog;
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import com.android.internal.annotations.VisibleForTesting;
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import com.android.internal.util.TrafficStatsConstants;
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import java.net.DatagramPacket;
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import java.net.DatagramSocket;
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import java.net.InetAddress;
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import java.net.InetSocketAddress;
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import java.net.UnknownHostException;
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import java.security.NoSuchAlgorithmException;
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import java.security.SecureRandom;
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import java.time.Duration;
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import java.time.Instant;
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import java.util.Objects;
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import java.util.Random;
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import java.util.function.Supplier;
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/**
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* Simple, single-use SNTP client class for retrieving network time.
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*
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* Sample usage:
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* <pre>SntpClient client = new SntpClient();
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* if (client.requestTime("time.foo.com")) {
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* long now = client.getNtpTime() + SystemClock.elapsedRealtime() - client.getNtpTimeReference();
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* }
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* </pre>
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*
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* <p>This class is not thread-safe.
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*
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* @hide
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*/
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public class SntpClient {
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private static final String TAG = "SntpClient";
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private static final boolean DBG = true;
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private static final int REFERENCE_TIME_OFFSET = 16;
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private static final int ORIGINATE_TIME_OFFSET = 24;
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private static final int RECEIVE_TIME_OFFSET = 32;
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private static final int TRANSMIT_TIME_OFFSET = 40;
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private static final int NTP_PACKET_SIZE = 48;
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public static final int STANDARD_NTP_PORT = 123;
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private static final int NTP_MODE_CLIENT = 3;
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private static final int NTP_MODE_SERVER = 4;
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private static final int NTP_MODE_BROADCAST = 5;
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private static final int NTP_VERSION = 3;
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private static final int NTP_LEAP_NOSYNC = 3;
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private static final int NTP_STRATUM_DEATH = 0;
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private static final int NTP_STRATUM_MAX = 15;
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// The source of the current system clock time, replaceable for testing.
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private final Supplier<Instant> mSystemTimeSupplier;
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private final Random mRandom;
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// The last offset calculated from an NTP server response
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private long mClockOffset;
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// The last system time computed from an NTP server response
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private long mNtpTime;
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// The value of SystemClock.elapsedRealtime() corresponding to mNtpTime / mClockOffset
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private long mNtpTimeReference;
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// The round trip (network) time in milliseconds
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private long mRoundTripTime;
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// Details of the NTP server used to obtain the time last.
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@Nullable private InetSocketAddress mServerSocketAddress;
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private static class InvalidServerReplyException extends Exception {
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public InvalidServerReplyException(String message) {
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super(message);
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}
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}
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@UnsupportedAppUsage
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public SntpClient() {
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this(Instant::now, defaultRandom());
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}
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@VisibleForTesting
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public SntpClient(Supplier<Instant> systemTimeSupplier, Random random) {
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mSystemTimeSupplier = Objects.requireNonNull(systemTimeSupplier);
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mRandom = Objects.requireNonNull(random);
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}
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/**
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* Sends an SNTP request to the given host and processes the response.
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*
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* @param host host name of the server.
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* @param port port of the server.
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* @param timeout network timeout in milliseconds. the timeout doesn't include the DNS lookup
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* time, and it applies to each individual query to the resolved addresses of
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* the NTP server.
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* @param network network over which to send the request.
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* @return true if the transaction was successful.
