I don't really understand how to read / write file...

# multiplatform

[Michal Klimczak]

I don't really understand how to read / write files in okio 3 multiplatform (specifically on ios). All examples show how to do it using FileSystem.SYSTEM which is only available on `jvm` . It's like everything is there when you have FileHandle or Sink, but the first step is vague. Any hints?

[mbonnin]

FileSystem.SYSTEM is also available for native

[mbonnin]

It's not for JS because there's no filesystem on the browser but there is NodeJsFileSystem in a separate artifact

[mbonnin]

So you can use expect /`actual`

[mbonnin]

More info there: https://github.com/square/okio/issues/1070

[Michal Klimczak]

hmm, in my iosMain source set I only have FileSystem.SYSTEM_TEMPORARY_DIRECTORY under FileSystem.Companion. iosMain.dependsOn(commonMain) and commonMain has implementation("com.squareup.okio:okio:3.0.0")

[Michal Klimczak]

maybe I have messed up my source sets some other way 🤔

[Michal Klimczak]

but you are right, it's there

[mbonnin]

Might one of these HMPP thing (https://kotlinlang.org/docs/mpp-share-on-platforms.html)

[Michal Klimczak]

I'm starting to think it's more of an IDE issue. I added the dependency directly to iosMain source set and it shows up red, but then when I navigate to the FileSystem class the SYSTEM is there.

[Michal Klimczak]

yeah, it builds just fine.
@Sebastian Sellmair [JB] you might be interested in this. This dependency from okio nativeMain sourceset is resolved properly by build system, but my iosMain source set doesn't see it in Android Studio (regardles of if I add the dependency to iosMain or commonMain).

val iosMain by creating {
            dependsOn(commonMain)
            iosArm64Main.dependsOn(this)
            iosX64Main.dependsOn(this)
            ...
            dependencies {
                implementation("com.squareup.okio:okio:3.0.0")
                ...
            }
        }

and

kotlin.mpp.enableGranularSourceSetsMetadata=true
kotlin.native.enableDependencyPropagation=false

[Sebastian Sellmair [JB]]

Hey! Thanks for pinging me.
Without looking into further details here, it seems that issues like this are expected.
OKIO does not publish in a hierarchical multiplatform compatible way and so tooling will not be able to distinguish symbols that are in “intermediate” source sets (like iosMain) from others.
So you can only use ‘commonMain’ APIs in iosMain or ios{Arch}Main apis in your ios{Arch}Main. The Kotlin Multiplatform team tried to help migrating OKIO to hmpp, however we can’t report significant progress there from our side.
Obviously, OKIO is still very close to our heart (Kotlin Multiplatform Team) and we’re monitoring OKIO and have branches on our hands with hmpp support.
In the end, this is square’s decision to migrate and there might be good reasons for them postponing it?

[Michal Klimczak]

Thanks for taking time to respond! In the meantime I found your PR in okio. Asked on #squarelibraries, maybe there are some plans

[Michal Klimczak]

any workarounds maybe? I tried some random things like creating a matching nativeMain source sets but it doesn't help

[Sebastian Sellmair [JB]]

There would be some workarounds I can think of, however those are rather complicated.
Is it feasible for you to expect/actual around that issue for now?

[Michal Klimczak]

I don't think expect/actual would help here, but it's not really that important, it builds, I can just work it out without code completion etc, so no need for big workarounds here.

I wonder though, the SYSTEM is not present in commonMain, nor it's an `expect/actual` static field. It's just something that is declared in the actual companion object FileSystem both in jvmMain and nativeMain. So why does my AS pick up the jvm variable and doesn't do it for native? I guess it has something to do with the fact that androidMain is already provided and I obtain the source set by getting , whereas iosMain is by creating?

[Sebastian Sellmair [JB]]

In short:
jvmMain and androidMain are “platform source sets”. Like iosArm64Main commonMain and platform source sets will be provided with symbols to analise against. Intermediate source sets have more complicated platform attributes, since them are shared across multiple platforms.

[Sebastian Sellmair [JB]]

Your intuitions are all correct in the “hmpp” world, the issue is just that OKIO does not publish in this mode. You either get commonMain, or platforms thats it. Tooling will not be provided with more ganularity!

[Michal Klimczak]

Makes sense, thank you :)