Blocking call when using swagger-ui found by Blockhound

[Simulacron-3]

Bug description

• I am doing dome check with Blockhound on my reactive application to see if there is no blocking call inside my code. If i try to user the swagger-ui page i get this error by Blockhound:

reactor.blockhound.BlockingOperationError: Blocking call! java.io.RandomAccessFile#readBytes
at java.base/java.io.RandomAccessFile.readBytes(RandomAccessFile.java)
Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException:
Error has been observed at the following site(s):
|_ checkpoint ⇢ org.springframework.boot.actuate.metrics.web.reactive.server.MetricsWebFilter [DefaultWebFilterChain]
|_ checkpoint ⇢ HTTP GET "/webjars/swagger-ui/index.html?configUrl=/v3/api-docs/swagger-config" [ExceptionHandlingWebHandler]
Stack trace:
at java.base/java.io.RandomAccessFile.readBytes(RandomAccessFile.java)
at java.base/java.io.RandomAccessFile.read(RandomAccessFile.java:406)
at java.base/java.io.RandomAccessFile.readFully(RandomAccessFile.java:470)
at java.base/java.util.zip.ZipFile$Source.readFullyAt(ZipFile.java:1298)
at java.base/java.util.zip.ZipFile$ZipFileInputStream.initDataOffset(ZipFile.java:997)
at java.base/java.util.zip.ZipFile$ZipFileInputStream.read(ZipFile.java:1012)
at java.base/java.util.zip.ZipFile$ZipFileInflaterInputStream.fill(ZipFile.java:467)
at java.base/java.util.zip.InflaterInputStream.read(InflaterInputStream.java:159)
at java.base/java.io.InputStream.readNBytes(InputStream.java:490)
at java.base/java.util.jar.JarFile.getBytes(JarFile.java:805)
at java.base/java.util.jar.JarFile.checkForSpecialAttributes(JarFile.java:1005)
at java.base/java.util.jar.JarFile.isMultiRelease(JarFile.java:388)
at java.base/java.util.jar.JarFile.getEntry(JarFile.java:507)
at java.base/sun.net.www.protocol.jar.URLJarFile.getEntry(URLJarFile.java:131)
at java.base/sun.net.www.protocol.jar.JarURLConnection.connect(JarURLConnection.java:137)
at java.base/sun.net.www.protocol.jar.JarURLConnection.getContentLengthLong(JarURLConnection.java:182)
at org.springframework.core.io.AbstractFileResolvingResource.isReadable(AbstractFileResolvingResource.java:109)
at org.springframework.web.reactive.resource.PathResourceResolver.getResource(PathResourceResolver.java:117)
at org.springframework.web.reactive.resource.PathResourceResolver.lambda$getResource$1(PathResourceResolver.java:99)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.drain(FluxConcatMap.java:367)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.onSubscribe(FluxConcatMap.java:211)
at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:161)
at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:86)
at reactor.core.publisher.MonoFromFluxOperator.subscribe(MonoFromFluxOperator.java:81)
at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
at reactor.core.publisher.Mono.subscribe(Mono.java:4213)
at reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onComplete(FluxSwitchIfEmpty.java:75)
at reactor.core.publisher.MonoNext$NextSubscriber.onComplete(MonoNext.java:96)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.drain(FluxConcatMap.java:359)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.onSubscribe(FluxConcatMap.java:211)
at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:161)
at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:86)
at reactor.core.publisher.Mono.subscribe(Mono.java:4213)
at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.drain(MonoIgnoreThen.java:172)
at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:56)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:150)
at reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:67)
at reactor.core.publisher.MonoNext$NextSubscriber.onNext(MonoNext.java:76)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.innerNext(FluxConcatMap.java:274)
at reactor.core.publisher.FluxConcatMap$ConcatMapInner.onNext(FluxConcatMap.java:851)
at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:121)
at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2344)
at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.request(FluxMapFuseable.java:162)
at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.set(Operators.java:2152)
at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onSubscribe(Operators.java:2026)
at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onSubscribe(FluxMapFuseable.java:90)
at reactor.core.publisher.MonoJust.subscribe(MonoJust.java:54)
at reactor.core.publisher.Mono.subscribe(Mono.java:4213)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.drain(FluxConcatMap.java:441)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.onSubscribe(FluxConcatMap.java:211)
at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:161)
at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:86)
at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
at reactor.core.publisher.Mono.subscribe(Mono.java:4213)
at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.drain(MonoIgnoreThen.java:172)
at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:56)
at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
at reactor.netty.http.server.HttpServerHandle.onStateChange(HttpServerHandle.java:65)
at reactor.netty.ReactorNetty$CompositeConnectionObserver.onStateChange(ReactorNetty.java:518)
at reactor.netty.tcp.TcpServerBind$ChildObserver.onStateChange(TcpServerBind.java:272)
at reactor.netty.http.server.HttpServerOperations.onInboundNext(HttpServerOperations.java:462)
at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:96)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)
at reactor.netty.http.server.HttpTrafficHandler.channelRead(HttpTrafficHandler.java:172)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)
at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:436)
at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:324)
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:296)
at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:251)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)
at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:714)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:650)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:576)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493)
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989)
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)

To Reproduce
Steps to reproduce the behavior:

• spring boot version 2.3.4-RELEASE
• springdoc-openapi-webflux-ui version1.4.8
• json
• to reproduce the problem you just need to add blockhound as dependency and activate it like this in your starter class
  public static void main(String[] args) { BlockHound.install(); SpringApplication.run(YuorApplication.class, args); }
  the you must try to access to the swagger html page
  Expected behavior
• i was expecting not to have a blocking call.(although i am not totally sure this is a issue i just want to understand what is happening)

Screenshots

Additional context

[bnasslahsen]

@Simulacron-3,

We are unable to reproduce your issue with the provided information.
If you can add a minimal reproducible sample, this ticket can be then reopened.

[Simulacron-3]

Hi, you can refer to this example code

https://github.com/Simulacron-3/SpringOpenAPIBlockhound.git

After the startup if you go to
http://localhost:8080/webjars/swagger-ui/index.html?configUrl=/v3/api-docs/swagger-config
you can find in the log the same stacktrace i have written in my previous post

[bnasslahsen]

@Simulacron-3,

Note that your project isn't even starting because your having this line on your pom.xml (scope provided):

• https://github.com/Simulacron-3/SpringOpenAPIBlockhound/blob/418ba4b1e7f17201eb613b17b0822607e0f467d5/pom.xml#L52

After removing scope provided: The application starts and the swagger url is accessible without any issue.