Can we use a C++ library from within a Zenoh plugin?

[PLeVasseur]

Hi there 👋

Was having an online discussion with @Mallets earlier today and wanted to make sure I understood correctly.

Related to some discussions occurring over on how to handle the architecture of our "transport bridge" component (called streamer) that bridges between various transports, e.g. Zenoh, SOME/IP for uProtocol.

We were discussing that using C++ code within a Zenoh plugin was not doable, but then it seemed to become it was possible when we clarified a bit further.

So I tried to write a little more detail around what we're trying to do. Is the following kind of architecture doable?

flowchart TB
    subgraph ide0 [zenohd]
    main-->ide1
    subgraph ide1 [streamer-plugin]
    a1[up-streamer-rust]-->ide2
    a1[up-streamer-rust]-->ide3
    subgraph ide2 [OS thread]
    a2[up-client-zenoh-rust]
    end
    subgraph ide3 [OS thread]
    subgraph ide4 [Rust bridge e.g. up-client-someip-rust using cxx]
    a3[up-client-someip-cpp]
    end
    end
    end
    end

Loading

[evshary]

Hi @PLeVasseur
I think what Luca means is we can use C++ to run in Zenoh router mode, and then load the plugins, which are written in Rust.
Maybe I can provide the example, hopefully tomorrow.
@Mallets Please correct me if I'm wrong.

[Mallets]

That's correct. A plugin has a Rust interface. Plugin code then can link other libraries (e.g. C/C++) but those libraries do not have access to the Zenoh C/C++ API since they are running in plugin-space.

[PLeVasseur]

Sure, I'm trying to piece it together 🙂

In this case though, the only C++ code is a C++ library wrapped in Rust code related to a different transport protocol, nothing to do with Zenoh, right?

Would the above architecture work in that case?

Or maybe I missed the point haha

[PLeVasseur]

@evshary -- I'm all for learning more about the approach you're outlining if @Mallets says what I'm proposing won't work

[Mallets]

Correct. An example of such approach is the ROS2 plugin where the C-based CycloneDDS library is used to communicate over DDS. CycloneDDS though does not call anything related to Zenoh.

[PLeVasseur]

Okay, the picture is coming together.

So to be super clear and pedantic about this, over here in the ROS2 plugin we call dds_create_participant (wrapped in unsafe of course), which is the same C function from the eclipse-cyclonedds project, right?

[JEnoch]

Correct: the CycloneDDS C code is wrapped into Rust in the cyclors crate using the bindgen tool in the build.rs file.
And the ROS2 plugin depends on cyclors.

[PLeVasseur]

Perfect! Thank you everyone for pitching in to help me understand 🙂

Only question is how the heck to Mark as answer multiple of them haha