David K. Bainbridge | 215e024 | 2017-09-05 23:18:24 -0700 | [diff] [blame] | 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 | |
| 5 | package ipv4 |
| 6 | |
| 7 | import ( |
| 8 | "encoding/binary" |
| 9 | "fmt" |
| 10 | "net" |
| 11 | "runtime" |
| 12 | "syscall" |
| 13 | |
| 14 | "golang.org/x/net/internal/socket" |
| 15 | ) |
| 16 | |
| 17 | const ( |
| 18 | Version = 4 // protocol version |
| 19 | HeaderLen = 20 // header length without extension headers |
| 20 | maxHeaderLen = 60 // sensible default, revisit if later RFCs define new usage of version and header length fields |
| 21 | ) |
| 22 | |
| 23 | type HeaderFlags int |
| 24 | |
| 25 | const ( |
| 26 | MoreFragments HeaderFlags = 1 << iota // more fragments flag |
| 27 | DontFragment // don't fragment flag |
| 28 | ) |
| 29 | |
| 30 | // A Header represents an IPv4 header. |
| 31 | type Header struct { |
| 32 | Version int // protocol version |
| 33 | Len int // header length |
| 34 | TOS int // type-of-service |
| 35 | TotalLen int // packet total length |
| 36 | ID int // identification |
| 37 | Flags HeaderFlags // flags |
| 38 | FragOff int // fragment offset |
| 39 | TTL int // time-to-live |
| 40 | Protocol int // next protocol |
| 41 | Checksum int // checksum |
| 42 | Src net.IP // source address |
| 43 | Dst net.IP // destination address |
| 44 | Options []byte // options, extension headers |
| 45 | } |
| 46 | |
| 47 | func (h *Header) String() string { |
| 48 | if h == nil { |
| 49 | return "<nil>" |
| 50 | } |
| 51 | 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) |
| 52 | } |
| 53 | |
| 54 | // Marshal returns the binary encoding of h. |
| 55 | func (h *Header) Marshal() ([]byte, error) { |
| 56 | if h == nil { |
| 57 | return nil, syscall.EINVAL |
| 58 | } |
| 59 | if h.Len < HeaderLen { |
| 60 | return nil, errHeaderTooShort |
| 61 | } |
| 62 | hdrlen := HeaderLen + len(h.Options) |
| 63 | b := make([]byte, hdrlen) |
| 64 | b[0] = byte(Version<<4 | (hdrlen >> 2 & 0x0f)) |
| 65 | b[1] = byte(h.TOS) |
| 66 | flagsAndFragOff := (h.FragOff & 0x1fff) | int(h.Flags<<13) |
| 67 | switch runtime.GOOS { |
| 68 | case "darwin", "dragonfly", "netbsd": |
| 69 | socket.NativeEndian.PutUint16(b[2:4], uint16(h.TotalLen)) |
| 70 | socket.NativeEndian.PutUint16(b[6:8], uint16(flagsAndFragOff)) |
| 71 | case "freebsd": |
| 72 | if freebsdVersion < 1100000 { |
| 73 | socket.NativeEndian.PutUint16(b[2:4], uint16(h.TotalLen)) |
| 74 | socket.NativeEndian.PutUint16(b[6:8], uint16(flagsAndFragOff)) |
| 75 | } else { |
| 76 | binary.BigEndian.PutUint16(b[2:4], uint16(h.TotalLen)) |
| 77 | binary.BigEndian.PutUint16(b[6:8], uint16(flagsAndFragOff)) |
| 78 | } |
| 79 | default: |
| 80 | binary.BigEndian.PutUint16(b[2:4], uint16(h.TotalLen)) |
| 81 | binary.BigEndian.PutUint16(b[6:8], uint16(flagsAndFragOff)) |
