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/crypto"
    "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 (
    blockInsertTimer = metrics.NewRegisteredTimer("chain/inserts", nil)

    ErrNoGenesis = errors.New("Genesis not found in chain")
)

const (
    bodyCacheLimit      = 256
    blockCacheLimit     = 256
    maxFutureBlocks     = 256
    maxTimeFutureBlocks = 30
    badBlockLimit       = 10
    triesInMemory       = 128

    // BlockChainVersion ensures that an incompatible database forces a resync from scratch.
    BlockChainVersion = 3
)

// CacheConfig contains the configuration values for the trie caching/pruning
// that's resident in a blockchain.
type CacheConfig struct {
    Disabled      bool          // Whether to disable trie write caching (archive node)
    TrieNodeLimit int           // Memory limit (MB) at which to flush the current in-memory trie to disk
    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
    scope         event.SubscriptionScope
    genesisBlock  *types.Block

    mu      sync.RWMutex // global mutex for locking chain operations
    chainmu sync.RWMutex // blockchain insertion lock
    procmu  sync.RWMutex // block processor lock

    checkpoint       int          // checkpoint counts towards the new checkpoint
    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
    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
    processor Processor // block processor interface
    validator Validator // block and state validator 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.
}

// 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{
            TrieNodeLimit: 256 * 1024 * 1024,
            TrieTimeLimit: 5 * time.Minute,
        }
    }
    bodyCache, _ := lru.New(bodyCacheLimit)
    bodyRLPCache, _ := lru.New(bodyCacheLimit)
    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.NewDatabase(db),
        quit:           make(chan struct{}),
        shouldPreserve: shouldPreserve,
        bodyCache:      bodyCache,
        bodyRLPCache:   bodyRLPCache,
        blockCache:     blockCache,
        futureBlocks:   futureBlocks,
        engine:         engine,
        vmConfig:       vmConfig,
        badBlocks:      badBlocks,
    }
    bc.SetValidator(NewBlockValidator(chainConfig, bc, engine))
    bc.SetProcessor(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
    }
    if err := bc.loadLastState(); err != nil {
        return nil, err
    }
    // 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
}

// 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
        }
    }
    // Everything seems to be fine, set as the head block
    bc.currentBlock.Store(currentBlock)

    // 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)
    if head := rawdb.ReadHeadFastBlockHash(bc.db); head != (common.Hash{}) {
        if block := bc.GetBlockByHash(head); block != nil {
            bc.currentFastBlock.Store(block)
        }
    }

    // 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(currentHeader.Time.Int64(), 0)))
    log.Info("Loaded most recent local full block", "number", currentBlock.Number(), "hash", currentBlock.Hash(), "td", blockTd, "age", common.PrettyAge(time.Unix(currentBlock.Time().Int64(), 0)))
    log.Info("Loaded most recent local fast block", "number", currentFastBlock.Number(), "hash", currentFastBlock.Hash(), "td", fastTd, "age", common.PrettyAge(time.Unix(currentFastBlock.Time().Int64(), 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.mu.Lock()
    defer bc.mu.Unlock()

    // Rewind the header chain, deleting all block bodies until then
    delFn := func(db rawdb.DatabaseDeleter, hash common.Hash, num uint64) {
        rawdb.DeleteBody(db, hash, num)
    }
    bc.hc.SetHead(head, delFn)
    currentHeader := bc.hc.CurrentHeader()

