ChannelPipeline.java

/*
 * 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.util.concurrent.DefaultEventExecutorGroup;
import io.netty.util.concurrent.EventExecutor;
import io.netty.util.concurrent.EventExecutorGroup;

import java.net.ConnectException;
import java.net.SocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SocketChannel;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NoSuchElementException;


/**
 * A list of {@link ChannelHandler}s which handles or intercepts inbound events and outbound operations of a
 * {@link Channel}.  {@link ChannelPipeline} implements an advanced form of the
 * <a href="http://www.oracle.com/technetwork/java/interceptingfilter-142169.html">Intercepting Filter</a> pattern
 * to give a user full control over how an event is handled and how the {@link ChannelHandler}s in a pipeline
 * interact with each other.
 *
 * <h3>Creation of a pipeline</h3>
 *
 * Each channel has its own pipeline and it is created automatically when a new channel is created.
 *
 * <h3>How an event flows in a pipeline</h3>
 *
 * The following diagram describes how I/O events are processed by {@link ChannelHandler}s in a {@link ChannelPipeline}
 * typically. An I/O event is handled by a {@link ChannelHandler} and is forwarded by the {@link ChannelHandler} which
 * handled the event to the {@link ChannelHandler} which is placed right next to it. A {@link ChannelHandler} can also
 * trigger an arbitrary I/O event if necessary.  To forward or trigger an event, a {@link ChannelHandler} calls the
 * event propagation methods defined in {@link ChannelHandlerContext}, such as
 * {@link ChannelHandlerContext#fireChannelRead(Object)} and {@link ChannelHandlerContext#write(Object)}.
 * <pre>
 *                                                 I/O Request
 *                                            via {@link Channel} or
 *                                        {@link ChannelHandlerContext}
 *                                                      |
 *  +---------------------------------------------------+---------------+
 *  |                           ChannelPipeline         |               |
 *  |                                                  \|/              |
 *  |    +----------------------------------------------+----------+    |
 *  |    |                   ChannelHandler  N                     |    |
 *  |    +----------+-----------------------------------+----------+    |
 *  |              /|\                                  |               |
 *  |               |                                  \|/              |
 *  |    +----------+-----------------------------------+----------+    |
 *  |    |                   ChannelHandler N-1                    |    |
 *  |    +----------+-----------------------------------+----------+    |
 *  |              /|\                                  .               |
 *  |               .                                   .               |
 *  | ChannelHandlerContext.fireIN_EVT() ChannelHandlerContext.OUT_EVT()|
 *  |          [method call]                      [method call]         |
 *  |               .                                   .               |
 *  |               .                                  \|/              |
 *  |    +----------+-----------------------------------+----------+    |
 *  |    |                   ChannelHandler  2                     |    |
 *  |    +----------+-----------------------------------+----------+    |
 *  |              /|\                                  |               |
 *  |               |                                  \|/              |
 *  |    +----------+-----------------------------------+----------+    |
 *  |    |                   ChannelHandler  1                     |    |
 *  |    +----------+-----------------------------------+----------+    |
 *  |              /|\                                  |               |
 *  +---------------+-----------------------------------+---------------+
 *                  |                                  \|/
 *  +---------------+-----------------------------------+---------------+
 *  |               |                                   |               |
 *  |       [ Socket.read() ]                    [ Socket.write() ]     |
 *  |                                                                   |
 *  |  Netty Internal I/O Threads (Transport Implementation)            |
 *  +-------------------------------------------------------------------+
 * </pre>
 * An inbound event is handled by the {@link ChannelHandler}s in the bottom-up direction as shown on the left side of
 * the diagram.  An inbound event is usually triggered by the I/O thread on the bottom of the diagram so that the
 * {@link ChannelHandler}s are notified when the state of a {@link Channel} changes (e.g. newly established connections
