Subscriptions and variable getters

[mfwre]

Hi,

I'm very new to OPC in general, so this might be a trivial question.

I have a Weintek OPC server which reads data from a PLC.
Since this device is on a "isolated" network I desided to program a bridge OPC UA (srv) server that exposes some values read on the Weintek device.

What I did is:
On srv I've set up of different

VariableBuilder::new(&node_id, server_attr, server_attr)
    .property_of(/* ... */)
    .data_type(/* ... */)
    /* I tried with and without these settings
    .historizing(true)
    .history_readable()
    .minimum_sampling_interval(500f64)
    */
    .has_type_definition(VariableTypeId::PropertyType)
    .value_getter(AttrFnGetter::new_boxed(
        move |_, _, _, _, _, _| -> Result<Option<DataValue>, StatusCode> {
            /* following client.read() call is a connection from the bridge server
              * to the Weintek server
              * */
            let session = client.read();
            session
                .read(
                    &[NodeId::new(2, weintek_node_srting_id).into()],
                    TimestampsToReturn::Server,
                    1.0,
                 )
                 .map(|v| v.into_iter().nth(0))
        },
    ))
    .insert(address_space);

On another OPC client I tried to subscribe to these nodes via

let subscription_id = session.write()
    .create_subscription(
        2000.0,
        10,
        30,
        0,
        0,
        true,
        DataChangeCallback::new(|changed_data| {
            println!("Data change:");
            changed_data.iter().for_each(|i| println!("{i:#?}"));
        }),
    )
    .unwrap();

// followed by a
session.write()
    .create_monitored_items(
         subscription_id,
         TimestampsToReturn::Server,
         &items // Vec<MonitoredItemCreateRequest> created from the NodeIds
     )
    .unwrap();

Session::run(session)

The code compiles and runs. On srv, if I use some tools like opcua-commander, I see the values of the nodes set up with .value_getter correctly change.

I don't see however prints made by the DataChangeCallback. Hence the question: can I subscribe to Variables which value lies behind a getter?

Other somewhat related questions: what is the point of creating a ObjectTypeBuilder, assigning some variables via VariableBuilder instead of simply creating directly the object with a ObjectBuilder?

The last one isn't that much a question. But feel free to suggest other ways to solve my bridging solution. I'm still new to automation

[mfwre]

It appears I was the coconut all along.
Since I was coding a PoC I wrote all piece of code in a single main.rs file.

Putting all the setting up the subscription and monitored items calls in a separated expression block fixed the issue. The subscription fires DataChangeCallback events now.