/*

  * Copyright (c) 2008, 2012, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.  Oracle designates this

  * particular file as subject to the "Classpath" exception as provided

  * by Oracle in the LICENSE file that accompanied this code.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  */

 package sun.invoke.anon;

 import java.io.IOException;

 import java.lang.reflect.InvocationTargetException;

 import java.lang.reflect.Method;

 import sun.misc.IOUtils;

 /**

  * Anonymous class loader.  Will load any valid classfile, producing

  * a {@link Class} metaobject, without installing that class in the

  * system dictionary.  Therefore, {@link Class#forName(String)} will never

  * produce a reference to an anonymous class.

  * <p>

  * The access permissions of the anonymous class are borrowed from

  * a <em>host class</em>.  The new class behaves as if it were an

  * inner class of the host class.  It can access the host's private

  * members, if the creator of the class loader has permission to

  * do so (or to create accessible reflective objects).

  * <p>

  * When the anonymous class is loaded, elements of its constant pool

  * can be patched to new values.  This provides a hook to pre-resolve

  * named classes in the constant pool to other classes, including

  * anonymous ones.  Also, string constants can be pre-resolved to

  * any reference.  (The verifier treats non-string, non-class reference

  * constants as plain objects.)

  *  <p>

  * Why include the patching function?  It makes some use cases much easier.

  * Second, the constant pool needed some internal patching anyway,

  * to anonymize the loaded class itself.  Finally, if you are going

  * to use this seriously, you'll want to build anonymous classes

  * on top of pre-existing anonymous classes, and that requires patching.

  *

  * <p>%%% TO-DO:

  * <ul>

  * <li>needs better documentation</li>

  * <li>needs more security work (for safe delegation)</li>

  * <li>needs a clearer story about error processing</li>

  * <li>patch member references also (use ';' as delimiter char)</li>

  * <li>patch method references to (conforming) method handles</li>

  * </ul>

  *

  * @author jrose

  * @author Remi Forax

  * @see <a href="http://blogs.sun.com/jrose/entry/anonymous_classes_in_the_vm">

  *      http://blogs.sun.com/jrose/entry/anonymous_classes_in_the_vm</a>

  */

 public class AnonymousClassLoader {

     final Class<?> hostClass;

     // Privileged constructor.

     private AnonymousClassLoader(Class<?> hostClass) {

         this.hostClass = hostClass;

     }

     public static AnonymousClassLoader make(sun.misc.Unsafe unsafe, Class<?> hostClass) {

         if (unsafe == null)  throw new NullPointerException();

         return new AnonymousClassLoader(hostClass);

     }

     public Class<?> loadClass(byte[] classFile) {

         if (defineAnonymousClass == null) {

             // no JVM support; try to fake an approximation

             try {

                 return fakeLoadClass(new ConstantPoolParser(classFile).createPatch());

             } catch (InvalidConstantPoolFormatException ee) {

                 throw new IllegalArgumentException(ee);

             }

         }

         return loadClass(classFile, null);

     }

     public Class<?> loadClass(ConstantPoolPatch classPatch) {

         if (defineAnonymousClass == null) {

             // no JVM support; try to fake an approximation

             return fakeLoadClass(classPatch);

         }

         Object[] patches = classPatch.patchArray;

         // Convert class names (this late in the game)

         // to use slash '/' instead of dot '.'.

         // Java likes dots, but the JVM likes slashes.

         for (int i = 0; i < patches.length; i++) {

             Object value = patches[i];

             if (value != null) {

                 byte tag = classPatch.getTag(i);

                 switch (tag) {

                 case ConstantPoolVisitor.CONSTANT_Class:

                     if (value instanceof String) {

                         if (patches == classPatch.patchArray)

                             patches = patches.clone();

                         patches[i] = ((String)value).replace('.', '/');

                     }

                     break;

                 case ConstantPoolVisitor.CONSTANT_Fieldref:

                 case ConstantPoolVisitor.CONSTANT_Methodref:

                 case ConstantPoolVisitor.CONSTANT_InterfaceMethodref:

                 case ConstantPoolVisitor.CONSTANT_NameAndType:

                     // When/if the JVM supports these patches,

                     // we'll probably need to reformat them also.

