New submission from Hiroshi Miura <[email protected]>:
When decompressing a particular archive, result become truncated a last word.
A test data attached is uncompressed size is 12800 bytes, and compressed using
LZMA1+BCJ algorithm into 11327 bytes.
The data is a payload of a 7zip archive.
Here is a pytest code to reproduce it.
:: code-block::
def test_lzma_raw_decompressor_lzmabcj():
filters = []
filters.append({'id': lzma.FILTER_X86})
filters.append(lzma._decode_filter_properties(lzma.FILTER_LZMA1,
b']\x00\x00\x01\x00'))
decompressor = lzma.LZMADecompressor(format=lzma.FORMAT_RAW,
filters=filters)
with testdata_path.joinpath('lzmabcj.bin').open('rb') as infile:
out = decompressor.decompress(infile.read(11327))
assert len(out) == 12800
test become failure that len(out) become 12796 bytes, which lacks last 4 bytes,
which should be b'\x00\x00\x00\x00'
When specifying a filters as a single LZMA1 decompression, I got an expected
length of data, 12800 bytes.(*1)
When creating a test data with LZMA2+BCJ and examines it, I got an expected
data.
When specifying a filters as a single LZMA2 decompression against LZMA2+BCJ
payload, a result is perfectly as same as (*1) data.
It indicate us that a pipeline of LZMA1/LZMA2 --> BCJ is in doubt.
After investigation and understanding that _lzmamodule.c is a thin wrapper of
liblzma, I found the problem can be reproduced in liblzma.
I've reported it to upstream xz-devel ML with a test code
https://www.mail-archive.com/[email protected]/msg00370.html
----------
components: Extension Modules
files: lzmabcj.bin
messages: 373008
nosy: miurahr
priority: normal
severity: normal
status: open
title: LZMADecompressor.decompress(FORMAT_RAW) truncate output when input is
paticular LZMA+BCJ data
versions: Python 3.6, Python 3.7, Python 3.8, Python 3.9
Added file: https://bugs.python.org/file49296/lzmabcj.bin
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<https://bugs.python.org/issue41210>
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