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108 lines
4.1 KiB
108 lines
4.1 KiB
// Copyright 2021 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package core
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import (
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crand "crypto/rand"
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"errors"
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"math/big"
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mrand "math/rand"
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"github.com/ethereum/go-ethereum/common"
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"github.com/ethereum/go-ethereum/common/math"
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"github.com/ethereum/go-ethereum/core/types"
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"github.com/ethereum/go-ethereum/log"
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"github.com/ethereum/go-ethereum/params"
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)
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// ChainReader defines a small collection of methods needed to access the local
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// blockchain during header verification. It's implemented by both blockchain
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// and lightchain.
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type ChainReader interface {
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// Config retrieves the header chain's chain configuration.
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Config() *params.ChainConfig
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// GetTd returns the total difficulty of a local block.
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GetTd(common.Hash, uint64) *big.Int
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}
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// ForkChoice is the fork chooser based on the highest total difficulty of the
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// chain(the fork choice used in the eth1) and the external fork choice (the fork
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// choice used in the eth2). This main goal of this ForkChoice is not only for
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// offering fork choice during the eth1/2 merge phase, but also keep the compatibility
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// for all other proof-of-work networks.
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type ForkChoice struct {
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chain ChainReader
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rand *mrand.Rand
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// preserve is a helper function used in td fork choice.
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// Miners will prefer to choose the local mined block if the
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// local td is equal to the extern one. It can be nil for light
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// client
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preserve func(header *types.Header) bool
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}
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func NewForkChoice(chainReader ChainReader, preserve func(header *types.Header) bool) *ForkChoice {
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// Seed a fast but crypto originating random generator
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seed, err := crand.Int(crand.Reader, big.NewInt(math.MaxInt64))
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if err != nil {
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log.Crit("Failed to initialize random seed", "err", err)
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}
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return &ForkChoice{
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chain: chainReader,
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rand: mrand.New(mrand.NewSource(seed.Int64())),
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preserve: preserve,
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}
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}
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// ReorgNeeded returns whether the reorg should be applied
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// based on the given external header and local canonical chain.
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// In the td mode, the new head is chosen if the corresponding
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// total difficulty is higher. In the extern mode, the trusted
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// header is always selected as the head.
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func (f *ForkChoice) ReorgNeeded(current *types.Header, header *types.Header) (bool, error) {
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var (
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localTD = f.chain.GetTd(current.Hash(), current.Number.Uint64())
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externTd = f.chain.GetTd(header.Hash(), header.Number.Uint64())
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)
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if localTD == nil || externTd == nil {
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return false, errors.New("missing td")
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}
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// Accept the new header as the chain head if the transition
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// is already triggered. We assume all the headers after the
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// transition come from the trusted consensus layer.
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if ttd := f.chain.Config().TerminalTotalDifficulty; ttd != nil && ttd.Cmp(externTd) <= 0 {
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return true, nil
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}
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// If the total difficulty is higher than our known, add it to the canonical chain
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// Second clause in the if statement reduces the vulnerability to selfish mining.
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// Please refer to http://www.cs.cornell.edu/~ie53/publications/btcProcFC.pdf
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reorg := externTd.Cmp(localTD) > 0
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if !reorg && externTd.Cmp(localTD) == 0 {
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number, headNumber := header.Number.Uint64(), current.Number.Uint64()
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if number < headNumber {
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reorg = true
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} else if number == headNumber {
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var currentPreserve, externPreserve bool
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if f.preserve != nil {
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currentPreserve, externPreserve = f.preserve(current), f.preserve(header)
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}
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reorg = !currentPreserve && (externPreserve || f.rand.Float64() < 0.5)
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}
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}
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return reorg, nil
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}
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