// 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" "golang.org/x/net/internal/socket" ) const ( Version = 4 // protocol version HeaderLen = 20 // header length without extension headers ) 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. // // The returned slice is in the format used by a raw IP socket on the // local system. // This may differ from the wire format, depending on the system. func (h *Header) Marshal() ([]byte, error) { if h == nil { return nil, errNilHeader } 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", "ios", "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 stores the result in h. // // The provided b must be in the format used by a raw IP socket on the // local system. // This may differ from the wire format, depending on the system. func (h *Header) Parse(b []byte) error { if h == nil || b == nil { return errNilHeader } if len(b) < HeaderLen { return errHeaderTooShort } hdrlen := int(b[0]&0x0f) << 2 if len(b) < hdrlen { return errExtHeaderTooShort } 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", "ios", "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. // // The provided b must be in the format used by a raw IP socket on the // local system. // This may differ from the wire format, depending on the system. func ParseHeader(b []byte) (*Header, error) { h := new(Header) if err := h.Parse(b); err != nil { return nil, err } return h, nil }