eth: port the synchronisation algo to eth/62

1 files changed, 580 insertions, 94 deletions

diff --git a/eth/downloader/downloader.go b/eth/downloader/downloader.go
index b28879ee6..0e8529756 100644
--- a/eth/downloader/downloader.go
+++ b/eth/downloader/downloader.go
@@ -26,12 +26,10 @@ import (
 	"time"
 
 	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/event"
 	"github.com/ethereum/go-ethereum/logger"
 	"github.com/ethereum/go-ethereum/logger/glog"
-	"gopkg.in/fatih/set.v0"
 )
 
 const (
@@ -40,40 +38,44 @@ const (
 )
 
 var (
-	MinHashFetch     = 512 // Minimum amount of hashes to not consider a peer stalling
 	MaxHashFetch     = 512 // Amount of hashes to be fetched per retrieval request
 	MaxBlockFetch    = 128 // Amount of blocks to be fetched per retrieval request
-	MaxHeaderFetch   = 256 // Amount of block headers to be fetched per retrieval request
+	MaxHeaderFetch   = 192 // Amount of block headers to be fetched per retrieval request
+	MaxBodyFetch     = 128 // Amount of block bodies to be fetched per retrieval request
 	MaxStateFetch    = 384 // Amount of node state values to allow fetching per request
 	MaxReceiptsFetch = 384 // Amount of transaction receipts to allow fetching per request
 
-	hashTTL         = 5 * time.Second  // Time it takes for a hash request to time out
-	blockSoftTTL    = 3 * time.Second  // Request completion threshold for increasing or decreasing a peer's bandwidth
-	blockHardTTL    = 3 * blockSoftTTL // Maximum time allowance before a block request is considered expired
-	crossCheckCycle = time.Second      // Period after which to check for expired cross checks
+	hashTTL      = 5 * time.Second  // [eth/61] Time it takes for a hash request to time out
+	blockSoftTTL = 3 * time.Second  // [eth/61] Request completion threshold for increasing or decreasing a peer's bandwidth
+	blockHardTTL = 3 * blockSoftTTL // [eth/61] Maximum time allowance before a block request is considered expired
+	headerTTL    = 5 * time.Second  // [eth/62] Time it takes for a header request to time out
+	bodySoftTTL  = 3 * time.Second  // [eth/62] Request completion threshold for increasing or decreasing a peer's bandwidth
+	bodyHardTTL  = 3 * bodySoftTTL  // [eth/62] Maximum time allowance before a block body request is considered expired
 
-	maxQueuedHashes = 256 * 1024 // Maximum number of hashes to queue for import (DOS protection)
-	maxBannedHashes = 4096       // Number of bannable hashes before phasing old ones out
-	maxBlockProcess = 256        // Number of blocks to import at once into the chain
+	maxQueuedHashes  = 256 * 1024 // [eth/61] Maximum number of hashes to queue for import (DOS protection)
+	maxQueuedHeaders = 256 * 1024 // [eth/62] Maximum number of headers to queue for import (DOS protection)
+	maxBlockProcess  = 256        // Number of blocks to import at once into the chain
 )
 
 var (
-	errBusy             = errors.New("busy")
-	errUnknownPeer      = errors.New("peer is unknown or unhealthy")
-	errBadPeer          = errors.New("action from bad peer ignored")
-	errStallingPeer     = errors.New("peer is stalling")
-	errBannedHead       = errors.New("peer head hash already banned")
-	errNoPeers          = errors.New("no peers to keep download active")
-	errPendingQueue     = errors.New("pending items in queue")
-	errTimeout          = errors.New("timeout")
-	errEmptyHashSet     = errors.New("empty hash set by peer")
-	errPeersUnavailable = errors.New("no peers available or all peers tried for block download process")
-	errAlreadyInPool    = errors.New("hash already in pool")
-	errInvalidChain     = errors.New("retrieved hash chain is invalid")
-	errCrossCheckFailed = errors.New("block cross-check failed")
-	errCancelHashFetch  = errors.New("hash fetching canceled (requested)")
-	errCancelBlockFetch = errors.New("block downloading canceled (requested)")
-	errNoSyncActive     = errors.New("no sync active")
+	errBusy              = errors.New("busy")
+	errUnknownPeer       = errors.New("peer is unknown or unhealthy")
+	errBadPeer           = errors.New("action from bad peer ignored")
+	errStallingPeer      = errors.New("peer is stalling")
+	errNoPeers           = errors.New("no peers to keep download active")
+	errPendingQueue      = errors.New("pending items in queue")
+	errTimeout           = errors.New("timeout")
+	errEmptyHashSet      = errors.New("empty hash set by peer")
+	errEmptyHeaderSet    = errors.New("empty header set by peer")
+	errPeersUnavailable  = errors.New("no peers available or all peers tried for block download process")
+	errAlreadyInPool     = errors.New("hash already in pool")
+	errInvalidChain      = errors.New("retrieved hash chain is invalid")
+	errInvalidBody       = errors.New("retrieved block body is invalid")
+	errCancelHashFetch   = errors.New("hash fetching canceled (requested)")
+	errCancelBlockFetch  = errors.New("block downloading canceled (requested)")
+	errCancelHeaderFetch = errors.New("block header fetching canceled (requested)")
+	errCancelBodyFetch   = errors.New("block body downloading canceled (requested)")
+	errNoSyncActive      = errors.New("no sync active")
 )
 
