[GitHub] [skywalking] thas1024 opened a new issue, #10776: [Bug]

["thas1024 (via GitHub)" <gi...@apache.org>]

thas1024 opened a new issue, #10776:
URL: https://github.com/apache/skywalking/issues/10776

   ### Search before asking
   
   - [X] I had searched in the [issues](https://github.com/apache/skywalking/issues?q=is%3Aissue) and found no similar issues.
   
   
   ### Apache SkyWalking Component
   
   Java Agent (apache/skywalking-java)
   
   ### What happened
   
   在使用spring-mvc5和skywalking-java-agent进行链路追踪的过程中，我发现了一个问题：当springmvc中Controller的方法返回ResponseBodyEmitter类型，并通过异步方式发送响应结果时，链路追踪无法正确地传递到最终阶段。例如，以下是一个典型的Controller方法：
   
   @RequestMapping("/test")
   public ResponseBodyEmitter test() {
   
   ResponseBodyEmitter emitter = new ResponseBodyEmitter();
   // gprc invoke 已加入链路追踪
   /** 
   stub.invoke(request, new StreamObserver<String>() {
   
   @Override
   public void onNext(String value) {
   // 异步输出正确响应
   emitter.send(value);
   }
   
   @Override
   public void onError(Throwable t) {
   // 异步输出异常
   emitter.completeWithError(t);
   }
   
   @Override
   public void onComplete() {
   emitter.complete();
   }
   
   })
   **/
   return emitter;
   }
   当异步调用出现异常时，我希望通过spring的全局异常处理器来捕获异常，并将异常信息转换为JSON格式返回给前端。但是，我发现spring的全局异常处理器获取到的TraceId并不是该请求最初生成的TraceId，而是一个全新的ID。
   
   为了找出原因，我阅读了skywalking和springmvc的源码，发现了以下情况：
   
   skywalking通过org.apache.skywalking.apm.plugin.tomcat10x.TomcatInvokeInterceptor拦截了org.apache.catalina.core.StandardHostValve类的invoke方法，在方法调用前创建Span，在方法调用后结束这个Span。
   springmvc对异步响应有特殊的处理逻辑。当DispatcherServlet.dispatch方法遇到异步响应时，会直接返回，不会执行后续的逻辑。当异步响应完成时，会通过Tomcat的Async_Dispatch机制重新触发dispatch的过程，也就是StandardHostValve类的invoke方法会再次执行。因此，请求的生命周期变成了：请求开始->方法处理->请求结束->…->异步响应->请求开始->响应结果/异常处理->请求结束。
   Async_Dispatch产生的第二次请求没有携带第一次请求的链路追踪信息，因此被skywalking视为一个独立的请求，生成了一个全新的TraceID。
   根据上述分析，如果异步响应正常返回结果，则不会有问题，因为没有额外的方法调用过程，只是将结果输出到HTTP响应中。但是如果异步响应出现异常，则无法将异常处理过程加入到链路追踪中，也就无法在JSON格式的错误信息中添加请求的TraceId。
   
   
   
   ### What you expected to happen
   
   在这种异步响应的场景下，通过将链路追踪过程体现完整
   
   ### How to reproduce
   
   要解决这个问题，可能需要参考HttpClient->HttpServer的链路追踪方式，即在第一次请求中将链路追踪信息添加到Request的Header中，在Async_Dispatch时从Header中获取并传递。除了ResponseBodyEmitter外，还有DeferredResultMethodReturnValueHandler也存在类似的问题。
   
   ### Anything else
   
   _No response_
   
   ### Are you willing to submit PR?
   
   - [ ] Yes I am willing to submit a PR!
   
   ### Code of Conduct
   
   - [X] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)
   


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[GitHub] [skywalking] wu-sheng closed issue #10776: [Bug]

["wu-sheng (via GitHub)" <gi...@apache.org>]

wu-sheng closed issue #10776: [Bug] 
URL: https://github.com/apache/skywalking/issues/10776


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[GitHub] [skywalking] wu-sheng commented on issue #10776: [Bug]

["wu-sheng (via GitHub)" <gi...@apache.org>]

wu-sheng commented on issue #10776:
URL: https://github.com/apache/skywalking/issues/10776#issuecomment-1538106925

   We only accept issues/PRs in English. And in a generally reading, this seems a discussion, not a bug.


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