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msg.go
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msg.go
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// DNS packet assembly, see RFC 1035. Converting from - Unpack() -
// and to - Pack() - wire format.
// All the packers and unpackers take a (msg []byte, off int)
// and return (off1 int, ok bool). If they return ok==false, they
// also return off1==len(msg), so that the next unpacker will
// also fail. This lets us avoid checks of ok until the end of a
// packing sequence.
package dns
//go:generate go run msg_generate.go
//go:generate go run compress_generate.go
import (
crand "crypto/rand"
"encoding/binary"
"fmt"
"math/big"
"math/rand"
"strconv"
"sync"
)
const (
maxCompressionOffset = 2 << 13 // We have 14 bits for the compression pointer
maxDomainNameWireOctets = 255 // See RFC 1035 section 2.3.4
)
// Errors defined in this package.
var (
ErrAlg error = &Error{err: "bad algorithm"} // ErrAlg indicates an error with the (DNSSEC) algorithm.
ErrAuth error = &Error{err: "bad authentication"} // ErrAuth indicates an error in the TSIG authentication.
ErrBuf error = &Error{err: "buffer size too small"} // ErrBuf indicates that the buffer used is too small for the message.
ErrConnEmpty error = &Error{err: "conn has no connection"} // ErrConnEmpty indicates a connection is being used before it is initialized.
ErrExtendedRcode error = &Error{err: "bad extended rcode"} // ErrExtendedRcode ...
ErrFqdn error = &Error{err: "domain must be fully qualified"} // ErrFqdn indicates that a domain name does not have a closing dot.
ErrId error = &Error{err: "id mismatch"} // ErrId indicates there is a mismatch with the message's ID.
ErrKeyAlg error = &Error{err: "bad key algorithm"} // ErrKeyAlg indicates that the algorithm in the key is not valid.
ErrKey error = &Error{err: "bad key"}
ErrKeySize error = &Error{err: "bad key size"}
ErrLongDomain error = &Error{err: fmt.Sprintf("domain name exceeded %d wire-format octets", maxDomainNameWireOctets)}
ErrNoSig error = &Error{err: "no signature found"}
ErrPrivKey error = &Error{err: "bad private key"}
ErrRcode error = &Error{err: "bad rcode"}
ErrRdata error = &Error{err: "bad rdata"}
ErrRRset error = &Error{err: "bad rrset"}
ErrSecret error = &Error{err: "no secrets defined"}
ErrShortRead error = &Error{err: "short read"}
ErrSig error = &Error{err: "bad signature"} // ErrSig indicates that a signature can not be cryptographically validated.
ErrSoa error = &Error{err: "no SOA"} // ErrSOA indicates that no SOA RR was seen when doing zone transfers.
ErrTime error = &Error{err: "bad time"} // ErrTime indicates a timing error in TSIG authentication.
ErrTruncated error = &Error{err: "failed to unpack truncated message"} // ErrTruncated indicates that we failed to unpack a truncated message. We unpacked as much as we had so Msg can still be used, if desired.
)
// Id by default, returns a 16 bits random number to be used as a
// message id. The random provided should be good enough. This being a
// variable the function can be reassigned to a custom function.
// For instance, to make it return a static value:
//
// dns.Id = func() uint16 { return 3 }
var Id = id
var (
idLock sync.Mutex
idRand *rand.Rand
)
// id returns a 16 bits random number to be used as a
// message id. The random provided should be good enough.
func id() uint16 {
idLock.Lock()
if idRand == nil {
// This (partially) works around
// https://github.com/golang/go/issues/11833 by only
// seeding idRand upon the first call to id.
var seed int64
var buf [8]byte
if _, err := crand.Read(buf[:]); err == nil {
seed = int64(binary.LittleEndian.Uint64(buf[:]))
} else {
seed = rand.Int63()
}
idRand = rand.New(rand.NewSource(seed))
}
// The call to idRand.Uint32 must be within the
// mutex lock because *rand.Rand is not safe for
// concurrent use.
//
// There is no added performance overhead to calling
// idRand.Uint32 inside a mutex lock over just
// calling rand.Uint32 as the global math/rand rng
// is internally protected by a sync.Mutex.
id := uint16(idRand.Uint32())
idLock.Unlock()
return id
}
// MsgHdr is a a manually-unpacked version of (id, bits).
type MsgHdr struct {
Id uint16
Response bool
Opcode int
Authoritative bool
Truncated bool
RecursionDesired bool
RecursionAvailable bool
Zero bool
AuthenticatedData bool
CheckingDisabled bool
Rcode int
}
// Msg contains the layout of a DNS message.
type Msg struct {
MsgHdr
Compress bool `json:"-"` // If true, the message will be compressed when converted to wire format.