 * and closed connections) or the inbound data was read from a remote peer.  If an inbound event goes beyond the
 * {@link ChannelHandler} at the top of the diagram, it is discarded and logged, depending on your loglevel.
 *
 * <p>
 * An outbound event is handled by the {@link ChannelHandler}s in the top-down direction as shown on the right side of
 * the diagram.  An outbound event is usually triggered by your code that requests an outbound I/O operation, such as
 * a write request and a connection attempt.  If an outbound event goes beyond the {@link ChannelHandler} at the
 * bottom of the diagram, it is handled by an I/O thread associated with the {@link Channel}. The I/O thread often
 * performs the actual output operation such as {@link SocketChannel#write(ByteBuffer)}.
 * <p>
 *
 * <h3>Forwarding an event to the next handler</h3>
 *
 * As explained briefly above, a {@link ChannelHandler} has to invoke the event propagation methods in
 * {@link ChannelHandlerContext} to forward an event to its next handler.  Those methods include:
 * <ul>
 * <li>Inbound event propagation methods:
 *     <ul>
 *     <li>{@link ChannelHandlerContext#fireChannelRegistered()}</li>
 *     <li>{@link ChannelHandlerContext#fireChannelActive()}</li>
 *     <li>{@link ChannelHandlerContext#fireChannelRead(Object)}</li>
 *     <li>{@link ChannelHandlerContext#fireChannelReadComplete()}</li>
 *     <li>{@link ChannelHandlerContext#fireExceptionCaught(Throwable)}</li>
 *     <li>{@link ChannelHandlerContext#fireUserEventTriggered(Object)}</li>
 *     <li>{@link ChannelHandlerContext#fireChannelWritabilityChanged()}</li>
 *     <li>{@link ChannelHandlerContext#fireChannelInactive()}</li>
 *     </ul>
 * </li>
 * <li>Outbound event propagation methods:
 *     <ul>
 *     <li>{@link ChannelHandlerContext#bind(SocketAddress, ChannelPromise)}</li>
 *     <li>{@link ChannelHandlerContext#connect(SocketAddress, SocketAddress, ChannelPromise)}</li>
 *     <li>{@link ChannelHandlerContext#write(Object, ChannelPromise)}</li>
 *     <li>{@link ChannelHandlerContext#flush()}</li>
 *     <li>{@link ChannelHandlerContext#read()}</li>
 *     <li>{@link ChannelHandlerContext#disconnect(ChannelPromise)}</li>
 *     <li>{@link ChannelHandlerContext#close(ChannelPromise)}</li>
 *     </ul>
 * </li>
 * </ul>
 *
 * and the following example shows how the event propagation is usually done:
 *
 * <pre>
 * public class MyInboundHandler extends {@link ChannelHandlerAdapter} {
 *     {@code @Override}
 *     public void channelActive({@link ChannelHandlerContext} ctx) {
 *         System.out.println("Connected!");
 *         ctx.fireChannelActive();
 *     }
 * }
 *
 * public clas MyOutboundHandler extends {@link ChannelHandlerAdapter} {
 *     {@code @Override}
 *     public void close({@link ChannelHandlerContext} ctx, {@link ChannelPromise} promise) {
 *         System.out.println("Closing ..");
 *         ctx.close(promise);
 *     }
 * }
 * </pre>
 *
 * <h3>Building a pipeline</h3>
 * <p>
 * A user is supposed to have one or more {@link ChannelHandler}s in a pipeline to receive I/O events (e.g. read) and
 * to request I/O operations (e.g. write and close).  For example, a typical server will have the following handlers
 * in each channel's pipeline, but your mileage may vary depending on the complexity and characteristics of the
 * protocol and business logic:
 *
 * <ol>
 * <li>Protocol Decoder - translates binary data (e.g. {@link ByteBuf}) into a Java object.</li>
 * <li>Protocol Encoder - translates a Java object into binary data.</li>
 * <li>Business Logic Handler - performs the actual business logic (e.g. database access).</li>
 * </ol>
 *
 * and it could be represented as shown in the following example:
 *
 * <pre>
 * static final {@link EventExecutorGroup} group = new {@link DefaultEventExecutorGroup}(16);
 * ...
 *
 * {@link ChannelPipeline} pipeline = ch.pipeline();
 *
 * pipeline.addLast("decoder", new MyProtocolDecoder());
 * pipeline.addLast("encoder", new MyProtocolEncoder());
 *
 * // Tell the pipeline to run MyBusinessLogicHandler's event handler methods
 * // in a different thread than an I/O thread so that the I/O thread is not blocked by
 * // a time-consuming task.
 * // If your business logic is fully asynchronous or finished very quickly, you don't
 * // need to specify a group.
 * pipeline.addLast(group, "handler", new MyBusinessLogicHandler());
 * </pre>
 *
 * <h3>Thread safety</h3>
 * <p>
 * A {@link ChannelHandler} can be added or removed at any time because a {@link ChannelPipeline} is thread safe.
 * For example, you can insert an encryption handler when sensitive information is about to be exchanged, and remove it
 * after the exchange.
 */
public interface ChannelPipeline extends Iterable<Entry<String, ChannelHandler>> {

