Support for automatic reconnection to server

[MacherelR]

Hello,
Sorry for annoyment because maybe my question is a bit dumb... But I've worked now for three weeks with this wonderful library and I'm starting to get really used to !
There's still a point I can't figure out, even by wandering around the source codes:
How and where is the automatic reconnection handled ?
In fact, I've observed that there's the _monitor_server_loop method that checks whether server is alive (and therefore also connection), and I've used it to catch connection loss exceptions in my own API using the asyncua library. But what I couldn't get ahold of is how is it that when I simply reconnect my network, the connection to the server is reinitialized and how could I get this information inside my API code ?

Hope this is clear enough, if not, please let me know if I should provide any further informations !

Thanks

Rémy

[schroeder-]

We have sample here: https://github.com/FreeOpcUa/opcua-asyncio/blob/master/examples/client-reconnect.py
As short answer just call client.check_connection() this will throw an exception if the connection is lost.

[oroulet]

havin a connect inside a try/excep sounds really like abad idea. You need osme kind of loop.

e fastAPI app or any other framework that proposes an API (here the purpose is to be able to add and remove subscriptions while running,

I have zero ideas what a fastAPI is, but if you want to maintain a connection you need some kind of loop in your server (and you already have some loop because asyncua has background tasks).

[MacherelR]

FastAPI is simply a way to declare an API in python. I had to use this because in my use case I need to be able to add or remove subscriptions on the run. For example I should launch the service without any subscription inside a docker container, and then be able to add a subscription to a chosen node (but this can come later on). This is why I used FastAPI so I can implement api calls such as Subscribe_to_node(nodeid) that then uses the client.create_subscription() method to add a subscription.
The problem that in fastAPI there's no "main" code which could be run into a while True and a with statement for the client (which would, as in the examples be very useful to handle errors), that's why I'm encountering so many troubles to handle connection errors.
I don't know if you heard of any implementations like this one (being able to add/remove subscriptions on the run), and if yes would you please redirect me to one of those ?

[AndreasHeine]

@MacherelR be careful the number of subscription which you can create is limited by the opc ua server (ServerCapabilities.OperationLimits) so don't use many subscriptions! use one subscription which dynamically added and removed MonitoredItems instead only if you reach the MaxMonitoredItemsPerSubscription limit create a new Subscription!

[schroeder-]

maybe just have a global task which does the connection handling.
Something like this:

async def opc_ua_connection_loop():
    client = ... # init client
    while True:
        try:
           with client:
               ... # Subscripe usw.
              while 1:
                  ...
                 client.check_connection()
       except ....:
               ....


opc_ua_task = None

@app.on_event("startup")
async def startup_event():
        opc_ua_task = asyncio.create_task(opc_ua_connection_loop())

[MacherelR]

@AndreasHeine I misspelled before but that's what I'm doing sorry for inconvenience !
@schroeder- I'll try this method with a single main loop and try to handle the adding and removing of subscriptions inside it, I'll get back to you when I've implemented it ! Thanks :)