1155 lines
30 KiB
Go
1155 lines
30 KiB
Go
// DNS packet assembly, see RFC 1035. Converting from - Unpack() -
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// and to - Pack() - wire format.
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// All the packers and unpackers take a (msg []byte, off int)
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// and return (off1 int, ok bool). If they return ok==false, they
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// also return off1==len(msg), so that the next unpacker will
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// also fail. This lets us avoid checks of ok until the end of a
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// packing sequence.
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package dns
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//go:generate go run msg_generate.go
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//go:generate go run compress_generate.go
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import (
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crand "crypto/rand"
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"encoding/binary"
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"fmt"
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"math/big"
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"math/rand"
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"strconv"
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"sync"
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)
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const (
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maxCompressionOffset = 2 << 13 // We have 14 bits for the compression pointer
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maxDomainNameWireOctets = 255 // See RFC 1035 section 2.3.4
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)
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// Errors defined in this package.
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var (
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ErrAlg error = &Error{err: "bad algorithm"} // ErrAlg indicates an error with the (DNSSEC) algorithm.
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ErrAuth error = &Error{err: "bad authentication"} // ErrAuth indicates an error in the TSIG authentication.
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ErrBuf error = &Error{err: "buffer size too small"} // ErrBuf indicates that the buffer used is too small for the message.
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ErrConnEmpty error = &Error{err: "conn has no connection"} // ErrConnEmpty indicates a connection is being used before it is initialized.
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ErrExtendedRcode error = &Error{err: "bad extended rcode"} // ErrExtendedRcode ...
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ErrFqdn error = &Error{err: "domain must be fully qualified"} // ErrFqdn indicates that a domain name does not have a closing dot.
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ErrId error = &Error{err: "id mismatch"} // ErrId indicates there is a mismatch with the message's ID.
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ErrKeyAlg error = &Error{err: "bad key algorithm"} // ErrKeyAlg indicates that the algorithm in the key is not valid.
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ErrKey error = &Error{err: "bad key"}
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ErrKeySize error = &Error{err: "bad key size"}
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ErrLongDomain error = &Error{err: fmt.Sprintf("domain name exceeded %d wire-format octets", maxDomainNameWireOctets)}
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ErrNoSig error = &Error{err: "no signature found"}
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ErrPrivKey error = &Error{err: "bad private key"}
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ErrRcode error = &Error{err: "bad rcode"}
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ErrRdata error = &Error{err: "bad rdata"}
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ErrRRset error = &Error{err: "bad rrset"}
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ErrSecret error = &Error{err: "no secrets defined"}
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ErrShortRead error = &Error{err: "short read"}
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ErrSig error = &Error{err: "bad signature"} // ErrSig indicates that a signature can not be cryptographically validated.
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ErrSoa error = &Error{err: "no SOA"} // ErrSOA indicates that no SOA RR was seen when doing zone transfers.
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ErrTime error = &Error{err: "bad time"} // ErrTime indicates a timing error in TSIG authentication.
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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.
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)
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// Id by default, returns a 16 bits random number to be used as a
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// message id. The random provided should be good enough. This being a
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// variable the function can be reassigned to a custom function.
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// For instance, to make it return a static value:
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//
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// dns.Id = func() uint16 { return 3 }
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var Id = id
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var (
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idLock sync.Mutex
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idRand *rand.Rand
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)
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// id returns a 16 bits random number to be used as a
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// message id. The random provided should be good enough.
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func id() uint16 {
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idLock.Lock()
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if idRand == nil {
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// This (partially) works around
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// https://github.com/golang/go/issues/11833 by only
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// seeding idRand upon the first call to id.
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var seed int64
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var buf [8]byte
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if _, err := crand.Read(buf[:]); err == nil {
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seed = int64(binary.LittleEndian.Uint64(buf[:]))
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} else {
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seed = rand.Int63()
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}
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idRand = rand.New(rand.NewSource(seed))
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}
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// The call to idRand.Uint32 must be within the
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// mutex lock because *rand.Rand is not safe for
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// concurrent use.
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//
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// There is no added performance overhead to calling
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// idRand.Uint32 inside a mutex lock over just
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// calling rand.Uint32 as the global math/rand rng
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// is internally protected by a sync.Mutex.
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id := uint16(idRand.Uint32())
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idLock.Unlock()
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return id
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}
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// MsgHdr is a a manually-unpacked version of (id, bits).
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type MsgHdr struct {
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Id uint16
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Response bool
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Opcode int
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Authoritative bool
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Truncated bool
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RecursionDesired bool
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RecursionAvailable bool
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Zero bool
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AuthenticatedData bool
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CheckingDisabled bool
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Rcode int
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}
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// Msg contains the layout of a DNS message.
