OPC auto-reconnect pattern

[mariohr]

Hi,

how to implement a OPC auto-reconnect pattern ??

Thanks

[msalafia]

What do you mean exactly? please, provide more details.

[mariohr]

thanks for response! today, if after start to monitoring some items and the OPC server goes down, and goes up, the client does not continue to publish values thru MQTT for example... the subscriptions and session do not reconnect ...

[msalafia]

Yes, this is probably due to missing reconnection mechanism in the platform. I suppose it can implemented in the following way.

In UAClient.cs try to apply the following changings:

• Declare these two variables in the UaClient class

const int ReconnectPeriod = 10;
private SessionReconnectHandler _reconnectHandler;

• Declare the following callback functions:

private void Client_KeepAlive(Session sender, KeepAliveEventArgs e)
        {
            if (e.Status != null && ServiceResult.IsNotGood(e.Status))
            {
                Console.WriteLine("{0} {1}/{2}", e.Status, sender.OutstandingRequestCount, sender.DefunctRequestCount);

                if (_reconnectHandler == null)
                {
                    Console.WriteLine("--- RECONNECTING ---");
                    _reconnectHandler = new SessionReconnectHandler();
                    _reconnectHandler.BeginReconnect(sender, ReconnectPeriod * 1000, Client_ReconnectComplete);
                }
            }
        }

private void Client_ReconnectComplete(object sender, EventArgs e)
        {
            // ignore callbacks from discarded objects.
            if (!Object.ReferenceEquals(sender, _reconnectHandler))
            {
                return;
            }

            var endpointUrl = _reconnectHandler.Session.Endpoint.EndpointUrl;
            _sessions[endpointUrl] = _reconnectHandler.Session; //<--- You have to remove 'readonly' from _session
            _reconnectHandler.Dispose();
            _reconnectHandler = null;

            Console.WriteLine("--- RECONNECTED ---");
        }

• Add the following instruction in function GetSessionAsync()

private async Task<Session> GetSessionAsync(string serverUrl)
        {
            lock (_sessions)
            {
                if (_sessions.ContainsKey(serverUrl)) return _sessions[serverUrl];
            }

            await CheckAndLoadConfiguration();
            EndpointDescription endpointDescription;
            try
            {
                endpointDescription = CoreClientUtils.SelectEndpoint(serverUrl, false, 15000);
            }
            catch (Exception e)
            {
                throw new DataSetNotAvailableException();
            }
            
            Console.WriteLine("    Selected endpoint uses: {0}",
                endpointDescription.SecurityPolicyUri.Substring(endpointDescription.SecurityPolicyUri.LastIndexOf('#') + 1));

            var endpointConfiguration = EndpointConfiguration.Create(_appConfiguration);

            var endpoint = new ConfiguredEndpoint(endpointDescription.Server, endpointConfiguration);
            endpoint.Update(endpointDescription);

            var s = await Session.Create(_appConfiguration,
                                             endpoint,
                                             true,
                                             false,
                                             _appConfiguration.ApplicationName + "_session",
                                             (uint)_appConfiguration.ClientConfiguration.DefaultSessionTimeout,
                                             null,
                                             null);
            s.KeepAlive += Client_KeepAlive;  // <----- ADD THIS!!!
            
            lock (_sessions)
            {
                if (_sessions.ContainsKey(serverUrl))
                    s = _sessions[serverUrl];
                else
                    _sessions.Add(serverUrl, s);
            }

            return s;
        }

I hope this work!