Question []Question // Holds the RR(s) of the question section.
Answer []RR // Holds the RR(s) of the answer section.
Ns []RR // Holds the RR(s) of the authority section.
Extra []RR // Holds the RR(s) of the additional section.
}
// ClassToString is a maps Classes to strings for each CLASS wire type.
var ClassToString = map[uint16]string{
ClassINET: "IN",
ClassCSNET: "CS",
ClassCHAOS: "CH",
ClassHESIOD: "HS",
ClassNONE: "NONE",
ClassANY: "ANY",
}
// OpcodeToString maps Opcodes to strings.
var OpcodeToString = map[int]string{
OpcodeQuery: "QUERY",
OpcodeIQuery: "IQUERY",
OpcodeStatus: "STATUS",
OpcodeNotify: "NOTIFY",
OpcodeUpdate: "UPDATE",
}
// RcodeToString maps Rcodes to strings.
var RcodeToString = map[int]string{
RcodeSuccess: "NOERROR",
RcodeFormatError: "FORMERR",
RcodeServerFailure: "SERVFAIL",
RcodeNameError: "NXDOMAIN",
RcodeNotImplemented: "NOTIMPL",
RcodeRefused: "REFUSED",
RcodeYXDomain: "YXDOMAIN", // See RFC 2136
RcodeYXRrset: "YXRRSET",
RcodeNXRrset: "NXRRSET",
RcodeNotAuth: "NOTAUTH",
RcodeNotZone: "NOTZONE",
RcodeBadSig: "BADSIG", // Also known as RcodeBadVers, see RFC 6891
// RcodeBadVers: "BADVERS",
RcodeBadKey: "BADKEY",
RcodeBadTime: "BADTIME",
RcodeBadMode: "BADMODE",
RcodeBadName: "BADNAME",
RcodeBadAlg: "BADALG",
RcodeBadTrunc: "BADTRUNC",
RcodeBadCookie: "BADCOOKIE",
}
// Domain names are a sequence of counted strings
// split at the dots. They end with a zero-length string.
// PackDomainName packs a domain name s into msg[off:].
// If compression is wanted compress must be true and the compression
// map needs to hold a mapping between domain names and offsets
// pointing into msg.
func PackDomainName(s string, msg []byte, off int, compression map[string]int, compress bool) (off1 int, err error) {
off1, _, err = packDomainName(s, msg, off, compression, compress)
return
}
func packDomainName(s string, msg []byte, off int, compression map[string]int, compress bool) (off1 int, labels int, err error) {
// special case if msg == nil
lenmsg := 256
if msg != nil {
lenmsg = len(msg)
}
ls := len(s)
if ls == 0 { // Ok, for instance when dealing with update RR without any rdata.
return off, 0, nil
}
// If not fully qualified, error out, but only if msg == nil #ugly
switch {
case msg == nil:
if s[ls-1] != '.' {
s += "."
ls++
}
case msg != nil:
if s[ls-1] != '.' {
return lenmsg, 0, ErrFqdn
}
}
// Each dot ends a segment of the name.
// We trade each dot byte for a length byte.
// Except for escaped dots (\.), which are normal dots.
// There is also a trailing zero.
// Compression
nameoffset := -1
pointer := -1
// Emit sequence of counted strings, chopping at dots.
begin := 0
bs := []byte(s)
roBs, bsFresh, escapedDot := s, true, false
for i := 0; i < ls; i++ {
if bs[i] == '\\' {
for j := i; j < ls-1; j++ {
bs[j] = bs[j+1]
}
ls--
if off+1 > lenmsg {
return lenmsg, labels, ErrBuf
}
// check for \DDD
if i+2 < ls && isDigit(bs[i]) && isDigit(bs[i+1]) && isDigit(bs[i+2]) {
bs[i] = dddToByte(bs[i:])
for j := i + 1; j < ls-2; j++ {
bs[j] = bs[j+2]
}
ls -= 2
}
escapedDot = bs[i] == '.'
