icmp: add extensions for MPLS

This change implements ICMP multi-part message marshaler, parser and
extensions for MPLS which are used for route trace applications as
described in RFC 4950.

API breaking changes:

type MessageBody interface, Len() int
type Extension interface, Len() int
type Extension interface, Marshal() ([]byte, error)

are replaced with

type MessageBody interface, Len(int) int
type Extension interface, Len(int) int
type Extension interface, Marshal(int) ([]byte, error)

Change-Id: Iee1f2e03916d49b8dfe3a89fe682c702d40ecc85
Reviewed-on: https://go-review.googlesource.com/2794
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 9 insertions, 10 deletions

diff --git a/icmp/dstunreach.go b/icmp/dstunreach.go
index d1905a9..01dc660 100644
--- a/icmp/dstunreach.go
+++ b/icmp/dstunreach.go
@@ -12,31 +12,30 @@ type DstUnreach struct {
 }
 
 // Len implements the Len method of MessageBody interface.
-func (p *DstUnreach) Len() int {
+func (p *DstUnreach) Len(proto int) int {
 	if p == nil {
 		return 0
 	}
-	return 4 + len(p.Data)
+	l, _ := multipartMessageBodyDataLen(proto, p.Data, p.Extensions)
+	return l
 }
 
 // Marshal implements the Marshal method of MessageBody interface.
 func (p *DstUnreach) Marshal(proto int) ([]byte, error) {
-	b := make([]byte, 4+len(p.Data))
-	copy(b[4:], p.Data)
-	return b, nil
+	return marshalMultipartMessageBody(proto, p.Data, p.Extensions)
 }
 
 // parseDstUnreach parses b as an ICMP destination unreachable message
 // body.
 func parseDstUnreach(proto int, b []byte) (MessageBody, error) {
-	bodyLen := len(b)
-	if bodyLen < 4 {
+	if len(b) < 4 {
 		return nil, errMessageTooShort
 	}
 	p := &DstUnreach{}
-	if bodyLen > 4 {
-		p.Data = make([]byte, bodyLen-4)
-		copy(p.Data, b[4:])
+	var err error
+	p.Data, p.Extensions, err = parseMultipartMessageBody(proto, b)
+	if err != nil {
+		return nil, err
 	}
 	return p, nil
 }