Method _read_frame

gunicorn/asgi/websocket.py:262–342

Read a single WebSocket frame. Returns: tuple: (opcode, payload) or None if connection closed

(self)

                })

    async def _read_frame(self):  # pylint: disable=too-many-return-statements
        """Read a single WebSocket frame.

        Returns:
            tuple: (opcode, payload) or None if connection closed
        """
        # Read frame header (2 bytes minimum)
        header = await self._read_exact(2)
        if not header:
            return None

        first_byte, second_byte = header[0], header[1]

        fin = (first_byte >> 7) & 1
        rsv1 = (first_byte >> 6) & 1
        rsv2 = (first_byte >> 5) & 1
        rsv3 = (first_byte >> 4) & 1
        opcode = first_byte & 0x0F

        # RSV bits must be 0 (no extensions)
        if rsv1 or rsv2 or rsv3:
            await self._send_close(CLOSE_PROTOCOL_ERROR, "RSV bits set")
            return None

        masked = (second_byte >> 7) & 1
        payload_len = second_byte & 0x7F

        # Client frames must be masked (RFC 6455)
        if not masked:
            await self._send_close(CLOSE_PROTOCOL_ERROR, "Frame not masked")
            return None

        # Extended payload length
        if payload_len == 126:
            ext_len = await self._read_exact(2)
            if not ext_len:
                return None
            payload_len = struct.unpack("!H", ext_len)[0]
        elif payload_len == 127:
            ext_len = await self._read_exact(8)
            if not ext_len:
                return None
            payload_len = struct.unpack("!Q", ext_len)[0]

        # Read masking key
        masking_key = await self._read_exact(4)
        if not masking_key:
            return None

        # Read payload
        payload = await self._read_exact(payload_len)
        if payload is None:
            return None

        # Unmask payload
        payload = self._unmask(payload, masking_key)

        # Handle fragmented messages