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type Msg struct {
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MsgHdr
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Compress bool `json:"-"` // If true, the message will be compressed when converted to wire format.
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Question []Question // Holds the RR(s) of the question section.
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Answer []RR // Holds the RR(s) of the answer section.
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Ns []RR // Holds the RR(s) of the authority section.
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Extra []RR // Holds the RR(s) of the additional section.
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}
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// ClassToString is a maps Classes to strings for each CLASS wire type.
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var ClassToString = map[uint16]string{
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ClassINET: "IN",
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ClassCSNET: "CS",
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ClassCHAOS: "CH",
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ClassHESIOD: "HS",
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ClassNONE: "NONE",
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ClassANY: "ANY",
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}
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// OpcodeToString maps Opcodes to strings.
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var OpcodeToString = map[int]string{
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OpcodeQuery: "QUERY",
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OpcodeIQuery: "IQUERY",
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OpcodeStatus: "STATUS",
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OpcodeNotify: "NOTIFY",
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OpcodeUpdate: "UPDATE",
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}
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// RcodeToString maps Rcodes to strings.
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var RcodeToString = map[int]string{
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RcodeSuccess: "NOERROR",
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RcodeFormatError: "FORMERR",
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RcodeServerFailure: "SERVFAIL",
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RcodeNameError: "NXDOMAIN",
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RcodeNotImplemented: "NOTIMPL",
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RcodeRefused: "REFUSED",
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RcodeYXDomain: "YXDOMAIN", // See RFC 2136
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RcodeYXRrset: "YXRRSET",
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RcodeNXRrset: "NXRRSET",
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RcodeNotAuth: "NOTAUTH",
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RcodeNotZone: "NOTZONE",
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RcodeBadSig: "BADSIG", // Also known as RcodeBadVers, see RFC 6891
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// RcodeBadVers: "BADVERS",
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RcodeBadKey: "BADKEY",
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RcodeBadTime: "BADTIME",
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RcodeBadMode: "BADMODE",
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RcodeBadName: "BADNAME",
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RcodeBadAlg: "BADALG",
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RcodeBadTrunc: "BADTRUNC",
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RcodeBadCookie: "BADCOOKIE",
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}
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// Domain names are a sequence of counted strings
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// split at the dots. They end with a zero-length string.
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// PackDomainName packs a domain name s into msg[off:].
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// If compression is wanted compress must be true and the compression
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// map needs to hold a mapping between domain names and offsets
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// pointing into msg.
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func PackDomainName(s string, msg []byte, off int, compression map[string]int, compress bool) (off1 int, err error) {
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off1, _, err = packDomainName(s, msg, off, compression, compress)
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return
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}
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func packDomainName(s string, msg []byte, off int, compression map[string]int, compress bool) (off1 int, labels int, err error) {
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// special case if msg == nil
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lenmsg := 256
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if msg != nil {
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lenmsg = len(msg)
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}
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ls := len(s)
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if ls == 0 { // Ok, for instance when dealing with update RR without any rdata.
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return off, 0, nil
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}
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// If not fully qualified, error out, but only if msg == nil #ugly
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switch {
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case msg == nil:
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if s[ls-1] != '.' {
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s += "."
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ls++
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}
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case msg != nil:
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if s[ls-1] != '.' {
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return lenmsg, 0, ErrFqdn
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}
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}
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// Each dot ends a segment of the name.
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// We trade each dot byte for a length byte.
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// Except for escaped dots (\.), which are normal dots.
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// There is also a trailing zero.
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// Compression
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nameoffset := -1
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pointer := -1
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// Emit sequence of counted strings, chopping at dots.
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begin := 0
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bs := []byte(s)
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roBs, bsFresh, escapedDot := s, true, false
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for i := 0; i < ls; i++ {
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if bs[i] == '\\' {
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for j := i; j < ls-1; j++ {
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bs[j] = bs[j+1]
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}
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ls--
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if off+1 > lenmsg {
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return lenmsg, labels, ErrBuf
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}
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// check for \DDD
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if i+2 < ls && isDigit(bs[i]) && isDigit(bs[i+1]) && isDigit(bs[i+2]) {
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bs[i] = dddToByte(bs[i:])
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for j := i + 1; j < ls-2; j++ {
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bs[j] = bs[j+2]
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}
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ls -= 2
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}
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escapedDot = bs[i] == '.'
