blockchain.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 implements the Ethereum consensus protocol.
package core

import (
	"errors"
	"fmt"
	"io"
	"math"
	"math/big"
	mrand "math/rand"
	"sort"
	"sync"
	"sync/atomic"
	"time"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/mclock"
	"github.com/ethereum/go-ethereum/common/prque"
	"github.com/ethereum/go-ethereum/consensus"
	"github.com/ethereum/go-ethereum/consensus/istanbul"
	"github.com/ethereum/go-ethereum/core/rawdb"
	"github.com/ethereum/go-ethereum/core/state"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/core/vm"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/event"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/metrics"
	"github.com/ethereum/go-ethereum/params"
	"github.com/ethereum/go-ethereum/rlp"
	"github.com/ethereum/go-ethereum/trie"
	lru "github.com/hashicorp/golang-lru"
)

var (
	headBlockGauge     = metrics.NewRegisteredGauge("chain/head/block", nil)
	headHeaderGauge    = metrics.NewRegisteredGauge("chain/head/header", nil)
	headFastBlockGauge = metrics.NewRegisteredGauge("chain/head/receipt", nil)

	accountReadTimer   = metrics.NewRegisteredTimer("chain/account/reads", nil)
	accountHashTimer   = metrics.NewRegisteredTimer("chain/account/hashes", nil)
	accountUpdateTimer = metrics.NewRegisteredTimer("chain/account/updates", nil)
	accountCommitTimer = metrics.NewRegisteredTimer("chain/account/commits", nil)

	storageReadTimer   = metrics.NewRegisteredTimer("chain/storage/reads", nil)
	storageHashTimer   = metrics.NewRegisteredTimer("chain/storage/hashes", nil)
	storageUpdateTimer = metrics.NewRegisteredTimer("chain/storage/updates", nil)
	storageCommitTimer = metrics.NewRegisteredTimer("chain/storage/commits", nil)

	blockInsertTimer     = metrics.NewRegisteredTimer("chain/inserts", nil)
	blockValidationTimer = metrics.NewRegisteredTimer("chain/validation", nil)
	blockExecutionTimer  = metrics.NewRegisteredTimer("chain/execution", nil)
	blockWriteTimer      = metrics.NewRegisteredTimer("chain/write", nil)
	blockReorgAddMeter   = metrics.NewRegisteredMeter("chain/reorg/drop", nil)
	blockReorgDropMeter  = metrics.NewRegisteredMeter("chain/reorg/add", nil)

	blockPrefetchExecuteTimer   = metrics.NewRegisteredTimer("chain/prefetch/executes", nil)
	blockPrefetchInterruptMeter = metrics.NewRegisteredMeter("chain/prefetch/interrupts", nil)

	errInsertionInterrupted = errors.New("insertion is interrupted")
)

const (
	bodyCacheLimit      = 256
	blockCacheLimit     = 256
	receiptsCacheLimit  = 32
	txLookupCacheLimit  = 1024
	maxFutureBlocks     = 256
	maxTimeFutureBlocks = 30
	badBlockLimit       = 10
	TriesInMemory       = 128

	// BlockChainVersion ensures that an incompatible database forces a resync from scratch.
	//
	// Changelog:
	//
	// - Version 4
	//   The following incompatible database changes were added:
	//   * the `BlockNumber`, `TxHash`, `TxIndex`, `BlockHash` and `Index` fields of log are deleted
	//   * the `Bloom` field of receipt is deleted
	//   * the `BlockIndex` and `TxIndex` fields of txlookup are deleted
	// - Version 5
	//  The following incompatible database changes were added:
	//    * the `TxHash`, `GasCost`, and `ContractAddress` fields are no longer stored for a receipt
	//    * the `TxHash`, `GasCost`, and `ContractAddress` fields are computed by looking up the
	//      receipts' corresponding block
	// - Version 6
	//  The following incompatible database changes were added:
	//    * Transaction lookup information stores the corresponding block number instead of block hash
	// - Version 7
	//  The following incompatible database changes were added:
	//    * Use freezer as the ancient database to maintain all ancient data
	BlockChainVersion uint64 = 7
)

// CacheConfig contains the configuration values for the trie caching/pruning
// that's resident in a blockchain.
type CacheConfig struct {
	TrieCleanLimit      int           // Memory allowance (MB) to use for caching trie nodes in memory
	TrieCleanNoPrefetch bool          // Whether to disable heuristic state prefetching for followup blocks
	TrieDirtyLimit      int           // Memory limit (MB) at which to start flushing dirty trie nodes to disk
	TrieDirtyDisabled   bool          // Whether to disable trie write caching and GC altogether (archive node)
	TrieTimeLimit       time.Duration // Time limit after which to flush the current in-memory trie to disk
}

// BlockChain represents the canonical chain given a database with a genesis
// block. The Blockchain manages chain imports, reverts, chain reorganisations.
//
// Importing blocks in to the block chain happens according to the set of rules
// defined by the two stage Validator. Processing of blocks is done using the
// Processor which processes the included transaction. The validation of the state
// is done in the second part of the Validator. Failing results in aborting of
// the import.
//
// The BlockChain also helps in returning blocks from **any** chain included
// in the database as well as blocks that represents the canonical chain. It's
// important to note that GetBlock can return any block and does not need to be
// included in the canonical one where as GetBlockByNumber always represents the
// canonical chain.
type BlockChain struct {
	chainConfig *params.ChainConfig // Chain & network configuration
	cacheConfig *CacheConfig        // Cache configuration for pruning

	db     ethdb.Database // Low level persistent database to store final content in
	triegc *prque.Prque   // Priority queue mapping block numbers to tries to gc
	gcproc time.Duration  // Accumulates canonical block processing for trie dumping

	hc            *HeaderChain
	rmLogsFeed    event.Feed
	chainFeed     event.Feed
	chainSideFeed event.Feed
	chainHeadFeed event.Feed
	logsFeed      event.Feed
	blockProcFeed event.Feed
	scope         event.SubscriptionScope
	genesisBlock  *types.Block

	chainmu sync.RWMutex // blockchain insertion lock

	currentBlock     atomic.Value // Current head of the block chain
	currentFastBlock atomic.Value // Current head of the fast-sync chain (may be above the block chain!)

	stateCache    state.Database // State database to reuse between imports (contains state cache)
	bodyCache     *lru.Cache     // Cache for the most recent block bodies
	bodyRLPCache  *lru.Cache     // Cache for the most recent block bodies in RLP encoded format
	receiptsCache *lru.Cache     // Cache for the most recent receipts per block
	blockCache    *lru.Cache     // Cache for the most recent entire blocks
	txLookupCache *lru.Cache     // Cache for the most recent transaction lookup data.
	futureBlocks  *lru.Cache     // future blocks are blocks added for later processing

	quit    chan struct{} // blockchain quit channel
	running int32         // running must be called atomically
	// procInterrupt must be atomically called
	procInterrupt int32          // interrupt signaler for block processing
	wg            sync.WaitGroup // chain processing wait group for shutting down

	engine     consensus.Engine
	validator  Validator  // Block and state validator interface
	prefetcher Prefetcher // Block state prefetcher interface
	processor  Processor  // Block transaction processor interface
	vmConfig   vm.Config

	badBlocks       *lru.Cache                     // Bad block cache
	shouldPreserve  func(*types.Block) bool        // Function used to determine whether should preserve the given block.
	terminateInsert func(common.Hash, uint64) bool // Testing hook used to terminate ancient receipt chain insertion.
}

// NewBlockChain returns a fully initialised block chain using information
// available in the database. It initialises the default Ethereum Validator and
// Processor.
func NewBlockChain(db ethdb.Database, cacheConfig *CacheConfig, chainConfig *params.ChainConfig, engine consensus.Engine, vmConfig vm.Config, shouldPreserve func(block *types.Block) bool) (*BlockChain, error) {
	if cacheConfig == nil {
		cacheConfig = &CacheConfig{
			TrieCleanLimit: 256,
			TrieDirtyLimit: 256,
			TrieTimeLimit:  5 * time.Minute,
		}
	}
	bodyCache, _ := lru.New(bodyCacheLimit)
	bodyRLPCache, _ := lru.New(bodyCacheLimit)
	receiptsCache, _ := lru.New(receiptsCacheLimit)
	blockCache, _ := lru.New(blockCacheLimit)
	txLookupCache, _ := lru.New(txLookupCacheLimit)
	futureBlocks, _ := lru.New(maxFutureBlocks)
	badBlocks, _ := lru.New(badBlockLimit)

	bc := &BlockChain{
		chainConfig:    chainConfig,
		cacheConfig:    cacheConfig,
		db:             db,
		triegc:         prque.New(nil),
		stateCache:     state.NewDatabaseWithCache(db, cacheConfig.TrieCleanLimit),
		quit:           make(chan struct{}),
		shouldPreserve: shouldPreserve,
		bodyCache:      bodyCache,
		bodyRLPCache:   bodyRLPCache,
		receiptsCache:  receiptsCache,
		blockCache:     blockCache,
		txLookupCache:  txLookupCache,
		futureBlocks:   futureBlocks,
		engine:         engine,
		vmConfig:       vmConfig,
		badBlocks:      badBlocks,
	}
	bc.validator = NewBlockValidator(chainConfig, bc, engine)
	bc.prefetcher = newStatePrefetcher(chainConfig, bc, engine)
	bc.processor = NewStateProcessor(chainConfig, bc, engine)

	var err error
	bc.hc, err = NewHeaderChain(db, chainConfig, engine, bc.getProcInterrupt)
	if err != nil {
		return nil, err
	}
	bc.genesisBlock = bc.GetBlockByNumber(0)
	if bc.genesisBlock == nil {
		return nil, ErrNoGenesis
	}

	var nilBlock *types.Block
	bc.currentBlock.Store(nilBlock)
	bc.currentFastBlock.Store(nilBlock)

	// Initialize the chain with ancient data if it isn't empty.
	if bc.empty() {
		rawdb.InitDatabaseFromFreezer(bc.db)
	}

	if err := bc.loadLastState(); err != nil {
		return nil, err
	}
	// The first thing the node will do is reconstruct the verification data for
	// the head block. Might as well do it in advance.
	bc.engine.VerifyHeader(bc, bc.CurrentHeader(), true)

	if frozen, err := bc.db.Ancients(); err == nil && frozen > 0 {
		var (
			needRewind bool
			low        uint64
		)
		// The head full block may be rolled back to a very low height due to
		// blockchain repair. If the head full block is even lower than the ancient
		// chain, truncate the ancient store.
		fullBlock := bc.CurrentBlock()
		if fullBlock != nil && fullBlock != bc.genesisBlock && fullBlock.NumberU64() < frozen-1 {
			needRewind = true
			low = fullBlock.NumberU64()
		}
		// In fast sync, it may happen that ancient data has been written to the
		// ancient store, but the LastFastBlock has not been updated, truncate the
		// extra data here.
		fastBlock := bc.CurrentFastBlock()
		if fastBlock != nil && fastBlock.NumberU64() < frozen-1 {
			needRewind = true
			if fastBlock.NumberU64() < low || low == 0 {
				low = fastBlock.NumberU64()
			}
		}
		if needRewind {
			var hashes []common.Hash
			previous := bc.CurrentHeader().Number.Uint64()
			for i := low + 1; i <= bc.CurrentHeader().Number.Uint64(); i++ {
				hashes = append(hashes, rawdb.ReadCanonicalHash(bc.db, i))
			}
			bc.Rollback(hashes, true)
			log.Warn("Truncate ancient chain", "from", previous, "to", low)
		}
	}
	// Check the current state of the block hashes and make sure that we do not have any of the bad blocks in our chain
	for hash := range BadHashes {
		if header := bc.GetHeaderByHash(hash); header != nil {
			// get the canonical block corresponding to the offending header's number
			headerByNumber := bc.GetHeaderByNumber(header.Number.Uint64())
			// make sure the headerByNumber (if present) is in our current canonical chain
			if headerByNumber != nil && headerByNumber.Hash() == header.Hash() {
				log.Error("Found bad hash, rewinding chain", "number", header.Number, "hash", header.ParentHash)
				bc.SetHead(header.Number.Uint64() - 1)
				log.Error("Chain rewind was successful, resuming normal operation")
			}
		}
	}
	// Take ownership of this particular state
	go bc.update()
	return bc, nil
}

func (bc *BlockChain) getProcInterrupt() bool {
	return atomic.LoadInt32(&bc.procInterrupt) == 1
}

