docs: updated readme

README.md

@@ -4,55 +4,125 @@ this is a simple crate built around [jni-rs](https://github.com/jni-rs/jni-rs) t
 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
+just specify package and class on your function, and done!
 
 ```rust
 #[jni_toolbox::jni(package = "your.package.path", class = "ContainerClass")]
-fn your_function_name(arg: i32) -> Result<(), String> {
-	// your code here
+fn your_function_name(arg: String) -> Result<Vec<String>, String> {
+	Ok(arg.split('/').map(|x| x.to_string()).collect())
 }
 ```
 
-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!)
+every type that must go into/from Java must implement `IntoJava` or `FromJava` (methods will receive a `&mut JNIEnv` and can return errors).
+most primitives already have them implemented. conversions are automatic and the wrapper function will invoke IntoJava/FromJava for every type,
+passing an environment reference.
+
+
+Errors are thrown automatically when a `Result` is an error. For your errors to work, you must implement the `JniToolboxError` trait for your errors,
+(which just returns the path to your Java error class) and then make a Java error wrapper which can be constructed with a single string argument.
+functions returning `Result`s will automatically have their return value unwrapped and, if is an err, throw an exception and return early.
+
+to throw simple exceptions, it's possible to use the `exception` attribute. just pass your exception's path (must be constructable with a single string argument!)
+
+to return pointer type values, add the `ptr` attribute
 
-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:
 ```rust
-#[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(())
+#[jni(package = "mp.code", class = "Client", ptr)]
+fn connect(config: Config) -> Result<Client, ConnectionError> {
+	tokio().block_on(Client::connect(config))
 }
 ```
 
-gets turned into this couple of functions:
+gets turned into these two functions:
+
+<details><summary>show macro expansion</summary>
+
 ```rust
-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(())
+fn connect(config: Config) -> Result<Client, ConnectionError> {
+	tokio().block_on(Client::connect(config))
 }
 
 #[no_mangle]
-pub extern "system" fn Java_mp_code_Client_connect<'local>(env: JNIEnv, host: JString) -> () {
-  match connect(env, cacca) {
+#[allow(unused_mut)]
+pub extern "system" fn Java_mp_code_Client_connect<'local>(
+	mut env: jni::JNIEnv<'local>,
+	_class: jni::objects::JClass<'local>,
+	mut config: <Config as jni_toolbox::FromJava<'local>>::T,
+) -> <Client as jni_toolbox::IntoJava<'local>>::T {
+	use jni_toolbox::{FromJava, IntoJava, JniToolboxError};
+	let mut env_copy = unsafe { env.unsafe_clone() };
+	let config_new = match jni_toolbox::from_java_static::<Config>(&mut env, config) {
 		Ok(x) => x,
 		Err(e) => {
-      $crate::panicking::panic_fmt($crate::const_format_args!("error in JNI!"));
+			let _ = env.throw_new(
+				"java/lang/RuntimeException",
+				$crate::__export::must_use({
+					let res = $crate::fmt::format($crate::__export::format_args!("{e:?}"));
+					res
+				}),
+			);
+			return std::ptr::null_mut();
 		}
+	};
+	match connect(config_new) {
+		Err(e) => match env_copy.find_class(e.jclass()) {
+			Err(e) => {
+				$crate::panicking::panic_fmt($crate::const_format_args!(
+					"error throwing Java exception -- failed resolving error class: {e}"
+				));
+			}
+			Ok(class) => match env_copy.new_string($crate::__export::must_use({
+				let res = $crate::fmt::format($crate::__export::format_args!("{e:?}"));
+				res
+			})) {
+				Err(e) => {
+					$crate::panicking::panic_fmt($crate::const_format_args!(
+						"error throwing Java exception --  failed creating error string: {e}"
+					));
+				}
+				Ok(msg) => match env_copy.new_object(
+					class,
+					"(Ljava/lang/String;)V",
+					&[jni::objects::JValueGen::Object(&msg)],
+				) {
+					Err(e) => {
+						$crate::panicking::panic_fmt($crate::const_format_args!(
+							"error throwing Java exception -- failed creating object: {e}"
+						));
+					}
+					Ok(obj) => match env_copy.throw(jni::objects::JThrowable::from(obj)) {
+						Err(e) => {
+							$crate::panicking::panic_fmt($crate::const_format_args!(
+								"error throwing Java exception -- failed throwing: {e}"
+							));
+						}
+						Ok(_) => return std::ptr::null_mut(),
+					},
+				},
+			},
+		},
+		Ok(ret) => match ret.into_java(&mut env_copy) {
+			Ok(fin) => return fin,
+			Err(e) => {
+				let _ = env_copy.throw_new(
+					"java/lang/RuntimeException",
+					$crate::__export::must_use({
+						let res = $crate::fmt::format($crate::__export::format_args!("{e:?}"));
+						res
+					}),
+				);
+				return std::ptr::null_mut();
+			}
+		},
 	}
 }
 ```
 
+</details>
+
 
 ## status
 this crate is rather early and intended mostly to maintain [`codemp`](https://github.com/hexedtech/codemp) java bindings, however it's also quite small and only runs at comptime, so should be rather safe to use