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 * Copyright (c) 2008, 2010, 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

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 */

package sun.dyn.util;

import java.lang.reflect.Modifier;

import static java.lang.reflect.Modifier.*;

/**

 * This class centralizes information about the JVM's linkage access control.

 * @author jrose

 */

public class VerifyAccess {

    private VerifyAccess() { }  // cannot instantiate

    private static final int PACKAGE_ONLY = 0;

    private static final int ALL_ACCESS_MODES = (PUBLIC|PRIVATE|PROTECTED|PACKAGE_ONLY);

    private static final boolean ALLOW_NESTMATE_ACCESS = false;

    /**

     * Evaluate the JVM linkage rules for access to the given method

     * on behalf of a caller class which proposes to perform the access.

     * Return true if the caller class has privileges to invoke a method

     * or access a field with the given properties.

     * This requires an accessibility check of the referencing class,

     * plus an accessibility check of the member within the class,

     * which depends on the member's modifier flags.

     * <p>

     * The relevant properties include the defining class ({@code defc})

     * of the member, and its modifier flags ({@code mods}).

     * Also relevant is the class used to make the initial symbolic reference

     * to the member ({@code refc}).  If this latter class is not distinguished,

     * the defining class should be passed for both arguments ({@code defc == refc}).

     * <h3>JVM Specification, 5.4.4 "Access Control"</h3>

     * A field or method R is accessible to a class or interface D if

     * and only if any of the following conditions is true:<ul>

     * <li>R is public.

     * <li>R is protected and is declared in a class C, and D is either

     *     a subclass of C or C itself.  Furthermore, if R is not

     *     static, then the symbolic reference to R must contain a

     *     symbolic reference to a class T, such that T is either a

     *     subclass of D, a superclass of D or D itself.

     * <li>R is either protected or has default access (that is,

     *     neither public nor protected nor private), and is declared

     *     by a class in the same runtime package as D.

     * <li>R is private and is declared in D.

     * </ul>

     * This discussion of access control omits a related restriction

     * on the target of a protected field access or method invocation

     * (the target must be of class D or a subtype of D). That

     * requirement is checked as part of the verification process

     * (5.4.1); it is not part of link-time access control.

     * @param refc the class used in the symbolic reference to the proposed member

     * @param defc the class in which the proposed member is actually defined

     * @param mods modifier flags for the proposed member

     * @param lookupClass the class for which the access check is being made

     * @return true iff the the accessing class can access such a member

     */

    public static boolean isMemberAccessible(Class<?> refc,  // symbolic ref class

                                             Class<?> defc,  // actual def class

                                             int      mods,  // actual member mods

                                             Class<?> lookupClass) {

        // Usually refc and defc are the same, but if they differ, verify them both.

        if (refc != defc) {

            if (!isClassAccessible(refc, lookupClass)) {

                // Note that defc is verified in the switch below.

                return false;

            }

            if ((mods & (ALL_ACCESS_MODES|STATIC)) == (PROTECTED|STATIC)) {

                // Apply the special rules for refc here.

                if (!isRelatedClass(refc, lookupClass))

                    return isSamePackage(defc, lookupClass);

                // If refc == defc, the call to isPublicSuperClass will do

                // the whole job, since in that case refc (as defc) will be

                // a superclass of the lookup class.

            }

        }

        if (defc == lookupClass)

            return true;        // easy check; all self-access is OK

        switch (mods & ALL_ACCESS_MODES) {

        case PUBLIC:

            if (refc != defc)  return true;  // already checked above

            return isClassAccessible(refc, lookupClass);

        case PROTECTED:

            return isSamePackage(defc, lookupClass) || isPublicSuperClass(defc, lookupClass);

        case PACKAGE_ONLY:

            return isSamePackage(defc, lookupClass);

        case PRIVATE:

            // Loosened rules for privates follows access rules for inner classes.

            return (ALLOW_NESTMATE_ACCESS &&

                    isSamePackageMember(defc, lookupClass));

        default:

            throw new IllegalArgumentException("bad modifiers: "+Modifier.toString(mods));

        }

    }

    static boolean isRelatedClass(Class<?> refc, Class<?> lookupClass) {

        return (refc == lookupClass ||

                refc.isAssignableFrom(lookupClass) ||

                lookupClass.isAssignableFrom(refc));

    }

    static boolean isPublicSuperClass(Class<?> defc, Class<?> lookupClass) {

        return isPublic(defc.getModifiers()) && defc.isAssignableFrom(lookupClass);

    }

    /**

     * Evaluate the JVM linkage rules for access to the given class on behalf of caller.

     * <h3>JVM Specification, 5.4.4 "Access Control"</h3>

     * A class or interface C is accessible to a class or interface D

     * if and only if either of the following conditions are true:<ul>

     * <li>C is public.

     * <li>C and D are members of the same runtime package.

     * </ul>

     * @param refc the symbolic reference class to which access is being checked (C)

     * @param lookupClass the class performing the lookup (D)

     */

    public static boolean isClassAccessible(Class<?> refc, Class<?> lookupClass) {

        int mods = refc.getModifiers();

        if (isPublic(mods))

            return true;

        if (isSamePackage(lookupClass, refc))

            return true;

        return false;

    }

    /**

     * Test if two classes have the same class loader and package qualifier.

     * @param class1

     * @param class2

     * @return whether they are in the same package

     */

    public static boolean isSamePackage(Class<?> class1, Class<?> class2) {

        if (class1 == class2)

            return true;

        if (!loadersAreRelated(class1.getClassLoader(), class2.getClassLoader()))

            return false;

        String name1 = class1.getName(), name2 = class2.getName();

        int dot = name1.lastIndexOf('.');

        if (dot != name2.lastIndexOf('.'))

            return false;

        for (int i = 0; i < dot; i++) {

            if (name1.charAt(i) != name2.charAt(i))

                return false;

        }

        return true;

    }

    /**

     * Test if two classes are defined as part of the same package member (top-level class).

     * If this is true, they can share private access with each other.

     * @param class1

     * @param class2

     * @return whether they are identical or nested together

     */

    public static boolean isSamePackageMember(Class<?> class1, Class<?> class2) {

        if (class1 == class2)

            return true;

        if (!isSamePackage(class1, class2))

            return false;

        if (getOutermostEnclosingClass(class1) != getOutermostEnclosingClass(class2))

            return false;

        return true;

    }

    private static Class<?> getOutermostEnclosingClass(Class<?> c) {

        Class<?> pkgmem = c;

        for (Class<?> enc = c; (enc = enc.getEnclosingClass()) != null; )

            pkgmem = enc;

        return pkgmem;

    }

    private static boolean loadersAreRelated(ClassLoader loader1, ClassLoader loader2) {

        if (loader1 == loader2 || loader1 == null || loader2 == null) {

            return true;

        }

        for (ClassLoader scan1 = loader1;

                scan1 != null; scan1 = scan1.getParent()) {

            if (scan1 == loader2)  return true;

        }

        for (ClassLoader scan2 = loader2;

                scan2 != null; scan2 = scan2.getParent()) {

            if (scan2 == loader1)  return true;

        }

        return false;

    }

}