def upload_file(
        self, filename, bucket, key, callback=None, extra_args=None
    ):
        """Upload a file to an S3 object.

        Variants have also been injected into S3 client, Bucket and Object.
        You don't have to use S3Transfer.upload_file() directly.
        """
        if extra_args is None:
            extra_args = {}
        self._validate_all_known_args(extra_args, self.ALLOWED_UPLOAD_ARGS)
        events = self._client.meta.events
        events.register_first(
            'request-created.s3',
            disable_upload_callbacks,
            unique_id='s3upload-callback-disable',
        )
        events.register_last(
            'request-created.s3',
            enable_upload_callbacks,
            unique_id='s3upload-callback-enable',
        )
        if (
            self._osutil.get_file_size(filename)
            >= self._config.multipart_threshold
        ):
            self._multipart_upload(filename, bucket, key, callback, extra_args)
        else:
            self._put_object(filename, bucket, key, callback, extra_args)