core-it-support/core-it-javaagent/src/main/java/org/apache/maven/coreits/javaagent/mng5669/Premain.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.maven.coreits.javaagent.mng5669;

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.lang.instrument.Instrumentation;
import java.security.ProtectionDomain;

import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.commons.AdviceAdapter;

/**
 *
 * @author Robert Scholte
 *
 */
public class Premain {
    public static void premain(String agentArgs, Instrumentation inst) {
        inst.addTransformer(new ClassFileTransformer() {

            public byte[] transform(
                    ClassLoader loader,
                    String className,
                    Class<?> classBeingRedefined,
                    ProtectionDomain protectionDomain,
                    byte[] classfileBuffer)
                    throws IllegalClassFormatException {
                if ("org/apache/maven/model/io/DefaultModelReader".equals(className)) {
                    ClassReader r = new ClassReader(classfileBuffer);
                    final ClassWriter w = new ClassWriter(Opcodes.ASM6);

                    ClassVisitor v = new DefaultModelReaderVisitor(Opcodes.ASM6, w);

                    r.accept(v, ClassReader.EXPAND_FRAMES);
                    return w.toByteArray();
                } else {
                    return classfileBuffer;
                }
            }
        });
    }

    private static class DefaultModelReaderVisitor extends ClassVisitor {
        DefaultModelReaderVisitor(int api, org.objectweb.asm.ClassVisitor cv) {
            super(api, cv);
        }

        @Override
        public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
            MethodVisitor mv = cv.visitMethod(access, name, desc, signature, exceptions);
            if ("getSource".equals(name)) {
                return new GetSourceMethodAdvice(Opcodes.ASM6, mv, access, name, desc);
            } else {
                return mv;
            }
        }
    }

    // org.apache.maven.model.io.DefaultModelReader.getSource(Map<String, ?>)
    private static class GetSourceMethodAdvice extends AdviceAdapter {
        GetSourceMethodAdvice(int api, MethodVisitor mv, int access, String name, String desc) {
            super(api, mv, access, name, desc);
        }

        @Override
        protected void onMethodEnter() {
            // System.out.println( options ),
            mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
            mv.visitVarInsn(ALOAD, 1);
            mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/Object;)V", false);
        }
    }
}