bridgedb/parse/__init__.py

   1 # -*- coding: utf-8 -*-
   2 #
   3 # This file is part of BridgeDB, a Tor bridge distribution system.
   4 #
   5 # :authors: Isis Lovecruft 0xA3ADB67A2CDB8B35 <isis@torproject.org>
   6 #           please also see AUTHORS file
   7 # :copyright: (c) 2013 Isis Lovecruft
   8 #             (c) 2007-2013, The Tor Project, Inc.
   9 #             (c) 2007-2013, all entities within the AUTHORS file
  10 # :license: 3-clause BSD, see included LICENSE for information
  11
  12 '''Package containing modules for parsing data.
  13
  14 .. py:module:: bridgedb.parse
  15     :synopsis: Package containing modules for parsing data.
  16 '''
  17
  18 from __future__ import absolute_import
  19 from __future__ import print_function
  20 from __future__ import unicode_literals
  21
  22 import binascii
  23
  24
  25 class InvalidBase64(ValueError):
  26     """Raised if parsing or decoding cannot continue due to invalid base64."""
  27
  28
  29 def padBase64(b64string):
  30     """Re-add any stripped equals sign character padding to a b64 string.
  31
  32     :param string b64string: A base64-encoded string which might have had its
  33         trailing equals sign (``=``) padding removed.
  34     :raises ValueError: if there was any error while manipulating the string.
  35     :returns: A properly-padded (according to the base64 spec: :rfc:`4648`)
  36         string.
  37     """
  38     addchars  = 0
  39     try:
  40         b64string = b64string.strip()
  41         remainder = len(b64string) % 4
  42         if 2 <= remainder <= 3:
  43             addchars = 4 - remainder
  44     except AttributeError as error:
  45         raise ValueError(error)
  46     else:
  47         if not addchars:
  48             raise ValueError("Invalid base64-encoded string: %r" % b64string)
  49         b64string += '=' * addchars
  50
  51     return b64string
  52
  53 def parseUnpaddedBase64(field):
  54     """Parse an unpadded, base64-encoded field.
  55
  56     The **field** will be re-padded, if need be, and then base64 decoded.
  57
  58     :param str field: Should be some base64-encoded thing, with any trailing
  59         ``=``-characters removed.
  60     :raises InvalidBase64: if there is an error in either unpadding or decoding
  61         **field**.
  62     :rtype: str
  63     :returns: The base64-decoded **field**.
  64     """
  65     if field.endswith('='):
  66         raise InvalidBase64("Unpadded, base64-encoded networkstatus field "\
  67                             "must not end with '=': %r" % field)
  68
  69     try:
  70         paddedField = padBase64(field)  # Add the trailing equals sign back in
  71     except ValueError as error:
  72         raise InvalidBase64(error)
  73
  74     debasedField = binascii.a2b_base64(paddedField)
  75     if not debasedField:
  76         raise InvalidBase64("Base64-encoded networkstatus field %r is invalid!"
  77                             % field)
  78
  79     return debasedField