path: root/core/test/state.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 test

import (
    "bytes"
    "errors"
    "sort"
    "sync"
    "time"

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

var (
    // ErrDuplicatedChange means the change request is already applied.
    ErrDuplicatedChange = errors.New("duplicated change")
    // ErrForkedCRS means a different CRS for one round is proposed.
    ErrForkedCRS = errors.New("forked CRS")
    // ErrMissingPreviousCRS means previous CRS not found when
    // proposing a specific round of CRS.
    ErrMissingPreviousCRS = errors.New("missing previous CRS")
    // ErrUnknownStateChangeType means a StateChangeType is not recognized.
    ErrUnknownStateChangeType = errors.New("unknown state change type")
    // ErrProposerMPKIsReady means a proposer of one mpk is ready.
    ErrProposerMPKIsReady = errors.New("proposer mpk is ready")
    // ErrProposerIsFinal means a proposer of one complaint is finalized.
    ErrProposerIsFinal = errors.New("proposer is final")
    // ErrStateConfigNotEqual means configuration part of two states is not
    // equal.
    ErrStateConfigNotEqual = errors.New("config not equal")
    // ErrStateLocalFlagNotEqual means local flag of two states is not equal.
    ErrStateLocalFlagNotEqual = errors.New("local flag not equal")
    // ErrStateNodeSetNotEqual means node sets of two states are not equal.
    ErrStateNodeSetNotEqual = errors.New("node set not equal")
    // ErrStateDKGComplaintsNotEqual means DKG complaints for two states are not
    // equal.
    ErrStateDKGComplaintsNotEqual = errors.New("dkg complaints not equal")
    // ErrStateDKGMasterPublicKeysNotEqual means DKG master public keys of two
    // states are not equal.
    ErrStateDKGMasterPublicKeysNotEqual = errors.New(
        "dkg master public keys not equal")
    // ErrStateDKGMPKReadysNotEqual means DKG readys of two states are not
    // equal.
    ErrStateDKGMPKReadysNotEqual = errors.New("dkg readys not equal")
    // ErrStateDKGFinalsNotEqual means DKG finalizations of two states are not
    // equal.
    ErrStateDKGFinalsNotEqual = errors.New("dkg finalizations not equal")
    // ErrStateCRSsNotEqual means CRSs of two states are not equal.
    ErrStateCRSsNotEqual = errors.New("crs not equal")
    // ErrStateDKGResetCountNotEqual means dkgResetCount of two states are not
    // equal.
    ErrStateDKGResetCountNotEqual = errors.New("dkg reset count not equal")
    // ErrStatePendingChangesNotEqual means pending change requests of two
    // states are not equal.
    ErrStatePendingChangesNotEqual = errors.New("pending changes not equal")
    // ErrChangeWontApply means the state change won't be applied for some
    // reason.
    ErrChangeWontApply = errors.New("change won't apply")
    // ErrNotInRemoteMode means callers attempts to call functions for remote
    // mode when the State instance is still in local mode.
    ErrNotInRemoteMode = errors.New(
        "attempting to use remote functions in local mode")
)

type crsAdditionRequest struct {
    Round uint64      `json:"round"`
    CRS   common.Hash `json:"crs"`
}

// State emulates what the global state in governace contract on a fullnode.
type State struct {
    // Configuration related.
    lambdaBA         time.Duration
    lambdaDKG        time.Duration
    notarySetSize    uint32
    roundInterval    uint64
    minBlockInterval time.Duration
    // Nodes
    nodes map[types.NodeID]crypto.PublicKey
    // DKG & CRS
    dkgComplaints       map[uint64]map[types.NodeID][]*typesDKG.Complaint
    dkgMasterPublicKeys map[uint64]map[types.NodeID]*typesDKG.MasterPublicKey
    dkgReadys           map[uint64]map[types.NodeID]*typesDKG.MPKReady
    dkgFinals           map[uint64]map[types.NodeID]*typesDKG.Finalize
    crs                 []common.Hash
    dkgResetCount       map[uint64]uint64
    // Other stuffs
    local           bool
    logger          common.Logger
    lock            sync.RWMutex
    appliedRequests map[common.Hash]struct{}
    // Pending change requests.
    ownRequests    map[common.Hash]*StateChangeRequest
    globalRequests map[common.Hash]*StateChangeRequest
}

