Introduction

OPC Data Client components may, under certain circumstances, display a user interface "by itself", without you having to make a specific method call. Such unsolicited user interaction only happens when the current process is running in user interactive mode, as reported by the Environment.UserInteractive Property. In non-interactive mode, the components assume reasonable default user responses. In addition, you can turn off specific user interactions by setting corresponding parameters in the code.

Usually, these are notifications or confirmations related to conditions that cannot be anticipated upfront, such as the certificate exchange in the OPC UA connection process. As OPC Data Client controls the connections and diconnections automatically, and when subscriptions are in effect, also makes re-connections, you - as a developer - cannot generally predict when such user interaction may be needed.

Interaction Types

There are following situations that may trigger an unsolicited user interaction related to OPC Unified Architecture (OPC UA) operations:

• Issues while checking or creating an application instance certificate. These are rare, and usually only happen when the application runs for the first time. These can be turned off or on by the AllowUserInteraction Property of the EasyUAApplication.ApplicationParameters.InstanceCertificateGenerationParameters. See also Providing OPC UA Client Instance Certificate.
• When HTTPS communication is used, failed validation of server's HTTPS certificate. The user is prompted whether he/she wants to accept the certificate anyway. This prompt can be turned off or on by the AllowUserAcceptCertificate Property of HttpsCertificateAcceptancePolicy Property of EngineParameters Property of EasyUAClient.SharedParameters Property. See also Trusting OPC UA Server HTTPS Certificate.
• Failed validation of OPC UA server's instance certificate. The user is prompted whether he/she wants to accept the certificate anyway. This prompt can be turned off or on by the AllowUserAcceptCertificate Property of CertificateAcceptancePolicy Property of EngineParameters Property of EasyUAClient.SharedParameters Property. Alternatively, the certificate acceptance policy can be overridden for a specific endpoint by setting it to a non-null value in CertificateAcceptancePolicy Property. See also Trusting OPC UA Server Instance Certificate. The user can also choose to trust the certificate permanently. With this choice, the certificate is copied to the trusted peers certificate store (and removed from the rejected certificates store). Note that the user running the application must have sufficient permissions to add the certificate to the trusted peers certificate store.
• The effective host name in endpoint URL returned by the server does not match any of the domain names in the server certificate. This may be an indication of a spoofing attempt. The user is prompted whether he/she wants to allow the endpoint anyway. This prompt can be turned off or on by the AllowEndpointDomainPrompt Property of UAClientSessionParameters Class.

There is no unsolicited user interaction related to OPC Classic operations.

Interaction Providers

The way OPC Data Client presents the unsolicited user interaction depends on the environment your application is running in. There is an interaction provider for each such supported environment. OPC Data Client interrogates the available interaction providers to see which one should perform the interaction, selects the appropriate interaction provider and then uses it to actually communicate with the user. Following interaction providers are available:

• Console Interaction Provider. Used in console applications.
• Windows Forms Interaction Provider. Used on Microsoft Windows in applications that have windowed user interface.
• Null Interaction Provider. This provider is used if OPC Data Client cannot find any other interaction provider for the current environment.

Each interaction provider (except for the Null Interaction Provider) can be turned on or off, and may have additional configurable parameters.

Example

// This example shows how to completely turn off interaction in a console application.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

using System;
using OpcLabs.EasyOpc.UA;
using OpcLabs.EasyOpc.UA.Engine;
using OpcLabs.EasyOpc.UA.OperationModel;

namespace UADocExamples.Interaction
{
    partial class ConsoleInteraction
    {
        public static void TurnOff()
        {
            // Do not implicitly trust any endpoint URLs. 
            EasyUAClient.SharedParameters.EngineParameters.CertificateAcceptancePolicy.TrustedEndpointUrlStrings.Clear();

            // Completely disable the console interaction.
            EasyUAClient.SharedParameters.PluginSetups.FindName("UAConsoleInteraction").Enabled = false;

            // Define which server we will work with.
            UAEndpointDescriptor endpointDescriptor = "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer";
            // Require secure connection, in order to enforce the certificate check.
            endpointDescriptor.EndpointSelectionPolicy = UAMessageSecurityModes.Secure;
            
            // Instantiate the client object.
            var client = new EasyUAClient();

            UAAttributeData attributeData;
            try
            {
                // Obtain attribute data.
                // The operation will fail, unless you set up mutual trust using certificate stores.
                attributeData = client.Read(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853");
            }
            catch (UAException uaException)
            {
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException().Message);
                return;
            }

            // Display results.
            Console.WriteLine("Value: {0}", attributeData.Value);
            Console.WriteLine("ServerTimestamp: {0}", attributeData.ServerTimestamp);
            Console.WriteLine("SourceTimestamp: {0}", attributeData.SourceTimestamp);
            Console.WriteLine("StatusCode: {0}", attributeData.StatusCode);
        }
    }
}

