Source Code for Module dns.rdataclass

  1  # Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license 
  2   
  3  # Copyright (C) 2001-2017 Nominum, Inc. 
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 17   
 18  """DNS Rdata Classes.""" 
 19   
 20  import re 
 21   
 22  import dns.exception 
 23   
 24  RESERVED0 = 0 
 25  IN = 1 
 26  CH = 3 
 27  HS = 4 
 28  NONE = 254 
 29  ANY = 255 
 30   
 31  _by_text = { 
 32      'RESERVED0': RESERVED0, 
 33      'IN': IN, 
 34      'CH': CH, 
 35      'HS': HS, 
 36      'NONE': NONE, 
 37      'ANY': ANY 
 38  } 
 39   
 40  # We construct the inverse mapping programmatically to ensure that we 
 41  # cannot make any mistakes (e.g. omissions, cut-and-paste errors) that 
 42  # would cause the mapping not to be true inverse. 
 43   
 44  _by_value = {y: x for x, y in _by_text.items()} 
 45   
 46  # Now that we've built the inverse map, we can add class aliases to 
 47  # the _by_text mapping. 
 48   
 49  _by_text.update({ 
 50      'INTERNET': IN, 
 51      'CHAOS': CH, 
 52      'HESIOD': HS 
 53  }) 
 54   
 55  _metaclasses = { 
 56      NONE: True, 
 57      ANY: True 
 58  } 
 59   
 60  _unknown_class_pattern = re.compile('CLASS([0-9]+)$', re.I) 
 61   
 62   
 63 -class UnknownRdataclass(dns.exception.DNSException): 
 64      """A DNS class is unknown.""" 
 65   
 66   
 67 -def from_text(text): 
 68      """Convert text into a DNS rdata class value. 
 69   
 70      The input text can be a defined DNS RR class mnemonic or 
 71      instance of the DNS generic class syntax. 
 72   
 73      For example, "IN" and "CLASS1" will both result in a value of 1. 
 74   
 75      Raises ``dns.rdatatype.UnknownRdataclass`` if the class is unknown. 
 76   
 77      Raises ``ValueError`` if the rdata class value is not >= 0 and <= 65535. 
 78   
 79      Returns an ``int``. 
 80      """ 
 81   
 82      value = _by_text.get(text.upper()) 
 83      if value is None: 
 84          match = _unknown_class_pattern.match(text) 
 85          if match is None: 
 86              raise UnknownRdataclass 
 87          value = int(match.group(1)) 
 88          if value < 0 or value > 65535: 
 89              raise ValueError("class must be between >= 0 and <= 65535") 
 90      return value 
 91   
 92   
 93 -def to_text(value): 
 94      """Convert a DNS rdata type value to text. 
 95   
 96      If the value has a known mnemonic, it will be used, otherwise the 
 97      DNS generic class syntax will be used. 
 98   
 99      Raises ``ValueError`` if the rdata class value is not >= 0 and <= 65535. 
100   
101      Returns a ``str``. 
102      """ 
103   
104      if value < 0 or value > 65535: 
105          raise ValueError("class must be between >= 0 and <= 65535") 
106      text = _by_value.get(value) 
107      if text is None: 
108          text = 'CLASS' + repr(value) 
109      return text 
110   
111   
112 -def is_metaclass(rdclass): 
113      """True if the specified class is a metaclass. 
114   
115      The currently defined metaclasses are ANY and NONE. 
116   
117      *rdclass* is an ``int``. 
118      """ 
119   
120      if rdclass in _metaclasses: 
121          return True 
122      return False 
123