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package dns
import (
"errors"
"net"
"strconv"
"strings"
)
const hexDigit = "0123456789abcdef"
// Everything is assumed in ClassINET.
// SetReply creates a reply message from a request message.
func (dns *Msg) SetReply(request *Msg) *Msg {
dns.Id = request.Id
dns.Response = true
dns.Opcode = request.Opcode
if dns.Opcode == OpcodeQuery {
dns.RecursionDesired = request.RecursionDesired // Copy rd bit
dns.CheckingDisabled = request.CheckingDisabled // Copy cd bit
}
dns.Rcode = RcodeSuccess
if len(request.Question) > 0 {
dns.Question = make([]Question, 1)
dns.Question[0] = request.Question[0]
}
return dns
}
// SetQuestion creates a question message, it sets the Question
// section, generates an Id and sets the RecursionDesired (RD)
// bit to true.
func (dns *Msg) SetQuestion(z string, t uint16) *Msg {
dns.Id = Id()
dns.RecursionDesired = true
dns.Question = make([]Question, 1)
dns.Question[0] = Question{z, t, ClassINET}
return dns
}
// SetNotify creates a notify message, it sets the Question
// section, generates an Id and sets the Authoritative (AA)
// bit to true.
func (dns *Msg) SetNotify(z string) *Msg {
dns.Opcode = OpcodeNotify
dns.Authoritative = true
dns.Id = Id()
dns.Question = make([]Question, 1)
dns.Question[0] = Question{z, TypeSOA, ClassINET}
return dns
}
// SetRcode creates an error message suitable for the request.
func (dns *Msg) SetRcode(request *Msg, rcode int) *Msg {
dns.SetReply(request)
dns.Rcode = rcode
return dns
}
// SetRcodeFormatError creates a message with FormError set.
func (dns *Msg) SetRcodeFormatError(request *Msg) *Msg {
dns.Rcode = RcodeFormatError
dns.Opcode = OpcodeQuery
dns.Response = true
dns.Authoritative = false
dns.Id = request.Id
return dns
}
// SetUpdate makes the message a dynamic update message. It
// sets the ZONE section to: z, TypeSOA, ClassINET.
func (dns *Msg) SetUpdate(z string) *Msg {
dns.Id = Id()
dns.Response = false
dns.Opcode = OpcodeUpdate
dns.Compress = false // BIND9 cannot handle compression
dns.Question = make([]Question, 1)
dns.Question[0] = Question{z, TypeSOA, ClassINET}
return dns
}
// SetIxfr creates message for requesting an IXFR.
func (dns *Msg) SetIxfr(z string, serial uint32, ns, mbox string) *Msg {
dns.Id = Id()
dns.Question = make([]Question, 1)
dns.Ns = make([]RR, 1)
s := new(SOA)
s.Hdr = RR_Header{z, TypeSOA, ClassINET, defaultTtl, 0}
s.Serial = serial
s.Ns = ns
s.Mbox = mbox
dns.Question[0] = Question{z, TypeIXFR, ClassINET}
dns.Ns[0] = s
return dns
}
// SetAxfr creates message for requesting an AXFR.
func (dns *Msg) SetAxfr(z string) *Msg {
dns.Id = Id()
dns.Question = make([]Question, 1)
dns.Question[0] = Question{z, TypeAXFR, ClassINET}
return dns
}
// SetTsig appends a TSIG RR to the message.
// This is only a skeleton TSIG RR that is added as the last RR in the
// additional section. The TSIG is calculated when the message is being send.
func (dns *Msg) SetTsig(z, algo string, fudge uint16, timesigned int64) *Msg {
t := new(TSIG)
t.Hdr = RR_Header{z, TypeTSIG, ClassANY, 0, 0}
t.Algorithm = algo
t.Fudge = fudge
t.TimeSigned = uint64(timesigned)
t.OrigId = dns.Id
dns.Extra = append(dns.Extra, t)
return dns
}
// SetEdns0 appends a EDNS0 OPT RR to the message.
