eth, rpc: standardize the chain sync progress counters

eth/downloader/downloader.go

@@ -130,10 +130,9 @@ type Downloader struct {
 	interrupt int32 // Atomic boolean to signal termination
 
 	// Statistics
-	importStart time.Time // Instance when the last blocks were taken from the cache
-	importQueue []*Block  // Previously taken blocks to check import progress
-	importDone  int       // Number of taken blocks already imported from the last batch
-	importLock  sync.Mutex
+	syncStatsOrigin uint64       // Origin block number where syncing started at
+	syncStatsHeight uint64       // Highest block number known when syncing started
+	syncStatsLock   sync.RWMutex // Lock protecting the sync stats fields
 
 	// Callbacks
 	hasBlock    hashCheckFn      // Checks if a block is present in the chain
@@ -161,6 +160,7 @@ type Downloader struct {
 	cancelLock sync.RWMutex  // Lock to protect the cancel channel in delivers
 
 	// 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
 	chainInsertHook func([]*Block)        // Method to call upon inserting a chain of blocks (possibly in multiple invocations)
 }
@@ -192,27 +192,14 @@ func New(mux *event.TypeMux, hasBlock hashCheckFn, getBlock blockRetrievalFn, he
 	}
 }
 
-// Stats retrieves the current status of the downloader.
-func (d *Downloader) Stats() (pending int, cached int, importing int, estimate time.Duration) {
-	// Fetch the download status
-	pending, cached = d.queue.Size()
+// Boundaries retrieves the synchronisation boundaries, specifically the origin
+// block where synchronisation started at (may have failed/suspended) and the
+// latest known block which the synchonisation targets.
+func (d *Downloader) Boundaries() (uint64, uint64) {
+	d.syncStatsLock.RLock()
+	defer d.syncStatsLock.RUnlock()
 
-	// Figure out the import progress
-	d.importLock.Lock()
-	defer d.importLock.Unlock()
-
-	for len(d.importQueue) > 0 && d.hasBlock(d.importQueue[0].RawBlock.Hash()) {
-		d.importQueue = d.importQueue[1:]
-		d.importDone++
-	}
-	importing = len(d.importQueue)
-
-	// Make an estimate on the total sync
-	estimate = 0
-	if d.importDone > 0 {
-		estimate = time.Since(d.importStart) / time.Duration(d.importDone) * time.Duration(pending+cached+importing)
-	}
-	return
+	return d.syncStatsOrigin, d.syncStatsHeight
 }
 
 // Synchronising returns whether the downloader is currently retrieving blocks.
@@ -333,14 +320,29 @@ func (d *Downloader) syncWithPeer(p *peer, hash common.Hash, td *big.Int) (err e
 
 	switch {
 	case p.version == eth61:
-		// Old eth/61, use forward, concurrent hash and block retrieval algorithm
-		number, err := d.findAncestor61(p)
+		// Look up the sync boundaries: the common ancestor and the target block
+		latest, err := d.fetchHeight61(p)
+		if err != nil {
+			return err
+		}
+		origin, err := d.findAncestor61(p)
 		if err != nil {
 			return err
 		}
+		d.syncStatsLock.Lock()
+		if d.syncStatsHeight <= origin || d.syncStatsOrigin > origin {
+			d.syncStatsOrigin = origin
+		}
+		d.syncStatsHeight = latest
+		d.syncStatsLock.Unlock()
+
+		// Initiate the sync using a  concurrent hash and block retrieval algorithm
+		if d.syncInitHook != nil {
+			d.syncInitHook(origin, latest)
+		}
 		errc := make(chan error, 2)
-		go func() { errc <- d.fetchHashes61(p, td, number+1) }()
-		go func() { errc <- d.fetchBlocks61(number + 1) }()
+		go func() { errc <- d.fetchHashes61(p, td, origin+1) }()
+		go func() { errc <- d.fetchBlocks61(origin + 1) }()
 
