commonMain.io.github.xxfast.kstore.file.FileCodec.kt Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of kstore-file Show documentation

A tiny Kotlin multiplatform library that assists in saving and restoring objects to and from disk using kotlinx.coroutines, kotlinx.serialisation and okio

The newest version!

package io.github.xxfast.kstore.file


import io.github.xxfast.kstore.Codec
import io.github.xxfast.kstore.DefaultJson
import kotlinx.io.buffered
import kotlinx.io.files.FileNotFoundException
import kotlinx.io.files.Path
import kotlinx.io.files.SystemFileSystem
import kotlinx.serialization.ExperimentalSerializationApi
import kotlinx.serialization.KSerializer
import kotlinx.serialization.Serializable
import kotlinx.serialization.json.Json
import kotlinx.serialization.serializer

import kotlinx.serialization.json.io.decodeFromSource as decode
import kotlinx.serialization.json.io.encodeToSink as encode

/**
 * Creates a store with [FileCodec] with json serializer
 * @param file path to the file that is managed by this store
 * @param json JSON Serializer to use. defaults to [DefaultJson]
 * @return store that contains a value of type [T]
 */
public inline fun  FileCodec(
  file: Path,
  tempFile: Path = Path("$file.temp"),
  json: Json = DefaultJson,
): FileCodec = FileCodec(
  file = file,
  tempFile = tempFile,
  json = json,
  serializer = json.serializersModule.serializer(),
)

public class FileCodec(
  private val file: Path,
  private val tempFile: Path,
  private val json: Json,
  private val serializer: KSerializer,
) : Codec {
  /**
   * Decodes the file to a value.
   * If the file does not exist, null is returned.
   * @return optional value that is decoded
   */
  @OptIn(ExperimentalSerializationApi::class)
  override suspend fun decode(): T? =
    try {
      SystemFileSystem.source(file).buffered().use { json.decode(serializer, it) }
    } catch (e: FileNotFoundException) {
      null
    }

  /**
   * Encodes the given value to the file.
   * If the value is null, the file is deleted.
   * If the encoding fails, the temp file is deleted.
   * If the encoding succeeds, the temp file is atomically moved to the target file - completing the transaction.
   * @param value optional value to encode
   */
  @OptIn(ExperimentalSerializationApi::class)
  override suspend fun encode(value: T?) {
    if (value == null) {
      SystemFileSystem.delete(file, mustExist = false)
      return
    }

    try {
      SystemFileSystem.sink(tempFile).buffered().use { json.encode(serializer, value, it) }
    } catch (e: Throwable) {
      SystemFileSystem.delete(tempFile, mustExist = false)
      throw e
    }

    SystemFileSystem.atomicMove(source = tempFile, destination = file)
  }
}