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*/
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public boolean requestTime(String host, int port, int timeout, Network network) {
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final Network networkForResolv = network.getPrivateDnsBypassingCopy();
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try {
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final InetAddress[] addresses = networkForResolv.getAllByName(host);
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for (int i = 0; i < addresses.length; i++) {
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if (requestTime(addresses[i], port, timeout, networkForResolv)) {
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return true;
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}
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}
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} catch (UnknownHostException e) {
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Log.w(TAG, "Unknown host: " + host);
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EventLogTags.writeNtpFailure(host, e.toString());
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}
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if (DBG) Log.d(TAG, "request time failed");
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return false;
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}
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public boolean requestTime(InetAddress address, int port, int timeout, Network network) {
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DatagramSocket socket = null;
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final int oldTag = TrafficStats.getAndSetThreadStatsTag(
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TrafficStatsConstants.TAG_SYSTEM_NTP);
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try {
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socket = new DatagramSocket();
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network.bindSocket(socket);
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socket.setSoTimeout(timeout);
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byte[] buffer = new byte[NTP_PACKET_SIZE];
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DatagramPacket request = new DatagramPacket(buffer, buffer.length, address, port);
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// set mode = 3 (client) and version = 3
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// mode is in low 3 bits of first byte
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// version is in bits 3-5 of first byte
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buffer[0] = NTP_MODE_CLIENT | (NTP_VERSION << 3);
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// get current time and write it to the request packet
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final Instant requestTime = mSystemTimeSupplier.get();
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final Timestamp64 requestTimestamp = Timestamp64.fromInstant(requestTime);
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final Timestamp64 randomizedRequestTimestamp =
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requestTimestamp.randomizeSubMillis(mRandom);
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final long requestTicks = SystemClock.elapsedRealtime();
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writeTimeStamp(buffer, TRANSMIT_TIME_OFFSET, randomizedRequestTimestamp);
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socket.send(request);
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// read the response
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DatagramPacket response = new DatagramPacket(buffer, buffer.length);
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socket.receive(response);
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final long responseTicks = SystemClock.elapsedRealtime();
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final Instant responseTime = requestTime.plusMillis(responseTicks - requestTicks);
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final Timestamp64 responseTimestamp = Timestamp64.fromInstant(responseTime);
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// extract the results
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final byte leap = (byte) ((buffer[0] >> 6) & 0x3);
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final byte mode = (byte) (buffer[0] & 0x7);
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final int stratum = (int) (buffer[1] & 0xff);
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final Timestamp64 referenceTimestamp = readTimeStamp(buffer, REFERENCE_TIME_OFFSET);
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final Timestamp64 originateTimestamp = readTimeStamp(buffer, ORIGINATE_TIME_OFFSET);
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final Timestamp64 receiveTimestamp = readTimeStamp(buffer, RECEIVE_TIME_OFFSET);
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final Timestamp64 transmitTimestamp = readTimeStamp(buffer, TRANSMIT_TIME_OFFSET);
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/* Do validation according to RFC */
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checkValidServerReply(leap, mode, stratum, transmitTimestamp, referenceTimestamp,
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randomizedRequestTimestamp, originateTimestamp);
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long totalTransactionDurationMillis = responseTicks - requestTicks;
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long serverDurationMillis =
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Duration64.between(receiveTimestamp, transmitTimestamp).toDuration().toMillis();
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long roundTripTimeMillis = totalTransactionDurationMillis - serverDurationMillis;
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Duration clockOffsetDuration = calculateClockOffset(requestTimestamp,
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receiveTimestamp, transmitTimestamp, responseTimestamp);
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long clockOffsetMillis = clockOffsetDuration.toMillis();
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EventLogTags.writeNtpSuccess(
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address.toString(), roundTripTimeMillis, clockOffsetMillis);
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if (DBG) {
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Log.d(TAG, "round trip: " + roundTripTimeMillis + "ms, "
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+ "clock offset: " + clockOffsetMillis + "ms");
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}
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// save our results - use the times on this side of the network latency
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// (response rather than request time)
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mClockOffset = clockOffsetMillis;
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mNtpTime = responseTime.plus(clockOffsetDuration).toEpochMilli();
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mNtpTimeReference = responseTicks;
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mRoundTripTime = roundTripTimeMillis;
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mServerSocketAddress = new InetSocketAddress(address, port);
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} catch (Exception e) {
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EventLogTags.writeNtpFailure(address.toString(), e.toString());
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if (DBG) Log.d(TAG, "request time failed: " + e);
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return false;
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} finally {
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if (socket != null) {
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socket.close();
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}
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TrafficStats.setThreadStatsTag(oldTag);
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}
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return true;
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}
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/** Performs the NTP clock offset calculation. */
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@VisibleForTesting
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public static Duration calculateClockOffset(Timestamp64 clientRequestTimestamp,
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Timestamp64 serverReceiveTimestamp, Timestamp64 serverTransmitTimestamp,
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Timestamp64 clientResponseTimestamp) {
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// According to RFC4330:
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// t is the system clock offset (the adjustment we are trying to find)
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// t = ((T2 - T1) + (T3 - T4)) / 2
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//
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// Which is:
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// t = (([server]receiveTimestamp - [client]requestTimestamp)
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// + ([server]transmitTimestamp - [client]responseTimestamp)) / 2
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//
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// See the NTP spec and tests: the numeric types used are deliberate:
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// + Duration64.between() uses 64-bit arithmetic (32-bit for the seconds).
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// + plus() / dividedBy() use Duration, which isn't the double precision floating point
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// used in NTPv4, but is good enough.
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return Duration64.between(clientRequestTimestamp, serverReceiveTimestamp)
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.plus(Duration64.between(clientResponseTimestamp, serverTransmitTimestamp))
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.dividedBy(2);
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}
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@Deprecated
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@UnsupportedAppUsage
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public boolean requestTime(String host, int timeout) {
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Log.w(TAG, "Shame on you for calling the hidden API requestTime()!");
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return false;
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}
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/**
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* Returns the offset calculated to apply to the client clock to arrive at {@link #getNtpTime()}
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*/
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@VisibleForTesting
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public long getClockOffset() {
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return mClockOffset;
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}
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/**
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* Returns the time computed from the NTP transaction.