 		// If any fetcher fails, cancel the other
 		if err := <-errc; err != nil {
@@ -351,14 +353,29 @@ func (d *Downloader) syncWithPeer(p *peer, hash common.Hash, td *big.Int) (err e
 		return <-errc
 
 	case p.version >= eth62:
-		// New eth/62, use forward, concurrent header and block body retrieval algorithm
-		number, err := d.findAncestor(p)
+		// Look up the sync boundaries: the common ancestor and the target block
+		latest, err := d.fetchHeight(p)
 		if err != nil {
 			return err
 		}
+		origin, err := d.findAncestor(p)
+		if err != nil {
+			return err
+		}
+		d.syncStatsLock.Lock()
+		if d.syncStatsHeight <= origin || d.syncStatsOrigin > origin {
+			d.syncStatsOrigin = origin
+		}
+		d.syncStatsHeight = latest
+		d.syncStatsLock.Unlock()
+
+		// Initiate the sync using a  concurrent hash and block retrieval algorithm
+		if d.syncInitHook != nil {
+			d.syncInitHook(origin, latest)
+		}
 		errc := make(chan error, 2)
-		go func() { errc <- d.fetchHeaders(p, td, number+1) }()
-		go func() { errc <- d.fetchBodies(number + 1) }()
+		go func() { errc <- d.fetchHeaders(p, td, origin+1) }()
+		go func() { errc <- d.fetchBodies(origin + 1) }()
 
 		// If any fetcher fails, cancel the other
 		if err := <-errc; err != nil {
@@ -401,6 +418,50 @@ func (d *Downloader) Terminate() {
 	d.cancel()
 }
 
+// fetchHeight61 retrieves the head block of the remote peer to aid in estimating
+// the total time a pending synchronisation would take.
+func (d *Downloader) fetchHeight61(p *peer) (uint64, error) {
+	glog.V(logger.Debug).Infof("%v: retrieving remote chain height", p)
+
+	// Request the advertised remote head block and wait for the response
+	go p.getBlocks([]common.Hash{p.head})
+
+	timeout := time.After(blockSoftTTL)
+	for {
+		select {
+		case <-d.cancelCh:
+			return 0, 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 <-d.hashCh:
+			// Out of bounds hashes received, ignore them
+
+		case blockPack := <-d.blockCh:
+			// Discard anything not from the origin peer
+			if blockPack.peerId != p.id {
+				glog.V(logger.Debug).Infof("Received blocks from incorrect peer(%s)", blockPack.peerId)
+				break
+			}
+			// Make sure the peer actually gave something valid
+			blocks := blockPack.blocks
+			if len(blocks) != 1 {
+				glog.V(logger.Debug).Infof("%v: invalid number of head blocks: %d != 1", p, len(blocks))
+				return 0, errBadPeer
+			}
+			return blocks[0].NumberU64(), nil
+
+		case <-timeout:
+			glog.V(logger.Debug).Infof("%v: head block timeout", p)
+			return 0, errTimeout
+		}
+	}
+}
+
 // 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.
@@ -776,6 +837,50 @@ func (d *Downloader) fetchBlocks61(from uint64) error {
 	}
 }
 
+// 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 *peer) (uint64, error) {
+	glog.V(logger.Debug).Infof("%v: retrieving remote chain height", p)
+
+	// Request the advertised remote head block and wait for the response
+	go p.getRelHeaders(p.head, 1, 0, false)
+
+	timeout := time.After(headerTTL)
+	for {
+		select {
+		case <-d.cancelCh:
+			return 0, errCancelBlockFetch
+
+		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 number of head headers: %d != 1", p, len(headers))
+				return 0, errBadPeer
+			}
+			return headers[0].Number.Uint64(), nil
+
+		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
+		}
+	}
+}
+
 // 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.
@@ -1203,16 +1308,10 @@ func (d *Downloader) process() {
 			d.process()
 		}
 	}()
-	// Release the lock upon exit (note, before checking for reentry!), and set
+	// Release the lock upon exit (note, before checking for reentry!)
 	// the import statistics to zero.
-	defer func() {
-		d.importLock.Lock()
-		d.importQueue = nil
-		d.importDone = 0
-		d.importLock.Unlock()
+	defer atomic.StoreInt32(&d.processing, 0)
 