 // hashCheckFn is a callback type for verifying a hash's presence in the local chain.
@@ -91,28 +93,36 @@ type chainInsertFn func(types.Blocks) (int, error)
 // peerDropFn is a callback type for dropping a peer detected as malicious.
 type peerDropFn func(id string)
 
+// hashPack is a batch of block hashes returned by a peer (eth/61).
+type hashPack struct {
+	peerId string
+	hashes []common.Hash
+}
+
+// blockPack is a batch of blocks returned by a peer (eth/61).
 type blockPack struct {
 	peerId string
 	blocks []*types.Block
 }
 
-type hashPack struct {
-	peerId string
-	hashes []common.Hash
+// headerPack is a batch of block headers returned by a peer.
+type headerPack struct {
+	peerId  string
+	headers []*types.Header
 }
 
-type crossCheck struct {
-	expire time.Time
-	parent common.Hash
+// bodyPack is a batch of block bodies returned by a peer.
+type bodyPack struct {
+	peerId       string
+	transactions [][]*types.Transaction
+	uncles       [][]*types.Header
 }
 
 type Downloader struct {
 	mux *event.TypeMux
 
-	queue  *queue                      // Scheduler for selecting the hashes to download
-	peers  *peerSet                    // Set of active peers from which download can proceed
-	checks map[common.Hash]*crossCheck // Pending cross checks to verify a hash chain
-	banned *set.Set                    // Set of hashes we've received and banned
+	queue *queue   // Scheduler for selecting the hashes to download
+	peers *peerSet // Set of active peers from which download can proceed
 
 	interrupt int32 // Atomic boolean to signal termination
 
@@ -137,12 +147,18 @@ type Downloader struct {
 
 	// Channels
 	newPeerCh chan *peer
-	hashCh    chan hashPack  // Channel receiving inbound hashes
-	blockCh   chan blockPack // Channel receiving inbound blocks
-	processCh chan bool      // Channel to signal the block fetcher of new or finished work
+	hashCh    chan hashPack   // [eth/61] Channel receiving inbound hashes
+	blockCh   chan blockPack  // [eth/61] Channel receiving inbound blocks
+	headerCh  chan headerPack // [eth/62] Channel receiving inbound block headers
+	bodyCh    chan bodyPack   // [eth/62] Channel receiving inbound block bodies
+	processCh chan bool       // Channel to signal the block fetcher of new or finished work
 
 	cancelCh   chan struct{} // Channel to cancel mid-flight syncs
 	cancelLock sync.RWMutex  // Lock to protect the cancel channel in delivers
+
+	// Testing hooks
+	bodyFetchHook   func([]*types.Header) // Method to call upon starting a block body fetch
+	chainInsertHook func([]*Block)        // Method to call upon inserting a chain of blocks (possibly in multiple invocations)
 }
 
 // Block is an origin-tagged blockchain block.
@@ -153,8 +169,7 @@ type Block struct {
 
 // New creates a new downloader to fetch hashes and blocks from remote peers.
 func New(mux *event.TypeMux, hasBlock hashCheckFn, getBlock blockRetrievalFn, headBlock headRetrievalFn, insertChain chainInsertFn, dropPeer peerDropFn) *Downloader {
-	// Create the base downloader
-	downloader := &Downloader{
+	return &Downloader{
 		mux:         mux,
 		queue:       newQueue(),
 		peers:       newPeerSet(),
@@ -166,14 +181,10 @@ func New(mux *event.TypeMux, hasBlock hashCheckFn, getBlock blockRetrievalFn, he
 		newPeerCh:   make(chan *peer, 1),
 		hashCh:      make(chan hashPack, 1),
 		blockCh:     make(chan blockPack, 1),
+		headerCh:    make(chan headerPack, 1),
+		bodyCh:      make(chan bodyPack, 1),
 		processCh:   make(chan bool, 1),
 	}
-	// Inject all the known bad hashes
-	downloader.banned = set.New()
-	for hash, _ := range core.BadHashes {
-		downloader.banned.Add(hash)
-	}
-	return downloader
 }
 
 // Stats retrieves the current status of the downloader.
@@ -206,15 +217,12 @@ func (d *Downloader) Synchronising() bool {
 
