path: root/consensus/ethash/consensus.go

// 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 ethash

import (
    "bytes"
    "errors"
    "fmt"
    "math/big"
    "runtime"
    "sync/atomic"
    "time"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/common/math"
    "github.com/ethereum/go-ethereum/consensus"
    "github.com/ethereum/go-ethereum/consensus/misc"
    "github.com/ethereum/go-ethereum/core/state"
    "github.com/ethereum/go-ethereum/core/types"
    "github.com/ethereum/go-ethereum/params"
    set "gopkg.in/fatih/set.v0"
)

// Ethash proof-of-work protocol constants.
var (
    blockReward *big.Int = big.NewInt(5e+18) // Block reward in wei for successfully mining a block
    maxUncles            = 2                 // Maximum number of uncles allowed in a single block
)

var (
    ErrInvalidChain      = errors.New("invalid header chain")
    ErrTooManyUncles     = errors.New("too many uncles")
    ErrDuplicateUncle    = errors.New("duplicate uncle")
    ErrUncleIsAncestor   = errors.New("uncle is ancestor")
    ErrDanglingUncle     = errors.New("uncle's parent is not ancestor")
    ErrNonceOutOfRange   = errors.New("nonce out of range")
    ErrInvalidDifficulty = errors.New("non-positive difficulty")
    ErrInvalidMixDigest  = errors.New("invalid mix digest")
    ErrInvalidPoW        = errors.New("invalid proof-of-work")
)

// VerifyHeader checks whether a header conforms to the consensus rules of the
// stock Ethereum ethash engine.
func (ethash *Ethash) VerifyHeader(chain consensus.ChainReader, header *types.Header, seal bool) error {
    // If we're running a full engine faking, accept any input as valid
    if ethash.fakeFull {
        return nil
    }
    // Short circuit if the header is known, or it's parent not
    number := header.Number.Uint64()
    if chain.GetHeader(header.Hash(), number) != nil {
        return nil
    }
    parent := chain.GetHeader(header.ParentHash, number-1)
    if parent == nil {
        return consensus.ErrUnknownAncestor
    }
    // Sanity checks passed, do a proper verification
    return ethash.verifyHeader(chain, header, parent, false, seal)
}

// 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.
func (ethash *Ethash) VerifyHeaders(chain consensus.ChainReader, headers []*types.Header, seals []bool) (chan<- struct{}, <-chan error) {
    // If we're running a full engine faking, accept any input as valid
    if ethash.fakeFull {
        abort, results := make(chan struct{}), make(chan error, len(headers))
        for i := 0; i < len(headers); i++ {
            results <- nil
        }
        return abort, results
    }
    // Spawn as many workers as allowed threads
    workers := runtime.GOMAXPROCS(0)
    if len(headers) < workers {
        workers = len(headers)
    }
    // Create a task channel and spawn the verifiers
    type result struct {
        index int
        err   error
    }
    inputs := make(chan int, workers)
    outputs := make(chan result, len(headers))

    var badblock uint64
    for i := 0; i < workers; i++ {
        go func() {
            for index := range inputs {
                // If we've found a bad block already before this, stop validating
                if bad := atomic.LoadUint64(&badblock); bad != 0 && bad <= headers[index].Number.Uint64() {
                    outputs <- result{index: index, err: ErrInvalidChain}
                    continue
                }
                // We need to look up the first parent
                var parent *types.Header
                if index == 0 {
                    parent = chain.GetHeader(headers[0].ParentHash, headers[0].Number.Uint64()-1)
                } else if headers[index-1].Hash() == headers[index].ParentHash {
                    parent = headers[index-1]
                }
                // Ensure the validation is useful and execute it
                var failure error
                switch {
                case chain.GetHeader(headers[index].Hash(), headers[index].Number.Uint64()-1) != nil:
                    outputs <- result{index: index, err: nil}
                case parent == nil:
                    failure = consensus.ErrUnknownAncestor
                    outputs <- result{index: index, err: failure}
                default:
                    failure = ethash.verifyHeader(chain, headers[index], parent, false, seals[index])
                    outputs <- result{index: index, err: failure}
                }
                // If a validation failure occurred, mark subsequent blocks invalid
                if failure != nil {
                    number := headers[index].Number.Uint64()
                    if prev := atomic.LoadUint64(&badblock); prev == 0 || prev > number {
                        // This two step atomic op isn't thread-safe in that `badblock` might end
                        // up slightly higher than the block number of the first failure (if many
                        // workers try to write at the same time), but it's fine as we're mostly
                        // interested to avoid large useless work, we don't care about 1-2 extra
                        // runs. Doing "full thread safety" would involve mutexes, which would be
                        // a noticeable sync overhead on the fast spinning worker routines.
                        atomic.StoreUint64(&badblock, number)
                    }
                }
            }
        }()
    }
    // Feed item indices to the workers until done, sorting and feeding the results to the caller
    dones := make([]bool, len(headers))
    errors := make([]error, len(headers))

    abort := make(chan struct{})
    returns := make(chan error, len(headers))

    go func() {
        defer close(inputs)

        input, output := 0, 0
        for i := 0; i < len(headers)*2; i++ {
            var res result

