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