/*
* 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.io.InputStream;
import java.io.OutputStream;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.handler.execution.ExecutionHandler;
import org.jboss.netty.handler.execution.OrderedMemoryAwareThreadPoolExecutor;
import org.jboss.netty.handler.ssl.SslHandler;
/**
* A list of {@link ChannelHandler}s which handles or intercepts
* {@link ChannelEvent}s of a {@link Channel}. {@link ChannelPipeline}
* implements an advanced form of the
* <a href="http://java.sun.com/blueprints/corej2eepatterns/Patterns/InterceptingFilter.html">Intercepting
* Filter</a> pattern to give a user full control over how an event is handled
* and how the {@link ChannelHandler}s in the pipeline interact with each other.
*
* <h3>Creation of a pipeline</h3>
*
* For each new channel, a new pipeline must be created and attached to the
* channel. Once attached, the coupling between the channel and the pipeline
* is permanent; the channel cannot attach another pipeline to it nor detach
* the current pipeline from it.
* <p>
* The recommended way to create a new pipeline is to use the helper methods in
* {@link Channels} rather than calling an individual implementation's
* constructor:
* <pre>
* import static org.jboss.netty.channel.{@link Channels}.*;
* {@link ChannelPipeline} pipeline = pipeline(); // same with Channels.pipeline()
* </pre>
*
* <h3>How an event flows in a pipeline</h3>
*
* The following diagram describes how {@link ChannelEvent}s are processed by
* {@link ChannelHandler}s in a {@link ChannelPipeline} typically.
* A {@link ChannelEvent} can be handled by either a {@link ChannelUpstreamHandler}
* or a {@link ChannelDownstreamHandler} and be forwarded to the closest
* handler by calling {@link ChannelHandlerContext#sendUpstream(ChannelEvent)}
* or {@link ChannelHandlerContext#sendDownstream(ChannelEvent)}. The meaning
* of the event is interpreted somewhat differently depending on whether it is
* going upstream or going downstream. Please refer to {@link ChannelEvent} for
* more information.
* <pre>
* I/O Request
* via {@link Channel} or
* {@link ChannelHandlerContext}
* |
* +----------------------------------------+---------------+
* | ChannelPipeline | |
* | \|/ |
* | +----------------------+ +-----------+------------+ |
* | | Upstream Handler N | | Downstream Handler 1 | |
* | +----------+-----------+ +-----------+------------+ |
* | /|\ | |
* | | \|/ |
* | +----------+-----------+ +-----------+------------+ |
* | | Upstream Handler N-1 | | Downstream Handler 2 | |
* | +----------+-----------+ +-----------+------------+ |
* | /|\ . |
* | . . |
* | [ sendUpstream() ] [ sendDownstream() ] |
* | [ + INBOUND data ] [ + OUTBOUND data ] |
* | . . |
* | . \|/ |
* | +----------+-----------+ +-----------+------------+ |
* | | Upstream Handler 2 | | Downstream Handler M-1 | |
* | +----------+-----------+ +-----------+------------+ |
* | /|\ | |
* | | \|/ |
* | +----------+-----------+ +-----------+------------+ |
* | | Upstream Handler 1 | | Downstream Handler M | |
* | +----------+-----------+ +-----------+------------+ |
* | /|\ | |
* +-------------+--------------------------+---------------+
* | \|/
* +-------------+--------------------------+---------------+
* | | | |
* | [ Socket.read() ] [ Socket.write() ] |
* | |
* | Netty Internal I/O Threads (Transport Implementation) |
* +--------------------------------------------------------+
* </pre>
* An upstream event is handled by the upstream handlers in the bottom-up
* direction as shown on the left side of the diagram. An upstream handler
* usually handles the inbound data generated by the I/O thread on the bottom
* of the diagram. The inbound data is often read from a remote peer via the
* actual input operation such as {@link InputStream#read(byte[])}.
* If an upstream event goes beyond the top upstream handler, it is discarded
* silently.
* <p>
* A downstream event is handled by the downstream handler in the top-down
* direction as shown on the right side of the diagram. A downstream handler
* usually generates or transforms the outbound traffic such as write requests.