bsFresh = false
continue
}
if bs[i] == '.' {
if i > 0 && bs[i-1] == '.' && !escapedDot {
// two dots back to back is not legal
return lenmsg, labels, ErrRdata
}
if i-begin >= 1<<6 { // top two bits of length must be clear
return lenmsg, labels, ErrRdata
}
// off can already (we're in a loop) be bigger than len(msg)
// this happens when a name isn't fully qualified
if off+1 > lenmsg {
return lenmsg, labels, ErrBuf
}
if msg != nil {
msg[off] = byte(i - begin)
}
offset := off
off++
for j := begin; j < i; j++ {
if off+1 > lenmsg {
return lenmsg, labels, ErrBuf
}
if msg != nil {
msg[off] = bs[j]
}
off++
}
if compress && !bsFresh {
roBs = string(bs)
bsFresh = true
}
// Don't try to compress '.'
// We should only compress when compress it true, but we should also still pick
// up names that can be used for *future* compression(s).
if compression != nil && roBs[begin:] != "." {
if p, ok := compression[roBs[begin:]]; !ok {
// Only offsets smaller than this can be used.
if offset < maxCompressionOffset {
compression[roBs[begin:]] = offset
}
} else {
// The first hit is the longest matching dname
// keep the pointer offset we get back and store
// the offset of the current name, because that's
// where we need to insert the pointer later
// If compress is true, we're allowed to compress this dname
if pointer == -1 && compress {
pointer = p // Where to point to
nameoffset = offset // Where to point from
break
}
}
}
labels++
begin = i + 1
}
escapedDot = false
}
// Root label is special
if len(bs) == 1 && bs[0] == '.' {
return off, labels, nil
}
// If we did compression and we find something add the pointer here
if pointer != -1 {
// Clear the msg buffer after the pointer location, otherwise
// packDataNsec writes the wrong data to msg.
tainted := msg[nameoffset:off]
for i := range tainted {
tainted[i] = 0
}
// We have two bytes (14 bits) to put the pointer in
// if msg == nil, we will never do compression
binary.BigEndian.PutUint16(msg[nameoffset:], uint16(pointer^0xC000))
off = nameoffset + 1
goto End
}
if msg != nil && off < len(msg) {
msg[off] = 0
}
End:
off++
return off, labels, nil
}
// Unpack a domain name.
// In addition to the simple sequences of counted strings above,
// domain names are allowed to refer to strings elsewhere in the
// packet, to avoid repeating common suffixes when returning
// many entries in a single domain. The pointers are marked
// by a length byte with the top two bits set. Ignoring those
// two bits, that byte and the next give a 14 bit offset from msg[0]
// where we should pick up the trail.
// Note that if we jump elsewhere in the packet,
// we return off1 == the offset after the first pointer we found,
// which is where the next record will start.
// In theory, the pointers are only allowed to jump backward.
// We let them jump anywhere and stop jumping after a while.
// UnpackDomainName unpacks a domain name into a string.
func UnpackDomainName(msg []byte, off int) (string, int, error) {
s := make([]byte, 0, 64)
off1 := 0
lenmsg := len(msg)
maxLen := maxDomainNameWireOctets
ptr := 0 // number of pointers followed
Loop:
for {
if off >= lenmsg {
return "", lenmsg, ErrBuf
}
c := int(msg[off])
off++
switch c & 0xC0 {
case 0x00:
if c == 0x00 {
// end of name
break Loop
}
// literal string
if off+c > lenmsg {
return "", lenmsg, ErrBuf
}
for j := off; j < off+c; j++ {
switch b := msg[j]; b {
case '.', '(', ')', ';', ' ', '@':
fallthrough
case '"', '\\':
s = append(s, '\\', b)
// presentation-format \X escapes add an extra byte
maxLen++
default:
if b < 32 || b >= 127 { // unprintable, use \DDD
var buf [3]byte
bufs := strconv.AppendInt(buf[:0], int64(b), 10)
s = append(s, '\\')
for i := len(bufs); i < 3; i++ {
s = append(s, '0')
}
s = append(s, bufs...)
// presentation-format \DDD escapes add 3 extra bytes
maxLen += 3
} else {
s = append(s, b)
}
}
}
s = append(s, '.')
off += c
case 0xC0:
// pointer to somewhere else in msg.
// remember location after first ptr,
// since that's how many bytes we consumed.
