OPC Studio User's Guide and Reference
OPC UA Local Discovery
Client and Subscriber Development > Development Models > Imperative Programming Model > Imperative Programming Model for OPC Data (Classic and UA) > Browsing for Information (OPC Data) > Discovering OPC UA Servers > OPC UA Local Discovery

OPC Data Client-UA allows you to work with so called OPC-UA Local Discovery Server(s). OPC-UA Local Discovery Server is a special OPC-UA service that provides information about other OPC-UA servers available.

The term "local discovery" might be misleading sometimes. OPC UA Local Discovery is not just for discovering OPC UA servers that reside on the same computer as where your OPC UA client is. OPC UA Local Discover allows you to discover servers on a remote computer as well, provided that you know the host name of the computer, and the OPC UA Local Discovery Server is running on that remote computer.

If you want to retrieve a list of OPC Unified Architecture servers registered on a local or remote computer, call the DiscoverLocalServers method, passing it the name or address of the remote machine.

You will receive back a UADiscoveryElementCollection object, which is collection of UADiscoveryElement-s. Each element contains a server's discovery URL. The discovery URL is the main piece of information that you can further use if you want to connect to that OPC-UA server. Each UADiscoveryElement contains information gathered about one OPC server found by the discovery process, including things like the application name, application type, its Product URI etc.

.NET

// This example shows how to obtain application URLs of all OPC Unified Architecture servers on a given machine.
//
// 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.Discovery;
using OpcLabs.EasyOpc.UA.OperationModel;

namespace UADocExamples._EasyUAClient
{
    class DiscoverLocalServers
    {
        public static void Overload1()
        {
            // Instantiate the client object.
            var client = new EasyUAClient();

            // Obtain collection of server elements.
            UADiscoveryElementCollection discoveryElementCollection;
            try
            {
                discoveryElementCollection = client.DiscoverLocalServers("opcua.demo-this.com");
            }
            catch (UAException uaException)
            {
                Console.WriteLine($"*** Failure: {uaException.GetBaseException().Message}");
                return;
            }

            // Display results.
            foreach (UADiscoveryElement discoveryElement in discoveryElementCollection)
                Console.WriteLine($"discoveryElementCollection[\"{discoveryElement.DiscoveryUriString}\"].ApplicationUriString: {discoveryElement.ApplicationUriString}");

            
            // Example output:
            //
            //discoveryElementCollection["opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"].ApplicationUriString: urn: DEMO - 5:UA Sample Server
            //discoveryElementCollection["http://opcua.demo-this.com:51211/UA/SampleServer"].ApplicationUriString: urn: DEMO - 5:UA Sample Server
            //discoveryElementCollection["https://opcua.demo-this.com:51212/UA/SampleServer/"].ApplicationUriString: urn: DEMO - 5:UA Sample Server
            //discoveryElementCollection["http://opcua.demo-this.com:62543/Quickstarts/AlarmConditionServer"].ApplicationUriString: urn: opcua.demo - this.com:Quickstart Alarm Condition Server
            //discoveryElementCollection["opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer"].ApplicationUriString: urn: opcua.demo - this.com:Quickstart Alarm Condition Server
        }
    }
}

# This example shows how to obtain application URLs of all OPC Unified Architecture servers on a given machine.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

#requires -Version 5.1
using namespace OpcLabs.EasyOpc.UA
using namespace OpcLabs.EasyOpc.UA.Discovery
using namespace OpcLabs.EasyOpc.UA.OperationModel

# The path below assumes that the current directory is [ProductDir]/Examples-NET/PowerShell/Windows .
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcUA.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcUAComponents.dll"

# Instantiate the client object.
$client = New-Object EasyUAClient

# Obtain collection of server elements.
try {
    $discoveryElementCollection = [IEasyUAClientExtension]::DiscoverLocalServers($client, "opcua.demo-this.com")
}
catch [UAException] {
    Write-Host "*** Failure: $($PSItem.Exception.GetBaseException().Message)"
    return
}

# Display results.
foreach ($discoveryElement in $discoveryElementCollection) {
    Write-Host "discoveryElementCollection[`"$($discoveryElement.DiscoveryUriString)`"].ApplicationUriString: $($discoveryElement.ApplicationUriString)"
}


