// 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 import ( "crypto/rand" "encoding/binary" "fmt" "math/big" "strconv" "strings" ) const ( maxCompressionOffset = 2 << 13 // We have 14 bits for the compression pointer maxDomainNameWireOctets = 255 // See RFC 1035 section 2.3.4 // This is the maximum number of compression pointers that should occur in a // semantically valid message. Each label in a domain name must be at least one // octet and is separated by a period. The root label won't be represented by a // compression pointer to a compression pointer, hence the -2 to exclude the // smallest valid root label. // // It is possible to construct a valid message that has more compression pointers // than this, and still doesn't loop, by pointing to a previous pointer. This is // not something a well written implementation should ever do, so we leave them // to trip the maximum compression pointer check. maxCompressionPointers = (maxDomainNameWireOctets+1)/2 - 2 // This is the maximum length of a domain name in presentation format. The // maximum wire length of a domain name is 255 octets (see above), with the // maximum label length being 63. The wire format requires one extra byte over // the presentation format, reducing the number of octets by 1. Each label in // the name will be separated by a single period, with each octet in the label // expanding to at most 4 bytes (\DDD). If all other labels are of the maximum // length, then the final label can only be 61 octets long to not exceed the // maximum allowed wire length. maxDomainNamePresentationLength = 61*4 + 1 + 63*4 + 1 + 63*4 + 1 + 63*4 + 1 ) // 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. ) // Id by default returns a 16-bit random number to be used as a message id. The // number is drawn from a cryptographically secure random number generator. // This being a variable the function can be reassigned to a custom function. // For instance, to make it return a static value for testing: // // dns.Id = func() uint16 { return 3 } var Id = id // id returns a 16 bits random number to be used as a // message id. The random provided should be good enough. func id() uint16 { var output uint16 err := binary.Read(rand.Reader, binary.BigEndian, &output) if err != nil { panic("dns: reading random id failed: " + err.Error()) } return output } // 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: "NOTIMP", 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", } // compressionMap is used to allow a more efficient compression map // to be used for internal packDomainName calls without changing the // signature or functionality of public API. // // In particular, map[string]uint16 uses 25% less per-entry memory // than does map[string]int. type compressionMap struct { ext map[string]int // external callers int map[string]uint16 // internal callers } func (m compressionMap) valid() bool { return m.int != nil || m.ext != nil } func (m compressionMap) insert(s string, pos int) { if m.ext != nil { m.ext[s] = pos } else { m.int[s] = uint16(pos) } } func (m compressionMap) find(s string) (int, bool) { if m.ext != nil { pos, ok := m.ext[s] return pos, ok } pos, ok := m.int[s] return int(pos), ok } // 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) { return packDomainName(s, msg, off, compressionMap{ext: compression}, compress) } func packDomainName(s string, msg []byte, off int, compression compressionMap, compress bool) (off1 int, err error) { // XXX: A logical copy of this function exists in IsDomainName and // should be kept in sync with this function. ls := len(s) if ls == 0 { // Ok, for instance when dealing with update RR without any rdata. return off, nil } // If not fully qualified, error out. if !IsFqdn(s) { return len(msg), 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 pointer := -1 // Emit sequence of counted strings, chopping at dots. var ( begin int compBegin int compOff int bs []byte wasDot bool ) loop: for i := 0; i < ls; i++ { var c byte if bs == nil { c = s[i] } else { c = bs[i] } switch c { case '\\': if off+1 > len(msg) { return len(msg), ErrBuf } if bs == nil { bs = []byte(s) } // check for \DDD if i+3 < ls && isDigit(bs[i+1]) && isDigit(bs[i+2]) && isDigit(bs[i+3]) { bs[i] = dddToByte(bs[i+1:]) copy(bs[i+1:ls-3], bs[i+4:]) ls -= 3 compOff += 3 } else { copy(bs[i:ls-1], bs[i+1:]) ls-- compOff++ } wasDot = false case '.': if wasDot { // two dots back to back is not legal return len(msg), ErrRdata } wasDot = true labelLen := i - begin if labelLen >= 1<<6 { // top two bits of length must be clear return len(msg), 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+labelLen > len(msg) { return len(msg), ErrBuf } // Don't try to compress '.' // We should only compress when compress is true, but we should also still pick // up names that can be used for *future* compression(s). if compression.valid() && !isRootLabel(s, bs, begin, ls) { if p, ok := compression.find(s[compBegin:]); ok { // 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 compress { pointer = p // Where to point to break loop } } else if off < maxCompressionOffset { // Only offsets smaller