| 82 | } |
| 83 | binary.BigEndian.PutUint16(b[4:6], uint16(h.ID)) |
| 84 | b[8] = byte(h.TTL) |
| 85 | b[9] = byte(h.Protocol) |
| 86 | binary.BigEndian.PutUint16(b[10:12], uint16(h.Checksum)) |
| 87 | if ip := h.Src.To4(); ip != nil { |
| 88 | copy(b[12:16], ip[:net.IPv4len]) |
| 89 | } |
| 90 | if ip := h.Dst.To4(); ip != nil { |
| 91 | copy(b[16:20], ip[:net.IPv4len]) |
| 92 | } else { |
| 93 | return nil, errMissingAddress |
| 94 | } |
| 95 | if len(h.Options) > 0 { |
| 96 | copy(b[HeaderLen:], h.Options) |
| 97 | } |
| 98 | return b, nil |
| 99 | } |
| 100 | |
| 101 | // Parse parses b as an IPv4 header and sotres the result in h. |
| 102 | func (h *Header) Parse(b []byte) error { |
| 103 | if h == nil || len(b) < HeaderLen { |
| 104 | return errHeaderTooShort |
| 105 | } |
| 106 | hdrlen := int(b[0]&0x0f) << 2 |
| 107 | if hdrlen > len(b) { |
| 108 | return errBufferTooShort |
| 109 | } |
| 110 | h.Version = int(b[0] >> 4) |
| 111 | h.Len = hdrlen |
| 112 | h.TOS = int(b[1]) |
| 113 | h.ID = int(binary.BigEndian.Uint16(b[4:6])) |
| 114 | h.TTL = int(b[8]) |
| 115 | h.Protocol = int(b[9]) |
| 116 | h.Checksum = int(binary.BigEndian.Uint16(b[10:12])) |
| 117 | h.Src = net.IPv4(b[12], b[13], b[14], b[15]) |
| 118 | h.Dst = net.IPv4(b[16], b[17], b[18], b[19]) |
| 119 | switch runtime.GOOS { |
| 120 | case "darwin", "dragonfly", "netbsd": |
| 121 | h.TotalLen = int(socket.NativeEndian.Uint16(b[2:4])) + hdrlen |
| 122 | h.FragOff = int(socket.NativeEndian.Uint16(b[6:8])) |
| 123 | case "freebsd": |
| 124 | if freebsdVersion < 1100000 { |
| 125 | h.TotalLen = int(socket.NativeEndian.Uint16(b[2:4])) |
| 126 | if freebsdVersion < 1000000 { |
| 127 | h.TotalLen += hdrlen |
| 128 | } |
| 129 | h.FragOff = int(socket.NativeEndian.Uint16(b[6:8])) |
| 130 | } else { |
| 131 | h.TotalLen = int(binary.BigEndian.Uint16(b[2:4])) |
| 132 | h.FragOff = int(binary.BigEndian.Uint16(b[6:8])) |
| 133 | } |
| 134 | default: |
| 135 | h.TotalLen = int(binary.BigEndian.Uint16(b[2:4])) |
| 136 | h.FragOff = int(binary.BigEndian.Uint16(b[6:8])) |
| 137 | } |
| 138 | h.Flags = HeaderFlags(h.FragOff&0xe000) >> 13 |
| 139 | h.FragOff = h.FragOff & 0x1fff |
| 140 | optlen := hdrlen - HeaderLen |
| 141 | if optlen > 0 && len(b) >= hdrlen { |
| 142 | if cap(h.Options) < optlen { |
| 143 | h.Options = make([]byte, optlen) |
| 144 | } else { |
| 145 | h.Options = h.Options[:optlen] |
| 146 | } |
| 147 | copy(h.Options, b[HeaderLen:hdrlen]) |
| 148 | } |
| 149 | return nil |
| 150 | } |
| 151 | |
| 152 | // ParseHeader parses b as an IPv4 header. |
| 153 | func ParseHeader(b []byte) (*Header, error) { |
| 154 | h := new(Header) |
| 155 | if err := h.Parse(b); err != nil { |
| 156 | return nil, err |
| 157 | } |
| 158 | return h, nil |
| 159 | } |