def __init__(
        self,
        fin: int = 0,
        rsv1: int = 0,
        rsv2: int = 0,
        rsv3: int = 0,
        opcode: int = OPCODE_TEXT,
        mask_value: int = 1,
        data: Union[str, bytes, None] = "",
    ) -> None:
        """
        Constructor for ABNF. Please check RFC for arguments.
        """
        self.fin = fin
        self.rsv1 = rsv1
        self.rsv2 = rsv2
        self.rsv3 = rsv3
        self.opcode = opcode
        self.mask_value = mask_value
        if data is None:
            data = ""
        self.data = data
        self.get_mask_key = os.urandom

        Constructor for ABNF. Please check RFC for arguments.
        
websocket/_abnf.py