 // RegisterPeer injects a new download peer into the set of block source to be
 // used for fetching hashes and blocks from.
-func (d *Downloader) RegisterPeer(id string, version int, head common.Hash, getRelHashes relativeHashFetcherFn, getAbsHashes absoluteHashFetcherFn, getBlocks blockFetcherFn) error {
-	// If the peer wants to send a banned hash, reject
-	if d.banned.Has(head) {
-		glog.V(logger.Debug).Infoln("Register rejected, head hash banned:", id)
-		return errBannedHead
-	}
-	// Otherwise try to construct and register the peer
+func (d *Downloader) RegisterPeer(id string, version int, head common.Hash,
+	getRelHashes relativeHashFetcherFn, getAbsHashes absoluteHashFetcherFn, getBlocks blockFetcherFn, // eth/61 callbacks, remove when upgrading
+	getRelHeaders relativeHeaderFetcherFn, getAbsHeaders absoluteHeaderFetcherFn, getBlockBodies blockBodyFetcherFn) error {
+
 	glog.V(logger.Detail).Infoln("Registering peer", id)
-	if err := d.peers.Register(newPeer(id, version, head, getRelHashes, getAbsHashes, getBlocks)); err != nil {
+	if err := d.peers.Register(newPeer(id, version, head, getRelHashes, getAbsHashes, getBlocks, getRelHeaders, getAbsHeaders, getBlockBodies)); err != nil {
 		glog.V(logger.Error).Infoln("Register failed:", err)
 		return err
 	}
@@ -235,7 +243,7 @@ func (d *Downloader) UnregisterPeer(id string) error {
 // Synchronise tries to sync up our local block chain with a remote peer, both
 // adding various sanity checks as well as wrapping it with various log entries.
 func (d *Downloader) Synchronise(id string, head common.Hash, td *big.Int) {
-	glog.V(logger.Detail).Infof("Attempting synchronisation: %v, head 0x%x, TD %v", id, head[:4], td)
+	glog.V(logger.Detail).Infof("Attempting synchronisation: %v, head [%x…], TD %v", id, head[:4], td)
 
 	switch err := d.synchronise(id, head, td); err {
 	case nil:
@@ -244,7 +252,7 @@ func (d *Downloader) Synchronise(id string, head common.Hash, td *big.Int) {
 	case errBusy:
 		glog.V(logger.Detail).Infof("Synchronisation already in progress")
 
-	case errTimeout, errBadPeer, errStallingPeer, errBannedHead, errEmptyHashSet, errPeersUnavailable, errInvalidChain, errCrossCheckFailed:
+	case errTimeout, errBadPeer, errStallingPeer, errEmptyHashSet, errEmptyHeaderSet, errPeersUnavailable, errInvalidChain:
 		glog.V(logger.Debug).Infof("Removing peer %v: %v", id, err)
 		d.dropPeer(id)
 
@@ -270,10 +278,6 @@ func (d *Downloader) synchronise(id string, hash common.Hash, td *big.Int) error
 	}
 	defer atomic.StoreInt32(&d.synchronising, 0)
 
-	// If the head hash is banned, terminate immediately
-	if d.banned.Has(hash) {
-		return errBannedHead
-	}
 	// Post a user notification of the sync (only once per session)
 	if atomic.CompareAndSwapInt32(&d.notified, 0, 1) {
 		glog.V(logger.Info).Infoln("Block synchronisation started")
@@ -285,7 +289,6 @@ func (d *Downloader) synchronise(id string, hash common.Hash, td *big.Int) error
 	// Reset the queue and peer set to clean any internal leftover state
 	d.queue.Reset()
 	d.peers.Reset()
-	d.checks = make(map[common.Hash]*crossCheck)
 
 	// Create cancel channel for aborting mid-flight
 	d.cancelLock.Lock()
@@ -320,17 +323,37 @@ func (d *Downloader) syncWithPeer(p *peer, hash common.Hash, td *big.Int) (err e
 		}
 	}()
 
-	glog.V(logger.Debug).Infof("Synchronizing with the network using: %s, eth/%d", p.id, p.version)
-	switch p.version {
-	case eth61:
+	glog.V(logger.Debug).Infof("Synchronising with the network using: %s [eth/%d]", p.id, p.version)
+	defer glog.V(logger.Debug).Infof("Synchronisation terminated")
+
+	switch {
+	case p.version == eth61:
 		// Old eth/61, use forward, concurrent hash and block retrieval algorithm
+		number, err := d.findAncestor61(p)
+		if err != nil {
+			return err
+		}
+		errc := make(chan error, 2)
+		go func() { errc <- d.fetchHashes61(p, td, number+1) }()
+		go func() { errc <- d.fetchBlocks61(number + 1) }()
+
+		// If any fetcher fails, cancel the other
+		if err := <-errc; err != nil {
+			d.cancel()
+			<-errc
+			return err
+		}
+		return <-errc
+
+	case p.version >= eth62:
+		// New eth/62, use forward, concurrent header and block body retrieval algorithm
 		number, err := d.findAncestor(p)
 		if err != nil {
 			return err
 		}
 		errc := make(chan error, 2)
-		go func() { errc <- d.fetchHashes(p, td, number+1) }()
-		go func() { errc <- d.fetchBlocks(number + 1) }()
+		go func() { errc <- d.fetchHeaders(p, td, number+1) }()
+		go func() { errc <- d.fetchBodies(number + 1) }()
 
 		// If any fetcher fails, cancel the other
 		if err := <-errc; err != nil {
@@ -373,17 +396,17 @@ func (d *Downloader) Terminate() {
 	d.cancel()
 }
 
-// findAncestor tries to locate the common ancestor block of the local chain and
+// findAncestor61 tries to locate the common ancestor block of the local chain and
 // a remote peers blockchain. In the general case when our node was in sync and
 // on the correct chain, checking the top N blocks should already get us a match.
-// In the rare scenario when we ended up on a long soft fork (i.e. none of the
-// head blocks match), we do a binary search to find the common ancestor.
-func (d *Downloader) findAncestor(p *peer) (uint64, error) {
+// In the rare scenario when we ended up on a long reorganization (i.e. none of
+// the head blocks match), we do a binary search to find the common ancestor.
+func (d *Downloader) findAncestor61(p *peer) (uint64, error) {
 	glog.V(logger.Debug).Infof("%v: looking for common ancestor", p)
 
