Fix Asynchronous Dispatch Logic in AwsAsyncContext with Spring's DispatcherServlet

[leekib]

*Issue #, if available: #630

*Description of changes:

Problem

While examining #630, I found an issue within the asynchronous dispatch logic of AwsAsyncContext when interacting with Spring's DispatcherServlet.

• Premature Re-dispatch: Currently, AwsAsyncContext prematurly triggers re-dispatch.
  When handling asynchronous requests with DispatcherServlet, DispatcherServlet'sdoDispatch should be called to complete the initial request. Only after the initial request concludes, should the doDispatch be called again for re-dispatch. However, in the present implementation, this sequence is disrupted. During the processing of the initial request by the doDispatch method, the dispatch method of AwsAsyncContext is invoked, which in turn directly calls the doFilter method for immediate re-dispatch. This leads to premature execution of the re-dispatch before the post-processing logic of doDispatch(which is handling the initial request) is executed.

• EntityManager Bind Timing Issue: While using Spring JPA, due to the aforementioned issue, an error arises when trying to bind the EntityManager to threadLocal during the preHandle phase of the re-dispatch. This is because the EntityManager is already bound from the initial request, and the post-processing logic meant to unbind it hasn't been executed yet. As a result, attempting to bind it again triggers the following error:

Value [org.springframework.orm.jpa.EntityManagerHolder@38a6ca39] already bound to key [org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean@39296cef].

Changes

To resolve this, I made modifications to the SpringBootLambdaContainerHandler::handleRequest and AwsAsyncContext::dispatch by referencing the way requests are handled in apache.coyote.AbstractProcessorLight::process.
The snippet for the proposed solution is as follows:

protected void handleRequest(HttpServletRequest containerRequest, AwsHttpServletResponse containerResponse, Context lambdaContext) throws Exception {
    // ... [other code]
    doFilter(containerRequest, containerResponse, reqServlet);
    //added addtional filter logic
    if(requiresAsyncReDispatch(containerRequest)) {
        doFilter(containerRequest, containerResponse, reqServlet);
    }
    // ... [other code]
}

public void dispatch() {
    // ... [other code]
    //added dispatchStarted flag
    if (!dispatchStarted.get()) {
        dispatchStarted.set(true);
    } else {
        dispatched.set(true);
    // removed the line that directly calls doFilter
        notifyListeners(NotificationType.START_ASYNC, null);
    }
    // ... [other code]
}

By ensuring that the post-processing of the initial request is complete and only then re-invoking the doFilter when necessary, we can bypass the issues mentioned above.

I have not yet added test cases, and there are two test cases marked with @disable since AwsAsyncContext no longer maps requests to the servlet. I think we can talk about this solution or potentially explore better approaches.

By submitting this pull request

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I confirm that I've made a best effort attempt to update all relevant documentation.

[mbfreder]

Thanks for your contribution. I will review this today and let you know.

[mbfreder]

Looks good to me. Could you add tests, please?

[leekib]

I added test cases

[deki]

How do we plan to deal with the @Disabled test cases? I've not worked much with WebFlux but we need to make sure that the things implemented in #239 are still working.

[leekib]

How do we plan to deal with the @Disabled test cases? I've not worked much with WebFlux but we need to make sure that the things implemented in #239 are still working.

The two @Disabled test cases are testing whether AwsAsyncContext's dispatch correctly maps to the right servlet.
Specifically, it's testing this line to see whether the right servlet is input when calling doFilter.

However, in my commit, this line has removed from the dispatch function, and the responsibility for mapping the servlet has now shifted from AwsAsyncContext to SpringBootLambdaContainerHandler. I believe the disabled cases are adequately covered in the test cases of aws-serverless-java-container-springboot and springboot3.

However, as you pointed out, I seem to have overlooked testing whether the request path is properly amended when dispatch is called in AwsAsyncContextTest. I've added that test.

[leekib]

I missed that both springboot3 and spring handle async requests the same way. After looking over it again, I've updated the SpringLambdaContainerHandler in aws-serverless-java-container-spring and added some tests.

[leekib]

@deki Any further feedback on my update?

[deki]

AwsAsyncContext no longer depends on the AwsLambdaServletContainerHandler could you please remove the unused variable as well?

[deki]

Hey @2012160085,
sorry for the delay, I saw your comment on #630 and had therefore de-prioritized this PR.

I read https://jakarta.ee/specifications/servlet/6.0/jakarta-servlet-spec-6.0#asynchronous-processing, looked at https://github.com/apache/tomcat/blob/main/java/org/apache/catalina/core/AsyncContextImpl.java and noticed we may required additional fixes. The async processing capability should work within aws-serverless-java-container-core but with the proposed change you made calling filters exclusive to -spring and -springboot3. Filters for apps running -jersey and other potential implementations would no longer be called or am I missing something?

[leekib]

Hey @2012160085, sorry for the delay, I saw your comment on #630 and had therefore de-prioritized this PR.

I read https://jakarta.ee/specifications/servlet/6.0/jakarta-servlet-spec-6.0#asynchronous-processing, looked at https://github.com/apache/tomcat/blob/main/java/org/apache/catalina/core/AsyncContextImpl.java and noticed we may required additional fixes. The async processing capability should work within aws-serverless-java-container-core but with the proposed change you made calling filters exclusive to -spring and -springboot3. Filters for apps running -jersey and other potential implementations would no longer be called or am I missing something?

You seem to be correct based on what I've reviewed. I will take a closer look into this

[deki]

@2012160085 just a heads up, we are planning to release 2.0.0 at the end of this month. are you still working on it so we can include it?

[leekib]

@2012160085 just a heads up, we are planning to release 2.0.0 at the end of this month. are you still working on it so we can include it?

I haven't been able to focus on this recently, but I will make sure to wrap it up by the end of the month.

[leekib]

@2012160085 just a heads up, we are planning to release 2.0.0 at the end of this month. are you still working on it so we can include it?

@deki I think I've wrapped it up.

• Modified the serverless-java-container-core to revise the ReDispatch logic.
  I relocated the ReDispatch logic from springboot3 and spring to the serverless-java-container-core, ensuring that the ReDispatch logic now operates exclusively within the serverless-java-container-core.
• Added JpaAppTest to serverless-java-container-springboot3, which was initially failing with JPA dependencies but now succeeds after my modifications. Additionally, I added asynchronous request test cases to Spring.

[deki]

Thanks again for your contribution, @2012160085!