github.com/klaytn/klaytn@v1.10.2/consensus/clique/clique.go

// Modifications Copyright 2019 The klaytn Authors
// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum 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 go-ethereum 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 go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
//
// This file is derived from go-ethereum/consensus/clique/clique.go (2018/06/04).
// Modified and improved for the klaytn development.

package clique

import (
	"bytes"
	"errors"
	"math/big"
	"math/rand"
	"sync"
	"time"

	lru "github.com/hashicorp/golang-lru"
	"github.com/klaytn/klaytn/accounts"
	"github.com/klaytn/klaytn/blockchain/state"
	"github.com/klaytn/klaytn/blockchain/types"
	"github.com/klaytn/klaytn/common"
	"github.com/klaytn/klaytn/common/hexutil"
	"github.com/klaytn/klaytn/consensus"
	"github.com/klaytn/klaytn/crypto"
	"github.com/klaytn/klaytn/crypto/sha3"
	"github.com/klaytn/klaytn/governance"
	"github.com/klaytn/klaytn/log"
	"github.com/klaytn/klaytn/networks/rpc"
	"github.com/klaytn/klaytn/params"
	"github.com/klaytn/klaytn/rlp"
	"github.com/klaytn/klaytn/storage/database"
)

const (
	checkpointInterval = 1024 // Number of blocks after which to save the vote snapshot to the database
	inmemorySnapshots  = 128  // Number of recent vote snapshots to keep in memory
	inmemorySignatures = 4096 // Number of recent block signatures to keep in memory

	wiggleTime = 500 * time.Millisecond // Random delay (per signer) to allow concurrent signers
)

// Clique proof-of-authority protocol constants.
var (
	epochLength = uint64(30000) // Default number of blocks after which to checkpoint and reset the pending votes
	blockPeriod = uint64(15)    // Default minimum difference between two consecutive block's timestamps

	ExtraVanity = 32                     // Fixed number of extra-data prefix bytes reserved for signer vanity
	ExtraSeal   = crypto.SignatureLength // Fixed number of extra-data suffix bytes reserved for signer seal

	nonceAuthVote = hexutil.MustDecode("0xffffffffffffffff") // Magic nonce number to vote on adding a new signer
	nonceDropVote = hexutil.MustDecode("0x0000000000000000") // Magic nonce number to vote on removing a signer.

	scoreInTurn = big.NewInt(2) // Block blockscore for in-turn signatures
	scoreNoTurn = big.NewInt(1) // Block blockscore for out-of-turn signatures
)

var logger = log.NewModuleLogger(log.ConsensusClique)

// Various error messages to mark blocks invalid. These should be private to
// prevent engine specific errors from being referenced in the remainder of the
// codebase, inherently breaking if the engine is swapped out. Please put common
// error types into the consensus package.
var (
	// errUnknownBlock is returned when the list of signers is requested for a block
	// that is not part of the local blockchain.
	errUnknownBlock = errors.New("unknown block")

	// errInvalidCheckpointBeneficiary is returned if a checkpoint/epoch transition
	// block has a beneficiary set to non-zeroes.
	errInvalidCheckpointBeneficiary = errors.New("beneficiary in checkpoint block non-zero")

	// errInvalidVote is returned if a nonce value is something else that the two
	// allowed constants of 0x00..0 or 0xff..f.
	errInvalidVote = errors.New("vote nonce not 0x00..0 or 0xff..f")

	// errInvalidCheckpointVote is returned if a checkpoint/epoch transition block
	// has a vote nonce set to non-zeroes.
	errInvalidCheckpointVote = errors.New("vote nonce in checkpoint block non-zero")

	// errMissingVanity is returned if a block's extra-data section is shorter than
	// 32 bytes, which is required to store the signer vanity.
	errMissingVanity = errors.New("extra-data 32 byte vanity prefix missing")

	// errMissingSignature is returned if a block's extra-data section doesn't seem
	// to contain a 65 byte secp256k1 signature.
	errMissingSignature = errors.New("extra-data 65 byte signature suffix missing")

	// errExtraSigners is returned if non-checkpoint block contain signer data in
	// their extra-data fields.
	errExtraSigners = errors.New("non-checkpoint block contains extra signer list")

	// errInvalidCheckpointSigners is returned if a checkpoint block contains an
	// invalid list of signers (i.e. non divisible by 20 bytes).
	errInvalidCheckpointSigners = errors.New("invalid signer list on checkpoint block")

