From 54b6cfa9a9e5b861a9930af873580d6dc20f773c Mon Sep 17 00:00:00 2001 From: The Android Open Source Project Date: Tue, 21 Oct 2008 07:00:00 -0700 Subject: Initial Contribution --- core/java/android/net/SntpClient.java | 201 ++++++++++++++++++++++++++++++++++ 1 file changed, 201 insertions(+) create mode 100644 core/java/android/net/SntpClient.java (limited to 'core/java/android/net/SntpClient.java') diff --git a/core/java/android/net/SntpClient.java b/core/java/android/net/SntpClient.java new file mode 100644 index 0000000..28134b2 --- /dev/null +++ b/core/java/android/net/SntpClient.java @@ -0,0 +1,201 @@ +/* + * 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 android.net; + +import android.os.SystemClock; +import android.util.Config; +import android.util.Log; + +import java.io.IOException; +import java.net.DatagramPacket; +import java.net.DatagramSocket; +import java.net.InetAddress; + +/** + * {@hide} + * + * Simple SNTP client class for retrieving network time. + * + * Sample usage: + * 
SntpClient client = new SntpClient();
+ * if (client.requestTime("time.foo.com")) {
+ *     long now = client.getNtpTime() + SystemClock.elapsedRealtime() - client.getNtpTimeReference();
+ * }
+ *
+ */ +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; + + /** + * 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) { + try { + DatagramSocket 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); + socket.close(); + + // 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); + long clockOffset = (receiveTime - originateTime) + (transmitTime - responseTime); + if (Config.LOGD) Log.d(TAG, "round trip: " + roundTripTime + " ms"); + if (Config.LOGD) Log.d(TAG, "clock offset: " + clockOffset + " ms"); + + // save our results + mNtpTime = requestTime + clockOffset; + mNtpTimeReference = requestTicks; + mRoundTripTime = roundTripTime; + } catch (Exception e) { + if (Config.LOGD) Log.d(TAG, "request time failed: " + e); + return false; + } + + 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; + } + + /** + * 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); + } +} -- cgit v1.1