dex: copy fetcher and downloader from eth

1 files changed, 1684 insertions, 0 deletions

diff --git a/dex/downloader/downloader.go b/dex/downloader/downloader.go
new file mode 100644
index 000000000..0383a3709
--- /dev/null
+++ b/dex/downloader/downloader.go
@@ -0,0 +1,1684 @@
+// 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 downloader contains the manual full chain synchronisation.
+package downloader
+
+import (
+	"errors"
+	"fmt"
+	"math/big"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	ethereum "github.com/dexon-foundation/dexon"
+	"github.com/dexon-foundation/dexon/common"
+	"github.com/dexon-foundation/dexon/core/rawdb"
+	"github.com/dexon-foundation/dexon/core/types"
+	"github.com/dexon-foundation/dexon/ethdb"
+	"github.com/dexon-foundation/dexon/event"
+	"github.com/dexon-foundation/dexon/log"
+	"github.com/dexon-foundation/dexon/metrics"
+	"github.com/dexon-foundation/dexon/params"
+)
+
+var (
+	MaxHashFetch    = 512 // Amount of hashes to be fetched per retrieval request
+	MaxBlockFetch   = 128 // Amount of blocks to be fetched per retrieval request
+	MaxHeaderFetch  = 192 // Amount of block headers to be fetched per retrieval request
+	MaxSkeletonSize = 128 // Number of header fetches to need for a skeleton assembly
+	MaxBodyFetch    = 128 // Amount of block bodies to be fetched per retrieval request
+	MaxReceiptFetch = 256 // Amount of transaction receipts to allow fetching per request
+	MaxStateFetch   = 384 // Amount of node state values to allow fetching per request
+
+	MaxForkAncestry  = 3 * params.EpochDuration // Maximum chain reorganisation
+	rttMinEstimate   = 2 * time.Second          // Minimum round-trip time to target for download requests
+	rttMaxEstimate   = 20 * time.Second         // Maximum round-trip time to target for download requests
+	rttMinConfidence = 0.1                      // Worse confidence factor in our estimated RTT value
+	ttlScaling       = 3                        // Constant scaling factor for RTT -> TTL conversion
+	ttlLimit         = time.Minute              // Maximum TTL allowance to prevent reaching crazy timeouts
+
+	qosTuningPeers   = 5    // Number of peers to tune based on (best peers)
+	qosConfidenceCap = 10   // Number of peers above which not to modify RTT confidence
+	qosTuningImpact  = 0.25 // Impact that a new tuning target has on the previous value
+
+	maxQueuedHeaders  = 32 * 1024 // [eth/62] Maximum number of headers to queue for import (DOS protection)
+	maxHeadersProcess = 2048      // Number of header download results to import at once into the chain
+	maxResultsProcess = 2048      // Number of content download results to import at once into the chain
+
+	reorgProtThreshold   = 48 // Threshold number of recent blocks to disable mini reorg protection
+	reorgProtHeaderDelay = 2  // Number of headers to delay delivering to cover mini reorgs
+
+	fsHeaderCheckFrequency = 100             // Verification frequency of the downloaded headers during fast sync
+	fsHeaderSafetyNet      = 2048            // Number of headers to discard in case a chain violation is detected
+	fsHeaderForceVerify    = 24              // Number of headers to verify before and after the pivot to accept it
+	fsHeaderContCheck      = 3 * time.Second // Time interval to check for header continuations during state download
+	fsMinFullBlocks        = 64              // Number of blocks to retrieve fully even in fast sync
+)
+
+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")
+	errNoPeers                 = errors.New("no peers to keep download active")
+	errTimeout                 = errors.New("timeout")
+	errEmptyHeaderSet          = errors.New("empty header set by peer")
+	errPeersUnavailable        = errors.New("no peers available or all tried for download")
+	errInvalidAncestor         = errors.New("retrieved ancestor is invalid")
+	errInvalidChain            = errors.New("retrieved hash chain is invalid")
+	errInvalidBlock            = errors.New("retrieved block is invalid")
+	errInvalidBody             = errors.New("retrieved block body is invalid")
+	errInvalidReceipt          = errors.New("retrieved receipt is invalid")
+	errCancelBlockFetch        = errors.New("block download canceled (requested)")
+	errCancelHeaderFetch       = errors.New("block header download canceled (requested)")
+	errCancelBodyFetch         = errors.New("block body download canceled (requested)")
+	errCancelReceiptFetch      = errors.New("receipt download canceled (requested)")
+	errCancelStateFetch        = errors.New("state data download canceled (requested)")
+	errCancelHeaderProcessing  = errors.New("header processing canceled (requested)")
+	errCancelContentProcessing = errors.New("content processing canceled (requested)")
+	errNoSyncActive            = errors.New("no sync active")
+	errTooOld                  = errors.New("peer doesn't speak recent enough protocol version (need version >= 62)")
+)
+
+type Downloader struct {
+	mode SyncMode       // Synchronisation mode defining the strategy used (per sync cycle)
+	mux  *event.TypeMux // Event multiplexer to announce sync operation events
+
+	queue   *queue   // Scheduler for selecting the hashes to download
+	peers   *peerSet // Set of active peers from which download can proceed
+	stateDB ethdb.Database
+
+	rttEstimate   uint64 // Round trip time to target for download requests
+	rttConfidence uint64 // Confidence in the estimated RTT (unit: millionths to allow atomic ops)
+
+	// Statistics
+	syncStatsChainOrigin uint64 // Origin block number where syncing started at
+	syncStatsChainHeight uint64 // Highest block number known when syncing started
+	syncStatsState       stateSyncStats
+	syncStatsLock        sync.RWMutex // Lock protecting the sync stats fields
+
+	lightchain LightChain
+	blockchain BlockChain
+
+	// Callbacks
+	dropPeer peerDropFn // Drops a peer for misbehaving
+
+	// Status
+	synchroniseMock func(id string, hash common.Hash) error // Replacement for synchronise during testing
+	synchronising   int32
+	notified        int32
+	committed       int32
+
+	// Channels
+	headerCh      chan dataPack        // [eth/62] Channel receiving inbound block headers
+	bodyCh        chan dataPack        // [eth/62] Channel receiving inbound block bodies
+	receiptCh     chan dataPack        // [eth/63] Channel receiving inbound receipts
+	bodyWakeCh    chan bool            // [eth/62] Channel to signal the block body fetcher of new tasks
+	receiptWakeCh chan bool            // [eth/63] Channel to signal the receipt fetcher of new tasks
+	headerProcCh  chan []*types.Header // [eth/62] Channel to feed the header processor new tasks
+
+	// for stateFetcher
+	stateSyncStart chan *stateSync
+	trackStateReq  chan *stateReq
+	stateCh        chan dataPack // [eth/63] Channel receiving inbound node state data
+
+	// Cancellation and termination
+	cancelPeer string         // Identifier of the peer currently being used as the master (cancel on drop)
+	cancelCh   chan struct{}  // Channel to cancel mid-flight syncs
+	cancelLock sync.RWMutex   // Lock to protect the cancel channel and peer in delivers
+	cancelWg   sync.WaitGroup // Make sure all fetcher goroutines have exited.
+
+	quitCh   chan struct{} // Quit channel to signal termination
+	quitLock sync.RWMutex  // Lock to prevent double closes
+
+	// Testing hooks
+	syncInitHook     func(uint64, uint64)  // Method to call upon initiating a new sync run
+	bodyFetchHook    func([]*types.Header) // Method to call upon starting a block body fetch
+	receiptFetchHook func([]*types.Header) // Method to call upon starting a receipt fetch
+	chainInsertHook  func([]*fetchResult)  // Method to call upon inserting a chain of blocks (possibly in multiple invocations)
+}
+
+// LightChain encapsulates functions required to synchronise a light chain.
+type LightChain interface {
+	// HasHeader verifies a header's presence in the local chain.
+	HasHeader(common.Hash, uint64) bool
+
+	// GetHeaderByHash retrieves a header from the local chain.
+	GetHeaderByHash(common.Hash) *types.Header
+
+	// CurrentHeader retrieves the head header from the local chain.
+	CurrentHeader() *types.Header
+
+	// GetTd returns the total difficulty of a local block.
+	GetTd(common.Hash, uint64) *big.Int
+
+	// InsertHeaderChain inserts a batch of headers into the local chain.