	// errMismatchingCheckpointSigners is returned if a checkpoint block contains a
	// list of signers different than the one the local node calculated.
	errMismatchingCheckpointSigners = errors.New("mismatching signer list on checkpoint block")

	// errInvalidBlockScore is returned if the blockScore of a block neither 1 or 2.
	errInvalidBlockScore = errors.New("invalid blockscore")

	// errWrongBlockScore is returned if the blockScore of a block doesn't match the
	// turn of the signer.
	errWrongBlockScore = errors.New("wrong blockScore")

	// ErrInvalidTimestamp is returned if the timestamp of a block is lower than
	// the previous block's timestamp + the minimum block period.
	ErrInvalidTimestamp = errors.New("invalid timestamp")

	// errInvalidVotingChain is returned if an authorization list is attempted to
	// be modified via out-of-range or non-contiguous headers.
	errInvalidVotingChain = errors.New("invalid voting chain")

	// errUnauthorizedSigner is returned if a header is signed by a non-authorized entity.
	errUnauthorizedSigner = errors.New("unauthorized signer")

	// errRecentlySigned is returned if a header is signed by an authorized entity
	// that already signed a header recently, thus is temporarily not allowed to.
	errRecentlySigned = errors.New("recently signed")

	// errWaitTransactions is returned if an empty block is attempted to be sealed
	// on an instant chain (0 second period). It's important to refuse these as the
	// block reward is zero, so an empty block just bloats the chain... fast.
	errWaitTransactions = errors.New("waiting for transactions")
)

// SignerFn is a signer callback function to request a hash to be signed by a
// backing account.
type SignerFn func(accounts.Account, []byte) ([]byte, error)

// sigHash returns the hash which is used as input for the proof-of-authority
// signing. It is the hash of the entire header apart from the 65 byte signature
// contained at the end of the extra data.
//
// Note, the method requires the extra data to be at least 65 bytes, otherwise it
// panics. This is done to avoid accidentally using both forms (signature present
// or not), which could be abused to produce different hashes for the same header.
func sigHash(header *types.Header) (hash common.Hash) {
	hasher := sha3.NewKeccak256()

	rlp.Encode(hasher, []interface{}{
		header.ParentHash,
		header.Root,
		header.TxHash,
		header.ReceiptHash,
		header.Bloom,
		header.BlockScore,
		header.Number,
		header.GasUsed,
		header.Time,
		header.Extra[:len(header.Extra)-crypto.SignatureLength], // Yes, this will panic if extra is too short
	})
	hasher.Sum(hash[:0])
	return hash
}

// ecrecover extracts the Klaytn account address from a signed header.
func ecrecover(header *types.Header, sigcache *lru.ARCCache) (common.Address, error) {
	// If the signature's already cached, return that
	hash := header.Hash()
	if address, known := sigcache.Get(hash); known {
		return address.(common.Address), nil
	}
	// Retrieve the signature from the header extra-data
	if len(header.Extra) < ExtraSeal {
		return common.Address{}, errMissingSignature
	}
	signature := header.Extra[len(header.Extra)-ExtraSeal:]

	// Recover the public key and the Klaytn address
	pubkey, err := crypto.Ecrecover(sigHash(header).Bytes(), signature)
	if err != nil {
		return common.Address{}, err
	}
	var signer common.Address
	copy(signer[:], crypto.Keccak256(pubkey[1:])[12:])

	sigcache.Add(hash, signer)
	return signer, nil
}

// Clique is the proof-of-authority consensus engine proposed to support the
// Klaytn testnet following the Baobab attacks.
type Clique struct {
	config *params.CliqueConfig // Consensus engine configuration parameters
	db     database.DBManager   // Database to store and retrieve snapshot checkpoints

	recents    *lru.ARCCache // Snapshots for recent block to speed up reorgs
	signatures *lru.ARCCache // Signatures of recent blocks to speed up mining

	proposals map[common.Address]bool // Current list of proposals we are pushing

	signer common.Address // Klaytn address of the signing key
	signFn SignerFn       // Signer function to authorize hashes with
	lock   sync.RWMutex   // Protects the signer fields

	// The fields below are for testing only
	fakeBlockScore bool // Skip blockScore verifications
}

