def unread_data(self, data: bytes) -> None:
        """rollback reading some data from stream, inserting it to buffer head."""
        warnings.warn(
            "unread_data() is deprecated "
            "and will be removed in future releases (#3260)",
            DeprecationWarning,
            stacklevel=2,
        )
        if not data:
            return

        if self._buffer_offset:
            self._buffer[0] = self._buffer[0][self._buffer_offset :]
            self._buffer_offset = 0
        self._size += len(data)
        self._cursor -= len(data)
        self._buffer.appendleft(data)
        self._eof_counter = 0
rollback reading some data from stream, inserting it to buffer head.
lib/aiohttp/streams.py