Want to combine the best between Flutter, a cross-platform hot-reload rapid-development UI toolkit, and Rust, a language empowering everyone to build reliable and efficient software? Here it comes!
Vec<u8>(Uint8List), Vec<T>(List<T>), any custom struct(class)s, and even recursive structs (e.g. a tree node).What you write down (in Rust):
```rust
pub fn my_function(a: MyTreeNode, b: SomeOtherStruct) -> Result
// you can use structs (even recursive)
pub struct TreeNode { pub value: String, pub children: Vec
With bindings automatically generated, you can simply use the following API in Flutter/Dart. Nothing more.
dart
Future<Uint8List> myFunction(MyTreeNode a, SomeOtherStruct b);
Remark: Why FutureΒ in Flutter: Flutter is single-threaded. If not using future, just like what you do with plain-old Flutter bindings, your UI will be stuckΒ as long as your Rust code is executing. If your Rust code run for a second, your UI will fully freeze for one second.
cbindgen: cargo install cbindgen (may need latest version, thanks @gmorenz)ffigen: dart pub global activate ffigen, and install LLVM.cargo install flutter_rust_bridge_codegen.flutter_rust_bridge = "1.0" (where 1.0 should be the latest version) to Rust's Cargo.toml.flutter_rust_bridge: ^1.0 (same as above, should be latest version) to Flutter/Dart's pubspec.yaml under the section of dependencies.shell
flutter_rust_bridge_codegen --rust-input path/to/your/api.rs --dart-output path/to/file/being/bridge_generated.dart
(For more options, use --help; To see what types and function signatures can you write in Rust, have a look at this example.) (For Windows, you may need \\ instead of / for paths.)
Use the class in the generated .dart file, as if it is a normal Flutter/Dart class! (The abstract class at the top of the generated file.)
Want to see a Flutter tutorial with UI? See the tutorial section below. Want pure-Dart example? Here is another tutorial.
Remark: If you are interested, why abstractclass can be used - it is because of the factory language feature.
This library has CI that runs Valgrind automatically on the setup that a Dart program calls a Rust program using this package, so memory problems should be found by Valgrind. (Notice that, even when running a simple hello-world Dart program, Valgrind will report hundreds of errors. See this Dart lang issue for more details. Therefore, I both look at "definitely lost" in Valgrind, and manually search things related to this library - if all reported errors are unrelated to this library then we are safe.)
In addition, Flutter integration tests are also done in CI. This ensures a real Flutter application using this library does not suffer from problems.
Most of the code are written in safe Rust. The unsafe code mainly comes from support::box_from_leak_ptr and support::vec_from_leak_ptr. They are used for pointers and arrays, and I follow the high-upvoted answers and official doc when writing down that few lines of code.
I use this library heavily in my own Flutter project (yplusplus, or why++). That app is in production and it works quite well. If I observe any problems, I will fix it in this library.
The CI also runs the run_codegen workflow, which ensure that the code generator can compile and generate desired results. Lastly, the CI also runs formatters and linters (fmt, clippy, dart analyze, dart format), and linters can also catch some common problems.
Remark: The flutter_ios_test and flutter_android_test sections of the CI workflow can also be useful, if you want details of each command.
Please install Flutter, install Rust, and have some familiarity with them. Then run git clone https://github.com/fzyzcjy/flutter_rust_bridge, and my example is in frb_example/with_flutter.
Remark: I have generated the source code already (in quickstart), so this step is optional. Even if you do it, you should not see anything changed.
Install it: cargo install flutter_rust_bridge_codegen.
Run it: flutter_rust_bridge_codegen --rust-input frb_example/with_flutter/rust/src/api.rs --dart-output frb_example/with_flutter/lib/bridge_generated.dart --c-output frb_example/with_flutter/ios/Runner/bridge_generated.h. (See CI workflow as a reference.) (For Windows, you may need \\ instead of / for paths.)
With this app, you will see a Mandelbrot set plotted in Flutter UI and generated by Rust algorithm.
Run cargo ndk -o ../android/app/src/main/jniLibs build. Then run the Flutter app normally as is taught in official tutorial. For example, flutter run.
Remark: Since my quickstart app is so baremetal, I do not integrate the Rust building process into Flutter building process. But you can look at this tutorial to easily do that.
Modify Cargo.toml to change cdylib to staticlib. (Again, this is baremetal example so it is done manually. For your project, you can automate it.)
Run cargo lipo && cp target/universal/debug/libflutter_rust_bridge_example.a ../ios/Runner to build Rust and copy the static library. Then run the Flutter app normally as is taught in official tutorial. For example, flutter run. (Similarly, this tutorial can automate the process.)
Have a look at the function arguments and return types in this file: api.rs. With this library, we have a generated API that resides at generated_api.dart (of course, that is auto generated, and you can use it in other Dart code).
modIf you are adding this lib to your own existing code, please put mod generated_wire; (where generated_wire is the name of the wire file that you choose) into your lib.rs or main.rs. Only by doing this, Rust can understand that this generated file is a part of your project.
Dart SDK >=2.14.0 is needed not by this library, but by the latest version of the ffigen tool. Therefore, write sdk: ">=2.14.0 <3.0.0" in the environment section of pubspec.yaml. If you do not want that, consider installing a older version of the ffigen tool.