// New creates a Clique proof-of-authority consensus engine with the initial
// signers set to the ones provided by the user.
func New(config *params.CliqueConfig, db database.DBManager) *Clique {
	// Set any missing consensus parameters to their defaults
	conf := *config
	if conf.Epoch == 0 {
		conf.Epoch = epochLength
	}
	// Allocate the snapshot caches and create the engine
	recents, _ := lru.NewARC(inmemorySnapshots)
	signatures, _ := lru.NewARC(inmemorySignatures)

	return &Clique{
		config:     &conf,
		db:         db,
		recents:    recents,
		signatures: signatures,
		proposals:  make(map[common.Address]bool),
	}
}

// Author implements consensus.Engine, returning the Klaytn address recovered
// from the signature in the header's extra-data section.
func (c *Clique) Author(header *types.Header) (common.Address, error) {
	return ecrecover(header, c.signatures)
}

// CanVerifyHeadersConcurrently returns true if concurrent header verification possible, otherwise returns false.
func (c *Clique) CanVerifyHeadersConcurrently() bool {
	return true
}

// PreprocessHeaderVerification prepares header verification for heavy computation before synchronous header verification such as ecrecover.
func (c *Clique) PreprocessHeaderVerification(headers []*types.Header) (chan<- struct{}, <-chan error) {
	panic("this method is not used for Clique engine")
}

// VerifyHeader checks whether a header conforms to the consensus rules.
func (c *Clique) VerifyHeader(chain consensus.ChainReader, header *types.Header, seal bool) error {
	return c.verifyHeader(chain, header, nil)
}

// VerifyHeaders is similar to VerifyHeader, but verifies a batch of headers. The
// method returns a quit channel to abort the operations and a results channel to
// retrieve the async verifications (the order is that of the input slice).
func (c *Clique) VerifyHeaders(chain consensus.ChainReader, headers []*types.Header, seals []bool) (chan<- struct{}, <-chan error) {
	abort := make(chan struct{})
	results := make(chan error, len(headers))

	go func() {
		for i, header := range headers {
			err := c.verifyHeader(chain, header, headers[:i])

			select {
			case <-abort:
				return
			case results <- err:
			}
		}
	}()
	return abort, results
}

// verifyHeader checks whether a header conforms to the consensus rules.The
// caller may optionally pass in a batch of parents (ascending order) to avoid
// looking those up from the database. This is useful for concurrently verifying
// a batch of new headers.
func (c *Clique) verifyHeader(chain consensus.ChainReader, header *types.Header, parents []*types.Header) error {
	if header.Number == nil {
		return errUnknownBlock
	}
	number := header.Number.Uint64()

	// Don't waste time checking blocks from the future
	if header.Time.Cmp(big.NewInt(time.Now().Unix())) > 0 {
		return consensus.ErrFutureBlock
	}
	// Check that the extra-data contains both the vanity and signature
	if len(header.Extra) < ExtraVanity {
		return errMissingVanity
	}
	if len(header.Extra) < ExtraVanity+ExtraSeal {
		return errMissingSignature
	}
	// Ensure that the extra-data contains a signer list on checkpoint, but none otherwise
	signersBytes := len(header.Extra) - ExtraVanity - ExtraSeal
	checkpoint := (number % c.config.Epoch) == 0
	if !checkpoint && signersBytes != 0 {
		return errExtraSigners
	}
	if checkpoint && signersBytes%common.AddressLength != 0 {
		return errInvalidCheckpointSigners
	}
	// Ensure that the block's blockScore is meaningful (may not be correct at this point)
	if number > 0 {
		if header.BlockScore == nil || (header.BlockScore.Cmp(scoreInTurn) != 0 && header.BlockScore.Cmp(scoreNoTurn) != 0) {
			return errInvalidBlockScore
		}
	}
	// All basic checks passed, verify cascading fields
	return c.verifyCascadingFields(chain, header, parents)
}

// verifyCascadingFields verifies all the header fields that are not standalone,
// rather depend on a batch of previous headers. The caller may optionally pass
// in a batch of parents (ascending order) to avoid looking those up from the
// database. This is useful for concurrently verifying a batch of new headers.
func (c *Clique) verifyCascadingFields(chain consensus.ChainReader, header *types.Header, parents []*types.Header) error {
	// The genesis block is the always valid dead-end
	number := header.Number.Uint64()
	if number == 0 {
		return nil
	}
	// Ensure that the block's timestamp isn't too close to it's parent
	var parent *types.Header
	if len(parents) > 0 {
		parent = parents[len(parents)-1]
	} else {
		parent = chain.GetHeader(header.ParentHash, number-1)
	}
	if parent == nil || parent.Number.Uint64() != number-1 || parent.Hash() != header.ParentHash {
		return consensus.ErrUnknownAncestor
	}
	if parent.Time.Uint64()+c.config.Period > header.Time.Uint64() {
		return ErrInvalidTimestamp
	}
	// Retrieve the snapshot needed to verify this header and cache it
	snap, err := c.snapshot(chain, number-1, header.ParentHash, parents)
	if err != nil {
		return err
	}
	// If the block is a checkpoint block, verify the signer list
	if number%c.config.Epoch == 0 {
		signers := make([]byte, len(snap.Signers)*common.AddressLength)
		for i, signer := range snap.signers() {
			copy(signers[i*common.AddressLength:], signer[:])
		}
		extraSuffix := len(header.Extra) - ExtraSeal
		if !bytes.Equal(header.Extra[ExtraVanity:extraSuffix], signers) {
			return errInvalidCheckpointSigners
		}
	}
	// All basic checks passed, verify the seal and return
	return c.verifySeal(chain, header, parents)
}