    /**
     * Inserts a {@link ChannelHandler} at the first position of this pipeline.
     *
     * @param name     the name of the handler to insert first. {@code null} to let the name auto-generated.
     * @param handler  the handler to insert first
     *
     * @throws IllegalArgumentException
     *         if there's an entry with the same name already in the pipeline
     * @throws NullPointerException
     *         if the specified handler is {@code null}
     */
    ChannelPipeline addFirst(String name, ChannelHandler handler);

    /**
     * Inserts a {@link ChannelHandler} at the first position of this pipeline.
     *
     * @param group    the {@link EventExecutorGroup} which will be used to execute the {@link ChannelHandler}
     *                 methods
     * @param name     the name of the handler to insert first. {@code null} to let the name auto-generated.
     * @param handler  the handler to insert first
     *
     * @throws IllegalArgumentException
     *         if there's an entry with the same name already in the pipeline
     * @throws NullPointerException
     *         if the specified handler is {@code null}
     */
    ChannelPipeline addFirst(EventExecutorGroup group, String name, ChannelHandler handler);

    /**
     * Inserts a {@link ChannelHandler} at the first position of this pipeline.
     *
     * @param invoker  the {@link ChannelHandlerInvoker} which invokes the {@code handler}s event handler methods
     * @param name     the name of the handler to insert first. {@code null} to let the name auto-generated.
     * @param handler  the handler to insert first
     *
     * @throws IllegalArgumentException
     *         if there's an entry with the same name already in the pipeline
     * @throws NullPointerException
     *         if the specified handler is {@code null}
     */
    ChannelPipeline addFirst(ChannelHandlerInvoker invoker, String name, ChannelHandler handler);

    /**
     * Appends a {@link ChannelHandler} at the last position of this pipeline.
     *
     * @param name     the name of the handler to append. {@code null} to let the name auto-generated.
     * @param handler  the handler to append
     *
     * @throws IllegalArgumentException
     *         if there's an entry with the same name already in the pipeline
     * @throws NullPointerException
     *         if the specified handler is {@code null}
     */
    ChannelPipeline addLast(String name, ChannelHandler handler);

    /**
     * Appends a {@link ChannelHandler} at the last position of this pipeline.
     *
     * @param group    the {@link EventExecutorGroup} which will be used to execute the {@link ChannelHandler}
     *                 methods
     * @param name     the name of the handler to append. {@code null} to let the name auto-generated.
     * @param handler  the handler to append
     *
     * @throws IllegalArgumentException
     *         if there's an entry with the same name already in the pipeline
     * @throws NullPointerException
     *         if the specified handler is {@code null}
     */
    ChannelPipeline addLast(EventExecutorGroup group, String name, ChannelHandler handler);