// NewState constructs an State instance with genesis information, including:
//  - node set
//  - crs
func NewState(
    dkgDelayRound uint64,
    nodePubKeys []crypto.PublicKey,
    lambda time.Duration,
    logger common.Logger,
    local bool) *State {
    nodes := make(map[types.NodeID]crypto.PublicKey)
    for _, key := range nodePubKeys {
        nodes[types.NewNodeID(key)] = key
    }
    genesisCRS := crypto.Keccak256Hash([]byte("__ DEXON"))
    crs := make([]common.Hash, dkgDelayRound+1)
    for i := range crs {
        crs[i] = genesisCRS
        genesisCRS = crypto.Keccak256Hash(genesisCRS[:])
    }
    return &State{
        local:            local,
        logger:           logger,
        lambdaBA:         lambda,
        lambdaDKG:        lambda * 10,
        roundInterval:    1000,
        minBlockInterval: 4 * lambda,
        crs:              crs,
        nodes:            nodes,
        notarySetSize:    uint32(len(nodes)),
        ownRequests:      make(map[common.Hash]*StateChangeRequest),
        globalRequests:   make(map[common.Hash]*StateChangeRequest),
        dkgReadys: make(
            map[uint64]map[types.NodeID]*typesDKG.MPKReady),
        dkgFinals: make(
            map[uint64]map[types.NodeID]*typesDKG.Finalize),
        dkgComplaints: make(
            map[uint64]map[types.NodeID][]*typesDKG.Complaint),
        dkgMasterPublicKeys: make(
            map[uint64]map[types.NodeID]*typesDKG.MasterPublicKey),
        dkgResetCount:   make(map[uint64]uint64),
        appliedRequests: make(map[common.Hash]struct{}),
    }
}

// SwitchToRemoteMode turn this State instance into remote mode: all changes
// are pending, and need to be packed/unpacked to apply. Once this state switch
// to remote mode, there would be no way to switch back to local mode.
func (s *State) SwitchToRemoteMode() {
    s.lock.Lock()
    defer s.lock.Unlock()
    s.local = false
}

// Snapshot returns configration that could be snapshotted.
func (s *State) Snapshot() (*types.Config, []crypto.PublicKey) {
    s.lock.RLock()
    defer s.lock.RUnlock()
    // Clone a node set.
    nodes := make([]crypto.PublicKey, 0, len(s.nodes))
    for _, key := range s.nodes {
        nodes = append(nodes, key)
    }
    cfg := &types.Config{
        LambdaBA:         s.lambdaBA,
        LambdaDKG:        s.lambdaDKG,
        NotarySetSize:    s.notarySetSize,
        RoundLength:      s.roundInterval,
        MinBlockInterval: s.minBlockInterval,
    }
    s.logger.Info("Snapshot config", "config", cfg)
    return cfg, nodes
}

// AttachLogger allows to attach custom logger.
func (s *State) AttachLogger(logger common.Logger) {
    s.logger = logger
}

