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/*
 * 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.AttributeKey;
import io.netty.util.AttributeMap;
import io.netty.util.concurrent.EventExecutor;
import io.netty.util.concurrent.FutureListener;

import java.net.ConnectException;
import java.net.SocketAddress;
import java.nio.channels.Channels;

/**
 * Enables a {@link ChannelHandler} to interact with its {@link ChannelPipeline}
 * and other handlers.  A handler can notify the next {@link ChannelHandler} in the {@link ChannelPipeline},
 * modify the {@link ChannelPipeline} it belongs to dynamically.
 *
 * 

Notify

* * 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. * *

Modifying a pipeline

* * 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. * *

Retrieving for later use

* * You can keep the {@link ChannelHandlerContext} for later use, such as * triggering an event outside the handler methods, even from a different thread. *
 * public class MyHandler extends {@link ChannelDuplexHandler} {
 *
 *     private {@link ChannelHandlerContext} ctx;
 *
 *     public void beforeAdd({@link ChannelHandlerContext} ctx) {
 *         this.ctx = ctx;
 *     }
 *
 *     public void login(String username, password) {
 *         ctx.write(new LoginMessage(username, password));
 *     }
 *     ...
 * }
 * 
* *

Storing stateful information

* * {@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. * *

A handler can have more than one context

* * 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. *

* 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: *

 * public class FactorialHandler extends {@link ChannelInboundHandlerAdapter}<{@link Integer}> {
 *
 *   private final {@link AttributeKey}<{@link Integer}> counter =
 *           new {@link AttributeKey}<{@link Integer}>("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));
 *   }
 * }
 *
 * // 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 (as an (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);
 * 
* *

Additional resources worth reading

*

* 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 { /** * Return the {@link Channel} which is bound to the {@link ChannelHandlerContext}. */ Channel channel(); /** * The {@link EventExecutor} that is used to dispatch the events. This can also be used to directly * submit tasks that get executed in the event loop. For more information please refer to the * {@link EventExecutor} javadoc. */ 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(); /** * A {@link Channel} was registered to its {@link EventLoop}. * * This will result in having the {@link ChannelInboundHandler#channelRegistered(ChannelHandlerContext)} method * called of the next {@link ChannelInboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelHandlerContext fireChannelRegistered(); /** * A {@link Channel} was unregistered from its {@link EventLoop}. * * This will result in having the {@link ChannelInboundHandler#channelUnregistered(ChannelHandlerContext)} method * called of the next {@link ChannelInboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelHandlerContext fireChannelUnregistered(); /** * A {@link Channel} is active now, which means it is connected. * * This will result in having the {@link ChannelInboundHandler#channelActive(ChannelHandlerContext)} method * called of the next {@link ChannelInboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelHandlerContext fireChannelActive(); /** * A {@link Channel} is inactive now, which means it is closed. * * This will result in having the {@link ChannelInboundHandler#channelInactive(ChannelHandlerContext)} method * called of the next {@link ChannelInboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelHandlerContext fireChannelInactive(); /** * A {@link Channel} received an {@link Throwable} in one of its inbound operations. * * This will result in having the {@link ChannelInboundHandler#exceptionCaught(ChannelHandlerContext, Throwable)} * method called of the next {@link ChannelInboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelHandlerContext fireExceptionCaught(Throwable cause); /** * A {@link Channel} received an user defined event. * * This will result in having the {@link ChannelInboundHandler#userEventTriggered(ChannelHandlerContext, Object)} * method called of the next {@link ChannelInboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelHandlerContext fireUserEventTriggered(Object evt); /** * A {@link Channel} received a message. * * This will result in having the {@link ChannelInboundHandler#channelRead(ChannelHandlerContext, Object)} * method called of the next {@link ChannelInboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelHandlerContext fireChannelRead(Object msg); /** * Triggers an {@link ChannelInboundHandler#channelReadComplete(ChannelHandlerContext)} * event to the next {@link ChannelInboundHandler} in the {@link ChannelPipeline}. */ ChannelHandlerContext fireChannelReadComplete(); /** * Triggers an {@link ChannelInboundHandler#channelWritabilityChanged(ChannelHandlerContext)} * event to the next {@link ChannelInboundHandler} in the {@link ChannelPipeline}. */ ChannelHandlerContext fireChannelWritabilityChanged(); /** * Request to bind to the given {@link SocketAddress} and notify the {@link ChannelFuture} once the operation * completes, either because the operation was successful or because of an error. *

