KTOR-7620 Make Url class @serializable and JVM Serializable

In our project we had to define our own UrlSerializer. It would be much nicer to have this in the Ktor library itself, so it works out of the box (similar to how Cookie was recently extended).

Also, types like Url and Cookie should be java.io.Serializable. Otherwise Android crashes when using those types as e.g. screen arguments. This happens very quickly when Url is used indirectly as part of a data class where we wanted type safety.

Author: wkornewald

ktor-http/build.gradle.kts

@@ -14,5 +14,12 @@ kotlin {
                 api(libs.kotlinx.serialization.core)
             }
         }
+        jvmTest {
+            dependencies {
+                implementation(project(":ktor-shared:ktor-junit"))
+                implementation(project(":ktor-shared:ktor-serialization:ktor-serialization-kotlinx"))
+                implementation(project(":ktor-shared:ktor-serialization:ktor-serialization-kotlinx:ktor-serialization-kotlinx-json"))
+            }
+        }
     }
 }

ktor-http/common/src/io/ktor/http/Cookie.kt

@@ -6,6 +6,7 @@ package io.ktor.http
 
 import io.ktor.util.*
 import io.ktor.util.date.*
+import io.ktor.utils.io.*
 import kotlinx.serialization.*
 import kotlin.jvm.*
 
@@ -37,7 +38,17 @@ public data class Cookie(
     val secure: Boolean = false,
     val httpOnly: Boolean = false,
     val extensions: Map<String, String?> = emptyMap()
-)
+) : JvmSerializable {
+    private fun writeReplace(): Any = JvmSerializerReplacement(CookieJvmSerializer, this)
+}
+
+internal object CookieJvmSerializer : JvmSerializer<Cookie> {
+    override fun jvmSerialize(value: Cookie): ByteArray =
+        renderSetCookieHeader(value).encodeToByteArray()
+
+    override fun jvmDeserialize(value: ByteArray): Cookie =
+        parseServerSetCookieHeader(value.decodeToString())
+}
 
 /**
  * Cooke encoding strategy

ktor-http/common/src/io/ktor/http/URLProtocol.kt

@@ -5,13 +5,14 @@
 package io.ktor.http
 
 import io.ktor.util.*
+import io.ktor.utils.io.*
 
 /**
  * Represents URL protocol
  * @property name of protocol (schema)
  * @property defaultPort default port for protocol or `-1` if not known
  */
-public data class URLProtocol(val name: String, val defaultPort: Int) {
+public data class URLProtocol(val name: String, val defaultPort: Int) : JvmSerializable {
     init {
         require(name.all { it.isLowerCase() }) { "All characters should be lower case" }
     }

ktor-http/common/src/io/ktor/http/Url.kt

@@ -4,6 +4,11 @@
 
 package io.ktor.http
 
+import io.ktor.utils.io.*
+import kotlinx.serialization.*
+import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.encoding.*
+
 /**
  * Represents an immutable URL
  *
@@ -18,6 +23,7 @@ package io.ktor.http
  * @property password password part of URL
  * @property trailingQuery keep trailing question character even if there are no query parameters
  */
+@Serializable(with = UrlSerializer::class)
 public class Url internal constructor(
     protocol: URLProtocol?,
     public val host: String,
@@ -29,7 +35,7 @@ public class Url internal constructor(
     public val password: String?,
     public val trailingQuery: Boolean,
     private val urlString: String
-) {
+) : JvmSerializable {
     init {
         require(specifiedPort in 0..65535) {
             "Port must be between 0 and 65535, or $DEFAULT_PORT if not set. Provided: $specifiedPort"
@@ -222,9 +228,19 @@ public class Url internal constructor(
         return urlString.hashCode()
     }
 
+    private fun writeReplace(): Any = JvmSerializerReplacement(UrlJvmSerializer, this)
+
     public companion object
 }
 
+internal object UrlJvmSerializer : JvmSerializer<Url> {
+    override fun jvmSerialize(value: Url): ByteArray =
+        value.toString().encodeToByteArray()
+
+    override fun jvmDeserialize(value: ByteArray): Url =
+        Url(value.decodeToString())
+}
+
 /**
  * [Url] authority.
  */
@@ -254,3 +270,14 @@ internal val Url.encodedUserAndPassword: String
     get() = buildString {
         appendUserAndPassword(encodedUser, encodedPassword)
     }
+
+public class UrlSerializer : KSerializer<Url> {
+    override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("Url", PrimitiveKind.STRING)
+
+    override fun deserialize(decoder: Decoder): Url =
+        Url(decoder.decodeString())
+
+    override fun serialize(encoder: Encoder, value: Url) {
+        encoder.encodeString(value.toString())
+    }
+}