 	// Request out head blocks to short circuit ancestor location
 	head := d.headBlock().NumberU64()
-	from := int64(head) - int64(MaxHashFetch)
+	from := int64(head) - int64(MaxHashFetch) + 1
 	if from < 0 {
 		from = 0
 	}
@@ -422,6 +445,12 @@ func (d *Downloader) findAncestor(p *peer) (uint64, error) {
 		case <-d.blockCh:
 			// Out of bounds blocks received, ignore them
 
+		case <-d.headerCh:
+			// Out of bounds eth/62 block headers received, ignore them
+
+		case <-d.bodyCh:
+			// Out of bounds eth/62 block bodies received, ignore them
+
 		case <-timeout:
 			glog.V(logger.Debug).Infof("%v: head hash timeout", p)
 			return 0, errTimeout
@@ -429,7 +458,7 @@ func (d *Downloader) findAncestor(p *peer) (uint64, error) {
 	}
 	// If the head fetch already found an ancestor, return
 	if !common.EmptyHash(hash) {
-		glog.V(logger.Debug).Infof("%v: common ancestor: #%d [%x]", p, number, hash[:4])
+		glog.V(logger.Debug).Infof("%v: common ancestor: #%d [%x…]", p, number, hash[:4])
 		return number, nil
 	}
 	// Ancestor not found, we need to binary search over our chain
@@ -468,7 +497,7 @@ func (d *Downloader) findAncestor(p *peer) (uint64, error) {
 					break
 				}
 				if block.NumberU64() != check {
-					glog.V(logger.Debug).Infof("%v: non requested hash #%d [%x], instead of #%d", p, block.NumberU64(), block.Hash().Bytes()[:4], check)
+					glog.V(logger.Debug).Infof("%v: non requested hash #%d [%x…], instead of #%d", p, block.NumberU64(), block.Hash().Bytes()[:4], check)
 					return 0, errBadPeer
 				}
 				start = check
@@ -476,6 +505,12 @@ func (d *Downloader) findAncestor(p *peer) (uint64, error) {
 			case <-d.blockCh:
 				// Out of bounds blocks received, ignore them
 
+			case <-d.headerCh:
+				// Out of bounds eth/62 block headers received, ignore them
+
+			case <-d.bodyCh:
+				// Out of bounds eth/62 block bodies received, ignore them
+
 			case <-timeout:
 				glog.V(logger.Debug).Infof("%v: search hash timeout", p)
 				return 0, errTimeout
@@ -485,9 +520,9 @@ func (d *Downloader) findAncestor(p *peer) (uint64, error) {
 	return start, nil
 }
 
-// fetchHashes keeps retrieving hashes from the requested number, until no more
+// fetchHashes61 keeps retrieving hashes from the requested number, until no more
 // are returned, potentially throttling on the way.
-func (d *Downloader) fetchHashes(p *peer, td *big.Int, from uint64) error {
+func (d *Downloader) fetchHashes61(p *peer, td *big.Int, from uint64) error {
 	glog.V(logger.Debug).Infof("%v: downloading hashes from #%d", p, from)
 
 	// Create a timeout timer, and the associated hash fetcher
@@ -510,6 +545,12 @@ func (d *Downloader) fetchHashes(p *peer, td *big.Int, from uint64) error {
 		case <-d.cancelCh:
 			return errCancelHashFetch
 
+		case <-d.headerCh:
+			// Out of bounds eth/62 block headers received, ignore them
+
+		case <-d.bodyCh:
+			// Out of bounds eth/62 block bodies received, ignore them
+
 		case hashPack := <-d.hashCh:
 			// Make sure the active peer is giving us the hashes
 			if hashPack.peerId != p.id {
@@ -548,7 +589,7 @@ func (d *Downloader) fetchHashes(p *peer, td *big.Int, from uint64) error {
 			// Otherwise insert all the new hashes, aborting in case of junk
 			glog.V(logger.Detail).Infof("%v: inserting %d hashes from #%d", p, len(hashPack.hashes), from)
 
-			inserts := d.queue.Insert(hashPack.hashes, true)
+			inserts := d.queue.Insert61(hashPack.hashes, true)
 			if len(inserts) != len(hashPack.hashes) {
 				glog.V(logger.Debug).Infof("%v: stale hashes", p)
 				return errBadPeer
@@ -573,10 +614,10 @@ func (d *Downloader) fetchHashes(p *peer, td *big.Int, from uint64) error {
 	}
 }
 
-// fetchBlocks iteratively downloads the scheduled hashes, taking any available
+// fetchBlocks61 iteratively downloads the scheduled hashes, taking any available
 // peers, reserving a chunk of blocks for each, waiting for delivery and also
 // periodically checking for timeouts.
-func (d *Downloader) fetchBlocks(from uint64) error {
+func (d *Downloader) fetchBlocks61(from uint64) error {
 	glog.V(logger.Debug).Infof("Downloading blocks from #%d", from)
 	defer glog.V(logger.Debug).Infof("Block download terminated")
 
@@ -595,24 +636,30 @@ func (d *Downloader) fetchBlocks(from uint64) error {
 		case <-d.cancelCh:
 			return errCancelBlockFetch
 
