def decode_header(cls, stream):
        """
        Decode a WebSocket header.

        :param stream: A file like object that can be 'read' from.
        :returns: A `Header` instance.
        """
        read = stream.read
        data = read(2)
        if len(data) != 2:
            raise WebSocketError("Unexpected EOF while decoding header")
        first_byte, second_byte = struct.unpack('!BB', data)
        header = cls(
            fin=first_byte & cls.FIN_MASK == cls.FIN_MASK,
            opcode=first_byte & cls.OPCODE_MASK,
            flags=first_byte & cls.HEADER_FLAG_MASK,
            length=second_byte & cls.LENGTH_MASK)
        has_mask = second_byte & cls.MASK_MASK == cls.MASK_MASK
        if header.opcode > 0x07:
            if not header.fin:
                raise WebSocketError('Received fragmented control frame: {0!r}'.format(data))
            # Control frames MUST have a payload length of 125 bytes or less
            if header.length > 125:
                raise FrameTooLargeException('Control frame cannot be larger than 125 bytes: {0!r}'.format(data))
        if header.length == 126:
            # 16 bit length
            data = read(2)
            if len(data) != 2:
                raise WebSocketError('Unexpected EOF while decoding header')
            header.length = struct.unpack('!H', data)[0]
        elif header.length == 127:
            # 64 bit length
            data = read(8)
            if len(data) != 8:
                raise WebSocketError('Unexpected EOF while decoding header')
            header.length = struct.unpack('!Q', data)[0]
        if has_mask:
            mask = read(4)
            if len(mask) != 4:
                raise WebSocketError('Unexpected EOF while decoding header')
            header.mask = mask
        return header

        Decode a WebSocket header.

        :param stream: A file like object that can be 'read' from.
        :returns: A `Header` instance.
        
ws4redis/websocket.py