QueryServers Method (_EasyUAGlobalDiscoveryClient)

(Depreciated) Finds server applications that meet the specified filters.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
Sub QueryServers( _
   ByVal gdsEndpointDescriptor As Object, _
   ByVal startingRecordId As Integer, _
   ByVal maximumRecordsToReturn As Integer, _
   ByVal applicationName As String, _
   ByVal applicationUriString As String, _
   ByVal productUriString As String, _
   ByVal serverCapabilities As Object, _
   ByRef lastCounterResetTime As Date, _
   ByRef serverOnNetworkArray As Object _
)

'Usage
 
Dim instance As _EasyUAGlobalDiscoveryClient
Dim gdsEndpointDescriptor As Object
Dim startingRecordId As Integer
Dim maximumRecordsToReturn As Integer
Dim applicationName As String
Dim applicationUriString As String
Dim productUriString As String
Dim serverCapabilities As Object
Dim lastCounterResetTime As Date
Dim serverOnNetworkArray As Object
 
instance.QueryServers(gdsEndpointDescriptor, startingRecordId, maximumRecordsToReturn, applicationName, applicationUriString, productUriString, serverCapabilities, lastCounterResetTime, serverOnNetworkArray)

void QueryServers( 
   object gdsEndpointDescriptor,
   int startingRecordId,
   int maximumRecordsToReturn,
   string applicationName,
   string applicationUriString,
   string productUriString,
   object serverCapabilities,
   out DateTime lastCounterResetTime,
   out object serverOnNetworkArray
)

void QueryServers( 
   Object^ gdsEndpointDescriptor,
   int startingRecordId,
   int maximumRecordsToReturn,
   String^ applicationName,
   String^ applicationUriString,
   String^ productUriString,
   Object^ serverCapabilities,
   [Out] DateTime lastCounterResetTime,
   [Out] Object^ serverOnNetworkArray
)

Parameters

gdsEndpointDescriptor: Endpoint descriptor. Identifies the OPC-UA server. The server must be a Global Directory Server (GDS).
startingRecordId: Only records with an identifier greater than this number will be returned.
Specify 0 to start with the first record in the database.
maximumRecordsToReturn: The maximum number of records to return in the response.
0 indicates that there is no limit.
applicationName: The ApplicationName of the applications to return.
Supports the syntax used by the LIKE FilterOperator described in Part 4.
Not used if an empty string is specified. The filter is only applied to the default ApplicationName.
applicationUriString: The ApplicationUri of the servers to return.
Supports the syntax used by the LIKE FilterOperator described in Part 4.
Not used if an empty string is specified.
productUriString: The ProductUri of the servers to return.
Supports the syntax used by the LIKE FilterOperator described in Part 4.
Not used if an empty string is specified.
serverCapabilities: The capabilities supported by the applications returned. If no server capabilities are provided this filter is not used.
lastCounterResetTime: The last time the counters were reset.
serverOnNetworkArray: A list of Servers which meet the criteria (OpcLabs.EasyOpc.UA.Discovery.UAServerOnNetwork).

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

There are higher-level methods that are easier to use and can be used instead. Have a look e.g. at:

OpcLabs.EasyOpc.UA.IEasyUAClientExtension.DiscoverGlobalApplications and its overloads,
OpcLabs.EasyOpc.UA.IEasyUAClientExtension.DiscoverGlobalServers and its overloads.
OpcLabs.EasyOpc.UA.IEasyUAClient.Discover and OpcLabs.EasyOpc.UA.Discovery.UAGlobalApplicationDiscoveryQuery.

Example

.NET

// Shows how to find server applications that meet the specified filters, using the global discovery client.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

using System;
using OpcLabs.EasyOpc.UA.Discovery;
using OpcLabs.EasyOpc.UA.Gds;
using OpcLabs.EasyOpc.UA.OperationModel;

namespace UADocExamples.Gds._EasyUAGlobalDiscoveryClient
{
    class QueryServers
    {
        public static void Main1()
        {
            // Instantiate the global discovery client object
            var globalDiscoveryClient = new EasyUAGlobalDiscoveryClient();

            // Find all servers registered in the GDS.
            UAServerOnNetwork[] serverOnNetworkArray;
            try
            {
                globalDiscoveryClient.QueryServers(
                    gdsEndpointDescriptor:"opc.tcp://opcua.demo-this.com:58810/GlobalDiscoveryServer",
                    startingRecordId:0,
                    maximumRecordsToReturn:0,
                    applicationName:"",
                    applicationUriString:"",
                    productUriString:"",
                    serverCapabilities:new string[0],
                    lastCounterResetTime:out _,
                    serverOnNetworkArray:out serverOnNetworkArray);
            }
            catch (UAException uaException)
            {
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException().Message);
                return;
            }