    /**
     * Appends a {@link ChannelHandler} at the last position of this pipeline.
     *
     * @param invoker  the {@link ChannelHandlerInvoker} which invokes the {@code handler}s event handler methods
     * @param name     the name of the handler to append. {@code null} to let the name auto-generated.
     * @param handler  the handler to append
     *
     * @throws IllegalArgumentException
     *         if there's an entry with the same name already in the pipeline
     * @throws NullPointerException
     *         if the specified handler is {@code null}
     */
    ChannelPipeline addLast(ChannelHandlerInvoker invoker, String name, ChannelHandler handler);

    /**
     * Inserts a {@link ChannelHandler} before an existing handler of this
     * pipeline.
     *
     * @param baseName  the name of the existing handler
     * @param name      the name of the handler to insert before. {@code null} to let the name auto-generated.
     * @param handler   the handler to insert before
     *
     * @throws NoSuchElementException
     *         if there's no such entry with the specified {@code baseName}
     * @throws IllegalArgumentException
     *         if there's an entry with the same name already in the pipeline
     * @throws NullPointerException
     *         if the specified baseName or handler is {@code null}
     */
    ChannelPipeline addBefore(String baseName, String name, ChannelHandler handler);

    /**
     * Inserts a {@link ChannelHandler} before an existing handler of this
     * pipeline.
     *
     * @param group     the {@link EventExecutorGroup} which will be used to execute the {@link ChannelHandler}
     *                  methods
     * @param baseName  the name of the existing handler
     * @param name      the name of the handler to insert before. {@code null} to let the name auto-generated.
     * @param handler   the handler to insert before
     *
     * @throws NoSuchElementException
     *         if there's no such entry with the specified {@code baseName}
     * @throws IllegalArgumentException
     *         if there's an entry with the same name already in the pipeline
     * @throws NullPointerException
     *         if the specified baseName or handler is {@code null}
     */
    ChannelPipeline addBefore(EventExecutorGroup group, String baseName, String name, ChannelHandler handler);

    /**
     * Inserts a {@link ChannelHandler} before an existing handler of this
     * pipeline.
     *
     * @param invoker   the {@link ChannelHandlerInvoker} which invokes the {@code handler}s event handler methods
     * @param baseName  the name of the existing handler
     * @param name      the name of the handler to insert before. {@code null} to let the name auto-generated.
     * @param handler   the handler to insert before
     *
     * @throws NoSuchElementException
     *         if there's no such entry with the specified {@code baseName}
     * @throws IllegalArgumentException
     *         if there's an entry with the same name already in the pipeline
     * @throws NullPointerException
     *         if the specified baseName or handler is {@code null}
     */
    ChannelPipeline addBefore(ChannelHandlerInvoker invoker, String baseName, String name, ChannelHandler handler);

    /**
     * Inserts a {@link ChannelHandler} after an existing handler of this
     * pipeline.
     *
     * @param baseName  the name of the existing handler
     * @param name      the name of the handler to insert after. {@code null} to let the name auto-generated.
     * @param handler   the handler to insert after
     *
     * @throws NoSuchElementException
     *         if there's no such entry with the specified {@code baseName}
     * @throws IllegalArgumentException
     *         if there's an entry with the same name already in the pipeline
     * @throws NullPointerException
     *         if the specified baseName or handler is {@code null}
     */
    ChannelPipeline addAfter(String baseName, String name, ChannelHandler handler);

    /**
     * Inserts a {@link ChannelHandler} after an existing handler of this
     * pipeline.
     *
     * @param group     the {@link EventExecutorGroup} which will be used to execute the {@link ChannelHandler}
     *                  methods
     * @param baseName  the name of the existing handler
     * @param name      the name of the handler to insert after. {@code null} to let the name auto-generated.
     * @param handler   the handler to insert after
     *
     * @throws NoSuchElementException
     *         if there's no such entry with the specified {@code baseName}
     * @throws IllegalArgumentException
     *         if there's an entry with the same name already in the pipeline
     * @throws NullPointerException
     *         if the specified baseName or handler is {@code null}
     */
    ChannelPipeline addAfter(EventExecutorGroup group, String baseName, String name, ChannelHandler handler);