func (s *State) unpackPayload(
    raw *rawStateChangeRequest) (v interface{}, err error) {
    switch raw.Type {
    case StateAddCRS:
        v = &crsAdditionRequest{}
        err = rlp.DecodeBytes(raw.Payload, v)
    case StateAddDKGComplaint:
        v = &typesDKG.Complaint{}
        err = rlp.DecodeBytes(raw.Payload, v)
    case StateAddDKGMasterPublicKey:
        v = &typesDKG.MasterPublicKey{}
        err = rlp.DecodeBytes(raw.Payload, v)
    case StateAddDKGMPKReady:
        v = &typesDKG.MPKReady{}
        err = rlp.DecodeBytes(raw.Payload, v)
    case StateAddDKGFinal:
        v = &typesDKG.Finalize{}
        err = rlp.DecodeBytes(raw.Payload, v)
    case StateResetDKG:
        var tmp common.Hash
        err = rlp.DecodeBytes(raw.Payload, &tmp)
        v = tmp
    case StateChangeLambdaBA:
        var tmp uint64
        err = rlp.DecodeBytes(raw.Payload, &tmp)
        v = tmp
    case StateChangeLambdaDKG:
        var tmp uint64
        err = rlp.DecodeBytes(raw.Payload, &tmp)
        v = tmp
    case StateChangeRoundLength:
        var tmp uint64
        err = rlp.DecodeBytes(raw.Payload, &tmp)
        v = tmp
    case StateChangeMinBlockInterval:
        var tmp uint64
        err = rlp.DecodeBytes(raw.Payload, &tmp)
        v = tmp
    case StateChangeNotarySetSize:
        var tmp uint32
        err = rlp.DecodeBytes(raw.Payload, &tmp)
        v = tmp
    case StateAddNode:
        var tmp []byte
        err = rlp.DecodeBytes(raw.Payload, &tmp)
        v = tmp
    default:
        err = ErrUnknownStateChangeType
    }
    if err != nil {
        return
    }
    return
}

func (s *State) unpackRequests(
    b []byte) (reqs []*StateChangeRequest, err error) {
    // Try to unmarshal this byte stream into []*StateChangeRequest.
    rawReqs := []*rawStateChangeRequest{}
    if err = rlp.DecodeBytes(b, &rawReqs); err != nil {
        return
    }
    for _, r := range rawReqs {
        var payload interface{}
        if payload, err = s.unpackPayload(r); err != nil {
            return
        }
        reqs = append(reqs, &StateChangeRequest{
            Type:      r.Type,
            Payload:   payload,
            Hash:      r.Hash,
            Timestamp: r.Timestamp,
        })
    }
    return
}