// GetVMConfig returns the block chain VM config.
func (bc *BlockChain) GetVMConfig() *vm.Config {
	return &bc.vmConfig
}

// empty returns an indicator whether the blockchain is empty.
// Note, it's a special case that we connect a non-empty ancient
// database with an empty node, so that we can plugin the ancient
// into node seamlessly.
func (bc *BlockChain) empty() bool {
	genesis := bc.genesisBlock.Hash()
	for _, hash := range []common.Hash{rawdb.ReadHeadBlockHash(bc.db), rawdb.ReadHeadHeaderHash(bc.db), rawdb.ReadHeadFastBlockHash(bc.db)} {
		if hash != genesis {
			return false
		}
	}
	return true
}

// GetDatabase returns the block chain's database
func (bc *BlockChain) GetDatabase() ethdb.Database {
	return bc.db
}

// loadLastState loads the last known chain state from the database. This method
// assumes that the chain manager mutex is held.
func (bc *BlockChain) loadLastState() error {
	// Restore the last known head block
	head := rawdb.ReadHeadBlockHash(bc.db)
	if head == (common.Hash{}) {
		// Corrupt or empty database, init from scratch
		log.Warn("Empty database, resetting chain")
		return bc.Reset()
	}
	// Make sure the entire head block is available
	currentBlock := bc.GetBlockByHash(head)
	if currentBlock == nil {
		// Corrupt or empty database, init from scratch
		log.Warn("Head block missing, resetting chain", "hash", head)
		return bc.Reset()
	}
	// Make sure the state associated with the block is available
	if _, err := state.New(currentBlock.Root(), bc.stateCache); err != nil {
		// Dangling block without a state associated, init from scratch
		log.Warn("Head state missing, repairing chain", "number", currentBlock.Number(), "hash", currentBlock.Hash())
		if err := bc.repair(&currentBlock); err != nil {
			return err
		}
		rawdb.WriteHeadBlockHash(bc.db, currentBlock.Hash())
	}
	// Everything seems to be fine, set as the head block
	bc.currentBlock.Store(currentBlock)
	headBlockGauge.Update(int64(currentBlock.NumberU64()))

	// Restore the last known head header
	currentHeader := currentBlock.Header()
	if head := rawdb.ReadHeadHeaderHash(bc.db); head != (common.Hash{}) {
		if header := bc.GetHeaderByHash(head); header != nil {
			currentHeader = header
		}
	}
	log.Debug(fmt.Sprintf("Loading Last State: %v", currentHeader.Number))
	bc.hc.SetCurrentHeader(currentHeader)

	// Restore the last known head fast block
	bc.currentFastBlock.Store(currentBlock)
	headFastBlockGauge.Update(int64(currentBlock.NumberU64()))

	if head := rawdb.ReadHeadFastBlockHash(bc.db); head != (common.Hash{}) {
		if block := bc.GetBlockByHash(head); block != nil {
			bc.currentFastBlock.Store(block)
			headFastBlockGauge.Update(int64(block.NumberU64()))
		}
	}
	// Issue a status log for the user
	currentFastBlock := bc.CurrentFastBlock()

	headerTd := bc.GetTd(currentHeader.Hash(), currentHeader.Number.Uint64())
	blockTd := bc.GetTd(currentBlock.Hash(), currentBlock.NumberU64())
	fastTd := bc.GetTd(currentFastBlock.Hash(), currentFastBlock.NumberU64())

	log.Info("Loaded most recent local header", "number", currentHeader.Number, "hash", currentHeader.Hash(), "td", headerTd, "age", common.PrettyAge(time.Unix(int64(currentHeader.Time), 0)))
	log.Info("Loaded most recent local full block", "number", currentBlock.Number(), "hash", currentBlock.Hash(), "td", blockTd, "age", common.PrettyAge(time.Unix(int64(currentBlock.Time()), 0)))
	log.Info("Loaded most recent local fast block", "number", currentFastBlock.Number(), "hash", currentFastBlock.Hash(), "td", fastTd, "age", common.PrettyAge(time.Unix(int64(currentFastBlock.Time()), 0)))

	return nil
}

// SetHead rewinds the local chain to a new head. In the case of headers, everything
// above the new head will be deleted and the new one set. In the case of blocks
// though, the head may be further rewound if block bodies are missing (non-archive
// nodes after a fast sync).
func (bc *BlockChain) SetHead(head uint64) error {
	log.Warn("Rewinding blockchain", "target", head)

	bc.chainmu.Lock()
	defer bc.chainmu.Unlock()

	updateFn := func(db ethdb.KeyValueWriter, header *types.Header) {
		// Rewind the block chain, ensuring we don't end up with a stateless head block
		if currentBlock := bc.CurrentBlock(); currentBlock != nil && header.Number.Uint64() < currentBlock.NumberU64() {
			newHeadBlock := bc.GetBlock(header.Hash(), header.Number.Uint64())
			if newHeadBlock == nil {
				newHeadBlock = bc.genesisBlock
			} else {
				if _, err := state.New(newHeadBlock.Root(), bc.stateCache); err != nil {
					// Rewound state missing, rolled back to before pivot, reset to genesis
					newHeadBlock = bc.genesisBlock
				}
			}
			rawdb.WriteHeadBlockHash(db, newHeadBlock.Hash())
			bc.currentBlock.Store(newHeadBlock)
			headBlockGauge.Update(int64(newHeadBlock.NumberU64()))
		}

		// Rewind the fast block in a simpleton way to the target head
		if currentFastBlock := bc.CurrentFastBlock(); currentFastBlock != nil && header.Number.Uint64() < currentFastBlock.NumberU64() {
			newHeadFastBlock := bc.GetBlock(header.Hash(), header.Number.Uint64())
			// If either blocks reached nil, reset to the genesis state
			if newHeadFastBlock == nil {
				newHeadFastBlock = bc.genesisBlock
			}
			rawdb.WriteHeadFastBlockHash(db, newHeadFastBlock.Hash())
			bc.currentFastBlock.Store(newHeadFastBlock)
			headFastBlockGauge.Update(int64(newHeadFastBlock.NumberU64()))
		}
	}

	// Rewind the header chain, deleting all block bodies until then
	delFn := func(db ethdb.KeyValueWriter, hash common.Hash, num uint64) {
		// Ignore the error here since light client won't hit this path
		frozen, _ := bc.db.Ancients()
		if num+1 <= frozen {
			// Truncate all relative data(header, total difficulty, body, receipt
			// and canonical hash) from ancient store.
			if err := bc.db.TruncateAncients(num + 1); err != nil {
				log.Crit("Failed to truncate ancient data", "number", num, "err", err)
			}

			// Remove the hash <-> number mapping from the active store.
			rawdb.DeleteHeaderNumber(db, hash)
		} else {
			// Remove relative body and receipts from the active store.
			// The header, total difficulty and canonical hash will be
			// removed in the hc.SetHead function.
			rawdb.DeleteBody(db, hash, num)
			rawdb.DeleteReceipts(db, hash, num)
		}
		// Todo(rjl493456442) txlookup, bloombits, etc
	}
	bc.hc.SetHead(head, updateFn, delFn)

	// Clear out any stale content from the caches
	bc.bodyCache.Purge()
	bc.bodyRLPCache.Purge()
	bc.receiptsCache.Purge()
	bc.blockCache.Purge()
	bc.txLookupCache.Purge()
	bc.futureBlocks.Purge()

	return bc.loadLastState()
}

// FastSyncCommitHead sets the current head block to the one defined by the hash
// irrelevant what the chain contents were prior.
func (bc *BlockChain) FastSyncCommitHead(hash common.Hash) error {
	// Make sure that both the block as well at its state trie exists
	block := bc.GetBlockByHash(hash)
	if block == nil {
		return fmt.Errorf("non existent block [%x…]", hash[:4])
	}
	if _, err := trie.NewSecure(block.Root(), bc.stateCache.TrieDB()); err != nil {
		return err
	}
	// If all checks out, manually set the head block
	bc.chainmu.Lock()
	bc.currentBlock.Store(block)
	headBlockGauge.Update(int64(block.NumberU64()))
	bc.chainmu.Unlock()

	log.Info("Committed new head block", "number", block.Number(), "hash", hash)
	return nil
}

// CurrentBlock retrieves the current head block of the canonical chain. The
// block is retrieved from the blockchain's internal cache.
func (bc *BlockChain) CurrentBlock() *types.Block {
	return bc.currentBlock.Load().(*types.Block)
}

// CurrentFastBlock retrieves the current fast-sync head block of the canonical
// chain. The block is retrieved from the blockchain's internal cache.
func (bc *BlockChain) CurrentFastBlock() *types.Block {
	return bc.currentFastBlock.Load().(*types.Block)
}

// Validator returns the current validator.
func (bc *BlockChain) Validator() Validator {
	return bc.validator
}

// Processor returns the current processor.
func (bc *BlockChain) Processor() Processor {
	return bc.processor
}

// State returns a new mutable state based on the current HEAD block.
func (bc *BlockChain) State() (*state.StateDB, error) {
	return bc.StateAt(bc.CurrentBlock().Root())
}

// StateAt returns a new mutable state based on a particular point in time.
func (bc *BlockChain) StateAt(root common.Hash) (*state.StateDB, error) {
	return state.New(root, bc.stateCache)
}

// StateCache returns the caching database underpinning the blockchain instance.
func (bc *BlockChain) StateCache() state.Database {
	return bc.stateCache
}

// Reset purges the entire blockchain, restoring it to its genesis state.
func (bc *BlockChain) Reset() error {
	return bc.ResetWithGenesisBlock(bc.genesisBlock)
}

// ResetWithGenesisBlock purges the entire blockchain, restoring it to the
// specified genesis state.
func (bc *BlockChain) ResetWithGenesisBlock(genesis *types.Block) error {
	// Dump the entire block chain and purge the caches
	if err := bc.SetHead(0); err != nil {
		return err
	}
	bc.chainmu.Lock()
	defer bc.chainmu.Unlock()

	// Prepare the genesis block and reinitialise the chain
	if err := bc.hc.WriteTd(genesis.Hash(), genesis.NumberU64(), genesis.TotalDifficulty()); err != nil {
		log.Crit("Failed to write genesis block TD", "err", err)
	}
	rawdb.WriteBlock(bc.db, genesis)

	bc.genesisBlock = genesis
	bc.insert(bc.genesisBlock)
	bc.currentBlock.Store(bc.genesisBlock)
	headBlockGauge.Update(int64(bc.genesisBlock.NumberU64()))

	bc.hc.SetGenesis(bc.genesisBlock.Header())
	bc.hc.SetCurrentHeader(bc.genesisBlock.Header())
	bc.currentFastBlock.Store(bc.genesisBlock)
	headFastBlockGauge.Update(int64(bc.genesisBlock.NumberU64()))

	return nil
}

// repair tries to repair the current blockchain by rolling back the current block
// until one with associated state is found. This is needed to fix incomplete db
// writes caused either by crashes/power outages, or simply non-committed tries.
//
// This method only rolls back the current block. The current header and current
// fast block are left intact.
func (bc *BlockChain) repair(head **types.Block) error {
	for {
		// Abort if we've rewound to a head block that does have associated state
		if _, err := state.New((*head).Root(), bc.stateCache); err == nil {
			log.Info("Rewound blockchain to past state", "number", (*head).Number(), "hash", (*head).Hash())
			return nil
		}
		// Otherwise rewind one block and recheck state availability there
		block := bc.GetBlock((*head).ParentHash(), (*head).NumberU64()-1)
		if block == nil {
			return fmt.Errorf("missing block %d [%x]", (*head).NumberU64()-1, (*head).ParentHash())
		}
		*head = block
	}
}

