Confusing WebClient exception message in case of Reactor-Netty `PrematureCloseException` during response

[david0]

We are using WebClient+netty. We have run into
reactor.netty.http.client.PrematureCloseException: Connection prematurely closed DURING response.

Unfortunately the WebClientResponseException.getMessage() will just return
200 OK from POST http://localhost:50457/foo
in this case, not giving any helpful detail what the problem was.

Maybe the original exception message (Connection prematurely closed DURING response) should be shown or just some generic An error happend while reading the response? Everything would be better than 200 OK from ...

[simonbasle]

If you'd like us to spend some time investigating, please take the time to provide a complete minimal sample (something that we can unzip or git clone, build, and deploy) that reproduces the problem. At a very minimum, more details like the full stacktrace.

Please also have a look at this FAQ from the Reactor-Netty project: https://projectreactor.io/docs/netty/release/reference/index.html#faq.connection-closed

[david0]

Thanks for the link, was not aware of that (but i was able to reproduce it with curl nevertheless).

Please find a example here that reproduces this error: https://github.com/david0/mre-spring-issue-33127-webclient/blob/main/src/test/java/com/github/david0/webclient_prematureend/WebclientTest.java#L29

Example stacktrace:

org.springframework.web.reactive.function.client.WebClientResponseException: 200 OK from POST http://localhost:54029/
	at org.springframework.web.reactive.function.client.WebClientResponseException.create(WebClientResponseException.java:323)
	at org.springframework.web.reactive.function.client.DefaultClientResponse.lambda$createException$1(DefaultClientResponse.java:214)
	at reactor.core.publisher.FluxMap$MapSubscriber.onNext(FluxMap.java:106)
	at reactor.core.publisher.FluxOnErrorReturn$ReturnSubscriber.onError(FluxOnErrorReturn.java:199)
	at reactor.core.publisher.FluxDefaultIfEmpty$DefaultIfEmptySubscriber.onError(FluxDefaultIfEmpty.java:156)
	at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.onError(FluxOnAssembly.java:544)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onError(FluxMapFuseable.java:142)
	at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onError(FluxContextWrite.java:121)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableConditionalSubscriber.onError(FluxMapFuseable.java:340)
	at reactor.core.publisher.FluxFilterFuseable$FilterFuseableConditionalSubscriber.onError(FluxFilterFuseable.java:382)
	at reactor.core.publisher.MonoCollect$CollectSubscriber.onError(MonoCollect.java:135)
	at reactor.core.publisher.FluxMap$MapSubscriber.onError(FluxMap.java:134)
	at reactor.core.publisher.FluxPeek$PeekSubscriber.onError(FluxPeek.java:222)
	at reactor.core.publisher.FluxMap$MapSubscriber.onError(FluxMap.java:134)
	at reactor.core.publisher.Operators.error(Operators.java:198)
	at reactor.netty.channel.FluxReceive.startReceiver(FluxReceive.java:177)
	at reactor.netty.channel.FluxReceive.subscribe(FluxReceive.java:147)
	at reactor.core.publisher.InternalFluxOperator.subscribe(InternalFluxOperator.java:68)
	at reactor.netty.ByteBufFlux.subscribe(ByteBufFlux.java:340)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4568)
	at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:103)
	at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.onError(FluxOnAssembly.java:544)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onError(MonoFlatMap.java:180)
	at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onError(FluxContextWrite.java:121)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableConditionalSubscriber.onError(FluxMapFuseable.java:340)
	at reactor.core.publisher.FluxFilterFuseable$FilterFuseableConditionalSubscriber.onError(FluxFilterFuseable.java:382)
	at reactor.core.publisher.MonoCollect$CollectSubscriber.onError(MonoCollect.java:135)
	at reactor.core.publisher.FluxMap$MapSubscriber.onError(FluxMap.java:134)
	at reactor.core.publisher.FluxPeek$PeekSubscriber.onError(FluxPeek.java:222)
	at reactor.core.publisher.FluxMap$MapSubscriber.onError(FluxMap.java:134)
	at reactor.netty.channel.FluxReceive.onInboundError(FluxReceive.java:465)
	at reactor.netty.channel.ChannelOperations.onInboundError(ChannelOperations.java:515)
	at reactor.netty.http.client.HttpClientOperations.onInboundClose(HttpClientOperations.java:328)
	at reactor.netty.channel.ChannelOperationsHandler.channelInactive(ChannelOperationsHandler.java:73)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:303)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:281)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:274)
	at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelInactive(CombinedChannelDuplexHandler.java:418)
	at io.netty.handler.codec.ByteToMessageDecoder.channelInputClosed(ByteToMessageDecoder.java:412)
	at io.netty.handler.codec.ByteToMessageDecoder.channelInactive(ByteToMessageDecoder.java:377)
	at io.netty.handler.codec.http.HttpClientCodec$Decoder.channelInactive(HttpClientCodec.java:410)
	at io.netty.channel.CombinedChannelDuplexHandler.channelInactive(CombinedChannelDuplexHandler.java:221)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:303)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:281)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:274)
	at io.netty.channel.DefaultChannelPipeline$HeadContext.channelInactive(DefaultChannelPipeline.java:1402)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:301)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:281)
	at io.netty.channel.DefaultChannelPipeline.fireChannelInactive(DefaultChannelPipeline.java:900)
	at io.netty.channel.AbstractChannel$AbstractUnsafe$7.run(AbstractChannel.java:811)
	at io.netty.util.concurrent.AbstractEventExecutor.runTask(AbstractEventExecutor.java:173)
	at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:166)
	at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:469)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:566)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:994)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.base/java.lang.Thread.run(Thread.java:840)
	Suppressed: java.lang.Exception: #block terminated with an error