+	InsertHeaderChain([]*types.Header, int) (int, error)
+
+	// Rollback removes a few recently added elements from the local chain.
+	Rollback([]common.Hash)
+}
+
+// BlockChain encapsulates functions required to sync a (full or fast) blockchain.
+type BlockChain interface {
+	LightChain
+
+	// HasBlock verifies a block's presence in the local chain.
+	HasBlock(common.Hash, uint64) bool
+
+	// GetBlockByHash retrieves a block from the local chain.
+	GetBlockByHash(common.Hash) *types.Block
+
+	// CurrentBlock retrieves the head block from the local chain.
+	CurrentBlock() *types.Block
+
+	// CurrentFastBlock retrieves the head fast block from the local chain.
+	CurrentFastBlock() *types.Block
+
+	// FastSyncCommitHead directly commits the head block to a certain entity.
+	FastSyncCommitHead(common.Hash) error
+
+	// InsertChain inserts a batch of blocks into the local chain.
+	InsertChain(types.Blocks) (int, error)
+
+	// InsertReceiptChain inserts a batch of receipts into the local chain.
+	InsertReceiptChain(types.Blocks, []types.Receipts) (int, error)
+}
+
+// New creates a new downloader to fetch hashes and blocks from remote peers.
+func New(mode SyncMode, stateDb ethdb.Database, mux *event.TypeMux, chain BlockChain, lightchain LightChain, dropPeer peerDropFn) *Downloader {
+	if lightchain == nil {
+		lightchain = chain
+	}
+
+	dl := &Downloader{
+		mode:           mode,
+		stateDB:        stateDb,
+		mux:            mux,
+		queue:          newQueue(),
+		peers:          newPeerSet(),
+		rttEstimate:    uint64(rttMaxEstimate),
+		rttConfidence:  uint64(1000000),
+		blockchain:     chain,
+		lightchain:     lightchain,
+		dropPeer:       dropPeer,
+		headerCh:       make(chan dataPack, 1),
+		bodyCh:         make(chan dataPack, 1),
+		receiptCh:      make(chan dataPack, 1),
+		bodyWakeCh:     make(chan bool, 1),
+		receiptWakeCh:  make(chan bool, 1),
+		headerProcCh:   make(chan []*types.Header, 1),
+		quitCh:         make(chan struct{}),
+		stateCh:        make(chan dataPack),
+		stateSyncStart: make(chan *stateSync),
+		syncStatsState: stateSyncStats{
+			processed: rawdb.ReadFastTrieProgress(stateDb),
+		},
+		trackStateReq: make(chan *stateReq),
+	}
+	go dl.qosTuner()
+	go dl.stateFetcher()
+	return dl
+}
+
+// Progress retrieves the synchronisation boundaries, specifically the origin
+// block where synchronisation started at (may have failed/suspended); the block
+// or header sync is currently at; and the latest known block which the sync targets.
+//
+// In addition, during the state download phase of fast synchronisation the number
+// of processed and the total number of known states are also returned. Otherwise
+// these are zero.
+func (d *Downloader) Progress() ethereum.SyncProgress {
+	// Lock the current stats and return the progress
+	d.syncStatsLock.RLock()
+	defer d.syncStatsLock.RUnlock()
+
+	current := uint64(0)
+	switch d.mode {
+	case FullSync:
+		current = d.blockchain.CurrentBlock().NumberU64()
+	case FastSync:
+		current = d.blockchain.CurrentFastBlock().NumberU64()
+	case LightSync:
+		current = d.lightchain.CurrentHeader().Number.Uint64()
+	}
+	return ethereum.SyncProgress{
+		StartingBlock: d.syncStatsChainOrigin,
+		CurrentBlock:  current,
+		HighestBlock:  d.syncStatsChainHeight,
+		PulledStates:  d.syncStatsState.processed,
+		KnownStates:   d.syncStatsState.processed + d.syncStatsState.pending,
+	}
+}
+
+// Synchronising returns whether the downloader is currently retrieving blocks.
+func (d *Downloader) Synchronising() bool {
+	return atomic.LoadInt32(&d.synchronising) > 0
+}
+
+// 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, peer Peer) error {
+	logger := log.New("peer", id)
+	logger.Trace("Registering sync peer")
+	if err := d.peers.Register(newPeerConnection(id, version, peer, logger)); err != nil {
+		logger.Error("Failed to register sync peer", "err", err)
+		return err
+	}
+	d.qosReduceConfidence()
+
+	return nil
+}
+
+// RegisterLightPeer injects a light client peer, wrapping it so it appears as a regular peer.
+func (d *Downloader) RegisterLightPeer(id string, version int, peer LightPeer) error {
+	return d.RegisterPeer(id, version, &lightPeerWrapper{peer})
+}
+
+// UnregisterPeer remove a peer from the known list, preventing any action from
+// the specified peer. An effort is also made to return any pending fetches into
+// the queue.
+func (d *Downloader) UnregisterPeer(id string) error {
+	// Unregister the peer from the active peer set and revoke any fetch tasks
+	logger := log.New("peer", id)
+	logger.Trace("Unregistering sync peer")
+	if err := d.peers.Unregister(id); err != nil {
+		logger.Error("Failed to unregister sync peer", "err", err)
+		return err
+	}
+	d.queue.Revoke(id)
+
+	// If this peer was the master peer, abort sync immediately
+	d.cancelLock.RLock()
+	master := id == d.cancelPeer
+	d.cancelLock.RUnlock()
+
+	if master {
+		d.cancel()
+	}
+	return nil
+}
+
+// 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, mode SyncMode) error {
+	err := d.synchronise(id, head, td, mode)
+	switch err {
+	case nil:
+	case errBusy:
+
+	case errTimeout, errBadPeer, errStallingPeer,
+		errEmptyHeaderSet, errPeersUnavailable, errTooOld,
+		errInvalidAncestor, errInvalidChain:
+		log.Warn("Synchronisation failed, dropping peer", "peer", id, "err", err)
+		if d.dropPeer == nil {
+			// The dropPeer method is nil when `--copydb` is used for a local copy.
+			// Timeouts can occur if e.g. compaction hits at the wrong time, and can be ignored
+			log.Warn("Downloader wants to drop peer, but peerdrop-function is not set", "peer", id)
+		} else {
+			d.dropPeer(id)
+		}
+	default:
+		log.Warn("Synchronisation failed, retrying", "err", err)
+	}
+	return err
+}
+
+// synchronise will select the peer and use it for synchronising. If an empty string is given
+// it will use the best peer possible and synchronize if its TD is higher than our own. If any of the
+// checks fail an error will be returned. This method is synchronous
+func (d *Downloader) synchronise(id string, hash common.Hash, td *big.Int, mode SyncMode) error {
+	// Mock out the synchronisation if testing
+	if d.synchroniseMock != nil {
+		return d.synchroniseMock(id, hash)
+	}
+	// Make sure only one goroutine is ever allowed past this point at once
+	if !atomic.CompareAndSwapInt32(&d.synchronising, 0, 1) {
+		return errBusy
+	}
+	defer atomic.StoreInt32(&d.synchronising, 0)
+
+	// Post a user notification of the sync (only once per session)
+	if atomic.CompareAndSwapInt32(&d.notified, 0, 1) {
+		log.Info("Block synchronisation started")
+	}
+	// Reset the queue, peer set and wake channels to clean any internal leftover state
+	d.queue.Reset()
+	d.peers.Reset()
+
+	for _, ch := range []chan bool{d.bodyWakeCh, d.receiptWakeCh} {
+		select {
+		case <-ch:
+		default:
+		}
+	}
+	for _, ch := range []chan dataPack{d.headerCh, d.bodyCh, d.receiptCh} {
+		for empty := false; !empty; {
+			select {
+			case <-ch:
+			default:
+				empty = true
+			}
+		}
+	}
+	for empty := false; !empty; {
+		select {
+		case <-d.headerProcCh:
+		default:
+			empty = true
+		}
+	}
+	// Create cancel channel for aborting mid-flight and mark the master peer
+	d.cancelLock.Lock()
+	d.cancelCh = make(chan struct{})
+	d.cancelPeer = id
+	d.cancelLock.Unlock()
+
+	defer d.Cancel() // No matter what, we can't leave the cancel channel open
+
+	// Set the requested sync mode, unless it's forbidden
+	d.mode = mode
+
+	// Retrieve the origin peer and initiate the downloading process
+	p := d.peers.Peer(id)
+	if p == nil {
+		return errUnknownPeer
+	}
+	return d.syncWithPeer(p, hash, td)
+}
+
+// syncWithPeer starts a block synchronization based on the hash chain from the
+// specified peer and head hash.
