OPC Studio User's Guide and Reference
OpenStream(IEasyUAFileTransfer,UAEndpointDescriptor,UANamedNodeDescriptor) Method
Example 



OpcLabs.EasyOpcUA Assembly > OpcLabs.EasyOpc.UA.IO.Extensions Namespace > IEasyUAFileTransferExtension2 Class > OpenStream Method : OpenStream(IEasyUAFileTransfer,UAEndpointDescriptor,UANamedNodeDescriptor) Method
The OPC UA file transfer object that will perform the operation.

This is typically the OpcLabs.EasyOpc.UA.FileTransfer.EasyUAFileTransferClient object.

The value of this parameter cannot be null (Nothing in Visual Basic).

Endpoint descriptor. Identifies the OPC-UA server.

Because the OpcLabs.EasyOpc.UA.UAEndpointDescriptor has implicit conversions from System.String and System.Uri, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a string (representing the endpoint URL, or a so-called OPC UA endpoint descriptor string), or a System.Uri object, in place of this parameter, and the corresponding endpoint descriptor will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the OpcLabs.EasyOpc.UA.UAEndpointDescriptor.FromString or OpcLabs.EasyOpc.UA.UAEndpointDescriptor.FromUri static method instead.

Also, because the OpcLabs.EasyOpc.UA.Discovery.UAApplicationElement and OpcLabs.EasyOpc.UA.Discovery.UADiscoveryElement have an implicit conversion to OpcLabs.EasyOpc.UA.UAEndpointDescriptor, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a OpcLabs.EasyOpc.UA.Discovery.UAApplicationElement or OpcLabs.EasyOpc.UA.Discovery.UADiscoveryElement (results from OPC UA discovery) in place of this parameter, and the corresponding endpoint descriptor will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can convert a (non-null) OpcLabs.EasyOpc.UA.Discovery.UAApplicationElement or OpcLabs.EasyOpc.UA.Discovery.UADiscoveryElement to OpcLabs.EasyOpc.UA.UAEndpointDescriptor using the OpcLabs.EasyOpc.UA.Discovery.UAApplicationElement.ToUAEndpointDescriptor or OpcLabs.EasyOpc.UA.Discovery.UADiscoveryElement.ToUAEndpointDescriptor method instead.

If you are using OPC Wizard (for server development), an implicit conversion from OpcLabs.EasyOpc.UA.EasyUAServerCore can be used in the same way to simply pass the server object in place of this parameter, which will use its OpcLabs.EasyOpc.UA.EasyUAServerCore.EffectiveServerDescriptor property for the connection.

The value of this parameter cannot be null (Nothing in Visual Basic).

The named node descriptor of the file on which the stream should be opened.

Because the OpcLabs.EasyOpc.UA.Navigation.UANamedNodeDescriptor has an implicit conversion from OpcLabs.EasyOpc.UA.UANodeDescriptor, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a OpcLabs.EasyOpc.UA.UANodeDescriptor (containing the final node descriptor) in place of this parameter, and the corresponding OPC UA named node descriptor will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the OpcLabs.EasyOpc.UA.Navigation.UANamedNodeDescriptor.FromUANodeDescriptor static method instead.

The value of this parameter cannot be null (Nothing in Visual Basic).

Opens a System.IO.Stream on the specified OPC UA file, using default open mode.
Syntax
'Declaration
 
<ExtensionAttribute()>
<NotNullAttribute()>
Public Overloads Shared Function OpenStream( _
   ByVal fileTransfer As IEasyUAFileTransfer, _
   ByVal endpointDescriptor As UAEndpointDescriptor, _
   ByVal fileNamedNodeDescriptor As UANamedNodeDescriptor _
) As Stream
'Usage
 
Dim fileTransfer As IEasyUAFileTransfer
Dim endpointDescriptor As UAEndpointDescriptor
Dim fileNamedNodeDescriptor As UANamedNodeDescriptor
Dim value As Stream
 
value = IEasyUAFileTransferExtension2.OpenStream(fileTransfer, endpointDescriptor, fileNamedNodeDescriptor)

Parameters

fileTransfer
The OPC UA file transfer object that will perform the operation.

