How to use the xandikos.store.open_by_extension function in xandikos

def _scan_uids(self):
        removed = set(self._fname_to_uid.keys())
        for (name, content_type, etag) in self.iter_with_etag():
            if name in removed:
                removed.remove(name)
            if (name in self._fname_to_uid and
                    self._fname_to_uid[name][0] == etag):
                continue
            fi = open_by_extension(self._get_raw(name, etag), name,
                                   self.extra_file_handlers)
            try:
                uid = fi.get_uid()
            except KeyError:
                logger.warning('No UID found in file %s', name)
                uid = None
            except InvalidFileContents:
                logging.warning('Unable to parse file %s', name)
                uid = None
            except NotImplementedError:
                # This file type doesn't support UIDs
                uid = None
            self._fname_to_uid[name] = (etag, uid)
            if uid is not None:
                self._uid_to_fname[uid] = (name, etag)
        for name in removed:

def _scan_uids(self):
        removed = set(self._fname_to_uid.keys())
        for (name, mode, sha) in self._iterblobs():
            etag = sha.decode('ascii')
            if name in removed:
                removed.remove(name)
            if (name in self._fname_to_uid and
                    self._fname_to_uid[name][0] == etag):
                continue
            blob = self.repo.object_store[sha]
            fi = open_by_extension(blob.chunked, name,
                                   self.extra_file_handlers)
            try:
                uid = fi.get_uid()
            except KeyError:
                logger.warning('No UID found in file %s', name)
                uid = None
            except InvalidFileContents:
                logging.warning('Unable to parse file %s', name)
                uid = None
            except NotImplementedError:
                # This file type doesn't support UIDs
                uid = None
            self._fname_to_uid[name] = (etag, uid)
            if uid is not None:
                self._uid_to_fname[uid] = (name, etag)
        for name in removed:

:param etag: Optional mandatory etag of object to remove
        :raise NoSuchItem: when the item doesn't exist
        :raise InvalidETag: If the specified ETag doesn't match the curren
        """
        tree = self._get_current_tree()
        name_enc = name.encode(DEFAULT_ENCODING)
        try:
            current_sha = tree[name_enc][1]
        except KeyError:
            raise NoSuchItem(name)
        if etag is not None and current_sha != etag.encode('ascii'):
            raise InvalidETag(name, etag, current_sha.decode('ascii'))
        del tree[name_enc]
        self.repo.object_store.add_objects([(tree, '')])
        if message is None:
            fi = open_by_extension(
                self.repo.object_store[current_sha].chunked, name,
                self.extra_file_handlers)
            message = "Delete " + fi.describe(name)
        self._commit_tree(tree.id, message.encode(DEFAULT_ENCODING),
                          author=author)

replace_etag=None):
        """Import a single object.

        :param name: name of the object
        :param content_type: Content type
        :param data: serialized object as list of bytes
        :param message: Commit message
        :param author: Optional author
        :param replace_etag: optional etag of object to replace
        :raise InvalidETag: when the name already exists but with different
                            etag
        :raise DuplicateUidError: when the uid already exists
        :return: etag
        """
        if content_type is None:
            fi = open_by_extension(data, name, self.extra_file_handlers)
        else:
            fi = open_by_content_type(
                data, content_type, self.extra_file_handlers)
        if name is None:
            name = str(uuid.uuid4())
            extension = MIMETYPES.guess_extension(content_type)
            if extension is not None:
                name += extension
        fi.validate()
        try:
            uid = fi.get_uid()
        except (KeyError, NotImplementedError):
            uid = None
        self._check_duplicate(uid, name, replace_etag)
        if message is None:
            try:

replace_etag=None):
        """Import a single object.

        :param name: name of the object
        :param content_type: Content type
        :param data: serialized object as list of bytes
        :param message: Commit message
        :param author: Optional author
        :param replace_etag: optional etag of object to replace
        :raise InvalidETag: when the name already exists but with different
                            etag
        :raise DuplicateUidError: when the uid already exists
        :return: etag
        """
        if content_type is None:
            fi = open_by_extension(data, name, self.extra_file_handlers)
        else:
            fi = open_by_content_type(
                data, content_type, self.extra_file_handlers)
        if name is None:
            name = str(uuid.uuid4())
            extension = MIMETYPES.guess_extension(content_type)
            if extension is not None:
                name += extension
        fi.validate()
        try:
            uid = fi.get_uid()
        except (KeyError, NotImplementedError):
            uid = None
        self._check_duplicate(uid, name, replace_etag)

        # TODO(jelmer): Check that extensions match content type: