Source code for dfvfs.file_io.cpio_file_io

# -*- 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