# Example output:
#
#discoveryElementCollection["opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"].ApplicationUriString: urn:DEMO-5:UA Sample Server
#discoveryElementCollection["http://opcua.demo-this.com:51211/UA/SampleServer"].ApplicationUriString: urn:DEMO-5:UA Sample Server
#discoveryElementCollection["https://opcua.demo-this.com:51212/UA/SampleServer/"].ApplicationUriString: urn:DEMO-5:UA Sample Server
#discoveryElementCollection["http://opcua.demo-this.com:62543/Quickstarts/AlarmConditionServer"].ApplicationUriString: urn:opcua.demo-this.com:Quickstart Alarm Condition Server
#discoveryElementCollection["opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer"].ApplicationUriString: urn:opcua.demo-this.com:Quickstart Alarm Condition Server


# This example shows how to obtain application URLs of all OPC Unified Architecture servers on the specified host.
#
# 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.OperationModel import *


# Instantiate the client object.
client = EasyUAClient()

# Obtain collection of server elements.
try:
    discoveryElementCollection = IEasyUAClientExtension.DiscoverLocalServers(client, 'opcua.demo-this.com')
except UAException as uaException:
    print('*** Failure: ' + uaException.GetBaseException().Message)
    exit()

# Display results.
for discoveryElement in discoveryElementCollection:
    print('DiscoveryElementCollection["', discoveryElement.DiscoveryUriString, '"].ApplicationUriString: ', 
          discoveryElement.ApplicationUriString, sep='')

' This example shows how to obtain application URLs of all OPC Unified Architecture servers on a given machine.
'
' 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.Discovery
Imports OpcLabs.EasyOpc.UA.OperationModel

Namespace _EasyUAClient
    Friend Class DiscoverLocalServers
        Public Shared Sub Overload1()
            ' Instantiate the client object
            Dim client = New EasyUAClient()

            ' Obtain collection of server elements
            Dim discoveryElementCollection As UADiscoveryElementCollection
            Try
                discoveryElementCollection = client.DiscoverLocalServers("opcua.demo-this.com")
            Catch uaException As UAException
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException.Message)
                Exit Sub
            End Try

            ' Display results
            For Each discoveryElement As UADiscoveryElement In discoveryElementCollection
                Console.WriteLine("discoveryElementCollection[""{0}""].ApplicationUriString: {1}", _
                                  discoveryElement.DiscoveryUriString, discoveryElement.ApplicationUriString)
            Next discoveryElement

            ' Example output:
            'discoveryElementCollection["opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"].ApplicationUriString: urn:Test-PC:UA Sample Server
            'discoveryElementCollection["http://opcua.demo-this.com:51211/UA/SampleServer"].ApplicationUriString: urn:Test-PC:UA Sample Server
        End Sub
    End Class
End Namespace

COM

// This example shows how to obtain application URLs of all OPC Unified Architecture servers on the specified host.
//
// Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

#include "stdafx.h"    // Includes "QuickOpc.h", and other commonly used files
#include "DiscoverLocalServers.h"

namespace _EasyUAClient
{
    void DiscoverLocalServers::Main()
    {
        // Initialize the COM library
        CoInitializeEx(NULL, COINIT_MULTITHREADED);
        {
            // Instantiate the client object
            _EasyUAClientPtr ClientPtr(__uuidof(EasyUAClient));

            // Obtain collection of server elements
            _UADiscoveryElementCollectionPtr DiscoveryElementsPtr = ClientPtr->DiscoverLocalServers(L"opcua.demo-this.com");
    
            // Display results
            IEnumVARIANTPtr EnumDiscoveryElementPtr = DiscoveryElementsPtr->GetEnumerator();
            _variant_t vDiscoveryElement;
            while (EnumDiscoveryElementPtr->Next(1, &vDiscoveryElement, NULL) == S_OK)
            {
                _UADiscoveryElementPtr DiscoveryElementPtr(vDiscoveryElement);
                _tprintf(_T("DiscoveryElementCollection[\"%s\"]: "), (LPCTSTR)CW2CT(DiscoveryElementPtr->DiscoveryUriString));
                _tprintf(_T("%s\n"), (LPCTSTR)CW2CT(DiscoveryElementPtr->ApplicationUriString));
                vDiscoveryElement.Clear();
            }
        }
         // Release all interface pointers BEFORE calling CoUninitialize()
        CoUninitialize();
    }
}

