path: root/core/consensus.go

// 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 (
    "context"
    "encoding/hex"
    "fmt"
    "sync"
    "time"

    "github.com/dexon-foundation/dexon-consensus-core/common"
    "github.com/dexon-foundation/dexon-consensus-core/core/blockdb"
    "github.com/dexon-foundation/dexon-consensus-core/core/crypto"
    "github.com/dexon-foundation/dexon-consensus-core/core/types"
    typesDKG "github.com/dexon-foundation/dexon-consensus-core/core/types/dkg"
)

// Errors for consensus core.
var (
    ErrProposerNotInNodeSet = fmt.Errorf(
        "proposer is not in node set")
    ErrIncorrectHash = fmt.Errorf(
        "hash of block is incorrect")
    ErrIncorrectSignature = fmt.Errorf(
        "signature of block is incorrect")
    ErrGenesisBlockNotEmpty = fmt.Errorf(
        "genesis block should be empty")
    ErrUnknownBlockProposed = fmt.Errorf(
        "unknown block is proposed")
    ErrIncorrectAgreementResultPosition = fmt.Errorf(
        "incorrect agreement result position")
    ErrNotEnoughVotes = fmt.Errorf(
        "not enought votes")
    ErrIncorrectVoteBlockHash = fmt.Errorf(
        "incorrect vote block hash")
    ErrIncorrectVoteType = fmt.Errorf(
        "incorrect vote type")
    ErrIncorrectVotePosition = fmt.Errorf(
        "incorrect vote position")
    ErrIncorrectVoteProposer = fmt.Errorf(
        "incorrect vote proposer")
    ErrIncorrectBlockRandomnessResult = fmt.Errorf(
        "incorrect block randomness result")
)

// consensusBAReceiver implements agreementReceiver.
type consensusBAReceiver struct {
    // TODO(mission): consensus would be replaced by lattice and network.
    consensus        *Consensus
    agreementModule  *agreement
    chainID          uint32
    changeNotaryTime time.Time
    round            uint64
    restartNotary    chan bool
}

func (recv *consensusBAReceiver) ProposeVote(vote *types.Vote) {
    go func() {
        if err := recv.agreementModule.prepareVote(vote); err != nil {
            recv.consensus.logger.Error("Failed to prepare vote", "error", err)
            return
        }
        if err := recv.agreementModule.processVote(vote); err != nil {
            recv.consensus.logger.Error("Failed to process vote", "error", err)
            return
        }
        recv.consensus.logger.Debug("Calling Network.BroadcastVote",
            "vote", vote)
        recv.consensus.network.BroadcastVote(vote)
    }()
}

func (recv *consensusBAReceiver) ProposeBlock() common.Hash {
    block := recv.consensus.proposeBlock(recv.chainID, recv.round)
    if block == nil {
        recv.consensus.logger.Error("unable to propose block")
        return nullBlockHash
    }
    if err := recv.consensus.preProcessBlock(block); err != nil {
        recv.consensus.logger.Error("Failed to pre-process block", "error", err)
        return common.Hash{}
    }
    recv.consensus.logger.Debug("Calling Network.BroadcastBlock", "block", block)
    recv.consensus.network.BroadcastBlock(block)
    return block.Hash
}

func (recv *consensusBAReceiver) ConfirmBlock(
    hash common.Hash, votes map[types.NodeID]*types.Vote) {
    var block *types.Block
    if (hash == common.Hash{}) {
        recv.consensus.logger.Info("Empty block is confirmed",
            "position", recv.agreementModule.agreementID())
        var err error
        block, err = recv.consensus.proposeEmptyBlock(recv.chainID)
        if err != nil {
            recv.consensus.logger.Error("Propose empty block failed", "error", err)
            return
        }
    } else {
        var exist bool
        block, exist = recv.consensus.baModules[recv.chainID].
            findCandidateBlockNoLock(hash)
        if !exist {
            recv.consensus.logger.Error("Unknown block confirmed",
                "hash", hash,
                "chainID", recv.chainID)
            ch := make(chan *types.Block)
            func() {
                recv.consensus.lock.Lock()
                defer recv.consensus.lock.Unlock()
                recv.consensus.baConfirmedBlock[hash] = ch
            }()
            recv.consensus.network.PullBlocks(common.Hashes{hash})
            go func() {
                block = <-ch
                recv.consensus.logger.Info("Receive unknown block",
                    "hash", hash,
                    "chainID", recv.chainID)
                recv.agreementModule.addCandidateBlock(block)
                recv.ConfirmBlock(block.Hash, votes)
            }()
            return
        }
    }
    recv.consensus.ccModule.registerBlock(block)
    voteList := make([]types.Vote, 0, len(votes))
    for _, vote := range votes {
        if vote.BlockHash != hash {
            continue
        }
        voteList = append(voteList, *vote)
    }
    result := &types.AgreementResult{
        BlockHash: block.Hash,
        Position:  block.Position,
        Votes:     voteList,
    }
    recv.consensus.logger.Debug("Calling Network.BroadcastAgreementResult",
        "result", result)
    recv.consensus.network.BroadcastAgreementResult(result)
    if err := recv.consensus.processBlock(block); err != nil {
        recv.consensus.logger.Error("Failed to process block", "error", err)
        return
    }
    if block.Timestamp.After(recv.changeNotaryTime) {
        recv.round++
        recv.restartNotary <- true
    } else {
        recv.restartNotary <- false
    }
}

