+++ /dev/null
-// Copyright (c) 2013-2014 The btcsuite developers
-// Use of this source code is governed by an ISC
-// license that can be found in the LICENSE file.
-
-package blockchain
-
-import (
- "math"
- "sort"
- "sync"
- "time"
-)
-
-const (
- // maxAllowedOffsetSeconds is the maximum number of seconds in either
- // direction that local clock will be adjusted. When the median time
- // of the network is outside of this range, no offset will be applied.
- maxAllowedOffsetSecs = 70 * 60 // 1 hour 10 minutes
-
- // similarTimeSecs is the number of seconds in either direction from the
- // local clock that is used to determine that it is likley wrong and
- // hence to show a warning.
- similarTimeSecs = 5 * 60 // 5 minutes
-)
-
-var (
- // maxMedianTimeEntries is the maximum number of entries allowed in the
- // median time data. This is a variable as opposed to a constant so the
- // test code can modify it.
- maxMedianTimeEntries = 200
-)
-
-// MedianTimeSource provides a mechanism to add several time samples which are
-// used to determine a median time which is then used as an offset to the local
-// clock.
-type MedianTimeSource interface {
- // AdjustedTime returns the current time adjusted by the median time
- // offset as calculated from the time samples added by AddTimeSample.
- AdjustedTime() time.Time
-
- // AddTimeSample adds a time sample that is used when determining the
- // median time of the added samples.
- AddTimeSample(id string, timeVal time.Time)
-
- // Offset returns the number of seconds to adjust the local clock based
- // upon the median of the time samples added by AddTimeData.
- Offset() time.Duration
-}
-
-// int64Sorter implements sort.Interface to allow a slice of 64-bit integers to
-// be sorted.
-type int64Sorter []int64
-
-// Len returns the number of 64-bit integers in the slice. It is part of the
-// sort.Interface implementation.
-func (s int64Sorter) Len() int {
- return len(s)
-}
-
-// Swap swaps the 64-bit integers at the passed indices. It is part of the
-// sort.Interface implementation.
-func (s int64Sorter) Swap(i, j int) {
- s[i], s[j] = s[j], s[i]
-}
-
-// Less returns whether the 64-bit integer with index i should sort before the
-// 64-bit integer with index j. It is part of the sort.Interface
-// implementation.
-func (s int64Sorter) Less(i, j int) bool {
- return s[i] < s[j]
-}
-
-// medianTime provides an implementation of the MedianTimeSource interface.
-// It is limited to maxMedianTimeEntries includes the same buggy behavior as
-// the time offset mechanism in Bitcoin Core. This is necessary because it is
-// used in the consensus code.
-type medianTime struct {
- mtx sync.Mutex
- knownIDs map[string]struct{}
- offsets []int64
- offsetSecs int64
- invalidTimeChecked bool
-}
-
-// Ensure the medianTime type implements the MedianTimeSource interface.
-var _ MedianTimeSource = (*medianTime)(nil)
-
-// AdjustedTime returns the current time adjusted by the median time offset as
-// calculated from the time samples added by AddTimeSample.
-//
-// This function is safe for concurrent access and is part of the
-// MedianTimeSource interface implementation.
-func (m *medianTime) AdjustedTime() time.Time {
- m.mtx.Lock()
- defer m.mtx.Unlock()
-
- // Limit the adjusted time to 1 second precision.
- now := time.Unix(time.Now().Unix(), 0)
- return now.Add(time.Duration(m.offsetSecs) * time.Second)
-}
-
-// AddTimeSample adds a time sample that is used when determining the median
-// time of the added samples.
-//
-// This function is safe for concurrent access and is part of the
-// MedianTimeSource interface implementation.
-func (m *medianTime) AddTimeSample(sourceID string, timeVal time.Time) {
- m.mtx.Lock()
- defer m.mtx.Unlock()
-
- // Don't add time data from the same source.
