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JMockit is a Java toolkit for developer (unit/integration) testing. It contains mocking APIs and other tools, supporting both JUnit and TestNG. The mocking APIs allow all kinds of Java code, without testability restrictions, to be tested in isolation from selected dependencies.

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/*
 * Copyright (c) 2006-2012 Rogério Liesenfeld
 * This file is subject to the terms of the MIT license (see LICENSE.txt).
 */
package mockit.internal.capturing;

import java.lang.instrument.*;
import java.security.*;
import java.util.*;

import mockit.external.asm4.*;
import mockit.internal.*;
import mockit.internal.state.*;
import mockit.internal.util.*;

final class CaptureTransformer implements ClassFileTransformer
{
   private final CapturedType metadata;
   private final String capturedType;
   private final CaptureOfImplementations modifierFactory;
   private final SuperTypeCollector superTypeCollector;
   private final Map transformedClasses;
   private boolean inactive;

   CaptureTransformer(CapturedType metadata, CaptureOfImplementations modifierFactory, boolean forTestClass)
   {
      this.metadata = metadata;
      capturedType = Type.getInternalName(metadata.baseType);
      this.modifierFactory = modifierFactory;
      superTypeCollector = new SuperTypeCollector();
      transformedClasses = forTestClass ? new HashMap(2) : null;
   }

   void deactivate()
   {
      inactive = true;

      if (transformedClasses != null) {
         RedefinitionEngine redefinitionEngine = new RedefinitionEngine();

         for (Map.Entry classNameAndOriginalBytecode : transformedClasses.entrySet()) {
            String className = classNameAndOriginalBytecode.getKey();
            byte[] originalBytecode = classNameAndOriginalBytecode.getValue();
            redefinitionEngine.restoreToDefinition(className, originalBytecode);
         }

         transformedClasses.clear();
      }
   }

   public byte[] transform(
      ClassLoader loader, String internalClassName, Class classBeingRedefined, ProtectionDomain protectionDomain,
      byte[] classfileBuffer)
   {
      if (
         inactive || classBeingRedefined != null || TestRun.getCurrentTestInstance() == null ||
         internalClassName.startsWith("mockit/internal/"))
      {
         return null;
      }

      String className = internalClassName.replace('/', '.');

      if (!metadata.isToBeCaptured(className)) {
         return null;
      }

      ClassReader cr = new ClassReader(classfileBuffer);

      try {
         cr.accept(superTypeCollector, ClassReader.SKIP_DEBUG);
      }
      catch (VisitInterruptedException ignore) {
         if (superTypeCollector.classExtendsCapturedType) {
            return modifyAndRegisterClass(loader, className, cr);
         }
      }

      return null;
   }

   private byte[] modifyAndRegisterClass(ClassLoader loader, String className, ClassReader cr)
   {
      ClassVisitor modifier = modifierFactory.createModifier(loader, cr, capturedType);
      cr.accept(modifier, 0);

      byte[] originalBytecode = cr.b;

      if (transformedClasses == null) {
         TestRun.mockFixture().addTransformedClass(className, originalBytecode);
      }
      else {
         transformedClasses.put(className, originalBytecode);
      }

      return modifier.toByteArray();
   }

   private final class SuperTypeCollector extends ClassVisitor
   {
      boolean classExtendsCapturedType;

      @Override
      public void visit(int version, int access, String name, String signature, String superName, String[] interfaces)
      {
         classExtendsCapturedType = false;

         if (capturedType.equals(superName)) {
            classExtendsCapturedType = true;
         }
         else {
            for (String itfc : interfaces) {
               if (capturedType.equals(itfc)) {
                  classExtendsCapturedType = true;
                  break;
               }
            }
         }

         if (!classExtendsCapturedType && !"java/lang/Object".equals(superName)) {
            String superClassName = superName.replace('/', '.');
            ClassReader cr = ClassFile.createClassFileReader(superClassName);
            cr.accept(superTypeCollector, ClassReader.SKIP_DEBUG);
         }

         throw VisitInterruptedException.INSTANCE;
      }
   }
}