github.com/reapchain/go-reapchain@v0.2.15-0.20210609012950-9735c110c705/consensus/podc/backend/engine.go

// Copyright 2017 AMIS Technologies
// 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/>.

package backend

import (
	"bytes"
	"crypto/ecdsa"
	"errors"
	"math/big"
	"math/rand"
	"time"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/hexutil"
	"github.com/ethereum/go-ethereum/consensus"
	"github.com/ethereum/go-ethereum/consensus/podc"
	podcCore "github.com/ethereum/go-ethereum/consensus/podc/core"
	"github.com/ethereum/go-ethereum/consensus/podc/validator"
	"github.com/ethereum/go-ethereum/core/state"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/crypto/sha3"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/rlp"
	"github.com/ethereum/go-ethereum/rpc"
)

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
)

var (
	// errInvalidProposal is returned when a prposal is malformed.
	errInvalidProposal = errors.New("invalid proposal")
	// errInvalidSignature is returned when given signature is not signed by given
	// address.
	errInvalidSignature = errors.New("invalid signature")
	// errUnknownBlock is returned when the list of validators is requested for a block
	// that is not part of the local blockchain.
	errUnknownBlock = errors.New("unknown block")
	// errUnauthorized is returned if a header is signed by a non authorized entity.
	errUnauthorized = errors.New("unauthorized")
	// errInvalidDifficulty is returned if the difficulty of a block is not 1
	errInvalidDifficulty = errors.New("invalid difficulty")
	// errInvalidExtraDataFormat is returned when the extra data format is incorrect
	errInvalidExtraDataFormat = errors.New("invalid extra data format")
	// errInvalidMixDigest is returned if a block's mix digest is not Istanbul digest.
	errInvalidMixDigest = errors.New("invalid Istanbul mix digest")
	// errInvalidNonce is returned if a block's nonce is invalid
	errInvalidNonce = errors.New("invalid nonce")
	// errInvalidUncleHash is returned if a block contains an non-empty uncle list.
	errInvalidUncleHash = errors.New("non empty uncle hash")
	// errInconsistentValidatorSet is returned if the validator set is inconsistent
	errInconsistentValidatorSet = errors.New("non empty uncle hash")
	// 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")
	// 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")
	// errInvalidCommittedSeals is returned if the committed seal is not signed by any of parent validators.
	errInvalidCommittedSeals = errors.New("invalid committed seals")
	// errEmptyCommittedSeals is returned if the field of committed seals is zero.
	errEmptyCommittedSeals = errors.New("zero committed seals")
)
var (
	defaultDifficulty = big.NewInt(1)
	nilUncleHash      = types.CalcUncleHash(nil) // Always Keccak256(RLP([])) as uncles are meaningless outside of PoW.
	emptyNonce        = types.BlockNonce{}
	now               = time.Now

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

// Author retrieves the Ethereum address of the account that minted the given
// block, which may be different from the header's coinbase if a consensus
// engine is based on signatures.

func (sb *simpleBackend) Author(header *types.Header) (common.Address, error) {
	return ecrecover(header)
}

// VerifyHeader checks whether a header conforms to the consensus rules of a
// given engine. Verifying the seal may be done optionally here, or explicitly
// via the VerifySeal method.
func (sb *simpleBackend) VerifyHeader(chain consensus.ChainReader, header *types.Header, seal bool) error {
	return sb.verifyHeader(chain, header, nil)
}

// 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 (sb *simpleBackend) verifyHeader(chain consensus.ChainReader, header *types.Header, parents []*types.Header) error {
	if header.Number == nil {
		return errUnknownBlock
	}

	// Don't waste time checking blocks from the future
	if header.Time.Cmp(big.NewInt(now().Unix())) > 0 {
		log.Debug("future block", "header.Time", header.Time, "now", big.NewInt(now().Unix()))
		return consensus.ErrFutureBlock
	}

	// Ensure that the extra data format is satisfied
	// ExtraData 포맷만 확인함.
	if _, err := types.ExtractPoDCExtra(header); err != nil {
		return errInvalidExtraDataFormat
	}

