ntp

Documentation

Overview

Package ntp provides an implementation of a Simple NTP (SNTP) client capable of querying the current time from a remote NTP server. See RFC5905 (https://tools.ietf.org/html/rfc5905) for more details.

This approach grew out of a go-nuts post by Michael Hofmann: https://groups.google.com/forum/?fromgroups#!topic/golang-nuts/FlcdMU5fkLQ

Index

• Constants
• func TimeFuncFromContext(ctx context.Context) func() time.Time
• type LeapIndicator
• type Options
• type Response
  • func Exchange(ctx context.Context, dialer N.Dialer, serverAddress M.Socksaddr) (*Response, error)
  • func (r *Response) Validate() error
• type Service
  • func NewService(options Options) *Service
  • func (s *Service) Close() error
  • func (s *Service) Start() error
  • func (s *Service) TimeFunc() func() time.Time
• type TimeService

Constants

const (
	// LeapNoWarning indicates no impending leap second.
	LeapNoWarning LeapIndicator = 0

	// LeapAddSecond indicates the last minute of the day has 61 seconds.
	LeapAddSecond = 1

	// LeapDelSecond indicates the last minute of the day has 59 seconds.
	LeapDelSecond = 2

	// LeapNotInSync indicates an unsynchronized leap second.
	LeapNotInSync = 3
)

const TimeLayout = "2006-01-02 15:04:05 -0700"

Functions

func TimeFuncFromContext

func TimeFuncFromContext(ctx context.Context) func() time.Time

Types

type LeapIndicator

type LeapIndicator uint8

The LeapIndicator is used to warn if a leap second should be inserted or deleted in the last minute of the current month.

type Options

type Options struct {
	Context  context.Context
	Server   M.Socksaddr
	Interval time.Duration
	Dialer   N.Dialer
	Logger   logger.Logger
}

type Response

type Response struct {
	// Time is the transmit time reported by the server just before it
	// responded to the client's NTP query.
	Time time.Time

	// ClockOffset is the estimated offset of the client clock relative to
	// the server. Add this to the client's system clock time to obtain a
	// more accurate time.
	ClockOffset time.Duration

	// RTT is the measured round-trip-time delay estimate between the client
	// and the server.
	RTT time.Duration

	// Precision is the reported precision of the server's clock.
	Precision time.Duration

	// Stratum is the "stratum level" of the server. The smaller the number,
	// the closer the server is to the reference clock. Stratum 1 servers are
	// attached directly to the reference clock. A stratum value of 0
	// indicates the "kiss of death," which typically occurs when the client
	// issues too many requests to the server in a short period of time.
	Stratum uint8

	// ReferenceID is a 32-bit identifier identifying the server or
	// reference clock.
	ReferenceID uint32

	// ReferenceTime is the time when the server's system clock was last
	// set or corrected.
	ReferenceTime time.Time

	// RootDelay is the server's estimated aggregate round-trip-time delay to
	// the stratum 1 server.
	RootDelay time.Duration

	// RootDispersion is the server's estimated maximum measurement error
	// relative to the stratum 1 server.
	RootDispersion time.Duration

	// RootDistance is an estimate of the total synchronization distance
	// between the client and the stratum 1 server.
	RootDistance time.Duration

	// Leap indicates whether a leap second should be added or removed from
	// the current month's last minute.
	Leap LeapIndicator

	// MinError is a lower bound on the error between the client and server
	// clocks. When the client and server are not synchronized to the same
	// clock, the reported timestamps may appear to violate the principle of
	// causality. In other words, the NTP server's response may indicate
	// that a message was received before it was sent. In such cases, the
	// minimum error may be useful.
	MinError time.Duration

	// KissCode is a 4-character string describing the reason for a
	// "kiss of death" response (stratum = 0). For a list of standard kiss
	// codes, see https://tools.ietf.org/html/rfc5905#section-7.4.
	KissCode string

	// Poll is the maximum interval between successive NTP polling messages.
	// It is not relevant for simple NTP clients like this one.
	Poll time.Duration
}

A Response contains time data, some of which is returned by the NTP server and some of which is calculated by the client.

func Exchange

func Exchange(ctx context.Context, dialer N.Dialer, serverAddress M.Socksaddr) (*Response, error)

func (*Response) Validate

func (r *Response) Validate() error

Validate checks if the response is valid for the purposes of time synchronization.

type Service

type Service struct {
	// contains filtered or unexported fields
}

func NewService

func NewService(options Options) *Service

func (*Service) Close

func (s *Service) Close() error

func (*Service) Start

func (s *Service) Start() error

func (*Service) TimeFunc

func (s *Service) TimeFunc() func() time.Time

type TimeService

type TimeService interface {
	TimeFunc() func() time.Time
}