than maxCompressionOffset can be used. compression.insert(s[compBegin:], off) } } // The following is covered by the length check above. msg[off] = byte(labelLen) if bs == nil { copy(msg[off+1:], s[begin:i]) } else { copy(msg[off+1:], bs[begin:i]) } off += 1 + labelLen begin = i + 1 compBegin = begin + compOff default: wasDot = false } } // Root label is special if isRootLabel(s, bs, 0, ls) { return off, 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 binary.BigEndian.PutUint16(msg[off:], uint16(pointer^0xC000)) return off + 2, nil } if off < len(msg) { msg[off] = 0 } return off + 1, nil } // isRootLabel returns whether s or bs, from off to end, is the root // label ".". // // If bs is nil, s will be checked, otherwise bs will be checked. func isRootLabel(s string, bs []byte, off, end int) bool { if bs == nil { return s[off:end] == "." } return end-off == 1 && bs[off] == '.' } // 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. It returns // the name, the new offset into msg and any error that occurred. // // When an error is encountered, the unpacked name will be discarded // and len(msg) will be returned as the offset. func UnpackDomainName(msg []byte, off int) (string, int, error) { s := make([]byte, 0, maxDomainNamePresentationLength) off1 := 0 lenmsg := len(msg) budget := 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 } budget -= c + 1 // +1 for the label separator if budget <= 0 { return "", lenmsg, ErrLongDomain } for _, b := range msg[off : off+c] { if isDomainNameLabelSpecial(b) { s = append(s, '\\', b) } else if b < ' ' || b > '~' { s = append(s, escapeByte(b)...) } 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 > maxCompressionPointers { 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 { return ".", off1, nil } 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 _, s := range txt { if len(s) > len(tmp) { return offset, ErrBuf } offset, err = packTxtString(s, 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 { _ = s[2] // bounds check hint to compiler; see golang.org/issue/14808 return byte((s[0]-'0')*100 + (s[1]-'0')*10 + (s[2] - '0')) } func dddStringToByte(s string) byte { _ = s[2] // bounds check hint to compiler; see golang.org/issue/14808 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) { headerEnd, off1, err := packRR(rr, msg, off, compressionMap{ext: compression}, compress) if err == nil { // packRR no longer sets the Rdlength field on the rr, but // callers might be expecting it so we set it here. rr.Header().Rdlength = uint16(off1 - headerEnd) } return off1, err } func packRR(rr RR, msg []byte, off int, compression compressionMap, compress bool) (headerEnd int, off1 int, err error) { if rr == nil { return len(msg), len(msg), &Error{err: "nil rr"} } headerEnd, err = rr.Header().packHeader(msg, off, compression, compress) if err != nil { return headerEnd, len(msg), err } off1, err = rr.pack(msg, headerEnd, compression, compress) if err != nil { return headerEnd, len(msg), err } rdlength := off1 - headerEnd if int(uint16(rdlength)) != rdlength { // overflow return headerEnd, len(msg), ErrRdata } // The RDLENGTH field is the last field in the header and we set it here. binary.BigEndian.PutUint16(msg[headerEnd-2:], uint16(rdlength)) return headerEnd, off1, nil } // 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) { if newFn, ok := TypeToRR[h.Rrtype]; ok { rr = newFn() *rr.Header() = h } else { rr = &RFC3597{Hdr: h} } if noRdata(h) { return rr, off, nil } end := off + int(h.Rdlength) off, err = rr.unpack(msg, off) if err != nil { return nil, end, err } if off != end { return &h, end, &Error{err: "bad rdlength"} } return rr, off, nil } // 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 { 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) { // If this message can't be compressed, avoid filling the // compression map and creating garbage. if dns.Compress && dns.isCompressible() { compression := make(map[string]uint16) // Compression pointer mappings. return dns.packBufferWithCompressionMap(buf, compressionMap{int: compression}, true) } return dns.packBufferWithCompressionMap(buf, compressionMap{}, false) } // packBufferWithCompressionMap packs a Msg, using the given buffer buf. func (dns *Msg) packBufferWithCompressionMap(buf []byte, compression compressionMap, compress bool) (msg []byte, err error) { if dns.Rcode < 0 || dns.Rcode > 0xFFF { return nil, ErrRcode } // Set extended rcode unconditionally if we have an opt, this will allow // reseting the extended rcode bits if they need to. if opt := dns.IsEdns0(); opt != nil { opt.SetExtendedRcode(uint16(dns.Rcode)) } else if dns.Rcode > 0xF { // If Rcode is an extended one and opt is nil, error out. return nil, ErrExtendedRcode } // Convert convenient Msg into wire-like Header. var dh 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 } dh.Qdcount = uint16(len(dns.Question)) dh.Ancount = uint16(len(dns.Answer)) dh.Nscount = uint16(len(dns.Ns)) dh.Arcount = uint16(len(dns.Extra)) // We need the uncompressed length here, because we first pack it and then compress it. msg = buf uncompressedLen := msgLenWithCompressionMap(dns, nil) 