// Export writes the active chain to the given writer.
func (bc *BlockChain) Export(w io.Writer) error {
	return bc.ExportN(w, uint64(0), bc.CurrentBlock().NumberU64())
}

// ExportN writes a subset of the active chain to the given writer.
func (bc *BlockChain) ExportN(w io.Writer, first uint64, last uint64) error {
	bc.chainmu.RLock()
	defer bc.chainmu.RUnlock()

	if first > last {
		return fmt.Errorf("export failed: first (%d) is greater than last (%d)", first, last)
	}
	log.Info("Exporting batch of blocks", "count", last-first+1)

	start, reported := time.Now(), time.Now()
	for nr := first; nr <= last; nr++ {
		block := bc.GetBlockByNumber(nr)
		if block == nil {
			return fmt.Errorf("export failed on #%d: not found", nr)
		}
		if err := block.EncodeRLP(w); err != nil {
			return err
		}
		if time.Since(reported) >= statsReportLimit {
			log.Info("Exporting blocks", "exported", block.NumberU64()-first, "elapsed", common.PrettyDuration(time.Since(start)))
			reported = time.Now()
		}
	}
	return nil
}

// insert injects a new head block into the current block chain. This method
// assumes that the block is indeed a true head. It will also reset the head
// header and the head fast sync block to this very same block if they are older
// or if they are on a different side chain.
//
// Note, this function assumes that the `mu` mutex is held!
func (bc *BlockChain) insert(block *types.Block) {
	log.Debug(fmt.Sprintf("Inserting %v", block.Number()))
	// If the block is on a side chain or an unknown one, force other heads onto it too
	updateHeads := rawdb.ReadCanonicalHash(bc.db, block.NumberU64()) != block.Hash()

	// Add the block to the canonical chain number scheme and mark as the head
	rawdb.WriteCanonicalHash(bc.db, block.Hash(), block.NumberU64())
	rawdb.WriteHeadBlockHash(bc.db, block.Hash())

	bc.currentBlock.Store(block)
	headBlockGauge.Update(int64(block.NumberU64()))

	// If the block is better than our head or is on a different chain, force update heads
	if updateHeads {
		bc.hc.SetCurrentHeader(block.Header())
		rawdb.WriteHeadFastBlockHash(bc.db, block.Hash())

		bc.currentFastBlock.Store(block)
		headFastBlockGauge.Update(int64(block.NumberU64()))
	}
}

// Genesis retrieves the chain's genesis block.
func (bc *BlockChain) Genesis() *types.Block {
	return bc.genesisBlock
}

// GetBody retrieves a block body (transactions) from the database by
// hash, caching it if found.
func (bc *BlockChain) GetBody(hash common.Hash) *types.Body {
	// Short circuit if the body's already in the cache, retrieve otherwise
	if cached, ok := bc.bodyCache.Get(hash); ok {
		body := cached.(*types.Body)
		return body
	}
	number := bc.hc.GetBlockNumber(hash)
	if number == nil {
		return nil
	}
	body := rawdb.ReadBody(bc.db, hash, *number)
	if body == nil {
		return nil
	}
	// Cache the found body for next time and return
	bc.bodyCache.Add(hash, body)
	return body
}

// GetBodyRLP retrieves a block body in RLP encoding from the database by hash,
// caching it if found.
func (bc *BlockChain) GetBodyRLP(hash common.Hash) rlp.RawValue {
	// Short circuit if the body's already in the cache, retrieve otherwise
	if cached, ok := bc.bodyRLPCache.Get(hash); ok {
		return cached.(rlp.RawValue)
	}
	number := bc.hc.GetBlockNumber(hash)
	if number == nil {
		return nil
	}
	body := rawdb.ReadBodyRLP(bc.db, hash, *number)
	if len(body) == 0 {
		return nil
	}
	// Cache the found body for next time and return
	bc.bodyRLPCache.Add(hash, body)
	return body
}

// HasBlock checks if a block is fully present in the database or not.
func (bc *BlockChain) HasBlock(hash common.Hash, number uint64) bool {
	if bc.blockCache.Contains(hash) {
		return true
	}
	return rawdb.HasBody(bc.db, hash, number)
}

// HasFastBlock checks if a fast block is fully present in the database or not.
func (bc *BlockChain) HasFastBlock(hash common.Hash, number uint64) bool {
	if !bc.HasBlock(hash, number) {
		return false
	}
	if bc.receiptsCache.Contains(hash) {
		return true
	}
	return rawdb.HasReceipts(bc.db, hash, number)
}

// HasState checks if state trie is fully present in the database or not.
func (bc *BlockChain) HasState(hash common.Hash) bool {
	_, err := bc.stateCache.OpenTrie(hash)
	return err == nil
}

// HasBlockAndState checks if a block and associated state trie is fully present
// in the database or not, caching it if present.
func (bc *BlockChain) HasBlockAndState(hash common.Hash, number uint64) bool {
	// Check first that the block itself is known
	block := bc.GetBlock(hash, number)
	if block == nil {
		return false
	}
	return bc.HasState(block.Root())
}

// GetBlock retrieves a block from the database by hash and number,
// caching it if found.
func (bc *BlockChain) GetBlock(hash common.Hash, number uint64) *types.Block {
	// Short circuit if the block's already in the cache, retrieve otherwise
	if block, ok := bc.blockCache.Get(hash); ok {
		return block.(*types.Block)
	}
	block := rawdb.ReadBlock(bc.db, hash, number)
	if block == nil {
		return nil
	}
	// Cache the found block for next time and return
	bc.blockCache.Add(block.Hash(), block)
	return block
}

// GetBlockByHash retrieves a block from the database by hash, caching it if found.
func (bc *BlockChain) GetBlockByHash(hash common.Hash) *types.Block {
	number := bc.hc.GetBlockNumber(hash)
	if number == nil {
		return nil
	}
	return bc.GetBlock(hash, *number)
}

// GetBlockByNumber retrieves a block from the database by number, caching it
// (associated with its hash) if found.
func (bc *BlockChain) GetBlockByNumber(number uint64) *types.Block {
	hash := rawdb.ReadCanonicalHash(bc.db, number)
	if hash == (common.Hash{}) {
		return nil
	}
	return bc.GetBlock(hash, number)
}

// GetReceiptsByHash retrieves the receipts for all transactions in a given block.
func (bc *BlockChain) GetReceiptsByHash(hash common.Hash) types.Receipts {
	if receipts, ok := bc.receiptsCache.Get(hash); ok {
		return receipts.(types.Receipts)
	}
	number := rawdb.ReadHeaderNumber(bc.db, hash)
	if number == nil {
		return nil
	}
	receipts := rawdb.ReadReceipts(bc.db, hash, *number, bc.chainConfig)
	if receipts == nil {
		return nil
	}
	bc.receiptsCache.Add(hash, receipts)
	return receipts
}

// GetBlocksFromHash returns the block corresponding to hash and up to n-1 ancestors.
// [deprecated by eth/62]
func (bc *BlockChain) GetBlocksFromHash(hash common.Hash, n int) (blocks []*types.Block) {
	number := bc.hc.GetBlockNumber(hash)
	if number == nil {
		return nil
	}
	for i := 0; i < n; i++ {
		block := bc.GetBlock(hash, *number)
		if block == nil {
			break
		}
		blocks = append(blocks, block)
		hash = block.ParentHash()
		*number--
	}
	return
}

// TrieNode retrieves a blob of data associated with a trie node (or code hash)
// either from ephemeral in-memory cache, or from persistent storage.
func (bc *BlockChain) TrieNode(hash common.Hash) ([]byte, error) {
	return bc.stateCache.TrieDB().Node(hash)
}

// Stop stops the blockchain service. If any imports are currently in progress
// it will abort them using the procInterrupt.
func (bc *BlockChain) Stop() {
	if !atomic.CompareAndSwapInt32(&bc.running, 0, 1) {
		return
	}
	// Unsubscribe all subscriptions registered from blockchain
	bc.scope.Close()
	close(bc.quit)
	atomic.StoreInt32(&bc.procInterrupt, 1)

	bc.wg.Wait()

	// Ensure the state of a recent block is also stored to disk before exiting.
	// We're writing three different states to catch different restart scenarios:
	//  - HEAD:     So we don't need to reprocess any blocks in the general case
	//  - HEAD-1:   So we don't do large reorgs if our HEAD becomes an uncle
	//  - HEAD-127: So we have a hard limit on the number of blocks reexecuted
	if !bc.cacheConfig.TrieDirtyDisabled {
		triedb := bc.stateCache.TrieDB()

		for _, offset := range []uint64{0, 1, TriesInMemory - 1} {
			if number := bc.CurrentBlock().NumberU64(); number > offset {
				recent := bc.GetBlockByNumber(number - offset)

				log.Info("Writing cached state to disk", "block", recent.Number(), "hash", recent.Hash(), "root", recent.Root())
				if err := triedb.Commit(recent.Root(), true); err != nil {
					log.Error("Failed to commit recent state trie", "err", err)
				}
			}
		}
		for !bc.triegc.Empty() {
			triedb.Dereference(bc.triegc.PopItem().(common.Hash))
		}
		if size, _ := triedb.Size(); size != 0 {
			log.Error("Dangling trie nodes after full cleanup")
		}
	}
	log.Info("Blockchain manager stopped")
}

func (bc *BlockChain) procFutureBlocks() {
	blocks := make([]*types.Block, 0, bc.futureBlocks.Len())
	for _, hash := range bc.futureBlocks.Keys() {
		if block, exist := bc.futureBlocks.Peek(hash); exist {
			blocks = append(blocks, block.(*types.Block))
		}
	}
	if len(blocks) > 0 {
		sort.Slice(blocks, func(i, j int) bool {
			return blocks[i].NumberU64() < blocks[j].NumberU64()
		})
		// Insert one by one as chain insertion needs contiguous ancestry between blocks
		for i := range blocks {
			bc.InsertChain(blocks[i : i+1])
		}
	}
}

// WriteStatus status of write
type WriteStatus byte

const (
	NonStatTy WriteStatus = iota
	CanonStatTy
	SideStatTy
)