+func (d *Downloader) syncWithPeer(p *peerConnection, hash common.Hash, td *big.Int) (err error) {
+	d.mux.Post(StartEvent{})
+	defer func() {
+		// reset on error
+		if err != nil {
+			d.mux.Post(FailedEvent{err})
+		} else {
+			d.mux.Post(DoneEvent{})
+		}
+	}()
+	if p.version < 62 {
+		return errTooOld
+	}
+
+	log.Debug("Synchronising with the network", "peer", p.id, "eth", p.version, "head", hash, "td", td, "mode", d.mode)
+	defer func(start time.Time) {
+		log.Debug("Synchronisation terminated", "elapsed", time.Since(start))
+	}(time.Now())
+
+	// Look up the sync boundaries: the common ancestor and the target block
+	latest, err := d.fetchHeight(p)
+	if err != nil {
+		return err
+	}
+	height := latest.Number.Uint64()
+
+	origin, err := d.findAncestor(p, height)
+	if err != nil {
+		return err
+	}
+	d.syncStatsLock.Lock()
+	if d.syncStatsChainHeight <= origin || d.syncStatsChainOrigin > origin {
+		d.syncStatsChainOrigin = origin
+	}
+	d.syncStatsChainHeight = height
+	d.syncStatsLock.Unlock()
+
+	// Ensure our origin point is below any fast sync pivot point
+	pivot := uint64(0)
+	if d.mode == FastSync {
+		if height <= uint64(fsMinFullBlocks) {
+			origin = 0
+		} else {
+			pivot = height - uint64(fsMinFullBlocks)
+			if pivot <= origin {
+				origin = pivot - 1
+			}
+		}
+	}
+	d.committed = 1
+	if d.mode == FastSync && pivot != 0 {
+		d.committed = 0
+	}
+	// Initiate the sync using a concurrent header and content retrieval algorithm
+	d.queue.Prepare(origin+1, d.mode)
+	if d.syncInitHook != nil {
+		d.syncInitHook(origin, height)
+	}
+
+	fetchers := []func() error{
+		func() error { return d.fetchHeaders(p, origin+1, pivot) }, // Headers are always retrieved
+		func() error { return d.fetchBodies(origin + 1) },          // Bodies are retrieved during normal and fast sync
+		func() error { return d.fetchReceipts(origin + 1) },        // Receipts are retrieved during fast sync
+		func() error { return d.processHeaders(origin+1, pivot, td) },
+	}
+	if d.mode == FastSync {
+		fetchers = append(fetchers, func() error { return d.processFastSyncContent(latest) })
+	} else if d.mode == FullSync {
+		fetchers = append(fetchers, d.processFullSyncContent)
+	}
+	return d.spawnSync(fetchers)
+}
+
+// spawnSync runs d.process and all given fetcher functions to completion in
+// separate goroutines, returning the first error that appears.
+func (d *Downloader) spawnSync(fetchers []func() error) error {
+	errc := make(chan error, len(fetchers))
+	d.cancelWg.Add(len(fetchers))
+	for _, fn := range fetchers {
+		fn := fn
+		go func() { defer d.cancelWg.Done(); errc <- fn() }()
+	}
+	// Wait for the first error, then terminate the others.
+	var err error
+	for i := 0; i < len(fetchers); i++ {
+		if i == len(fetchers)-1 {
+			// Close the queue when all fetchers have exited.
+			// This will cause the block processor to end when
+			// it has processed the queue.
+			d.queue.Close()
+		}
+		if err = <-errc; err != nil {
+			break
+		}
+	}
+	d.queue.Close()
+	d.Cancel()
+	return err
+}
+
+// cancel aborts all of the operations and resets the queue. However, cancel does
+// not wait for the running download goroutines to finish. This method should be
+// used when cancelling the downloads from inside the downloader.
+func (d *Downloader) cancel() {
+	// Close the current cancel channel
+	d.cancelLock.Lock()
+	if d.cancelCh != nil {
+		select {
+		case <-d.cancelCh:
+			// Channel was already closed
+		default:
+			close(d.cancelCh)
+		}
+	}
+	d.cancelLock.Unlock()
+}
+
+// Cancel aborts all of the operations and waits for all download goroutines to
+// finish before returning.
+func (d *Downloader) Cancel() {
+	d.cancel()
+	d.cancelWg.Wait()
+}
+
+// Terminate interrupts the downloader, canceling all pending operations.
+// The downloader cannot be reused after calling Terminate.
+func (d *Downloader) Terminate() {
+	// Close the termination channel (make sure double close is allowed)
+	d.quitLock.Lock()
+	select {
+	case <-d.quitCh:
+	default:
+		close(d.quitCh)
+	}
+	d.quitLock.Unlock()
+
+	// Cancel any pending download requests
+	d.Cancel()
+}
+
+// fetchHeight retrieves the head header of the remote peer to aid in estimating
+// the total time a pending synchronisation would take.
+func (d *Downloader) fetchHeight(p *peerConnection) (*types.Header, error) {
+	p.log.Debug("Retrieving remote chain height")
+
+	// Request the advertised remote head block and wait for the response
+	head, _ := p.peer.Head()
+	go p.peer.RequestHeadersByHash(head, 1, 0, false)
+
+	ttl := d.requestTTL()
+	timeout := time.After(ttl)
+	for {
+		select {
+		case <-d.cancelCh:
+			return nil, errCancelBlockFetch
+
+		case packet := <-d.headerCh:
+			// Discard anything not from the origin peer
+			if packet.PeerId() != p.id {
+				log.Debug("Received headers from incorrect peer", "peer", packet.PeerId())
+				break
+			}
+			// Make sure the peer actually gave something valid
+			headers := packet.(*headerPack).headers
+			if len(headers) != 1 {
+				p.log.Debug("Multiple headers for single request", "headers", len(headers))
+				return nil, errBadPeer
+			}
+			head := headers[0]
+			p.log.Debug("Remote head header identified", "number", head.Number, "hash", head.Hash())
+			return head, nil
+
+		case <-timeout:
+			p.log.Debug("Waiting for head header timed out", "elapsed", ttl)
+			return nil, errTimeout
+
+		case <-d.bodyCh:
+		case <-d.receiptCh:
+			// Out of bounds delivery, ignore
+		}
+	}
+}
+
+// findAncestor tries to locate the common ancestor link 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 links should already get us a match.
+// In the rare scenario when we ended up on a long reorganisation (i.e. none of
+// the head links match), we do a binary search to find the common ancestor.