func (recv *consensusBAReceiver) PullBlocks(hashes common.Hashes) {
    recv.consensus.logger.Debug("Calling Network.PullBlocks", "hashes", hashes)
    recv.consensus.network.PullBlocks(hashes)
}

// consensusDKGReceiver implements dkgReceiver.
type consensusDKGReceiver struct {
    ID           types.NodeID
    gov          Governance
    authModule   *Authenticator
    nodeSetCache *NodeSetCache
    cfgModule    *configurationChain
    network      Network
    logger       common.Logger
}

// ProposeDKGComplaint proposes a DKGComplaint.
func (recv *consensusDKGReceiver) ProposeDKGComplaint(
    complaint *typesDKG.Complaint) {
    if err := recv.authModule.SignDKGComplaint(complaint); err != nil {
        recv.logger.Error("Failed to sign DKG complaint", "error", err)
        return
    }
    recv.logger.Debug("Calling Governace.AddDKGComplaint",
        "complaint", complaint)
    recv.gov.AddDKGComplaint(complaint.Round, complaint)
}

// ProposeDKGMasterPublicKey propose a DKGMasterPublicKey.
func (recv *consensusDKGReceiver) ProposeDKGMasterPublicKey(
    mpk *typesDKG.MasterPublicKey) {
    if err := recv.authModule.SignDKGMasterPublicKey(mpk); err != nil {
        recv.logger.Error("Failed to sign DKG master public key", "error", err)
        return
    }
    recv.logger.Debug("Calling Governance.AddDKGMasterPublicKey", "key", mpk)
    recv.gov.AddDKGMasterPublicKey(mpk.Round, mpk)
}

// ProposeDKGPrivateShare propose a DKGPrivateShare.
func (recv *consensusDKGReceiver) ProposeDKGPrivateShare(
    prv *typesDKG.PrivateShare) {
    if err := recv.authModule.SignDKGPrivateShare(prv); err != nil {
        recv.logger.Error("Failed to sign DKG private share", "error", err)
        return
    }
    receiverPubKey, exists := recv.nodeSetCache.GetPublicKey(prv.ReceiverID)
    if !exists {
        recv.logger.Error("Public key for receiver not found",
            "receiver", prv.ReceiverID.String()[:6])
        return
    }
    if prv.ReceiverID == recv.ID {
        go func() {
            if err := recv.cfgModule.processPrivateShare(prv); err != nil {
                recv.logger.Error("Failed to process self private share", "prvShare", prv)
            }
        }()
    } else {
        recv.logger.Debug("Calling Network.SendDKGPrivateShare",
            "receiver", hex.EncodeToString(receiverPubKey.Bytes()))
        recv.network.SendDKGPrivateShare(receiverPubKey, prv)
    }
}

// ProposeDKGAntiNackComplaint propose a DKGPrivateShare as an anti complaint.
func (recv *consensusDKGReceiver) ProposeDKGAntiNackComplaint(
    prv *typesDKG.PrivateShare) {
    if prv.ProposerID == recv.ID {
        if err := recv.authModule.SignDKGPrivateShare(prv); err != nil {
            recv.logger.Error("Failed sign DKG private share", "error", err)
            return
        }
    }
    recv.logger.Debug("Calling Network.BroadcastDKGPrivateShare", "share", prv)
    recv.network.BroadcastDKGPrivateShare(prv)
}

