Merge pull request #467 from vivint-smarthome/fix-457

Properly proxy truncated responses

exchanger/exchanger.go

@@ -26,6 +26,18 @@ func (f Func) Exchange(m *dns.Msg, addr string) (*dns.Msg, time.Duration, error)
 // A Decorator adds a layer of behaviour to a given Exchanger.
 type Decorator func(Exchanger) Exchanger
 
+// IgnoreErrTruncated is a Decorator which causes dns.ErrTruncated to be ignored
+var IgnoreErrTruncated Decorator = func(ex Exchanger) Exchanger {
+	return Func(func(m *dns.Msg, a string) (r *dns.Msg, rtt time.Duration, err error) {
+		r, rtt, err = ex.Exchange(m, a)
+		if err == dns.ErrTruncated {
+			// Ignore
+			err = nil
+		}
+		return
+	})
+}
+
 // Decorate decorates an Exchanger with the given Decorators.
 func Decorate(ex Exchanger, ds ...Decorator) Exchanger {
 	decorated := ex

resolver/resolver.go

@@ -76,6 +76,7 @@ func exchangers(timeout time.Duration, protos ...string) map[string]exchanger.Ex
 				ReadTimeout:  timeout,
 				WriteTimeout: timeout,
 			},
+			exchanger.IgnoreErrTruncated,
 			exchanger.ErrorLogging(logging.Error),
 			exchanger.Instrumentation(
 				logging.CurLog.NonMesosForwarded,
@@ -447,8 +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
 	}
 

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) {