How to write "Display Name" and "Description" to Node

[Aposeltof]

First thanks a lot for this module! It's really great.

For the moment we have used the browse and write value functions. Everything works fine.
The next step is to understand how to change a "display name" and "description" of an existing Node.

Can you help me ?

I try it like that for the moment :

func (s *instanceOPCClient) WriteDisplayNameByID(displayName string, ns uint16, id uint32) (success bool) {
	//Get Node id
	nid := ua.NewNumericNodeID(ns, id)

	//Open Node
	node := s.inst.uaClient.Node(nid)

	//Read current Node value to check it
	_, err := node.Value()
	if rslog.Check(err, slpOPC) {
		//Create a Variant from value
		variant, err := ua.NewVariant(displayName)
		if rslog.Check(err, slpOPC) {
			//Create a Write Request
			req := &ua.WriteRequest{
				NodesToWrite: []*ua.WriteValue{
					{
						NodeID:      nid,
						AttributeID: ua.AttributeIDDisplayName,
						Value: &ua.DataValue{
							EncodingMask: ua.DataValueValue,
							Value:        variant,
						},
					},
				},
			}

			//Write value to node
			_, err = s.inst.uaClient.Write(req)
			return rslog.Check(err, slpOPC)
		}
	}
	return false
}

[siscia]

Glancing at the code I don't see any obvious error.

I guess it didn't work, what error did you get?

[magiconair]

As a general Go comment: try to avoid nesting if statements and don't use helpers for error checking. It makes code harder to read since the idiomatic way of writing this is to fail fast. For example:

The other thing is that you should check the result code of the Write operation. If err != nil then that means that the Write operation has failed as a whole (e.g. server down, session closed, ...) but since you can update multiple nodes at the same time you need to check the resp.Results array for each node you've written.

func WriteDisplayNameByID(c *Client, displayName string, ns uint16, id uint32) error {
	// Get Node id
	nid := ua.NewNumericNodeID(ns, id)

	// Open Node
	node := c.Node(nid)

	// Read current Node value to check it
	_, err := node.Value()
	if err != nil {
		return err
	}

	// Create a Variant from value
	value, err := ua.NewVariant(displayName)
	if err != nil {
		return err
	}

	req := &ua.WriteRequest{
		NodesToWrite: []*ua.WriteValue{
			{
				NodeID:      nid,
				AttributeID: ua.AttributeIDDisplayName,
				Value: &ua.DataValue{
					EncodingMask: ua.DataValueValue,
					Value:        value,
				},
			},
		},
	}

	resp, err := c.Write(req)
	if err != nil {
		return err
	}

	if resp.Results[0] != ua.StatusOK {
		return resp.Results[0]
	}

	return nil
}

[magiconair]

As an aside: It might make sense to have a helper for setting attributes on the Node instance. Something like n.SetAttribute(attrID ua.AttributeID, value interface{}) error

[Aposeltof]

Yes it would be great

[Aposeltof]

Thanks for answering @magiconair and @siscia also for the general feedback.

I tried your code @magiconair .

I get the next message error :
The attribute is not supported for the specified Node. StatusBadAttributeIDInvalid (0x80350000)

But it was because of the commented part.

Now I have the error
User does not have permission to perform the requested operation. StatusBadUserAccessDenied (0x801F0000)

But I think it's more a node configuration error on the server side.
I will try to correct it and try again.

func WriteDisplayNameByID(c *opcua.Client, displayName string, ns uint16, id uint32) error {
	// Get Node id
	nid := ua.NewNumericNodeID(ns, id)

	// Open Node
	//	node := c.Node(nid)

	// Read current Node value to check it
	//_, err := node.Value()
	//if err != nil {
	//		return err
	//}

	// Create a Variant from value
	value, err := ua.NewVariant(displayName)
	if err != nil {
		return err
	}

	req := &ua.WriteRequest{
		NodesToWrite: []*ua.WriteValue{
			{
				NodeID:      nid,
				AttributeID: ua.AttributeIDDisplayName,
				Value: &ua.DataValue{
					EncodingMask: ua.DataValueValue,
					Value:        value,
				},
			},
		},
	}

	resp, err := c.Write(req)
	if err != nil {
		return err
	}

	if resp.Results[0] != ua.StatusOK { 
		return resp.Results[0] //  // Here come the user access error
	}

	return nil
}

[Aposeltof]

Hello, it works now.

On the Client side in Go :
I read and modify the display name attribute which is a "Localized.Text".
I convert it to a Variant then I can write it via the WriteRequest.

Server side:
I have to configure the "Write Mask" of the node so that the Display Name can be modified (Code 64).

The code

func WriteDisplayNameByID(c *opcua.Client, displayName string, ns uint16, id uint32) error {
	// Get Node id
	nid := ua.NewNumericNodeID(ns, id)

	// Open Node
	node := c.Node(nid)

	// Read current DisplayName
	dName, err := node.DisplayName()
	if err != nil {
		return err
	}

	//Change text
	dName.Text = displayName

	// Create a Variant from dName (Struct LocalizedText)
	value, err := ua.NewVariant(dName)
	if err != nil {
		return err
	}

	req := &ua.WriteRequest{
		NodesToWrite: []*ua.WriteValue{
			{
				NodeID:      nid,
				AttributeID: ua.AttributeIDDisplayName,
				Value: &ua.DataValue{
					EncodingMask: ua.DataValueValue,
					Value:        value,
				},
			},
		},
	}

	resp, err := c.Write(req)
	if err != nil {
		return err
	}

	if resp.Results[0] != ua.StatusOK {
		return resp.Results[0]
	}

	return nil
}