// ProposeDKGFinalize propose a DKGFinalize message.
func (recv *consensusDKGReceiver) ProposeDKGFinalize(final *typesDKG.Finalize) {
    if err := recv.authModule.SignDKGFinalize(final); err != nil {
        recv.logger.Error("Faield to sign DKG finalize", "error", err)
        return
    }
    recv.logger.Debug("Calling Governance.AddDKGFinalize", "final", final)
    recv.gov.AddDKGFinalize(final.Round, final)
}

// Consensus implements DEXON Consensus algorithm.
type Consensus struct {
    // Node Info.
    ID            types.NodeID
    authModule    *Authenticator
    currentConfig *types.Config

    // BA.
    baModules        []*agreement
    receivers        []*consensusBAReceiver
    baConfirmedBlock map[common.Hash]chan<- *types.Block

    // DKG.
    dkgRunning int32
    dkgReady   *sync.Cond
    cfgModule  *configurationChain

    // Dexon consensus v1's modules.
    lattice  *Lattice
    ccModule *compactionChain

    // Interfaces.
    db        blockdb.BlockDatabase
    app       Application
    gov       Governance
    network   Network
    tickerObj Ticker

    // Misc.
    dMoment       time.Time
    nodeSetCache  *NodeSetCache
    round         uint64
    roundToNotify uint64
    lock          sync.RWMutex
    ctx           context.Context
    ctxCancel     context.CancelFunc
    event         *common.Event
    logger        common.Logger
}

// NewConsensus construct an Consensus instance.
func NewConsensus(
    dMoment time.Time,
    app Application,
    gov Governance,
    db blockdb.BlockDatabase,
    network Network,
    prv crypto.PrivateKey,
    logger common.Logger) *Consensus {

    // TODO(w): load latest blockHeight from DB, and use config at that height.
    var (
        round uint64
        // round 0 and 1 are decided at beginning.
        roundToNotify = round + 2
    )
    logger.Debug("Calling Governance.Configuration", "round", round)
    config := gov.Configuration(round)
    nodeSetCache := NewNodeSetCache(gov)
    logger.Debug("Calling Governance.CRS", "round", round)
    crs := gov.CRS(round)
    // Setup acking by information returned from Governace.
    nodes, err := nodeSetCache.GetNodeSet(round)
    if err != nil {
        panic(err)
    }
    // Setup auth module.
    authModule := NewAuthenticator(prv)
    // Check if the application implement Debug interface.
    debugApp, _ := app.(Debug)
    // Init lattice.
    lattice := NewLattice(
        dMoment, config, authModule, app, debugApp, db, logger)
    // Init configuration chain.
    ID := types.NewNodeID(prv.PublicKey())
    recv := &consensusDKGReceiver{
        ID:           ID,
        gov:          gov,
        authModule:   authModule,
        nodeSetCache: nodeSetCache,
        network:      network,
        logger:       logger,
    }
    cfgModule := newConfigurationChain(
        ID,
        recv,
        gov,
        logger)
    recv.cfgModule = cfgModule
    // Construct Consensus instance.
    con := &Consensus{
        ID:               ID,
        currentConfig:    config,
        ccModule:         newCompactionChain(gov),
        lattice:          lattice,
        app:              app,
        gov:              gov,
        db:               db,
        network:          network,
        tickerObj:        newTicker(gov, round, TickerBA),
        baConfirmedBlock: make(map[common.Hash]chan<- *types.Block),
        dkgReady:         sync.NewCond(&sync.Mutex{}),
        cfgModule:        cfgModule,
        dMoment:          dMoment,
        nodeSetCache:     nodeSetCache,
        authModule:       authModule,
        event:            common.NewEvent(),
        logger:           logger,
        roundToNotify:    roundToNotify,
    }

    validLeader := func(block *types.Block) bool {
        return lattice.SanityCheck(block) == nil
    }

    con.baModules = make([]*agreement, config.NumChains)
    con.receivers = make([]*consensusBAReceiver, config.NumChains)
    for i := uint32(0); i < config.NumChains; i++ {
        chainID := i
        recv := &consensusBAReceiver{
            consensus:     con,
            chainID:       chainID,
            restartNotary: make(chan bool, 1),
        }
        agreementModule := newAgreement(
            con.ID,
            recv,
            nodes.IDs,
            newLeaderSelector(crs, validLeader),
            con.authModule,
        )
        // Hacky way to make agreement module self contained.
        recv.agreementModule = agreementModule
        recv.changeNotaryTime = dMoment
        con.baModules[chainID] = agreementModule
        con.receivers[chainID] = recv
    }
    return con
}

