Solace - How to create ISubscription instance to be used by Session.CreateFlow method - solace

Question

I am trying to create a subscriber for my durable topic endpoint in solace via .NET APIs.
I have the below method where in I am trying to create a flow for my durable topic endpoint. I don't understand what is the need for ISubscription instance in the Session.CreateFlow method. (https://docs.solace.com/API-Developer-Online-Ref-Documentation/net/html/a548a98a-9134-c167-2517-192a26ceed77.htm)
How do I create an instance of ISubscription and what should it be?
public void Start()
{
//Create a instance of a durable topic endpoint
topic = ContextFactory.Instance.CreateDurableTopicEndpointEx(topicName);
FlowProperties flowProps = new FlowProperties();
flowProps.FlowStartState = false;
if (selector != null)
{
flowProps.Selector = selector;
}
flowProps.AckMode = ackMode == AckMode.ClientAcknowledge ? MessageAckMode.ClientAck : MessageAckMode.AutoAck;
if (windowSize.HasValue)
{
flowProps.WindowSize = windowSize.Value;
}
flow = session.CreateFlow(flowProps, topic, null, HandleFlowMessageEvent, HandleFlowEvent);
flow.Start();
}
I am currently passing it as null and I get the error
subscription must be non-null when endpoint is of type ITopicEndpoint
Secondly, I have a message handler for my flow event and session event, so when a message comes through which handler would it invoke. I would expect that I handle the message in the FlowMessageHandler as I am connecting to a durable topic endpoint. Please can someone shed more light on this?
//session message event handler
session = context.CreateSession(sessionProperties, HandleSessionMessageEvent, HandleSessionEvent);
//Flow message event handler
flow = session.CreateFlow(flowProps, topic, null, HandleFlowMessageEvent, HandleFlowEvent);

Answer 1

For a durable topic endpoint, if you have multiple subscribers then each would have to register with a unique subscription name (you can give any name as you like) so that the broker can maintain a durable connection with the specific subscriber. Even if the subscriber is down for a while and reconnects, it will not lose out on messages in the interim. The broker will push the messages to the subscriber. You can create a subscriber via the Solace Admin client or via code. Solace Admin -> Select the VPN -> Choose Endpoint tab -> select Durable Topic Endpoint -> click the + sign to create a subscriber -> ensure that consume is chosen for 'All other Permissions'.
The messages are sent to the session handler first and then to the flow handler. So you can access the messages from both the handlers.