KTOR-7698 Make ServiceLoader.load calls optimizable by R8

ktor-client/ktor-client-core/jvm/src/io/ktor/client/HttpClientJvm.kt

@@ -1,10 +1,11 @@
 /*
- * Copyright 2014-2019 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
+ * Copyright 2014-2024 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
  */
 
 package io.ktor.client
 
 import io.ktor.client.engine.*
+import io.ktor.util.reflect.*
 import io.ktor.utils.io.*
 import java.util.*
 
@@ -34,12 +35,8 @@ public interface HttpClientEngineContainer {
     public val factory: HttpClientEngineFactory<*>
 }
 
-/**
- * Workaround for dummy android [ClassLoader].
- */
-private val engines: List<HttpClientEngineContainer> = HttpClientEngineContainer::class.java.let {
-    ServiceLoader.load(it, it.classLoader).toList()
-}
+@OptIn(InternalAPI::class)
+private val engines = loadService<HttpClientEngineContainer>()
 
 private val FACTORY = engines.firstOrNull()?.factory ?: error(
     "Failed to find HTTP client engine implementation in the classpath: consider adding client engine dependency. " +

ktor-client/ktor-client-plugins/ktor-client-json/jvm/src/io/ktor/client/plugins/json/DefaultJvm.kt

@@ -1,24 +1,22 @@
 /*
- * Copyright 2014-2021 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
+ * Copyright 2014-2024 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
  */
 
 package io.ktor.client.plugins.json
 
-import java.util.*
+import io.ktor.util.reflect.*
+import io.ktor.utils.io.*
 
+@OptIn(InternalAPI::class)
 @Suppress("DEPRECATION_ERROR")
 public actual fun defaultSerializer(): JsonSerializer {
-    val serializers = ServiceLoader.load(JsonSerializer::class.java)
-        .toList()
-
-    if (serializers.isEmpty()) {
-        error(
-            """Fail to find serializer. Consider to add one of the following dependencies: 
- - ktor-client-gson
- - ktor-client-json
- - ktor-client-serialization"""
-        )
-    }
-
-    return serializers.maxByOrNull { it::javaClass.name }!!
+    val serializers = loadService<JsonSerializer>()
+    return serializers.maxByOrNull { it::javaClass.name } ?: error(
+        """
+        Failed to find serializer. Consider adding one of the following dependencies: 
+         - ktor-client-gson
+         - ktor-client-json
+         - ktor-client-serialization
+        """.trimIndent()
+    )
 }

ktor-client/ktor-client-tests/jvm/src/io/ktor/client/tests/utils/ClientLoaderJvm.kt

@@ -1,11 +1,13 @@
 /*
- * Copyright 2014-2022 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
+ * Copyright 2014-2024 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
  */
 
 package io.ktor.client.tests.utils
 
 import io.ktor.client.*
 import io.ktor.client.engine.*
+import io.ktor.util.reflect.*
+import io.ktor.utils.io.*
 import kotlinx.coroutines.*
 import kotlinx.coroutines.debug.*
 import java.util.*
@@ -16,11 +18,8 @@ import kotlin.time.Duration.Companion.seconds
  */
 actual abstract class ClientLoader actual constructor(val timeoutSeconds: Int) {
 
-    private val engines: List<HttpClientEngineContainer> by lazy {
-        HttpClientEngineContainer::class.java.let { engineContainerClass ->
-            ServiceLoader.load(engineContainerClass, engineContainerClass.classLoader).toList()
-        }
-    }
+    @OptIn(InternalAPI::class)
+    private val engines: Iterable<HttpClientEngineContainer> by lazy { loadService<HttpClientEngineContainer>() }
 
     /**
      * Perform test against all clients from dependencies.

ktor-server/ktor-server-core/jvm/src/io/ktor/server/config/ConfigLoadersJvm.kt

@@ -1,11 +1,12 @@
 /*
- * Copyright 2014-2022 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
+ * Copyright 2014-2024 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
  */
 
 package io.ktor.server.config
 
 import io.ktor.server.engine.*
-import java.util.*
+import io.ktor.util.reflect.*
+import io.ktor.utils.io.*
 
 internal actual val CONFIG_PATH: List<String>
     get() = listOfNotNull(
@@ -14,6 +15,5 @@ internal actual val CONFIG_PATH: List<String>
         getEnvironmentProperty("config.url"),
     )
 
