path: root/core/block_validator.go

// Copyright 2014 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 core

import (
    "fmt"
    "math/big"
    "time"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/core/state"
    "github.com/ethereum/go-ethereum/core/types"
    "github.com/ethereum/go-ethereum/logger/glog"
    "github.com/ethereum/go-ethereum/params"
    "github.com/ethereum/go-ethereum/pow"
    "gopkg.in/fatih/set.v0"
)

var (
    ExpDiffPeriod = big.NewInt(100000)
    big10         = big.NewInt(10)
    bigMinus99    = big.NewInt(-99)
)

// BlockValidator is responsible for validating block headers, uncles and
// processed state.
//
// BlockValidator implements Validator.
type BlockValidator struct {
    bc  *BlockChain // Canonical block chain
    Pow pow.PoW     // Proof of work used for validating
}

// NewBlockValidator returns a new block validator which is safe for re-use
func NewBlockValidator(blockchain *BlockChain, pow pow.PoW) *BlockValidator {
    validator := &BlockValidator{
        Pow: pow,
        bc:  blockchain,
    }
    return validator
}

// ValidateBlock validates the given block's header and uncles and verifies the
// the block header's transaction and uncle roots.
//
// ValidateBlock does not validate the header's pow. The pow work validated
// separately so we can process them in parallel.
//
// ValidateBlock also validates and makes sure that any previous state (or present)
// state that might or might not be present is checked to make sure that fast
// sync has done it's job proper. This prevents the block validator form accepting
// false positives where a header is present but the state is not.
func (v *BlockValidator) ValidateBlock(block *types.Block) error {
    if v.bc.HasBlock(block.Hash()) {
        if _, err := state.New(block.Root(), v.bc.chainDb); err == nil {
            return &KnownBlockError{block.Number(), block.Hash()}
        }
    }
    parent := v.bc.GetBlock(block.ParentHash())
    if parent == nil {
        return ParentError(block.ParentHash())
    }
    if _, err := state.New(parent.Root(), v.bc.chainDb); err != nil {
        return ParentError(block.ParentHash())
    }

    header := block.Header()
    // validate the block header
    if err := ValidateHeader(v.Pow, header, parent.Header(), false, false); err != nil {
        return err
    }
    // verify the uncles are correctly rewarded
    if err := v.VerifyUncles(block, parent); err != nil {
        return err
    }

    // Verify UncleHash before running other uncle validations
    unclesSha := types.CalcUncleHash(block.Uncles())
    if unclesSha != header.UncleHash {
        return fmt.Errorf("invalid uncles root hash. received=%x calculated=%x", header.UncleHash, unclesSha)
    }

    // The transactions Trie's root (R = (Tr [[i, RLP(T1)], [i, RLP(T2)], ... [n, RLP(Tn)]]))
    // can be used by light clients to make sure they've received the correct Txs
    txSha := types.DeriveSha(block.Transactions())
    if txSha != header.TxHash {
        return fmt.Errorf("invalid transaction root hash. received=%x calculated=%x", header.TxHash, txSha)
    }

    return nil
}

// ValidateState validates the various changes that happen after a state
// transition, such as amount of used gas, the receipt roots and the state root
// itself. ValidateState returns a database batch if the validation was a success
// otherwise nil and an error is returned.
func (v *BlockValidator) ValidateState(block, parent *types.Block, statedb *state.StateDB, receipts types.Receipts, usedGas *big.Int) (err error) {
    header := block.Header()
    if block.GasUsed().Cmp(usedGas) != 0 {
        return ValidationError(fmt.Sprintf("gas used error (%v / %v)", block.GasUsed(), usedGas))
    }
    // Validate the received block's bloom with the one derived from the generated receipts.
    // For valid blocks this should always validate to true.
    rbloom := types.CreateBloom(receipts)
    if rbloom != header.Bloom {
        return fmt.Errorf("unable to replicate block's bloom=%x vs calculated bloom=%x", header.Bloom, rbloom)
    }
    // Tre receipt Trie's root (R = (Tr [[H1, R1], ... [Hn, R1]]))
    receiptSha := types.DeriveSha(receipts)
    if receiptSha != header.ReceiptHash {
        return fmt.Errorf("invalid receipt root hash. received=%x calculated=%x", header.ReceiptHash, receiptSha)
    }
    // Validate the state root against the received state root and throw
    // an error if they don't match.
    if root := statedb.IntermediateRoot(); header.Root != root {
        return fmt.Errorf("invalid merkle root: header=%x computed=%x", header.Root, root)
    }
    return nil
}

// VerifyUncles verifies the given block's uncles and applies the Ethereum
// consensus rules to the various block headers included; it will return an
// error if any of the included uncle headers were invalid. It returns an error
// if the validation failed.
func (v *BlockValidator) VerifyUncles(block, parent *types.Block) error {
    // validate that there at most 2 uncles included in this block
    if len(block.Uncles()) > 2 {
        return ValidationError("Block can only contain maximum 2 uncles (contained %v)", len(block.Uncles()))
    }

    uncles := set.New()
    ancestors := make(map[common.Hash]*types.Block)
    for _, ancestor := range v.bc.GetBlocksFromHash(block.ParentHash(), 7) {
        ancestors[ancestor.Hash()] = ancestor
        // Include ancestors uncles in the uncle set. Uncles must be unique.
        for _, uncle := range ancestor.Uncles() {
            uncles.Add(uncle.Hash())
        }
    }
    ancestors[block.Hash()] = block
    uncles.Add(block.Hash())

    for i, uncle := range block.Uncles() {
        hash := uncle.Hash()
        if uncles.Has(hash) {
            // Error not unique
            return UncleError("uncle[%d](%x) not unique", i, hash[:4])
        }
        uncles.Add(hash)