// This example shows how to obtain application URLs of all OPC Unified Architecture servers on the specified host.
//
// Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

class procedure DiscoverLocalServers.Main;
var
  Client: EasyUAClient;
  Count: Cardinal;
  Element: OleVariant;
  DiscoveryElement: _UADiscoveryElement;
  DiscoveryElementEnumerator: IEnumVariant;
  DiscoveryElements: _UADiscoveryElementCollection;
begin
  // Instantiate the client object
  Client := CoEasyUAClient.Create;

  // Obtain collection of server elements
  DiscoveryElements := Client.DiscoverLocalServers('opcua.demo-this.com');

  // Display results
  DiscoveryElementEnumerator := DiscoveryElements.GetEnumerator;
  while (DiscoveryElementEnumerator.Next(1, Element, Count) = S_OK) do
  begin
    DiscoveryElement := IUnknown(Element) as _UADiscoveryElement;
    WriteLn(
      'DiscoveryElements["',
      DiscoveryElement.DiscoveryUriString,
      '".ApplicationUriString: ',
      DiscoveryElement.ApplicationUriString);
  end;
end;

// This example shows how to obtain application URLs of all OPC Unified Architecture servers on the specified host.
//
// Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

class procedure DiscoverLocalServers.Main;
var
  Client: OpcLabs_EasyOpcUA_TLB._EasyUAClient;
  Count: Cardinal;
  Element: OleVariant;
  DiscoveryElement: _UADiscoveryElement;
  DiscoveryElementEnumerator: IEnumVariant;
  DiscoveryElements: _UADiscoveryElementCollection;
begin
  // Instantiate the client object
  Client := CoEasyUAClient.Create;

  // Obtain collection of server elements
  try
    DiscoveryElements := Client.DiscoverLocalServers('opcua.demo-this.com');
  except
    on E: EOleException do
    begin
      WriteLn(Format('*** Failure: %s', [E.GetBaseException.Message]));
      Exit;
    end;
  end;

  // Display results
  DiscoveryElementEnumerator := DiscoveryElements.GetEnumerator;
  while (DiscoveryElementEnumerator.Next(1, Element, Count) = S_OK) do
  begin
    DiscoveryElement := IUnknown(Element) as _UADiscoveryElement;
    WriteLn(
      'DiscoveryElements["',
      DiscoveryElement.DiscoveryUriString,
      '".ApplicationUriString: ',
      DiscoveryElement.ApplicationUriString);
  end;
end;

// This example shows how to obtain application URLs of all OPC Unified Architecture servers on the specified host.
//
// Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

// Instantiate the client object
$Client = new COM("OpcLabs.EasyOpc.UA.EasyUAClient");

// Obtain collection of server elements
try
{
    $DiscoveryElementCollection = $Client->DiscoverLocalServers("opcua.demo-this.com");
}
catch (com_exception $e)
{
    printf("*** Failure: %s\n", $e->getMessage());
}

// Display results
foreach ($DiscoveryElementCollection as $DiscoveryElement)
{
    printf("DiscoveryElementCollection[\"s\"].ApplicationUriStrings\n", 
        $DiscoveryElement->DiscoveryUriString, $DiscoveryElement->ApplicationUriString);
}

# This example shows how to obtain application URLs of all OPC Unified Architecture servers on the specified host.
#
# The Python for Windows (pywin32) extensions package is needed. Install it using "pip install pypiwin32".
# CAUTION: We now recommend using Python.NET package instead. Full set of examples with Python.NET is available!
#
# Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
import win32com.client
from pywintypes import com_error

# Instantiate the client object
client = win32com.client.Dispatch('OpcLabs.EasyOpc.UA.EasyUAClient') 

# Obtain collection of server elements
try:
    discoveryElementCollection = client.DiscoverLocalServers('opcua.demo-this.com')
except com_error as e:
    print('*** Failure: ' + e.args[2][1] + ': ' + e.args[2][2])
    exit()

