Got "Content type application/json is not supported" exception when the class to serialize/unserialize is in the function

[scorsi]

Hello,

I don't know if it is an expected result but here is something that didn't work and how to solve it.
I spent a lot of time to fix that.
Did the same with ktor-gson or ktor-jackson.

Ktor Version

1.0.1

Ktor Engine Used(client or server and name)

ktor-server-netty

JVM Version, Operating System and Relevant Context

jdk1.8.0_17 on macOS Mojave 10.14.1

Feedback

I'm getting

io.ktor.features.UnsupportedMediaTypeException: Content type application/json is not supported
	at io.ktor.features.ContentNegotiation$Feature$install$3.invokeSuspend(ContentNegotiation.kt:100)
	at io.ktor.features.ContentNegotiation$Feature$install$3.invoke(ContentNegotiation.kt)
	at io.ktor.util.pipeline.SuspendFunctionGun.loop(PipelineContext.kt:248)
	at io.ktor.util.pipeline.SuspendFunctionGun.access$loop(PipelineContext.kt:63)
	at io.ktor.util.pipeline.SuspendFunctionGun.proceed(PipelineContext.kt:111)
	at io.ktor.util.pipeline.SuspendFunctionGun.execute(PipelineContext.kt:131)
	at io.ktor.util.pipeline.Pipeline.execute(Pipeline.kt:24)
	at io.ktor.request.ApplicationReceiveFunctionsKt.receive(ApplicationReceiveFunctions.kt:68)
	at something.SomethingKt.notes(something.kt:176)
	at something.SomethingKt$api$1.invokeSuspend(something.kt:8)
	at something.SomethingKt$api$1.invoke(something.kt)
	at io.ktor.util.pipeline.SuspendFunctionGun.loop(PipelineContext.kt:248)
	at io.ktor.util.pipeline.SuspendFunctionGun.access$loop(PipelineContext.kt:63)
	at io.ktor.util.pipeline.SuspendFunctionGun.proceed(PipelineContext.kt:111)
	at io.ktor.util.pipeline.SuspendFunctionGun.execute(PipelineContext.kt:131)
	at io.ktor.util.pipeline.Pipeline.execute(Pipeline.kt:24)
	at io.ktor.routing.Routing.executeResult(Routing.kt:148)
	at io.ktor.routing.Routing.interceptor(Routing.kt:29)
	at io.ktor.routing.Routing$Feature$install$1.invokeSuspend(Routing.kt:93)
	at io.ktor.routing.Routing$Feature$install$1.invoke(Routing.kt)
	at io.ktor.util.pipeline.SuspendFunctionGun.loop(PipelineContext.kt:248)
	at io.ktor.util.pipeline.SuspendFunctionGun.access$loop(PipelineContext.kt:63)
	at io.ktor.util.pipeline.SuspendFunctionGun.proceed(PipelineContext.kt:111)
	at io.ktor.features.ContentNegotiation$Feature$install$1.invokeSuspend(ContentNegotiation.kt:60)
	at io.ktor.features.ContentNegotiation$Feature$install$1.invoke(ContentNegotiation.kt)
	at io.ktor.util.pipeline.SuspendFunctionGun.loop(PipelineContext.kt:248)
	at io.ktor.util.pipeline.SuspendFunctionGun.access$loop(PipelineContext.kt:63)
	at io.ktor.util.pipeline.SuspendFunctionGun.proceed(PipelineContext.kt:111)
	at io.ktor.features.CallLogging$Feature$install$2.invokeSuspend(CallLogging.kt:124)
	at io.ktor.features.CallLogging$Feature$install$2.invoke(CallLogging.kt)
	at io.ktor.util.pipeline.SuspendFunctionGun.loop(PipelineContext.kt:248)
	at io.ktor.util.pipeline.SuspendFunctionGun.access$loop(PipelineContext.kt:63)
	at io.ktor.util.pipeline.SuspendFunctionGun.proceed(PipelineContext.kt:111)
	at io.ktor.util.pipeline.SuspendFunctionGun.execute(PipelineContext.kt:131)
	at io.ktor.util.pipeline.Pipeline.execute(Pipeline.kt:24)
	at io.ktor.server.engine.DefaultEnginePipelineKt$defaultEnginePipeline$2.invokeSuspend(DefaultEnginePipeline.kt:80)
	at io.ktor.server.engine.DefaultEnginePipelineKt$defaultEnginePipeline$2.invoke(DefaultEnginePipeline.kt)
	at io.ktor.util.pipeline.SuspendFunctionGun.loop(PipelineContext.kt:248)
	at io.ktor.util.pipeline.SuspendFunctionGun.access$loop(PipelineContext.kt:63)
	at io.ktor.util.pipeline.SuspendFunctionGun.proceed(PipelineContext.kt:111)
	at io.ktor.util.pipeline.SuspendFunctionGun.execute(PipelineContext.kt:131)
	at io.ktor.util.pipeline.Pipeline.execute(Pipeline.kt:24)
	at io.ktor.server.netty.NettyApplicationCallHandler$handleRequest$1.invokeSuspend(NettyApplicationCallHandler.kt:31)
	at io.ktor.server.netty.NettyApplicationCallHandler$handleRequest$1.invoke(NettyApplicationCallHandler.kt)

This code will throw:

fun Application.config() {
    install(ContentNegotiation) {
        gson {
            serializeNulls()
        }
    }
    // ...
}
fun Application.routes() {
    routing {
        post("/something") {
            data class Foo(var bar: Int)
            data class Bar(var foo: Int)
            val foo = call.receive<Foo>()
            val bar = Bar(foo.bar)
            call.respond(bar)
        }
        // ...
    }
}

This code will works:

data class Foo(var bar: Int)
data class Bar(var foo: Int)

fun Application.config() {
    install(ContentNegotiation) {
        gson {
            serializeNulls()
        }
    }
    // ...
}
fun Application.routes() {
    routing {
        post("/something") {
            val foo = call.receive<Foo>()
            val bar = Bar(foo.bar)
            call.respond(bar)
        }
        // ...
    }
}

[cy6erGn0m]

GSON does never deserialize local and anonymous classes thus returns null. Unfortunately ktor doesn't support null deserialization for now so it simply throws UnsupportedMediaTypeException that is confusing.

[cy6erGn0m]

Fixed