Merge pull request #2081 from zsfelfoldi/light-chain

core: create a header chain structure shared by full and light clients

4 files changed, 575 insertions, 345 deletions

diff --git a/core/blockchain.go b/core/blockchain.go
index 79648869c..83299ceec 100644
--- a/core/blockchain.go
+++ b/core/blockchain.go
@@ -18,11 +18,9 @@
 package core
 
 import (
-	crand "crypto/rand"
 	"errors"
 	"fmt"
 	"io"
-	"math"
 	"math/big"
 	mrand "math/rand"
 	"runtime"
@@ -82,24 +80,22 @@ const (
 // included in the canonical one where as GetBlockByNumber always represents the
 // canonical chain.
 type BlockChain struct {
+	hc           *HeaderChain
 	chainDb      ethdb.Database
 	eventMux     *event.TypeMux
 	genesisBlock *types.Block
-	// Last known total difficulty
+
 	mu      sync.RWMutex
 	chainmu sync.RWMutex
 	tsmu    sync.RWMutex
 	procmu  sync.RWMutex
 
-	checkpoint       int           // checkpoint counts towards the new checkpoint
-	currentHeader    *types.Header // Current head of the header chain (may be above the block chain!)
-	currentBlock     *types.Block  // Current head of the block chain
-	currentFastBlock *types.Block  // Current head of the fast-sync chain (may be above the block chain!)
+	checkpoint       int          // checkpoint counts towards the new checkpoint
+	currentBlock     *types.Block // Current head of the block chain
+	currentFastBlock *types.Block // Current head of the fast-sync chain (may be above the block chain!)
 
-	headerCache  *lru.Cache // Cache for the most recent block headers
 	bodyCache    *lru.Cache // Cache for the most recent block bodies
 	bodyRLPCache *lru.Cache // Cache for the most recent block bodies in RLP encoded format
-	tdCache      *lru.Cache // Cache for the most recent block total difficulties
 	blockCache   *lru.Cache // Cache for the most recent entire blocks
 	futureBlocks *lru.Cache // future blocks are blocks added for later processing
 
@@ -110,7 +106,6 @@ type BlockChain struct {
 	wg            sync.WaitGroup
 
 	pow       pow.PoW
-	rand      *mrand.Rand
 	processor Processor
 	validator Validator
 }
@@ -119,10 +114,8 @@ type BlockChain struct {
 // available in the database. It initialiser the default Ethereum Validator and
 // Processor.
 func NewBlockChain(chainDb ethdb.Database, pow pow.PoW, mux *event.TypeMux) (*BlockChain, error) {
-	headerCache, _ := lru.New(headerCacheLimit)
 	bodyCache, _ := lru.New(bodyCacheLimit)
 	bodyRLPCache, _ := lru.New(bodyCacheLimit)
-	tdCache, _ := lru.New(tdCacheLimit)
 	blockCache, _ := lru.New(blockCacheLimit)
 	futureBlocks, _ := lru.New(maxFutureBlocks)
 
@@ -130,22 +123,21 @@ func NewBlockChain(chainDb ethdb.Database, pow pow.PoW, mux *event.TypeMux) (*Bl
 		chainDb:      chainDb,
 		eventMux:     mux,
 		quit:         make(chan struct{}),
-		headerCache:  headerCache,
 		bodyCache:    bodyCache,
 		bodyRLPCache: bodyRLPCache,
-		tdCache:      tdCache,
 		blockCache:   blockCache,
 		futureBlocks: futureBlocks,
 		pow:          pow,
 	}
-	// Seed a fast but crypto originating random generator
-	seed, err := crand.Int(crand.Reader, big.NewInt(math.MaxInt64))
+	bc.SetValidator(NewBlockValidator(bc, pow))
+	bc.SetProcessor(NewStateProcessor(bc))
+
+	gv := func() HeaderValidator { return bc.Validator() }
+	var err error
+	bc.hc, err = NewHeaderChain(chainDb, gv, bc.getProcInterrupt)
 	if err != nil {
 		return nil, err
 	}
-	bc.rand = mrand.New(mrand.NewSource(seed.Int64()))
-	bc.SetValidator(NewBlockValidator(bc, pow))
-	bc.SetProcessor(NewStateProcessor(bc))
 
 	bc.genesisBlock = bc.GetBlockByNumber(0)
 	if bc.genesisBlock == nil {
@@ -171,6 +163,10 @@ func NewBlockChain(chainDb ethdb.Database, pow pow.PoW, mux *event.TypeMux) (*Bl
 	return bc, nil
 }
 
+func (self *BlockChain) getProcInterrupt() bool {
+	return atomic.LoadInt32(&self.procInterrupt) == 1
+}
+
 // loadLastState loads the last known chain state from the database. This method
 // assumes that the chain manager mutex is held.
 func (self *BlockChain) loadLastState() error {
@@ -189,12 +185,13 @@ func (self *BlockChain) loadLastState() error {
 		}
 	}
 	// Restore the last known head header
-	self.currentHeader = self.currentBlock.Header()
+	currentHeader := self.currentBlock.Header()
 	if head := GetHeadHeaderHash(self.chainDb); head != (common.Hash{}) {
 		if header := self.GetHeader(head); header != nil {
-			self.currentHeader = header
+			currentHeader = header
 		}
 	}
+	self.hc.SetCurrentHeader(currentHeader)
 	// Restore the last known head fast block
 	self.currentFastBlock = self.currentBlock
 	if head := GetHeadFastBlockHash(self.chainDb); head != (common.Hash{}) {
@@ -203,11 +200,11 @@ func (self *BlockChain) loadLastState() error {
 		}
 	}
 	// Issue a status log and return
-	headerTd := self.GetTd(self.currentHeader.Hash())
+	headerTd := self.GetTd(self.hc.CurrentHeader().Hash())
 	blockTd := self.GetTd(self.currentBlock.Hash())
 	fastTd := self.GetTd(self.currentFastBlock.Hash())
 
-	glog.V(logger.Info).Infof("Last header: #%d [%x…] TD=%v", self.currentHeader.Number, self.currentHeader.Hash().Bytes()[:4], headerTd)
+	glog.V(logger.Info).Infof("Last header: #%d [%x…] TD=%v", self.hc.CurrentHeader().Number, self.hc.CurrentHeader().Hash().Bytes()[:4], headerTd)
 	glog.V(logger.Info).Infof("Last block: #%d [%x…] TD=%v", self.currentBlock.Number(), self.currentBlock.Hash().Bytes()[:4], blockTd)
 	glog.V(logger.Info).Infof("Fast block: #%d [%x…] TD=%v", self.currentFastBlock.Number(), self.currentFastBlock.Hash().Bytes()[:4], fastTd)
 
@@ -222,71 +219,35 @@ func (bc *BlockChain) SetHead(head uint64) {
 	bc.mu.Lock()
 	defer bc.mu.Unlock()
 
-	// Figure out the highest known canonical headers and/or blocks
-	height := uint64(0)
-	if bc.currentHeader != nil {
-		if hh := bc.currentHeader.Number.Uint64(); hh > height {
-			height = hh
-		}
-	}
-	if bc.currentBlock != nil {
-		if bh := bc.currentBlock.NumberU64(); bh > height {
-			height = bh
-		}
-	}
-	if bc.currentFastBlock != nil {
-		if fbh := bc.currentFastBlock.NumberU64(); fbh > height {
-			height = fbh
-		}
-	}
-	// Gather all the hashes that need deletion
-	drop := make(map[common.Hash]struct{})
-
-	for bc.currentHeader != nil && bc.currentHeader.Number.Uint64() > head {
-		drop[bc.currentHeader.Hash()] = struct{}{}
-		bc.currentHeader = bc.GetHeader(bc.currentHeader.ParentHash)
-	}
-	for bc.currentBlock != nil && bc.currentBlock.NumberU64() > head {
-		drop[bc.currentBlock.Hash()] = struct{}{}
-		bc.currentBlock = bc.GetBlock(bc.currentBlock.ParentHash())
-	}
-	for bc.currentFastBlock != nil && bc.currentFastBlock.NumberU64() > head {
-		drop[bc.currentFastBlock.Hash()] = struct{}{}
-		bc.currentFastBlock = bc.GetBlock(bc.currentFastBlock.ParentHash())
-	}
-	// Roll back the canonical chain numbering
-	for i := height; i > head; i-- {
-		DeleteCanonicalHash(bc.chainDb, i)
-	}
-	// Delete everything found by the above rewind
-	for hash, _ := range drop {
-		DeleteHeader(bc.chainDb, hash)
+	delFn := func(hash common.Hash) {
 		DeleteBody(bc.chainDb, hash)
-		DeleteTd(bc.chainDb, hash)
 	}
+	bc.hc.SetHead(head, delFn)
+
 	// Clear out any stale content from the caches
-	bc.headerCache.Purge()
 	bc.bodyCache.Purge()
 	bc.bodyRLPCache.Purge()
 	bc.blockCache.Purge()
 	bc.futureBlocks.Purge()
 
 	// Update all computed fields to the new head
+	if bc.currentBlock != nil && bc.hc.CurrentHeader().Number.Uint64() < bc.currentBlock.NumberU64() {
+		bc.currentBlock = bc.GetBlock(bc.hc.CurrentHeader().Hash())
+	}
+	if bc.currentFastBlock != nil && bc.hc.CurrentHeader().Number.Uint64() < bc.currentFastBlock.NumberU64() {
+		bc.currentFastBlock = bc.GetBlock(bc.hc.CurrentHeader().Hash())
+	}
+
 	if bc.currentBlock == nil {
 		bc.currentBlock = bc.genesisBlock
 	}
-	if bc.currentHeader == nil {
-		bc.currentHeader = bc.genesisBlock.Header()
-	}
 	if bc.currentFastBlock == nil {
 		bc.currentFastBlock = bc.genesisBlock
 	}
+
 	if err := WriteHeadBlockHash(bc.chainDb, bc.currentBlock.Hash()); err != nil {
 		glog.Fatalf("failed to reset head block hash: %v", err)
 	}
-	if err := WriteHeadHeaderHash(bc.chainDb, bc.currentHeader.Hash()); err != nil {
-		glog.Fatalf("failed to reset head header hash: %v", err)
-	}
 	if err := WriteHeadFastBlockHash(bc.chainDb, bc.currentFastBlock.Hash()); err != nil {
 		glog.Fatalf("failed to reset head fast block hash: %v", err)
 	}
@@ -329,15 +290,6 @@ func (self *BlockChain) LastBlockHash() common.Hash {
 	return self.currentBlock.Hash()
 }
 
-// CurrentHeader retrieves the current head header of the canonical chain. The
-// header is retrieved from the blockchain's internal cache.
-func (self *BlockChain) CurrentHeader() *types.Header {
-	self.mu.RLock()
-	defer self.mu.RUnlock()
-
-	return self.currentHeader
-}
-
 // CurrentBlock retrieves the current head block of the canonical chain. The
 // block is retrieved from the blockchain's internal cache.
 func (self *BlockChain) CurrentBlock() *types.Block {
@@ -425,7 +377,8 @@ func (bc *BlockChain) ResetWithGenesisBlock(genesis *types.Block) {
 	bc.genesisBlock = genesis
 	bc.insert(bc.genesisBlock)
 	bc.currentBlock = bc.genesisBlock
-	bc.currentHeader = bc.genesisBlock.Header()
+	bc.hc.SetGenesis(bc.genesisBlock.Header())
+	bc.hc.SetCurrentHeader(bc.genesisBlock.Header())
 	bc.currentFastBlock = bc.genesisBlock
 }
 
@@ -483,10 +436,7 @@ func (bc *BlockChain) insert(block *types.Block) {
 
 	// If the block is better than out head or is on a different chain, force update heads
 	if updateHeads {
-		if err := WriteHeadHeaderHash(bc.chainDb, block.Hash()); err != nil {
-			glog.Fatalf("failed to insert head header hash: %v", err)
-		}
-		bc.currentHeader = block.Header()
+		bc.hc.SetCurrentHeader(block.Header())
 
 		if err := WriteHeadFastBlockHash(bc.chainDb, block.Hash()); err != nil {
 			glog.Fatalf("failed to insert head fast block hash: %v", err)
@@ -500,38 +450,6 @@ func (bc *BlockChain) Genesis() *types.Block {
 	return bc.genesisBlock
 }
 
-// HasHeader checks if a block header is present in the database or not, caching
-// it if present.
-func (bc *BlockChain) HasHeader(hash common.Hash) bool {
-	return bc.GetHeader(hash) != nil
-}
-
-// GetHeader retrieves a block header from the database by hash, caching it if
-// found.
-func (self *BlockChain) GetHeader(hash common.Hash) *types.Header {
-	// Short circuit if the header's already in the cache, retrieve otherwise
-	if header, ok := self.headerCache.Get(hash); ok {
-		return header.(*types.Header)
-	}
-	header := GetHeader(self.chainDb, hash)
-	if header == nil {
-		return nil
-	}
-	// Cache the found header for next time and return
-	self.headerCache.Add(header.Hash(), header)
-	return header
-}
-
-// GetHeaderByNumber retrieves a block header from the database by number,
-// caching it (associated with its hash) if found.
-func (self *BlockChain) GetHeaderByNumber(number uint64) *types.Header {
-	hash := GetCanonicalHash(self.chainDb, number)
-	if hash == (common.Hash{}) {
-		return nil
-	}
-	return self.GetHeader(hash)
-}
-
 // GetBody retrieves a block body (transactions and uncles) from the database by
 // hash, caching it if found.
 func (self *BlockChain) GetBody(hash common.Hash) *types.Body {
@@ -565,22 +483,6 @@ func (self *BlockChain) GetBodyRLP(hash common.Hash) rlp.RawValue {
 	return body
 }
 
-// GetTd retrieves a block's total difficulty in the canonical chain from the
-// database by hash, caching it if found.
-func (self *BlockChain) GetTd(hash common.Hash) *big.Int {
-	// Short circuit if the td's already in the cache, retrieve otherwise
-	if cached, ok := self.tdCache.Get(hash); ok {
-		return cached.(*big.Int)
-	}
-	td := GetTd(self.chainDb, hash)
-	if td == nil {
-		return nil
-	}
-	// Cache the found body for next time and return
-	self.tdCache.Add(hash, td)
-	return td
-}
-
 // HasBlock checks if a block is fully present in the database or not, caching
 // it if present.
 func (bc *BlockChain) HasBlock(hash common.Hash) bool {
@@ -625,28 +527,6 @@ func (self *BlockChain) GetBlockByNumber(number uint64) *types.Block {
 	return self.GetBlock(hash)
 }
 
-// GetBlockHashesFromHash retrieves a number of block hashes starting at a given
-// hash, fetching towards the genesis block.
-func (self *BlockChain) GetBlockHashesFromHash(hash common.Hash, max uint64) []common.Hash {
-	// Get the origin header from which to fetch
-	header := self.GetHeader(hash)
-	if header == nil {
-		return nil
-	}
-	// Iterate the headers until enough is collected or the genesis reached
-	chain := make([]common.Hash, 0, max)
-	for i := uint64(0); i < max; i++ {
-		if header = self.GetHeader(header.ParentHash); header == nil {
-			break
-		}
-		chain = append(chain, header.Hash())
-		if header.Number.Cmp(common.Big0) == 0 {
-			break
-		}
-	}
-	return chain
-}
-
 // [deprecated by eth/62]
 // GetBlocksFromHash returns the block corresponding to hash and up to n-1 ancestors.
 func (self *BlockChain) GetBlocksFromHash(hash common.Hash, n int) (blocks []*types.Block) {
@@ -698,195 +578,15 @@ func (self *BlockChain) procFutureBlocks() {
 	}
 }
 
