From aba8346bd6c533ffb144258118e1100ff31e2cb5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E4=B8=96=E7=95=8C?= <i@sekai.icu>
Date: Fri, 6 Feb 2026 22:28:30 +0800
Subject: [PATCH] Fix DNS cache lock goroutine leak

The cache deduplication in Client.Exchange uses a channel-based lock
per DNS question. Waiting goroutines blocked on <-cond without context
awareness, causing them to accumulate indefinitely when the owning
goroutine's transport call stalls. Add select on ctx.Done() so waiters
respect context cancellation and timeouts.
---
 dns/client.go | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/dns/client.go b/dns/client.go
index 939ca48c..2982d11c 100644
--- a/dns/client.go
+++ b/dns/client.go
@@ -144,7 +144,11 @@ func (c *Client) Exchange(ctx context.Context, transport adapter.DNSTransport, m
 		if c.cache != nil {
 			cond, loaded := c.cacheLock.LoadOrStore(question, make(chan struct{}))
 			if loaded {
-				<-cond
+				select {
+				case <-cond:
+				case <-ctx.Done():
+					return nil, ctx.Err()
+				}
 			} else {
 				defer func() {
 					c.cacheLock.Delete(question)
@@ -154,7 +158,11 @@ func (c *Client) Exchange(ctx context.Context, transport adapter.DNSTransport, m
 		} else if c.transportCache != nil {
 			cond, loaded := c.transportCacheLock.LoadOrStore(question, make(chan struct{}))
 			if loaded {
-				<-cond
+				select {
+				case <-cond:
+				case <-ctx.Done():
+					return nil, ctx.Err()
+				}
 			} else {
 				defer func() {
 					c.transportCacheLock.Delete(question)