-		atomic.StoreInt32(&d.processing, 0)
-	}()
 	// Repeat the processing as long as there are blocks to import
 	for {
 		// Fetch the next batch of blocks
@@ -1223,13 +1322,6 @@ func (d *Downloader) process() {
 		if d.chainInsertHook != nil {
 			d.chainInsertHook(blocks)
 		}
-		// Reset the import statistics
-		d.importLock.Lock()
-		d.importStart = time.Now()
-		d.importQueue = blocks
-		d.importDone = 0
-		d.importLock.Unlock()
-
 		// Actually import the blocks
 		glog.V(logger.Debug).Infof("Inserting chain with %d blocks (#%v - #%v)\n", len(blocks), blocks[0].RawBlock.Number(), blocks[len(blocks)-1].RawBlock.Number())
 		for len(blocks) != 0 {

eth/downloader/downloader_test.go

@@ -20,6 +20,7 @@ import (
 	"errors"
 	"fmt"
 	"math/big"
+	"sync"
 	"sync/atomic"
 	"testing"
 	"time"
@@ -99,6 +100,8 @@ type downloadTester struct {
 	peerHashes   map[string][]common.Hash                // Hash chain belonging to different test peers
 	peerBlocks   map[string]map[common.Hash]*types.Block // Blocks belonging to different test peers
 	peerChainTds map[string]map[common.Hash]*big.Int     // Total difficulties of the blocks in the peer chains
+
+	lock sync.RWMutex
 }
 
 // newTester creates a new downloader test mocker.
@@ -118,8 +121,8 @@ func newTester() *downloadTester {
 
 // sync starts synchronizing with a remote peer, blocking until it completes.
 func (dl *downloadTester) sync(id string, td *big.Int) error {
+	dl.lock.RLock()
 	hash := dl.peerHashes[id][0]
-
 	// If no particular TD was requested, load from the peer's blockchain
 	if td == nil {
 		td = big.NewInt(1)
@@ -127,14 +130,19 @@ func (dl *downloadTester) sync(id string, td *big.Int) error {
 			td = diff
 		}
 	}
-	err := dl.downloader.synchronise(id, hash, td)
+	dl.lock.RUnlock()
 
+	err := dl.downloader.synchronise(id, hash, td)
 	for {
 		// If the queue is empty and processing stopped, break
 		hashes, blocks := dl.downloader.queue.Size()
 		if hashes+blocks == 0 && atomic.LoadInt32(&dl.downloader.processing) == 0 {
 			break
 		}
+		// If there are queued blocks, but the head is missing, it's a stale leftover
+		if hashes+blocks > 0 && atomic.LoadInt32(&dl.downloader.processing) == 0 && dl.downloader.queue.GetHeadBlock() == nil {
+			break
+		}
 		// Otherwise sleep a bit and retry
 		time.Sleep(time.Millisecond)
 	}
@@ -143,26 +151,41 @@ func (dl *downloadTester) sync(id string, td *big.Int) error {
 
 // hasBlock checks if a block is pres	ent in the testers canonical chain.
 func (dl *downloadTester) hasBlock(hash common.Hash) bool {
+	dl.lock.RLock()
+	defer dl.lock.RUnlock()
+
 	return dl.getBlock(hash) != nil
 }
 
 // getBlock retrieves a block from the testers canonical chain.
 func (dl *downloadTester) getBlock(hash common.Hash) *types.Block {
+	dl.lock.RLock()
+	defer dl.lock.RUnlock()
+
 	return dl.ownBlocks[hash]
 }
 
 // headBlock retrieves the current head block from the canonical chain.
 func (dl *downloadTester) headBlock() *types.Block {
+	dl.lock.RLock()
+	defer dl.lock.RUnlock()
+
 	return dl.getBlock(dl.ownHashes[len(dl.ownHashes)-1])
 }
 
 // getTd retrieves the block's total difficulty from the canonical chain.
 func (dl *downloadTester) getTd(hash common.Hash) *big.Int {
+	dl.lock.RLock()
+	defer dl.lock.RUnlock()
+
 	return dl.ownChainTd[hash]
 }
 
 // insertChain injects a new batch of blocks into the simulated chain.
 func (dl *downloadTester) insertChain(blocks types.Blocks) (int, error) {
+	dl.lock.Lock()
+	defer dl.lock.Unlock()
+
 	for i, block := range blocks {
 		if _, ok := dl.ownBlocks[block.ParentHash()]; !ok {
 			return i, errors.New("unknown parent")
@@ -183,9 +206,12 @@ func (dl *downloadTester) newPeer(id string, version int, hashes []common.Hash,
 // specific delay time on processing the network packets sent to it, simulating
 // potentially slow network IO.
 func (dl *downloadTester) newSlowPeer(id string, version int, hashes []common.Hash, blocks map[common.Hash]*types.Block, delay time.Duration) error {
+	dl.lock.Lock()
+	defer dl.lock.Unlock()
+
 	err := dl.downloader.RegisterPeer(id, version, hashes[0],
 		dl.peerGetRelHashesFn(id, delay), dl.peerGetAbsHashesFn(id, delay), dl.peerGetBlocksFn(id, delay),
-		nil, dl.peerGetAbsHeadersFn(id, delay), dl.peerGetBodiesFn(id, delay))
+		dl.peerGetRelHeadersFn(id, delay), dl.peerGetAbsHeadersFn(id, delay), dl.peerGetBodiesFn(id, delay))
 	if err == nil {
 		// Assign the owned hashes and blocks to the peer (deep copy)
 		dl.peerHashes[id] = make([]common.Hash, len(hashes))
@@ -207,6 +233,9 @@ func (dl *downloadTester) newSlowPeer(id string, version int, hashes []common.Ha
 