// also, don't follow too many pointers --
// maybe there's a loop.
if off >= lenmsg {
return "", lenmsg, ErrBuf
}
c1 := msg[off]
off++
if ptr == 0 {
off1 = off
}
if ptr++; ptr > 10 {
return "", lenmsg, &Error{err: "too many compression pointers"}
}
// pointer should guarantee that it advances and points forwards at least
// but the condition on previous three lines guarantees that it's
// at least loop-free
off = (c^0xC0)<<8 | int(c1)
default:
// 0x80 and 0x40 are reserved
return "", lenmsg, ErrRdata
}
}
if ptr == 0 {
off1 = off
}
if len(s) == 0 {
s = []byte(".")
} else if len(s) >= maxLen {
// error if the name is too long, but don't throw it away
return string(s), lenmsg, ErrLongDomain
}
return string(s), off1, nil
}
func packTxt(txt []string, msg []byte, offset int, tmp []byte) (int, error) {
if len(txt) == 0 {
if offset >= len(msg) {
return offset, ErrBuf
}
msg[offset] = 0
return offset, nil
}
var err error
for i := range txt {
if len(txt[i]) > len(tmp) {
return offset, ErrBuf
}
offset, err = packTxtString(txt[i], msg, offset, tmp)
if err != nil {
return offset, err
}
}
return offset, nil
}
func packTxtString(s string, msg []byte, offset int, tmp []byte) (int, error) {
lenByteOffset := offset
if offset >= len(msg) || len(s) > len(tmp) {
return offset, ErrBuf
}
offset++
bs := tmp[:len(s)]
copy(bs, s)
for i := 0; i < len(bs); i++ {
if len(msg) <= offset {
return offset, ErrBuf
}
if bs[i] == '\\' {
i++
if i == len(bs) {
break
}
// check for \DDD
if i+2 < len(bs) && isDigit(bs[i]) && isDigit(bs[i+1]) && isDigit(bs[i+2]) {
msg[offset] = dddToByte(bs[i:])
i += 2
} else {
msg[offset] = bs[i]
}
} else {
msg[offset] = bs[i]
}
offset++
}
l := offset - lenByteOffset - 1
if l > 255 {
return offset, &Error{err: "string exceeded 255 bytes in txt"}
}
msg[lenByteOffset] = byte(l)
return offset, nil
}
func packOctetString(s string, msg []byte, offset int, tmp []byte) (int, error) {
if offset >= len(msg) || len(s) > len(tmp) {
return offset, ErrBuf
}
bs := tmp[:len(s)]
copy(bs, s)
for i := 0; i < len(bs); i++ {
if len(msg) <= offset {
return offset, ErrBuf
}
if bs[i] == '\\' {
i++
if i == len(bs) {
break
}
// check for \DDD
if i+2 < len(bs) && isDigit(bs[i]) && isDigit(bs[i+1]) && isDigit(bs[i+2]) {
msg[offset] = dddToByte(bs[i:])
i += 2
} else {
msg[offset] = bs[i]
}
} else {
msg[offset] = bs[i]
}
offset++
}
return offset, nil
}
func unpackTxt(msg []byte, off0 int) (ss []string, off int, err error) {
off = off0
var s string
for off < len(msg) && err == nil {
s, off, err = unpackString(msg, off)
if err == nil {
ss = append(ss, s)
}
}
return
}
// Helpers for dealing with escaped bytes
func isDigit(b byte) bool { return b >= '0' && b <= '9' }
func dddToByte(s []byte) byte {
return byte((s[0]-'0')*100 + (s[1]-'0')*10 + (s[2] - '0'))
}
func dddStringToByte(s string) byte {
return byte((s[0]-'0')*100 + (s[1]-'0')*10 + (s[2] - '0'))
}
// Helper function for packing and unpacking
func intToBytes(i *big.Int, length int) []byte {
buf := i.Bytes()
if len(buf) < length {
b := make([]byte, length)
copy(b[length-len(buf):], buf)
return b
}
return buf
}
// PackRR packs a resource record rr into msg[off:].
