36
36
maxHeaderLen = 60 // sensible default, revisit if later RFCs define new usage of version and header length fields
42
posTOS headerField = 1 // type-of-service
43
posTotalLen = 2 // packet total length
44
posID = 4 // identification
45
posFragOff = 6 // fragment offset
46
posTTL = 8 // time-to-live
47
posProtocol = 9 // next protocol
48
posChecksum = 10 // checksum
49
posSrc = 12 // source address
50
posDst = 16 // destination address
40
posTOS = 1 // type-of-service
41
posTotalLen = 2 // packet total length
42
posID = 4 // identification
43
posFragOff = 6 // fragment offset
44
posTTL = 8 // time-to-live
45
posProtocol = 9 // next protocol
46
posChecksum = 10 // checksum
47
posSrc = 12 // source address
48
posDst = 16 // destination address
54
MoreFragments HeaderFlags = 1 << iota // more fragments flag
55
DontFragment // don't fragment flag
53
58
// A Header represents an IPv4 header.
54
59
type Header struct {
55
Version int // protocol version
56
Len int // header length
57
TOS int // type-of-service
58
TotalLen int // packet total length
59
ID int // identification
60
FragOff int // fragment offset
61
TTL int // time-to-live
62
Protocol int // next protocol
63
Checksum int // checksum
64
Src net.IP // source address
65
Dst net.IP // destination address
66
Options []byte // options, extension headers
60
Version int // protocol version
61
Len int // header length
62
TOS int // type-of-service
63
TotalLen int // packet total length
64
ID int // identification
65
Flags HeaderFlags // flags
66
FragOff int // fragment offset
67
TTL int // time-to-live
68
Protocol int // next protocol
69
Checksum int // checksum
70
Src net.IP // source address
71
Dst net.IP // destination address
72
Options []byte // options, extension headers
69
75
func (h *Header) String() string {
73
return fmt.Sprintf("ver: %v, hdrlen: %v, tos: %#x, totallen: %v, id: %#x, fragoff: %#x, ttl: %v, proto: %v, cksum: %#x, src: %v, dst: %v", h.Version, h.Len, h.TOS, h.TotalLen, h.ID, h.FragOff, h.TTL, h.Protocol, h.Checksum, h.Src, h.Dst)
79
return fmt.Sprintf("ver: %v, hdrlen: %v, tos: %#x, totallen: %v, id: %#x, flags: %#x, fragoff: %#x, ttl: %v, proto: %v, 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)
76
82
// Please refer to the online manual; IP(4) on Darwin, FreeBSD and
89
95
b := make([]byte, hdrlen)
90
96
b[0] = byte(Version<<4 | (hdrlen >> 2 & 0x0f))
91
97
b[posTOS] = byte(h.TOS)
98
flagsAndFragOff := (h.FragOff & 0x1fff) | int(h.Flags<<13)
92
99
if supportsNewIPInput {
93
100
b[posTotalLen], b[posTotalLen+1] = byte(h.TotalLen>>8), byte(h.TotalLen)
94
b[posFragOff], b[posFragOff+1] = byte(h.FragOff>>8), byte(h.FragOff)
101
b[posFragOff], b[posFragOff+1] = byte(flagsAndFragOff>>8), byte(flagsAndFragOff)
96
103
*(*uint16)(unsafe.Pointer(&b[posTotalLen : posTotalLen+1][0])) = uint16(h.TotalLen)
97
*(*uint16)(unsafe.Pointer(&b[posFragOff : posFragOff+1][0])) = uint16(h.FragOff)
104
*(*uint16)(unsafe.Pointer(&b[posFragOff : posFragOff+1][0])) = uint16(flagsAndFragOff)
99
106
b[posID], b[posID+1] = byte(h.ID>>8), byte(h.ID)
100
107
b[posTTL] = byte(h.TTL)