# -*- coding: utf-8 -*-
"""The GUID Partition Table (GPT) file-like object implementation."""
import os
from dfvfs.file_io import file_io
from dfvfs.lib import errors
from dfvfs.resolver import resolver
[docs]
class GPTFile(file_io.FileIO):
"""File input/output (IO) object using pyvsgpt."""
[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(GPTFile, self).__init__(resolver_context, path_spec)
self._current_offset = None
self._file_object = None
self._file_system = None
self._partition_offset = None
self._partition_size = None
self._vsgpt_partition = None
def _Close(self):
"""Closes the file-like object."""
self._current_offset = None
self._partition_offset = None
self._partition_size = None
self._vsgpt_partition = None
self._file_object = None
self._file_system = None
def _Open(self, mode='rb'):
"""Opens the file-like object defined by path specification.
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.
"""
file_system = resolver.Resolver.OpenFileSystem(
self._path_spec, resolver_context=self._resolver_context)
entry_index = file_system.GetEntryIndexByPathSpec(self._path_spec)
if entry_index is None:
raise errors.PathSpecError(
'Unable to retrieve entry index from path specification.')
vsgpt_volume = file_system.GetGPTVolume()
if not vsgpt_volume.has_partition_with_identifier(entry_index):
raise errors.PathSpecError(
f'Missing GPT partition with entry index: {entry_index:d}')
self._file_system = file_system
self._vsgpt_partition = vsgpt_volume.get_partition_by_identifier(
entry_index)
# Note that using pass-through IO in Python is faster than using
# the vsgpt_partition read and seek methods.
self._file_object = resolver.Resolver.OpenFileObject(
self._path_spec.parent, resolver_context=self._resolver_context)
self._current_offset = 0
self._partition_offset = self._vsgpt_partition.get_volume_offset()
self._partition_size = self._vsgpt_partition.get_size()
# 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._partition_offset < 0 or self._partition_size < 0:
raise IOError('Invalid partition 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._partition_size:
return b''
if size is None:
size = self._partition_size
if self._current_offset + size > self._partition_size:
size = self._partition_size - self._current_offset
self._file_object.seek(
self._partition_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._partition_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 partition.
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 partition.
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._partition_size