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fix(beacon): add per-nodeID rate limit to Discover endpoint updates (PILOT-334) #14

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fix(beacon): add per-nodeID rate limit to Discover endpoint updates (PILOT-334) #14

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33 changes: 29 additions & 4 deletions server.go
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,8 @@ type Server struct {
punchRateMu sync.Mutex // protects punchSourceLast
punchSourceLast map[string]time.Time // source IP → last allowed punch time
lastPunchTime atomic.Int64 // UnixNano of last global punch (rate limit)
discoverRateMu sync.Mutex // protects discoverRateLast
discoverRateLast map[uint32]time.Time // nodeID → last allowed discover endpoint update

// Peer mesh (gossip)
beaconID uint32
Expand Down Expand Up @@ -116,6 +118,7 @@ const (
maxPunchPerSecond = 10 // global hard cap on punch commands per second
punchPerSourceInterval = time.Second // min interval between punches from same source
punchRateCleanupInterval = 5 * time.Minute // how often stale source entries are swept
discoverMinInterval = 30 * time.Second // min interval between endpoint updates from same nodeID
)

func New() *Server {
Expand All @@ -132,7 +135,8 @@ func NewWithPeers(beaconID uint32, peers []string) *Server {
relayCh: make(chan relayJob, relayQueueSize),
beaconID: beaconID,
done: make(chan struct{}),
punchSourceLast: make(map[string]time.Time),
punchSourceLast: make(map[string]time.Time),
discoverRateLast: make(map[uint32]time.Time),
}
emptyPeers := make(map[uint32]*net.UDPAddr)
s.peerNodes.Store(&emptyPeers)
Expand Down Expand Up @@ -500,9 +504,20 @@ func (s *Server) handleDiscover(data []byte, remote *net.UDPAddr) {

nodeID := binary.BigEndian.Uint32(data[0:4])

// Record this node's observed public endpoint. Sharded — no global lock.
if _, atCap := s.nodes.Upsert(nodeID, remote, time.Now(), maxBeaconNodes); atCap {
return // shard at capacity — drop silently
// Per-nodeID endpoint update rate limit — prevents a single
// nodeID from flapping its endpoint via rapid Discover messages.
s.discoverRateMu.Lock()
if last, ok := s.discoverRateLast[nodeID]; ok && time.Since(last) < discoverMinInterval {
s.discoverRateMu.Unlock()
// Rate-limited: skip the Upsert but still reply with the
// observed address so the node learns its public endpoint.
} else {
s.discoverRateLast[nodeID] = time.Now()
s.discoverRateMu.Unlock()
// Record this node's observed public endpoint. Sharded — no global lock.
if _, atCap := s.nodes.Upsert(nodeID, remote, time.Now(), maxBeaconNodes); atCap {
return // shard at capacity — drop silently
}
}

slog.Debug("beacon discover", "node_id", nodeID, "addr", remote)
Expand Down Expand Up @@ -941,6 +956,16 @@ func (s *Server) reapStaleNodes() {
}
}
s.punchRateMu.Unlock()

// Sweep stale discover-rate entries.
s.discoverRateMu.Lock()
discoverCutoff := time.Now().Add(-discoverMinInterval * 2)
for id, last := range s.discoverRateLast {
if last.Before(discoverCutoff) {
delete(s.discoverRateLast, id)
}
}
s.discoverRateMu.Unlock()
}

// --- Gossip ---
Expand Down
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