// Equal checks equality between State instance.
func (s *State) Equal(other *State) error {
    // Check configuration part.
    configEqual := s.lambdaBA == other.lambdaBA &&
        s.lambdaDKG == other.lambdaDKG &&
        s.notarySetSize == other.notarySetSize &&
        s.roundInterval == other.roundInterval &&
        s.minBlockInterval == other.minBlockInterval
    if !configEqual {
        return ErrStateConfigNotEqual
    }
    // Check local flag.
    if s.local != other.local {
        return ErrStateLocalFlagNotEqual
    }
    // Check node set.
    if len(s.nodes) != len(other.nodes) {
        return ErrStateNodeSetNotEqual
    }
    for nID, key := range s.nodes {
        otherKey, exists := other.nodes[nID]
        if !exists {
            return ErrStateNodeSetNotEqual
        }
        if bytes.Compare(key.Bytes(), otherKey.Bytes()) != 0 {
            return ErrStateNodeSetNotEqual
        }
    }
    // Check DKG Complaints, here I assume the addition sequence of complaints
    // proposed by one node would be identical on each node (this should be true
    // when state change requests are carried by blocks and executed in order).
    if len(s.dkgComplaints) != len(other.dkgComplaints) {
        return ErrStateDKGComplaintsNotEqual
    }
    for round, compsForRound := range s.dkgComplaints {
        otherCompsForRound, exists := other.dkgComplaints[round]
        if !exists {
            return ErrStateDKGComplaintsNotEqual
        }
        if len(compsForRound) != len(otherCompsForRound) {
            return ErrStateDKGComplaintsNotEqual
        }
        for nID, comps := range compsForRound {
            otherComps, exists := otherCompsForRound[nID]
            if !exists {
                return ErrStateDKGComplaintsNotEqual
            }
            if len(comps) != len(otherComps) {
                return ErrStateDKGComplaintsNotEqual
            }
            for idx, comp := range comps {
                if !comp.Equal(otherComps[idx]) {
                    return ErrStateDKGComplaintsNotEqual
                }
            }
        }
    }
    // Check DKG master public keys.
    if len(s.dkgMasterPublicKeys) != len(other.dkgMasterPublicKeys) {
        return ErrStateDKGMasterPublicKeysNotEqual
    }
    for round, mKeysForRound := range s.dkgMasterPublicKeys {
        otherMKeysForRound, exists := other.dkgMasterPublicKeys[round]
        if !exists {
            return ErrStateDKGMasterPublicKeysNotEqual
        }
        if len(mKeysForRound) != len(otherMKeysForRound) {
            return ErrStateDKGMasterPublicKeysNotEqual
        }
        for nID, mKey := range mKeysForRound {
            otherMKey, exists := otherMKeysForRound[nID]
            if !exists {
                return ErrStateDKGMasterPublicKeysNotEqual
            }
            if !mKey.Equal(otherMKey) {
                return ErrStateDKGMasterPublicKeysNotEqual
            }
        }
    }
    // Check DKG readys.
    if len(s.dkgReadys) != len(other.dkgReadys) {
        return ErrStateDKGMPKReadysNotEqual
    }
    for round, readysForRound := range s.dkgReadys {
        otherReadysForRound, exists := other.dkgReadys[round]
        if !exists {
            return ErrStateDKGMPKReadysNotEqual
        }
        if len(readysForRound) != len(otherReadysForRound) {
            return ErrStateDKGMPKReadysNotEqual
        }
        for nID, ready := range readysForRound {
            otherReady, exists := otherReadysForRound[nID]
            if !exists {
                return ErrStateDKGMPKReadysNotEqual
            }
            if !ready.Equal(otherReady) {
                return ErrStateDKGMPKReadysNotEqual
            }
        }
    }
    // Check DKG finals.
    if len(s.dkgFinals) != len(other.dkgFinals) {
        return ErrStateDKGFinalsNotEqual
    }
    for round, finalsForRound := range s.dkgFinals {
        otherFinalsForRound, exists := other.dkgFinals[round]
        if !exists {
            return ErrStateDKGFinalsNotEqual
        }
        if len(finalsForRound) != len(otherFinalsForRound) {
            return ErrStateDKGFinalsNotEqual
        }
        for nID, final := range finalsForRound {
            otherFinal, exists := otherFinalsForRound[nID]
            if !exists {
                return ErrStateDKGFinalsNotEqual
            }
            if !final.Equal(otherFinal) {
                return ErrStateDKGFinalsNotEqual
            }
        }
    }
    // Check CRS part.
    if len(s.crs) != len(other.crs) {
        return ErrStateCRSsNotEqual
    }
    for idx, crs := range s.crs {
        if crs != other.crs[idx] {
            return ErrStateCRSsNotEqual
        }
    }
    // Check dkgResetCount.
    if len(s.dkgResetCount) != len(other.dkgResetCount) {
        return ErrStateDKGResetCountNotEqual
    }
    for idx, count := range s.dkgResetCount {
        if count != other.dkgResetCount[idx] {
            return ErrStateDKGResetCountNotEqual
        }
    }
    // Check pending changes.
    checkPending := func(
        src, target map[common.Hash]*StateChangeRequest) error {
        if len(src) != len(target) {
            return ErrStatePendingChangesNotEqual
        }
        for k, v := range src {
            otherV, exists := target[k]
            if !exists {
                return ErrStatePendingChangesNotEqual
            }
            if err := v.Equal(otherV); err != nil {
                return err
            }
        }
        return nil
    }
    if err := checkPending(s.ownRequests, other.ownRequests); err != nil {
        return err
    }
    if err := checkPending(s.globalRequests, other.globalRequests); err != nil {
        return err
    }
    return nil
}

