SNTP获取时间源统一时间
时间记录：2019-9-30
最近在进行时间戳的服务的阅读的时候发现了我们通常会使用一个公用的时间源作为一个标准的时间，我们知道在windows中有一个网络时间同步的功能那里使用的同步的时间源就是基于一种协议的网络的时间的请求。通常在作为网络的时间机器的时间的依据是一个量子时间钟，这个时间的误差在2000万年的误差很小。我们不做研究在这里，我们这里主要了解下时间的网络的协议的格式以及数据的传输的方式，在进行获取网络时间的时候如何进行网络的时间的获取(这里以java的方式来进行请求)
我们首先建立自己的时间源服务，这里使用的是ntp，然后就是不同版本的rfc的协议的格式，然后就是在java下如何进行时间的获取(其实只要了解其的网络的协议的格式就可以了，不仅仅是局限于语言)
搭建自己的时间源
环境描述：我这里是基于虚拟机的操作
安装
yum install ntp
配置ntp
vi /etc/ntp.conf
找到service，添加自己的地址127.0.0.1，将其余的上游注释，也可以使用其余上游
我们只需要指定当前的时间源为服务的时间源，在实际的环境中通常会有多级的时间源，这里也可以进行简单的配置
时间源服务的默认端口为123
时间源的数据格式
时间源服务的协议的报文格式服从RFC标准
从下面的NtpMessage中有得知支持所有版本的NTP和SNTP
This class represents a NTP message, as specified in RFC 2030. The message format is compatible with all versions of NTP and SNTP.
协议介绍这一块不做具体的研究了，平时使用的不多，主要记录下，存在这样一个东西
java的时间数据的获取
sntp使用的是UDP的网络协议，进行数据的传输，在java中封装组合了UDP协议的DatagramSocket的api进行网络的请求。然后我们需要知道对应的网络协议的数据格式，就可以进行数据的交互，将对应的数据格式转换为自己需要的，可以理解的数据，实际上就是对一对的数据进行持久化的封装，以供自己的需求和使用，java中有现成的javasntpclient.源地址链接，我们尝试使用此项进行网络的时间源的数据的获取。其中主要的是NtpMessage的封装，为了跟方便的使用
package com.huo.time;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.text.DecimalFormat;
/**
* NtpClient - an NTP client for Java. This program connects to an NTP server
* and prints the response to the console.
*
* The local clock offset calculation is implemented according to the SNTP
* algorithm specified in RFC 2030.
*
* Note that on windows platforms, the curent time-of-day timestamp is limited
* to an resolution of 10ms and adversely affects the accuracy of the results.
*
*
* This code is copyright (c) Adam Buckley 2004
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the Free
* Software Foundation; either version 2 of the License, or (at your option)
* any later version. A HTML version of the GNU General Public License can be
* seen at http://www.gnu.org/licenses/gpl.html
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
*
* @author Adam Buckley
*/
public class SntpClient
{
public static void main(String[] args) throws IOException
{
String serverName = "192.168.195.128";
// Process command-line args
// if(args.length==1)
// {
// serverName = args[0];
// }
// else
// {
// printUsage();
// return;
// }
// Send request
DatagramSocket socket = new DatagramSocket();
InetAddress address = InetAddress.getByName(serverName);
byte[] buf = new NtpMessage().toByteArray();
DatagramPacket packet =
new DatagramPacket(buf, buf.length, address, 123);
// Set the transmit timestamp *just* before sending the packet
// ToDo: Does this actually improve performance or not?
