io.netty.bootstrap.ChannelInitializerExtension Maven / Gradle / Ivy
/*
* Copyright 2023 The Netty Project
*
* The Netty Project licenses this file to you under the Apache License,
* version 2.0 (the "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at:
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*/
package io.netty.bootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ServerChannel;
/**
* A channel initializer extension make it possible to enforce rules and apply modifications across multiple,
* disconnected uses of Netty within the same JVM process.
*
* For instance, application-level firewall rules can be injected into all uses of Netty within an application,
* without making changes to such uses that are otherwise outside the purview of the application code,
* such as 3rd-party libraries.
*
* Channel initializer extensions are not enabled by default, because of their power to influence Netty
* pipelines across libraries, frameworks, and use-cases.
* Extensions must be explicitly enabled by setting the {@value #EXTENSIONS_SYSTEM_PROPERTY} to {@code serviceload}.
*
* All channel initializer extensions that are available on the classpath will be
* {@linkplain java.util.ServiceLoader#load(Class) service-loaded} and used by all {@link AbstractBootstrap} subclasses.
*
* Note that this feature will not work for Netty uses that are shaded and relocated into other libraries.
* The classes in a relocated Netty library are technically distinct and incompatible types. This means the
* service-loader in non-relocated Netty will not see types from a relocated Netty, and vice versa.
*/
public abstract class ChannelInitializerExtension {
/**
* The name of the system property that control initializer extensions.
*
* These extensions can potentially be a security liability, so they are disabled by default.
*
* To enable the extensions, application operators can explicitly opt in by setting this system property to the
* value {@code serviceload}. This will enable all the extensions that are available through the service loader
* mechanism.
*
* To load and log (at INFO level) all available extensions without actually running them, set this system property
* to the value {@code log}.
*/
public static final String EXTENSIONS_SYSTEM_PROPERTY = "io.netty.bootstrap.extensions";
/**
* Get the "priority" of this extension. If multiple extensions are avilable, then they will be called in their
* priority order, from lowest to highest.
*
* Implementers are encouraged to pick a number between {@code -100.0} and {@code 100.0}, where extensions that have
* no particular opinion on their priority are encouraged to return {@code 0.0}.
*
* Extensions with lower priority will get called first, while extensions with greater priority may be able to
* observe the effects of extensions with lesser priority.
*
* Note that if multiple extensions have the same priority, then their relative order will be unpredictable.
* As such, implementations should always take into consideration that other extensions might be called before
* or after them.
*
* Override this method to specify your own priority.
* The default implementation just returns {@code 0}.
*
* @return The priority.
*/
public double priority() {
return 0;
}
/**
* Called by {@link Bootstrap} after the initialization of the given client channel.
*
* The method is allowed to modify the handlers in the pipeline, the channel attributes, or the channel options.
* The method must refrain from doing any I/O, or from closing the channel.
*
* Override this method to add your own callback logic.
* The default implementation does nothing.
*
* @param channel The channel that was initialized.
*/
public void postInitializeClientChannel(Channel channel) {
}
/**
* Called by {@link ServerBootstrap} after the initialization of the given server listener channel.
* The listener channel is responsible for invoking the {@code accept(2)} system call,
* and for producing child channels.
*
* The method is allowed to modify the handlers in the pipeline, the channel attributes, or the channel options.
* The method must refrain from doing any I/O, or from closing the channel.
*
* Override this method to add your own callback logic.
* The default implementation does nothing.
*
* @param channel The channel that was initialized.
*/
public void postInitializeServerListenerChannel(ServerChannel channel) {
}
/**
* Called by {@link ServerBootstrap} after the initialization of the given child channel.
* A child channel is a newly established connection from a client to the server.
*
* The method is allowed to modify the handlers in the pipeline, the channel attributes, or the channel options.
* The method must refrain from doing any I/O, or from closing the channel.
*
* Override this method to add your own callback logic.
* The default implementation does nothing.
*
* @param channel The channel that was initialized.
*/
public void postInitializeServerChildChannel(Channel channel) {
}
}