github.com/neatlab/neatio@v1.7.3-0.20220425043230-d903e92fcc75/network/p2p/discover/ntp.go (about)

     1  package discover
     2  
     3  import (
     4  	"fmt"
     5  	"net"
     6  	"sort"
     7  	"time"
     8  
     9  	"github.com/neatlab/neatio/chain/log"
    10  )
    11  
    12  const (
    13  	ntpPool   = "pool.ntp.org"
    14  	ntpChecks = 3
    15  )
    16  
    17  type durationSlice []time.Duration
    18  
    19  func (s durationSlice) Len() int           { return len(s) }
    20  func (s durationSlice) Less(i, j int) bool { return s[i] < s[j] }
    21  func (s durationSlice) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
    22  
    23  func checkClockDrift() {
    24  	drift, err := sntpDrift(ntpChecks)
    25  	if err != nil {
    26  		return
    27  	}
    28  	if drift < -driftThreshold || drift > driftThreshold {
    29  		log.Warn(fmt.Sprintf("System clock seems off by %v, which can prevent network connectivity", drift))
    30  		log.Warn("Please enable network time synchronisation in system settings.")
    31  	} else {
    32  		log.Debug("NTP sanity check done", "drift", drift)
    33  	}
    34  }
    35  
    36  func sntpDrift(measurements int) (time.Duration, error) {
    37  	addr, err := net.ResolveUDPAddr("udp", ntpPool+":123")
    38  	if err != nil {
    39  		return 0, err
    40  	}
    41  	request := make([]byte, 48)
    42  	request[0] = 3<<3 | 3
    43  
    44  	drifts := []time.Duration{}
    45  	for i := 0; i < measurements+2; i++ {
    46  		conn, err := net.DialUDP("udp", nil, addr)
    47  		if err != nil {
    48  			return 0, err
    49  		}
    50  		defer conn.Close()
    51  
    52  		sent := time.Now()
    53  		if _, err = conn.Write(request); err != nil {
    54  			return 0, err
    55  		}
    56  		conn.SetDeadline(time.Now().Add(5 * time.Second))
    57  
    58  		reply := make([]byte, 48)
    59  		if _, err = conn.Read(reply); err != nil {
    60  			return 0, err
    61  		}
    62  		elapsed := time.Since(sent)
    63  
    64  		sec := uint64(reply[43]) | uint64(reply[42])<<8 | uint64(reply[41])<<16 | uint64(reply[40])<<24
    65  		frac := uint64(reply[47]) | uint64(reply[46])<<8 | uint64(reply[45])<<16 | uint64(reply[44])<<24
    66  
    67  		nanosec := sec*1e9 + (frac*1e9)>>32
    68  
    69  		t := time.Date(1900, 1, 1, 0, 0, 0, 0, time.UTC).Add(time.Duration(nanosec)).Local()
    70  
    71  		drifts = append(drifts, sent.Sub(t)+elapsed/2)
    72  	}
    73  	sort.Sort(durationSlice(drifts))
    74  
    75  	drift := time.Duration(0)
    76  	for i := 1; i < len(drifts)-1; i++ {
    77  		drift += drifts[i]
    78  	}
    79  	return drift / time.Duration(measurements), nil
    80  }