jni-toolbox

this is a simple crate built around jni-rs to automatically generate JNI-compatible extern functions

it also wraps functions returning Result<>, making short-circuiting easy

usage

you must implement JniToolboxError trait for your errors, so that they can be converted to Java errors

you will need to define classes for them, and implement JniToolboxError returning the class path

alternatively, an exception class can be specified with the exception attribute

then just annotate your functions with

#[jni_toolbox::jni(package = "your.package.path", class = "ContainerClass")]
fn your_function_name(arg: i32) -> Result<(), String> {
	// your code here
}

by specifying package and class, this crate will write an appropriate wrapper with the right function name. If inner function returns a Result<>, wrapper will also handle it. (currently just panics, soon will throw exceptions!)

note that input/output arguments must be natively FFI safe: there will be no hidden translations! you will have to un-marshal strings yourself

examples

the following function:

#[jni_toolbox::jni(package = "mp.code", class = "Client")]
fn connect(env: JNIEnv, cacca: JString) -> Result<(), ConnectionError> {
  let config = codemp::api::Config::new("asd".into(), "dsa".into());
  tokio().block_on(codemp::Client::connect(config))?;
  Ok(())
}

gets turned into this couple of functions:

fn connect(env: JNIEnv, host: JString) -> Result<(), ConnectionError> {
  let config = codemp::api::Config::new("mail@example.net".into(), "dont-use-this-password".into());
  tokio::runtime::current().block_on(codemp::Client::connect(config))?;
  Ok(())
}

#[no_mangle]
pub extern "system" fn Java_mp_code_Client_connect<'local>(env: JNIEnv, host: JString) -> () {
  match connect(env, cacca) {
    Ok(x) => x,
    Err(e) => {
      $crate::panicking::panic_fmt($crate::const_format_args!("error in JNI!"));
    }
  }
}

status

this crate is rather early and intended mostly to maintain codemp java bindings, however it's also quite small and only runs at comptime, so should be rather safe to use