--- /dev/null
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ipv4
+
+import (
+ "encoding/binary"
+ "fmt"
+ "net"
+ "runtime"
+ "syscall"
+
+ "golang.org/x/net/internal/socket"
+)
+
+const (
+ Version = 4 // protocol version
+ HeaderLen = 20 // header length without extension headers
+ maxHeaderLen = 60 // sensible default, revisit if later RFCs define new usage of version and header length fields
+)
+
+type HeaderFlags int
+
+const (
+ MoreFragments HeaderFlags = 1 << iota // more fragments flag
+ DontFragment // don't fragment flag
+)
+
+// A Header represents an IPv4 header.
+type Header struct {
+ Version int // protocol version
+ Len int // header length
+ TOS int // type-of-service
+ TotalLen int // packet total length
+ ID int // identification
+ Flags HeaderFlags // flags
+ FragOff int // fragment offset
+ TTL int // time-to-live
+ Protocol int // next protocol
+ Checksum int // checksum
+ Src net.IP // source address
+ Dst net.IP // destination address
+ Options []byte // options, extension headers
+}
+
+func (h *Header) String() string {
+ if h == nil {
+ return "<nil>"
+ }
+ 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)
+}
+
+// Marshal returns the binary encoding of h.
+func (h *Header) Marshal() ([]byte, error) {
+ if h == nil {
+ return nil, syscall.EINVAL
+ }
+ if h.Len < HeaderLen {
+ return nil, errHeaderTooShort
+ }
+ hdrlen := HeaderLen + len(h.Options)
+ b := make([]byte, hdrlen)
+ b[0] = byte(Version<<4 | (hdrlen >> 2 & 0x0f))
+ b[1] = byte(h.TOS)
+ flagsAndFragOff := (h.FragOff & 0x1fff) | int(h.Flags<<13)
+ switch runtime.GOOS {
+ case "darwin", "dragonfly", "netbsd":
+ socket.NativeEndian.PutUint16(b[2:4], uint16(h.TotalLen))
+ socket.NativeEndian.PutUint16(b[6:8], uint16(flagsAndFragOff))
+ case "freebsd":
+ if freebsdVersion < 1100000 {
+ socket.NativeEndian.PutUint16(b[2:4], uint16(h.TotalLen))
+ socket.NativeEndian.PutUint16(b[6:8], uint16(flagsAndFragOff))
+ } else {
+ binary.BigEndian.PutUint16(b[2:4], uint16(h.TotalLen))
+ binary.BigEndian.PutUint16(b[6:8], uint16(flagsAndFragOff))
+ }
+ default:
+ binary.BigEndian.PutUint16(b[2:4], uint16(h.TotalLen))
+ binary.BigEndian.PutUint16(b[6:8], uint16(flagsAndFragOff))
+ }
+ binary.BigEndian.PutUint16(b[4:6], uint16(h.ID))
+ b[8] = byte(h.TTL)
+ b[9] = byte(h.Protocol)
+ binary.BigEndian.PutUint16(b[10:12], uint16(h.Checksum))
+ if ip := h.Src.To4(); ip != nil {
+ copy(b[12:16], ip[:net.IPv4len])
+ }
+ if ip := h.Dst.To4(); ip != nil {
+ copy(b[16:20], ip[:net.IPv4len])
+ } else {
+ return nil, errMissingAddress
+ }
+ if len(h.Options) > 0 {
+ copy(b[HeaderLen:], h.Options)
+ }
+ return b, nil
+}
+
+// Parse parses b as an IPv4 header and sotres the result in h.
+func (h *Header) Parse(b []byte) error {
+ if h == nil || len(b) < HeaderLen {
+ return errHeaderTooShort
+ }
+ hdrlen := int(b[0]&0x0f) << 2
+ if hdrlen > len(b) {
+ return errBufferTooShort
+ }
+ h.Version = int(b[0] >> 4)
+ h.Len = hdrlen
+ h.TOS = int(b[1])
+ h.ID = int(binary.BigEndian.Uint16(b[4:6]))
+ h.TTL = int(b[8])
+ h.Protocol = int(b[9])
+ h.Checksum = int(binary.BigEndian.Uint16(b[10:12]))
+ h.Src = net.IPv4(b[12], b[13], b[14], b[15])
+ h.Dst = net.IPv4(b[16], b[17], b[18], b[19])
+ switch runtime.GOOS {
+ case "darwin", "dragonfly", "netbsd":
+ h.TotalLen = int(socket.NativeEndian.Uint16(b[2:4])) + hdrlen
+ h.FragOff = int(socket.NativeEndian.Uint16(b[6:8]))
+ case "freebsd":
+ if freebsdVersion < 1100000 {
+ h.TotalLen = int(socket.NativeEndian.Uint16(b[2:4]))
+ if freebsdVersion < 1000000 {
+ h.TotalLen += hdrlen
+ }
+ h.FragOff = int(socket.NativeEndian.Uint16(b[6:8]))
+ } else {
+ h.TotalLen = int(binary.BigEndian.Uint16(b[2:4]))
+ h.FragOff = int(binary.BigEndian.Uint16(b[6:8]))
+ }
+ default:
+ h.TotalLen = int(binary.BigEndian.Uint16(b[2:4]))
+ h.FragOff = int(binary.BigEndian.Uint16(b[6:8]))
+ }
+ h.Flags = HeaderFlags(h.FragOff&0xe000) >> 13
+ h.FragOff = h.FragOff & 0x1fff
+ optlen := hdrlen - HeaderLen
+ if optlen > 0 && len(b) >= hdrlen {
+ if cap(h.Options) < optlen {
+ h.Options = make([]byte, optlen)
+ } else {
+ h.Options = h.Options[:optlen]
+ }
+ copy(h.Options, b[HeaderLen:hdrlen])
+ }
+ return nil
+}
+
+// ParseHeader parses b as an IPv4 header.
+func ParseHeader(b []byte) (*Header, error) {
+ h := new(Header)
+ if err := h.Parse(b); err != nil {
+ return nil, err
+ }
+ return h, nil
+}
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