226 lines
8.3 KiB
Python
226 lines
8.3 KiB
Python
######################## BEGIN LICENSE BLOCK ########################
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#
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# Contributor(s):
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# Jason Zavaglia
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#
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# This library is free software; you can redistribute it and/or
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# modify it under the terms of the GNU Lesser General Public
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# License as published by the Free Software Foundation; either
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# version 2.1 of the License, or (at your option) any later version.
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#
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# This library is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# Lesser General Public License for more details.
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#
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# You should have received a copy of the GNU Lesser General Public
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# License along with this library; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
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# 02110-1301 USA
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######################### END LICENSE BLOCK #########################
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from typing import List, Union
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from .charsetprober import CharSetProber
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from .enums import ProbingState
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class UTF1632Prober(CharSetProber):
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"""
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This class simply looks for occurrences of zero bytes, and infers
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whether the file is UTF16 or UTF32 (low-endian or big-endian)
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For instance, files looking like ( \0 \0 \0 [nonzero] )+
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have a good probability to be UTF32BE. Files looking like ( \0 [nonzero] )+
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may be guessed to be UTF16BE, and inversely for little-endian varieties.
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"""
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# how many logical characters to scan before feeling confident of prediction
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MIN_CHARS_FOR_DETECTION = 20
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# a fixed constant ratio of expected zeros or non-zeros in modulo-position.
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EXPECTED_RATIO = 0.94
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def __init__(self) -> None:
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super().__init__()
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self.position = 0
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self.zeros_at_mod = [0] * 4
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self.nonzeros_at_mod = [0] * 4
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self._state = ProbingState.DETECTING
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self.quad = [0, 0, 0, 0]
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self.invalid_utf16be = False
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self.invalid_utf16le = False
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self.invalid_utf32be = False
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self.invalid_utf32le = False
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self.first_half_surrogate_pair_detected_16be = False
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self.first_half_surrogate_pair_detected_16le = False
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self.reset()
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def reset(self) -> None:
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super().reset()
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self.position = 0
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self.zeros_at_mod = [0] * 4
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self.nonzeros_at_mod = [0] * 4
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self._state = ProbingState.DETECTING
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self.invalid_utf16be = False
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self.invalid_utf16le = False
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self.invalid_utf32be = False
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self.invalid_utf32le = False
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self.first_half_surrogate_pair_detected_16be = False
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self.first_half_surrogate_pair_detected_16le = False
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self.quad = [0, 0, 0, 0]
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@property
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def charset_name(self) -> str:
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if self.is_likely_utf32be():
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return "utf-32be"
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if self.is_likely_utf32le():
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return "utf-32le"
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if self.is_likely_utf16be():
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return "utf-16be"
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if self.is_likely_utf16le():
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return "utf-16le"
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# default to something valid
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return "utf-16"
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@property
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def language(self) -> str:
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return ""
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def approx_32bit_chars(self) -> float:
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return max(1.0, self.position / 4.0)
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def approx_16bit_chars(self) -> float:
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return max(1.0, self.position / 2.0)
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def is_likely_utf32be(self) -> bool:
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approx_chars = self.approx_32bit_chars()
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return approx_chars >= self.MIN_CHARS_FOR_DETECTION and (
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self.zeros_at_mod[0] / approx_chars > self.EXPECTED_RATIO
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and self.zeros_at_mod[1] / approx_chars > self.EXPECTED_RATIO
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and self.zeros_at_mod[2] / approx_chars > self.EXPECTED_RATIO
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and self.nonzeros_at_mod[3] / approx_chars > self.EXPECTED_RATIO
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and not self.invalid_utf32be
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)
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def is_likely_utf32le(self) -> bool:
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approx_chars = self.approx_32bit_chars()
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return approx_chars >= self.MIN_CHARS_FOR_DETECTION and (
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self.nonzeros_at_mod[0] / approx_chars > self.EXPECTED_RATIO
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and self.zeros_at_mod[1] / approx_chars > self.EXPECTED_RATIO
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and self.zeros_at_mod[2] / approx_chars > self.EXPECTED_RATIO
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and self.zeros_at_mod[3] / approx_chars > self.EXPECTED_RATIO
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and not self.invalid_utf32le
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)
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def is_likely_utf16be(self) -> bool:
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approx_chars = self.approx_16bit_chars()
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return approx_chars >= self.MIN_CHARS_FOR_DETECTION and (
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(self.nonzeros_at_mod[1] + self.nonzeros_at_mod[3]) / approx_chars
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> self.EXPECTED_RATIO
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and (self.zeros_at_mod[0] + self.zeros_at_mod[2]) / approx_chars
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> self.EXPECTED_RATIO
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and not self.invalid_utf16be
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)
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def is_likely_utf16le(self) -> bool:
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approx_chars = self.approx_16bit_chars()
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return approx_chars >= self.MIN_CHARS_FOR_DETECTION and (
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(self.nonzeros_at_mod[0] + self.nonzeros_at_mod[2]) / approx_chars
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> self.EXPECTED_RATIO
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and (self.zeros_at_mod[1] + self.zeros_at_mod[3]) / approx_chars
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> self.EXPECTED_RATIO
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and not self.invalid_utf16le
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)
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def validate_utf32_characters(self, quad: List[int]) -> None:
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"""
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Validate if the quad of bytes is valid UTF-32.