NtpMessage.encodeTimestamp(packet.getData(), 40,
(System.currentTimeMillis()/1000.0) + 2208988800.0);
socket.send(packet);
// Get response
System.out.println("NTP request sent, waiting for response...\n");
packet = new DatagramPacket(buf, buf.length);
socket.receive(packet);
// Immediately record the incoming timestamp
double destinationTimestamp =
(System.currentTimeMillis()/1000.0) + 2208988800.0;
// Process response
NtpMessage msg = new NtpMessage(packet.getData());
// Corrected, according to RFC2030 errata
double roundTripDelay = (destinationTimestamp-msg.originateTimestamp) -
(msg.transmitTimestamp-msg.receiveTimestamp);
double localClockOffset =
((msg.receiveTimestamp - msg.originateTimestamp) +
(msg.transmitTimestamp - destinationTimestamp)) / 2;
// Display response
System.out.println("NTP server: " + serverName);
System.out.println(msg.toString());
System.out.println("Dest. timestamp: " +
NtpMessage.timestampToString(destinationTimestamp));
System.out.println("Round-trip delay: " +
new DecimalFormat("0.00").format(roundTripDelay*1000) + " ms");
System.out.println("Local clock offset: " +
new DecimalFormat("0.00").format(localClockOffset*1000) + " ms");
socket.close();
}
/**
* Prints usage
*/
static void printUsage()
{
System.out.println(
"NtpClient - an NTP client for Java.\n" +
"\n" +
"This program connects to an NTP server and prints the response to the console.\n" +
"\n" +
"\n" +
"Usage: java NtpClient server\n" +
"\n" +
"\n" +
"This program is copyright (c) Adam Buckley 2004 and distributed under the terms\n" +
"of the GNU General Public License. This program is distributed in the hope\n" +
"that it will be useful, but WITHOUT ANY WARRANTY; without even the implied\n" +
"warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU\n" +
"General Public License available at http://www.gnu.org/licenses/gpl.html for\n" +
"more details.");
}
}
package com.huo.time;
import java.text.DecimalFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
/**
* This class represents a NTP message, as specified in RFC 2030. The message
* format is compatible with all versions of NTP and SNTP.
*
* This class does not support the optional authentication protocol, and
* ignores the key ID and message digest fields.
*
* For convenience, this class exposes message values as native Java types, not
* the NTP-specified data formats. For example, timestamps are
* stored as doubles (as opposed to the NTP unsigned 64-bit fixed point
* format).
*
* However, the contructor NtpMessage(byte[]) and the method toByteArray()
* allow the import and export of the raw NTP message format.
*
*
* Usage example
*
* // Send message
* DatagramSocket socket = new DatagramSocket();
* InetAddress address = InetAddress.getByName("ntp.cais.rnp.br");
* byte[] buf = new NtpMessage().toByteArray();
* DatagramPacket packet = new DatagramPacket(buf, buf.length, address, 123);
* socket.send(packet);
*
* // Get response
* socket.receive(packet);
* System.out.println(msg.toString());
*
*
* This code is copyright (c) Adam Buckley 2004
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the Free
* Software Foundation; either version 2 of the License, or (at your option)
* any later version. A HTML version of the GNU General Public License can be
* seen at http://www.gnu.org/licenses/gpl.html
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
*
*
* Comments for member variables are taken from RFC2030 by David Mills,
* University of Delaware.
*
* Number format conversion code in NtpMessage(byte[] array) and toByteArray()
* inspired by http://www.pps.jussieu.fr/~jch/enseignement/reseaux/
* NTPMessage.java which is copyright (c) 2003 by Juliusz Chroboczek
*
* @author Adam Buckley
*/
public class NtpMessage
{
/**
* This is a two-bit code warning of an impending leap second to be
* inserted/deleted in the last minute of the current day. It's values
* may be as follows:
*
* Value Meaning
* ----- -------
* 0 no warning
* 1 last minute has 61 seconds
* 2 last minute has 59 seconds)
* 3 alarm condition (clock not synchronized)
*/
public byte leapIndicator = 0;
/**
* This value indicates the NTP/SNTP version number. The version number
* is 3 for Version 3 (IPv4 only) and 4 for Version 4 (IPv4, IPv6 and OSI).
* If necessary to distinguish between IPv4, IPv6 and OSI, the
* encapsulating context must be inspected.
*/
public byte version = 3;
/**
* This value indicates the mode, with values defined as follows:
*
* Mode Meaning
* ---- -------
* 0 reserved
* 1 symmetric active
* 2 symmetric passive
* 3 client
* 4 server
* 5 broadcast
* 6 reserved for NTP control message
* 7 reserved for private use
*
* In unicast and anycast modes, the client sets this field to 3 (client)
* in the request and the server sets it to 4 (server) in the reply. In
* multicast mode, the server sets this field to 5 (broadcast).
*/
public byte mode = 0;
/**
* This value indicates the stratum level of the local clock, with values
* defined as follows:
*
* Stratum Meaning
* ----------------------------------------------
* 0 unspecified or unavailable
* 1 primary reference (e.g., radio clock)
* 2-15 secondary reference (via NTP or SNTP)
* 16-255 reserved
*/
public short stratum = 0;
/**
* This value indicates the maximum interval between successive messages,
* in seconds to the nearest power of two. The values that can appear in
* this field presently range from 4 (16 s) to 14 (16284 s); however, most
* applications use only the sub-range 6 (64 s) to 10 (1024 s).
