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Reading 'null' JSON response via WebClient fails in v5.2.x #23935

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Reading 'null' JSON response via WebClient fails in v5.2.x#23935
Assignees
poutsma
Labels
in: webIssues in web modules (web, webmvc, webflux, websocket)type: regressionA bug that is also a regression
Milestone
5.2.2
@ckubik-monster

Description

@ckubik-monster
ckubik-monster
opened on Nov 5, 2019

WebClient is not able to read null JSON response in both v5.2.0 and v5.2.1, however at least in v5.1.x it works as expected and empty result was correctly retrieved.

Code to reproduce the problem

Sample project with the failing test:
webclient-null-json-sample.zip

import static org.junit.jupiter.api.Assertions.assertNull;

import java.io.IOException;
import java.util.Map;
import okhttp3.mockwebserver.MockResponse;
import okhttp3.mockwebserver.MockWebServer;
import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.web.reactive.function.client.WebClient;

class WebClientJsonNullTest {

  //dependency: com.squareup.okhttp3:mockwebserver:4.2.2
  private static MockWebServer mockWebServer;

  @BeforeAll
  public static void startMockWebServer() throws IOException {
    mockWebServer = new MockWebServer();
    mockWebServer.start();
  }

  @AfterAll
  public static void shutdownMockWebServer() throws IOException {
    mockWebServer.shutdown();
  }

  //this test is failing in v5.2, in v5.1 passes
  @Test
  void nullJsonResponse_shouldBeReadAsEmpty() {
    WebClient webClient = WebClient.builder().build();

    mockWebServer.enqueue(new MockResponse()
        .setResponseCode(200)
        .setHeader(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
        .setBody("null"));

    Map<?, ?> result = webClient.get()
        .uri(mockWebServer.url("/").uri())
        .retrieve()
        .bodyToMono(Map.class)
        .block();
    assertNull(result);
  }
}

Following NPE is thrown:


java.lang.NullPointerException: The mapper returned a null value.

	at java.base/java.util.Objects.requireNonNull(Objects.java:246)
	Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
	|_ checkpoint ⇢ Body from GET http://localhost:54097/ [DefaultClientResponse]
Stack trace:
		at java.base/java.util.Objects.requireNonNull(Objects.java:246)
		at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:107)
		at reactor.core.publisher.FluxContextStart$ContextStartSubscriber.onNext(FluxContextStart.java:103)
		at reactor.core.publisher.FluxContextStart$ContextStartSubscriber.onNext(FluxContextStart.java:103)
		at reactor.core.publisher.FluxMapFuseable$MapFuseableConditionalSubscriber.onNext(FluxMapFuseable.java:287)
		at reactor.core.publisher.FluxFilterFuseable$FilterFuseableConditionalSubscriber.onNext(FluxFilterFuseable.java:330)
		at reactor.core.publisher.Operators$MonoSubscriber.complete(Operators.java:1592)
		at reactor.core.publisher.MonoCollect$CollectSubscriber.onComplete(MonoCollect.java:145)
		at reactor.core.publisher.FluxMap$MapSubscriber.onComplete(FluxMap.java:136)
		at reactor.core.publisher.FluxPeek$PeekSubscriber.onComplete(FluxPeek.java:252)
		at reactor.core.publisher.FluxPeek$PeekSubscriber.onComplete(FluxPeek.java:252)
		at reactor.core.publisher.FluxMap$MapSubscriber.onComplete(FluxMap.java:136)
		at reactor.netty.channel.FluxReceive.terminateReceiver(FluxReceive.java:397)
		at reactor.netty.channel.FluxReceive.drainReceiver(FluxReceive.java:197)
		at reactor.netty.channel.FluxReceive.onInboundComplete(FluxReceive.java:345)
		at reactor.netty.channel.ChannelOperations.onInboundComplete(ChannelOperations.java:363)
		at reactor.netty.channel.ChannelOperations.terminate(ChannelOperations.java:412)
		at reactor.netty.http.client.HttpClientOperations.onInboundNext(HttpClientOperations.java:556)
		at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:91)
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
		at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
		at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:102)
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
		at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
		at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:438)
		at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:328)
		at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:302)
		at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:253)
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
		at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
		at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1421)
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
		at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:930)
		at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:163)
		at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:697)
		at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:632)
		at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:549)
		at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:511)
		at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:918)
		at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
		at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
		at java.base/java.lang.Thread.run(Thread.java:834)
	Suppressed: java.lang.Exception: #block terminated with an error
		at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:93)
		at reactor.core.publisher.Mono.block(Mono.java:1663)
		at WebClientJsonNullTest.nullJsonResponse_shouldBeReadAsEmpty(WebClientJsonNullTest.java:43)
		at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
		at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
		at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
		at java.base/java.lang.reflect.Method.invoke(Method.java:566)
		at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:675)
		at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
		at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:125)
		at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:132)
		at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:124)
		at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:74)
		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:104)
		at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:62)
		at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:43)
		at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:35)
		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$6(TestMethodTestDescriptor.java:202)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:198)
		at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:135)
		at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:69)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:135)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
		at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
		at java.base/java.util.ArrayList.forEach(ArrayList.java:1540)
		at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
		at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
		at java.base/java.util.ArrayList.forEach(ArrayList.java:1540)
		at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
		at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
		at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
		at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
		at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
		at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
		at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:229)
		at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$6(DefaultLauncher.java:197)
		at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:211)
		at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:191)
		at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:128)
		at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:69)
		at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
		at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
		at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

That null comes from decoding JSON response body via Jackson2JsonDecoder.

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in: webIssues in web modules (web, webmvc, webflux, websocket)type: regressionA bug that is also a regression

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