From 9c7fad9521e4728631b5bc802610dcd7fbd2b51d Mon Sep 17 00:00:00 2001
From: Daniel Liu <139250065@qq.com>
Date: Tue, 14 Jul 2026 15:26:03 +0800
Subject: [PATCH] p2p/enode: fallback to v6 ports for selected ipv4 endpoint

When IPv4 is selected as the preferred address but only UDP6/TCP6 ports are present in ENR, the previous logic left UDP/TCP as zero and produced a non-usable endpoint.

Load IPv4 ports first and fall back to UDP6/TCP6 ports only when the IPv4 keys are missing, matching the existing missing-key fallback semantics in function `setIP6`.

Add a regression test covering the mixed-stack case where IPv4 is selected while only IPv6-family ports are populated.
---
 p2p/enode/node.go      |  8 ++++++--
 p2p/enode/node_test.go | 14 ++++++++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/p2p/enode/node.go b/p2p/enode/node.go
index dafde51d6a..5c71d5bd95 100644
--- a/p2p/enode/node.go
+++ b/p2p/enode/node.go
@@ -114,8 +114,12 @@ func (n *Node) setIP4(ip netip.Addr) {
 }
 
 func (n *Node) setIPv4Ports() {
-	n.Load((*enr.UDP)(&n.udp))
-	n.Load((*enr.TCP)(&n.tcp))
+	if err := n.Load((*enr.UDP)(&n.udp)); err != nil {
+		n.Load((*enr.UDP6)(&n.udp))
+	}
+	if err := n.Load((*enr.TCP)(&n.tcp)); err != nil {
+		n.Load((*enr.TCP6)(&n.tcp))
+	}
 }
 
 func (n *Node) setIP6(ip netip.Addr) {
diff --git a/p2p/enode/node_test.go b/p2p/enode/node_test.go
index 51bc4ebe15..340aa8e2cf 100644
--- a/p2p/enode/node_test.go
+++ b/p2p/enode/node_test.go
@@ -229,6 +229,20 @@ func TestNodeEndpoints(t *testing.T) {
 			wantIP:  netip.MustParseAddr("192.168.2.2"),
 			wantUDP: 30304,
 		},
+		{
+			name: "ipv4-selected-falls-back-to-ipv6-family-ports",
+			node: func() *Node {
+				var r enr.Record
+				r.Set(enr.IPv4Addr(netip.MustParseAddr("99.22.33.1")))
+				r.Set(enr.IPv6Addr(netip.MustParseAddr("fd00::abcd:1")))
+				r.Set(enr.UDP6(30306))
+				r.Set(enr.TCP6(30307))
+				return SignNull(&r, id)
+			}(),
+			wantIP:  netip.MustParseAddr("99.22.33.1"),
+			wantUDP: 30306,
+			wantTCP: 30307,
+		},
 		{
 			name: "ipv4-quic",
 			node: func() *Node {