*/
public byte pollInterval = 0;
/**
* This value indicates the precision of the local clock, in seconds to
* the nearest power of two. The values that normally appear in this field
* range from -6 for mains-frequency clocks to -20 for microsecond clocks
* found in some workstations.
*/
public byte precision = 0;
/**
* This value indicates the total roundtrip delay to the primary reference
* source, in seconds. Note that this variable can take on both positive
* and negative values, depending on the relative time and frequency
* offsets. The values that normally appear in this field range from
* negative values of a few milliseconds to positive values of several
* hundred milliseconds.
*/
public double rootDelay = 0;
/**
* This value indicates the nominal error relative to the primary reference
* source, in seconds. The values that normally appear in this field
* range from 0 to several hundred milliseconds.
*/
public double rootDispersion = 0;
/**
* This is a 4-byte array identifying the particular reference source.
* In the case of NTP Version 3 or Version 4 stratum-0 (unspecified) or
* stratum-1 (primary) servers, this is a four-character ASCII string, left
* justified and zero padded to 32 bits. In NTP Version 3 secondary
* servers, this is the 32-bit IPv4 address of the reference source. In NTP
* Version 4 secondary servers, this is the low order 32 bits of the latest
* transmit timestamp of the reference source. NTP primary (stratum 1)
* servers should set this field to a code identifying the external
* reference source according to the following list. If the external
* reference is one of those listed, the associated code should be used.
* Codes for sources not listed can be contrived as appropriate.
*
* Code External Reference Source
* ---- -------------------------
* LOCL uncalibrated local clock used as a primary reference for
* a subnet without external means of synchronization
* PPS atomic clock or other pulse-per-second source
* individually calibrated to national standards
* ACTS NIST dialup modem service
* USNO USNO modem service
* PTB PTB (Germany) modem service
* TDF Allouis (France) Radio 164 kHz
* DCF Mainflingen (Germany) Radio 77.5 kHz
* MSF Rugby (UK) Radio 60 kHz
* WWV Ft. Collins (US) Radio 2.5, 5, 10, 15, 20 MHz
* WWVB Boulder (US) Radio 60 kHz
* WWVH Kaui Hawaii (US) Radio 2.5, 5, 10, 15 MHz
* CHU Ottawa (Canada) Radio 3330, 7335, 14670 kHz
* LORC LORAN-C radionavigation system
* OMEG OMEGA radionavigation system
* GPS Global Positioning Service
* GOES Geostationary Orbit Environment Satellite
*/
public byte[] referenceIdentifier = {0, 0, 0, 0};
/**
* This is the time at which the local clock was last set or corrected, in
* seconds since 00:00 1-Jan-1900.
*/
public double referenceTimestamp = 0;
/**
* This is the time at which the request departed the client for the
* server, in seconds since 00:00 1-Jan-1900.
*/
public double originateTimestamp = 0;
/**
* This is the time at which the request arrived at the server, in seconds
* since 00:00 1-Jan-1900.
*/
public double receiveTimestamp = 0;
/**
* This is the time at which the reply departed the server for the client,
* in seconds since 00:00 1-Jan-1900.
*/
public double transmitTimestamp = 0;
/**
* Constructs a new NtpMessage from an array of bytes.
*/
public NtpMessage(byte[] array)
{
// See the packet format diagram in RFC 2030 for details
leapIndicator = (byte) ((array[0] >> 6) & 0x3);
version = (byte) ((array[0] >> 3) & 0x7);
mode = (byte) (array[0] & 0x7);
stratum = unsignedByteToShort(array[1]);
pollInterval = array[2];
precision = array[3];
rootDelay = (array[4] * 256.0) +
unsignedByteToShort(array[5]) +
(unsignedByteToShort(array[6]) / 256.0) +
(unsignedByteToShort(array[7]) / 65536.0);
rootDispersion = (unsignedByteToShort(array[8]) * 256.0) +
unsignedByteToShort(array[9]) +
(unsignedByteToShort(array[10]) / 256.0) +
(unsignedByteToShort(array[11]) / 65536.0);
referenceIdentifier[0] = array[12];
referenceIdentifier[1] = array[13];
referenceIdentifier[2] = array[14];
referenceIdentifier[3] = array[15];
referenceTimestamp = decodeTimestamp(array, 16);
originateTimestamp = decodeTimestamp(array, 24);
receiveTimestamp = decodeTimestamp(array, 32);
transmitTimestamp = decodeTimestamp(array, 40);
}
/**
* Constructs a new NtpMessage in client -> server mode, and sets the
* transmit timestamp to the current time.
