HTTP & paths confusion

[spembo]

Im trying to build an STM32 dev board-based battery monitor, to send battery values to an RPI signal k server via HTTP.

I have an HTTP client running on the dev board and can do the GET endpoints, GET self, and POST login fine.
Login request returns 200 and the token from the server - all good!

Then when I try to send a delta to batteries/0/current (for example) I get a response (405 not allowed):
"PUT not supported for electrical.batteries.0.current"

If I use a web browser on my PC and try:
http://IP:PORT/signalk/v1/api/vessels/self/electrical
I get:
"Cannot GET /signalk/v1/api/vessels/self/electrical"

And when I log into the server via web browser and open the "data browser" tab, there are no paths for electrical or anything else showing (like they show in the demo server).

So I guess somewhere in the server I need to set up all these paths, so that I can send updates to them???

I've been through the documentation for hours and cannot see anything on how to set these paths up.

I see in FAQ:
"PUT is for making changes that have some real world consequences, like turning on the anchor light. For PUT requests to work there must be a PUT handler registered for the path in question, that carries out the action, like turning the light on or off."
"Sensor data / new values for something are sent as delta messages over the WebSocket connection."

So how do you create a path then set up a PUT handler for a path?

Also, does this mean it is not possible to send something like battery data over HTTP?
Must you use web sockets?
The specification seems to say TCP, UDP, HTTP or Websockets could be used for sending deltas?

Any help with this would be very appreciated because this seems like a really simple thing I am missing and I feel a bit stupid at the moment!

[sbender9]

Yes, you must use WebSockets to send deltas.

[spembo]

Hi Scott, thanks for getting back to me so quickly.

So if I send the data via web socket will the server then automatically create that path?
It well then appear in the "data browser" tab from that point forward?

Or is there some other alternative of creating the full model within the server before sending data to it?

I have been through the documentation and gihub pages many times and cant see instructions on this, but if they are available a link to then would be very helpful, if you have it?

[spembo]

Sorry I have one more question, In the specification it states:

"PUT is for making changes that have some real world consequences, like turning on the anchor light. For PUT requests to work there must be a PUT handler registered for the path in question, that carries out the action, like turning the light on or off."

If I were to try and make a PUT request to an anchor light, I would still face the problem I have now, which is no path or PUT handler in the server.
So how do I add the path and put handler for this? Or find instructions on how to do so?

Thanks in advance

[sbender9]

In the case of an anchor light, there would be a plugin or something that has registered to handle a PUT and would be sending deltas related to that path. Switching related plugins do this.

Your use case would not use PUT. You just need to report on the vale of something. You cant PUT to battery current just like you can't PUT to wind speed. We can't change the wind speed. Only report on it.

When you send a delta for a any path, it will show up in the server and in the data browser. They won't be there until something sends a delta.

[tkurki]

Sending delta over ws is the same as sending a delta with Data Fiddler in the Admin UI, so you can try things out there.

[spembo]

Thank you both for your replies. That makes sense now.

[datadu-de]

Sending delta over ws is the same as sending a delta with Data Fiddler in the Admin UI, so you can try things out there.

on that note, as a noobie to SignalK may I ask, is there a specific reason, why a sensor cannot POST a data point to SK?
When I read about the API, the way GET works is perfectly clear, but when I looked ad how to get data in, it was confusing, why there's no POST interfaces for data points.
should this case be handled by a plugin that receives POST requests?

[sbender9]

POST is a very inefficient way to get data in. And I'm sure there were other reasons behind the decision.

You can do this: https://github.com/SignalK/signalk-server/wiki/FAQ:-Frequently-Asked-Questions#how-to-send-data-from-a-script-to-node-red

[spembo]

Thank you both for your replies. That makes sense now.