flutter macos support

[unsuitable001]

This PR intends to add macOS support for flutter. macOS support for Dart CLI is already present.

Related #5

cc @dcharkes

[unsuitable001]

Weirdly, while running in Flutter mode, macOS trying to locate the binary from:

libUri: file:///Users/unsuitable001/Library/Containers/dev.google.cronetExample/Data/libcronet.86.0.4240.198.dylib

hence, it fails to load the binary.

However, in Dart CLI mode it tries to locate from:

libUri: file:///Users/unsuitable001/development/projects/cronet.dart/libcronet.86.0.4240.198.dylib

which is the correct location.

[unsuitable001]

Reference: flutter/flutter#61950

[dcharkes]

Would you mind mentioning which files are generated by flutter create and were not modified to ease the reviewing? :)

[dcharkes]

*** -> **

[unsuitable001]

Oh right 😅. I forgot. Doing that in an hour.

[dcharkes]

I don't see a macos folder outside the example. (Apparently I need better eyes!) The way you have set it up requires all your users on MacOS to repeat your steps.

Instead, run flutter create -t plugin --platforms=macos . on the root and modify the podspec to include the dylibs. For example for mylib_dylib including two dylibs:

#
# 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 'FlutterMacOS'

  s.platform = :osx, '10.11'
  s.pod_target_xcconfig = { 'DEFINES_MODULE' => 'YES' }
  s.vendored_libraries = 'Frameworks/libmylib_dylib.dylib', 'Frameworks/libmylib_dylib_dependency.dylib'
  s.swift_version = '5.0'
end

Note that the dylibs must be in the macos/Frameworks folder, podspec does not allow them to be in a parent folder of macos.

That way we do not modify any other changes in the example project. (Other than maybe flutter create --platforms=macos . and flutter clean.) So your users on MacOS can just import your library and be done with it.

[dcharkes]

Missing s.vendored_libraries here.

[unsuitable001]

Oow! Now I got it. My first time using mac's build system. 😅

[unsuitable001]

I added that and is getting copied into the Framework subdirectory under the app's installation directory. But, it seems like mac is trying to find the dylib from some other path dyld: Library not loaded: @executable_path/libcronet.86.0.4240.198.dylib. I'm yet to figure out how to change it. I tried setting DYLD_LIBRARY_PATH and LD_RUNPATH_SEARCH_PATHS. But, didn't work.

[dcharkes]

Try just libcronet.86.0.4240.198.dylib by name instead of with @executable_path/.

[unsuitable001]

I'm trying to load it without @executable_path. It is getting added by itself. And, this error is happening just before our app's launch. So, I guess podspec is maybe.. dynamically linking our dylibs?
(Even if in that case, I'm unsure why it will fail to locate itself).

[dcharkes]

My CMakeLists.txt:

add_library(mylib_dylib SHARED mylib_dylib.c)

set_target_properties(mylib_dylib PROPERTIES
    PUBLIC_HEADER mylib_dylib.h
    OUTPUT_NAME "mylib_dylib"
    XCODE_ATTRIBUTE_CODE_SIGN_IDENTITY "35FA16FED6F78C492D1D7DE64CB5DDDDC6A0C138"
    # Set the install name of the dylib to the path of where it will be in the app bundle.
    XCODE_ATTRIBUTE_LD_DYLIB_INSTALL_NAME "@executable_path/Frameworks/libmylib_dylib.dylib"
)

And then I open it by name in Dart when running in Flutter apps:

DynamicLibrary.open(dylibFileName(libName));` // libmylib_dylib.dylib

Maybe the combination of that?

[unsuitable001]

We're not building cronet from source files. Can we add it to cmake file?

[unsuitable001]

@dcharkes
It seems like a widespread issue in a few of the latest MacOS/iOS versions. Reading other related issues, I tried to use use_frameworks! and use_modular_headers! in the Podfile. Though some of them got lucky with this hack, I wasn't one of them (along with few others).

I'm experimenting with the issue. Meanwhile, if you get time, can try running the build on your machine maybe..? If the same error happens in your machine too?

And, is there any way to just copy the dylib and not linking it? So that it doesn't get loaded automatically and we can get the scope of loading it from Dart (by experimenting with the path).

[dcharkes]

We're not building cronet from source files.

install_name_tool can be used to investigate the "install name" for dylibs which are already compiled.

https://stackoverflow.com/questions/33991581/install-name-tool-to-update-a-executable-to-search-for-dylib-in-mac-os-x

[unsuitable001]

Just curious, if #32 can help me resolve this mess :)

[dcharkes]

Yes, with my experience iOS and MacOS should be almost identical. :)

[Sunbreak]

Any update?