path: root/core/headerchain.go

// Copyright 2015 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"
	"fmt"
	"math"
	"math/big"
	mrand "math/rand"
	"sync/atomic"
	"time"

	"github.com/ava-labs/coreth/consensus"
	"github.com/ava-labs/coreth/core/rawdb"
	"github.com/ava-labs/coreth/core/types"
	"github.com/ava-labs/coreth/params"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/log"
	lru "github.com/hashicorp/golang-lru"
)

const (
	headerCacheLimit = 512
	tdCacheLimit     = 1024
	numberCacheLimit = 2048
)

// HeaderChain implements the basic block header chain logic that is shared by
// core.BlockChain and light.LightChain. It is not usable in itself, only as
// a part of either structure.
//
// HeaderChain is responsible for maintaining the header chain including the
// header query and updating.
//
// The components maintained by headerchain includes: (1) total difficult
// (2) header (3) block hash -> number mapping (4) canonical number -> hash mapping
// and (5) head header flag.
//
// It is not thread safe either, the encapsulating chain structures should do
// the necessary mutex locking/unlocking.
type HeaderChain struct {
	config *params.ChainConfig

	chainDb       ethdb.Database
	genesisHeader *types.Header

	currentHeader     atomic.Value // Current head of the header chain (may be above the block chain!)
	currentHeaderHash common.Hash  // Hash of the current head of the header chain (prevent recomputing all the time)

	headerCache *lru.Cache // Cache for the most recent block headers
	tdCache     *lru.Cache // Cache for the most recent block total difficulties
	numberCache *lru.Cache // Cache for the most recent block numbers

	procInterrupt func() bool

	rand   *mrand.Rand
	engine consensus.Engine
}

// NewHeaderChain creates a new HeaderChain structure. ProcInterrupt points
// to the parent's interrupt semaphore.
func NewHeaderChain(chainDb ethdb.Database, config *params.ChainConfig, engine consensus.Engine, procInterrupt func() bool) (*HeaderChain, error) {
	headerCache, _ := lru.New(headerCacheLimit)
	tdCache, _ := lru.New(tdCacheLimit)
	numberCache, _ := lru.New(numberCacheLimit)

	// Seed a fast but crypto originating random generator
	seed, err := crand.Int(crand.Reader, big.NewInt(math.MaxInt64))
	if err != nil {
		return nil, err
	}

	hc := &HeaderChain{
		config:        config,
		chainDb:       chainDb,
		headerCache:   headerCache,
		tdCache:       tdCache,
		numberCache:   numberCache,
		procInterrupt: procInterrupt,
		rand:          mrand.New(mrand.NewSource(seed.Int64())),
		engine:        engine,
	}

	hc.genesisHeader = hc.GetHeaderByNumber(0)
	if hc.genesisHeader == nil {
		return nil, ErrNoGenesis
	}

	hc.currentHeader.Store(hc.genesisHeader)
	if head := rawdb.ReadHeadBlockHash(chainDb); head != (common.Hash{}) {
		if chead := hc.GetHeaderByHash(head); chead != nil {
			hc.currentHeader.Store(chead)
		}
	}
	hc.currentHeaderHash = hc.CurrentHeader().Hash()
	headHeaderGauge.Update(hc.CurrentHeader().Number.Int64())

	return hc, nil
}

// GetBlockNumber retrieves the block number belonging to the given hash
// from the cache or database
func (hc *HeaderChain) GetBlockNumber(hash common.Hash) *uint64 {
	if cached, ok := hc.numberCache.Get(hash); ok {
		number := cached.(uint64)
		return &number
	}
	number := rawdb.ReadHeaderNumber(hc.chainDb, hash)
	if number != nil {
		hc.numberCache.Add(hash, *number)
	}
	return number
}

// WriteHeader writes a header into the local chain, given that its parent is
// already known. If the total difficulty of the newly inserted header becomes
// greater than the current known TD, the canonical chain is re-routed.
//
// Note: This method is not concurrent-safe with inserting blocks simultaneously
// into the chain, as side effects caused by reorganisations cannot be emulated
// without the real blocks. Hence, writing headers directly should only be done
// in two scenarios: pure-header mode of operation (light clients), or properly
// separated header/block phases (non-archive clients).
func (hc *HeaderChain) WriteHeader(header *types.Header) (status WriteStatus, err error) {
	// Cache some values to prevent constant recalculation
	var (
		hash   = header.Hash()
		number = header.Number.Uint64()
	)
	// Calculate the total difficulty of the header
	ptd := hc.GetTd(header.ParentHash, number-1)
	if ptd == nil {
		return NonStatTy, consensus.ErrUnknownAncestor
	}
	head := hc.CurrentHeader().Number.Uint64()
	localTd := hc.GetTd(hc.currentHeaderHash, head)
	externTd := new(big.Int).Add(header.Difficulty, ptd)

	// Irrelevant of the canonical status, write the td and header to the database
	//
	// Note all the components of header(td, hash->number index and header) should
	// be written atomically.
	headerBatch := hc.chainDb.NewBatch()
	rawdb.WriteTd(headerBatch, hash, number, externTd)
	rawdb.WriteHeader(headerBatch, header)
	if err := headerBatch.Write(); err != nil {
		log.Crit("Failed to write header into disk", "err", err)
	}
	// 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 {
		if header.Number.Uint64() < head {
			reorg = true
		} else if header.Number.Uint64() == head {
			reorg = mrand.Float64() < 0.5
		}
	}
	if reorg {
		// If the header can be added into canonical chain, adjust the
		// header chain markers(canonical indexes and head header flag).
		//
		// Note all markers should be written atomically.

		// Delete any canonical number assignments above the new head
		markerBatch := hc.chainDb.NewBatch()
		for i := number + 1; ; i++ {
			hash := rawdb.ReadCanonicalHash(hc.chainDb, i)
			if hash == (common.Hash{}) {
				break
			}
			rawdb.DeleteCanonicalHash(markerBatch, i)
		}

		// Overwrite any stale canonical number assignments
		var (
			headHash   = header.ParentHash
			headNumber = header.Number.Uint64() - 1
			headHeader = hc.GetHeader(headHash, headNumber)
		)
		for rawdb.ReadCanonicalHash(hc.chainDb, headNumber) != headHash {
			rawdb.WriteCanonicalHash(markerBatch, headHash, headNumber)

			headHash = headHeader.ParentHash
			headNumber = headHeader.Number.Uint64() - 1
			headHeader = hc.GetHeader(headHash, headNumber)
		}
		// Extend the canonical chain with the new header
		rawdb.WriteCanonicalHash(markerBatch, hash, number)
		rawdb.WriteHeadHeaderHash(markerBatch, hash)
		if err := markerBatch.Write(); err != nil {
			log.Crit("Failed to write header markers into disk", "err", err)
		}
		// Last step update all in-memory head header markers
		hc.currentHeaderHash = hash
		hc.currentHeader.Store(types.CopyHeader(header))
		headHeaderGauge.Update(header.Number.Int64())

		status = CanonStatTy
	} else {
		status = SideStatTy
	}
	hc.tdCache.Add(hash, externTd)
	hc.headerCache.Add(hash, header)
	hc.numberCache.Add(hash, number)
	return
}

// WhCallback is a callback function for inserting individual headers.
// A callback is used for two reasons: first, in a LightChain, status should be
// processed and light chain events sent, while in a BlockChain this is not
// necessary since chain events are sent after inserting blocks. Second, the
// header writes should be protected by the parent chain mutex individually.
type WhCallback func(*