"""The operating system file-like object implementation."""
import stat
import os
import pysmdev
from dfvfs.file_io import file_io
from dfvfs.lib import definitions
from dfvfs.lib import errors
[docs]
class OSFile(file_io.FileIO):
"""File input/output (IO) object that uses the operating system."""
[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().__init__(resolver_context, path_spec)
self._file_object = None
self._size = 0
def _Close(self):
"""Closes the file-like object."""
self._file_object.close()
self._file_object = None
def _Open(self):
"""Opens the file-like object defined by path specification.
Raises:
AccessError: if the access to open the file was denied.
MountPointError: if the mount point specified in the path specification
does not exist.
OSError: if the file-like object could not be opened.
PathSpecError: if the path specification is incorrect.
"""
location = getattr(self._path_spec, "location", None)
if self._path_spec.HasParent():
parent_path_spec = self._path_spec.parent
if parent_path_spec.type_indicator != definitions.TYPE_INDICATOR_MOUNT:
raise errors.PathSpecError(
"Unsupported path specification with parent."
)
mount_path_spec = self._resolver_context.GetMountPoint(
parent_path_spec.identifier
)
if not mount_path_spec:
raise errors.MountPointError(
f"No such mount point: {parent_path_spec.identifier:s}"
)
if (
mount_path_spec.type_indicator != definitions.TYPE_INDICATOR_OS
or mount_path_spec.parent
):
raise errors.MountPointError(
"Unsupported mount point path specification."
)
mount_path = mount_path_spec.location
if mount_path[-1] == os.path.sep:
mount_path = mount_path[:-1]
# Cannot use os.path.join() here since location is prefixed with a path
# segment separator.
location = "".join([mount_path, location])
if location is None:
raise errors.PathSpecError("Path specification missing location.")
# Windows does not support running os.stat on device files so we use
# libsmdev to do an initial check.
try:
is_device = pysmdev.check_device(location)
except OSError as exception:
# Since os.stat() will not recognize Windows device file names and
# will return '[Error 87] The parameter is incorrect' we check here
# if pysmdev exception message contains ' access denied ' and raise
# AccessError instead.
if " access denied " in str(exception):
raise errors.AccessError(
f"Access denied to file: {location:s} with error: {exception!s}"
)
is_device = False
if not is_device:
try:
stat_info = os.stat(location)
except OSError as exception:
raise OSError(f"Unable to open file with error: {exception!s}")
# In case the libsmdev check is not able to detect the device also use
# the stat information.
if stat.S_ISCHR(stat_info.st_mode) or stat.S_ISBLK(stat_info.st_mode):
is_device = True
if is_device:
smdev_handle = pysmdev.handle()
smdev_handle.open(location, mode="r")
self._file_object = smdev_handle
self._size = smdev_handle.media_size
else:
# pylint: disable=consider-using-with
self._file_object = open(
location,
mode="rb",
)
self._size = stat_info.st_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:
OSError: if the read failed.
"""
if not self._is_open:
raise OSError("Not opened.")
if size is None:
size = self._size - self._file_object.tell()
return self._file_object.read(size)
[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:
OSError: if the seek failed.
"""
if not self._is_open:
raise OSError("Not opened.")
# For a yet unknown reason a Python file-like object on Windows allows for
# invalid whence values to be passed to the seek function. This check
# makes sure the behavior of the function is the same on all platforms.
if whence not in (os.SEEK_CUR, os.SEEK_END, os.SEEK_SET):
raise OSError("Unsupported whence.")
self._file_object.seek(offset, whence)
[docs]
def get_offset(self):
"""Retrieves the current offset into the file-like object.
Returns:
int: current offset into the file-like object.
Raises:
OSError: if the file-like object has not been opened.
"""
if not self._is_open:
raise OSError("Not opened.")
return self._file_object.tell()
[docs]
def get_size(self):
"""Retrieves the size of the file-like object.
Returns:
int: size of the file-like object data.
Raises:
OSError: if the file-like object has not been opened.
"""
if not self._is_open:
raise OSError("Not opened.")
return self._size