# -*- coding: utf-8 -*-
"""The CPIO extracted file-like object implementation."""
import os
from dfvfs.file_io import file_io
from dfvfs.resolver import resolver
[docs]
class CPIOFile(file_io.FileIO):
"""File input/output (IO) object using CPIOArchiveFile."""
[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(CPIOFile, self).__init__(resolver_context, path_spec)
self._cpio_archive_file = None
self._cpio_archive_file_entry = None
self._current_offset = 0
self._file_system = None
self._size = 0
def _Close(self):
"""Closes the file-like object."""
self._cpio_archive_file_entry = None
self._cpio_archive_file = 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)
file_entry = file_system.GetFileEntryByPathSpec(self._path_spec)
if not file_entry:
raise IOError('Unable to retrieve file entry.')
self._file_system = file_system
self._cpio_archive_file = self._file_system.GetCPIOArchiveFile()
self._cpio_archive_file_entry = file_entry.GetCPIOArchiveFileEntry()
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._current_offset >= self._cpio_archive_file_entry.data_size:
return b''
file_offset = (
self._cpio_archive_file_entry.data_offset + self._current_offset)
read_size = self._cpio_archive_file_entry.data_size - self._current_offset
read_size = min(read_size, size)
data = self._cpio_archive_file.ReadDataAtOffset(file_offset, read_size)
# It is possible the that returned data size is not the same as the
# requested data size. At this layer we don't care and this discrepancy
# should be dealt with on a higher layer if necessary.
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 whence == os.SEEK_CUR:
offset += self._current_offset
elif whence == os.SEEK_END:
offset += self._cpio_archive_file_entry.data_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 CPIO archived file.
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 CPIO archived file.
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._cpio_archive_file_entry.data_size