observe property deserialized value (may) not (be) completely consistent #1294
Description
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.