1/*
2 * Copyright (c) 2015, Oracle and/or its affiliates. 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.  Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26package jdk.dynalink.linker;
27
28import java.security.Permission;
29import java.util.List;
30import java.util.ServiceLoader;
31import java.util.function.Supplier;
32import jdk.dynalink.DynamicLinkerFactory;
33
34/**
35 * A class acting as a supplier of guarding dynamic linkers that can be
36 * automatically loaded by other language runtimes. Language runtimes wishing
37 * to export their own linkers should subclass this class and implement the
38 * {@link #get()} method to return a list of exported linkers and declare the
39 * subclass in
40 * {@code /META-INF/services/jdk.dynalink.linker.GuardingDynamicLinkerExporter}
41 * resource of their distribution (typically, JAR file) so that dynamic linker
42 * factories can discover them using the {@link ServiceLoader} mechanism. Note
43 * that instantiating this class is tied to a security check for the
44 * {@code RuntimePermission("dynalink.exportLinkersAutomatically")} when a
45 * security manager is present, to ensure that only trusted runtimes can
46 * automatically export their linkers into other runtimes.
47 * @see DynamicLinkerFactory#setClassLoader(ClassLoader)
48 */
49public abstract class GuardingDynamicLinkerExporter implements Supplier<List<GuardingDynamicLinker>> {
50    /**
51     * The name of the runtime permission for creating instances of this class.
52     * Granting this permission to a language runtime allows it to export its
53     * linkers for automatic loading into other language runtimes.
54     */
55    public static final String AUTOLOAD_PERMISSION_NAME = "dynalink.exportLinkersAutomatically";
56
57    private static final Permission AUTOLOAD_PERMISSION = new RuntimePermission(AUTOLOAD_PERMISSION_NAME);
58
59    /**
60     * Creates a new linker exporter. If there is a security manager installed
61     * checks for the
62     * {@code RuntimePermission("dynalink.exportLinkersAutomatically")} runtime
63     * permission. This ensures only language runtimes granted this permission
64     * will be allowed to export their linkers for automatic loading.
65     * @throws SecurityException if the necessary runtime permission is not
66     * granted.
67     */
68    protected GuardingDynamicLinkerExporter() {
69        final SecurityManager sm = System.getSecurityManager();
70        if (sm != null) {
71            sm.checkPermission(AUTOLOAD_PERMISSION);
72        }
73    }
74}
75