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// Copyright 2018 The dexon-consensus-core Authors
// This file is part of the dexon-consensus-core library.
//
// The dexon-consensus-core 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-core 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-core library. If not, see
// <http://www.gnu.org/licenses/>.
package core
import (
"errors"
"time"
"github.com/dexon-foundation/dexon-consensus-core/core/types"
)
// consensusTimestamp is for Concensus Timestamp Algorithm.
type consensusTimestamp struct {
chainTimestamps []time.Time
// This part keeps configs for each round.
numChainsForRounds []uint32
numChainsRoundBase uint64
// dMoment represents the genesis time.
dMoment 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")
)
// newConsensusTimestamp creates timestamper object.
func newConsensusTimestamp(
dMoment time.Time, numChains uint32) *consensusTimestamp {
return &consensusTimestamp{
numChainsForRounds: []uint32{numChains},
numChainsRoundBase: uint64(0),
dMoment: dMoment,
}
}
// 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.numChainsForRounds))+ct.numChainsRoundBase {
return ErrRoundNotIncreasing
}
ct.numChainsForRounds = append(ct.numChainsForRounds, config.NumChains)
return nil
}
func (ct *consensusTimestamp) getNumChains(round uint64) uint32 {
roundIndex := round - ct.numChainsRoundBase
return ct.numChainsForRounds[roundIndex]
}
// ProcessBlocks is the entry function.
func (ct *consensusTimestamp) processBlocks(blocks []*types.Block) (err error) {
for _, block := range blocks {
numChains := ct.getNumChains(block.Position.Round)
// Fulfill empty time slots with d-moment. This part also means
// each time we increasing number of chains, we can't increase over
// 49% of previous number of chains.
for uint32(len(ct.chainTimestamps)) < numChains {
ct.chainTimestamps = append(ct.chainTimestamps, ct.dMoment)
}
ts := ct.chainTimestamps[:numChains]
if block.Finalization.Timestamp, err = getMedianTime(ts); err != nil {
return
}
if !block.Timestamp.After(ct.chainTimestamps[block.Position.ChainID]) {
return ErrTimestampNotIncrease
}
ct.chainTimestamps[block.Position.ChainID] = block.Timestamp
// Purge configs for older rounds, rounds of blocks from total ordering
// would increase.
if block.Position.Round > ct.numChainsRoundBase {
ct.numChainsRoundBase++
ct.numChainsForRounds = ct.numChainsForRounds[1:]
}
}
return
}
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