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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:
 *
 *   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.channel;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import io.netty.channel.socket.DatagramChannel;
import io.netty.channel.socket.DatagramPacket;
import io.netty.channel.socket.ServerSocketChannel;
import io.netty.channel.socket.SocketChannel;
import io.netty.util.AttributeMap;

import java.net.InetSocketAddress;
import java.net.SocketAddress;


/**
 * A nexus to a network socket or a component which is capable of I/O
 * operations such as read, write, connect, and bind.
 * 

* A channel provides a user: *

    *
  • the current state of the channel (e.g. is it open? is it connected?),
  • *
  • the {@linkplain ChannelConfig configuration parameters} of the channel (e.g. receive buffer size),
  • *
  • the I/O operations that the channel supports (e.g. read, write, connect, and bind), and
  • *
  • the {@link ChannelPipeline} which handles all I/O events and requests * associated with the channel.
  • *
* *

All I/O operations are asynchronous.

*

* All I/O operations in Netty are asynchronous. It means any I/O calls will * return immediately with no guarantee that the requested I/O operation has * been completed at the end of the call. Instead, you will be returned with * a {@link ChannelFuture} instance which will notify you when the requested I/O * operation has succeeded, failed, or canceled. * *

Channels are hierarchical

*

* A {@link Channel} can have a {@linkplain #parent() parent} depending on * how it was created. For instance, a {@link SocketChannel}, that was accepted * by {@link ServerSocketChannel}, will return the {@link ServerSocketChannel} * as its parent on {@link #parent()}. *

* The semantics of the hierarchical structure depends on the transport * implementation where the {@link Channel} belongs to. For example, you could * write a new {@link Channel} implementation that creates the sub-channels that * share one socket connection, as BEEP and * SSH do. * *

Downcast to access transport-specific operations

*

* Some transports exposes additional operations that is specific to the * transport. Down-cast the {@link Channel} to sub-type to invoke such * operations. For example, with the old I/O datagram transport, multicast * join / leave operations are provided by {@link DatagramChannel}. * *

Release resources

*

* It is important to call {@link #close()} or {@link #close(ChannelPromise)} to release all * resources once you are done with the {@link Channel}. This ensures all resources are * released in a proper way, i.e. filehandles. */ public interface Channel extends AttributeMap, ChannelOutboundInvoker, Comparable { /** * Returns the globally unique identifier of this {@link Channel}. */ ChannelId id(); /** * Return the {@link EventLoop} this {@link Channel} was registered to. */ EventLoop eventLoop(); /** * Returns the parent of this channel. * * @return the parent channel. * {@code null} if this channel does not have a parent channel. */ Channel parent(); /** * Returns the configuration of this channel. */ ChannelConfig config(); /** * Returns {@code true} if the {@link Channel} is open and may get active later */ boolean isOpen(); /** * Returns {@code true} if the {@link Channel} is registered with an {@link EventLoop}. */ boolean isRegistered(); /** * Return {@code true} if the {@link Channel} is active and so connected. */ boolean isActive(); /** * Return the {@link ChannelMetadata} of the {@link Channel} which describe the nature of the {@link Channel}. */ ChannelMetadata metadata(); /** * Returns the local address where this channel is bound to. The returned * {@link SocketAddress} is supposed to be down-cast into more concrete * type such as {@link InetSocketAddress} to retrieve the detailed * information. * * @return the local address of this channel. * {@code null} if this channel is not bound. */ SocketAddress localAddress(); /** * Returns the remote address where this channel is connected to. The * returned {@link SocketAddress} is supposed to be down-cast into more * concrete type such as {@link InetSocketAddress} to retrieve the detailed * information. * * @return the remote address of this channel. * {@code null} if this channel is not connected. * If this channel is not connected but it can receive messages * from arbitrary remote addresses (e.g. {@link DatagramChannel}, * use {@link DatagramPacket#recipient()} to determine * the origination of the received message as this method will * return {@code null}. */ SocketAddress remoteAddress(); /** * Returns the {@link ChannelFuture} which will be notified when this * channel is closed. This method always returns the same future instance. */ ChannelFuture closeFuture(); /** * Returns {@code true} if and only if the I/O thread will perform the * requested write operation immediately. Any write requests made when * this method returns {@code false} are queued until the I/O thread is * ready to process the queued write requests. */ boolean isWritable(); /** * Get how many bytes can be written until {@link #isWritable()} returns {@code false}. * This quantity will always be non-negative. If {@link #isWritable()} is {@code false} then 0. */ long bytesBeforeUnwritable(); /** * Get how many bytes must be drained from underlying buffers until {@link #isWritable()} returns {@code true}. * This quantity will always be non-negative. If {@link #isWritable()} is {@code true} then 0. */ long bytesBeforeWritable(); /** * Returns an internal-use-only object that provides unsafe operations. */ Unsafe unsafe(); /** * Return the assigned {@link ChannelPipeline}. */ ChannelPipeline pipeline(); /** * Return the assigned {@link ByteBufAllocator} which will be used to allocate {@link ByteBuf}s. */ ByteBufAllocator alloc(); @Override Channel read(); @Override Channel flush(); /** * Unsafe operations that should never be called from user-code. These methods * are only provided to implement the actual transport, and must be invoked from an I/O thread except for the * following methods: *

