Spring WebTestClient.post MULTIPART_FORM_DATA causes Blockhound BlockingOperationError

Affects: Spring Boot 2.4.5 (Spring Framework 5.3.6)

I am using Spring Boot 2.4.5 (Spring Framework 5.3.6) with io.projectreactor.tools:blockhound-junit-platform.

I recently got into a blocking call issue in following code.

String csv = Files.readString(Paths.get("src/test/resources/sample.csv"));
WebTestClient.bindToRouterFunction(routerFunction).build()
                    .post()
                    .uri("/csvUpload")
                    .contentType(MediaType.MULTIPART_FORM_DATA)
                    .accept(MediaType.APPLICATION_JSON)
                    .body(BodyInserters.fromMultipartData("csv", csv))
                    .exchange()
                    .expectStatus()
                    .isNoContent();

And the exception trace is below:

Blocking call! java.io.FileInputStream#readBytes; nested exception is reactor.blockhound.BlockingOperationError: Blocking call! java.io.FileInputStream#readBytes
org.springframework.web.reactive.function.client.WebClientRequestException: Blocking call! java.io.FileInputStream#readBytes; nested exception is reactor.blockhound.BlockingOperationError: Blocking call! java.io.FileInputStream#readBytes
    at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.lambda$wrapException$9(ExchangeFunctions.java:141)
    at reactor.core.publisher.MonoErrorSupplied.subscribe(MonoErrorSupplied.java:70)
    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)
    at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:103)
    at reactor.core.publisher.FluxPeek$PeekSubscriber.onError(FluxPeek.java:221)
    at reactor.core.publisher.FluxPeek$PeekSubscriber.onError(FluxPeek.java:221)
    at reactor.core.publisher.FluxMap$MapSubscriber.onError(FluxMap.java:132)
    at reactor.core.publisher.MonoSubscribeOn$SubscribeOnSubscriber.onError(MonoSubscribeOn.java:152)
    at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onError(MonoIgnoreThen.java:270)
    at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:106)
    at reactor.core.publisher.Operators.error(Operators.java:197)
    at reactor.core.publisher.MonoError.subscribe(MonoError.java:52)
    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)
    at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:103)
    at reactor.core.publisher.MonoWhen$WhenCoordinator.signalError(MonoWhen.java:172)
    at reactor.core.publisher.MonoWhen$WhenInner.onError(MonoWhen.java:288)
    at reactor.core.publisher.SinkEmptyMulticast.subscribe(SinkEmptyMulticast.java:168)
    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)
    at reactor.core.publisher.MonoWhen$WhenCoordinator.subscribe(MonoWhen.java:160)
    at reactor.core.publisher.MonoWhen.subscribe(MonoWhen.java:99)
    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)
    at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:255)
    at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:51)
    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)
    at reactor.core.publisher.MonoSubscribeOn$SubscribeOnSubscriber.run(MonoSubscribeOn.java:126)
    at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:84)
    at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:37)
    at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
    at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at java.base/java.lang.Thread.run(Thread.java:834)
    Suppressed: java.lang.Exception: #block terminated with an error
        at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:139)
        at reactor.core.publisher.Mono.block(Mono.java:1727)
        at org.springframework.test.web.reactive.server.DefaultWebTestClient$DefaultRequestBodyUriSpec.exchange(DefaultWebTestClient.java:358)
        at my.group.router.handler.CsvApiHandlerTest.shouldImportCsvSuccessfully(CsvApiHandlerTest.java:76)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:688)
        at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
        at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
        at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
        at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)
        at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)
        at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
        at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
        at org.junit.jupiter.engine.execution.InvocationInterceptorChain$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.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
        at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
        at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:210)
        at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
        at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:206)
        at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:131)
        at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:65)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
        at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
        at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
        at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
        at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
        at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
        at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
        at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
        at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