// TSIG should always the last RR in a message.
func (dns *Msg) SetEdns0(udpsize uint16, do bool) *Msg {
e := new(OPT)
e.Hdr.Name = "."
e.Hdr.Rrtype = TypeOPT
e.SetUDPSize(udpsize)
if do {
e.SetDo()
}
dns.Extra = append(dns.Extra, e)
return dns
}
// IsTsig checks if the message has a TSIG record as the last record
// in the additional section. It returns the TSIG record found or nil.
func (dns *Msg) IsTsig() *TSIG {
if len(dns.Extra) > 0 {
if dns.Extra[len(dns.Extra)-1].Header().Rrtype == TypeTSIG {
return dns.Extra[len(dns.Extra)-1].(*TSIG)
}
}
return nil
}
// IsEdns0 checks if the message has a EDNS0 (OPT) record, any EDNS0
// record in the additional section will do. It returns the OPT record
// found or nil.
func (dns *Msg) IsEdns0() *OPT {
// RFC 6891, Section 6.1.1 allows the OPT record to appear
// anywhere in the additional record section, but it's usually at
// the end so start there.
for i := len(dns.Extra) - 1; i >= 0; i-- {
if dns.Extra[i].Header().Rrtype == TypeOPT {
return dns.Extra[i].(*OPT)
}
}
return nil
}
// popEdns0 is like IsEdns0, but it removes the record from the message.
func (dns *Msg) popEdns0() *OPT {
// RFC 6891, Section 6.1.1 allows the OPT record to appear
// anywhere in the additional record section, but it's usually at
// the end so start there.
for i := len(dns.Extra) - 1; i >= 0; i-- {
if dns.Extra[i].Header().Rrtype == TypeOPT {
opt := dns.Extra[i].(*OPT)
dns.Extra = append(dns.Extra[:i], dns.Extra[i+1:]...)
return opt
}
}
return nil
}
// IsDomainName checks if s is a valid domain name, it returns the number of
// labels and true, when a domain name is valid. Note that non fully qualified
// domain name is considered valid, in this case the last label is counted in
// the number of labels. When false is returned the number of labels is not
// defined. Also note that this function is extremely liberal; almost any
// string is a valid domain name as the DNS is 8 bit protocol. It checks if each
// label fits in 63 characters and that the entire name will fit into the 255
// octet wire format limit.
func IsDomainName(s string) (labels int, ok bool) {
// XXX: The logic in this function was copied from packDomainName and
// should be kept in sync with that function.
const lenmsg = 256
if len(s) == 0 { // Ok, for instance when dealing with update RR without any rdata.
return 0, false
}
s = Fqdn(s)
// Each dot ends a segment of the name. Except for escaped dots (\.), which
// are normal dots.
var (
off int
begin int
wasDot bool
)
for i := 0; i < len(s); i++ {
switch s[i] {
case '\\':
if off+1 > lenmsg {
return labels, false
}
// check for \DDD
if i+3 < len(s) && isDigit(s[i+1]) && isDigit(s[i+2]) && isDigit(s[i+3]) {
i += 3
begin += 3
} else {
i++
begin++
}
wasDot = false
case '.':
if wasDot {
// two dots back to back is not legal
return labels, false
}
wasDot = true
labelLen := i - begin
if labelLen >= 1<<6 { // top two bits of length must be clear
return labels, false
}
// off can already (we're in a loop) be bigger than lenmsg
// this happens when a name isn't fully qualified
off += 1 + labelLen
if off > lenmsg {
return labels, false
}
labels++
begin = i + 1
default:
wasDot = false
}
}
return labels, true
}
// IsSubDomain checks if child is indeed a child of the parent. If child and parent
// are the same domain true is returned as well.
func IsSubDomain(parent, child string) bool {
// Entire child is contained in parent
return CompareDomainName(parent, child) == CountLabel(parent)
}
// IsMsg sanity checks buf and returns an error if it isn't a valid DNS packet.
