Add FFI and JNI support to Swift and Kotlin by tarrinneal · Pull Request #11352 · flutter/packages

tarrinneal · 2026-03-25T18:52:22Z

This PR introduces optional Native Interop to Pigeon, enabling direct communication between Dart and native code without the overhead of traditional MethodChannel serialization. It leverages FFI (Foreign Function Interface) for Swift (iOS/macOS) and JNI (Java Native Interface) for Kotlin (Android).

This represents a significant architectural shift, moving from message-based passing to direct memory sharing and function calls. It also updates the concurrency model for asynchronous methods, moving from completion handlers/callbacks to modern language features: async/await in Swift and Coroutines in Kotlin.

Generators Covered

Swift Generator: Updated to support FFI bindings and async/await for asynchronous methods.
Kotlin Generator: Updated to support JNI bindings and Kotlin Coroutines for asynchronous methods.
Dart Generator: Updated to handle the generated interop bindings on the Dart side.

What's In Scope

Infrastructure: Added core support for useFfi and useJni options.
Automation: Implemented multi-step generation flows that automatically invoke jnigen and ffigen to produce final bindings.
Config Generation: Added jnigen_config_generator.dart and ffigen_config_generator.dart to generate the necessary configuration files for the external tools.
Documentation: Added a detailed native_interop_guide.md explaining prerequisites, setup, and usage.
Tests: Added ni_tests.dart and associated generated files and integration tests to verify the feature.

What's Out of Scope

Other Languages: This PR specifically targets Swift and Kotlin for the Native Interop feature. Support for Objective-C, C++, and GObject is not included in this interop implementation, and may not be in the future.
Performance Optimization for Complex Classes: As noted in the guide, there is a known performance regression when transferring complex classes with many fields compared to MethodChannel Pigeon. This PR delivers the functional infrastructure, but optimizing this specific case is left for follow-up work.
Non-instant released data. Currently all data that is sent over host or flutter api surfaces is converted to the correct shape and type for the language it is moving toward and the data created in the other language is then discarded. This presents some inefficiencies and potential workflows that are not yet available.

work toward flutter/flutter#182230
design doc flutter/flutter#181430

…ent other generated files

stuartmorgan-g

Some very early review notes; since it's going to be a long review I thought I should post things incrementally. So far I've mostly just looked at the smaller bits, not the full generators yet (and not the tests).

Please also add a real PR description, with issue references and a high level overview of the PR (what it does, what generators it covers, what's in and out of scope here, etc.)

stuartmorgan-g

Still working, but here's another incremental comment drop.

stuartmorgan-g · 2026-04-23T17:01:50Z

We should consider changing to two example apps, one that uses method-channel-based Pigeon, and one that use the FFI-based Pigeon. I would expect the common use case to just be one or the other, so putting both in the same app could be confusing.

Do we have the infrastructure to handle two example apps?

Yes, if you have example/thing1/ and example/thing2/ as example apps, our tooling will understand that and do things with both of them.

stuartmorgan-g · 2026-04-23T17:06:41Z

+// #enddocregion config
+@HostApi()
+abstract class NativeInteropExampleApi {
+  void doSomething();


I'm not actually seeing any generated code corresponding to this. Is this file unused except for excerpting? If so that's pretty confusing for anyone looking at the example to see how to use this.

stuartmorgan-g · 2026-04-23T19:31:44Z

Does this need to be checked in? If so we should use some kind of naming convention for it to indicate that it's generated if possible.

stuartmorgan-g · 2026-04-23T19:34:44Z

      expect(listEquals(echoObject, list), true);
    });

+    // // Currently need set up


stuartmorgan-g · 2026-04-23T19:36:36Z

+  override fun noop() {
+    api?.let {
+      try {
+        return api!!.noop()


My Kotlin-fu is not strong, but surely there's a way to do a guard that doesn't require force unwrapping.

stuartmorgan-g · 2026-04-23T19:45:05Z

+      return '';
+    }
+    typeArgumentString += '>';
+    return typeArgumentString;


You can do final typeArgumentString; at the top, make the internals assignments instead of +=, and then return '<$typeArgumentString>';. That avoids the reassignable variable and the string concatenation.

stuartmorgan-g · 2026-04-24T13:39:03Z

+        indent.writeln('}');
+      } else {
+        indent.format('''
+  var sdkPath = '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk';


We can punt on it for now, but at some point we'll need to figure out how to allow configuring iOS vs macOS vs both as SDK options.

stuartmorgan-g · 2026-04-24T13:52:05Z

+    final indent = Indent();
+    indent.writeln('// ignore_for_file: prefer_const_constructors');
+    indent.writeln("import 'package:jnigen/jnigen.dart';");
+    indent.writeln("import 'package:logging/logging.dart';");


When we write these configs, we should also parse the pubspec and check that these dependencies exist, and if not either add them automatically, or tell the user they should add them. (Same for ffigen.)