-type writeStatus byte
+type WriteStatus byte
 
 const (
-	NonStatTy writeStatus = iota
+	NonStatTy WriteStatus = iota
 	CanonStatTy
 	SplitStatTy
 	SideStatTy
 )
 
-// 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 (self *BlockChain) writeHeader(header *types.Header) error {
-	self.wg.Add(1)
-	defer self.wg.Done()
-
-	// Calculate the total difficulty of the header
-	ptd := self.GetTd(header.ParentHash)
-	if ptd == nil {
-		return ParentError(header.ParentHash)
-	}
-
-	localTd := self.GetTd(self.currentHeader.Hash())
-	externTd := new(big.Int).Add(header.Difficulty, ptd)
-
-	// Make sure no inconsistent state is leaked during insertion
-	self.mu.Lock()
-	defer self.mu.Unlock()
-
-	// 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
-		for i := header.Number.Uint64() + 1; GetCanonicalHash(self.chainDb, i) != (common.Hash{}); i++ {
-			DeleteCanonicalHash(self.chainDb, i)
-		}
-		// Overwrite any stale canonical number assignments
-		head := self.GetHeader(header.ParentHash)
-		for GetCanonicalHash(self.chainDb, head.Number.Uint64()) != head.Hash() {
-			WriteCanonicalHash(self.chainDb, head.Hash(), head.Number.Uint64())
-			head = self.GetHeader(head.ParentHash)
-		}
-		// Extend the canonical chain with the new header
-		if err := WriteCanonicalHash(self.chainDb, header.Hash(), header.Number.Uint64()); err != nil {
-			glog.Fatalf("failed to insert header number: %v", err)
-		}
-		if err := WriteHeadHeaderHash(self.chainDb, header.Hash()); err != nil {
-			glog.Fatalf("failed to insert head header hash: %v", err)
-		}
-		self.currentHeader = types.CopyHeader(header)
-	}
-	// Irrelevant of the canonical status, write the header itself to the database
-	if err := WriteTd(self.chainDb, header.Hash(), externTd); err != nil {
-		glog.Fatalf("failed to write header total difficulty: %v", err)
-	}
-	if err := WriteHeader(self.chainDb, header); err != nil {
-		glog.Fatalf("filed to write header contents: %v", err)
-	}
-	return nil
-}
-
-// 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 verfy nonces, as well as
-// because nonces can be verified sparsely, not needing to check each.
-func (self *BlockChain) InsertHeaderChain(chain []*types.Header, checkFreq int) (int, error) {
-	self.wg.Add(1)
-	defer self.wg.Done()
-
-	// Make sure only one thread manipulates the chain at once
-	self.chainmu.Lock()
-	defer self.chainmu.Unlock()
-
-	// Collect some import statistics to report on
-	stats := struct{ processed, ignored int }{}
-	start := time.Now()
-
-	// Generate the list of headers that should be POW verified
-	verify := make([]bool, len(chain))
-	for i := 0; i < len(verify)/checkFreq; i++ {
-		index := i*checkFreq + self.rand.Intn(checkFreq)
-		if index >= len(verify) {
-			index = len(verify) - 1
-		}
-		verify[index] = true
-	}
-	verify[len(verify)-1] = true // Last should always be verified to avoid junk
-
-	// Create the header verification task queue and worker functions
-	tasks := make(chan int, len(chain))
-	for i := 0; i < len(chain); i++ {
-		tasks <- i
-	}
-	close(tasks)
-
-	errs, failed := make([]error, len(tasks)), int32(0)
-	process := func(worker int) {
-		for index := range tasks {
-			header, hash := chain[index], chain[index].Hash()
-
-			// Short circuit insertion if shutting down or processing failed
-			if atomic.LoadInt32(&self.procInterrupt) == 1 {
-				return
-			}
-			if atomic.LoadInt32(&failed) > 0 {
-				return
-			}
-			// Short circuit if the header is bad or already known
-			if BadHashes[hash] {
-				errs[index] = BadHashError(hash)
-				atomic.AddInt32(&failed, 1)
-				return
-			}
-			if self.HasHeader(hash) {
-				continue
-			}
-			// Verify that the header honors the chain parameters
-			checkPow := verify[index]
-
-			var err error
-			if index == 0 {
-				err = self.Validator().ValidateHeader(header, self.GetHeader(header.ParentHash), checkPow)
-			} else {
-				err = self.Validator().ValidateHeader(header, chain[index-1], checkPow)
-			}
-			if err != nil {
-				errs[index] = err
-				atomic.AddInt32(&failed, 1)
-				return
-			}
-		}
-	}
-	// Start as many worker threads as goroutines allowed
-	pending := new(sync.WaitGroup)
-	for i := 0; i < runtime.GOMAXPROCS(0); i++ {
-		pending.Add(1)
-		go func(id int) {
-			defer pending.Done()
-			process(id)
-		}(i)
-	}
-	pending.Wait()
-
-	// If anything failed, report
-	if failed > 0 {
-		for i, err := range errs {
-			if err != nil {
-				return i, err
-			}
-		}
-	}
-	// All headers passed verification, import them into the database
-	for i, header := range chain {
-		// Short circuit insertion if shutting down
-		if atomic.LoadInt32(&self.procInterrupt) == 1 {
-			glog.V(logger.Debug).Infoln("premature abort during header chain processing")
-			break
-		}
-		hash := header.Hash()
-
-		// If the header's already known, skip it, otherwise store
-		if self.HasHeader(hash) {
-			stats.ignored++
-			continue
-		}
-		if err := self.writeHeader(header); err != nil {
-			return i, err
-		}
-		stats.processed++
-	}
-	// Report some public statistics so the user has a clue what's going on
-	first, last := chain[0], chain[len(chain)-1]
-	glog.V(logger.Info).Infof("imported %d header(s) (%d ignored) in %v. #%v [%x… / %x…]", stats.processed, stats.ignored,
-		time.Since(start), last.Number, first.Hash().Bytes()[:4], last.Hash().Bytes()[:4])
-
-	return 0, nil
-}
-
 // Rollback is designed to remove a chain of links from the database that aren't
 // certain enough to be valid.
 func (self *BlockChain) Rollback(chain []common.Hash) {
@@ -896,9 +596,8 @@ func (self *BlockChain) Rollback(chain []common.Hash) {
 	for i := len(chain) - 1; i >= 0; i-- {
 		hash := chain[i]
 