-public actual val configLoaders: List<ConfigLoader> = ConfigLoader::class.java.let {
-    ServiceLoader.load(it, it.classLoader).toList()
-}
+@OptIn(InternalAPI::class)
+public actual val configLoaders: List<ConfigLoader> = loadService<ConfigLoader>().toList()

ktor-shared/ktor-serialization/ktor-serialization-kotlinx/common/src/io/ktor/serialization/kotlinx/Extensions.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2022 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
+ * Copyright 2014-2024 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
  */
 
 package io.ktor.serialization.kotlinx
@@ -11,7 +11,7 @@ import io.ktor.utils.io.*
 import io.ktor.utils.io.charsets.*
 import kotlinx.serialization.*
 
-internal expect val providers: List<KotlinxSerializationExtensionProvider>
+internal expect val providers: Iterable<KotlinxSerializationExtensionProvider>
 
 internal fun extensions(format: SerialFormat): List<KotlinxSerializationExtension> =
     providers.mapNotNull { it.extension(format) }

ktor-shared/ktor-serialization/ktor-serialization-kotlinx/jsAndWasmShared/src/io/ktor/serialization/kotlinx/ExtensionsJs.kt

@@ -1,8 +1,8 @@
 /*
- * Copyright 2014-2022 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
+ * Copyright 2014-2024 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
  */
 
 package io.ktor.serialization.kotlinx
 
-internal actual val providers: List<KotlinxSerializationExtensionProvider>
+internal actual val providers: Iterable<KotlinxSerializationExtensionProvider>
     get() = emptyList()

ktor-shared/ktor-serialization/ktor-serialization-kotlinx/jvm/src/io/ktor/serialization/kotlinx/ExtensionsJvm.kt

@@ -1,12 +1,12 @@
 /*
- * Copyright 2014-2022 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
+ * Copyright 2014-2024 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
  */
 
 package io.ktor.serialization.kotlinx
 
-import java.util.*
+import io.ktor.util.reflect.*
+import io.ktor.utils.io.*
 
-internal actual val providers: List<KotlinxSerializationExtensionProvider> =
-    KotlinxSerializationExtensionProvider::class.java.let {
-        ServiceLoader.load(it, it.classLoader).toList()
-    }
+@OptIn(InternalAPI::class)
+internal actual val providers: Iterable<KotlinxSerializationExtensionProvider> =
+    loadService<KotlinxSerializationExtensionProvider>()

ktor-shared/ktor-serialization/ktor-serialization-kotlinx/posix/src/io/ktor/serialization/kotlinx/ExtensionsNative.kt

@@ -1,13 +1,13 @@
 /*
- * Copyright 2014-2022 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
+ * Copyright 2014-2024 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
  */
 
 package io.ktor.serialization.kotlinx
 
 import io.ktor.utils.io.*
 
 private val _providers: MutableList<KotlinxSerializationExtensionProvider> = mutableListOf()
-internal actual val providers: List<KotlinxSerializationExtensionProvider> = _providers
+internal actual val providers: Iterable<KotlinxSerializationExtensionProvider> = _providers
 
 @InternalAPI
 public fun addExtensionProvider(provider: KotlinxSerializationExtensionProvider) {

ktor-utils/jvm/src/io/ktor/util/reflect/ServiceLoader.kt

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2014-2024 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package io.ktor.util.reflect
+
+import io.ktor.utils.io.*
+import java.util.*
+
+/**
+ * Loads implementations of service [T] using [ServiceLoader.load].
+ *
+ * NOTE: ServiceLoader should use specific call convention to be optimized by R8 on Android:
+ * `ServiceLoader.load(X.class, X.class.getClassLoader()).iterator()`
+ * See: https://r8.googlesource.com/r8/+/refs/heads/main/src/main/java/com/android/tools/r8/ir/optimize/ServiceLoaderRewriter.java
+ */
+@InternalAPI
+public inline fun <reified T> loadService(): Iterable<T> {
+    val iterator = ServiceLoader.load(
+        T::class.java,
+        T::class.java.classLoader,
+    ).iterator()
+
+    return Iterable { iterator }
+}