core: implement insert chain, headerchain logic

3 files changed, 521 insertions, 0 deletions

diff --git a/core/blockchain.go b/core/blockchain.go
index 8bf680c38..293bb88f4 100644
--- a/core/blockchain.go
+++ b/core/blockchain.go
@@ -29,6 +29,7 @@ import (
 	"time"
 
 	coreCommon "github.com/dexon-foundation/dexon-consensus/common"
+	dexCore "github.com/dexon-foundation/dexon-consensus/core"
 	coreTypes "github.com/dexon-foundation/dexon-consensus/core/types"
 	"github.com/hashicorp/golang-lru"
 
@@ -145,6 +146,8 @@ type BlockChain struct {
 
 	roundHeightMap sync.Map
 
+	verifierCache *dexCore.TSigVerifierCache
+
 	confirmedBlockInitMu sync.Mutex
 	confirmedBlocks      map[uint32]map[coreCommon.Hash]*blockInfo
 	addressNonce         map[uint32]map[common.Address]uint64
@@ -231,6 +234,9 @@ func NewBlockChain(db ethdb.Database, cacheConfig *CacheConfig, chainConfig *par
 		}
 	}
 
+	gov := NewGovernance(bc)
+	bc.verifierCache = dexCore.NewTSigVerifierCache(gov, 5)
+
 	// Take ownership of this particular state
 	go bc.update()
 	return bc, nil
@@ -1007,6 +1013,9 @@ func (bc *BlockChain) InsertReceiptChain(blockChain types.Blocks, receiptChain [
 			bytes += batch.ValueSize()
 			batch.Reset()
 		}
+		if _, ok := bc.GetRoundHeight(block.Round()); !ok {
+			bc.storeRoundHeight(block.Round(), block.NumberU64())
+		}
 	}
 	if batch.ValueSize() > 0 {
 		bytes += batch.ValueSize()
@@ -1527,6 +1536,205 @@ func (bc *BlockChain) insertSidechain(block *types.Block, it *insertIterator) (i
 	return 0, nil, nil, nil
 }
 
+// InsertChain2 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) InsertChain2(chain types.Blocks) (int, error) {
+	n, events, logs, err := bc.insertChain2(chain)
+	bc.PostChainEvents(events, logs)
+	return n, err
+}
+
+// insertChain2 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) insertChain2(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 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 := bc.hc.verifyTSig(block.Header(), bc.verifierCache)
+		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 := time.Now().Unix() + maxTimeFutureBlocks
+			if block.Time() > uint64(max) {
+				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.insertChain2(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)
+		if _, ok := bc.GetRoundHeight(block.Round()); !ok {
+			bc.storeRoundHeight(block.Round(), block.NumberU64())
+		}
+	}
+	// 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
+}
+
 func (bc *BlockChain) ProcessPendingBlock(block *types.Block, witness *coreTypes.Witness) (*common.Hash, error) {
 	n, events, logs, err := bc.processPendingBlock(block, witness)
 	bc.PostChainEvents(events, logs)
@@ -2014,6 +2222,24 @@ func (bc *BlockChain) InsertHeaderChain(chain []*types.Header, checkFreq int) (i
 	return bc.hc.InsertHeaderChain(chain, whFunc, start)
 }
 
