[New-bugs-announce] [issue27517] LZMACompressor and LZMADecompressor raise exceptions if given empty strings twice

[Benjamin Fogle]

New submission from Benjamin Fogle:

To reproduce:

>>> import lzma
>>> c = lzma.LZMACompressor()
>>> c.compress(b'')
b'\xfd7zXZ\x00\x00\x04\xe6\xd6\xb4F'
>>> c.compress(b'')
b''
>>> c.compress(b'')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
_lzma.LZMAError: Insufficient buffer space
>>> d = lzma.LZMADecompressor()
>>> d.decompress(b'')
b''
>>> d.decompress(b'')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
_lzma.LZMAError: Insufficient buffer space

This can occur anytime during compression/decompression when an empty string is passed twice in a row.

The problem is that that liblzma interprets a call to lzma_code() with avail_in == 0 as a buffer full condition. The second time in a row it encounters this, it returns LZMA_BUF_ERROR as per documentation. The attached patch prevents this condition from occurring.

----------
components: Extension Modules
files: lzma.patch
keywords: patch
messages: 270451
nosy: benfogle
priority: normal
severity: normal
status: open
title: LZMACompressor and LZMADecompressor raise exceptions if given empty strings twice
type: behavior
versions: Python 3.3, Python 3.4, Python 3.5, Python 3.6
Added file: http://bugs.python.org/file43727/lzma.patch

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<http://bugs.python.org/issue27517>
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