如何处理 reactor-netty 在 spring-webflux 中终止请求？

Question

We have a spring-webflux application running on spring-boot-starter-webflux:jar:2.1.5.RELEASE and reactor-netty:jar:0.8.8.RELEASE . When a reactive client goes away (k8s pod killed or the client subscription is disposed off) before the request is completed, we see the server simply stops processing the request and no more application logs related to that request are seen. However, reactive-netty prints a trace log indicating that the channel is inactive and will be terminated.

Is there anything we can do to handle this termination gracefully? We would ideally like to respond to a cancellation signal from reactor.

2020-03-18T16:46:40.372Z TRACE --- [reactor-http-epoll-2] r.n.c.ChannelOperations : [id: 0x4cad974b, L:/<SERVER_IP_ADDRESS>:8080 ! R:/<SOME_OTHER_IP_ADDRESS>:55436] Disposing ChannelOperation from a channel
java.lang.Exception: ChannelOperation terminal stack
    at reactor.netty.channel.ChannelOperations.terminate(ChannelOperations.java:391)
    at reactor.netty.channel.ChannelOperations.onInboundClose(ChannelOperations.java:360)
    at reactor.netty.channel.ChannelOperationsHandler.channelInactive(ChannelOperationsHandler.java:72)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:257)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:243)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:236)
    at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelInactive(CombinedChannelDuplexHandler.java:420)
    at io.netty.handler.codec.ByteToMessageDecoder.channelInputClosed(ByteToMessageDecoder.java:393)
    at io.netty.handler.codec.ByteToMessageDecoder.channelInactive(ByteToMessageDecoder.java:358)
    at io.netty.channel.CombinedChannelDuplexHandler.channelInactive(CombinedChannelDuplexHandler.java:223)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:257)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:243)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:236)
    at io.netty.channel.DefaultChannelPipeline$HeadContext.channelInactive(DefaultChannelPipeline.java:1416)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:257)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:243)
    at io.netty.channel.DefaultChannelPipeline.fireChannelInactive(DefaultChannelPipeline.java:912)
    at io.netty.channel.AbstractChannel$AbstractUnsafe$8.run(AbstractChannel.java:816)
    at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163)
    at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:416)
    at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:331)
    at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:918)
    at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
    at java.base/java.lang.Thread.run(Thread.java:834)

Answer 1

The doOnCancel operator allows for a callback to be provided when a subscription is cancelled. This is different from the doOnEach operator which is run only when the subscription completes or errors out.

https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Mono.html#doOnCancel-java.lang.Runnable-