Remove vss2dbc mapping for sensor

[erikbosch]

Related to #23

Current CAN provider implementation always subscribe to target value for "vss2dbc". That does not really make sense for sensors, as they do not have target values. Remove it from example mapping and give a warning

[SebastianSchildt]

I am not sure what this code does or want to say.

"relevant to use"

The menaing is "vss2dbc only supported for actuators", right? However if it is right, this code does nothing, it just prints something, shouldn"t it ignore such amppings then?

So I not fully get what happens actually if there is a mapping of vss2dbc for a sensor

[erikbosch]

Below is the code that manages subscription. As of today I do not think that you get an error if trying to subscribe to target value for a sensor/attribute. (Alternatively we discard any error message we receive, but I do not think that is the case.)

This code gives a warning if using vss2dbc on a sensor or attribute, but it does not ignore the vss2dbc statement or give an error. So it is just a hint to the user that they maybe should refactor their mapping file. We could be more intrusive:

• We could ignore the vss2dbc after giving warning. Practical behavior would be the same as we anyway do not get any updates for sensors/attributes. The only difference would be if there are errors inside the vss2dbc statement, today that would result in errors, if we ignore it they would be no errors either.
• We could give an error and exit.

And we could rephrase the warning but keep the rest intact if we would like. Any opinion?

async def subscribe(self, vss_names: List[str], callback):
        """Create a subscription and invoke the callback when data received."""
        entries: List[SubscribeEntry] = []
        for name in vss_names:
            # Always subscribe to target
            subscribe_entry = SubscribeEntry(name, View.FIELDS, [Field.ACTUATOR_TARGET])
            log.info("Subscribe entry: %s", subscribe_entry)
            entries.append(subscribe_entry)

        # If there is a path VSSClient will request a secure connection
        if self._tls and self._root_ca_path:
            root_path: Optional[Path] = Path(self._root_ca_path)
        else:
            root_path = None

        async with VSSClient(self._ip, self._port, token=self._token,
                             root_certificates=root_path, tls_server_name=self._tls_server_name) as client:
            async for updates in client.subscribe(entries=entries):
                log.debug(f"Received update of length {len(updates)}")
                await callback(updates)

[SebastianSchildt]

I think the "best way" is printing a waring and actually dropping the mapping.
The API not giving an error when subscribing target for a sensor could be seen as an error, and f that ever changes might break tis code. So I think dropping such mappings is better.

On the other hand, I don"t want to overcomplicate this PR, so I can also follow any of the other suggestions.
(Failing with exit might also be good, as it at least points to a problem early)

[erikbosch]

Solution changed to exit if using vss2dbc on something not an actuator

[SebastianSchildt]

lgtm 🦘