2 files changed, 34 insertions, 6 deletions
diff --git a/request/request.go b/request/request.go
index 2ce2c7acc..9672edeb1 100644
--- a/request/request.go
+++ b/request/request.go
@@ -180,11 +180,11 @@ const (
 	ScrubDone
 )
 
-// Scrub scrubs the reply message so that it will fit the client's buffer. If even after dropping
-// the additional section, it still does not fit the TC bit will be set on the message. Note,
-// the TC bit will be set regardless of protocol, even TCP message will get the bit, the client
-// should then retry with pigeons.
-// TODO(referral).
+// Scrub scrubs the reply message so that it will fit the client's buffer. If
+// even after dropping the additional section it does not fit, the answer will
+// be cleared and the TC bit will be set on the message. Note, the TC bit will
+// be set regardless of protocol, even TCP message will get the bit, the client
+// should then retry with pigeons. TODO(referral).
 func (r *Request) Scrub(reply *dns.Msg) (*dns.Msg, Result) {
 	size := r.Size()
 	l := reply.Len()
@@ -200,8 +200,9 @@ func (r *Request) Scrub(reply *dns.Msg) (*dns.Msg, Result) {
 	if size >= l {
 		return reply, ScrubDone
 	}
-	// Still?!! does not fit.
+
 	reply.Truncated = true
+	reply.Answer = nil
 	return reply, ScrubDone
 }
 
diff --git a/request/request_test.go b/request/request_test.go
index 2311d89ea..49b825627 100644
--- a/request/request_test.go
+++ b/request/request_test.go
@@ -1,6 +1,7 @@
 package request
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/coredns/coredns/plugin/test"
@@ -60,6 +61,32 @@ func TestRequestMalformed(t *testing.T) {
 	}
 }
 
+func TestRequestScrub(t *testing.T) {
+	m := new(dns.Msg)
+	m.SetQuestion("large.example.com.", dns.TypeSRV)
+	req := Request{W: &test.ResponseWriter{}, Req: m}
+
+	reply := new(dns.Msg)
+	reply.SetReply(m)
+	for i := 1; i < 200; i++ {
+		reply.Answer = append(reply.Answer, test.SRV(fmt.Sprintf(
+			"large.example.com. 10 IN SRV 0 0 80 10-0-0-%d.default.pod.k8s.example.com.",
+			i,
+		)))
+	}
+
+	msg, got := req.Scrub(reply)
+	if want := ScrubDone; want != got {
+		t.Errorf("want scrub result %d, got %d", want, got)
+	}
+	if want, got := req.Size(), msg.Len(); want < got {
+		t.Errorf("want scrub to reduce message length below %d bytes, got %d bytes", want, got)
+	}
+	if !msg.Truncated {
+		t.Errorf("want scrub to set truncated bit")
+	}
+}
+
 func BenchmarkRequestDo(b *testing.B) {
 	st := testRequest()