*/
public NtpMessage()
{
// Note that all the other member variables are already set with
// appropriate default values.
this.mode = 3;
this.transmitTimestamp = (System.currentTimeMillis()/1000.0) + 2208988800.0;
}
/**
* This method constructs the data bytes of a raw NTP packet.
*/
public byte[] toByteArray()
{
// All bytes are automatically set to 0
byte[] p = new byte[48];
p[0] = (byte) (leapIndicator << 6 | version << 3 | mode);
p[1] = (byte) stratum;
p[2] = (byte) pollInterval;
p[3] = (byte) precision;
// root delay is a signed 16.16-bit FP, in Java an int is 32-bits
int l = (int) (rootDelay * 65536.0);
p[4] = (byte) ((l >> 24) & 0xFF);
p[5] = (byte) ((l >> 16) & 0xFF);
p[6] = (byte) ((l >> 8) & 0xFF);
p[7] = (byte) (l & 0xFF);
// root dispersion is an unsigned 16.16-bit FP, in Java there are no
// unsigned primitive types, so we use a long which is 64-bits
long ul = (long) (rootDispersion * 65536.0);
p[8] = (byte) ((ul >> 24) & 0xFF);
p[9] = (byte) ((ul >> 16) & 0xFF);
p[10] = (byte) ((ul >> 8) & 0xFF);
p[11] = (byte) (ul & 0xFF);
p[12] = referenceIdentifier[0];
p[13] = referenceIdentifier[1];
p[14] = referenceIdentifier[2];
p[15] = referenceIdentifier[3];
encodeTimestamp(p, 16, referenceTimestamp);
encodeTimestamp(p, 24, originateTimestamp);
encodeTimestamp(p, 32, receiveTimestamp);
encodeTimestamp(p, 40, transmitTimestamp);
return p;
}
/**
* Returns a string representation of a NtpMessage
*/
public String toString()
{
String precisionStr =
new DecimalFormat("0.#E0").format(Math.pow(2, precision));
return "Leap indicator: " + leapIndicator + "\n" +
"Version: " + version + "\n" +
"Mode: " + mode + "\n" +
"Stratum: " + stratum + "\n" +
"Poll: " + pollInterval + "\n" +
"Precision: " + precision + " (" + precisionStr + " seconds)\n" +
"Root delay: " + new DecimalFormat("0.00").format(rootDelay*1000) + " ms\n" +
"Root dispersion: " + new DecimalFormat("0.00").format(rootDispersion*1000) + " ms\n" +
"Reference identifier: " + referenceIdentifierToString(referenceIdentifier, stratum, version) + "\n" +
"Reference timestamp: " + timestampToString(referenceTimestamp) + "\n" +
"Originate timestamp: " + timestampToString(originateTimestamp) + "\n" +
"Receive timestamp: " + timestampToString(receiveTimestamp) + "\n" +
"Transmit timestamp: " + timestampToString(transmitTimestamp);
}
/**
* Converts an unsigned byte to a short. By default, Java assumes that
* a byte is signed.
*/
public static short unsignedByteToShort(byte b)
{
if((b & 0x80)==0x80) return (short) (128 + (b & 0x7f));
else return (short) b;
}
/**
* Will read 8 bytes of a message beginning at pointer
* and return it as a double, according to the NTP 64-bit timestamp
* format.
