Stream: general

Topic: Passing an exported resource into an imported function - wit

Mendy Berger (Jul 30 2024 at 16:47):

Is it possible to use a resource exported from a world as an parameter for an imported function?
I'm trying to have the guest create a resource and pass in into a function provided by the host.

Here's the wit I currently have:

package webidl:browser;

interface custom-element-export {
    resource define-element-base {
        connected-callback: func();
    }
}

interface custom-element-import {
    use custom-element-export.{define-element-base};
    define: func(name: string, options: define-element-base);
}

world browser {
    export start: func();
    export custom-element-export;
    import custom-element-import;
}

When generating the bindings with wit-bindgen, it seems to be creating two distinct define-element-basetypes, one for the import and another one for the export.

Joel Dice (Jul 30 2024 at 16:48):

No, it's not possible: https://github.com/WebAssembly/component-model/issues/272

Joel Dice (Jul 30 2024 at 16:51):

AFAIK, the only way to emulate that kind of callback is to export functions which take e.g. u32 handles which the guest can use as indexes into a table of state objects.

Mendy Berger (Jul 30 2024 at 16:55):

Okay, so no ergonomic way to do this.
I have an alternative idea which only requires imports that I can use instead. Not gonna be as nice, but not too bad either.
Thanks @Joel Dice for the quick response!

Last updated: Dec 23 2024 at 12:05 UTC