Extension to add attributes to root span

[iamrakesh]

Hi,
My application uses Apache Wicket and I am trying to write an extension to add additional attributes to root span; values of these additional attributes is based on my application runtime state.
I wrote simple extension (based on default io.opentelemetry.javaagent.instrumentation.wicket.RequestHandlerExecutorInstrumentation), and my advice looks like below
public static class ExecuteAdvice { @Advice.OnMethodExit(suppress = Throwable.class) public static void onExit(@Advice.Argument(0) IRequestHandler handler) { HttpServerRoute.update( Java8BytecodeBridge.currentContext(), CONTROLLER, SERVER_SPAN_NAME, (IPageClassRequestHandler) handler); Span rootSpan = LocalRootSpan.fromContextOrNull(Java8BytecodeBridge.rootContext()); if (rootSpan == null) { return; } rootSpan.setAttribute("my.attribute", "Extension works"); } }
Extension is built and configured using 'otel.javaagent.extensions' property. I've enabled 'otel.javaagent.debug' and I dont see any errors during deployment/startup.

But with above implementation I dont see my custom attribute getting added to tracing.
Is there anything I am missing or doing it wrong way ?

[laurit]

Java8BytecodeBridge.rootContext() returns an empty context and LocalRootSpan.fromContextOrNull will always return null. Try using Java8BytecodeBridge.currentContext() instead. For debugging you can add System.err.println statements to see which branch was taken in your code.

[iamrakesh]

I tried above suggestion and still could not see the custom attribute; then started taking a look at the opentelemetry debug log, and I see below exception while loading my custom instrumentation, some how I overlooked this obvious error earlier.

[otel.javaagent 2023-12-29 11:15:19:575 +0530] [main] DEBUG io.opentelemetry.javaagent.tooling.instrumentation.InstrumentationLoader - Loading instrumentation wicket-requests [class io.github.iamrakesh.otel.wicket.instrumentation.WicketInstrumentationModule]
[otel.javaagent 2023-12-29 11:15:19:583 +0530] [main] ERROR io.opentelemetry.javaagent.tooling.instrumentation.InstrumentationLoader - Unable to load instrumentation wicket-requests [class io.github.iamrakesh.otel.wicket.instrumentation.WicketInstrumentationModule]
java.lang.NoClassDefFoundError: org/apache/wicket/core/request/handler/IPageRequestHandler
at io.github.iamrakesh.otel.wicket.instrumentation.RequestHandlerInstrumentation.(RequestHandlerInstrumentation.java:26)
at io.github.iamrakesh.otel.wicket.instrumentation.WicketInstrumentationModule.typeInstrumentations(WicketInstrumentationModule.java:49)
at io.opentelemetry.javaagent.tooling.instrumentation.InstrumentationModuleInstaller.install(InstrumentationModuleInstaller.java:69)
at io.opentelemetry.javaagent.tooling.instrumentation.InstrumentationLoader.extend(InstrumentationLoader.java:44)
at io.opentelemetry.javaagent.tooling.AgentInstaller.installBytebuddyAgent(AgentInstaller.java:175)
at io.opentelemetry.javaagent.tooling.AgentInstaller.installBytebuddyAgent(AgentInstaller.java:101)
at io.opentelemetry.javaagent.tooling.AgentStarterImpl.start(AgentStarterImpl.java:98)
at io.opentelemetry.javaagent.bootstrap.AgentInitializer$1.run(AgentInitializer.java:53)
at io.opentelemetry.javaagent.bootstrap.AgentInitializer$1.run(AgentInitializer.java:47)
at io.opentelemetry.javaagent.bootstrap.AgentInitializer.execute(AgentInitializer.java:64)
at io.opentelemetry.javaagent.bootstrap.AgentInitializer.initialize(AgentInitializer.java:46)
at io.opentelemetry.javaagent.OpenTelemetryAgent.startAgent(OpenTelemetryAgent.java:57)
at io.opentelemetry.javaagent.OpenTelemetryAgent.premain(OpenTelemetryAgent.java:45)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at java.instrument/sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:513)
at java.instrument/sun.instrument.InstrumentationImpl.loadClassAndCallPremain(InstrumentationImpl.java:525)
Caused by: java.lang.ClassNotFoundException: org.apache.wicket.core.request.handler.IPageRequestHandler
at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:476)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:594)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:527)
... 19 more

I do have this class added to additional helper classes in the module, below is my module impl.
`
@autoservice(InstrumentationModule.class)
public final class WicketInstrumentationModule extends InstrumentationModule {
....

@OverRide
public List getAdditionalHelperClassNames() {
return Arrays.asList(
"io.opentelemetry.javaagent.extension.instrumentation.TypeInstrumentation",
"org.apache.wicket.request.cycle.RequestCycle",
"org.apache.wicket.WicketRuntimeException",
"org.apache.wicket.request.component.IRequestablePage",
"org.apache.wicket.core.request.handler.IPageRequestHandler",
"org.apache.wicket.request.component.IRequestablePage");
}
}
I am using 'otel.javaagent.configuration-file' system property and the property file, contains below entry for loading extension
otel.javaagent.extensions=/otel-extension-1.0-SNAPSHOT.jar
`
When my extension is built, I get three JARs

• opentelemetry-javaagent.jar
• otel-extension-1.0-SNAPSHOT.jar
• otel-extension-1.0-SNAPSHOT-all.jar

I am using the second JAR from above list in my configuration.
what could have caused the ClassNotFoundException ?
Any help is appreciated, Thank you.

[iamrakesh]

Complete code I am trying is available at https://github.com/iamrakesh/otel-extensions/tree/main/wicket

[laurit]

Your main mistake is https://github.com/iamrakesh/otel-extensions/blob/db43d64d1794fc53191da00820aad91f744c2ea3/wicket/src/main/java/io/github/iamrakesh/otel/wicket/instrumentation/RequestHandlerInstrumentation.java#L25 If you had placed it in a separate class as the original code does it would have worked. The problem is that instrumentation code contains 2 kinds of classes. Classes that are used to set up the instrumentation and classes that are injected into the application class loader (documentation calls these helper classes). Helper classes can use classes from the instrumented framework but other classes can not. Here you have created a dependency from a class that is used to set up the instrumentation to wicket classes that are not available inside the agent.
https://github.com/iamrakesh/otel-extensions/blob/db43d64d1794fc53191da00820aad91f744c2ea3/wicket/src/main/java/io/github/iamrakesh/otel/wicket/instrumentation/WicketInstrumentationModule.java#L52 doesn't make sense, instead of that add

  @Override
  public boolean isHelperClass(String className) {
    return className.startsWith("io.github.iamrakesh.otel.wicket");
  }

The https://github.com/iamrakesh/otel-extensions/blob/db43d64d1794fc53191da00820aad91f744c2ea3/wicket/build.gradle#L7 takes care of figuring out which helper classes you are using, you only need to tell what package they are in (agent does not use it because classes in io.opentelemetry.javaagent.instrumentation are automatically considered as helper classes). You don't need to list wicket classes as helper classes, only your own classes.
Another thing that does not make sense to me is copying the route logic from the instrumentation that is bundled in the agent. Multiple advice can be applied to the same class, you could rely on the agent to apply that instrumentation unless you plan to modify it.

[iamrakesh]

Thank you for looking into the example source and for pointing the problems with the implementation. Following your suggestions/fixes helped and I was able to get the example working.
Regarding the 'route login' (WicketServerSpanNaming) being a copy from the original implementation, intention indeed is to modify and customize span name preparation.
Thank you (y)