p2p/discover: shuffle in appendLiveNodes

p2p/discover/common.go

@@ -100,6 +100,7 @@ type ReadPacket struct {
 type randomSource interface {
 	Intn(int) int
 	Int63n(int64) int64
+	Shuffle(int, func(int, int))
 }
 
 // reseedingRandom is a random number generator that tracks when it was last re-seeded.
@@ -130,3 +131,9 @@ func (r *reseedingRandom) Int63n(n int64) int64 {
 	defer r.mu.Unlock()
 	return r.cur.Int63n(n)
 }
+
+func (r *reseedingRandom) Shuffle(n int, swap func(i, j int)) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	r.cur.Shuffle(n, swap)
+}

p2p/discover/table.go

@@ -79,7 +79,7 @@ type Table struct {
 	refreshReq      chan chan struct{}
 	revalResponseCh chan revalidationResponse
 	addNodeCh       chan addNodeOp
-	addNodeHandled  chan 1bool
+	addNodeHandled  chan bool
 	trackRequestCh  chan trackRequestOp
 	initDone        chan struct{}
 	closeReq        chan struct{}
@@ -279,12 +279,17 @@ func (tab *Table) appendLiveNodes(dist uint, result []*enode.Node) []*enode.Node
 	}
 
 	tab.mutex.Lock()
-	defer tab.mutex.Unlock()
 	for _, n := range tab.bucketAtDistance(int(dist)).entries {
 		if n.isValidatedLive {
 			result = append(result, n.Node)
 		}
 	}
+	tab.mutex.Unlock()
+
+	// Shuffle result to avoid always returning same nodes in FINDNODE/v5.
+	tab.rand.Shuffle(len(result), func(i, j int) {
+		result[i], result[j] = result[j], result[i]
+	})
 	return result
 }