// 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 { // 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 := 0; i < 3-len(bufs); i++ { s = append(s, '0') } for _, r := range bufs { s = append(s, r) } // 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 = unpackTxtString(msg, off) if err == nil { ss = append(ss, s) } } return } func unpackTxtString(msg []byte, offset int) (string, int, error) { if offset+1 > len(msg) { return "", offset, &Error{err: "overflow unpacking txt"} } l := int(msg[offset]) if offset+l+1 > len(msg) { return "", offset, &Error{err: "overflow unpacking txt"} } s := make([]byte, 0, l) for _, b := range msg[offset+1 : offset+1+l] { switch b { case '"', '\\': s = append(s, '\\', b) default: if b < 32 || b > 127 { // unprintable var buf [3]byte bufs := strconv.AppendInt(buf[:0], int64(b), 10) s = append(s, '\\') for i := 0; i < 3-len(bufs); i++ { s = append(s, '0') } for _, r := range bufs { s = append(s, r) } } else { s = append(s, b) } } } offset += 1 + l return string(s), offset, nil } // 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')) } // 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 } 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 " 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) { // We use a similar function in tsig.go's stripTsig. var ( dh Header compression map[string]int ) if dns.Compress { compression = make(map[string]int) // Compression pointer mappings } 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)) dns.Rcode &= 0xF } // Convert convenient Msg into wire-like Header. dh.Id = dns.Id dh.Bits = uint16(dns.Opcode)<<11 | uint16(dns.Rcode) 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 " 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) } // 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. l := 12 // Message header is always 12 bytes if compress { compression := map[string]int{} for _, r := range dns.Question { l += r.len() compressionLenHelper(compression, r.Name) } l += compressionLenSlice(compression, dns.Answer) l += compressionLenSlice(compression, dns.Ns) l += compressionLenSlice(compression, dns.Extra) } else { 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(c map[string]int, rs []RR) int { var l int for _, r := range rs { if r == nil { continue } l += r.len() k, ok := compressionLenSearch(c, r.Header().Name) if ok { l += 1 - k } compressionLenHelper(c, r.Header().Name) k, ok = compressionLenSearchType(c, r) if ok { l += 1 - k } compressionLenHelperType(c, r) } return l } // Put the parts of the name in the compression map. func compressionLenHelper(c map[string]int, s string) { pref := "" lbs := Split(s) for j := len(lbs) - 1; j >= 0; j-- { pref = s[lbs[j]:] if _, ok := c[pref]; !ok { c[pref] = len(pref) } } } // Look for each part in the compression map and returns its length, // keep on searching so we get the longest match. func compressionLenSearch(c map[string]int, s string) (int, bool) { off := 0 end := false if s == "" { // don't bork on bogus data return 0, false } for { if _, ok := c[s[off:]]; ok { return len(s[off:]), true } if end { break } off, end = NextLabel(s, off) } return 0, false } // Copy returns a new RR which is a deep-copy of r. func Copy(r RR) RR { r1 := r.copy(); return r1 } // Len returns the length (in octets) of the uncompressed RR in wire format. func Len(r RR) int { return r.len() } // Copy returns a new *Msg which is a deep-copy of dns. func (dns *Msg) Copy() *Msg { return dns.CopyTo(new(Msg)) } // CopyTo copies the contents to the provided message using a deep-copy and returns the copy. func (dns *Msg) CopyTo(r1 *Msg) *Msg { r1.MsgHdr = dns.MsgHdr r1.Compress = dns.Compress if len(dns.Question) > 0 { r1.Question = make([]Question, len(dns.Question)) copy(r1.Question, dns.Question) // TODO(miek): Question is an immutable value, ok to do a shallow-copy } rrArr := make([]RR, len(dns.Answer)+len(dns.Ns)+len(dns.Extra)) var rri int if len(dns.Answer) > 0 { rrbegin := rri for i := 0; i < len(dns.Answer); i++ { rrArr[rri] = dns.Answer[i].copy() rri++ } r1.Answer = rrArr[rrbegin:rri:rri] } if len(dns.Ns) > 0 { rrbegin := rri for i := 0; i < len(dns.Ns); i++ { rrArr[rri] = dns.Ns[i].copy() rri++ } r1.Ns = rrArr[rrbegin:rri:rri] } if len(dns.Extra) > 0 { rrbegin := rri for i := 0; i < len(dns.Extra); i++ { rrArr[rri] = dns.Extra[i].copy() rri++ } r1.Extra = rrArr[rrbegin:rri:rri] } return r1 } func (q *Question) pack(msg []byte, off int, compression map[string]int, compress bool) (int, error) { off, err := PackDomainName(q.Name, msg, off, compression, compress) if err != nil { return off, err } off, err = packUint16(q.Qtype, msg, off) if err != nil { return off, err } off, err = packUint16(q.Qclass, msg, off) if err != nil { return off, err } return off, nil } func unpackQuestion(msg []byte, off int) (Question, int, error) { var ( q Question err error ) q.Name, off, err = UnpackDomainName(msg, off) if err != nil { return q, off, err } if off == len(msg) { return q, off, nil } q.Qtype, off, err = unpackUint16(msg, off) if err != nil { return q, off, err } if off == len(msg) { return q, off, nil } q.Qclass, off, err = unpackUint16(msg, off) if off == len(msg) { return q, off, nil } return q, off, err } func (dh *Header) pack(msg []byte, off int, compression map[string]int, compress bool) (int, error) { off, err := packUint16(dh.Id, msg, off) if err != nil { return off, err } off, err = packUint16(dh.Bits, msg, off) if err != nil { return off, err } off, err = packUint16(dh.Qdcount, msg, off) if err != nil { return off, err } off, err = packUint16(dh.Ancount, msg, off) if err != nil { return off, err } off, err = packUint16(dh.Nscount, msg, off) if err != nil { return off, err } off, err = packUint16(dh.Arcount, msg, off) return off, err } func unpackMsgHdr(msg []byte, off int) (Header, int, error) { var ( dh Header err error ) dh.Id, off, err = unpackUint16(msg, off) if err != nil { return dh, off, err } dh.Bits, off, err = unpackUint16(msg, off) if err != nil { return dh, off, err } dh.Qdcount, off, err = unpackUint16(msg, off) if err != nil { return dh, off, err } dh.Ancount, off, err = unpackUint16(msg, off) if err != nil { return dh, off, err } dh.Nscount, off, err = unpackUint16(msg, off) if err != nil { return dh, off, err } dh.Arcount, off, err = unpackUint16(msg, off) return dh, off, err }