From b788e266a795486eaa5c4151724ef3ea9d1cfd0e Mon Sep 17 00:00:00 2001
From: healthykim <bsbs8645@snu.ac.kr>
Date: Tue, 17 Mar 2026 16:22:07 +0900
Subject: [PATCH] add remote2 flag

---
 cmd/devp2p/discv5cmd.go                   |  2 ++
 cmd/devp2p/internal/v5test/discv5tests.go |  6 ++++++
 cmd/devp2p/internal/v5test/framework.go   | 22 ++++++++++++++++++----
 cmd/devp2p/runtest.go                     |  5 +++++
 4 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/cmd/devp2p/discv5cmd.go b/cmd/devp2p/discv5cmd.go
index dd253dd082..0e5be792e3 100644
--- a/cmd/devp2p/discv5cmd.go
+++ b/cmd/devp2p/discv5cmd.go
@@ -69,6 +69,7 @@ var (
 			testTAPFlag,
 			testListen1Flag,
 			testListen2Flag,
+			testRemote2Flag,
 		},
 	}
 	discv5ListenCommand = &cli.Command{
@@ -127,6 +128,7 @@ func discv5Test(ctx *cli.Context) error {
 		Dest:    getNodeArg(ctx),
 		Listen1: ctx.String(testListen1Flag.Name),
 		Listen2: ctx.String(testListen2Flag.Name),
+		Remote2: ctx.String(testRemote2Flag.Name),
 	}
 	return runTests(ctx, suite.AllTests())
 }
diff --git a/cmd/devp2p/internal/v5test/discv5tests.go b/cmd/devp2p/internal/v5test/discv5tests.go
index efe9144069..f04905a1ca 100644
--- a/cmd/devp2p/internal/v5test/discv5tests.go
+++ b/cmd/devp2p/internal/v5test/discv5tests.go
@@ -33,6 +33,7 @@ import (
 type Suite struct {
 	Dest             *enode.Node
 	Listen1, Listen2 string // listening addresses
+	Remote2          string // remote node address for l2 (if different from Dest)
 }
 
 func (s *Suite) listen1(log logger) (*conn, net.PacketConn) {
@@ -44,6 +45,11 @@ func (s *Suite) listen1(log logger) (*conn, net.PacketConn) {
 func (s *Suite) listen2(log logger) (*conn, net.PacketConn, net.PacketConn) {
 	c := newConn(s.Dest, log)
 	l1, l2 := c.listen(s.Listen1), c.listen(s.Listen2)
+	if s.Remote2 != "" {
+		c.listenerRemoteAddr = map[net.PacketConn]*net.UDPAddr{
+			l2: {IP: net.ParseIP(s.Remote2), Port: s.Dest.UDP()},
+		}
+	}
 	return c, l1, l2
 }
 
diff --git a/cmd/devp2p/internal/v5test/framework.go b/cmd/devp2p/internal/v5test/framework.go
index 92a5048150..fc3c73dd24 100644
--- a/cmd/devp2p/internal/v5test/framework.go
+++ b/cmd/devp2p/internal/v5test/framework.go
@@ -65,6 +65,8 @@ type conn struct {
 	log       logger
 	codec     *v5wire.Codec
 	idCounter uint32
+
+	listenerRemoteAddr map[net.PacketConn]*net.UDPAddr // per-listener remote address override
 }
 
 type logger interface {
@@ -198,16 +200,25 @@ func (tc *conn) findnode(c net.PacketConn, dists []uint) ([]*enode.Node, error)
 	return results, nil
 }
 
+// remoteAddrFor returns the remote address to use for the given listener.
+func (tc *conn) remoteAddrFor(c net.PacketConn) *net.UDPAddr {
+	if addr, ok := tc.listenerRemoteAddr[c]; ok {
+		return addr
+	}
+	return tc.remoteAddr
+}
+
 // write sends a packet on the given connection.
 func (tc *conn) write(c net.PacketConn, p v5wire.Packet, challenge *v5wire.Whoareyou) v5wire.Nonce {
+	sendAddr := tc.remoteAddrFor(c)
 	packet, nonce, err := tc.codec.Encode(tc.remote.ID(), tc.remoteAddr.String(), p, challenge)
 	if err != nil {
 		panic(fmt.Errorf("can't encode %v packet: %v", p.Name(), err))
 	}
-	if _, err := c.WriteTo(packet, tc.remoteAddr); err != nil {
+	if _, err := c.WriteTo(packet, sendAddr); err != nil {
 		tc.logf("Can't send %s: %v", p.Name(), err)
 	} else {
-		tc.logf(">> %s", p.Name())
+		tc.logf(">> %s (to %v)", p.Name(), sendAddr)
 	}
 	return nonce
 }
@@ -218,11 +229,14 @@ func (tc *conn) read(c net.PacketConn) v5wire.Packet {
 	if err := c.SetReadDeadline(time.Now().Add(waitTime)); err != nil {
 		return &readError{err}
 	}
-	n, fromAddr, err := c.ReadFrom(buf)
+	n, _, err := c.ReadFrom(buf)
 	if err != nil {
 		return &readError{err}
 	}
-	_, _, p, err := tc.codec.Decode(buf[:n], fromAddr.String())
+	// Always use remoteAddr for codec session lookup, even if the actual sender
+	// address differs (e.g. in multi-network setups where packets are routed
+	// through a different interface).
+	_, _, p, err := tc.codec.Decode(buf[:n], tc.remoteAddr.String())
 	if err != nil {
 		return &readError{err}
 	}
diff --git a/cmd/devp2p/runtest.go b/cmd/devp2p/runtest.go
index c40a4b8a01..24f121f0a1 100644
--- a/cmd/devp2p/runtest.go
+++ b/cmd/devp2p/runtest.go
@@ -77,6 +77,11 @@ var (
 		Value:    v4test.Listen2,
 		Category: flags.TestingCategory,
 	}
+	testRemote2Flag = &cli.StringFlag{
+		Name:     "remote2",
+		Usage:    "Remote node address for second listener (overrides default remote address)",
+		Category: flags.TestingCategory,
+	}
 )
 
 func runTests(ctx *cli.Context, tests []utesting.Test) error {