+func (d *Downloader) findAncestor(p *peerConnection, height uint64) (uint64, error) {
+	// Figure out the valid ancestor range to prevent rewrite attacks
+	floor, ceil := int64(-1), d.lightchain.CurrentHeader().Number.Uint64()
+
+	if d.mode == FullSync {
+		ceil = d.blockchain.CurrentBlock().NumberU64()
+	} else if d.mode == FastSync {
+		ceil = d.blockchain.CurrentFastBlock().NumberU64()
+	}
+	if ceil >= MaxForkAncestry {
+		floor = int64(ceil - MaxForkAncestry)
+	}
+	p.log.Debug("Looking for common ancestor", "local", ceil, "remote", height)
+
+	// Request the topmost blocks to short circuit binary ancestor lookup
+	head := ceil
+	if head > height {
+		head = height
+	}
+	from := int64(head) - int64(MaxHeaderFetch)
+	if from < 0 {
+		from = 0
+	}
+	// Span out with 15 block gaps into the future to catch bad head reports
+	limit := 2 * MaxHeaderFetch / 16
+	count := 1 + int((int64(ceil)-from)/16)
+	if count > limit {
+		count = limit
+	}
+	go p.peer.RequestHeadersByNumber(uint64(from), count, 15, false)
+
+	// Wait for the remote response to the head fetch
+	number, hash := uint64(0), common.Hash{}
+
+	ttl := d.requestTTL()
+	timeout := time.After(ttl)
+
+	for finished := false; !finished; {
+		select {
+		case <-d.cancelCh:
+			return 0, errCancelHeaderFetch
+
+		case packet := <-d.headerCh:
+			// Discard anything not from the origin peer
+			if packet.PeerId() != p.id {
+				log.Debug("Received headers from incorrect peer", "peer", packet.PeerId())
+				break
+			}
+			// Make sure the peer actually gave something valid
+			headers := packet.(*headerPack).headers
+			if len(headers) == 0 {
+				p.log.Warn("Empty head header set")
+				return 0, errEmptyHeaderSet
+			}
+			// Make sure the peer's reply conforms to the request
+			for i := 0; i < len(headers); i++ {
+				if number := headers[i].Number.Int64(); number != from+int64(i)*16 {
+					p.log.Warn("Head headers broke chain ordering", "index", i, "requested", from+int64(i)*16, "received", number)
+					return 0, errInvalidChain
+				}
+			}
+			// Check if a common ancestor was found
+			finished = true
+			for i := len(headers) - 1; i >= 0; i-- {
+				// Skip any headers that underflow/overflow our requested set
+				if headers[i].Number.Int64() < from || headers[i].Number.Uint64() > ceil {
+					continue
+				}
+				// Otherwise check if we already know the header or not
+				h := headers[i].Hash()
+				n := headers[i].Number.Uint64()
+				if (d.mode == FullSync && d.blockchain.HasBlock(h, n)) || (d.mode != FullSync && d.lightchain.HasHeader(h, n)) {
+					number, hash = n, h
+
+					// If every header is known, even future ones, the peer straight out lied about its head
+					if number > height && i == limit-1 {
+						p.log.Warn("Lied about chain head", "reported", height, "found", number)
+						return 0, errStallingPeer
+					}
+					break
+				}
+			}
+
+		case <-timeout:
+			p.log.Debug("Waiting for head header timed out", "elapsed", ttl)
+			return 0, errTimeout
+
+		case <-d.bodyCh:
+		case <-d.receiptCh:
+			// Out of bounds delivery, ignore
+		}
+	}
+	// If the head fetch already found an ancestor, return
+	if hash != (common.Hash{}) {
+		if int64(number) <= floor {
+			p.log.Warn("Ancestor below allowance", "number", number, "hash", hash, "allowance", floor)
+			return 0, errInvalidAncestor
+		}
+		p.log.Debug("Found common ancestor", "number", number, "hash", hash)
+		return number, nil
+	}
+	// Ancestor not found, we need to binary search over our chain
+	start, end := uint64(0), head
+	if floor > 0 {
+		start = uint64(floor)
+	}
+	for start+1 < end {
+		// Split our chain interval in two, and request the hash to cross check
+		check := (start + end) / 2
+
+		ttl := d.requestTTL()
+		timeout := time.After(ttl)
+
+		go p.peer.RequestHeadersByNumber(check, 1, 0, false)
+
+		// Wait until a reply arrives to this request
+		for arrived := false; !arrived; {
+			select {
+			case <-d.cancelCh:
+				return 0, errCancelHeaderFetch
+
+			case packer := <-d.headerCh:
+				// Discard anything not from the origin peer
+				if packer.PeerId() != p.id {
+					log.Debug("Received headers from incorrect peer", "peer", packer.PeerId())
+					break
+				}
+				// Make sure the peer actually gave something valid
+				headers := packer.(*headerPack).headers
+				if len(headers) != 1 {
+					p.log.Debug("Multiple headers for single request", "headers", len(headers))
+					return 0, errBadPeer
+				}
+				arrived = true
+
+				// Modify the search interval based on the response
+				h := headers[0].Hash()
+				n := headers[0].Number.Uint64()
+				if (d.mode == FullSync && !d.blockchain.HasBlock(h, n)) || (d.mode != FullSync && !d.lightchain.HasHeader(h, n)) {
+					end = check
+					break
+				}
+				header := d.lightchain.GetHeaderByHash(h) // Independent of sync mode, header surely exists
+				if header.Number.Uint64() != check {
+					p.log.Debug("Received non requested header", "number", header.Number, "hash", header.Hash(), "request", check)
+					return 0, errBadPeer
+				}
+				start = check
+				hash = h
+
+			case <-timeout:
+				p.log.Debug("Waiting for search header timed out", "elapsed", ttl)
+				return 0, errTimeout
+
+			case <-d.bodyCh:
+			case <-d.receiptCh:
+				// Out of bounds delivery, ignore
+			}
+		}
+	}
+	// Ensure valid ancestry and return
+	if int64(start) <= floor {
+		p.log.Warn("Ancestor below allowance", "number", start, "hash", hash, "allowance", floor)
+		return 0, errInvalidAncestor
+	}
+	p.log.Debug("Found common ancestor", "number", start, "hash", hash)
+	return start, nil
+}
+
+// fetchHeaders keeps retrieving headers concurrently from the number
+// requested, until no more are returned, potentially throttling on the way. To
+// facilitate concurrency but still protect against malicious nodes sending bad
+// headers, we construct a header chain skeleton using the "origin" peer we are
+// syncing with, and fill in the missing headers using anyone else. Headers from
+// other peers are only accepted if they map cleanly to the skeleton. If no one
+// can fill in the skeleton - not even the origin peer - it's assumed invalid and
+// the origin is dropped.
+func (d *Downloader) fetchHeaders(p *peerConnection, from uint64, pivot uint64) error {
+	p.log.Debug("Directing header downloads", "origin", from)
+	defer p.log.Debug("Header download terminated")
+
+	// Create a timeout timer, and the associated header fetcher
+	skeleton := true            // Skeleton assembly phase or finishing up
+	request := time.Now()       // time of the last skeleton fetch request
+	timeout := time.NewTimer(0) // timer to dump a non-responsive active peer
+	<-timeout.C                 // timeout channel should be initially empty
+	defer timeout.Stop()
+
+	var ttl time.Duration
+	getHeaders := func(from uint64) {
+		request = time.Now()
+
+		ttl = d.requestTTL()
+		timeout.Reset(ttl)
+
+		if skeleton {
+			p.log.Trace("Fetching skeleton headers", "count", MaxHeaderFetch, "from", from)
+			go p.peer.RequestHeadersByNumber(from+uint64(MaxHeaderFetch)-1, MaxSkeletonSize, MaxHeaderFetch-1, false)
+		} else {
+			p.log.Trace("Fetching full headers", "count", MaxHeaderFetch, "from", from)
+			go p.peer.RequestHeadersByNumber(from, MaxHeaderFetch, 0, false)
+		}
+	}
+	// Start pulling the header chain skeleton until all is done
+	getHeaders(from)
+
+	for {
+		select {
+		case <-d.cancelCh:
+			return errCancelHeaderFetch
+
+		case packet := <-d.headerCh:
+			// Make sure the active peer is giving us the skeleton headers
+			if packet.PeerId() != p.id {
+				log.Debug("Received skeleton from incorrect peer", "peer", packet.PeerId())
+				break
+			}
+			headerReqTimer.UpdateSince(request)
+			timeout.Stop()
+
+			// If the skeleton's finished, pull any remaining head headers directly from the origin
+			if packet.Items() == 0 && skeleton {
+				skeleton = false
+				getHeaders(from)
+				continue
+			}
+			// If no more headers are inbound, notify the content fetchers and return
+			if packet.Items() == 0 {
+				// Don't abort header fetches while the pivot is downloading
+				if atomic.LoadInt32(&d.committed) == 0 && pivot <= from {
+					p.log.Debug("No headers, waiting for pivot commit")
+					select {
+					case <-time.After(fsHeaderContCheck):
+						getHeaders(from)
+						continue
+					case <-d.cancelCh:
+						return errCancelHeaderFetch
+					}
+				}
+				// Pivot done (or not in fast sync) and no more headers, terminate the process
+				p.log.Debug("No more headers available")
+				select {
+				case d.headerProcCh <- nil:
+					return nil
+				case <-d.cancelCh:
+					return errCancelHeaderFetch
+				}
+			}
+			headers := packet.(*headerPack).headers
+
+			// If we received a skeleton batch, resolve internals concurrently
+			if skeleton {
+				filled, proced, err := d.fillHeaderSkeleton(from, headers)
+				if err != nil {
+					p.log.Debug("Skeleton chain invalid", "err", err)
+					return errInvalidChain
+				}
+				headers = filled[proced:]
+				from += uint64(proced)
+			} else {
+				// If we're closing in on the chain head, but haven't yet reached it, delay
+				// the last few headers so mini reorgs on the head don't cause invalid hash
+				// chain errors.
