From 328ef60b856f75bf664fb103bc54674d962bef2e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A9ter=20Szil=C3=A1gyi?= <peterke@gmail.com>
Date: Fri, 5 Jun 2015 12:37:48 +0300
Subject: [PATCH] eth/downloader: differentiate stale and nonexistent
 deliveries

---
 eth/downloader/downloader.go | 50 ++++++++++++++++++++++++------------
 eth/downloader/queue.go      | 15 ++++++++---
 2 files changed, 46 insertions(+), 19 deletions(-)

diff --git a/eth/downloader/downloader.go b/eth/downloader/downloader.go
index 626f47b7b..cc1ceb637 100644
--- a/eth/downloader/downloader.go
+++ b/eth/downloader/downloader.go
@@ -422,28 +422,46 @@ out:
 			// in a reasonable time frame, ignore it's message.
 			if peer := d.peers.Peer(blockPack.peerId); peer != nil {
 				// Deliver the received chunk of blocks, and demote in case of errors
-				if err := d.queue.Deliver(blockPack.peerId, blockPack.blocks); err != nil {
-					if err == ErrInvalidChain {
-						// The hash chain is invalid (blocks are not ordered properly), abort
-						return err
+				err := d.queue.Deliver(blockPack.peerId, blockPack.blocks)
+				switch err {
+				case nil:
+					// If no blocks were delivered, demote the peer (need the delivery above)
+					if len(blockPack.blocks) == 0 {
+						peer.Demote()
+						peer.SetIdle()
+						glog.V(logger.Detail).Infof("%s: no blocks delivered", peer)
+						break
 					}
-					// Peer did deliver, but some blocks were off, penalize
+					// All was successful, promote the peer
+					peer.Promote()
+					peer.SetIdle()
+					glog.V(logger.Detail).Infof("%s: delivered %d blocks", peer, len(blockPack.blocks))
+
+				case ErrInvalidChain:
+					// The hash chain is invalid (blocks are not ordered properly), abort
+					return err
+
+				case errNoFetchesPending:
+					// Peer probably timed out with its delivery but came through
+					// in the end, demote, but allow to to pull from this peer.
 					peer.Demote()
 					peer.SetIdle()
-					glog.V(logger.Detail).Infof("%s: block delivery failed: %v", peer, err)
-					break
-				}
-				// If no blocks were delivered, demote the peer (above code is needed to mark the packet done!)
-				if len(blockPack.blocks) == 0 {
+					glog.V(logger.Detail).Infof("%s: out of bound delivery", peer)
+
+				case errStaleDelivery:
+					// Delivered something completely else than requested, usually
+					// caused by a timeout and delivery during a new sync cycle.
+					// Don't set it to idle as the original request should still be
+					// in flight.
+					peer.Demote()
+					glog.V(logger.Detail).Infof("%s: stale delivery", peer)
+
+				default:
+					// Peer did something semi-useful, demote but keep it around
 					peer.Demote()
 					peer.SetIdle()
-					glog.V(logger.Detail).Infof("%s: no blocks delivered", peer)
-					break
+					glog.V(logger.Detail).Infof("%s: delivery partially failed: %v", peer, err)
 				}
-				// All was successful, promote the peer
-				peer.Promote()
-				peer.SetIdle()
-				glog.V(logger.Detail).Infof("%s: delivered %d blocks", peer, len(blockPack.blocks))
 			}
 		case <-ticker.C:
 			// Check for bad peers. Bad peers may indicate a peer not responding
diff --git a/eth/downloader/queue.go b/eth/downloader/queue.go
index 02fa667f1..671ffe51b 100644
--- a/eth/downloader/queue.go
+++ b/eth/downloader/queue.go
@@ -20,6 +20,11 @@ const (
 	blockCacheLimit = 8 * MaxBlockFetch // Maximum number of blocks to cache before throttling the download
 )
 
+var (
+	errNoFetchesPending = errors.New("no fetches pending")
+	errStaleDelivery    = errors.New("stale delivery")
+)
+
 // fetchRequest is a currently running block retrieval operation.
 type fetchRequest struct {
 	Peer   *peer               // Peer to which the request was sent
@@ -293,7 +298,7 @@ func (q *queue) Deliver(id string, blocks []*types.Block) (err error) {
 	// Short circuit if the blocks were never requested
 	request := q.pendPool[id]
 	if request == nil {
-		return errors.New("no fetches pending")
+		return errNoFetchesPending
 	}
 	delete(q.pendPool, id)
 
@@ -309,7 +314,7 @@ func (q *queue) Deliver(id string, blocks []*types.Block) (err error) {
 		// Skip any blocks that were not requested
 		hash := block.Hash()
 		if _, ok := request.Hashes[hash]; !ok {
-			errs = append(errs, fmt.Errorf("non-requested block %v", hash))
+			errs = append(errs, fmt.Errorf("non-requested block %x", hash))
 			continue
 		}
 		// If a requested block falls out of the range, the hash chain is invalid
@@ -326,11 +331,15 @@ func (q *queue) Deliver(id string, blocks []*types.Block) (err error) {
 		delete(q.hashPool, hash)
 		q.blockPool[hash] = int(block.NumberU64())
 	}
-	// Return all failed fetches to the queue
+	// Return all failed or missing fetches to the queue
 	for hash, index := range request.Hashes {
 		q.hashQueue.Push(hash, float32(index))
 	}
+	// If none of the blocks were good, it's a stale delivery
 	if len(errs) != 0 {
+		if len(errs) == len(blocks) {
+			return errStaleDelivery
+		}
 		return fmt.Errorf("multiple failures: %v", errs)
 	}
 	return nil