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package dhcpv4
import (
"bytes"
"errors"
"fmt"
)
// ErrShortByteStream is an error that is thrown any time a short byte stream is
// detected during option parsing.
var ErrShortByteStream = errors.New("short byte stream")
// ErrZeroLengthByteStream is an error that is thrown any time a zero-length
// byte stream is encountered.
var ErrZeroLengthByteStream = errors.New("zero-length byte stream")
// MagicCookie is the magic 4-byte value at the beginning of the list of options
// in a DHCPv4 packet.
var MagicCookie = []byte{99, 130, 83, 99}
// OptionCode is a single byte representing the code for a given Option.
type OptionCode byte
// Option is an interface that all DHCP v4 options adhere to.
type Option interface {
Code() OptionCode
ToBytes() []byte
Length() int
String() string
}
// ParseOption parses a sequence of bytes as a single DHCPv4 option, returning
// the specific option structure or error, if any.
func ParseOption(data []byte) (Option, error) {
if len(data) == 0 {
return nil, errors.New("invalid zero-length DHCPv4 option")
}
var (
opt Option
err error
)
switch OptionCode(data[0]) {
case OptionDHCPMessageType:
opt, err = ParseOptMessageType(data)
case OptionParameterRequestList:
opt, err = ParseOptParameterRequestList(data)
case OptionRequestedIPAddress:
opt, err = ParseOptRequestedIPAddress(data)
case OptionServerIdentifier:
opt, err = ParseOptServerIdentifier(data)
case OptionMaximumDHCPMessageSize:
opt, err = ParseOptMaximumDHCPMessageSize(data)
case OptionClassIdentifier:
opt, err = ParseOptClassIdentifier(data)
default:
opt, err = ParseOptionGeneric(data)
}
if err != nil {
return nil, err
}
return opt, nil
}
// OptionsFromBytes parses a sequence of bytes until the end and builds a list
// of options from it. The sequence must contain the Magic Cookie. Returns an
// error if any invalid option or length is found.
func OptionsFromBytes(data []byte) ([]Option, error) {
if len(data) < len(MagicCookie) {
return nil, errors.New("invalid options: shorter than 4 bytes")
}
if !bytes.Equal(data[:len(MagicCookie)], MagicCookie) {
return nil, fmt.Errorf("invalid magic cookie: %v", data[:len(MagicCookie)])
}
opts, err := OptionsFromBytesWithoutMagicCookie(data[len(MagicCookie):])
if err != nil {
return nil, err
}
return opts, nil
}
// OptionsFromBytesWithoutMagicCookie parses a sequence of bytes until the end
// and builds a list of options from it. The sequence should not contain the
// DHCP magic cookie. Returns an error if any invalid option or length is found.
func OptionsFromBytesWithoutMagicCookie(data []byte) ([]Option, error) {
options := make([]Option, 0, 10)
idx := 0
for {
if idx == len(data) {
break
}
// This should never happen.
if idx > len(data) {
return nil, errors.New("read past the end of options")
}
opt, err := ParseOption(data[idx:])
idx++
if err != nil {
return nil, err
}
options = append(options, opt)
// Options with zero length have no length byte, so here we handle the
// ones with nonzero length
if opt.Length() > 0 {
idx++
}
idx += opt.Length()
}
return options, nil
}
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