Help with session disconnect sending and receiving requests from client

[VedanthaKasturi]

I am new to OPC so please bear with me. Also Thanks to this amazing project for being open-source and the lively community!

Background Information

I am working on a client-side code in C++ whose job is to get sensor information from a magnet system controlled by a PLC. I will also occasionally send some commands to turn on and turn off things. I have followed the client examples in the documentation to develop the code. The OPC send and receive commands are handled by a class called OPCmanager and the user end functions are done by another class called magnetControl. The connect part in the OPCmanager looks like this:

bool OpcManager::connectToServer() {
    MagnetControlClient = UA_Client_new();
    UA_ClientConfig *magnetClientConfig = UA_Client_getConfig(MagnetControlClient);

    UA_ClientConfig_setDefault(magnetClientConfig);

    std::string serverAddress = "opc.tcp://" + ServerIpAddress + ":" + std::to_string(PortNumber);

    UA_StatusCode retval = UA_Client_connect(MagnetControlClient, serverAddress.c_str());

    if(retval != UA_STATUSCODE_GOOD) {
        if(loggingEnabled)
            UA_LOG_ERROR(UA_Log_Stdout, UA_LOGCATEGORY_SESSION, "Could not connect to server at %s", serverAddress.c_str());

        UA_Client_delete(MagnetControlClient);
        return false;
    } else {
        if(loggingEnabled)
            UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_SESSION, "Connected to server at %s", serverAddress.c_str());
    }

    return true;
}

Description of Issue

I have a while loop which reads nodes and writes to nodes inside a while loop whenever the user requests it. I was able to access the nodes but sometimes I have an error and I can't send any additional requests until I disconnect and reconnect to the server:

[2024-04-12 17:13:43.755 (UTC+0200)] info/userland Turning Off Power Converter
[2024-04-12 17:13:43.758 (UTC+0200)] info/client Received a ServiceFault response
[2024-04-12 17:13:43.758 (UTC+0200)] warn/client Session no longer valid. A new Session is created for the next Service request but we do not re-send the current request.
[2024-04-12 17:13:43.758 (UTC+0200)] info/client Client Status: ChannelState: Open, SessionState: Closed, ConnectStatus: Good
[2024-04-12 17:13:43.758 (UTC+0200)] error/userland Could not write the value. StatusCode 80250000

From the documentation I understand I might need to use perhaps "UA_Client_run_iterate" but I am not sure how and if thats enough since I have no idea when my next request might be. should I call it once every loop with no timeout? is there another way to keep the session open? or is this error not related to this? I could really use your guidance.

Checklist

Please provide the following information:

• open62541 Version (release number or git tag): main (1.3.10 and 1.4.0)
• Other OPC UA SDKs used (client or server): none
• Operating system: Linux and Mac OS Sonoma
• Logs (with UA_LOGLEVEL set as low as necessary) attached
• Wireshark network dump attached
• Self-contained code example attached
• Critical issue

[jpfr]

You can call _run with a fixed interval.
Or you get from the clients eventloop the timestamp of the next scheduled action.
Then you can keep track of time yourself.

Or you just open a separate thread to do the cyclic _run.