Unpack native lib only once. (#6)

skiko/build.gradle.kts

 import kotlin.text.capitalize
+import org.gradle.crypto.checksum.Checksum
 
 plugins {
     kotlin("multiplatform") version "1.3.72"
     `cpp-library`
     `maven-publish`
+    id("org.gradle.crypto.checksum") version "1.1.0"
 }
 
 val isCIBuild = project.hasProperty("teamcity")
@@ -246,8 +248,18 @@ val skikoJvmJar: Provider<Jar> by tasks.registering(Jar::class) {
     from(kotlin.jvm().compilations["main"].output.allOutputs)
 }
 
+val createChecksums by project.tasks.registering(org.gradle.crypto.checksum.Checksum::class) {
+    val linkTask = project.tasks.named("linkRelease${target.capitalize()}")
+    dependsOn(linkTask)
+    files = linkTask.get().outputs.files.filter { it.isFile } +
+            if (target == "windows") files("$skiaDir/out/Release-x64/icudtl.dat") else files()
+    algorithm = Checksum.Algorithm.SHA256
+    outputDir = file("$buildDir/checksums")
+}
+
 val skikoJvmRuntimeJar by project.tasks.registering(Jar::class) {
     archiveBaseName.set("skiko-$target")
+    dependsOn(createChecksums)
     from(skikoJvmJar.map { zipTree(it.archiveFile) })
     from(project.tasks.named("linkRelease${target.capitalize()}").map {
         it.outputs.files.filter { it.isFile }
@@ -255,6 +267,7 @@ val skikoJvmRuntimeJar by project.tasks.registering(Jar::class) {
     if (target == "windows") {
         from(files("$skiaDir/out/Release-x64/icudtl.dat"))
     }
+    from(createChecksums.get().outputs.files)
 }
 
 project.tasks.register<JavaExec>("run") {

skiko/src/jvmMain/kotlin/org/jetbrains/skiko/Library.kt

 package org.jetbrains.skiko
 
+import java.io.BufferedReader
+import java.io.InputStreamReader
 import java.io.File
 import java.nio.file.Files
 import java.nio.file.StandardCopyOption
 
-// based on https://github.com/JetBrains/skija/blob/bc6e0531021e4ff839c07196e0336d6456ed7520/src/main/java/org/jetbrains/skija/Library.java
 object Library {
     private var loaded = false
 
-    // https://github.com/adamheinrich/native-utils/blob/e6a39489662846a77504634b6fafa4995ede3b1d/src/main/java/cz/adamh/utils/NativeUtils.java
+    private val cacheDir = "${System.getProperty("user.home")}/.skiko/"
+
+    private fun loadOrGet(path: String, resource: String, isLibrary: Boolean) {
+        File(cacheDir).mkdirs()
+        val resourceName = if (isLibrary) System.mapLibraryName(resource) else resource
+        val hash = Library::class.java.getResourceAsStream("$path$resourceName.sha256").use {
+            BufferedReader(InputStreamReader(it)).lines().toArray()[0] as String
+        }
+
+        val fileName = if (isLibrary) System.mapLibraryName(hash) else hash
+        val file = File(cacheDir, fileName)
+        // TODO: small race change when multiple Compose apps are started first time, can handle with atomic rename.
+        if (!file.exists()) {
+            Library::class.java.getResourceAsStream("$path$resourceName").use { input ->
+                Files.copy(input, file.toPath(), StandardCopyOption.REPLACE_EXISTING)
+            }
+        }
+        if (isLibrary) {
+            System.load(file.absolutePath)
+        }
+    }
+
     @Synchronized
     fun load(resourcePath: String, name: String) {
         if (loaded) return
 
-        val libFileName = System.mapLibraryName(name)
-        val url = Library::class.java.getResource(resourcePath + libFileName)
-
-        val tempRoot = File(System.getProperty("java.io.tmpdir"))
-        val tempDir = tempRoot.resolve("skiko_" + System.nanoTime()).apply { mkdirs() }
-        val libFile = when {
-            url == null -> error("Library $libFileName is not found in $resourcePath")
-            url.protocol == "file" -> File(url.toURI())
-            else -> url.openStream().use { input ->
-                File(tempDir, libFileName).also {
-                    it.deleteOnExit()
-                    Files.copy(input, it.toPath(), StandardCopyOption.REPLACE_EXISTING)
-                }
-            }
-        }
+        loadOrGet(resourcePath, name, true)
         val loadIcu = System.getProperty("os.name").toLowerCase().startsWith("win")
-        val icuData = "icudtl.dat"
         if (loadIcu) {
-            val icuUrl = Library::class.java.getResource(resourcePath + icuData)
-            icuUrl.openStream().use { input ->
-                File(tempDir, icuData).also {
-                    it.deleteOnExit()
-                    Files.copy(input, it.toPath(), StandardCopyOption.REPLACE_EXISTING)
-                }
-            }
+            loadOrGet(resourcePath, "icudtl.dat", false)
         }
-        System.load(libFile.absolutePath)
         loaded = true
 
         // we have to set this property to avoid render flickering.