+				if n := len(headers); n > 0 {
+					// Retrieve the current head we're at
+					head := uint64(0)
+					if d.mode == LightSync {
+						head = d.lightchain.CurrentHeader().Number.Uint64()
+					} else {
+						head = d.blockchain.CurrentFastBlock().NumberU64()
+						if full := d.blockchain.CurrentBlock().NumberU64(); head < full {
+							head = full
+						}
+					}
+					// If the head is way older than this batch, delay the last few headers
+					if head+uint64(reorgProtThreshold) < headers[n-1].Number.Uint64() {
+						delay := reorgProtHeaderDelay
+						if delay > n {
+							delay = n
+						}
+						headers = headers[:n-delay]
+					}
+				}
+			}
+			// Insert all the new headers and fetch the next batch
+			if len(headers) > 0 {
+				p.log.Trace("Scheduling new headers", "count", len(headers), "from", from)
+				select {
+				case d.headerProcCh <- headers:
+				case <-d.cancelCh:
+					return errCancelHeaderFetch
+				}
+				from += uint64(len(headers))
+				getHeaders(from)
+			} else {
+				// No headers delivered, or all of them being delayed, sleep a bit and retry
+				p.log.Trace("All headers delayed, waiting")
+				select {
+				case <-time.After(fsHeaderContCheck):
+					getHeaders(from)
+					continue
+				case <-d.cancelCh:
+					return errCancelHeaderFetch
+				}
+			}
+
+		case <-timeout.C:
+			if d.dropPeer == nil {
+				// The dropPeer method is nil when `--copydb` is used for a local copy.
+				// Timeouts can occur if e.g. compaction hits at the wrong time, and can be ignored
+				p.log.Warn("Downloader wants to drop peer, but peerdrop-function is not set", "peer", p.id)
+				break
+			}
+			// Header retrieval timed out, consider the peer bad and drop
+			p.log.Debug("Header request timed out", "elapsed", ttl)
+			headerTimeoutMeter.Mark(1)
+			d.dropPeer(p.id)
+
+			// Finish the sync gracefully instead of dumping the gathered data though
+			for _, ch := range []chan bool{d.bodyWakeCh, d.receiptWakeCh} {
+				select {
+				case ch <- false:
+				case <-d.cancelCh:
+				}
+			}
+			select {
+			case d.headerProcCh <- nil:
+			case <-d.cancelCh:
+			}
+			return errBadPeer
+		}
+	}
+}
+
+// fillHeaderSkeleton concurrently retrieves headers from all our available peers
+// and maps them to the provided skeleton header chain.
+//
+// Any partial results from the beginning of the skeleton is (if possible) forwarded
+// immediately to the header processor to keep the rest of the pipeline full even
+// in the case of header stalls.
+//
+// The method returns the entire filled skeleton and also the number of headers
+// already forwarded for processing.
+func (d *Downloader) fillHeaderSkeleton(from uint64, skeleton []*types.Header) ([]*types.Header, int, error) {
+	log.Debug("Filling up skeleton", "from", from)
+	d.queue.ScheduleSkeleton(from, skeleton)
+
+	var (
+		deliver = func(packet dataPack) (int, error) {
+			pack := packet.(*headerPack)
+			return d.queue.DeliverHeaders(pack.peerID, pack.headers, d.headerProcCh)
+		}
+		expire   = func() map[string]int { return d.queue.ExpireHeaders(d.requestTTL()) }
+		throttle = func() bool { return false }
+		reserve  = func(p *peerConnection, count int) (*fetchRequest, bool, error) {
+			return d.queue.ReserveHeaders(p, count), false, nil
+		}
+		fetch    = func(p *peerConnection, req *fetchRequest) error { return p.FetchHeaders(req.From, MaxHeaderFetch) }
+		capacity = func(p *peerConnection) int { return p.HeaderCapacity(d.requestRTT()) }
+		setIdle  = func(p *peerConnection, accepted int) { p.SetHeadersIdle(accepted) }
+	)
+	err := d.fetchParts(errCancelHeaderFetch, d.headerCh, deliver, d.queue.headerContCh, expire,
+		d.queue.PendingHeaders, d.queue.InFlightHeaders, throttle, reserve,
+		nil, fetch, d.queue.CancelHeaders, capacity, d.peers.HeaderIdlePeers, setIdle, "headers")
+
+	log.Debug("Skeleton fill terminated", "err", err)
+
+	filled, proced := d.queue.RetrieveHeaders()
+	return filled, proced, err
+}
+
+// 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 {
+	log.Debug("Downloading block bodies", "origin", from)
+
+	var (
+		deliver = func(packet dataPack) (int, error) {
+			pack := packet.(*bodyPack)
+			return d.queue.DeliverBodies(pack.peerID, pack.transactions, pack.uncles)
+		}
+		expire   = func() map[string]int { return d.queue.ExpireBodies(d.requestTTL()) }
+		fetch    = func(p *peerConnection, req *fetchRequest) error { return p.FetchBodies(req) }
+		capacity = func(p *peerConnection) int { return p.BlockCapacity(d.requestRTT()) }
+		setIdle  = func(p *peerConnection, accepted int) { p.SetBodiesIdle(accepted) }
+	)
+	err := d.fetchParts(errCancelBodyFetch, d.bodyCh, deliver, d.bodyWakeCh, expire,
+		d.queue.PendingBlocks, d.queue.InFlightBlocks, d.queue.ShouldThrottleBlocks, d.queue.ReserveBodies,
+		d.bodyFetchHook, fetch, d.queue.CancelBodies, capacity, d.peers.BodyIdlePeers, setIdle, "bodies")
+
+	log.Debug("Block body download terminated", "err", err)
+	return err
+}
+
+// fetchReceipts iteratively downloads the scheduled block receipts, taking any
+// available peers, reserving a chunk of receipts for each, waiting for delivery
+// and also periodically checking for timeouts.
+func (d *Downloader) fetchReceipts(from uint64) error {
+	log.Debug("Downloading transaction receipts", "origin", from)
+
+	var (
+		deliver = func(packet dataPack) (int, error) {
+			pack := packet.(*receiptPack)
+			return d.queue.DeliverReceipts(pack.peerID, pack.receipts)
+		}
+		expire   = func() map[string]int { return d.queue.ExpireReceipts(d.requestTTL()) }
+		fetch    = func(p *peerConnection, req *fetchRequest) error { return p.FetchReceipts(req) }
+		capacity = func(p *peerConnection) int { return p.ReceiptCapacity(d.requestRTT()) }
+		setIdle  = func(p *peerConnection, accepted int) { p.SetReceiptsIdle(accepted) }
+	)
+	err := d.fetchParts(errCancelReceiptFetch, d.receiptCh, deliver, d.receiptWakeCh, expire,
+		d.queue.PendingReceipts, d.queue.InFlightReceipts, d.queue.ShouldThrottleReceipts, d.queue.ReserveReceipts,
+		d.receiptFetchHook, fetch, d.queue.CancelReceipts, capacity, d.peers.ReceiptIdlePeers, setIdle, "receipts")
+
+	log.Debug("Transaction receipt download terminated", "err", err)
+	return err
+}
+
+// fetchParts iteratively downloads scheduled block parts, taking any available
+// peers, reserving a chunk of fetch requests for each, waiting for delivery and
+// also periodically checking for timeouts.
+//
+// As the scheduling/timeout logic mostly is the same for all downloaded data
+// types, this method is used by each for data gathering and is instrumented with
+// various callbacks to handle the slight differences between processing them.