-		if self.currentHeader.Hash() == hash {
-			self.currentHeader = self.GetHeader(self.currentHeader.ParentHash)
-			WriteHeadHeaderHash(self.chainDb, self.currentHeader.Hash())
+		if self.hc.CurrentHeader().Hash() == hash {
+			self.hc.SetCurrentHeader(self.GetHeader(self.hc.CurrentHeader().ParentHash))
 		}
 		if self.currentFastBlock.Hash() == hash {
 			self.currentFastBlock = self.GetBlock(self.currentFastBlock.ParentHash())
@@ -1055,7 +754,7 @@ func (self *BlockChain) InsertReceiptChain(blockChain types.Blocks, receiptChain
 }
 
 // WriteBlock writes the block to the chain.
-func (self *BlockChain) WriteBlock(block *types.Block) (status writeStatus, err error) {
+func (self *BlockChain) WriteBlock(block *types.Block) (status WriteStatus, err error) {
 	self.wg.Add(1)
 	defer self.wg.Done()
 
@@ -1427,3 +1126,89 @@ func reportBlock(block *types.Block, err error) {
 	}
 	go ReportBlock(block, 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 verfy nonces, as well as
+// because nonces can be verified sparsely, not needing to check each.
+func (self *BlockChain) InsertHeaderChain(chain []*types.Header, checkFreq int) (int, error) {
+	// Make sure only one thread manipulates the chain at once
+	self.chainmu.Lock()
+	defer self.chainmu.Unlock()
+
+	self.wg.Add(1)
+	defer self.wg.Done()
+
+	whFunc := func(header *types.Header) error {
+		self.mu.Lock()
+		defer self.mu.Unlock()
+
+		_, err := self.hc.WriteHeader(header)
+		return err
+	}
+
+	return self.hc.InsertHeaderChain(chain, checkFreq, whFunc)
+}
+
+// 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 (self *BlockChain) writeHeader(header *types.Header) error {
+	self.wg.Add(1)
+	defer self.wg.Done()
+
+	self.mu.Lock()
+	defer self.mu.Unlock()
+
+	_, err := self.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 (self *BlockChain) CurrentHeader() *types.Header {
+	self.mu.RLock()
+	defer self.mu.RUnlock()
+
+	return self.hc.CurrentHeader()
+}
+
+// GetTd retrieves a block's total difficulty in the canonical chain from the
+// database by hash, caching it if found.
+func (self *BlockChain) GetTd(hash common.Hash) *big.Int {
+	return self.hc.GetTd(hash)
+}
+
+// GetHeader retrieves a block header from the database by hash, caching it if
+// found.
+func (self *BlockChain) GetHeader(hash common.Hash) *types.Header {
+	return self.hc.GetHeader(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) bool {
+	return bc.hc.HasHeader(hash)
+}
+
+// GetBlockHashesFromHash retrieves a number of block hashes starting at a given
+// hash, fetching towards the genesis block.
+func (self *BlockChain) GetBlockHashesFromHash(hash common.Hash, max uint64) []common.Hash {
+	return self.hc.GetBlockHashesFromHash(hash, max)
+}
+
+// GetHeaderByNumber retrieves a block header from the database by number,
+// caching it (associated with its hash) if found.
+func (self *BlockChain) GetHeaderByNumber(number uint64) *types.Header {
+	return self.hc.GetHeaderByNumber(number)
+}
diff --git a/core/blockchain_test.go b/core/blockchain_test.go
index a7d3ea56e..310751cca 100644
--- a/core/blockchain_test.go
+++ b/core/blockchain_test.go
@@ -472,11 +472,16 @@ func makeBlockChainWithDiff(genesis *types.Block, d []int, seed byte) []*types.B
 
