Class org.teavm.platform.Platform is not supported on current target (WASM_GC)

[bertung]

How to do this on WASM_GC target?

//data is  an Int8Array
public ArrayBufferView onData(JSObject data) {
         return (ArrayBufferView)Platform.getPlatformObject(data);
}

[konsoletyper]

You should not do this on ANY target. Platform is an implementation detail you should not know of and you should not even add this artifact as a compile-time dependency

[bertung]

Okay, how do I pass Int8Array as byte[] from javascript > java ?

[konsoletyper]

It depends. For example, when you call a JavaScript method which produces byte[], you need to declare the method as:

native byte[] callJsMethod();

You may also need to put @JSByRef annotation to avoid unnecessary copy. However, this won't work in WasmGC even in theory - you can't just pass Int8Array to WasmGC. See https://teavm.org/docs/runtime/jso.html

[konsoletyper]

Alternatively, you can reorganize you API to expect JS code to fill Int8Array you provide to it. In which case you can pass direct ByteBuffer to JS method to avoid copying.

[bertung]

could you provide a simple example how to fill Int8Array passed from Javascript to a Java method?

[konsoletyper]

It's not that straigtforward in case of Wasm GC backend due to limitations of Wasm. You can try to receive it as Int8Array from Java side and call batch set method, which is unfortunately lacking in existing Int8Array declarations - but you can workaround it by providing your own static method like

@JSBody(params = { "array", "data" }, script = "array.set(data);")
static void set(Int8Array array, byte[] data);

Note that you SHOULD fill this data array first and then use single call to fill the entire Int8Array. Otherwise, if you decide to fill it byte-by-byte, you'll get bad performance.

Note that even in this case you'll get a slightly worse performance than is JS due to need to copy data array internally. Direct ByteBuffer would be the fasted way.

[bertung]

This sounds good but I still need a piece of code. Lets say, I have an Int8Array populated in javascript and I want to pass that to a java method.

 //will this work in WebAssembly-GC?
 @JSBody(params = {"service"}, script = "window['postEvent'] = service.postEvent;")
 static native void export(JSObject service);

  public class Services implements JSObject {
    public void postEvent(JSObject data) {
        //data is Int8Array , how do I cast JSObject to Int8Array here
    }

    public void postEventAlternative(Int8Array data) {
        //how about this? is it auto boxed?
    }
  }

export(new Services());

in javascript, I make a call

window['postEvent'](new Int8Array([1,2,3,4,5]);

[konsoletyper]

//data is Int8Array , how do I cast JSObject to Int8Array here

Just (Int8Array) data

but overall it's not the correct way. Try something like

@JSBody(params = {"service"}, script = "window['postEvent'] = service.postEvent;")
 static native void export(Services service);

  public class Services {
    @JSExport
    public void postEvent(JSObject data) {
  
    }
  }

Finally, you can just create a module

public class Services {
  @JSExport
  public static void postEvent(JSObject data) {
    // ...
  }
}

and set Services as a main class (you don't need main method). Instead of main, your WasmGC module will provide postEvent method.

[bertung]

Great many thanks

[bertung]

One more thing,

how I do convert Int8Array to ByteBuffer fast?

Can I hack it like this?

@JSBody(params = { "array"}, script = "return array")
static Buffer set(Int8Array array);

[konsoletyper]

You can't. But you can allocate a direct ByteBuffer and convert it to Int8Array. Use something like Int8Array.fromJavaBuffer or define your native method that takes ByteBuffer and produces Int8Array as described in https://teavm.org/docs/runtime/jso.html