    *
  • {@link #localAddress()}
  • *
  • {@link #remoteAddress()}
  • *
  • {@link #closeForcibly()}
  • *
  • {@link #register(EventLoop, ChannelPromise)}
  • *
  • {@link #deregister(ChannelPromise)}
  • *
  • {@link #voidPromise()}
  • *
*/ interface Unsafe { /** * Return the assigned {@link RecvByteBufAllocator.Handle} which will be used to allocate {@link ByteBuf}'s when * receiving data. */ RecvByteBufAllocator.Handle recvBufAllocHandle(); /** * Return the {@link SocketAddress} to which is bound local or * {@code null} if none. */ SocketAddress localAddress(); /** * Return the {@link SocketAddress} to which is bound remote or * {@code null} if none is bound yet. */ SocketAddress remoteAddress(); /** * Register the {@link Channel} of the {@link ChannelPromise} and notify * the {@link ChannelFuture} once the registration was complete. */ void register(EventLoop eventLoop, ChannelPromise promise); /** * Bind the {@link SocketAddress} to the {@link Channel} of the {@link ChannelPromise} and notify * it once its done. */ void bind(SocketAddress localAddress, ChannelPromise promise); /** * Connect the {@link Channel} of the given {@link ChannelFuture} with the given remote {@link SocketAddress}. * If a specific local {@link SocketAddress} should be used it need to be given as argument. Otherwise just * pass {@code null} to it. * * The {@link ChannelPromise} will get notified once the connect operation was complete. */ void connect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise); /** * Disconnect the {@link Channel} of the {@link ChannelFuture} and notify the {@link ChannelPromise} once the * operation was complete. */ void disconnect(ChannelPromise promise); /** * Close the {@link Channel} of the {@link ChannelPromise} and notify the {@link ChannelPromise} once the * operation was complete. */ void close(ChannelPromise promise); /** * Closes the {@link Channel} immediately without firing any events. Probably only useful * when registration attempt failed. */ void closeForcibly(); /** * Deregister the {@link Channel} of the {@link ChannelPromise} from {@link EventLoop} and notify the * {@link ChannelPromise} once the operation was complete. */ void deregister(ChannelPromise promise); /** * Schedules a read operation that fills the inbound buffer of the first {@link ChannelInboundHandler} in the * {@link ChannelPipeline}. If there's already a pending read operation, this method does nothing. */ void beginRead(); /** * Schedules a write operation. */ void write(Object msg, ChannelPromise promise); /** * Flush out all write operations scheduled via {@link #write(Object, ChannelPromise)}. */ void flush(); /** * Return a special ChannelPromise which can be reused and passed to the operations in {@link Unsafe}. * It will never be notified of a success or error and so is only a placeholder for operations * that take a {@link ChannelPromise} as argument but for which you not want to get notified. */ ChannelPromise voidPromise(); /** * Returns the {@link ChannelOutboundBuffer} of the {@link Channel} where the pending write requests are stored. */ ChannelOutboundBuffer outboundBuffer(); } }




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