File size: 8,505 Bytes
065fee7 |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 |
######################## BEGIN LICENSE BLOCK ########################
#
# Contributor(s):
# Jason Zavaglia
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
# 02110-1301 USA
######################### END LICENSE BLOCK #########################
from typing import List, Union
from .charsetprober import CharSetProber
from .enums import ProbingState
class UTF1632Prober(CharSetProber):
"""
This class simply looks for occurrences of zero bytes, and infers
whether the file is UTF16 or UTF32 (low-endian or big-endian)
For instance, files looking like ( \0 \0 \0 [nonzero] )+
have a good probability to be UTF32BE. Files looking like ( \0 [nonzero] )+
may be guessed to be UTF16BE, and inversely for little-endian varieties.
"""
# how many logical characters to scan before feeling confident of prediction
MIN_CHARS_FOR_DETECTION = 20
# a fixed constant ratio of expected zeros or non-zeros in modulo-position.
EXPECTED_RATIO = 0.94
def __init__(self) -> None:
super().__init__()
self.position = 0
self.zeros_at_mod = [0] * 4
self.nonzeros_at_mod = [0] * 4
self._state = ProbingState.DETECTING
self.quad = [0, 0, 0, 0]
self.invalid_utf16be = False
self.invalid_utf16le = False
self.invalid_utf32be = False
self.invalid_utf32le = False
self.first_half_surrogate_pair_detected_16be = False
self.first_half_surrogate_pair_detected_16le = False
self.reset()
def reset(self) -> None:
super().reset()
self.position = 0
self.zeros_at_mod = [0] * 4
self.nonzeros_at_mod = [0] * 4
self._state = ProbingState.DETECTING
self.invalid_utf16be = False
self.invalid_utf16le = False
self.invalid_utf32be = False
self.invalid_utf32le = False
self.first_half_surrogate_pair_detected_16be = False
self.first_half_surrogate_pair_detected_16le = False
self.quad = [0, 0, 0, 0]
@property
def charset_name(self) -> str:
if self.is_likely_utf32be():
return "utf-32be"
if self.is_likely_utf32le():
return "utf-32le"
if self.is_likely_utf16be():
return "utf-16be"
if self.is_likely_utf16le():
return "utf-16le"
# default to something valid
return "utf-16"
@property
def language(self) -> str:
return ""
def approx_32bit_chars(self) -> float:
return max(1.0, self.position / 4.0)
def approx_16bit_chars(self) -> float:
return max(1.0, self.position / 2.0)
def is_likely_utf32be(self) -> bool:
approx_chars = self.approx_32bit_chars()
return approx_chars >= self.MIN_CHARS_FOR_DETECTION and (
self.zeros_at_mod[0] / approx_chars > self.EXPECTED_RATIO
and self.zeros_at_mod[1] / approx_chars > self.EXPECTED_RATIO
and self.zeros_at_mod[2] / approx_chars > self.EXPECTED_RATIO
and self.nonzeros_at_mod[3] / approx_chars > self.EXPECTED_RATIO
and not self.invalid_utf32be
)
def is_likely_utf32le(self) -> bool:
approx_chars = self.approx_32bit_chars()
return approx_chars >= self.MIN_CHARS_FOR_DETECTION and (
self.nonzeros_at_mod[0] / approx_chars > self.EXPECTED_RATIO
and self.zeros_at_mod[1] / approx_chars > self.EXPECTED_RATIO
and self.zeros_at_mod[2] / approx_chars > self.EXPECTED_RATIO
and self.zeros_at_mod[3] / approx_chars > self.EXPECTED_RATIO
and not self.invalid_utf32le
)
def is_likely_utf16be(self) -> bool:
approx_chars = self.approx_16bit_chars()
return approx_chars >= self.MIN_CHARS_FOR_DETECTION and (
(self.nonzeros_at_mod[1] + self.nonzeros_at_mod[3]) / approx_chars
> self.EXPECTED_RATIO
and (self.zeros_at_mod[0] + self.zeros_at_mod[2]) / approx_chars
> self.EXPECTED_RATIO
and not self.invalid_utf16be
)
def is_likely_utf16le(self) -> bool:
approx_chars = self.approx_16bit_chars()
return approx_chars >= self.MIN_CHARS_FOR_DETECTION and (
(self.nonzeros_at_mod[0] + self.nonzeros_at_mod[2]) / approx_chars
> self.EXPECTED_RATIO
and (self.zeros_at_mod[1] + self.zeros_at_mod[3]) / approx_chars
> self.EXPECTED_RATIO
and not self.invalid_utf16le
)
def validate_utf32_characters(self, quad: List[int]) -> None:
"""
Validate if the quad of bytes is valid UTF-32.