+func (bc *BlockChain) InsertHeaderChain2(chain []*types.HeaderWithGovState, verifierCache *dexCore.TSigVerifierCache) (int, error) {
+	start := time.Now()
+	bc.chainmu.Lock()
+	defer bc.chainmu.Unlock()
+
+	bc.wg.Add(1)
+	defer bc.wg.Done()
+
+	whFunc := func(header *types.HeaderWithGovState) error {
+		bc.mu.Lock()
+		defer bc.mu.Unlock()
+		_, err := bc.hc.WriteHeader2(header)
+		return err
+	}
+
+	return bc.hc.InsertHeaderChain2(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.
diff --git a/core/governance.go b/core/governance.go
new file mode 100644
index 000000000..261db1e75
--- /dev/null
+++ b/core/governance.go
@@ -0,0 +1,102 @@
+package core
+
+import (
+	"math/big"
+	"time"
+
+	dexCore "github.com/dexon-foundation/dexon-consensus/core"
+	coreTypes "github.com/dexon-foundation/dexon-consensus/core/types"
+	dkgTypes "github.com/dexon-foundation/dexon-consensus/core/types/dkg"
+
+	"github.com/dexon-foundation/dexon/core/vm"
+	"github.com/dexon-foundation/dexon/log"
+	"github.com/dexon-foundation/dexon/rlp"
+)
+
+type Governance struct {
+	bc *BlockChain
+}
+
+func NewGovernance(bc *BlockChain) *Governance {
+	return &Governance{bc: bc}
+}
+
+func (g *Governance) getHeadHelper() *vm.GovernanceStateHelper {
+	headState, err := g.bc.State()
+	if err != nil {
+		log.Error("get head state fail", "err", err)
+		panic(err)
+	}
+	return &vm.GovernanceStateHelper{headState}
+}
+
+func (g *Governance) getConfigHelper(round uint64) *vm.GovernanceStateHelper {
+	if round < dexCore.ConfigRoundShift {
+		round = 0
+	} else {
+		round -= dexCore.ConfigRoundShift
+	}
+	return g.getHelperAtRound(round)
+}
+
+func (g *Governance) getHelperAtRound(round uint64) *vm.GovernanceStateHelper {
+	headHelper := g.getHeadHelper()
+	height := headHelper.RoundHeight(big.NewInt(int64(round))).Uint64()
+	header := g.bc.GetHeaderByNumber(height)
+	s, err := g.bc.StateAt(header.Root)
+	if err != nil {
+		log.Error("get state fail", "err", err)
+		panic(err)
+	}
+	return &vm.GovernanceStateHelper{s}
+}
+
+func (g *Governance) Configuration(round uint64) *coreTypes.Config {
+	helper := g.getConfigHelper(round)
+	c := helper.Configuration()
+	return &coreTypes.Config{
+		NumChains:        c.NumChains,
+		LambdaBA:         time.Duration(c.LambdaBA) * time.Millisecond,
+		LambdaDKG:        time.Duration(c.LambdaDKG) * time.Millisecond,
+		K:                int(c.K),
+		PhiRatio:         c.PhiRatio,
+		NotarySetSize:    c.NotarySetSize,
+		DKGSetSize:       c.DKGSetSize,
+		RoundInterval:    time.Duration(c.RoundInterval) * time.Millisecond,
+		MinBlockInterval: time.Duration(c.MinBlockInterval) * time.Millisecond,
+	}
+}
+
+func (g *Governance) DKGComplaints(round uint64) []*dkgTypes.Complaint {
+	headHelper := g.getHeadHelper()
+	var dkgComplaints []*dkgTypes.Complaint
+	for _, pk := range headHelper.DKGComplaints(big.NewInt(int64(round))) {
+		x := new(dkgTypes.Complaint)
+		if err := rlp.DecodeBytes(pk, x); err != nil {
+			panic(err)
+		}
+		dkgComplaints = append(dkgComplaints, x)
+	}
+	return dkgComplaints
+}
+
+func (g *Governance) DKGMasterPublicKeys(round uint64) []*dkgTypes.MasterPublicKey {
+	headHelper := g.getHeadHelper()
+	var dkgMasterPKs []*dkgTypes.MasterPublicKey
+	for _, pk := range headHelper.DKGMasterPublicKeys(big.NewInt(int64(round))) {
+		x := new(dkgTypes.MasterPublicKey)
+		if err := rlp.DecodeBytes(pk, x); err != nil {
+			panic(err)
+		}
+		dkgMasterPKs = append(dkgMasterPKs, x)
+	}
+	return dkgMasterPKs
+}
+
+func (g *Governance) IsDKGFinal(round uint64) bool {
+	headHelper := g.getHeadHelper()
+	configHelper := g.getConfigHelper(round)
+	threshold := 2*configHelper.DKGSetSize().Uint64()/3 + 1
+	count := headHelper.DKGFinalizedsCount(big.NewInt(int64(round))).Uint64()
+	return count >= threshold
+}
diff --git a/core/headerchain.go b/core/headerchain.go
index 76ca1c1dd..a57e509ca 100644
--- a/core/headerchain.go
+++ b/core/headerchain.go
@@ -26,13 +26,20 @@ import (
 	"sync/atomic"
 	"time"
 
