discovery: revamp recent rejects map

Similar to the prior commit, in this commit, we move to using a basic
LRU cache to store the set of prior rejected messages.

discovery/gossiper.go

@@ -44,6 +44,11 @@ const (
 	// maxPrematureUpdates tracks the max amount of premature channel
 	// updates that we'll hold onto.
 	maxPrematureUpdates = 100
+
+	// maxRejectedUpdates tracks the max amount of rejected channel updates
+	// we'll maintain. This is the global size across all peers. We'll
+	// allocate ~3 MB max to the cache.
+	maxRejectedUpdates = 10_000
 )
 
 var (
@@ -287,6 +292,33 @@ func (c *cachedNetworkMsg) Size() (uint64, error) {
 	return uint64(len(c.msgs)), nil
 }
 
+// rejectCacheKey is the cache key that we'll use to track announcements we've
+// recently rejected.
+type rejectCacheKey struct {
+	pubkey [33]byte
+	chanID uint64
+}
+
+// newRejectCacheKey returns a new cache key for the reject cache.
+func newRejectCacheKey(cid uint64, pub [33]byte) rejectCacheKey {
+	k := rejectCacheKey{
+		chanID: cid,
+		pubkey: pub,
+	}
+
+	return k
+}
+
+// cachedReject is the empty value used to track the value for rejects.
+type cachedReject struct {
+}
+
+// Size returns the "size" of an entry. We return 1 as we just want to limit
+// the total size.
+func (c *cachedReject) Size() (uint64, error) {
+	return 1, nil
+}
+
 // AuthenticatedGossiper is a subsystem which is responsible for receiving
 // announcements, validating them and applying the changes to router, syncing
 // lightning network with newly connected nodes, broadcasting announcements
@@ -345,8 +377,7 @@ type AuthenticatedGossiper struct {
 	// consistent between when the DB is first read until it's written.
 	channelMtx *multimutex.Mutex
 
-	rejectMtx     sync.RWMutex
+	recentRejects *lru.Cache
-	recentRejects map[uint64]struct{}
 
 	// syncMgr is a subsystem responsible for managing the gossip syncers
 	// for peers currently connected. When a new peer is connected, the
@@ -388,7 +419,7 @@ func New(cfg Config, selfKeyDesc *keychain.KeyDescriptor) *AuthenticatedGossiper
 		chanPolicyUpdates:       make(chan *chanPolicyUpdateRequest),
 		prematureChannelUpdates: lru.NewCache(maxPrematureUpdates),
 		channelMtx:              multimutex.NewMutex(),
-		recentRejects:           make(map[uint64]struct{}),
+		recentRejects:           lru.NewCache(maxRejectedUpdates),
 		chanUpdateRateLimiter:   make(map[uint64][2]*rate.Limiter),
 	}
 
@@ -1036,7 +1067,9 @@ func (d *AuthenticatedGossiper) networkHandler() {
 
 			// If this message was recently rejected, then we won't
 			// attempt to re-process it.
-			if d.isRecentlyRejectedMsg(announcement.msg) {
+			if announcement.isRemote && d.isRecentlyRejectedMsg(
+				announcement.msg, announcement.peer.PubKey(),
+			) {
 				announcement.err <- fmt.Errorf("recently " +
 					"rejected")
 				continue
@@ -1202,22 +1235,23 @@ func (d *AuthenticatedGossiper) PruneSyncState(peer route.Vertex) {
 
 // isRecentlyRejectedMsg returns true if we recently rejected a message, and
 // false otherwise, This avoids expensive reprocessing of the message.
-func (d *AuthenticatedGossiper) isRecentlyRejectedMsg(msg lnwire.Message) bool {
+func (d *AuthenticatedGossiper) isRecentlyRejectedMsg(msg lnwire.Message,
-	d.rejectMtx.RLock()
+	peerPub [33]byte) bool {
-	defer d.rejectMtx.RUnlock()
 
+	var scid uint64
 	switch m := msg.(type) {
 	case *lnwire.ChannelUpdate:
-		_, ok := d.recentRejects[m.ShortChannelID.ToUint64()]
+		scid = m.ShortChannelID.ToUint64()
-		return ok
 
 	case *lnwire.ChannelAnnouncement:
-		_, ok := d.recentRejects[m.ShortChannelID.ToUint64()]
+		scid = m.ShortChannelID.ToUint64()
-		return ok
 
 	default:
 		return false
 	}
+
+	_, err := d.recentRejects.Get(newRejectCacheKey(scid, peerPub))
+	return err != cache.ErrElementNotFound
 }
 
 // retransmitStaleAnns examines all outgoing channels that the source node is
@@ -1640,9 +1674,11 @@ func (d *AuthenticatedGossiper) processNetworkAnnouncement(
 				d.cfg.ChainHash)
 			log.Errorf(err.Error())
 
