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edns.go
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edns.go
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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.OPT)
// o.Hdr.Name = "." // MUST be the root zone, per definition.
// o.Hdr.Rrtype = dns.TypeOPT
//
// The rdata of an OPT RR consists out of a slice of EDNS0 interfaces. Currently
// only a few have been standardized: EDNS0_NSID (RFC 5001) and EDNS0_SUBNET (draft). Note that
// these options may be combined in an OPT RR.
// Basic use pattern for a server to check if (and which) options are set:
//
// // o is a dns.OPT
// for _, s := range o.Options {
// switch e := s.(type) {
// case *dns.EDNS0_NSID:
// // do stuff with e.Nsid
// case *dns.EDNS0_SUBNET:
// // access e.Family, e.Address, etc.
// }
// }
package dns
import (
"encoding/hex"
"errors"
"net"
"strconv"
)
// EDNS0 Option codes.
const (
EDNS0LLQ = 0x1 // not used
EDNS0UL = 0x2 // not used
EDNS0UPDATELEASE = 0x2 // update lease draft
EDNS0NSID = 0x3 // nsid (RFC5001)
EDNS0SUBNET = 0x50fa // client-subnet draft
_DO = 1 << 7 // dnssec ok
)
type OPT struct {
Hdr RR_Header
Option []EDNS0 `dns:"opt"`
}
func (rr *OPT) Header() *RR_Header {
return &rr.Hdr
}
func (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()
case *EDNS0_UPDATE_LEASE:
s += "\n; LEASE: " + o.String()
}
}
return s
}
func (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 *OPT) Copy() RR {
return &OPT{*rr.Hdr.CopyHeader(), rr.Option}
}
// Version returns the EDNS version used. Only zero is defined.
func (rr *OPT) Version() uint8 {
return uint8(rr.Hdr.Ttl & 0x00FF00FFFF)
}
// SetVersion sets the version of EDNS. This is usually zero.
func (rr *OPT) SetVersion(v uint8) {
rr.Hdr.Ttl = rr.Hdr.Ttl&0xFF00FFFF | uint32(v)
}
// UDPSize returns the UDP buffer size.
func (rr *OPT) UDPSize() uint16 {
return rr.Hdr.Class
}
// SetUDPSize sets the UDP buffer size.
func (rr *OPT) SetUDPSize(size uint16) {
rr.Hdr.Class = size
}
// Do returns the value of the DO (DNSSEC OK) bit.
func (rr *OPT) Do() bool {
return byte(rr.Hdr.Ttl>>8)&_DO == _DO
}
// SetDo sets the DO (DNSSEC OK) bit.
func (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 options 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. When seding a request Nsid must be set to the empty string
// The identifier is an opaque string encoded as hex.
// Basic use pattern for creating an nsid option:
//
// o := new(dns.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.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
}
// The UPDATE_LEASE EDNS0 (draft RFC) option is used to tell the server to set
// an expiration on an update RR. This is helpful for clients that cannot clean
// up after themselves. This is a draft RFC and more information can be found at
// http://files.dns-sd.org/draft-sekar-dns-ul.txt
//
// o := new(dns.OPT)
// o.Hdr.Name = "."
// o.Hdr.Rrtype = dns.TypeOPT
// e := new(dns.EDNS0_UPDATE_LEASE)
// e.Code = dns.EDNS0UPDATELEASE
// e.Lease = 120 // in seconds
// o.Option = append(o.Option, e)
type EDNS0_UPDATE_LEASE struct {
Code uint16 // Always EDNS0UPDATELEASE
Lease uint32
}
func (e *EDNS0_UPDATE_LEASE) Option() uint16 {
return EDNS0UPDATELEASE
}
// Copied: http://golang.org/src/pkg/net/dnsmsg.go
func (e *EDNS0_UPDATE_LEASE) pack() ([]byte, error) {
b := make([]byte, 4)
b[0] = byte(e.Lease >> 24)
b[1] = byte(e.Lease >> 16)
b[2] = byte(e.Lease >> 8)
b[3] = byte(e.Lease)
return b, nil
}
func (e *EDNS0_UPDATE_LEASE) unpack(b []byte) {
e.Lease = uint32(b[0])<<24 | uint32(b[1])<<16 | uint32(b[2])<<8 | uint32(b[3])
}
func (e *EDNS0_UPDATE_LEASE) String() string {
return strconv.Itoa(int(e.Lease))
}