Obtain jni_fn locally

app/src/main/jni_fn/.gitignore

@@ -0,0 +1,2 @@
+/target
+Cargo.lock

app/src/main/jni_fn/Cargo.toml

@@ -0,0 +1,22 @@
+[package]
+name = "jni_fn"
+version = "0.1.0"
+authors = ["Anton Lazarev <https://antonok.com>"]
+edition = "2021"
+description = "JNI-compatible method signature generator"
+repository = "https://gitlab.com/antonok/jni_fn"
+readme = "README.md"
+keywords = ["jni", "java", "jvm", "android", "ndk"]
+categories = ["api-bindings", "development-tools::procedural-macro-helpers"]
+license = "MIT OR Apache-2.0"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+syn = { version = "1.0.109", features = ["full"] }
+quote = "*"
+proc-macro2 = "*"
+
+[dev-dependencies]
+jni = "0.19.0"

app/src/main/jni_fn/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2021 Anton Lazarev
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

app/src/main/jni_fn/src/lib.rs

@@ -0,0 +1,398 @@
+//! JNI-compatible method signature generator for Rust libraries.
+//!
+//! This crate was designed for use with the [`jni`](https://crates.io/crates/jni) crate, which
+//! exposes JNI-compatible type bindings. Although it's possible to use `jni` without `jni_fn`, the
+//! procedural macro defined here will make it easier to write the method signatures correctly.
+//!
+//! See the `jni_fn` attribute macro documentation below for more info and usage examples.
+
+#![deny(missing_docs)]
+#![deny(unsafe_code)]
+
+use proc_macro2::TokenStream;
+use quote::ToTokens;
+use syn::spanned::Spanned;
+
+/// Annotate a function with this procedural macro attribute to expose it over the JNI.
+///
+/// This attribute takes a single string literal as an argument, specifying the package namespace
+/// this function should be placed under.
+///
+/// ```
+/// use jni::{ JNIEnv, objects::{ JClass, JString }, sys::jstring };
+/// use jni_fn::jni_fn;
+///
+/// #[jni_fn("com.example.RustBindings")]
+/// pub fn sayHello(env: JNIEnv, _: JClass, name: JString) -> jstring {
+///     let name_javastr = env.get_string(name).unwrap();
+///     let name = name_javastr.to_str().unwrap();
+///
+///     env.new_string(format!("Hello, {}!", name))
+///         .expect("Couldn't create java string!")
+///         .into_inner()
+/// }
+/// ```
+///
+/// The `sayHello` function will automatically be expanded to have the correct ABI specification
+/// and the appropriate JNI-compatible name, i.e. in this case -
+/// `Java_com_example_RustBindings_sayHello`.
+///
+/// Then it can be accessed by, for example, Kotlin code as follows:
+/// ```kotlin
+/// package com.example.RustBindings
+///
+/// class RustBindings {
+///     private external fun sayHello(name: String): String
+///
+///     fun greetWorld() {
+///         println(sayHello("world"))
+///     }
+/// }
+/// ```
+#[proc_macro_attribute]
+pub fn jni_fn(
+    attr: proc_macro::TokenStream,
+    item: proc_macro::TokenStream,
+) -> proc_macro::TokenStream {
+    jni_fn2(attr.into(), item.into()).into()
+}
+
+/// Deals exclusively with `proc_macro2::TokenStream` instead of `proc_macro::TokenStream`,
+/// allowing it and all interior functionality to be unit tested.
+fn jni_fn2(attr: TokenStream, item: TokenStream) -> TokenStream {
+    let attr_span = attr.span();
+    let item_span = item.span();
+
+    let mut function: syn::ItemFn = match syn::parse2(item) {
+        Ok(f) => f,
+        Err(_e) => {
+            return syn::Error::new(
+                item_span,
+                "The `jni_fn` attribute can only be applied to `fn` items",
+            )
+            .to_compile_error()
+        }
+    };
+
+    let namespace = match syn::parse2::<syn::LitStr>(attr) {
+        Ok(n) => n,
+        Err(_e) => return syn::Error::new(attr_span, "The `jni_fn` attribute must have a single string literal supplied to specify the namespace").to_compile_error(),
+    }.value();
+
+    if !valid_namespace(&namespace) {
+        return syn::Error::new(
+            attr_span,
+            "Invalid package namespace supplied to `jni_fn` attribute",
+        )
+        .to_compile_error();
+    }
+
+    let orig_fn_name = function.sig.ident.to_string();
+
+    function.sig.ident = syn::Ident::new(
+        &create_jni_fn_name(&namespace, &orig_fn_name),
+        function.sig.ident.span(),
+    );
+
+    function.attrs.push(syn::Attribute {
+        pound_token: Default::default(),
+        style: syn::AttrStyle::Outer,
+        bracket_token: Default::default(),
+        path: syn::parse_str("no_mangle").unwrap(),
+        tokens: TokenStream::new(),
+    });
+    function.attrs.push(syn::Attribute {
+        pound_token: Default::default(),
+        style: syn::AttrStyle::Outer,
+        bracket_token: Default::default(),
+        path: syn::parse_str("allow").unwrap(),
+        tokens: quote::quote! { (non_snake_case) },