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

    // Rewind the block chain, ensuring we don't end up with a stateless head block
    if currentBlock := bc.CurrentBlock(); currentBlock != nil && currentHeader.Number.Uint64() < currentBlock.NumberU64() {
        bc.currentBlock.Store(bc.GetBlock(currentHeader.Hash(), currentHeader.Number.Uint64()))
    }
    if currentBlock := bc.CurrentBlock(); currentBlock != nil {
        if _, err := state.New(currentBlock.Root(), bc.stateCache); err != nil {
            // Rewound state missing, rolled back to before pivot, reset to genesis
            bc.currentBlock.Store(bc.genesisBlock)
        }
    }
    // Rewind the fast block in a simpleton way to the target head
    if currentFastBlock := bc.CurrentFastBlock(); currentFastBlock != nil && currentHeader.Number.Uint64() < currentFastBlock.NumberU64() {
        bc.currentFastBlock.Store(bc.GetBlock(currentHeader.Hash(), currentHeader.Number.Uint64()))
    }
    // If either blocks reached nil, reset to the genesis state
    if currentBlock := bc.CurrentBlock(); currentBlock == nil {
        bc.currentBlock.Store(bc.genesisBlock)
    }
    if currentFastBlock := bc.CurrentFastBlock(); currentFastBlock == nil {
        bc.currentFastBlock.Store(bc.genesisBlock)
    }
    currentBlock := bc.CurrentBlock()
    currentFastBlock := bc.CurrentFastBlock()

    rawdb.WriteHeadBlockHash(bc.db, currentBlock.Hash())
    rawdb.WriteHeadFastBlockHash(bc.db, currentFastBlock.Hash())

    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(), 0); err != nil {
        return err
    }
    // If all checks out, manually set the head block
    bc.mu.Lock()
    bc.currentBlock.Store(block)
    bc.mu.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)
}

// SetProcessor sets the processor required for making state modifications.
func (bc *BlockChain) SetProcessor(processor Processor) {
    bc.procmu.Lock()
    defer bc.procmu.Unlock()
    bc.processor = processor
}

// SetValidator sets the validator which is used to validate incoming blocks.
func (bc *BlockChain) SetValidator(validator Validator) {
    bc.procmu.Lock()
    defer bc.procmu.Unlock()
    bc.validator = validator
}

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

// Processor returns the current processor.
func (bc *BlockChain) Processor() Processor {
    bc.procmu.RLock()
    defer bc.procmu.RUnlock()
    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)
}

// 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.mu.Lock()
    defer bc.mu.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)
    bc.hc.SetGenesis(bc.genesisBlock.Header())
    bc.hc.SetCurrentHeader(bc.genesisBlock.Header())
    bc.currentFastBlock.Store(bc.genesisBlock)

    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
        (*head) = bc.GetBlock((*head).ParentHash(), (*head).NumberU64()-1)
    }
}

// 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.mu.RLock()
    defer bc.mu.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)

    // 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)
    }
}

// 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)
}

// 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 {
    number := rawdb.ReadHeaderNumber(bc.db, hash)
    if number == nil {
        return nil
    }
    return rawdb.ReadReceipts(bc.db, hash, *number)
}

// 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.Disabled {
        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.mu.Lock()
    defer bc.mu.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)
            bc.currentFastBlock.Store(newFastBlock)
            rawdb.WriteHeadFastBlockHash(bc.db, newFastBlock.Hash())
        }
        if currentBlock := bc.CurrentBlock(); currentBlock.Hash() == hash {
            newBlock := bc.GetBlock(currentBlock.ParentHash(), currentBlock.NumberU64()-1)
            bc.currentBlock.Store(newBlock)
            rawdb.WriteHeadBlockHash(bc.db, newBlock.Hash())
        }
    }
}

// SetReceiptsData computes all the non-consensus fields of the receipts
func SetReceiptsData(config *params.ChainConfig, block *types.Block, receipts types.Receipts) error {
    signer := types.MakeSigner(config, block.Number())

    transactions, logIndex := block.Transactions(), uint(0)
    if len(transactions) != len(receipts) {
        return errors.New("transaction and receipt count mismatch")
    }

    for j := 0; j < len(receipts); j++ {
        // The transaction hash can be retrieved from the transaction itself
        receipts[j].TxHash = transactions[j].Hash()

