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Read/write files using OPC UA Client
April 24, 2017
15:20, EET
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RoarF
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April 24, 2017
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Hi,

I wondering how file read (and write) works from the OPC UA Client. I have created a server with som files wich I can browse, but when i try to read them from the client. I’m asked for filehandle int. Don’t know what this should be. Is it possible to read/write files from the client at all?

April 24, 2017
16:09, EET
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Bjarne Boström
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Hi,

Please read UA specification v1.03 Part 5 Annex C on how the File Transfer works. As a quick summary you open a handle via the Open UaMethod and then pass the received int to Read/Write methods and operate on arrays of bytes and then close the handle via Close method. The handle marks a position in the file where the Read/Write operations are performed and can be changed via SetPosition method.

The graphical client does not have anything special built-in for supporting this feature, i.e. theoretically you could read the raw bytestrings, but it is not practical as they would only be displayed on the screen as numbers. However this might be something we could add to a future version (i.e. export to file/import file kind dialogs), if there are actual use-cases. I would also note that the current FileType definition in the UA spec lacks any kind of checksum options, therefore I’m not sure on how to check the read/write is succesful.

– Bjarne

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