This is typically the OpcLabs.EasyOpc.UA.FileTransfer.EasyUAFileTransferClient object.

The value of this parameter cannot be null (Nothing in Visual Basic).

endpointDescriptor
Endpoint descriptor. Identifies the OPC-UA server.

Because the OpcLabs.EasyOpc.UA.UAEndpointDescriptor has implicit conversions from System.String and System.Uri, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a string (representing the endpoint URL, or a so-called OPC UA endpoint descriptor string), or a System.Uri object, in place of this parameter, and the corresponding endpoint descriptor will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the OpcLabs.EasyOpc.UA.UAEndpointDescriptor.FromString or OpcLabs.EasyOpc.UA.UAEndpointDescriptor.FromUri static method instead.

Also, because the OpcLabs.EasyOpc.UA.Discovery.UAApplicationElement and OpcLabs.EasyOpc.UA.Discovery.UADiscoveryElement have an implicit conversion to OpcLabs.EasyOpc.UA.UAEndpointDescriptor, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a OpcLabs.EasyOpc.UA.Discovery.UAApplicationElement or OpcLabs.EasyOpc.UA.Discovery.UADiscoveryElement (results from OPC UA discovery) in place of this parameter, and the corresponding endpoint descriptor will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can convert a (non-null) OpcLabs.EasyOpc.UA.Discovery.UAApplicationElement or OpcLabs.EasyOpc.UA.Discovery.UADiscoveryElement to OpcLabs.EasyOpc.UA.UAEndpointDescriptor using the OpcLabs.EasyOpc.UA.Discovery.UAApplicationElement.ToUAEndpointDescriptor or OpcLabs.EasyOpc.UA.Discovery.UADiscoveryElement.ToUAEndpointDescriptor method instead.

If you are using OPC Wizard (for server development), an implicit conversion from OpcLabs.EasyOpc.UA.EasyUAServerCore can be used in the same way to simply pass the server object in place of this parameter, which will use its OpcLabs.EasyOpc.UA.EasyUAServerCore.EffectiveServerDescriptor property for the connection.

The value of this parameter cannot be null (Nothing in Visual Basic).

fileNamedNodeDescriptor
The named node descriptor of the file on which the stream should be opened.

Because the OpcLabs.EasyOpc.UA.Navigation.UANamedNodeDescriptor has an implicit conversion from OpcLabs.EasyOpc.UA.UANodeDescriptor, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a OpcLabs.EasyOpc.UA.UANodeDescriptor (containing the final node descriptor) in place of this parameter, and the corresponding OPC UA named node descriptor will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the OpcLabs.EasyOpc.UA.Navigation.UANamedNodeDescriptor.FromUANodeDescriptor static method instead.

The value of this parameter cannot be null (Nothing in Visual Basic).

Return Value

Returns a System.IO.Stream opened for access to the specified file.

This method never returns null (Nothing in Visual Basic).

Exceptions
ExceptionDescription

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.

An attempt to access a file that does not exist on disk has failed.

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.

An I/O error has occurred.

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

CAUTION: This method does not throw the usual OpcLabs.EasyOpc.UA.OperationModel.UAException. Instead, an System.IO.IOException is thrown in case of an error during the operation.

See OPC UA File Transfer internals for information about Stream buffering and Stream expansion.

Recommendation: Whenever possible, do not use this method directly, and use a higher-level abstraction instead. You can obtain a file provider (using GetFileProvider2), and make use of its methods, and methods available on the directory contents (obtained using Microsoft.Extensions.FileProviders.IFileProvider.GetDirectoryContents(System.String)) or file info (obtained using Microsoft.Extensions.FileProviders.IFileProvider.GetFileInfo(System.String)).

This is an extension method (info: C#, VB.NET). In languages that have support for extensions methods (such as C# and VB.NET), you can use the extension method as if it were a regular method on the object that is its first parameter. In other languages (such as with Python.NET), you will call the extension as a static method, and pass it the object on which it acts as its first parameter.