    /**
     * Inserts a {@link ChannelHandler} after an existing handler of this
     * pipeline.
     *
     * @param invoker   the {@link ChannelHandlerInvoker} which invokes the {@code handler}s event handler methods
     * @param baseName  the name of the existing handler
     * @param name      the name of the handler to insert after. {@code null} to let the name auto-generated.
     * @param handler   the handler to insert after
     *
     * @throws NoSuchElementException
     *         if there's no such entry with the specified {@code baseName}
     * @throws IllegalArgumentException
     *         if there's an entry with the same name already in the pipeline
     * @throws NullPointerException
     *         if the specified baseName or handler is {@code null}
     */
    ChannelPipeline addAfter(ChannelHandlerInvoker invoker, String baseName, String name, ChannelHandler handler);

    /**
     * Inserts a {@link ChannelHandler}s at the first position of this pipeline.
     *
     * @param handlers  the handlers to insert first
     *
     */
    ChannelPipeline addFirst(ChannelHandler... handlers);

    /**
     * Inserts a {@link ChannelHandler}s at the first position of this pipeline.
     *
     * @param group     the {@link EventExecutorGroup} which will be used to execute the {@link ChannelHandler}s
     *                  methods.
     * @param handlers  the handlers to insert first
     *
     */
    ChannelPipeline addFirst(EventExecutorGroup group, ChannelHandler... handlers);

    /**
     * Inserts a {@link ChannelHandler}s at the first position of this pipeline.
     *
     * @param invoker   the {@link ChannelHandlerInvoker} which invokes the {@code handler}s event handler methods
     * @param handlers  the handlers to insert first
     *
     */
    ChannelPipeline addFirst(ChannelHandlerInvoker invoker, ChannelHandler... handlers);

    /**
     * Inserts a {@link ChannelHandler}s at the last position of this pipeline.
     *
     * @param handlers  the handlers to insert last
     *
     */
    ChannelPipeline addLast(ChannelHandler... handlers);

    /**
     * Inserts a {@link ChannelHandler}s at the last position of this pipeline.
     *
     * @param group     the {@link EventExecutorGroup} which will be used to execute the {@link ChannelHandler}s
     *                  methods.
     * @param handlers  the handlers to insert last
     *
     */
    ChannelPipeline addLast(EventExecutorGroup group, ChannelHandler... handlers);

    /**
     * Inserts a {@link ChannelHandler}s at the last position of this pipeline.
     *
     * @param invoker   the {@link ChannelHandlerInvoker} which invokes the {@code handler}s event handler methods
     * @param handlers  the handlers to insert last
     *
     */
    ChannelPipeline addLast(ChannelHandlerInvoker invoker, ChannelHandler... handlers);

    /**
     * Removes the specified {@link ChannelHandler} from this pipeline.
     *
     * @param  handler          the {@link ChannelHandler} to remove
     *
     * @throws NoSuchElementException
     *         if there's no such handler in this pipeline
     * @throws NullPointerException
     *         if the specified handler is {@code null}
     */
    ChannelPipeline remove(ChannelHandler handler);

    /**
     * Removes the {@link ChannelHandler} with the specified name from this pipeline.
     *
     * @param  name             the name under which the {@link ChannelHandler} was stored.
     *
     * @return the removed handler
     *
     * @throws NoSuchElementException
     *         if there's no such handler with the specified name in this pipeline
     * @throws NullPointerException
     *         if the specified name is {@code null}
     */
    ChannelHandler remove(String name);

    /**
     * Removes the {@link ChannelHandler} of the specified type from this pipeline.
     *
     * @param <T>           the type of the handler
     * @param handlerType   the type of the handler
     *
     * @return the removed handler
     *
     * @throws NoSuchElementException
     *         if there's no such handler of the specified type in this pipeline
     * @throws NullPointerException
     *         if the specified handler type is {@code null}
     */
    <T extends ChannelHandler> T remove(Class<T> handlerType);