# Display results
for discoveryElement in discoveryElementCollection:
    print('DiscoveryElementCollection["', discoveryElement.DiscoveryUriString, '"].ApplicationUriString: ', 
          discoveryElement.ApplicationUriString)

REM This example shows how to obtain application URLs of all OPC Unified Architecture servers on the specified host.
REM
REM Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Public Sub DiscoverLocalServers_Main_Command_Click()
    OutputText = ""

    ' Instantiate the client object
    Dim Client As New EasyUAClient

    ' Obtain collection of server elements
    On Error Resume Next
    Dim DiscoveryElementCollection As UADiscoveryElementCollection
    Set DiscoveryElementCollection = Client.DiscoverLocalServers("opcua.demo-this.com")
    If Err.Number <> 0 Then
        OutputText = OutputText & "*** Failure: " & Err.Source & ": " & Err.Description & vbCrLf
        Exit Sub
    End If
    On Error GoTo 0
    
    ' Display results
    Dim DiscoveryElement As UADiscoveryElement: For Each DiscoveryElement In DiscoveryElementCollection
        OutputText = OutputText & "DiscoveryElementCollection[""" & DiscoveryElement.DiscoveryUriString & """].ApplicationUriString: " & _
            DiscoveryElement.applicationUriString & vbCrLf
    Next
End Sub

Rem This example shows how to obtain application URLs of all OPC Unified Architecture servers on the specified host.
Rem
Rem Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Option Explicit

' Instantiate the client object
Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.UA.EasyUAClient")

' Obtain collection of server elements
On Error Resume Next
Dim DiscoveryElementCollection: Set DiscoveryElementCollection = Client.DiscoverLocalServers("opcua.demo-this.com")
If Err.Number <> 0 Then
    WScript.Echo "*** Failure: " & Err.Source & ": " & Err.Description
    WScript.Quit
End If
On Error Goto 0

' Display results
Dim DiscoveryElement: For Each DiscoveryElement In DiscoveryElementCollection
    WScript.Echo "DiscoveryElementCollection[""" & DiscoveryElement.DiscoveryUriString & """].ApplicationUriString: " & _
        DiscoveryElement.ApplicationUriString
Next

 

In .NET, if you want to connect to the discovered OPC server later in your code by calling other methods, use the built-in conversion of UADiscoveryElement to UAEndpointDescriptor, and pass the resulting object as an endpointDescriptor argument either directly to some other method call.

When performing a local discovery of OPC-UA servers, the component attempts to connect to multiple possible discovery endpoints in parallel, speeding up the discovery. This behavior is controlled by the ParallelDiscovery property in the UADiscoveryParameters object. The endpoints that the components attempts to use for discovery on a given host (either sequentially, or in parallel), are given by the DiscoveryUriTemplateStrings property of the UAHostParameters.

You can also bypass the use of UAHostParameters, and call the DiscoverLocalServers overload that takes an input array or URL strings to attempt discovery on.

There are also DiscoverLocalApplications methods, which allow you to specify the application types you are interested in, using the combination of flags from the UAApplicationTypes enumeration. This can be useful e.g. if you want to do hierarchical discovery and return also the discovery servers (which are not returned by default).

The FindLocalApplications method can be used, if you want to interrogate specific discovery endpoints.

.NET

// This example shows how to obtain application URLs of all OPC Unified Architecture servers, using specified discovery URI
// strings.
//
// 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.Discovery;
using OpcLabs.EasyOpc.UA.OperationModel;

namespace UADocExamples._EasyUAClient
{
    class FindLocalApplications
    {
        public static void Main1()
        {

            string[] discoveryUriStrings =
            {
                "opc.tcp://opcua.demo-this.com:4840/UADiscovery",
                "http://opcua.demo-this.com/UADiscovery/Default.svc",
                "http://opcua.demo-this.com:52601/UADiscovery"
            };

            // Instantiate the client object.
            var client = new EasyUAClient();

            // Obtain collection of application elements.
            UADiscoveryElementCollection discoveryElementCollection;
            try
            {
                discoveryElementCollection = client.FindLocalApplications(discoveryUriStrings, UAApplicationTypes.Server);
            }
            catch (UAException uaException)
            {
                Console.WriteLine($"*** Failure: {uaException.GetBaseException().Message}");
                return;
            }

