The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2008 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 | |
| 17 | package android.net; |
| 18 | |
| 19 | import android.os.SystemClock; |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 20 | import android.util.Log; |
| 21 | |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 22 | import java.net.DatagramPacket; |
| 23 | import java.net.DatagramSocket; |
| 24 | import java.net.InetAddress; |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 25 | import java.util.Arrays; |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 26 | |
| 27 | /** |
| 28 | * {@hide} |
| 29 | * |
| 30 | * Simple SNTP client class for retrieving network time. |
| 31 | * |
| 32 | * Sample usage: |
| 33 | * <pre>SntpClient client = new SntpClient(); |
| 34 | * if (client.requestTime("time.foo.com")) { |
| 35 | * long now = client.getNtpTime() + SystemClock.elapsedRealtime() - client.getNtpTimeReference(); |
| 36 | * } |
| 37 | * </pre> |
| 38 | */ |
| 39 | public class SntpClient |
| 40 | { |
| 41 | private static final String TAG = "SntpClient"; |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 42 | private static final boolean DBG = true; |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 43 | |
| 44 | private static final int REFERENCE_TIME_OFFSET = 16; |
| 45 | private static final int ORIGINATE_TIME_OFFSET = 24; |
| 46 | private static final int RECEIVE_TIME_OFFSET = 32; |
| 47 | private static final int TRANSMIT_TIME_OFFSET = 40; |
| 48 | private static final int NTP_PACKET_SIZE = 48; |
| 49 | |
| 50 | private static final int NTP_PORT = 123; |
| 51 | private static final int NTP_MODE_CLIENT = 3; |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 52 | private static final int NTP_MODE_SERVER = 4; |
| 53 | private static final int NTP_MODE_BROADCAST = 5; |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 54 | private static final int NTP_VERSION = 3; |
| 55 | |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 56 | private static final int NTP_LEAP_NOSYNC = 3; |
| 57 | private static final int NTP_STRATUM_DEATH = 0; |
| 58 | private static final int NTP_STRATUM_MAX = 15; |
| 59 | |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 60 | // Number of seconds between Jan 1, 1900 and Jan 1, 1970 |
| 61 | // 70 years plus 17 leap days |
| 62 | private static final long OFFSET_1900_TO_1970 = ((365L * 70L) + 17L) * 24L * 60L * 60L; |
| 63 | |
| 64 | // system time computed from NTP server response |
| 65 | private long mNtpTime; |
| 66 | |
| 67 | // value of SystemClock.elapsedRealtime() corresponding to mNtpTime |
| 68 | private long mNtpTimeReference; |
| 69 | |
| 70 | // round trip time in milliseconds |
| 71 | private long mRoundTripTime; |
| 72 | |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 73 | private static class InvalidServerReplyException extends Exception { |
| 74 | public InvalidServerReplyException(String message) { |
| 75 | super(message); |
| 76 | } |
| 77 | } |
| 78 | |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 79 | /** |
| 80 | * Sends an SNTP request to the given host and processes the response. |
| 81 | * |
| 82 | * @param host host name of the server. |
| 83 | * @param timeout network timeout in milliseconds. |
| 84 | * @return true if the transaction was successful. |
| 85 | */ |
| 86 | public boolean requestTime(String host, int timeout) { |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 87 | InetAddress address = null; |
| 88 | try { |
| 89 | address = InetAddress.getByName(host); |
| 90 | } catch (Exception e) { |
| 91 | if (DBG) Log.d(TAG, "request time failed: " + e); |
| 92 | return false; |
| 93 | } |
| 94 | return requestTime(address, NTP_PORT, timeout); |
| 95 | } |
| 96 | |
| 97 | public boolean requestTime(InetAddress address, int port, int timeout) { |
Nick Kralevich | 2ed20f8 | 2010-12-13 14:32:17 -0800 | [diff] [blame] | 98 | DatagramSocket socket = null; |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 99 | try { |
Nick Kralevich | 2ed20f8 | 2010-12-13 14:32:17 -0800 | [diff] [blame] | 100 | socket = new DatagramSocket(); |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 101 | socket.setSoTimeout(timeout); |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 102 | byte[] buffer = new byte[NTP_PACKET_SIZE]; |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 103 | DatagramPacket request = new DatagramPacket(buffer, buffer.length, address, port); |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 104 | |