 // dropPeer simulates a hard peer removal from the connection pool.
 func (dl *downloadTester) dropPeer(id string) {
+	dl.lock.Lock()
+	defer dl.lock.Unlock()
+
 	delete(dl.peerHashes, id)
 	delete(dl.peerBlocks, id)
 	delete(dl.peerChainTds, id)
@@ -221,6 +250,9 @@ func (dl *downloadTester) peerGetRelHashesFn(id string, delay time.Duration) fun
 	return func(head common.Hash) error {
 		time.Sleep(delay)
 
+		dl.lock.RLock()
+		defer dl.lock.RUnlock()
+
 		// Gather the next batch of hashes
 		hashes := dl.peerHashes[id]
 		result := make([]common.Hash, 0, MaxHashFetch)
@@ -250,6 +282,9 @@ func (dl *downloadTester) peerGetAbsHashesFn(id string, delay time.Duration) fun
 	return func(head uint64, count int) error {
 		time.Sleep(delay)
 
+		dl.lock.RLock()
+		defer dl.lock.RUnlock()
+
 		// Gather the next batch of hashes
 		hashes := dl.peerHashes[id]
 		result := make([]common.Hash, 0, count)
@@ -271,6 +306,10 @@ func (dl *downloadTester) peerGetAbsHashesFn(id string, delay time.Duration) fun
 func (dl *downloadTester) peerGetBlocksFn(id string, delay time.Duration) func([]common.Hash) error {
 	return func(hashes []common.Hash) error {
 		time.Sleep(delay)
+
+		dl.lock.RLock()
+		defer dl.lock.RUnlock()
+
 		blocks := dl.peerBlocks[id]
 		result := make([]*types.Block, 0, len(hashes))
 		for _, hash := range hashes {
@@ -284,6 +323,27 @@ func (dl *downloadTester) peerGetBlocksFn(id string, delay time.Duration) func([
 	}
 }
 
+// peerGetRelHeadersFn constructs a GetBlockHeaders function based on a hashed
+// origin; associated with a particular peer in the download tester. The returned
+// function can be used to retrieve batches of headers from the particular peer.
+func (dl *downloadTester) peerGetRelHeadersFn(id string, delay time.Duration) func(common.Hash, int, int, bool) error {
+	return func(origin common.Hash, amount int, skip int, reverse bool) error {
+		// Find the canonical number of the hash
+		dl.lock.RLock()
+		number := uint64(0)
+		for num, hash := range dl.peerHashes[id] {
+			if hash == origin {
+				number = uint64(len(dl.peerHashes[id]) - num - 1)
+				break
+			}
+		}
+		dl.lock.RUnlock()
+
+		// Use the absolute header fetcher to satisfy the query
+		return dl.peerGetAbsHeadersFn(id, delay)(number, amount, skip, reverse)
+	}
+}
+
 // peerGetAbsHeadersFn constructs a GetBlockHeaders function based on a numbered
 // origin; associated with a particular peer in the download tester. The returned
 // function can be used to retrieve batches of headers from the particular peer.
@@ -291,6 +351,9 @@ func (dl *downloadTester) peerGetAbsHeadersFn(id string, delay time.Duration) fu
 	return func(origin uint64, amount int, skip int, reverse bool) error {
 		time.Sleep(delay)
 
