forked from insomniacslk/dublin-traceroute
/
ipv4.go
249 lines (223 loc) · 5.38 KB
/
ipv4.go
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/* SPDX-License-Identifier: BSD-2-Clause */
package net
/*
import (
"bytes"
"encoding/binary"
"errors"
"net"
)
// Version4 is IP version 4
var Version4 = 4
// MinIPv4HeaderLen is the minimum IPv4 header length
var MinIPv4HeaderLen = 20
// Flag is an IPv4 flag type
type Flag byte
// IPv4 flags
var (
DontFragment = 2
MoreFragments = 4
)
// Option is an IP option
type Option [4]byte
// NewIPv4 constructs a new IPv4 header from a sequence of bytes
func NewIPv4(b []byte) (*IPv4, error) {
var h IPv4
if err := h.UnmarshalBinary(b); err != nil {
return nil, err
}
return &h, nil
}
// IPv4 is the IPv4 header
type IPv4 struct {
Version int
HeaderLen int
DiffServ int
TotalLen int
ID int
Flags int
FragOff int
TTL int
Proto IPProto
Checksum int
Src net.IP
Dst net.IP
Options []Option
next Layer
// IP in ICMP, if set, won't make the parser fail on short packets
IPinICMP bool
}
// Next returns the next layer
func (h IPv4) Next() Layer {
return h.next
}
// SetNext sets the next layer
func (h *IPv4) SetNext(l Layer) {
h.next = l
}
// MarshalBinary serializes the layer
func (h IPv4) MarshalBinary() ([]byte, error) {
var b bytes.Buffer
// Version check
if h.Version == 0 {
h.Version = Version4
}
if h.Version != Version4 {
return nil, errors.New("invalid version")
}
// IHL checks
h.HeaderLen = 5 + len(h.Options)
if h.HeaderLen > 0xff || h.HeaderLen < 5 {
return nil, errors.New("invalid ip header length")
}
binary.Write(&b, binary.BigEndian, byte(h.Version<<4)|byte(h.HeaderLen))
// Differentiated Services (DSCP, ECN)
if h.DiffServ < 0 || h.DiffServ > 0x3f {
return nil, errors.New("invalid differentiated services")
}
binary.Write(&b, binary.BigEndian, byte(h.DiffServ))
// Total length (header + data)
// marshal the payload to know the length
next := h.Next()
var (
payload []byte
err error
)
if next != nil {
payload, err = next.MarshalBinary()
if err != nil {
return nil, err
}
}
h.TotalLen = h.HeaderLen*4 + len(payload)
if h.TotalLen < 0 || h.TotalLen > 0xffff {
return nil, errors.New("invalid total length")
}
binary.Write(&b, binary.BigEndian, uint16(h.TotalLen))
// ID
if h.ID < 0 || h.ID > 0xffff {
return nil, errors.New("invalid ID")
}
binary.Write(&b, binary.BigEndian, uint16(h.ID))
// Flags
if h.Flags < 0 || h.Flags > 0x7 || h.Flags&0x1 != 0 {
return nil, errors.New("invalid flags")
}
var u16 = uint16(h.Flags << 13)
// Fragment offset
if h.FragOff < 0 || h.FragOff > 0x1fff {
return nil, errors.New("invalid fragment offset")
}
u16 |= uint16(h.FragOff & 0x1fff)
binary.Write(&b, binary.BigEndian, u16)
// TTL
if h.TTL < 0 || h.TTL > 0xff {
return nil, errors.New("invalid TTL")
}
binary.Write(&b, binary.BigEndian, uint8(h.TTL))
// Protocol
if h.Proto < 0 || h.Proto > 0xff {
return nil, errors.New("invalid protocol")
}
if h.Proto == 0 {
switch next.(type) {
case *UDP:
h.Proto = ProtoUDP
case *ICMP:
h.Proto = ProtoICMP
}
}
binary.Write(&b, binary.BigEndian, uint8(h.Proto))
// Checksum - left to 0, filled in by the platform
if h.Checksum < 0 || h.Checksum > 0xffff {
return nil, errors.New("invalid checksum")
}
binary.Write(&b, binary.BigEndian, uint16(h.Checksum))
// src and dst addresses
if h.Src == nil {
h.Src = net.IPv4zero
}
if h.Dst == nil {
h.Dst = net.IPv4zero
}
binary.Write(&b, binary.BigEndian, h.Src.To4())
binary.Write(&b, binary.BigEndian, h.Dst.To4())
// Options
for _, opt := range h.Options {
binary.Write(&b, binary.BigEndian, opt)
}
ret := append(b.Bytes(), payload...)
return ret, nil
}
// IsFragment returns whether this packet is a fragment of a larger packet.
func (h IPv4) IsFragment() bool {
return h.Flags&MoreFragments != 0 || h.FragOff != 0
}
// UnmarshalBinary deserializes the raw bytes to an IPv4 header
func (h *IPv4) UnmarshalBinary(b []byte) error {
if len(b) < MinIPv4HeaderLen {
return errors.New("short ipv4 header")
}
var (
u8 byte
u16 [2]byte
u32 [4]byte
)
buf := bytes.NewBuffer(b)
u8, _ = buf.ReadByte()
h.Version = int(u8 >> 4)
if h.Version != Version4 {
return errors.New("invalid version")
}
h.HeaderLen = int(u8 & 0xf)
if len(b) < h.HeaderLen*4 {
return errors.New("short ipv4 header")
}
u8, _ = buf.ReadByte()
h.DiffServ = int(u8)
buf.Read(u16[:])
h.TotalLen = int(binary.BigEndian.Uint16(u16[:]))
buf.Read(u16[:])
h.ID = int(binary.BigEndian.Uint16(u16[:]))
buf.Read(u16[:])
tmp := binary.BigEndian.Uint16(u16[:])
h.Flags = int((tmp >> 13) & 0x1f)
h.FragOff = int(tmp & 0x1fff)
u8, _ = buf.ReadByte()
h.TTL = int(u8)
u8, _ = buf.ReadByte()
h.Proto = IPProto(u8)
buf.Read(u16[:])
h.Checksum = int(binary.BigEndian.Uint16(u16[:]))
buf.Read(u32[:])
h.Src = append([]byte{}, u32[:]...)
buf.Read(u32[:])
h.Dst = append([]byte{}, u32[:]...)
h.Options = make([]Option, 0, h.HeaderLen-5)
for i := 0; i < cap(h.Options); i++ {
buf.Read(u32[:])
h.Options = append(h.Options, Option(u32))
}
// payload
if len(b) < h.TotalLen && !h.IPinICMP {
return errors.New("invalid IPv4 packet: payload too short")
}
payload := b[h.HeaderLen*4 : h.TotalLen]
if h.Proto == ProtoUDP && !h.IsFragment() {
u, err := NewUDP(payload)
if err != nil {
return err
}
h.next = u
} else if h.Proto == ProtoICMP {
i, err := NewICMP(payload)
if err != nil {
return err
}
h.next = i
} else {
h.next = &Raw{Data: payload}
}
return nil
}
*/