text: # Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license
  
  # Copyright (C) 2010, 2011 Nominum, Inc.
  #
  # Permission to use, copy, modify, and distribute this software and its
  # documentation for any purpose with or without fee is hereby granted,
  # provided that the above copyright notice and this permission notice
  # appear in all copies.
  #
  # THE SOFTWARE IS PROVIDED "AS IS" AND NOMINUM DISCLAIMS ALL WARRANTIES
  # WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  # MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NOMINUM BE LIABLE FOR
  # ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  # WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  # ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
  # OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  
  import struct
  import binascii
  
  import dns.dnssectypes
  import dns.immutable
  import dns.rdata
  import dns.rdatatype
  
  
  @dns.immutable.immutable
  class DSBase(dns.rdata.Rdata):
  
      """Base class for rdata that is like a DS record"""
  
      __slots__ = ['key_tag', 'algorithm', 'digest_type', 'digest']
  
      # Digest types registry: https://www.iana.org/assignments/ds-rr-types/ds-rr-types.xhtml
      _digest_length_by_type = {
          1: 20,  # SHA-1, RFC 3658 Sec. 2.4
          2: 32,  # SHA-256, RFC 4509 Sec. 2.2
          3: 32,  # GOST R 34.11-94, RFC 5933 Sec. 4 in conjunction with RFC 4490 Sec. 2.1
          4: 48,  # SHA-384, RFC 6605 Sec. 2
      }
  
      def __init__(self, rdclass, rdtype, key_tag, algorithm, digest_type,
                   digest):
          super().__init__(rdclass, rdtype)
          self.key_tag = self._as_uint16(key_tag)
          self.algorithm = dns.dnssectypes.Algorithm.make(algorithm)
          self.digest_type = self._as_uint8(digest_type)
          self.digest = self._as_bytes(digest)
          try:
              if len(self.digest) != self._digest_length_by_type[self.digest_type]:
                  raise ValueError('digest length inconsistent with digest type')
          except KeyError:
              if self.digest_type == 0:  # reserved, RFC 3658 Sec. 2.4
                  raise ValueError('digest type 0 is reserved')
  
      def to_text(self, origin=None, relativize=True, **kw):
          kw = kw.copy()
          chunksize = kw.pop('chunksize', 128)
          return '%d %d %d %s' % (self.key_tag, self.algorithm,
                                  self.digest_type,
                                  dns.rdata._hexify(self.digest,
                                                    chunksize=chunksize,
                                                    **kw))
  
      @classmethod
      def from_text(cls, rdclass, rdtype, tok, origin=None, relativize=True,
                    relativize_to=None):
          key_tag = tok.get_uint16()
          algorithm = tok.get_string()
          digest_type = tok.get_uint8()
          digest = tok.concatenate_remaining_identifiers().encode()
          digest = binascii.unhexlify(digest)
          return cls(rdclass, rdtype, key_tag, algorithm, digest_type,
                     digest)
  
      def _to_wire(self, file, compress=None, origin=None, canonicalize=False):
          header = struct.pack("!HBB", self.key_tag, self.algorithm,
                               self.digest_type)
          file.write(header)
          file.write(self.digest)
  
      @classmethod
      def from_wire_parser(cls, rdclass, rdtype, parser, origin=None):
          header = parser.get_struct("!HBB")
          digest = parser.get_remaining()
          return cls(rdclass, rdtype, header[0], header[1], header[2], digest)
  