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lzg.py
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lzg.py
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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
from __future__ import annotations
from typing import Union
import enum
import re
from refinery.units import Unit, RefineryPartialResult
from refinery.lib.structures import MemoryFile, StructReader, Struct
class LZGMethod(enum.IntEnum):
COPY = 0
LZG1 = 1
class LZGCheckSum:
def __init__(self, reader: Union[bytearray, StructReader[bytearray]], size: int = 0):
if not isinstance(reader, StructReader):
reader = StructReader(reader)
self.reader = reader
self._a = 1
self._b = 0
if size:
self.process(size)
def __int__(self):
return ((self._b << 0x10) | self._a)
def process(self, size: int) -> None:
a = self._a
b = self._b
for c in self.reader.read_exactly(size):
a = (a + c) & 0xFFFF
b = (b + a) & 0xFFFF
self._a = a
self._b = b
class LZGStream(Struct):
_LENGTH_DECODE = list(range(2, 30))
_LENGTH_DECODE.extend((35, 48, 72, 128))
def __init__(self, reader: StructReader[memoryview]):
self._body = reader
magic = reader.peek(3)
if magic == B'LZG':
self.has_magic = True
reader.seekrel(3)
else:
self.has_magic = False
with reader.be:
dec = reader.u32()
enc = reader.u32()
if enc > dec and not self.has_magic:
enc, dec = dec, enc
self.encoded_size = enc
self.decoded_size = dec
self.checksum = reader.u32()
if reader.remaining_bytes < self.encoded_size:
raise EOFError(F'Header announces buffer size of {self.encoded_size}, but only {reader.remaining_bytes} remain in buffer')
if reader.remaining_bytes == self.encoded_size:
if self._checks():
self.method = None
return
raise ValueError('Invalid checksum or truncated buffer.')
method = reader.u8()
try:
self.method = LZGMethod(method)
except ValueError:
self.method = None
if self._checks():
raise ValueError(F'Invalid method code {method}.')
reader.seekrel(-1)
self.encoded_size -= 1
if self.method is LZGMethod.COPY and self.encoded_size != self.decoded_size:
raise ValueError('Header indicates method COPY but encoded and decoded size are different.')
if self._checks():
return
self._handle_invalid_checksum()
def _checks(self):
checker = LZGCheckSum(StructReader(self._body.peek()))
checker.process(self.encoded_size)
for tolerance in range(8):
if int(checker) == self.checksum:
self.encoded_size += tolerance
return True
checker.process(1)
else:
return False
def _find_checksum(self, data: bytearray) -> int:
a = 1
b = 0
t = self.checksum
for k, c in enumerate(data):
a = (a + c) & 0xFFFF
b = (b + a) & 0xFFFF
s = ((b << 0x10) | a)
if s == t:
return k
return -1
def _handle_invalid_checksum(self):
offsets = {}
for k in range(16):
offset = self._find_checksum(self._body.peek())
if offset >= 0:
offsets[offset] = k + 1
self._body.seekrel(1)
if not offsets:
raise ValueError('Invalid checksum and no working offsets could be found.')
else:
closest = min(offsets, key=lambda k: abs(self.encoded_size - k))
skip = offsets[closest]
raise ValueError(
F'Checksum failed; a valid checksum can be obtained by skipping {skip} bytes and then reading {closest}. '
F'According to the header, the size of the encoded data is {self.encoded_size}.')
def decompress(self) -> bytearray:
if self._body is None:
raise RuntimeError('The decompress method can only be called once.')
reader = self._body
self._body = None
if self.method is LZGMethod.COPY:
return reader.read(self.encoded_size)
end = reader.tell() + self.encoded_size
out = MemoryFile(bytearray())
markers = reader.read(4)
pattern = re.compile(B'[%s]' % re.escape(markers), flags=re.DOTALL)
pos = reader.tell()
while reader.tell() < end:
pos = reader.tell()
hop = pattern.search(reader.getbuffer(), pos)
if hop is None:
out.write(reader.read(end - pos))
break
hop = hop.start()
out.write(reader.read(hop - pos))
code = reader.u8()
arg1 = reader.u8()
if not arg1:
out.write_byte(code)
continue
elif code == markers[0]:
length = self._LENGTH_DECODE[arg1 & 0x1F]
b2 = reader.u8()
offset = ((arg1 & 0xE0) << 11) | (b2 << 8) | reader.u8()
offset += 2056
elif code == markers[1]:
length = self._LENGTH_DECODE[arg1 & 0x1F]
b2 = reader.u8()
offset = ((arg1 & 0xE0) << 3) | b2
offset += 8
elif code == markers[2]:
length = (arg1 >> 6) + 3
offset = (arg1 & 0x3F) + 8
elif code == markers[3]:
length = self._LENGTH_DECODE[arg1 & 0x1F]
offset = (arg1 >> 5) + 1
else:
raise RuntimeError
out.replay(offset, length)
return out.getbuffer()
class lzg(Unit):
"""
LZG decompression.
"""
def process(self, data: bytearray):
stream = LZGStream(data)
out = stream.decompress()
if len(out) != stream.decoded_size:
msg = F'LZG header announced {stream.decoded_size} bytes, but decompressed buffer had size {len(out)}.'
raise RefineryPartialResult(msg, out)
return out
@classmethod
def handles(cls, data: bytearray):
if data[:3] == B'LZG':
return True