Hacking through WrapFS #207
Description
Disclaimer: This might be long for something stupid or simple. Please be patient :-)
As discussed in #204 - I am trying to write a custom FS that caches files and directories. For the same I needed a custom file wrapper that does setup and teardown stuff. This is how it looks like:
class _custom_file_wrapper(object):
"""This is a custom file class that does some setup and teardown stuff.."""
def __init__(self,
file_system,
parent_fs,
path,
mode,
buffering=-1,
encoding=None,
newline='',
line_buffering=False):
print('We should see this message when a new file is created!!')
self._file = parent_fs.openbin(path=path,
mode=mode,
buffering=buffering,
encoding=encoding)
# do some setUp stuff with _file.
print('Filesystem: {}, Parent File system: {}'.format(file_system, parent_fs))
def __enter__(self):
return self._file
def __exit__(self, exc_type, exc_value, traceback):
self.close()
return False
def close(self):
# do some tearDown stuff for the _file object.
print('Closing File ....')
self._file.close()
def __getattr__(self, item):
return getattr(self._file, item)My WrapFS wraps an OSFS instance and overwrites functionality such as open and openbin to use the above _custom_file_wrapper object. This works fine when the essential methods are called but when non-essential methods such as move or copy are called, my _custom_file_wrapper is ignored. Below is how my custom WrapFS instance looks like:
class TestFileSystem(WrapFS):
def __init__(self, path):
super(TestFileSystem, self).__init__(open_fs(path)) # wrap osfs at path
self._wrap_fs._meta['supports_rename'] = False
# ^^^ not sure if this is required as a custom getmeta() is defined below.
# But still - to be safe.
def getmeta(self, namespace="standard"):
"""Defined so that os.rename is never used."""
self.check()
meta = self.delegate_fs().getmeta(namespace=namespace)
meta['supports_rename'] = False
return meta
def openbin(self, path, mode="r", buffering=-1, **options):
print('Inside openbin of TestFileSystem. This is a test!')
return _custom_file_wrapper(parent_fs=self.delegate_fs(),
file_system=self,
path=path,
mode=Mode(mode).to_platform_bin(),
buffering=buffering)
# NOTE: open() is similar. I omitted it's definition since `move()` uses move.move_file which would
# neither use open() or openbin()When run together, the following result is obtained (Link to gist)
Starting FS test
Listing files/directories in cwd: ['another.py', 'test.py']
Rename is False. os.rename should not be used
Inside openbin of TestFileSystem. This is a test!
We should see this message when a new file is created!!
Filesystem: <osfs '/home/abhinav/demo'>, Parent File system: <osfs '/home/abhinav/demo'>
Closing File ....
------------- Start Move --------------
------------- Stop Move --------------
Stopping FS testAs seen from above output, my custom defined essesntial methods were not invoked during the call of move().
Problem:
The reason for this is that all methods defined in WrapFS call the underlying OSFS methods.
I was hoping that in it's implementation, only essential methods would be allowed to do so.