Regression with serialization using list of types that have registered contextual serializers

[rasharab]

This seems to be an issue in the kotlinx serialization land, but I'm not sure where the boundary ends between Ktor ContentNegotation plugin and Kotlinx serialization.

We have noticed a regression that was introduced with Ktor 2.2.* and kotlinx.serialization 1.4.1+ when serializing/deserializing lists of Contextual types, and it seems to be related to serialization caching.

The regression produces the following error:

Class 'ArrayList' is not registered for polymorphic serialization in the scope of 'List'.
To be registered automatically, class 'ArrayList' has to be '@Serializable', and the base class 'List' has to be sealed and '@Serializable'.
Alternatively, register the serializer for 'ArrayList' explicitly in a corresponding SerializersModule.
kotlinx.serialization.SerializationException: Class 'ArrayList' is not registered for polymorphic serialization in the scope of 'List'.
To be registered automatically, class 'ArrayList' has to be '@Serializable', and the base class 'List' has to be sealed and '@Serializable'.
Alternatively, register the serializer for 'ArrayList' explicitly in a corresponding SerializersModule.
	at app//kotlinx.serialization.internal.Abst

We believe the above exception is a byproduct of changes in this pr to implement a caching layer for serializers:

2825e21

In particular, this conditional:

https://github.com/Kotlin/kotlinx.serialization/blame/84d4af04a688286ad1b51a72130ccda691caff75/core/commonMain/src/kotlinx/serialization/Serializers.kt#L200

The supplied testbed was working at Ktor 2.1.3 and Kotlinx Serialization 1.4.0.

TESTBED:

You can configure the versions here:

https://github.com/NextChapterSoftware/kotlinx-serialization-bug/blob/cefc82ad210cbd683c8327188f9d8a8d5119af00/kotlinx-serialization-bug/build.gradle.kts#L18

// Good Versions
//val ktorVersion = "2.1.3"
//val kotlinxSerializationVersion = "1.4.0"

// Regression Versions
val ktorVersion = "2.3.1"
val kotlinxSerializationVersion = "1.5.1"

You should run this file:

https://github.com/NextChapterSoftware/kotlinx-serialization-bug/blob/main/kotlinx-serialization-bug/src/test/kotlin/TestSerialization.kt

import io.ktor.client.call.body
import io.ktor.client.plugins.contentnegotiation.ContentNegotiation
import io.ktor.client.plugins.defaultRequest
import io.ktor.client.request.post
import io.ktor.client.request.setBody
import io.ktor.http.ContentType
import io.ktor.http.contentType
import io.ktor.server.plugins.contentnegotiation.ContentNegotiation as ServerCN
import io.ktor.serialization.kotlinx.json.json
import io.ktor.serialization.kotlinx.serializerForTypeInfo
import io.ktor.server.application.*
import io.ktor.server.application.call
import io.ktor.server.request.receive
import io.ktor.server.response.respond
import io.ktor.server.routing.post
import io.ktor.server.routing.routing
import io.ktor.server.testing.testApplication
import kotlinx.serialization.KSerializer
import kotlinx.serialization.descriptors.PrimitiveKind.STRING
import kotlinx.serialization.descriptors.PrimitiveSerialDescriptor
import kotlinx.serialization.descriptors.SerialDescriptor
import kotlinx.serialization.encoding.Decoder
import kotlinx.serialization.encoding.Encoder
import kotlinx.serialization.json.Json
import kotlinx.serialization.modules.SerializersModule
import org.junit.jupiter.api.Assertions
import org.junit.jupiter.api.Test
import java.util.UUID

object UUIDAdapter : KSerializer<UUID> {
    override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("UUID", STRING)

    override fun serialize(encoder: Encoder, value: UUID) {
        encoder.encodeString(value.toString())
    }

    override fun deserialize(decoder: Decoder): UUID {
        return UUID.fromString(decoder.decodeString())
    }
}

class TestSerialization {
    @Test
    fun `test serialization regression for list of type with contextual adapter`() = testApplication {
        val testHttpClient = createClient {
            install(ContentNegotiation) {
                json(
                    Json {
                        serializersModule = SerializersModule {
                            contextual(UUID::class, UUIDAdapter)
                        }
                    }
                )
            }
            defaultRequest {
                contentType(ContentType.Application.Json)
            }
        }
        application {
            install(ServerCN) {
                json(
                    Json {
                        serializersModule = SerializersModule {
                            contextual(UUID::class, UUIDAdapter)
                        }
                    }
                )
            }
            routing {
                post("/echoUUIDs") {
                    val bytes = call.receive<List<UUID>>()
                    call.respond(bytes.toString())
                }
            }
        }

        val response = testHttpClient.post("/echoUUIDs") {
            setBody(listOf(UUID.randomUUID(), UUID.randomUUID()))
        }

        val result = response.body<String>()
        Assertions.assertTrue(result.isNotEmpty())
    }
}