 func chm(genesis *types.Block, db ethdb.Database) *BlockChain {
 	var eventMux event.TypeMux
-	bc := &BlockChain{chainDb: db, genesisBlock: genesis, eventMux: &eventMux, pow: FakePow{}, rand: rand.New(rand.NewSource(0))}
-	bc.headerCache, _ = lru.New(100)
+	bc := &BlockChain{
+		chainDb: db,
+		genesisBlock: genesis,
+		eventMux: &eventMux,
+		pow: FakePow{},
+	}
+	valFn := func() HeaderValidator { return bc.Validator() }
+	bc.hc, _ = NewHeaderChain(db, valFn, bc.getProcInterrupt)
 	bc.bodyCache, _ = lru.New(100)
 	bc.bodyRLPCache, _ = lru.New(100)
-	bc.tdCache, _ = lru.New(100)
 	bc.blockCache, _ = lru.New(100)
 	bc.futureBlocks, _ = lru.New(100)
 	bc.SetValidator(bproc{})
diff --git a/core/headerchain.go b/core/headerchain.go
new file mode 100644
index 000000000..8528801a7
--- /dev/null
+++ b/core/headerchain.go
@@ -0,0 +1,432 @@
+// Copyright 2015 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 (
+	crand "crypto/rand"
+	"math"
+	"math/big"
+	mrand "math/rand"
+	"runtime"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/ethdb"
+	"github.com/ethereum/go-ethereum/logger"
+	"github.com/ethereum/go-ethereum/logger/glog"
+	"github.com/ethereum/go-ethereum/pow"
+	"github.com/hashicorp/golang-lru"
+)
+
+// HeaderChain implements the basic block header chain logic that is shared by
+// core.BlockChain and light.LightChain. It is not usable in itself, only as
+// a part of either structure.
+// It is not thread safe either, the encapsulating chain structures should do
+// the necessary mutex locking/unlocking.
+type HeaderChain struct {
+	chainDb       ethdb.Database
+	genesisHeader *types.Header
+
+	currentHeader *types.Header // Current head of the header chain (may be above the block chain!)
+	headerCache   *lru.Cache    // Cache for the most recent block headers
+	tdCache       *lru.Cache    // Cache for the most recent block total difficulties
+
+	procInterrupt  func() bool
+
+	rand         *mrand.Rand
+	getValidator getHeaderValidatorFn
+}
+
+// getHeaderValidatorFn returns a HeaderValidator interface
+type getHeaderValidatorFn func() HeaderValidator
+
+// NewHeaderChain creates a new HeaderChain structure.
+//  getValidator should return the parent's validator
+//  procInterrupt points to the parent's interrupt semaphore
+//  wg points to the parent's shutdown wait group
+func NewHeaderChain(chainDb ethdb.Database, getValidator getHeaderValidatorFn, procInterrupt func() bool) (*HeaderChain, error) {
+	headerCache, _ := lru.New(headerCacheLimit)
+	tdCache, _ := lru.New(tdCacheLimit)
+
+	// Seed a fast but crypto originating random generator
+	seed, err := crand.Int(crand.Reader, big.NewInt(math.MaxInt64))
+	if err != nil {
+		return nil, err
+	}
+
+	hc := &HeaderChain{
+		chainDb:       chainDb,
+		headerCache:   headerCache,
+		tdCache:       tdCache,
+		procInterrupt: procInterrupt,
+		rand:          mrand.New(mrand.NewSource(seed.Int64())),
+		getValidator:  getValidator,
+	}
+
+	hc.genesisHeader = hc.GetHeaderByNumber(0)
+	if hc.genesisHeader == nil {
+		genesisBlock, err := WriteDefaultGenesisBlock(chainDb)
+		if err != nil {
+			return nil, err
+		}
+		glog.V(logger.Info).Infoln("WARNING: Wrote default ethereum genesis block")
+		hc.genesisHeader = genesisBlock.Header()
+	}
+
+	hc.currentHeader = hc.genesisHeader
+	if head := GetHeadBlockHash(chainDb); head != (common.Hash{}) {
+		if chead := hc.GetHeader(head); chead != nil {
+			hc.currentHeader = chead
+		}
+	}
+
+	return hc, nil
+}
+
+// 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 (hc *HeaderChain) WriteHeader(header *types.Header) (status WriteStatus, err error) {
+	// Calculate the total difficulty of the header
+	ptd := hc.GetTd(header.ParentHash)
+	if ptd == nil {
+		return NonStatTy, ParentError(header.ParentHash)
+	}
+	localTd := hc.GetTd(hc.currentHeader.Hash())
+	externTd := new(big.Int).Add(header.Difficulty, ptd)
+
+	// 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
+		for i := header.Number.Uint64() + 1; GetCanonicalHash(hc.chainDb, i) != (common.Hash{}); i++ {
+			DeleteCanonicalHash(hc.chainDb, i)
+		}
+		// Overwrite any stale canonical number assignments
+		head := hc.GetHeader(header.ParentHash)
+		for GetCanonicalHash(hc.chainDb, head.Number.Uint64()) != head.Hash() {
+			WriteCanonicalHash(hc.chainDb, head.Hash(), head.Number.Uint64())
+			head = hc.GetHeader(head.ParentHash)
+		}
+		// Extend the canonical chain with the new header
+		if err := WriteCanonicalHash(hc.chainDb, header.Hash(), header.Number.Uint64()); err != nil {
+			glog.Fatalf("failed to insert header number: %v", err)
+		}
+		if err := WriteHeadHeaderHash(hc.chainDb, header.Hash()); err != nil {
+			glog.Fatalf("failed to insert head header hash: %v", err)
+		}
+		hc.currentHeader = types.CopyHeader(header)
+		status = CanonStatTy
+	} else {
+		status = SideStatTy
+	}
+	// Irrelevant of the canonical status, write the header itself to the database
