core: rework blockchain import #17973

core/blockchain.go

@@ -741,16 +741,21 @@ func (bc *BlockChain) ExportN(w io.Writer, first uint64, last uint64) error {
 	}
 	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
 }
 
@@ -865,6 +870,12 @@ func (bc *BlockChain) HasFastBlock(hash common.Hash, number uint64) bool {
 	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
+}
+
 // HasFullState checks if state trie is fully present in the database or not.
 func (bc *BlockChain) HasFullState(block *types.Block) bool {
 	_, err := bc.stateCache.OpenTrie(block.Root())
@@ -1565,6 +1576,18 @@ func (bc *BlockChain) writeBlockWithState(block *types.Block, receipts []*types.
 	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 := big.NewInt(time.Now().Unix() + maxTimeFutureBlocks)
+	if block.Time().Cmp(max) > 0 {
+		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
@@ -1580,7 +1603,7 @@ func (bc *BlockChain) InsertChain(chain types.Blocks) (int, error) {
 	// Do a sanity check that the provided chain is actually ordered and linked
 	for i := 1; i < len(chain); i++ {
 		block, prev := chain[i], chain[i-1]
-		if block.NumberU64() != chain[i-1].NumberU64()+1 || block.ParentHash() != chain[i-1].Hash() {
+		if block.NumberU64() != prev.NumberU64()+1 || block.ParentHash() != prev.Hash() {
 			// Chain broke ancestry, log a messge (programming error) and skip insertion
 			log.Error("Non contiguous block insert",
 				"number", block.Number(),
@@ -1618,6 +1641,9 @@ func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, []
 		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.
@@ -1639,11 +1665,52 @@ func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, []
 	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)
+	// Peek the error for the first block to decide the directing import logic
+	it := newInsertIterator(chain, results, bc.Validator())
 
-	// Iterate over the blocks and insert when the verifier permits
-	for i, block := range chain {
+	block, err := it.next()
+	switch {
+	// First block is pruned, insert as sidechain and reorg only if TD grows enough
+	case err == consensus.ErrPrunedAncestor:
+		return bc.insertSidechain(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) {
+			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
+
+	// 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.
+	case err == ErrKnownBlock:
+		// Skip all known blocks that behind us
+		current := bc.CurrentBlock().NumberU64()
+
+		for block != nil && err == ErrKnownBlock && current >= block.NumberU64() {
+			stats.ignored++
+			block, err = it.next()
+		}
+		// Falls through to the block import
+
+	// 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; 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")
@@ -1652,87 +1719,19 @@ func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, []
 		// If the header is a banned one, straight out abort
 		if BadHashes[block.Hash()] {
 			bc.reportBlock(block, nil, ErrBlacklistedHash)
-			return i, events, coalescedLogs, ErrBlacklistedHash
+			return it.index, events, coalescedLogs, ErrBlacklistedHash
 		}
-		// Wait for the block's verification to complete
-		bstart := time.Now()
+		// Retrieve the parent block and it's state to execute on top
+		start := 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.HasFullState(parent) {
-				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]
-			}
-			log.Debug("Number block need calculated again", "number", block.NumberU64(), "hash", block.Hash().Hex(), "winners", len(winner))
-			// Import all the pruned blocks to make the state available
-			// During reorg, we use verifySeals=false
-			_, evs, logs, err := bc.insertChain(winner, false)
-			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
-		}
-		var parent *types.Block
-		if i == 0 {
+		parent := it.previous()
+		if parent == nil {
 			parent = bc.GetBlock(block.ParentHash(), block.NumberU64()-1)
-		} else {
-			parent = chain[i-1]
 		}
 		// Create a new statedb using the parent block and report an error if it fails.
 		statedb, err := state.New(parent.Root(), bc.stateCache)
 		if err != nil {
-			return i, events, coalescedLogs, err
+			return it.index, events, coalescedLogs, err
 		}
 		// Process block using the parent state as reference point.
 		t0 := time.Now()
@@ -1740,29 +1739,29 @@ func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, []
 		tradingState, lendingState, err := bc.processTradingAndLendingStates(isTIPXDCXReceiver, block, parent, statedb)
 		if err != nil {
 			bc.reportBlock(block, nil, err)
-			return i, events, coalescedLogs, err
+			return it.index, events, coalescedLogs, err
 		}
 		feeCapacity := state.GetTRC21FeeCapacityFromStateWithCache(parent.Root(), statedb)
 		receipts, logs, usedGas, err := bc.processor.Process(block, statedb, tradingState, bc.vmConfig, feeCapacity)
 		t1 := time.Now()
 		if err != nil {
 			bc.reportBlock(block, receipts, err)
-			return i, events, coalescedLogs, err
+			return it.index, events, coalescedLogs, err
 		}
 		// Validate the state using the default validator
 		err = bc.Validator().ValidateState(block, parent, statedb, receipts, usedGas)
 		if err != nil {
 			bc.reportBlock(block, receipts, err)
-			return i, events, coalescedLogs, err
+			return it.index, events, coalescedLogs, err
 		}
 		t2 := time.Now()
-		proctime := time.Since(bstart)
+		proctime := time.Since(start)
 