+		dl.lock.RLock()
+		defer dl.lock.RUnlock()
+
 		// Gather the next batch of hashes
 		hashes := dl.peerHashes[id]
 		blocks := dl.peerBlocks[id]
@@ -315,6 +378,10 @@ func (dl *downloadTester) peerGetAbsHeadersFn(id string, delay time.Duration) fu
 func (dl *downloadTester) peerGetBodiesFn(id string, delay time.Duration) func([]common.Hash) error {
 	return func(hashes []common.Hash) error {
 		time.Sleep(delay)
+
+		dl.lock.RLock()
+		defer dl.lock.RUnlock()
+
 		blocks := dl.peerBlocks[id]
 
 		transactions := make([][]*types.Transaction, 0, len(hashes))
@@ -384,13 +451,23 @@ func testThrottling(t *testing.T, protocol int) {
 		errc <- tester.sync("peer", nil)
 	}()
 	// Iteratively take some blocks, always checking the retrieval count
-	for len(tester.ownBlocks) < targetBlocks+1 {
+	for {
+		// Check the retrieval count synchronously (! reason for this ugly block)
+		tester.lock.RLock()
+		retrieved := len(tester.ownBlocks)
+		tester.lock.RUnlock()
+		if retrieved >= targetBlocks+1 {
+			break
+		}
 		// Wait a bit for sync to throttle itself
 		var cached int
 		for start := time.Now(); time.Since(start) < time.Second; {
 			time.Sleep(25 * time.Millisecond)
 
