# -*- coding: utf-8 -*-
"""The compressed stream file-like object implementation."""
import os
from dfvfs.compression import manager as compression_manager
from dfvfs.file_io import file_io
from dfvfs.lib import errors
from dfvfs.resolver import resolver
[docs]
class CompressedStream(file_io.FileIO):
"""File input/output (IO) object of a compressed stream."""
# The size of the compressed data buffer.
_COMPRESSED_DATA_BUFFER_SIZE = 8 * 1024 * 1024
[docs]
def __init__(self, resolver_context, path_spec):
"""Initializes a file input/output (IO) object.
Args:
resolver_context (Context): resolver context.
path_spec (PathSpec): a path specification.
"""
super(CompressedStream, self).__init__(resolver_context, path_spec)
self._compression_method = None
self._file_object = None
self._compressed_data = b''
self._current_offset = 0
self._decompressor = None
self._realign_offset = True
self._uncompressed_data = b''
self._uncompressed_data_offset = 0
self._uncompressed_data_size = 0
self._uncompressed_stream_size = None
def _Close(self):
"""Closes the file-like object.
If the file-like object was passed in the init function the compressed
stream file-like object does not control the file-like object and should not
actually close it.
"""
self._compressed_data = b''
self._file_object = None
self._decompressor = None
self._uncompressed_data = b''
def _GetDecompressor(self):
"""Retrieves the decompressor.
Returns:
Decompressor: decompressor.
"""
return compression_manager.CompressionManager.GetDecompressor(
self._compression_method)
def _GetUncompressedStreamSize(self):
"""Retrieves the uncompressed stream size.
Returns:
int: uncompressed stream size.
"""
self._file_object.seek(0, os.SEEK_SET)
self._decompressor = self._GetDecompressor()
self._uncompressed_data = b''
compressed_data_offset = 0
compressed_data_size = self._file_object.get_size()
uncompressed_stream_size = 0
while compressed_data_offset < compressed_data_size:
read_count = self._ReadCompressedData(self._COMPRESSED_DATA_BUFFER_SIZE)
if read_count == 0:
break
compressed_data_offset += read_count
uncompressed_stream_size += self._uncompressed_data_size
return uncompressed_stream_size
def _Open(self, mode='rb'):
"""Opens the file-like object.
Args:
mode (Optional[str]): file access mode.
Raises:
AccessError: if the access to open the file was denied.
IOError: if the file-like object could not be opened.
OSError: if the file-like object could not be opened.
PathSpecError: if the path specification is incorrect.
"""
if not self._path_spec.HasParent():
raise errors.PathSpecError(
'Unsupported path specification without parent.')
self._compression_method = getattr(
self._path_spec, 'compression_method', None)
if self._compression_method is None:
raise errors.PathSpecError(
'Path specification missing compression method.')
self._file_object = resolver.Resolver.OpenFileObject(
self._path_spec.parent, resolver_context=self._resolver_context)
def _AlignUncompressedDataOffset(self, uncompressed_data_offset):
"""Aligns the compressed file with the uncompressed data offset.
Args:
uncompressed_data_offset (int): uncompressed data offset.
"""
self._file_object.seek(0, os.SEEK_SET)
self._decompressor = self._GetDecompressor()
self._uncompressed_data = b''
compressed_data_offset = 0
compressed_data_size = self._file_object.get_size()
while compressed_data_offset < compressed_data_size:
read_count = self._ReadCompressedData(self._COMPRESSED_DATA_BUFFER_SIZE)
if read_count == 0:
break
compressed_data_offset += read_count
if uncompressed_data_offset < self._uncompressed_data_size:
self._uncompressed_data_offset = uncompressed_data_offset
break
uncompressed_data_offset -= self._uncompressed_data_size
def _ReadCompressedData(self, read_size):
"""Reads compressed data from the file-like object.
Args:
read_size (int): number of bytes of compressed data to read.
Returns:
int: number of bytes of compressed data read.