            // If there are tasks left, push to workers
            if input < len(headers) {
                select {
                case inputs <- input:
                    input++
                    continue
                case <-abort:
                    return
                case res = <-outputs:
                }
            } else {
                // Otherwise keep waiting for results
                select {
                case <-abort:
                    return
                case res = <-outputs:
                }
            }
            // A result arrived, save and propagate if next
            dones[res.index], errors[res.index] = true, res.err
            for output < len(headers) && dones[output] {
                returns <- errors[output]
                output++
            }
        }
    }()
    return abort, returns
}

// VerifyUncles verifies that the given block's uncles conform to the consensus
// rules of the stock Ethereum ethash engine.
func (ethash *Ethash) VerifyUncles(chain consensus.ChainReader, block *types.Block) error {
    // If we're running a full engine faking, accept any input as valid
    if ethash.fakeFull {
        return nil
    }
    // Verify that there are at most 2 uncles included in this block
    if len(block.Uncles()) > maxUncles {
        return ErrTooManyUncles
    }
    // Gather the set of past uncles and ancestors
    uncles, ancestors := set.New(), make(map[common.Hash]*types.Header)

    number, parent := block.NumberU64()-1, block.ParentHash()
    for i := 0; i < 7; i++ {
        ancestor := chain.GetBlock(parent, number)
        if ancestor == nil {
            break
        }
        ancestors[ancestor.Hash()] = ancestor.Header()
        for _, uncle := range ancestor.Uncles() {
            uncles.Add(uncle.Hash())
        }
        parent, number = ancestor.ParentHash(), number-1
    }
    ancestors[block.Hash()] = block.Header()
    uncles.Add(block.Hash())

    // Verify each of the uncles that it's recent, but not an ancestor
    for _, uncle := range block.Uncles() {
        // Make sure every uncle is rewarded only once
        hash := uncle.Hash()
        if uncles.Has(hash) {
            return ErrDuplicateUncle
        }
        uncles.Add(hash)

        // Make sure the uncle has a valid ancestry
        if ancestors[hash] != nil {
            return ErrUncleIsAncestor
        }
        if ancestors[uncle.ParentHash] == nil || uncle.ParentHash == block.ParentHash() {
            return ErrDanglingUncle
        }
        if err := ethash.verifyHeader(chain, uncle, ancestors[uncle.ParentHash], true, true); err != nil {
            return err
        }
    }
    return nil
}

// verifyHeader checks whether a header conforms to the consensus rules of the
// stock Ethereum ethash engine.
//
// See YP section 4.3.4. "Block Header Validity"
func (ethash *Ethash) verifyHeader(chain consensus.ChainReader, header, parent *types.Header, uncle bool, seal bool) error {
    // Ensure that the header's extra-data section is of a reasonable size
    if uint64(len(header.Extra)) > params.MaximumExtraDataSize {
        return fmt.Errorf("extra-data too long: %d > %d", len(header.Extra), params.MaximumExtraDataSize)
    }
    // Verify the header's timestamp
    if uncle {
        if header.Time.Cmp(math.MaxBig256) > 0 {
            return consensus.ErrLargeBlockTime
        }
    } else {
        if header.Time.Cmp(big.NewInt(time.Now().Unix())) > 0 {
            return consensus.ErrFutureBlock
        }
    }
    if header.Time.Cmp(parent.Time) <= 0 {
        return consensus.ErrZeroBlockTime
    }
    // Verify the block's difficulty based in it's timestamp and parent's difficulty
    expected := CalcDifficulty(chain.Config(), header.Time.Uint64(), parent.Time.Uint64(), parent.Number, parent.Difficulty)
    if expected.Cmp(header.Difficulty) != 0 {
        return fmt.Errorf("invalid difficulty: have %v, want %v", header.Difficulty, expected)
    }
    // Verify that the gas limit remains within allowed bounds
    diff := new(big.Int).Set(parent.GasLimit)
    diff = diff.Sub(diff, header.GasLimit)
    diff.Abs(diff)

    limit := new(big.Int).Set(parent.GasLimit)
    limit = limit.Div(limit, params.GasLimitBoundDivisor)

