Reading files

Read files with FileKit Core in Kotlin Multiplatform

Introduction

FileKit Core provides a consistent API for reading files across all platforms. The PlatformFile class offers multiple methods to read the contents of a file, from simple byte arrays to more complex streaming operations.

Reading as ByteArray

Supported on Android, iOS, macOS, JVM, Kotlin/Native Linux, JS and WASM targets

The most common way to read a file is to use the readBytes() suspend function, which returns the file contents as a ByteArray:

val file = PlatformFile("/path/to/file.pdf")

// Read the file as bytes
val bytes: ByteArray = file.readBytes()

Reading as String

Supported on Android, iOS, macOS, JVM, Kotlin/Native Linux, JS and WASM targets

For text files, you can use the readString() suspend function, which returns the file contents as a String:

val file = PlatformFile("/path/to/file.txt")

// Read the file as a string
val text: String = file.readString()
println(text)

Using Source

Supported on Android, iOS, macOS, JVM and Kotlin/Native Linux targets

For more advanced use cases or when working with large files, you can use the source() method from kotlinx-io to get a raw source:

val file = PlatformFile("/path/to/large-file.dat")

// Get a raw source for the file
val source = file.source().buffered()

// Use the source to read in chunks
source.use { bufferedSource ->
    // Read a line
    val line = bufferedSource.readLine()

    // Read a specific number of bytes
    val bytesRead = bufferedSource.readByteArray(1024)

    // Read until EOF
    while (!bufferedSource.exhausted()) {
        // Process data...
    }
}

Error Handling

When reading files, you should handle potential errors:

try {
    val file = PlatformFile("/path/to/file.txt")
    val bytes = file.readBytes()
} catch (e: FileNotFoundException) {
    println("File not found: ${e.message}")
} catch (e: IOException) {
    println("Error reading file: ${e.message}")
}

Example: Reading Different File Types

suspend fun readDifferentFiles() {
    // Read a text file
    val textFile = PlatformFile(FileKit.filesDir, "document.txt")
    val text = textFile.readString()
    
    // Read an image file
    val imageFile = PlatformFile(FileKit.filesDir, "image.jpg")
    val imageBytes = imageFile.readBytes()
    // Process image bytes...
    
    // Read a JSON file
    val jsonFile = PlatformFile(FileKit.filesDir, "config.json")
    val jsonString = jsonFile.readString()
    // Parse JSON...
}

See also: Writing Files for information on how to write to files after reading them.