How to use the pypsexec.rpc.ContextElement function in pypsexec

def test_create_message(self):
        message = BindPDU()
        message['pfx_flags'].set_flag(PFlags.PFC_MAYBE)
        packed_drep = DataRepresentationFormat()
        packed_drep['integer_character'] = \
            IntegerCharacterRepresentation.ASCII_LITTLE_ENDIAN
        packed_drep['floating_point'] = FloatingPointRepresentation.IEEE
        message['packed_drep'] = packed_drep
        message['call_id'] = 4
        message['assoc_group_id'] = 2
        con_elem = ContextElement()
        con_elem['context_id'] = 1
        syntax = SyntaxIdElement()
        syntax['uuid'] = uuid.UUID(bytes=b"\xff" * 16)
        con_elem['abstract_syntax'] = syntax
        con_elem['transfer_syntaxes'] = [syntax]
        message['context_elems'] = [con_elem]
        expected = b"\x05" \
                   b"\x00" \
                   b"\x0b" \
                   b"\x40" \
                   b"\x10" \
                   b"\x00" \
                   b"\x00" \
                   b"\x00" \
                   b"\x48\x00" \
                   b"\x00\x00" \

def test_parse_message(self):
        actual = ContextElement()
        data = b"\x04\x00" \
               b"\x02" \
               b"\x00" \
               b"\xff\xff\xff\xff\xff\xff\xff\xff" \
               b"\xff\xff\xff\xff\xff\xff\xff\xff" \
               b"\x00\x00\x00\x00" \
               b"\xee\xee\xee\xee\xee\xee\xee\xee" \
               b"\xee\xee\xee\xee\xee\xee\xee\xee" \
               b"\x00\x00\x00\x00" \
               b"\xdd\xdd\xdd\xdd\xdd\xdd\xdd\xdd" \
               b"\xdd\xdd\xdd\xdd\xdd\xdd\xdd\xdd" \
               b"\x00\x00\x00\x00"
        data = actual.unpack(data)
        assert len(actual) == 64
        assert data == b""
        assert actual['context_id'].get_value() == 4

def test_create_message(self):
        message = ContextElement()
        message['context_id'] = 4
        syntax1 = SyntaxIdElement()
        syntax1['uuid'] = uuid.UUID(bytes=b"\xff" * 16)
        syntax2 = SyntaxIdElement()
        syntax2['uuid'] = uuid.UUID(bytes=b"\xee" * 16)
        syntax3 = SyntaxIdElement()
        syntax3['uuid'] = uuid.UUID(bytes=b"\xdd" * 16)
        message['abstract_syntax'] = syntax1
        message['transfer_syntaxes'] = [syntax2, syntax3]
        expected = b"\x04\x00" \
                   b"\x02" \
                   b"\x00" \
                   b"\xff\xff\xff\xff\xff\xff\xff\xff" \
                   b"\xff\xff\xff\xff\xff\xff\xff\xff" \
                   b"\x00\x00\x00\x00" \
                   b"\xee\xee\xee\xee\xee\xee\xee\xee" \

context_ndr = ContextElement()
        context_ndr['context_id'] = 0
        context_ndr['abstract_syntax'] = SyntaxIdElement()
        context_ndr['abstract_syntax']['uuid'] = \
            uuid.UUID("367ABB81-9844-35F1-AD32-98F038001003")
        context_ndr['abstract_syntax']['version'] = 2

        # https://msdn.microsoft.com/en-us/library/cc243843.aspx
        ndr_syntax = SyntaxIdElement()
        ndr_syntax['uuid'] = uuid.UUID("8a885d04-1ceb-11c9-9fe8-08002b104860")
        ndr_syntax['version'] = 2
        context_ndr['transfer_syntaxes'] = [
            ndr_syntax
        ]

        context_bind = ContextElement()
        context_bind['context_id'] = 1
        context_bind['abstract_syntax'] = SyntaxIdElement()
        context_bind['abstract_syntax']['uuid'] = \
            uuid.UUID("367ABB81-9844-35F1-AD32-98F038001003")
        context_bind['abstract_syntax']['version'] = 2