        // The contract address can be derived from the transaction itself
        if transactions[j].To() == nil {
            // Deriving the signer is expensive, only do if it's actually needed
            from, _ := types.Sender(signer, transactions[j])
            receipts[j].ContractAddress = crypto.CreateAddress(from, transactions[j].Nonce())
        }
        // The used gas can be calculated based on previous receipts
        if j == 0 {
            receipts[j].GasUsed = receipts[j].CumulativeGasUsed
        } else {
            receipts[j].GasUsed = receipts[j].CumulativeGasUsed - receipts[j-1].CumulativeGasUsed
        }
        // The derived log fields can simply be set from the block and transaction
        for k := 0; k < len(receipts[j].Logs); k++ {
            receipts[j].Logs[k].BlockNumber = block.NumberU64()
            receipts[j].Logs[k].BlockHash = block.Hash()
            receipts[j].Logs[k].TxHash = receipts[j].TxHash
            receipts[j].Logs[k].TxIndex = uint(j)
            receipts[j].Logs[k].Index = logIndex
            logIndex++
        }
    }
    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) (int, error) {
    bc.wg.Add(1)
    defer bc.wg.Done()

    // Do a sanity check that the provided chain is actually ordered and linked
    for i := 1; i < len(blockChain); i++ {
        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])
        }
    }

    var (
        stats = struct{ processed, ignored int32 }{}
        start = time.Now()
        bytes = 0
        batch = bc.db.NewBatch()
    )
    for i, block := range blockChain {
        receipts := receiptChain[i]
        // Short circuit insertion if shutting down or processing failed
        if atomic.LoadInt32(&bc.procInterrupt) == 1 {
            return 0, nil
        }
        // 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])
        }
        // Skip if the entire data is already known
        if bc.HasBlock(block.Hash(), block.NumberU64()) {
            stats.ignored++
            continue
        }
        // Compute all the non-consensus fields of the receipts
        if err := SetReceiptsData(bc.chainConfig, block, receipts); err != nil {
            return i, fmt.Errorf("failed to set receipts data: %v", err)
        }
        // Write all the data out into the database
        rawdb.WriteBody(batch, block.Hash(), block.NumberU64(), block.Body())
        rawdb.WriteReceipts(batch, block.Hash(), block.NumberU64(), receipts)
        rawdb.WriteTxLookupEntries(batch, block)

        stats.processed++

        if batch.ValueSize() >= ethdb.IdealBatchSize {
            if err := batch.Write(); err != nil {
                return 0, err
            }
            bytes += batch.ValueSize()
            batch.Reset()
        }
    }
    if batch.ValueSize() > 0 {
        bytes += batch.ValueSize()
        if err := batch.Write(); err != nil {
            return 0, err
        }
    }

    // Update the head fast sync block if better
    bc.mu.Lock()
    head := blockChain[len(blockChain)-1]
    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)
        }
    }
    bc.mu.Unlock()

    context := []interface{}{
        "count", stats.processed, "elapsed", common.PrettyDuration(time.Since(start)),
        "number", head.Number(), "hash", head.Hash(), "age", common.PrettyAge(time.Unix(head.Time().Int64(), 0)),
        "size", common.StorageSize(bytes),
    }
    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
}

// 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.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
    bc.mu.Lock()
    defer bc.mu.Unlock()

    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.Disabled {
        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.TrieNodeLimit) * 1024 * 1024
            )
            if nodes > limit || imgs > 4*1024*1024 {
                triedb.Cap(limit - ethdb.IdealBatchSize)
            }
            // Find the next state trie we need to commit
            header := bc.GetHeaderByNumber(current - triesInMemory)
            chosen := header.Number.Uint64()

            // If we exceeded out time allowance, flush an entire trie to disk
            if bc.gcproc > bc.cacheConfig.TrieTimeLimit {
                // 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, block.NumberU64(), 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
}

// 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) {
    n, events, logs, err := bc.insertChain(chain)
    bc.PostChainEvents(events, logs)
    return n, err
}

