(Enhance class java.net.URL error)Cannot inject auxiliary class into bootstrap loader using reflection

[YANGJINJUE]

import net.bytebuddy.description.method.MethodDescription;
import net.bytebuddy.matcher.ElementMatcher;
import net.bytebuddy.matcher.ElementMatchers;
import org.apache.skywalking.apm.agent.core.plugin.interceptor.ConstructorInterceptPoint;
import org.apache.skywalking.apm.agent.core.plugin.interceptor.InstanceMethodsInterceptPoint;
import org.apache.skywalking.apm.agent.core.plugin.interceptor.StaticMethodsInterceptPoint;
import org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.ClassEnhancePluginDefine;
import org.apache.skywalking.apm.agent.core.plugin.match.ClassMatch;

public class JavaNetUrlInstrumentation extends ClassEnhancePluginDefine {
    private static final String ENHANCE_CLASS = "java.net.URL";
    private static final String INTERCEPT_METHOD_CLASS = "org.apache.skywalking.apm.plugin.java.net.url.interceptor.JavaNetUrlMethodInterceptor";
    private static final String INTERCEPT_CONSTRUCTOR_CLASS = "org.apache.skywalking.apm.plugin.java.net.url.interceptor.JavaNetUrlConstructorInterceptor";

    @Override
    protected ClassMatch enhanceClass() {
        return byName(ENHANCE_CLASS);
    }

    @Override
    public ConstructorInterceptPoint[] getConstructorsInterceptPoints() {
        return new ConstructorInterceptPoint[]{
                new ConstructorInterceptPoint() {
                    @Override
                    public ElementMatcher<MethodDescription> getConstructorMatcher() {
                        return ElementMatchers.takesArgument(0, String.class);
                    }

                    @Override
                    public String getConstructorInterceptor() {
                        return INTERCEPT_CONSTRUCTOR_CLASS;
                    }
                }
        };
    }

    @Override
    public InstanceMethodsInterceptPoint[] getInstanceMethodsInterceptPoints() {
        return new InstanceMethodsInterceptPoint[]{
                new InstanceMethodsInterceptPoint() {
                    @Override
                    public ElementMatcher<MethodDescription> getMethodsMatcher() {
                        return named("openStream");
                    }

                    @Override
                    public String getMethodsInterceptor() {
                        return INTERCEPT_METHOD_CLASS;
                    }

                    @Override
                    public boolean isOverrideArgs() {
                        return false;
                    }
                },
                new InstanceMethodsInterceptPoint() {
                    @Override
                    public ElementMatcher<MethodDescription> getMethodsMatcher() {
                        return named("getContent");
                    }

                    @Override
                    public String getMethodsInterceptor() {
                        return INTERCEPT_METHOD_CLASS;
                    }

                    @Override
                    public boolean isOverrideArgs() {
                        return false;
                    }
                }
        };
    }

    @Override
    public StaticMethodsInterceptPoint[] getStaticMethodsInterceptPoints() {
        return new StaticMethodsInterceptPoint[0];
    }
}

[YANGJINJUE]

2023-09-27 19:31:01.894 ERROR main SkyWalkingAgent : Enhance class java.net.URL error.
java.lang.IllegalStateException: Cannot inject auxiliary class into bootstrap loader using reflection
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$InjectionStrategy$UsingReflection.resolve(AgentBuilder.java:3334)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$InitializationStrategy$SelfInjection$Split$Dispatcher.register(AgentBuilder.java:3146)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.doTransform(AgentBuilder.java:10328)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.transform(AgentBuilder.java:10263)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.access$1600(AgentBuilder.java:10029)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$LegacyVmDispatcher.run(AgentBuilder.java:10648)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$LegacyVmDispatcher.run(AgentBuilder.java:10595)
at java.security.AccessController.doPrivileged(Native Method)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.transform(AgentBuilder.java:10186)
at org.apache.skywalking.apm.agent.core.plugin.bytebuddy.CacheableTransformerDecorator$1.transform(CacheableTransformerDecorator.java:94)
at sun.instrument.TransformerManager.transform(TransformerManager.java:188)
at sun.instrument.InstrumentationImpl.transform(InstrumentationImpl.java:428)
at sun.instrument.InstrumentationImpl.retransformClasses0(Native Method)
at sun.instrument.InstrumentationImpl.retransformClasses(InstrumentationImpl.java:144)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$RedefinitionStrategy$Dispatcher$ForJava6CapableVm.retransformClasses(AgentBuilder.java:6869)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$RedefinitionStrategy$Collector$ForRetransformation.doApply(AgentBuilder.java:7148)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$RedefinitionStrategy$Collector.apply(AgentBuilder.java:6993)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$RedefinitionStrategy.apply(AgentBuilder.java:4855)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$Default.doInstall(AgentBuilder.java:9463)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$Default.installOn(AgentBuilder.java:9384)
at org.apache.skywalking.apm.agent.SkyWalkingAgent.premain(SkyWalkingAgent.java:121)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:386)
at sun.instrument.InstrumentationImpl.loadClassAndCallPremain(InstrumentationImpl.java:401)

[wu-sheng]

Read the doc about this, https://skywalking.apache.org/docs/skywalking-java/next/en/setup/service-agent/java-agent/java-plugin-development-guide/#bootstrap-class-instrumentation

And I highly doubt this instrumentation would work. Because you can't instrument class used by the agent kernel.

[wu-sheng]

I have no idea what this means. And I assume you are not using the latest, because L157 now is only the method declaration.

[YANGJINJUE]

I apologize, the previous null pointer error was because I didn't override the getStaticMethodsInterceptPoints method. I have added it now, and there are no errors during runtime. However, it is not generating any traces. I placed a breakpoint in the following code,
public class JavaNetUrlConstructorInterceptor implements InstanceConstructorInterceptor

but it didn't take effect.

[wu-sheng]

I said before, And I highly doubt this instrumentation would work. Because you can't instrument class used by the agent kernel.

[YANGJINJUE]

I didn't quite understand your point. There are no runtime errors anymore, but I can't hit the breakpoint inside the constructor. It seems like the interceptor isn't taking effect. What should I do?

[wu-sheng]

A class can't be instrumented if it is already used. This is the limitation of any booting agent.