// Run starts running DEXON Consensus.
func (con *Consensus) Run(initBlock *types.Block) {
    // Setup context.
    con.ctx, con.ctxCancel = context.WithCancel(context.Background())
    con.ccModule.init(initBlock)
    // TODO(jimmy-dexon): change AppendConfig to add config for specific round.
    for i := uint64(0); i < initBlock.Position.Round; i++ {
        con.logger.Debug("Calling Governance.Configuration", "round", i+1)
        cfg := con.gov.Configuration(i + 1)
        if err := con.lattice.AppendConfig(i+1, cfg); err != nil {
            panic(err)
        }
    }
    con.logger.Debug("Calling Network.ReceiveChan")
    go con.processMsg(con.network.ReceiveChan())
    // Sleep until dMoment come.
    time.Sleep(con.dMoment.Sub(time.Now().UTC()))
    con.cfgModule.registerDKG(con.round, int(con.currentConfig.DKGSetSize)/3+1)
    con.event.RegisterTime(con.dMoment.Add(con.currentConfig.RoundInterval/4),
        func(time.Time) {
            con.runDKGTSIG(con.round)
        })
    round1 := uint64(1)
    con.logger.Debug("Calling Governance.Configuration", "round", round1)
    con.lattice.AppendConfig(round1, con.gov.Configuration(round1))
    con.initialRound(con.dMoment)
    ticks := make([]chan struct{}, 0, con.currentConfig.NumChains)
    for i := uint32(0); i < con.currentConfig.NumChains; i++ {
        tick := make(chan struct{})
        ticks = append(ticks, tick)
        go con.runBA(i, tick)
    }

    // Reset ticker.
    <-con.tickerObj.Tick()
    <-con.tickerObj.Tick()
    for {
        <-con.tickerObj.Tick()
        for _, tick := range ticks {
            go func(tick chan struct{}) { tick <- struct{}{} }(tick)
        }
    }
}

func (con *Consensus) runBA(chainID uint32, tick <-chan struct{}) {
    // TODO(jimmy-dexon): move this function inside agreement.
    agreement := con.baModules[chainID]
    recv := con.receivers[chainID]
    recv.restartNotary <- true
    nIDs := make(map[types.NodeID]struct{})
    // Reset ticker
    <-tick
BALoop:
    for {
        select {
        case <-con.ctx.Done():
            break BALoop
        default:
        }
        select {
        case newNotary := <-recv.restartNotary:
            if newNotary {
                recv.changeNotaryTime =
                    recv.changeNotaryTime.Add(con.currentConfig.RoundInterval)
                nodes, err := con.nodeSetCache.GetNodeSet(recv.round)
                if err != nil {
                    panic(err)
                }
                con.logger.Debug("Calling Governance.Configuration",
                    "round", recv.round)
                con.logger.Debug("Calling Governance.CRS", "round", recv.round)
                nIDs = nodes.GetSubSet(
                    int(con.gov.Configuration(recv.round).NotarySetSize),
                    types.NewNotarySetTarget(con.gov.CRS(recv.round), chainID))
            }
            nextPos := con.lattice.NextPosition(chainID)
            nextPos.Round = recv.round
            agreement.restart(nIDs, nextPos)
        default:
        }
        if agreement.pullVotes() {
            pos := agreement.agreementID()
            con.logger.Debug("Calling Network.PullVotes for syncing votes",
                "position", pos)
            con.network.PullVotes(pos)
        }
        err := agreement.nextState()
        if err != nil {
            con.logger.Error("Failed to proceed to next state",
                "nodeID", con.ID.String(),
                "error", err)
            break BALoop
        }
        for i := 0; i < agreement.clocks(); i++ {
            // Priority select for agreement.done().
            select {
            case <-agreement.done():
                continue BALoop
            default:
            }
            select {
            case <-agreement.done():
                continue BALoop
            case <-tick:
            }
        }
    }
}