    /**
     * Removes the first {@link ChannelHandler} in this pipeline.
     *
     * @return the removed handler
     *
     * @throws NoSuchElementException
     *         if this pipeline is empty
     */
    ChannelHandler removeFirst();

    /**
     * Removes the last {@link ChannelHandler} in this pipeline.
     *
     * @return the removed handler
     *
     * @throws NoSuchElementException
     *         if this pipeline is empty
     */
    ChannelHandler removeLast();

    /**
     * Replaces the specified {@link ChannelHandler} with a new handler in this pipeline.
     *
     * @param  oldHandler    the {@link ChannelHandler} to be replaced
     * @param  newName       the name under which the replacement should be added.
     *                       {@code null} to use the same name with the handler being replaced.
     * @param  newHandler    the {@link ChannelHandler} which is used as replacement
     *
     * @return itself

     * @throws NoSuchElementException
     *         if the specified old handler does not exist in this pipeline
     * @throws IllegalArgumentException
     *         if a handler with the specified new name already exists in this
     *         pipeline, except for the handler to be replaced
     * @throws NullPointerException
     *         if the specified old handler or new handler is {@code null}
     */
    ChannelPipeline replace(ChannelHandler oldHandler, String newName, ChannelHandler newHandler);

    /**
     * Replaces the {@link ChannelHandler} of the specified name with a new handler in this pipeline.
     *
     * @param  oldName       the name of the {@link ChannelHandler} to be replaced
     * @param  newName       the name under which the replacement should be added.
     *                       {@code null} to use the same name with the handler being replaced.
     * @param  newHandler    the {@link ChannelHandler} which is used as replacement
     *
     * @return the removed handler
     *
     * @throws NoSuchElementException
     *         if the handler with the specified old name does not exist in this pipeline
     * @throws IllegalArgumentException
     *         if a handler with the specified new name already exists in this
     *         pipeline, except for the handler to be replaced
     * @throws NullPointerException
     *         if the specified old handler or new handler is {@code null}
     */
    ChannelHandler replace(String oldName, String newName, ChannelHandler newHandler);

    /**
     * Replaces the {@link ChannelHandler} of the specified type with a new handler in this pipeline.
     *
     * @param  oldHandlerType   the type of the handler to be removed
     * @param  newName          the name under which the replacement should be added.
     *                          {@code null} to use the same name with the handler being replaced.
     * @param  newHandler       the {@link ChannelHandler} which is used as replacement
     *
     * @return the removed handler
     *
     * @throws NoSuchElementException
     *         if the handler of the specified old handler type does not exist
     *         in this pipeline
     * @throws IllegalArgumentException
     *         if a handler with the specified new name already exists in this
     *         pipeline, except for the handler to be replaced
     * @throws NullPointerException
     *         if the specified old handler or new handler is {@code null}
     */
    <T extends ChannelHandler> T replace(Class<T> oldHandlerType, String newName,
                                         ChannelHandler newHandler);

    /**
     * Returns the first {@link ChannelHandler} in this pipeline.
     *
     * @return the first handler.  {@code null} if this pipeline is empty.
     */
    ChannelHandler first();

    /**
     * Returns the context of the first {@link ChannelHandler} in this pipeline.
     *
     * @return the context of the first handler.  {@code null} if this pipeline is empty.
     */
    ChannelHandlerContext firstContext();

    /**
     * Returns the last {@link ChannelHandler} in this pipeline.
     *
     * @return the last handler.  {@code null} if this pipeline is empty.
     */
    ChannelHandler last();

    /**
     * Returns the context of the last {@link ChannelHandler} in this pipeline.
     *
     * @return the context of the last handler.  {@code null} if this pipeline is empty.
     */
    ChannelHandlerContext lastContext();