UTF-32 is valid in the range 0x00000000 - 0x0010FFFF
excluding 0x0000D800 - 0x0000DFFF
https://en.wikipedia.org/wiki/UTF-32
"""
if (
quad[0] != 0
or quad[1] > 0x10
or (quad[0] == 0 and quad[1] == 0 and 0xD8 <= quad[2] <= 0xDF)
):
self.invalid_utf32be = True
if (
quad[3] != 0
or quad[2] > 0x10
or (quad[3] == 0 and quad[2] == 0 and 0xD8 <= quad[1] <= 0xDF)
):
self.invalid_utf32le = True
def validate_utf16_characters(self, pair: List[int]) -> None:
"""
Validate if the pair of bytes is valid UTF-16.
UTF-16 is valid in the range 0x0000 - 0xFFFF excluding 0xD800 - 0xFFFF
with an exception for surrogate pairs, which must be in the range
0xD800-0xDBFF followed by 0xDC00-0xDFFF
https://en.wikipedia.org/wiki/UTF-16
"""
if not self.first_half_surrogate_pair_detected_16be:
if 0xD8 <= pair[0] <= 0xDB:
self.first_half_surrogate_pair_detected_16be = True
elif 0xDC <= pair[0] <= 0xDF:
self.invalid_utf16be = True
else:
if 0xDC <= pair[0] <= 0xDF:
self.first_half_surrogate_pair_detected_16be = False
else:
self.invalid_utf16be = True
if not self.first_half_surrogate_pair_detected_16le:
if 0xD8 <= pair[1] <= 0xDB:
self.first_half_surrogate_pair_detected_16le = True
elif 0xDC <= pair[1] <= 0xDF:
self.invalid_utf16le = True
else:
if 0xDC <= pair[1] <= 0xDF:
self.first_half_surrogate_pair_detected_16le = False
else:
self.invalid_utf16le = True
def feed(self, byte_str: Union[bytes, bytearray]) -> ProbingState:
for c in byte_str:
mod4 = self.position % 4
self.quad[mod4] = c
if mod4 == 3:
self.validate_utf32_characters(self.quad)
self.validate_utf16_characters(self.quad[0:2])
self.validate_utf16_characters(self.quad[2:4])
if c == 0:
self.zeros_at_mod[mod4] += 1
else:
self.nonzeros_at_mod[mod4] += 1
self.position += 1
return self.state
@property
def state(self) -> ProbingState:
if self._state in {ProbingState.NOT_ME, ProbingState.FOUND_IT}:
# terminal, decided states
return self._state
if self.get_confidence() > 0.80:
self._state = ProbingState.FOUND_IT
elif self.position > 4 * 1024:
# if we get to 4kb into the file, and we can't conclude it's UTF,
# let's give up
self._state = ProbingState.NOT_ME
return self._state
def get_confidence(self) -> float:
return (
0.85
if (
self.is_likely_utf16le()
or self.is_likely_utf16be()
or self.is_likely_utf32le()
or self.is_likely_utf32be()
)
else 0.00
)
|