path: root/core/consensus-timestamp.go

// Copyright 2018 The dexon-consensus Authors
// This file is part of the dexon-consensus library.
//
// The dexon-consensus library is free software: you can redistribute it
// and/or modify it under the terms of the GNU Lesser General Public License as
// published by the Free Software Foundation, either version 3 of the License,
// or (at your option) any later version.
//
// The dexon-consensus library is distributed in the hope that it will be
// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
// General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the dexon-consensus library. If not, see
// <http://www.gnu.org/licenses/>.

package core

import (
    "errors"
    "time"

    "github.com/dexon-foundation/dexon-consensus/core/types"
)

// consensusTimestamp is for Concensus Timestamp Algorithm.
type consensusTimestamp struct {
    chainTimestamps []time.Time

    // This part keeps configs for each round.
    numChainsOfRounds []uint32
    numChainsBase     uint64

    // dMoment represents the genesis time.
    dMoment time.Time
    // lastTimestamp represents previous assigned consensus timestamp.
    lastTimestamp time.Time
}

var (
    // ErrTimestampNotIncrease would be reported if the timestamp is not strickly
    // increasing on the same chain.
    ErrTimestampNotIncrease = errors.New("timestamp is not increasing")
    // ErrNoRoundConfig for no round config found.
    ErrNoRoundConfig = errors.New("no round config found")
    // ErrConsensusTimestampRewind would be reported if the generated timestamp
    // is rewinded.
    ErrConsensusTimestampRewind = errors.New("consensus timestamp rewind")
)

// newConsensusTimestamp creates timestamper object.
func newConsensusTimestamp(
    dMoment time.Time, round uint64, numChains uint32) *consensusTimestamp {

    ts := make([]time.Time, numChains)
    for i := range ts {
        ts[i] = dMoment
    }
    return &consensusTimestamp{
        numChainsOfRounds: []uint32{numChains},
        numChainsBase:     round,
        dMoment:           dMoment,
        chainTimestamps:   ts,
    }
}

// appendConfig appends a configuration for upcoming round. When you append
// a config for round R, next time you can only append the config for round R+1.
func (ct *consensusTimestamp) appendConfig(
    round uint64, config *types.Config) error {

    if round != uint64(len(ct.numChainsOfRounds))+ct.numChainsBase {
        return ErrRoundNotIncreasing
    }
    ct.numChainsOfRounds = append(ct.numChainsOfRounds, config.NumChains)
    return nil
}

func (ct *consensusTimestamp) resizeChainTimetamps(numChain uint32) {
    l := uint32(len(ct.chainTimestamps))
    if numChain > l {
        for i := l; i < numChain; i++ {
            ct.chainTimestamps = append(ct.chainTimestamps, ct.dMoment)
        }
    } else if numChain < l {
        ct.chainTimestamps = ct.chainTimestamps[:numChain]
    }
}

// ProcessBlocks is the entry function.
func (ct *consensusTimestamp) processBlocks(blocks []*types.Block) (err error) {
    for _, block := range blocks {
        // Rounds might interleave within rounds if no configuration change
        // occurs. And it is limited to one round, that is, round r can only
        // interleave with r-1 and r+1.
        round := block.Position.Round
        if ct.numChainsBase == round || ct.numChainsBase+1 == round {
            // Normal case, no need to modify chainTimestamps.
        } else if ct.numChainsBase+2 == round {
            if len(ct.numChainsOfRounds) < 2 {
                return ErrNoRoundConfig
            }
            ct.numChainsBase++
            ct.numChainsOfRounds = ct.numChainsOfRounds[1:]
            if ct.numChainsOfRounds[0] > ct.numChainsOfRounds[1] {
                ct.resizeChainTimetamps(ct.numChainsOfRounds[0])
            } else {
                ct.resizeChainTimetamps(ct.numChainsOfRounds[1])
            }
        } else {
            // Error if round < base or round > base + 2.
            return ErrInvalidRoundID
        }
        ts := ct.chainTimestamps[:ct.numChainsOfRounds[round-ct.numChainsBase]]
        if block.Finalization.Timestamp, err = getMedianTime(ts); err != nil {
            return
        }
        if block.Timestamp.Before(ct.chainTimestamps[block.Position.ChainID]) {
            return ErrTimestampNotIncrease
        }
        ct.chainTimestamps[block.Position.ChainID] = block.Timestamp
        if block.Finalization.Timestamp.Before(ct.lastTimestamp) {
            block.Finalization.Timestamp = ct.lastTimestamp
        } else {
            ct.lastTimestamp = block.Finalization.Timestamp
        }
    }
    return
}

func (ct *consensusTimestamp) isSynced() bool {
    numChain := ct.numChainsOfRounds[0]
    for i := uint32(0); i < numChain; i++ {
        if ct.chainTimestamps[i].Equal(ct.dMoment) {
            return false
        }
    }
    return true
}