How to control the return StatusCode from a UAMethod call on the server

[piperoc]

I am writing a simulation in which the client will call a method that has no OutputArguments.
If the server validates the InputArgument successfully (according to some rules) then the call should return 0 (Good), otherwise it will return something like BadInvalidArgument.

I know this "hijacking" of the status code is not a great idea. But I'm simulating a commercial server that implemented that logic (don't do it) and I have no choice.

This would not be a problem in other languages and SDK's (like C and the open62541) where the method callbacks are designed to return a StatusCode.

This Python API seems to be designed to return the Output arguments instead (which I kind of like because of Python ability to return multiple results). However, how can I control the result of a call on the server?

Thanks for any help.
Cos

[schroeder-]

Raise the corresponding error for BadInvalidArgument do this:

raise BadInvalidArgument

[piperoc]

Thank you @schroeder- .

Here's a short example (cut down version of the examples):

import asyncio
import logging

from asyncua import ua, uamethod, Server



# method to be exposed through server
def func(parent, variant):
    print("func method call with parameters: ", variant.Value)
    ret = False
    if variant.Value == 42:
        raise ua.UaStatusCodeError(ua.StatusCodes.BadInvalidArgument)
    if variant.Value % 2 == 0:
        ret = True
    return [ua.Variant(ret, ua.VariantType.Boolean)]


async def main():
    logging.basicConfig(level=logging.WARN)

    # now set up our server
    server = Server()
    await server.init()
    # server.set_endpoint("opc.tcp://localhost:4840/freeopcua/server/")
    server.set_endpoint("opc.tcp://0.0.0.0:48404/freeopcua/server/")
    server.set_server_name("FreeOpcUa Example Server")

    # set up our own namespace
    uri = "http://examples.freeopcua.github.io"
    idx = await server.register_namespace(uri)

    # get Objects node, this is where we should put our custom stuff
    objects = server.nodes.objects

    # populating our address space
    await objects.add_folder(idx, "myEmptyFolder")
    myobj = await objects.add_object(idx, "MyObject")
    myvar = await myobj.add_variable(idx, "MyVariable", 6.7)
    await myvar.set_writable()  # Set MyVariable to be writable by clients
    myarrayvar = await myobj.add_variable(idx, "myarrayvar", [6.7, 7.9])
    await myobj.add_variable(
        idx, "myStronglytTypedVariable", ua.Variant([], ua.VariantType.UInt32)
    )
    await myobj.add_property(idx, "myproperty", "I am a property")
    
    await myobj.add_method(idx, "mymethod", func, [ua.VariantType.Int64], [ua.VariantType.Boolean])
    
    async with server:
        while True:
            await asyncio.sleep(1)


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

I might not have understood your answer completely (sorry). The client still reports just a BadUnexpectedError .
Thank you again

[schroeder-]

Sry my bad just return the StatusCode:

def func(parent, variant):
    print("func method call with parameters: ", variant.Value)
    ret = False
    if variant.Value == 42:
        return ua.StatusCodes.BadInvalidArgument
    if variant.Value % 2 == 0:
        ret = True
    return [ua.Variant(ret, ua.VariantType.Boolean)]

[piperoc]

That's the first thing I tried but it gives me TypeError: object of type 'int' has no len()

[piperoc]

I changed my code to do:

import asyncio
import logging

from asyncua import ua, uamethod, Server
from asyncua.ua.uaerrors import BadInvalidArgument


# method to be exposed through server
def func(parent, variant):
    print("func method call with parameters: ", variant.Value)
    ret = False
    if variant.Value == 42:
        raise BadInvalidArgument
    if variant.Value % 2 == 0:
        ret = True
    return [ua.Variant(ret, ua.VariantType.Boolean)]

[...]

which seems to work on the server side, but UAExpert still gives me BadUnexpectedError

[piperoc]

also tried other clients, same behavior

[schroeder-]

You have to wrap the error code in ua.StatusCode:

 def func(parent, variant):
    print("func method call with parameters: ", variant.Value)
    ret = False
    if variant.Value == 42:
        return ua.StatusCode(ua.StatusCodes.BadInvalidArgument)
    if variant.Value % 2 == 0:
        ret = True
    return [ua.Variant(ret, ua.VariantType.Boolean)]

[piperoc]

That's it, Thank you !!!