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*
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* @return time value computed from NTP server response.
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*/
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@UnsupportedAppUsage
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public long getNtpTime() {
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return mNtpTime;
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}
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/**
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* Returns the reference clock value (value of SystemClock.elapsedRealtime())
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* corresponding to the NTP time.
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*
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* @return reference clock corresponding to the NTP time.
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*/
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@UnsupportedAppUsage
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public long getNtpTimeReference() {
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return mNtpTimeReference;
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}
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/**
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* Returns the round trip time of the NTP transaction
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*
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* @return round trip time in milliseconds.
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*/
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@UnsupportedAppUsage
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public long getRoundTripTime() {
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return mRoundTripTime;
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}
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/**
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* Returns the address of the NTP server used in the NTP transaction
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*/
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@Nullable
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public InetSocketAddress getServerSocketAddress() {
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return mServerSocketAddress;
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}
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private static void checkValidServerReply(
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byte leap, byte mode, int stratum, Timestamp64 transmitTimestamp,
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Timestamp64 referenceTimestamp, Timestamp64 randomizedRequestTimestamp,
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Timestamp64 originateTimestamp) throws InvalidServerReplyException {
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if (leap == NTP_LEAP_NOSYNC) {
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throw new InvalidServerReplyException("unsynchronized server");
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}
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if ((mode != NTP_MODE_SERVER) && (mode != NTP_MODE_BROADCAST)) {
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throw new InvalidServerReplyException("untrusted mode: " + mode);
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}
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if ((stratum == NTP_STRATUM_DEATH) || (stratum > NTP_STRATUM_MAX)) {
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throw new InvalidServerReplyException("untrusted stratum: " + stratum);
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}
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if (!randomizedRequestTimestamp.equals(originateTimestamp)) {
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throw new InvalidServerReplyException(
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"originateTimestamp != randomizedRequestTimestamp");
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}
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if (transmitTimestamp.equals(Timestamp64.ZERO)) {
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throw new InvalidServerReplyException("zero transmitTimestamp");
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}
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if (referenceTimestamp.equals(Timestamp64.ZERO)) {
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throw new InvalidServerReplyException("zero referenceTimestamp");
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}
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}
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/**
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* Reads an unsigned 32 bit big endian number from the given offset in the buffer.
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*/
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private long readUnsigned32(byte[] buffer, int offset) {
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int i0 = buffer[offset++] & 0xFF;
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int i1 = buffer[offset++] & 0xFF;
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int i2 = buffer[offset++] & 0xFF;
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int i3 = buffer[offset] & 0xFF;
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int bits = (i0 << 24) | (i1 << 16) | (i2 << 8) | i3;
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return bits & 0xFFFF_FFFFL;
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}
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/**
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* Reads the NTP time stamp from the given offset in the buffer.
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*/
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private Timestamp64 readTimeStamp(byte[] buffer, int offset) {
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long seconds = readUnsigned32(buffer, offset);
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int fractionBits = (int) readUnsigned32(buffer, offset + 4);
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return Timestamp64.fromComponents(seconds, fractionBits);
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}
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/**
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* Writes the NTP time stamp at the given offset in the buffer.
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*/
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private void writeTimeStamp(byte[] buffer, int offset, Timestamp64 timestamp) {
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long seconds = timestamp.getEraSeconds();
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// write seconds in big endian format
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buffer[offset++] = (byte) (seconds >>> 24);
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buffer[offset++] = (byte) (seconds >>> 16);
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buffer[offset++] = (byte) (seconds >>> 8);
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buffer[offset++] = (byte) (seconds);
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int fractionBits = timestamp.getFractionBits();
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// write fraction in big endian format
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buffer[offset++] = (byte) (fractionBits >>> 24);
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buffer[offset++] = (byte) (fractionBits >>> 16);
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buffer[offset++] = (byte) (fractionBits >>> 8);
|
||
|
|
buffer[offset] = (byte) (fractionBits);
|
||
|
|
}
|
||
|
|
|
||
|
|
private static Random defaultRandom() {
|
||
|
|
Random random;
|
||
|
|
try {
|
||
|
|
random = SecureRandom.getInstanceStrong();
|
||
|
|
} catch (NoSuchAlgorithmException e) {
|
||
|
|
// This should never happen.
|
||
|
|
Slog.wtf(TAG, "Unable to access SecureRandom", e);
|
||
|
|
random = new Random(System.currentTimeMillis());
|
||
|
|
}
|
||
|
|
return random;
|
||
|
|
}
|
||
|
|
}
|