preserve upstream truncation state

mesosphere · Aug 26, 2016 · 60bc1f5 · 60bc1f5
1 parent b086677
commit 60bc1f5
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Showing 2 changed files with 15 additions and 4 deletions.
diff --git a/resolver/resolver.go b/resolver/resolver.go
@@ -448,8 +448,10 @@ func truncate(m *dns.Msg, udp bool) *dns.Msg {
 		max = int(opt.UDPSize())
 	}
 
-	m.Truncated = m.Len() > max
-	if !m.Truncated {
+	furtherTruncation := m.Len() > max
+	m.Truncated = m.Truncated || furtherTruncation
+
+	if !furtherTruncation {
 		return m
 	}
 

diff --git a/resolver/resolver_test.go b/resolver/resolver_test.go
@@ -418,17 +418,26 @@ func TestMultiError(t *testing.T) {
 }
 
 func TestTruncate(t *testing.T) {
-	tm := newTruncated()
+	tm := *newTruncated()
 	if !tm.Truncated {
 		t.Fatal("Message not truncated")
 	}
 	if l := tm.Len(); l > 512 {
-		t.Fatalf("Message to large: %d bytes", l)
+		t.Fatalf("Message too large: %d bytes", l)
 	}
+	tm2 := *truncate(&tm, true)
+	if !tm2.Truncated {
+		t.Fatal("Original truncation status was not preseved")
+	}
+	if tm2.Len() != tm.Len() {
+		t.Fatal("Further modification to already truncated message")
+	}
+
 	tm.Answer = append(tm.Answer, genA(1)...)
 	if l := tm.Len(); l < 512 {
 		t.Fatalf("Message to small after adding answers: %d bytes", l)
 	}
+
 }
 
 func BenchmarkTruncate(b *testing.B) {