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verify_header.go
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verify_header.go
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package types
import (
"bytes"
"errors"
"fmt"
"math/big"
"runtime"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/common/math"
"github.com/ethereum/go-ethereum/core/types"
"github.com/ethereum/go-ethereum/params"
)
// VerifySeal checks whether a block satisfies the PoW difficulty requirements,
// either using the usual ethash cache for it, or alternatively using a full DAG
// to make remote mining fast.
func (ethash *Ethash) VerifySeal(header *types.Header, fulldag bool) error {
// Ensure that we have a valid difficulty for the block
if header.Difficulty.Sign() <= 0 {
return ErrWrongDifficulty
}
// Recompute the digest and PoW values
number := header.Number.Uint64()
var (
digest []byte
result []byte
)
// If fast-but-heavy PoW verification was requested, use an ethash dataset
if fulldag {
dataset := ethash.dataset(number, true)
if dataset.generated() {
digest, result = hashimotoFull(dataset.dataset, ethash.SealHash(header).Bytes(), header.Nonce.Uint64())
// Datasets are unmapped in a finalizer. Ensure that the dataset stays alive
// until after the call to hashimotoFull so it's not unmapped while being used.
runtime.KeepAlive(dataset)
} else {
// Dataset not yet generated, don't hang, use a cache instead
fulldag = false
}
}
// If slow-but-light PoW verification was requested (or DAG not yet ready), use an ethash cache
if !fulldag {
cache := ethash.cache(number)
size := datasetSize(number)
if ethash.config.PowMode == ModeTest {
size = 32 * 1024
}
digest, result = hashimotoLight(size, cache.cache, ethash.SealHash(header).Bytes(), header.Nonce.Uint64())
// Caches are unmapped in a finalizer. Ensure that the cache stays alive
// until after the call to hashimotoLight so it's not unmapped while being used.
runtime.KeepAlive(cache)
}
// Verify the calculated values against the ones provided in the header
if !bytes.Equal(header.MixDigest[:], digest) {
return ErrInvalidMixDigest
}
target := new(big.Int).Div(two256, header.Difficulty)
if new(big.Int).SetBytes(result).Cmp(target) > 0 {
return ErrWrongDifficulty
}
return nil
}
// Some weird constants to avoid constant memory allocs for them.
var (
expDiffPeriod = big.NewInt(100000)
big1 = big.NewInt(1)
big2 = big.NewInt(2)
big9 = big.NewInt(9)
bigMinus99 = big.NewInt(-99)
)
// makeDifficultyCalculator creates a difficultyCalculator with the given bomb-delay.
// the difficulty is calculated with Byzantium rules, which differs from Homestead in
// how uncles affect the calculation
func makeDifficultyCalculator(bombDelay *big.Int) func(time uint64, parent *Header) *big.Int {
// Note, the calculations below looks at the parent number, which is 1 below
// the block number. Thus we remove one from the delay given
bombDelayFromParent := new(big.Int).Sub(bombDelay, big1)
return func(time uint64, parent *Header) *big.Int {
// https://github.com/ethereum/EIPs/issues/100.
// algorithm:
// diff = (parent_diff +
// (parent_diff / 2048 * max((2 if len(parent.uncles) else 1) - ((timestamp - parent.timestamp) // 9), -99))
// ) + 2^(periodCount - 2)
bigTime := new(big.Int).SetUint64(time)
bigParentTime := new(big.Int).SetUint64(parent.Time)
// holds intermediate values to make the algo easier to read & audit
x := new(big.Int)
y := new(big.Int)
// (2 if len(parent_uncles) else 1) - (block_timestamp - parent_timestamp) // 9
x.Sub(bigTime, bigParentTime)
x.Div(x, big9)
if parent.ToEthHeader().UncleHash == types.EmptyUncleHash {
x.Sub(big1, x)
} else {
x.Sub(big2, x)
}
// max((2 if len(parent_uncles) else 1) - (block_timestamp - parent_timestamp) // 9, -99)
if x.Cmp(bigMinus99) < 0 {
x.Set(bigMinus99)
}
// parent_diff + (parent_diff / 2048 * max((2 if len(parent.uncles) else 1) - ((timestamp - parent.timestamp) // 9), -99))
y.Div(parent.ToEthHeader().Difficulty, params.DifficultyBoundDivisor)
x.Mul(y, x)
x.Add(parent.ToEthHeader().Difficulty, x)
// minimum difficulty can ever be (before exponential factor)
if x.Cmp(params.MinimumDifficulty) < 0 {
x.Set(params.MinimumDifficulty)
}
// calculate a fake block number for the ice-age delay
// Specification: https://eips.ethereum.org/EIPS/eip-1234
fakeBlockNumber := new(big.Int)
if parent.ToEthHeader().Number.Cmp(bombDelayFromParent) >= 0 {
fakeBlockNumber = fakeBlockNumber.Sub(parent.ToEthHeader().Number, bombDelayFromParent)
}
// for the exponential factor
periodCount := fakeBlockNumber
periodCount.Div(periodCount, expDiffPeriod)
// the exponential factor, commonly referred to as "the bomb"
// diff = diff + 2^(periodCount - 2)
if periodCount.Cmp(big1) > 0 {
y.Sub(periodCount, big2)
y.Exp(big2, y, nil)
x.Add(x, y)
}
return x
}
}
const (
BaseFeeChangeDenominator = 8 // Bounds the amount the base fee can change between blocks.