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bsFresh = false
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continue
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}
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if bs[i] == '.' {
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if i > 0 && bs[i-1] == '.' && !escapedDot {
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// two dots back to back is not legal
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return lenmsg, labels, ErrRdata
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}
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if i-begin >= 1<<6 { // top two bits of length must be clear
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return lenmsg, labels, ErrRdata
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}
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// off can already (we're in a loop) be bigger than len(msg)
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// this happens when a name isn't fully qualified
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if off+1 > lenmsg {
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return lenmsg, labels, ErrBuf
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}
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if msg != nil {
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msg[off] = byte(i - begin)
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}
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offset := off
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off++
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for j := begin; j < i; j++ {
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if off+1 > lenmsg {
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return lenmsg, labels, ErrBuf
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}
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if msg != nil {
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msg[off] = bs[j]
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}
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off++
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}
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if compress && !bsFresh {
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roBs = string(bs)
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bsFresh = true
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}
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// Don't try to compress '.'
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// We should only compress when compress it true, but we should also still pick
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// up names that can be used for *future* compression(s).
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if compression != nil && roBs[begin:] != "." {
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if p, ok := compression[roBs[begin:]]; !ok {
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// Only offsets smaller than this can be used.
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if offset < maxCompressionOffset {
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compression[roBs[begin:]] = offset
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}
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} else {
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// The first hit is the longest matching dname
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// keep the pointer offset we get back and store
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// the offset of the current name, because that's
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// where we need to insert the pointer later
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// If compress is true, we're allowed to compress this dname
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if pointer == -1 && compress {
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pointer = p // Where to point to
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nameoffset = offset // Where to point from
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break
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}
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}
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}
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labels++
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begin = i + 1
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}
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escapedDot = false
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}
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// Root label is special
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if len(bs) == 1 && bs[0] == '.' {
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return off, labels, nil
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}
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// If we did compression and we find something add the pointer here
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if pointer != -1 {
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// We have two bytes (14 bits) to put the pointer in
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// if msg == nil, we will never do compression
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binary.BigEndian.PutUint16(msg[nameoffset:], uint16(pointer^0xC000))
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off = nameoffset + 1
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goto End
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}
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if msg != nil && off < len(msg) {
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msg[off] = 0
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}
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End:
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off++
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return off, labels, nil
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}
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// Unpack a domain name.
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// In addition to the simple sequences of counted strings above,
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// domain names are allowed to refer to strings elsewhere in the
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// packet, to avoid repeating common suffixes when returning
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// many entries in a single domain. The pointers are marked
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// by a length byte with the top two bits set. Ignoring those
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// two bits, that byte and the next give a 14 bit offset from msg[0]
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// where we should pick up the trail.
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// Note that if we jump elsewhere in the packet,
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// we return off1 == the offset after the first pointer we found,
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// which is where the next record will start.
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// In theory, the pointers are only allowed to jump backward.
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// We let them jump anywhere and stop jumping after a while.
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// UnpackDomainName unpacks a domain name into a string.
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func UnpackDomainName(msg []byte, off int) (string, int, error) {
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s := make([]byte, 0, 64)
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off1 := 0
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lenmsg := len(msg)
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maxLen := maxDomainNameWireOctets
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ptr := 0 // number of pointers followed
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Loop:
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for {
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if off >= lenmsg {
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return "", lenmsg, ErrBuf
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}
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c := int(msg[off])
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off++
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switch c & 0xC0 {
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case 0x00:
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if c == 0x00 {
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// end of name
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break Loop
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}
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// literal string
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if off+c > lenmsg {
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return "", lenmsg, ErrBuf
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}
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for j := off; j < off+c; j++ {
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switch b := msg[j]; b {
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case '.', '(', ')', ';', ' ', '@':
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fallthrough
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case '"', '\\':
|
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s = append(s, '\\', b)
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// presentation-format \X escapes add an extra byte
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maxLen++
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default:
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if b < 32 || b >= 127 { // unprintable, use \DDD
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var buf [3]byte
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bufs := strconv.AppendInt(buf[:0], int64(b), 10)
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s = append(s, '\\')
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for i := 0; i < 3-len(bufs); i++ {
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s = append(s, '0')
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}
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for _, r := range bufs {
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s = append(s, r)
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}
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// presentation-format \DDD escapes add 3 extra bytes
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maxLen += 3
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} else {
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s = append(s, b)
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}
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}
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}
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s = append(s, '.')
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off += c
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case 0xC0:
|
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// pointer to somewhere else in msg.
|
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// remember location after first ptr,
|
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// since that's how many bytes we consumed.
|
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// also, don't follow too many pointers --
|
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// maybe there's a loop.
|
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if off >= lenmsg {
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return "", lenmsg, ErrBuf
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}
|
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c1 := msg[off]
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off++
|
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if ptr == 0 {
|
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off1 = off
|
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}
|
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if ptr++; ptr > 10 {
|
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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 "<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) {
|
|
// 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 "<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) }
|
|
|
|
// 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
|
|
}
|