    if diff.Cmp(limit) >= 0 || header.GasLimit.Cmp(params.MinGasLimit) < 0 {
        return fmt.Errorf("invalid gas limit: have %v, want %v += %v", header.GasLimit, parent.GasLimit, limit)
    }
    // Verify that the block number is parent's +1
    if diff := new(big.Int).Sub(header.Number, parent.Number); diff.Cmp(big.NewInt(1)) != 0 {
        return consensus.ErrInvalidNumber
    }
    // Verify the engine specific seal securing the block
    if seal {
        if err := ethash.VerifySeal(chain, header); err != nil {
            return err
        }
    }
    // If all checks passed, validate any special fields for hard forks
    if err := misc.VerifyDAOHeaderExtraData(chain.Config(), header); err != nil {
        return err
    }
    if err := misc.VerifyForkHashes(chain.Config(), header, uncle); err != nil {
        return err
    }
    return nil
}

// CalcDifficulty is the difficulty adjustment algorithm. It returns the difficulty
// that a new block should have when created at time given the parent block's time
// and difficulty.
//
// TODO (karalabe): Move the chain maker into this package and make this private!
func CalcDifficulty(config *params.ChainConfig, time, parentTime uint64, parentNumber, parentDiff *big.Int) *big.Int {
    if config.IsHomestead(new(big.Int).Add(parentNumber, common.Big1)) {
        return calcDifficultyHomestead(time, parentTime, parentNumber, parentDiff)
    }
    return calcDifficultyFrontier(time, parentTime, parentNumber, parentDiff)
}

// Some weird constants to avoid constant memory allocs for them.
var (
    expDiffPeriod = big.NewInt(100000)
    big10         = big.NewInt(10)
    bigMinus99    = big.NewInt(-99)
)

// calcDifficultyHomestead is the difficulty adjustment algorithm. It returns
// the difficulty that a new block should have when created at time given the
// parent block's time and difficulty. The calculation uses the Homestead rules.
func calcDifficultyHomestead(time, parentTime uint64, parentNumber, parentDiff *big.Int) *big.Int {
    // https://github.com/ethereum/EIPs/blob/master/EIPS/eip-2.mediawiki
    // algorithm:
    // diff = (parent_diff +
    //         (parent_diff / 2048 * max(1 - (block_timestamp - parent_timestamp) // 10, -99))
    //        ) + 2^(periodCount - 2)

    bigTime := new(big.Int).SetUint64(time)
    bigParentTime := new(big.Int).SetUint64(parentTime)

    // holds intermediate values to make the algo easier to read & audit
    x := new(big.Int)
    y := new(big.Int)

    // 1 - (block_timestamp -parent_timestamp) // 10
    x.Sub(bigTime, bigParentTime)
    x.Div(x, big10)
    x.Sub(common.Big1, x)

    // max(1 - (block_timestamp - parent_timestamp) // 10, -99)))
    if x.Cmp(bigMinus99) < 0 {
        x.Set(bigMinus99)
    }
    // (parent_diff + parent_diff // 2048 * max(1 - (block_timestamp - parent_timestamp) // 10, -99))
    y.Div(parentDiff, params.DifficultyBoundDivisor)
    x.Mul(y, x)
    x.Add(parentDiff, x)

    // minimum difficulty can ever be (before exponential factor)
    if x.Cmp(params.MinimumDifficulty) < 0 {
        x.Set(params.MinimumDifficulty)
    }
    // for the exponential factor
    periodCount := new(big.Int).Add(parentNumber, common.Big1)
    periodCount.Div(periodCount, expDiffPeriod)

    // the exponential factor, commonly referred to as "the bomb"
    // diff = diff + 2^(periodCount - 2)
    if periodCount.Cmp(common.Big1) > 0 {
        y.Sub(periodCount, common.Big2)
        y.Exp(common.Big2, y, nil)
        x.Add(x, y)
    }
    return x
}