	// Ensure that the coinbase is valid
	if header.Nonce != (emptyNonce) && !bytes.Equal(header.Nonce[:], nonceAuthVote) && !bytes.Equal(header.Nonce[:], nonceDropVote) {
		return errInvalidNonce
	}
	// Ensure that the mix digest is zero as we don't have fork protection currently
	if header.MixDigest != types.PoDCDigest {
		return errInvalidMixDigest
	}
	// Ensure that the block doesn't contain any uncles which are meaningless in Istanbul
	if header.UncleHash != nilUncleHash {
		return errInvalidUncleHash
	}
	// Ensure that the block's difficulty is meaningful (may not be correct at this point)
	if header.Difficulty == nil || header.Difficulty.Cmp(defaultDifficulty) != 0 {
		return errInvalidDifficulty
	}

	return sb.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 (sb *simpleBackend) 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()+sb.config.BlockPeriod > header.Time.Uint64() {
		return errInvalidTimestamp
	}
	// Verify validators in extraData. Validators in snapshot and extraData should be the same.
	snap, err := sb.snapshot(chain, number-1, header.ParentHash, parents)
	if err != nil {
		return err
	}
	validators := make([]byte, len(snap.validators())*common.AddressLength)
	for i, validator := range snap.validators() {
		copy(validators[i*common.AddressLength:], validator[:])
	}
	if err := sb.verifySigner(chain, header, parents); err != nil {
		return err
	}

	return sb.verifyCommittedSeals(chain, header, parents)
}

// VerifyHeaders is similar to VerifyHeader, but verifies a batch of headers
// concurrently. 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 (sb *simpleBackend) 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 := sb.verifyHeader(chain, header, headers[:i])

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

// VerifyUncles verifies that the given block's uncles conform to the consensus
// rules of a given engine.
func (sb *simpleBackend) VerifyUncles(chain consensus.ChainReader, block *types.Block) error {
	if len(block.Uncles()) > 0 {
		return errInvalidUncleHash
	}
	return nil
}

// verifySigner checks whether the signer is in parent's validator set
func (sb *simpleBackend) verifySigner(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 := sb.snapshot(chain, number-1, header.ParentHash, parents)
	if err != nil {
		return err
	}

	// resolve the authorization key and check against signers
	signer, err := ecrecover(header)
	if err != nil {
		return err
	}

	// Signer should be in the validator set of previous block's extraData.
	if _, v := snap.ValSet.GetByAddress(signer); v == nil {
		return errUnauthorized
	}
	return nil
}

// verifyCommittedSeals checks whether every committed seal is signed by one of the parent's validators

func (sb *simpleBackend) verifyCommittedSeals(chain consensus.ChainReader, header *types.Header, parents []*types.Header) error {
	number := header.Number.Uint64()
	// We don't need to verify committed seals in the genesis block
	if number == 0 {
		return nil
	}

	// Retrieve the snapshot needed to verify this header and cache it
	snap, err := sb.snapshot(chain, number-1, header.ParentHash, parents)
	if err != nil {
		return err
	}

	extra, err := types.ExtractPoDCExtra(header)
	if err != nil {
		return err
	}
	// The length of Committed seals should be larger than 0
	if len(extra.CommittedSeal) == 0 {
		return errEmptyCommittedSeals
	}

	validators := snap.ValSet.Copy()
	// Check whether the committed seals are generated by parent's validators
	validSeal := 0
	proposalSeal := podcCore.PrepareCommittedSeal(header.Hash())
	// 1. Get committed seals from current header
	for _, seal := range extra.CommittedSeal {
		// 2. Get the original address by seal and parent block hash
		addr, err := podc.GetSignatureAddress(proposalSeal, seal)
		if err != nil {
			sb.logger.Error("not a valid address", "err", err)
			return errInvalidSignature
		}
		// Every validator can have only one seal. If more than one seals are signed by a
		// validator, the validator cannot be found and errInvalidCommittedSeals is returned.
		if validators.RemoveValidator(addr) {
			validSeal += 1
		} else {
			return errInvalidCommittedSeals
		}
	}

	// The length of validSeal should be larger than number of faulty node + 1
	if validSeal <= 2*snap.ValSet.F() {
		return errInvalidCommittedSeals
	}

	return nil
}

// VerifySeal checks whether the crypto seal on a header is valid according to
// the consensus rules of the given engine.
func (sb *simpleBackend) VerifySeal(chain consensus.ChainReader, header *types.Header) error {
	// get parent header and ensure the signer is in parent's validator set
	number := header.Number.Uint64()
	if number == 0 {
		return errUnknownBlock
	}

	// ensure that the difficulty equals to defaultDifficulty
	if header.Difficulty.Cmp(defaultDifficulty) != 0 {
		return errInvalidDifficulty
	}
	return sb.verifySigner(chain, header, nil)
}

