"kotlin.IllegalStateException: Fail to send body. Content has type: class kotlinx.serialization.json.JsonObject, but OutgoingContent expected." when acceptContentTypes and contentType are differents

Ktor Version and Engine Used (client or server and name) 1.3.2, client Curl or IOS

Describe the bug IllegalStateException is thrown when acceptContentTypes and contentType are different. When both are same, the client call is ok and http response is correct.

To Reproduce Steps to reproduce the behavior:

@Serializable
data class User(
    val email: String,
    val password: String
)

@UnstableDefault
@KtorExperimentalAPI
class Sample {
    val client: HttpClient by lazy {
        HttpClient(Curl.create()) {
            expectSuccess = false

            install(JsonFeature) {
                acceptContentTypes = listOf(
                    ContentType.parse("application/vnd.any.response+json")
                )
                serializer = KotlinxSerializer()
            }
        }
    }
}

@ImplicitReflectionSerializer
@KtorExperimentalAPI
@UnstableDefault
fun main() = runBlocking {
    val response: HttpResponse = Sample().client.put {
        url("https://httpbin.org/put")
        contentType(
            ContentType.parse("application/vnd.any+json")
        )
        body = Json(JsonConfiguration.Stable).toJson(User("[e-mail]", "password1234"))
    }

    println(response.readText())
}

Uncaught Kotlin exception: kotlin.IllegalStateException: Fail to send body. Content has type: class kotlinx.serialization.json.JsonObject, but OutgoingContent expected.
        at 0   untitled.kexe                       0x00000001002e6317 kfun:kotlin.Throwable.<init>(kotlin.String?)kotlin.Throwable + 87 (/Users/teamcity3/buildAgent/work/4d622a065c544371/runtime/src/main/kotlin/kotlin/Throwable.kt:22:37)
        at 1   untitled.kexe                       0x00000001002df5d5 kfun:kotlin.Exception.<init>(kotlin.String?)kotlin.Exception + 85 (/Users/teamcity3/buildAgent/work/4d622a065c544371/runtime/src/main/kotlin/kotlin/Exceptions.kt:23:44)
        at 2   untitled.kexe                       0x00000001002df775 kfun:kotlin.RuntimeException.<init>(kotlin.String?)kotlin.RuntimeException + 85 (/Users/teamcity3/buildAgent/work/4d622a065c544371/runtime/src/main/kotlin/kotlin/Exceptions.kt:34:44)
        at 3   untitled.kexe                       0x00000001002dfc35 kfun:kotlin.IllegalStateException.<init>(kotlin.String?)kotlin.IllegalStateException + 85 (/Users/teamcity3/buildAgent/work/4d622a065c544371/runtime/src/main/kotlin/kotlin/Exceptions.kt:70:44)
        at 4   untitled.kexe                       0x00000001005d0206 kfun:io.ktor.client.features.HttpSend.Feature.$install$lambda-0COROUTINE$26.invokeSuspend#internal + 5270 (/Users/teamcity3/buildAgent/work/4d622a065c544371/backend.native/build/stdlib/kotlin/util/Preconditions.kt:98:15)
        at 5   untitled.kexe                       0x00000001005d0728 kfun:io.ktor.client.features.HttpSend.Feature.$install$lambda-0COROUTINE$26.invoke#internal + 312 (/opt/buildAgent/work/a85294440dc5c6e/ktor-client/ktor-client-core/common/src/io/ktor/client/features/HttpSend.kt:72:71)
        at 6   untitled.kexe                       0x0000000100549d22 kfun:io.ktor.util.pipeline.SuspendFunctionGun.loop#internal + 1122 (/opt/buildAgent/work/a85294440dc5c6e/ktor-utils/common/src/io/ktor/util/pipeline/PipelineContext.kt:207:0)
        at 7   untitled.kexe                       0x000000010054937b kfun:io.ktor.util.pipeline.SuspendFunctionGun.proceed#internal + 395 (/opt/buildAgent/work/a85294440dc5c6e/ktor-utils/common/src/io/ktor/util/pipeline/PipelineContext.kt:18:0)