            // Display results.
            foreach (UADiscoveryElement discoveryElement in discoveryElementCollection)
                Console.WriteLine($"discoveryElementCollection[\"{discoveryElement.DiscoveryUriString}\"].ApplicationUriString: {discoveryElement.ApplicationUriString}");


            // Example output:
            //discoveryElementCollection["http://opcua.demo-this.com:62543/Quickstarts/AlarmConditionServer"].ApplicationUriString: urn:opcua.demo-this.com:Quickstart Alarm Condition Server
            //discoveryElementCollection["opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer"].ApplicationUriString: urn:opcua.demo-this.com:Quickstart Alarm Condition Server
            //discoveryElementCollection["opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"].ApplicationUriString: urn:opcua.demo-this.com:UA Sample Server
            //discoveryElementCollection["http://opcua.demo-this.com:51211/UA/SampleServer"].ApplicationUriString: urn:opcua.demo-this.com:UA Sample Server
            //discoveryElementCollection["https://opcua.demo-this.com:51212/UA/SampleServer/"].ApplicationUriString: urn:opcua.demo-this.com:UA Sample Server
            //discoveryElementCollection["opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"].ApplicationUriString: urn:Test-PC:UA Sample Server
        }
    }
}

# This example shows how to obtain application URLs of all OPC Unified Architecture servers, using specified discovery URI
# strings.
#
# Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

#requires -Version 5.1
using namespace OpcLabs.EasyOpc.UA
using namespace OpcLabs.EasyOpc.UA.Discovery
using namespace OpcLabs.EasyOpc.UA.OperationModel

# The path below assumes that the current directory is [ProductDir]/Examples-NET/PowerShell/Windows .
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcUA.dll"
Add-Type -Path "../../../Components/Opclabs.QuickOpc/net472/OpcLabs.EasyOpcUAComponents.dll"

$discoveryUriStrings = @(
    "opc.tcp://opcua.demo-this.com:4840/UADiscovery",
    "http://opcua.demo-this.com/UADiscovery/Default.svc",
    "http://opcua.demo-this.com:52601/UADiscovery")

# Instantiate the client object.
$client = New-Object EasyUAClient

# Obtain collection of application elements.
try {
    $discoveryElementCollection = [IEasyUAClientExtension]::FindLocalApplications($client, 
        $discoveryUriStrings, [UAApplicationTypes]::Server)
}
catch [UAException] {
    Write-Host "*** Failure: $($PSItem.Exception.GetBaseException().Message)"
    return
}

# Display results.
foreach ($discoveryElement in $discoveryElementCollection) {
    Write-Host "discoveryElementCollection[`"$($discoveryElement.DiscoveryUriString)`"].ApplicationUriString: $($discoveryElement.ApplicationUriString)"
}


# Example output:
#
#discoveryElementCollection["http://opcua.demo-this.com:62543/Quickstarts/AlarmConditionServer"].ApplicationUriString: urn:opcua.demo-this.com:Quickstart Alarm Condition Server
#discoveryElementCollection["opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer"].ApplicationUriString: urn:opcua.demo-this.com:Quickstart Alarm Condition Server
#discoveryElementCollection["opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"].ApplicationUriString: urn:opcua.demo-this.com:UA Sample Server
#discoveryElementCollection["http://opcua.demo-this.com:51211/UA/SampleServer"].ApplicationUriString: urn:opcua.demo-this.com:UA Sample Server
#discoveryElementCollection["https://opcua.demo-this.com:51212/UA/SampleServer/"].ApplicationUriString: urn:opcua.demo-this.com:UA Sample Server
#discoveryElementCollection["opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"].ApplicationUriString: urn:Test-PC:UA Sample Server


# This example shows how to obtain application URLs of all OPC Unified Architecture servers, using specified discovery
# URI strings.
#
# 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.Discovery import *
from OpcLabs.EasyOpc.UA.OperationModel import *


discoveryUriStrings = [
    'opc.tcp://opcua.demo-this.com:4840/UADiscovery',
    'http://opcua.demo-this.com/UADiscovery/Default.svc',
    'http://opcua.demo-this.com:52601/UADiscovery'
]

