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Apache Commons Net library contains a collection of network utilities and protocol implementations.
Supported protocols include: Echo, Finger, FTP, NNTP, NTP, POP3(S), SMTP(S), Telnet, Whois
package org.apache.commons.net.ntp;
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.util.ArrayList;
import java.util.List;
/**
* Wrapper class to network time packet messages (NTP, etc) that computes
* related timing info and stats.
*/
public class TimeInfo {
private final NtpV3Packet message;
private List comments;
private Long delayMillis;
private Long offsetMillis;
/**
* time at which time message packet was received by local machine
*/
private final long returnTimeMillis;
/**
* flag indicating that the TimeInfo details was processed and delay/offset were computed
*/
private boolean detailsComputed;
/**
* Create TimeInfo object with raw packet message and destination time received.
*
* @param message NTP message packet
* @param returnTimeMillis destination receive time
* @throws IllegalArgumentException if message is null
*/
public TimeInfo(final NtpV3Packet message, final long returnTimeMillis) {
this(message, returnTimeMillis, null, true);
}
/**
* Create TimeInfo object with raw packet message and destination time received.
*
* @param message NTP message packet
* @param returnTimeMillis destination receive time
* @param comments List of errors/warnings identified during processing
* @throws IllegalArgumentException if message is null
*/
public TimeInfo(final NtpV3Packet message, final long returnTimeMillis, final List comments)
{
this(message, returnTimeMillis, comments, true);
}
/**
* Create TimeInfo object with raw packet message and destination time received.
* Auto-computes details if computeDetails flag set otherwise this is delayed
* until computeDetails() is called. Delayed computation is for fast
* intialization when sub-millisecond timing is needed.
*
* @param msgPacket NTP message packet
* @param returnTimeMillis destination receive time
* @param doComputeDetails flag to pre-compute delay/offset values
* @throws IllegalArgumentException if message is null
*/
public TimeInfo(final NtpV3Packet msgPacket, final long returnTimeMillis, final boolean doComputeDetails)
{
this(msgPacket, returnTimeMillis, null, doComputeDetails);
}
/**
* Create TimeInfo object with raw packet message and destination time received.
* Auto-computes details if computeDetails flag set otherwise this is delayed
* until computeDetails() is called. Delayed computation is for fast
* intialization when sub-millisecond timing is needed.
*
* @param message NTP message packet
* @param returnTimeMillis destination receive time
* @param comments list of comments used to store errors/warnings with message
* @param doComputeDetails flag to pre-compute delay/offset values
* @throws IllegalArgumentException if message is null
*/
public TimeInfo(final NtpV3Packet message, final long returnTimeMillis, final List comments,
final boolean doComputeDetails)
{
if (message == null) {
throw new IllegalArgumentException("message cannot be null");
}
this.returnTimeMillis = returnTimeMillis;
this.message = message;
this.comments = comments;
if (doComputeDetails) {
computeDetails();
}
}
/**
* Add comment (error/warning) to list of comments associated
* with processing of NTP parameters. If comment list not create
* then one will be created.
*
* @param comment the comment
*/
public void addComment(final String comment)
{
if (comments == null) {
comments = new ArrayList<>();
}
comments.add(comment);
}
/**
* Compute and validate details of the NTP message packet. Computed
* fields include the offset and delay.
*/
public void computeDetails()
{
if (detailsComputed) {
return; // details already computed - do nothing
}
detailsComputed = true;
if (comments == null) {
comments = new ArrayList<>();
}
final TimeStamp origNtpTime = message.getOriginateTimeStamp();
final long origTimeMillis = origNtpTime.getTime();
// Receive Time is time request received by server (t2)
final TimeStamp rcvNtpTime = message.getReceiveTimeStamp();
final long rcvTimeMillis = rcvNtpTime.getTime();
// Transmit time is time reply sent by server (t3)
final TimeStamp xmitNtpTime = message.getTransmitTimeStamp();
final long xmitTimeMillis = xmitNtpTime.getTime();
/*
* Round-trip network delay and local clock offset (or time drift) is calculated
* according to this standard NTP equation:
*
* LocalClockOffset = ((ReceiveTimestamp - OriginateTimestamp) +
* (TransmitTimestamp - DestinationTimestamp)) / 2
*
* equations from RFC-1305 (NTPv3)
* roundtrip delay = (t4 - t1) - (t3 - t2)
* local clock offset = ((t2 - t1) + (t3 - t4)) / 2
*
* It takes into account network delays and assumes that they are symmetrical.
*
* Note the typo in SNTP RFCs 1769/2030 which state that the delay
* is (T4 - T1) - (T2 - T3) with the "T2" and "T3" switched.