// Clone returns a copied State instance.
func (s *State) Clone() (copied *State) {
    // Clone configuration parts.
    copied = &State{
        lambdaBA:         s.lambdaBA,
        lambdaDKG:        s.lambdaDKG,
        notarySetSize:    s.notarySetSize,
        roundInterval:    s.roundInterval,
        minBlockInterval: s.minBlockInterval,
        local:            s.local,
        logger:           s.logger,
        nodes:            make(map[types.NodeID]crypto.PublicKey),
        dkgComplaints: make(
            map[uint64]map[types.NodeID][]*typesDKG.Complaint),
        dkgMasterPublicKeys: make(
            map[uint64]map[types.NodeID]*typesDKG.MasterPublicKey),
        dkgReadys:       make(map[uint64]map[types.NodeID]*typesDKG.MPKReady),
        dkgFinals:       make(map[uint64]map[types.NodeID]*typesDKG.Finalize),
        appliedRequests: make(map[common.Hash]struct{}),
    }
    // Nodes
    for nID, key := range s.nodes {
        copied.nodes[nID] = key
    }
    // DKG & CRS
    for round, complaintsForRound := range s.dkgComplaints {
        copied.dkgComplaints[round] =
            make(map[types.NodeID][]*typesDKG.Complaint)
        for nID, comps := range complaintsForRound {
            tmpComps := []*typesDKG.Complaint{}
            for _, comp := range comps {
                tmpComps = append(tmpComps, CloneDKGComplaint(comp))
            }
            copied.dkgComplaints[round][nID] = tmpComps
        }
    }
    for round, mKeysForRound := range s.dkgMasterPublicKeys {
        copied.dkgMasterPublicKeys[round] =
            make(map[types.NodeID]*typesDKG.MasterPublicKey)
        for nID, mKey := range mKeysForRound {
            copied.dkgMasterPublicKeys[round][nID] =
                CloneDKGMasterPublicKey(mKey)
        }
    }
    for round, readysForRound := range s.dkgReadys {
        copied.dkgReadys[round] = make(map[types.NodeID]*typesDKG.MPKReady)
        for nID, ready := range readysForRound {
            copied.dkgReadys[round][nID] = CloneDKGMPKReady(ready)
        }
    }
    for round, finalsForRound := range s.dkgFinals {
        copied.dkgFinals[round] = make(map[types.NodeID]*typesDKG.Finalize)
        for nID, final := range finalsForRound {
            copied.dkgFinals[round][nID] = CloneDKGFinalize(final)
        }
    }
    for _, crs := range s.crs {
        copied.crs = append(copied.crs, crs)
    }
    copied.dkgResetCount = make(map[uint64]uint64, len(s.dkgResetCount))
    for round, count := range s.dkgResetCount {
        copied.dkgResetCount[round] = count
    }
    for hash := range s.appliedRequests {
        copied.appliedRequests[hash] = struct{}{}
    }
    // Pending Changes
    copied.ownRequests = make(map[common.Hash]*StateChangeRequest)
    for k, req := range s.ownRequests {
        copied.ownRequests[k] = req.Clone()
    }
    copied.globalRequests = make(map[common.Hash]*StateChangeRequest)
    for k, req := range s.globalRequests {
        copied.globalRequests[k] = req.Clone()
    }
    return
}

type reqByTime []*StateChangeRequest

func (req reqByTime) Len() int      { return len(req) }
func (req reqByTime) Swap(i, j int) { req[i], req[j] = req[j], req[i] }
func (req reqByTime) Less(i, j int) bool {
    return req[i].Timestamp < req[j].Timestamp
}

// Apply change requests, this function would also
// be called when we extract these request from delivered blocks.
func (s *State) Apply(reqsAsBytes []byte) (err error) {
    if len(reqsAsBytes) == 0 {
        return
    }
    // Try to unmarshal this byte stream into []*StateChangeRequest.
    reqs, err := s.unpackRequests(reqsAsBytes)
    if err != nil {
        return
    }
    sort.Sort(reqByTime(reqs))
    s.lock.Lock()
    defer s.lock.Unlock()
    for _, req := range reqs {
        s.logger.Debug("Apply Request", "req", req)
        // Remove this request from pending set once it's about to apply.
        delete(s.globalRequests, req.Hash)
        delete(s.ownRequests, req.Hash)
        if _, exist := s.appliedRequests[req.Hash]; exist {
            continue
        }
        if err = s.isValidRequest(req); err != nil {
            if err == ErrDuplicatedChange {
                err = nil
                continue
            }
            return
        }
        if err = s.applyRequest(req); err != nil {
            return
        }
        s.appliedRequests[req.Hash] = struct{}{}
    }
    return
}