// CreateSnapshot does not return a snapshot but creates a new snapshot at a given point in time.
func (c *Clique) CreateSnapshot(chain consensus.ChainReader, number uint64, hash common.Hash, parents []*types.Header) error {
	_, err := c.snapshot(chain, number, hash, parents)
	return err
}

// snapshot retrieves the authorization snapshot at a given point in time.
func (c *Clique) snapshot(chain consensus.ChainReader, number uint64, hash common.Hash, parents []*types.Header) (*Snapshot, error) {
	// Search for a snapshot in memory or on disk for checkpoints
	var (
		headers []*types.Header
		snap    *Snapshot
	)
	for snap == nil {
		// If an in-memory snapshot was found, use that
		if s, ok := c.recents.Get(hash); ok {
			snap = s.(*Snapshot)
			break
		}
		// If an on-disk checkpoint snapshot can be found, use that
		if number%checkpointInterval == 0 {
			if s, err := loadSnapshot(c.config, c.signatures, c.db, hash); err == nil {
				logger.Trace("Loaded voting snapshot from disk", "number", number, "hash", hash)
				snap = s
				break
			}
		}
		// If we're at block zero, make a snapshot
		if number == 0 {
			genesis := chain.GetHeaderByNumber(0)
			if err := c.VerifyHeader(chain, genesis, false); err != nil {
				return nil, err
			}
			signers := make([]common.Address, (len(genesis.Extra)-ExtraVanity-ExtraSeal)/common.AddressLength)
			for i := 0; i < len(signers); i++ {
				copy(signers[i][:], genesis.Extra[ExtraVanity+i*common.AddressLength:])
			}
			snap = newSnapshot(c.config, c.signatures, 0, genesis.Hash(), signers)
			if err := snap.store(c.db); err != nil {
				return nil, err
			}
			logger.Trace("Stored genesis voting snapshot to disk")
			break
		}
		// No snapshot for this header, gather the header and move backward
		var header *types.Header
		if len(parents) > 0 {
			// If we have explicit parents, pick from there (enforced)
			header = parents[len(parents)-1]
			if header.Hash() != hash || header.Number.Uint64() != number {
				return nil, consensus.ErrUnknownAncestor
			}
			parents = parents[:len(parents)-1]
		} else {
			// No explicit parents (or no more left), reach out to the database
			header = chain.GetHeader(hash, number)
			if header == nil {
				return nil, consensus.ErrUnknownAncestor
			}
		}
		headers = append(headers, header)
		number, hash = number-1, header.ParentHash
	}
	// Previous snapshot found, apply any pending headers on top of it
	for i := 0; i < len(headers)/2; i++ {
		headers[i], headers[len(headers)-1-i] = headers[len(headers)-1-i], headers[i]
	}
	snap, err := snap.apply(headers)
	if err != nil {
		return nil, err
	}
	c.recents.Add(snap.Hash, snap)

	// If we've generated a new checkpoint snapshot, save to disk
	if snap.Number%checkpointInterval == 0 && len(headers) > 0 {
		if err = snap.store(c.db); err != nil {
			return nil, err
		}
		logger.Trace("Stored voting snapshot to disk", "number", snap.Number, "hash", snap.Hash)
	}
	return snap, err
}

// GetConsensusInfo is not used for Clique engine
func (c *Clique) GetConsensusInfo(block *types.Block) (consensus.ConsensusInfo, error) {
	return consensus.ConsensusInfo{}, nil
}

// VerifySeal implements consensus.Engine, checking whether the signature contained
// in the header satisfies the consensus protocol requirements.
func (c *Clique) VerifySeal(chain consensus.ChainReader, header *types.Header) error {
	return c.verifySeal(chain, header, nil)
}