+//
+// The instrumentation parameters:
+//  - errCancel:   error type to return if the fetch operation is cancelled (mostly makes logging nicer)
+//  - deliveryCh:  channel from which to retrieve downloaded data packets (merged from all concurrent peers)
+//  - deliver:     processing callback to deliver data packets into type specific download queues (usually within `queue`)
+//  - wakeCh:      notification channel for waking the fetcher when new tasks are available (or sync completed)
+//  - expire:      task callback method to abort requests that took too long and return the faulty peers (traffic shaping)
+//  - pending:     task callback for the number of requests still needing download (detect completion/non-completability)
+//  - inFlight:    task callback for the number of in-progress requests (wait for all active downloads to finish)
+//  - throttle:    task callback to check if the processing queue is full and activate throttling (bound memory use)
+//  - reserve:     task callback to reserve new download tasks to a particular peer (also signals partial completions)
+//  - fetchHook:   tester callback to notify of new tasks being initiated (allows testing the scheduling logic)
+//  - fetch:       network callback to actually send a particular download request to a physical remote peer
+//  - cancel:      task callback to abort an in-flight download request and allow rescheduling it (in case of lost peer)
+//  - capacity:    network callback to retrieve the estimated type-specific bandwidth capacity of a peer (traffic shaping)
+//  - idle:        network callback to retrieve the currently (type specific) idle peers that can be assigned tasks
+//  - setIdle:     network callback to set a peer back to idle and update its estimated capacity (traffic shaping)
+//  - kind:        textual label of the type being downloaded to display in log mesages
+func (d *Downloader) fetchParts(errCancel error, deliveryCh chan dataPack, deliver func(dataPack) (int, error), wakeCh chan bool,
+	expire func() map[string]int, pending func() int, inFlight func() bool, throttle func() bool, reserve func(*peerConnection, int) (*fetchRequest, bool, error),
+	fetchHook func([]*types.Header), fetch func(*peerConnection, *fetchRequest) error, cancel func(*fetchRequest), capacity func(*peerConnection) int,
+	idle func() ([]*peerConnection, int), setIdle func(*peerConnection, int), kind string) error {
+
+	// Create a ticker to detect expired retrieval tasks
+	ticker := time.NewTicker(100 * time.Millisecond)
+	defer ticker.Stop()
+
+	update := make(chan struct{}, 1)
+
+	// Prepare the queue and fetch block parts until the block header fetcher's done
+	finished := false
+	for {
+		select {
+		case <-d.cancelCh:
+			return errCancel
+
+		case packet := <-deliveryCh:
+			// If the peer was previously banned and failed to deliver its pack
+			// in a reasonable time frame, ignore its message.
+			if peer := d.peers.Peer(packet.PeerId()); peer != nil {
+				// Deliver the received chunk of data and check chain validity
+				accepted, err := deliver(packet)
+				if err == errInvalidChain {
+					return err
+				}
+				// Unless a peer delivered something completely else than requested (usually
+				// caused by a timed out request which came through in the end), set it to
+				// idle. If the delivery's stale, the peer should have already been idled.
+				if err != errStaleDelivery {
+					setIdle(peer, accepted)
+				}
+				// Issue a log to the user to see what's going on
+				switch {
+				case err == nil && packet.Items() == 0:
+					peer.log.Trace("Requested data not delivered", "type", kind)
+				case err == nil:
+					peer.log.Trace("Delivered new batch of data", "type", kind, "count", packet.Stats())
+				default:
+					peer.log.Trace("Failed to deliver retrieved data", "type", kind, "err", err)
+				}
+			}
+			// Blocks assembled, try to update the progress
+			select {
+			case update <- struct{}{}:
+			default:
+			}
+
+		case cont := <-wakeCh:
+			// 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 fetch request timeouts and demote the responsible peers
+			for pid, fails := range expire() {
+				if peer := d.peers.Peer(pid); peer != nil {
+					// If a lot of retrieval elements expired, we might have overestimated the remote peer or perhaps
+					// ourselves. Only reset to minimal throughput but don't drop just yet. If even the minimal times
+					// out that sync wise we need to get rid of the peer.
+					//
+					// The reason the minimum threshold is 2 is because the downloader tries to estimate the bandwidth
+					// and latency of a peer separately, which requires pushing the measures capacity a bit and seeing
+					// how response times reacts, to it always requests one more than the minimum (i.e. min 2).
+					if fails > 2 {
+						peer.log.Trace("Data delivery timed out", "type", kind)
+						setIdle(peer, 0)
+					} else {
+						peer.log.Debug("Stalling delivery, dropping", "type", kind)
+						if d.dropPeer == nil {
+							// The dropPeer method is nil when `--copydb` is used for a local copy.
+							// Timeouts can occur if e.g. compaction hits at the wrong time, and can be ignored
+							peer.log.Warn("Downloader wants to drop peer, but peerdrop-function is not set", "peer", pid)
+						} else {
+							d.dropPeer(pid)
+						}
+					}
+				}
+			}
+			// If there's nothing more to fetch, wait or terminate
+			if pending() == 0 {
+				if !inFlight() && finished {
+					log.Debug("Data fetching completed", "type", kind)
+					return nil
+				}
+				break
+			}
+			// Send a download request to all idle peers, until throttled
+			progressed, throttled, running := false, false, inFlight()
+			idles, total := idle()
+
+			for _, peer := range idles {
+				// Short circuit if throttling activated
+				if throttle() {
+					throttled = true
+					break
+				}
+				// Short circuit if there is no more available task.
+				if pending() == 0 {
+					break
+				}
+				// Reserve a chunk of fetches for a peer. A nil can mean either that
+				// no more headers are available, or that the peer is known not to
+				// have them.
+				request, progress, err := reserve(peer, capacity(peer))
+				if err != nil {
+					return err
+				}
+				if progress {
+					progressed = true
+				}
+				if request == nil {
+					continue
+				}
+				if request.From > 0 {
+					peer.log.Trace("Requesting new batch of data", "type", kind, "from", request.From)
+				} else {
+					peer.log.Trace("Requesting new batch of data", "type", kind, "count", len(request.Headers), "from", request.Headers[0].Number)
+				}
+				// Fetch the chunk and make sure any errors return the hashes to the queue
+				if fetchHook != nil {
+					fetchHook(request.Headers)
+				}
+				if err := fetch(peer, request); err != nil {
+					// Although we could try and make an attempt to fix this, this error really
+					// means that we've double allocated a fetch task to a peer. If that is the
+					// case, the internal state of the downloader and the queue is very wrong so
+					// better hard crash and note the error instead of silently accumulating into
+					// a much bigger issue.
+					panic(fmt.Sprintf("%v: %s fetch assignment failed", peer, kind))
+				}
+				running = true
+			}
+			// Make sure that we have peers available for fetching. If all peers have been tried
+			// and all failed throw an error
+			if !progressed && !throttled && !running && len(idles) == total && pending() > 0 {
+				return errPeersUnavailable
+			}
+		}
+	}
+}
+
+// processHeaders takes batches of retrieved headers from an input channel and
+// keeps processing and scheduling them into the header chain and downloader's
+// queue until the stream ends or a failure occurs.
+func (d *Downloader) processHeaders(origin uint64, pivot uint64, td *big.Int) error {
+	// Keep a count of uncertain headers to roll back
+	rollback := []*types.Header{}
+	defer func() {
+		if len(rollback) > 0 {
+			// Flatten the headers and roll them back
+			hashes := make([]common.Hash, len(rollback))
+			for i, header := range rollback {
+				hashes[i] = header.Hash()
+			}
+			lastHeader, lastFastBlock, lastBlock := d.lightchain.CurrentHeader().Number, common.Big0, common.Big0
+			if d.mode != LightSync {
+				lastFastBlock = d.blockchain.CurrentFastBlock().Number()
+				lastBlock = d.blockchain.CurrentBlock().Number()
+			}
+			d.lightchain.Rollback(hashes)
+			curFastBlock, curBlock := common.Big0, common.Big0
+			if d.mode != LightSync {
+				curFastBlock = d.blockchain.CurrentFastBlock().Number()
+				curBlock = d.blockchain.CurrentBlock().Number()
+			}
+			log.Warn("Rolled back headers", "count", len(hashes),
+				"header", fmt.Sprintf("%d->%d", lastHeader, d.lightchain.CurrentHeader().Number),
+				"fast", fmt.Sprintf("%d->%d", lastFastBlock, curFastBlock),
+				"block", fmt.Sprintf("%d->%d", lastBlock, curBlock))
+		}
+	}()
+
+	// Wait for batches of headers to process
+	gotHeaders := false
+
+	for {
+		select {
+		case <-d.cancelCh:
+			return errCancelHeaderProcessing
+
+		case headers := <-d.headerProcCh:
+			// Terminate header processing if we synced up
+			if len(headers) == 0 {
+				// Notify everyone that headers are fully processed
+				for _, ch := range []chan bool{d.bodyWakeCh, d.receiptWakeCh} {
+					select {
+					case ch <- false:
+					case <-d.cancelCh:
+					}
+				}
+				// If no headers were retrieved at all, the peer violated its TD promise that it had a
+				// better chain compared to ours. The only exception is if its 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 d.mode != LightSync {
+					head := d.blockchain.CurrentBlock()
+					if !gotHeaders && td.Cmp(d.blockchain.GetTd(head.Hash(), head.NumberU64())) > 0 {
+						return errStallingPeer
+					}
+				}
+				// If fast or light syncing, ensure promised headers are indeed delivered. This is
+				// needed to detect scenarios where an attacker feeds a bad pivot and then bails out
+				// of delivering the post-pivot blocks that would flag the invalid content.
