From 99f84ae56e75126dd77e5de4fae2ea034a468ca1 Mon Sep 17 00:00:00 2001
From: Matthijs Mekking <github@pletterpet.nl>
Date: Mon, 30 Jan 2017 11:53:01 +0100
Subject: [PATCH] return errTruncated after setting header bits (#442)

---
 msg.go | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/msg.go b/msg.go
index d99c2ddf..0d8cc6fb 100644
--- a/msg.go
+++ b/msg.go
@@ -759,9 +759,6 @@ func (dns *Msg) Unpack(msg []byte) (err error) {
 	if dh, off, err = unpackMsgHdr(msg, off); err != nil {
 		return err
 	}
-	if off == len(msg) {
-		return ErrTruncated
-	}
 
 	dns.Id = dh.Id
 	dns.Response = (dh.Bits & _QR) != 0
@@ -775,6 +772,10 @@ func (dns *Msg) Unpack(msg []byte) (err error) {
 	dns.CheckingDisabled = (dh.Bits & _CD) != 0
 	dns.Rcode = int(dh.Bits & 0xF)
 
+	if off == len(msg) {
+		return ErrTruncated
+	}
+
 	// Optimistically use the count given to us in the header
 	dns.Question = make([]Question, 0, int(dh.Qdcount))