eth/downloader: fix deliveries to check for sync cancels

eth/downloader/downloader.go

@@ -70,7 +70,9 @@ type Downloader struct {
 	newPeerCh chan *peer
 	hashCh    chan hashPack
 	blockCh   chan blockPack
-	cancelCh  chan struct{}
+
+	cancelCh   chan struct{} // Channel to cancel mid-flight syncs
+	cancelLock sync.RWMutex  // Lock to protect the cancel channel in delivers
 }
 
 func New(hasBlock hashCheckFn, getBlock getBlockFn) *Downloader {
@@ -83,6 +85,9 @@ func New(hasBlock hashCheckFn, getBlock getBlockFn) *Downloader {
 		hashCh:    make(chan hashPack, 1),
 		blockCh:   make(chan blockPack, 1),
 	}
+	// Set the initial downloader state as canceled (sanity check)
+	downloader.cancelCh = make(chan struct{})
+	close(downloader.cancelCh)
 
 	return downloader
 }
@@ -123,8 +128,10 @@ func (d *Downloader) Synchronise(id string, hash common.Hash) error {
 	}
 	defer atomic.StoreInt32(&d.synchronising, 0)
 
-	// Create cancel channel for aborting midflight
+	// Create cancel channel for aborting mid-flight
+	d.cancelLock.Lock()
 	d.cancelCh = make(chan struct{})
+	d.cancelLock.Unlock()
 
 	// Abort if the queue still contains some leftover data
 	if _, cached := d.queue.Size(); cached > 0 && d.queue.GetHeadBlock() != nil {
@@ -421,9 +428,18 @@ func (d *Downloader) DeliverBlocks(id string, blocks []*types.Block) error {
 	if atomic.LoadInt32(&d.synchronising) == 0 {
 		return errNoSyncActive
 	}
-	d.blockCh <- blockPack{id, blocks}
+	// Deliver or abort if the sync is canceled while queuing
+	d.cancelLock.RLock()
+	cancel := d.cancelCh
+	d.cancelLock.RUnlock()
 
-	return nil
+	select {
+	case d.blockCh <- blockPack{id, blocks}:
+		return nil
+
+	case <-cancel:
+		return errNoSyncActive
+	}
 }
 
 // DeliverHashes injects a new batch of hashes received from a remote node into
@@ -434,11 +450,16 @@ func (d *Downloader) DeliverHashes(id string, hashes []common.Hash) error {
 	if atomic.LoadInt32(&d.synchronising) == 0 {
 		return errNoSyncActive
 	}
-	if glog.V(logger.Debug) && len(hashes) != 0 {
-		from, to := hashes[0], hashes[len(hashes)-1]
-		glog.V(logger.Debug).Infof("adding %d (T=%d) hashes [ %x / %x ] from: %s\n", len(hashes), d.queue.Pending(), from[:4], to[:4], id)
-	}
-	d.hashCh <- hashPack{id, hashes}
+	// Deliver or abort if the sync is canceled while queuing
+	d.cancelLock.RLock()
+	cancel := d.cancelCh
+	d.cancelLock.RUnlock()
 
-	return nil
+	select {
+	case d.hashCh <- hashPack{id, hashes}:
+		return nil
+
+	case <-cancel:
+		return errNoSyncActive
+	}
 }