Skip to content
Permalink
671094279e
Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?
Go to file
 
 
Cannot retrieve contributors at this time
108 lines (99 sloc) 4.13 KB
// Copyright 2021 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 (
crand "crypto/rand"
"errors"
"math/big"
mrand "math/rand"
"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/log"
"github.com/ethereum/go-ethereum/params"
)
// ChainReader defines a small collection of methods needed to access the local
// blockchain during header verification. It's implemented by both blockchain
// and lightchain.
type ChainReader interface {
// Config retrieves the header chain's chain configuration.
Config() *params.ChainConfig
// GetTd returns the total difficulty of a local block.
GetTd(common.Hash, uint64) *big.Int
}
// ForkChoice is the fork chooser based on the highest total difficulty of the
// chain(the fork choice used in the eth1) and the external fork choice (the fork
// choice used in the eth2). This main goal of this ForkChoice is not only for
// offering fork choice during the eth1/2 merge phase, but also keep the compatibility
// for all other proof-of-work networks.
type ForkChoice struct {
chain ChainReader
rand *mrand.Rand
// preserve is a helper function used in td fork choice.
// Miners will prefer to choose the local mined block if the
// local td is equal to the extern one. It can be nil for light
// client
preserve func(header *types.Header) bool
}
func NewForkChoice(chainReader ChainReader, preserve func(header *types.Header) bool) *ForkChoice {
// Seed a fast but crypto originating random generator
seed, err := crand.Int(crand.Reader, big.NewInt(math.MaxInt64))
if err != nil {
log.Crit("Failed to initialize random seed", "err", err)
}
return &ForkChoice{
chain: chainReader,
rand: mrand.New(mrand.NewSource(seed.Int64())),
preserve: preserve,
}
}
// ReorgNeeded returns whether the reorg should be applied
// based on the given external header and local canonical chain.
// In the td mode, the new head is chosen if the corresponding
// total difficulty is higher. In the extern mode, the trusted
// header is always selected as the head.
func (f *ForkChoice) ReorgNeeded(current *types.Header, header *types.Header) (bool, error) {
var (
localTD = f.chain.GetTd(current.Hash(), current.Number.Uint64())
externTd = f.chain.GetTd(header.Hash(), header.Number.Uint64())
)
if localTD == nil || externTd == nil {
return false, errors.New("missing td")
}
// Accept the new header as the chain head if the transition
// is already triggered. We assume all the headers after the
// transition come from the trusted consensus layer.
if ttd := f.chain.Config().TerminalTotalDifficulty; ttd != nil && ttd.Cmp(externTd) <= 0 {
return true, nil
}
// If the total difficulty is higher than our known, add it to the canonical chain
// Second clause in the if statement reduces the vulnerability to selfish mining.
// Please refer to http://www.cs.cornell.edu/~ie53/publications/btcProcFC.pdf
reorg := externTd.Cmp(localTD) > 0
if !reorg && externTd.Cmp(localTD) == 0 {
number, headNumber := header.Number.Uint64(), current.Number.Uint64()
if number < headNumber {
reorg = true
} else if number == headNumber {
var currentPreserve, externPreserve bool
if f.preserve != nil {
currentPreserve, externPreserve = f.preserve(current), f.preserve(header)
}
reorg = !currentPreserve && (externPreserve || f.rand.Float64() < 0.5)
}
}
return reorg, nil
}