observe property deserialized value (may) not (be) completely consistent

[VigneshVSV]

The observable change events are pushed through HTTP SSE in may case. The following is the property affordance:

"position": {
      "title": "position",
      "description": "current position, write operation does not cause movement but overwrite register value.",
      "type": "number",
      "forms": [
        {
          "href": "https://localhost:8080/linear-stage/position",
          "op": "readproperty",
          "htv:methodName": "GET",
          "contentType": "application/json"
        },
        {
          "href": "https://localhost:8080/linear-stage/position",
          "op": "writeproperty",
          "htv:methodName": "PUT",
          "contentType": "application/json"
        },
        {
          "href": "https://localhost:8080/linear-stage/position/change-event",
          "subprotocol": "sse",
          "op": "observeproperty",
          "htv:methodName": "GET",
          "contentType": "text/plain"
        }
      ],
      "observable": true
    }

Either using text/plain or application/json as contentType , one still only retrieves the entire event object, not the event.data

Web browser gives the following output as expected from the event-stream. Server set header is text/event-stream:

data: 20.36

data: 20.005

data: 19.585

data: 19.07

data: 18.4825

data: 17.83

data: 17.0825

But what I get from node-wot (please ignore the stringification)

movements.tsx:24 Position changed to:
movements.tsx:25 "{\"type\":\"message\",\"data\":\"17.1025\",\"lastEventId\":\"\",\"origin\":\"https://localhost:8080\"}"
movements.tsx:24 Position changed to:
movements.tsx:25 "{\"type\":\"message\",\"data\":\"17.70375\",\"lastEventId\":\"\",\"origin\":\"https://localhost:8080\"}"
movements.tsx:24 Position changed to:
movements.tsx:25 "{\"type\":\"message\",\"data\":\"18.36\",\"lastEventId\":\"\",\"origin\":\"https://localhost:8080\"}"
movements.tsx:24 Position changed to:
movements.tsx:25 "{\"type\":\"message\",\"data\":\"18.96375\",\"lastEventId\":\"\",\"origin\":\"https://localhost:8080\"}"
movements.tsx:24 Position changed to:
movements.tsx:25 "{\"type\":\"message\",\"data\":\"19.48375\",\"lastEventId\":\"\",\"origin\":\"https://localhost:8080\"}"
movements.tsx:24 Position changed to:
movements.tsx:25 "{\"type\":\"message\",\"data\":\"19.92625\",\"lastEventId\":\"\",\"origin\":\"https://localhost:8080\"}"
movements.tsx:24 Position changed to:
movements.tsx:25 "{\"type\":\"message\",\"data\":\"20.3\",\"lastEventId\":\"\",\"origin\":\"https://localhost:8080\"}"
movements.tsx:24 Position changed to:
movements.tsx:25 "{\"type\":\"message\",\"data\":\"20.59\",\"lastEventId\":\"\",\"origin\":\"https://localhost:8080\"}"
movements.tsx:24 Position changed to:
movements.tsx:25 "{\"type\":\"message\",\"data\":\"20.7825\",\"lastEventId\":\"\",\"origin\":\"https://localhost:8080\"}"
movements.tsx:24 Position changed to:
movements.tsx:25 "{\"type\":\"message\",\"data\":\"20.915\",\"lastEventId\":\"\",\"origin\":\"https://localhost:8080\"}"
movements.tsx:24 Position changed to:
movements.tsx:25 "{\"type\":\"message\",\"data\":\"20.9925\",\"lastEventId\":\"\",\"origin\":\"https://localhost:8080\"}"
movements.tsx:24 Position changed to:
movements.tsx:25 "{\"type\":\"message\",\"data\":\"21.0\",\"lastEventId\":\"\",\"origin\":\"https://localhost:8080\"}"

client side code is like this:

const updatePosition = async (data) => {
      try {
          data.ignoreValidation = true 
          console.log("Position changed to:") 
          console.log(JSON.stringify(await data.value()))
      } catch (error) {
          console.error("Cannot read the observed property position");
          console.error(error);
      }
}

const subscribe = async() => {
      await motor.observeProperty('position', updatePosition) // motor is the node-wot client
      console.log("subscribed to motor position")
} 

setting ignoreValidation to false causes schema error as well

Position changed to:
movements.tsx:26 Cannot read the observed property position
Error: Invalid value according to DataSchema
    at InteractionOutput.<anonymous> (wot-bundle.min.js:69486:23)

I think the schema error is one reason why the event.data object must be returned instead of the event object itself.

[VigneshVSV]

Please ignore my JSON.stringify. I think that was an error from my side, but the general point might be correct.

[danielpeintner]

IF the object is returned (compared to the actual event data) it clarifies also why DataSchema validation fails.
Anyhow, I will not have time to look into it the next 2 weeks.

[VigneshVSV]

No hurry, the data is still accessible.

[danielpeintner]

Can you share your file movements.tsx with us?
I assume you call emitPropertyChange() right? I would like to see how this is done...

Thanks!

[VigneshVSV]

The data is sent from my backend in python, not node-wot server side. I mainly use node-wot as a client. The payload is a simple number in this case.

Is this what you wanted to know? The file is here anyway : https://gitlab.com/node-clients/phymotion-controllers-app/-/blob/main/src/components/movements.tsx?ref_type=heads