From 518354e7ebd3362315f02f34a6a9ce21131f8fc9 Mon Sep 17 00:00:00 2001
From: Dreamacro <305009791@qq.com>
Date: Tue, 24 Mar 2020 10:13:53 +0800
Subject: [PATCH] Fix: dns request panic and close #527

---
 dns/resolver.go | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/dns/resolver.go b/dns/resolver.go
index dc526a7b..f1f51a98 100644
--- a/dns/resolver.go
+++ b/dns/resolver.go
@@ -115,7 +115,7 @@ func (r *Resolver) Exchange(m *D.Msg) (msg *D.Msg, err error) {
 		}
 	}()
 
-	ret, err, _ := r.group.Do(q.String(), func() (interface{}, error) {
+	ret, err, shared := r.group.Do(q.String(), func() (interface{}, error) {
 		isIPReq := isIPRequest(q)
 		if isIPReq {
 			return r.fallbackExchange(m)
@@ -126,6 +126,9 @@ func (r *Resolver) Exchange(m *D.Msg) (msg *D.Msg, err error) {
 
 	if err == nil {
 		msg = ret.(*D.Msg)
+		if shared {
+			msg = msg.Copy()
+		}
 	}
 
 	return