fix the whole database (except backups) was corrupted and the applica…

…tion cannot be reopened if the application is previously killed while writing files

src/jvmMain/kotlin/com/sunnychung/application/multiplatform/hellohttp/manager/FileManager.kt

@@ -10,6 +10,7 @@ import okio.buffer
 import okio.sink
 import okio.source
 import java.io.File
+import java.io.IOException
 import java.io.OutputStream
 import java.util.concurrent.ConcurrentHashMap
 
@@ -41,15 +42,24 @@ class FileManager {
 
     suspend fun writeToFile(file: File, writeOperation: (OutputStream) -> Unit) {
         withLock(file) {
-            file.sink().buffer().use {
-                it.write(magicBytes)
-                it.write(byteArrayOf(separatorByte))
-                it.write(fileSchemaVersion.toString().toByteArray())
-                it.write(byteArrayOf(separatorByte))
+            file.outputStream().use { fileOutputStream ->
+                val fileLock = fileOutputStream.channel.tryLock()
+                    ?: throw IOException("Cannot lock file ${file.absolutePath} for writing")
+
+                try {
+                    file.sink().buffer().use {
+                        it.write(magicBytes)
+                        it.write(byteArrayOf(separatorByte))
+                        it.write(fileSchemaVersion.toString().toByteArray())
+                        it.write(byteArrayOf(separatorByte))
 
-                val outputStream = it.outputStream().buffered()
-                writeOperation(outputStream)
-                outputStream.flush() // must
+                        val outputStream = it.outputStream().buffered()
+                        writeOperation(outputStream)
+                        outputStream.flush() // must
+                    }
+                } finally {
+                    fileLock.release()
+                }
             }
         }
     }

src/jvmMain/kotlin/com/sunnychung/application/multiplatform/hellohttp/manager/PersistenceManager.kt

@@ -19,6 +19,7 @@ import kotlinx.serialization.ExperimentalSerializationApi
 import kotlinx.serialization.KSerializer
 import kotlinx.serialization.cbor.Cbor
 import java.io.File
+import java.io.IOException
 import java.util.concurrent.ConcurrentHashMap
 
 @OptIn(ExperimentalSerializationApi::class)
@@ -53,11 +54,21 @@ class PersistenceManager {
 //            file = file,
 //            content = bytes
 //        )
+        val tmpFile = File(file.parentFile, "${file.name}.tmp")
+        if (tmpFile.exists() && !tmpFile.canWrite()) {
+            throw IOException("File ${tmpFile.absolutePath} is not writeable")
+        }
         fileManager.writeToFile(
-            file = file,
+            file = tmpFile,
         ) { outStream ->
             codecCustomizedWriter.encodeToStream(serializer, document, outStream)
         }
+        if (file.exists() && !file.delete()) {
+            throw IOException("File ${file.absolutePath} cannot be deleted for new content")
+        }
+        if (!tmpFile.renameTo(file)) {
+            throw IOException("File ${tmpFile.absolutePath} cannot be renamed to ${file.name}")
+        }
     }
 
     internal suspend inline fun <T> readFile(relativePath: String, serializer: KSerializer<T>): T? {