+    });
+
+    if function.sig.abi.is_some() {
+        return syn::Error::new(function.sig.abi.span(), "Don't specify an ABI for `jni_fn` attributed functions - the correct ABI will be added automatically").to_compile_error();
+    }
+    function.sig.abi = Some(syn::Abi {
+        extern_token: Default::default(),
+        name: Some(syn::LitStr::new("system", function.sig.ident.span())),
+    });
+
+    if !matches!(function.vis, syn::Visibility::Public(_)) {
+        return syn::Error::new(
+            function.vis.span(),
+            "`jni_fn` attributed functions must have public visibility (`pub`)",
+        )
+        .to_compile_error();
+    }
+
+    function.into_token_stream()
+}
+
+/// Ensures that `namespace` appears roughly like a valid package name.
+///
+/// A package name is a '.'-separated identifier list.
+///
+/// Identifiers are described in section 3.8 of the Java language specification, although some
+/// JVM-compatible languages have slightly different restrictions on what is considered a valid
+/// identifier. This function attempts to catch obviously incorrect strings.
+///
+/// Please submit an issue report or patch to make this more permissive if it's required for
+/// valid JVM code! Otherwise, making it more restrictive is appreciated as long as it's confirmed
+/// to work with multiple JVM-compatible languages.
+fn valid_namespace(namespace: &str) -> bool {
+    /// These shouldn't occur _anywhere_ in the package name.
+    const FORBIDDEN_CHARS: &[char] = &[
+        ' ', ',', ':', ';', '|', '\\', '/', '!', '@', '#', '%', '^', '&', '*', '(', ')', '{', '}',
+        '[', ']', '-', '`', '~', '\t', '\n', '\r',
+    ];
+
+    for c in FORBIDDEN_CHARS {
+        if namespace.contains(*c) {
+            return false;
+        }
+    }
+
+    fn is_valid_ident(ident: &str) -> bool {
+        /// These shouldn't occur as the first character of an identifier.
+        const FORBIDDEN_START_CHARS: &[char] = &['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'];
+
+        if ident.is_empty() {
+            return false;
+        }
+
+        for c in FORBIDDEN_START_CHARS {
+            if ident.starts_with(*c) {
+                return false;
+            }
+        }
+
+        true
+    }
+
+    for ident in namespace.split('.') {
+        if !is_valid_ident(ident) {
+            return false;
+        }
+    }
+
+    true
+}
+
+/// Creates a JNI-compatible function name from the given namespace and function name.
+/// This does _not_ transform the provided function name into `snakeCase` if it's not already; but
+/// `#[allow(non_snake_case)]` should be added to prevent errors.
+///
+/// Importantly, any underscores in the original namespace or function name need to be replaced by
+/// "_1", and then dot separators need to be turned into underscores.
+fn create_jni_fn_name(namespace: &str, fn_name: &str) -> String {
+    let namespace_underscored = namespace.replace('_', "_1").replace('.', "_");
+    let fn_name_underscored = fn_name.replace('_', "_1");
+    format!("Java_{}_{}", namespace_underscored, fn_name_underscored)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_create_jni_fn_name() {
+        assert_eq!(
+            create_jni_fn_name("com.example.Foo", "init"),
+            "Java_com_example_Foo_init"
+        );
+        assert_eq!(
+            create_jni_fn_name("com.example.Bar", "closeIt"),
+            "Java_com_example_Bar_closeIt"
+        );
+        assert_eq!(
+            create_jni_fn_name("com.example.Bar", "close_it"),
+            "Java_com_example_Bar_close_1it"
+        );
+        assert_eq!(
+            create_jni_fn_name(
+                "org.signal.client.internal.Native",
+                "IdentityKeyPair_Deserialize"
+            ),
+            "Java_org_signal_client_internal_Native_IdentityKeyPair_1Deserialize"
+        );
+    }
+
+    #[test]
+    fn test_valid_namespace() {
+        assert!(valid_namespace("com.example.Foo"));
+        assert!(valid_namespace("com.antonok.kb"));
+        assert!(valid_namespace("org.signal.client.internal.Native"));
+        assert!(valid_namespace("net.under_score"));
+        assert!(!valid_namespace("com example Foo"));
+        assert!(!valid_namespace(" com.example.Foo"));
+        assert!(!valid_namespace("com.example.Foo "));
+        assert!(!valid_namespace("com.example.1Foo"));
+    }
+
+    #[test]
+    fn test_code_generation() {
+        let attr = quote::quote! {
+            "com.example.Bar"
+        };
+        let source = quote::quote! {
+            pub fn close_it(env: JNIEnv, _: JClass, filename: JString) -> jboolean {
+                unimplemented!()
+            }
+        };
+
+        let expanded = jni_fn2(attr.into(), source.into());
+
+        assert_eq!(
