C#-only way to declare wasm imports and exports

[SteveSandersonMS]

Currently to declare a custom WebAssembly import or export you have to write C code, e.g., https://github.com/SteveSandersonMS/dotnet-wasi-sdk/blob/main/src/Wasi.AspNetCore.Server.CustomHost/native/server_interop.c#L7-L17

We should make it possible to declare such imports/exports using just C# only without any native code.

At a basic level this could be achieved fairly easily by codegenerating the equivalent C code that uses the Mono embedding APIs to invoke C#. However going further, we'd want to be able to receive and return nontrivial types, which probably involves a C# sourcegenerator for WIT.

[inkeliz]

There's any simpler example of how use export/import, when using the C?

[SteveSandersonMS]

No, https://github.com/SteveSandersonMS/dotnet-wasi-sdk/blob/main/src/Wasi.AspNetCore.Server.CustomHost/native/server_interop.c is about as simple as it gets. That's why we should make a simpler mechanism with C# only.

[inkeliz]

I understand the motivation to add C#-only. I'm trying to figure out how server_interop.c works.

Just to make sure, I need to have the Mono toolchain and compile the my_interop.c? The README mention that "You can optionally include other native sources such as .c files in the compilation.", but I'm struggling to understand how to make my C code interact with Mono and get compiled. 🧐

[SteveSandersonMS]

No, you don't need Mono. No other build tools are needed. Just reference your .c file with WasiNativeFileReference like the Wasi.AspNetCore.Server.CustomHost project does, and it will be included in the compilation.

[flavio]

There's any simpler example of how use export/import, when using the C?

@inkeliz: you might want to take a look at https://github.com/flavio/wapc-guest-dotnet/blob/main/src/WapcGuest/native/wapc_ffi.c
This is a smaller example.

I hope that helps!

[inkeliz]

Thank you, @flavio. I think that will be very useful for any future readers. My primary concern was how to compile that, since I'm not familiar with C#/Dotnet, so I'm not sure how things are suppose to compile. 😅

I manage to use force the compilation including the WasiNativeFileReference, as @SteveSandersonMS said. However, I need to include that into the .csproj directly. I'm not sure why the build folder doesn't work, where is the result. Since that is just for testing, not a library, I think it's fine.

[SteveSandersonMS]

I need to include that into the .csproj directly

Good, that's the right thing to do if you're just testing! Having .props/.targets files that get bundled into a NuGet package is only for people shipping NuGet packages - it's nothing specific to dotnet-wasi-sdk but more of a general NuGet/MSBuild pattern.

[ChristianWeyer]

Maybe the experimental LLVM-based approach could be a way forward...?
https://github.com/dotnet/runtimelab/blob/feature/NativeAOT-LLVM/docs/using-nativeaot/compiling.md#webassembly-native-libraries

.cc @SteveSandersonMS

[ghost]

``Hello, i do have an unresolved doubt:
is there a way, when for example compiling with wasi a classlib (.dll), to mark as exported the methods i want and use those methods importing the .wasm file in an application via wasmtime for example?

I tried, for ease of testing, to build a classlib with a generic method

namespace wasmlibrary;
public static class Class1
{
    public static int method(int i)
    {
        return i++;
    }
}

and in another console project use wasmtime.net to load the module

 using (var engine = new Engine())
        using (var store = new Store(engine))
        using (var linker = new Linker(engine))
        using (var module = Module.FromFile(engine, "../../../../wasmlibrary/bin/Debug/net7.0/wasmlibrary.wasm"))
        {
            linker.DefineWasi();  
            dynamic instance = linker.Instantiate(store, module);
            var run = instance.GetFunction<int, int>("method");
        }

but, debugging, module only exports the basic methods (malloc, free, _run, etc..), and run is null, meaning that the method is not exported.

thanks to everyone in advance!

[iwate]

I tried exporting wasi-wasm function by using ILCompiler.LLVM. And it worked.

https://github.com/iwate/learn-wasm-with-dotnet/tree/main/challenge09/wasilib