+	dexCore "github.com/dexon-foundation/dexon-consensus/core"
+	coreCrypto "github.com/dexon-foundation/dexon-consensus/core/crypto"
+	coreTypes "github.com/dexon-foundation/dexon-consensus/core/types"
+
 	"github.com/dexon-foundation/dexon/common"
 	"github.com/dexon-foundation/dexon/consensus"
 	"github.com/dexon-foundation/dexon/core/rawdb"
 	"github.com/dexon-foundation/dexon/core/types"
+	"github.com/dexon-foundation/dexon/crypto"
 	"github.com/dexon-foundation/dexon/ethdb"
 	"github.com/dexon-foundation/dexon/log"
 	"github.com/dexon-foundation/dexon/params"
+	"github.com/dexon-foundation/dexon/rlp"
+	"github.com/dexon-foundation/dexon/trie"
 	"github.com/hashicorp/golang-lru"
 )
 
@@ -297,6 +304,192 @@ func (hc *HeaderChain) InsertHeaderChain(chain []*types.Header, writeHeader WhCa
 	return 0, nil
 }
 
+func (hc *HeaderChain) WriteHeader2(header *types.HeaderWithGovState) (status WriteStatus, err error) {
+	// Cache some values to prevent constant recalculation
+	var (
+		hash   = header.Hash()
+		number = header.Number.Uint64()
+	)
+	// Calculate the total difficulty of the header
+	ptd := hc.GetTd(header.ParentHash, number-1)
+	if ptd == nil {
+		return NonStatTy, consensus.ErrUnknownAncestor
+	}
+	localTd := hc.GetTd(hc.currentHeaderHash, hc.CurrentHeader().Number.Uint64())
+	externTd := new(big.Int).Add(header.Difficulty, ptd)
+
+	// Irrelevant of the canonical status, write the td and header to the database
+	if err := hc.WriteTd(hash, number, externTd); err != nil {
+		log.Crit("Failed to write header total difficulty", "err", err)
+	}
+	rawdb.WriteHeader(hc.chainDb, header.Header)
+
+	// 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
+	if externTd.Cmp(localTd) > 0 || (externTd.Cmp(localTd) == 0 && mrand.Float64() < 0.5) {
+		// Delete any canonical number assignments above the new head
+		batch := hc.chainDb.NewBatch()
+		for i := number + 1; ; i++ {
+			hash := rawdb.ReadCanonicalHash(hc.chainDb, i)
+			if hash == (common.Hash{}) {
+				break
+			}
+			rawdb.DeleteCanonicalHash(batch, i)
+		}
+		batch.Write()
+
+		// Overwrite any stale canonical number assignments
+		var (
+			headHash   = header.ParentHash
+			headNumber = header.Number.Uint64() - 1
+			headHeader = hc.GetHeader(headHash, headNumber)
+		)
+		for rawdb.ReadCanonicalHash(hc.chainDb, headNumber) != headHash {
+			rawdb.WriteCanonicalHash(hc.chainDb, headHash, headNumber)
+
+			headHash = headHeader.ParentHash
+			headNumber = headHeader.Number.Uint64() - 1
+			headHeader = hc.GetHeader(headHash, headNumber)
+		}
+		// Extend the canonical chain with the new header
+		rawdb.WriteCanonicalHash(hc.chainDb, hash, number)
+		rawdb.WriteHeadHeaderHash(hc.chainDb, hash)
+
+		hc.currentHeaderHash = hash
+		hc.currentHeader.Store(types.CopyHeader(header.Header))
+
+		status = CanonStatTy
+	} else {
+		status = SideStatTy
+	}
+
+	hc.headerCache.Add(hash, header.Header)
+	hc.numberCache.Add(hash, number)
+
+	// Store the govState
+	if govState := header.GovState; govState != nil {
+		batch := hc.chainDb.NewBatch()
+		for _, node := range govState.Proof {
+			batch.Put(crypto.Keccak256(node), node)
+		}
+		if err := batch.Write(); err != nil {
+			panic(fmt.Errorf("DB write error: %v", err))
+		}
+
+		triedb := trie.NewDatabase(hc.chainDb)
+		t, err := trie.New(common.Hash{}, triedb)
+		if err != nil {
+			panic(err)
+		}
+
+		for _, kv := range govState.Storage {
+			t.TryUpdate(kv[0], kv[1])
+		}
+		t.Commit(nil)
+		triedb.Commit(t.Hash(), false)
