rust如何使用Java GraalVM在Java代码和嵌入式WASM代码之间传递字符串作为参数和返回值

Question

我想将一个字符串作为参数从Java代码传递到WASM代码，并将一个字符串从WASM代码返回到Java。 在GraalVM WASM reference后面没有显示如何实现这一点

Rust编译成example.wasm的示例代码：

#[no_mangle]
pub extern fn main() -> *const u8 {
    "Hello world!".as_ptr()
}

使用GraalVM polyglot API嵌入WASM的Java代码：

byte[] binary = readBytes("example.wasm");
Context.Builder contextBuilder = Context.newBuilder("wasm");
Source.Builder sourceBuilder = Source.newBuilder("wasm", ByteSequence.create(binary), "example");
Source source = sourceBuilder.build();
Context context = contextBuilder.build();

context.eval(source);

Value mainFunction = context.getBindings("wasm").getMember("main").getMember("main");
System.out.println("Returned: " + mainFunction.execute());

但是，运行此程序时，会打印以下内容：

Returned: 1048641

我希望它能打印Returned: Hello world!

正在尝试mainFunction.execute().asString()

Exception in thread "main" java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.springframework.boot.loader.MainMethodRunner.run(MainMethodRunner.java:49)
    at org.springframework.boot.loader.Launcher.launch(Launcher.java:108)
    at org.springframework.boot.loader.Launcher.launch(Launcher.java:58)
    at org.springframework.boot.loader.JarLauncher.main(JarLauncher.java:88)
Caused by: java.lang.ClassCastException: Cannot convert '1048641'(language: Java, type: java.lang.Integer) to Java type 'java.lang.String' using Value.asString(): Invalid coercion. You can ensure that the value can be converted using Value.isString().
    at org.graalvm.truffle/com.oracle.truffle.polyglot.PolyglotEngineException.classCast(PolyglotEngineException.java:154)
    at org.graalvm.truffle/com.oracle.truffle.polyglot.PolyglotValue.cannotConvert(PolyglotValue.java:1261)
    at org.graalvm.truffle/com.oracle.truffle.polyglot.PolyglotValue.invalidCastPrimitive(PolyglotValue.java:686)
    at org.graalvm.truffle/com.oracle.truffle.polyglot.PolyglotValue.asStringUnsupported(PolyglotValue.java:658)
    at org.graalvm.truffle/com.oracle.truffle.polyglot.PolyglotValue.asString(PolyglotValue.java:649)
    at org.graalvm.truffle/com.oracle.truffle.polyglot.PolyglotValue$PrimitiveValue.asString(PolyglotValue.java:4016)
    at org.graalvm.sdk/org.graalvm.polyglot.Value.asString(Value.java:952)
    at org.example.wasmhost.WasmHostApplication.main(WasmHostApplication.java:63)
    ... 8 more

我的java是：

$ java -version
openjdk version "11.0.11" 2021-04-20
OpenJDK Runtime Environment GraalVM CE 21.1.0 (build 11.0.11+8-jvmci-21.1-b05)
OpenJDK 64-Bit Server VM GraalVM CE 21.1.0 (build 11.0.11+8-jvmci-21.1-b05, mixed mode, sharing)