		at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:104)
		at reactor.core.publisher.Mono.block(Mono.java:1779)
		at com.github.david0.webclient_prematureend.WebclientTest.lambda$test$3(WebclientTest.java:38)
		at org.junit.jupiter.api.AssertThrows.assertThrows(AssertThrows.java:53)
		at org.junit.jupiter.api.AssertThrows.assertThrows(AssertThrows.java:35)
		at org.junit.jupiter.api.Assertions.assertThrows(Assertions.java:3115)
		at com.github.david0.webclient_prematureend.WebclientTest.test(WebclientTest.java:35)
		at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
		at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
		at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
		at java.base/java.lang.reflect.Method.invoke(Method.java:568)
		at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:728)
		at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
		at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
		at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:156)
		at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:147)
		at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:86)
		at org.junit.jupiter.engine.execution.InterceptingExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(InterceptingExecutableInvoker.java:103)
		at org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.lambda$invoke$0(InterceptingExecutableInvoker.java:93)
		at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
		at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
		at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
		at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
		at org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.invoke(InterceptingExecutableInvoker.java:92)
		at org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.invoke(InterceptingExecutableInvoker.java:86)
		at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$7(TestMethodTestDescriptor.java:218)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:214)
		at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:139)
		at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:69)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:151)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
		at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
		at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
		at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
		at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
		at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
		at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
		at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
		at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:35)
		at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
		at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:54)
		at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:198)
		at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:169)
		at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:93)
		at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:58)
		at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:141)
		at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:57)
		at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:103)
		at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:85)
		at org.junit.platform.launcher.core.DelegatingLauncher.execute(DelegatingLauncher.java:47)
		at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.processAllTestClasses(JUnitPlatformTestClassProcessor.java:119)
		at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.access$000(JUnitPlatformTestClassProcessor.java:94)
		at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor.stop(JUnitPlatformTestClassProcessor.java:89)
		at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.stop(SuiteTestClassProcessor.java:62)
		at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
		at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
		at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
		at java.base/java.lang.reflect.Method.invoke(Method.java:568)
		at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
		at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
		at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:33)
		at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:94)
		at jdk.proxy1/jdk.proxy1.$Proxy2.stop(Unknown Source)
		at org.gradle.api.internal.tasks.testing.worker.TestWorker$3.run(TestWorker.java:193)
		at org.gradle.api.internal.tasks.testing.worker.TestWorker.executeAndMaintainThreadName(TestWorker.java:129)
		at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:100)
		at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:60)
		at org.gradle.process.internal.worker.child.ActionExecutionWorker.execute(ActionExecutionWorker.java:56)
		at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:119)
		at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:66)
		at worker.org.gradle.process.internal.worker.GradleWorkerMain.run(GradleWorkerMain.java:69)
		at worker.org.gradle.process.internal.worker.GradleWorkerMain.main(GradleWorkerMain.java:74)
Caused by: reactor.netty.http.client.PrematureCloseException: Connection prematurely closed DURING response
	Suppressed: The stacktrace has been enhanced by Reactor, refer to additional information below: 
Error has been observed at the following site(s):
	*__checkpoint ⇢ Body from POST http://localhost:54029/ [DefaultClientResponse]
	*__checkpoint ⇢ Body from POST http://localhost:54029/ [DefaultClientResponse]
Original Stack Trace:

[simonbasle]

Mmh the faq I have provided is perhaps not that relevant, as it is about a PrematureCloseException with "BEFORE response" message, not DURING response.

I think this is more symptomatic of an issue on the remote server's side (which could be triggered by the payload on your client side). The test you have provided is representative of that, as it triggers an IO error in the wiremock server by writing a content-length header then an incomplete body that doesn't match.

However the exception message's signal-to-noise ratio seems a bit off balance here, indeed. I'll discuss with the team how we can best improve the situation without masking the need for an actual root cause investigation on the user's part.