// AddRequestsFromOthers add requests from others, they won't be packed by
// 'PackOwnRequests'.
func (s *State) AddRequestsFromOthers(reqsAsBytes []byte) (err error) {
    if s.local {
        err = ErrNotInRemoteMode
        return
    }
    reqs, err := s.unpackRequests(reqsAsBytes)
    if err != nil {
        return
    }
    s.lock.Lock()
    defer s.lock.Unlock()
    for _, req := range reqs {
        s.globalRequests[req.Hash] = req
    }
    return
}

// PackRequests pack all current pending requests, include those from others.
func (s *State) PackRequests() (b []byte, err error) {
    if s.local {
        // Convert own requests to global one for packing.
        if _, err = s.PackOwnRequests(); err != nil {
            return
        }
    }
    // Pack requests in global pool.
    packed := []*StateChangeRequest{}
    s.lock.Lock()
    defer s.lock.Unlock()
    for _, v := range s.globalRequests {
        s.logger.Debug("Pack Request", "req", v)
        packed = append(packed, v)
    }
    return rlp.EncodeToBytes(packed)
}

// PackOwnRequests pack current pending requests as byte slice, which
// could be sent as blocks' payload and unmarshall back to apply.
//
// Once a request is packed as own request, it would be turned into a normal
// pending request and won't be packed by this function. This would ensure
// each request broadcasted(gossip) once.
//
// This function is not required to call in local mode.
func (s *State) PackOwnRequests() (b []byte, err error) {
    packed := []*StateChangeRequest{}
    s.lock.Lock()
    defer s.lock.Unlock()
    for k, v := range s.ownRequests {
        delete(s.ownRequests, k)
        s.globalRequests[k] = v
        packed = append(packed, v)
    }
    if b, err = rlp.EncodeToBytes(packed); err != nil {
        return
    }
    return
}

// isValidRequest checks if this request is valid to proceed or not.
func (s *State) isValidRequest(req *StateChangeRequest) error {
    // NOTE: there would be no lock in this helper, callers should be
    //       responsible for acquiring appropriate lock.
    switch req.Type {
    case StateAddDKGMPKReady:
        ready := req.Payload.(*typesDKG.MPKReady)
        if ready.Reset != s.dkgResetCount[ready.Round] {
            return ErrChangeWontApply
        }
    case StateAddDKGFinal:
        final := req.Payload.(*typesDKG.Finalize)
        if final.Reset != s.dkgResetCount[final.Round] {
            return ErrChangeWontApply
        }
    case StateAddDKGMasterPublicKey:
        mpk := req.Payload.(*typesDKG.MasterPublicKey)
        if mpk.Reset != s.dkgResetCount[mpk.Round] {
            return ErrChangeWontApply
        }
        // If we've received identical MPK, ignore it.
        mpkForRound, exists := s.dkgMasterPublicKeys[mpk.Round]
        if exists {
            if oldMpk, exists := mpkForRound[mpk.ProposerID]; exists {
                if !oldMpk.Equal(mpk) {
                    return ErrDuplicatedChange
                }
                return ErrChangeWontApply
            }
        }
        // If we've received MPK from that proposer, we would ignore
        // its mpk.
        if _, exists := s.dkgReadys[mpk.Round][mpk.ProposerID]; exists {
            return ErrProposerMPKIsReady
        }
    case StateAddDKGComplaint:
        comp := req.Payload.(*typesDKG.Complaint)
        if comp.Reset != s.dkgResetCount[comp.Round] {
            return ErrChangeWontApply
        }
        // If we've received DKG final from that proposer, we would ignore
        // its complaint.
        if _, exists := s.dkgFinals[comp.Round][comp.ProposerID]; exists {
            return ErrProposerIsFinal
        }
        // If we've received identical complaint, ignore it.
        compForRound, exists := s.dkgComplaints[comp.Round]
        if !exists {
            break
        }
        comps, exists := compForRound[comp.ProposerID]
        if !exists {
            break
        }
        for _, tmpComp := range comps {
            if tmpComp == comp {
                return ErrDuplicatedChange
            }
        }
    case StateAddCRS:
        crsReq := req.Payload.(*crsAdditionRequest)
        if uint64(len(s.crs)) > crsReq.Round {
            if !s.crs[crsReq.Round].Equal(crsReq.CRS) {
                return ErrForkedCRS
            }
            return ErrDuplicatedChange
        } else if uint64(len(s.crs)) == crsReq.Round {
            return nil
        } else {
            return ErrMissingPreviousCRS
        }
    case StateResetDKG:
        newCRS := req.Payload.(common.Hash)
        if s.crs[len(s.crs)-1].Equal(newCRS) {
            return ErrDuplicatedChange
        }
        // TODO(mission): find a smart way to make sure the caller call request
        //                this change with correct resetCount.
    }
    return nil
}