+				//
+				// This check cannot be executed "as is" for full imports, since blocks may still be
+				// queued for processing when the header download completes. However, as long as the
+				// peer gave us something useful, we're already happy/progressed (above check).
+				if d.mode == FastSync || d.mode == LightSync {
+					head := d.lightchain.CurrentHeader()
+					if td.Cmp(d.lightchain.GetTd(head.Hash(), head.Number.Uint64())) > 0 {
+						return errStallingPeer
+					}
+				}
+				// Disable any rollback and return
+				rollback = nil
+				return nil
+			}
+			// Otherwise split the chunk of headers into batches and process them
+			gotHeaders = true
+
+			for len(headers) > 0 {
+				// Terminate if something failed in between processing chunks
+				select {
+				case <-d.cancelCh:
+					return errCancelHeaderProcessing
+				default:
+				}
+				// Select the next chunk of headers to import
+				limit := maxHeadersProcess
+				if limit > len(headers) {
+					limit = len(headers)
+				}
+				chunk := headers[:limit]
+
+				// In case of header only syncing, validate the chunk immediately
+				if d.mode == FastSync || d.mode == LightSync {
+					// Collect the yet unknown headers to mark them as uncertain
+					unknown := make([]*types.Header, 0, len(headers))
+					for _, header := range chunk {
+						if !d.lightchain.HasHeader(header.Hash(), header.Number.Uint64()) {
+							unknown = append(unknown, header)
+						}
+					}
+					// If we're importing pure headers, verify based on their recentness
+					frequency := fsHeaderCheckFrequency
+					if chunk[len(chunk)-1].Number.Uint64()+uint64(fsHeaderForceVerify) > pivot {
+						frequency = 1
+					}
+					if n, err := d.lightchain.InsertHeaderChain(chunk, frequency); err != nil {
+						// If some headers were inserted, add them too to the rollback list
+						if n > 0 {
+							rollback = append(rollback, chunk[:n]...)
+						}
+						log.Debug("Invalid header encountered", "number", chunk[n].Number, "hash", chunk[n].Hash(), "err", err)
+						return errInvalidChain
+					}
+					// All verifications passed, store newly found uncertain headers
+					rollback = append(rollback, unknown...)
+					if len(rollback) > fsHeaderSafetyNet {
+						rollback = append(rollback[:0], rollback[len(rollback)-fsHeaderSafetyNet:]...)
+					}
+				}
+				// Unless we're doing light chains, schedule the headers for associated content retrieval
+				if d.mode == FullSync || d.mode == FastSync {
+					// If we've reached the allowed number of pending headers, stall a bit
+					for d.queue.PendingBlocks() >= maxQueuedHeaders || d.queue.PendingReceipts() >= maxQueuedHeaders {
+						select {
+						case <-d.cancelCh:
+							return errCancelHeaderProcessing
+						case <-time.After(time.Second):
+						}
+					}
+					// Otherwise insert the headers for content retrieval
+					inserts := d.queue.Schedule(chunk, origin)
+					if len(inserts) != len(chunk) {
+						log.Debug("Stale headers")
+						return errBadPeer
+					}
+				}
+				headers = headers[limit:]
+				origin += uint64(limit)
+			}
+
+			// Update the highest block number we know if a higher one is found.
+			d.syncStatsLock.Lock()
+			if d.syncStatsChainHeight < origin {
+				d.syncStatsChainHeight = origin - 1
+			}
+			d.syncStatsLock.Unlock()
+
+			// Signal the content downloaders of the availablility of new tasks
+			for _, ch := range []chan bool{d.bodyWakeCh, d.receiptWakeCh} {
+				select {
+				case ch <- true:
+				default:
+				}
+			}
+		}
+	}
+}
+
+// processFullSyncContent takes fetch results from the queue and imports them into the chain.
+func (d *Downloader) processFullSyncContent() error {
+	for {
+		results := d.queue.Results(true)
+		if len(results) == 0 {
+			return nil
+		}
+		if d.chainInsertHook != nil {
+			d.chainInsertHook(results)
+		}
+		if err := d.importBlockResults(results); err != nil {
+			return err
+		}
+	}
+}
+
+func (d *Downloader) importBlockResults(results []*fetchResult) error {
+	// Check for any early termination requests
+	if len(results) == 0 {
+		return nil
+	}
+	select {
+	case <-d.quitCh:
+		return errCancelContentProcessing
+	default:
+	}
+	// Retrieve the a batch of results to import
+	first, last := results[0].Header, results[len(results)-1].Header
+	log.Debug("Inserting downloaded chain", "items", len(results),
+		"firstnum", first.Number, "firsthash", first.Hash(),
+		"lastnum", last.Number, "lasthash", last.Hash(),
+	)
+	blocks := make([]*types.Block, len(results))
+	for i, result := range results {
+		blocks[i] = types.NewBlockWithHeader(result.Header).WithBody(result.Transactions, result.Uncles)
+	}
+	if index, err := d.blockchain.InsertChain(blocks); err != nil {
+		log.Debug("Downloaded item processing failed", "number", results[index].Header.Number, "hash", results[index].Header.Hash(), "err", err)
+		return errInvalidChain
+	}
+	return nil
+}
+
+// processFastSyncContent takes fetch results from the queue and writes them to the
+// database. It also controls the synchronisation of state nodes of the pivot block.
+func (d *Downloader) processFastSyncContent(latest *types.Header) error {
+	// Start syncing state of the reported head block. This should get us most of
+	// the state of the pivot block.
+	stateSync := d.syncState(latest.Root)
+	defer stateSync.Cancel()
+	go func() {
+		if err := stateSync.Wait(); err != nil && err != errCancelStateFetch {
+			d.queue.Close() // wake up WaitResults
+		}
+	}()
+	// Figure out the ideal pivot block. Note, that this goalpost may move if the
+	// sync takes long enough for the chain head to move significantly.
+	pivot := uint64(0)
+	if height := latest.Number.Uint64(); height > uint64(fsMinFullBlocks) {
+		pivot = height - uint64(fsMinFullBlocks)
+	}
+	// To cater for moving pivot points, track the pivot block and subsequently
+	// accumulated download results separately.
+	var (
+		oldPivot *fetchResult   // Locked in pivot block, might change eventually
+		oldTail  []*fetchResult // Downloaded content after the pivot
+	)
+	for {
+		// Wait for the next batch of downloaded data to be available, and if the pivot
+		// block became stale, move the goalpost
+		results := d.queue.Results(oldPivot == nil) // Block if we're not monitoring pivot staleness
+		if len(results) == 0 {
+			// If pivot sync is done, stop
+			if oldPivot == nil {
+				return stateSync.Cancel()
+			}
+			// If sync failed, stop
+			select {
+			case <-d.cancelCh:
+				return stateSync.Cancel()
+			default:
+			}
+		}
+		if d.chainInsertHook != nil {
+			d.chainInsertHook(results)
+		}
+		if oldPivot != nil {
+			results = append(append([]*fetchResult{oldPivot}, oldTail...), results...)
