Persistent/Reliable sessions

[Haeavar]

We would like to use the OpcPublisher for reliable OPC UA telemetry transfer. Currently, if the OpcPublisher is restarted (due to update/maintenance or others) the session and subscriptions are gone and the OpcPublisher reconnects to the OPC UA server with a new session. This (might) result in lost OPC UA data - for all data occurred between the disconnect and new connect (with the same subscriptions).

What we need is a call to TransferSubscriptions on OpcPublisher start as well. This would reactivated the old session (as long as the OPC UA server has the sessions as well) and all queued data would be available.

Of course, this could only work if in the meantime the subscriptions has not changed and so on.

Describe the solution you'd like

• A commandline option PersistentSessions (default: false) which activates the persistance of sessions
• The session information should be stored in the file system (a commandline option for the PersistentSessionsPath)
• On OpcPublisher start the session information should be loaded (if available and active)
• Create the session with these information and call the TransferSubscriptions
• If possible, apply the pn.json if its changed in the meantime
• For any error, create a new session