From 03d7306558eb9f74f48cdda2c8a4205058988e5e Mon Sep 17 00:00:00 2001
From: Tom Thorogood <me+github@tomthorogood.co.uk>
Date: Wed, 28 Nov 2018 01:08:33 +1030
Subject: [PATCH] Fix NotImp RCode string (#819)

* Fix NOTIMP typo in RcodeToString

RFC 6895 lists RCODE 4 as NotImp.

* Accept legacy NOTIMPL spelling in StringToRcode
---
 msg.go     | 2 +-
 reverse.go | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/msg.go b/msg.go
index 7f151f12..4208eb45 100644
--- a/msg.go
+++ b/msg.go
@@ -150,7 +150,7 @@ var RcodeToString = map[int]string{
 	RcodeFormatError:    "FORMERR",
 	RcodeServerFailure:  "SERVFAIL",
 	RcodeNameError:      "NXDOMAIN",
-	RcodeNotImplemented: "NOTIMPL",
+	RcodeNotImplemented: "NOTIMP",
 	RcodeRefused:        "REFUSED",
 	RcodeYXDomain:       "YXDOMAIN", // See RFC 2136
 	RcodeYXRrset:        "YXRRSET",
diff --git a/reverse.go b/reverse.go
index f6e7a47a..1f0e2b2a 100644
--- a/reverse.go
+++ b/reverse.go
@@ -12,6 +12,11 @@ var StringToOpcode = reverseInt(OpcodeToString)
 // StringToRcode is a map of rcodes to strings.
 var StringToRcode = reverseInt(RcodeToString)
 
+func init() {
+	// Preserve previous NOTIMP typo, see github.com/miekg/dns/issues/733.
+	StringToRcode["NOTIMPL"] = RcodeNotImplemented
+}
+
 // Reverse a map
 func reverseInt8(m map[uint8]string) map[string]uint8 {
 	n := make(map[string]uint8, len(m))