// calcDifficultyFrontier is the difficulty adjustment algorithm. It returns the
// difficulty that a new block should have when created at time given the parent
// block's time and difficulty. The calculation uses the Frontier rules.
func calcDifficultyFrontier(time, parentTime uint64, parentNumber, parentDiff *big.Int) *big.Int {
    diff := new(big.Int)
    adjust := new(big.Int).Div(parentDiff, params.DifficultyBoundDivisor)
    bigTime := new(big.Int)
    bigParentTime := new(big.Int)

    bigTime.SetUint64(time)
    bigParentTime.SetUint64(parentTime)

    if bigTime.Sub(bigTime, bigParentTime).Cmp(params.DurationLimit) < 0 {
        diff.Add(parentDiff, adjust)
    } else {
        diff.Sub(parentDiff, adjust)
    }
    if diff.Cmp(params.MinimumDifficulty) < 0 {
        diff.Set(params.MinimumDifficulty)
    }

    periodCount := new(big.Int).Add(parentNumber, common.Big1)
    periodCount.Div(periodCount, expDiffPeriod)
    if periodCount.Cmp(common.Big1) > 0 {
        // diff = diff + 2^(periodCount - 2)
        expDiff := periodCount.Sub(periodCount, common.Big2)
        expDiff.Exp(common.Big2, expDiff, nil)
        diff.Add(diff, expDiff)
        diff = math.BigMax(diff, params.MinimumDifficulty)
    }
    return diff
}

// VerifySeal implements consensus.Engine, checking whether the given block satisfies
// the PoW difficulty requirements.
func (ethash *Ethash) VerifySeal(chain consensus.ChainReader, header *types.Header) error {
    // If we're running a fake PoW, accept any seal as valid
    if ethash.fakeMode {
        time.Sleep(ethash.fakeDelay)
        if ethash.fakeFail == header.Number.Uint64() {
            return ErrInvalidPoW
        }
        return nil
    }
    // If we're running a shared PoW, delegate verification to it
    if ethash.shared != nil {
        return ethash.shared.VerifySeal(chain, header)
    }
    // Sanity check that the block number is below the lookup table size (60M blocks)
    number := header.Number.Uint64()
    if number/epochLength >= uint64(len(cacheSizes)) {
        // Go < 1.7 cannot calculate new cache/dataset sizes (no fast prime check)
        return ErrNonceOutOfRange
    }
    // Ensure that we have a valid difficulty for the block
    if header.Difficulty.Sign() <= 0 {
        return ErrInvalidDifficulty
    }
    // Recompute the digest and PoW value and verify against the header
    cache := ethash.cache(number)

    size := datasetSize(number)
    if ethash.tester {
        size = 32 * 1024
    }
    digest, result := hashimotoLight(size, cache, header.HashNoNonce().Bytes(), header.Nonce.Uint64())
    if !bytes.Equal(header.MixDigest[:], digest) {
        return ErrInvalidMixDigest
    }
    target := new(big.Int).Div(maxUint256, header.Difficulty)
    if new(big.Int).SetBytes(result).Cmp(target) > 0 {
        return ErrInvalidPoW
    }
    return nil
}

// Prepare implements consensus.Engine, initializing the difficulty field of a
// header to conform to the ethash protocol. The changes are done inline.
func (ethash *Ethash) Prepare(chain consensus.ChainReader, header *types.Header) error {
    parent := chain.GetHeader(header.ParentHash, header.Number.Uint64()-1)
    if parent == nil {
        return consensus.ErrUnknownAncestor
    }
    header.Difficulty = CalcDifficulty(chain.Config(), header.Time.Uint64(),
        parent.Time.Uint64(), parent.Number, parent.Difficulty)

    return nil
}

// Finalize implements consensus.Engine, accumulating the block and uncle rewards,
// setting the final state and assembling the block.
func (ethash *Ethash) Finalize(chain consensus.ChainReader, header *types.Header, state *state.StateDB, txs []*types.Transaction, uncles []*types.Header, receipts []*types.Receipt) (*types.Block, error) {
    // Accumulate any block and uncle rewards and commit the final state root
    AccumulateRewards(state, header, uncles)
    header.Root = state.IntermediateRoot(chain.Config().IsEIP158(header.Number))

    // Header seems complete, assemble into a block and return
    return types.NewBlock(header, txs, uncles, receipts), nil
}

// Some weird constants to avoid constant memory allocs for them.
var (
    big8  = big.NewInt(8)
    big32 = big.NewInt(32)
)

// AccumulateRewards credits the coinbase of the given block with the mining
// reward. The total reward consists of the static block reward and rewards for
// included uncles. The coinbase of each uncle block is also rewarded.
//
// TODO (karalabe): Move the chain maker into this package and make this private!
func AccumulateRewards(state *state.StateDB, header *types.Header, uncles []*types.Header) {
    reward := new(big.Int).Set(blockReward)
    r := new(big.Int)
    for _, uncle := range uncles {
        r.Add(uncle.Number, big8)
        r.Sub(r, header.Number)
        r.Mul(r, blockReward)
        r.Div(r, big8)
        state.AddBalance(uncle.Coinbase, r)

        r.Div(blockReward, big32)
        reward.Add(reward, r)
    }
    state.AddBalance(header.Coinbase, reward)
}