+		case <-d.headerCh:
+			// Out of bounds eth/62 block headers received, ignore them
+
+		case <-d.bodyCh:
+			// Out of bounds eth/62 block bodies received, ignore them
+
 		case blockPack := <-d.blockCh:
 			// If the peer was previously banned and failed to deliver it's pack
 			// in a reasonable time frame, ignore it's message.
 			if peer := d.peers.Peer(blockPack.peerId); peer != nil {
 				// Deliver the received chunk of blocks, and demote in case of errors
-				err := d.queue.Deliver(blockPack.peerId, blockPack.blocks)
+				err := d.queue.Deliver61(blockPack.peerId, blockPack.blocks)
 				switch err {
 				case nil:
 					// If no blocks were delivered, demote the peer (need the delivery above)
 					if len(blockPack.blocks) == 0 {
 						peer.Demote()
-						peer.SetIdle()
+						peer.SetIdle61()
 						glog.V(logger.Detail).Infof("%s: no blocks delivered", peer)
 						break
 					}
 					// All was successful, promote the peer and potentially start processing
 					peer.Promote()
-					peer.SetIdle()
+					peer.SetIdle61()
 					glog.V(logger.Detail).Infof("%s: delivered %d blocks", peer, len(blockPack.blocks))
 					go d.process()
 
@@ -624,7 +671,7 @@ func (d *Downloader) fetchBlocks(from uint64) error {
 					// Peer probably timed out with its delivery but came through
 					// in the end, demote, but allow to to pull from this peer.
 					peer.Demote()
-					peer.SetIdle()
+					peer.SetIdle61()
 					glog.V(logger.Detail).Infof("%s: out of bound delivery", peer)
 
 				case errStaleDelivery:
@@ -638,7 +685,7 @@ func (d *Downloader) fetchBlocks(from uint64) error {
 				default:
 					// Peer did something semi-useful, demote but keep it around
 					peer.Demote()
-					peer.SetIdle()
+					peer.SetIdle61()
 					glog.V(logger.Detail).Infof("%s: delivery partially failed: %v", peer, err)
 					go d.process()
 				}
@@ -696,7 +743,7 @@ func (d *Downloader) fetchBlocks(from uint64) error {
 				// Reserve a chunk of hashes for a peer. A nil can mean either that
 				// no more hashes are available, or that the peer is known not to
 				// have them.
-				request := d.queue.Reserve(peer, peer.Capacity())
+				request := d.queue.Reserve61(peer, peer.Capacity())
 				if request == nil {
 					continue
 				}
@@ -704,7 +751,7 @@ func (d *Downloader) fetchBlocks(from uint64) error {
 					glog.Infof("%s: requesting %d blocks", peer, len(request.Hashes))
 				}
 				// Fetch the chunk and make sure any errors return the hashes to the queue
-				if err := peer.Fetch(request); err != nil {
+				if err := peer.Fetch61(request); err != nil {
 					glog.V(logger.Error).Infof("%v: fetch failed, rescheduling", peer)
 					d.queue.Cancel(request)
 				}
@@ -718,6 +765,401 @@ func (d *Downloader) fetchBlocks(from uint64) error {
 	}
 }
 
