# -*- coding: utf-8 -*-
"""The operating system attribute implementation."""
import os
try:
import xattr
except ImportError:
xattr = None
from dfvfs.vfs import attribute
[docs]
class OSExtendedAttribute(attribute.Attribute):
"""Extended attribute that uses the operating system."""
[docs]
def __init__(self, location, name):
"""Initializes an attribute.
Args:
location (str): path of the file.
name (str): name of the extended attribute.
"""
super(OSExtendedAttribute, self).__init__()
self._current_offset = 0
self._data = xattr.getxattr(location, name)
self._location = location
self._name = name
self._size = len(self._data)
@property
def name(self):
"""str: name."""
return self._name
# 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 input/output (IO) object.
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 size is None:
size = self._size
data = self._data[self._current_offset:self._current_offset + size]
self._current_offset += len(data)
return data
[docs]
def seek(self, offset, whence=os.SEEK_SET):
"""Seeks to an offset within the file input/output (IO) object.
Args:
offset (int): offset to seek.
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 whence == os.SEEK_CUR:
offset += self._current_offset
elif whence == os.SEEK_END:
offset = self._size - offset
elif whence != os.SEEK_SET:
raise IOError('Invalid whence')
if offset < 0:
raise IOError('Invalid offset')
self._current_offset = offset
# get_offset() is preferred above tell() by the libbfio layer used in libyal.
[docs]
def get_offset(self):
"""Retrieves the current offset into the file input/output (IO) object.
Returns:
int: current offset into the file input/output (IO) object.
"""
return self._current_offset
# Pythonesque alias for get_offset().
[docs]
def tell(self):
"""Retrieves the current offset into the file input/output (IO) object."""
return self.get_offset()
[docs]
def get_size(self):
"""Retrieves the size of the file input/output (IO) object.
Returns:
int: size of the file input/output (IO) object.
"""
return self._size
[docs]
def seekable(self):
"""Determines if a file input/output (IO) object is seekable.
Returns:
bool: True since a file IO object provides a seek method.
"""
return True