text: package dns
  
  import (
  	"errors"
  	"net"
  	"strconv"
  )
  
  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 {
  	// EDNS0 is at the end of the additional section, start there.
  	// We might want to change this to *only* look at the last two
  	// records. So we see TSIG and/or OPT - this a slightly bigger
  	// change though.
  	for i := len(dns.Extra) - 1; i >= 0; i-- {
  		if dns.Extra[i].Header().Rrtype == TypeOPT {
  			return dns.Extra[i].(*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, but there is no length check for the entire
  // string s. I.e.  a domain name longer than 255 characters is considered valid.
  func IsDomainName(s string) (labels int, ok bool) {
  	_, labels, err := packDomainName(s, nil, 0, nil, false)
  	return labels, err == nil
  }
  
  // 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) < 12 {
  		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 {
  	l := len(s)
  	if l == 0 {
  		return false
  	}
  	return s[l-1] == '.'
  }
  
  // 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 + "."
  }
  
  // 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 ip.To4() != nil {
  		return strconv.Itoa(int(ip[15])) + "." + strconv.Itoa(int(ip[14])) + "." + strconv.Itoa(int(ip[13])) + "." +
  			strconv.Itoa(int(ip[12])) + ".in-addr.arpa.", nil
  	}
  	// Must be IPv6
  	buf := make([]byte, 0, len(ip)*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])
  		buf = append(buf, '.')
  		buf = append(buf, hexDigit[v>>4])
  		buf = append(buf, '.')
  	}
  	// 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, specically 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))
  }
  