// verifySeal checks whether the signature contained in the header satisfies the
// consensus protocol requirements. The method accepts an optional list of parent
// headers that aren't yet part of the local blockchain to generate the snapshots
// from.
func (c *Clique) verifySeal(chain consensus.ChainReader, header *types.Header, parents []*types.Header) error {
	// Verifying the genesis block is not supported
	number := header.Number.Uint64()
	if number == 0 {
		return errUnknownBlock
	}
	// Retrieve the snapshot needed to verify this header and cache it
	snap, err := c.snapshot(chain, number-1, header.ParentHash, parents)
	if err != nil {
		return err
	}

	// Resolve the authorization key and check against signers
	signer, err := ecrecover(header, c.signatures)
	if err != nil {
		logger.Error("ecrecover signer", "addr", signer, "err", err)
		return err
	}
	if _, ok := snap.Signers[signer]; !ok {
		return errUnauthorizedSigner
	}
	for seen, recent := range snap.Recents {
		if recent == signer {
			// Signer is among recents, only fail if the current block doesn't shift it out
			if limit := uint64(len(snap.Signers)/2 + 1); seen > number-limit {
				return errRecentlySigned
			}
		}
	}
	// Ensure that the blockScore corresponds to the turn-ness of the signer
	if !c.fakeBlockScore {
		inturn := snap.inturn(header.Number.Uint64(), signer)
		if inturn && header.BlockScore.Cmp(scoreInTurn) != 0 {
			return errInvalidBlockScore
		}
		if !inturn && header.BlockScore.Cmp(scoreNoTurn) != 0 {
			return errInvalidBlockScore
		}
	}
	return nil
}

// Prepare implements consensus.Engine, preparing all the consensus fields of the
// header for running the transactions on top.
func (c *Clique) Prepare(chain consensus.ChainReader, header *types.Header) error {
	// If the block isn't a checkpoint, cast a random vote (good enough for now)
	number := header.Number.Uint64()
	// Assemble the voting snapshot to check which votes make sense
	snap, err := c.snapshot(chain, number-1, header.ParentHash, nil)
	if err != nil {
		return err
	}
	if number%c.config.Epoch != 0 {
		c.lock.RLock()

		// Gather all the proposals that make sense voting on
		addresses := make([]common.Address, 0, len(c.proposals))
		for address, authorize := range c.proposals {
			if snap.validVote(address, authorize) {
				addresses = append(addresses, address)
			}
		}
		// If there's pending proposals, cast a vote on them
		if len(addresses) > 0 {
			vote := new(governance.GovernanceVote)
			addr := addresses[rand.Intn(len(addresses))]
			if c.proposals[addr] == true {
				vote.Key = "addvalidator"
			} else {
				vote.Key = "removevalidator"
			}
			vote.Value = addr
			encoded, err := rlp.EncodeToBytes(vote)
			if err != nil {
				logger.Error("Failed to RLP Encode a vote", "vote", vote)
			}
			header.Vote = encoded
		}
		c.lock.RUnlock()
	}
	// Set the correct blockScore
	header.BlockScore = CalcBlockScore(snap, c.signer)

	// Ensure the extra data has all it's components
	if len(header.Extra) < ExtraVanity {
		header.Extra = append(header.Extra, bytes.Repeat([]byte{0x00}, ExtraVanity-len(header.Extra))...)
	}
	header.Extra = header.Extra[:ExtraVanity]

	if number%c.config.Epoch == 0 {
		for _, signer := range snap.signers() {
			header.Extra = append(header.Extra, signer[:]...)
		}
	}
	header.Extra = append(header.Extra, make([]byte, ExtraSeal)...)

	// Ensure the timestamp has the correct delay
	parent := chain.GetHeader(header.ParentHash, number-1)
	if parent == nil {
		return consensus.ErrUnknownAncestor
	}
	// set header's timestamp
	header.Time = new(big.Int).Add(parent.Time, new(big.Int).SetUint64(c.config.Period))
	header.TimeFoS = parent.TimeFoS
	if header.Time.Int64() < time.Now().Unix() {
		t := time.Now()
		header.Time = big.NewInt(t.Unix())
		header.TimeFoS = uint8((t.UnixNano() / 1000 / 1000 / 10) % 100)
	}
	return nil
}

