Init Flutter plugin project

flutter create --template=plugin --platform=android,ios,linux,macos,windows --org com.pkgorg -a kotlin -i swift pkgname

Update pubspec.yaml:

dependencies:
  # ...
  ffi: ^2.0.1
  flutter_rust_bridge: ^1.65.0
# ...
dev_dependencies:
  # ...
  ffigen: ^6.1.2

Write Rust impl

cargo new pkgname --lib

• Add to a folder in root dir of plugin project.
• Update Cargo.toml:

[lib]
crate-type = ["staticlib", "cdylib"]

Init Android

android/build.gradle:

sourceSets {
    // ...
    main.jniLibs.srcDirs = ['src/main/jniLibs']
}

Init Linux

linux/CMakeLists.txt at the bottom:

set(pkgname_bundled_libraries
    "${CMAKE_CURRENT_SOURCE_DIR}/libpkgname.so"
    # ...

Init macOS

macos/pkgname.podspec:

s.vendored_libraries = 'Libs/**/*'

IMPORTANT: XCode strips the code from the library so you need to make sure it bundles.

macos/Classes/SwiftpkgnamePlugin.swift

public static func register(with registrar: FlutterPluginRegistrar) {
    // ...
    let _ = dummy()
}

public static func dummy() -> Int64
{ return dummy_method_to_enforce_bundling() }

Init iOS

ios/pkgname.podspec:

s.vendored_frameworks = 'Frameworks/**/*.xcframework'
s.static_framework = true # This allows us to use the static library we built.

IMPORTANT: XCode strips the code from the library so you need to make sure it bundles.

Objective-C: ios/Classes/pkgnamePlugin.m

...
#import "../Classes/bridge_generated.h"
...
@implementation pkgnamePlugin
+ (void)registerWithRegistrar:(NSObject<FlutterPluginRegistrar>*)registrar {
  dummy_method_to_enforce_bundling(); // <--- Insert this to prevent stripping.
  [SwiftpkgnamePlugin registerWithRegistrar:registrar];
}
@end

Swift: ios/Classes/SwiftpkgnamePlugin.swift

public static func register(with registrar: FlutterPluginRegistrar) {
    // ...
    let _ = dummy()
}

public static func dummy() -> Int64
{ return dummy_method_to_enforce_bundling() }

Init Windows

windows/CMakeLists.txt:

set(pkgname_bundled_libraries
    "${CMAKE_CURRENT_SOURCE_DIR}/pkgname.dll"
    # ...

Flutter->Rust Codegen

flutter_rust_bridge_codegen \
    --rust-input ./rust/src/lib.rs \
    --dart-output ./lib/src/bridge_generated.dart \
    --dart-decl-output ./lib/src/bridge_definitions.dart \
    --c-output ./rust/src/bridge_generated.h

• Copy and move ./rust/src/bridge_generated.h to ./macos/Classes and ./ios/Classes
• Fix any errors.
• Move everything in the folder to a subfolder called src
• Add this file to lib/src
• Create API for users.

NOTE: If codegen fails with incorrect signatures, try this:

export CPATH="$(clang -v 2>&1 | grep "Selected GCC installation" | rev | cut -d' ' -f1 | rev)/include"

Export Android Libs

rustup target add aarch64-linux-android armv7-linux-androideabi x86_64-linux-android i686-linux-android

cargo install cargo-ndk

cargo ndk -t arm64-v8a -t armeabi-v7a -t x86 -t x86_64 -o ../android/src/main/jniLibs build --release

Export Linux Lib

rustup target add x86_64-unknown-linux-gnu

cargo build --release --target x86_64-unknown-linux-gnu

Move the exported file to ./linux

Export macOS Libs

rustup target add aarch64-apple-darwin x86_64-apple-darwin

cargo build --release --target aarch64-apple-darwin

cargo build --release --target x86_64-apple-darwin

lipo "target/aarch64-apple-darwin/release/libpkgname.a" "target/x86_64-apple-darwin/release/libpkgname.a" -output "libpkgname.a" -create

Move the exported file to ./macos/Libs

Export iOS Libs

rustup target add aarch64-apple-ios aarch64-apple-ios-sim x86_64-apple-ios

cargo build --release --target aarch64-apple-ios

cargo build --release --target aarch64-apple-ios-sim

cargo build --release --target x86_64-apple-ios

lipo "target/aarch64-apple-ios-sim/release/libpkgname.a" "target/x86_64-apple-ios/release/libpkgname.a" -output "libpkgname.a" -create

xcodebuild -create-xcframework -library ./target/aarch64-apple-ios/release/libpkgname.a -library ./libpkgname.a -output pkgname.xcframework

Move the framework to ./ios/Frameworks

Export Windows Libs

rustup target add x86_64-pc-windows-msvc

cargo build --release --target x86_64-pc-windows-msvc

Move the exported file to ./windows

Updating the project

• Run code gen above.
• Export all libs again.

Publish to pub.dev

pub.dev does not allow projects to be over 100MB. This means you cannot include the libraries when publishing. To fix this, you can use the tutorial here.