ktor-http/jvm/test/io/ktor/tests/http/SerializableTest.kt

@@ -0,0 +1,24 @@
+// ktlint-disable filename
+/*
+ * Copyright 2014-2019 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package io.ktor.tests.http
+
+import io.ktor.http.*
+import io.ktor.junit.*
+import kotlin.test.*
+
+class SerializableTest {
+    @Test
+    fun urlTest() {
+        val url = Url("https://localhost/path?key=value#fragment")
+        assertEquals(url, assertSerializable(url))
+    }
+
+    @Test
+    fun cookieTest() {
+        val cookie = Cookie("key", "value")
+        assertEquals(cookie, assertSerializable(cookie))
+    }
+}

ktor-io/common/src/io/ktor/utils/io/JvmSerializable.kt

@@ -0,0 +1,16 @@
+/*
+ * 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.utils.io
+
+public expect interface JvmSerializable
+
+public interface JvmSerializer<T> : JvmSerializable {
+    public fun jvmSerialize(value: T): ByteArray
+    public fun jvmDeserialize(value: ByteArray): T
+}
+
+public expect fun <T : Any> JvmSerializerReplacement(serializer: JvmSerializer<T>, value: T): Any
+
+internal object DummyJvmSimpleSerializerReplacement

ktor-io/jsAndWasmShared/src/io/ktor/utils/io/JvmSerializable.jsAndWasmShared.kt

@@ -0,0 +1,11 @@
+/*
+ * 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.utils.io
+
+/** Alias for `java.io.Serializable` on JVM. Empty interface otherwise. */
+public actual interface JvmSerializable
+
+public actual fun <T : Any> JvmSerializerReplacement(serializer: JvmSerializer<T>, value: T): Any =
+    DummyJvmSimpleSerializerReplacement

ktor-io/jvm/src/io/ktor/utils/io/JvmSerializable.jvm.kt

@@ -0,0 +1,42 @@
+/*
+ * 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.utils.io
+
+import java.io.*
+
+public actual typealias JvmSerializable = Serializable
+
+@Suppress("UNCHECKED_CAST")
+public actual fun <T : Any> JvmSerializerReplacement(serializer: JvmSerializer<T>, value: T): Any =
+    DefaultJvmSerializerReplacement(serializer, value)
+
+@PublishedApi // IMPORTANT: changing the class name would result in serialization incompatibility
+internal class DefaultJvmSerializerReplacement<T : Any>(
+    private var serializer: JvmSerializer<T>?,
+    private var value: T?
+) : Externalizable {
+    constructor() : this(null, null)
+
+    override fun writeExternal(out: ObjectOutput) {
+        println("writeExternal $value")
+        out.writeObject(serializer)
+        out.writeObject(serializer!!.jvmSerialize(value!!))
+    }
+
+    @Suppress("UNCHECKED_CAST")
+    override fun readExternal(`in`: ObjectInput) {
+        println("readExternal")
+        serializer = `in`.readObject() as JvmSerializer<T>
+        println(serializer)
+        value = serializer!!.jvmDeserialize(`in`.readObject() as ByteArray)
+    }
+
+    private fun readResolve(): Any =
+        value!!
+
+    companion object {
+        private const val serialVersionUID: Long = 0L
+    }
+}

ktor-io/src/desktopMain/kotlin/io/ktor/utils/io/JvmSerializable.desktop.kt

@@ -0,0 +1,11 @@
+/*
+ * 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.utils.io
+
+/** Alias for `java.io.Serializable` on JVM. Empty interface otherwise. */
+public actual interface JvmSerializable
+
+public actual fun <T : Any> JvmSerializerReplacement(serializer: JvmSerializer<T>, value: T): Any =
+    DummyJvmSimpleSerializerReplacement

ktor-io/src/nixMain/kotlin/io/ktor/utils/io/JvmSerializable.nix.kt

@@ -0,0 +1,11 @@
+/*
+ * 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.utils.io
+
+/** Alias for `java.io.Serializable` on JVM. Empty interface otherwise. */
+public actual interface JvmSerializable
+
+public actual fun <T : Any> JvmSerializerReplacement(serializer: JvmSerializer<T>, value: T): Any =
+    DummyJvmSimpleSerializerReplacement

ktor-shared/ktor-junit/jvm/src/io/ktor/junit/Assertions.kt

@@ -4,6 +4,8 @@
 
 package io.ktor.junit
 
+import java.io.*
+
 /**
  * Convenience function for asserting on all elements of a collection.
  */
@@ -29,3 +31,10 @@ fun <T> assertAll(collection: Iterable<T>, assertion: (T) -> Unit) {
         }
     )
 }
+
+inline fun <reified T : Any> assertSerializable(obj: T): T {
+    val encoded = ByteArrayOutputStream().also {
+        ObjectOutputStream(it).writeObject(obj)
+    }.toByteArray()
+    return ObjectInputStream(encoded.inputStream()).readObject() as T
+}