        at 8   untitled.kexe                       0x00000001005ccdec kfun:io.ktor.client.features.HttpRequestLifecycle.Feature.$install$lambda-0COROUTINE$25.invokeSuspend#internal + 1212 (/opt/buildAgent/work/a85294440dc5c6e/ktor-client/ktor-client-core/common/src/io/ktor/client/features/HttpRequestLifecycle.kt:34:21)
        at 9   untitled.kexe                       0x00000001005cd508 kfun:io.ktor.client.features.HttpRequestLifecycle.Feature.$install$lambda-0COROUTINE$25.invoke#internal + 312 (/opt/buildAgent/work/a85294440dc5c6e/ktor-client/ktor-client-core/common/src/io/ktor/client/features/HttpRequestLifecycle.kt:28:73)
        at 10  untitled.kexe                       0x0000000100549d22 kfun:io.ktor.util.pipeline.SuspendFunctionGun.loop#internal + 1122 (/opt/buildAgent/work/a85294440dc5c6e/ktor-utils/common/src/io/ktor/util/pipeline/PipelineContext.kt:207:0)
        at 11  untitled.kexe                       0x000000010054937b kfun:io.ktor.util.pipeline.SuspendFunctionGun.proceed#internal + 395 (/opt/buildAgent/work/a85294440dc5c6e/ktor-utils/common/src/io/ktor/util/pipeline/PipelineContext.kt:18:0)
        at 12  untitled.kexe                       0x00000001005497da kfun:io.ktor.util.pipeline.SuspendFunctionGun.execute#internal + 474 (/opt/buildAgent/work/a85294440dc5c6e/ktor-utils/common/src/io/ktor/util/pipeline/PipelineContext.kt:183:16)
        at 13  untitled.kexe                       0x0000000100543909 kfun:io.ktor.util.pipeline.Pipeline.execute(TContext;TSubject)TSubject + 361 (/opt/buildAgent/work/a85294440dc5c6e/ktor-utils/common/src/io/ktor/util/pipeline/Pipeline.kt:27:41)
        at 14  untitled.kexe                       0x00000001005a44ed kfun:io.ktor.client.HttpClient.$executeCOROUTINE$0.invokeSuspend(kotlin.Result<kotlin.Any?>)kotlin.Any? + 653 (/opt/buildAgent/work/a85294440dc5c6e/ktor-client/ktor-client-core/common/src/io/ktor/client/HttpClient.kt:164:25)
        at 15  untitled.kexe                       0x00000001005a4834 kfun:io.ktor.client.HttpClient.execute(io.ktor.client.request.HttpRequestBuilder)io.ktor.client.call.HttpClientCall + 308 (/opt/buildAgent/work/a85294440dc5c6e/ktor-client/ktor-client-core/common/src/io/ktor/client/HttpClient.kt:163:13)
        at 16  untitled.kexe                       0x00000001005e0c0f kfun:io.ktor.client.statement.HttpStatement.$executeUnsafeCOROUTINE$96.invokeSuspend(kotlin.Result<kotlin.Any?>)kotlin.Any? + 943 (/opt/buildAgent/work/a85294440dc5c6e/ktor-client/ktor-client-core/common/src/io/ktor/client/statement/HttpStatement.kt:104:27)
        at 17  untitled.kexe                       0x00000001005e0f1b kfun:io.ktor.client.statement.HttpStatement.executeUnsafe$ktor-client-core()io.ktor.client.statement.HttpResponse + 235 (/opt/buildAgent/work/a85294440dc5c6e/ktor-client/ktor-client-core/common/src/io/ktor/client/statement/HttpStatement.kt:101:22)
        at 18  untitled.kexe                       0x00000001005dfbbb kfun:io.ktor.client.statement.HttpStatement.$executeCOROUTINE$93.invokeSuspend(kotlin.Result<kotlin.Any?>)kotlin.Any? + 1259 (/opt/buildAgent/work/a85294440dc5c6e/ktor-client/ktor-client-core/common/src/io/ktor/client/statement/HttpStatement.kt:43:38)
        at 19  untitled.kexe                       0x00000001005e0584 kfun:io.ktor.client.statement.HttpStatement.execute(kotlin.coroutines.SuspendFunction1<io.ktor.client.statement.HttpResponse,T>){0<kotlin.Any?>}Generic + 308 (/opt/buildAgent/work/a85294440dc5c6e/ktor-client/ktor-client-core/common/src/io/ktor/client/statement/HttpStatement.kt:42:13)
