AwsServletContext violates Servlet Spec by throwing UnsupportedOperationException

[Koella1337]

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Serverless Java Container version: 1.6

Implementations: Core

Framework version: SpringBoot 2 v1.7-SNAPSHOT

Frontend service: HTTP API

Deployment method: SAM

Scenario

I'm trying to instrument an AWS Lambda function with a Java agent containing a Servlet instrumentation. In the instrumentation of Filter#init(FilterConfig), the agent calls getServletContext() (via reflection) on the FilterConfig, which returns a com.amazonaws.serverless.proxy.internal.servlet.AwsServletContext object. Then, again via reflection, the agent calls getServletContextName().

Expected behavior

getServletContextName() returns a name or null as per the Servlet spec:
https://javaee.github.io/javaee-spec/javadocs/javax/servlet/ServletContext.html#getServletContextName--

Actual behavior

getServletContextName() throws an UnsupportedOperationException (wrapped in an InvocationTargetException due to reflection).

Steps to reproduce

1. Instantiate an AwsServletContext object.
2. Call getServletContextName() on it.

Log output

Not the full logs since they're not relevant, but here's the InvocationTargetException i got when discovering this issue:

2022-02-04 13:51:12.139 UTC [00000001] [ServletIntrospection] Exception in introspection method "registerFilter". java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.base/java.lang.reflect.Method.invoke(Unknown Source)
at agent.introspection.util.classvalue.MethodClassValue.invoke(MethodClassValue.java:71)
at agent.introspection.servlet.ServletIntrospection.getServletContextName(ServletIntrospection.java:382)
at agent.introspection.servlet.ServletIntrospection.registerFilter(ServletIntrospection.java:178)
at agent.introspection.servlet.ServletIntrospectionWrapper.registerFilter(ServletIntrospectionWrapper.java:188)
at org.springframework.web.filter.GenericFilterBean.init(GenericFilterBean.java)
at com.amazonaws.serverless.proxy.internal.servlet.FilterHolder.init(FilterHolder.java:89)
at com.amazonaws.serverless.proxy.internal.servlet.FilterChainHolder.doFilter(FilterChainHolder.java:86)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
at com.amazonaws.serverless.proxy.internal.servlet.FilterChainHolder.doFilter(FilterChainHolder.java:90)
at com.amazonaws.serverless.proxy.internal.servlet.AwsLambdaServletContainerHandler.doFilter(AwsLambdaServletContainerHandler.java:156)
at com.amazonaws.serverless.proxy.spring.SpringBootLambdaContainerHandler.handleRequest(SpringBootLambdaContainerHandler.java:180)
at com.amazonaws.serverless.proxy.spring.SpringBootLambdaContainerHandler.handleRequest(SpringBootLambdaContainerHandler.java:53)
at com.amazonaws.serverless.proxy.internal.LambdaContainerHandler.proxy(LambdaContainerHandler.java:211)
at com.amazonaws.serverless.proxy.internal.LambdaContainerHandler.proxyStream(LambdaContainerHandler.java:254)
at <censored>
at <censored>
at java.base/java.lang.Class.forName0(Native Method)
at java.base/java.lang.Class.forName(Unknown Source)
at lambdainternal.HandlerInfo.fromString(HandlerInfo.java:33)
at lambdainternal.AWSLambda.findUserMethods(AWSLambda.java:109)
at lambdainternal.AWSLambda.startRuntime(AWSLambda.java:230)
at lambdainternal.AWSLambda.startRuntime(AWSLambda.java:199)
at lambdainternal.AWSLambda.main(AWSLambda.java:193)
Caused by: java.lang.UnsupportedOperationException
at com.amazonaws.serverless.proxy.internal.servlet.AwsServletContext.getServletContextName(AwsServletContext.java:314)
... 28 more

[deki]

Thanks for reporting this. I'm afraid there a several places where this library doesn't comply with the Spec as we are not offering a full servlet container.
However in this case returning null should be fine.

[deki]

Fixed, will be part of next release.