// Prepare initializes the consensus fields of a block header according to the
// rules of a particular engine. The changes are executed inline.
func (sb *simpleBackend) Prepare(chain consensus.ChainReader, header *types.Header) error {
	// unused fields, force to set to empty
	header.Coinbase = common.Address{}
	header.Nonce = emptyNonce
	header.MixDigest = types.PoDCDigest //

	// copy the parent extra data as the header extra data
	number := header.Number.Uint64()
	parent := chain.GetHeader(header.ParentHash, number-1)
	if parent == nil {
		return consensus.ErrUnknownAncestor
	}
	// use the same difficulty for all blocks
	header.Difficulty = defaultDifficulty

	// Assemble the voting snapshot
	snap, err := sb.snapshot(chain, number-1, header.ParentHash, nil)
	if err != nil {
		return err
	}

	sb.candidatesLock.RLock()
	var addresses []common.Address
	var authorizes []bool
	for address, authorize := range sb.candidates {
		if snap.checkVote(address, authorize) {
			addresses = append(addresses, address)
			authorizes = append(authorizes, authorize)
		}
	}
	sb.candidatesLock.RUnlock()

	// pick one of the candidates randomly
	if len(addresses) > 0 {
		index := rand.Intn(len(addresses))
		// add validator voting in coinbase
		header.Coinbase = addresses[index]
		if authorizes[index] {
			copy(header.Nonce[:], nonceAuthVote)
		} else {
			copy(header.Nonce[:], nonceDropVote)
		}
	}
	extra, err := prepareExtra(header, snap.validators())
	if err != nil {
		return err
	}
	header.Extra = extra
	return nil
}

// Finalize runs any post-transaction state modifications (e.g. block rewards)
// and assembles the final block.
//
// Note, the block header and state database might be updated to reflect any
// consensus rules that happen at finalization (e.g. block rewards).
func (sb *simpleBackend) Finalize(chain consensus.ChainReader, header *types.Header, state *state.StateDB, txs []*types.Transaction,
	uncles []*types.Header, receipts []*types.Receipt) (*types.Block, error) {
	// No block rewards in Istanbul, so the state remains as is and uncles are dropped
	header.Root = state.IntermediateRoot(chain.Config().IsEIP158(header.Number))
	header.UncleHash = nilUncleHash

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

// Seal generates a new block for the given input block with the local miner's
// seal place on top.
func (sb *simpleBackend) Seal(chain consensus.ChainReader, block *types.Block, stop <-chan struct{}) (*types.Block, error) {
	log.Debug("Seal")
	// update the block header timestamp and signature and propose the block to core engine
	header := block.Header()
	number := header.Number.Uint64()

	// Bail out if we're unauthorized to sign a block
	snap, err := sb.snapshot(chain, number-1, header.ParentHash, nil)
	if err != nil {
		return nil, err
	}
	if _, v := snap.ValSet.GetByAddress(sb.address); v == nil {
		return nil, errUnauthorized
	}

	parent := chain.GetHeader(header.ParentHash, number-1)
	if parent == nil {
		return nil, consensus.ErrUnknownAncestor
	}
	block, err = sb.updateBlock(parent, block)
	if err != nil {
		return nil, err
	}

	log.Debug("before waiting", "block time", time.Unix(block.Header().Time.Int64(), 0).Format("01-02|15:04:05.000"))
	// wait for the timestamp of header, use this to adjust the block period
	pause := int64(100000000) //100ms delay more, workaround for race condition during block time validation
	delay := time.Unix(block.Header().Time.Int64(), pause).Sub(now())
	select {
	case <-time.After(delay):
	case <-stop:
		return nil, nil
	}
	log.Debug("after waiting")

	// get the proposed block hash and clear it if the seal() is completed.
	sb.sealMu.Lock()
	sb.proposedBlockHash = block.Hash()
	clear := func() {
		sb.proposedBlockHash = common.Hash{}
		sb.sealMu.Unlock()
	}
	defer clear()

	// post block into PoDC engine
	// 엔진에 블럭을 붙인다.
	go sb.EventMux().Post(podc.RequestEvent{
		Proposal: block,
	})

	for {
		select {
		case result := <-sb.commitCh:
			// if the block hash and the hash from channel are the same,
			// return the result. Otherwise, keep waiting the next hash.
			if block.Hash() == result.Hash() {
				return result, nil
			}
		case <-stop:
			return nil, nil
		}
	}
}

// update timestamp and signature of the block based on its number of transactions
func (sb *simpleBackend) updateBlock(parent *types.Header, block *types.Block) (*types.Block, error) {
	// set block period based the number of tx
	var period uint64
	if len(block.Transactions()) == 0 {
		period = sb.config.BlockPauseTime
	} else {
		period = sb.config.BlockPeriod
	}

