1// Copyright 2015 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package icmp
6
7import "encoding/binary"
8
9// MPLSLabel represents an MPLS label stack entry.
10type MPLSLabel struct {
11	Label int  // label value
12	TC    int  // traffic class; formerly experimental use
13	S     bool // bottom of stack
14	TTL   int  // time to live
15}
16
17const (
18	classMPLSLabelStack        = 1
19	typeIncomingMPLSLabelStack = 1
20)
21
22// MPLSLabelStack represents an MPLS label stack.
23type MPLSLabelStack struct {
24	Class  int // extension object class number
25	Type   int // extension object sub-type
26	Labels []MPLSLabel
27}
28
29// Len implements the Len method of Extension interface.
30func (ls *MPLSLabelStack) Len(proto int) int {
31	return 4 + (4 * len(ls.Labels))
32}
33
34// Marshal implements the Marshal method of Extension interface.
35func (ls *MPLSLabelStack) Marshal(proto int) ([]byte, error) {
36	b := make([]byte, ls.Len(proto))
37	if err := ls.marshal(proto, b); err != nil {
38		return nil, err
39	}
40	return b, nil
41}
42
43func (ls *MPLSLabelStack) marshal(proto int, b []byte) error {
44	l := ls.Len(proto)
45	binary.BigEndian.PutUint16(b[:2], uint16(l))
46	b[2], b[3] = classMPLSLabelStack, typeIncomingMPLSLabelStack
47	off := 4
48	for _, ll := range ls.Labels {
49		b[off], b[off+1], b[off+2] = byte(ll.Label>>12), byte(ll.Label>>4&0xff), byte(ll.Label<<4&0xf0)
50		b[off+2] |= byte(ll.TC << 1 & 0x0e)
51		if ll.S {
52			b[off+2] |= 0x1
53		}
54		b[off+3] = byte(ll.TTL)
55		off += 4
56	}
57	return nil
58}
59
60func parseMPLSLabelStack(b []byte) (Extension, error) {
61	ls := &MPLSLabelStack{
62		Class: int(b[2]),
63		Type:  int(b[3]),
64	}
65	for b = b[4:]; len(b) >= 4; b = b[4:] {
66		ll := MPLSLabel{
67			Label: int(b[0])<<12 | int(b[1])<<4 | int(b[2])>>4,
68			TC:    int(b[2]&0x0e) >> 1,
69			TTL:   int(b[3]),
70		}
71		if b[2]&0x1 != 0 {
72			ll.S = true
73		}
74		ls.Labels = append(ls.Labels, ll)
75	}
76	return ls, nil
77}
78