Remark: The valgrind_test section of the CI workflow can also be useful, if you want details of each command and want to see Valgrind configuration.
Unlike the previous tutorial, this one integrates Rust with pure Dart instead of Flutter.
Please install Dart, install Rust, and have some familiarity with them. Then run git clone https://github.com/fzyzcjy/flutter_rust_bridge, and my example is in frb_example/pure_dart.
Remark: I have generated the source code already (in quickstart), so this step is optional. Even if you do it, you should not see anything changed.
Install it: cargo install flutter_rust_bridge_codegen.
Run it: flutter_rust_bridge_codegen --rust-input frb_example/pure_dart/rust/src/api.rs --dart-output frb_example/pure_dart/dart/lib/bridge_generated.dart (See CI workflow as a reference.) (For Windows, you may need \\ instead of / for paths.)
You may run frb_example/pure_dart/dart/lib/main.dart as a normal Dart program, except that you should provide the dynamic linked library of the Rust code (for simplicity, here I only demonstrate the approach for dynamic linked library, but you can for sure use other methods). The detailed steps are as follows.
Run cargo build in frb_example/pure_dart/rust to build the Rust code into a .so file. Then run dart frb_example/pure_dart/dart/lib/main.dart frb_example/pure_dart/rust/target/debug/libflutter_rust_bridge_example.so to run the Dart program with Rust .so file. (If on MacOS, Rust may indeed generate .dylib, so change the last command to use ...dylib instead of ...so,)
P.S. You will only see some tests passing - no fancy UI or functionality in this example.
Simply add --help to see full documentation.
```shell flutterrustbridge_codegen
USAGE:
flutterrustbridge_codegen [OPTIONS] --dart-output
FLAGS: -h, --help Prints help information -V, --version Prints version information
OPTIONS:
-r, --rust-input
This library is nothing but a code generator that helps your Flutter/Dart functions call Rust functions. Therefore, you may refer to external materials to learn Flutter, learn Rust, learn Flutter FFI (Dart FFI) and so on. With material on the Internet, you will know how to create a mobile application using Flutter, and how that app can call Rust functions via Dart FFI (in the C ABI). Then this package comes in, and ease you from the burden to write down tons of boilerplate code ;)
By default, the DefaultExecutor is used. When Dart calls Rust, the DefaultExecutor use a simple thread pool to execute the real Rust functions. By doing this, Rust function that needs to run for a long time (more than a few frames) will never make the UI stuck.
However, you can implement your own Executor doing whatever you want. In order to do this, implement the Executor trait, and create a variable named FLUTTER_RUST_BRIDGE_EXECUTOR in the Rust input file (probably using lazy_static).
I suggest that you can start with the Flutter example first, and modify it to satisfy your needs. It can serve as a template for new projects. It is run against CI so we are sure it works.
Indeed, this library is nothing but a code generator that helps your Flutter/Dart functions call Rust functions. Therefore, "how to create a Flutter app that can run Rust code" is actually out of the scope of this library, and there are already several tutorials on the Internet.
However, I can sketch the outline of what to do if you want to set up a new Flutter+Rust project as follows.
Step 1: Create a new Flutter project (or use an existing one). The Dart SDK should be >=2.14.0 if you want to use the latest ffigen tool.
Step 2: Create a new Rust project, say, at directory rust under the Flutter project.
Step 3: Edit Cargo.toml and add:
[lib]
name = "flutter_rust_bridge_example" # whatever you like
crate-type = ["cdylib"] # <-- notice this type. `cdylib` for android, and `staticlib` for iOS. I write down a script to change it before build.
Step 4: Follow the standard steps of "how iOS uses static libraries". For example, in XCode, edit Strip Style in Build Settings to Debugging Symbols. Also, add your libyour_generate_file.a to Link Binary With Libraries in Build Phases. Add binding.h to Copy Bundle Resources. Add #import "binding.h" to Runner-Bridging-Header. Last but not least, add a never-to-be-executed dummy function in Swift that calls any of the generated C bindings. This lib has already generated a dummy method for you, so you simply need to add print("dummy_value=\(dummy_method_to_enforce_bundling())"); to swift file's override func application(...) {}, and this will prevent symbol stripping - especially in the release build for iOS (i.e. when building ipa file or releasing to App Store). Notice that, we have to use that dummy_method_to_enforce_bundling(), otherwise the symbols will not maintain in the release build, and Flutter will complain it cannot find the symbols.
Lastly, in order to build Rust automatically when you are building Flutter, follow this tutorial.
I plan to support the following features. Of course, if you want to have other features, feel free to make an issue or PR.
async in Rust (currently only async in Dart). Should be quite easy to implement; I have not done it because my use case currently does not includ that, but feel free to PR.Streams, which is a powerful abstraction. Should also be easy to implement.Firstly, welcome, and thanks for your contributions! If you want to contribute, feel free to create a Pull Request. If you need some ideas of what to contribute, have a look at the Issues section of this repository. The code is covered by CI, and please ensure the CI passes - which often catches bugs. To release a new version, bump several versions, and write down a changelog: vim frb_codegen/Cargo.toml && vim frb_rust/Cargo.toml && vim frb_dart/pubspec.yaml && vim frb_dart/CHANGELOG.md