Advice of byte buddy throw java.lang.ClassNotFoundException when using my own class in the custom instrumentation

[bgong-mdsol]

Hi all,
I like to write my own instrumentation to add some attributes based on http request. I write a helper class to build additional attributes, and get the exception java.lang.ClassNotFoundException when call it in Advice of byte buddy:

@Advice.OnMethodEnter(suppress = Throwable.class)
public static void onEnter( 
    @Advice.Argument(0) ServletRequest request,
    @Advice.Argument(1) ServletResponse response) {
    if (!(request instanceof HttpServletRequest) || !(response instanceof HttpServletResponse)) {
       return;
    }
    try {
       AttributesHelper.testing((HttpServletRequest) request);
    } catch (Throwable t) {
       System.out.println("ERROR: " + t.getCause());
    }
}

public static class AttributesHelper { 
    public static void testing(HttpServletRequest httpRequest) {
        System.out.println("This is AttributesHelper");
    }
}

When I run my app with the custom otel javaagent, got the error below, any suggestion?
ERROR: java.lang.ClassNotFoundException: my.javaagent.instrumentation.servlet.AttributesHelper

[iNikem]

Maybe this will hetlp: https://github.com/open-telemetry/opentelemetry-java-instrumentation/blob/main/docs/contributing/writing-instrumentation-module.md#ishelperclass ?

[bgong-mdsol]

Thanks @iNikem,
I refer the doc and example to create my instrumentation, But I can't use my own class in @Advice-annotated methods because of java.lang.ClassNotFoundException .

I looked the existing instrumentation which is calling the method from different class in in @Advice-annotated methods , such as https://github.com/open-telemetry/opentelemetry-java-instrumentation/blob/main/instrumentation/spring/spring-scheduling-3.1/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/spring/scheduling/TaskInstrumentation.java#L35

I am wonder if I missed any configuration or runtime dependence in my gradle project.

[iNikem]

@mateuszrzeszutek Can you help here?

[mateuszrzeszutek]

Hey @bgong-mdsol ,

Are you writing your instrumentation in a fork of this project or a distro/extension/repackage? The isHelperClass(String) method mentioned by @iNikem is called by our compile-time "muzzle" extension, which is not yet available for usage outside of this project.

As a workaround, please try manually adding all names of the classes that you use to the getMuzzleHelperClassNames() method, e.g.:

public List<String> getMuzzleHelperClassNames() {
  return Collections.singletonList("my.javaagent.instrumentation.servlet.AttributesHelper");
}

This method is normally (well, normally in this project) generated automatically by the muzzle compile-time plugin, but if you don't use it you might have to write it yourself.

[bgong-mdsol]

👍 It works! Thanks a lot @mateuszrzeszutek and @iNikem