// Rollback is designed to remove a chain of links from the database that aren't
// certain enough to be valid.
func (bc *BlockChain) Rollback(chain []common.Hash, fullHeaderChainAvailable bool) {
	bc.chainmu.Lock()
	defer bc.chainmu.Unlock()

	for i := len(chain) - 1; i >= 0; i-- {
		hash := chain[i]

		currentHeader := bc.hc.CurrentHeader()
		if currentHeader.Hash() == hash {
			bc.hc.SetCurrentHeader(bc.GetHeader(currentHeader.ParentHash, currentHeader.Number.Uint64()-1))
		}
		if currentFastBlock := bc.CurrentFastBlock(); currentFastBlock.Hash() == hash {
			newFastBlock := bc.GetBlock(currentFastBlock.ParentHash(), currentFastBlock.NumberU64()-1)
			rawdb.WriteHeadFastBlockHash(bc.db, newFastBlock.Hash())
			bc.currentFastBlock.Store(newFastBlock)
			headFastBlockGauge.Update(int64(newFastBlock.NumberU64()))
		}
		if currentBlock := bc.CurrentBlock(); currentBlock.Hash() == hash {
			newBlock := bc.GetBlock(currentBlock.ParentHash(), currentBlock.NumberU64()-1)
			rawdb.WriteHeadBlockHash(bc.db, newBlock.Hash())
			bc.currentBlock.Store(newBlock)
			headBlockGauge.Update(int64(newBlock.NumberU64()))
		}
	}
	// Truncate ancient data which exceeds the current header.
	//
	// Notably, it can happen that system crashes without truncating the ancient data
	// but the head indicator has been updated in the active store. Regarding this issue,
	// system will self recovery by truncating the extra data during the setup phase.
	if err := bc.truncateAncient(bc.hc.CurrentHeader().Number.Uint64()); err != nil {
		log.Crit("Truncate ancient store failed", "err", err)
	}
}

// truncateAncient rewinds the blockchain to the specified header and deletes all
// data in the ancient store that exceeds the specified header.
func (bc *BlockChain) truncateAncient(head uint64) error {
	frozen, err := bc.db.Ancients()
	if err != nil {
		return err
	}
	// Short circuit if there is no data to truncate in ancient store.
	if frozen <= head+1 {
		return nil
	}
	// Truncate all the data in the freezer beyond the specified head
	if err := bc.db.TruncateAncients(head + 1); err != nil {
		return err
	}
	// Clear out any stale content from the caches
	bc.hc.headerCache.Purge()
	bc.hc.tdCache.Purge()
	bc.hc.numberCache.Purge()
	// Clear out any stale content from the caches
	bc.bodyCache.Purge()
	bc.bodyRLPCache.Purge()
	bc.receiptsCache.Purge()
	bc.blockCache.Purge()
	bc.txLookupCache.Purge()
	bc.futureBlocks.Purge()

	log.Info("Rewind ancient data", "number", head)
	return nil
}

// numberHash is just a container for a number and a hash, to represent a block
type numberHash struct {
	number uint64
	hash   common.Hash
}

// InsertReceiptChain attempts to complete an already existing header chain with
// transaction and receipt data.
func (bc *BlockChain) InsertReceiptChain(blockChain types.Blocks, receiptChain []types.Receipts, ancientLimit uint64) (int, error) {
	// We don't require the chainMu here since we want to maximize the
	// concurrency of header insertion and receipt insertion.
	bc.wg.Add(1)
	defer bc.wg.Done()

	var (
		ancientBlocks, liveBlocks     types.Blocks
		ancientReceipts, liveReceipts []types.Receipts
	)
	// Do a sanity check that the provided chain is actually ordered and linked
	for i := 0; i < len(blockChain); i++ {
		if i != 0 {
			if blockChain[i].NumberU64() != blockChain[i-1].NumberU64()+1 || blockChain[i].ParentHash() != blockChain[i-1].Hash() {
				log.Error("Non contiguous receipt insert", "number", blockChain[i].Number(), "hash", blockChain[i].Hash(), "parent", blockChain[i].ParentHash(),
					"prevnumber", blockChain[i-1].Number(), "prevhash", blockChain[i-1].Hash())
				return 0, fmt.Errorf("non contiguous insert: item %d is #%d [%x…], item %d is #%d [%x…] (parent [%x…])", i-1, blockChain[i-1].NumberU64(),
					blockChain[i-1].Hash().Bytes()[:4], i, blockChain[i].NumberU64(), blockChain[i].Hash().Bytes()[:4], blockChain[i].ParentHash().Bytes()[:4])
			}
		}
		if blockChain[i].NumberU64() <= ancientLimit {
			ancientBlocks, ancientReceipts = append(ancientBlocks, blockChain[i]), append(ancientReceipts, receiptChain[i])
		} else {
			liveBlocks, liveReceipts = append(liveBlocks, blockChain[i]), append(liveReceipts, receiptChain[i])
		}
	}

	var (
		stats = struct{ processed, ignored int32 }{}
		start = time.Now()
		size  = 0
	)
	// updateHead updates the head fast sync block if the inserted blocks are better
	// and returns a indicator whether the inserted blocks are canonical.
	updateHead := func(head *types.Block) bool {
		bc.chainmu.Lock()

		// Rewind may have occurred, skip in that case.
		if bc.CurrentHeader().Number.Cmp(head.Number()) >= 0 {
			currentFastBlock, td := bc.CurrentFastBlock(), bc.GetTd(head.Hash(), head.NumberU64())
			if bc.GetTd(currentFastBlock.Hash(), currentFastBlock.NumberU64()).Cmp(td) < 0 {
				rawdb.WriteHeadFastBlockHash(bc.db, head.Hash())
				bc.currentFastBlock.Store(head)
				headFastBlockGauge.Update(int64(head.NumberU64()))
				bc.chainmu.Unlock()
				return true
			}
		}
		bc.chainmu.Unlock()
		return false
	}
	// writeAncient writes blockchain and corresponding receipt chain into ancient store.
	//
	// this function only accepts canonical chain data. All side chain will be reverted
	// eventually.
	writeAncient := func(blockChain types.Blocks, receiptChain []types.Receipts) (int, error) {
		var (
			previous = bc.CurrentFastBlock()
			batch    = bc.db.NewBatch()
		)
		// If any error occurs before updating the head or we are inserting a side chain,
		// all the data written this time wll be rolled back.
		defer func() {
			if previous != nil {
				if err := bc.truncateAncient(previous.NumberU64()); err != nil {
					log.Crit("Truncate ancient store failed", "err", err)
				}
			}
		}()
		var deleted []*numberHash
		for i, block := range blockChain {
			// Short circuit insertion if shutting down or processing failed
			if atomic.LoadInt32(&bc.procInterrupt) == 1 {
				return 0, errInsertionInterrupted
			}
			// Short circuit insertion if it is required(used in testing only)
			if bc.terminateInsert != nil && bc.terminateInsert(block.Hash(), block.NumberU64()) {
				return i, errors.New("insertion is terminated for testing purpose")
			}
			// Short circuit if the owner header is unknown
			if !bc.HasHeader(block.Hash(), block.NumberU64()) {
				return i, fmt.Errorf("containing header #%d [%x…] unknown", block.Number(), block.Hash().Bytes()[:4])
			}
			var (
				start  = time.Now()
				logged = time.Now()
				count  int
			)
			// Migrate all ancient blocks. This can happen if someone upgrades from Geth
			// 1.8.x to 1.9.x mid-fast-sync. Perhaps we can get rid of this path in the
			// long term.
			for {
				// We can ignore the error here since light client won't hit this code path.
				frozen, _ := bc.db.Ancients()
				if frozen >= block.NumberU64() {
					break
				}
				h := rawdb.ReadCanonicalHash(bc.db, frozen)
				b := rawdb.ReadBlock(bc.db, h, frozen)
				size += rawdb.WriteAncientBlock(bc.db, b, rawdb.ReadReceipts(bc.db, h, frozen, bc.chainConfig), rawdb.ReadTd(bc.db, h, frozen))
				count += 1

				// Always keep genesis block in active database.
				if b.NumberU64() != 0 {
					deleted = append(deleted, &numberHash{b.NumberU64(), b.Hash()})
				}
				if time.Since(logged) > 8*time.Second {
					log.Info("Migrating ancient blocks", "count", count, "elapsed", common.PrettyDuration(time.Since(start)))
					logged = time.Now()
				}
				// Don't collect too much in-memory, write it out every 100K blocks
				if len(deleted) > 100000 {

					// Sync the ancient store explicitly to ensure all data has been flushed to disk.
					if err := bc.db.Sync(); err != nil {
						return 0, err
					}
					// Wipe out canonical block data.
					for _, nh := range deleted {
						rawdb.DeleteBlockWithoutNumber(batch, nh.hash, nh.number)
						rawdb.DeleteCanonicalHash(batch, nh.number)
					}
					if err := batch.Write(); err != nil {
						return 0, err
					}
					batch.Reset()
					// Wipe out side chain too.
					for _, nh := range deleted {
						for _, hash := range rawdb.ReadAllHashes(bc.db, nh.number) {
							rawdb.DeleteBlock(batch, hash, nh.number)
						}
					}
					if err := batch.Write(); err != nil {
						return 0, err
					}
					batch.Reset()
					deleted = deleted[0:]
				}
			}
			if count > 0 {
				log.Info("Migrated ancient blocks", "count", count, "elapsed", common.PrettyDuration(time.Since(start)))
			}
			// Flush data into ancient database.
			size += rawdb.WriteAncientBlock(bc.db, block, receiptChain[i], bc.GetTd(block.Hash(), block.NumberU64()))
			rawdb.WriteTxLookupEntries(batch, block)

			stats.processed++
		}
		// Flush all tx-lookup index data.
		size += batch.ValueSize()
		if err := batch.Write(); err != nil {
			return 0, err
		}
		batch.Reset()

		// Sync the ancient store explicitly to ensure all data has been flushed to disk.
		if err := bc.db.Sync(); err != nil {
			return 0, err
		}
		if !updateHead(blockChain[len(blockChain)-1]) {
			return 0, errors.New("side blocks can't be accepted as the ancient chain data")
		}
		previous = nil // disable rollback explicitly

		// Wipe out canonical block data.
		for _, nh := range deleted {
			rawdb.DeleteBlockWithoutNumber(batch, nh.hash, nh.number)
			rawdb.DeleteCanonicalHash(batch, nh.number)
		}
		for _, block := range blockChain {
			// Always keep genesis block in active database.
			if block.NumberU64() != 0 {
				rawdb.DeleteBlockWithoutNumber(batch, block.Hash(), block.NumberU64())
				rawdb.DeleteCanonicalHash(batch, block.NumberU64())
			}
		}
		if err := batch.Write(); err != nil {
			return 0, err
		}
		batch.Reset()

		// Wipe out side chain too.
		for _, nh := range deleted {
			for _, hash := range rawdb.ReadAllHashes(bc.db, nh.number) {
				rawdb.DeleteBlock(batch, hash, nh.number)
			}
		}
		for _, block := range blockChain {
			// Always keep genesis block in active database.
			if block.NumberU64() != 0 {
				for _, hash := range rawdb.ReadAllHashes(bc.db, block.NumberU64()) {
					rawdb.DeleteBlock(batch, hash, block.NumberU64())
				}
			}
		}
		if err := batch.Write(); err != nil {
			return 0, err
		}
		return 0, nil
	}
	// writeLive writes blockchain and corresponding receipt chain into active store.
	writeLive := func(blockChain types.Blocks, receiptChain []types.Receipts) (int, error) {
		batch := bc.db.NewBatch()
		for i, block := range blockChain {
			// Short circuit insertion if shutting down or processing failed
			if atomic.LoadInt32(&bc.procInterrupt) == 1 {
				return 0, errInsertionInterrupted
			}
			// Short circuit if the owner header is unknown
			if !bc.HasHeader(block.Hash(), block.NumberU64()) {
				return i, fmt.Errorf("containing header #%d [%x…] unknown", block.Number(), block.Hash().Bytes()[:4])
			}
			if bc.HasBlock(block.Hash(), block.NumberU64()) {
				stats.ignored++
				continue
			}
			// Write all the data out into the database
			rawdb.WriteBody(batch, block.Hash(), block.NumberU64(), block.Body())
			rawdb.WriteReceipts(batch, block.Hash(), block.NumberU64(), receiptChain[i])
			rawdb.WriteTxLookupEntries(batch, block)

			stats.processed++
			if batch.ValueSize() >= ethdb.IdealBatchSize {
				if err := batch.Write(); err != nil {
					return 0, err
				}
				size += batch.ValueSize()
				batch.Reset()
			}
		}
		if batch.ValueSize() > 0 {
			size += batch.ValueSize()
			if err := batch.Write(); err != nil {
				return 0, err
			}
		}
		updateHead(blockChain[len(blockChain)-1])
		return 0, nil
	}
	// Write downloaded chain data and corresponding receipt chain data.
	if len(ancientBlocks) > 0 {
		if n, err := writeAncient(ancientBlocks, ancientReceipts); err != nil {
			if err == errInsertionInterrupted {
				return 0, nil
			}
			return n, err
		}
	}
	if len(liveBlocks) > 0 {
		if n, err := writeLive(liveBlocks, liveReceipts); err != nil {
			if err == errInsertionInterrupted {
				return 0, nil
			}
			return n, err
		}
	}

	head := blockChain[len(blockChain)-1]
	context := []interface{}{
		"count", stats.processed, "elapsed", common.PrettyDuration(time.Since(start)),
		"number", head.Number(), "hash", head.Hash(), "age", common.PrettyAge(time.Unix(int64(head.Time()), 0)),
		"size", common.StorageSize(size),
	}
	if stats.ignored > 0 {
		context = append(context, []interface{}{"ignored", stats.ignored}...)
	}
	log.Info("Imported new block receipts", context...)

