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



OpcLabs.EasyOpcUA Assembly > OpcLabs.EasyOpc.UA.IO.Extensions Namespace > IEasyUAFileTransferExtension2 Class > OpenStream Method : OpenStream(IEasyUAFileTransfer,UAEndpointDescriptor,UANamedNodeDescriptor,UAOpenFileModes) Method
The OPC UA file transfer object that will perform the operation.
Endpoint descriptor. Identifies the OPC-UA server.
The named node descriptor of the file on which the stream should be opened.
Indicates whether the file should be opened only for read operations or for read and write operations and where the initial position is set.
Opens a System.IO.Stream on the specified OPC UA file.
Syntax
'Declaration
 
<ExtensionAttribute()>
<NotNullAttribute()>
Public Overloads Shared Function OpenStream( _
   ByVal fileTransfer As IEasyUAFileTransfer, _
   ByVal endpointDescriptor As UAEndpointDescriptor, _
   ByVal fileNamedNodeDescriptor As UANamedNodeDescriptor, _
   ByVal openFileModes As UAOpenFileModes _
) As Stream
'Usage
 
Dim fileTransfer As IEasyUAFileTransfer
Dim endpointDescriptor As UAEndpointDescriptor
Dim fileNamedNodeDescriptor As UANamedNodeDescriptor
Dim openFileModes As UAOpenFileModes
Dim value As Stream
 
value = IEasyUAFileTransferExtension2.OpenStream(fileTransfer, endpointDescriptor, fileNamedNodeDescriptor, openFileModes)

Parameters

fileTransfer
The OPC UA file transfer object that will perform the operation.
endpointDescriptor
Endpoint descriptor. Identifies the OPC-UA server.
fileNamedNodeDescriptor
The named node descriptor of the file on which the stream should be opened.
openFileModes
Indicates whether the file should be opened only for read operations or for read and write operations and where the initial position is set.

Return Value

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

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

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.

Example

.NET

// 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 .

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 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 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.')
' 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 .

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
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