// Finalize implements consensus.Engine and returns the final block.
func (c *Clique) Finalize(chain consensus.ChainReader, header *types.Header, state *state.StateDB, txs []*types.Transaction, receipts []*types.Receipt) (*types.Block, error) {
	// No block rewards in PoA, so the state remains as is
	header.Root = state.IntermediateRoot(true)

	// Assemble and return the final block for sealing
	return types.NewBlock(header, txs, receipts), nil
}

// Authorize injects a private key into the consensus engine to mint new blocks
// with.
func (c *Clique) Authorize(signer common.Address, signFn SignerFn) {
	c.lock.Lock()
	defer c.lock.Unlock()

	c.signer = signer
	c.signFn = signFn
}

// Seal implements consensus.Engine, attempting to create a sealed block using
// the local signing credentials.
func (c *Clique) Seal(chain consensus.ChainReader, block *types.Block, stop <-chan struct{}) (*types.Block, error) {
	header := block.Header()

	// Sealing the genesis block is not supported
	number := header.Number.Uint64()
	if number == 0 {
		return nil, errUnknownBlock
	}
	// For 0-period chains, refuse to seal empty blocks (no reward but would spin sealing)
	if c.config.Period == 0 && len(block.Transactions()) == 0 {
		return nil, errWaitTransactions
	}
	// Don't hold the signer fields for the entire sealing procedure
	c.lock.RLock()
	signer, signFn := c.signer, c.signFn
	c.lock.RUnlock()

	// Bail out if we're unauthorized to sign a block
	snap, err := c.snapshot(chain, number-1, header.ParentHash, nil)
	if err != nil {
		return nil, err
	}
	if _, authorized := snap.Signers[signer]; !authorized {
		return nil, errUnauthorizedSigner
	}
	// If we're amongst the recent signers, wait for the next block
	for seen, recent := range snap.Recents {
		if recent == signer {
			// Signer is among recents, only wait if the current block doesn't shift it out
			if limit := uint64(len(snap.Signers)/2 + 1); number < limit || seen > number-limit {
				logger.Info("Signed recently, must wait for others")
				<-stop
				return nil, nil
			}
		}
	}
	// Sweet, the protocol permits us to sign the block, wait for our time
	delay := time.Unix(header.Time.Int64(), 0).Sub(time.Now()) // nolint: gosimple
	if header.BlockScore.Cmp(scoreNoTurn) == 0 {
		// It's not our turn explicitly to sign, delay it a bit
		wiggle := time.Duration(len(snap.Signers)/2+1) * wiggleTime
		delay += time.Duration(rand.Int63n(int64(wiggle)))

		logger.Trace("Out-of-turn signing requested", "wiggle", common.PrettyDuration(wiggle))
	}
	logger.Trace("Waiting for slot to sign and propagate", "delay", common.PrettyDuration(delay))

	select {
	case <-stop:
		return nil, nil
	case <-time.After(delay):
	}
	// Sign all the things!
	sighash, err := signFn(accounts.Account{Address: signer}, sigHash(header).Bytes())
	if err != nil {
		return nil, err
	}
	copy(header.Extra[len(header.Extra)-ExtraSeal:], sighash)

	return block.WithSeal(header), nil
}

// CalcBlockScore is the blockScore adjustment algorithm. It returns the blockScore
// that a new block should have based on the previous blocks in the chain and the
// current signer.
func (c *Clique) CalcBlockScore(chain consensus.ChainReader, time uint64, parent *types.Header) *big.Int {
	snap, err := c.snapshot(chain, parent.Number.Uint64(), parent.Hash(), nil)
	if err != nil {
		return nil
	}
	return CalcBlockScore(snap, c.signer)
}

// CalcBlockScore is the blockScore adjustment algorithm. It returns the blockScore
// that a new block should have based on the previous blocks in the chain and the
// current signer.
func CalcBlockScore(snap *Snapshot, signer common.Address) *big.Int {
	if snap.inturn(snap.Number+1, signer) {
		return new(big.Int).Set(scoreInTurn)
	}
	return new(big.Int).Set(scoreNoTurn)
}

// APIs implements consensus.Engine, returning the user facing RPC API to allow
// controlling the signer voting.
func (c *Clique) APIs(chain consensus.ChainReader) []rpc.API {
	return []rpc.API{{
		Namespace: "clique",
		Version:   "1.0",
		Service:   &API{chain: chain, clique: c},
		Public:    false,
	}}
}

// Protocol implements consensus.Engine.Protocol
func (c *Clique) Protocol() consensus.Protocol {
	return consensus.KlayProtocol
}