Robert Greenwalt | bf7de39 | 2010-04-21 17:09:38 -0700 | [diff] [blame] | 105 | // set mode = 3 (client) and version = 3 |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 106 | // mode is in low 3 bits of first byte |
| 107 | // version is in bits 3-5 of first byte |
| 108 | buffer[0] = NTP_MODE_CLIENT | (NTP_VERSION << 3); |
| 109 | |
| 110 | // get current time and write it to the request packet |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 111 | final long requestTime = System.currentTimeMillis(); |
| 112 | final long requestTicks = SystemClock.elapsedRealtime(); |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 113 | writeTimeStamp(buffer, TRANSMIT_TIME_OFFSET, requestTime); |
| 114 | |
| 115 | socket.send(request); |
Robert Greenwalt | bf7de39 | 2010-04-21 17:09:38 -0700 | [diff] [blame] | 116 | |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 117 | // read the response |
| 118 | DatagramPacket response = new DatagramPacket(buffer, buffer.length); |
| 119 | socket.receive(response); |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 120 | final long responseTicks = SystemClock.elapsedRealtime(); |
| 121 | final long responseTime = requestTime + (responseTicks - requestTicks); |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 122 | |
| 123 | // extract the results |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 124 | final byte leap = (byte) ((buffer[0] >> 6) & 0x3); |
| 125 | final byte mode = (byte) (buffer[0] & 0x7); |
| 126 | final int stratum = (int) (buffer[1] & 0xff); |
| 127 | final long originateTime = readTimeStamp(buffer, ORIGINATE_TIME_OFFSET); |
| 128 | final long receiveTime = readTimeStamp(buffer, RECEIVE_TIME_OFFSET); |
| 129 | final long transmitTime = readTimeStamp(buffer, TRANSMIT_TIME_OFFSET); |
| 130 | |
| 131 | /* do sanity check according to RFC */ |
| 132 | // TODO: validate originateTime == requestTime. |
| 133 | checkValidServerReply(leap, mode, stratum, transmitTime); |
| 134 | |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 135 | long roundTripTime = responseTicks - requestTicks - (transmitTime - receiveTime); |
Robert Greenwalt | 499a121 | 2010-04-15 12:31:55 -0700 | [diff] [blame] | 136 | // receiveTime = originateTime + transit + skew |
| 137 | // responseTime = transmitTime + transit - skew |
| 138 | // clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime))/2 |
| 139 | // = ((originateTime + transit + skew - originateTime) + |
| 140 | // (transmitTime - (transmitTime + transit - skew)))/2 |
| 141 | // = ((transit + skew) + (transmitTime - transmitTime - transit + skew))/2 |
| 142 | // = (transit + skew - transit + skew)/2 |
| 143 | // = (2 * skew)/2 = skew |
| 144 | long clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime))/2; |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 145 | if (DBG) { |
| 146 | Log.d(TAG, "round trip: " + roundTripTime + "ms, " + |
| 147 | "clock offset: " + clockOffset + "ms"); |
| 148 | } |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 149 | |
Robert Greenwalt | 499a121 | 2010-04-15 12:31:55 -0700 | [diff] [blame] | 150 | // save our results - use the times on this side of the network latency |
| 151 | // (response rather than request time) |
| 152 | mNtpTime = responseTime + clockOffset; |
| 153 | mNtpTimeReference = responseTicks; |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 154 | mRoundTripTime = roundTripTime; |
| 155 | } catch (Exception e) { |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 156 | if (DBG) Log.d(TAG, "request time failed: " + e); |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 157 | return false; |
Nick Kralevich | 2ed20f8 | 2010-12-13 14:32:17 -0800 | [diff] [blame] | 158 | } finally { |
| 159 | if (socket != null) { |
| 160 | socket.close(); |
| 161 | } |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 162 | } |
| 163 | |
| 164 | return true; |
| 165 | } |
| 166 | |
| 167 | /** |
| 168 | * Returns the time computed from the NTP transaction. |
| 169 | * |
| 170 | * @return time value computed from NTP server response. |
| 171 | */ |
| 172 | public long getNtpTime() { |
| 173 | return mNtpTime; |
| 174 | } |
| 175 | |
| 176 | /** |
| 177 | * Returns the reference clock value (value of SystemClock.elapsedRealtime()) |
| 178 | * corresponding to the NTP time. |
| 179 | * |
| 180 | * @return reference clock corresponding to the NTP time. |
| 181 | */ |
