/*
* Copyright 2011 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 org.jboss.netty.channel;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.channels.NotYetConnectedException;
import java.nio.channels.SelectionKey;
import org.jboss.netty.channel.socket.DatagramChannel;
import org.jboss.netty.channel.socket.ServerSocketChannel;
import org.jboss.netty.channel.socket.SocketChannel;
import org.jboss.netty.channel.socket.nio.NioSocketChannelConfig;
/**
* A nexus to a network socket or a component which is capable of I/O
* operations such as read, write, connect, and bind.
* <p>
* A channel provides a user:
* <ul>
* <li>the current state of the channel (e.g. is it open? is it connected?),</li>
* <li>the {@linkplain ChannelConfig configuration parameters} of the channel (e.g. receive buffer size),</li>
* <li>the I/O operations that the channel supports (e.g. read, write, connect, and bind), and</li>
* <li>the {@link ChannelPipeline} which handles all {@linkplain ChannelEvent I/O events and requests}
* associated with the channel.</li>
* </ul>
*
* <h3>All I/O operations are asynchronous.</h3>
* <p>
* 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.
*
* <h3>Channels are hierarchical</h3>
* <p>
* A {@link Channel} can have a {@linkplain #getParent() 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 #getParent()}.
* <p>
* 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 <a href="http://beepcore.org/">BEEP</a> and
* <a href="http://en.wikipedia.org/wiki/Secure_Shell">SSH</a> do.
*
* <h3>Downcast to access transport-specific operations</h3>
* <p>
* 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}.
*
* <h3>InterestOps</h3>
* <p>
* A {@link Channel} has a property called {@link #getInterestOps() interestOps}
* which is similar to that of {@link SelectionKey#interestOps() NIO SelectionKey}.
* It is represented as a <a href="http://en.wikipedia.org/wiki/Bit_field">bit
* field</a> which is composed of the two flags.
* <ul>
* <li>{@link #OP_READ} - If set, a message sent by a remote peer will be read
* immediately. If unset, the message from the remote peer will not be read
* until the {@link #OP_READ} flag is set again (i.e. read suspension).</li>
* <li>{@link #OP_WRITE} - If set, a write request will not be sent to a remote
* peer until the {@link #OP_WRITE} flag is cleared and the write request
* will be pending in a queue. If unset, the write request will be flushed
* out as soon as possible from the queue.</li>
* <li>{@link #OP_READ_WRITE} - This is a combination of {@link #OP_READ} and
* {@link #OP_WRITE}, which means only write requests are suspended.</li>
* <li>{@link #OP_NONE} - This is a combination of (NOT {@link #OP_READ}) and
* (NOT {@link #OP_WRITE}), which means only read operation is suspended.</li>
* </ul>
* </p><p>
* You can set or clear the {@link #OP_READ} flag to suspend and resume read
* operation via {@link #setReadable(boolean)}.
* </p><p>
* Please note that you cannot suspend or resume write operation just like you
* can set or clear {@link #OP_READ}. The {@link #OP_WRITE} flag is read only
* and provided simply as a mean to tell you if the size of pending write
* requests exceeded a certain threshold or not so that you don't issue too many
* pending writes that lead to an {@link OutOfMemoryError}. For example, the
* NIO socket transport uses the {@code writeBufferLowWaterMark} and
* {@code writeBufferHighWaterMark} properties in {@link NioSocketChannelConfig}
* to determine when to set or clear the {@link #OP_WRITE} flag.
* </p>
*
* @apiviz.landmark
* @apiviz.composedOf org.jboss.netty.channel.ChannelConfig
* @apiviz.composedOf org.jboss.netty.channel.ChannelPipeline
*
* @apiviz.exclude ^org\.jboss\.netty\.channel\.([a-z]+\.)+[^\.]+Channel$
*/
public interface Channel extends Comparable<Channel> {
/**
* The {@link #getInterestOps() interestOps} value which tells that only
* read operation has been suspended.
*/
int OP_NONE = 0;
/**
* The {@link #getInterestOps() interestOps} value which tells that neither
* read nor write operation has been suspended.
*/
int OP_READ = 1;
/**
* The {@link #getInterestOps() interestOps} value which tells that both
* read and write operation has been suspended.
*/
int OP_WRITE = 4;
/**
* The {@link #getInterestOps() interestOps} value which tells that only
* write operation has been suspended.
*/
int OP_READ_WRITE = OP_READ | OP_WRITE;
/**
* Returns the unique integer ID of this channel.
*/
Integer getId();
/**
* Returns the {@link ChannelFactory} which created this channel.
*/
ChannelFactory getFactory();
/**
* Returns the parent of this channel.
*
* @return the parent channel.
* {@code null} if this channel does not have a parent channel.
*/
Channel getParent();
/**
* Returns the configuration of this channel.
*/
ChannelConfig getConfig();
/**
* Returns the {@link ChannelPipeline} which handles {@link ChannelEvent}s
* associated with this channel.
*/
ChannelPipeline getPipeline();
/**
* Returns {@code true} if and only if this channel is open.