                     // Meanwhile, let the class loader create the error.

                     break;

                 }

             }

         }

         return loadClass(classPatch.outer.classFile, classPatch.patchArray);

     }

     private Class<?> loadClass(byte[] classFile, Object[] patchArray) {

         try {

             return (Class<?>)

                 defineAnonymousClass.invoke(unsafe,

                                             hostClass, classFile, patchArray);

         } catch (Exception ex) {

             throwReflectedException(ex);

             throw new RuntimeException("error loading into "+hostClass, ex);

         }

     }

     private static void throwReflectedException(Exception ex) {

         if (ex instanceof InvocationTargetException) {

             Throwable tex = ((InvocationTargetException)ex).getTargetException();

             if (tex instanceof Error)

                 throw (Error) tex;

             ex = (Exception) tex;

         }

         if (ex instanceof RuntimeException) {

             throw (RuntimeException) ex;

         }

     }

     private Class<?> fakeLoadClass(ConstantPoolPatch classPatch) {

         // Implementation:

         // 1. Make up a new name nobody has used yet.

         // 2. Inspect the tail-header of the class to find the this_class index.

         // 3. Patch the CONSTANT_Class for this_class to the new name.

         // 4. Add other CP entries required by (e.g.) string patches.

         // 5. Flatten Class constants down to their names, making sure that

         //    the host class loader can pick them up again accurately.

         // 6. Generate the edited class file bytes.

         //

         // Potential limitations:

         // * The class won't be truly anonymous, and may interfere with others.

         // * Flattened class constants might not work, because of loader issues.

         // * Pseudo-string constants will not flatten down to real strings.

         // * Method handles will (of course) fail to flatten to linkage strings.

         if (true)  throw new UnsupportedOperationException("NYI");

         Object[] cpArray;

         try {

             cpArray = classPatch.getOriginalCP();

         } catch (InvalidConstantPoolFormatException ex) {

             throw new RuntimeException(ex);

         }

         int thisClassIndex = classPatch.getParser().getThisClassIndex();

         String thisClassName = (String) cpArray[thisClassIndex];

         synchronized (AnonymousClassLoader.class) {

             thisClassName = thisClassName+"\\|"+(++fakeNameCounter);

         }

         classPatch.putUTF8(thisClassIndex, thisClassName);

         byte[] classFile = null;

         return unsafe.defineClass(null, classFile, 0, classFile.length,

                                   hostClass.getClassLoader(),

                                   hostClass.getProtectionDomain());

     }

     private static int fakeNameCounter = 99999;

     // ignore two warnings on this line:

     private static sun.misc.Unsafe unsafe = sun.misc.Unsafe.getUnsafe();

     // preceding line requires that this class be on the boot class path

     static private final Method defineAnonymousClass;

     static {

         Method dac = null;

         Class<? extends sun.misc.Unsafe> unsafeClass = unsafe.getClass();

         try {

             dac = unsafeClass.getMethod("defineAnonymousClass",

                                         Class.class,

                                         byte[].class,

                                         Object[].class);

         } catch (Exception ee) {

             dac = null;

         }

         defineAnonymousClass = dac;

     }

     private static void noJVMSupport() {

         throw new UnsupportedOperationException("no JVM support for anonymous classes");

     }

     private static native Class<?> loadClassInternal(Class<?> hostClass,

                                                      byte[] classFile,

                                                      Object[] patchArray);

     public static byte[] readClassFile(Class<?> templateClass) throws IOException {

         String templateName = templateClass.getName();

         int lastDot = templateName.lastIndexOf('.');

         java.net.URL url = templateClass.getResource(templateName.substring(lastDot+1)+".class");

         java.net.URLConnection connection = url.openConnection();

         int contentLength = connection.getContentLength();

         if (contentLength < 0)

             throw new IOException("invalid content length "+contentLength);

         return IOUtils.readFully(connection.getInputStream(), contentLength, true);

     }

 }