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@ -16,7 +16,7 @@ import (
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"time"
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)
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type mode byte
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type mode uint8
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const (
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reserved mode = 0 + iota
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@ -39,40 +39,53 @@ var (
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ntpEpoch = time.Date(1900, 1, 1, 0, 0, 0, 0, time.UTC)
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)
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type ntpTime struct {
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Seconds uint32
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Fraction uint32
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}
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// An ntpTime is a 64-bit fixed-point (Q32.32) representation of the number of
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// seconds elapsed since the NTP epoch.
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type ntpTime uint64
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func (t ntpTime) Time() time.Time {
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return ntpEpoch.Add(t.sinceEpoch())
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// Duration interprets the fixed-point ntpTime as a number of elapsed seconds
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// and returns the corresponding time.Duration value.
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func (t ntpTime) Duration() time.Duration {
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sec := (t >> 32) * nanoPerSec
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frac := (t & 0xffffffff) * nanoPerSec >> 32
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return time.Duration(sec + frac)
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}
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// sinceEpoch converts the ntpTime record t into a duration since the NTP
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// epoch time (Jan 1, 1900).
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func (t ntpTime) sinceEpoch() time.Duration {
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sec := time.Duration(t.Seconds) * time.Second
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frac := time.Duration(uint64(t.Fraction) * nanoPerSec >> 32)
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return sec + frac
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// Time interprets the fixed-point ntpTime as a an absolute time and returns
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// the corresponding time.Time value.
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func (t ntpTime) Time() time.Time {
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return ntpEpoch.Add(t.Duration())
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}
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// toNtpTime converts the time value t into an ntpTime representation.
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// toNtpTime converts the time.Time value t into its 64-bit fixed-point
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// ntpTime representation.
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func toNtpTime(t time.Time) ntpTime {
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nsec := uint64(t.Sub(ntpEpoch))
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return ntpTime{
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Seconds: uint32(nsec / nanoPerSec),
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Fraction: uint32((nsec % nanoPerSec) << 32 / nanoPerSec),
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sec := nsec / nanoPerSec
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frac := (nsec - sec*nanoPerSec) << 32 / nanoPerSec
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return ntpTime(sec<<32 | frac)
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}
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// An ntpTimeShort is a 32-bit fixed-point (Q16.16) representation of the
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// number of seconds elapsed since the NTP epoch.
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type ntpTimeShort uint32
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// Duration interprets the fixed-point ntpTimeShort as a number of elapsed
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// seconds and returns the corresponding time.Duration value.
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func (t ntpTimeShort) Duration() time.Duration {
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sec := (t >> 16) * nanoPerSec
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frac := (t & 0xffff) * nanoPerSec >> 16
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return time.Duration(sec + frac)
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}
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// msg is an internal representation of an NTP packet.
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type msg struct {
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LiVnMode byte // Leap Indicator (2) + Version (3) + Mode (3)
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Stratum byte
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Poll byte
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Precision byte
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RootDelay uint32
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RootDispersion uint32
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LiVnMode uint8 // Leap Indicator (2) + Version (3) + Mode (3)
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Stratum uint8
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Poll int8
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Precision int8
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RootDelay ntpTimeShort
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RootDispersion ntpTimeShort
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ReferenceID uint32
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ReferenceTime ntpTime
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OriginTime ntpTime
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@ -87,7 +100,7 @@ func (m *msg) setVersion(v int) {
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// setMode sets the NTP protocol mode on the message.
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func (m *msg) setMode(md mode) {
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m.LiVnMode = (m.LiVnMode & 0xf8) | byte(md)
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m.LiVnMode = (m.LiVnMode & 0xf8) | uint8(md)
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}
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// A Response contains time data, some of which is returned by the NTP server
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@ -96,7 +109,12 @@ type Response struct {
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Time time.Time // receive time reported by the server
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RTT time.Duration // round-trip time between client and server
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ClockOffset time.Duration // local clock offset relative to server
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Poll time.Duration // maximum polling interval
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Precision time.Duration // precision of server's system clock
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Stratum uint8 // stratum level of NTP server's clock
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ReferenceID uint32 // server's reference ID
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RootDelay time.Duration // server's RTT to the reference clock
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RootDispersion time.Duration // server's dispersion to the reference clock
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}
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// Query returns information from the remote NTP server specifed as host. NTP
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@ -112,7 +130,12 @@ func Query(host string, version int) (*Response, error) {
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Time: m.ReceiveTime.Time(),
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RTT: rtt(m.OriginTime, m.ReceiveTime, m.TransmitTime, now),
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ClockOffset: offset(m.OriginTime, m.ReceiveTime, m.TransmitTime, now),
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Poll: toInterval(m.Poll),
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Precision: toInterval(m.Precision),
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Stratum: m.Stratum,
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ReferenceID: m.ReferenceID,
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RootDelay: m.RootDelay.Duration(),
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RootDispersion: m.RootDispersion.Duration(),
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}
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// https://tools.ietf.org/html/rfc5905#section-7.3
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@ -204,3 +227,14 @@ func offset(t1, t2, t3, t4 ntpTime) time.Duration {
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b := t3.Time().Sub(t4.Time())
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return (a + b) / time.Duration(2)
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}
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func toInterval(t int8) time.Duration {
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switch {
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case t > 0:
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return time.Duration(uint64(time.Second) << uint(t))
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case t < 0:
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return time.Duration(uint64(time.Second) >> uint(-t))
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default:
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return time.Second
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}
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}
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