1 files changed, 29 insertions, 2 deletions
diff --git a/eth/downloader/queue.go b/eth/downloader/queue.go
index 4d1aa4e93..adbc2a0d0 100644
--- a/eth/downloader/queue.go
+++ b/eth/downloader/queue.go
@@ -31,6 +31,17 @@ func newqueue() *queue {
 	}
 }
 
+func (c *queue) reset() {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	c.hashPool.Clear()
+	c.fetchPool.Clear()
+	c.blockHashes.Clear()
+	c.blocks = nil
+	c.fetching = make(map[string]*chunk)
+}
+
 // reserve a `max` set of hashes for `p` peer.
 func (c *queue) get(p *peer, max int) *chunk {
 	c.mu.Lock()
@@ -45,22 +56,32 @@ func (c *queue) get(p *peer, max int) *chunk {
 	// Create a new set of hashes
 	hashes, i := set.New(), 0
 	c.hashPool.Each(func(v interface{}) bool {
+		// break on limit
 		if i == limit {
 			return false
 		}
+		// skip any hashes that have previously been requested from the peer
+		if p.ignored.Has(v) {
+			return true
+		}
 
 		hashes.Add(v)
 		i++
 
 		return true
 	})
+	// if no hashes can be requested return a nil chunk
+	if hashes.Size() == 0 {
+		return nil
+	}
+
 	// remove the fetchable hashes from hash pool
 	c.hashPool.Separate(hashes)
 	c.fetchPool.Merge(hashes)
 
 	// Create a new chunk for the seperated hashes. The time is being used
 	// to reset the chunk (timeout)
-	chunk := &chunk{hashes, time.Now()}
+	chunk := &chunk{p, hashes, time.Now()}
 	// register as 'fetching' state
 	c.fetching[p.id] = chunk
 
@@ -92,6 +113,12 @@ func (c *queue) deliver(id string, blocks []*types.Block) {
 	// If the chunk was never requested simply ignore it
 	if chunk != nil {
 		delete(c.fetching, id)
+		// check the length of the returned blocks. If the length of blocks is 0
+		// we'll assume the peer doesn't know about the chain.
+		if len(blocks) == 0 {
+			// So we can ignore the blocks we didn't know about
+			chunk.peer.ignored.Merge(chunk.hashes)
+		}
 
 		// seperate the blocks and the hashes
 		blockHashes := chunk.fetchedHashes(blocks)
@@ -99,7 +126,6 @@ func (c *queue) deliver(id string, blocks []*types.Block) {
 		c.blockHashes.Merge(blockHashes)
 		// Add the blocks
 		c.blocks = append(c.blocks, blocks...)
-
 		// Add back whatever couldn't be delivered
 		c.hashPool.Merge(chunk.hashes)
 		c.fetchPool.Separate(chunk.hashes)
@@ -115,6 +141,7 @@ func (c *queue) put(hashes *set.Set) {
 }
 
 type chunk struct {
+	peer   *peer
 	hashes *set.Set
 	itime  time.Time
 }