[iOS] Failed to load dynamic library dylib using the dart:ffi

[Aquarian-Age]

I compiled the libgo.so with go code, and it works fine with ffi calls on Android. On iOS, how do I invoke this compiled libgo.so?

On flutter.cn website, it is not very clear about the use of third-party libraries for ffi calls. For example, using go code should be compiled to
libxxx.a or libxxx.so? Compiled libxxx.a or libxxx.so? Where is it in the iOS directory? How should it be called?

[exaby73]

Hello @Aquarian-Age. Have you gone through the steps provided on https://docs.flutter.dev/development/platform-integration/ios/c-interop

[Aquarian-Age]

Hello @Aquarian-Age. Have you gone through the steps provided on https://docs.flutter.dev/development/platform-integration/ios/c-interop

---

Yes, already seen. Already searched some on the Internet, still do not understand. Maybe my level is too low 😂
It would be nice to have an example.

[dcharkes]

If you have an already compiled library: https://docs.flutter.dev/development/platform-integration/ios/c-interop#closed-source-third-party-library

Dynamic libraries are lib<name>.dylib on MacOS and iOS. (Not lib<name>.so as on Linux/Android.)

#
# To learn more about a Podspec see http://guides.cocoapods.org/syntax/podspec.html.
# Run `pod lib lint mylib_dylib.podspec` to validate before publishing.
#
Pod::Spec.new do |s|
  s.name             = 'mylib_dylib'
  s.version          = '0.0.1'
  s.summary          = 'A new flutter plugin project.'
  s.description      = <<-DESC
A new flutter plugin project.
                       DESC
  s.homepage         = 'http://example.com'
  s.license          = { :file => '../LICENSE' }
  s.author           = { 'Your Company' => 'email@example.com' }
  s.source           = { :path => '.' }
  s.source_files = 'Classes/**/*'
  s.dependency 'Flutter'
  s.platform = :ios, '10.0'
  # TODO(dacoharkes): exclude i386 again, and enable simulator on Mac M1.
  s.pod_target_xcconfig = {
    'DEFINES_MODULE' => 'YES',
    'EXCLUDED_ARCHS[sdk=iphonesimulator*]' => 'arm64'
  }
  s.vendored_libraries = 'Frameworks/libmylib_dylib.dylib', 'Frameworks/libmylib_dylib_dependency.dylib'
  s.swift_version = '5.0'
end

[exaby73]

@dcharkes Can this be concluded to be a documentation issue, or would you consider this an invalid issue?

[Aquarian-Age]

cannot find .dylib

dylib的编译脚本

add method

---

Both golib.dylib and golibsimulator.dylib have been tried, the same error content

[huycozy]

@Aquarian-Age Please provide a completed and minimal reproducible code sample so that we may verify this. Also, please provide the output of flutter doctor -v and the error log in quoting format so that we may verify it. Thanks!

[Aquarian-Age]

@Aquarian-Age Please provide a completed and minimal reproducible code sample so that we may verify this. Also, please provide the output of flutter doctor -v and the error log in quoting format so that we may verify it. Thanks!

• sample
  https://github.com/Aquarian-Age/golang-flutter/tree/amrta/goffi

[huycozy]

@Aquarian-Age thanks for providing the sample code. I also see the same error when running it. Labeling this issue for further insights from the team.

Logs

======== Exception caught by widgets library =======================================================
The following ArgumentError was thrown building FFiExample(dirty, state: _FFiExampleState#fa443):
Invalid argument(s): Failed to load dynamic library 'golibsimulator.dylib': dlopen(golibsimulator.dylib, 0x0001): tried: '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRootgolibsimulator.dylib' (errno=2), '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/usr/lib/swift/golibsimulator.dylib' (errno=2), '/usr/lib/swift/golibsimulator.dylib' (errno=2, not in dyld cache), '/Users/huynq/Library/Developer/CoreSimulator/Devices/B5C9F133-A0DA-4F5E-BF54-DFFF9A9BFFA6/data/Containers/Bundle/Application/B7924F97-4106-4FA3-B50A-7DAD0EDCE11F/Runner.app/Frameworks/golibsimulator.dylib' (errno=2), '/usr/lib/golibsimulator.dylib' (errno=2, not in dyld cache), 'golibsimulator.dylib' (errno=2), '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/usr/lib/golibsimulator.dylib' (errno=2)

