ReadFile Method (IEasyUAFileTransfer)

Reads a part of the file, starting from the current file position.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<NotNullAttribute()>
Function ReadFile( _
   ByVal endpointDescriptor As UAEndpointDescriptor, _
   ByVal fileNodeDescriptor As UANodeDescriptor, _
   ByVal fileHandle As UAFileHandle, _
   ByVal length As Integer _
) As Byte()

'Usage
 
Dim instance As IEasyUAFileTransfer
Dim endpointDescriptor As UAEndpointDescriptor
Dim fileNodeDescriptor As UANodeDescriptor
Dim fileHandle As UAFileHandle
Dim length As Integer
Dim value() As Byte
 
value = instance.ReadFile(endpointDescriptor, fileNodeDescriptor, fileHandle, length)

[NotNull()]
byte[] ReadFile( 
   UAEndpointDescriptor endpointDescriptor,
   UANodeDescriptor fileNodeDescriptor,
   UAFileHandle fileHandle,
   int length
)

[NotNull()]
array<byte>^ ReadFile( 
   UAEndpointDescriptor^ endpointDescriptor,
   UANodeDescriptor^ fileNodeDescriptor,
   UAFileHandle^ fileHandle,
   int length
)

Parameters

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 ToUAEndpointDescriptor or 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).

fileNodeDescriptor

Node descriptor of the OPC UA file.

Because the OpcLabs.EasyOpc.UA.UANodeDescriptor has implicit conversions from OpcLabs.EasyOpc.UA.AddressSpace.UANodeId, OpcLabs.EasyOpc.UA.AddressSpace.UANodeElement, OpcLabs.EasyOpc.UA.Navigation.UABrowsePath and System.String, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a OpcLabs.EasyOpc.UA.AddressSpace.UANodeId object (representing the Id of the OPC UA node), a node element object (from OPC UA browsing), OpcLabs.EasyOpc.UA.Navigation.UABrowsePath object (representing OPC UA absolute browse path), or a string (with expanded node Id text) in place of this parameter, and the corresponding 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.UANodeDescriptor.FromString, OpcLabs.EasyOpc.UA.UANodeDescriptor.FromUABrowsePath, OpcLabs.EasyOpc.UA.UANodeDescriptor.FromUANodeElement or OpcLabs.EasyOpc.UA.UANodeDescriptor.FromUANodeId static method instead.

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

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

fileHandle

A handle indicating the access request and thus indirectly the position inside the file.

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

length

Defines the length in bytes that should be returned, starting from the current position of the file handle. If the end of file is reached, all data until the end of the file is returned. The server is allowed to return fewer data than specified length. Only positive values are allowed.

Return Value

Returns the data read from the file. If the returned array is empty (zero length), it indicates that the end of the file is reached.

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

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.
System.ArgumentOutOfRangeException	The value of an argument is outside the allowable range of values as defined by the invoked method. 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.

System.ArgumentOutOfRangeException

The value of an argument is outside the allowable range of values as defined by the invoked method.

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 corresponds to (but is not fully identical with) the OPC UA File Transfer Method .

The fileNodeDescriptor must be an existing node in the server, of object type OpcLabs.EasyOpc.UA.AddressSpace.Standard.UAObjectTypeIds.FileType.

The file position is advanced by the number of bytes read.

Recommendation: Whenever possible, do not use this method directly, and use a higher-level abstraction instead. You can create System.IO.Stream objects for accessing the file data by using methods like OpcLabs.EasyOpc.UA.IO.Extensions.IEasyUAFileTransferExtension2.OpenOrCreateStream, or obtain them through a file provider (using IEasyUAFileTransferExtension.GetFileProvider2 or IEasyUAFileTransferExtension.GetWritableFileProvider).

Example

CSharp
VB.NET
Python

// Shows how to read different sections from an OPC UA file, using the file transfer client.
// 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 OpcLabs.EasyOpc.UA;
using OpcLabs.EasyOpc.UA.FileTransfer;
using OpcLabs.EasyOpc.UA.OperationModel;

namespace UADocExamples.FileTransfer._EasyUAFileTransferClient
{
    class ReadAndSetFilePosition
    {
        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();

            // Open the file, read two separate sections of it, and close it.
            try
            {
                Console.WriteLine("Opening file...");
                using (UAFileHandle fileHandle = fileTransferClient.OpenFile(endpointDescriptor, fileNodeDescriptor, UAOpenFileModes.Read))
                {
                    Console.WriteLine("Reading first file section...");
                    byte[] bytes1 = fileTransferClient.ReadFile(endpointDescriptor, fileNodeDescriptor, fileHandle, length:16);
                    Console.WriteLine($"First section: {BitConverter.ToString(bytes1)}");

                    Console.WriteLine("Reading second file section...");
                    byte[] bytes2 = fileTransferClient.ReadFile(endpointDescriptor, fileNodeDescriptor, fileHandle, length: 10);
                    Console.WriteLine($"Second section: {BitConverter.ToString(bytes2)}");

