mirror of
https://github.com/prometheus/node_exporter.git
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33f99c4fc1
Uses godep to vendor dependencies. Godeps is not necessary during build, golang's new vendor support is used instead.
114 lines
2.7 KiB
Go
114 lines
2.7 KiB
Go
// Copyright 2015 Brett Vickers.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package ntp provides a simple mechanism for querying the current time
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// from a remote NTP server. This package only supports NTP client mode
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// behavior and version 4 of the NTP protocol. See RFC 5905.
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// Approach inspired by go-nuts post by Michael Hofmann:
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// https://groups.google.com/forum/?fromgroups#!topic/golang-nuts/FlcdMU5fkLQ
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package ntp
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import (
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"encoding/binary"
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"net"
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"time"
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)
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type mode byte
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const (
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reserved mode = 0 + iota
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symmetricActive
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symmetricPassive
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client
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server
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broadcast
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controlMessage
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reservedPrivate
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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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func (t ntpTime) UTC() time.Time {
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nsec := uint64(t.Seconds)*1e9 + (uint64(t.Fraction) * 1e9 >> 32)
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return time.Date(1900, 1, 1, 0, 0, 0, 0, time.UTC).Add(time.Duration(nsec))
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}
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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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ReferenceId uint32
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ReferenceTime ntpTime
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OriginTime ntpTime
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ReceiveTime ntpTime
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TransmitTime ntpTime
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}
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// SetVersion sets the NTP protocol version on the message.
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func (m *msg) SetVersion(v byte) {
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m.LiVnMode = (m.LiVnMode & 0xc7) | v<<3
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}
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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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}
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// Time returns the "receive time" from the remote NTP server
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// specifed as host. NTP client mode is used.
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func getTime(host string, version byte) (time.Time, error) {
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if version < 2 || version > 4 {
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panic("ntp: invalid version number")
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}
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raddr, err := net.ResolveUDPAddr("udp", host+":123")
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if err != nil {
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return time.Now(), err
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}
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con, err := net.DialUDP("udp", nil, raddr)
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if err != nil {
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return time.Now(), err
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}
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defer con.Close()
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con.SetDeadline(time.Now().Add(5 * time.Second))
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m := new(msg)
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m.SetMode(client)
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m.SetVersion(version)
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err = binary.Write(con, binary.BigEndian, m)
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if err != nil {
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return time.Now(), err
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}
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err = binary.Read(con, binary.BigEndian, m)
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if err != nil {
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return time.Now(), err
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}
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t := m.ReceiveTime.UTC().Local()
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return t, nil
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}
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// TimeV returns the "receive time" from the remote NTP server
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// specifed as host. Use the NTP client mode with the requested
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// version number (2, 3, or 4).
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func TimeV(host string, version byte) (time.Time, error) {
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return getTime(host, version)
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}
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// Time returns the "receive time" from the remote NTP server
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// specifed as host. NTP client mode version 4 is used.
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func Time(host string) (time.Time, error) {
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return getTime(host, 4)
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}
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