skywalking: Webflux plugin throw ClassCastException when defining a filter

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• Why do you submit this issue?
• Question or discussion
• Bug
• Requirement
• Feature or performance improvement

---

Bug

• Which version of SkyWalking, OS and JRE? apm-webflux-5.x-plugin-6.4.0-SNAPSHOT, centos7, jdk8

• What happen? I define a filter:

@Component
public class MyFilter implements WebFilter {

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
        return chain.filter(new MyServerWebExchangeDecorator(exchange));
    }

    public static class MyServerWebExchangeDecorator extends ServerWebExchangeDecorator {
        public MyServerWebExchangeDecorator(ServerWebExchange delegate) {
            super(delegate);
        }
    }

}

@RestController
public class HelloController {

    @GetMapping("/hello")
    public Mono<String> hello() {
        return Mono.just("Hello World");
    }

}

and the plugin will throw ClassCastException:

DEBUG 2019-09-02 09:42:53:591 reactor-http-nio-2 AbstractClassEnhancePluginDefine :  prepare to enhance class org.springframework.web.server.adapter.DefaultServerWebExchange by org.apache.skywalking.apm.plugin.spring.webflux.v5.define.DefaultServerWebExchangeInstrumentation.
DEBUG 2019-09-02 09:42:53:592 reactor-http-nio-2 AbstractClassEnhancePluginDefine :  enhance class org.springframework.web.server.adapter.DefaultServerWebExchange by org.apache.skywalking.apm.plugin.spring.webflux.v5.define.DefaultServerWebExchangeInstrumentation completely.
DEBUG 2019-09-02 09:42:53:592 reactor-http-nio-2 SkyWalkingAgent :  Finish the prepare stage for org.springframework.web.server.adapter.DefaultServerWebExchange.
DEBUG 2019-09-02 09:42:53:598 reactor-http-nio-2 SkyWalkingAgent :  On Transformation class org.springframework.web.server.adapter.DefaultServerWebExchange.
ERROR 2019-09-02 09:42:53:631 reactor-http-nio-2 InstMethodsInter :  class[class org.springframework.web.reactive.DispatcherHandler] before method[handle] intercept failure
java.lang.ClassCastException: com.example.MyFilter$MyServerWebExchangeDecorator cannot be cast to org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.EnhancedInstance
	at org.apache.skywalking.apm.plugin.spring.webflux.v5.DispatcherHandlerHandleMethodInterceptor.beforeMethod(DispatcherHandlerHandleMethodInterceptor.java:51)
	at org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.InstMethodsInter.intercept(InstMethodsInter.java:82)
	at org.springframework.web.reactive.DispatcherHandler.handle(DispatcherHandler.java)
	at org.springframework.web.server.handler.DefaultWebFilterChain.lambda$filter$0(DefaultWebFilterChain.java:122)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:44)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
	at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44)
	at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44)
	at reactor.core.publisher.MonoPeekTerminal.subscribe(MonoPeekTerminal.java:61)
	at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44)
	at reactor.core.publisher.Mono.subscribe(Mono.java:3848)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.drain(MonoIgnoreThen.java:172)
	at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:56)
	at reactor.core.publisher.MonoPeekFuseable.subscribe(MonoPeekFuseable.java:70)
	at reactor.core.publisher.MonoPeekTerminal.subscribe(MonoPeekTerminal.java:61)
	at reactor.netty.http.server.HttpServerHandle.onStateChange(HttpServerHandle.java:64)
	at reactor.netty.tcp.TcpServerBind$ChildObserver.onStateChange(TcpServerBind.java:226)
	at reactor.netty.http.server.HttpServerOperations.onInboundNext(HttpServerOperations.java:442)
	at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:91)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
	at reactor.netty.http.server.HttpTrafficHandler.channelRead(HttpTrafficHandler.java:161)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
	at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:438)
	at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:323)
	at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:297)
	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$HeadContext.channelRead(DefaultChannelPipeline.java:1408)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
	at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:930)
	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:163)
	at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:682)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:617)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:534)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:496)
	at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:906)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at java.lang.Thread.run(Thread.java:748)

and can fix it by HierarchyMatch in DefaultServerWebExchangeInstrumentation:

public class DefaultServerWebExchangeInstrumentation extends ClassInstanceMethodsEnhancePluginDefine {

    @Override
    protected ClassMatch enhanceClass() {
        return byHierarchyMatch(new String[] {"org.springframework.web.server.ServerWebExchange"});
    }
    ......
}