/*
 * Copyright 1997-2009 Sun Microsystems, Inc.  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.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

package java.security;

import java.util.HashMap;
import java.util.ArrayList;
import java.net.URL;

import sun.security.util.Debug;

/**
 * This class extends ClassLoader with additional support for defining
 * classes with an associated code source and permissions which are
 * retrieved by the system policy by default.
 *
 * @author  Li Gong
 * @author  Roland Schemers
 */
public class SecureClassLoader extends ClassLoader {
    /*
     * If initialization succeed this is set to true and security checks will
     * succeed. Otherwise the object is not initialized and the object is
     * useless.
     */
    private final boolean initialized;

    // HashMap that maps CodeSource to ProtectionDomain
    // @GuardedBy("pdcache")
    private final HashMap<CodeSource, ProtectionDomain> pdcache =
                        new HashMap<CodeSource, ProtectionDomain>(11);

    private static final Debug debug = Debug.getInstance("scl");

    static {
        ClassLoader.registerAsParallelCapable();
    }

    /**
     * Creates a new SecureClassLoader using the specified parent
     * class loader for delegation.
     *
     * <p>If there is a security manager, this method first
     * calls the security manager's <code>checkCreateClassLoader</code>
     * method  to ensure creation of a class loader is allowed.
     * <p>
     * @param parent the parent ClassLoader
     * @exception  SecurityException  if a security manager exists and its
     *             <code>checkCreateClassLoader</code> method doesn't allow
     *             creation of a class loader.
     * @see SecurityManager#checkCreateClassLoader
     */
    protected SecureClassLoader(ClassLoader parent) {
        super(parent);
        // this is to make the stack depth consistent with 1.1
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkCreateClassLoader();
        }
        initialized = true;
    }

    /**
     * Creates a new SecureClassLoader using the default parent class
     * loader for delegation.
     *
     * <p>If there is a security manager, this method first
     * calls the security manager's <code>checkCreateClassLoader</code>
     * method  to ensure creation of a class loader is allowed.
     *
     * @exception  SecurityException  if a security manager exists and its
     *             <code>checkCreateClassLoader</code> method doesn't allow
     *             creation of a class loader.
     * @see SecurityManager#checkCreateClassLoader
     */
    protected SecureClassLoader() {
        super();
        // this is to make the stack depth consistent with 1.1
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkCreateClassLoader();
        }
        initialized = true;
    }

    /**
     * Converts an array of bytes into an instance of class Class,
     * with an optional CodeSource. Before the
     * class can be used it must be resolved.
     * <p>
     * If a non-null CodeSource is supplied a ProtectionDomain is
     * constructed and associated with the class being defined.
     * <p>
     * @param      name the expected name of the class, or <code>null</code>
     *                  if not known, using '.' and not '/' as the separator
     *                  and without a trailing ".class" suffix.
     * @param      b    the bytes that make up the class data. The bytes in
     *             positions <code>off</code> through <code>off+len-1</code>
     *             should have the format of a valid class file as defined
     *             by the
     *             <a href="http://java.sun.com/docs/books/vmspec/">Java
     *             Virtual Machine Specification</a>.
     * @param      off  the start offset in <code>b</code> of the class data
     * @param      len  the length of the class data
     * @param      cs   the associated CodeSource, or <code>null</code> if none
     * @return the <code>Class</code> object created from the data,
     *         and optional CodeSource.
     * @exception  ClassFormatError if the data did not contain a valid class
     * @exception  IndexOutOfBoundsException if either <code>off</code> or
     *             <code>len</code> is negative, or if
     *             <code>off+len</code> is greater than <code>b.length</code>.
     *
     * @exception  SecurityException if an attempt is made to add this class
     *             to a package that contains classes that were signed by
     *             a different set of certificates than this class, or if
     *             the class name begins with "java.".
     */
    protected final Class<?> defineClass(String name,
                                         byte[] b, int off, int len,
                                         CodeSource cs)
    {
        return defineClass(name, b, off, len, getProtectionDomain(cs));
    }

    /**
     * Converts a {@link java.nio.ByteBuffer <tt>ByteBuffer</tt>}
     * into an instance of class <tt>Class</tt>, with an optional CodeSource.
     * Before the class can be used it must be resolved.
     * <p>
     * If a non-null CodeSource is supplied a ProtectionDomain is
     * constructed and associated with the class being defined.
     * <p>
     * @param      name the expected name of the class, or <code>null</code>
     *                  if not known, using '.' and not '/' as the separator
     *                  and without a trailing ".class" suffix.
     * @param      b    the bytes that make up the class data.  The bytes from positions
     *                  <tt>b.position()</tt> through <tt>b.position() + b.limit() -1</tt>
     *                  should have the format of a valid class file as defined by the
     *                  <a href="http://java.sun.com/docs/books/vmspec/">Java Virtual
     *                  Machine Specification</a>.
     * @param      cs   the associated CodeSource, or <code>null</code> if none
     * @return the <code>Class</code> object created from the data,
     *         and optional CodeSource.
     * @exception  ClassFormatError if the data did not contain a valid class
     * @exception  SecurityException if an attempt is made to add this class
     *             to a package that contains classes that were signed by
     *             a different set of certificates than this class, or if
     *             the class name begins with "java.".
     *
     * @since  1.5
     */
    protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
                                         CodeSource cs)
    {
        return defineClass(name, b, getProtectionDomain(cs));
    }

    /**
     * Returns the permissions for the given CodeSource object.
     * <p>
     * This method is invoked by the defineClass method which takes
     * a CodeSource as an argument when it is constructing the
     * ProtectionDomain for the class being defined.
     * <p>
     * @param codesource the codesource.
     *
     * @return the permissions granted to the codesource.
     *
     */
    protected PermissionCollection getPermissions(CodeSource codesource)
    {
        check();
        return new Permissions(); // ProtectionDomain defers the binding
    }

    /*
     * Returned cached ProtectionDomain for the specified CodeSource.
     */
    private ProtectionDomain getProtectionDomain(CodeSource cs) {
        if (cs == null)
            return null;

        ProtectionDomain pd = null;
        synchronized (pdcache) {
            pd = pdcache.get(cs);
            if (pd == null) {
                PermissionCollection perms = getPermissions(cs);
                pd = new ProtectionDomain(cs, perms, this, null);
                pdcache.put(cs, pd);
                if (debug != null) {
                    debug.println(" getPermissions "+ pd);
                    debug.println("");
                }
            }
        }
        return pd;
    }

    /*
     * Check to make sure the class loader has been initialized.
     */
    private void check() {
        if (!initialized) {
            throw new SecurityException("ClassLoader object not initialized");
        }
    }

}
