Illegal hardware instruction java - when calling Rust code from Java

[tomislavhoman]

I am making a test project to get familiar with the library before using it in production and I have a problem when calling a Rust function that returns custom struct to the Java code. I have a simple java client called JavaClient and the error I get when calling Rust code is illegal hardware instruction java JavaClient.

Here is the sample Java client:

// JavaClient.java
public class JavaClient {
    private static native RustResult2 stringLengthComplexGenerated(String input);

    static {
        System.loadLibrary("java_bridge");
    }

    public static void main(String[] args) {
        System.out.println("Hello from Java");

        String input = "12345678";
        String shortInput = "1234";
         // With generated models 
        RustResult2 result4 = stringLengthComplexGenerated(input);
        System.out.printf("Length of the long string (gen, models) %s is: %d, returned error is %s\n", input, result4.length, result4.error);

        RustResult2 result5 = stringLengthComplexGenerated(shortInput);
        System.out.printf("Length of the short string (gen, models) %s is: %d, returned error is %s\n", shortInput, result5.length, result5.error);
    }
}

// RustResult2.java
public class RustResult2 {
    public int length;
    public String error;

    public RustResult2(int length, String error) {
        this.length = length;
        this.error = error;
    }
} 

And here is the Rust lib:

// Cargo.toml
[package]
name = "java-bridge"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[lib]
crate-type = ["cdylib"]

[dependencies]
rust-lib = { path = "../rust-lib" }
# robusta_jni = "0.2.1"
robusta_jni = { path = "../../robusta" }
jni = "0.19.0"


// lib.rs
use robusta_jni::bridge;

#[bridge]
mod jni {
    use robusta_jni::convert::{FromJavaValue, IntoJavaValue, Signature, TryFromJavaValue, TryIntoJavaValue};
    use robusta_jni::jni::errors::Error as JniError;
    use robusta_jni::jni::errors::Result as JniResult;
    use robusta_jni::jni::objects::{AutoLocal, JValue};
    use robusta_jni::jni::sys::jobject;
    use robusta_jni::jni::JNIEnv;
    use rust_lib::{string_length_complex_internal, string_length_internal};

    #[derive(Signature, IntoJavaValue, TryIntoJavaValue, FromJavaValue, TryFromJavaValue)]
    #[package()]
    pub struct RustResult2<'env: 'borrow, 'borrow> {
        #[instance]
        raw: AutoLocal<'env, 'borrow>,
        length: i32,
        error: String,
    }

    // impl<'env: 'borrow, 'borrow> IntoJavaValue<'env> for RustResult2<'env, 'borrow> {
        // type Target = jobject;
        // fn into(self, env: &JNIEnv<'env>) -> Self::Target {

        //     let length = self.length;
        //     let error = self.error;

        //     let env: &'_ ::robusta_jni::jni::JNIEnv<'_> = env;
        //     let res = env
        //         .new_object(
        //             "RustResult2",
        //             [
        //                 "(",
        //                 <i32 as ::robusta_jni::convert::TryIntoJavaValue>::SIG_TYPE,
        //                 <String as ::robusta_jni::convert::TryIntoJavaValue>::SIG_TYPE,
        //                 ")",
        //                 "V",
        //             ]
        //                 .join(""),
        //             &[
        //                 ::std::convert::Into::into(
        //                     <i32 as ::robusta_jni::convert::TryIntoJavaValue>::try_into(
        //                         length,
        //                         &env,
        //                     ).unwrap(),
        //                 ),
        //                 ::std::convert::Into::into(
        //                     <String as ::robusta_jni::convert::TryIntoJavaValue>::try_into(
        //                         error,
        //                         &env,
        //                     ).unwrap(),
        //                 ),
        //             ],
        //         );
        //     res.unwrap().into_inner()
        // }
    // }

    impl<'env: 'borrow, 'borrow> RustResult2<'env, 'borrow> {
        #[constructor]
        pub extern "java" fn new(env: &'borrow JNIEnv<'env>, length: i32, error: String) -> JniResult<Self> {} 
    }

    #[derive(Signature)]
    #[package()]
    pub struct JavaClient;

    impl<'env: 'borrow, 'borrow> JavaClient {

        #[call_type(unchecked)]
        pub extern "jni" fn stringLengthComplexGenerated(
            env: &'borrow JNIEnv<'env>,
            input: String,
        ) -> RustResult2<'env, 'borrow> {
            let result = string_length_complex_internal(&input);
            let (length, error) = match result {
                Result::Ok(length) => {
                    (length.try_into().unwrap(), "".to_owned())
                }
                Result::Err(error) => {
                    (-1, error.to_owned())
                }
            };

            let res = RustResult2::new(env, length, error).unwrap();
            println!("Result is (length: {}, error: {})", res.length, res.error);
            res
        }
    }
}

I get the error when using IntoJavaValue in derive attribute. If I remove it and manually do the conversion (commented code) then it works. The expanded code for the IntoJavaValue is this:

#[automatically_derived]
    impl<'env: 'borrow, 'borrow> ::robusta_jni::convert::IntoJavaValue<'env>
    for RustResult2<'env, 'borrow> {
        type Target = ::robusta_jni::jni::objects::JObject<'env>;
        fn into(self, env: &::robusta_jni::jni::JNIEnv<'env>) -> Self::Target {
            ::robusta_jni::convert::IntoJavaValue::into(self, env)
        }
    }

If I copy that code instead of my manual implementation I get the same error in the runtime and recursion warning from Rust, so that might be the issue. That "illegal hardware instruction" might actually be stack overflow.