Source code for dfvfs.file_io.data_range_io

# -*- 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