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Client-based NodeSet Export

The OPC UA .NET Standard stack provides the ability to export the address space from an OPC UA server to a NodeSet2 XML file using the client library. This allows you to browse a server's address space and save it to a file that can be used for documentation, analysis, or import into other systems.

Overview

The client-based NodeSet export feature enables:

  • Browsing and collecting nodes from an OPC UA server
  • Converting client-side node representations (INode) to server-side representations (NodeState)
  • Exporting nodes to standard NodeSet2 XML format
  • Round-tripping: exported NodeSets can be imported using existing import functionality

Usage

Basic Example

using System.IO;
using Opc.Ua;
using Opc.Ua.Client;

// Connect to server and create session
var session = await Session.CreateAsync(/*...*/);

// Browse to collect nodes
var browser = new Browser(session)
{
    BrowseDirection = BrowseDirection.Forward,
    ReferenceTypeId = ReferenceTypeIds.HierarchicalReferences,
    IncludeSubtypes = true,
    NodeClassMask = 0
};

var nodesToBrowse = new NodeIdCollection { ObjectIds.Server };
var allNodes = new List<INode>();

// Browse and collect nodes
ReferenceDescriptionCollection references = await browser.BrowseAsync(nodesToBrowse[0]);

foreach (ReferenceDescription reference in references)
{
    INode node = await session.NodeCache.FindAsync(reference.NodeId);
    if (node != null)
    {
        allNodes.Add(node);
    }
}

// Export to NodeSet2 file
using (var stream = new FileStream("exported-nodeset.xml", FileMode.Create))
{
    var systemContext = new SystemContext(telemetry)
    {
        NamespaceUris = session.NamespaceUris,
        ServerUris = session.ServerUris
    };

    CoreClientUtils.ExportNodesToNodeSet2(systemContext, allNodes, stream);
}

Using the Console Reference Client

The console reference client (ClientSamples class) includes a helper method for exporting nodes:

// Browse and collect nodes using the existing helper
IList<INode> nodes = await clientSamples.FetchAllNodesNodeCacheAsync(
    uaClient,
    ObjectIds.ObjectsFolder,  // Starting node
    fetchTree: true,           // Recursively browse the tree
    addRootNode: true,         // Include the root node
    filterUATypes: true,       // Filter out namespace 0 nodes
    clearNodeCache: true
);

// Export to NodeSet2 file
clientSamples.ExportNodesToNodeSet2(session, nodes, "address-space.xml");

Supported Node Types

The export functionality supports all standard OPC UA node types:

  • Object nodes - Objects and their properties
  • Variable nodes - Variables with their values and data types
  • Method nodes - Methods with their executable status
  • ObjectType nodes - Object type definitions
  • VariableType nodes - Variable type definitions
  • DataType nodes - Data type definitions
  • ReferenceType nodes - Reference type definitions
  • View nodes - View definitions

Features

Node Attributes Exported

For each node, the following attributes are exported (where applicable):

  • NodeId
  • BrowseName
  • DisplayName
  • Description
  • WriteMask and UserWriteMask
  • References to other nodes
  • Type-specific attributes (e.g., DataType for variables, EventNotifier for objects)

Namespace Handling

The export functionality properly handles:

  • Multiple namespaces
  • Namespace URIs are included in the exported NodeSet
  • NodeIds are correctly mapped to namespace indices

References

All references between nodes are preserved in the export, including:

  • Hierarchical references (e.g., HasComponent, HasProperty)
  • Type definition references (e.g., HasTypeDefinition)
  • Organizing references
  • Custom reference types

Limitations

  • The export creates a snapshot of the address space at the time of browsing
  • Dynamic values are captured as they exist at export time
  • Not all server-specific internal state may be preserved
  • Complex type definitions require the complex types system to be loaded

API Reference

CoreClientUtils.ExportNodesToNodeSet2

public static void ExportNodesToNodeSet2(
    ISystemContext context,
    IList<INode> nodes,
    Stream outputStream)

Parameters:

  • context - System context containing namespace and server URI information
  • nodes - List of nodes to export
  • outputStream - Stream to write the NodeSet2 XML to

Exceptions:

  • ArgumentNullException - If any parameter is null

ClientSamples.ExportNodesToNodeSet2

public void ExportNodesToNodeSet2(
    ISession session,
    IList<INode> nodes,
    string filePath)

Parameters:

  • session - Active session to use for namespace information
  • nodes - List of nodes to export
  • filePath - Path where the NodeSet2 XML file will be saved

Related Topics

Examples

For complete examples of using the NodeSet export functionality, see:

  • Tests/Opc.Ua.Client.Tests/NodeSetExportTest.cs - Unit tests demonstrating various export scenarios
  • Applications/ConsoleReferenceClient/ClientSamples.cs - Integration in the reference client

See Also