So I've been going back and forth with this
in https://github.com/golang/go/issues/105808.
Syncthing on Android consists of two parts, one is the actual android
UI/wrapper, and second is GOOS=linux GOARCH=arm Go binary that the android
UI starts and manipulates using a rest API.
>From the Go binary, we need to call into Java and get a file descriptor to
file on the SD card with write permissions.
Normal os.Open doesn't cut it, as permissions on the sdcard are managed via
Storage Access Framework, so we have to go through that in Java call a few
other functions to get a writable fd.
In Go terms I expect to do something like this
import (
"Java/android/content/ContentProvider"
"Java/android/content/Intent"
)
func Open(name string) (*os.File, error) {
//Java/Go pseudo code
try {
var contentProvider = ContentProvider
<https://developer.android.com/reference/android/content/ContentProvider.html#ContentProvider()>
();
// Get write permissions
contentProvider.getContext().getContentResolver().
takePersistableUriPermission(name, Intent.FLAG_GRANT_WRITE_URI_PERMISSION |
Intent.FLAG_GRANT_READ_URI_PERMISSION);
// At this point it probably doesn't matter if we get the FD using
Java or Go...
var fdFromJava = contentProvider.openFile(name).getFd();
return os.NewFile(fdFromJava, name), nil
} catch {
return nil, errors.New("welp")
}
}
Elias on the ticket suggests that forward gomobile bind should be enough,
yet I can't comprehend on how this is the case and how this would work, as
all examples of forward bindings I find show calling Go from Java not the
other way around.
As in, the call is initiated from Java side, which should not be the case
in this case, as we are running in a Go binary.
Can someone provide more clarity on how this can be achieved?
Even if we do reverse bindings, can we actually make all the calls we want
without having an activity in the current process/JVM?
Unrelated, but I thought I'll give gomobile bind a test to see what I end
up with and I get the following:
c:\gopath\src\github.com\syncthing\syncthing\lib\fs>gomobile bind
gomobile: go build -pkgdir=c:\gopath\pkg\gomobile/pkg_android_arm -buildmode
=c-shared -o=C:\Users\Audrius\AppData\Local\Temp\gomobile-work-804905487\
android\src\main\jniLibs\armeabi-v7a\libgojni.so C:\Users\Audrius\AppData\
Local\Temp\gomobile-work-804905487\androidlib\main.go failed: exit status 2
#
_/C_/Users/Audrius/AppData/Local/Temp/gomobile-work-804905487/gomobile_bind
C:\Users\Audrius\AppData\Local\Temp\gomobile-work-804905487\gomobile_bind\
go_fsmain.go:243: cannot use (*proxyfs_Filesystem)(_v_ref) (type *
proxyfs_Filesystem) as type fs.Filesystem in assignment:
*proxyfs_Filesystem does not implement fs.Filesystem (missing Chmod
method)
C:\Users\Audrius\AppData\Local\Temp\gomobile-work-804905487\gomobile_bind\
go_fsmain.go:722: cannot use (*proxyfs_FileInfo)(res_0_ref) (type *
proxyfs_FileInfo) as type fs.FileInfo in assignment:
*proxyfs_FileInfo does not implement fs.FileInfo (missing ModTime
method)
C:\Users\Audrius\AppData\Local\Temp\gomobile-work-804905487\gomobile_bind\
go_fsmain.go:1170: cannot use (*proxyfs_FileInfo)(res_0_ref) (type *
proxyfs_FileInfo) as type fs.FileInfo in assignment:
*proxyfs_FileInfo does not implement fs.FileInfo (missing ModTime
method)
C:\Users\Audrius\AppData\Local\Temp\gomobile-work-804905487\gomobile_bind\
go_fsmain.go:1284: cannot use (*proxyfs_FileInfo)(res_0_ref) (type *
proxyfs_FileInfo) as type fs.FileInfo in assignment:
*proxyfs_FileInfo does not implement fs.FileInfo (missing ModTime
method)
C:\Users\Audrius\AppData\Local\Temp\gomobile-work-804905487\gomobile_bind\
go_fsmain.go:1465: cannot use (*proxyfs_Filesystem)(_param_next_ref) (type *
proxyfs_Filesystem) as type fs.Filesystem in assignment:
*proxyfs_Filesystem does not implement fs.Filesystem (missing Chmod
method)
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