When I inject classes into the JAR package specified by -Dotel.javaagent.extensions, the application JAR can load the bytecode of these classes, but the instantiation triggers an infinite recursive call

[fcabbage]

Detail information: I extend Dubbo's probe in the otel-agent-ext JAR package.
This is my InstrumentationModule and the extended probe:

@AutoService(InstrumentationModule.class)
public class DubboProbeInstrumentationModule extends InstrumentationModule implements ExperimentalInstrumentationModule {

    public DubboProbeInstrumentationModule() {
        super("apache-dubbo-probe", "apache-dubbo-probe-3.3.0");
        System.out.println("DubboProbeInstrumentationModule");
    }

    @Override
    public void registerHelperResources(HelperResourceBuilder helperResourceBuilder) {
        System.out.println("registerHelperResources");
        helperResourceBuilder.register(
                "META-INF/org.apache.dubbo.qos.probe.StartupProbe");
        if (!isIndyModule()) {
            // For indy module the proxy-bytecode will be injected as resource by injectClasses()
            helperResourceBuilder.registerForAllClassLoaders(
                    "com/cabbage/demo/otel/agent/ext/mvn/dubbo/probe/OtelAgentExtStartupProbe.class");
        }
    }

    @Override
    public ElementMatcher.Junction<ClassLoader> classLoaderMatcher() {
        System.out.println("classLoaderMatcher");
        return hasClassesNamed("org.apache.dubbo.qos.probe.StartupProbe");
    }

    @Override
    public void injectClasses(ClassInjector injector) {
        System.out.println("injectClasses");
        injector
                .proxyBuilder(
                        "com.cabbage.demo.otel.agent.ext.mvn.dubbo.probe.OtelAgentExtStartupProbe")
                .inject(InjectionMode.CLASS_ONLY);
    }

    @Override
    public List<TypeInstrumentation> typeInstrumentations() {
        System.out.println("typeInstrumentations");
        return singletonList(new ResourceInjectingTypeInstrumentation());
    }

    // A type instrumentation is needed to trigger resource injection.
    public static class ResourceInjectingTypeInstrumentation implements TypeInstrumentation {
        @Override
        public ElementMatcher<TypeDescription> typeMatcher() {
            System.out.println("typeMatcher");
            return named("org.apache.dubbo.common.extension.ExtensionLoader");
        }

        @Override
        public void transform(TypeTransformer transformer) {
            System.out.println("transform");
            // Nothing to transform, this type instrumentation is only used for injecting resources.
        }
    }

    @Override
    public boolean isIndyModule() {
        System.out.println("isIndyModule");
        return true;
    }
}

@Activate
@AutoService(StartupProbe.class)
public final class OtelAgentExtStartupProbe implements StartupProbe {

    @Override
    public boolean check() {
        System.out.println(this.getClass().getName());
        return true;
    }

}

This is the error message of the application JAR package when executing the probe command:

Caused by: java.lang.StackOverflowError: null
	at java.base/java.lang.invoke.DirectMethodHandle.allocateInstance(DirectMethodHandle.java:482) ~[na:na]
	at com.cabbage.demo.otel.agent.ext.mvn.dubbo.probe.OtelAgentExtStartupProbe.<init>(Unknown Source) ~[opentelemetry-javaagent.jar:na]
	at com.cabbage.demo.otel.agent.ext.mvn.dubbo.probe.OtelAgentExtStartupProbe.<init>(Unknown Source) ~[opentelemetry-javaagent.jar:na]
	at com.cabbage.demo.otel.agent.ext.mvn.dubbo.probe.OtelAgentExtStartupProbe.<init>(Unknown Source) ~[opentelemetry-javaagent.jar:na]

And this is the probe class modified at runtime:

ClassLoader:
+-jdk.internal.loader.ClassLoaders$AppClassLoader@2626b418
  +-jdk.internal.loader.ClassLoaders$PlatformClassLoader@4f5b08d

Location:
/D:/WorkPlace/Code/Java/OpenTelemetry/agent/opentelemetry-javaagent.jar

/*
 * Decompiled with CFR.
 *
 * Could not load the following classes:
 *  io.opentelemetry.javaagent.bootstrap.IndyBootstrapDispatcher
 *  io.opentelemetry.javaagent.bootstrap.InstrumentationProxy
 */
package com.cabbage.demo.otel.agent.ext.mvn.dubbo.probe;

import io.opentelemetry.javaagent.bootstrap.IndyBootstrapDispatcher;
import io.opentelemetry.javaagent.bootstrap.InstrumentationProxy;
import org.apache.dubbo.common.extension.Activate;
import org.apache.dubbo.qos.probe.StartupProbe;

@Activate(group={}, value={}, before={}, after={}, order=0, onClass={})
public class OtelAgentExtStartupProbe
implements StartupProbe,
InstrumentationProxy {
    private final Object delegate = IndyBootstrapDispatcher.bootstrap("ctor", new Object[]{"proxy", "com.cabbage.demo.otel.agent.ext.mvn.dubbo.probe.DubboProbeInstrumentationModule", "com.cabbage.demo.otel.agent.ext.mvn.dubbo.probe.OtelAgentExtStartupProbe", "constructor"});

    @Override
    public boolean check() {
        return (boolean)IndyBootstrapDispatcher.bootstrap("check", new Object[]{"proxy", "com.cabbage.demo.otel.agent.ext.mvn.dubbo.probe.DubboProbeInstrumentationModule", "com.cabbage.demo.otel.agent.ext.mvn.dubbo.probe.OtelAgentExtStartupProbe", "virtual"}, this.delegate);
    }

    public /* synthetic */ Object __getIndyProxyDelegate() {
        return this.delegate;
    }
}

[steverao]

Could you introduce something about your purpose?

[fcabbage]

I plan to extend Dubbo using its SPI mechanism (such as Dubbo Filter). In the source code of otel-agent, I found that classes can be injected into application JAR files through the injectClasses method, and these injected classes can be discovered by Dubbo's SPI mechanism (io.opentelemetry.javaagent.instrumentation.apachedubbo.v2_7). Therefore, I referenced a similar implementation method to build my own extension (Dubbo Probe). The difference is that I do this by the opentelemetry-javaagent-extension JAR, not in otel-agent JAR.