* This will result in having the * {@link ChannelOutboundHandler#bind(ChannelHandlerContext, SocketAddress, ChannelPromise)} method * called of the next {@link ChannelOutboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelFuture bind(SocketAddress localAddress); /** * Request to connect to the given {@link SocketAddress} and notify the {@link ChannelFuture} once the operation * completes, either because the operation was successful or because of an error. *

* If the connection fails because of a connection timeout, the {@link ChannelFuture} will get failed with * a {@link ConnectTimeoutException}. If it fails because of connection refused a {@link ConnectException} * will be used. *

* This will result in having the * {@link ChannelOutboundHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)} * method called of the next {@link ChannelOutboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelFuture connect(SocketAddress remoteAddress); /** * Request to connect to the given {@link SocketAddress} while bind to the localAddress and notify the * {@link ChannelFuture} once the operation completes, either because the operation was successful or because of * an error. *

* This will result in having the * {@link ChannelOutboundHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)} * method called of the next {@link ChannelOutboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress); /** * Request to disconnect from the remote peer and notify the {@link ChannelFuture} once the operation completes, * either because the operation was successful or because of an error. *

* This will result in having the * {@link ChannelOutboundHandler#disconnect(ChannelHandlerContext, ChannelPromise)} * method called of the next {@link ChannelOutboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelFuture disconnect(); /** * Request to close the {@link Channel} and notify the {@link ChannelFuture} once the operation completes, * either because the operation was successful or because of * an error. * * After it is closed it is not possible to reuse it again. *

* This will result in having the * {@link ChannelOutboundHandler#close(ChannelHandlerContext, ChannelPromise)} * method called of the next {@link ChannelOutboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelFuture close(); /** * Request to deregister from the previous assigned {@link EventExecutor} and notify the * {@link ChannelFuture} once the operation completes, either because the operation was successful or because of * an error. *

* This will result in having the * {@link ChannelOutboundHandler#deregister(ChannelHandlerContext, ChannelPromise)} * method called of the next {@link ChannelOutboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. * */ ChannelFuture deregister(); /** * Request to bind to the given {@link SocketAddress} and notify the {@link ChannelFuture} once the operation * completes, either because the operation was successful or because of an error. * * The given {@link ChannelPromise} will be notified. *

* This will result in having the * {@link ChannelOutboundHandler#bind(ChannelHandlerContext, SocketAddress, ChannelPromise)} method * called of the next {@link ChannelOutboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise); /** * Request to connect to the given {@link SocketAddress} and notify the {@link ChannelFuture} once the operation * completes, either because the operation was successful or because of an error. * * The given {@link ChannelFuture} will be notified. * *

* If the connection fails because of a connection timeout, the {@link ChannelFuture} will get failed with * a {@link ConnectTimeoutException}. If it fails because of connection refused a {@link ConnectException} * will be used. *

* This will result in having the * {@link ChannelOutboundHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)} * method called of the next {@link ChannelOutboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelFuture connect(SocketAddress remoteAddress, ChannelPromise promise); /** * Request to connect to the given {@link SocketAddress} while bind to the localAddress and notify the * {@link ChannelFuture} once the operation completes, either because the operation was successful or because of * an error. * * The given {@link ChannelPromise} will be notified and also returned. *

* This will result in having the * {@link ChannelOutboundHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)} * method called of the next {@link ChannelOutboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise); /** * Request to disconnect from the remote peer and notify the {@link ChannelFuture} once the operation completes, * either because the operation was successful or because of an error. * * The given {@link ChannelPromise} will be notified. *

