def read_block(f, block_header_size_, check_type, outfile):
start_pos = f.tell() - 1
filters, compressed_size, uncompressed_size = read_block_header(
f, block_header_size_, check_type)
fpos, opos = f.tell(), outfile.tell()
filters[0](f, outfile, filters[1:])
actual_compressed_size = f.tell() - fpos
uncompressed_actual_size = outfile.tell() - opos
if uncompressed_size is not None and uncompressed_size != uncompressed_actual_size:
raise InvalidXZ('Uncompressed size for block does not match')
if compressed_size is not None and compressed_size != actual_compressed_size:
raise InvalidXZ('Compressed size for block does not match')
padding_count = f.tell() % 4
if padding_count:
padding_count = 4 - padding_count
padding = f.read(padding_count)
if len(padding) != padding_count:
raise InvalidXZ('Block is not aligned')
if padding.lstrip(b'\0'):
raise InvalidXZ('Block padding has non null bytes')
if check_type:
q = f.read(filters[0].crc.size)
if not filters[0].crc.check(q):
raise InvalidXZ('CRC for data does not match')
return Block(f.tell() - padding_count - start_pos,
uncompressed_actual_size)
def read_stream_footer(f, check_type, index_size):
crc, = unpack(b'<I', f.read(4))
raw = f.read(6)
backward_size, stream_flags1, stream_flags2 = unpack(b'<I2B', raw)
if stream_flags1 != 0 or stream_flags2 & 0xf0 != 0 or stream_flags2 & 0xf != check_type:
raise InvalidXZ('Footer stream flags != header stream flags')
backward_size = 4 * (1 + backward_size)
if backward_size != index_size:
raise InvalidXZ('Footer backward size != actual index size')
if f.read(2) != FOOTER_MAGIC:
raise InvalidXZ('Stream footer has incorrect magic bytes')
if crc != crc32(raw):
raise InvalidXZ('Stream footer CRC mismatch')
def read_stream_header(f):
try:
magic, stream_flags1, stream_flags2, crc = unpack(
b'<6s2BI', f.read(12))
except struct_error as e:
raise NotXZ('Not an XZ file. Invalid stream header: ' % e)
if magic != HEADER_MAGIC:
raise NotXZ('Not an XZ file. Header Magic is: %r' % magic)
if stream_flags1 != 0:
raise InvalidXZ('Stream flags first byte is not null')
check_type, reserved = 0x0f & stream_flags2, 0xf0 & stream_flags2
if reserved != 0:
raise InvalidXZ('Stream flags reserved bits not null')
if crc32(bytes(bytearray([stream_flags1, stream_flags2]))) != crc:
raise InvalidXZ('Stream flags header CRC incorrect')
return check_type
def decompress(raw, outfile=None):
'''
Decompress the specified data.
:param raw: A bytestring or a file-like object open for reading
:outfile: A file like object open for writing.
The decompressed data is written into it. If not specified then a SpooledTemporaryFile
is created and returned by this function.
'''
if isinstance(raw, bytes):
raw = BytesIO(raw)
outfile = outfile or SpooledTemporaryFile(50 * 1024 * 1024,
'_xz_decompress')
while True:
read_stream(raw, outfile)
pos = raw.tell()
trail = raw.read(1024)
if len(trail) < 20:
break
idx = trail.find(HEADER_MAGIC)
if idx == -1:
break
if idx > -1:
# Found another stream
raw.seek(pos)
if idx:
padding = raw.read(idx)
if padding.lstrip(b'\0') or len(padding) % 4:
raise InvalidXZ('Found trailing garbage between streams')
return outfile
def read_block_header(f, block_header_size_, check_type):
block_header_size = 4 * (ord(block_header_size_) + 1)
if block_header_size < 8:
raise InvalidXZ('Invalid block header size: %d' % block_header_size)
header, crc = unpack(b'<%dsI' % (block_header_size - 5),
f.read(block_header_size - 1))
if crc != crc32(block_header_size_ + header):
raise InvalidXZ('Block header CRC mismatch')
block_flags = ord(header[0])
number_of_filters = (0x03 & block_flags) + 1
if not (0 < number_of_filters <= 4):
raise InvalidXZ('Invalid number of filters: %d' % number_of_filters)