+		}
+		// Split around the pivot block and process the two sides via fast/full sync
+		if atomic.LoadInt32(&d.committed) == 0 {
+			latest = results[len(results)-1].Header
+			if height := latest.Number.Uint64(); height > pivot+2*uint64(fsMinFullBlocks) {
+				log.Warn("Pivot became stale, moving", "old", pivot, "new", height-uint64(fsMinFullBlocks))
+				pivot = height - uint64(fsMinFullBlocks)
+			}
+		}
+		P, beforeP, afterP := splitAroundPivot(pivot, results)
+		if err := d.commitFastSyncData(beforeP, stateSync); err != nil {
+			return err
+		}
+		if P != nil {
+			// If new pivot block found, cancel old state retrieval and restart
+			if oldPivot != P {
+				stateSync.Cancel()
+
+				stateSync = d.syncState(P.Header.Root)
+				defer stateSync.Cancel()
+				go func() {
+					if err := stateSync.Wait(); err != nil && err != errCancelStateFetch {
+						d.queue.Close() // wake up WaitResults
+					}
+				}()
+				oldPivot = P
+			}
+			// Wait for completion, occasionally checking for pivot staleness
+			select {
+			case <-stateSync.done:
+				if stateSync.err != nil {
+					return stateSync.err
+				}
+				if err := d.commitPivotBlock(P); err != nil {
+					return err
+				}
+				oldPivot = nil
+
+			case <-time.After(time.Second):
+				oldTail = afterP
+				continue
+			}
+		}
+		// Fast sync done, pivot commit done, full import
+		if err := d.importBlockResults(afterP); err != nil {
+			return err
+		}
+	}
+}
+
+func splitAroundPivot(pivot uint64, results []*fetchResult) (p *fetchResult, before, after []*fetchResult) {
+	for _, result := range results {
+		num := result.Header.Number.Uint64()
+		switch {
+		case num < pivot:
+			before = append(before, result)
+		case num == pivot:
+			p = result
+		default:
+			after = append(after, result)
+		}
+	}
+	return p, before, after
+}
+
+func (d *Downloader) commitFastSyncData(results []*fetchResult, stateSync *stateSync) error {
+	// Check for any early termination requests
+	if len(results) == 0 {
+		return nil
+	}
+	select {
+	case <-d.quitCh:
+		return errCancelContentProcessing
+	case <-stateSync.done:
+		if err := stateSync.Wait(); err != nil {
+			return err
+		}
+	default:
+	}
+	// Retrieve the a batch of results to import
+	first, last := results[0].Header, results[len(results)-1].Header
+	log.Debug("Inserting fast-sync blocks", "items", len(results),
+		"firstnum", first.Number, "firsthash", first.Hash(),
+		"lastnumn", last.Number, "lasthash", last.Hash(),
+	)
+	blocks := make([]*types.Block, len(results))
+	receipts := make([]types.Receipts, len(results))
+	for i, result := range results {
+		blocks[i] = types.NewBlockWithHeader(result.Header).WithBody(result.Transactions, result.Uncles)
+		receipts[i] = result.Receipts
+	}
+	if index, err := d.blockchain.InsertReceiptChain(blocks, receipts); err != nil {
+		log.Debug("Downloaded item processing failed", "number", results[index].Header.Number, "hash", results[index].Header.Hash(), "err", err)
+		return errInvalidChain
+	}
+	return nil
+}
+
+func (d *Downloader) commitPivotBlock(result *fetchResult) error {
+	block := types.NewBlockWithHeader(result.Header).WithBody(result.Transactions, result.Uncles)
+	log.Debug("Committing fast sync pivot as new head", "number", block.Number(), "hash", block.Hash())
+	if _, err := d.blockchain.InsertReceiptChain([]*types.Block{block}, []types.Receipts{result.Receipts}); err != nil {
+		return err
+	}
+	if err := d.blockchain.FastSyncCommitHead(block.Hash()); err != nil {
+		return err
+	}
+	atomic.StoreInt32(&d.committed, 1)
+	return nil
+}
+
+// DeliverHeaders injects a new batch of block headers received from a remote
+// node into the download schedule.
+func (d *Downloader) DeliverHeaders(id string, headers []*types.Header) (err error) {
+	return d.deliver(id, d.headerCh, &headerPack{id, headers}, headerInMeter, headerDropMeter)
+}
+
+// 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) (err error) {
+	return d.deliver(id, d.bodyCh, &bodyPack{id, transactions, uncles}, bodyInMeter, bodyDropMeter)
+}
+
+// DeliverReceipts injects a new batch of receipts received from a remote node.
+func (d *Downloader) DeliverReceipts(id string, receipts [][]*types.Receipt) (err error) {
+	return d.deliver(id, d.receiptCh, &receiptPack{id, receipts}, receiptInMeter, receiptDropMeter)
+}
+
+// DeliverNodeData injects a new batch of node state data received from a remote node.
+func (d *Downloader) DeliverNodeData(id string, data [][]byte) (err error) {
+	return d.deliver(id, d.stateCh, &statePack{id, data}, stateInMeter, stateDropMeter)
+}
+
+// deliver injects a new batch of data received from a remote node.
+func (d *Downloader) deliver(id string, destCh chan dataPack, packet dataPack, inMeter, dropMeter metrics.Meter) (err error) {
+	// Update the delivery metrics for both good and failed deliveries
+	inMeter.Mark(int64(packet.Items()))
+	defer func() {
+		if err != nil {
+			dropMeter.Mark(int64(packet.Items()))
+		}
+	}()
+	// Deliver or abort if the sync is canceled while queuing
+	d.cancelLock.RLock()
+	cancel := d.cancelCh
+	d.cancelLock.RUnlock()
+	if cancel == nil {
+		return errNoSyncActive
+	}
+	select {
+	case destCh <- packet:
+		return nil
+	case <-cancel:
+		return errNoSyncActive
+	}
+}
+
+// qosTuner is the quality of service tuning loop that occasionally gathers the
+// peer latency statistics and updates the estimated request round trip time.
+func (d *Downloader) qosTuner() {
+	for {
+		// Retrieve the current median RTT and integrate into the previoust target RTT
+		rtt := time.Duration((1-qosTuningImpact)*float64(atomic.LoadUint64(&d.rttEstimate)) + qosTuningImpact*float64(d.peers.medianRTT()))
+		atomic.StoreUint64(&d.rttEstimate, uint64(rtt))
+
+		// A new RTT cycle passed, increase our confidence in the estimated RTT
+		conf := atomic.LoadUint64(&d.rttConfidence)
+		conf = conf + (1000000-conf)/2
+		atomic.StoreUint64(&d.rttConfidence, conf)
+
+		// Log the new QoS values and sleep until the next RTT
+		log.Debug("Recalculated downloader QoS values", "rtt", rtt, "confidence", float64(conf)/1000000.0, "ttl", d.requestTTL())
+		select {
+		case <-d.quitCh:
+			return
+		case <-time.After(rtt):
+		}
+	}
+}
+
+// qosReduceConfidence is meant to be called when a new peer joins the downloader's
+// peer set, needing to reduce the confidence we have in out QoS estimates.
+func (d *Downloader) qosReduceConfidence() {
+	// If we have a single peer, confidence is always 1
+	peers := uint64(d.peers.Len())
+	if peers == 0 {
+		// Ensure peer connectivity races don't catch us off guard
+		return
+	}
+	if peers == 1 {
+		atomic.StoreUint64(&d.rttConfidence, 1000000)
+		return
+	}
+	// If we have a ton of peers, don't drop confidence)
+	if peers >= uint64(qosConfidenceCap) {
+		return
+	}
+	// Otherwise drop the confidence factor
+	conf := atomic.LoadUint64(&d.rttConfidence) * (peers - 1) / peers
+	if float64(conf)/1000000 < rttMinConfidence {
+		conf = uint64(rttMinConfidence * 1000000)
+	}
+	atomic.StoreUint64(&d.rttConfidence, conf)
+
+	rtt := time.Duration(atomic.LoadUint64(&d.rttEstimate))
+	log.Debug("Relaxed downloader QoS values", "rtt", rtt, "confidence", float64(conf)/1000000.0, "ttl", d.requestTTL())
+}
+
+// requestRTT returns the current target round trip time for a download request
+// to complete in.
+//
+// Note, the returned RTT is .9 of the actually estimated RTT. The reason is that
+// the downloader tries to adapt queries to the RTT, so multiple RTT values can
+// be adapted to, but smaller ones are preferred (stabler download stream).
+func (d *Downloader) requestRTT() time.Duration {
+	return time.Duration(atomic.LoadUint64(&d.rttEstimate)) * 9 / 10
+}
+
+// requestTTL returns the current timeout allowance for a single download request
+// to finish under.
+func (d *Downloader) requestTTL() time.Duration {
+	var (
+		rtt  = time.Duration(atomic.LoadUint64(&d.rttEstimate))
+		conf = float64(atomic.LoadUint64(&d.rttConfidence)) / 1000000.0
+	)
+	ttl := time.Duration(ttlScaling) * time.Duration(float64(rtt)/conf)
+	if ttl > ttlLimit {
+		ttl = ttlLimit
+	}
+	return ttl
+}