/*
* Copyright 2012 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:
*
* http://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.channel;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import io.netty.util.Attribute;
import io.netty.util.AttributeKey;
import io.netty.util.AttributeMap;
import io.netty.util.concurrent.EventExecutor;
import java.nio.channels.Channels;
/**
* Enables a {@link ChannelHandler} to interact with its {@link ChannelPipeline}
* and other handlers. Among other things a handler can notify the next {@link ChannelHandler} in the
* {@link ChannelPipeline} as well as modify the {@link ChannelPipeline} it belongs to dynamically.
*
* <h3>Notify</h3>
*
* You can notify the closest handler in the same {@link ChannelPipeline} by calling one of the various methods
* provided here.
*
* Please refer to {@link ChannelPipeline} to understand how an event flows.
*
* <h3>Modifying a pipeline</h3>
*
* You can get the {@link ChannelPipeline} your handler belongs to by calling
* {@link #pipeline()}. A non-trivial application could insert, remove, or
* replace handlers in the pipeline dynamically at runtime.
*
* <h3>Retrieving for later use</h3>
*
* You can keep the {@link ChannelHandlerContext} for later use, such as
* triggering an event outside the handler methods, even from a different thread.
* <pre>
* public class MyHandler extends {@link ChannelDuplexHandler} {
*
* <b>private {@link ChannelHandlerContext} ctx;</b>
*
* public void beforeAdd({@link ChannelHandlerContext} ctx) {
* <b>this.ctx = ctx;</b>
* }
*
* public void login(String username, password) {
* ctx.write(new LoginMessage(username, password));
* }
* ...
* }
* </pre>
*
* <h3>Storing stateful information</h3>
*
* {@link #attr(AttributeKey)} allow you to
* store and access stateful information that is related with a handler and its
* context. Please refer to {@link ChannelHandler} to learn various recommended
* ways to manage stateful information.
*
* <h3>A handler can have more than one context</h3>
*
* Please note that a {@link ChannelHandler} instance can be added to more than
* one {@link ChannelPipeline}. It means a single {@link ChannelHandler}
* instance can have more than one {@link ChannelHandlerContext} and therefore
* the single instance can be invoked with different
* {@link ChannelHandlerContext}s if it is added to one or more
* {@link ChannelPipeline}s more than once.
* <p>
* For example, the following handler will have as many independent {@link AttributeKey}s
* as how many times it is added to pipelines, regardless if it is added to the
* same pipeline multiple times or added to different pipelines multiple times:
* <pre>
* public class FactorialHandler extends {@link ChannelInboundHandlerAdapter} {
*
* private final {@link AttributeKey}<{@link Integer}> counter = {@link AttributeKey}.valueOf("counter");
*
* // This handler will receive a sequence of increasing integers starting
* // from 1.
* {@code @Override}
* public void channelRead({@link ChannelHandlerContext} ctx, Object msg) {
* Integer a = ctx.attr(counter).get();
*
* if (a == null) {
* a = 1;
* }
*
* attr.set(a * (Integer) msg);
* }
* }
*
* // Different context objects are given to "f1", "f2", "f3", and "f4" even if
* // they refer to the same handler instance. Because the FactorialHandler
* // stores its state in a context object (using an {@link AttributeKey}), the factorial is
* // calculated correctly 4 times once the two pipelines (p1 and p2) are active.
* FactorialHandler fh = new FactorialHandler();
*
* {@link ChannelPipeline} p1 = {@link Channels}.pipeline();
* p1.addLast("f1", fh);
* p1.addLast("f2", fh);
*
* {@link ChannelPipeline} p2 = {@link Channels}.pipeline();
* p2.addLast("f3", fh);
* p2.addLast("f4", fh);
* </pre>
*
* <h3>Additional resources worth reading</h3>
* <p>
* Please refer to the {@link ChannelHandler}, and
* {@link ChannelPipeline} to find out more about inbound and outbound operations,
* what fundamental differences they have, how they flow in a pipeline, and how to handle
* the operation in your application.
*/
public interface ChannelHandlerContext extends AttributeMap, ChannelInboundInvoker, ChannelOutboundInvoker {
/**
* Return the {@link Channel} which is bound to the {@link ChannelHandlerContext}.
*/
Channel channel();
/**
* Returns the {@link EventExecutor} which is used to execute an arbitrary task.
*/
EventExecutor executor();
/**
* The unique name of the {@link ChannelHandlerContext}.The name was used when then {@link ChannelHandler}
* was added to the {@link ChannelPipeline}. This name can also be used to access the registered
* {@link ChannelHandler} from the {@link ChannelPipeline}.
*/
String name();
/**
* The {@link ChannelHandler} that is bound this {@link ChannelHandlerContext}.
*/
ChannelHandler handler();
/**
* Return {@code true} if the {@link ChannelHandler} which belongs to this context was removed
* from the {@link ChannelPipeline}. Note that this method is only meant to be called from with in the
* {@link EventLoop}.
*/
boolean isRemoved();
@Override
ChannelHandlerContext fireChannelRegistered();
@Override
ChannelHandlerContext fireChannelUnregistered();
@Override
ChannelHandlerContext fireChannelActive();
@Override
ChannelHandlerContext fireChannelInactive();
@Override
ChannelHandlerContext fireExceptionCaught(Throwable cause);
@Override
ChannelHandlerContext fireUserEventTriggered(Object evt);
@Override
ChannelHandlerContext fireChannelRead(Object msg);
@Override
ChannelHandlerContext fireChannelReadComplete();
@Override
ChannelHandlerContext fireChannelWritabilityChanged();
@Override
ChannelHandlerContext read();
@Override
ChannelHandlerContext flush();
/**
* Return the assigned {@link ChannelPipeline}
*/
ChannelPipeline pipeline();
/**
* Return the assigned {@link ByteBufAllocator} which will be used to allocate {@link ByteBuf}s.
*/
ByteBufAllocator alloc();
/**
* @deprecated Use {@link Channel#attr(AttributeKey)}
*/
@Deprecated
@Override
<T> Attribute<T> attr(AttributeKey<T> key);
/**
* @deprecated Use {@link Channel#hasAttr(AttributeKey)}
*/
@Deprecated
@Override
<T> boolean hasAttr(AttributeKey<T> key);
}