However, I took slightly different steps to make it more simple. In the following code, replace the names in the GitHub URLs accordingly.

Android

• Add CMakeLists.txt to ./android.
• Edit build.gradle.

CMakeLists.txt:

cmake_minimum_required(VERSION 3.10)

# Download the binaries from GitHub.
# The version of the release from GitHub.
set(Version "1.0.0")
set(LibPath "${CMAKE_CURRENT_SOURCE_DIR}/src/main/jniLibs")

if(NOT EXISTS "${LibPath}/arm64-v8a/libpkgname.so")
  file(DOWNLOAD
    "https://github.com/username/pkgname/blob/v${Version}/android/src/main/jniLibs/arm64-v8a/libpkgname.so?raw=true"
    "${LibPath}/arm64-v8a/libpkgname.so"
    TLS_VERIFY ON
  )

  file(DOWNLOAD
    "https://github.com/username/pkgname/blob/v${Version}/android/src/main/jniLibs/armeabi-v7a/libpkgname.so?raw=true"
    "${LibPath}/armeabi-v7a/libpkgname.so"
    TLS_VERIFY ON
  )

  file(DOWNLOAD
    "https://github.com/username/pkgname/blob/v${Version}/android/src/main/jniLibs/x86/libpkgname.so?raw=true"
    "${LibPath}/x86/libpkgname.so"
    TLS_VERIFY ON
  )

  file(DOWNLOAD
    "https://github.com/username/pkgname/blob/v${Version}/android/src/main/jniLibs/x86_64/libpkgname.so?raw=true"
    "${LibPath}/x86_64/libpkgname.so"
    TLS_VERIFY ON
  )
endif()

build.gradle:

android {
    // ...
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
}

Linux

Add this to linux/CMakeLists.txt:

# Download the binary from GitHub.
set(Version "1.0.0")
set(LibPath "${CMAKE_CURRENT_SOURCE_DIR}/libpkgname.so")
if(NOT EXISTS ${LibPath})
  file(DOWNLOAD
    "https://github.com/username/pkgname/blob/v${Version}/linux/libpkgname.so?raw=true"
    ${LibPath}
    TLS_VERIFY ON
  )
endif()

macOS

Add this to macos/pkgname.podspec:

# Download the binary from GitHub.
version = "1.0.0"
lib_url = "https://github.com/username/pkgname/blob/v#{version}/macos/Libs/libpkgname.a?raw=true"

`
mkdir Libs
cd Libs
if [ ! -f libpkgname.a ]
then
  curl -L "#{lib_url}" -o libpkgname.a
fi
cd ..
`

iOS

Add this to ios/pkgname.podspec:

# Download the binaries from GitHub.
version = "1.0.0"
lib_url = "https://github.com/username/pkgname/blob/v#{version}/ios/Frameworks/pkgname.xcframework"

`
mkdir Frameworks
cd Frameworks
if [ ! -d pkgname.xcframework ]
then
  mkdir pkgname.xcframework
  cd pkgname.xcframework
  mkdir ios-arm64
  mkdir ios-arm64_x86_64-simulator
  curl -L "#{lib_url}/Info.plist?raw=true" -o Info.plist
  curl -L "#{lib_url}/ios-arm64/libpkgname.a?raw=true" -o ios-arm64/libpkgname.a
  curl -L "#{lib_url}/ios-arm64_x86_64-simulator/libpkgname.a?raw=true" -o ios-arm64_x86_64-simulator/libpkgname.a
fi
cd ../..
`

Windows

Add this to windows/CMakeLists.txt:

# Download the binary from GitHub.
set(Version "1.0.0")
set(LibPath "${CMAKE_CURRENT_SOURCE_DIR}/pkgname.dll")
if(NOT EXISTS ${LibPath})
  file(DOWNLOAD
    "https://github.com/username/pkgname/blob/v${Version}/windows/pkgname.dll?raw=true"
    ${LibPath}
    TLS_VERIFY ON
  )
endif()

Notes

Here are issues that I ran into, with solutions that may help you:

OpenSSL

I had trouble building this dependency on a few platforms.

In your Cargo.toml, add an openssl-sys dependency with the vendored feature.

• Linux: Install Perl and Perl CPAN
• Windows: Install Strawberry Perl
• iOS: The vendored feature does not work on the aarch64-apple-ios-sim target, so you need to use these environment variables when building. The OPENSSL_INCLUDE_DIR points to the include folder in the openssl source, so update this to wherever you cloned it.
  • OPENSSL_STATIC=1
  • OPENSSL_LIB_DIR=/usr/local/lib
  • OPENSSL_INCLUDE_DIR=~/Downloads/openssl/include
  • OPENSSL_NO_VENDOR=1

Clone openssl and run the Configure script.

iOS Missing Symbols

In my project, I had a Rust dependency to Apple's coreaudio API. When I tried to build the Flutter app, it would always give me multiple missing symbol errors. I was able to fix this by adding a framework to the example app's Runner project. Make sure the framework is not being embeded.

Examples

If you are unsure of how something is implemented, feel free to checkout my project simple_audio.