// runDKGTSIG starts running DKG+TSIG protocol.
func (con *Consensus) runDKGTSIG(round uint64) {
    con.dkgReady.L.Lock()
    defer con.dkgReady.L.Unlock()
    if con.dkgRunning != 0 {
        return
    }
    con.dkgRunning = 1
    go func() {
        startTime := time.Now().UTC()
        defer func() {
            con.dkgReady.L.Lock()
            defer con.dkgReady.L.Unlock()
            con.dkgReady.Broadcast()
            con.dkgRunning = 2
            DKGTime := time.Now().Sub(startTime)
            if DKGTime.Nanoseconds() >=
                con.currentConfig.RoundInterval.Nanoseconds()/2 {
                con.logger.Warn("Your computer cannot finish DKG on time!",
                    "nodeID", con.ID.String())
            }
        }()
        if err := con.cfgModule.runDKG(round); err != nil {
            panic(err)
        }
        nodes, err := con.nodeSetCache.GetNodeSet(round)
        if err != nil {
            panic(err)
        }
        con.logger.Debug("Calling Governance.Configuration", "round", round)
        hash := HashConfigurationBlock(
            nodes.IDs,
            con.gov.Configuration(round),
            common.Hash{},
            con.cfgModule.prevHash)
        psig, err := con.cfgModule.preparePartialSignature(
            round, hash)
        if err != nil {
            panic(err)
        }
        if err = con.authModule.SignDKGPartialSignature(psig); err != nil {
            panic(err)
        }
        if err = con.cfgModule.processPartialSignature(psig); err != nil {
            panic(err)
        }
        con.logger.Debug("Calling Network.BroadcastDKGPartialSignature",
            "proposer", psig.ProposerID,
            "round", psig.Round,
            "hash", psig.Hash)
        con.network.BroadcastDKGPartialSignature(psig)
        if _, err = con.cfgModule.runBlockTSig(round, hash); err != nil {
            panic(err)
        }
    }()
}

func (con *Consensus) runCRS() {
    // Start running next round CRS.
    con.logger.Debug("Calling Governance.CRS", "round", con.round)
    psig, err := con.cfgModule.preparePartialSignature(
        con.round, con.gov.CRS(con.round))
    if err != nil {
        con.logger.Error("Failed to prepare partial signature", "error", err)
    } else if err = con.authModule.SignDKGPartialSignature(psig); err != nil {
        con.logger.Error("Failed to sign DKG partial signature", "error", err)
    } else if err = con.cfgModule.processPartialSignature(psig); err != nil {
        con.logger.Error("Failed to process partial signature", "error", err)
    } else {
        con.logger.Debug("Calling Network.BroadcastDKGPartialSignature",
            "proposer", psig.ProposerID,
            "round", psig.Round,
            "hash", psig.Hash)
        con.network.BroadcastDKGPartialSignature(psig)
        con.logger.Debug("Calling Governance.CRS", "round", con.round)
        crs, err := con.cfgModule.runCRSTSig(con.round, con.gov.CRS(con.round))
        if err != nil {
            con.logger.Error("Failed to run CRS Tsig", "error", err)
        } else {
            con.logger.Debug("Calling Governance.ProposeCRS",
                "round", con.round+1,
                "crs", hex.EncodeToString(crs))
            con.gov.ProposeCRS(con.round+1, crs)
        }
    }
}

func (con *Consensus) initialRound(startTime time.Time) {
    select {
    case <-con.ctx.Done():
        return
    default:
    }
    con.logger.Debug("Calling Governance.Configuration", "round", con.round)
    con.currentConfig = con.gov.Configuration(con.round)

    con.event.RegisterTime(startTime.Add(con.currentConfig.RoundInterval/2),
        func(time.Time) {
            go func() {
                con.runCRS()
                ticker := newTicker(con.gov, con.round, TickerDKG)
                <-ticker.Tick()
                // Normally, gov.CRS would return non-nil. Use this for in case of
                // unexpected network fluctuation and ensure the robustness.
                for (con.gov.CRS(con.round+1) == common.Hash{}) {
                    con.logger.Info("CRS is not ready yet. Try again later...",
                        "nodeID", con.ID)
                    time.Sleep(500 * time.Millisecond)
                }
                con.cfgModule.registerDKG(
                    con.round+1, int(con.currentConfig.DKGSetSize/3)+1)
            }()
        })
    con.event.RegisterTime(startTime.Add(con.currentConfig.RoundInterval*2/3),
        func(time.Time) {
            func() {
                con.dkgReady.L.Lock()
                defer con.dkgReady.L.Unlock()
                con.dkgRunning = 0
            }()
            con.runDKGTSIG(con.round + 1)
        })
    con.event.RegisterTime(startTime.Add(con.currentConfig.RoundInterval),
        func(time.Time) {
            // Change round.
            con.round++
            con.logger.Debug("Calling Governance.Configuration",
                "round", con.round+1)
            con.lattice.AppendConfig(con.round+1, con.gov.Configuration(con.round+1))
            con.initialRound(startTime.Add(con.currentConfig.RoundInterval))
        })
}