// insertChain will execute the actual chain insertion and event aggregation. The
// only reason this method exists as a separate one is to make locking cleaner
// with deferred statements.
func (bc *BlockChain) insertChain(chain types.Blocks) (int, []interface{}, []*types.Log, error) {
    // Sanity check that we have something meaningful to import
    if len(chain) == 0 {
        return 0, nil, nil, nil
    }
    // Do a sanity check that the provided chain is actually ordered and linked
    for i := 1; i < len(chain); i++ {
        if chain[i].NumberU64() != chain[i-1].NumberU64()+1 || chain[i].ParentHash() != chain[i-1].Hash() {
            // Chain broke ancestry, log a message (programming error) and skip insertion
            log.Error("Non contiguous block insert", "number", chain[i].Number(), "hash", chain[i].Hash(),
                "parent", chain[i].ParentHash(), "prevnumber", chain[i-1].Number(), "prevhash", chain[i-1].Hash())

            return 0, nil, nil, fmt.Errorf("non contiguous insert: item %d is #%d [%x…], item %d is #%d [%x…] (parent [%x…])", i-1, chain[i-1].NumberU64(),
                chain[i-1].Hash().Bytes()[:4], i, chain[i].NumberU64(), chain[i].Hash().Bytes()[:4], chain[i].ParentHash().Bytes()[:4])
        }
    }
    // Pre-checks passed, start the full block imports
    bc.wg.Add(1)
    defer bc.wg.Done()

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

    // 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] = true
    }
    abort, results := bc.engine.VerifyHeaders(bc, headers, seals)
    defer close(abort)

    // Start a parallel signature recovery (signer will fluke on fork transition, minimal perf loss)
    senderCacher.recoverFromBlocks(types.MakeSigner(bc.chainConfig, chain[0].Number()), chain)

    // Iterate over the blocks and insert when the verifier permits
    for i, block := range chain {
        // 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 i, events, coalescedLogs, ErrBlacklistedHash
        }
        // Wait for the block's verification to complete
        bstart := time.Now()

        err := <-results
        if err == nil {
            err = bc.Validator().ValidateBody(block)
        }
        switch {
        case err == ErrKnownBlock:
            // Block and state both already known. However if the current block is below
            // this number we did a rollback and we should reimport it nonetheless.
            if bc.CurrentBlock().NumberU64() >= block.NumberU64() {
                stats.ignored++
                continue
            }

        case err == consensus.ErrFutureBlock:
            // Allow up to MaxFuture second in the future blocks. If this limit is exceeded
            // the chain is discarded and processed at a later time if given.
            max := big.NewInt(time.Now().Unix() + maxTimeFutureBlocks)
            if block.Time().Cmp(max) > 0 {
                return i, events, coalescedLogs, fmt.Errorf("future block: %v > %v", block.Time(), max)
            }
            bc.futureBlocks.Add(block.Hash(), block)
            stats.queued++
            continue

        case err == consensus.ErrUnknownAncestor && bc.futureBlocks.Contains(block.ParentHash()):
            bc.futureBlocks.Add(block.Hash(), block)
            stats.queued++
            continue

        case err == consensus.ErrPrunedAncestor:
            // Block competing with the canonical chain, store in the db, but don't process
            // until the competitor TD goes above the canonical TD
            currentBlock := bc.CurrentBlock()
            localTd := bc.GetTd(currentBlock.Hash(), currentBlock.NumberU64())
            externTd := new(big.Int).Add(bc.GetTd(block.ParentHash(), block.NumberU64()-1), block.Difficulty())
            if localTd.Cmp(externTd) > 0 {
                if err = bc.WriteBlockWithoutState(block, externTd); err != nil {
                    return i, events, coalescedLogs, err
                }
                continue
            }
            // Competitor chain beat canonical, gather all blocks from the common ancestor
            var winner []*types.Block