 		// Write the block to the chain and get the status.
 		status, err := bc.writeBlockWithState(block, receipts, statedb, tradingState, lendingState)
 		t3 := time.Now()
 		if err != nil {
-			return i, events, coalescedLogs, err
+			return it.index, events, coalescedLogs, err
 		}
 
 		// Update the metrics subsystem with all the measurements
@@ -1779,7 +1778,7 @@ func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, []
 		trieAccess := statedb.AccountReads + statedb.AccountHashes + statedb.AccountUpdates + statedb.AccountCommits
 		trieAccess += statedb.StorageReads + statedb.StorageHashes + statedb.StorageUpdates + statedb.StorageCommits
 
-		blockInsertTimer.UpdateSince(bstart)
+		blockInsertTimer.UpdateSince(start)
 		blockExecutionTimer.Update(t1.Sub(t0) - trieAccess)
 		blockValidationTimer.Update(t2.Sub(t1))
 		blockWriteTimer.Update(t3.Sub(t2))
@@ -1787,7 +1786,7 @@ func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, []
 		switch status {
 		case CanonStatTy:
 			log.Debug("Inserted new block from downloader", "number", block.Number(), "hash", block.Hash(), "uncles", len(block.Uncles()),
-				"txs", len(block.Transactions()), "gas", block.GasUsed(), "elapsed", common.PrettyDuration(time.Since(bstart)))
+				"txs", len(block.Transactions()), "gas", block.GasUsed(), "elapsed", common.PrettyDuration(time.Since(start)))
 
 			coalescedLogs = append(coalescedLogs, logs...)
 			events = append(events, ChainEvent{block, block.Hash(), logs})
@@ -1802,17 +1801,19 @@ func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, []
 			}
 		case SideStatTy:
 			log.Debug("Inserted forked block from downloader", "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()))
+				common.PrettyDuration(time.Since(start)), "txs", len(block.Transactions()), "gas", block.GasUsed(), "uncles", len(block.Uncles()))
 			events = append(events, ChainSideEvent{block})
 			bc.UpdateBlocksHashCache(block)
 		}
+		blockInsertTimer.UpdateSince(start)
 		stats.processed++
 		stats.usedGas += usedGas
+
 		dirty, _ := bc.stateCache.TrieDB().Size()
-		stats.report(chain, i, dirty)
+		stats.report(chain, it.index, dirty)
 		if bc.chainConfig.XDPoS != nil {
 			engine, _ := bc.Engine().(*XDPoS.XDPoS)
-			isEpochSwithBlock, _, err := engine.IsEpochSwitch(chain[i].Header()) // epoch block
+			isEpochSwithBlock, _, err := engine.IsEpochSwitch(block.Header()) // epoch block
 			if err != nil {
 				log.Error("[insertChain] Error while checking and notifying channel CheckpointCh if the incoming block is epoch switch block", "Hash", block.Hash(), "Number", block.Number())
 				bc.reportBlock(block, nil, err)
@@ -1822,12 +1823,142 @@ func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, []
 			}
 		}
 	}
+
+	// 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() {
 		log.Debug("New ChainHeadEvent ", "number", lastCanon.NumberU64(), "hash", lastCanon.Hash())
 		events = append(events, ChainHeadEvent{lastCanon})
 	}
-	return 0, events, coalescedLogs, nil
+	return it.index, events, coalescedLogs, nil
+}
+
+// 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(it *insertIterator) (int, []interface{}, []*types.Log, error) {
+	var (
+		externTd *big.Int
+		current  = bc.CurrentBlock().NumberU64()
+	)
+	// 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.
+	block, err := it.current(), 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 >= number {
+			if canonical := bc.GetBlockByNumber(number); 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("Inserted 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(bc.CurrentBlock().Hash(), current)
+	if localTd.Cmp(externTd) > 0 {
+		log.Info("Sidechain written to disk", "start", it.first().NumberU64(), "end", it.previous().NumberU64(), "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 := bc.GetHeader(it.previous().Hash(), it.previous().NumberU64())
+	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
 }
 