+// findAncestor tries to locate the common ancestor block of the local chain and
+// a remote peers blockchain. In the general case when our node was in sync and
+// on the correct chain, checking the top N blocks should already get us a match.
+// In the rare scenario when we ended up on a long reorganization (i.e. none of
+// the head blocks match), we do a binary search to find the common ancestor.
+func (d *Downloader) findAncestor(p *peer) (uint64, error) {
+	glog.V(logger.Debug).Infof("%v: looking for common ancestor", p)
+
+	// Request our head blocks to short circuit ancestor location
+	head := d.headBlock().NumberU64()
+	from := int64(head) - int64(MaxHeaderFetch) + 1
+	if from < 0 {
+		from = 0
+	}
+	go p.getAbsHeaders(uint64(from), MaxHeaderFetch, 0, false)
+
+	// Wait for the remote response to the head fetch
+	number, hash := uint64(0), common.Hash{}
+	timeout := time.After(hashTTL)
+
+	for finished := false; !finished; {
+		select {
+		case <-d.cancelCh:
+			return 0, errCancelHashFetch
+
+		case headerPack := <-d.headerCh:
+			// Discard anything not from the origin peer
+			if headerPack.peerId != p.id {
+				glog.V(logger.Debug).Infof("Received headers from incorrect peer(%s)", headerPack.peerId)
+				break
+			}
+			// Make sure the peer actually gave something valid
+			headers := headerPack.headers
+			if len(headers) == 0 {
+				glog.V(logger.Debug).Infof("%v: empty head header set", p)
+				return 0, errEmptyHeaderSet
+			}
+			// Check if a common ancestor was found
+			finished = true
+			for i := len(headers) - 1; i >= 0; i-- {
+				if d.hasBlock(headers[i].Hash()) {
+					number, hash = headers[i].Number.Uint64(), headers[i].Hash()
+					break
+				}
+			}
+
+		case <-d.bodyCh:
+			// Out of bounds block bodies received, ignore them
+
+		case <-d.hashCh:
+			// Out of bounds eth/61 hashes received, ignore them
+
+		case <-d.blockCh:
+			// Out of bounds eth/61 blocks received, ignore them
+
+		case <-timeout:
+			glog.V(logger.Debug).Infof("%v: head header timeout", p)
+			return 0, errTimeout
+		}
+	}
+	// If the head fetch already found an ancestor, return
+	if !common.EmptyHash(hash) {
+		glog.V(logger.Debug).Infof("%v: common ancestor: #%d [%x…]", p, number, hash[:4])
+		return number, nil
+	}
+	// Ancestor not found, we need to binary search over our chain
+	start, end := uint64(0), head
+	for start+1 < end {
+		// Split our chain interval in two, and request the hash to cross check
+		check := (start + end) / 2
+
+		timeout := time.After(hashTTL)
+		go p.getAbsHeaders(uint64(check), 1, 0, false)
+
+		// Wait until a reply arrives to this request
+		for arrived := false; !arrived; {
+			select {
+			case <-d.cancelCh:
+				return 0, errCancelHashFetch
+
+			case headerPack := <-d.headerCh:
+				// Discard anything not from the origin peer
+				if headerPack.peerId != p.id {
+					glog.V(logger.Debug).Infof("Received headers from incorrect peer(%s)", headerPack.peerId)
+					break
+				}
+				// Make sure the peer actually gave something valid
+				headers := headerPack.headers
+				if len(headers) != 1 {
+					glog.V(logger.Debug).Infof("%v: invalid search header set (%d)", p, len(headers))
+					return 0, errBadPeer
+				}
+				arrived = true
+
+				// Modify the search interval based on the response
+				block := d.getBlock(headers[0].Hash())
+				if block == nil {
+					end = check
+					break
+				}
+				if block.NumberU64() != check {
+					glog.V(logger.Debug).Infof("%v: non requested header #%d [%x…], instead of #%d", p, block.NumberU64(), block.Hash().Bytes()[:4], check)
+					return 0, errBadPeer
+				}
+				start = check
+
+			case <-d.bodyCh:
+				// Out of bounds block bodies received, ignore them
+
+			case <-d.hashCh:
+				// Out of bounds eth/61 hashes received, ignore them
+
+			case <-d.blockCh:
+				// Out of bounds eth/61 blocks received, ignore them
+
+			case <-timeout:
+				glog.V(logger.Debug).Infof("%v: search header timeout", p)
+				return 0, errTimeout
+			}
+		}
+	}
+	return start, nil
+}
+
+// fetchHeaders keeps retrieving headers from the requested number, until no more
+// are returned, potentially throttling on the way.
+func (d *Downloader) fetchHeaders(p *peer, td *big.Int, from uint64) error {
+	glog.V(logger.Debug).Infof("%v: downloading headers from #%d", p, from)
+	defer glog.V(logger.Debug).Infof("%v: header download terminated", p)
+
+	// Create a timeout timer, and the associated hash fetcher
+	timeout := time.NewTimer(0) // timer to dump a non-responsive active peer
+	<-timeout.C                 // timeout channel should be initially empty
+	defer timeout.Stop()
+
+	getHeaders := func(from uint64) {
+		glog.V(logger.Detail).Infof("%v: fetching %d headers from #%d", p, MaxHeaderFetch, from)
+
+		go p.getAbsHeaders(from, MaxHeaderFetch, 0, false)
+		timeout.Reset(headerTTL)
+	}
+	// Start pulling headers, until all are exhausted
+	getHeaders(from)
+	gotHeaders := false
+
+	for {
+		select {
+		case <-d.cancelCh:
+			return errCancelHeaderFetch
+
+		case <-d.hashCh:
+			// Out of bounds eth/61 hashes received, ignore them
+
+		case <-d.blockCh:
+			// Out of bounds eth/61 blocks received, ignore them
+
+		case headerPack := <-d.headerCh:
+			// Make sure the active peer is giving us the headers
+			if headerPack.peerId != p.id {
+				glog.V(logger.Debug).Infof("Received headers from incorrect peer (%s)", headerPack.peerId)
+				break
+			}
+			timeout.Stop()
+
+			// If no more headers are inbound, notify the body fetcher and return
+			if len(headerPack.headers) == 0 {
+				glog.V(logger.Debug).Infof("%v: no available headers", p)
+
+				select {
+				case d.processCh <- false:
+				case <-d.cancelCh:
+				}
+				// If no headers were retrieved at all, the peer violated it's TD promise that it had a
+				// better chain compared to ours. The only exception is if it's promised blocks were
+				// already imported by other means (e.g. fecher):
+				//
+				// R <remote peer>, L <local node>: Both at block 10
+				// R: Mine block 11, and propagate it to L
+				// L: Queue block 11 for import
+				// L: Notice that R's head and TD increased compared to ours, start sync
+				// L: Import of block 11 finishes
+				// L: Sync begins, and finds common ancestor at 11
+				// L: Request new headers up from 11 (R's TD was higher, it must have something)
+				// R: Nothing to give
+				if !gotHeaders && td.Cmp(d.headBlock().Td) > 0 {
+					return errStallingPeer
+				}
+				return nil
+			}
+			gotHeaders = true
+
+			// Otherwise insert all the new headers, aborting in case of junk
+			glog.V(logger.Detail).Infof("%v: inserting %d headers from #%d", p, len(headerPack.headers), from)
+
+			inserts := d.queue.Insert(headerPack.headers)
+			if len(inserts) != len(headerPack.headers) {
+				glog.V(logger.Debug).Infof("%v: stale headers", p)
+				return errBadPeer
+			}
+			// Notify the block fetcher of new headers, but stop if queue is full
+			cont := d.queue.Pending() < maxQueuedHeaders
+			select {
+			case d.processCh <- cont:
+			default:
+			}
+			if !cont {
+				return nil
+			}
+			// Queue not yet full, fetch the next batch
+			from += uint64(len(headerPack.headers))
+			getHeaders(from)
+
+		case <-timeout.C:
+			// Header retrieval timed out, consider the peer bad and drop
+			glog.V(logger.Debug).Infof("%v: header request timed out", p)
+			d.dropPeer(p.id)
+
+			// Finish the sync gracefully instead of dumping the gathered data though
+			select {
+			case d.processCh <- false:
+			default:
+			}
+			return nil
+		}
+	}
+}
+
+// fetchBodies iteratively downloads the scheduled block bodies, taking any
+// available peers, reserving a chunk of blocks for each, waiting for delivery
+// and also periodically checking for timeouts.
+func (d *Downloader) fetchBodies(from uint64) error {
+	glog.V(logger.Debug).Infof("Downloading block bodies from #%d", from)
+	defer glog.V(logger.Debug).Infof("Block body download terminated")
+
+	// Create a timeout timer for scheduling expiration tasks
+	ticker := time.NewTicker(100 * time.Millisecond)
+	defer ticker.Stop()
+
+	update := make(chan struct{}, 1)
+
+	// Prepare the queue and fetch block bodies until the block header fetcher's done
+	d.queue.Prepare(from)
+	finished := false
+
+	for {
+		select {
+		case <-d.cancelCh:
+			return errCancelBlockFetch
+
+		case <-d.hashCh:
+			// Out of bounds eth/61 hashes received, ignore them
+
+		case <-d.blockCh:
+			// Out of bounds eth/61 blocks received, ignore them
+
+		case bodyPack := <-d.bodyCh:
+			// If the peer was previously banned and failed to deliver it's pack
+			// in a reasonable time frame, ignore it's message.
+			if peer := d.peers.Peer(bodyPack.peerId); peer != nil {
+				// Deliver the received chunk of bodies, and demote in case of errors
+				err := d.queue.Deliver(bodyPack.peerId, bodyPack.transactions, bodyPack.uncles)
+				switch err {
+				case nil:
+					// If no blocks were delivered, demote the peer (need the delivery above)
+					if len(bodyPack.transactions) == 0 || len(bodyPack.uncles) == 0 {
+						peer.Demote()
+						peer.SetIdle()
+						glog.V(logger.Detail).Infof("%s: no block bodies delivered", peer)
+						break
+					}
+					// All was successful, promote the peer and potentially start processing
+					peer.Promote()
+					peer.SetIdle()
+					glog.V(logger.Detail).Infof("%s: delivered %d:%d block bodies", peer, len(bodyPack.transactions), len(bodyPack.uncles))
+					go d.process()
+
+				case errInvalidChain:
+					// The hash chain is invalid (blocks are not ordered properly), abort
+					return err
+
+				case errInvalidBody:
+					// The peer delivered something very bad, drop immediately
+					glog.V(logger.Error).Infof("%s: delivered invalid block, dropping", peer)
+					d.dropPeer(peer.id)
+
+				case errNoFetchesPending:
+					// Peer probably timed out with its delivery but came through
+					// in the end, demote, but allow to to pull from this peer.
+					peer.Demote()
+					peer.SetIdle()
+					glog.V(logger.Detail).Infof("%s: out of bound delivery", peer)
+
+				case errStaleDelivery:
+					// Delivered something completely else than requested, usually
+					// caused by a timeout and delivery during a new sync cycle.
+					// Don't set it to idle as the original request should still be
+					// in flight.
+					peer.Demote()
+					glog.V(logger.Detail).Infof("%s: stale delivery", peer)
+
+				default:
+					// Peer did something semi-useful, demote but keep it around
+					peer.Demote()
+					peer.SetIdle()
+					glog.V(logger.Detail).Infof("%s: delivery partially failed: %v", peer, err)
+					go d.process()
+				}
+			}
+			// Blocks assembled, try to update the progress
+			select {
+			case update <- struct{}{}:
+			default:
+			}
+
+		case cont := <-d.processCh:
+			// The header fetcher sent a continuation flag, check if it's done
+			if !cont {
+				finished = true
+			}
+			// Headers arrive, try to update the progress
+			select {
+			case update <- struct{}{}:
+			default:
+			}
+
+		case <-ticker.C:
+			// Sanity check update the progress
+			select {
+			case update <- struct{}{}:
+			default:
+			}
+
+		case <-update:
+			// Short circuit if we lost all our peers
+			if d.peers.Len() == 0 {
+				return errNoPeers
+			}
+			// Check for block body request timeouts and demote the responsible peers
+			for _, pid := range d.queue.Expire(bodyHardTTL) {
+				if peer := d.peers.Peer(pid); peer != nil {
+					peer.Demote()
+					glog.V(logger.Detail).Infof("%s: block body delivery timeout", peer)
+				}
+			}
+			// If there's noting more to fetch, wait or terminate
+			if d.queue.Pending() == 0 {
+				if d.queue.InFlight() == 0 && finished {
+					glog.V(logger.Debug).Infof("Block body fetching completed")
+					return nil
+				}
+				break
+			}
+			// Send a download request to all idle peers, until throttled
+			queuedEmptyBlocks, throttled := false, false
+			for _, peer := range d.peers.IdlePeers() {
+				// Short circuit if throttling activated
+				if d.queue.Throttle() {
+					throttled = true
+					break
+				}
+				// Reserve a chunk of hashes for a peer. A nil can mean either that
+				// no more hashes are available, or that the peer is known not to
+				// have them.
+				request, process, err := d.queue.Reserve(peer, peer.Capacity())
+				if err != nil {
+					return err
+				}
+				if process {
+					queuedEmptyBlocks = true
+					go d.process()
+				}
+				if request == nil {
+					continue
+				}
+				if glog.V(logger.Detail) {
+					glog.Infof("%s: requesting %d block bodies", peer, len(request.Headers))
+				}
+				// Fetch the chunk and make sure any errors return the hashes to the queue
+				if d.bodyFetchHook != nil {
+					d.bodyFetchHook(request.Headers)
+				}
+				if err := peer.Fetch(request); err != nil {
+					glog.V(logger.Error).Infof("%v: fetch failed, rescheduling", peer)
+					d.queue.Cancel(request)
+				}
+			}
+			// Make sure that we have peers available for fetching. If all peers have been tried
+			// and all failed throw an error
+			if !queuedEmptyBlocks && !throttled && d.queue.InFlight() == 0 {
+				return errPeersUnavailable
+			}
+		}
+	}
+}
+
 // process takes blocks from the queue and tries to import them into the chain.
 //
 // The algorithmic flow is as follows:
@@ -763,6 +1205,9 @@ func (d *Downloader) process() {
 		if len(blocks) == 0 {
 			return
 		}
+		if d.chainInsertHook != nil {
+			d.chainInsertHook(blocks)
+		}
 		// Reset the import statistics
 		d.importLock.Lock()
 		d.importStart = time.Now()
@@ -796,9 +1241,31 @@ func (d *Downloader) process() {
 	}
 }
 