        at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
        at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
        at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
        at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
        at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
        at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
        at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
        at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:108)
        at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)
        at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)
        at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)
        at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)
        at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:96)
        at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:75)
        at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.processAllTestClasses(JUnitPlatformTestClassProcessor.java:99)
        at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.access$000(JUnitPlatformTestClassProcessor.java:79)
        at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor.stop(JUnitPlatformTestClassProcessor.java:75)
        at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.stop(SuiteTestClassProcessor.java:61)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
        at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
        at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:33)
        at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:94)
        at com.sun.proxy.$Proxy5.stop(Unknown Source)
        at org.gradle.api.internal.tasks.testing.worker.TestWorker.stop(TestWorker.java:135)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
        at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
        at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:182)
        at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:164)
        at org.gradle.internal.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:414)
        at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:64)
        at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:48)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
        at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:56)
        at java.base/java.lang.Thread.run(Unknown Source)
Caused by: reactor.blockhound.BlockingOperationError: Blocking call! java.io.FileInputStream#readBytes
    at java.base/java.io.FileInputStream.readBytes(FileInputStream.java)
    at java.base/java.io.FileInputStream.read(FileInputStream.java:279)
    at java.base/java.io.FilterInputStream.read(FilterInputStream.java:133)
    at java.base/sun.security.provider.NativePRNG$RandomIO.readFully(NativePRNG.java:424)
    at java.base/sun.security.provider.NativePRNG$RandomIO.ensureBufferValid(NativePRNG.java:526)
    at java.base/sun.security.provider.NativePRNG$RandomIO.implNextBytes(NativePRNG.java:545)
    at java.base/sun.security.provider.NativePRNG.engineNextBytes(NativePRNG.java:220)
    at java.base/java.security.SecureRandom.nextBytes(SecureRandom.java:751)
    at java.base/java.security.SecureRandom.next(SecureRandom.java:808)
    at java.base/java.util.Random.nextInt(Random.java:390)
    at org.springframework.util.MimeTypeUtils.generateMultipartBoundary(MimeTypeUtils.java:390)
    at org.springframework.http.codec.multipart.MultipartWriterSupport.generateMultipartBoundary(MultipartWriterSupport.java:104)
    at org.springframework.http.codec.multipart.MultipartHttpMessageWriter.writeMultipart(MultipartHttpMessageWriter.java:185)
    at org.springframework.http.codec.multipart.MultipartHttpMessageWriter.lambda$write$0(MultipartHttpMessageWriter.java:158)
    at reactor.core.publisher.FluxFlatMap.trySubscribeScalarMap(FluxFlatMap.java:152)
    at reactor.core.publisher.MonoFlatMap.subscribeOrReturn(MonoFlatMap.java:53)
    at reactor.core.publisher.Mono.subscribe(Mono.java:4135)
    at reactor.core.publisher.Mono.subscribeWith(Mono.java:4265)
    at reactor.core.publisher.Mono.subscribe(Mono.java:4121)
    at reactor.core.publisher.Mono.subscribe(Mono.java:4057)
    at org.springframework.test.web.reactive.server.HttpHandlerConnector.doConnect(HttpHandlerConnector.java:112)
    at org.springframework.test.web.reactive.server.HttpHandlerConnector.lambda$connect$0(HttpHandlerConnector.java:79)
    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:44)
    ... 9 more

Comment From: sbrannen

Related issues:

21176
21512
26955

Comment From: rstoyanchev

WebTestClient is expected to be called directly from test methods where the thread isn't marked as non-blocking and therefore I would not expect the given code snippet to block in those circumstances. The stacktrace, however, seems to indicate there is more going on with surrounding code that uses multicast sink and error handling?

Comment From: spring-projects-issues

If you would like us to look at this issue, please provide the requested information. If the information is not provided within the next 7 days this issue will be closed.

Comment From: spring-projects-issues

Closing due to lack of requested feedback. If you would like us to look at this issue, please provide the requested information and we will re-open the issue.

Spring WebTestClient.post MULTIPART_FORM_DATA causes Blockhound BlockingOperationError

21176

21512

26955