        at 20  untitled.kexe                       0x00000001005e06f4 kfun:io.ktor.client.statement.HttpStatement.execute()io.ktor.client.statement.HttpResponse + 228 (/opt/buildAgent/work/a85294440dc5c6e/ktor-client/ktor-client-core/common/src/io/ktor/client/statement/HttpStatement.kt:58:43)
        at 21  untitled.kexe                       0x000000010028c905 kfun:sample.$main$lambda-0COROUTINE$0.invokeSuspend#internal + 6117 (/opt/buildAgent/work/a85294440dc5c6e/ktor-client/ktor-client-core/common/src/io/ktor/client/statement/HttpStatement.kt:71:32)
        at 22  untitled.kexe                       0x00000001003068dc kfun:kotlin.coroutines.native.internal.BaseContinuationImpl.resumeWith(kotlin.Result<kotlin.Any?>) + 700 (/Users/teamcity3/buildAgent/work/4d622a065c544371/runtime/src/main/kotlin/kotlin/coroutines/ContinuationImpl.kt:26:0)
        at 23  untitled.kexe                       0x0000000100467d0a kfun:kotlinx.coroutines.DispatchedTask.run() + 2570 (/opt/buildAgent/work/44ec6e850d5c63f0/kotlinx-coroutines-core/common/src/internal/DispatchedTask.kt:42:0)
        at 24  untitled.kexe                       0x000000010044241d kfun:kotlinx.coroutines.EventLoopImplBase.processNextEvent()kotlin.Long + 813 (/opt/buildAgent/work/44ec6e850d5c63f0/kotlinx-coroutines-core/common/src/EventLoop.common.kt:272:20)
        at 25  untitled.kexe                       0x00000001004748f8 kfun:kotlinx.coroutines.BlockingCoroutine.joinBlocking#internal + 1864 (/opt/buildAgent/work/44ec6e850d5c63f0/kotlinx-coroutines-core/native/src/Builders.kt:65:44)
        at 26  untitled.kexe                       0x0000000100473aaf kfun:kotlinx.coroutines.runBlocking(kotlin.coroutines.CoroutineContext;kotlin.coroutines.SuspendFunction1<kotlinx.coroutines.CoroutineScope,T>){0<kotlin.Any?>}Generic + 1231 (/opt/buildAgent/work/44ec6e850d5c63f0/kotlinx-coroutines-core/native/src/Builders.kt:50:22)
        at 27  untitled.kexe                       0x0000000100473fca kfun:kotlinx.coroutines.runBlocking$default(kotlin.coroutines.CoroutineContext?;kotlin.coroutines.SuspendFunction1<kotlinx.coroutines.CoroutineScope,T>;kotlin.Int){0<kotlin.Any?>}Generic + 330 (/opt/buildAgent/work/44ec6e850d5c63f0/kotlinx-coroutines-core/native/src/Builders.kt:33:8)
        at 28  untitled.kexe                       0x000000010028aff2 kfun:sample.main() + 162 (/Users/niccheva/code/kotlin/untitled/src/macosMain/kotlin/sample/SampleMacos.kt:47:14)
        at 29  untitled.kexe                       0x000000010028e06a Konan_start + 138 (/Users/niccheva/code/kotlin/untitled/src/macosMain/kotlin/sample/SampleMacos.kt:47:1)

Expected behavior Expected client call to works when accept and content type are different.

[niccheva]

The same code with ktor 1.3.0 produce:

kotlin.ClassCastException: kotlinx.serialization.json.JsonObject cannot be cast to io.ktor.client.call.HttpClientCall

But also works if accept and content type are same

[dmitrievanthony]

Well, that’s the truth. I confused about everything. I spent some time investigating the JsonFeature code and realized that acceptedContentTypes there should contain all content types (received and sent) that should be serialized.

In your example, you mention in the feature that it should work only with application/vnd.any.response+json, but at the same time you send application/vnd.any+json and assume it should be serialized also.

I would recommend you to fix it the following way:

            install(JsonFeature) {
                acceptContentTypes = listOf(
                    ContentType.parse("application/vnd.any.response+json"),
                    ContentType.parse("application/vnd.any+json")
                )
                serializer = KotlinxSerializer()
            }