            parent := bc.GetBlock(block.ParentHash(), block.NumberU64()-1)
            for !bc.HasState(parent.Root()) {
                winner = append(winner, parent)
                parent = bc.GetBlock(parent.ParentHash(), parent.NumberU64()-1)
            }
            for j := 0; j < len(winner)/2; j++ {
                winner[j], winner[len(winner)-1-j] = winner[len(winner)-1-j], winner[j]
            }
            // Import all the pruned blocks to make the state available
            bc.chainmu.Unlock()
            _, evs, logs, err := bc.insertChain(winner)
            bc.chainmu.Lock()
            events, coalescedLogs = evs, logs

            if err != nil {
                return i, events, coalescedLogs, err
            }

        case err != nil:
            bc.reportBlock(block, nil, err)
            return i, events, coalescedLogs, err
        }
        // Create a new statedb using the parent block and report an
        // error if it fails.
        var parent *types.Block
        if i == 0 {
            parent = bc.GetBlock(block.ParentHash(), block.NumberU64()-1)
        } else {
            parent = chain[i-1]
        }
        state, err := state.New(parent.Root(), bc.stateCache)
        if err != nil {
            return i, events, coalescedLogs, err
        }
        // Process block using the parent state as reference point.
        receipts, logs, usedGas, err := bc.processor.Process(block, state, bc.vmConfig)
        if err != nil {
            bc.reportBlock(block, receipts, err)
            return i, events, coalescedLogs, err
        }
        // Validate the state using the default validator
        err = bc.Validator().ValidateState(block, parent, state, receipts, usedGas)
        if err != nil {
            bc.reportBlock(block, receipts, err)
            return i, events, coalescedLogs, err
        }
        proctime := time.Since(bstart)

        // Write the block to the chain and get the status.
        status, err := bc.WriteBlockWithState(block, receipts, state)
        if err != nil {
            return i, events, coalescedLogs, err
        }
        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(bstart)))

            coalescedLogs = append(coalescedLogs, logs...)
            blockInsertTimer.UpdateSince(bstart)
            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(bstart)), "txs", len(block.Transactions()), "gas", block.GasUsed(), "uncles", len(block.Uncles()))

            blockInsertTimer.UpdateSince(bstart)
            events = append(events, ChainSideEvent{block})
        }
        stats.processed++
        stats.usedGas += usedGas

        cache, _ := bc.stateCache.TrieDB().Size()
        stats.report(chain, i, cache)
    }
    // 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 0, events, coalescedLogs, nil
}

// insertStats tracks and reports on block insertion.
type insertStats struct {
    queued, processed, ignored int
    usedGas                    uint64
    lastIndex                  int
    startTime                  mclock.AbsTime
}

// statsReportLimit is the time limit during import and export after which we
// always print out progress. This avoids the user wondering what's going on.
const statsReportLimit = 8 * time.Second

// report prints statistics if some number of blocks have been processed
// or more than a few seconds have passed since the last message.
func (st *insertStats) report(chain []*types.Block, index int, cache common.StorageSize) {
    // Fetch the timings for the batch
    var (
        now     = mclock.Now()
        elapsed = time.Duration(now) - time.Duration(st.startTime)
    )
    // If we're at the last block of the batch or report period reached, log
    if index == len(chain)-1 || elapsed >= statsReportLimit {
        var (
            end = chain[index]
            txs = countTransactions(chain[st.lastIndex : index+1])
        )
        context := []interface{}{
            "blocks", st.processed, "txs", txs, "mgas", float64(st.usedGas) / 1000000,
            "elapsed", common.PrettyDuration(elapsed), "mgasps", float64(st.usedGas) * 1000 / float64(elapsed),
            "number", end.Number(), "hash", end.Hash(),
        }
        if timestamp := time.Unix(end.Time().Int64(), 0); time.Since(timestamp) > time.Minute {
            context = append(context, []interface{}{"age", common.PrettyAge(timestamp)}...)
        }
        context = append(context, []interface{}{"cache", cache}...)

        if st.queued > 0 {
            context = append(context, []interface{}{"queued", st.queued}...)
        }
        if st.ignored > 0 {
            context = append(context, []interface{}{"ignored", st.ignored}...)
        }
        log.Info("Imported new chain segment", context...)

