Package dns :: Module rdataclass |
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# Source Code for Module dns.rdataclass

      1  # Copyright (C) 2001-2007, 2009-2011 Nominum, Inc.
      2  #
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      4  # documentation for any purpose with or without fee is hereby granted,
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      8  # THE SOFTWARE IS PROVIDED "AS IS" AND NOMINUM DISCLAIMS ALL WARRANTIES
      9  # WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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     14  # OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
     15
     16  """DNS Rdata Classes.
     17
     18  @var _by_text: The rdata class textual name to value mapping
     19  @type _by_text: dict
     20  @var _by_value: The rdata class value to textual name mapping
     21  @type _by_value: dict
     22  @var _metaclasses: If an rdataclass is a metaclass, there will be a mapping
     23  whose key is the rdatatype value and whose value is True in this dictionary.
     24  @type _metaclasses: dict"""
     25
     26  import re
     27
     28  import dns.exception
     29
     30  RESERVED0 = 0
     31  IN = 1
     32  CH = 3
     33  HS = 4
     34  NONE = 254
     35  ANY = 255
     36
     37  _by_text = {
     38      'RESERVED0': RESERVED0,
     39      'IN': IN,
     40      'CH': CH,
     41      'HS': HS,
     42      'NONE': NONE,
     43      'ANY': ANY
     44  }
     45
     46  # We construct the inverse mapping programmatically to ensure that we
     47  # cannot make any mistakes (e.g. omissions, cut-and-paste errors) that
     48  # would cause the mapping not to be true inverse.
     49
     50  _by_value = dict((y, x) for x, y in _by_text.items())
     51
     52  # Now that we've built the inverse map, we can add class aliases to
     53  # the _by_text mapping.
     54
     55  _by_text.update({
     56      'INTERNET': IN,
     57      'CHAOS': CH,
     58      'HESIOD': HS
     59  })
     60
     61  _metaclasses = {
     62      NONE: True,
     63      ANY: True
     64  }
     65
     66  _unknown_class_pattern = re.compile('CLASS([0-9]+)$', re.I)
     67
     68
     69 -class UnknownRdataclass(dns.exception.DNSException):
     70
     71      """A DNS class is unknown."""
     72
     73
     74 -def from_text(text):
     75      """Convert text into a DNS rdata class value.
     76      @param text: the text
     77      @type text: string
     78      @rtype: int
     79      @raises dns.rdataclass.UnknownRdataclass: the class is unknown
     80      @raises ValueError: the rdata class value is not >= 0 and <= 65535
     81      """
     82
     83      value = _by_text.get(text.upper())
     84      if value is None:
     85          match = _unknown_class_pattern.match(text)
     86          if match is None:
     87              raise UnknownRdataclass
     88          value = int(match.group(1))
     89          if value < 0 or value > 65535:
     90              raise ValueError("class must be between >= 0 and <= 65535")
     91      return value
     92
     93
     94 -def to_text(value):
     95      """Convert a DNS rdata class to text.
     96      @param value: the rdata class value
     97      @type value: int
     98      @rtype: string
     99      @raises ValueError: the rdata class value is not >= 0 and <= 65535
    100      """
    101
    102      if value < 0 or value > 65535:
    103          raise ValueError("class must be between >= 0 and <= 65535")
    104      text = _by_value.get(value)
    105      if text is None:
    106          text = 'CLASS' + repr(value)
    107      return text
    108
    109
    110 -def is_metaclass(rdclass):
    111      """True if the class is a metaclass.
    112      @param rdclass: the rdata class
    113      @type rdclass: int
    114      @rtype: bool"""
    115
    116      if rdclass in _metaclasses:
    117          return True
    118      return False
    119