How to avoid NoClassDefFoundError when using ByteBuddy to implement OpenTracing

Question

I'm trying to implement a Java Agent that can easily be added to the commandline of some of our legacy services to enable distributed tracing using the OpenTracing API. I'm using ByteBuddy (1.9.12) and hitting NoClassDefFoundErrors when the instrumented code runs for the following scenarios so far:

1. instrumented a class in the java.util.concurrent package: can't find the GlobalTracer since the Java Agent was only in the app classpath. I got around this temporarily by adding the Java Agent that includes the tracing APIs to the bootstrap classpath on the commandline (Java 8 only), but I'd like to be able to do that programmatically. Looking for the right way to do that. (Edit: this is solved by using the Boot-Class-Path option in the manifest file of the Java Agent--just put the filename--no path--of the Java Agent JAR itself.)
2. instrumented a custom network client class: can't find a class in the custom network packages from my Intercept class (during byte code injection) since the network client packages aren't in the Java Agent JAR. I'm looking for the "right way" to structure things at a high level to avoid this.

Code for scenario 2:

public class NettyAgentRule implements AgentRule {

    public Iterable<? extends AgentBuilder> buildAgent(AgentBuilder agentBuilder) {
        return Arrays.asList(agentBuilder
                .type(hasSuperType(named("org.jboss.netty.bootstrap.Bootstrap")))
                .transform((builder, typeDescription, classLoader, module) -> {
                    return builder.visit(Advice.to(NettyAgentRule.class).on(named("setPipelineFactory")));
                }));
    }

    @Advice.OnMethodEnter
    public static void enter(final @Advice.Origin String origin,
                            final @Advice.This Object thiz,
                            @Advice.Argument(value = 0, readOnly = false, typing = Assigner.Typing.DYNAMIC) Object parameter) {
        parameter = NettyAgentIntercept.enter(thiz, parameter);
    }
}

where the Error happens in the NettyAgentIntercept class, which references Netty classes.

I've researched how the OpenTracing 'contrib' SpecialAgent handles these scenarios and it has quite a bit of custom classloading going on, which is tightly coupled to their build structure (JARs within the JAR following a naming convention). This would be nice to avoid if possible.

Example exception stack from scenario 2:

java.lang.NoClassDefFoundError: org/jboss/netty/channel/ChannelPipelineFactory
2019-07-05 18:52:21,10613       at com.example.tracing.netty.NettyAgentIntercept.enter(NettyAgentIntercept.java:9)
2019-07-05 18:52:21,10613       at org.jboss.netty.bootstrap.Bootstrap.setPipelineFactory(Bootstrap.java:251)
2019-07-05 18:52:21,10616       at com.example.lib.util.net.NettyCore.<init>(NettyCore.java:176)
2019-07-05 18:52:21,10616       at com.example.lib.util.net.NetClient.getInstance(NetClient.java:125)
2019-07-05 18:52:21,10617       at com.example.lib.util.net.NetClient.getInstance(NetClient.java:147)
2019-07-05 18:52:21,10617       at com.example.lib.util.net.NetClient.getInstance(NetClient.java:55)
2019-07-05 18:52:21,10617       at com.example.component.Component.main(Component.java:155)
2019-07-05 18:52:21,10618       at com.example.lib.util.invoke.ComponentThread.run(ComponentThread.java:21)

I have also tried the following code as recommended in

byte-buddy throws java.lang.ClassNotFoundException: javax.servlet.http.HttpServlet

but it results in the same sort of exception:

public Iterable<? extends AgentBuilder> buildAgent(AgentBuilder agentBuilder) {
        return Arrays.asList(agentBuilder
                .type(hasSuperType(named("org.jboss.netty.bootstrap.Bootstrap")))
                .transform(new AgentBuilder.Transformer.ForAdvice()
                        .include(getClass().getClassLoader())
                        .advice(named("setPipelineFactory"),"com.example.tracing.netty.NettyAgentAdvice")
                ));

    }

where the advice class is

package com.example.tracing.netty;

import org.jboss.netty.bootstrap.ClientBootstrap;
import org.jboss.netty.channel.ChannelPipeline;
import org.jboss.netty.channel.ChannelPipelineFactory;

import net.bytebuddy.asm.Advice;
import net.bytebuddy.implementation.bytecode.assign.Assigner;

public class NettyAgentAdvice {

    @Advice.OnMethodEnter
    public static void enter(final @Advice.Origin String origin,
                            final @Advice.This Object thiz,
                            @Advice.Argument(value = 0, readOnly = false, typing = Assigner.Typing.DYNAMIC) Object parameter) {
        parameter = enter(thiz, parameter);
    }

    public static ChannelPipelineFactory enter(Object thiz, Object returned) {
        ChannelPipelineFactory pipelineFactory = (ChannelPipelineFactory) returned;
        if (thiz instanceof ClientBootstrap) {
            return () -> {
                ChannelPipeline pipeline = pipelineFactory.getPipeline();
                if (pipeline.get(TracingHandler.class) == null) {
                    pipeline.addLast("tracing", new TracingHandler());
                }
                return pipeline;
            };
        }
        return pipelineFactory;
    }
}

Answer 1

Byte Buddy has an advice adapter for the agent builder that avoids class loading and reflection to avoid the error you are seeing: AgentBuilder.Transformer.ForAdvice.

This transformer will use a TypePool to resolve advice classes from the target class loader and any class loader that you add to represent classes.