dht: Limit the size of peer discovery backlog

dht/dht.go

@@ -156,7 +156,7 @@ func (n *Node) DefinitelyGood() bool {
 	if len(n.id) != 20 {
 		return false
 	}
-	// No reason to think ill of them if they've never responded.
+	// No reason to think ill of them if they've never been queried.
 	if n.lastSentQuery.IsZero() {
 		return true
 	}

dht/getpeers.go

@@ -17,7 +17,10 @@ type peerDiscovery struct {
 	infoHash   string
 }
 
-const parallelQueries = 100
+const (
+	parallelQueries = 100
+	backlogMaxLen   = 10000
+)
 
 func (me *peerDiscovery) Close() {
 	me.peerStream.Close()
@@ -43,12 +46,29 @@ func (s *Server) GetPeers(infoHash string) (*peerStream, error) {
 		peerStream: &peerStream{
 			Values: make(chan peerStreamValue),
 			stop:   make(chan struct{}),
+			values: make(chan peerStreamValue),
 		},
 		triedAddrs: make(map[string]struct{}, 500),
 		backlog:    make(map[string]net.Addr, parallelQueries),
 		server:     s,
 		infoHash:   infoHash,
 	}
+	// Function ferries from values to Values until discovery is halted.
+	go func() {
+		defer close(disc.Values)
+		for {
+			select {
+			case psv := <-disc.values:
+				select {
+				case disc.Values <- psv:
+				case <-disc.stop:
+					return
+				}
+			case <-disc.stop:
+				return
+			}
+		}
+	}()
 	disc.mu.Lock()
 	for _, addr := range startAddrs {
 		disc.contact(addr)
@@ -72,7 +92,9 @@ func (me *peerDiscovery) gotNodeAddr(addr net.Addr) {
 		return
 	}
 	if me.pending >= parallelQueries {
-		me.backlog[addr.String()] = addr
+		if len(me.backlog) < backlogMaxLen {
+			me.backlog[addr.String()] = addr
+		}
 	} else {
 		me.contact(addr)
 	}
@@ -89,7 +111,6 @@ func (me *peerDiscovery) contact(addr net.Addr) {
 
 func (me *peerDiscovery) transactionClosed() {
 	me.pending--
-	// log.Printf("pending: %d", me.pending)
 	for key, addr := range me.backlog {
 		if me.pending >= parallelQueries {
 			break
@@ -140,7 +161,7 @@ func (me *peerDiscovery) getPeers(addr net.Addr) error {
 				}()
 				copy(nodeInfo.ID[:], id)
 				select {
-				case me.peerStream.Values <- peerStreamValue{
+				case me.peerStream.values <- peerStreamValue{
 					Peers:    vs,
 					NodeInfo: nodeInfo,
 				}:
@@ -157,10 +178,6 @@ func (me *peerDiscovery) getPeers(addr net.Addr) error {
 	return nil
 }
 
-func (me *peerDiscovery) streamValue(psv peerStreamValue) {
-	me.peerStream.Values <- psv
-}
-
 type peerStreamValue struct {
 	Peers    []util.CompactPeer // Peers given in get_peers response.
 	NodeInfo                    // The node that gave the response.
@@ -169,6 +186,8 @@ type peerStreamValue struct {
 type peerStream struct {
 	mu     sync.Mutex
 	Values chan peerStreamValue
+	// Inner chan is set to nil when on close.
+	values chan peerStreamValue
 	stop   chan struct{}
 }
 
@@ -179,6 +198,5 @@ func (ps *peerStream) Close() {
 	case <-ps.stop:
 	default:
 		close(ps.stop)
-		close(ps.Values)
 	}
 }