1 /*

     2  * Copyright 2008-2009 Sun Microsystems, Inc.  All Rights Reserved.

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

     4  *

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

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

     7  * published by the Free Software Foundation.  Sun designates this

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

     9  * by Sun in the LICENSE file that accompanied this code.

    10  *

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

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

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

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

    15  * accompanied this code).

    16  *

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

    18  * 2 along with this work; if not, write to the Free Software Foundation,

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

    20  *

    21  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

    22  * CA 95054 USA or visit www.sun.com if you need additional information or

    23  * have any questions.

    24  */

    25 

    26 package sun.dyn;

    27 

    28 import sun.reflect.Reflection;

    29 

    30 /**

    31  * Access control to this package.

    32  * Classes in other packages can attempt to acquire the access token,

    33  * but will fail if they are not recognized as friends.

    34  * Certain methods in this package, although public, require a non-null

    35  * access token in order to proceed; they act like package-private methods.

    36  * @author jrose

    37  */

    38 

    39 public class Access {

    40 

    41     private Access() { }

    42 

    43     /**

    44      * The heart of this pattern:  The list of classes which are

    45      * permitted to acquire the access token, and become honorary

    46      * members of this package.

    47      */

    48     private static final String[] FRIENDS = {

    49         "java.dyn.", "sun.dyn."

    50     };

    51 

    52     /**

    53      * The following object is NOT public.  That's the point of the pattern.

    54      * It is package-private, so that any member of this package

    55      * can acquire the access token, and give it away to trusted friends.

    56      */

    57     static final Access TOKEN = new Access();

    58 

    59     /**

    60      * @return Access.TOKEN, if the caller is a friend of this package

    61      */

    62     public static Access getToken() {

    63         Class<?> callc = Reflection.getCallerClass(2);

    64         if (isFriend(callc))

    65             return TOKEN;

    66         else

    67             throw new IllegalAccessError("bad caller: " + callc);

    68     }

    69 

    70     /** Is the given name the name of a class which could be our friend? */

    71     public static boolean isFriendName(String name) {

    72         for (String friend : FRIENDS) {

    73             if (name.startsWith(friend))

    74                 return true;

    75         }

    76         return false;

    77     }

    78 

    79     /** Is the given class a friend?  True if {@link #isFriendName},

    80      *  and the given class also shares a class loader with us.

    81      */

    82     public static boolean isFriend(Class<?> c) {

    83         return isFriendName(c.getName()) && c.getClassLoader() == CLASS_LOADER;

    84     }

    85 

    86     private static final ClassLoader CLASS_LOADER = Access.class.getClassLoader();

    87 

    88     /**

    89      * Throw an IllegalAccessError if the caller does not possess

    90      * the Access.TOKEN.

    91      * @param must be Access.TOKEN

    92      */

    93     public static void check(Access token) {

    94         if (token == null)

    95             fail();

    96         // else it must be the unique Access.TOKEN

    97         assert(token == Access.TOKEN);

    98     }

    99     private static void fail() {

   100         final int CALLER_DEPTH = 3;

   101         // 0: Reflection.getCC, 1: this.fail, 2: Access.*, 3: caller

   102         Class<?> callc = Reflection.getCallerClass(CALLER_DEPTH);

   103         throw new IllegalAccessError("bad caller: " + callc);

   104     }

   105 

   106     static {

   107         //sun.reflect.Reflection.registerMethodsToFilter(MH.class, "getToken");

   108     }

   109 }