Source code for dfvfs.file_io.gpt_file_io

# -*- 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