-			d.rejectMtx.Lock()
+			key := newRejectCacheKey(
-			d.recentRejects[msg.ShortChannelID.ToUint64()] = struct{}{}
+				msg.ShortChannelID.ToUint64(),
-			d.rejectMtx.Unlock()
+				nMsg.peer.PubKey(),
+			)
+			_, _ = d.recentRejects.Put(key, &cachedReject{})
 
 			nMsg.err <- err
 			return nil, false
@@ -1680,9 +1716,12 @@ func (d *AuthenticatedGossiper) processNetworkAnnouncement(
 			if err := routing.ValidateChannelAnn(msg); err != nil {
 				err := fmt.Errorf("unable to validate "+
 					"announcement: %v", err)
-				d.rejectMtx.Lock()
+
-				d.recentRejects[msg.ShortChannelID.ToUint64()] = struct{}{}
+				key := newRejectCacheKey(
-				d.rejectMtx.Unlock()
+					msg.ShortChannelID.ToUint64(),
+					nMsg.peer.PubKey(),
+				)
+				_, _ = d.recentRejects.Put(key, &cachedReject{})
 
 				log.Error(err)
 				nMsg.err <- err
@@ -1753,9 +1792,13 @@ func (d *AuthenticatedGossiper) processNetworkAnnouncement(
 				// see if we get any new announcements.
 				anns, rErr := d.processRejectedEdge(msg, proof)
 				if rErr != nil {
-					d.rejectMtx.Lock()
+
-					d.recentRejects[msg.ShortChannelID.ToUint64()] = struct{}{}
+					key := newRejectCacheKey(
-					d.rejectMtx.Unlock()
+						msg.ShortChannelID.ToUint64(),
+						nMsg.peer.PubKey(),
+					)
+					_, _ = d.recentRejects.Put(key, &cachedReject{})
+
 					nMsg.err <- rErr
 					return nil, false
 				}
@@ -1777,9 +1820,11 @@ func (d *AuthenticatedGossiper) processNetworkAnnouncement(
 				log.Tracef("Router rejected channel "+
 					"edge: %v", err)
 
-				d.rejectMtx.Lock()
+				key := newRejectCacheKey(
-				d.recentRejects[msg.ShortChannelID.ToUint64()] = struct{}{}
+					msg.ShortChannelID.ToUint64(),
-				d.rejectMtx.Unlock()
+					nMsg.peer.PubKey(),
+				)
+				_, _ = d.recentRejects.Put(key, &cachedReject{})
 			}
 
 			nMsg.err <- err
@@ -1862,9 +1907,11 @@ func (d *AuthenticatedGossiper) processNetworkAnnouncement(
 				d.cfg.ChainHash)
 			log.Errorf(err.Error())
 
-			d.rejectMtx.Lock()
+			key := newRejectCacheKey(
-			d.recentRejects[msg.ShortChannelID.ToUint64()] = struct{}{}
+				msg.ShortChannelID.ToUint64(),
-			d.rejectMtx.Unlock()
+				nMsg.peer.PubKey(),
+			)
+			_, _ = d.recentRejects.Put(key, &cachedReject{})
 
 			nMsg.err <- err
 			return nil, false
@@ -1952,21 +1999,23 @@ func (d *AuthenticatedGossiper) processNetworkAnnouncement(
 				shortChanID,
 			)
 			switch {
-			// Nothing in the cache yeyt, we can just directly
+			// Nothing in the cache yet, we can just directly
 			// insert this element.
 			case err == cache.ErrElementNotFound:
-				d.prematureChannelUpdates.Put(shortChanID, &cachedNetworkMsg{
+				_, _ = d.prematureChannelUpdates.Put(
-					msgs: []*networkMsg{nMsg},
+					shortChanID, &cachedNetworkMsg{
-				})
+						msgs: []*networkMsg{nMsg},
+					})
 
 			// There's already something in the cache, so we'll
-			// combine the set of messagesa into a single value.
+			// combine the set of messages into a single value.
 			default:
 				msgs := earlyMsgs.(*cachedNetworkMsg).msgs
 				msgs = append(msgs, nMsg)
-				d.prematureChannelUpdates.Put(shortChanID, &cachedNetworkMsg{
+				_, _ = d.prematureChannelUpdates.Put(
-					msgs: msgs,
+					shortChanID, &cachedNetworkMsg{
-				})
+						msgs: msgs,
+					})
 			}
 
 			log.Debugf("Got ChannelUpdate for edge not found in "+
@@ -1984,9 +2033,12 @@ func (d *AuthenticatedGossiper) processNetworkAnnouncement(
 			log.Error(err)
 			nMsg.err <- err
 
-			d.rejectMtx.Lock()
+			key := newRejectCacheKey(
-			d.recentRejects[msg.ShortChannelID.ToUint64()] = struct{}{}
+				msg.ShortChannelID.ToUint64(),
-			d.rejectMtx.Unlock()
+				nMsg.peer.PubKey(),
+			)
+			_, _ = d.recentRejects.Put(key, &cachedReject{})
+
 			return nil, false
 		}
 
@@ -2089,9 +2141,13 @@ func (d *AuthenticatedGossiper) processNetworkAnnouncement(
 				routing.ErrIgnored) {
 				log.Debug(err)
 			} else if err != routing.ErrVBarrierShuttingDown {
-				d.rejectMtx.Lock()
+
-				d.recentRejects[msg.ShortChannelID.ToUint64()] = struct{}{}
+				key := newRejectCacheKey(
-				d.rejectMtx.Unlock()
+					msg.ShortChannelID.ToUint64(),
+					nMsg.peer.PubKey(),
+				)
+				_, _ = d.recentRejects.Put(key, &cachedReject{})
+
 				log.Error(err)
 			}