DiscoverLocalServers Method (

Discovers available OPC-UA servers and returns information about them, using the specified discovery host.

This method uses the so-called Local Discovery Server (LDS). You can influence how the discovery works using the properties in static SharedParameters.

Invokes the FindServers service.

See also in Knowledge Base: Technical note-OPC UA Discovery in QuickOPC.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<ElementsNotNullAttribute()>
<NotNullAttribute()>
Function DiscoverLocalServers( _
   ByVal discoveryHost As String _
) As UADiscoveryElementCollection

'Usage
 
Dim instance As _EasyUAClient
Dim discoveryHost As String
Dim value As UADiscoveryElementCollection
 
value = instance.DiscoverLocalServers(discoveryHost)

[ElementsNotNull()]
[NotNull()]
UADiscoveryElementCollection DiscoverLocalServers( 
   string discoveryHost
)

[ElementsNotNull()]
[NotNull()]
UADiscoveryElementCollection^ DiscoverLocalServers( 
   String^ discoveryHost
)

Parameters

discoveryHost: The name of the machine that runs the discovery server that will be used for discovery task.

Return Value

Returns a collection of application elements (servers, OpcLabs.EasyOpc.UA.Discovery.UADiscoveryElement).

Exceptions

Exception Description

Exception	Description
System.ArgumentNullException	A `null` reference (`Nothing` in Visual Basic) is passed to a method that does not accept it as a valid argument. This is a usage error, i.e. it will never occur (the exception will not be thrown) in a correctly written program. Your code should not catch this exception.
OpcLabs.EasyOpc.UA.OperationModel.UAException	The OPC UA operation has failed. This operation exception in uniformly used to allow common handling of various kinds of errors. The System.Exception.InnerException always contains information about the actual error cause. This is an operation error that depends on factors external to your program, and thus cannot be always avoided. Your code must handle it appropriately.

System.ArgumentNullException

A null reference (Nothing in Visual Basic) is passed to a method that does not accept it as a valid argument.

This is a usage error, i.e. it will never occur (the exception will not be thrown) in a correctly written program. Your code should not catch this exception.

OpcLabs.EasyOpc.UA.OperationModel.UAException

The OPC UA operation has failed. This operation exception in uniformly used to allow common handling of various kinds of errors. The System.Exception.InnerException always contains information about the actual error cause.

This is an operation error that depends on factors external to your program, and thus cannot be always avoided. Your code must handle it appropriately.

Remarks

This method uses the so-called Local Discovery Server (LDS). You can influence how the discovery works using the properties in static SharedParameters.

Invokes the FindServers service.

See also in Knowledge Base: Technical note-OPC UA Discovery in QuickOPC.

Example

.NET

// This example shows how to obtain application URLs of all OPC Unified Architecture servers on a given machine.

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.

#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.

# 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.

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

C++
Free Pascal
Object Pascal
PHP
Python
Visual Basic (VB 6.0)
VBScript

// This example shows how to obtain application URLs of all OPC Unified Architecture servers on the specified host.

#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.

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.

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.

// 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!
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.

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.

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

Requirements

Target Platforms: .NET Framework: Windows 10 (selected versions), Windows 11 (selected versions), Windows Server 2016, Windows Server 2022; .NET: Linux, macOS, Microsoft Windows

Reference

_EasyUAClient Interface
_EasyUAClient Members

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