* This will result in having the * {@link ChannelOutboundHandler#disconnect(ChannelHandlerContext, ChannelPromise)} * method called of the next {@link ChannelOutboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelFuture disconnect(ChannelPromise promise); /** * Request to close the {@link Channel} and notify the {@link ChannelFuture} once the operation completes, * either because the operation was successful or because of * an error. * * After it is closed it is not possible to reuse it again. * The given {@link ChannelPromise} will be notified. *

* This will result in having the * {@link ChannelOutboundHandler#close(ChannelHandlerContext, ChannelPromise)} * method called of the next {@link ChannelOutboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelFuture close(ChannelPromise promise); /** * Request to deregister from the previous assigned {@link EventExecutor} and notify the * {@link ChannelFuture} once the operation completes, either because the operation was successful or because of * an error. * * The given {@link ChannelPromise} will be notified. *

* This will result in having the * {@link ChannelOutboundHandler#deregister(ChannelHandlerContext, ChannelPromise)} * method called of the next {@link ChannelOutboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelFuture deregister(ChannelPromise promise); /** * Request to Read data from the {@link Channel} into the first inbound buffer, triggers an * {@link ChannelInboundHandler#channelRead(ChannelHandlerContext, Object)} event if data was * read, and triggers a * {@link ChannelInboundHandler#channelReadComplete(ChannelHandlerContext) channelReadComplete} event so the * handler can decide to continue reading. If there's a pending read operation already, this method does nothing. *

* This will result in having the * {@link ChannelOutboundHandler#read(ChannelHandlerContext)} * method called of the next {@link ChannelOutboundHandler} contained in the {@link ChannelPipeline} of the * {@link Channel}. */ ChannelHandlerContext read(); /** * Request to write a message via this {@link ChannelHandlerContext} through the {@link ChannelPipeline}. * This method will not request to actual flush, so be sure to call {@link #flush()} * once you want to request to flush all pending data to the actual transport. */ ChannelFuture write(Object msg); /** * Request to write a message via this {@link ChannelHandlerContext} through the {@link ChannelPipeline}. * This method will not request to actual flush, so be sure to call {@link #flush()} * once you want to request to flush all pending data to the actual transport. */ ChannelFuture write(Object msg, ChannelPromise promise); /** * Request to flush all pending messages via this ChannelOutboundInvoker. */ ChannelHandlerContext flush(); /** * Shortcut for call {@link #write(Object, ChannelPromise)} and {@link #flush()}. */ ChannelFuture writeAndFlush(Object msg, ChannelPromise promise); /** * Shortcut for call {@link #write(Object)} and {@link #flush()}. */ ChannelFuture writeAndFlush(Object msg); /** * Return the assigned {@link ChannelPipeline} */ ChannelPipeline pipeline(); /** * Return the assigned {@link ByteBufAllocator} which will be used to allocate {@link ByteBuf}s. */ ByteBufAllocator alloc(); /** * Return a new {@link ChannelPromise}. */ ChannelPromise newPromise(); /** * Return an new {@link ChannelProgressivePromise} */ ChannelProgressivePromise newProgressivePromise(); /** * Create a new {@link ChannelFuture} which is marked as succeeded already. So {@link ChannelFuture#isSuccess()} * will return {@code true}. All {@link FutureListener} added to it will be notified directly. Also * every call of blocking methods will just return without blocking. */ ChannelFuture newSucceededFuture(); /** * Create a new {@link ChannelFuture} which is marked as failed already. So {@link ChannelFuture#isSuccess()} * will return {@code false}. All {@link FutureListener} added to it will be notified directly. Also * every call of blocking methods will just return without blocking. */ ChannelFuture newFailedFuture(Throwable cause); /** * Return a special ChannelPromise which can be reused for different operations. *

* It's only supported to use * it for {@link ChannelHandlerContext#write(Object, ChannelPromise)}. *

*

* Be aware that the returned {@link ChannelPromise} will not support most operations and should only be used * if you want to save an object allocation for every write operation. You will not be able to detect if the * operation was complete, only if it failed as the implementation will call * {@link ChannelPipeline#fireExceptionCaught(Throwable)} in this case. *

* Be aware this is an expert feature and should be used with care! */ ChannelPromise voidPromise(); }




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