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// EDNS0
//
// EDNS0 is an extension mechanism for the DNS defined in RFC 2671. It defines a
// standard RR type, the OPT RR, which is then completely abused.
// Basic use pattern for creating an (empty) OPT RR:
//
// o := new(dns.RR_OPT)
// o.Hdr.Name = "."
// o.Hdr.Rrtype = dns.TypeOPT
//
package dns
import (
"encoding/hex"
"errors"
"net"
"strconv"
)
// EDNS0 Option codes.
const (
_ = iota
EDNS0LLQ // not used
EDNS0UL // not used
EDNS0NSID // nsid (RFC5001)
EDNS0SUBNET = 0x50fa // client-subnet draft
_DO = 1 << 7 // dnssec ok
)
type RR_OPT struct {
Hdr RR_Header
Option []EDNS0 `dns:"opt"`
}
func (rr *RR_OPT) Header() *RR_Header {
return &rr.Hdr
}
func (rr *RR_OPT) String() string {
s := "\n;; OPT PSEUDOSECTION:\n; EDNS: version " + strconv.Itoa(int(rr.Version())) + "; "
if rr.Do() {
s += "flags: do; "
} else {
s += "flags: ; "
}
s += "udp: " + strconv.Itoa(int(rr.UDPSize()))
for _, o := range rr.Option {
switch o.(type) {
case *EDNS0_NSID:
s += "\n; NSID: " + o.String()
h, e := o.Pack()
var r string
if e == nil {
for _, c := range h {
r += "(" + string(c) + ")"
}
s += " " + r
}
case *EDNS0_SUBNET:
s += "\n; SUBNET: " + o.String()
}
}
return s
}
func (rr *RR_OPT) Len() int {
l := rr.Hdr.Len()
for i := 0; i < len(rr.Option); i++ {
lo, _ := rr.Option[i].Pack()
l += 2 + len(lo)
}
return l
}
func (rr *RR_OPT) Copy() RR {
return &RR_OPT{*rr.Hdr.CopyHeader(), rr.Option}
}
// Version returns the EDNS version used. Only zero is defined.
func (rr *RR_OPT) Version() uint8 {
return uint8(rr.Hdr.Ttl & 0x00FF00FFFF)
}
// SetVersion sets the version of EDNS. This is usually zero.
func (rr *RR_OPT) SetVersion(v uint8) {
rr.Hdr.Ttl = rr.Hdr.Ttl&0xFF00FFFF | uint32(v)
}
// UDPSize returns the UDP buffer size.
func (rr *RR_OPT) UDPSize() uint16 {
return rr.Hdr.Class
}
// SetUDPSize sets the UDP buffer size.
func (rr *RR_OPT) SetUDPSize(size uint16) {
rr.Hdr.Class = size
}
// Do returns the value of the DO (DNSSEC OK) bit.
func (rr *RR_OPT) Do() bool {
return byte(rr.Hdr.Ttl>>8)&_DO == _DO
}
// SetDo sets the DO (DNSSEC OK) bit.
func (rr *RR_OPT) SetDo() {
b1 := byte(rr.Hdr.Ttl >> 24)
b2 := byte(rr.Hdr.Ttl >> 16)
b3 := byte(rr.Hdr.Ttl >> 8)
b4 := byte(rr.Hdr.Ttl)
b3 |= _DO // Set it
rr.Hdr.Ttl = uint32(b1)<<24 | uint32(b2)<<16 | uint32(b3)<<8 | uint32(b4)
}
// EDNS0 defines an EDNS0 Option. An OPT RR can have multiple option appended to
// it. Basic use pattern for adding an option to and OPT RR:
//
// // o is the OPT RR, e is the EDNS0 option
// o.Option = append(o.Option, e)
type EDNS0 interface {
// Option returns the option code for the option.
Option() uint16
// Pack returns the bytes of the option data.
Pack() ([]byte, error)
// Unpack sets the data as found in the buffer. Is also sets
// the length of the slice as the length of the option data.
Unpack([]byte)
// String returns the string representation of the option.
String() string
}
// The nsid EDNS0 option is used to retrieve some sort of nameserver
// identifier. The identifier is an opaque string encoded has hex.
// Basic use pattern for creating an nsid option:
//
// o := new(dns.RR_OPT)
// o.Hdr.Name = "."
