def _on_frame_start(self, data):
        header, payloadlen = struct.unpack("BB", data)
        self._final_frame = header & 0x80
        reserved_bits = header & 0x70
        self._frame_opcode = header & 0xf
        self._frame_opcode_is_control = self._frame_opcode & 0x8
        if reserved_bits:
            # client is using as-yet-undefined extensions; abort
            self._abort()
            return
        self._masked_frame = bool(payloadlen & 0x80)
        payloadlen = payloadlen & 0x7f
        if self._frame_opcode_is_control and payloadlen >= 126:
            # control frames must have payload < 126
            self._abort()
            return
        try:
            if payloadlen < 126:
                self._frame_length = payloadlen
                if self._masked_frame:
                    self.stream.read_bytes(4, self._on_masking_key)
                else:
                    self.stream.read_bytes(self._frame_length, self._on_frame_data)
            elif payloadlen == 126:
                self.stream.read_bytes(2, self._on_frame_length_16)
            elif payloadlen == 127:
                self.stream.read_bytes(8, self._on_frame_length_64)
        except StreamClosedError:
            self._abort()
dataset/ETHPy150Open RobotWebTools/rosbridge_suite/rosbridge_server/src/tornado/websocket.py/WebSocketProtocol13._on_frame_start/original