	// set header timestamp
	header := block.Header()
	header.Time = new(big.Int).Add(parent.Time, new(big.Int).SetUint64(period))
	time := now().Unix()
	if header.Time.Int64() < time {
		header.Time = big.NewInt(time)
	}
	// sign the hash
	seal, err := sb.Sign(sigHash(header).Bytes())
	if err != nil {
		return nil, err
	}

	err = writeSeal(header, seal)
	if err != nil {
		return nil, err
	}

	return block.WithSeal(header), nil
}

// APIs returns the RPC APIs this consensus engine provides.
func (sb *simpleBackend) APIs(chain consensus.ChainReader) []rpc.API {

	return []rpc.API{{
		Namespace: "PoDC", //PoDC와 Web3ext.go Namespace PoDC 여기서 연결 ?
		Version:   "1.0",
		Service:   &API{chain: chain, podc: sb}, /* podc */
		Public:    true,
	}}

}

// HandleMsg implements consensus.PoDC.HandleMsg

func (sb *simpleBackend) HandleMsg(pubKey *ecdsa.PublicKey, data []byte) error {
	addr := crypto.PubkeyToAddress(*pubKey)
	// get the latest snapshot
	curHeader := sb.chain.CurrentHeader()
	snap, err := sb.snapshot(sb.chain, curHeader.Number.Uint64(), curHeader.Hash(), nil)
	if err != nil {
		sb.logger.Error("Cannot get latest snapshot", "err", err)
		return err
	}

	isInValSet := true
	if _, val := snap.ValSet.GetByAddress(addr); val == nil {
		//if len(curHeader.Extra)!= 0 {
		//	sb.logger.Error("Not in validator set", "peerAddr", addr)
		//}
		//return podc.ErrUnauthorizedAddress
		isInValSet = false
	}

	if isInValSet {
		go sb.podcEventMux.Post(podc.MessageEvent{
			Payload: data,
		})
	}

	return nil
}

// NewChainHead implements consensus.PoDC.NewChainHead
// 새로 블럭체인 헤더를 받는다. // 합의 시작되기 전에,
func (sb *simpleBackend) NewChainHead(block *types.Block) {
	snap, err := sb.snapshot(sb.chain, block.NumberU64(), block.Hash(), nil)
	if err != nil {
		log.Error("NewChainHead - Cannot get latest snapshot", "err", err)
		return
	}
	if _, val := snap.ValSet.GetByAddress(sb.Address()); val == nil {
		//log.Debug("NewChainHead - Normal node")
		return
	}

	p, err := sb.Author(block.Header())
	if err != nil {
		log.Error("Failed to get block proposer", "err", err)
		return
	}
	go sb.podcEventMux.Post(podc.FinalCommittedEvent{
		Proposal: block,
		Proposer: p,
	})
}

// Start implements consensus
func (sb *simpleBackend) Start(chain consensus.ChainReader, inserter func(block *types.Block) error) error { //?
	sb.chain = chain
	sb.inserter = inserter
	sb.core = podcCore.New(sb, sb.config)

	curHeader := chain.CurrentHeader()
	lastSequence := new(big.Int).Set(curHeader.Number)
	lastProposer := common.Address{}

	if lastSequence.Cmp(common.Big0) > 0 {
		p, err := sb.Author(curHeader)
		if err != nil {
			return err
		}
		lastProposer = p
	}
	block := chain.GetBlock(curHeader.Hash(), lastSequence.Uint64())
	return sb.core.Start(lastSequence, lastProposer, block)
}

// Stop implements consensus.Istanbul.Stop
func (sb *simpleBackend) Stop() error {
	if sb.core != nil {
		return sb.core.Stop()
	}
	return nil
}