-// DeliverBlocks injects a new batch of blocks received from a remote node.
+// DeliverHashes61 injects a new batch of hashes received from a remote node into
+// the download schedule. This is usually invoked through the BlockHashesMsg by
+// the protocol handler.
+func (d *Downloader) DeliverHashes61(id string, hashes []common.Hash) error {
+	// Make sure the downloader is active
+	if atomic.LoadInt32(&d.synchronising) == 0 {
+		return errNoSyncActive
+	}
+	// Deliver or abort if the sync is canceled while queuing
+	d.cancelLock.RLock()
+	cancel := d.cancelCh
+	d.cancelLock.RUnlock()
+
+	select {
+	case d.hashCh <- hashPack{id, hashes}:
+		return nil
+
+	case <-cancel:
+		return errNoSyncActive
+	}
+}
+
+// DeliverBlocks61 injects a new batch of blocks received from a remote node.
 // This is usually invoked through the BlocksMsg by the protocol handler.
-func (d *Downloader) DeliverBlocks(id string, blocks []*types.Block) error {
+func (d *Downloader) DeliverBlocks61(id string, blocks []*types.Block) error {
 	// Make sure the downloader is active
 	if atomic.LoadInt32(&d.synchronising) == 0 {
 		return errNoSyncActive
@@ -817,10 +1284,9 @@ func (d *Downloader) DeliverBlocks(id string, blocks []*types.Block) error {
 	}
 }
 