| 182 | public long getNtpTimeReference() { |
| 183 | return mNtpTimeReference; |
| 184 | } |
| 185 | |
| 186 | /** |
| 187 | * Returns the round trip time of the NTP transaction |
| 188 | * |
| 189 | * @return round trip time in milliseconds. |
| 190 | */ |
| 191 | public long getRoundTripTime() { |
| 192 | return mRoundTripTime; |
| 193 | } |
| 194 | |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 195 | private static void checkValidServerReply( |
| 196 | byte leap, byte mode, int stratum, long transmitTime) |
| 197 | throws InvalidServerReplyException { |
| 198 | if (leap == NTP_LEAP_NOSYNC) { |
| 199 | throw new InvalidServerReplyException("unsynchronized server"); |
| 200 | } |
| 201 | if ((mode != NTP_MODE_SERVER) && (mode != NTP_MODE_BROADCAST)) { |
| 202 | throw new InvalidServerReplyException("untrusted mode: " + mode); |
| 203 | } |
| 204 | if ((stratum == NTP_STRATUM_DEATH) || (stratum > NTP_STRATUM_MAX)) { |
| 205 | throw new InvalidServerReplyException("untrusted stratum: " + stratum); |
| 206 | } |
| 207 | if (transmitTime == 0) { |
| 208 | throw new InvalidServerReplyException("zero transmitTime"); |
| 209 | } |
| 210 | } |
| 211 | |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 212 | /** |
| 213 | * Reads an unsigned 32 bit big endian number from the given offset in the buffer. |
| 214 | */ |
| 215 | private long read32(byte[] buffer, int offset) { |
| 216 | byte b0 = buffer[offset]; |
| 217 | byte b1 = buffer[offset+1]; |
| 218 | byte b2 = buffer[offset+2]; |
| 219 | byte b3 = buffer[offset+3]; |
| 220 | |
| 221 | // convert signed bytes to unsigned values |
| 222 | int i0 = ((b0 & 0x80) == 0x80 ? (b0 & 0x7F) + 0x80 : b0); |
| 223 | int i1 = ((b1 & 0x80) == 0x80 ? (b1 & 0x7F) + 0x80 : b1); |
| 224 | int i2 = ((b2 & 0x80) == 0x80 ? (b2 & 0x7F) + 0x80 : b2); |
| 225 | int i3 = ((b3 & 0x80) == 0x80 ? (b3 & 0x7F) + 0x80 : b3); |
| 226 | |
| 227 | return ((long)i0 << 24) + ((long)i1 << 16) + ((long)i2 << 8) + (long)i3; |
| 228 | } |
| 229 | |
| 230 | /** |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 231 | * Reads the NTP time stamp at the given offset in the buffer and returns |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 232 | * it as a system time (milliseconds since January 1, 1970). |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 233 | */ |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 234 | private long readTimeStamp(byte[] buffer, int offset) { |
| 235 | long seconds = read32(buffer, offset); |
| 236 | long fraction = read32(buffer, offset + 4); |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 237 | // Special case: zero means zero. |
| 238 | if (seconds == 0 && fraction == 0) { |
| 239 | return 0; |
| 240 | } |
| 241 | return ((seconds - OFFSET_1900_TO_1970) * 1000) + ((fraction * 1000L) / 0x100000000L); |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 242 | } |
| 243 | |
| 244 | /** |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 245 | * Writes system time (milliseconds since January 1, 1970) as an NTP time stamp |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 246 | * at the given offset in the buffer. |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 247 | */ |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 248 | private void writeTimeStamp(byte[] buffer, int offset, long time) { |
Jerry Wong | 32d52f3 | 2015-10-06 22:18:11 -0700 | [diff] [blame] | 249 | // Special case: zero means zero. |
| 250 | if (time == 0) { |
| 251 | Arrays.fill(buffer, offset, offset + 8, (byte) 0x00); |
| 252 | return; |
| 253 | } |
| 254 | |
The Android Open Source Project | 9066cfe | 2009-03-03 19:31:44 -0800 | [diff] [blame] | 255 | long seconds = time / 1000L; |
| 256 | long milliseconds = time - seconds * 1000L; |
| 257 | seconds += OFFSET_1900_TO_1970; |
| 258 | |
| 259 | // write seconds in big endian format |
| 260 | buffer[offset++] = (byte)(seconds >> 24); |
| 261 | buffer[offset++] = (byte)(seconds >> 16); |
| 262 | buffer[offset++] = (byte)(seconds >> 8); |
| 263 | buffer[offset++] = (byte)(seconds >> 0); |
| 264 | |
| 265 | long fraction = milliseconds * 0x100000000L / 1000L; |
| 266 | // write fraction in big endian format |
| 267 | buffer[offset++] = (byte)(fraction >> 24); |
| 268 | buffer[offset++] = (byte)(fraction >> 16); |
| 269 | buffer[offset++] = (byte)(fraction >> 8); |
| 270 | // low order bits should be random data |
| 271 | buffer[offset++] = (byte)(Math.random() * 255.0); |
| 272 | } |
| 273 | } |