    /**
     * Returns the {@link ChannelHandler} with the specified name in this
     * pipeline.
     *
     * @return the handler with the specified name.
     *         {@code null} if there's no such handler in this pipeline.
     */
    ChannelHandler get(String name);

    /**
     * Returns the {@link ChannelHandler} of the specified type in this
     * pipeline.
     *
     * @return the handler of the specified handler type.
     *         {@code null} if there's no such handler in this pipeline.
     */
    <T extends ChannelHandler> T get(Class<T> handlerType);

    /**
     * Returns the context object of the specified {@link ChannelHandler} in
     * this pipeline.
     *
     * @return the context object of the specified handler.
     *         {@code null} if there's no such handler in this pipeline.
     */
    ChannelHandlerContext context(ChannelHandler handler);

    /**
     * Returns the context object of the {@link ChannelHandler} with the
     * specified name in this pipeline.
     *
     * @return the context object of the handler with the specified name.
     *         {@code null} if there's no such handler in this pipeline.
     */
    ChannelHandlerContext context(String name);

    /**
     * Returns the context object of the {@link ChannelHandler} of the
     * specified type in this pipeline.
     *
     * @return the context object of the handler of the specified type.
     *         {@code null} if there's no such handler in this pipeline.
     */
    ChannelHandlerContext context(Class<? extends ChannelHandler> handlerType);

    /**
     * Returns the {@link Channel} that this pipeline is attached to.
     *
     * @return the channel. {@code null} if this pipeline is not attached yet.
     */
    Channel channel();

    /**
     * Returns the {@link List} of the handler names.
     */
    List<String> names();

    /**
     * Converts this pipeline into an ordered {@link Map} whose keys are
     * handler names and whose values are handlers.
     */
    Map<String, ChannelHandler> toMap();

    /**
     * A {@link Channel} was registered to its {@link EventLoop}.
     *
     * This will result in having the  {@link ChannelHandler#channelRegistered(ChannelHandlerContext)} method
     * called of the next  {@link ChannelHandler} contained in the  {@link ChannelPipeline} of the
     * {@link Channel}.
     */
    ChannelPipeline fireChannelRegistered();

    /**
     * A {@link Channel} was unregistered from its {@link EventLoop}.
     *
     * This will result in having the  {@link ChannelHandler#channelUnregistered(ChannelHandlerContext)} method
     * called of the next  {@link ChannelHandler} contained in the  {@link ChannelPipeline} of the
     * {@link Channel}.
     */
    ChannelPipeline fireChannelUnregistered();

    /**
     * A {@link Channel} is active now, which means it is connected.
     *
     * This will result in having the  {@link ChannelHandler#channelActive(ChannelHandlerContext)} method
     * called of the next  {@link ChannelHandler} contained in the  {@link ChannelPipeline} of the
     * {@link Channel}.
     */
    ChannelPipeline fireChannelActive();

    /**
     * A {@link Channel} is inactive now, which means it is closed.
     *
     * This will result in having the  {@link ChannelHandler#channelInactive(ChannelHandlerContext)} method
     * called of the next  {@link ChannelHandler} contained in the  {@link ChannelPipeline} of the
     * {@link Channel}.
     */
    ChannelPipeline fireChannelInactive();

    /**
     * A {@link Channel} received an {@link Throwable} in one of its inbound operations.
     *
     * This will result in having the  {@link ChannelHandler#exceptionCaught(ChannelHandlerContext, Throwable)}
     * method  called of the next  {@link ChannelHandler} contained in the  {@link ChannelPipeline} of the
     * {@link Channel}.
     */
    ChannelPipeline fireExceptionCaught(Throwable cause);

    /**
     * A {@link Channel} received an user defined event.
     *
     * This will result in having the  {@link ChannelHandler#userEventTriggered(ChannelHandlerContext, Object)}
     * method  called of the next  {@link ChannelHandler} contained in the  {@link ChannelPipeline} of the
     * {@link Channel}.
     */
    ChannelPipeline fireUserEventTriggered(Object event);

