Running OPC UA server and adding dynamic tags.

[aashay987]

Hi,

I needed some assistance with a personal project where I am developing an OPC server, that would dynamically add tags on client subscription. Below is my current implementation, but I see that the connection with the client is not persistent (UAExpert). I often see errors like.

Error 'BadTimeout' was returned during OpenSecureChannel
Error 'BadSessionIdInvalid' was returned during ActivateSession

Later a new session starts.

import logging
import asyncio

try:
    from IPython import embed
except ImportError:
    import code

    def embed():
        vars = globals()
        vars.update(locals())
        shell = code.InteractiveConsole(vars)
        shell.interact()


from asyncua import Server,ua
from asyncua.common.callback import CallbackType
l = []
myobj = None

async def create_monitored_items(event, dispatcher):
    global myobj
    for idx in range(len(event.response_params)):
        nodeId = event.request_params.ItemsToCreate[idx].ItemToMonitor.NodeId
        if nodeId.Identifier not in l and myobj is not None:
            l.append(nodeId.Identifier)
            try: 
                var_nodeid = ua.NodeId(str(nodeId.Identifier), idx)
                myvar = await myobj.add_variable(nodeid=var_nodeid,bname=str(nodeId.Identifier),val=0)
                await myvar.set_writable()
            except:
                print('Error :', nodeId.Identifier)


async def main():
    server = Server()
    await server.init()

    server.set_endpoint("opc.tcp://0.0.0.0:4840/freeopcua/server/")
    server.set_server_name("FreeOpcUa Example Server")

    uri = "http://examples.freeopcua.github.io"
    idx = await server.register_namespace(uri)

    objects = server.nodes.objects

    await server.start()

    global myobj
    myobj = await objects.add_object(idx, "Test1")


    
    
    # Create Callback for item event
    server.subscribe_server_callback(CallbackType.ItemSubscriptionCreated, create_monitored_items)

    while True:
        await asyncio.sleep(1)

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

The objective is for the client to be able to subscribe to around 30,000 nodes and ensure a resilient connection.