// 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/>.
// Package clique implements the proof-of-authority consensus engine.
package clique
import (
"bytes"
"errors"
"math/big"
"math/rand"
"sync"
"time"
"github.com/ethereum/go-ethereum/accounts"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/common/hexutil"
"github.com/ethereum/go-ethereum/consensus"
"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/ethdb"
"github.com/ethereum/go-ethereum/log"
"github.com/ethereum/go-ethereum/params"
"github.com/ethereum/go-ethereum/rlp"
"github.com/ethereum/go-ethereum/rpc"
lru "github.com/hashicorp/golang-lru"
)
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 = 65 // 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.
uncleHash = types.CalcUncleHash(nil) // Always Keccak256(RLP([])) as uncles are meaningless outside of PoW.
diffInTurn = big.NewInt(2) // Block difficulty for in-turn signatures
diffNoTurn = big.NewInt(1) // Block difficulty for out-of-turn signatures
)
// 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 suffix signature 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, or not the correct
// ones).
errInvalidCheckpointSigners = errors.New("invalid signer list on checkpoint block")
// errInvalidMixDigest is returned if a block's mix digest is non-zero.
errInvalidMixDigest = errors.New("non-zero mix digest")
// errInvalidUncleHash is returned if a block contains an non-empty uncle list.
errInvalidUncleHash = errors.New("non empty uncle hash")
// errInvalidDifficulty is returned if the difficulty of a block is not either
// of 1 or 2, or if the value does not match the turn of the signer.
errInvalidDifficulty = errors.New("invalid difficulty")
// 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")
// errUnauthorized is returned if a header is signed by a non-authorized entity.
errUnauthorized = errors.New("unauthorized")
)
// 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.UncleHash,
header.Coinbase,
header.Root,
header.TxHash,
header.ReceiptHash,
header.Bloom,
header.Difficulty,
header.Number,
header.GasLimit,
header.GasUsed,
header.Time,
header.Extra[:len(header.Extra)-65], // Yes, this will panic if extra is too short
header.MixDigest,
header.Nonce,
})
hasher.Sum(hash[:0])
return hash
}
// ecrecover extracts the Ethereum 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 Ethereum 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
// Ethereum testnet following the Ropsten attacks.
type Clique struct {
config *params.CliqueConfig // Consensus engine configuration parameters
db ethdb.Database // 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 // Ethereum address of the signing key
signFn SignerFn // Signer function to authorize hashes with
lock sync.RWMutex // Protects the signer fields
}
// 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 ethdb.Database) *Clique {
// Set any missing consensus parameters to their defaults
conf := *config
if conf.Epoch == 0 {
conf.Epoch = epochLength
}
if conf.Period == 0 {
conf.Period = blockPeriod
}
// 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 Ethereum 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)
}
// 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
}
// Checkpoint blocks need to enforce zero beneficiary
checkpoint := (number % c.config.Epoch) == 0
if checkpoint && header.Coinbase != (common.Address{}) {
return errInvalidCheckpointBeneficiary
}
// Nonces must be 0x00..0 or 0xff..f, zeroes enforced on checkpoints
if !bytes.Equal(header.Nonce[:], nonceAuthVote) && !bytes.Equal(header.Nonce[:], nonceDropVote) {
return errInvalidVote
}
if checkpoint && !bytes.Equal(header.Nonce[:], nonceDropVote) {
return errInvalidCheckpointVote
}
// 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
if !checkpoint && signersBytes != 0 {
return errExtraSigners
}
if checkpoint && signersBytes%common.AddressLength != 0 {
return errInvalidCheckpointSigners
}
// Ensure that the mix digest is zero as we don't have fork protection currently
if header.MixDigest != (common.Hash{}) {
return errInvalidMixDigest
}
// Ensure that the block doesn't contain any uncles which are meaningless in PoA
if header.UncleHash != uncleHash {
return errInvalidUncleHash
}
// Ensure that the block's difficulty is meaningful (may not be correct at this point)
if number > 0 {
if header.Difficulty == nil || (header.Difficulty.Cmp(diffInTurn) != 0 && header.Difficulty.Cmp(diffNoTurn) != 0) {
return errInvalidDifficulty
}
}
// 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)
}
// 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 {
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 {
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
}
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
}
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
}
log.Trace("Stored voting snapshot to disk", "number", snap.Number, "hash", snap.Hash)
}
return snap, err
}
// VerifyUncles implements consensus.Engine, always returning an error for any
// uncles as this consensus mechanism doesn't permit uncles.
func (c *Clique) VerifyUncles(chain consensus.ChainReader, block *types.Block) error {
if len(block.Uncles()) > 0 {
return errors.New("uncles not allowed")
}
return 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 {
return err
}
if _, ok := snap.Signers[signer]; !ok {
return errUnauthorized
}
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 errUnauthorized
}
}
}
// Ensure that the difficulty corresponds to the turn-ness of the signer
inturn := snap.inturn(header.Number.Uint64(), signer)
if inturn && header.Difficulty.Cmp(diffInTurn) != 0 {
return errInvalidDifficulty
}
if !inturn && header.Difficulty.Cmp(diffNoTurn) != 0 {
return errInvalidDifficulty
}
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)
header.Coinbase = common.Address{}
header.Nonce = types.BlockNonce{}
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 {
header.Coinbase = addresses[rand.Intn(len(addresses))]
if c.proposals[header.Coinbase] {
copy(header.Nonce[:], nonceAuthVote)
} else {
copy(header.Nonce[:], nonceDropVote)
}
}
c.lock.RUnlock()
}
// Set the correct difficulty
header.Difficulty = diffNoTurn
if snap.inturn(header.Number.Uint64(), c.signer) {
header.Difficulty = diffInTurn
}
// 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)...)
// Mix digest is reserved for now, set to empty
header.MixDigest = common.Hash{}
// Ensure the timestamp has the correct delay
parent := chain.GetHeader(header.ParentHash, number-1)
if parent == nil {
return consensus.ErrUnknownAncestor
}
header.Time = new(big.Int).Add(parent.Time, new(big.Int).SetUint64(c.config.Period))
if header.Time.Int64() < time.Now().Unix() {
header.Time = big.NewInt(time.Now().Unix())
}
return nil
}
// Finalize implements consensus.Engine, ensuring no uncles are set, nor block
// rewards given, and returns the final block.
func (c *Clique) 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 PoA, so the state remains as is and uncles are dropped
header.Root = state.IntermediateRoot(chain.Config().IsEIP158(header.Number))
header.UncleHash = types.CalcUncleHash(nil)
// Assemble and return the final block for sealing
return types.NewBlock(header, txs, nil, 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
}
// 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, errUnauthorized
}
// 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 {
log.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())
if header.Difficulty.Cmp(diffNoTurn) == 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)))
log.Trace("Out-of-turn signing requested", "wiggle", common.PrettyDuration(wiggle))
}
log.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
}
// 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,
}}
}
