KMPFile

A Kotlin Multiplatform File implementation that mimics the Java File API.

KMPFile wraps kotlinx.io for some operations including streams.

Compatibility

KMPFile targets the following platforms:

Android (File, Uri)
JVM
Apple (iOS, macOS, tvOS, watchOS) (largely untested)
Linux (arm64, x64) (largely untested)
Android NDK (arm32, arm64, x86, x64) (largely untested)
Windows (MinGW x64) (largely untested)

Installation

Add the dependency to your commonMain source set:

sourceSets {
    val commonMain by getting {
        dependencies {
            implementation("dev.zwander:kmpfile:VERSION")
            // Convenience functions for converting from FileKit to KMPFile.
            // Supports the same platforms as FileKit, minus JS and WASM.
            implementation("dev.zwander:kmpfile-filekit:VERSION")
            // Convenience functions for converting between kotlinx.io and okio
            // Sources and Sinks.
            // Supports the same platforms as okio, minus JS and WASM.
            implementation("dev.zwander:kmpfile-okio:VERSION")
        }
    }
}

Usage

The base type you want to use in your code (e.g., when specifying function arguments) is IPlatformFile. This interface contains all the supported functions of KMPFile.

suspend fun someFileOperation(input: IPlatformFile, output: IPlatformFile) {
    //...
}

There are two classes that implement IPlatformFile: PlatformFile and PlatformUriFile.

PlatformFile

This class is available on all platforms and is meant to deal with files directly.

On Android and the JVM, PlatformFile wraps Java's File. On Apple platforms, it wraps NSURL.

PlatformFile contains multiple constructors to create instances directly from common code. You can create a PlatformFile from a file path, from a parent path and child file name, from a parent file and child file name, and even wrap a Java File or Apple NSURL directly from your common source.

PlatformUriFile

This class is only available on Android, but implements IPlatformFile so it can be used in the same way as PlatformFile.

PlatformUriFile is made for doing Uri-based file management on Android. You can't directly create an instance from common code, but there are convenience functions for doing so.

Convenience Functions

If you have a string that could represent either a file path or Uri, you can use FileUtils.fromString() to create the appropriate IPlatformFile instance for it.

// This will create a PlatformUriFile instance on Android.
val uriFile = FileUtils.fromString(input = "content://media/some_file_id", isDirectory = false)

// This will create a PlatformFile instance on all platforms.
val realFile = FileUtils.fromString(input = "/path/to/some_file.txt", isDirectory = false)

Specifying whether the referenced path is a directory is necessary for consistent behavior with Android Uris and on Apple platforms.

Platform Differences

File management on one platform isn't perfectly analogous to management on another, so not every function of IPlatformFile may be available or identical in behavior.

For details on the differences between platforms and which functions aren't supported on which platform, check out the comments on IPlatformFile.

Picking Files

KMPFile doesn't provide file picker functionality, but the FileKit can be used with KMPFile.

KMPFile provides an extension module dev.zwander:kmpfile-filekit that you can implement to provide extension functions to convert FileKit files to KMPFile files.

val fileKitDirectory = FileKit.pickDirectory()
val fileKitFile = FileKit.pickFile()

val kmpFileDirectory = fileKitDirectory.toKmpFile()
val kmpFileFile = fileKitFile.toKmpFile()

On Android, toKmpFile() will return a PlatformUriFile instance, since FileKit's file on Android only handles Uris.

PlatformUriFile implements IPlatformFile so this is largely invisible to usages in the common source set. You can create your own instances of PlatformUriFile from the Android source set.

Okio Compatibility

KMPFile uses kotlinx.io internally for many functions, including data streaming. If your project uses Okio, you can add kmpfile-okio to convert between the two libraries.

val file: IPlatformFile = PlatformFile("/some/path.txt")
    
// Convert kotlinx.io streams to okio streams.
val okioSource: okio.Source? = file.openInputStream()?.toOkioSource()
val okioSink: okio.Sink? = file.openOutputStream()?.toOkioSink()

// Convert okio streams to kotlinx.io streams.
val kotlinSource: kotlinx.io.RawSource? = okioSource?.toKotlinSource()
val kotlinSink: kotlinx.io.RawSink? = okioSink?.toKotlinSink()

These haven't been tested for performance and may cause issues with transfer speeds. Unfortunately neither library is very extensible, so KMPFile needs to use intermediate buffers with each operation.

zacharee/KMPFile