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Java agent performing instrumentation for scala-grading.
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/* NEST (New Scala Test)
 * Copyright 2007-2015 LAMP/EPFL
 * @author Grzegorz Kossakowski
 */

package ch.epfl.lamp.instragent;

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

import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassWriter;

public class ASMTransformer implements ClassFileTransformer {

    private final String[] shouldTransformPrefixes;

    public ASMTransformer() {
        String prefixesStr = System.getProperty(
            "ch.epfl.lamp.instragent.classprefixes", "");
        shouldTransformPrefixes = prefixesStr.split(":");
    }

    private boolean shouldTransform(String className) {
        return
            shouldTransformPrefixExists(className) &&
            // do not instrument instrumentation logic (in order to avoid infinite recursion)
            !className.startsWith("ch/epfl/lamp/instragent/") &&
            !className.startsWith("ch/epfl/lamp/grading/");
    }

    private boolean shouldTransformPrefixExists(String className) {
        for (String prefix : shouldTransformPrefixes)
            if (className.startsWith(prefix))
                return true;
        return false;
    }

    public byte[] transform(final ClassLoader classLoader, String className,
        Class classBeingRedefined, ProtectionDomain protectionDomain,
        byte[] classfileBuffer) {

        if (shouldTransform(className)) {
            ClassWriter writer = new ClassWriter(
                ClassWriter.COMPUTE_FRAMES | ClassWriter.COMPUTE_MAXS) {

                // this is copied verbatim from the superclass,
                // except that we use the outer class loader
                @Override protected String getCommonSuperClass(
                    final String type1, final String type2) {

                    Class c, d;
                    try {
                        c = Class.forName(type1.replace('/', '.'), false, classLoader);
                        d = Class.forName(type2.replace('/', '.'), false, classLoader);
                    } catch (Exception e) {
                        throw new RuntimeException(e.toString());
                    }
                    if (c.isAssignableFrom(d)) {
                        return type1;
                    }
                    if (d.isAssignableFrom(c)) {
                        return type2;
                    }
                    if (c.isInterface() || d.isInterface()) {
                        return "java/lang/Object";
                    } else {
                        do {
                            c = c.getSuperclass();
                        } while (!c.isAssignableFrom(d));
                        return c.getName().replace('.', '/');
                    }
                }
            };
            ProfilerVisitor visitor = new ProfilerVisitor(writer);
            ClassReader reader = new ClassReader(classfileBuffer);
            reader.accept(visitor, 0);
            return writer.toByteArray();
        } else {
            return classfileBuffer;
        }
    }
}