// Stop the Consensus core.
func (con *Consensus) Stop() {
    for _, a := range con.baModules {
        a.stop()
    }
    con.event.Reset()
    con.ctxCancel()
}

func (con *Consensus) processMsg(msgChan <-chan interface{}) {
MessageLoop:
    for {
        var msg interface{}
        select {
        case msg = <-msgChan:
        case <-con.ctx.Done():
            return
        }

        switch val := msg.(type) {
        case *types.Block:
            if ch, exist := func() (chan<- *types.Block, bool) {
                con.lock.RLock()
                defer con.lock.RUnlock()
                ch, e := con.baConfirmedBlock[val.Hash]
                return ch, e
            }(); exist {
                if err := con.lattice.SanityCheck(val); err != nil {
                    if err == ErrRetrySanityCheckLater {
                        err = nil
                    } else {
                        con.logger.Error("SanityCheck failed", "error", err)
                        continue MessageLoop
                    }
                }
                func() {
                    con.lock.Lock()
                    defer con.lock.Unlock()
                    // In case of multiple delivered block.
                    if _, exist := con.baConfirmedBlock[val.Hash]; !exist {
                        return
                    }
                    delete(con.baConfirmedBlock, val.Hash)
                    ch <- val
                }()
            } else if val.IsFinalized() {
                // For sync mode.
                if err := con.processFinalizedBlock(val); err != nil {
                    con.logger.Error("Failed to process finalized block",
                        "error", err)
                }
            } else {
                if err := con.preProcessBlock(val); err != nil {
                    con.logger.Error("Failed to pre process block",
                        "error", err)
                }
            }
        case *types.Vote:
            if err := con.ProcessVote(val); err != nil {
                con.logger.Error("Failed to process vote",
                    "error", err)
            }
        case *types.AgreementResult:
            if err := con.ProcessAgreementResult(val); err != nil {
                con.logger.Error("Failed to process agreement result",
                    "error", err)
            }
        case *types.BlockRandomnessResult:
            if err := con.ProcessBlockRandomnessResult(val); err != nil {
                con.logger.Error("Failed to process block randomness result",
                    "error", err)
            }
        case *typesDKG.PrivateShare:
            if err := con.cfgModule.processPrivateShare(val); err != nil {
                con.logger.Error("Failed to process private share",
                    "error", err)
            }

        case *typesDKG.PartialSignature:
            if err := con.cfgModule.processPartialSignature(val); err != nil {
                con.logger.Error("Failed to process partial signature",
                    "error", err)
            }
        }
    }
}

func (con *Consensus) proposeBlock(chainID uint32, round uint64) *types.Block {
    block := &types.Block{
        Position: types.Position{
            ChainID: chainID,
            Round:   round,
        },
    }
    if err := con.prepareBlock(block, time.Now().UTC()); err != nil {
        con.logger.Error("Failed to prepare block", "error", err)
        return nil
    }
    return block
}

func (con *Consensus) proposeEmptyBlock(
    chainID uint32) (*types.Block, error) {
    block := &types.Block{
        Position: types.Position{
            ChainID: chainID,
        },
    }
    if err := con.lattice.PrepareEmptyBlock(block); err != nil {
        return nil, err
    }
    return block, nil
}

// ProcessVote is the entry point to submit ont vote to a Consensus instance.
func (con *Consensus) ProcessVote(vote *types.Vote) (err error) {
    v := vote.Clone()
    err = con.baModules[v.Position.ChainID].processVote(v)
    return err
}