# Instantiate the client object.
client = EasyUAClient()

# Obtain collection of application elements.
try:
    discoveryElementCollection = IEasyUAClientExtension.FindLocalApplications(client,
        discoveryUriStrings, UAApplicationTypes.Server)
except UAException as uaException:
    print('*** Failure: ' + uaException.GetBaseException().Message)
    exit()

# Display results.
for discoveryElement in discoveryElementCollection:
    print('DiscoveryElementCollection["', discoveryElement.DiscoveryUriString, '"].ApplicationUriString: ',
          discoveryElement.ApplicationUriString, sep='')

' This example shows how to obtain application URLs of all OPC Unified Architecture servers, using specified discovery URI strings.
'
' 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.Discovery
Imports OpcLabs.EasyOpc.UA.OperationModel

Namespace _EasyUAClient
    Friend Class FindLocalApplications
        Public Shared Sub Main1()
            Dim discoveryUriStrings() As String =
            { _
                "opc.tcp://opcua.demo-this.com:4840/UADiscovery", _
                "http://opcua.demo-this.com/UADiscovery/Default.svc", _
                "http://opcua.demo-this.com:52601/UADiscovery" _
            }

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

            ' Obtain collection of application elements
            Dim discoveryElementCollection As UADiscoveryElementCollection
            Try
                discoveryElementCollection = client.FindLocalApplications(discoveryUriStrings, UAApplicationTypes.Server)
            Catch uaException As UAException
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException.Message)
                Exit Sub
            End Try

            ' Display results
            For Each discoveryElement As UADiscoveryElement In discoveryElementCollection
                Console.WriteLine("discoveryElementCollection[""{0}""].ApplicationUriString: {1}", _
                    discoveryElement.DiscoveryUriString, discoveryElement.ApplicationUriString)
            Next discoveryElement

            ' Example output:
            'discoveryElementCollection["http://opcua.demo-this.com:62543/Quickstarts/AlarmConditionServer"].ApplicationUriString: urn:opcua.demo-this.com:Quickstart Alarm Condition Server
            'discoveryElementCollection["opc.tcp://opcua.demo-this.com:62544/Quickstarts/AlarmConditionServer"].ApplicationUriString: urn:opcua.demo-this.com:Quickstart Alarm Condition Server
            'discoveryElementCollection["opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"].ApplicationUriString: urn:opcua.demo-this.com:UA Sample Server
            'discoveryElementCollection["http://opcua.demo-this.com:51211/UA/SampleServer"].ApplicationUriString: urn:opcua.demo-this.com:UA Sample Server
            'discoveryElementCollection["https://opcua.demo-this.com:51212/UA/SampleServer/"].ApplicationUriString: urn:opcua.demo-this.com:UA Sample Server
            'discoveryElementCollection["opc.tcp://opcua.demo-this.com:51210/UA/SampleServer"].ApplicationUriString: urn:Test-PC:UA Sample Server
        End Sub
    End Class
End Namespace

COM

// This example shows how to obtain application URLs of all OPC Unified Architecture servers, using specified discovery URI strings.
//
// Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

class procedure FindLocalApplications.Main;
const
  UAApplicationTypes_Server = 1;
var
  Client: OpcLabs_EasyOpcUA_TLB._EasyUAClient;
  Count: Cardinal;
  Element: OleVariant;
  DiscoveryElement: _UADiscoveryElement;
  DiscoveryElementEnumerator: IEnumVariant;
  DiscoveryElements: _UADiscoveryElementCollection;
  DiscoveryUriStrings: OleVariant;
begin
  DiscoveryUriStrings := VarArrayCreate([0, 2], varVariant);
  DiscoveryUriStrings[0] := 'opc.tcp://opcua.demo-this.com:4840/UADiscovery';
  DiscoveryUriStrings[1] := 'http://opcua.demo-this.com/UADiscovery/Default.svc';
  DiscoveryUriStrings[2] := 'http://opcua.demo-this.com:52601/UADiscovery';

  // Instantiate the client object
  Client := CoEasyUAClient.Create;

  // Obtain collection of application elements
  try
    DiscoveryElements := Client.FindLocalApplications(DiscoveryUriStrings, UAApplicationTypes_Server);
  except
    on E: EOleException do
    begin
      WriteLn(Format('*** Failure: %s', [E.GetBaseException.Message]));
      Exit;
    end;
  end;

