/*

 * Copyright (c) 2016, 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 jdk.dynalink;

import java.lang.invoke.MethodHandles;

import java.lang.invoke.MethodHandles.Lookup;

import java.util.Objects;

/**

 * Provides security-checked access to a {@code MethodHandles.Lookup} object.

 * See {@link #getLookup()} for details.

 */

public class SecureLookupSupplier {

    /**

     * The name of a runtime permission required to successfully invoke the

     * {@link #getLookup()} method.

     */

    public static final String GET_LOOKUP_PERMISSION_NAME = "dynalink.getLookup";

    private static final RuntimePermission GET_LOOKUP_PERMISSION = new RuntimePermission(SecureLookupSupplier.GET_LOOKUP_PERMISSION_NAME);

    private final MethodHandles.Lookup lookup;

    /**

     * Creates a new secure lookup supplier, securing the passed lookup.

     * @param lookup the lookup to secure. Can not be null.

     * @throws NullPointerException if null is passed.

     */

    public SecureLookupSupplier(final MethodHandles.Lookup lookup) {

        this.lookup = Objects.requireNonNull(lookup, "lookup");

    }

    /**

     * Returns the lookup secured by this {@code SecureLookupSupplier}.

     * @return the lookup secured by this {@code SecureLookupSupplier}.

     * @throws SecurityException if the secured lookup isn't the

     * {@link MethodHandles#publicLookup()}, and a security manager is present,

     * and a check for {@code RuntimePermission("dynalink.getLookup")} fails.

     */

    public final Lookup getLookup() {

        final SecurityManager sm = System.getSecurityManager();

        if (sm != null && lookup != MethodHandles.publicLookup()) {

            sm.checkPermission(GET_LOOKUP_PERMISSION);

        }

        return lookup;

    }

    /**

     * Returns the value of {@link #getLookup()} without a security check. Can

     * be used by subclasses to access the lookup quickly.

     * @return same as returned value of {@link #getLookup()}.

     */

    protected final Lookup getLookupPrivileged() {

        return lookup;

    }

}