+++ /dev/null
-// Contains the NTP time drift detection via the SNTP protocol:
-// https://tools.ietf.org/html/rfc4330
-
-package discover
-
-import (
- "fmt"
- "net"
- "sort"
- "strings"
- "time"
-
- log "github.com/sirupsen/logrus"
-)
-
-const (
- ntpPool = "pool.ntp.org" // ntpPool is the NTP server to query for the current time
- ntpChecks = 3 // Number of measurements to do against the NTP server
-)
-
-// durationSlice attaches the methods of sort.Interface to []time.Duration,
-// sorting in increasing order.
-type durationSlice []time.Duration
-
-func (s durationSlice) Len() int { return len(s) }
-func (s durationSlice) Less(i, j int) bool { return s[i] < s[j] }
-func (s durationSlice) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
-
-// checkClockDrift queries an NTP server for clock drifts and warns the user if
-// one large enough is detected.
-func checkClockDrift() {
- drift, err := sntpDrift(ntpChecks)
- if err != nil {
- return
- }
- if drift < -driftThreshold || drift > driftThreshold {
- warning := fmt.Sprintf("System clock seems off by %v, which can prevent network connectivity", drift)
- howtofix := fmt.Sprintf("Please enable network time synchronisation in system settings")
- separator := strings.Repeat("-", len(warning))
-
- log.Warn(separator)
- log.Warn(warning)
- log.Warn(howtofix)
- log.Warn(separator)
- } else {
- log.Debug(fmt.Sprintf("Sanity NTP check reported %v drift, all ok", drift))
- }
-}
-
-// sntpDrift does a naive time resolution against an NTP server and returns the
-// measured drift. This method uses the simple version of NTP. It's not precise
-// but should be fine for these purposes.
-//
-// Note, it executes two extra measurements compared to the number of requested
-// ones to be able to discard the two extremes as outliers.
-func sntpDrift(measurements int) (time.Duration, error) {
- // Resolve the address of the NTP server
- addr, err := net.ResolveUDPAddr("udp", ntpPool+":123")
- if err != nil {
- return 0, err
- }
- // Construct the time request (empty package with only 2 fields set):
- // Bits 3-5: Protocol version, 3
- // Bits 6-8: Mode of operation, client, 3
- request := make([]byte, 48)
- request[0] = 3<<3 | 3
-
- // Execute each of the measurements
- drifts := []time.Duration{}
- for i := 0; i < measurements+2; i++ {
- // Dial the NTP server and send the time retrieval request
- conn, err := net.DialUDP("udp", nil, addr)
- if err != nil {
- return 0, err
- }
- defer conn.Close()
-
- sent := time.Now()
- if _, err = conn.Write(request); err != nil {
- return 0, err
- }
- // Retrieve the reply and calculate the elapsed time
- conn.SetDeadline(time.Now().Add(5 * time.Second))
-
- reply := make([]byte, 48)
- if _, err = conn.Read(reply); err != nil {
- return 0, err
- }
- elapsed := time.Since(sent)
-
- // Reconstruct the time from the reply data
- sec := uint64(reply[43]) | uint64(reply[42])<<8 | uint64(reply[41])<<16 | uint64(reply[40])<<24
- frac := uint64(reply[47]) | uint64(reply[46])<<8 | uint64(reply[45])<<16 | uint64(reply[44])<<24
-
- nanosec := sec*1e9 + (frac*1e9)>>32
-
- t := time.Date(1900, 1, 1, 0, 0, 0, 0, time.UTC).Add(time.Duration(nanosec)).Local()
-
- // Calculate the drift based on an assumed answer time of RRT/2
- drifts = append(drifts, sent.Sub(t)+elapsed/2)
- }
- // Calculate average drif (drop two extremities to avoid outliers)
- sort.Sort(durationSlice(drifts))
-
- drift := time.Duration(0)
- for i := 1; i < len(drifts)-1; i++ {
- drift += drifts[i]
- }
- return drift / time.Duration(measurements), nil
-}
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