Example
// Shows how to read different sections from an OPC UA file stream.
// Note: Consider using a higher-level abstraction, OPC UA file provider, instead.
//
// Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
// OPC client and subscriber examples in C# on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-CSharp .
// Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
// a commercial license in order to use Online Forums, and we reply to every post.

using System;
using System.IO;
using OpcLabs.EasyOpc.UA;
using OpcLabs.EasyOpc.UA.FileTransfer;
using OpcLabs.EasyOpc.UA.IO.Extensions;

namespace UADocExamples.FileTransfer._UAFileStream
{
    class ReadAndSeek
    {
        public static void Main1()
        {
            // Unified Automation .NET based demo server (UaNETServer/UaServerNET.exe)
            UAEndpointDescriptor endpointDescriptor = "opc.tcp://localhost:48030";

            // A node that represents an instance of OPC UA FileType object.
            UANodeDescriptor fileNodeDescriptor = "nsu=http://www.unifiedautomation.com/DemoServer/ ;s=Demo.Files.TextFile";
            
            // Instantiate the file transfer client object
            var fileTransferClient = new EasyUAFileTransferClient();

            try
            {
                // Get a stream object that corresponds to an OPC UA file.
                Console.WriteLine("Opening the file for reading...");
                using (Stream stream = fileTransferClient.OpenStream(endpointDescriptor, fileNodeDescriptor))
                {
                    // The OPC UA file stream object behaves like any other stream in .NET.

                    Console.WriteLine("Reading first section of a stream...");
                    var buffer1 = new byte[16];
                    int bytesRead1 = stream.Read(buffer1, 0, buffer1.Length);
                    Console.WriteLine($"{bytesRead1} bytes read, buffer: {BitConverter.ToString(buffer1)}");

                    Console.WriteLine("Reading second section of a stream...");
                    var buffer2 = new byte[10];
                    int bytesRead2 = stream.Read(buffer2, 0, buffer2.Length);
                    Console.WriteLine($"{bytesRead2} bytes read, buffer: {BitConverter.ToString(buffer2)}");

                    Console.WriteLine("Seeking...");
                    stream.Seek(100, SeekOrigin.Begin);

                    Console.WriteLine("Reading third section of a stream...");
                    var buffer3 = new byte[20];
                    int bytesRead3 = stream.Read(buffer3, 0, buffer3.Length);
                    Console.WriteLine($"{bytesRead3} bytes read, buffer: {BitConverter.ToString(buffer3)}");
                }
            }
            // OPC UA errors encountered during opening of a UA file stream and operations on such stream are transformed
            // to IOException-s.
            catch (IOException ioException)
            {
                Console.WriteLine("*** Failure: {0}", ioException.GetBaseException().Message);
                return;
            }

            Console.WriteLine();
            Console.WriteLine("Finished...");
        }
    }
}
' Shows how to read different sections from an OPC UA file stream.
' Note: Consider using a higher-level abstraction, OPC UA file provider, instead.
'
' Find all latest examples here: https://opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Latest/examples.html .
' OPC client and subscriber examples in VB.NET on GitHub: https://github.com/OPCLabs/Examples-QuickOPC-VBNET .
' Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
' a commercial license in order to use Online Forums, and we reply to every post.

Imports System.IO
Imports OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.FileTransfer
Imports OpcLabs.EasyOpc.UA.IO.Extensions

Namespace FileTransfer._UAFileStream

    Friend Class ReadAndSeek

        Public Shared Sub Main1()

            ' Unified Automation .NET based demo server (UaNETServer/UaServerNET.exe)
            Dim endpointDescriptor As UAEndpointDescriptor = "opc.tcp://localhost:48030"

            ' A node that represents an instance of OPC UA FileType object.
            Dim fileNodeDescriptor As UANodeDescriptor = "nsu=http://www.unifiedautomation.com/DemoServer/ ;s=Demo.Files.TextFile"

            ' Instantiate the file transfer client object
            Dim fileTransferClient = New EasyUAFileTransferClient

            Try
                ' Get a stream object that corresponds to an OPC UA file.
                Console.WriteLine("Opening the file for reading...")
                Using stream As Stream = fileTransferClient.OpenStream(endpointDescriptor, fileNodeDescriptor)
                    ' Get a stream object that corresponds to an OPC UA file.
                    Console.WriteLine("Reading first section of a stream...")
                    Dim buffer1(16 - 1) As Byte
                    Dim bytesRead1 As Integer = stream.Read(buffer1, 0, buffer1.Length)
                    Console.WriteLine($"{bytesRead1} bytes read, buffer: {BitConverter.ToString(buffer1)}")