 func (bc *BlockChain) InsertBlock(block *types.Block) error {
@@ -2060,61 +2191,6 @@ func (bc *BlockChain) insertBlock(block *types.Block) ([]interface{}, []*types.L
 	return 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 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, dirty 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", dirty}...)
-
-		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
-}
-
 // collectLogs collects the logs that were generated or removed during
 // the processing of a block. These logs are later announced as deleted or reborn.
 func (bc *BlockChain) collectLogs(b *types.Block, removed bool) []*types.Log {

core/blockchain_insert.go

@@ -0,0 +1,143 @@
+// Copyright 2018 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package core
+
+import (
+	"time"
+
+	"github.com/XinFinOrg/XDPoSChain/common"
+	"github.com/XinFinOrg/XDPoSChain/common/mclock"
+	"github.com/XinFinOrg/XDPoSChain/core/types"
+	"github.com/XinFinOrg/XDPoSChain/log"
+)
+
+// 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 {
+		// Count the number of transactions in this segment
+		var txs int
+		for _, block := range chain[st.lastIndex : index+1] {
+			txs += len(block.Transactions())
+		}
+		end := chain[index]
+
+		// Assemble the log context and send it to the logger
+		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...)
+
+		// Bump the stats reported to the next section
+		*st = insertStats{startTime: now, lastIndex: index + 1}
+	}
+}
+
+// insertIterator is a helper to assist during chain import.
+type insertIterator struct {
+	chain     types.Blocks
+	results   <-chan error
+	index     int
+	validator Validator
+}
+
+// newInsertIterator creates a new iterator based on the given blocks, which are
+// assumed to be a contiguous chain.
+func newInsertIterator(chain types.Blocks, results <-chan error, validator Validator) *insertIterator {
+	return &insertIterator{
+		chain:     chain,
+		results:   results,
+		index:     -1,
+		validator: validator,
+	}
+}
+
+// next returns the next block in the iterator, along with any potential validation
+// error for that block. When the end is reached, it will return (nil, nil).
+func (it *insertIterator) next() (*types.Block, error) {
+	if it.index+1 >= len(it.chain) {
+		it.index = len(it.chain)
+		return nil, nil
+	}
+	it.index++
+	if err := <-it.results; err != nil {
+		return it.chain[it.index], err
+	}
+	return it.chain[it.index], it.validator.ValidateBody(it.chain[it.index])
+}
+
+// current returns the current block that's being processed.
+func (it *insertIterator) current() *types.Block {
+	if it.index < 0 || it.index+1 >= len(it.chain) {
+		return nil
+	}
+	return it.chain[it.index]
+}
+
+// previous returns the previous block was being processed, or nil
+func (it *insertIterator) previous() *types.Block {
+	if it.index < 1 {
+		return nil
+	}
+	return it.chain[it.index-1]
+}
+
+// first returns the first block in the it.
+func (it *insertIterator) first() *types.Block {
+	return it.chain[0]
+}
+
+// remaining returns the number of remaining blocks.
+func (it *insertIterator) remaining() int {
+	return len(it.chain) - it.index
+}
+
+// processed returns the number of processed blocks.
+func (it *insertIterator) processed() int {
+	return it.index + 1
+}