Source Code for Module dns.wiredata

 1  # Copyright (C) 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. 
 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 Wire Data Helper""" 
17   
18   
19  import dns.exception 
20  from ._compat import binary_type, string_types 
21   
22  # Figure out what constant python passes for an unspecified slice bound. 
23  # It's supposed to be sys.maxint, yet on 64-bit windows sys.maxint is 2^31 - 1 
24  # but Python uses 2^63 - 1 as the constant.  Rather than making pointless 
25  # extra comparisons, duplicating code, or weakening WireData, we just figure 
26  # out what constant Python will use. 
27   
28   
29 -class _SliceUnspecifiedBound(str): 
30   
31 -    def __getslice__(self, i, j): 
32          return j 
33   
34  _unspecified_bound = _SliceUnspecifiedBound('')[1:] 
35   
36   
37 -class WireData(binary_type): 
38      # WireData is a string with stricter slicing 
39   
40 -    def __getitem__(self, key): 
41          try: 
42              if isinstance(key, slice): 
43                  return WireData(super(WireData, self).__getitem__(key)) 
44              return bytearray(self.unwrap())[key] 
45          except IndexError: 
46              raise dns.exception.FormError 
47   
48 -    def __getslice__(self, i, j): 
49          try: 
50              if j == _unspecified_bound: 
51                  # handle the case where the right bound is unspecified 
52                  j = len(self) 
53              if i < 0 or j < 0: 
54                  raise dns.exception.FormError 
55              # If it's not an empty slice, access left and right bounds 
56              # to make sure they're valid 
57              if i != j: 
58                  super(WireData, self).__getitem__(i) 
59                  super(WireData, self).__getitem__(j - 1) 
60              return WireData(super(WireData, self).__getslice__(i, j)) 
61          except IndexError: 
62              raise dns.exception.FormError 
63   
64 -    def __iter__(self): 
65          i = 0 
66          while 1: 
67              try: 
68                  yield self[i] 
69                  i += 1 
70              except dns.exception.FormError: 
71                  raise StopIteration 
72   
73 -    def unwrap(self): 
74          return binary_type(self) 
75   
76   
77 -def maybe_wrap(wire): 
78      if isinstance(wire, WireData): 
79          return wire 
80      elif isinstance(wire, binary_type): 
81          return WireData(wire) 
82      elif isinstance(wire, string_types): 
83          return WireData(wire.encode()) 
84      raise ValueError("unhandled type %s" % type(wire)) 
85