1# Protocol Buffers - Google's data interchange format
2# Copyright 2008 Google Inc.  All rights reserved.
3# https://developers.google.com/protocol-buffers/
4#
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6# modification, are permitted provided that the following conditions are
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8#
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18#
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29# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30
31#PY25 compatible for GAE.
32#
33"""Encoding related utilities."""
34
35import re
36import sys  ##PY25
37
38# Lookup table for utf8
39_cescape_utf8_to_str = [chr(i) for i in xrange(0, 256)]
40_cescape_utf8_to_str[9] = r'\t'  # optional escape
41_cescape_utf8_to_str[10] = r'\n'  # optional escape
42_cescape_utf8_to_str[13] = r'\r'  # optional escape
43_cescape_utf8_to_str[39] = r"\'"  # optional escape
44
45_cescape_utf8_to_str[34] = r'\"'  # necessary escape
46_cescape_utf8_to_str[92] = r'\\'  # necessary escape
47
48# Lookup table for non-utf8, with necessary escapes at (o >= 127 or o < 32)
49_cescape_byte_to_str = ([r'\%03o' % i for i in xrange(0, 32)] +
50                        [chr(i) for i in xrange(32, 127)] +
51                        [r'\%03o' % i for i in xrange(127, 256)])
52_cescape_byte_to_str[9] = r'\t'  # optional escape
53_cescape_byte_to_str[10] = r'\n'  # optional escape
54_cescape_byte_to_str[13] = r'\r'  # optional escape
55_cescape_byte_to_str[39] = r"\'"  # optional escape
56
57_cescape_byte_to_str[34] = r'\"'  # necessary escape
58_cescape_byte_to_str[92] = r'\\'  # necessary escape
59
60
61def CEscape(text, as_utf8):
62  """Escape a bytes string for use in an ascii protocol buffer.
63
64  text.encode('string_escape') does not seem to satisfy our needs as it
65  encodes unprintable characters using two-digit hex escapes whereas our
66  C++ unescaping function allows hex escapes to be any length.  So,
67  "\0011".encode('string_escape') ends up being "\\x011", which will be
68  decoded in C++ as a single-character string with char code 0x11.
69
70  Args:
71    text: A byte string to be escaped
72    as_utf8: Specifies if result should be returned in UTF-8 encoding
73  Returns:
74    Escaped string
75  """
76  # PY3 hack: make Ord work for str and bytes:
77  # //platforms/networking/data uses unicode here, hence basestring.
78  Ord = ord if isinstance(text, basestring) else lambda x: x
79  if as_utf8:
80    return ''.join(_cescape_utf8_to_str[Ord(c)] for c in text)
81  return ''.join(_cescape_byte_to_str[Ord(c)] for c in text)
82
83
84_CUNESCAPE_HEX = re.compile(r'(\\+)x([0-9a-fA-F])(?![0-9a-fA-F])')
85_cescape_highbit_to_str = ([chr(i) for i in range(0, 127)] +
86                           [r'\%03o' % i for i in range(127, 256)])
87
88
89def CUnescape(text):
90  """Unescape a text string with C-style escape sequences to UTF-8 bytes."""
91
92  def ReplaceHex(m):
93    # Only replace the match if the number of leading back slashes is odd. i.e.
94    # the slash itself is not escaped.
95    if len(m.group(1)) & 1:
96      return m.group(1) + 'x0' + m.group(2)
97    return m.group(0)
98
99  # This is required because the 'string_escape' encoding doesn't
100  # allow single-digit hex escapes (like '\xf').
101  result = _CUNESCAPE_HEX.sub(ReplaceHex, text)
102
103  if sys.version_info[0] < 3:  ##PY25
104##!PY25  if str is bytes:  # PY2
105    return result.decode('string_escape')
106  result = ''.join(_cescape_highbit_to_str[ord(c)] for c in result)
107  return (result.encode('ascii')  # Make it bytes to allow decode.
108          .decode('unicode_escape')
109          # Make it bytes again to return the proper type.
110          .encode('raw_unicode_escape'))
111