Spring webclient throws “Only one connection receive subscriber allowed” when response does not contain media type header

Question

Refer the test case at which simulates the issue. https://github.com/nischit7/my-exp-webflux-stream/blob/master/src/test/java/com/example/spring/stream/controller/MoreThanOnSubscriberTest.java

In essence, I am bringing up a mock server which is supposed to return NO media type header.

On running that test, I get an error - java.lang.IllegalStateException: Only one connection receive subscriber allowed.

at reactor.netty.channel.FluxReceive.startReceiver(FluxReceive.java:277)
at reactor.netty.channel.FluxReceive.subscribe(FluxReceive.java:127)
at reactor.core.publisher.FluxMap.subscribe(FluxMap.java:62)
at reactor.netty.ByteBufFlux.subscribe(ByteBufFlux.java:290)
at reactor.core.publisher.FluxMap.subscribe(FluxMap.java:62)
at reactor.core.publisher.FluxMap.subscribe(FluxMap.java:62)
at reactor.core.publisher.Flux.subscribe(Flux.java:7734)
at reactor.core.publisher.FluxConcatArray$ConcatArraySubscriber.onComplete(FluxConcatArray.java:207)
at reactor.core.publisher.MonoIgnoreElements$IgnoreElementsSubscriber.onComplete(MonoIgnoreElements.java:81)
at reactor.core.publisher.MonoIgnoreElements$IgnoreElementsSubscriber.onComplete(MonoIgnoreElements.java:81)
at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onComplete(Operators.java:1713)
at reactor.core.publisher.FluxMap$MapSubscriber.onComplete(FluxMap.java:136)
at reactor.core.publisher.FluxMap$MapSubscriber.onComplete(FluxMap.java:136)
at reactor.core.publisher.FluxMap$MapSubscriber.onComplete(FluxMap.java:136)
at reactor.netty.channel.FluxReceive.terminateReceiver(FluxReceive.java:378)
at reactor.netty.channel.FluxReceive.drainReceiver(FluxReceive.java:202)
at reactor.netty.channel.FluxReceive.onInboundComplete(FluxReceive.java:343)
at reactor.netty.channel.ChannelOperations.onInboundComplete(ChannelOperations.java:325)
at reactor.netty.channel.ChannelOperations.terminate(ChannelOperations.java:372)
at reactor.netty.http.client.HttpClientOperations.onInboundNext(HttpClientOperations.java:522)
at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:141)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:102)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:438)
at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:310)
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:284)
at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:253)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1434)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:965)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:163)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:628)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:563)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:480)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:442)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884)
at java.lang.Thread.run(Thread.java:748)
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:1475)
    at com.example.spring.stream.controller.MoreThanOnSubscriberTest.moreThanOneSubscriberError(MoreThanOnSubscriberTest.java:83)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.execution.junit.IdeaTestRunner$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)

Note the line number 69 in that test class. I have intentionally commented it. Now uncomment the line and re-rerun the test case. This time, it should be successful. Comment that line again.

Now another interesting thing to note. When you change the version of spring-webflux to 5.0.10.RELEASE, you should see it successful. Change the version of spring-webflix to 5.1.1.RELEASE, it will fail. So obviously something has changed. I do see spring finds no content-type response header and defaults it to octet stream. After which I have not digged further, why it fails.

Any help is appreciated.

Answer 1

Seems like this issue has now been resolved. I had logged this bug with spring community https://jira.spring.io/browse/SPR-17482 . The ticked has been marked resolved with fix coming in spring-webflux 5.1.3.