// snapshot retrieves the authorization snapshot at a given point in time.
func (sb *simpleBackend) 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 := sb.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(sb.config.Epoch, sb.db, hash); err == nil {
				if s.ValSet.Size() == 0 {
					block := chain.GetHeaderByNumber(number)
					podcExtra, err := types.ExtractPoDCExtra(block)
					if err != nil {
						return nil, err
					}
					s.ValSet = validator.NewSet(podcExtra.Validators, sb.config.ProposerPolicy)
					//snap = newSnapshot(sb.config.Epoch, number, block.Hash(), validator.NewSet(podcExtra.Validators, sb.config.ProposerPolicy))
					//log.Debug("Updated validator list to voting snapshot", "number", number, "hash", hash, "block.Hash()", block.Hash())
				}
				log.Trace("Loaded voting snapshot form disk", "number", number, "hash", hash)
				snap = s
				break
			}
		}
		// If we're at block zero, make a snapshot
		if number == 0 {
			log.Info("If we're at block zero, make a snapshot", "If we're at block zero, make a snapshot", "blcok zero and make a snapshot in engine.go")
			genesis := chain.GetHeaderByNumber(0)
			if err := sb.VerifyHeader(chain, genesis, false); err != nil {
				return nil, err
			}
			podcExtra, err := types.ExtractPoDCExtra(genesis)
			if err != nil {
				log.Debug("genesis podcExtra error", "err", err)
				return nil, err
			}
			log.Info("genesis podcExtra", "podcExtra", podcExtra)
			// istanbulExtra.Validators 는 20바이트 계정 주소 목록
			snap = newSnapshot(sb.config.Epoch, 0, genesis.Hash(), validator.NewSet(podcExtra.Validators, sb.config.ProposerPolicy))
			if err := snap.store(sb.db); err != nil {
				return nil, err
			}
			log.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
	}
	sb.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(sb.db); err != nil {
			return nil, err
		}
		log.Trace("Stored voting snapshot to disk", "number", snap.Number, "hash", snap.Hash)
	}
	return snap, err
}

// FIXME: Need to update this for Istanbul  -> ?
// sigHash returns the hash which is used as input for the Istanbul
// 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()

	// Clean seal is required for calculating proposer seal.
	rlp.Encode(hasher, types.PoDCFilteredHeader(header, false))
	hasher.Sum(hash[:0])
	return hash
}

// ecrecover extracts the Ethereum account address from a signed header.
func ecrecover(header *types.Header) (common.Address, error) {
	// Retrieve the signature from the header extra-data
	podcExtra, err := types.ExtractPoDCExtra(header)
	if err != nil {
		return common.Address{}, err
	}
	return podc.GetSignatureAddress(sigHash(header).Bytes(), podcExtra.Seal)
}

// prepareExtra returns a extra-data of the given header and validators
func prepareExtra(header *types.Header, vals []common.Address) ([]byte, error) {
	var buf bytes.Buffer

	// compensate the lack bytes if header.Extra is not enough IstanbulExtraVanity bytes.
	if len(header.Extra) < types.PoDCExtraVanity {
		header.Extra = append(header.Extra, bytes.Repeat([]byte{0x00}, types.PoDCExtraVanity-len(header.Extra))...)
	}
	buf.Write(header.Extra[:types.PoDCExtraVanity])

	ist := &types.PoDCExtra{
		Validators:    vals,
		Seal:          []byte{},
		CommittedSeal: [][]byte{},
	}

	payload, err := rlp.EncodeToBytes(&ist)
	if err != nil {
		return nil, err
	}
	return append(buf.Bytes(), payload...), nil
}

// writeSeal writes the extra-data field of the given header with the given seals.
// suggest to rename to writeSeal.
func writeSeal(h *types.Header, seal []byte) error {
	if len(seal)%types.PoDCExtraSeal != 0 {
		return errInvalidSignature
	}

	podcExtra, err := types.ExtractPoDCExtra(h)
	if err != nil {
		return err
	}

	podcExtra.Seal = seal
	payload, err := rlp.EncodeToBytes(&podcExtra)
	if err != nil {
		return err
	}

	h.Extra = append(h.Extra[:types.PoDCExtraVanity], payload...)
	return nil
}

// writeCommittedSeals writes the extra-data field of a block header with given committed seals.
func writeCommittedSeals(h *types.Header, committedSeals []byte) error {
	if len(committedSeals)%types.PoDCExtraSeal != 0 {
		return errInvalidCommittedSeals
	}

	podcExtra, err := types.ExtractPoDCExtra(h)
	if err != nil {
		return err
	}

	podcExtra.CommittedSeal = make([][]byte, len(committedSeals)/types.PoDCExtraSeal)
	for i := 0; i < len(podcExtra.CommittedSeal); i++ {
		podcExtra.CommittedSeal[i] = make([]byte, types.PoDCExtraSeal)
		copy(podcExtra.CommittedSeal[i][:], committedSeals[i*types.PoDCExtraSeal:])
	}

	payload, err := rlp.EncodeToBytes(&podcExtra)
	if err != nil {
		return err
	}

	h.Extra = append(h.Extra[:types.PoDCExtraVanity], payload...)
	return nil
}