Same for the runtime dependencies (jni, objective_c)

stuartmorgan-g

I tried playing with this in local_auth_android, and ran into some issues pretty quickly, although I may have been holding it wrong. I would definitely recommend trying to do an initial conversion of a plugin (that one already uses kotlin generation) to see if things work.

stuartmorgan-g · 2026-04-24T15:00:07Z

+    if (generatorOptions.useJni) {
+      indent.writeln('import androidx.annotation.Keep');
+    }
    indent.writeln('import io.flutter.plugin.common.BasicMessageChannel');


We should make all of these conditional; they are unused when using JNI.

stuartmorgan-g · 2026-04-24T15:13:51Z

+    if (generatorOptions.package != null && !generatorOptions.useJni) {
      indent.writeln('package ${generatorOptions.package}');
    }


Were you including the namepace in the class list in the jnigen config file?

We definitely want to use the package namespace if we are going to avoid a lot of disruption to clients.

stuartmorgan-g · 2026-04-24T15:16:15Z

+@ConfigurePigeon(
+  PigeonOptions(
+    dartOptions: DartOptions(),
+    kotlinOptions: KotlinOptions(useJni: true),


The docs say appDirectory is required with JNI, but this isn't using it. And using it didn't work for me, unless I was doing something wrong. What's the right way to configure at the Pigeon level for a standard plugin-with-example?

good point. appDirectory in the tests is encoded with a default value so isn't required. That's clearly confusing though so I'll add it here. What was the behavior you were seeing? This didn't do anything at all? were the jnigen bindings not showing up? not in the right folder?

IIRC it was trying to find the example in ./ so jnigen failed? I'll have to try again from scratch since I foolishly didn't capture the details.

ok, don't worry about it until I push up changes, I'm looking into it already.

tarrinneal added 30 commits October 29, 2025 19:00

kotlin jni impementation

b9b0b5e

analyzer

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test fixes w jetski

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Merge branch 'main' of https://github.com/flutter/packages into Kamyshin

f636cdb

remove future code

72a305e

Merge branch 'main' of https://github.com/flutter/packages into Kamyshin

4e59659

Merge branch 'main' of https://github.com/flutter/packages into Kamyshin

e22c55a

Merge remote-tracking branch 'origin/Frillback' into Kamyshin

3f0be1d

minor cleanup

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Merge branch 'main' of https://github.com/flutter/packages into Kamyshin

e0f23a9

omit types

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Merge branch 'main' of https://github.com/flutter/packages into Kamyshin

aa01700

format

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flutter api

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fix swift optional bug

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add nullable tests and more sync tests

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flutter api async methods

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error handling and tests

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basic thread tests

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fix swftFunction

b0cd2ec

add back tests for named/optional params

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Merge branch 'main' of https://github.com/flutter/packages into Kamyshin

850cb2e

fix const gen adapter classes

9bb4bc5

performance improvements to typedData and isEquals

0c7ef63

stuff that I'm going to move to a different branch

110ab70

Improve efficiency in some methods

82065a8

analyze this

9861c00

format

11daedd

less repeating, and less listing

e197fc0

allow individual class types to not have colliding hashes

cbf4096

tarrinneal added 2 commits March 30, 2026 21:12

readme and bump jnigen version, remove script

246b1a3

rename enum for number type in swift

6951605

tarrinneal added CICD Run CI/CD and removed CICD Run CI/CD labels Mar 31, 2026

fix lints and refine multi step generation code

d47a1ad

tarrinneal added CICD Run CI/CD and removed CICD Run CI/CD labels Apr 2, 2026

tarrinneal added 3 commits April 2, 2026 16:56

add missing args to cli tool, change jnigen build process to not prev…

f422d9d

…ent other generated files

Merge branch 'main' of https://github.com/flutter/packages into Kamyshin

835f8f5

gen

d765ce7

github-actions Bot added CICD Run CI/CD and removed CICD Run CI/CD platform-linux platform-windows labels Apr 9, 2026

stuartmorgan-g reviewed Apr 15, 2026

View reviewed changes

nits and nats

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github-actions Bot removed the CICD Run CI/CD label Apr 16, 2026

tarrinneal added 2 commits April 16, 2026 20:39

Merge branch 'main' of https://github.com/flutter/packages into Kamyshin

5c53127

remove build apk

aa7372b

stuartmorgan-g reviewed Apr 24, 2026

View reviewed changes

fix jni kotlin package

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flutter-dashboard Bot added the CICD Run CI/CD label Apr 28, 2026

relative paths and appDir comments

e202db9

github-actions Bot removed the CICD Run CI/CD label Apr 28, 2026

uncoment comments

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tarrinneal mentioned this pull request Apr 30, 2026

[pigeon] updates toString and isNullish methods #11625

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flutter-dashboard Bot added the CICD Run CI/CD label Apr 30, 2026

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stuartmorgan-g May 1, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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tarrinneal commented Mar 25, 2026 •

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