// The checking is performed on the binary payload.
func IsMsg(buf []byte) error {
// Header
if len(buf) < headerSize {
return errors.New("dns: bad message header")
}
// Header: Opcode
// TODO(miek): more checks here, e.g. check all header bits.
return nil
}
// IsFqdn checks if a domain name is fully qualified.
func IsFqdn(s string) bool {
s2 := strings.TrimSuffix(s, ".")
if s == s2 {
return false
}
i := strings.LastIndexFunc(s2, func(r rune) bool {
return r != '\\'
})
// Test whether we have an even number of escape sequences before
// the dot or none.
return (len(s2)-i)%2 != 0
}
// IsRRset checks if a set of RRs is a valid RRset as defined by RFC 2181.
// This means the RRs need to have the same type, name, and class. Returns true
// if the RR set is valid, otherwise false.
func IsRRset(rrset []RR) bool {
if len(rrset) == 0 {
return false
}
if len(rrset) == 1 {
return true
}
rrHeader := rrset[0].Header()
rrType := rrHeader.Rrtype
rrClass := rrHeader.Class
rrName := rrHeader.Name
for _, rr := range rrset[1:] {
curRRHeader := rr.Header()
if curRRHeader.Rrtype != rrType || curRRHeader.Class != rrClass || curRRHeader.Name != rrName {
// Mismatch between the records, so this is not a valid rrset for
//signing/verifying
return false
}
}
return true
}
// Fqdn return the fully qualified domain name from s.
// If s is already fully qualified, it behaves as the identity function.
func Fqdn(s string) string {
if IsFqdn(s) {
return s
}
return s + "."
}
// CanonicalName returns the domain name in canonical form. A name in canonical
// form is lowercase and fully qualified. See Section 6.2 in RFC 4034.
func CanonicalName(s string) string {
return strings.ToLower(Fqdn(s))
}
// Copied from the official Go code.
// ReverseAddr returns the in-addr.arpa. or ip6.arpa. hostname of the IP
// address suitable for reverse DNS (PTR) record lookups or an error if it fails
// to parse the IP address.
func ReverseAddr(addr string) (arpa string, err error) {
ip := net.ParseIP(addr)
if ip == nil {
return "", &Error{err: "unrecognized address: " + addr}
}
if v4 := ip.To4(); v4 != nil {
buf := make([]byte, 0, net.IPv4len*4+len("in-addr.arpa."))
// Add it, in reverse, to the buffer
for i := len(v4) - 1; i >= 0; i-- {
buf = strconv.AppendInt(buf, int64(v4[i]), 10)
buf = append(buf, '.')
}
// Append "in-addr.arpa." and return (buf already has the final .)
buf = append(buf, "in-addr.arpa."...)
return string(buf), nil
}
// Must be IPv6
buf := make([]byte, 0, net.IPv6len*4+len("ip6.arpa."))
// Add it, in reverse, to the buffer
for i := len(ip) - 1; i >= 0; i-- {
v := ip[i]
buf = append(buf, hexDigit[v&0xF], '.', hexDigit[v>>4], '.')
}
// Append "ip6.arpa." and return (buf already has the final .)
buf = append(buf, "ip6.arpa."...)
return string(buf), nil
}
// String returns the string representation for the type t.
func (t Type) String() string {
if t1, ok := TypeToString[uint16(t)]; ok {
return t1
}
return "TYPE" + strconv.Itoa(int(t))
}
// String returns the string representation for the class c.
func (c Class) String() string {
if s, ok := ClassToString[uint16(c)]; ok {
// Only emit mnemonics when they are unambiguous, specially ANY is in both.
if _, ok := StringToType[s]; !ok {
return s
}
}
return "CLASS" + strconv.Itoa(int(c))
}
// String returns the string representation for the name n.
func (n Name) String() string {
return sprintName(string(n))
}