+			tester.downloader.queue.lock.RLock()
 			cached = len(tester.downloader.queue.blockPool)
+			tester.downloader.queue.lock.RUnlock()
+
 			if cached == blockCacheLimit || len(tester.ownBlocks)+cached+int(atomic.LoadUint32(&blocked)) == targetBlocks+1 {
 				break
 			}
@@ -727,3 +804,259 @@ func testBlockBodyAttackerDropping(t *testing.T, protocol int) {
 		}
 	}
 }
+
+// Tests that synchronisation boundaries (origin block number and highest block
+// number) is tracked and updated correctly.
+func TestSyncBoundaries61(t *testing.T) { testSyncBoundaries(t, 61) }
+func TestSyncBoundaries62(t *testing.T) { testSyncBoundaries(t, 62) }
+func TestSyncBoundaries63(t *testing.T) { testSyncBoundaries(t, 63) }
+func TestSyncBoundaries64(t *testing.T) { testSyncBoundaries(t, 64) }
+
+func testSyncBoundaries(t *testing.T, protocol int) {
+	// Create a small enough block chain to download
+	targetBlocks := blockCacheLimit - 15
+	hashes, blocks := makeChain(targetBlocks, 0, genesis)
+
+	// Set a sync init hook to catch boundary changes
+	starting := make(chan struct{})
+	progress := make(chan struct{})
+
+	tester := newTester()
+	tester.downloader.syncInitHook = func(origin, latest uint64) {
+		starting <- struct{}{}
+		<-progress
+	}
+	// Retrieve the sync boundaries and ensure they are zero (pristine sync)
+	if origin, latest := tester.downloader.Boundaries(); origin != 0 || latest != 0 {
+		t.Fatalf("Pristine boundary mismatch: have %v/%v, want %v/%v", origin, latest, 0, 0)
+	}
+	// Synchronise half the blocks and check initial boundaries
+	tester.newPeer("peer-half", protocol, hashes[targetBlocks/2:], blocks)
+	pending := new(sync.WaitGroup)
+	pending.Add(1)
+
+	go func() {
+		defer pending.Done()
+		if err := tester.sync("peer-half", nil); err != nil {
+			t.Fatalf("failed to synchronise blocks: %v", err)
+		}
+	}()
+	<-starting
+	if origin, latest := tester.downloader.Boundaries(); origin != 0 || latest != uint64(targetBlocks/2+1) {
+		t.Fatalf("Initial boundary mismatch: have %v/%v, want %v/%v", origin, latest, 0, targetBlocks/2+1)
+	}
+	progress <- struct{}{}
+	pending.Wait()
+
+	// Synchronise all the blocks and check continuation boundaries
+	tester.newPeer("peer-full", protocol, hashes, blocks)
+	pending.Add(1)
+
+	go func() {
+		defer pending.Done()
+		if err := tester.sync("peer-full", nil); err != nil {
+			t.Fatalf("failed to synchronise blocks: %v", err)
+		}
+	}()
+	<-starting
+	if origin, latest := tester.downloader.Boundaries(); origin != uint64(targetBlocks/2+1) || latest != uint64(targetBlocks) {
+		t.Fatalf("Completing boundary mismatch: have %v/%v, want %v/%v", origin, latest, targetBlocks/2+1, targetBlocks)
+	}
+	progress <- struct{}{}
+	pending.Wait()
+}
+
+// Tests that synchronisation boundaries (origin block number and highest block
+// number) is tracked and updated correctly in case of a fork (or manual head
+// revertal).
+func TestForkedSyncBoundaries61(t *testing.T) { testForkedSyncBoundaries(t, 61) }
+func TestForkedSyncBoundaries62(t *testing.T) { testForkedSyncBoundaries(t, 62) }
+func TestForkedSyncBoundaries63(t *testing.T) { testForkedSyncBoundaries(t, 63) }
+func TestForkedSyncBoundaries64(t *testing.T) { testForkedSyncBoundaries(t, 64) }
+
+func testForkedSyncBoundaries(t *testing.T, protocol int) {
+	// Create a forked chain to simulate origin revertal
+	common, fork := MaxHashFetch, 2*MaxHashFetch
+	hashesA, hashesB, blocksA, blocksB := makeChainFork(common+fork, fork, genesis)
+
+	// Set a sync init hook to catch boundary changes
+	starting := make(chan struct{})
+	progress := make(chan struct{})
+
+	tester := newTester()
+	tester.downloader.syncInitHook = func(origin, latest uint64) {
+		starting <- struct{}{}
+		<-progress
+	}
+	// Retrieve the sync boundaries and ensure they are zero (pristine sync)
+	if origin, latest := tester.downloader.Boundaries(); origin != 0 || latest != 0 {
+		t.Fatalf("Pristine boundary mismatch: have %v/%v, want %v/%v", origin, latest, 0, 0)
+	}
+	// Synchronise with one of the forks and check boundaries
+	tester.newPeer("fork A", protocol, hashesA, blocksA)
+	pending := new(sync.WaitGroup)
+	pending.Add(1)
+
+	go func() {
+		defer pending.Done()
+		if err := tester.sync("fork A", nil); err != nil {
+			t.Fatalf("failed to synchronise blocks: %v", err)
+		}
+	}()
+	<-starting
+	if origin, latest := tester.downloader.Boundaries(); origin != 0 || latest != uint64(len(hashesA)-1) {
+		t.Fatalf("Initial boundary mismatch: have %v/%v, want %v/%v", origin, latest, 0, len(hashesA)-1)
+	}
+	progress <- struct{}{}
+	pending.Wait()
+
+	// Simulate a successful sync above the fork
+	tester.downloader.syncStatsOrigin = tester.downloader.syncStatsHeight
+
+	// Synchronise with the second fork and check boundary resets
+	tester.newPeer("fork B", protocol, hashesB, blocksB)
+	pending.Add(1)
+
+	go func() {
+		defer pending.Done()
+		if err := tester.sync("fork B", nil); err != nil {
+			t.Fatalf("failed to synchronise blocks: %v", err)
+		}
+	}()
+	<-starting
+	if origin, latest := tester.downloader.Boundaries(); origin != uint64(common) || latest != uint64(len(hashesB)-1) {
