1// Copyright 2012 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 ipv4
6
7import (
8	"encoding/binary"
9	"fmt"
10	"net"
11	"runtime"
12
13	"golang.org/x/net/internal/socket"
14)
15
16const (
17	Version   = 4  // protocol version
18	HeaderLen = 20 // header length without extension headers
19)
20
21type HeaderFlags int
22
23const (
24	MoreFragments HeaderFlags = 1 << iota // more fragments flag
25	DontFragment                          // don't fragment flag
26)
27
28// A Header represents an IPv4 header.
29type Header struct {
30	Version  int         // protocol version
31	Len      int         // header length
32	TOS      int         // type-of-service
33	TotalLen int         // packet total length
34	ID       int         // identification
35	Flags    HeaderFlags // flags
36	FragOff  int         // fragment offset
37	TTL      int         // time-to-live
38	Protocol int         // next protocol
39	Checksum int         // checksum
40	Src      net.IP      // source address
41	Dst      net.IP      // destination address
42	Options  []byte      // options, extension headers
43}
44
45func (h *Header) String() string {
46	if h == nil {
47		return "<nil>"
48	}
49	return fmt.Sprintf("ver=%d hdrlen=%d tos=%#x totallen=%d id=%#x flags=%#x fragoff=%#x ttl=%d proto=%d cksum=%#x src=%v dst=%v", h.Version, h.Len, h.TOS, h.TotalLen, h.ID, h.Flags, h.FragOff, h.TTL, h.Protocol, h.Checksum, h.Src, h.Dst)
50}
51
52// Marshal returns the binary encoding of h.
53//
54// The returned slice is in the format used by a raw IP socket on the
55// local system.
56// This may differ from the wire format, depending on the system.
57func (h *Header) Marshal() ([]byte, error) {
58	if h == nil {
59		return nil, errNilHeader
60	}
61	if h.Len < HeaderLen {
62		return nil, errHeaderTooShort
63	}
64	hdrlen := HeaderLen + len(h.Options)
65	b := make([]byte, hdrlen)
66	b[0] = byte(Version<<4 | (hdrlen >> 2 & 0x0f))
67	b[1] = byte(h.TOS)
68	flagsAndFragOff := (h.FragOff & 0x1fff) | int(h.Flags<<13)
69	switch runtime.GOOS {
70	case "darwin", "ios", "dragonfly", "netbsd":
71		socket.NativeEndian.PutUint16(b[2:4], uint16(h.TotalLen))
72		socket.NativeEndian.PutUint16(b[6:8], uint16(flagsAndFragOff))
73	case "freebsd":
74		if freebsdVersion < 1100000 {
75			socket.NativeEndian.PutUint16(b[2:4], uint16(h.TotalLen))
76			socket.NativeEndian.PutUint16(b[6:8], uint16(flagsAndFragOff))
77		} else {
78			binary.BigEndian.PutUint16(b[2:4], uint16(h.TotalLen))
79			binary.BigEndian.PutUint16(b[6:8], uint16(flagsAndFragOff))
80		}
81	default:
82		binary.BigEndian.PutUint16(b[2:4], uint16(h.TotalLen))
83		binary.BigEndian.PutUint16(b[6:8], uint16(flagsAndFragOff))
84	}
85	binary.BigEndian.PutUint16(b[4:6], uint16(h.ID))
86	b[8] = byte(h.TTL)
87	b[9] = byte(h.Protocol)
88	binary.BigEndian.PutUint16(b[10:12], uint16(h.Checksum))
89	if ip := h.Src.To4(); ip != nil {
90		copy(b[12:16], ip[:net.IPv4len])
91	}
92	if ip := h.Dst.To4(); ip != nil {
93		copy(b[16:20], ip[:net.IPv4len])
94	} else {
95		return nil, errMissingAddress
96	}
97	if len(h.Options) > 0 {
98		copy(b[HeaderLen:], h.Options)
99	}
100	return b, nil
101}
102
103// Parse parses b as an IPv4 header and stores the result in h.
104//
105// The provided b must be in the format used by a raw IP socket on the
106// local system.
107// This may differ from the wire format, depending on the system.
108func (h *Header) Parse(b []byte) error {
109	if h == nil || b == nil {
110		return errNilHeader
111	}
112	if len(b) < HeaderLen {
113		return errHeaderTooShort
114	}
115	hdrlen := int(b[0]&0x0f) << 2
116	if len(b) < hdrlen {
117		return errExtHeaderTooShort
118	}
119	h.Version = int(b[0] >> 4)
120	h.Len = hdrlen
121	h.TOS = int(b[1])
122	h.ID = int(binary.BigEndian.Uint16(b[4:6]))
123	h.TTL = int(b[8])
124	h.Protocol = int(b[9])
125	h.Checksum = int(binary.BigEndian.Uint16(b[10:12]))
126	h.Src = net.IPv4(b[12], b[13], b[14], b[15])
127	h.Dst = net.IPv4(b[16], b[17], b[18], b[19])
128	switch runtime.GOOS {
129	case "darwin", "ios", "dragonfly", "netbsd":
130		h.TotalLen = int(socket.NativeEndian.Uint16(b[2:4])) + hdrlen
131		h.FragOff = int(socket.NativeEndian.Uint16(b[6:8]))
132	case "freebsd":
133		if freebsdVersion < 1100000 {
134			h.TotalLen = int(socket.NativeEndian.Uint16(b[2:4]))
135			if freebsdVersion < 1000000 {
136				h.TotalLen += hdrlen
137			}
138			h.FragOff = int(socket.NativeEndian.Uint16(b[6:8]))
139		} else {
140			h.TotalLen = int(binary.BigEndian.Uint16(b[2:4]))
141			h.FragOff = int(binary.BigEndian.Uint16(b[6:8]))
142		}
143	default:
144		h.TotalLen = int(binary.BigEndian.Uint16(b[2:4]))
145		h.FragOff = int(binary.BigEndian.Uint16(b[6:8]))
146	}
147	h.Flags = HeaderFlags(h.FragOff&0xe000) >> 13
148	h.FragOff = h.FragOff & 0x1fff
149	optlen := hdrlen - HeaderLen
150	if optlen > 0 && len(b) >= hdrlen {
151		if cap(h.Options) < optlen {
152			h.Options = make([]byte, optlen)
153		} else {
154			h.Options = h.Options[:optlen]
155		}
156		copy(h.Options, b[HeaderLen:hdrlen])
157	}
158	return nil
159}
160
161// ParseHeader parses b as an IPv4 header.
162//
163// The provided b must be in the format used by a raw IP socket on the
164// local system.
165// This may differ from the wire format, depending on the system.
166func ParseHeader(b []byte) (*Header, error) {
167	h := new(Header)
168	if err := h.Parse(b); err != nil {
169		return nil, err
170	}
171	return h, nil
172}
173