def list_folder(self, path):
return SFTP_OP_UNSUPPORTED<EOL>
Return a list of files within a given folder.  The ``path`` will use
posix notation (``"/"`` separates folder names) and may be an absolute
or relative path.

The list of files is expected to be a list of `.SFTPAttributes`
objects, which are similar in structure to the objects returned by
``os.stat``.  In addition, each object should have its ``filename``
field filled in, since this is important to a directory listing and
not normally present in ``os.stat`` results.  The method
`.SFTPAttributes.from_stat` will usually do what you want.

In case of an error, you should return one of the ``SFTP_*`` error
codes, such as ``SFTP_PERMISSION_DENIED``.

:param str path: the requested path (relative or absolute) to be
    listed.
:return:
    a list of the files in the given folder, using `.SFTPAttributes`
    objects.

.. note::
    You should normalize the given ``path`` first (see the `os.path`
    module) and check appropriate permissions before returning the list
    of files.  Be careful of malicious clients attempting to use
    relative paths to escape restricted folders, if you're doing a
    direct translation from the SFTP server path to your local
    filesystem.