// o.Hdr.Rrtype = dns.TypeOPT
// e := new(dns.EDNS0_NSID)
// e.Code = dns.EDNS0NSID
// o.Option = append(o.Option, e)
type EDNS0_NSID struct {
Code uint16 // Always EDNS0NSID
Nsid string // This string needs to be hex encoded
}
func (e *EDNS0_NSID) Option() uint16 {
return EDNS0NSID
}
func (e *EDNS0_NSID) Pack() ([]byte, error) {
h, err := hex.DecodeString(e.Nsid)
if err != nil {
return nil, err
}
return h, nil
}
func (e *EDNS0_NSID) Unpack(b []byte) {
e.Nsid = hex.EncodeToString(b)
}
func (e *EDNS0_NSID) String() string {
return string(e.Nsid)
}
// The subnet EDNS0 option is used to give the remote nameserver
// an idea of where the client lives. It can then give back a different
// answer depending on the location or network topology.
// Basic use pattern for creating an subnet option:
//
// o := new(dns.RR_OPT)
// o.Hdr.Name = "."
// o.Hdr.Rrtype = dns.TypeOPT
// e := new(dns.EDNS0_SUBNET)
// e.Code = dns.EDNS0SUBNET
// e.Family = 1 // 1 for IPv4 source address, 2 for IPv6
// e.NetMask = 32 // 32 for IPV4, 128 for IPv6
// e.SourceScope = 0
// e.Address = net.ParseIP("127.0.0.1").To4() // for IPv4
// // e.Address = net.ParseIP("2001:7b8:32a::2") // for IPV6
// o.Option = append(o.Option, e)
type EDNS0_SUBNET struct {
Code uint16 // Always EDNS0SUBNET
Family uint16 // 1 for IP, 2 for IP6
SourceNetmask uint8
SourceScope uint8
Address net.IP
}
func (e *EDNS0_SUBNET) Option() uint16 {
return EDNS0SUBNET
}
func (e *EDNS0_SUBNET) Pack() ([]byte, error) {
b := make([]byte, 4)
b[0], b[1] = packUint16(e.Family)
b[2] = e.SourceNetmask
b[3] = e.SourceScope
switch e.Family {
case 1:
if e.SourceNetmask > net.IPv4len*8 {
return nil, errors.New("bad netmask")
}
ip := make([]byte, net.IPv4len)
a := e.Address.To4().Mask(net.CIDRMask(int(e.SourceNetmask), net.IPv4len*8))
for i := 0; i < net.IPv4len; i++ {
if i+1 > len(e.Address) {
break
}
ip[i] = a[i]
}
b = append(b, ip...)
case 2:
if e.SourceNetmask > net.IPv6len*8 {
return nil, errors.New("bad netmask")
}
ip := make([]byte, net.IPv6len)
a := e.Address.Mask(net.CIDRMask(int(e.SourceNetmask), net.IPv6len*8))
for i := 0; i < net.IPv6len; i++ {
if i+1 > len(e.Address) {
break
}
ip[i] = a[i]
}
b = append(b, ip...)
default:
return nil, errors.New("bad address family")
}
return b, nil
}
func (e *EDNS0_SUBNET) Unpack(b []byte) {
if len(b) < 8 {
return
}
e.Family, _ = unpackUint16(b, 0)
e.SourceNetmask = b[2]
e.SourceScope = b[3]
switch e.Family {
case 1:
if len(b) == 8 {
e.Address = net.IPv4(b[4], b[5], b[6], b[7])
}
case 2:
if len(b) == 20 {
e.Address = net.IP{b[4], b[4+1], b[4+2], b[4+3], b[4+4],
b[4+5], b[4+6], b[4+7], b[4+8], b[4+9], b[4+10],
b[4+11], b[4+12], b[4+13], b[4+14], b[4+15]}
}
}
return
}
func (e *EDNS0_SUBNET) String() (s string) {
if e.Address == nil {
s = "<nil>"
} else if e.Address.To4() != nil {
s = e.Address.String()
} else {
s = "[" + e.Address.String() + "]"
}
s += "/" + strconv.Itoa(int(e.SourceNetmask)) + "/" + strconv.Itoa(int(e.SourceScope))
return
}
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