suspend controller function returning Unit fails to serialize it

[tmapes]

Expected Behavior

If an @Controller function is both suspend-able and returns Unit i would expect no body to be written to the caller.

Actual Behaviour

Default behavior seems to be to throw a serialization exception, however various @SerdeImport combinations appear to sometimes serialize Unit as an empty object ({}).

Attached repo is the former.

If a controller function returns Unit but isn't suspend-able it works without issue, no body is returned and no exception is thrown.

Stack Trace

18:21:31.401 [kotlinx.coroutines.DefaultExecutor] ERROR i.m.http.server.RouteExecutor - Unexpected error occurred: Error encoding object [kotlin.Unit] to JSON: No serializable introspection present for type Unit. Consider adding Serdeable. Serializable annotate to type Unit. Alternatively if you are not in control of the project's source code, you can use @SerdeImport(Unit.class) to enable serialization of this type. io.micronaut.http.codec.CodecException: Error encoding object [kotlin.Unit] to JSON: No serializable introspection present for type Unit. Consider adding Serdeable. Serializable annotate to type Unit. Alternatively if you are not in control of the project's source code, you can use @SerdeImport(Unit.class) to enable serialization of this type. at io.micronaut.http.netty.body.NettyJsonHandler.writeTo(NettyJsonHandler.java:166) at io.micronaut.http.server.netty.RoutingInBoundHandler.writeNettyMessageBody(RoutingInBoundHandler.java:380) at io.micronaut.http.server.netty.RoutingInBoundHandler.encodeHttpResponse(RoutingInBoundHandler.java:358) at io.micronaut.http.server.netty.RoutingInBoundHandler.writeResponse(RoutingInBoundHandler.java:248) at io.micronaut.http.server.netty.NettyRequestLifecycle.lambda$handleNormal$0(NettyRequestLifecycle.java:101) at io.micronaut.http.reactive.execution.ReactorExecutionFlowImpl$1.onComplete(ReactorExecutionFlowImpl.java:121) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onComplete(Operators.java:2231) at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:159) at reactor.core.publisher.FluxMap$MapSubscriber.onNext(FluxMap.java:122) at reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:74) at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:158) at reactor.core.publisher.MonoCompletionStage$MonoCompletionStageSubscription.apply(MonoCompletionStage.java:121) at reactor.core.publisher.MonoCompletionStage$MonoCompletionStageSubscription.apply(MonoCompletionStage.java:67) at java.base/java.util.concurrent.CompletableFuture.uniHandle(CompletableFuture.java:934) at java.base/java.util.concurrent.CompletableFuture$UniHandle.tryFire(CompletableFuture.java:911) at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:510) at java.base/java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:2179) at io.micronaut.http.bind.binders.CustomContinuation.resumeWith(ContinuationArgumentBinder.kt:120) at kotlinx.coroutines.DispatchedTaskKt.resume(DispatchedTask.kt:175) at kotlinx.coroutines.DispatchedTaskKt.dispatch(DispatchedTask.kt:164) at kotlinx.coroutines.CancellableContinuationImpl.dispatchResume(CancellableContinuationImpl.kt:466) at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl(CancellableContinuationImpl.kt:500) at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl$default(CancellableContinuationImpl.kt:489) at kotlinx.coroutines.CancellableContinuationImpl.resumeUndispatched(CancellableContinuationImpl.kt:587) at kotlinx.coroutines.EventLoopImplBase$DelayedResumeTask.run(EventLoop.common.kt:490) at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:277) at kotlinx.coroutines.DefaultExecutor.run(DefaultExecutor.kt:105) at java.base/java.lang.Thread.run(Thread.java:1583) Caused by: io.micronaut.serde.exceptions.SerdeException: No serializable introspection present for type Unit. Consider adding Serdeable. Serializable annotate to type Unit. Alternatively if you are not in control of the project's source code, you can use @SerdeImport(Unit.class) to enable serialization of this type. at io.micronaut.serde.support.serializers.RuntimeTypeSerializer.lambda$getSerializer$0(RuntimeTypeSerializer.java:135) at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1708) at io.micronaut.serde.support.serializers.RuntimeTypeSerializer.getSerializer(RuntimeTypeSerializer.java:131) at io.micronaut.serde.support.serializers.RuntimeTypeSerializer.serialize(RuntimeTypeSerializer.java:76) at io.micronaut.serde.jackson.JacksonJsonMapper.writeValue(JacksonJsonMapper.java:187) at io.micronaut.serde.jackson.JacksonJsonMapper.writeValue0(JacksonJsonMapper.java:178) at io.micronaut.serde.jackson.JacksonJsonMapper.writeValue0(JacksonJsonMapper.java:173) at io.micronaut.serde.jackson.JacksonJsonMapper.writeValue(JacksonJsonMapper.java:259) at io.micronaut.http.netty.body.NettyJsonHandler.writeTo(NettyJsonHandler.java:163) ... 27 common frames omitted Caused by: io.micronaut.core.beans.exceptions.IntrospectionException: No serializable introspection present for type Unit. Consider adding Serdeable. Serializable annotate to type Unit. Alternatively if you are not in control of the project's source code, you can use @SerdeImport(Unit.class) to enable serialization of this type. at io.micronaut.serde.support.DefaultSerdeIntrospections.getSerializableIntrospection(DefaultSerdeIntrospections.java:111) at io.micronaut.serde.support.serializers.SerBean.(SerBean.java:116) at io.micronaut.serde.support.serializers.ObjectSerializer.lambda$getSerializableBean$0(ObjectSerializer.java:159) at io.micronaut.core.util.SupplierUtil$2.get(SupplierUtil.java:79) at io.micronaut.serde.support.serializers.ObjectSerializer.getSerializableBean(ObjectSerializer.java:164) at io.micronaut.serde.support.serializers.ObjectSerializer.createSpecificInternal(ObjectSerializer.java:104) at io.micronaut.serde.support.serializers.ObjectSerializer.createSpecific(ObjectSerializer.java:96) at io.micronaut.serde.jackson.JacksonJsonMapper.writeValue(JacksonJsonMapper.java:185) ... 31 common frames omitted