	return 0, nil
}

var lastWrite uint64

// writeBlockWithoutState writes only the block and its metadata to the database,
// but does not write any state. This is used to construct competing side forks
// up to the point where they exceed the canonical total difficulty.
func (bc *BlockChain) writeBlockWithoutState(block *types.Block, td *big.Int) (err error) {
	bc.wg.Add(1)
	defer bc.wg.Done()

	if err := bc.hc.WriteTd(block.Hash(), block.NumberU64(), td); err != nil {
		return err
	}
	rawdb.WriteBlock(bc.db, block)

	return nil
}

// writeKnownBlock updates the head block flag with a known block
// and introduces chain reorg if necessary.
func (bc *BlockChain) writeKnownBlock(block *types.Block) error {
	bc.wg.Add(1)
	defer bc.wg.Done()

	current := bc.CurrentBlock()
	if block.ParentHash() != current.Hash() {
		if err := bc.reorg(current, block); err != nil {
			return err
		}
	}
	// Write the positional metadata for transaction/receipt lookups.
	// Preimages here is empty, ignore it.
	rawdb.WriteTxLookupEntries(bc.db, block)

	bc.insert(block)
	return nil
}

// https://stackoverflow.com/questions/19105791/is-there-a-big-bitcount/32702348#32702348
func bitCount(n *big.Int) int {
	count := 0
	for _, v := range n.Bits() {
		count += popcount(uint64(v))
	}
	return count
}

// Straight and simple C to Go translation from https://en.wikipedia.org/wiki/Hamming_weight
func popcount(x uint64) int {
	const (
		m1  = 0x5555555555555555 //binary: 0101...
		m2  = 0x3333333333333333 //binary: 00110011..
		m4  = 0x0f0f0f0f0f0f0f0f //binary:  4 zeros,  4 ones ...
		h01 = 0x0101010101010101 //the sum of 256 to the power of 0,1,2,3...
	)
	x -= (x >> 1) & m1             //put count of each 2 bits into those 2 bits
	x = (x & m2) + ((x >> 2) & m2) //put count of each 4 bits into those 4 bits
	x = (x + (x >> 4)) & m4        //put count of each 8 bits into those 8 bits
	return int((x * h01) >> 56)    //returns left 8 bits of x + (x<<8) + (x<<16) + (x<<24) + ...
}

// updateUptime receives the currently accumulated uptime for all validators in an epoch and proceeds to update it
// based on which validators signed on the provided block by inspecting the block's parent bitmap
func updateUptime(uptime *istanbul.Uptime, blockNumber uint64, bitmap *big.Int, window uint64, epochNum uint64, epochSize uint64) *istanbul.Uptime {
	if uptime == nil {
		uptime = new(istanbul.Uptime)
		// The number of validators is upper bounded by 3/2 of the number of 1s in the bitmap
		// We multiply by 2 just to be extra cautious of off-by-one errors.
		validatorsSizeUpperBound := uint64(math.Ceil(float64(bitCount(bitmap)) * 2))
		uptime.Entries = make([]istanbul.UptimeEntry, validatorsSizeUpperBound)
	}

	valScoreTallyFirstBlockNum := istanbul.GetValScoreTallyFirstBlockNumber(epochNum, epochSize, window)
	valScoreTallyLastBlockNum := istanbul.GetValScoreTallyLastBlockNumber(epochNum, epochSize)

	// signedBlockWindowLastBlockNum is just the previous block
	signedBlockWindowLastBlockNum := blockNumber - 1
	signedBlockWindowFirstBlockNum := signedBlockWindowLastBlockNum - (window - 1)

	uptime.LatestBlock = blockNumber
	for i := 0; i < len(uptime.Entries); i++ {
		if bitmap.Bit(i) == 1 {
			// update their latest signed block
			uptime.Entries[i].LastSignedBlock = blockNumber - 1
		}

		// If we are within the validator uptime tally window, then update the validator's score
		// if its last signed block is within the lookback window
		if valScoreTallyFirstBlockNum <= blockNumber && blockNumber <= valScoreTallyLastBlockNum {
			lastSignedBlock := uptime.Entries[i].LastSignedBlock

			// Note that the second condition in the if condition is not necessary.  But it does
			// make the logic easier to understand.  (e.g. it's checking is lastSignedBlock is within
			// the range [signedBlockWindowFirstBlockNum, signedBlockWindowLastBlockNum])
			if signedBlockWindowFirstBlockNum <= lastSignedBlock && lastSignedBlock <= signedBlockWindowLastBlockNum {
				uptime.Entries[i].ScoreTally++
			}
		}
	}
	return uptime
}

// WriteBlockWithState writes the block and all associated state to the database.
func (bc *BlockChain) WriteBlockWithState(block *types.Block, receipts []*types.Receipt, state *state.StateDB) (status WriteStatus, err error) {
	bc.chainmu.Lock()
	defer bc.chainmu.Unlock()

	return bc.writeBlockWithState(block, receipts, state)
}

// writeBlockWithState writes the block and all associated state to the database,
// but is expects the chain mutex to be held.
func (bc *BlockChain) writeBlockWithState(block *types.Block, receipts []*types.Receipt, state *state.StateDB) (status WriteStatus, err error) {
	bc.wg.Add(1)
	defer bc.wg.Done()

	// We are going to update the uptime tally.
	// TODO find a better way of checking if it's istanbul
	if _, isIstanbul := bc.engine.(consensus.Istanbul); isIstanbul {
		// The epoch's first block's aggregated parent signatures is for the previous epoch's valset.
		// We can ignore updating the tally for that block.
		if !istanbul.IsFirstBlockOfEpoch(block.NumberU64(), bc.chainConfig.Istanbul.Epoch) {
			epochNum := istanbul.GetEpochNumber(block.NumberU64(), bc.chainConfig.Istanbul.Epoch)

			// Get the bitmap from the previous block
			extra, err := types.ExtractIstanbulExtra(block.Header())
			if err != nil {
				log.Error("Unable to extract istanbul extra", "func", "WriteBlockWithState", "blocknum", block.NumberU64(), "epoch", epochNum)
				return NonStatTy, errors.New("could not extract block header extra")
			}
			signedValidatorsBitmap := extra.ParentAggregatedSeal.Bitmap

			// Get the uptime scores
			uptime := rawdb.ReadAccumulatedEpochUptime(bc.db, epochNum)

			// We only update the uptime for blocks which are greater than the last block we saw.
			// This ensures that we do not count the same block twice for any reason.
			if uptime == nil || uptime.LatestBlock < block.NumberU64() {
				// Update the uptime scores
				uptime = updateUptime(uptime, block.NumberU64(), signedValidatorsBitmap, bc.chainConfig.Istanbul.LookbackWindow, epochNum, bc.chainConfig.Istanbul.Epoch)

				// Write the new uptime scores
				rawdb.WriteAccumulatedEpochUptime(bc.db, epochNum, uptime)
			} else {
				log.Trace("WritingBlockWithState with block number less than a block we previously wrote", "latestUptimeBlock", uptime.LatestBlock, "blockNumber", block.NumberU64())
			}
		}
	}

	// Calculate the total difficulty of the block
	ptd := bc.GetTd(block.ParentHash(), block.NumberU64()-1)
	if ptd == nil {
		return NonStatTy, consensus.ErrUnknownAncestor
	}
	// Make sure no inconsistent state is leaked during insertion
	currentBlock := bc.CurrentBlock()
	localTd := bc.GetTd(currentBlock.Hash(), currentBlock.NumberU64())
	externTd := big.NewInt(int64(block.NumberU64() + 1))

	// Irrelevant of the canonical status, write the block itself to the database
	if err := bc.hc.WriteTd(block.Hash(), block.NumberU64(), externTd); err != nil {
		return NonStatTy, err
	}
	rawdb.WriteBlock(bc.db, block)

	root, err := state.Commit(bc.chainConfig.IsEIP158(block.Number()))
	if err != nil {
		return NonStatTy, err
	}
	triedb := bc.stateCache.TrieDB()

	// If we're running an archive node, always flush
	if bc.cacheConfig.TrieDirtyDisabled {
		if err := triedb.Commit(root, false); err != nil {
			return NonStatTy, err
		}
	} else {
		// Full but not archive node, do proper garbage collection
		triedb.Reference(root, common.Hash{}) // metadata reference to keep trie alive
		bc.triegc.Push(root, -int64(block.NumberU64()))

		if current := block.NumberU64(); current > TriesInMemory {
			// If we exceeded our memory allowance, flush matured singleton nodes to disk
			var (
				nodes, imgs = triedb.Size()
				limit       = common.StorageSize(bc.cacheConfig.TrieDirtyLimit) * 1024 * 1024
			)
			if nodes > limit || imgs > 4*1024*1024 {
				triedb.Cap(limit - ethdb.IdealBatchSize)
			}
			// Find the next state trie we need to commit
			chosen := current - TriesInMemory

			// If we exceeded out time allowance, flush an entire trie to disk
			if bc.gcproc > bc.cacheConfig.TrieTimeLimit {
				// If the header is missing (canonical chain behind), we're reorging a low
				// diff sidechain. Suspend committing until this operation is completed.
				header := bc.GetHeaderByNumber(chosen)
				if header == nil {
					log.Warn("Reorg in progress, trie commit postponed", "number", chosen)
				} else {
					// If we're exceeding limits but haven't reached a large enough memory gap,
					// warn the user that the system is becoming unstable.
					if chosen < lastWrite+TriesInMemory && bc.gcproc >= 2*bc.cacheConfig.TrieTimeLimit {
						log.Info("State in memory for too long, committing", "time", bc.gcproc, "allowance", bc.cacheConfig.TrieTimeLimit, "optimum", float64(chosen-lastWrite)/TriesInMemory)
					}
					// Flush an entire trie and restart the counters
					triedb.Commit(header.Root, true)
					lastWrite = chosen
					bc.gcproc = 0
				}
			}
			// Garbage collect anything below our required write retention
			for !bc.triegc.Empty() {
				root, number := bc.triegc.Pop()
				if uint64(-number) > chosen {
					bc.triegc.Push(root, number)
					break
				}
				triedb.Dereference(root.(common.Hash))
			}
		}
	}