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, compress) if err != nil { return nil, err } for _, r := range dns.Question { off, err = r.pack(msg, off, compression, compress) if err != nil { return nil, err } } for _, r := range dns.Answer { _, off, err = packRR(r, msg, off, compression, compress) if err != nil { return nil, err } } for _, r := range dns.Ns { _, off, err = packRR(r, msg, off, compression, compress) if err != nil { return nil, err } } for _, r := range dns.Extra { _, off, err = packRR(r, msg, off, compression, compress) if err != nil { return nil, err } } return msg[:off], nil } func (dns *Msg) unpack(dh Header, msg []byte, off int) (err error) { // 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 { 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)) // Set extended Rcode if opt := dns.IsEdns0(); opt != nil { dns.Rcode |= opt.ExtendedRcode() } 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)) } return err } // Unpack unpacks a binary message to a Msg structure. func (dns *Msg) Unpack(msg []byte) (err error) { dh, off, err := unpackMsgHdr(msg, 0) if err != nil { return err } dns.setHdr(dh) return dns.unpack(dh, msg, off) } // 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 _, r := range dns.Question { s += r.String() + "\n" } } if len(dns.Answer) > 0 { s += "\n;; ANSWER SECTION:\n" for _, r := range dns.Answer { if r != nil { s += r.String() + "\n" } } } if len(dns.Ns) > 0 { s += "\n;; AUTHORITY SECTION:\n" for _, r := range dns.Ns { if r != nil { s += r.String() + "\n" } } } if len(dns.Extra) > 0 { s += "\n;; ADDITIONAL SECTION:\n" for _, r := range dns.Extra { if r != nil { s += r.String() + "\n" } } } return s } // isCompressible returns whether the msg may be compressible. func (dns *Msg) isCompressible() bool { // If we only have one question, there is nothing we can ever compress. return len(dns.Question) > 1 || len(dns.Answer) > 0 || len(dns.Ns) > 0 || len(dns.Extra) > 0 } // 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 { // If this message can't be compressed, avoid filling the // compression map and creating garbage. if dns.Compress && dns.isCompressible() { compression := make(map[string]struct{}) return msgLenWithCompressionMap(dns, compression) } return msgLenWithCompressionMap(dns, nil) } func msgLenWithCompressionMap(dns *Msg, compression map[string]struct{}) int { l := headerSize for _, r := range dns.Question { l += r.len(l, compression) } for _, r := range dns.Answer { if r != nil { l += r.len(l, compression) } } for _, r := range dns.Ns { if r != nil { l += r.len(l, compression) } } for _, r := range dns.Extra { if r != nil { l += r.len(l, compression) } } return l } func domainNameLen(s string, off int, compression map[string]struct{}, compress bool) int { if s == "" || s == "." { return 1 } escaped := strings.Contains(s, "\\") if compression != nil && (compress || off < maxCompressionOffset) { // compressionLenSearch will insert the entry into the compression // map if it doesn't contain it. if l, ok := compressionLenSearch(compression, s, off); ok && compress { if escaped { return escapedNameLen(s[:l]) + 2 } return l + 2 } } if escaped { return escapedNameLen(s) + 1 } return len(s) + 1 } func escapedNameLen(s string) int { nameLen := len(s) for i := 0; i < len(s); i++ { if s[i] != '\\' { continue } if i+3 < len(s) && isDigit(s[i+1]) && isDigit(s[i+2]) && isDigit(s[i+3]) { nameLen -= 3 i += 3 } else { nameLen-- i++ } } return nameLen } func compressionLenSearch(c map[string]struct{}, s string, msgOff int) (int, bool) { for off, end := 0, false; !end; off, end = NextLabel(s, off) { if _, ok := c[s[off:]]; ok { return off, true } if msgOff+off < maxCompressionOffset { c[s[off:]] = struct{}{} } } return 0, false } // Copy returns a new RR which is a deep-copy of r. func Copy(r RR) RR { return r.copy() } // Len returns the length (in octets) of the uncompressed RR in wire format. func Len(r RR) int { return r.len(0, nil) } // 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)) r1.Answer, rrArr = rrArr[:0:len(dns.Answer)], rrArr[len(dns.Answer):] r1.Ns, rrArr = rrArr[:0:len(dns.Ns)], rrArr[len(dns.Ns):] r1.Extra = rrArr[:0:len(dns.Extra)] for _, r := range dns.Answer { r1.Answer = append(r1.Answer, r.copy()) } for _, r := range dns.Ns { r1.Ns = append(r1.Ns, r.copy()) } for _, r := range dns.Extra { r1.Extra = append(r1.Extra, r.copy()) } return r1 } func (q *Question) pack(msg []byte, off int, compression compressionMap, 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 compressionMap, 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) if err != nil { return off, err } return off, nil } 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) if err != nil { return dh, off, err } return dh, off, nil } // setHdr set the header in the dns using the binary data in dh. func (dns *Msg) setHdr(dh Header) { 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 // _Z covers the zero bit, which should be zero; not sure why we set it to the opposite. dns.AuthenticatedData = dh.Bits&_AD != 0 dns.CheckingDisabled = dh.Bits&_CD != 0 dns.Rcode = int(dh.Bits & 0xF) }