Android使用NTP服务器获取当前时间
16lz
2021-01-26
前言
由于NTP服务在Android系统中已经存在，但是隐藏的系统API普通的开发手段无法调用。因此通过阅读相关源码就可以整理出我们自己可以使用的逻辑实现。
源码相关文件
-
frameworks/base/services/java/com/android/server/SystemServer.java
系统服务类，用于启动管理后续的系统服务，如NetworkTimeUpdateService -
frameworks/base/services/java/com/android/server/NetworkTimeUpdateService.java
通过onPollNetworkTime调用NtpTrustedTime.forceRefresh()获取NTP服务器时间 -
frameworks/base/core/java/android/util/NtpTrustedTime.java
创建SntpClient实例，调用SntpClient.requestTime()使用UDP协议请求网络时间 -
frameworks/base/core/java/android/net/SntpClient.java
发起服务器请求，并处理返回结果 -
frameworks/base/core/res/res/values/config.xml
Android系统配置ntpServer的文件路径
常用的可用的NTP服务器地址
基本官方通过这里查看https://www.pool.ntp.org/zh/zone/asia，但由于一些不可抗拒的原因有可能无法使用，目前整理出的可用的NTP服务器地址列表如下：
"ntp1.aliyun.com", "ntp2.aliyun.com", "ntp3.aliyun.com", "ntp4.aliyun.com", "ntp5.aliyun.com", "ntp6.aliyun.com", "ntp7.aliyun.com", "cn.pool.ntp.org", "cn.ntp.org.cn", "sg.pool.ntp.org", "tw.pool.ntp.org", "jp.pool.ntp.org", "hk.pool.ntp.org", "th.pool.ntp.org", "time.windows.com", "time.nist.gov", "time.apple.com", "time.asia.apple.com", "dns1.synet.edu.cn", "news.neu.edu.cn", "dns.sjtu.edu.cn", "dns2.synet.edu.cn", "ntp.glnet.edu.cn", "s2g.time.edu.cn", "ntp-sz.chl.la", "ntp.gwadar.cn", "3.asia.pool.ntp.org"复制整理SntpClient.java文件
拿出系统的源码是不能直接使用的，有一些内部日志输出的方法我们也不需要使用，因此替换成android.util.Log的输出结果如下，可直接使用
/* * 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 com.ziv.demo.ntptimeservice.services;import android.net.Network;import android.os.SystemClock;import android.util.Log;import java.net.DatagramPacket;import java.net.DatagramSocket;import java.net.InetAddress;import java.net.UnknownHostException;import java.util.Arrays;/** * 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 boolean DBG = true; 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_MODE_SERVER = 4; private static final int NTP_MODE_BROADCAST = 5; private static final int NTP_VERSION = 3; private static final int NTP_LEAP_NOSYNC = 3; private static final int NTP_STRATUM_DEATH = 0; private static final int NTP_STRATUM_MAX = 15; // 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 static class InvalidServerReplyException extends Exception { public InvalidServerReplyException(String message) { super(message); } } /** * 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; InetAddress address = null; try { address = InetAddress.getByName(host); socket = new DatagramSocket(); socket.setSoTimeout(timeout); 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 final long requestTime = System.currentTimeMillis(); final 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); final long responseTicks = SystemClock.elapsedRealtime(); final long responseTime = requestTime + (responseTicks - requestTicks); // extract the results final byte leap = (byte) ((buffer[0] >> 6) & 0x3); final byte mode = (byte) (buffer[0] & 0x7); final int stratum = (int) (buffer[1] & 0xff); final long originateTime = readTimeStamp(buffer, ORIGINATE_TIME_OFFSET); final long receiveTime = readTimeStamp(buffer, RECEIVE_TIME_OFFSET); final long transmitTime = readTimeStamp(buffer, TRANSMIT_TIME_OFFSET); /* do sanity check according to RFC */ // TODO: validate originateTime == requestTime. checkValidServerReply(leap, mode, stratum, transmitTime); long roundTripTime = responseTicks - requestTicks - (transmitTime - receiveTime); // receiveTime = originateTime + transit + skew // responseTime = transmitTime + transit - skew long 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 Log.d(TAG, "Request time form ntp server success, " + address.toString() + " ,roundTripTime: " + roundTripTime); if (DBG) { Log.d(TAG, "round trip: " + roundTripTime + "ms, " + "clock offset: " + clockOffset + "ms"); } // save our results - use the times on this side of the network latency // (response rather than request time) mNtpTime = responseTime + clockOffset; mNtpTimeReference = responseTicks; mRoundTripTime = roundTripTime; } catch (Exception e) {// if (DBG) {// Log.e(TAG, "Error address: " + address.toString());// } Log.e(TAG, "Request time from ntp server failed ,msg: " + e.getMessage()); 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; } private static void checkValidServerReply( byte leap, byte mode, int stratum, long transmitTime) throws InvalidServerReplyException { if (leap == NTP_LEAP_NOSYNC) { throw new InvalidServerReplyException("unsynchronized server"); } if ((mode != NTP_MODE_SERVER) && (mode != NTP_MODE_BROADCAST)) { throw new InvalidServerReplyException("untrusted mode: " + mode); } if ((stratum == NTP_STRATUM_DEATH) || (stratum > NTP_STRATUM_MAX)) { throw new InvalidServerReplyException("untrusted stratum: " + stratum); } if (transmitTime == 0) { throw new InvalidServerReplyException("zero transmitTime"); } } /** * 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); // Special case: zero means zero. if (seconds == 0 && fraction == 0) { return 0; } 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) { // Special case: zero means zero. if (time == 0) { Arrays.fill(buffer, offset, offset + 8, (byte) 0x00); return; } 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); }}使用示例
注意，一定要在非主线程调用，并添加网络访问权限
new Thread(){ @Override public void run() { SntpClient sntpClient = new SntpClient(); if (sntpClient.requestTime("cn.pool.ntp.org", 30000)) { long now = sntpClient.getNtpTime() + SystemClock.elapsedRealtime() - sntpClient.getNtpTimeReference(); Date current = new Date(now); Log.d(TAG, current.toString()); } }}.start();结束语
Github地址：https://github.com/Ziv-Android/NTPTimeServiceDemo
RTFSC(Read the Fucking Source Code)
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