	// Write other block data using a batch.
	batch := bc.db.NewBatch()
	rawdb.WriteReceipts(batch, block.Hash(), block.NumberU64(), receipts)

	// 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
	currentBlock = bc.CurrentBlock()
	if !reorg && externTd.Cmp(localTd) == 0 {
		// Split same-difficulty blocks by number, then preferentially select
		// the block generated by the local miner as the canonical block.
		if block.NumberU64() < currentBlock.NumberU64() {
			reorg = true
		} else if block.NumberU64() == currentBlock.NumberU64() {
			var currentPreserve, blockPreserve bool
			if bc.shouldPreserve != nil {
				currentPreserve, blockPreserve = bc.shouldPreserve(currentBlock), bc.shouldPreserve(block)
			}
			reorg = !currentPreserve && (blockPreserve || mrand.Float64() < 0.5)
		}
	}
	if reorg {
		// Reorganise the chain if the parent is not the head block
		if block.ParentHash() != currentBlock.Hash() {
			if err := bc.reorg(currentBlock, block); err != nil {
				return NonStatTy, err
			}
		}
		// Write the positional metadata for transaction/receipt lookups and preimages
		rawdb.WriteTxLookupEntries(batch, block)
		rawdb.WritePreimages(batch, state.Preimages())

		status = CanonStatTy
	} else {
		status = SideStatTy
	}
	if err := batch.Write(); err != nil {
		return NonStatTy, err
	}

	// Set new head.
	if status == CanonStatTy {
		bc.insert(block)
	}
	bc.futureBlocks.Remove(block.Hash())
	return status, nil
}

// addFutureBlock checks if the block is within the max allowed window to get
// accepted for future processing, and returns an error if the block is too far
// ahead and was not added.
func (bc *BlockChain) addFutureBlock(block *types.Block) error {
	max := uint64(time.Now().Unix() + maxTimeFutureBlocks)
	if block.Time() > max {
		return fmt.Errorf("future block timestamp %v > allowed %v", block.Time(), max)
	}
	bc.futureBlocks.Add(block.Hash(), block)
	return nil
}

// InsertChain attempts to insert the given batch of blocks in to the canonical
// chain or, otherwise, create a fork. If an error is returned it will return
// the index number of the failing block as well an error describing what went
// wrong.
//
// After insertion is done, all accumulated events will be fired.
func (bc *BlockChain) InsertChain(chain types.Blocks) (int, error) {
	// Sanity check that we have something meaningful to import
	if len(chain) == 0 {
		return 0, nil
	}

	bc.blockProcFeed.Send(true)
	defer bc.blockProcFeed.Send(false)

	// Remove already known canon-blocks
	var (
		block, prev *types.Block
	)
	// Do a sanity check that the provided chain is actually ordered and linked
	for i := 1; i < len(chain); i++ {
		block = chain[i]
		prev = chain[i-1]
		if block.NumberU64() != prev.NumberU64()+1 || block.ParentHash() != prev.Hash() {
			// Chain broke ancestry, log a message (programming error) and skip insertion
			log.Error("Non contiguous block insert", "number", block.Number(), "hash", block.Hash(),
				"parent", block.ParentHash(), "prevnumber", prev.Number(), "prevhash", prev.Hash())

			return 0, fmt.Errorf("non contiguous insert: item %d is #%d [%x…], item %d is #%d [%x…] (parent [%x…])", i-1, prev.NumberU64(),
				prev.Hash().Bytes()[:4], i, block.NumberU64(), block.Hash().Bytes()[:4], block.ParentHash().Bytes()[:4])
		}
	}
	// Pre-checks passed, start the full block imports
	bc.wg.Add(1)
	bc.chainmu.Lock()
	n, events, logs, err := bc.insertChain(chain, true)
	bc.chainmu.Unlock()
	bc.wg.Done()

	bc.PostChainEvents(events, logs)
	return n, err
}

// insertChain is the internal implementation of InsertChain, which assumes that
// 1) chains are contiguous, and 2) The chain mutex is held.
//
// This method is split out so that import batches that require re-injecting
// historical blocks can do so without releasing the lock, which could lead to
// racey behaviour. If a sidechain import is in progress, and the historic state
// is imported, but then new canon-head is added before the actual sidechain
// completes, then the historic state could be pruned again
func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, []interface{}, []*types.Log, error) {
	// If the chain is terminating, don't even bother starting up
	if atomic.LoadInt32(&bc.procInterrupt) == 1 {
		return 0, nil, nil, nil
	}
	// Start a parallel signature recovery (signer will fluke on fork transition, minimal perf loss)
	senderCacher.recoverFromBlocks(types.MakeSigner(bc.chainConfig, chain[0].Number()), chain)

	// A queued approach to delivering events. This is generally
	// faster than direct delivery and requires much less mutex
	// acquiring.
	var (
		stats         = insertStats{startTime: mclock.Now()}
		events        = make([]interface{}, 0, len(chain))
		lastCanon     *types.Block
		coalescedLogs []*types.Log
	)
	// Start the parallel header verifier
	headers := make([]*types.Header, len(chain))
	seals := make([]bool, len(chain))

	for i, block := range chain {
		headers[i] = block.Header()
		seals[i] = verifySeals
	}
	abort, results := bc.engine.VerifyHeaders(bc, headers, seals)
	defer close(abort)

	// Peek the error for the first block to decide the directing import logic
	it := newInsertIterator(chain, results, bc.validator)

	block, err := it.next()

	// Left-trim all the known blocks
	if err == ErrKnownBlock {
		// First block (and state) is known
		//   1. We did a roll-back, and should now do a re-import
		//   2. The block is stored as a sidechain, and is lying about it's stateroot, and passes a stateroot
		// 	    from the canonical chain, which has not been verified.
		// Skip all known blocks that are behind us
		var (
			current  = bc.CurrentBlock()
			localTd  = bc.GetTd(current.Hash(), current.NumberU64())
			externTd = bc.GetTd(block.ParentHash(), block.NumberU64()-1) // The first block can't be nil
		)
		for block != nil && err == ErrKnownBlock {
			externTd = new(big.Int).Add(externTd, big.NewInt(1))
			if localTd.Cmp(externTd) < 0 {
				break
			}
			log.Debug("Ignoring already known block", "number", block.Number(), "hash", block.Hash())
			stats.ignored++

			block, err = it.next()
		}
		// The remaining blocks are still known blocks, the only scenario here is:
		// During the fast sync, the pivot point is already submitted but rollback
		// happens. Then node resets the head full block to a lower height via `rollback`
		// and leaves a few known blocks in the database.
		//
		// When node runs a fast sync again, it can re-import a batch of known blocks via
		// `insertChain` while a part of them have higher total difficulty than current
		// head full block(new pivot point).
		for block != nil && err == ErrKnownBlock {
			log.Debug("Writing previously known block", "number", block.Number(), "hash", block.Hash())
			if err := bc.writeKnownBlock(block); err != nil {
				return it.index, nil, nil, err
			}
			lastCanon = block

			block, err = it.next()
		}
		// Falls through to the block import
	}
	switch {
	// First block is pruned, insert as sidechain and reorg only if TD grows enough
	case err == consensus.ErrPrunedAncestor:
		log.Debug("Pruned ancestor, inserting as sidechain", "number", block.Number(), "hash", block.Hash())
		return bc.insertSideChain(block, it)

	// First block is future, shove it (and all children) to the future queue (unknown ancestor)
	case err == consensus.ErrFutureBlock || (err == consensus.ErrUnknownAncestor && bc.futureBlocks.Contains(it.first().ParentHash())):
		for block != nil && (it.index == 0 || err == consensus.ErrUnknownAncestor) {
			log.Debug("Future block, postponing import", "number", block.Number(), "hash", block.Hash())
			if err := bc.addFutureBlock(block); err != nil {
				return it.index, events, coalescedLogs, err
			}
			block, err = it.next()
		}
		stats.queued += it.processed()
		stats.ignored += it.remaining()

		// If there are any still remaining, mark as ignored
		return it.index, events, coalescedLogs, err

	// Some other error occurred, abort
	case err != nil:
		bc.futureBlocks.Remove(block.Hash())
		stats.ignored += len(it.chain)
		bc.reportBlock(block, nil, err)
		return it.index, events, coalescedLogs, err
	}
	// No validation errors for the first block (or chain prefix skipped)
	for ; block != nil && err == nil || err == ErrKnownBlock; block, err = it.next() {
		// If the chain is terminating, stop processing blocks
		if atomic.LoadInt32(&bc.procInterrupt) == 1 {
			log.Debug("Premature abort during blocks processing")
			break
		}
		// If the header is a banned one, straight out abort
		if BadHashes[block.Hash()] {
			bc.reportBlock(block, nil, ErrBlacklistedHash)
			return it.index, events, coalescedLogs, ErrBlacklistedHash
		}
		// In this case, just skip the block we already validated it once fully
		// (and crashed), since its header and body was already in the database).
		if err == ErrKnownBlock {
			logger := log.Warn
			logger("Inserted known block", "number", block.Number(), "hash", block.Hash(), "txs", len(block.Transactions()), "gas", block.GasUsed(),
				"root", block.Root())

			if err := bc.writeKnownBlock(block); err != nil {
				return it.index, nil, nil, err
			}
			stats.processed++

			// We can assume that logs are empty here, since the only way for consecutive
			// blocks to have the same state is if there are no transactions.
			events = append(events, ChainEvent{block, block.Hash(), nil})
			lastCanon = block

			continue
		}
		// Retrieve the parent block and it's state to execute on top
		start := time.Now()

		parent := it.previous()
		if parent == nil {
			parent = bc.GetHeader(block.ParentHash(), block.NumberU64()-1)
		}
		statedb, err := state.New(parent.Root, bc.stateCache)
		if err != nil {
			return it.index, events, coalescedLogs, err
		}
		// If we have a followup block, run that against the current state to pre-cache
		// transactions and probabilistically some of the account/storage trie nodes.
		var followupInterrupt uint32

		if !bc.cacheConfig.TrieCleanNoPrefetch {
			if followup, err := it.peek(); followup != nil && err == nil {
				go func(start time.Time) {
					throwaway, _ := state.New(parent.Root, bc.stateCache)
					bc.prefetcher.Prefetch(followup, throwaway, bc.vmConfig, &followupInterrupt)

					blockPrefetchExecuteTimer.Update(time.Since(start))
					if atomic.LoadUint32(&followupInterrupt) == 1 {
						blockPrefetchInterruptMeter.Mark(1)
					}
				}(time.Now())
			}
		}
		// Process block using the parent state as reference point
		substart := time.Now()
		receipts, logs, usedGas, err := bc.processor.Process(block, statedb, bc.vmConfig)
		if err != nil {
			bc.reportBlock(block, receipts, err)
			atomic.StoreUint32(&followupInterrupt, 1)
			return it.index, events, coalescedLogs, err
		}
		// Update the metrics touched during block processing
		accountReadTimer.Update(statedb.AccountReads)     // Account reads are complete, we can mark them
		storageReadTimer.Update(statedb.StorageReads)     // Storage reads are complete, we can mark them
		accountUpdateTimer.Update(statedb.AccountUpdates) // Account updates are complete, we can mark them
		storageUpdateTimer.Update(statedb.StorageUpdates) // Storage updates are complete, we can mark them

		triehash := statedb.AccountHashes + statedb.StorageHashes // Save to not double count in validation
		trieproc := statedb.AccountReads + statedb.AccountUpdates
		trieproc += statedb.StorageReads + statedb.StorageUpdates

		blockExecutionTimer.Update(time.Since(substart) - trieproc - triehash)