        if ancestors[hash] != nil {
            branch := fmt.Sprintf("  O - %x\n  |\n", block.Hash())
            for h := range ancestors {
                branch += fmt.Sprintf("  O - %x\n  |\n", h)
            }
            glog.Infoln(branch)
            return UncleError("uncle[%d](%x) is ancestor", i, hash[:4])
        }

        if ancestors[uncle.ParentHash] == nil || uncle.ParentHash == parent.Hash() {
            return UncleError("uncle[%d](%x)'s parent is not ancestor (%x)", i, hash[:4], uncle.ParentHash[0:4])
        }

        if err := ValidateHeader(v.Pow, uncle, ancestors[uncle.ParentHash].Header(), true, true); err != nil {
            return ValidationError(fmt.Sprintf("uncle[%d](%x) header invalid: %v", i, hash[:4], err))
        }
    }

    return nil
}

// ValidateHeader validates the given header and, depending on the pow arg,
// checks the proof of work of the given header. Returns an error if the
// validation failed.
func (v *BlockValidator) ValidateHeader(header, parent *types.Header, checkPow bool) error {
    // Short circuit if the parent is missing.
    if parent == nil {
        return ParentError(header.ParentHash)
    }
    // Short circuit if the header's already known or its parent missing
    if v.bc.HasHeader(header.Hash()) {
        return nil
    }
    return ValidateHeader(v.Pow, header, parent, checkPow, false)
}

// Validates a header. Returns an error if the header is invalid.
//
// See YP section 4.3.4. "Block Header Validity"
func ValidateHeader(pow pow.PoW, header *types.Header, parent *types.Header, checkPow, uncle bool) error {
    if big.NewInt(int64(len(header.Extra))).Cmp(params.MaximumExtraDataSize) == 1 {
        return fmt.Errorf("Header extra data too long (%d)", len(header.Extra))
    }

    if uncle {
        if header.Time.Cmp(common.MaxBig) == 1 {
            return BlockTSTooBigErr
        }
    } else {
        if header.Time.Cmp(big.NewInt(time.Now().Unix())) == 1 {
            return BlockFutureErr
        }
    }
    if header.Time.Cmp(parent.Time) != 1 {
        return BlockEqualTSErr
    }

    expd := CalcDifficulty(header.Time.Uint64(), parent.Time.Uint64(), parent.Number, parent.Difficulty)
    if expd.Cmp(header.Difficulty) != 0 {
        return fmt.Errorf("Difficulty check failed for header %v, %v", header.Difficulty, expd)
    }

    a := new(big.Int).Set(parent.GasLimit)
    a = a.Sub(a, header.GasLimit)
    a.Abs(a)
    b := new(big.Int).Set(parent.GasLimit)
    b = b.Div(b, params.GasLimitBoundDivisor)
    if !(a.Cmp(b) < 0) || (header.GasLimit.Cmp(params.MinGasLimit) == -1) {
        return fmt.Errorf("GasLimit check failed for header %v (%v > %v)", header.GasLimit, a, b)
    }

    num := new(big.Int).Set(parent.Number)
    num.Sub(header.Number, num)
    if num.Cmp(big.NewInt(1)) != 0 {
        return BlockNumberErr
    }

    if checkPow {
        // Verify the nonce of the header. Return an error if it's not valid
        if !pow.Verify(types.NewBlockWithHeader(header)) {
            return &BlockNonceErr{header.Number, header.Hash(), header.Nonce.Uint64()}
        }
    }
    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.
func CalcDifficulty(time, parentTime uint64, parentNumber, parentDiff *big.Int) *big.Int {
    if params.IsHomestead(new(big.Int).Add(parentNumber, common.Big1)) {
        return calcDifficultyHomestead(time, parentTime, parentNumber, parentDiff)
    } else {
        return calcDifficultyFrontier(time, parentTime, parentNumber, parentDiff)
    }
}

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 = 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
}

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 = 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 = common.BigMax(diff, params.MinimumDifficulty)
    }

    return diff
}

// CalcGasLimit computes the gas limit of the next block after parent.
// The result may be modified by the caller.
// This is miner strategy, not consensus protocol.
func CalcGasLimit(parent *types.Block) *big.Int {
    // contrib = (parentGasUsed * 3 / 2) / 1024
    contrib := new(big.Int).Mul(parent.GasUsed(), big.NewInt(3))
    contrib = contrib.Div(contrib, big.NewInt(2))
    contrib = contrib.Div(contrib, params.GasLimitBoundDivisor)

    // decay = parentGasLimit / 1024 -1
    decay := new(big.Int).Div(parent.GasLimit(), params.GasLimitBoundDivisor)
    decay.Sub(decay, big.NewInt(1))

    /*
        strategy: gasLimit of block-to-mine is set based on parent's
        gasUsed value.  if parentGasUsed > parentGasLimit * (2/3) then we
        increase it, otherwise lower it (or leave it unchanged if it's right
        at that usage) the amount increased/decreased depends on how far away
        from parentGasLimit * (2/3) parentGasUsed is.
    */
    gl := new(big.Int).Sub(parent.GasLimit(), decay)
    gl = gl.Add(gl, contrib)
    gl.Set(common.BigMax(gl, params.MinGasLimit))

    // however, if we're now below the target (GenesisGasLimit) we increase the
    // limit as much as we can (parentGasLimit / 1024 -1)
    if gl.Cmp(params.GenesisGasLimit) < 0 {
        gl.Add(parent.GasLimit(), decay)
        gl.Set(common.BigMin(gl, params.GenesisGasLimit))
    }
    return gl
}