`up-zenoh-recorder` & `up-zenoh-utwin`: How are they initialized and given the Zenoh `Runtime` they will use?

[PLeVasseur]

Hey folks :wave:

Tagging in @mallets, @evshary, and @stevenhartley in particular.

From what I recall @evshary had started an experiment to see how we can start Zenoh plugins from within C++ or something to that effect. So I'd be interested to hear the parameters and outcome.

---

Given the topology diagram:

I wanted to drill down a little deeper:

1. How will the up-zenoh-utwin and up-zenoh-recorder plugins be initialized? a. From C++? b. From Rust?
2. Is it even possible to pass the plugins the Zenoh Runtime they will require, from C++?
3. If the plugins are initialized from C++, would the plugins need to have a C shim wrapped around them?
4. I suppose we would add a new way to instantiate a UPClientZenoh based on a Zenoh Session?

A first attempt at laying out these components:

classDiagram

    %% Very important to understand the mechanism by which:
    %%  The plugins written in Rust (up-zenoh-recorder &
    %%  up-zenoh-utwin) will be started
    %%
    %% If they are started in a way that they are called into
    %% by Rust code, that is ideal.
    %%
    %% If they are started from C++ code, then it's less clear
    %% how this would work, as the plugins need to be given
    %% an instance of the Zenoh Runtime in order to create their
    %% own Zenoh Session to use

    class z["Zenoh Runtime"] {

    }

    class uzr["up-zenoh-recorder"] {
        +UPClientZenoh up_client
        +new(Zenoh Runtime) Result<>
    }

    class uzu["up-zenoh-utwin"] {
        +UPClientZenoh up_client
        +new(Zenoh Runtime) Result<>
    }

    class usc["up-streamer-cpp"] {

    }

    style usc fill:#647687,color:#fff
    style uzr fill:#A0522D,color:#fff
    style uzu fill:#A0522D,color:#fff
    style z fill:#A0522D,color:#fff

    usc --* z: Initializes
    usc --* uzr: How are these plugins initialized? <br> From Rust or C++?
    usc --* uzu: How are these plugins initialized? <br> From Rust or C++?
    uzr ..> z: Takes copy of Runtime, <br> creates Zenoh Session <br> and uses that to <br> initialize held UPClientZenoh
    uzu ..> z: Takes copy of Runtime, <br> creates Zenoh Session <br> and uses that to <br> initialize held UPClientZenoh

[evshary]

Hi @PLeVasseur

1. How will the up-zenoh-utwin and up-zenoh-recorder plugins be initialized?
   • The plugins are written in Rust and can be loaded based on our configuration. zenoh-c is just a wrapper of Zenoh and the plugins are loaded in Zenoh.
2. Is it even possible to pass the plugins the Zenoh Runtime they will require, from C++?
   • While opening a session in C++, it'll load the plugins with its runtime directly.
3. If the plugins are initialized from C++, would the plugins need to have a C shim wrapped around them?
   • No, plugins are written in Rust in loaded by Zenoh. No need to consider C++.
4. I suppose we would add a new way to instantiate a UPClientZenoh based on a Zenoh Session?
   • Yes. Since we only have runtime in plugins, we need to get Session based on that runtime and initialize UPClientZenoh with that Session. I can create a PR to update this.

Also, here are some references for you:

• How to load plugins in C++
  • Using code: https://github.com/evshary/zenoh-cpp-example/blob/17060c33e2b8333014216fb65d96a38f512c1881/src/z_router.cxx#L83
  • Using config: https://github.com/eclipse-zenoh/zenoh/blob/7c64d99e9deb75070b8c3845e0a29b7027fb48e9/DEFAULT_CONFIG.json5#L377
• The plugin example:
  • https://github.com/eclipse-zenoh/zenoh/blob/7c64d99e9deb75070b8c3845e0a29b7027fb48e9/plugins/zenoh-plugin-example/src/lib.rs#L53
• Here are notes while building
  • https://github.com/evshary/zenoh-cpp-example/tree/17060c33e2b8333014216fb65d96a38f512c1881?tab=readme-ov-file#note

@Mallets Please correct me if I'm wrong.

[PLeVasseur]

Sounds to me based on @evshary's comment here and @Mallets's feedback on Slack that up-zenoh-utwin and up-zenoh-recorder can be standard Zenoh plugins written 100% in Rust.

Closing as resolved!