+	}
+	return
+}
+
+type Wh2Callback func(*types.HeaderWithGovState) error
+
+func (hc *HeaderChain) ValidateHeaderChain2(chain []*types.HeaderWithGovState, verifierCache *dexCore.TSigVerifierCache) (int, error) {
+	// Do a sanity check that the provided chain is actually ordered and linked
+	for i := 1; i < len(chain); i++ {
+		if chain[i].Number.Uint64() != chain[i-1].Number.Uint64()+1 || chain[i].ParentHash != chain[i-1].Hash() {
+			// Chain broke ancestry, log a message (programming error) and skip insertion
+			log.Error("Non contiguous header 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, fmt.Errorf("non contiguous insert: item %d is #%d [%x…], item %d is #%d [%x…] (parent [%x…])", i-1, chain[i-1].Number,
+				chain[i-1].Hash().Bytes()[:4], i, chain[i].Number, chain[i].Hash().Bytes()[:4], chain[i].ParentHash[:4])
+		}
+	}
+
+	// Iterate over the headers and ensure they all check out
+	for i, header := range chain {
+		// If the chain is terminating, stop processing blocks
+		if hc.procInterrupt() {
+			log.Debug("Premature abort during headers verification")
+			return 0, errors.New("aborted")
+		}
+
+		if err := hc.verifyTSig(header.Header, verifierCache); err != nil {
+			return i, err
+		}
+	}
+	return 0, nil
+}
+
+func (hc *HeaderChain) verifyTSig(header *types.Header, verifierCache *dexCore.TSigVerifierCache) error {
+	// If the header is a banned one, straight out abort
+	if BadHashes[header.Hash()] {
+		return ErrBlacklistedHash
+	}
+
+	if header.Round == 0 {
+		return nil
+	}
+
+	var dexconMeta coreTypes.Block
+	if err := rlp.DecodeBytes(header.DexconMeta, &dexconMeta); err != nil {
+		return err
+	}
+
+	v, ok, err := verifierCache.UpdateAndGet(header.Round)
+	if err != nil {
+		panic(err)
+	}
+
+	if !ok {
+		panic(fmt.Errorf("DKG of round %d is not finished", header.Round))
+	}
+
+	if !v.VerifySignature(dexconMeta.Hash, coreCrypto.Signature{
+		Type:      "bls",
+		Signature: header.Randomness}) {
+		return fmt.Errorf("signature invalid")
+	}
+	return nil
+}
+
+// InsertHeaderChain2 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 verfy nonces, as well as
+// because nonces can be verified sparsely, not needing to check each.
+func (hc *HeaderChain) InsertHeaderChain2(chain []*types.HeaderWithGovState, writeHeader Wh2Callback, start time.Time) (int, error) {
+	// Collect some import statistics to report on
+	stats := struct{ processed, ignored int }{}
+	// All headers passed verification, import them into the database
+	for i, header := range chain {
+		// Short circuit insertion if shutting down
+		if hc.procInterrupt() {
+			log.Debug("Premature abort during headers import")
+			return i, errors.New("aborted")
+		}
+		// If the header's already known, skip it, otherwise store
+		if hc.HasHeader(header.Hash(), header.Number.Uint64()) {
+			stats.ignored++
+			continue
+		}
+		if err := writeHeader(header); err != nil {
+			return i, err
+		}
+		stats.processed++
+	}
+	// Report some public statistics so the user has a clue what's going on
+	last := chain[len(chain)-1]
+	log.Info("Imported new block headers", "count", stats.processed, "elapsed", common.PrettyDuration(time.Since(start)),
+		"number", last.Number, "hash", last.Hash(), "ignored", stats.ignored)
+
+	return 0, nil
+}
+
 // GetBlockHashesFromHash retrieves a number of block hashes starting at a given
 // hash, fetching towards the genesis block.
 func (hc *HeaderChain) GetBlockHashesFromHash(hash common.Hash, max uint64) []common.Hash {