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// Package dhcpv6 provides encoding and decoding of DHCPv6 messages and
// options.
package dhcpv6
import (
"fmt"
"net"
"github.com/u-root/uio/uio"
)
type DHCPv6 interface {
Type() MessageType
ToBytes() []byte
String() string
Summary() string
LongString(indent int) string
IsRelay() bool
// GetInnerMessage returns the innermost encapsulated DHCPv6 message.
//
// If it is already a message, it will be returned. If it is a relay
// message, the encapsulated message will be recursively extracted.
GetInnerMessage() (*Message, error)
GetOption(code OptionCode) []Option
GetOneOption(code OptionCode) Option
AddOption(Option)
UpdateOption(Option)
}
// Modifier defines the signature for functions that can modify DHCPv6
// structures. This is used to simplify packet manipulation
type Modifier func(d DHCPv6)
// MessageFromBytes parses a DHCPv6 message from a byte stream.
func MessageFromBytes(data []byte) (*Message, error) {
buf := uio.NewBigEndianBuffer(data)
messageType := MessageType(buf.Read8())
if messageType == MessageTypeRelayForward || messageType == MessageTypeRelayReply {
return nil, fmt.Errorf("wrong message type")
}
d := &Message{
MessageType: messageType,
}
buf.ReadBytes(d.TransactionID[:])
if buf.Error() != nil {
return nil, fmt.Errorf("failed to parse DHCPv6 header: %w", buf.Error())
}
if err := d.Options.FromBytes(buf.Data()); err != nil {
return nil, err
}
return d, nil
}
// RelayMessageFromBytes parses a relay message from a byte stream.
func RelayMessageFromBytes(data []byte) (*RelayMessage, error) {
buf := uio.NewBigEndianBuffer(data)
messageType := MessageType(buf.Read8())
if messageType != MessageTypeRelayForward && messageType != MessageTypeRelayReply {
return nil, fmt.Errorf("wrong message type")
}
d := &RelayMessage{
MessageType: messageType,
HopCount: buf.Read8(),
}
d.LinkAddr = net.IP(buf.CopyN(net.IPv6len))
d.PeerAddr = net.IP(buf.CopyN(net.IPv6len))
if buf.Error() != nil {
return nil, fmt.Errorf("Error parsing RelayMessage header: %v", buf.Error())
}
// TODO: fail if no OptRelayMessage is present.
if err := d.Options.FromBytes(buf.Data()); err != nil {
return nil, err
}
return d, nil
}
// FromBytes reads a DHCPv6 message from a byte stream.
func FromBytes(data []byte) (DHCPv6, error) {
buf := uio.NewBigEndianBuffer(data)
messageType := MessageType(buf.Read8())
if buf.Error() != nil {
return nil, buf.Error()
}
if messageType == MessageTypeRelayForward || messageType == MessageTypeRelayReply {
return RelayMessageFromBytes(data)
} else {
return MessageFromBytes(data)
}
}
// NewMessage creates a new DHCPv6 message with default options
func NewMessage(modifiers ...Modifier) (*Message, error) {
tid, err := GenerateTransactionID()
if err != nil {
return nil, err
}
msg := &Message{
MessageType: MessageTypeSolicit,
TransactionID: tid,
}
// apply modifiers
for _, mod := range modifiers {
mod(msg)
}
return msg, nil
}
// DecapsulateRelay extracts the content of a relay message. It does not recurse
// if there are nested relay messages. Returns the original packet if is not not
// a relay message
func DecapsulateRelay(l DHCPv6) (DHCPv6, error) {
if !l.IsRelay() {
return l, nil
}
if rm := l.(*RelayMessage).Options.RelayMessage(); rm != nil {
return rm, nil
}
return nil, fmt.Errorf("malformed Relay message: no embedded message found")
}
// DecapsulateRelayIndex extracts the content of a relay message. It takes an
// integer as index (e.g. if 0 return the outermost relay, 1 returns the
// second, etc, and -1 returns the last). Returns the original packet if
// it is not not a relay message.
func DecapsulateRelayIndex(l DHCPv6, index int) (DHCPv6, error) {
if !l.IsRelay() {
return l, nil
}
if index < -1 {
return nil, fmt.Errorf("Invalid index: %d", index)
} else if index == -1 {
for {
d, err := DecapsulateRelay(l)
if err != nil {
return nil, err
}
if !d.IsRelay() {
return l, nil
}
l = d
}
}
for i := 0; i <= index; i++ {
d, err := DecapsulateRelay(l)
if err != nil {
return nil, err
}
l = d
}
return l, nil
}
// EncapsulateRelay creates a RelayMessage message containing the passed DHCPv6
// message as payload. The passed message type must be either RELAY_FORW or
// RELAY_REPL
func EncapsulateRelay(d DHCPv6, mType MessageType, linkAddr, peerAddr net.IP) (*RelayMessage, error) {
if mType != MessageTypeRelayForward && mType != MessageTypeRelayReply {
return nil, fmt.Errorf("Message type must be either RELAY_FORW or RELAY_REPL")
}
outer := RelayMessage{
MessageType: mType,
LinkAddr: linkAddr,
PeerAddr: peerAddr,
}
if d.IsRelay() {
relay := d.(*RelayMessage)
outer.HopCount = relay.HopCount + 1
} else {
outer.HopCount = 0
}
outer.AddOption(OptRelayMessage(d))
return &outer, nil
}
// GetTransactionID returns a transactionID of a message or its inner message
// in case of relay
func GetTransactionID(packet DHCPv6) (TransactionID, error) {
m, err := packet.GetInnerMessage()
if err != nil {
return TransactionID{0, 0, 0}, err
}
return m.TransactionID, nil
}
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