+		t.Fatalf("Forking boundary mismatch: have %v/%v, want %v/%v", origin, latest, common, len(hashesB)-1)
+	}
+	progress <- struct{}{}
+	pending.Wait()
+}
+
+// Tests that if synchronisation is aborted due to some failure, then the boundary
+// origin is not updated in the next sync cycle, as it should be considered the
+// continuation of the previous sync and not a new instance.
+func TestFailedSyncBoundaries61(t *testing.T) { testFailedSyncBoundaries(t, 61) }
+func TestFailedSyncBoundaries62(t *testing.T) { testFailedSyncBoundaries(t, 62) }
+func TestFailedSyncBoundaries63(t *testing.T) { testFailedSyncBoundaries(t, 63) }
+func TestFailedSyncBoundaries64(t *testing.T) { testFailedSyncBoundaries(t, 64) }
+
+func testFailedSyncBoundaries(t *testing.T, protocol int) {
+	// Create a small enough block chain to download
+	targetBlocks := blockCacheLimit - 15
+	hashes, blocks := makeChain(targetBlocks, 0, genesis)
+
+	// Set a sync init hook to catch boundary changes
+	starting := make(chan struct{})
+	progress := make(chan struct{})
+
+	tester := newTester()
+	tester.downloader.syncInitHook = func(origin, latest uint64) {
+		starting <- struct{}{}
+		<-progress
+	}
+	// Retrieve the sync boundaries and ensure they are zero (pristine sync)
+	if origin, latest := tester.downloader.Boundaries(); origin != 0 || latest != 0 {
+		t.Fatalf("Pristine boundary mismatch: have %v/%v, want %v/%v", origin, latest, 0, 0)
+	}
+	// Attempt a full sync with a faulty peer
+	tester.newPeer("faulty", protocol, hashes, blocks)
+	missing := targetBlocks / 2
+	delete(tester.peerBlocks["faulty"], hashes[missing])
+
+	pending := new(sync.WaitGroup)
+	pending.Add(1)
+
+	go func() {
+		defer pending.Done()
+		if err := tester.sync("faulty", nil); err == nil {
+			t.Fatalf("succeeded faulty synchronisation")
+		}
+	}()
+	<-starting
+	if origin, latest := tester.downloader.Boundaries(); origin != 0 || latest != uint64(targetBlocks) {
+		t.Fatalf("Initial boundary mismatch: have %v/%v, want %v/%v", origin, latest, 0, targetBlocks)
+	}
+	progress <- struct{}{}
+	pending.Wait()
+
+	// Synchronise with a good peer and check that the boundary origin remind the same after a failure
+	tester.newPeer("valid", protocol, hashes, blocks)
+	pending.Add(1)
+
+	go func() {
+		defer pending.Done()
+		if err := tester.sync("valid", nil); err != nil {
+			t.Fatalf("failed to synchronise blocks: %v", err)
+		}
+	}()
+	<-starting
+	if origin, latest := tester.downloader.Boundaries(); origin != 0 || latest != uint64(targetBlocks) {
+		t.Fatalf("Completing boundary mismatch: have %v/%v, want %v/%v", origin, latest, 0, targetBlocks)
+	}
+	progress <- struct{}{}
+	pending.Wait()
+}
+
+// Tests that if an attacker fakes a chain height, after the attack is detected,
+// the boundary height is successfully reduced at the next sync invocation.
+func TestFakedSyncBoundaries61(t *testing.T) { testFakedSyncBoundaries(t, 61) }
+func TestFakedSyncBoundaries62(t *testing.T) { testFakedSyncBoundaries(t, 62) }
+func TestFakedSyncBoundaries63(t *testing.T) { testFakedSyncBoundaries(t, 63) }
+func TestFakedSyncBoundaries64(t *testing.T) { testFakedSyncBoundaries(t, 64) }
+
+func testFakedSyncBoundaries(t *testing.T, protocol int) {
+	// Create a small block chain
+	targetBlocks := blockCacheLimit - 15
+	hashes, blocks := makeChain(targetBlocks+3, 0, genesis)
+
+	// Set a sync init hook to catch boundary changes
+	starting := make(chan struct{})
+	progress := make(chan struct{})
+
+	tester := newTester()
+	tester.downloader.syncInitHook = func(origin, latest uint64) {
+		starting <- struct{}{}
+		<-progress
+	}
+	// Retrieve the sync boundaries and ensure they are zero (pristine sync)
+	if origin, latest := tester.downloader.Boundaries(); origin != 0 || latest != 0 {
+		t.Fatalf("Pristine boundary mismatch: have %v/%v, want %v/%v", origin, latest, 0, 0)
+	}
+	//  Create and sync with an attacker that promises a higher chain than available
+	tester.newPeer("attack", protocol, hashes, blocks)
+	for i := 1; i < 3; i++ {
+		delete(tester.peerBlocks["attack"], hashes[i])
+	}
+
+	pending := new(sync.WaitGroup)
+	pending.Add(1)
+
+	go func() {
+		defer pending.Done()
+		if err := tester.sync("attack", nil); err == nil {
+			t.Fatalf("succeeded attacker synchronisation")
+		}
+	}()
+	<-starting
+	if origin, latest := tester.downloader.Boundaries(); origin != 0 || latest != uint64(targetBlocks+3) {
+		t.Fatalf("Initial boundary mismatch: have %v/%v, want %v/%v", origin, latest, 0, targetBlocks+3)
+	}
+	progress <- struct{}{}
+	pending.Wait()
+
+	// Synchronise with a good peer and check that the boundary height has been reduced to the true value
+	tester.newPeer("valid", protocol, hashes[3:], blocks)
+	pending.Add(1)
+
+	go func() {
+		defer pending.Done()
+		if err := tester.sync("valid", nil); err != nil {
+			t.Fatalf("failed to synchronise blocks: %v", err)
+		}
+	}()
+	<-starting
+	if origin, latest := tester.downloader.Boundaries(); origin != 0 || latest != uint64(targetBlocks) {
+		t.Fatalf("Initial boundary mismatch: have %v/%v, want %v/%v", origin, latest, 0, targetBlocks)
+	}
+	progress <- struct{}{}
+	pending.Wait()
+}