		// Validate the state using the default validator
		substart = time.Now()
		if err := bc.validator.ValidateState(block, statedb, receipts, usedGas); err != nil {
			bc.reportBlock(block, receipts, err)
			atomic.StoreUint32(&followupInterrupt, 1)
			return it.index, events, coalescedLogs, err
		}
		proctime := time.Since(start)

		// Update the metrics touched during block validation
		accountHashTimer.Update(statedb.AccountHashes) // Account hashes are complete, we can mark them
		storageHashTimer.Update(statedb.StorageHashes) // Storage hashes are complete, we can mark them

		blockValidationTimer.Update(time.Since(substart) - (statedb.AccountHashes + statedb.StorageHashes - triehash))

		// Write the block to the chain and get the status.
		substart = time.Now()
		status, err := bc.writeBlockWithState(block, receipts, statedb)
		if err != nil {
			atomic.StoreUint32(&followupInterrupt, 1)
			return it.index, events, coalescedLogs, err
		}
		atomic.StoreUint32(&followupInterrupt, 1)

		// Update the metrics touched during block commit
		accountCommitTimer.Update(statedb.AccountCommits) // Account commits are complete, we can mark them
		storageCommitTimer.Update(statedb.StorageCommits) // Storage commits are complete, we can mark them

		blockWriteTimer.Update(time.Since(substart) - statedb.AccountCommits - statedb.StorageCommits)
		blockInsertTimer.UpdateSince(start)

		switch status {
		case CanonStatTy:
			log.Debug("Inserted new block", "number", block.Number(), "txs", len(block.Transactions()), "gas", block.GasUsed(),
				"elapsed", common.PrettyDuration(time.Since(start)),
				"root", block.Root())

			coalescedLogs = append(coalescedLogs, logs...)
			events = append(events, ChainEvent{block, block.Hash(), logs})
			lastCanon = block

			// Only count canonical blocks for GC processing time
			bc.gcproc += proctime

		case SideStatTy:
			log.Debug("Inserted forked block", "number", block.Number(), "hash", block.Hash(),
				"elapsed", common.PrettyDuration(time.Since(start)),
				"txs", len(block.Transactions()), "gas", block.GasUsed(),
				"root", block.Root())
			events = append(events, ChainSideEvent{block})

		default:
			// This in theory is impossible, but lets be nice to our future selves and leave
			// a log, instead of trying to track down blocks imports that don't emit logs.
			log.Warn("Inserted block with unknown status", "number", block.Number(), "hash", block.Hash(),
				"elapsed", common.PrettyDuration(time.Since(start)),
				"txs", len(block.Transactions()), "gas", block.GasUsed(),
				"root", block.Root())
		}
		stats.processed++
		stats.usedGas += usedGas

		dirty, _ := bc.stateCache.TrieDB().Size()
		stats.report(chain, it.index, dirty)
	}
	// Any blocks remaining here? The only ones we care about are the future ones
	if block != nil && err == consensus.ErrFutureBlock {
		if err := bc.addFutureBlock(block); err != nil {
			return it.index, events, coalescedLogs, err
		}
		block, err = it.next()

		for ; block != nil && err == consensus.ErrUnknownAncestor; block, err = it.next() {
			if err := bc.addFutureBlock(block); err != nil {
				return it.index, events, coalescedLogs, err
			}
			stats.queued++
		}
	}
	stats.ignored += it.remaining()

	// Append a single chain head event if we've progressed the chain
	if lastCanon != nil && bc.CurrentBlock().Hash() == lastCanon.Hash() {
		events = append(events, ChainHeadEvent{lastCanon})
	}
	return it.index, events, coalescedLogs, err
}

// insertSideChain is called when an import batch hits upon a pruned ancestor
// error, which happens when a sidechain with a sufficiently old fork-block is
// found.
//
// The method writes all (header-and-body-valid) blocks to disk, then tries to
// switch over to the new chain if the TD exceeded the current chain.
func (bc *BlockChain) insertSideChain(block *types.Block, it *insertIterator) (int, []interface{}, []*types.Log, error) {
	var (
		externTd *big.Int
		current  = bc.CurrentBlock()
	)
	// The first sidechain block error is already verified to be ErrPrunedAncestor.
	// Since we don't import them here, we expect ErrUnknownAncestor for the remaining
	// ones. Any other errors means that the block is invalid, and should not be written
	// to disk.
	err := consensus.ErrPrunedAncestor
	for ; block != nil && (err == consensus.ErrPrunedAncestor); block, err = it.next() {
		// Check the canonical state root for that number
		if number := block.NumberU64(); current.NumberU64() >= number {
			canonical := bc.GetBlockByNumber(number)
			if canonical != nil && canonical.Hash() == block.Hash() {
				// Not a sidechain block, this is a re-import of a canon block which has it's state pruned

				externTd = bc.GetTd(block.Hash(), block.NumberU64())
				continue
			}
			if canonical != nil && canonical.Root() == block.Root() {
				// This is most likely a shadow-state attack. When a fork is imported into the
				// database, and it eventually reaches a block height which is not pruned, we
				// just found that the state already exist! This means that the sidechain block
				// refers to a state which already exists in our canon chain.
				//
				// If left unchecked, we would now proceed importing the blocks, without actually
				// having verified the state of the previous blocks.
				log.Warn("Sidechain ghost-state attack detected", "number", block.NumberU64(), "sideroot", block.Root(), "canonroot", canonical.Root())

				// If someone legitimately side-mines blocks, they would still be imported as usual. However,
				// we cannot risk writing unverified blocks to disk when they obviously target the pruning
				// mechanism.
				return it.index, nil, nil, errors.New("sidechain ghost-state attack")
			}
		}

		externTd = big.NewInt(int64(block.NumberU64() + 1))

		if !bc.HasBlock(block.Hash(), block.NumberU64()) {
			start := time.Now()
			if err := bc.writeBlockWithoutState(block, externTd); err != nil {
				return it.index, nil, nil, err
			}
			log.Debug("Injected sidechain block", "number", block.Number(), "hash", block.Hash(),
				"elapsed", common.PrettyDuration(time.Since(start)),
				"txs", len(block.Transactions()), "gas", block.GasUsed(),
				"root", block.Root())
		}
	}
	// At this point, we've written all sidechain blocks to database. Loop ended
	// either on some other error or all were processed. If there was some other
	// error, we can ignore the rest of those blocks.
	//
	// If the externTd was larger than our local TD, we now need to reimport the previous
	// blocks to regenerate the required state
	localTd := bc.GetTd(current.Hash(), current.NumberU64())
	if localTd.Cmp(externTd) > 0 {
		log.Info("Sidechain written to disk", "start", it.first().NumberU64(), "end", it.previous().Number, "sidetd", externTd, "localtd", localTd)
		return it.index, nil, nil, err
	}
	// Gather all the sidechain hashes (full blocks may be memory heavy)
	var (
		hashes  []common.Hash
		numbers []uint64
	)
	parent := it.previous()
	for parent != nil && !bc.HasState(parent.Root) {
		hashes = append(hashes, parent.Hash())
		numbers = append(numbers, parent.Number.Uint64())

		parent = bc.GetHeader(parent.ParentHash, parent.Number.Uint64()-1)
	}
	if parent == nil {
		return it.index, nil, nil, errors.New("missing parent")
	}
	// Import all the pruned blocks to make the state available
	var (
		blocks []*types.Block
		memory common.StorageSize
	)
	for i := len(hashes) - 1; i >= 0; i-- {
		// Append the next block to our batch
		block := bc.GetBlock(hashes[i], numbers[i])

		blocks = append(blocks, block)
		memory += block.Size()

		// If memory use grew too large, import and continue. Sadly we need to discard
		// all raised events and logs from notifications since we're too heavy on the
		// memory here.
		if len(blocks) >= 2048 || memory > 64*1024*1024 {
			log.Info("Importing heavy sidechain segment", "blocks", len(blocks), "start", blocks[0].NumberU64(), "end", block.NumberU64())
			if _, _, _, err := bc.insertChain(blocks, false); err != nil {
				return 0, nil, nil, err
			}
			blocks, memory = blocks[:0], 0

			// If the chain is terminating, stop processing blocks
			if atomic.LoadInt32(&bc.procInterrupt) == 1 {
				log.Debug("Premature abort during blocks processing")
				return 0, nil, nil, nil
			}
		}
	}
	if len(blocks) > 0 {
		log.Info("Importing sidechain segment", "start", blocks[0].NumberU64(), "end", blocks[len(blocks)-1].NumberU64())
		return bc.insertChain(blocks, false)
	}
	return 0, nil, nil, nil
}

// reorg takes two blocks, an old chain and a new chain and will reconstruct the
// blocks and inserts them to be part of the new canonical chain and accumulates
// potential missing transactions and post an event about them.
func (bc *BlockChain) reorg(oldBlock, newBlock *types.Block) error {
	var (
		newChain    types.Blocks
		oldChain    types.Blocks
		commonBlock *types.Block

		deletedTxs types.Transactions
		addedTxs   types.Transactions

		deletedLogs []*types.Log
		rebirthLogs []*types.Log

		// collectLogs collects the logs that were generated during the
		// processing of the block that corresponds with the given hash.
		// These logs are later announced as deleted or reborn
		collectLogs = func(hash common.Hash, removed bool) {
			number := bc.hc.GetBlockNumber(hash)
			if number == nil {
				return
			}
			receipts := rawdb.ReadReceipts(bc.db, hash, *number, bc.chainConfig)
			for _, receipt := range receipts {
				for _, log := range receipt.Logs {
					l := *log
					if removed {
						l.Removed = true
						deletedLogs = append(deletedLogs, &l)
					} else {
						rebirthLogs = append(rebirthLogs, &l)
					}
				}
			}
		}
	)
	// Reduce the longer chain to the same number as the shorter one
	if oldBlock.NumberU64() > newBlock.NumberU64() {
		// Old chain is longer, gather all transactions and logs as deleted ones
		for ; oldBlock != nil && oldBlock.NumberU64() != newBlock.NumberU64(); oldBlock = bc.GetBlock(oldBlock.ParentHash(), oldBlock.NumberU64()-1) {
			oldChain = append(oldChain, oldBlock)
			deletedTxs = append(deletedTxs, oldBlock.Transactions()...)
			collectLogs(oldBlock.Hash(), true)
		}
	} else {
		// New chain is longer, stash all blocks away for subsequent insertion
		for ; newBlock != nil && newBlock.NumberU64() != oldBlock.NumberU64(); newBlock = bc.GetBlock(newBlock.ParentHash(), newBlock.NumberU64()-1) {
			newChain = append(newChain, newBlock)
		}
	}
	if oldBlock == nil {
		return fmt.Errorf("invalid old chain")
	}
	if newBlock == nil {
		return fmt.Errorf("invalid new chain")
	}
	// Both sides of the reorg are at the same number, reduce both until the common
	// ancestor is found
	for {
		// If the common ancestor was found, bail out
		if oldBlock.Hash() == newBlock.Hash() {
			commonBlock = oldBlock
			break
		}
		// Remove an old block as well as stash away a new block
		oldChain = append(oldChain, oldBlock)
		deletedTxs = append(deletedTxs, oldBlock.Transactions()...)
		collectLogs(oldBlock.Hash(), true)

		newChain = append(newChain, newBlock)