The relevant error-causing widget was: 
  FFiExample FFiExample:file:///Users/huynq/Documents/NEVERCODE.IO/RepoduceProjects/OPClone/golang-flutter/goffi/lib/main.dart:9:16
When the exception was thrown, this was the stack: 
#0      _open (dart:ffi-patch/ffi_dynamic_library_patch.dart:12:43)
#1      new DynamicLibrary.open (dart:ffi-patch/ffi_dynamic_library_patch.dart:23:12)
#2      _FFiExampleState.build (package:goffi/main.dart:31:28)
#3      StatefulElement.build (package:flutter/src/widgets/framework.dart:4992:27)
#4      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4878:15)
#5      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:5050:11)
#6      Element.rebuild (package:flutter/src/widgets/framework.dart:4604:5)
#7      ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4859:5)
#8      StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:5041:11)
#9      ComponentElement.mount (package:flutter/src/widgets/framework.dart:4853:5)
#10     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3863:16)
#11     Element.updateChild (package:flutter/src/widgets/framework.dart:3592:18)
#12     RenderObjectToWidgetElement._rebuild (package:flutter/src/widgets/binding.dart:1195:16)
#13     RenderObjectToWidgetElement.mount (package:flutter/src/widgets/binding.dart:1164:5)
#14     RenderObjectToWidgetAdapter.attachToRenderTree.<anonymous closure> (package:flutter/src/widgets/binding.dart:1111:18)
#15     BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2605:19)
#16     RenderObjectToWidgetAdapter.attachToRenderTree (package:flutter/src/widgets/binding.dart:1110:13)
#17     WidgetsBinding.attachRootWidget (package:flutter/src/widgets/binding.dart:945:7)
#18     WidgetsBinding.scheduleAttachRootWidget.<anonymous closure> (package:flutter/src/widgets/binding.dart:925:7)
(elided 4 frames from class _RawReceivePortImpl, class _Timer, and dart:async-patch)
====================================================================================================

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[jmagman]

At a minimum this sounds like a request for documentation.

[jmagman]

Example app is actually on the https://docs.flutter.dev/development/platform-integration/ios/c-interop#compiled-dynamic-library path so shouldn't need a podspec. I linked and embedded the frameworks (though IRL this would need to be embedded differently on simulator vs physical device, i.e. using an xcframework):

Then I updated the open code to point to a real path (the error that's actually being displayed):
https://github.com/Aquarian-Age/golang-flutter/blob/078aa4aa0d11a17a94b4da72fb0be07cdeb85082/goffi/lib/main.dart#L31

      final executable = File(Platform.executable);
      final dyLibPath = '${executable.parent.path}/Frameworks/golibsimulator.dylib';
      final DynamicLibrary dylib = Platform.isIOS
          ? DynamicLibrary.open(dyLibPath)
          : DynamicLibrary.process();

That's indeed pointed to the right path in the installed app, but I'm getting not a mach-o file

Though it sure looks like one from otool.

I'm not sure how to get loading a pure dylib working, and even if you did I don't think it would be approved by the App Store--it needs to be packaged in a .framework bundle (I think), or be static. Which may be the real problem.

@dcharkes from your podspec example were you actually able to get this working with pure dylibs?

[dcharkes]

I'm not sure how to get loading a pure dylib working, and even if you did I don't think it would be approved by the App Store--it needs to be packaged in a .framework bundle (I think), or be static. Which may be the real problem.

@dcharkes from your podspec example were you actually able to get this working with pure dylibs?

Copying the .dylib in the Frameworks/ folder works for me locally. I've never published an app on the iOS store before, so I don't know if that works yes or no.

I've tried putting dylibs in an xcframework before, but I couldn't figure it out. I called xcodebuild -create-xcframework:

executable: 'xcodebuild',
arguments: [
  '-create-xcframework',
  for (final uri in srcUris) ...[
    '-library',
    uri.toFilePath(),
  ],
  '-output',
  targetUri.toFilePath(),
],

And then I tried adding it in the podspec as vendored_frameworks instead of vendored_libraries, but that resulted in:
[!] Invalid XCFramework slice type .dylib

[jmagman]

Copying the .dylib in the Frameworks/ folder works for me locally.

How did you DynamicLibrary.open it? I had to make it relative to Platform.executable. The iOS ffi code could really use a sample app.

@Aquarian-Age I recommend totally going the podspec path recommended in https://docs.flutter.dev/development/platform-integration/ios/c-interop#closed-source-third-party-library, which involves making a plugin (not a normal Flutter app, as your example as) and letting CocoaPods embed your precompiled code. I also don't think you're going to have a good time embedding a dylib on iOS, suggest converting it to a static library or making it a proper iOS framework bundle (that part has nothing to do with Flutter, it's an iOS restriction).

[Aquarian-Age]

Copying the .dylib in the Frameworks/ folder works for me locally.

How did you DynamicLibrary.open it? I had to make it relative to Platform.executable. The iOS ffi code could really use a sample app.

@Aquarian-Age I recommend totally going the podspec path recommended in https://docs.flutter.dev/development/platform-integration/ios/c-interop#closed-source-third-party-library, which involves making a plugin (not a normal Flutter app, as your example as) and letting CocoaPods embed your precompiled code. I also don't think you're going to have a good time embedding a dylib on iOS, suggest converting it to a static library or making it a proper iOS framework bundle (that part has nothing to do with Flutter, it's an iOS restriction).

---

The ffi method is no longer used. All code rewritten.

[jmagman]

Filed dart-lang/samples#162

[jmagman]

Also filed flutter/samples#1547 for Flutter app versions matching website instructions
https://docs.flutter.dev/development/platform-integration/ios/c-interop

[dcharkes]

making a plugin (not a normal Flutter app, as your example as)

I've never been able to get it to work with a normal Flutter app either, only with flutter create --template=plugin_ffi. The generated boilerplate + Flutter's own logic of doing extra build steps for plugins and FFI plugins are required.

[github-actions]

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.