rpc/api/admin.go

@@ -55,7 +55,6 @@ var (
 		"admin_exportChain":        (*adminApi).ExportChain,
 		"admin_importChain":        (*adminApi).ImportChain,
 		"admin_verbosity":          (*adminApi).Verbosity,
-		"admin_chainSyncStatus":    (*adminApi).ChainSyncStatus,
 		"admin_setSolc":            (*adminApi).SetSolc,
 		"admin_datadir":            (*adminApi).DataDir,
 		"admin_startRPC":           (*adminApi).StartRPC,
@@ -232,17 +231,6 @@ func (self *adminApi) Verbosity(req *shared.Request) (interface{}, error) {
 	return true, nil
 }
 
-func (self *adminApi) ChainSyncStatus(req *shared.Request) (interface{}, error) {
-	pending, cached, importing, estimate := self.ethereum.Downloader().Stats()
-
-	return map[string]interface{}{
-		"blocksAvailable":        pending,
-		"blocksWaitingForImport": cached,
-		"importing":              importing,
-		"estimate":               estimate.String(),
-	}, nil
-}
-
 func (self *adminApi) SetSolc(req *shared.Request) (interface{}, error) {
 	args := new(SetSolcArgs)
 	if err := self.coder.Decode(req.Params, &args); err != nil {

rpc/api/admin_js.go

@@ -143,10 +143,6 @@ web3._extend({
 		new web3._extend.Property({
 			name: 'datadir',
 			getter: 'admin_datadir'
-		}),
-		new web3._extend.Property({
-			name: 'chainSyncStatus',
-			getter: 'admin_chainSyncStatus'
 		})
 	]
 });

rpc/api/eth.go

@@ -55,6 +55,7 @@ var (
 		"eth_protocolVersion":                     (*ethApi).ProtocolVersion,
 		"eth_coinbase":                            (*ethApi).Coinbase,
 		"eth_mining":                              (*ethApi).IsMining,
+		"eth_syncing":                             (*ethApi).IsSyncing,
 		"eth_gasPrice":                            (*ethApi).GasPrice,
 		"eth_getStorage":                          (*ethApi).GetStorage,
 		"eth_storageAt":                           (*ethApi).GetStorage,
@@ -166,6 +167,20 @@ func (self *ethApi) IsMining(req *shared.Request) (interface{}, error) {
 	return self.xeth.IsMining(), nil
 }
 
+func (self *ethApi) IsSyncing(req *shared.Request) (interface{}, error) {
+	current := self.ethereum.ChainManager().CurrentBlock().NumberU64()
+	origin, height := self.ethereum.Downloader().Boundaries()
+
+	if current < height {
+		return map[string]interface{}{
+			"startingBlock": origin,
+			"currentBlock":  current,
+			"highestBlock":  height,
+		}, nil
+	}
+	return false, nil
+}
+
 func (self *ethApi) GasPrice(req *shared.Request) (interface{}, error) {
 	return newHexNum(self.xeth.DefaultGasPrice().Bytes()), nil
 }

rpc/api/eth_js.go

@@ -42,6 +42,10 @@ web3._extend({
 		new web3._extend.Property({
 			name: 'pendingTransactions',
 			getter: 'eth_pendingTransactions'
+		}),
+		new web3._extend.Property({
+			name: 'syncing',
+			getter: 'eth_syncing'
 		})
 	]
 });

rpc/api/utils.go

@@ -32,7 +32,6 @@ var (
 	AutoCompletion = map[string][]string{
 		"admin": []string{
 			"addPeer",
-			"chainSyncStatus",
 			"datadir",
 			"exportChain",
 			"getContractInfo",
@@ -99,6 +98,7 @@ var (
 			"sendRawTransaction",
 			"sendTransaction",
 			"sign",
+			"syncing",
 		},
 		"miner": []string{
 			"hashrate",