        *st = insertStats{startTime: now, lastIndex: index + 1}
    }
}

func countTransactions(chain []*types.Block) (c int) {
    for _, b := range chain {
        c += len(b.Transactions())
    }
    return c
}

// reorgs 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
        deletedLogs []*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.
        collectLogs = func(hash common.Hash) {
            // Coalesce logs and set 'Removed'.
            number := bc.hc.GetBlockNumber(hash)
            if number == nil {
                return
            }
            receipts := rawdb.ReadReceipts(bc.db, hash, *number)
            for _, receipt := range receipts {
                for _, log := range receipt.Logs {
                    del := *log
                    del.Removed = true
                    deletedLogs = append(deletedLogs, &del)
                }
            }
        }
    )

    // first reduce whoever is higher bound
    if oldBlock.NumberU64() > newBlock.NumberU64() {
        // reduce old chain
        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())
        }
    } else {
        // reduce new chain and append new chain blocks for inserting later on
        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")
    }

    for {
        if oldBlock.Hash() == newBlock.Hash() {
            commonBlock = oldBlock
            break
        }

        oldChain = append(oldChain, oldBlock)
        newChain = append(newChain, newBlock)
        deletedTxs = append(deletedTxs, oldBlock.Transactions()...)
        collectLogs(oldBlock.Hash())

        oldBlock, newBlock = bc.GetBlock(oldBlock.ParentHash(), oldBlock.NumberU64()-1), bc.GetBlock(newBlock.ParentHash(), newBlock.NumberU64()-1)
        if oldBlock == nil {
            return fmt.Errorf("Invalid old chain")
        }
        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, taking care of the proper incremental order
    var addedTxs types.Transactions
    for i := len(newChain) - 1; i >= 0; i-- {
        // insert the block in the canonical way, re-writing history
        bc.insert(newChain[i])
        // write lookup entries for hash based transaction/receipt searches
        rawdb.WriteTxLookupEntries(bc.db, newChain[i])
        addedTxs = append(addedTxs, newChain[i].Transactions()...)
    }
    // calculate the difference between deleted and added transactions
    diff := types.TxDifference(deletedTxs, addedTxs)
    // When transactions get deleted from the database that means the
    // receipts that were created in the fork must also be deleted
    batch := bc.db.NewBatch()
    for _, tx := range diff {
        rawdb.DeleteTxLookupEntry(batch, tx.Hash())
    }
    batch.Write()

    if len(deletedLogs) > 0 {
        go bc.rmLogsFeed.Send(RemovedLogsEvent{deletedLogs})
    }
    if len(oldChain) > 0 {
        go func() {
            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 _, receipt := range receipts {
        receiptString += fmt.Sprintf("\t%v\n", receipt)
    }
    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 {
        bc.mu.Lock()
        defer bc.mu.Unlock()

        _, err := bc.hc.WriteHeader(header)
        return err
    }

    return bc.hc.InsertHeaderChain(chain, whFunc, start)
}

// writeHeader writes a header into the local chain, given that its parent is
// already known. If the total difficulty of the newly inserted header becomes
// greater than the current known TD, the canonical chain is re-routed.
//
// Note: This method is not concurrent-safe with inserting blocks simultaneously
// into the chain, as side effects caused by reorganisations cannot be emulated
// without the real blocks. Hence, writing headers directly should only be done
// in two scenarios: pure-header mode of operation (light clients), or properly
// separated header/block phases (non-archive clients).
func (bc *BlockChain) writeHeader(header *types.Header) error {
    bc.wg.Add(1)
    defer bc.wg.Done()

    bc.mu.Lock()
    defer bc.mu.Unlock()

    _, err := bc.hc.WriteHeader(header)
    return err
}

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

    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))
}