// See PackDomainName for documentation about the compression.
func PackRR(rr RR, msg []byte, off int, compression map[string]int, compress bool) (off1 int, err error) {
if rr == nil {
return len(msg), &Error{err: "nil rr"}
}
off1, err = rr.pack(msg, off, compression, compress)
if err != nil {
return len(msg), err
}
// TODO(miek): Not sure if this is needed? If removed we can remove rawmsg.go as well.
if rawSetRdlength(msg, off, off1) {
return off1, nil
}
return off, ErrRdata
}
// UnpackRR unpacks msg[off:] into an RR.
func UnpackRR(msg []byte, off int) (rr RR, off1 int, err error) {
h, off, msg, err := unpackHeader(msg, off)
if err != nil {
return nil, len(msg), err
}
return UnpackRRWithHeader(h, msg, off)
}
// UnpackRRWithHeader unpacks the record type specific payload given an existing
// RR_Header.
func UnpackRRWithHeader(h RR_Header, msg []byte, off int) (rr RR, off1 int, err error) {
end := off + int(h.Rdlength)
if fn, known := typeToUnpack[h.Rrtype]; !known {
rr, off, err = unpackRFC3597(h, msg, off)
} else {
rr, off, err = fn(h, msg, off)
}
if off != end {
return &h, end, &Error{err: "bad rdlength"}
}
return rr, off, err
}
// unpackRRslice unpacks msg[off:] into an []RR.
// If we cannot unpack the whole array, then it will return nil
func unpackRRslice(l int, msg []byte, off int) (dst1 []RR, off1 int, err error) {
var r RR
// Don't pre-allocate, l may be under attacker control
var dst []RR
for i := 0; i < l; i++ {
off1 := off
r, off, err = UnpackRR(msg, off)
if err != nil {
off = len(msg)
break
}
// If offset does not increase anymore, l is a lie
if off1 == off {
l = i
break
}
dst = append(dst, r)
}
if err != nil && off == len(msg) {
dst = nil
}
return dst, off, err
}
// Convert a MsgHdr to a string, with dig-like headers:
//
//;; opcode: QUERY, status: NOERROR, id: 48404
//
//;; flags: qr aa rd ra;
func (h *MsgHdr) String() string {
if h == nil {
return "<nil> MsgHdr"
}
s := ";; opcode: " + OpcodeToString[h.Opcode]
s += ", status: " + RcodeToString[h.Rcode]
s += ", id: " + strconv.Itoa(int(h.Id)) + "\n"
s += ";; flags:"
if h.Response {
s += " qr"
}
if h.Authoritative {
s += " aa"
}
if h.Truncated {
s += " tc"
}
if h.RecursionDesired {
s += " rd"
}
if h.RecursionAvailable {
s += " ra"
}
if h.Zero { // Hmm
s += " z"
}
if h.AuthenticatedData {
s += " ad"
}
if h.CheckingDisabled {
s += " cd"
}
s += ";"
return s
}
// Pack packs a Msg: it is converted to to wire format.
// If the dns.Compress is true the message will be in compressed wire format.
func (dns *Msg) Pack() (msg []byte, err error) {
return dns.PackBuffer(nil)
}
// PackBuffer packs a Msg, using the given buffer buf. If buf is too small a new buffer is allocated.
func (dns *Msg) PackBuffer(buf []byte) (msg []byte, err error) {
var compression map[string]int
if dns.Compress {
compression = make(map[string]int) // Compression pointer mappings.
}
return dns.packBufferWithCompressionMap(buf, compression)
}
// packBufferWithCompressionMap packs a Msg, using the given buffer buf.
func (dns *Msg) packBufferWithCompressionMap(buf []byte, compression map[string]int) (msg []byte, err error) {
// We use a similar function in tsig.go's stripTsig.
var dh Header
if dns.Rcode < 0 || dns.Rcode > 0xFFF {
return nil, ErrRcode
}
if dns.Rcode > 0xF {
// Regular RCODE field is 4 bits
opt := dns.IsEdns0()
if opt == nil {
return nil, ErrExtendedRcode
}
opt.SetExtendedRcode(uint8(dns.Rcode >> 4))
}
// Convert convenient Msg into wire-like Header.
dh.Id = dns.Id
dh.Bits = uint16(dns.Opcode)<<11 | uint16(dns.Rcode&0xF)
if dns.Response {
dh.Bits |= _QR
}
if dns.Authoritative {
dh.Bits |= _AA
}
if dns.Truncated {
dh.Bits |= _TC
}
if dns.RecursionDesired {
dh.Bits |= _RD
}
if dns.RecursionAvailable {
dh.Bits |= _RA
}
if dns.Zero {
dh.Bits |= _Z
}
if dns.AuthenticatedData {
dh.Bits |= _AD
}
if dns.CheckingDisabled {
dh.Bits |= _CD
}
// Prepare variable sized arrays.
