# -*- coding: utf-8 -*-
"""The data range file-like object."""
import os
from dfvfs.file_io import file_io
from dfvfs.lib import errors
from dfvfs.resolver import resolver
[docs]
class DataRange(file_io.FileIO):
"""File input/output (IO) object that maps an in-file data range.
The data range object allows to expose a single partition within a full disk
image as a separate file-like object by mapping the data range (offset and
size) of the volume on top of the full disk image.
"""
[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(DataRange, self).__init__(resolver_context, path_spec)
self._current_offset = 0
self._file_object = None
self._range_offset = -1
self._range_size = -1
def _Close(self):
"""Closes the file-like object.
If the file-like object was passed in the init function the data range file-
like object does not control the file-like object and should not actually
close it.
"""
self._file_object = None
self._range_offset = -1
self._range_size = -1
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.')
range_offset = getattr(self._path_spec, 'range_offset', None)
range_size = getattr(self._path_spec, 'range_size', None)
if range_offset is None or range_size is None:
raise errors.PathSpecError(
'Path specification missing range offset and range size.')
self._SetRange(range_offset, range_size)
self._file_object = resolver.Resolver.OpenFileObject(
self._path_spec.parent, resolver_context=self._resolver_context)
def _SetRange(self, range_offset, range_size):
"""Sets the data range (offset and size).
The data range is used to map a range of data within one file
(e.g. a single partition within a full disk image) as a file-like object.
Args:
range_offset (int): start offset of the data range.
range_size (int): size of the data range.
Raises:
ValueError: if the range offset or range size is invalid.
"""
if range_offset < 0:
raise ValueError(
f'Invalid range offset: {range_offset:d} value out of bounds.')
if range_size < 0:
raise ValueError(
f'Invalid range size: {range_size:d} value out of bounds.')
self._range_offset = range_offset
self._range_size = range_size
self._current_offset = 0
# 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._range_offset < 0 or self._range_size < 0:
raise IOError('Invalid data range.')
if self._current_offset < 0:
raise IOError((
f'Invalid current offset: {self._current_offset:d} value less than '
f'zero.'))
if self._current_offset >= self._range_size:
return b''
if size is None:
size = self._range_size
if self._current_offset + size > self._range_size:
size = self._range_size - self._current_offset
self._file_object.seek(
self._range_offset + self._current_offset, os.SEEK_SET)
data = self._file_object.read(size)
self._current_offset += len(data)
return 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:
offset += self._range_size
elif whence != os.SEEK_SET:
raise IOError('Unsupported whence.')
if offset < 0:
raise IOError('Invalid offset value less than zero.')
self._current_offset = offset
[docs]
def get_offset(self):
"""Retrieves the current offset into the file-like object.
Returns:
int: current offset in the data range.
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 data range.
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._range_size