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package dns
import (
"encoding/hex"
"strconv"
)
const (
year68 = 1 << 31 // For RFC1982 (Serial Arithmetic) calculations in 32 bits.
defaultTtl = 3600 // Default internal TTL.
// DefaultMsgSize is the standard default for messages larger than 512 bytes.
DefaultMsgSize = 4096
// MinMsgSize is the minimal size of a DNS packet.
MinMsgSize = 512
// MaxMsgSize is the largest possible DNS packet.
MaxMsgSize = 65535
)
// Error represents a DNS error.
type Error struct{ err string }
func (e *Error) Error() string {
if e == nil {
return "dns: <nil>"
}
return "dns: " + e.err
}
// An RR represents a resource record.
type RR interface {
// Header returns the header of an resource record. The header contains
// everything up to the rdata.
Header() *RR_Header
// String returns the text representation of the resource record.
String() string
// copy returns a copy of the RR
copy() RR
// len returns the length (in octets) of the compressed or uncompressed RR in wire format.
//
// If compression is nil, the uncompressed size will be returned, otherwise the compressed
// size will be returned and domain names will be added to the map for future compression.
len(off int, compression map[string]struct{}) int
// pack packs the records RDATA into wire format. The header will
// already have been packed into msg.
pack(msg []byte, off int, compression compressionMap, compress bool) (off1 int, err error)
// unpack unpacks an RR from wire format.
//
// This will only be called on a new and empty RR type with only the header populated. It
// will only be called if the record's RDATA is non-empty.
unpack(msg []byte, off int) (off1 int, err error)
// parse parses an RR from zone file format.
//
// This will only be called on a new and empty RR type with only the header populated.
parse(c *zlexer, origin string) *ParseError
// isDuplicate returns whether the two RRs are duplicates.
isDuplicate(r2 RR) bool
}
// RR_Header is the header all DNS resource records share.
type RR_Header struct {
Name string `dns:"cdomain-name"`
Rrtype uint16
Class uint16
Ttl uint32
Rdlength uint16 // Length of data after header.
}
// Header returns itself. This is here to make RR_Header implements the RR interface.
func (h *RR_Header) Header() *RR_Header { return h }
// Just to implement the RR interface.
func (h *RR_Header) copy() RR { return nil }
func (h *RR_Header) String() string {
var s string
if h.Rrtype == TypeOPT {
s = ";"
// and maybe other things
}
s += sprintName(h.Name) + "\t"
s += strconv.FormatInt(int64(h.Ttl), 10) + "\t"
s += Class(h.Class).String() + "\t"
s += Type(h.Rrtype).String() + "\t"
return s
}
func (h *RR_Header) len(off int, compression map[string]struct{}) int {
l := domainNameLen(h.Name, off, compression, true)
l += 10 // rrtype(2) + class(2) + ttl(4) + rdlength(2)
return l
}
func (h *RR_Header) pack(msg []byte, off int, compression compressionMap, compress bool) (off1 int, err error) {
// RR_Header has no RDATA to pack.
return off, nil
}
func (h *RR_Header) unpack(msg []byte, off int) (int, error) {
panic("dns: internal error: unpack should never be called on RR_Header")
}
func (h *RR_Header) parse(c *zlexer, origin string) *ParseError {
panic("dns: internal error: parse should never be called on RR_Header")
}
// ToRFC3597 converts a known RR to the unknown RR representation from RFC 3597.
func (rr *RFC3597) ToRFC3597(r RR) error {
buf := make([]byte, Len(r))
headerEnd, off, err := packRR(r, buf, 0, compressionMap{}, false)
if err != nil {
return err
}
buf = buf[:off]
*rr = RFC3597{Hdr: *r.Header()}
rr.Hdr.Rdlength = uint16(off - headerEnd)
if noRdata(rr.Hdr) {
return nil
}
_, err = rr.unpack(buf, headerEnd)
return err
}
// fromRFC3597 converts an unknown RR representation from RFC 3597 to the known RR type.
func (rr *RFC3597) fromRFC3597(r RR) error {
hdr := r.Header()
*hdr = rr.Hdr
// Can't overflow uint16 as the length of Rdata is validated in (*RFC3597).parse.
// We can only get here when rr was constructed with that method.
hdr.Rdlength = uint16(hex.DecodedLen(len(rr.Rdata)))
if noRdata(*hdr) {
// Dynamic update.
return nil
}
// rr.pack requires an extra allocation and a copy so we just decode Rdata
// manually, it's simpler anyway.
msg, err := hex.DecodeString(rr.Rdata)
if err != nil {
return err
}
_, err = r.unpack(msg, 0)
return err
}
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