// applyRequest applies a single StateChangeRequest.
func (s *State) applyRequest(req *StateChangeRequest) error {
    // NOTE: there would be no lock in this helper, callers should be
    //       responsible for acquiring appropriate lock.
    switch req.Type {
    case StateAddNode:
        pubKey, err := ecdsa.NewPublicKeyFromByteSlice(req.Payload.([]byte))
        if err != nil {
            return err
        }
        s.nodes[types.NewNodeID(pubKey)] = pubKey
    case StateAddCRS:
        crsRequest := req.Payload.(*crsAdditionRequest)
        if crsRequest.Round != uint64(len(s.crs)) {
            return ErrDuplicatedChange
        }
        s.crs = append(s.crs, crsRequest.CRS)
    case StateAddDKGComplaint:
        comp := req.Payload.(*typesDKG.Complaint)
        if _, exists := s.dkgComplaints[comp.Round]; !exists {
            s.dkgComplaints[comp.Round] = make(
                map[types.NodeID][]*typesDKG.Complaint)
        }
        s.dkgComplaints[comp.Round][comp.ProposerID] = append(
            s.dkgComplaints[comp.Round][comp.ProposerID], comp)
    case StateAddDKGMasterPublicKey:
        mKey := req.Payload.(*typesDKG.MasterPublicKey)
        if _, exists := s.dkgMasterPublicKeys[mKey.Round]; !exists {
            s.dkgMasterPublicKeys[mKey.Round] = make(
                map[types.NodeID]*typesDKG.MasterPublicKey)
        }
        s.dkgMasterPublicKeys[mKey.Round][mKey.ProposerID] = mKey
    case StateAddDKGMPKReady:
        ready := req.Payload.(*typesDKG.MPKReady)
        if _, exists := s.dkgReadys[ready.Round]; !exists {
            s.dkgReadys[ready.Round] = make(map[types.NodeID]*typesDKG.MPKReady)
        }
        s.dkgReadys[ready.Round][ready.ProposerID] = ready
    case StateAddDKGFinal:
        final := req.Payload.(*typesDKG.Finalize)
        if _, exists := s.dkgFinals[final.Round]; !exists {
            s.dkgFinals[final.Round] = make(map[types.NodeID]*typesDKG.Finalize)
        }
        s.dkgFinals[final.Round][final.ProposerID] = final
    case StateResetDKG:
        round := uint64(len(s.crs) - 1)
        s.crs[round] = req.Payload.(common.Hash)
        s.dkgResetCount[round]++
        delete(s.dkgMasterPublicKeys, round)
        delete(s.dkgReadys, round)
        delete(s.dkgComplaints, round)
        delete(s.dkgFinals, round)
    case StateChangeLambdaBA:
        s.lambdaBA = time.Duration(req.Payload.(uint64))
    case StateChangeLambdaDKG:
        s.lambdaDKG = time.Duration(req.Payload.(uint64))
    case StateChangeRoundLength:
        s.roundInterval = req.Payload.(uint64)
    case StateChangeMinBlockInterval:
        s.minBlockInterval = time.Duration(req.Payload.(uint64))
    case StateChangeNotarySetSize:
        s.notarySetSize = req.Payload.(uint32)
    default:
        return errors.New("you are definitely kidding me")
    }
    return nil
}

