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Unpacking LZMA-compressed files from BSPs
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#!/usr/bin/python3 | |
import struct, lzma, sys | |
def unpack(fmt, stream): | |
''' | |
unpacks values from a stream | |
source: https://stackoverflow.com/a/17537253 | |
''' | |
size = struct.calcsize(fmt) | |
buf = stream.read(size) | |
return struct.unpack(fmt, buf) | |
if __name__ == "__main__": | |
import argparse, os | |
parser = argparse.ArgumentParser( | |
description="Decompressese an LZMA file extracted from a Source Engine BSP.", | |
usage='%(prog)s FILE') | |
parser.add_argument('filepath', metavar='FILE', help="file to decompress") | |
args = parser.parse_args() | |
if not os.path.isfile(args.filepath): | |
raise ValueError("file not defined") | |
with open(f'{args.filepath}', mode='rb') as f: | |
# id, actual_size, lzma_size, *properties = unpack('<III5B', f) | |
# properties can be unpacked directly, [0] = d, [1:4] = dict_size | |
# see LzmaProps_Decode in mp/src/utils/lzma/C/LzmaDec.c | |
header_id, actual_size, lzma_size, d, dict_size = unpack('<IIIBI', f) | |
if not header_id == 0x414D5A4C: | |
raise AssertionError('Not a valid Source Engine (PC) LZMA file') | |
if d >= (9 * 5 * 5): | |
raise AssertionError('throw SZ_ERROR_UNSUPPORTED') | |
lc, pb, lp = d % 9, (d // 9) // 5, (d // 9) % 5 | |
# TODO what filter do the other files use? | |
lzma_filter = [ | |
{ 'id': lzma.FILTER_LZMA1, 'dict_size': dict_size, 'lc': lc, 'lp': lp, 'pb': pb, 'preset': 6} | |
] | |
decompressor = lzma.LZMADecompressor(format = lzma.FORMAT_RAW, filters = lzma_filter) | |
stream_decompressed = decompressor.decompress(f.read(), max_length = actual_size) | |
sys.stdout.write(stream_decompressed.decode('ascii')) |
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