How to properly implement the reconnection to the server

[GaetanKorpys]

Type of issue

• Bug
• Enhancement
• Compliance
• Question
• Help wanted

Current Behavior

Hello, I have several questions about reconnection mecanism :

Doc about TransferSubscription :
"Transfer after session reconnect: The client SessionReconnectHandler can not reconnect to the existing session, it creates a new session and tries to transfer a subscription before recreating the full subscriptions."

• Does it mean that BeginReconnect will handle the creation of the subscription and monitored Item (not only the session) ? Even after a restart of the server (server is empty, subscriptions and monitored items are not persisted afer the restart) ?

• Is it possible to reconnect (subscription and monitored working) using BeginReconnect method when the session is closed on the server (du to timeout for example) ?
  If so, should the server implement DurableSubscription and TransferSubscription ?

In the sample, they use :
// support transfer
m_session.DeleteSubscriptionsOnClose = false;
m_session.TransferSubscriptionsOnReconnect = true;

I know sometimes the SDK send a new session with a different id from the previous one.
And in that case, my mind tell me that the sdk will transfer the subscriptions.

• When I call BeginReconnect, should I disable Keep Alive (e.CancelKeepAlive = True) even if the state is not ReconnectState.Triggered ?

That the case in the sample, but it means that BeginReconnect will moves to that state on her own ?
If so, then the client can not really log when the reconnect is starting (not completed) if i'm correct.

• When I set e.CancelKeepAlive at True, my method Session_KeepAlive continues to be trigger. I confirm that with logs. Do I missunderstand something in the use case ?

• Does ReconnectPeriod means that BeginReconnect will try to reconnect each ReconnectPeriod ?

Expected Behavior

No response

Steps To Reproduce

No response

Environment

- OS: Windows 11
- Environment: VS 2022
- Runtime: .Net 8
- Nuget Version: 1.5.376.213
- Component: /
- Server: /
- Client: my own implementation

Anything else?

Sample code from ConsoleReferenceClient :

///

/// Handles a keep alive event from a session and triggers a reconnect if necessary.
///

private void Session_KeepAlive(ISession session, KeepAliveEventArgs e)
{
try
{
// check for events from discarded sessions.
if (m_session == null || !m_session.Equals(session))
{
return;
}

    // start reconnect sequence on communication error.
    if (ServiceResult.IsBad(e.Status))
    {
        if (ReconnectPeriod <= 0)
        {
            Utils.LogWarning("KeepAlive status {0}, but reconnect is disabled.", e.Status);
            return;
        }

        var state = m_reconnectHandler.BeginReconnect(m_session, m_reverseConnectManager, ReconnectPeriod, Client_ReconnectComplete);
        if (state == SessionReconnectHandler.ReconnectState.Triggered)
        {
            Utils.LogInfo("KeepAlive status {0}, reconnect status {1}, reconnect period {2}ms.", e.Status, state, ReconnectPeriod);
        }
        else
        {
            Utils.LogInfo("KeepAlive status {0}, reconnect status {1}.", e.Status, state);
        }

        // cancel sending a new keep alive request, because reconnect is triggered.
        e.CancelKeepAlive = true;

        return;
    }
}
catch (Exception exception)
{
    Utils.LogError(exception, "Error in OnKeepAlive.");
}

}