question := dns.Question
answer := dns.Answer
ns := dns.Ns
extra := dns.Extra
dh.Qdcount = uint16(len(question))
dh.Ancount = uint16(len(answer))
dh.Nscount = uint16(len(ns))
dh.Arcount = uint16(len(extra))
// We need the uncompressed length here, because we first pack it and then compress it.
msg = buf
uncompressedLen := compressedLen(dns, false)
if packLen := uncompressedLen + 1; len(msg) < packLen {
msg = make([]byte, packLen)
}
// Pack it in: header and then the pieces.
off := 0
off, err = dh.pack(msg, off, compression, dns.Compress)
if err != nil {
return nil, err
}
for i := 0; i < len(question); i++ {
off, err = question[i].pack(msg, off, compression, dns.Compress)
if err != nil {
return nil, err
}
}
for i := 0; i < len(answer); i++ {
off, err = PackRR(answer[i], msg, off, compression, dns.Compress)
if err != nil {
return nil, err
}
}
for i := 0; i < len(ns); i++ {
off, err = PackRR(ns[i], msg, off, compression, dns.Compress)
if err != nil {
return nil, err
}
}
for i := 0; i < len(extra); i++ {
off, err = PackRR(extra[i], msg, off, compression, dns.Compress)
if err != nil {
return nil, err
}
}
return msg[:off], nil
}
// Unpack unpacks a binary message to a Msg structure.
func (dns *Msg) Unpack(msg []byte) (err error) {
var (
dh Header
off int
)
if dh, off, err = unpackMsgHdr(msg, off); err != nil {
return err
}
dns.Id = dh.Id
dns.Response = dh.Bits&_QR != 0
dns.Opcode = int(dh.Bits>>11) & 0xF
dns.Authoritative = dh.Bits&_AA != 0
dns.Truncated = dh.Bits&_TC != 0
dns.RecursionDesired = dh.Bits&_RD != 0
dns.RecursionAvailable = dh.Bits&_RA != 0
dns.Zero = dh.Bits&_Z != 0
dns.AuthenticatedData = dh.Bits&_AD != 0
dns.CheckingDisabled = dh.Bits&_CD != 0
dns.Rcode = int(dh.Bits & 0xF)
// If we are at the end of the message we should return *just* the
// header. This can still be useful to the caller. 9.9.9.9 sends these
// when responding with REFUSED for instance.
if off == len(msg) {
// reset sections before returning
dns.Question, dns.Answer, dns.Ns, dns.Extra = nil, nil, nil, nil
return nil
}
// Qdcount, Ancount, Nscount, Arcount can't be trusted, as they are
// attacker controlled. This means we can't use them to pre-allocate
// slices.
dns.Question = nil
for i := 0; i < int(dh.Qdcount); i++ {
off1 := off
var q Question
q, off, err = unpackQuestion(msg, off)
if err != nil {
// Even if Truncated is set, we only will set ErrTruncated if we
// actually got the questions
return err
}
if off1 == off { // Offset does not increase anymore, dh.Qdcount is a lie!
dh.Qdcount = uint16(i)
break
}
dns.Question = append(dns.Question, q)
}
dns.Answer, off, err = unpackRRslice(int(dh.Ancount), msg, off)
// The header counts might have been wrong so we need to update it
dh.Ancount = uint16(len(dns.Answer))
if err == nil {
dns.Ns, off, err = unpackRRslice(int(dh.Nscount), msg, off)
}
// The header counts might have been wrong so we need to update it
dh.Nscount = uint16(len(dns.Ns))
if err == nil {
dns.Extra, off, err = unpackRRslice(int(dh.Arcount), msg, off)
}
// The header counts might have been wrong so we need to update it
dh.Arcount = uint16(len(dns.Extra))
if off != len(msg) {
// TODO(miek) make this an error?
// use PackOpt to let people tell how detailed the error reporting should be?
