Failing to deserialize StructureDefinition from OPC-UA Server

Hello, I'm trying to read user-defined structure definitions from an S7-1212.  The objective is to subscribe to a variable with a user-defined structure type called "MyCustomType".

Subscribing to that variable fails in UaExpert 1.5 with the error "BadAttributeIdInvalid" when calling CreateMonitoredItems.  I haven't yet investigated why.

I'm using a `python-opcua` client to read the DataTypeDefinition of a DataType Node located in /Types/DataTypes/BaseDataType/Structure/SimaticStructures/MyCustomType

The response I get seems malformed, perhaps it is referencing an older version of the OPC-UA spec?  I am looking at OPC-UA 1.04 for definitions of StructureDefinition and StructureField.

I can't attach a packet capture here, but here's the ByteString returned by the S7-1212 OPC-UA server when querying the DataTypeDefinition attribute of MyCustomType:

0000   01 05 03 00 01 03 48 0d 00 00 00 00 01 00 00 00
0010   09 00 00 00 65 65 5f 73 74 61 74 75 73 02 00 00
0020   00 00 00 06 ff ff ff ff 00

"\x01\x05\x03\x00\x01\x03\x48\x0d\x00\x00\x00\x00\x01\x00\x00\x00\x09\x00\x00\x00\x65\x65\x5f\x73\x74\x61\x74\x75\x73\x02\x00\x00\x00\x00\x00\x06\xff\xff\xff\xff\x00"

The data looks correct, but truncated.  MyCustomType indeed contains a single field named "ee_status", but the buffer runs out before we can see the DataType of that field.

Hello,

really not familiar with OPC internal flow of data but what exactly you mean with truncated? What you mean with not correct datra from 2 pictures (one sequence with next sequence)? I recommend maybe also think that system on PC and PLC can be different due Endian system but this is my quick idea. Again, this is PLC Forum and ask (show) some PC SW programming in some other languages can be without answers. What result is if you use standard OPC UA SW as Siemens define?

Thanks for your reply Duris,

By truncated, I mean it appears as though the data has been cut short.  However, this isn't the problem because UAExpert is able to correctly decode the field of this structure:

In summary, on the S7-1212:

• UAExpert can read the StructureDefinition successfully.
  
• The python client I'm working with can't yet, or I'm using it incorrectly
  
• neither can subscribe to an OPC-UA Variable Node of type MyCustomType.
  

On an S7-1511:

• both python-opcua and UAExpert clients can subscribe to OPC-UA Variable nodes with custom structure types.
  
• This uses an older form of binary type encoding called "DataTypeDictionaries" (Superseded by DataTypeDefinition, but still included in OPC-UA 1.04)
  

Hello,

thnx for info, also something new to me. Maybe I try point you to S7-1200 firmware, can you tell us that version, also order number? Maybe this info can get you next...

S7-1212 FW: V.4.4.0

Thanks Einstein and Duris!  we'll try the FW update and see if that helps.

Einstein, are you referring to the number of bytes in the OPC-UA layer of the packet as is highlighted here in Wireshark?  I don't have enough information to answer your question.