            // Display results
            foreach (UAServerOnNetwork serverOnNetwork in serverOnNetworkArray)
            {
                Console.WriteLine();
                Console.WriteLine("Server name: {0}", serverOnNetwork.ServerName);
                Console.WriteLine("Discovery URL string: {0}", serverOnNetwork.DiscoveryUrlString);
                Console.WriteLine("Server capabilities: {0}", serverOnNetwork.ServerCapabilities);
            }
        }
    }
}

# Shows how to find server applications that meet the specified filters, using the global discovery client.
#
# 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 System import *
from OpcLabs.EasyOpc.UA import *
from OpcLabs.EasyOpc.UA.Discovery import *
from OpcLabs.EasyOpc.UA.Gds import *
from OpcLabs.EasyOpc.UA.OperationModel import *


# Define which GDS we will work with.
gdsEndpointDescriptor = UAEndpointDescriptor('opc.tcp://opcua.demo-this.com:58810/GlobalDiscoveryServer')

# Instantiate the global discovery client object.
globalDiscoveryClient = EasyUAGlobalDiscoveryClient()

# Find all servers registered in the GDS.
try:
    _, _, serverOnNetworkArray = globalDiscoveryClient.QueryServers(
        gdsEndpointDescriptor,
        0,  # startingRecordId
        0,  # maximumRecordsToReturn
        '', # applicationName
        '', # applicationUriString
        '', # productUriString
        Array.Empty[String](),  # serverCapabilities
        DateTime(), # out lastCounterResetTime
        Array.Empty[UAServerOnNetwork]()) # out serverOnNetworkArray
except UAException as uaException:
    print('*** Failure: ' + uaException.GetBaseException().Message)
    exit()

# Display results.
for serverOnNetwork in serverOnNetworkArray:
    print()
    print('Server name: ', serverOnNetwork.ServerName, sep='')
    print('Discovery URL string: ', serverOnNetwork.DiscoveryUrlString, sep='')
    print('Server capabilities: ', serverOnNetwork.ServerCapabilities, sep='')

print()
print('Finished.')

' Shows how to find server applications that meet the specified filters, using the global discovery client.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Imports OpcLabs.EasyOpc.UA.Discovery
Imports OpcLabs.EasyOpc.UA.Gds
Imports OpcLabs.EasyOpc.UA.OperationModel

Namespace Gds._EasyUAGlobalDiscoveryClient
    Friend Class QueryServers
        Public Shared Sub Main1()

            ' Instantiate the global discovery client object
            Dim globalDiscoveryClient = New EasyUAGlobalDiscoveryClient()

            ' Find all servers registered in the GDS.
            Dim serverOnNetworkArray() As UAServerOnNetwork = Nothing
            Try
                Dim lastCounterResetTime As DateTime
                globalDiscoveryClient.QueryServers(
                    gdsEndpointDescriptor:="opc.tcp://opcua.demo-this.com:58810/GlobalDiscoveryServer",
                    startingRecordId:=0,
                    maximumRecordsToReturn:=0,
                    applicationName:="",
                    applicationUriString:="",
                    productUriString:="",
                    serverCapabilities:=New String() {},
                    lastCounterResetTime:=lastCounterResetTime,
                    serverOnNetworkArray:=serverOnNetworkArray)
            Catch uaException As UAException
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException.Message)
                Exit Sub
            End Try

            ' Display results
            For Each serverOnNetwork As UAServerOnNetwork In serverOnNetworkArray
                Console.WriteLine()
                Console.WriteLine("Server name: {0}", serverOnNetwork.ServerName)
                Console.WriteLine("Discovery URL string: {0}", serverOnNetwork.DiscoveryUrlString)
                Console.WriteLine("Server capabilities: {0}", serverOnNetwork.ServerCapabilities)
            Next serverOnNetwork
        End Sub
    End Class
End Namespace

Object Pascal
Visual Basic (VB 6.0)