// ProcessAgreementResult processes the randomness request.
func (con *Consensus) ProcessAgreementResult(
    rand *types.AgreementResult) error {
    // Sanity Check.
    notarySet, err := con.nodeSetCache.GetNotarySet(
        rand.Position.Round, rand.Position.ChainID)
    if err != nil {
        return err
    }
    if len(rand.Votes) < len(notarySet)/3*2+1 {
        return ErrNotEnoughVotes
    }
    if len(rand.Votes) > len(notarySet) {
        return ErrIncorrectVoteProposer
    }
    for _, vote := range rand.Votes {
        if vote.BlockHash != rand.BlockHash {
            return ErrIncorrectVoteBlockHash
        }
        if vote.Type != types.VoteCom {
            return ErrIncorrectVoteType
        }
        if vote.Position != rand.Position {
            return ErrIncorrectVotePosition
        }
        if _, exist := notarySet[vote.ProposerID]; !exist {
            return ErrIncorrectVoteProposer
        }
        ok, err := verifyVoteSignature(&vote)
        if err != nil {
            return err
        }
        if !ok {
            return ErrIncorrectVoteSignature
        }
    }
    // Syncing BA Module.
    agreement := con.baModules[rand.Position.ChainID]
    aID := agreement.agreementID()
    if rand.Position.Newer(&aID) {
        con.logger.Info("Syncing BA", "position", rand.Position)
        nodes, err := con.nodeSetCache.GetNodeSet(rand.Position.Round)
        if err != nil {
            return err
        }
        con.logger.Debug("Calling Network.PullBlocks for syncing BA",
            "hash", rand.BlockHash)
        con.network.PullBlocks(common.Hashes{rand.BlockHash})
        nIDs := nodes.GetSubSet(
            int(con.gov.Configuration(rand.Position.Round).NotarySetSize),
            types.NewNotarySetTarget(
                con.gov.CRS(rand.Position.Round), rand.Position.ChainID))
        for _, vote := range rand.Votes {
            agreement.processVote(&vote)
        }
        agreement.restart(nIDs, rand.Position)
    }
    // Calculating randomness.
    if rand.Position.Round == 0 {
        return nil
    }
    if !con.ccModule.blockRegistered(rand.BlockHash) {
        return nil
    }
    if DiffUint64(con.round, rand.Position.Round) > 1 {
        return nil
    }
    // Sanity check done.
    if !con.cfgModule.touchTSigHash(rand.BlockHash) {
        return nil
    }
    con.logger.Debug("Calling Network.BroadcastAgreementResult", "result", rand)
    con.network.BroadcastAgreementResult(rand)
    dkgSet, err := con.nodeSetCache.GetDKGSet(rand.Position.Round)
    if err != nil {
        return err
    }
    if _, exist := dkgSet[con.ID]; !exist {
        return nil
    }
    psig, err := con.cfgModule.preparePartialSignature(rand.Position.Round, rand.BlockHash)
    if err != nil {
        return err
    }
    if err = con.authModule.SignDKGPartialSignature(psig); err != nil {
        return err
    }
    if err = con.cfgModule.processPartialSignature(psig); err != nil {
        return err
    }
    con.logger.Debug("Calling Network.BroadcastDKGPartialSignature",
        "proposer", psig.ProposerID,
        "round", psig.Round,
        "hash", psig.Hash)
    con.network.BroadcastDKGPartialSignature(psig)
    go func() {
        tsig, err := con.cfgModule.runTSig(rand.Position.Round, rand.BlockHash)
        if err != nil {
            if err != ErrTSigAlreadyRunning {
                con.logger.Error("Faield to run TSIG", "error", err)
            }
            return
        }
        result := &types.BlockRandomnessResult{
            BlockHash:  rand.BlockHash,
            Position:   rand.Position,
            Randomness: tsig.Signature,
        }
        if err := con.ProcessBlockRandomnessResult(result); err != nil {
            con.logger.Error("Failed to process randomness result",
                "error", err)
            return
        }
    }()
    return nil
}