*/
public static double decodeTimestamp(byte[] array, int pointer)
{
double r = 0.0;
for(int i=0; i<8; i++)
{
r += unsignedByteToShort(array[pointer+i]) * Math.pow(2, (3-i)*8);
}
return r;
}
/**
* Encodes a timestamp in the specified position in the message
*/
public static void encodeTimestamp(byte[] array, int pointer, double timestamp)
{
// Converts a double into a 64-bit fixed point
for(int i=0; i<8; i++)
{
// 2^24, 2^16, 2^8, .. 2^-32
double base = Math.pow(2, (3-i)*8);
// Capture byte value
array[pointer+i] = (byte) (timestamp / base);
// Subtract captured value from remaining total
timestamp = timestamp - (double) (unsignedByteToShort(array[pointer+i]) * base);
}
// From RFC 2030: It is advisable to fill the non-significant
// low order bits of the timestamp with a random, unbiased
// bitstring, both to avoid systematic roundoff errors and as
// a means of loop detection and replay detection.
array[7] = (byte) (Math.random()*255.0);
}
/**
* Returns a timestamp (number of seconds since 00:00 1-Jan-1900) as a
* formatted date/time string.
*/
public static String timestampToString(double timestamp)
{
if(timestamp==0) return "0";
// timestamp is relative to 1900, utc is used by Java and is relative
// to 1970
double utc = timestamp - (2208988800.0);
// milliseconds
long ms = (long) (utc * 1000.0);
// date/time
String date = new SimpleDateFormat("dd-MMM-yyyy HH:mm:ss").format(new Date(ms));
// fraction
double fraction = timestamp - ((long) timestamp);
String fractionSting = new DecimalFormat(".000000").format(fraction);
return date + fractionSting;
}
/**
* Returns a string representation of a reference identifier according
* to the rules set out in RFC 2030.
*/
public static String referenceIdentifierToString(byte[] ref, short stratum, byte version)
{
// From the RFC 2030:
// In the case of NTP Version 3 or Version 4 stratum-0 (unspecified)
// or stratum-1 (primary) servers, this is a four-character ASCII
// string, left justified and zero padded to 32 bits.
if(stratum==0 || stratum==1)
{
return new String(ref);
}
// In NTP Version 3 secondary servers, this is the 32-bit IPv4
// address of the reference source.
else if(version==3)
{
return unsignedByteToShort(ref[0]) + "." +
unsignedByteToShort(ref[1]) + "." +
unsignedByteToShort(ref[2]) + "." +
unsignedByteToShort(ref[3]);
}
// In NTP Version 4 secondary servers, this is the low order 32 bits
// of the latest transmit timestamp of the reference source.
else if(version==4)
{
return "" + ((unsignedByteToShort(ref[0]) / 256.0) +
(unsignedByteToShort(ref[1]) / 65536.0) +
(unsignedByteToShort(ref[2]) / 16777216.0) +
(unsignedByteToShort(ref[3]) / 4294967296.0));
}
return "";
}
}
测试结果
将ntpclient中的serviceName替换为192.168.195.128,结果为
NTP request sent, waiting for response...
NTP server: 192.168.195.128
Leap indicator: 3
Version: 3
Mode: 4
Stratum: 3
Poll: 3
Precision: -25 (3E-8 seconds)
Root delay: 41.81 ms
Root dispersion: 2214.39 ms
Reference identifier: 119.28.206.193
Reference timestamp: 14-十月-2019 23:36:18.240972
Originate timestamp: 14-十月-2019 23:36:36.530000
Receive timestamp: 14-十月-2019 23:36:34.489635
Transmit timestamp: 14-十月-2019 23:36:34.489730
Dest. timestamp: 14-十月-2019 23:36:36.531000
Round-trip delay: 0.91 ms
Local clock offset: -2040.82 ms
我们再使用windows提供的网络时间同步的地址，则替换serviceName为time.windows.com，结果为
NTP request sent, waiting for response...
NTP server: time.windows.com
Leap indicator: 0
Version: 3
Mode: 4
Stratum: 3
Poll: 0
Precision: -23 (1.2E-7 seconds)
Root delay: 19.26 ms
Root dispersion: 51.68 ms
Reference identifier: 25.66.230.5
Reference timestamp: 14-十月-2019 23:40:45.213007
Originate timestamp: 14-十月-2019 23:40:58.209000
Receive timestamp: 14-十月-2019 23:40:58.447006
Transmit timestamp: 14-十月-2019 23:40:58.447008
Dest. timestamp: 14-十月-2019 23:40:58.344000
Round-trip delay: 135.00 ms
Local clock offset: 170.51 ms
对不同的版本的协议的格式，只要修改对应的数据解析就可以使用了，也可以对不同版本的有着不同的解析方式，做到适应
总结： 时间源基本上在时间戳，证书的有效验证上使用的比较多，主要就是定一个标准，像国家授时中心也是同样的
时间记录：2019-10-1