    /**
     * A {@link Channel} received a message.
     *
     * This will result in having the {@link ChannelHandler#channelRead(ChannelHandlerContext, Object)}
     * method  called of the next {@link ChannelHandler} contained in the  {@link ChannelPipeline} of the
     * {@link Channel}.
     */
    ChannelPipeline fireChannelRead(Object msg);

    /**
     * Triggers an {@link ChannelHandler#channelWritabilityChanged(ChannelHandlerContext)}
     * event to the next {@link ChannelHandler} in the {@link ChannelPipeline}.
     */
    ChannelPipeline fireChannelReadComplete();

    /**
     * Triggers an {@link ChannelHandler#channelWritabilityChanged(ChannelHandlerContext)}
     * event to the next {@link ChannelHandler} in the {@link ChannelPipeline}.
     */
    ChannelPipeline 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.
     * <p>
     * This will result in having the
     * {@link ChannelHandler#bind(ChannelHandlerContext, SocketAddress, ChannelPromise)} method
     * called of the next {@link ChannelHandler} 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.
     * <p>
     * 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.
     * <p>
     * This will result in having the
     * {@link ChannelHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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.
     * <p>
     * This will result in having the
     * {@link ChannelHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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.
     * <p>
     * This will result in having the
     * {@link ChannelHandler#disconnect(ChannelHandlerContext, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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.
     * <p>
     * This will result in having the
     * {@link ChannelHandler#close(ChannelHandlerContext, ChannelPromise)}
     * method called of the next {@link ChannelHandler} contained in the  {@link ChannelPipeline} of the
     * {@link Channel}.
     */
    ChannelFuture close();

    /**
     * Request to deregister the {@link Channel} 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.
     * <p>
     * This will result in having the
     * {@link ChannelHandler#deregister(ChannelHandlerContext, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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.
     * <p>
     * This will result in having the
     * {@link ChannelHandler#bind(ChannelHandlerContext, SocketAddress, ChannelPromise)} method
     * called of the next {@link ChannelHandler} 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.
     *
     * <p>
     * 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.
     * <p>
     * This will result in having the
     * {@link ChannelHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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.
     * <p>
     * This will result in having the
     * {@link ChannelHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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.
     * <p>
     * This will result in having the
     * {@link ChannelHandler#disconnect(ChannelHandlerContext, ChannelPromise)}
     * method called of the next {@link ChannelHandler} contained in the  {@link ChannelPipeline} of the
     * {@link Channel}.
     */
    ChannelFuture disconnect(ChannelPromise promise);

    /**
     * Request to close the {@link Channel} bound to this {@link ChannelPipeline} 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.
     * <p>
     * This will result in having the
     * {@link ChannelHandler#close(ChannelHandlerContext, ChannelPromise)}
     * method called of the next {@link ChannelHandler} contained in the  {@link ChannelPipeline} of the
     * {@link Channel}.
     */
    ChannelFuture close(ChannelPromise promise);

    /**
     * Request to deregister the {@link Channel} bound this {@link ChannelPipeline} 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.
     * <p>ChannelOutboundHandler
     * This will result in having the
     * {@link ChannelHandler#deregister(ChannelHandlerContext, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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 ChannelHandler#channelRead(ChannelHandlerContext, Object)} event if data was
     * read, and triggers a
     * {@link ChannelHandler#channelReadComplete(ChannelHandlerContext) channelReadComplete} event so the
     * handler can decide to continue reading.  If there's a pending read operation already, this method does nothing.
     * <p>
     * This will result in having the
     * {@link ChannelHandler#read(ChannelHandlerContext)}
     * method called of the next {@link ChannelHandler} contained in the  {@link ChannelPipeline} of the
     * {@link Channel}.
     */
    ChannelPipeline read();

    /**
     * Request to write a message via this {@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 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.
     */
    ChannelPipeline 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);
}