// ProposeCRS propose a new CRS for a specific round.
func (s *State) ProposeCRS(round uint64, crs common.Hash) (err error) {
    err = s.RequestChange(StateAddCRS, &crsAdditionRequest{
        Round: round,
        CRS:   crs,
    })
    return
}

// RequestChange submits a state change request.
func (s *State) RequestChange(
    t StateChangeType, payload interface{}) (err error) {
    s.logger.Info("Request Change to State", "type", t, "value", payload)
    // Patch input parameter's type.
    switch t {
    case StateAddNode:
        payload = payload.(crypto.PublicKey).Bytes()
    case StateChangeLambdaBA,
        StateChangeLambdaDKG,
        StateChangeMinBlockInterval:
        payload = uint64(payload.(time.Duration))
    // These cases for for type assertion, make sure callers pass expected types.
    case StateAddCRS:
        payload = payload.(*crsAdditionRequest)
    case StateAddDKGMPKReady:
        payload = payload.(*typesDKG.MPKReady)
    case StateAddDKGFinal:
        payload = payload.(*typesDKG.Finalize)
    case StateAddDKGMasterPublicKey:
        payload = payload.(*typesDKG.MasterPublicKey)
    case StateAddDKGComplaint:
        payload = payload.(*typesDKG.Complaint)
    case StateResetDKG:
        payload = payload.(common.Hash)
    }
    req := NewStateChangeRequest(t, payload)
    s.lock.Lock()
    defer s.lock.Unlock()
    if s.local {
        if err = s.isValidRequest(req); err != nil {
            return
        }
        err = s.applyRequest(req)
    } else {
        if err = s.isValidRequest(req); err != nil {
            return
        }
        s.ownRequests[req.Hash] = req
    }
    return
}

// CRS access crs proposed for that round.
func (s *State) CRS(round uint64) common.Hash {
    s.lock.RLock()
    defer s.lock.RUnlock()
    if round >= uint64(len(s.crs)) {
        return common.Hash{}
    }
    return s.crs[round]
}

// DKGComplaints access current received dkg complaints for that round.
// This information won't be snapshot, thus can't be cached in test.Governance.
func (s *State) DKGComplaints(round uint64) []*typesDKG.Complaint {
    s.lock.RLock()
    defer s.lock.RUnlock()
    comps, exists := s.dkgComplaints[round]
    if !exists {
        return nil
    }
    tmpComps := make([]*typesDKG.Complaint, 0, len(comps))
    for _, compProp := range comps {
        for _, comp := range compProp {
            tmpComps = append(tmpComps, CloneDKGComplaint(comp))
        }
    }
    return tmpComps
}

// DKGMasterPublicKeys access current received dkg master public keys for that
// round. This information won't be snapshot, thus can't be cached in
// test.Governance.
func (s *State) DKGMasterPublicKeys(round uint64) []*typesDKG.MasterPublicKey {
    s.lock.RLock()
    defer s.lock.RUnlock()
    masterPublicKeys, exists := s.dkgMasterPublicKeys[round]
    if !exists {
        return nil
    }
    mpks := make([]*typesDKG.MasterPublicKey, 0, len(masterPublicKeys))
    for _, mpk := range masterPublicKeys {
        mpks = append(mpks, CloneDKGMasterPublicKey(mpk))
    }
    return mpks
}

// IsDKGMPKReady checks if current received dkg readys exceeds threshold.
// This information won't be snapshot, thus can't be cached in test.Governance.
func (s *State) IsDKGMPKReady(round uint64, threshold int) bool {
    s.lock.RLock()
    defer s.lock.RUnlock()
    return len(s.dkgReadys[round]) > threshold
}

// IsDKGFinal checks if current received dkg finals exceeds threshold.
// This information won't be snapshot, thus can't be cached in test.Governance.
func (s *State) IsDKGFinal(round uint64, threshold int) bool {
    s.lock.RLock()
    defer s.lock.RUnlock()
    return len(s.dkgFinals[round]) > threshold
}

// DKGResetCount returns the reset count for DKG of given round.
func (s *State) DKGResetCount(round uint64) uint64 {
    s.lock.RLock()
    defer s.lock.RUnlock()
    return s.dkgResetCount[round]
}