# This example shows how to completely turn off interaction in a console application.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
# OPC client and subscriber examples in Python on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-Python .
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc

# Import .NET namespaces.
from OpcLabs.EasyOpc.UA import *
from OpcLabs.EasyOpc.UA.Engine import *
from OpcLabs.EasyOpc.UA.OperationModel import *


# Do not implicitly trust any endpoint URLs. We want the user be asked explicitly.
EasyUAClient.SharedParameters.EngineParameters.CertificateAcceptancePolicy.TrustedEndpointUrlStrings.Clear()

# Completely disable the console interaction.
EasyUAClient.SharedParameters.PluginSetups.FindName('UAConsoleInteraction').Enabled = False

# Define which server we will work with.
endpointDescriptor = UAEndpointDescriptor('opc.tcp://opcua.demo-this.com:51210/UA/SampleServer')
# Require secure connection, in order to enforce the certificate check.
endpointDescriptor.EndpointSelectionPolicy = UAEndpointSelectionPolicy(UAMessageSecurityModes.Secure)

# Instantiate the client object.
client = EasyUAClient()

try:
    # Obtain attribute data.
    # The operation will fail, unless you set up mutual trust using certificate stores.
    attributeData = IEasyUAClientExtension.Read(client,
                                                endpointDescriptor,
                                                UANodeDescriptor('nsu=http://test.org/UA/Data/ ;i=10853'))
except UAException as uaException:
    print('*** Failure: ' + uaException.GetBaseException().Message)
    exit()

# Display results.
print('Value: ', attributeData.Value)
print('ServerTimestamp: ', attributeData.ServerTimestamp)
print('SourceTimestamp: ', attributeData.SourceTimestamp)
print('StatusCode: ', attributeData.StatusCode)

print()
print('Finished.')

' This example shows how to completely turn off interaction in a console application.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.Engine
Imports OpcLabs.EasyOpc.UA.OperationModel

Namespace Interaction
    Partial Friend Class ConsoleInteraction
        Public Shared Sub TurnOff()
            ' Do not implicitly trust any endpoint URLs. 
            EasyUAClient.SharedParameters.EngineParameters.CertificateAcceptancePolicy.TrustedEndpointUrlStrings.Clear()

            ' Completely disable the console interaction.
            EasyUAClient.SharedParameters.PluginSetups.FindName("UAConsoleInteraction").Enabled = False

            ' Define which server we will work with.
            Dim endpointDescriptor As UAEndpointDescriptor = "opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"
            ' Require secure connection, in order to enforce the certificate check.
            endpointDescriptor.EndpointSelectionPolicy = UAMessageSecurityModes.Secure

            ' Instantiate the client object.
            Dim client = New EasyUAClient()

            Dim attributeData As UAAttributeData
            Try
                ' Obtain attribute data.
                ' The operation will fail, unless you set up mutual trust using certificate stores.
                attributeData = client.Read(endpointDescriptor, "nsu=http://test.org/UA/Data/ ;i=10853")
            Catch uaException As UAException
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException.Message)
                Exit Sub
            End Try

            ' Display results.
            Console.WriteLine("Value: {0}", attributeData.Value)
            Console.WriteLine("ServerTimestamp: {0}", attributeData.ServerTimestamp)
            Console.WriteLine("SourceTimestamp: {0}", attributeData.SourceTimestamp)
            Console.WriteLine("StatusCode: {0}", attributeData.StatusCode)
        End Sub
    End Class
End Namespace

Interaction and Blocking

All unsolicited user interaction (with exception of rare messages and confirmations related to client application instance certificate checks) has a timeout associated with it, and a default user response is assumed should the user not respond in time. This means that under normal circumstances, the current activity cannot be blocked indefinitely if the user fails to respond. In fact, this behavior also guarantees that the activity will eventually proceed even if the Environment.UserInteractive Property incorrectly claimed that the process is running in user interactive mode. The timeout is configurable by the AcceptNotificationTimeout Property in the UAUserInteractionParameters Class. In order to obtain or modify this parameter, access the UserInteractionParameters Property of EngineParameters Property of EasyUAClient.SharedParameters Property.

Interaction and Licensing

When there is a problem with the license key, or when the trial license runtime expires. Instead, such problems are primarily reported as other errors, using the channels for the programming model used. For example, in Imperative Programming Model, the single-argument method throws an exception, a multiple-argument method returns the error in the Exception Property of the OperationResult Class, or with subscriptions, the error is reported in the Exception Property of the OperationEventArgs Class. It is up to the calling code to handle such situations.

In addition, in Windows Forms applications and certain other Windows desktop application, OPC Data Client components display a notification in Windows system tray for certain license-related issues:

• When a trial license is activated, a warning notification is displayed. Clicking on the notification shows further details.
• When the license is not valid, an error notification is displayed. Clicking on the notification shows further details about the issue.