+            format!("{}", expanded),
+            format!(
+                "{}",
+                quote::quote! {
+                    #[no_mangle]
+                    #[allow(non_snake_case)]
+                    pub extern "system" fn Java_com_example_Bar_close_1it (env: JNIEnv, _: JClass, filename: JString) -> jboolean {
+                        unimplemented!()
+                    }
+                }
+            )
+        );
+    }
+
+    #[test]
+    fn test_unsafe_fn() {
+        let attr = quote::quote! {
+            "com.example.Bar"
+        };
+        let source = quote::quote! {
+            pub unsafe fn close_it(env: JNIEnv, _: JClass, filename: JString) -> jboolean {
+                unimplemented!()
+            }
+        };
+
+        let expanded = jni_fn2(attr.into(), source.into());
+
+        assert_eq!(
+            format!("{}", expanded),
+            format!(
+                "{}",
+                quote::quote! {
+                    #[no_mangle]
+                    #[allow(non_snake_case)]
+                    pub unsafe extern "system" fn Java_com_example_Bar_close_1it (env: JNIEnv, _: JClass, filename: JString) -> jboolean {
+                        unimplemented!()
+                    }
+                }
+            )
+        );
+    }
+
+    #[test]
+    fn test_non_function() {
+        let attr = quote::quote! { "com.example.Foo" };
+        let source = quote::quote! {
+            enum NotAFunction {
+                Variant1,
+                Variant2(u8),
+            }
+        };
+
+        let expanded = jni_fn2(attr.into(), source.into());
+
+        assert_eq!(
+            format!("{}", expanded),
+            format!(
+                "{}",
+                quote::quote! {
+                    compile_error! { "The `jni_fn` attribute can only be applied to `fn` items" }
+                }
+            )
+        );
+    }
+
+    #[test]
+    fn test_empty_attribute() {
+        let attr = quote::quote! {};
+        let source = quote::quote! {
+            pub fn close_it(env: JNIEnv, _: JClass, filename: JString) -> jboolean {
+                unimplemented!()
+            }
+        };
+
+        let expanded = jni_fn2(attr.into(), source.into());
+
+        assert_eq!(
+            format!("{}", expanded),
+            format!(
+                "{}",
+                quote::quote! {
+                    compile_error! { "The `jni_fn` attribute must have a single string literal supplied to specify the namespace" }
+                }
+            )
+        );
+    }
+
+    #[test]
+    fn test_invalid_namespace() {
+        let attr = quote::quote! { "." };
+        let source = quote::quote! {
+            pub fn close_it(env: JNIEnv, _: JClass, filename: JString) -> jboolean {
+                unimplemented!()
+            }
+        };
+
+        let expanded = jni_fn2(attr.into(), source.into());
+
+        assert_eq!(
+            format!("{}", expanded),
+            format!(
+                "{}",
+                quote::quote! {
+                    compile_error! { "Invalid package namespace supplied to `jni_fn` attribute" }
+                }
+            )
+        );
+    }
+
+    #[test]
+    fn test_specified_abi() {
+        let attr = quote::quote! { "com.example.Foo" };
+        let source = quote::quote! {
+            pub extern "C" fn close_it(env: JNIEnv, _: JClass, filename: JString) -> jboolean {
+                unimplemented!()
+            }
+        };
+
+        let expanded = jni_fn2(attr.into(), source.into());
+
+        assert_eq!(
+            format!("{}", expanded),
+            format!(
+                "{}",
+                quote::quote! {
+                    compile_error! { "Don't specify an ABI for `jni_fn` attributed functions - the correct ABI will be added automatically" }
+                }
+            )
+        );
+    }
+
+    #[test]
+    fn test_wrong_visibility() {
+        let attr = quote::quote! { "com.example.Foo" };
+        let source = quote::quote! {
+            fn close_it(env: JNIEnv, _: JClass, filename: JString) -> jboolean {
+                unimplemented!()
+            }
+        };
+
+        let expanded = jni_fn2(attr.into(), source.into());
+
+        assert_eq!(
+            format!("{}", expanded),
+            format!(
+                "{}",
+                quote::quote! {
+                    compile_error! { "`jni_fn` attributed functions must have public visibility (`pub`)" }
+                }
+            )
+        );
+    }
+}

app/src/main/rust/Cargo.toml

@@ -17,7 +17,7 @@ jnix = "*"
 jnix-macros = "*"
 catch_panic = { path = "../catch_panic" }
 catch_panic_macros = { path = "../catch_panic_macros" }
-jni_fn = "*"
+jni_fn = { path = "../jni_fn" }
 
 [profile.release]
 strip = true