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1# Copyright (C) 2001-2007, 2009, 2010 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.
7#
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
18import dns.exception
19
20QUERY = 0
21IQUERY = 1
22STATUS = 2
23NOTIFY = 4
24UPDATE = 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
41class UnknownOpcode(dns.exception.DNSException):
42    """Raised if an opcode is unknown."""
43    pass
44
45def 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
63def 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
72def 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
80def 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
94def 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
105