eth/downloader: ignore orphan blocks in the downloader.

When blocks have been sorted and are being processed, orphan blocks
should be ignored and thrown out. The protocol handler is responsible
for downloading blocks which have missing parents.

eth/downloader/downloader.go

@@ -418,14 +418,16 @@ func (d *Downloader) process(peer *peer) error {
 	// link). We should at least check whihc queue match. This code could move
 	// to a seperate goroutine where it periodically checks for linked pieces.
 	types.BlockBy(types.Number).Sort(d.queue.blocks)
-	blocks := d.queue.blocks
+	if len(d.queue.blocks) == 0 {
-	if len(blocks) == 0 {
 		return nil
 	}
 
+	var (
+		blocks = d.queue.blocks
+		err    error
+	)
 	glog.V(logger.Debug).Infof("Inserting chain with %d blocks (#%v - #%v)\n", len(blocks), blocks[0].Number(), blocks[len(blocks)-1].Number())
 
-	var err error
 	// Loop untill we're out of blocks
 	for len(blocks) != 0 {
 		max := int(math.Min(float64(len(blocks)), 256))
@@ -435,9 +437,11 @@ func (d *Downloader) process(peer *peer) error {
 		var i int
 		i, err = d.insertChain(blocks[:max])
 		if err != nil && core.IsParentErr(err) {
-			glog.V(logger.Debug).Infof("Aborting process due to missing parent (%d)\n", i)
+			// Ignore the missing blocks. Handler should take care of anything that's missing.
+			glog.V(logger.Debug).Infof("Ignored block with missing parent (%d)\n", i)
+			blocks = blocks[i:]
 
-			break
+			continue
 		} else if err != nil {
 			// immediatly unregister the false peer but do not disconnect
 			d.UnregisterPeer(d.activePeer)