update ENR record with AutoNAT

Author: aarshkshah1992

beacon-chain/p2p/service.go

@@ -35,6 +35,7 @@ import (
 	"github.com/libp2p/go-libp2p/core/peer"
 	"github.com/libp2p/go-libp2p/core/protocol"
 	"github.com/multiformats/go-multiaddr"
+	manet "github.com/multiformats/go-multiaddr/net"
 	"github.com/patrickmn/go-cache"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
@@ -589,13 +590,54 @@ func (s *Service) subscribeReachabilityEvents() error {
 						"unreachable": multiaddrsToStrings(event.Unreachable),
 						"unknown":     multiaddrsToStrings(event.Unknown),
 					}).Info("Address reachability changed")
+
+					// Update ENR with reachable addresses if ENR has no addresses configured
+					if len(event.Reachable) > 0 {
+						s.updateENRFromReachableAddrs(event.Reachable)
+					}
 				}
 			}
 		}
 	}()
+
 	return nil
 }
 
+// updateENRFromReachableAddrs updates the ENR with IP addresses discovered
+// by AutoNAT if the ENR doesn't already have a static/fallback IP configured.
+func (s *Service) updateENRFromReachableAddrs(reachableAddrs []multiaddr.Multiaddr) {
+	// Skip if HostAddress was already configured
+	if s.cfg != nil && s.cfg.HostAddress != "" {
+		return
+	}
+
+	if s.dv5Listener == nil {
+		return
+	}
+
+	localNode := s.dv5Listener.LocalNode()
+
+	// Extract the first valid IP from reachable addresses
+	for _, addr := range reachableAddrs {
+		ip, err := manet.ToIP(addr)
+		if err != nil {
+			continue
+		}
+
+		// Validate the IP is either IPv4 or IPv6
+		if ip.To4() == nil && ip.To16() == nil {
+			continue
+		}
+
+		// Set fallback and static IP like we do for HostAddress
+		localNode.SetFallbackIP(ip)
+		localNode.SetStaticIP(ip)
+
+		log.WithField("ip", ip.String()).Info("Updated ENR IP from AutoNAT reachability")
+		return
+	}
+}
+
 func multiaddrsToStrings(addrs []multiaddr.Multiaddr) []string {
 	strs := make([]string, len(addrs))
 	for i, a := range addrs {