                    Console.WriteLine("Reading second section of a stream...")
                    Dim buffer2(10 - 1) As Byte
                    Dim bytesRead2 As Integer = stream.Read(buffer2, 0, buffer2.Length)
                    Console.WriteLine($"{bytesRead2} bytes read, buffer: {BitConverter.ToString(buffer2)}")

                    Console.WriteLine("Seeking...")
                    stream.Seek(100, SeekOrigin.Begin)

                    Console.WriteLine("Reading third section of a stream...")
                    Dim buffer3(20 - 1) As Byte
                    Dim bytesRead3 As Integer = stream.Read(buffer3, 0, buffer3.Length)
                    Console.WriteLine($"{bytesRead3} bytes read, buffer: {BitConverter.ToString(buffer3)}")
                End Using
                ' OPC UA errors encountered during opening of an UA file stream And operations on such stream are transformed
                ' to IOException-s.
            Catch ioException As IOException
                Console.WriteLine("*** Failure: {0}", ioException.GetBaseException.Message)
                Exit Sub
            End Try

            Console.WriteLine()
            Console.WriteLine("Finished...")
        End Sub
    End Class
End Namespace
# Shows how to read different sections from an OPC UA file stream.
# Note: Consider using a higher-level abstraction, OPC UA file provider, instead.
#
# 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 .
# Missing some example? Ask us for it on our Online Forums, https://www.opclabs.com/forum/index ! You do not have to own
# a commercial license in order to use Online Forums, and we reply to every post.
# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc

# Import .NET namespaces.
from System import *
from System.IO import *
from OpcLabs.EasyOpc.UA import *
from OpcLabs.EasyOpc.UA.FileTransfer import *
from OpcLabs.EasyOpc.UA.IO.Extensions import *
from OpcLabs.EasyOpc.UA.Navigation import *


# Unified Automation .NET based demo server (UaNETServer/UaServerNET.exe).
endpointDescriptor = UAEndpointDescriptor('opc.tcp://localhost:48030')

# A node that represents an instance of OPC UA FileType object.
fileNodeDescriptor = UANodeDescriptor('nsu=http://www.unifiedautomation.com/DemoServer/ ;s=Demo.Files.TextFile')

# Instantiate the file transfer client object.
fileTransferClient = EasyUAFileTransferClient()

stream = None
try:
    # Get a stream object that corresponds to an OPC UA file.
    print('Opening the file for reading...')
    stream = IEasyUAFileTransferExtension2.OpenStream(fileTransferClient,
                                                      endpointDescriptor,
                                                      UANamedNodeDescriptor(fileNodeDescriptor))

    # The OPC UA file stream object behaves like any other stream in .NET.

    print('Reading first section of a stream...')
    buffer1 = Array.CreateInstance(Byte, 16)
    bytesRead1, _ = stream.Read(buffer1, 0, buffer1.Length)
    print(bytesRead1, ' bytes read, buffer: ', BitConverter.ToString(buffer1), sep='')

    print('Reading second section of a stream...')
    buffer2 = Array.CreateInstance(Byte, 10)
    bytesRead2, _ = stream.Read(buffer2, 0, buffer2.Length)
    print(bytesRead2, ' bytes read, buffer: ', BitConverter.ToString(buffer2), sep='')

    print('Seeking...')
    stream.Seek(100, SeekOrigin.Begin)

    print('Reading third section of a stream...')
    buffer3 = Array.CreateInstance(Byte, 20)
    bytesRead3, _ = stream.Read(buffer3, 0, buffer3.Length)
    print(bytesRead3, ' bytes read, buffer: ', BitConverter.ToString(buffer3), sep='')

# OPC UA errors encountered during opening of a UA file stream and operations on such stream are transformed
# to IOException-s.
except IOException as ioException:
    print('*** Failure: ' + ioException.GetBaseException().Message)
    exit()

finally:
    stream and stream.Dispose()

print()
print('Finished.')
Requirements

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

See Also