Internal Server Error
io.micronaut.http.client.exceptions.HttpClientResponseException: Internal Server Error
at io.micronaut.http.client.netty.DefaultHttpClient$FullHttpResponseHandler.makeErrorFromRequestBody(DefaultHttpClient.java:2259)
at io.micronaut.http.client.netty.DefaultHttpClient$FullHttpResponseHandler.forwardResponseToPromise(DefaultHttpClient.java:2210)
at io.micronaut.http.client.netty.DefaultHttpClient$FullHttpResponseHandler.channelReadInstrumented(DefaultHttpClient.java:2179)
at io.micronaut.http.client.netty.DefaultHttpClient$FullHttpResponseHandler.channelReadInstrumented(DefaultHttpClient.java:2147)
at io.micronaut.http.client.netty.SimpleChannelInboundHandlerInstrumented.channelRead0(SimpleChannelInboundHandlerInstrumented.java:46)
at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:99)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:103)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:103)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:436)
at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:346)
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:318)
at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:251)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
at io.netty.channel.ChannelInboundHandlerAdapter.channelRead(ChannelInboundHandlerAdapter.java:93)
at io.micronaut.http.client.netty.ResettableReadTimeoutHandler$NextInterceptor.channelRead(ResettableReadTimeoutHandler.java:92)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
at io.netty.handler.timeout.IdleStateHandler.channelRead(IdleStateHandler.java:289)
at io.micronaut.http.client.netty.ResettableReadTimeoutHandler.channelRead(ResettableReadTimeoutHandler.java:64)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1407)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:440)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:918)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:788)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:724)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:650)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:562)
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:994)
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:1583)
Suppressed: java.lang.Exception: #block terminated with an error
at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:104)
at reactor.core.publisher.Flux.blockFirst(Flux.java:2766)
at io.micronaut.http.client.netty.DefaultHttpClient$1.exchange(DefaultHttpClient.java:571)
at io.micronaut.http.client.BlockingHttpClient.exchange(BlockingHttpClient.java:77)
at io.micronaut.http.client.BlockingHttpClient.exchange(BlockingHttpClient.java:106)
at com.example.UnitDemoTest.test_deleteAndReturnUnitdeleteAndReturnUnitSuspend(UnitDemoTest.kt:45)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at io.micronaut.test.extensions.junit5.MicronautJunit5Extension$2.proceed(MicronautJunit5Extension.java:142)
at io.micronaut.test.extensions.AbstractMicronautExtension.interceptEach(AbstractMicronautExtension.java:162)
at io.micronaut.test.extensions.AbstractMicronautExtension.interceptTest(AbstractMicronautExtension.java:119)
at io.micronaut.test.extensions.junit5.MicronautJunit5Extension.interceptTestMethod(MicronautJunit5Extension.java:129)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)

Steps To Reproduce

• Clone project
• Set JDK/JRE to 21
• Run included tests

./gradlew test

Environment Information

• macOS (arm)
• Java 21 & 17

Example Application

https://github.com/tmapes/mn-serde-unit

Version

4.5.0

[yawkat]

Can you try with 4.5.1? There was a related fix recently, not sure if it helps micronaut-projects/micronaut-core#10953

[tmapes]

@yawkat After some trial and error I was able to bump my local versions to the snapshots that include that PR but it didn't fix it.

After walking the call chain the RouteExecutor seems to think the return type despite explicitly being Unit in the controller, the isKotlinFunctionReturnTypeUnit value is being set to false.

Seems to come from this instanceof check, it's returning false.

[tmapes]

It's then causing the check here to become truthy, thus causing the body to be set to Unit

[graemerocher]

seems a core bug

[tmapes]

Noted, I'll move to core.