                    Console.WriteLine("Setting file position...");
                    fileTransferClient.SetFilePosition(endpointDescriptor, fileNodeDescriptor, fileHandle, position:100);

                    Console.WriteLine("Reading third file section...");
                    byte[] bytes3 = fileTransferClient.ReadFile(endpointDescriptor, fileNodeDescriptor, fileHandle, length: 20);
                    Console.WriteLine($"Third section: {BitConverter.ToString(bytes3)}");

                    Console.WriteLine("Closing file...");
                    fileTransferClient.CloseFile(endpointDescriptor, fileNodeDescriptor, fileHandle);
                }
            }
            catch (UAException uaException)
            {
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException().Message);
                return;
            }

            Console.WriteLine("Finished...");
        }
    }
}

' Shows how to read different sections from an OPC UA file, using the file transfer client.
' 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 OpcLabs.EasyOpc.UA
Imports OpcLabs.EasyOpc.UA.FileTransfer
Imports OpcLabs.EasyOpc.UA.OperationModel

Namespace FileTransfer._EasyUAFileTransferClient

    Friend Class ReadAndSetFilePosition

        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

            ' Open the file, read two separate sections of it, and close it.
            Try
                Console.WriteLine("Opening file...")
                Using fileHandle As UAFileHandle = fileTransferClient.OpenFile(endpointDescriptor, fileNodeDescriptor, UAOpenFileModes.Read)
                    Console.WriteLine("Reading first file section...")
                    Dim bytes1 As Byte() = fileTransferClient.ReadFile(endpointDescriptor, fileNodeDescriptor, fileHandle, 16)
                    Console.WriteLine($"First section: {BitConverter.ToString(bytes1)}")

                    Console.WriteLine("Reading second file section...")
                    Dim bytes2 As Byte() = fileTransferClient.ReadFile(endpointDescriptor, fileNodeDescriptor, fileHandle, 10)
                    Console.WriteLine($"Second section: {BitConverter.ToString(bytes2)}")

                    Console.WriteLine("Setting file position...")
                    fileTransferClient.SetFilePosition(endpointDescriptor, fileNodeDescriptor, fileHandle, 100)

                    Console.WriteLine("Reading third file section...")
                    Dim bytes3 As Byte() = fileTransferClient.ReadFile(endpointDescriptor, fileNodeDescriptor, fileHandle, 20)
                    Console.WriteLine($"Third section: {BitConverter.ToString(bytes3)}")

                    Console.WriteLine("Closing file...")
                    fileTransferClient.CloseFile(endpointDescriptor, fileNodeDescriptor, fileHandle)
                End Using
            Catch uaException As UAException
                Console.WriteLine("*** Failure: {0}", uaException.GetBaseException.Message)
                Exit Sub
            End Try

            Console.WriteLine("Finished...")
        End Sub
    End Class
End Namespace

# Shows how to read different sections from an OPC UA file, using the file transfer client.
# 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 OpcLabs.EasyOpc.UA import *
from OpcLabs.EasyOpc.UA.FileTransfer import *
from OpcLabs.EasyOpc.UA.OperationModel 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()

# Open the file, read two separate sections of it, and close it.
fileHandle = None
try:
    print('Opening file...')
    fileHandle = fileTransferClient.OpenFile(endpointDescriptor, fileNodeDescriptor, UAOpenFileModes.Read)

    print('Reading first file section...')
    bytes1 = fileTransferClient.ReadFile(endpointDescriptor, fileNodeDescriptor, fileHandle, 16)    # length
    print('First section: ', BitConverter.ToString(bytes1), sep='')

    print('Reading second file section...')
    bytes2 = fileTransferClient.ReadFile(endpointDescriptor, fileNodeDescriptor, fileHandle, 10)    # length
    print('Second section: ', BitConverter.ToString(bytes2), sep='')

    print('Setting file position...')
    fileTransferClient.SetFilePosition(endpointDescriptor, fileNodeDescriptor, fileHandle, 100) # position

    print('Reading third file section...')
    bytes3 = fileTransferClient.ReadFile(endpointDescriptor, fileNodeDescriptor, fileHandle, 20)    # length
    print('Third section: ', BitConverter.ToString(bytes3), sep='')

    print('Closing file...')
    fileTransferClient.CloseFile(endpointDescriptor, fileNodeDescriptor, fileHandle)

except UAException as uaException:
    print('*** Failure: ' + uaException.GetBaseException().Message)
    exit()

finally:
    fileHandle and fileHandle.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

Reference

IEasyUAFileTransfer Interface
IEasyUAFileTransfer Members
OpenStreamReader(IEasyUAFileTransfer,UAEndpointDescriptor,UANamedNodeDescriptor) Method
ReadAllBytes(IEasyUAFileTransfer,UAEndpointDescriptor,UANamedNodeDescriptor) Method
ReadAllText(IEasyUAFileTransfer,UAEndpointDescriptor,UANamedNodeDescriptor) Method
OpenFile Method
WriteFile Method

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