"""
compressed_data = self._file_object.read(read_size)
read_count = len(compressed_data)
self._compressed_data = b''.join([self._compressed_data, compressed_data])
self._uncompressed_data, self._compressed_data = (
self._decompressor.Decompress(self._compressed_data))
self._uncompressed_data_size = len(self._uncompressed_data)
return read_count
# Note: that the following functions do not follow the style guide
# because they are part of the file-like object interface.
# pylint: disable=invalid-name
[docs]
def read(self, size=None):
"""Reads a byte string from the file-like object at the current offset.
The function will read a byte string of the specified size or
all of the remaining data if no size was specified.
Args:
size (Optional[int]): number of bytes to read, where None is all
remaining data.
Returns:
bytes: data read.
Raises:
IOError: if the read failed.
OSError: if the read failed.
"""
if not self._is_open:
raise IOError('Not opened.')
if self._current_offset < 0:
raise IOError((
f'Invalid current offset: {self._current_offset:d} value less than '
f'zero.'))
if self._uncompressed_stream_size is None:
self._uncompressed_stream_size = self._GetUncompressedStreamSize()
if self._uncompressed_stream_size < 0:
raise IOError('Invalid uncompressed stream size.')
if self._current_offset >= self._uncompressed_stream_size:
return b''
if self._realign_offset:
self._AlignUncompressedDataOffset(self._current_offset)
self._realign_offset = False
if size is None:
size = self._uncompressed_stream_size
if self._current_offset + size > self._uncompressed_stream_size:
size = self._uncompressed_stream_size - self._current_offset
uncompressed_data = b''
if size == 0:
return uncompressed_data
while size > self._uncompressed_data_size:
uncompressed_data = b''.join([
uncompressed_data,
self._uncompressed_data[self._uncompressed_data_offset:]])
remaining_uncompressed_data_size = (
self._uncompressed_data_size - self._uncompressed_data_offset)
self._current_offset += remaining_uncompressed_data_size
size -= remaining_uncompressed_data_size
if self._current_offset >= self._uncompressed_stream_size:
break
read_count = self._ReadCompressedData(self._COMPRESSED_DATA_BUFFER_SIZE)
self._uncompressed_data_offset = 0
if read_count == 0:
break
if size > 0:
slice_start_offset = self._uncompressed_data_offset
slice_end_offset = slice_start_offset + size
uncompressed_data = b''.join([
uncompressed_data,
self._uncompressed_data[slice_start_offset:slice_end_offset]])
self._uncompressed_data_offset += size
self._current_offset += size
return uncompressed_data
[docs]
def seek(self, offset, whence=os.SEEK_SET):
"""Seeks to an offset within the file-like object.
Args:
offset (int): offset to seek to.
whence (Optional(int)): value that indicates whether offset is an absolute
or relative position within the file.
Raises:
IOError: if the seek failed.
OSError: if the seek failed.
"""
if not self._is_open:
raise IOError('Not opened.')
if self._current_offset < 0:
raise IOError((
f'Invalid current offset: {self._current_offset:d} value less than '
f'zero.'))
if whence == os.SEEK_CUR:
offset += self._current_offset
elif whence == os.SEEK_END:
if self._uncompressed_stream_size is None:
self._uncompressed_stream_size = self._GetUncompressedStreamSize()
if self._uncompressed_stream_size is None:
raise IOError('Invalid uncompressed stream size.')
offset += self._uncompressed_stream_size
elif whence != os.SEEK_SET:
raise IOError('Unsupported whence.')
if offset < 0:
raise IOError('Invalid offset value less than zero.')
if offset != self._current_offset:
self._current_offset = offset
self._realign_offset = True
[docs]
def get_offset(self):
"""Retrieves the current offset into the file-like object.
Returns:
int: current offset in the uncompressed stream.
Raises:
IOError: if the file-like object has not been opened.
OSError: if the file-like object has not been opened.
"""
if not self._is_open:
raise IOError('Not opened.')
return self._current_offset
[docs]
def get_size(self):
"""Retrieves the size of the file-like object.
Returns:
int: size of the uncompressed stream.
Raises:
IOError: if the file-like object has not been opened.
OSError: if the file-like object has not been opened.
"""
if not self._is_open:
raise IOError('Not opened.')
if self._uncompressed_stream_size is None:
self._uncompressed_stream_size = self._GetUncompressedStreamSize()
return self._uncompressed_stream_size