+	if err := WriteTd(hc.chainDb, header.Hash(), externTd); err != nil {
+		glog.Fatalf("failed to write header total difficulty: %v", err)
+	}
+	if err := WriteHeader(hc.chainDb, header); err != nil {
+		glog.Fatalf("failed to write header contents: %v", err)
+	}
+	return
+}
+
+// WhCallback is a callback function for inserting individual headers.
+// A callback is used for two reasons: first, in a LightChain, status should be
+// processed and light chain events sent, while in a BlockChain this is not
+// necessary since chain events are sent after inserting blocks. Second, the
+// header writes should be protected by the parent chain mutex individually.
+type WhCallback func(*types.Header) error
+
+// 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 verfy nonces, as well as
+// because nonces can be verified sparsely, not needing to check each.
+func (hc *HeaderChain) InsertHeaderChain(chain []*types.Header, checkFreq int, writeHeader WhCallback) (int, error) {
+	// Collect some import statistics to report on
+	stats := struct{ processed, ignored int }{}
+	start := time.Now()
+
+	// Generate the list of headers that should be POW verified
+	verify := make([]bool, len(chain))
+	for i := 0; i < len(verify)/checkFreq; i++ {
+		index := i*checkFreq + hc.rand.Intn(checkFreq)
+		if index >= len(verify) {
+			index = len(verify) - 1
+		}
+		verify[index] = true
+	}
+	verify[len(verify)-1] = true // Last should always be verified to avoid junk
+
+	// Create the header verification task queue and worker functions
+	tasks := make(chan int, len(chain))
+	for i := 0; i < len(chain); i++ {
+		tasks <- i
+	}
+	close(tasks)
+
+	errs, failed := make([]error, len(tasks)), int32(0)
+	process := func(worker int) {
+		for index := range tasks {
+			header, hash := chain[index], chain[index].Hash()
+
+			// Short circuit insertion if shutting down or processing failed
+			if hc.procInterrupt() {
+				return
+			}
+			if atomic.LoadInt32(&failed) > 0 {
+				return
+			}
+			// Short circuit if the header is bad or already known
+			if BadHashes[hash] {
+				errs[index] = BadHashError(hash)
+				atomic.AddInt32(&failed, 1)
+				return
+			}
+			if hc.HasHeader(hash) {
+				continue
+			}
+			// Verify that the header honors the chain parameters
+			checkPow := verify[index]
+
+			var err error
+			if index == 0 {
+				err = hc.getValidator().ValidateHeader(header, hc.GetHeader(header.ParentHash), checkPow)
+			} else {
+				err = hc.getValidator().ValidateHeader(header, chain[index-1], checkPow)
+			}
+			if err != nil {
+				errs[index] = err
+				atomic.AddInt32(&failed, 1)
+				return
+			}
+		}
+	}
+	// Start as many worker threads as goroutines allowed
+	pending := new(sync.WaitGroup)
+	for i := 0; i < runtime.GOMAXPROCS(0); i++ {
+		pending.Add(1)
+		go func(id int) {
+			defer pending.Done()
+			process(id)
+		}(i)
+	}
+	pending.Wait()
+
+	// If anything failed, report
+	if failed > 0 {
+		for i, err := range errs {
+			if err != nil {
+				return i, err
+			}
+		}
+	}
+	// All headers passed verification, import them into the database
+	for i, header := range chain {
+		// Short circuit insertion if shutting down
+		if hc.procInterrupt() {
+			glog.V(logger.Debug).Infoln("premature abort during header chain processing")
+			break
+		}
+		hash := header.Hash()
+
+		// If the header's already known, skip it, otherwise store
+		if hc.HasHeader(hash) {
+			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
+	first, last := chain[0], chain[len(chain)-1]
+	glog.V(logger.Info).Infof("imported %d header(s) (%d ignored) in %v. #%v [%x… / %x…]", stats.processed, stats.ignored,
+		time.Since(start), last.Number, first.Hash().Bytes()[:4], last.Hash().Bytes()[:4])
+
+	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 {
+	// Get the origin header from which to fetch
+	header := hc.GetHeader(hash)
+	if header == nil {
+		return nil
+	}
+	// Iterate the headers until enough is collected or the genesis reached
+	chain := make([]common.Hash, 0, max)
+	for i := uint64(0); i < max; i++ {
+		if header = hc.GetHeader(header.ParentHash); header == nil {
+			break
+		}
+		chain = append(chain, header.Hash())
+		if header.Number.Cmp(common.Big0) == 0 {
+			break
+		}
+	}
+	return chain
+}
+
+// GetTd retrieves a block's total difficulty in the canonical chain from the
+// database by hash, caching it if found.
+func (hc *HeaderChain) GetTd(hash common.Hash) *big.Int {
+	// Short circuit if the td's already in the cache, retrieve otherwise
+	if cached, ok := hc.tdCache.Get(hash); ok {
+		return cached.(*big.Int)
+	}
+	td := GetTd(hc.chainDb, hash)
+	if td == nil {
+		return nil
+	}
+	// Cache the found body for next time and return
+	hc.tdCache.Add(hash, td)
+	return td
+}
+
+// GetHeader retrieves a block header from the database by hash, caching it if
+// found.
+func (hc *HeaderChain) GetHeader(hash common.Hash) *types.Header {
+	// Short circuit if the header's already in the cache, retrieve otherwise