-// DeliverHashes injects a new batch of hashes received from a remote node into
-// the download schedule. This is usually invoked through the BlockHashesMsg by
-// the protocol handler.
-func (d *Downloader) DeliverHashes(id string, hashes []common.Hash) error {
+// DeliverHeaders injects a new batch of blck headers received from a remote
+// node into the download schedule.
+func (d *Downloader) DeliverHeaders(id string, headers []*types.Header) error {
 	// Make sure the downloader is active
 	if atomic.LoadInt32(&d.synchronising) == 0 {
 		return errNoSyncActive
@@ -831,7 +1297,27 @@ func (d *Downloader) DeliverHashes(id string, hashes []common.Hash) error {
 	d.cancelLock.RUnlock()
 
 	select {
-	case d.hashCh <- hashPack{id, hashes}:
+	case d.headerCh <- headerPack{id, headers}:
+		return nil
+
+	case <-cancel:
+		return errNoSyncActive
+	}
+}
+
+// DeliverBodies injects a new batch of block bodies received from a remote node.
+func (d *Downloader) DeliverBodies(id string, transactions [][]*types.Transaction, uncles [][]*types.Header) error {
+	// Make sure the downloader is active
+	if atomic.LoadInt32(&d.synchronising) == 0 {
+		return errNoSyncActive
+	}
+	// Deliver or abort if the sync is canceled while queuing
+	d.cancelLock.RLock()
+	cancel := d.cancelCh
+	d.cancelLock.RUnlock()
+
+	select {
+	case d.bodyCh <- bodyPack{id, transactions, uncles}:
 		return nil
 
 	case <-cancel: