Reading a quite complex extension object results in buffer problems

[pridi]

Discussed in https://github.com/FreeOpcUa/python-opcua/discussions/1354

^{Originally posted by pridi July 8, 2021} Hello everyone, I'm facing an issue when I try to read a structure like this (IcsEvoShifts in the picture):

When I try to get value before executing the load_type_definitions(), I correctly see in the body the bytes stream:

but after executing the load_type_definitions() and executing again the get_value(), I receive a Not enough data left in buffer:

raise NotEnoughData("Not enough data left in buffer, request for {0}, we have {1}".format(size, self)) opcua.common.utils.NotEnoughData: Not enough data left in buffer, request for 296960, we have Buffer(size:700,...

This is the very simple snipped code I have:

client.connect()

struct=client.get_node("s=IcsEvoShifts")
root = client.get_root_node()
objects = client.get_objects_node()
children = root.get_children()
child_of_children=children[0].get_children()
print("child_of_children  :",child_of_children)
c_child_of_children=child_of_children[3].get_children()
print("c_child_of_children  :", c_child_of_children)
structs = client.get_node(c_child_of_children[5])
before = struct.get_value()

client.load_type_definitions()

after = struct.get_value()

Could you please explain me what could the issue?

Thanks

[oroulet]

try with the sync API of asyncua instead of python-opcua . If you still get the issue I need to know the definitoin of that structures.

[pridi]

Thank you for your quick reply. Could you please help me to translate the previous snipped with asyncua? I'm quite new to it.

Thanks

[oroulet]

use asyncua library. The only changes should be to import from asyncua.sync import XXX instead of from opcua https://github.com/FreeOpcUa/opcua-asyncio

[oroulet]

aslre replace get_xx with read_xxx

[pridi]

I tried to use the provided demo code in the async repo. The results is the same.

import sys
import time
import logging
import asyncio

from asyncua import Client
from asyncua import ua


async def main():
    logging.basicConfig(level=logging.WARN)
    #async with Client("opc.tcp://asyncua.demo-this.com:51210/UA/SampleServer") as client:
    async with Client("opc.tcp://172.16.4.28:4840/") as client:

        uri = 'urn:unconfigured:application'
        idx = await client.get_namespace_index(uri)

        struct = await client.nodes.objects.get_child(f"{idx}:IcsEvoShifts")
        before = await struct.read_value()
        await client.load_type_definitions()  # scan server for custom structures and import them
        after = await struct.read_value()
        print("before", before)
        print("after", after)


if __name__ == "__main__":
    asyncio.run(main())

the error is the same:

[oroulet]

use load_data_type_definition() instead of load_type_definion()

[pridi]

Ok, now I do not have any more the error but the struct has not been decoded. I still see the bytes stream and not the decoded version.

Am I missing something?

[oroulet]

load_data_type_definitoin() is following the 1.04 spec. Your server probably does not support that verison of spec. What server are you using? Anyway honestly I do not have time debugging older spec version. I do not use them

[pridi]

For the version I have to ask to my customer (I don't know how to retrieve it with UAExpert...my bad!). You're right, if I use load_type_definitions() method and I look at the content of the returned variable, I see the complete and correct list of types of my struct. On the other side load_data_type_definitoin() is returning None. I was expecting that having the types (with load_type_definitions()) the decoding was producing in any case a good results.

[pridi]

@oroulet I've changed the PLC with a brand new Codesys PLC (V.3.15). Same structures as with the old PLC but the problem is totally the same.

[swamper123]

@pridi What OPC UA spec version does it support?

[KolbenKeule]

Hi, I need help too. I want to connct with an username and password but when I´m trying this with client.set_user("") client.set_password("*") I got an error with: asyncua.ua.uaerrors._auto.BadIdentityTokenInvalid: "The user identity token is not valid."(BadIdentityTokenInvalid) Can someone help me please? I don´t know what is wrong.

[AndreasHeine]

@KolbenKeule why do you post this on a half year old topic about extension objects?

Questions -> https://github.com/FreeOpcUa/python-opcua/discussions

[KolbenKeule]

Hi @AndreasHeine after your help. I try to code my own script but after 2 weeks I´m at the same positition like befor. Nothing works. :/

[AndreasHeine]

@KolbenKeule if nothing works its likely a misunderstanding/misuse of the technology. feel free to open issues or start discussions but remember this is all open source (supported by volunteers) means no one gets payed for that! i can only encourage you to at least read part 1 of the opc ua spec https://reference.opcfoundation.org/ as a starting point to get the basics and from then start asking the correct questions :wink: (opc ua is nothing you learn in 1h youtube tutorial ^^)