RE: Proposal for Remote Procedure Call extensions to VISS.

Hi,

so I feel the main issue here  is one of scope for VISS:

We definitely can have HTTP, “Classic”-Websocket, WAMP, MQTT, etc. as “transports”, and the VISS specification might just reference them as optional parts such as “IF you want to do REST with VISS ; HERE is how we suggest you do it, in case of WAMP map it like this, for MQTT….” A little bit like convergence layers in Bundle Protocol.

But the question really is should the underlying data model understand the notion of RPCs? If an actor is just a node in the tree you can write to, and what will really happen is sort of hidden. Or you introduce some “RPC” endpoints in the data model that expect some complex input data and specifying return values. My feeling is that the latter is too much. (It might make VISS a feature monster….). Maybe there is some middle ground, where one can define that there is an RPC mechanism (which means, transports need to have a support  a generic query/response scheme that can do more than “writeInt()->Done()”), but not defining/modelling detailed RPC signaturess in VSS?



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From: Ulf Bjorkengren <ulfbjorkengren@geotab.com>
Sent: Dienstag, 11. Februar 2020 09:36
To: Magnus Feuer <mfeuer1@jaguarlandrover.com>
Cc: public-automotive@w3.org
Subject: Re: Proposal for Remote Procedure Call extensions to VISS.

Thanks for the explanation.

I see this as a rather lightweight wrapper on top of VISS(/Gen2) that provides a different interface style. Which is fine with me, but I am doubtful in it being a formal part of the standard.
I also conclude that this is a different thing than WAMP that Gunnar mentioned.

BR
Ulf

On Mon, Feb 10, 2020 at 11:03 PM Magnus Feuer <mfeuer1@jaguarlandrover.com<mailto:mfeuer1@jaguarlandrover.com>> wrote:
I forgot the most important bit, the function call itself:

call_rpc("Vehicle.Cabin.Door.Row1.Left.Window.SetPosition", Position=50);

The argument (Position) can either be defined locally in the RPC definition, as per my previous email, or be a reference / anchor to a signal (tree) living somewhere else in the spec

/Magnus F.

-------------------
System Architect Manager
Jaguar Land Rover

Email: mfeuer1@jaguarlandrover.com<mailto:mfeuer1@jaguarlandrover.com>
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From: Magnus Feuer <mfeuer1@jaguarlandrover.com<mailto:mfeuer1@jaguarlandrover.com>>
Sent: Monday, February 10, 2020 13:52
To: Ulf Bjorkengren <ulfbjorkengren@geotab.com<mailto:ulfbjorkengren@geotab.com>>
Cc: public-automotive@w3.org<mailto:public-automotive@w3.org> <public-automotive@w3.org<mailto:public-automotive@w3.org>>
Subject: Re: Proposal for Remote Procedure Call extensions to VISS.


Ulf,

The idea is that the function name, and its arguments, live outside the VSS spec, driving our JLR principle of "RPC to actuate. Signal to sense". We are using a separate YAML file format for our service specifications.

That said, the idea of integrating function names into the VSS spec is probably worth exploring, although it may be too much feature packing into a single spec.

An RPC call in a VSS spec file would look something like:

# Signal to report window position
- Position:
  datatype: uint8
  type: sensor
  min: 0
  max: 100
  unit: percent
  description: Window position. 0 = Fully closed 100 = Fully opened.


# RPC to actuate window position
- SetPosition:
  type: rpc
  description: Move the window to a spcific position
  arguments:
    - TargetPosition:
      datatype: uint8
      min: 0
      max: 100
      unit: percent
      description: The target position to move the window to. 0 = Fully closed 100 = Fully opened.
  return:
    - Result:
      datatype: uint8
      description: The result code (from a standard set of result codes)

    - CurrentPosition:
      datatype: uint8
      min: 0
      max: 100
      unit: percent
      description: The position of the window at the start of the window move

Complex arguments (structs and nested structs) would look much like a signal tree.

Thoughts?

/Magnus F.



-------------------
System Architect Manager
Jaguar Land Rover

Email: mfeuer1@jaguarlandrover.com<mailto:mfeuer1@jaguarlandrover.com>
Mobile: +1 949 294 7871

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Jaguar Land Rover North America, LLC
1450 NW 18th Ave, Portland, OR 97209
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Business Details:
Jaguar Land Rover Limited
Registered Office: Abbey Road, Whitley, Coventry CV3 4LF
Registered in England No: 1672070

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From: Ulf Bjorkengren <ulfbjorkengren@geotab.com<mailto:ulfbjorkengren@geotab.com>>
Sent: Monday, February 10, 2020 02:20
To: Magnus Feuer <mfeuer1@jaguarlandrover.com<mailto:mfeuer1@jaguarlandrover.com>>
Cc: public-automotive@w3.org<mailto:public-automotive@w3.org> <public-automotive@w3.org<mailto:public-automotive@w3.org>>
Subject: Re: Proposal for Remote Procedure Call extensions to VISS.

Hi,

I think this could be an interesting extension to the standard.
At the same time I see it as a "wrapper" on the standard, which I do not think should be part of the normative standard, possible a non-normative note or the like.

I have a few comments on what is presented on https://github.com/PDXostc/viss-rpc.

- In "subscribe" calls the path is explicitly used, while in "call" calls this is implicit in the "function" parameter (which must then by the receiving server be mapped to a path). This means every leaf node in the tree would have to have a unique function value.
- In the "call" example the "arguments" filed contain the format of provided data. This format is known already by the server from the VSS metadata of this node. Providing it in the call open for the problem of mismatch with the metadata in the tree.

I do not think that neither this nor WAMP, or any other pub-sub solution, should replace HTTP and/or WebSocket as transports, but rather complement them.

BR
Ulf

On Fri, Feb 7, 2020 at 12:45 AM Magnus Feuer <mfeuer1@jaguarlandrover.com<mailto:mfeuer1@jaguarlandrover.com>> wrote:
All,

We have been exploring an extended VISS protocol that allows for remote procedure calls to be invoked over the same websocket that today runs signal pub/sub.
Since we believe this extension may be of use to the wider community, we would like to explore the possibility of expanding the W3C standard accordingly.

The proposal, and a working sample implementation, can be found at:

https://github.com/PDXostc/viss-rpc


All is open sourced under MPLv2.

This is in no way a completed spec. Things such as nested arguments (structs) and callbacks missing, so questions, proposals, and criticism would be much appreciated.

If we come to an agreement that this is the right way forward I will make sure that JLR matures code and documentation as needed to integrate them into the W3C standard.

Regards,

/Magnus F.

-------------------
System Architect Manager
Jaguar Land Rover

Email: mfeuer1@jaguarlandrover.com<mailto:mfeuer1@jaguarlandrover.com>
Mobile: +1 949 294 7871

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Jaguar Land Rover North America, LLC
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-------------------
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Registered Office: Abbey Road, Whitley, Coventry CV3 4LF
Registered in England No: 1672070

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Ulf Bjorkengren

Geotab

Senior Connectivity Strategist | Ph. D.

Mobile

+45 53562142

Visit

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--
Ulf Bjorkengren

Geotab

Senior Connectivity Strategist | Ph. D.

Mobile

+45 53562142

Visit

www.geotab.com<https://www.geotab.com/>