if block_flags & 0x3c != 0:
raise InvalidXZ('Non-zero reserved bits in block flags')
has_compressed_size = block_flags & 0x40
has_uncompressed_size = block_flags & 0x80
compressed_size = uncompressed_size = None
pos = 1
if has_compressed_size:
compressed_size, pos = decode_var_int2(header, pos)
if has_uncompressed_size:
uncompressed_size, pos = decode_var_int2(header, pos)
filters = []
while number_of_filters:
number_of_filters -= 1
filter_id, pos = decode_var_int2(header, pos)
size_of_properties, pos = decode_var_int2(header, pos)
if filter_id >= 0x4000000000000000:
raise InvalidXZ('Invalid filter id: %d' % filter_id)
if filter_id not in (LZMA2_FILTER_ID, DELTA_FILTER_ID):
raise InvalidXZ('Unsupported filter ID: 0x%x' % filter_id)
props = header[pos:pos + size_of_properties]
pos += size_of_properties
if len(props) != size_of_properties:
raise InvalidXZ('Incomplete filter properties')
if filter_id == LZMA2_FILTER_ID and number_of_filters:
raise InvalidXZ('LZMA2 filter must be the last filter')
elif filter_id == DELTA_FILTER_ID and not number_of_filters:
raise InvalidXZ('Delta filter cannot be the last filter')
filters.append(
(LZMA2Filter if filter_id == LZMA2_FILTER_ID else DeltaFilter)(
props, check_type))
padding = header[pos:]
if padding.lstrip(b'\0'):
raise InvalidXZ('Non-null block header padding: %r' % padding)
filters.reverse()
return filters, compressed_size, uncompressed_size
def __init__(self, props, check_type, bufsize=None):
if len(props) != 1:
raise InvalidXZ('Invalid properties length for LZMA2 filter')
props = ord(props)
self.dictionary_size = props & 0x3F
if props & 0xC0 != 0:
raise InvalidXZ('Invalid high bytes for LZMA2 filter properties')
self.props = props
if check_type in (0x1, 0x4):
self.crc = CRCChecker(check_type)
elif check_type == 0x0A:
self.crc = Sha256Checker()
else:
if check_type:
raise InvalidXZ('Unsupported CRC check type: %s' % check_type)
self.crc = DummyChecker()
if bufsize is None:
bufsize = self.BUFSIZE
self.bufsize = int(bufsize * 1024 * 1024)
def read_index(f):
pos = f.tell() - 1
number_of_records = decode_var_int(f)
while number_of_records:
number_of_records -= 1
unpadded_size = decode_var_int(f)
if unpadded_size < 1:
raise InvalidXZ('Invalid unpadded size in index: %d' %
unpadded_size)
yield Block(unpadded_size, decode_var_int(f))
if f.tell() % 4:
padding_count = 4 - f.tell() % 4
padding = f.read(padding_count)
if len(padding) != padding_count or padding.lstrip(b'\0'):
raise InvalidXZ('Incorrect Index padding')
epos = f.tell()
f.seek(pos)
raw = f.read(epos - pos)
crc, = unpack(b'<I', f.read(4))
if crc != crc32(raw):
raise InvalidXZ('Index field CRC mismatch')
def read_stream(f, outfile):
check_type = read_stream_header(f)
blocks, index = [], None
index_size = 0
while True:
sz = f.read(1)
if sz == b'\0':
pos = f.tell() - 1
index = tuple(read_index(f))
index_size = f.tell() - pos
break
else:
blocks.append(read_block(f, sz, check_type, outfile))
if index != tuple(blocks):
raise InvalidXZ('Index does not match actual blocks in file')
read_stream_footer(f, check_type, index_size)
def __call__(self, f, outfile, filters=()):
w = outfile.write
c = self.crc
def write(raw):
if filters:
raw = bytearray(raw)
for flt in filters:
raw = flt(raw)
raw = bytes(raw)
w(raw), c(raw)
try:
lzma.decompress2(f.read, f.seek, write, self.props, self.bufsize)
except lzma.error as e:
raise InvalidXZ(
'Failed to decode LZMA2 block with error code: %s' % e.message)
self.crc.finish()
def __init__(self, props, *args):
if len(props) != 1:
raise InvalidXZ('Invalid properties length for Delta filter')
self.distance = ord(props) + 1
self.pos = 0
self.history = bytearray(256)