From f218fef126d8842f4627102c8a63617f09116e79 Mon Sep 17 00:00:00 2001
From: Star Brilliant <m13253@hotmail.com>
Date: Sat, 14 Oct 2017 00:04:01 +0800
Subject: [PATCH] Fix EDNS0_SUBNET compatibility with dig (#530)

Do not complain about AddressFamily=0, if SubnetNetmask is also 0.

Fixes issue #529
---
 edns.go | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/edns.go b/edns.go
index 10d69f2c..a49f4b70 100644
--- a/edns.go
+++ b/edns.go
@@ -229,6 +229,12 @@ func (e *EDNS0_SUBNET) pack() ([]byte, error) {
 	b[2] = e.SourceNetmask
 	b[3] = e.SourceScope
 	switch e.Family {
+	case 0:
+		// "dig" sets AddressFamily to 0 if SourceNetmask is also 0
+		// We might don't need to complain either
+		if e.SourceNetmask != 0 {
+			return nil, errors.New("dns: bad address family")
+		}
 	case 1:
 		if e.SourceNetmask > net.IPv4len*8 {
 			return nil, errors.New("dns: bad netmask")
@@ -263,6 +269,13 @@ func (e *EDNS0_SUBNET) unpack(b []byte) error {
 	e.SourceNetmask = b[2]
 	e.SourceScope = b[3]
 	switch e.Family {
+	case 0:
+		// "dig" sets AddressFamily to 0 if SourceNetmask is also 0
+		// It's okay to accept such a packet
+		if e.SourceNetmask != 0 {
+			return errors.New("dns: bad address family")
+		}
+		e.Address = net.IPv4(0, 0, 0, 0)
 	case 1:
 		if e.SourceNetmask > net.IPv4len*8 || e.SourceScope > net.IPv4len*8 {
 			return errors.New("dns: bad netmask")