*/
boolean isOpen();
/**
* Returns {@code true} if and only if this channel is bound to a
* {@linkplain #getLocalAddress() local address}.
*/
boolean isBound();
/**
* Returns {@code true} if and only if this channel is connected to a
* {@linkplain #getRemoteAddress() remote address}.
*/
boolean isConnected();
/**
* 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 getLocalAddress();
/**
* 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 MessageEvent#getRemoteAddress()} to determine
* the origination of the received message as this method will
* return {@code null}.
*/
SocketAddress getRemoteAddress();
/**
* Sends a message to this channel asynchronously. If this channel was
* created by a connectionless transport (e.g. {@link DatagramChannel})
* and is not connected yet, you have to call {@link #write(Object, SocketAddress)}
* instead. Otherwise, the write request will fail with
* {@link NotYetConnectedException} and an {@code 'exceptionCaught'} event
* will be triggered.
*
* @param message the message to write
*
* @return the {@link ChannelFuture} which will be notified when the
* write request succeeds or fails
*
* @throws NullPointerException if the specified message is {@code null}
*/
ChannelFuture write(Object message);
/**
* Sends a message to this channel asynchronously. It has an additional
* parameter that allows a user to specify where to send the specified
* message instead of this channel's current remote address. If this
* channel was created by a connectionless transport (e.g. {@link DatagramChannel})
* and is not connected yet, you must specify non-null address. Otherwise,
* the write request will fail with {@link NotYetConnectedException} and
* an {@code 'exceptionCaught'} event will be triggered.
*
* @param message the message to write
* @param remoteAddress where to send the specified message.
* This method is identical to {@link #write(Object)}
* if {@code null} is specified here.
*
* @return the {@link ChannelFuture} which will be notified when the
* write request succeeds or fails
*
* @throws NullPointerException if the specified message is {@code null}
*/
ChannelFuture write(Object message, SocketAddress remoteAddress);
/**
* Binds this channel to the specified local address asynchronously.
*
* @param localAddress where to bind
*
* @return the {@link ChannelFuture} which will be notified when the
* bind request succeeds or fails
*
* @throws NullPointerException if the specified address is {@code null}
*/
ChannelFuture bind(SocketAddress localAddress);
/**
* Connects this channel to the specified remote address asynchronously.
*
* @param remoteAddress where to connect
*
* @return the {@link ChannelFuture} which will be notified when the
* connection request succeeds or fails
*
* @throws NullPointerException if the specified address is {@code null}
*/
ChannelFuture connect(SocketAddress remoteAddress);
/**
* Disconnects this channel from the current remote address asynchronously.
*
* @return the {@link ChannelFuture} which will be notified when the
* disconnection request succeeds or fails
*/
ChannelFuture disconnect();
/**
* Unbinds this channel from the current local address asynchronously.
*
* @return the {@link ChannelFuture} which will be notified when the
* unbind request succeeds or fails
*/
ChannelFuture unbind();
/**
* Closes this channel asynchronously. If this channel is bound or
* connected, it will be disconnected and unbound first. Once a channel
* is closed, it can not be open again. Calling this method on a closed
* channel has no effect. Please note that this method always returns the
* same future instance.
*
* @return the {@link ChannelFuture} which will be notified when the
* close request succeeds or fails
*/
ChannelFuture close();
/**
* Returns the {@link ChannelFuture} which will be notified when this
* channel is closed. This method always returns the same future instance.
*/
ChannelFuture getCloseFuture();
/**
* Returns the current {@code interestOps} of this channel.
*
* @return {@link #OP_NONE}, {@link #OP_READ}, {@link #OP_WRITE}, or
* {@link #OP_READ_WRITE}
*/
int getInterestOps();
/**
* Returns {@code true} if and only if the I/O thread will read a message
* from this channel. This method is a shortcut to the following code:
* <pre>
* return (getInterestOps() & OP_READ) != 0;
* </pre>
*/
boolean isReadable();
/**
* 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. This method is a shortcut
* to the following code:
* <pre>
* return (getInterestOps() & OP_WRITE) == 0;
* </pre>
*/
boolean isWritable();
/**
* Changes the {@code interestOps} of this channel asynchronously.
*
* @param interestOps the new {@code interestOps}
*
* @return the {@link ChannelFuture} which will be notified when the
* {@code interestOps} change request succeeds or fails
*/
ChannelFuture setInterestOps(int interestOps);
/**
* Suspends or resumes the read operation of the I/O thread asynchronously.
* This method is a shortcut to the following code:
* <pre>
* int interestOps = getInterestOps();
* if (readable) {
* setInterestOps(interestOps | OP_READ);
* } else {
* setInterestOps(interestOps & ~OP_READ);
* }
* </pre>
*
* @param readable {@code true} to resume the read operation and
* {@code false} to suspend the read operation
*
* @return the {@link ChannelFuture} which will be notified when the
* {@code interestOps} change request succeeds or fails
*/
ChannelFuture setReadable(boolean readable);
}