This project is a Flutter Plugin template.
It provides out-of-the box support for cross-compiling native Rust code for all available iOS and Android architectures and call it from plain Dart using Foreign Function Interface.
This template provides first class FFI support, the clean way.
aar
bundles or .framework
’sEdit your code within rust/src/lib.rs
and add any dependencies you need.
Make sure to annotate your exported functions with #[no_mangle]
and pub extern
so the function names can be matched from Dart.
Returning strings or structs may require using unsafe
blocks. Returned strings or structs will need to be free
’d from Dart.
$ANDROID_NDK_HOME
points to the NDK base folder
/Users/brickpop/Library/Android/sdk/ndk-bundle
on MacOS/home/brickpop/dev/android/ndk-bundle
on Linuxrust
folder:
make
to see the available actionsmake init
to install the Rust targetsmake all
to build the libraries and the .h
fileCargo.toml
Generated artifacts:
target/aarch64-linux-android/release/libexample.so
target/armv7-linux-androideabi/release/libexample.so
target/i686-linux-android/release/libexample.so
target/x86_64-linux-android/release/libexample.so
target/universal/release/libexample.a
target/bindings.h
Ensure that ios/mylib.podspec
includes the following directives:
...
s.source = { :path => '.' }
+ s.public_header_files = 'Classes**/*.h'
s.source_files = 'Classes/**/*'
+ s.static_framework = true
+ s.vendored_libraries = "**/*.a"
s.dependency 'Flutter'
s.platform = :ios, '8.0'
...
On flutter/ios
, place a symbolic link to the libexample.a
file
$ cd flutter/ios
$ ln -s ../rust/target/universal/release/libexample.a .
Append the generated function signatures from rust/target/bindings.h
into flutter/ios/Classes/MylibPlugin.h
$ cd flutter/ios
$ cat ../rust/target/bindings.h >> Classes/MylibPlugin.h
In our case, it will append char *rust_greeting(const char *to);
and void rust_cstr_free(char *s);
NOTE: By default, XCode will skip bundling the libexample.a
library if it detects that it is not being used. To force its inclusion, add dummy invocations in SwiftMylibPlugin.swift
that use every single native function that you use from Flutter:
...
public func dummyMethodToEnforceBundling() {
rust_greeting("...");
compress_jpeg_file("...");
compress_png_file("...");
// ...
// This code will force the bundler to use these functions, but will never be called
}
}
If you won’t be using Flutter channels, the rest of methods can be left empty.
Note: Support for avmv7, armv7s and i386 is deprecated. The targets can still be compiled with Rust 1.41 or earlier and by uncommenting the
make init
line onrust/makefile
Similarly as we did on iOS with libexample.a
, create symlinks pointing to the binary libraries on rust/target
.
You should have the following structure on flutter/android
for each architecture:
src
└── main
└── jniLibs
├── arm64-v8a
│ └── libexample.so@ -> ../../../../../rust/target/aarch64-linux-android/release/libexample.so
├── armeabi-v7a
│ └── libexample.so@ -> ../../../../../rust/target/armv7-linux-androideabi/release/libexample.so
├── x86
│ └── libexample.so@ -> ../../../../../rust/target/i686-linux-android/release/libexample.so
└── x86_64
└── libexample.so@ -> ../../../../../rust/target/x86_64-linux-android/release/libexample.so
As before, if you are not using Flutter channels, the methods within android/src/main/kotlin/org/mylib/mylib/MylibPlugin.kt
can be left empty.
To invoke the native code: load the library, locate the symbols and typedef
the Dart functions. You can automate this process from rust/target/bindings.h
or do it manually.
To use ffigen, add the dependency in pubspec.yaml
.
dev_dependencies:
flutter_test:
sdk: flutter
+ ffigen: ^1.2.0
Also, add the following lines at the end of pubspec.yaml
:
ffigen:
output: lib/bindings.dart
headers:
entry-points:
- rust/target/bindings.h
name: GreeterBindings
description: Dart bindings to call mylib functions
On MacOS:
brew install llvm
flutter pub run ffigen:setup -I/usr/local/opt/llvm/include -L/usr/local/opt/llvm/lib
On Linux:
sudo apt-get install -y clang libclang-dev
flutter pub run ffigen:setup
Generate lib/bindings.dart
:
flutter pub run ffigen
Finally, use the generated GreetingBindings
class. An example wrapper is available here.
Load the library:
final DynamicLibrary nativeExampleLib = Platform.isAndroid
? DynamicLibrary.open("libexample.so") // Load the dynamic library on Android
: DynamicLibrary.process(); // Load the static library on iOS
Find the symbols we want to use, with the appropriate Dart signatures:
final Pointer<Utf8> Function(Pointer<Utf8>) rustGreeting = nativeExampleLib
.lookup<NativeFunction<Pointer<Utf8> Function(Pointer<Utf8>)>>("rust_greeting")
.asFunction();
final void Function(Pointer<Utf8>) freeGreeting = nativeExampleLib
.lookup<NativeFunction<Void Function(Pointer<Utf8>)>>("rust_cstr_free")
.asFunction();
Call them:
// Prepare the parameters
final name = "John Smith";
final Pointer<Utf8> namePtr = Utf8.toUtf8(name);
print("- Calling rust_greeting with argument: $namePtr");
// Call rust_greeting
final Pointer<Utf8> resultPtr = rustGreeting(namePtr);
print("- Result pointer: $resultPtr");
final String greetingStr = Utf8.fromUtf8(resultPtr);
print("- Response string: $greetingStr");
When we are done using greetingStr
, tell Rust to free it, since the Rust implementation kept it alive for us to use it.
freeGreeting(resultPtr);
Author: brickpop
Source Code: https://github.com/brickpop/flutter-rust-ffi
#flutter #dart #mobile-apps #rust