ElasticityMultiplier = 2 // Bounds the maximum gas limit an EIP-1559 block may have.
InitialBaseFee = 1000000000 // Initial base fee for EIP-1559 blocks.
)
// VerifyEip1559Header verifies some header attributes which were changed in EIP-1559,
// - gas limit check
// - basefee check
func VerifyEip1559Header(parent, header *Header) error {
// Verify that the gas limit remains within allowed bounds
parentGasLimit := parent.ToEthHeader().GasLimit
if err := VerifyGaslimit(parentGasLimit, header.ToEthHeader().GasLimit); err != nil {
return err
}
// Verify the header is not malformed
if header.ToEthHeader().BaseFee == nil {
return fmt.Errorf("header is missing baseFee")
}
// Verify the baseFee is correct based on the parent header.
expectedBaseFee := CalcBaseFee(parent)
if header.ToEthHeader().BaseFee.Cmp(expectedBaseFee) != 0 {
return fmt.Errorf("invalid baseFee: have %s, want %s, parentBaseFee %s, parentGasUsed %d",
expectedBaseFee, header.ToEthHeader().BaseFee, parent.ToEthHeader().BaseFee, parent.ToEthHeader().GasUsed)
}
return nil
}
// VerifyGaslimit verifies the header gas limit according increase/decrease
// in relation to the parent gas limit.
func VerifyGaslimit(parentGasLimit, headerGasLimit uint64) error {
// Verify that the gas limit remains within allowed bounds
diff := int64(parentGasLimit) - int64(headerGasLimit)
if diff < 0 {
diff *= -1
}
limit := parentGasLimit / params.GasLimitBoundDivisor
if uint64(diff) >= limit {
return fmt.Errorf("invalid gas limit: have %d, want %d +-= %d", headerGasLimit, parentGasLimit, limit-1)
}
if headerGasLimit < params.MinGasLimit {
return errors.New("invalid gas limit below 5000")
}
return nil
}
// CalcBaseFee calculates the basefee of the header.
func CalcBaseFee(parent *Header) *big.Int {
var (
parentGasTarget = parent.ToEthHeader().GasLimit / ElasticityMultiplier
parentGasTargetBig = new(big.Int).SetUint64(parentGasTarget)
baseFeeChangeDenominator = new(big.Int).SetUint64(BaseFeeChangeDenominator)
)
// If the parent gasUsed is the same as the target, the baseFee remains unchanged.
if parent.ToEthHeader().GasUsed == parentGasTarget {
return new(big.Int).Set(parent.ToEthHeader().BaseFee)
}
if parent.ToEthHeader().GasUsed > parentGasTarget {
// If the parent block used more gas than its target, the baseFee should increase.
gasUsedDelta := new(big.Int).SetUint64(parent.ToEthHeader().GasUsed - parentGasTarget)
x := new(big.Int).Mul(parent.ToEthHeader().BaseFee, gasUsedDelta)
y := x.Div(x, parentGasTargetBig)
baseFeeDelta := math.BigMax(
x.Div(y, baseFeeChangeDenominator),
common.Big1,
)
return x.Add(parent.ToEthHeader().BaseFee, baseFeeDelta)
} else {
// Otherwise if the parent block used less gas than its target, the baseFee should decrease.
gasUsedDelta := new(big.Int).SetUint64(parentGasTarget - parent.ToEthHeader().GasUsed)
x := new(big.Int).Mul(parent.ToEthHeader().BaseFee, gasUsedDelta)
y := x.Div(x, parentGasTargetBig)
baseFeeDelta := x.Div(y, baseFeeChangeDenominator)
return math.BigMax(
x.Sub(parent.ToEthHeader().BaseFee, baseFeeDelta),
common.Big0,
)
}
}