- if _, exists := m.knownIDs[sourceID]; exists {
- return
- }
- m.knownIDs[sourceID] = struct{}{}
-
- // Truncate the provided offset to seconds and append it to the slice
- // of offsets while respecting the maximum number of allowed entries by
- // replacing the oldest entry with the new entry once the maximum number
- // of entries is reached.
- now := time.Unix(time.Now().Unix(), 0)
- offsetSecs := int64(timeVal.Sub(now).Seconds())
- numOffsets := len(m.offsets)
- if numOffsets == maxMedianTimeEntries && maxMedianTimeEntries > 0 {
- m.offsets = m.offsets[1:]
- numOffsets--
- }
- m.offsets = append(m.offsets, offsetSecs)
- numOffsets++
-
- // Sort the offsets so the median can be obtained as needed later.
- sortedOffsets := make([]int64, numOffsets)
- copy(sortedOffsets, m.offsets)
- sort.Sort(int64Sorter(sortedOffsets))
-
- offsetDuration := time.Duration(offsetSecs) * time.Second
- log.Debugf("Added time sample of %v (total: %v)", offsetDuration,
- numOffsets)
-
- // NOTE: The following code intentionally has a bug to mirror the
- // buggy behavior in Bitcoin Core since the median time is used in the
- // consensus rules.
- //
- // In particular, the offset is only updated when the number of entries
- // is odd, but the max number of entries is 200, an even number. Thus,
- // the offset will never be updated again once the max number of entries
- // is reached.
-
- // The median offset is only updated when there are enough offsets and
- // the number of offsets is odd so the middle value is the true median.
- // Thus, there is nothing to do when those conditions are not met.
- if numOffsets < 5 || numOffsets&0x01 != 1 {
- return
- }
-
- // At this point the number of offsets in the list is odd, so the
- // middle value of the sorted offsets is the median.
- median := sortedOffsets[numOffsets/2]
-
- // Set the new offset when the median offset is within the allowed
- // offset range.
- if math.Abs(float64(median)) < maxAllowedOffsetSecs {
- m.offsetSecs = median
- } else {
- // The median offset of all added time data is larger than the
- // maximum allowed offset, so don't use an offset. This
- // effectively limits how far the local clock can be skewed.
- m.offsetSecs = 0
-
- if !m.invalidTimeChecked {
- m.invalidTimeChecked = true
-
- // Find if any time samples have a time that is close
- // to the local time.
- var remoteHasCloseTime bool
- for _, offset := range sortedOffsets {
- if math.Abs(float64(offset)) < similarTimeSecs {
- remoteHasCloseTime = true
- break
- }
- }
-
- // Warn if none of the time samples are close.
- if !remoteHasCloseTime {
- log.Warnf("Please check your date and time " +
- "are correct! btcd will not work " +
- "properly with an invalid time")
- }
- }
- }
-
- medianDuration := time.Duration(m.offsetSecs) * time.Second
- log.Debugf("New time offset: %v", medianDuration)
-}
-
-// Offset returns the number of seconds to adjust the local clock based upon the
-// median of the time samples added by AddTimeData.
-//
-// This function is safe for concurrent access and is part of the
-// MedianTimeSource interface implementation.
-func (m *medianTime) Offset() time.Duration {
- m.mtx.Lock()
- defer m.mtx.Unlock()
-
- return time.Duration(m.offsetSecs) * time.Second
-}
-
-// NewMedianTime returns a new instance of concurrency-safe implementation of
-// the MedianTimeSource interface. The returned implementation contains the
-// rules necessary for proper time handling in the chain consensus rules and
-// expects the time samples to be added from the timestamp field of the version
-// message received from remote peers that successfully connect and negotiate.
-func NewMedianTime() MedianTimeSource {
- return &medianTime{
- knownIDs: make(map[string]struct{}),
- offsets: make([]int64, 0, maxMedianTimeEntries),
- }
-}
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