Cheers,

here's an Example of a possible bug I've found.

Could anyone confirm this or prove me an idiot, so I can either file a bug report or go kill myself in shame?

Using $sig or $class as method parameter only seems to work on nonstatic methods, on static methods I get a StackOverflow Error.

Have I missed something in the dicumentation or is that a serious bug?

I could reproduce this with the latest JRE6 and the current JRE7:

Using $sig:

instrumenting class: de/plush/brix/instrumentation/Main (995 bytes)

instrumenting class: javassist/runtime/Desc (3280 bytes)

Exception in thread "main" java.lang.StackOverflowError

at javassist.runtime.Desc.getParams(Desc.java)

at javassist.runtime.Desc.getParams(Desc.java)

at javassist.runtime.Desc.getParams(Desc.java)

[..]

Using $class:

instrumenting class: de/plush/brix/instrumentation/Main (995 bytes)

instrumenting class: javassist/runtime/Desc (3280 bytes)

Exception in thread "main" java.lang.StackOverflowError

at javassist.runtime.Desc.getClazz(Desc.java)

at javassist.runtime.Desc.getClazz(Desc.java)

[...]

Compile the following code, create JAR-File, have a manifest like:

Manifest-Version: 1.0

Ant-Version: Apache Ant 1.8.2

Created-By: 1.7.0_02-b13 (Oracle Corporation)

Premain-Class: de.plush.brix.instrumentation.Agent

Class-Path: javassist.jar

Start some Main.class with the jvm-arg:

-javaagent:${project_loc}\Agent.jar

And watch it happen.

package de.plush.brix.instrumentation;

public class Main {

void foo() {

  System.out.println("Hello world");

  }

public static void main(final String[] args) {

  new Main().foo();

}

}

package de.plush.brix.instrumentation;

import java.io.IOException;

import java.lang.instrument.ClassFileTransformer;

import java.lang.instrument.IllegalClassFormatException;

import java.lang.instrument.Instrumentation;

import java.lang.reflect.Modifier;

import java.security.ProtectionDomain;

import java.util.Arrays;

import javassist.ByteArrayClassPath;

import javassist.CannotCompileException;

import javassist.ClassPool;

import javassist.CtClass;

import javassist.CtMethod;

import javassist.NotFoundException;

public class Agent implements ClassFileTransformer {

public Agent(final String agentArgs, final Instrumentation instrumentation) {

  instrumentation.addTransformer(this);

}

public static void premain(final String agentArgs, final Instrumentation inst) {

  new Agent(agentArgs, inst);

}

public static void before(Class[] paramTypes) { //works

System.out.println("test passed");

}

public static void before(Class paramTypes) { //works

System.out.println("test passed");

}

public static void beforeStatic(Class[] paramTypes) { //stackOverflow

  System.out.println("test passed");

}

public static void beforeStatic2(Class paramTypes) { //stackOverflow

System.out.println("test passed");

}

@Override

public byte[] transform(final ClassLoader loader, final String className, final Class<?> classBeingRedefined, final ProtectionDomain protectionDomain,

final byte[] classfileBuffer) throws IllegalClassFormatException {

  System.out.println("instrumenting class: " + className + " (" + classfileBuffer.length + " bytes)");

  try {

  final String javaClassName = className.replace('/', '.');

  // turn bytecodes into a Javassist CtClass

  final CtClass clazz = createClass(classfileBuffer, javaClassName);

  // add output at the beginning and end of each method

  for (final CtMethod method : clazz.getMethods()) {

   if (!isInherited(javaClassName, method)) {

     if (Modifier.isStatic(method.getModifiers())) {

      method.insertBefore("{"+Agent.class.getName() + ".beforeStatic($sig);}"); // -- $sig kills it!

      // method.insertBefore("{"+Agent.class.getName() + ".beforeStatic2($class);}"); // -- $class kills it too!

     } else {

      method.insertBefore("{"+Agent.class.getName() + ".before($sig);}"); // -- works

      // method.insertBefore("{"+Agent.class.getName() + ".before2($class);}"); // --works too

    }

   }

  }

  return clazz.toBytecode();

} catch (final NotFoundException e) {

   throw new RuntimeException(e);

} catch (final CannotCompileException e) {

   if (!e.getMessage().contains("no method body")) {

    throw new RuntimeException(e);

   }

  // don't care

} catch (final IOException e) {

  throw new RuntimeException(e);

}

return classfileBuffer;

}

private boolean isInherited(final String javaClassName, final CtMethod method) {

  return !method.getLongName().startsWith(javaClassName);

}

private CtClass createClass(final byte[] classfileBuffer, final String javassistClassName) throws NotFoundException {

final ClassPool cp = ClassPool.getDefault();

cp.insertClassPath(new ByteArrayClassPath(javassistClassName, classfileBuffer));

final CtClass cc = cp.get(javassistClassName);

return cc;

}

}