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 calculates a block's finalization timestamp. Notice that
// the Finalization timestamps are increasing (but not strictly increasing).
// Instance functions:
// - processBlocks(blocks []*types.Block) error
//   called with blocks output from total ordering
// - appendConfig(round uint64, config *types.Config) error
//   called when a new config is known
// - synced() bool
//   called in sync mode
type consensusTimestamp struct {
    timestampsOfChains []time.Time

    // Stores number of chains for rounds.
    numChainsOfRounds []uint32
    numChainsBase     uint64

    // dMoment represents the genesis time.
    dMoment time.Time

    // lastTimestamp is the previous assigned consensus timestamp.
    lastTimestamp time.Time
}

var (
    // ErrTimestampNotIncrease for timestamp is not strictly increasing on one
    // chain.
    ErrTimestampNotIncrease = errors.New("timestamp is not increasing")
    // ErrNoRoundConfig for no round config found.
    ErrNoRoundConfig = errors.New("no round config found")
    // ErrConsensusTimestampRewind for rewinding timestamp.
    ErrConsensusTimestampRewind = errors.New("consensus timestamp rewind")
)

// newConsensusTimestamp creates consensus timestamp instance.
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,
        timestampsOfChains: 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
    }
    // This segment is to handle the corner case for config checking logic in
    // processBlock method.
    if len(ct.numChainsOfRounds) == 1 {
        if ct.numChainsOfRounds[0] > config.NumChains {
            ct.resizeTimetamps(ct.numChainsOfRounds[0])
        } else {
            ct.resizeTimetamps(config.NumChains)
        }
    }
    ct.numChainsOfRounds = append(ct.numChainsOfRounds, config.NumChains)
    return nil
}

func (ct *consensusTimestamp) resizeTimetamps(numChain uint32) {
    l := uint32(len(ct.timestampsOfChains))
    if numChain > l {
        for i := l; i < numChain; i++ {
            ct.timestampsOfChains = append(ct.timestampsOfChains, ct.dMoment)
        }
    } else if numChain < l {
        ct.timestampsOfChains = ct.timestampsOfChains[: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 timestampsOfChains.
        } else if ct.numChainsBase+2 == round {
            // Resize timestampsOfChains if block from r+2 comes, because the interleave
            // of rounds must be less than 1. Resize the size to
            // max(numChainsOfRounds[r+1], numChainsOfRounds[r+2]).
            if len(ct.numChainsOfRounds) < 2 {
                return ErrNoRoundConfig
            }
            ct.numChainsBase++
            ct.numChainsOfRounds = ct.numChainsOfRounds[1:]
            if ct.numChainsOfRounds[0] > ct.numChainsOfRounds[1] {
                ct.resizeTimetamps(ct.numChainsOfRounds[0])
            } else {
                ct.resizeTimetamps(ct.numChainsOfRounds[1])
            }
        } else {
            // Error if round < base or round > base + 2.
            return ErrInvalidRoundID
        }
        ts := ct.timestampsOfChains[:ct.numChainsOfRounds[round-ct.numChainsBase]]
        if block.Finalization.Timestamp, err = getMedianTime(ts); err != nil {
            return
        }
        if block.Timestamp.Before(ct.timestampsOfChains[block.Position.ChainID]) {
            return ErrTimestampNotIncrease
        }
        ct.timestampsOfChains[block.Position.ChainID] = block.Timestamp
        // If the finalization timestamp is before the last timestamp, set it to
        // the last one. Notice that the finalization timestamps are increasing but
        // not strictly increasing.
        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.timestampsOfChains[i].Equal(ct.dMoment) {
            return false
        }
    }
    return true
}