// Shows how to find server applications that meet the specified filters, using the global discovery client.
//
// Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

class procedure QueryServers.Main;
var
  ApplicationName: WideString;
  ApplicationUriString: WideString;
  GlobalDiscoveryClient: OpcLabs_EasyOpcUA_TLB._EasyUAGlobalDiscoveryClient;
  GdsEndpointDescriptor: _UAEndpointDescriptor;
  I: integer;
  LastCounterResetTime: TDateTime;
  MaximumRecordsToReturn: Integer;
  ProductUriString: WideString;
  ServerCapabilities: array of string;
  ServerOnNetwork: _UAServerOnNetwork;
  ServerOnNetworkArray: OleVariant;
  StartingRecordId: Integer;
begin
  // Define which GDS we will work with.
  GdsEndpointDescriptor := CoUAEndpointDescriptor.Create;
  GdsEndpointDescriptor.UrlString := 'opc.tcp://opcua.demo-this.com:58810/GlobalDiscoveryServer';

  // Instantiate the global discovery client object
  GlobalDiscoveryClient := CoEasyUAGlobalDiscoveryClient.Create;

  // Find all servers registered in the GDS.
  StartingRecordId := 0;
  MaximumRecordsToReturn := 0;
  ApplicationName := '';
  ApplicationUriString := '';
  ProductUriString := '';
  try
    GlobalDiscoveryClient.QueryServers(
      GdsEndpointDescriptor,
      StartingRecordId,
      MaximumRecordsToReturn,
      ApplicationName,
      ApplicationUriString,
      ProductUriString,
      ServerCapabilities,
      LastCounterResetTime,
      ServerOnNetworkArray);
  except
    on E: EOleException do
    begin
      WriteLn(Format('*** Failure: %s', [E.GetBaseException.Message]));
    end;
  end;

  // Display results
  for I := VarArrayLowBound(ServerOnNetworkArray,1) to VarArrayHighBound(ServerOnNetworkArray,1) do
  begin
    ServerOnNetwork := IUnknown(ServerOnNetworkArray[I]) as _UAServerOnNetwork;
    WriteLn;
    WriteLn('Server name: ', ServerOnNetwork.ServerName);
    WriteLn('Discovery URL string: ', ServerOnNetwork.DiscoveryUrlString);
    WriteLn('Server capabilities: ', ServerOnNetwork.ServerCapabilities.ToString);
  end;

end;

REM Shows how to find server applications that meet the specified filters, using the global discovery client.
REM
REM Find all latest examples here : https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .

Private Sub EasyUAGlobalDiscoveryClient_QueryServers_Main_Command_Click()
    OutputText = ""
    
    ' Define which GDS we will work with.
    Dim gdsEndpointDescriptor As New UAEndpointDescriptor
    gdsEndpointDescriptor.UrlString = "opc.tcp://opcua.demo-this.com:58810/GlobalDiscoveryServer"
    
    ' Instantiate the global discovery client object
    Dim globalDiscoveryClient As New EasyUAGlobalDiscoveryClient
    
    ' Find all servers registered in the GDS.
    Dim startingRecordId As Integer: startingRecordId = 0
    Dim maximumRecordsToReturn As Integer: maximumRecordsToReturn = 0
    Dim applicationName As String: applicationName = ""
    Dim applicationUriString As String: applicationUriString = ""
    Dim productUriString As String: productUriString = ""
    Dim serverCapabilities: serverCapabilities = Array()
    Dim lastCounterResetTime As Date
    Dim serverOnNetworkArray As Variant
    On Error Resume Next
    Dim applicationId As UANodeId
    Call globalDiscoveryClient.QueryServers( _
      gdsEndpointDescriptor, _
      startingRecordId, _
      maximumRecordsToReturn, _
      applicationName, _
      applicationUriString, _
      productUriString, _
      serverCapabilities, _
      lastCounterResetTime, _
      serverOnNetworkArray)
    If Err.Number <> 0 Then
        OutputText = OutputText & "*** Failure: " & Err.Source & ": " & Err.Description & vbCrLf
        Exit Sub
    End If
    On Error GoTo 0
    
    ' Display results
    Dim i: For i = LBound(serverOnNetworkArray) To UBound(serverOnNetworkArray)
        Dim serverOnNetwork As UAServerOnNetwork
        Set serverOnNetwork = serverOnNetworkArray(i)
        OutputText = OutputText & vbCrLf
        OutputText = OutputText & "ServerName name: " & serverOnNetwork.ServerName & vbCrLf
        OutputText = OutputText & "Discovery URL string: " & serverOnNetwork.DiscoveryUrlString & vbCrLf
        OutputText = OutputText & "Server capabilities: " & serverOnNetwork.serverCapabilities.ToString & vbCrLf
    Next
End Sub

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

_EasyUAGlobalDiscoveryClient Interface
_EasyUAGlobalDiscoveryClient Members

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