Wrong decoding on WPT Messages

[famnz]

Hello, for security reasons I can not uplad whole pcap files but I will try to give you as much context as I can, we use the wireshark plugin https://github.com/dspace-group/dsV2Gshark that base their decoding in cbexigen.
I,ve noticed that the message WPT_FinePositioningSetup when there is no SpecificDataContainer or LF_SystemSetupData is being decoded as ServiceSelectionRes

I've traced this issue because while encoding our message since there are no DataContainers after the NaturalOffset element we set the eventCode as 2 which means end element. But while decoding it treats it as EXI_ERROR__UNKNOWN_EVENT_CODE

https://raw.githubusercontent.com/dspace-group/dsV2Gshark/refs/heads/main/V2G_Libraries/Third_Party/cbv2g/iso-20/iso20_WPT_Decoder.c Line 21129

[barsnick]

Too bad GitHub cannot render or inline this large file's link as code:

https://github.com/dspace-group/dsV2Gshark/blob/0914449f0accf229763f8a642f58f625a9e02f70/V2G_Libraries/Third_Party/cbv2g/iso-20/iso20_WPT_Decoder.c#L21129

after the NaturalOffset element we set the eventCode as 2 which means end element

Whom do you mean with "we"? Who encoded this?

From a quick look, this code looks correct: The event code should be either 0 (in presence of a VendorSpecificDataContainer) or 1 (in case of END element).

You can try extracting the offending message and its neighbors from the PCAP using tshark. probably with something like
tshark -r input.pcap -Y "frame.number >= 27 && frame.number <= 29" -w output.pcap