Node.write_value an extentionObject ?

[fanno]

Hello

i am trying to write a scruture/object value to a node

value: is a TIMER class

@DataTypeRegistry.register
@dataclass
class TIMER:
    PRE: int = field(init=False, default=0, metadata={"ua_type": ua.VariantType.Int32})
    ACC: int = field(init=False, default=0, metadata={"ua_type": ua.VariantType.Int32})
    EN: bool = field(init=False, default=0, metadata={"ua_type": ua.VariantType.Boolean})
    DN: bool = field(init=False, default=0, metadata={"ua_type": ua.VariantType.Boolean})
    TT: bool = field(init=False, default=0, metadata={"ua_type": ua.VariantType.Boolean})

created (and i can see it in the opcua client)

                        snode, dtype_nodeid = await new_struct(
                            self.server,
                            self.getIDX(),
                            struct_name,
                            newFields
                        )

signal.NODE os the node referance
Note is created like this:

ot = await parent.add_variable(self.getIDX(), f"{tag.Name}", ua.Variant(getattr(ua, tag.DataType)(), ua.VariantType.ExtensionObject))

This works(because it is mutable, server timestamp ect is not updated but it works):

timer = await signal.NODE.read_value()
timer.ACC = value.ACC

how ever i would like to be able to do:

await signal.NODE.write_value(value) <---- i know this is wrong.

i would expect this to work ?

await signal.NODE.write_value(ua.Variant(ua.TIMER(value), ua.VariantType.ExtensionObject))

it appears to to work, atleast no errors when it set.

i get this dump when i try to access the tag in a opcua client. tried uaexpert and opcua-client both are the same

VariantType=<VariantType.ExtensionObject: 22>, Dimensions=None, is_array=False)
[2026-01-09 20:50:15,744, uaprocessor.py:165 - process_message() ] ERROR : Error while processing message
Traceback (most recent call last):
  File "C:\.....\asyncua\server\uaprocessor.py", line 147, in process_message
    return await self._process_message(typeid, requesthdr, seqhdr, body)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\.....\asyncua\server\uaprocessor.py", line 303, in _process_message
    self.send_response(requesthdr.RequestHandle, seqhdr, response)
  File "C:\.....\asyncua\server\uaprocessor.py", line 55, in send_response
    struct_to_binary(response), message_type=msgtype, request_id=seqhdr.RequestId
    ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 345, in struct_to_binary
    return serializer(obj)
           ^^^^^^^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 335, in serialize
    return b"".join(
           ^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 336, in <genexpr>
    serializer(enc_value(obj)) if name == "Encoding" else serializer(obj.__dict__[name])
                                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 412, in serialize
    return data_size + b"".join(type_serializer(el) for el in val)
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 412, in <genexpr>
    return data_size + b"".join(type_serializer(el) for el in val)
                                ^^^^^^^^^^^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 345, in struct_to_binary
    return serializer(obj)
           ^^^^^^^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 335, in serialize
    return b"".join(
           ^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 336, in <genexpr>
    serializer(enc_value(obj)) if name == "Encoding" else serializer(obj.__dict__[name])
                                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 286, in <lambda>
    return lambda val: b"" if val is None else serializer(val)
                                               ^^^^^^^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 500, in variant_to_binary
    body = pack_uatype(var.VariantType, var.Value)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 199, in pack_uatype
    return create_uatype_serializer(vtype)(value)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 587, in extensionobject_to_binary
    body = struct_to_binary(obj)
           ^^^^^^^^^^^^^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 345, in struct_to_binary
    return serializer(obj)
           ^^^^^^^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 335, in serialize
    return b"".join(
           ^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 336, in <genexpr>
    serializer(enc_value(obj)) if name == "Encoding" else serializer(obj.__dict__[name])
                                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\.....\asyncua\ua\ua_binary.py", line 136, in pack
    return struct.pack(self.format, data)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
struct.error: required argument is not an integer

i tried looking throw the source, but i am unsure what i am looking for =(

-Thanks

[fanno]

I figureed out i had to use the ua.TIMER() for my plc memory aswell then it works.

For anyone else who may have same problem

If writing a object it appers it MUST be a variant from ua.XXXXXX() for it to work.