Gerard Smit (Aug 26 2025 at 20:15): Gerard Smit (Aug 26 2025 at 20:15):Hey,
I'm trying to make a component in C#. I've followed the "Adder" docs and created a component.
I've compiled this component, and I see in the exports that the function docs:adder/add@0.1.0#add is exposed.
However, there are no components (that I can see in https://wa2.dev/exports).
When I try to call "docs:adder/add@0.1.0#add", I'm getting the error that the function cannot be found.
I've also tried multiple names (add etc.) without success:
using var engine = new Engine();
using var linker = new Linker(engine);
linker.AddWasiP2();
using var store = new Store(engine);
var bytes = File.ReadAllBytes("Wasm/Adder.wasm");
using var component = Component.Compile(engine, bytes);
var instance = component.CreateInstance(linker, store);
using var a = ComponentValue.CreateInt32(40);
using var b = ComponentValue.CreateInt32(2);
for (var i = 0; i < 10; i++)
{
using var result = instance.Call("docs:adder/add@0.1.0#add", [a, b]);
Assert.Equal(42, result.GetInt32(0));
}
With a component in WAT, the following works:
const string addIntModule =
"""
(component
(core module $AddModule
(func (export "return") (param i32) (param i32) (result i32)
local.get 0
local.get 1
i32.add
)
)
(core instance $add_instance (instantiate $AddModule))
(func (export "return") (param "a" s32) (param "b" s32) (result s32)
(canon lift
(core func $add_instance "return")
)
)
)
""";
using var engine = new Engine();
using var linker = new Linker(engine);
using var store = new Store(engine);
using var component = Component.Compile(engine, addIntModule);
var instance = component.CreateInstance(linker, store);
using var a = ComponentValue.CreateInt32(40);
using var b = ComponentValue.CreateInt32(2);
for (var i = 0; i < 10; i++)
{
using var result = instance.Call("return", [a, b]);
Assert.Equal(42, result.GetInt32(0));
}
So I'm not sure what I'm doing wrong :sweat_smile:
The Compile-method calls wasmtime_component_new which is OK I think.
Note: I'm implementing the component c-api in .NET, so I'm testing stuff out :slight_smile:
Gerard Smit (Aug 26 2025 at 20:29):It seems I can get docs:adder/add@0.1.0, and then I get a different error:
Export 'docs:adder/add@0.1.0' is not a function
So it looks like I need to get this export first, and then the function. I'm not sure what kind of export this is (e.g. a interface). And I'm also not sure if this is already implemented in the c-api. :thinking:
Gerard Smit (Aug 26 2025 at 20:46):Got it. I have to export the function directly:
package docs:adder@0.1.0;
world example {
export add: func(x: u32, y: u32) -> u32;
}
Then I can call the function directly with "add".
However now I'm getting a panic error :hmm:
Exit code is -1073740791 (thread '<unnamed>' panicked at crates\c-api\src\store.rs:110:39:
called `Option::unwrap()` on a `None` value
Got that as well. The store was not initialized with the WasiP2 context.
Now I'm getting C# exceptions. Progress :tada:
error while executing at wasm backtrace:
0: 0x8b366 - .tmp1wig0Y!S_P_CoreLib_System_Runtime_EH__DispatchException
1: 0x53c6c - .tmp1wig0Y!S_P_CoreLib_System_Runtime_EH__RhpThrowEx
2: 0x6dbd1 - .tmp1wig0Y!S_P_CoreLib_Internal_Runtime_CompilerHelpers_ThrowHelpers__ThrowNullReferenceException
3: 0x63e18 - .tmp1wig0Y!S_P_CoreLib_Internal_Runtime_CompilerHelpers_StartupCodeHelpers__InitializeGlobalTablesForModule
4: 0x98ead - .tmp1wig0Y!S_P_CoreLib_Internal_Runtime_CompilerHelpers_StartupCodeHelpers__InitializeModules
5: 0x24ba - .tmp1wig0Y!InitializeRuntime()
6: 0x5e3e - .tmp1wig0Y!Thread::ReversePInvokeAttachOrTrapThread(ReversePInvokeFrame*)
7: 0x5f4a - .tmp1wig0Y!RhpReversePInvokeAttachOrTrapThread2
8: 0x39a90 - .tmp1wig0Y!RhpReversePInvoke
9: 0x69eca - .tmp1wig0Y!Adder_ExampleWorld_exports_ExampleWorld__wasmExportAdd
note: using the `WASMTIME_BACKTRACE_DETAILS=1` environment variable may show more debugging information
Caused by:
wasm trap: uninitialized element
Nvm, that's a bug in the latest version in NativeAOT-LLVM. 10.0.0-alpha.1.25162.1 works without issues :tada:
Now I can run components in .NET Wasmtime :smile:
Joel Dice (Aug 26 2025 at 21:06):Congrats; I didn't think that was possible. Perhaps https://github.com/bytecodealliance/wasmtime-dotnet/issues/324 ought to be updated?
Gerard Smit (Aug 26 2025 at 21:10):I made a new library with ClangSharp (that generated C# bindings for headers) and then implemented a minimal wrapper around this. So it's not directly wasmtime-dotnet :slight_smile:
Gerard Smit (Aug 26 2025 at 21:12):There was an open issue about using ClangSharp: https://github.com/bytecodealliance/wasmtime-dotnet/issues/329
but with this, the structure is completely different. It was easier to start from scratch for me.
James Sturtevant (Aug 26 2025 at 22:05):awsome work! Someone started scratching out what it might look like in wasmtime-dotnet, but I was thinking that using clangsharp might be better approach here particuallary for the component model stuff. Do you think we could add a folder to wasmtime-dotnet and have low level API's exposed then add nice api on top?
James Sturtevant (Aug 26 2025 at 22:05):https://github.com/bytecodealliance/wasmtime-dotnet/pull/346
Gerard Smit (Aug 28 2025 at 13:48):If I want to add the component-model back to the main repo with a PR, it's gonna be a large one. :sweat_smile: Maybe I need to chop it down first.
But I'm still experimenting around.
I just made a source generator that converts the WIT-files:
package docs:adder@0.1.0;
world example {
export add: func(x: u32, y: u32) -> u32;
}
To callable methods:
// Create component instance (component = the compiled WASM file)
var instance = component.CreateInstance(linker, store);
// Wrap the instance around world 'example'
// The type 'Wit.docs.adder.example' is source generated.
var example = new Wit.docs.adder.example(instance);
// Call the method 'add'
var result = example.add(40, 2);
Last updated: Dec 06 2025 at 07:03 UTC