From 9bc7c59221d0bbe8cffd80311b077469c0edf6ca Mon Sep 17 00:00:00 2001
From: Johannes Kimmel <fff@bareminimum.eu>
Date: Tue, 14 Dec 2021 05:47:41 +0100
Subject: [PATCH] prepare SubTLV handling in PacketDecoder

---
 main.go    |  2 +-
 tlv/tlv.go | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/main.go b/main.go
index f9c68ec..414f469 100644
--- a/main.go
+++ b/main.go
@@ -90,7 +90,6 @@ func run(opt options) error {
 		var s tlv.PacketDecoder
 		s.Reset(b, src)
 		for s.Scan() {
-			var subtlv []byte
 			switch t := s.TLV().(type) {
 			case tlv.NextHop:
 				fmt.Printf("%12s %s\n", t.T(), t.Address)
@@ -122,6 +121,7 @@ func run(opt options) error {
 					fmt.Println("got nil TLV")
 				}
 			}
+			subtlv := s.SubTLV()
 			for len(subtlv) > 0 {
 				switch tlv.SubType(subtlv[0]) {
 				case tlv.SubTypeSourcePrefix:
diff --git a/tlv/tlv.go b/tlv/tlv.go
index 0b0a845..d70fa62 100644
--- a/tlv/tlv.go
+++ b/tlv/tlv.go
@@ -36,6 +36,10 @@ type TLV interface {
 
 type SubType uint8
 
+func (s SubType) IsMandatory() bool {
+	return s >= 128
+}
+
 const (
 	SubTypePad1         = SubType(0)
 	SubTypePadN         = SubType(1)
@@ -244,6 +248,12 @@ func (s *PacketDecoder) TLV() TLV {
 	}
 	return s.tlv
 }
+func (s *PacketDecoder) SubTLV() []byte {
+	if s.err != nil {
+		return nil
+	}
+	return s.subtlv
+}
 func (s *PacketDecoder) Err() error {
 	return s.err
 }