// println("dns: extra bytes in dns packet", off, "<", len(msg))
} else if dns.Truncated {
// Whether we ran into a an error or not, we want to return that it
// was truncated
err = ErrTruncated
}
return err
}
// Convert a complete message to a string with dig-like output.
func (dns *Msg) String() string {
if dns == nil {
return "<nil> MsgHdr"
}
s := dns.MsgHdr.String() + " "
s += "QUERY: " + strconv.Itoa(len(dns.Question)) + ", "
s += "ANSWER: " + strconv.Itoa(len(dns.Answer)) + ", "
s += "AUTHORITY: " + strconv.Itoa(len(dns.Ns)) + ", "
s += "ADDITIONAL: " + strconv.Itoa(len(dns.Extra)) + "\n"
if len(dns.Question) > 0 {
s += "\n;; QUESTION SECTION:\n"
for i := 0; i < len(dns.Question); i++ {
s += dns.Question[i].String() + "\n"
}
}
if len(dns.Answer) > 0 {
s += "\n;; ANSWER SECTION:\n"
for i := 0; i < len(dns.Answer); i++ {
if dns.Answer[i] != nil {
s += dns.Answer[i].String() + "\n"
}
}
}
if len(dns.Ns) > 0 {
s += "\n;; AUTHORITY SECTION:\n"
for i := 0; i < len(dns.Ns); i++ {
if dns.Ns[i] != nil {
s += dns.Ns[i].String() + "\n"
}
}
}
if len(dns.Extra) > 0 {
s += "\n;; ADDITIONAL SECTION:\n"
for i := 0; i < len(dns.Extra); i++ {
if dns.Extra[i] != nil {
s += dns.Extra[i].String() + "\n"
}
}
}
return s
}
// Len returns the message length when in (un)compressed wire format.
// If dns.Compress is true compression it is taken into account. Len()
// is provided to be a faster way to get the size of the resulting packet,
// than packing it, measuring the size and discarding the buffer.
func (dns *Msg) Len() int { return compressedLen(dns, dns.Compress) }
func compressedLenWithCompressionMap(dns *Msg, compression map[string]int) int {
l := 12 // Message header is always 12 bytes
for _, r := range dns.Question {
compressionLenHelper(compression, r.Name, l)
l += r.len()
}
l += compressionLenSlice(l, compression, dns.Answer)
l += compressionLenSlice(l, compression, dns.Ns)
l += compressionLenSlice(l, compression, dns.Extra)
return l
}
// compressedLen returns the message length when in compressed wire format
// when compress is true, otherwise the uncompressed length is returned.
func compressedLen(dns *Msg, compress bool) int {
// We always return one more than needed.
if compress {
compression := map[string]int{}
return compressedLenWithCompressionMap(dns, compression)
}
l := 12 // Message header is always 12 bytes
for _, r := range dns.Question {
l += r.len()
}
for _, r := range dns.Answer {
if r != nil {
l += r.len()
}
}
for _, r := range dns.Ns {
if r != nil {
l += r.len()
}
}
for _, r := range dns.Extra {
if r != nil {
l += r.len()
}
}
return l
}
func compressionLenSlice(lenp int, c map[string]int, rs []RR) int {
initLen := lenp
for _, r := range rs {
if r == nil {
continue
}
// TmpLen is to track len of record at 14bits boudaries
tmpLen := lenp
x := r.len()
// track this length, and the global length in len, while taking compression into account for both.
k, ok, _ := compressionLenSearch(c, r.Header().Name)
if ok {
// Size of x is reduced by k, but we add 1 since k includes the '.' and label descriptor take 2 bytes
// so, basically x:= x - k - 1 + 2
x += 1 - k
}
tmpLen += compressionLenHelper(c, r.Header().Name, tmpLen)
k, ok, _ = compressionLenSearchType(c, r)
if ok {
x += 1 - k
}
lenp += x
tmpLen = lenp
tmpLen += compressionLenHelperType(c, r, tmpLen)
}
return lenp - initLen
}
// Put the parts of the name in the compression map, return the size in bytes added in payload
func compressionLenHelper(c map[string]int, s string, currentLen int) int {
if currentLen > maxCompressionOffset {
// We won't be able to add any label that could be re-used later anyway
return 0
}
if _, ok := c[s]; ok {
return 0
}
initLen := currentLen
pref := ""
prev := s
lbs := Split(s)
for j := 0; j < len(lbs); j++ {
pref = s[lbs[j]:]
currentLen += len(prev) - len(pref)
prev = pref
if _, ok := c[pref]; !ok {
// If first byte label is within the first 14bits, it might be re-used later
if currentLen < maxCompressionOffset {
c[pref] = currentLen
}
} else {
added := currentLen - initLen
if j > 0 {