lib/dnspython/dns/opcode.py

   1 # Copyright (C) 2001-2007, 2009-2011 Nominum, Inc.
   2 #
   3 # Permission to use, copy, modify, and distribute this software and its
   4 # documentation for any purpose with or without fee is hereby granted,
   5 # provided that the above copyright notice and this permission notice
   6 # appear in all copies.
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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
  10 # MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NOMINUM BE LIABLE FOR
  11 # ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  12 # WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  13 # ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
  14 # OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  15
  16 """DNS Opcodes."""
  17
  18 import dns.exception
  19
  20 QUERY = 0
  21 IQUERY = 1
  22 STATUS = 2
  23 NOTIFY = 4
  24 UPDATE = 5
  25
  26 _by_text = {
  27     'QUERY' : QUERY,
  28     'IQUERY' : IQUERY,
  29     'STATUS' : STATUS,
  30     'NOTIFY' : NOTIFY,
  31     'UPDATE' : UPDATE
  32 }
  33
  34 # We construct the inverse mapping programmatically to ensure that we
  35 # cannot make any mistakes (e.g. omissions, cut-and-paste errors) that
  36 # would cause the mapping not to be true inverse.
  37
  38 _by_value = dict([(y, x) for x, y in _by_text.iteritems()])
  39
  40
  41 class UnknownOpcode(dns.exception.DNSException):
  42     """Raised if an opcode is unknown."""
  43     pass
  44
  45 def from_text(text):
  46     """Convert text into an opcode.
  47
  48     @param text: the textual opcode
  49     @type text: string
  50     @raises UnknownOpcode: the opcode is unknown
  51     @rtype: int
  52     """
  53
  54     if text.isdigit():
  55         value = int(text)
  56         if value >= 0 and value <= 15:
  57             return value
  58     value = _by_text.get(text.upper())
  59     if value is None:
  60         raise UnknownOpcode
  61     return value
  62
  63 def from_flags(flags):
  64     """Extract an opcode from DNS message flags.
  65
  66     @param flags: int
  67     @rtype: int
  68     """
  69
  70     return (flags & 0x7800) >> 11
  71
  72 def to_flags(value):
  73     """Convert an opcode to a value suitable for ORing into DNS message
  74     flags.
  75     @rtype: int
  76     """
  77
  78     return (value << 11) & 0x7800
  79
  80 def to_text(value):
  81     """Convert an opcode to text.
  82
  83     @param value: the opcdoe
  84     @type value: int
  85     @raises UnknownOpcode: the opcode is unknown
  86     @rtype: string
  87     """
  88
  89     text = _by_value.get(value)
  90     if text is None:
  91         text = str(value)
  92     return text
  93
  94 def is_update(flags):
  95     """True if the opcode in flags is UPDATE.
  96
  97     @param flags: DNS flags
  98     @type flags: int
  99     @rtype: bool
 100     """
 101
 102     if (from_flags(flags) == UPDATE):
 103         return True
 104     return False