  // Display results
  DiscoveryElementEnumerator := DiscoveryElements.GetEnumerator;
  while (DiscoveryElementEnumerator.Next(1, Element, Count) = S_OK) do
  begin
    DiscoveryElement := IUnknown(Element) as _UADiscoveryElement;
    WriteLn(
      'DiscoveryElements["',
      DiscoveryElement.DiscoveryUriString,
      '".ApplicationUriString: ',
      DiscoveryElement.ApplicationUriString);
  end;

  VarClear(DiscoveryUriStrings);
end;

REM This example shows how to obtain application URLs of all OPC Unified Architecture servers, using specified discovery URI strings.
REM
REM Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Public Sub FindLocalApplications_Main_Command_Click()
    OutputText = ""
    
    Dim DiscoveryUriStrings(2)
    DiscoveryUriStrings(0) = "opc.tcp://opcua.demo-this.com:4840/UADiscovery"
    DiscoveryUriStrings(1) = "http://opcua.demo-this.com/UADiscovery/Default.svc"
    DiscoveryUriStrings(2) = "http://opcua.demo-this.com:52601/UADiscovery"

    ' Instantiate the client object
    Dim Client As New EasyUAClient

    ' Obtain collection of application elements
    On Error Resume Next
    Dim DiscoveryElementCollection As UADiscoveryElementCollection
    Set DiscoveryElementCollection = Client.FindLocalApplications(DiscoveryUriStrings, UAApplicationTypes_Server)
    If Err.Number <> 0 Then
        OutputText = OutputText & "*** Failure: " & Err.Source & ": " & Err.Description & vbCrLf
        Exit Sub
    End If
    On Error GoTo 0
    
    ' Display results
    Dim DiscoveryElement As UADiscoveryElement: For Each DiscoveryElement In DiscoveryElementCollection
        OutputText = OutputText & "DiscoveryElementCollection[""" & DiscoveryElement.DiscoveryUriString & """].ApplicationUriString: " & _
            DiscoveryElement.applicationUriString & vbCrLf
    Next
End Sub

Rem This example shows how to obtain application URLs of all OPC Unified Architecture servers, using specified discovery URI strings.
Rem
Rem Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Option Explicit

Const UAApplicationTypes_Server = 1

Dim discoveryUriStrings(2)
discoveryUriStrings(0) = "opc.tcp://opcua.demo-this.com:4840/UADiscovery"
discoveryUriStrings(1) = "http://opcua.demo-this.com/UADiscovery/Default.svc"
discoveryUriStrings(2) = "http://opcua.demo-this.com:52601/UADiscovery"

' Instantiate the client object
Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.UA.EasyUAClient")

' Obtain collection of application elements
On Error Resume Next
Dim DiscoveryElementCollection: Set DiscoveryElementCollection = Client.FindLocalApplications(discoveryUriStrings, UAApplicationTypes_Server)
If Err.Number <> 0 Then
    WScript.Echo "*** Failure: " & Err.Source & ": " & Err.Description
    WScript.Quit
End If
On Error Goto 0

' Display results
Dim DiscoveryElement: For Each DiscoveryElement In DiscoveryElementCollection
    WScript.Echo "DiscoveryElementCollection[""" & DiscoveryElement.DiscoveryUriString & """].ApplicationUriString: " & _
        DiscoveryElement.ApplicationUriString
Next

 

Note that QuickOPC returns UADiscoveryElementCollection from all OPC UA discovery methods, but the amount of information contained in each returned UADiscoveryElement depends on the discovery approach used. For OPC UA Local Discovery, following primary properties of each UADiscoveryElement are filled in:

OPC UA Local Discovery Server (LDS) is not part of OPC Data Client installation.
See Also
OPC UA Network Discovery
OPC UA Global Discovery
Generalized OPC UA Discovery
Discovering OPC UA Servers
Browsing for Information (OPC Data)
Imperative Programming Model for OPC Data (Classic and UA)
Imperative Programming Model

Installed Examples - Web

Installed Examples - Web - UADiscoverServersWeb

 

 

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