path: root/core/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/big"
    mrand "math/rand"
    "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/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"
    "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)

    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
    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
    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)
    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,
        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
    }
    // 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 (ethash cache or clique voting snapshot). 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)
            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
}

// 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
        }
    }
    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.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
}

// GasLimit returns the gas limit of the current HEAD block.
func (bc *BlockChain) GasLimit() uint64 {
    return bc.CurrentBlock().GasLimit()
}

// 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.Difficulty()); 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) {
    // 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 and uncles) 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
}

// GetUnclesInChain retrieves all the uncles from a given block backwards until
// a specific distance is reached.
func (bc *BlockChain) GetUnclesInChain(block *types.Block, length int) []*types.Header {
    uncles := []*types.Header{}
    for i := 0; block != nil && i < length; i++ {
        uncles = append(uncles, block.Uncles()...)
        block = bc.GetBlock(block.ParentHash(), block.NumberU64()-1)
    }
    return uncles
}

// 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 {
        types.BlockBy(types.Number).Sort(blocks)

        // 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) {
    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.futureBlocks.Purge()

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

// 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) {
    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 {
        var isCanonical bool
        bc.chainmu.Lock()
        if td := bc.GetTd(head.Hash(), head.NumberU64()); td != nil { // Rewind may have occurred, skip in that case
            currentFastBlock := bc.CurrentFastBlock()
            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()))
                isCanonical = true
            }
        }
        bc.chainmu.Unlock()
        return isCanonical
    }
    // 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 types.Blocks
        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, b)
                }
                if time.Since(logged) > 8*time.Second {
                    log.Info("Migrating ancient blocks", "count", count, "elapsed", common.PrettyDuration(time.Since(start)))
                    logged = time.Now()
                }
            }
            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 _, block := range append(deleted, 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 _, block := range append(deleted, 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
}

// 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()

    // 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 := new(big.Int).Add(block.Difficulty(), ptd)

    // 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, block.Difficulty())
            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:
        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
        }
        // If the block is known (in the middle of the chain), it's a special case for
        // Clique blocks where they can share state among each other, so importing an
        // older block might complete the state of the subsequent one. 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.Debug
            if bc.chainConfig.Clique == nil {
                logger = log.Warn
            }
            logger("Inserted known block", "number", block.Number(), "hash", block.Hash(),
                "uncles", len(block.Uncles()), "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
            // Clique 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(), "hash", block.Hash(),
                "uncles", len(block.Uncles()), "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(),
                "diff", block.Difficulty(), "elapsed", common.PrettyDuration(time.Since(start)),
                "txs", len(block.Transactions()), "gas", block.GasUsed(), "uncles", len(block.Uncles()),
                "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(),
                "diff", block.Difficulty(), "elapsed", common.PrettyDuration(time.Since(start)),
                "txs", len(block.Transactions()), "gas", block.GasUsed(), "uncles", len(block.Uncles()),
                "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
                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")
            }
        }
        if externTd == nil {
            externTd = bc.GetTd(block.ParentHash(), block.NumberU64()-1)
        }
        externTd = new(big.Int).Add(externTd, block.Difficulty())

        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(),
                "diff", block.Difficulty(), "elapsed", common.PrettyDuration(time.Since(start)),
                "txs", len(block.Transactions()), "gas", block.GasUsed(), "uncles", len(block.Uncles()),
                "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.Debug
        if len(oldChain) > 63 {
            logFn = log.Warn
        }
        logFn("Chain split detected", "number", commonBlock.Number(), "hash", commonBlock.Hash(),
            "drop", len(oldChain), "dropfrom", oldChain[0].Hash(), "add", len(newChain), "addfrom", newChain[0].Hash())
    } 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
}

// 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.
//
// The verify parameter can be used to fine tune whether nonce verification
// should be done or not. The reason behind the optional check is because some
// of the header retrieval mechanisms already need to verify nonces, as well as
// because nonces can be verified sparsely, not needing to check each.
func (bc *BlockChain) InsertHeaderChain(chain []*types.Header, checkFreq int) (int, error) {
    start := time.Now()
    if i, err := bc.hc.ValidateHeaderChain(chain, checkFreq); 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)
}

// 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) {
    bc.chainmu.RLock()
    defer bc.chainmu.RUnlock()

    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)
}

// Config retrieves the blockchain's chain 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))
}