// ProcessBlockRandomnessResult processes the randomness result.
func (con *Consensus) ProcessBlockRandomnessResult(
    rand *types.BlockRandomnessResult) error {
    if rand.Position.Round == 0 {
        return nil
    }
    if !con.ccModule.blockRegistered(rand.BlockHash) {
        return nil
    }
    round := rand.Position.Round
    v, ok, err := con.ccModule.tsigVerifier.UpdateAndGet(round)
    if err != nil {
        return err
    }
    if !ok {
        return nil
    }
    if !v.VerifySignature(
        rand.BlockHash, crypto.Signature{Signature: rand.Randomness}) {
        return ErrIncorrectBlockRandomnessResult
    }
    con.logger.Debug("Calling Network.BroadcastRandomnessResult",
        "hash", rand.BlockHash,
        "position", rand.Position,
        "randomness", hex.EncodeToString(rand.Randomness))
    con.network.BroadcastRandomnessResult(rand)
    if err := con.ccModule.processBlockRandomnessResult(rand); err != nil {
        if err != ErrBlockNotRegistered {
            return err
        }
    }
    return nil
}

// preProcessBlock performs Byzantine Agreement on the block.
func (con *Consensus) preProcessBlock(b *types.Block) (err error) {
    if err = con.lattice.SanityCheck(b); err != nil {
        if err != ErrRetrySanityCheckLater {
            return
        }
    }
    if err = con.baModules[b.Position.ChainID].processBlock(b); err != nil {
        return err
    }
    return
}

// deliverBlock deliver a block to application layer.
func (con *Consensus) deliverBlock(b *types.Block) {
    // TODO(mission): clone types.FinalizationResult
    con.logger.Debug("Calling Application.BlockDelivered", "block", b)
    con.app.BlockDelivered(b.Hash, b.Finalization)
    if b.Position.Round+2 == con.roundToNotify {
        // Only the first block delivered of that round would
        // trigger this noitification.
        con.gov.NotifyRoundHeight(
            con.roundToNotify, b.Finalization.Height)
        con.roundToNotify++
    }
}

// processBlock is the entry point to submit one block to a Consensus instance.
func (con *Consensus) processBlock(block *types.Block) (err error) {
    if err = con.db.Put(*block); err != nil && err != blockdb.ErrBlockExists {
        return
    }
    con.lock.Lock()
    defer con.lock.Unlock()
    // Block processed by lattice can be out-of-order. But the output of lattice
    // (deliveredBlocks) cannot.
    deliveredBlocks, err := con.lattice.ProcessBlock(block)
    if err != nil {
        return
    }
    // Pass delivered blocks to compaction chain.
    for _, b := range deliveredBlocks {
        if err = con.ccModule.processBlock(b); err != nil {
            return
        }
        go con.event.NotifyTime(b.Finalization.Timestamp)
    }
    deliveredBlocks = con.ccModule.extractBlocks()
    for _, b := range deliveredBlocks {
        if err = con.db.Update(*b); err != nil {
            panic(err)
        }
        con.cfgModule.untouchTSigHash(b.Hash)
        con.deliverBlock(b)
    }
    if err = con.lattice.PurgeBlocks(deliveredBlocks); err != nil {
        return
    }
    return
}

// processFinalizedBlock is the entry point for syncing blocks.
func (con *Consensus) processFinalizedBlock(block *types.Block) (err error) {
    if err = con.lattice.SanityCheck(block); err != nil {
        return
    }
    con.ccModule.processFinalizedBlock(block)
    for {
        confirmed := con.ccModule.extractFinalizedBlocks()
        if len(confirmed) == 0 {
            break
        }
        if err = con.lattice.ctModule.processBlocks(confirmed); err != nil {
            return
        }
        for _, b := range confirmed {
            if err = con.db.Put(*b); err != nil {
                if err != blockdb.ErrBlockExists {
                    return
                }
                err = nil
            }
            con.deliverBlock(b)
        }
    }
    return
}

// PrepareBlock would setup header fields of block based on its ProposerID.
func (con *Consensus) prepareBlock(b *types.Block,
    proposeTime time.Time) (err error) {
    if err = con.lattice.PrepareBlock(b, proposeTime); err != nil {
        return
    }
    // TODO(mission): decide CRS by block's round, which could be determined by
    //                block's info (ex. position, timestamp).
    con.logger.Debug("Calling Governance.CRS", "round", 0)
    if err = con.authModule.SignCRS(b, con.gov.CRS(0)); err != nil {
        return
    }
    return
}

// PrepareGenesisBlock would setup header fields for genesis block.
func (con *Consensus) PrepareGenesisBlock(b *types.Block,
    proposeTime time.Time) (err error) {
    if err = con.prepareBlock(b, proposeTime); err != nil {
        return
    }
    if len(b.Payload) != 0 {
        err = ErrGenesisBlockNotEmpty
        return
    }
    return
}