From a0a32974813f86fa308fb38fd68d82a39cdcb159 Mon Sep 17 00:00:00 2001
From: Sahil Sojitra <sahilsojitra4555@gmail.com>
Date: Tue, 28 Apr 2026 14:42:50 +0530
Subject: [PATCH 1/2] fix: preserve next element when removing expired matchers

---
 p2p/discover/common.go | 15 +++++++++++++++
 p2p/discover/v4_udp.go | 11 ++++-------
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/p2p/discover/common.go b/p2p/discover/common.go
index 033b3d9517e..ada72317a46 100644
--- a/p2p/discover/common.go
+++ b/p2p/discover/common.go
@@ -20,9 +20,11 @@
 package discover
 
 import (
+	"container/list"
 	"crypto/ecdsa"
 	crand "crypto/rand"
 	"encoding/binary"
+	"iter"
 	"math/rand"
 	"net"
 	"net/netip"
@@ -146,3 +148,16 @@ func (r *reseedingRandom) Shuffle(n int, swap func(i, j int)) {
 	defer r.mu.Unlock()
 	r.cur.Shuffle(n, swap)
 }
+
+// iterList iterates over the elements of the given list.
+func iterList[T any](l *list.List) iter.Seq2[T, *list.Element] {
+	return func(yield func(T, *list.Element) bool) {
+		for el := l.Front(); el != nil; {
+			next := el.Next()
+			if !yield(el.Value.(T), el) {
+				return
+			}
+			el = next
+		}
+	}
+}
diff --git a/p2p/discover/v4_udp.go b/p2p/discover/v4_udp.go
index c9fe6f624a5..588da24cb92 100644
--- a/p2p/discover/v4_udp.go
+++ b/p2p/discover/v4_udp.go
@@ -452,9 +452,8 @@ func (t *UDPv4) loop() {
 		}
 		// Start the timer so it fires when the next pending reply has expired.
 		now := time.Now()
-		for el := plist.Front(); el != nil; el = el.Next() {
-			nextTimeout = el.Value.(*replyMatcher)
-			if dist := nextTimeout.deadline.Sub(now); dist < 2*respTimeout {
+		for p, el := range iterList[*replyMatcher](plist) {
+			if dist := p.deadline.Sub(now); dist < 2*respTimeout {
 				timeout.Reset(dist)
 				return
 			}
@@ -484,8 +483,7 @@ func (t *UDPv4) loop() {
 
 		case r := <-t.gotreply:
 			var matched bool // whether any replyMatcher considered the reply acceptable.
-			for el := plist.Front(); el != nil; el = el.Next() {
-				p := el.Value.(*replyMatcher)
+			for p, el := range iterList[*replyMatcher](plist) {
 				if p.from == r.from && p.ptype == r.data.Kind() && p.ip == r.ip {
 					ok, requestDone := p.callback(r.data)
 					matched = matched || ok
@@ -505,8 +503,7 @@ func (t *UDPv4) loop() {
 			nextTimeout = nil
 
 			// Notify and remove callbacks whose deadline is in the past.
-			for el := plist.Front(); el != nil; el = el.Next() {
-				p := el.Value.(*replyMatcher)
+			for p, el := range iterList[*replyMatcher](plist) {
 				if now.After(p.deadline) || now.Equal(p.deadline) {
 					p.errc <- errTimeout
 					plist.Remove(el)

From 04e045f8d38070e36561e0f9371ca515937b14dc Mon Sep 17 00:00:00 2001
From: Sahil Sojitra <sahilsojitra4555@gmail.com>
Date: Thu, 30 Apr 2026 09:35:53 +0530
Subject: [PATCH 2/2] fix: restore nextTimeout tracking in resetTimeout

---
 p2p/discover/v4_udp.go | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/p2p/discover/v4_udp.go b/p2p/discover/v4_udp.go
index 588da24cb92..daf1eb261f0 100644
--- a/p2p/discover/v4_udp.go
+++ b/p2p/discover/v4_udp.go
@@ -453,6 +453,7 @@ func (t *UDPv4) loop() {
 		// Start the timer so it fires when the next pending reply has expired.
 		now := time.Now()
 		for p, el := range iterList[*replyMatcher](plist) {
+			nextTimeout = p
 			if dist := p.deadline.Sub(now); dist < 2*respTimeout {
 				timeout.Reset(dist)
 				return
@@ -460,7 +461,7 @@ func (t *UDPv4) loop() {
 			// Remove pending replies whose deadline is too far in the
 			// future. These can occur if the system clock jumped
 			// backwards after the deadline was assigned.
-			nextTimeout.errc <- errClockWarp
+			p.errc <- errClockWarp
 			plist.Remove(el)
 		}
 		nextTimeout = nil