*/
if (origNtpTime.ntpValue() == 0)
{
// without originate time cannot determine when packet went out
// might be via a broadcast NTP packet...
if (xmitNtpTime.ntpValue() != 0)
{
offsetMillis = Long.valueOf(xmitTimeMillis - returnTimeMillis);
comments.add("Error: zero orig time -- cannot compute delay");
} else {
comments.add("Error: zero orig time -- cannot compute delay/offset");
}
} else if (rcvNtpTime.ntpValue() == 0 || xmitNtpTime.ntpValue() == 0) {
comments.add("Warning: zero rcvNtpTime or xmitNtpTime");
// assert destTime >= origTime since network delay cannot be negative
if (origTimeMillis > returnTimeMillis) {
comments.add("Error: OrigTime > DestRcvTime");
} else {
// without receive or xmit time cannot figure out processing time
// so delay is simply the network travel time
delayMillis = Long.valueOf(returnTimeMillis - origTimeMillis);
}
// TODO: is offset still valid if rcvNtpTime=0 || xmitNtpTime=0 ???
// Could always hash origNtpTime (sendTime) but if host doesn't set it
// then it's an malformed ntp host anyway and we don't care?
// If server is in broadcast mode then we never send out a query in first place...
if (rcvNtpTime.ntpValue() != 0)
{
// xmitTime is 0 just use rcv time
offsetMillis = Long.valueOf(rcvTimeMillis - origTimeMillis);
} else if (xmitNtpTime.ntpValue() != 0)
{
// rcvTime is 0 just use xmitTime time
offsetMillis = Long.valueOf(xmitTimeMillis - returnTimeMillis);
}
} else
{
long delayValueMillis = returnTimeMillis - origTimeMillis;
// assert xmitTime >= rcvTime: difference typically < 1ms
if (xmitTimeMillis < rcvTimeMillis)
{
// server cannot send out a packet before receiving it...
comments.add("Error: xmitTime < rcvTime"); // time-travel not allowed
} else
{
// subtract processing time from round-trip network delay
final long deltaMillis = xmitTimeMillis - rcvTimeMillis;
// in normal cases the processing delta is less than
// the total roundtrip network travel time.
if (deltaMillis <= delayValueMillis)
{
delayValueMillis -= deltaMillis; // delay = (t4 - t1) - (t3 - t2)
} else
{
// if delta - delayValue == 1 ms then it's a round-off error
// e.g. delay=3ms, processing=4ms
if (deltaMillis - delayValueMillis == 1)
{
// delayValue == 0 -> local clock saw no tick change but destination clock did
if (delayValueMillis != 0)
{
comments.add("Info: processing time > total network time by 1 ms -> assume zero delay");
delayValueMillis = 0;
}
} else {
comments.add("Warning: processing time > total network time");
}
}
}
delayMillis = Long.valueOf(delayValueMillis);
if (origTimeMillis > returnTimeMillis) {
comments.add("Error: OrigTime > DestRcvTime");
}
offsetMillis = Long.valueOf(((rcvTimeMillis - origTimeMillis) + (xmitTimeMillis - returnTimeMillis)) / 2);
}
}
/**
* Return list of comments (if any) during processing of NTP packet.
*
* @return List or null if not yet computed
*/
public List getComments()
{
return comments;
}
/**
* Get round-trip network delay. If null then could not compute the delay.
*
* @return Long or null if delay not available.
*/
public Long getDelay()
{
return delayMillis;
}
/**
* Get clock offset needed to adjust local clock to match remote clock. If null then could not
* compute the offset.
*
* @return Long or null if offset not available.
*/
public Long getOffset()
{
return offsetMillis;
}
/**
* Returns NTP message packet.
*
* @return NTP message packet.
*/
public NtpV3Packet getMessage()
{
return message;
}
/**
* Get host address from message datagram if available
* @return host address of available otherwise null
* @since 3.4
*/
public InetAddress getAddress() {
final DatagramPacket pkt = message.getDatagramPacket();
return pkt == null ? null : pkt.getAddress();
}
/**
* Returns time at which time message packet was received by local machine.
*
* @return packet return time.
*/
public long getReturnTime()
{
return returnTimeMillis;
}
/**
* Compares this object against the specified object.
* The result is true if and only if the argument is
* not null and is a TimeStamp object that
* contains the same values as this object.
*
* @param obj the object to compare with.
* @return true if the objects are the same;
* false otherwise.
* @since 3.4
*/
@Override
public boolean equals(final Object obj)
{
if (this == obj) {
return true;
}
if (obj == null || getClass() != obj.getClass()) {
return false;
}
final TimeInfo other = (TimeInfo) obj;
return returnTimeMillis == other.returnTimeMillis && message.equals(other.message);
}
/**
* Computes a hashcode for this object. The result is the exclusive
* OR of the return time and the message hash code.
*
* @return a hash code value for this object.
* @since 3.4
*/
@Override
public int hashCode()
{
final int prime = 31;
int result = (int)returnTimeMillis;
result = prime * result + message.hashCode();
return result;
}
}