        # https://msdn.microsoft.com/en-us/library/cc243715.aspx
        # uuid prefix = 6CB71C2C-9812-4540
        # uuid prefix bytes = b'\x2c\x1c\xb7\x6c\x12\x98\x40\x45'
        # BindTimeFeatureNegotiateBitmask
        # https://msdn.microsoft.com/en-us/library/cc243884.aspx
        # SecurityContextMultiplexingSupported = 0x01
        # KeepConnectionOnOrphanSupported = 0x02
        # version number is 1
        bind_syntax = SyntaxIdElement()
        bind_syntax['uuid'] = b'\x2c\x1c\xb7\x6c\x12\x98\x40\x45' \

default=lambda s: len(s['transfer_syntaxes'].get_value())
            )),
            ('reserved', IntField(size=1)),
            ('abstract_syntax', StructureField(
                structure_type=SyntaxIdElement
            )),
            ('transfer_syntaxes', ListField(
                list_type=StructureField(
                    size=20,
                    structure_type=SyntaxIdElement
                ),
                list_count=lambda s: s['n_transfer_syn'].get_value(),
                size=lambda s: s['n_transfer_syn'].get_value() * 20
            )),
        ])
        super(ContextElement, self).__init__()

0,
                           ShareAccess.FILE_SHARE_READ |
                           ShareAccess.FILE_SHARE_WRITE |
                           ShareAccess.FILE_SHARE_DELETE,
                           CreateDisposition.FILE_OPEN,
                           CreateOptions.FILE_NON_DIRECTORY_FILE)

        # we need to bind svcctl to SCManagerW over DCE/RPC
        bind = BindPDU()
        bind['pfx_flags'].set_flag(PFlags.PFC_FIRST_FRAG)
        bind['pfx_flags'].set_flag(PFlags.PFC_LAST_FRAG)
        bind['packed_drep'] = DataRepresentationFormat()
        bind['call_id'] = self.call_id
        self.call_id += 1

        context_ndr = ContextElement()
        context_ndr['context_id'] = 0
        context_ndr['abstract_syntax'] = SyntaxIdElement()
        context_ndr['abstract_syntax']['uuid'] = \
            uuid.UUID("367ABB81-9844-35F1-AD32-98F038001003")
        context_ndr['abstract_syntax']['version'] = 2

        # https://msdn.microsoft.com/en-us/library/cc243843.aspx
        ndr_syntax = SyntaxIdElement()
        ndr_syntax['uuid'] = uuid.UUID("8a885d04-1ceb-11c9-9fe8-08002b104860")
        ndr_syntax['version'] = 2
        context_ndr['transfer_syntaxes'] = [
            ndr_syntax
        ]

        context_bind = ContextElement()
        context_bind['context_id'] = 1

def _unpack_context_elems(self, structure, data):
        context_elems = []
        while data != b"":
            context_elem = ContextElement()
            data = context_elem.unpack(data)
            context_elems.append(context_elem)

        return context_elems

)),
            ('max_recv_frag', IntField(
                size=2,
                default=4280
            )),
            ('assoc_group_id', IntField(size=4)),
            # p_context_list_t
            ('n_context_elem', IntField(
                size=1,
                default=lambda s: len(s['context_elems'].get_value())
            )),
            ('reserved', IntField(size=1)),
            ('reserved2', IntField(size=2)),
            ('context_elems', ListField(
                list_count=lambda s: s['n_context_elem'].get_value(),
                list_type=StructureField(structure_type=ContextElement),
                unpack_func=lambda s, d: self._unpack_context_elems(s, d)
            )),
            ('auth_verifier', BytesField(
                size=lambda s: s['auth_length'].get_value()
            ))
        ])
        super(BindPDU, self).__init__()