+	if header, ok := hc.headerCache.Get(hash); ok {
+		return header.(*types.Header)
+	}
+	header := GetHeader(hc.chainDb, hash)
+	if header == nil {
+		return nil
+	}
+	// Cache the found header for next time and return
+	hc.headerCache.Add(header.Hash(), header)
+	return header
+}
+
+// HasHeader checks if a block header is present in the database or not, caching
+// it if present.
+func (hc *HeaderChain) HasHeader(hash common.Hash) bool {
+	return hc.GetHeader(hash) != nil
+}
+
+// GetHeaderByNumber retrieves a block header from the database by number,
+// caching it (associated with its hash) if found.
+func (hc *HeaderChain) GetHeaderByNumber(number uint64) *types.Header {
+	hash := GetCanonicalHash(hc.chainDb, number)
+	if hash == (common.Hash{}) {
+		return nil
+	}
+	return hc.GetHeader(hash)
+}
+
+// CurrentHeader retrieves the current head header of the canonical chain. The
+// header is retrieved from the HeaderChain's internal cache.
+func (hc *HeaderChain) CurrentHeader() *types.Header {
+	return hc.currentHeader
+}
+
+// SetCurrentHeader sets the current head header of the canonical chain.
+func (hc *HeaderChain) SetCurrentHeader(head *types.Header) {
+	if err := WriteHeadHeaderHash(hc.chainDb, head.Hash()); err != nil {
+		glog.Fatalf("failed to insert head header hash: %v", err)
+	}
+	hc.currentHeader = head
+}
+
+// DeleteCallback is a callback function that is called by SetHead before
+// each header is deleted.
+type DeleteCallback func(common.Hash)
+
+// SetHead rewinds the local chain to a new head. Everything above the new head
+// will be deleted and the new one set.
+func (hc *HeaderChain) SetHead(head uint64, delFn DeleteCallback) {
+	height := uint64(0)
+	if hc.currentHeader != nil {
+		height = hc.currentHeader.Number.Uint64()
+	}
+
+	for hc.currentHeader != nil && hc.currentHeader.Number.Uint64() > head {
+		hash := hc.currentHeader.Hash()
+		if delFn != nil {
+			delFn(hash)
+		}
+		DeleteHeader(hc.chainDb, hash)
+		DeleteTd(hc.chainDb, hash)
+		hc.currentHeader = hc.GetHeader(hc.currentHeader.ParentHash)
+	}
+	// Roll back the canonical chain numbering
+	for i := height; i > head; i-- {
+		DeleteCanonicalHash(hc.chainDb, i)
+	}
+	// Clear out any stale content from the caches
+	hc.headerCache.Purge()
+	hc.tdCache.Purge()
+
+	if hc.currentHeader == nil {
+		hc.currentHeader = hc.genesisHeader
+	}
+	if err := WriteHeadHeaderHash(hc.chainDb, hc.currentHeader.Hash()); err != nil {
+		glog.Fatalf("failed to reset head header hash: %v", err)
+	}
+}
+
+// SetGenesis sets a new genesis block header for the chain
+func (hc *HeaderChain) SetGenesis(head *types.Header) {
+	hc.genesisHeader = head
+}
+
+// headerValidator is responsible for validating block headers
+//
+// headerValidator implements HeaderValidator.
+type headerValidator struct {
+	hc  *HeaderChain // Canonical header chain
+	Pow pow.PoW      // Proof of work used for validating
+}
+
+// NewBlockValidator returns a new block validator which is safe for re-use
+func NewHeaderValidator(chain *HeaderChain, pow pow.PoW) HeaderValidator {
+	return &headerValidator{
+		Pow: pow,
+		hc:  chain,
+	}
+}
+
+// ValidateHeader validates the given header and, depending on the pow arg,
+// checks the proof of work of the given header. Returns an error if the
+// validation failed.
+func (v *headerValidator) ValidateHeader(header, parent *types.Header, checkPow bool) error {
+	// Short circuit if the parent is missing.
+	if parent == nil {
+		return ParentError(header.ParentHash)
+	}
+	// Short circuit if the header's already known or its parent missing
+	if v.hc.HasHeader(header.Hash()) {
+		return nil
+	}
+	return ValidateHeader(v.Pow, header, parent, checkPow, false)
+}
diff --git a/core/types.go b/core/types.go
index 027f628b1..60eb15662 100644
--- a/core/types.go
+++ b/core/types.go
@@ -38,14 +38,22 @@ import (
 // ValidateHeader validates the given header and parent and returns an error
 // if it failed to do so.
 //
-// ValidateStack validates the given statedb and optionally the receipts and
+// ValidateState validates the given statedb and optionally the receipts and
 // gas used. The implementor should decide what to do with the given input.
 type Validator interface {
+	HeaderValidator
 	ValidateBlock(block *types.Block) error
-	ValidateHeader(header, parent *types.Header, checkPow bool) error
 	ValidateState(block, parent *types.Block, state *state.StateDB, receipts types.Receipts, usedGas *big.Int) error
 }
 
+// HeaderValidator is an interface for validating headers only
+//
+// ValidateHeader validates the given header and parent and returns an error
+// if it failed to do so.
+type HeaderValidator interface {
+	ValidateHeader(header, parent *types.Header, checkPow bool) error
+}
+
 // Processor is an interface for processing blocks using a given initial state.
 //
 // Process takes the block to be processed and the statedb upon which the