1 /*
2 * Copyright 2023 The Netty Project
3 *
4 * The Netty Project licenses this file to you under the Apache License,
5 * version 2.0 (the "License"); you may not use this file except in compliance
6 * with the License. You may obtain a copy of the License at:
7 *
8 * https://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13 * License for the specific language governing permissions and limitations
14 * under the License.
15 */
16 package io.netty.bootstrap;
17
18 import io.netty.channel.Channel;
19 import io.netty.channel.ServerChannel;
20
21 /**
22 * A channel initializer extension make it possible to enforce rules and apply modifications across multiple,
23 * disconnected uses of Netty within the same JVM process.
24 * <p>
25 * For instance, application-level firewall rules can be injected into all uses of Netty within an application,
26 * without making changes to such uses that are otherwise outside the purview of the application code,
27 * such as 3rd-party libraries.
28 * <p>
29 * Channel initializer extensions are <em>not</em> enabled by default, because of their power to influence Netty
30 * pipelines across libraries, frameworks, and use-cases.
31 * Extensions must be explicitly enabled by setting the {@value #EXTENSIONS_SYSTEM_PROPERTY} to {@code serviceload}.
32 * <p>
33 * All channel initializer extensions that are available on the classpath will be
34 * {@linkplain java.util.ServiceLoader#load(Class) service-loaded} and used by all {@link AbstractBootstrap} subclasses.
35 * <p>
36 * Note that this feature will not work for Netty uses that are shaded <em>and relocated</em> into other libraries.
37 * The classes in a relocated Netty library are technically distinct and incompatible types. This means the
38 * service-loader in non-relocated Netty will not see types from a relocated Netty, and vice versa.
39 */
40 public abstract class ChannelInitializerExtension {
41 /**
42 * The name of the system property that control initializer extensions.
43 * <p>
44 * These extensions can potentially be a security liability, so they are disabled by default.
45 * <p>
46 * To enable the extensions, application operators can explicitly opt in by setting this system property to the
47 * value {@code serviceload}. This will enable all the extensions that are available through the service loader
48 * mechanism.
49 * <p>
50 * To load and log (at INFO level) all available extensions without actually running them, set this system property
51 * to the value {@code log}.
52 */
53 public static final String EXTENSIONS_SYSTEM_PROPERTY = "io.netty.bootstrap.extensions";
54
55 /**
56 * Get the "priority" of this extension. If multiple extensions are avilable, then they will be called in their
57 * priority order, from lowest to highest.
58 * <p>
59 * Implementers are encouraged to pick a number between {@code -100.0} and {@code 100.0}, where extensions that have
60 * no particular opinion on their priority are encouraged to return {@code 0.0}.
61 * <p>
62 * Extensions with lower priority will get called first, while extensions with greater priority may be able to
63 * observe the effects of extensions with lesser priority.
64 * <p>
65 * Note that if multiple extensions have the same priority, then their relative order will be unpredictable.
66 * As such, implementations should always take into consideration that other extensions might be called before
67 * or after them.
68 * <p>
69 * Override this method to specify your own priority.
70 * The default implementation just returns {@code 0}.
71 *
72 * @return The priority.
73 */
74 public double priority() {
75 return 0;
76 }
77
78 /**
79 * Called by {@link Bootstrap} after the initialization of the given client channel.
80 * <p>
81 * The method is allowed to modify the handlers in the pipeline, the channel attributes, or the channel options.
82 * The method must refrain from doing any I/O, or from closing the channel.
83 * <p>
84 * Override this method to add your own callback logic.
85 * The default implementation does nothing.
86 *
87 * @param channel The channel that was initialized.
88 */
89 public void postInitializeClientChannel(Channel channel) {
90 }
91
92 /**
93 * Called by {@link ServerBootstrap} after the initialization of the given server listener channel.
94 * The listener channel is responsible for invoking the {@code accept(2)} system call,
95 * and for producing child channels.
96 * <p>
97 * The method is allowed to modify the handlers in the pipeline, the channel attributes, or the channel options.
98 * The method must refrain from doing any I/O, or from closing the channel.
99 * <p>
100 * Override this method to add your own callback logic.
101 * The default implementation does nothing.
102 *
103 * @param channel The channel that was initialized.
104 */
105 public void postInitializeServerListenerChannel(ServerChannel channel) {
106 }
107
108 /**
109 * Called by {@link ServerBootstrap} after the initialization of the given child channel.
110 * A child channel is a newly established connection from a client to the server.
111 * <p>
112 * The method is allowed to modify the handlers in the pipeline, the channel attributes, or the channel options.
113 * The method must refrain from doing any I/O, or from closing the channel.
114 * <p>
115 * Override this method to add your own callback logic.
116 * The default implementation does nothing.
117 *
118 * @param channel The channel that was initialized.
119 */
120 public void postInitializeServerChildChannel(Channel channel) {
121 }
122 }