		// Step back with both chains
		oldBlock = bc.GetBlock(oldBlock.ParentHash(), oldBlock.NumberU64()-1)
		if oldBlock == nil {
			return fmt.Errorf("invalid old chain")
		}
		newBlock = bc.GetBlock(newBlock.ParentHash(), newBlock.NumberU64()-1)
		if newBlock == nil {
			return fmt.Errorf("invalid new chain")
		}
	}
	// Ensure the user sees large reorgs
	if len(oldChain) > 0 && len(newChain) > 0 {
		logFn := log.Info
		msg := "Chain reorg detected"
		if len(oldChain) > 63 {
			msg = "Large chain reorg detected"
			logFn = log.Warn
		}
		logFn(msg, "number", commonBlock.Number(), "hash", commonBlock.Hash(),
			"drop", len(oldChain), "dropfrom", oldChain[0].Hash(), "add", len(newChain), "addfrom", newChain[0].Hash())
		blockReorgAddMeter.Mark(int64(len(newChain)))
		blockReorgDropMeter.Mark(int64(len(oldChain)))
	} else {
		log.Error("Impossible reorg, please file an issue", "oldnum", oldBlock.Number(), "oldhash", oldBlock.Hash(), "newnum", newBlock.Number(), "newhash", newBlock.Hash())
	}
	// Insert the new chain(except the head block(reverse order)),
	// taking care of the proper incremental order.
	for i := len(newChain) - 1; i >= 1; i-- {
		// Insert the block in the canonical way, re-writing history
		bc.insert(newChain[i])

		// Collect reborn logs due to chain reorg
		collectLogs(newChain[i].Hash(), false)

		// Write lookup entries for hash based transaction/receipt searches
		rawdb.WriteTxLookupEntries(bc.db, newChain[i])
		addedTxs = append(addedTxs, newChain[i].Transactions()...)
	}
	// When transactions get deleted from the database, the receipts that were
	// created in the fork must also be deleted
	batch := bc.db.NewBatch()
	for _, tx := range types.TxDifference(deletedTxs, addedTxs) {
		rawdb.DeleteTxLookupEntry(batch, tx.Hash())
	}
	// Delete any canonical number assignments above the new head
	number := bc.CurrentBlock().NumberU64()
	for i := number + 1; ; i++ {
		hash := rawdb.ReadCanonicalHash(bc.db, i)
		if hash == (common.Hash{}) {
			break
		}
		rawdb.DeleteCanonicalHash(batch, i)
	}
	batch.Write()
	// If any logs need to be fired, do it now. In theory we could avoid creating
	// this goroutine if there are no events to fire, but realistcally that only
	// ever happens if we're reorging empty blocks, which will only happen on idle
	// networks where performance is not an issue either way.
	//
	// TODO(karalabe): Can we get rid of the goroutine somehow to guarantee correct
	// event ordering?
	go func() {
		if len(deletedLogs) > 0 {
			bc.rmLogsFeed.Send(RemovedLogsEvent{deletedLogs})
		}
		if len(rebirthLogs) > 0 {
			bc.logsFeed.Send(rebirthLogs)
		}
		if len(oldChain) > 0 {
			for _, block := range oldChain {
				bc.chainSideFeed.Send(ChainSideEvent{Block: block})
			}
		}
	}()
	return nil
}

// PostChainEvents iterates over the events generated by a chain insertion and
// posts them into the event feed.
// TODO: Should not expose PostChainEvents. The chain events should be posted in WriteBlock.
func (bc *BlockChain) PostChainEvents(events []interface{}, logs []*types.Log) {
	// post event logs for further processing
	if logs != nil {
		bc.logsFeed.Send(logs)
	}
	for _, event := range events {
		switch ev := event.(type) {
		case ChainEvent:
			bc.chainFeed.Send(ev)

		case ChainHeadEvent:
			bc.chainHeadFeed.Send(ev)

		case ChainSideEvent:
			bc.chainSideFeed.Send(ev)
		}
	}
}

func (bc *BlockChain) update() {
	futureTimer := time.NewTicker(5 * time.Second)
	defer futureTimer.Stop()
	for {
		select {
		case <-futureTimer.C:
			bc.procFutureBlocks()
		case <-bc.quit:
			return
		}
	}
}

// BadBlocks returns a list of the last 'bad blocks' that the client has seen on the network
func (bc *BlockChain) BadBlocks() []*types.Block {
	blocks := make([]*types.Block, 0, bc.badBlocks.Len())
	for _, hash := range bc.badBlocks.Keys() {
		if blk, exist := bc.badBlocks.Peek(hash); exist {
			block := blk.(*types.Block)
			blocks = append(blocks, block)
		}
	}
	return blocks
}

// HasBadBlock returns whether the block with the hash is a bad block
func (bc *BlockChain) HasBadBlock(hash common.Hash) bool {
	return bc.badBlocks.Contains(hash)
}

// addBadBlock adds a bad block to the bad-block LRU cache
func (bc *BlockChain) addBadBlock(block *types.Block) {
	bc.badBlocks.Add(block.Hash(), block)
}

// reportBlock logs a bad block error.
func (bc *BlockChain) reportBlock(block *types.Block, receipts types.Receipts, err error) {
	bc.addBadBlock(block)

	var receiptString string
	for i, receipt := range receipts {
		receiptString += fmt.Sprintf("\t %d: cumulative: %v gas: %v contract: %v status: %v tx: %v logs: %v bloom: %x state: %x\n",
			i, receipt.CumulativeGasUsed, receipt.GasUsed, receipt.ContractAddress.Hex(),
			receipt.Status, receipt.TxHash.Hex(), receipt.Logs, receipt.Bloom, receipt.PostState)
	}
	log.Error(fmt.Sprintf(`
########## BAD BLOCK #########
Chain config: %v

Number: %v
Hash: 0x%x
%v

Error: %v
##############################
`, bc.chainConfig, block.Number(), block.Hash(), receiptString, err))
}

// InsertHeaderChain attempts to insert the given header chain in to the local
// chain, possibly creating a reorg. If an error is returned, it will return the
// index number of the failing header as well an error describing what went wrong.
func (bc *BlockChain) InsertHeaderChain(chain []*types.Header, checkFreq int, contiguousHeaders bool) (int, error) {
	start := time.Now()
	if i, err := bc.hc.ValidateHeaderChain(chain, checkFreq, true); err != nil {
		return i, err
	}

	// Make sure only one thread manipulates the chain at once
	bc.chainmu.Lock()
	defer bc.chainmu.Unlock()

	bc.wg.Add(1)
	defer bc.wg.Done()

	whFunc := func(header *types.Header) error {
		_, err := bc.hc.WriteHeader(header)
		return err
	}
	return bc.hc.InsertHeaderChain(chain, whFunc, start)
}

// CurrentHeader retrieves the current head header of the canonical chain. The
// header is retrieved from the HeaderChain's internal cache.
func (bc *BlockChain) CurrentHeader() *types.Header {
	return bc.hc.CurrentHeader()
}

// GetTd retrieves a block's total difficulty in the canonical chain from the
// database by hash and number, caching it if found.
func (bc *BlockChain) GetTd(hash common.Hash, number uint64) *big.Int {
	return bc.hc.GetTd(hash, number)
}

// GetTdByHash retrieves a block's total difficulty in the canonical chain from the
// database by hash, caching it if found.
func (bc *BlockChain) GetTdByHash(hash common.Hash) *big.Int {
	return bc.hc.GetTdByHash(hash)
}

// GetHeader retrieves a block header from the database by hash and number,
// caching it if found.
func (bc *BlockChain) GetHeader(hash common.Hash, number uint64) *types.Header {
	return bc.hc.GetHeader(hash, number)
}

// GetHeaderByHash retrieves a block header from the database by hash, caching it if
// found.
func (bc *BlockChain) GetHeaderByHash(hash common.Hash) *types.Header {
	return bc.hc.GetHeaderByHash(hash)
}

// HasHeader checks if a block header is present in the database or not, caching
// it if present.
func (bc *BlockChain) HasHeader(hash common.Hash, number uint64) bool {
	return bc.hc.HasHeader(hash, number)
}

// GetCanonicalHash returns the canonical hash for a given block number
func (bc *BlockChain) GetCanonicalHash(number uint64) common.Hash {
	return bc.hc.GetCanonicalHash(number)
}

// GetBlockHashesFromHash retrieves a number of block hashes starting at a given
// hash, fetching towards the genesis block.
func (bc *BlockChain) GetBlockHashesFromHash(hash common.Hash, max uint64) []common.Hash {
	return bc.hc.GetBlockHashesFromHash(hash, max)
}

// GetAncestor retrieves the Nth ancestor of a given block. It assumes that either the given block or
// a close ancestor of it is canonical. maxNonCanonical points to a downwards counter limiting the
// number of blocks to be individually checked before we reach the canonical chain.
//
// Note: ancestor == 0 returns the same block, 1 returns its parent and so on.
func (bc *BlockChain) GetAncestor(hash common.Hash, number, ancestor uint64, maxNonCanonical *uint64) (common.Hash, uint64) {
	return bc.hc.GetAncestor(hash, number, ancestor, maxNonCanonical)
}

// GetHeaderByNumber retrieves a block header from the database by number,
// caching it (associated with its hash) if found.
func (bc *BlockChain) GetHeaderByNumber(number uint64) *types.Header {
	return bc.hc.GetHeaderByNumber(number)
}

// GetTransactionLookup retrieves the lookup associate with the given transaction
// hash from the cache or database.
func (bc *BlockChain) GetTransactionLookup(hash common.Hash) *rawdb.LegacyTxLookupEntry {
	// Short circuit if the txlookup already in the cache, retrieve otherwise
	if lookup, exist := bc.txLookupCache.Get(hash); exist {
		return lookup.(*rawdb.LegacyTxLookupEntry)
	}
	tx, blockHash, blockNumber, txIndex := rawdb.ReadTransaction(bc.db, hash)
	if tx == nil {
		return nil
	}
	lookup := &rawdb.LegacyTxLookupEntry{BlockHash: blockHash, BlockIndex: blockNumber, Index: txIndex}
	bc.txLookupCache.Add(hash, lookup)
	return lookup
}

// Config retrieves the chain's fork configuration.
func (bc *BlockChain) Config() *params.ChainConfig { return bc.chainConfig }

// Engine retrieves the blockchain's consensus engine.
func (bc *BlockChain) Engine() consensus.Engine { return bc.engine }

// SubscribeRemovedLogsEvent registers a subscription of RemovedLogsEvent.
func (bc *BlockChain) SubscribeRemovedLogsEvent(ch chan<- RemovedLogsEvent) event.Subscription {
	return bc.scope.Track(bc.rmLogsFeed.Subscribe(ch))
}

// SubscribeChainEvent registers a subscription of ChainEvent.
func (bc *BlockChain) SubscribeChainEvent(ch chan<- ChainEvent) event.Subscription {
	return bc.scope.Track(bc.chainFeed.Subscribe(ch))
}

// SubscribeChainHeadEvent registers a subscription of ChainHeadEvent.
func (bc *BlockChain) SubscribeChainHeadEvent(ch chan<- ChainHeadEvent) event.Subscription {
	return bc.scope.Track(bc.chainHeadFeed.Subscribe(ch))
}

// SubscribeChainSideEvent registers a subscription of ChainSideEvent.
func (bc *BlockChain) SubscribeChainSideEvent(ch chan<- ChainSideEvent) event.Subscription {
	return bc.scope.Track(bc.chainSideFeed.Subscribe(ch))
}

// SubscribeLogsEvent registers a subscription of []*types.Log.
func (bc *BlockChain) SubscribeLogsEvent(ch chan<- []*types.Log) event.Subscription {
	return bc.scope.Track(bc.logsFeed.Subscribe(ch))
}

// SubscribeBlockProcessingEvent registers a subscription of bool where true means
// block processing has started while false means it has stopped.
func (bc *BlockChain) SubscribeBlockProcessingEvent(ch chan<- bool) event.Subscription {
	return bc.scope.Track(bc.blockProcFeed.Subscribe(ch))
}