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UTF-32 is valid in the range 0x00000000 - 0x0010FFFF
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excluding 0x0000D800 - 0x0000DFFF
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https://en.wikipedia.org/wiki/UTF-32
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"""
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if (
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quad[0] != 0
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or quad[1] > 0x10
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or (quad[0] == 0 and quad[1] == 0 and 0xD8 <= quad[2] <= 0xDF)
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):
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self.invalid_utf32be = True
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if (
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quad[3] != 0
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or quad[2] > 0x10
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or (quad[3] == 0 and quad[2] == 0 and 0xD8 <= quad[1] <= 0xDF)
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):
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self.invalid_utf32le = True
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def validate_utf16_characters(self, pair: List[int]) -> None:
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"""
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Validate if the pair of bytes is valid UTF-16.
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UTF-16 is valid in the range 0x0000 - 0xFFFF excluding 0xD800 - 0xFFFF
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with an exception for surrogate pairs, which must be in the range
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0xD800-0xDBFF followed by 0xDC00-0xDFFF
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https://en.wikipedia.org/wiki/UTF-16
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"""
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if not self.first_half_surrogate_pair_detected_16be:
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if 0xD8 <= pair[0] <= 0xDB:
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self.first_half_surrogate_pair_detected_16be = True
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elif 0xDC <= pair[0] <= 0xDF:
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self.invalid_utf16be = True
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else:
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if 0xDC <= pair[0] <= 0xDF:
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self.first_half_surrogate_pair_detected_16be = False
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else:
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self.invalid_utf16be = True
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if not self.first_half_surrogate_pair_detected_16le:
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if 0xD8 <= pair[1] <= 0xDB:
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self.first_half_surrogate_pair_detected_16le = True
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elif 0xDC <= pair[1] <= 0xDF:
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self.invalid_utf16le = True
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else:
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if 0xDC <= pair[1] <= 0xDF:
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self.first_half_surrogate_pair_detected_16le = False
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else:
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self.invalid_utf16le = True
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def feed(self, byte_str: Union[bytes, bytearray]) -> ProbingState:
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for c in byte_str:
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mod4 = self.position % 4
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self.quad[mod4] = c
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if mod4 == 3:
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self.validate_utf32_characters(self.quad)
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self.validate_utf16_characters(self.quad[0:2])
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self.validate_utf16_characters(self.quad[2:4])
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if c == 0:
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self.zeros_at_mod[mod4] += 1
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else:
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self.nonzeros_at_mod[mod4] += 1
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self.position += 1
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return self.state
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@property
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def state(self) -> ProbingState:
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if self._state in {ProbingState.NOT_ME, ProbingState.FOUND_IT}:
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# terminal, decided states
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return self._state
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if self.get_confidence() > 0.80:
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self._state = ProbingState.FOUND_IT
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elif self.position > 4 * 1024:
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# if we get to 4kb into the file, and we can't conclude it's UTF,
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# let's give up
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self._state = ProbingState.NOT_ME
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return self._state
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def get_confidence(self) -> float:
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return (
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0.85
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if (
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self.is_likely_utf16le()
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or self.is_likely_utf16be()
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or self.is_likely_utf32le()
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or self.is_likely_utf32be()
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)
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else 0.00
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)
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