* If a downstream event goes beyond the bottom downstream handler, 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 OutputStream#write(byte[])}.
* <p>
* For example, let us assume that we created the following pipeline:
* <pre>
* {@link ChannelPipeline} p = {@link Channels}.pipeline();
* p.addLast("1", new UpstreamHandlerA());
* p.addLast("2", new UpstreamHandlerB());
* p.addLast("3", new DownstreamHandlerA());
* p.addLast("4", new DownstreamHandlerB());
* p.addLast("5", new UpstreamHandlerX());
* </pre>
* In the example above, the class whose name starts with {@code Upstream} means
* it is an upstream handler. The class whose name starts with
* {@code Downstream} means it is a downstream handler.
* <p>
* In the given example configuration, the handler evaluation order is 1, 2, 3,
* 4, 5 when an event goes upstream. When an event goes downstream, the order
* is 5, 4, 3, 2, 1. On top of this principle, {@link ChannelPipeline} skips
* the evaluation of certain handlers to shorten the stack depth:
* <ul>
* <li>3 and 4 don't implement {@link ChannelUpstreamHandler}, and therefore the
* actual evaluation order of an upstream event will be: 1, 2, and 5.</li>
* <li>1, 2, and 5 don't implement {@link ChannelDownstreamHandler}, and
* therefore the actual evaluation order of a downstream event will be:
* 4 and 3.</li>
* <li>If 5 extended {@link SimpleChannelHandler} which implements both
* {@link ChannelUpstreamHandler} and {@link ChannelDownstreamHandler}, the
* evaluation order of an upstream and a downstream event could be 125 and
* 543 respectively.</li>
* </ul>
*
* <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 ChannelBuffer})
* into a Java object.</li>
* <li>Protocol Encoder - translates a Java object into binary data.</li>
* <li>{@link ExecutionHandler} - applies a thread model.</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>
* {@link ChannelPipeline} pipeline = {@link Channels#pipeline() Channels.pipeline()};
* pipeline.addLast("decoder", new MyProtocolDecoder());
* pipeline.addLast("encoder", new MyProtocolEncoder());
* pipeline.addLast("executor", new {@link ExecutionHandler}(new {@link OrderedMemoryAwareThreadPoolExecutor}(16, 1048576, 1048576)));
* pipeline.addLast("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 a
* {@link SslHandler} when sensitive information is about to be exchanged,
* and remove it after the exchange.
*
* <h3>Pitfall</h3>
* <p>
* Due to the internal implementation detail of the current default
* {@link ChannelPipeline}, the following code does not work as expected if
* <tt>FirstHandler</tt> is the last handler in the pipeline:
* <pre>
* public class FirstHandler extends {@link SimpleChannelUpstreamHandler} {
*
* {@code @Override}
* public void messageReceived({@link ChannelHandlerContext} ctx, {@link MessageEvent} e) {
* // Remove this handler from the pipeline,
* ctx.getPipeline().remove(this);
* // And let SecondHandler handle the current event.
* ctx.getPipeline().addLast("2nd", new SecondHandler());
* ctx.sendUpstream(e);
* }
* }
* </pre>
* To implement the expected behavior, you have to add <tt>SecondHandler</tt>
* before the removal or make sure there is at least one more handler between
* <tt>FirstHandler</tt> and <tt>SecondHandler</tt>.
*
* @apiviz.landmark
* @apiviz.composedOf org.jboss.netty.channel.ChannelHandlerContext
* @apiviz.owns org.jboss.netty.channel.ChannelHandler
* @apiviz.uses org.jboss.netty.channel.ChannelSink - - sends events downstream
*/
public interface ChannelPipeline {
/**
* Inserts a {@link ChannelHandler} at the first position of this pipeline.
*
* @param name the name of the handler to insert first
* @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 name or handler is {@code null}
*/
void addFirst(String name, ChannelHandler handler);
/**
* Appends a {@link ChannelHandler} at the last position of this pipeline.
*
* @param name the name of the handler to append
* @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 name or handler is {@code null}
*/
void addLast(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
* @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, name, or handler is {@code null}
*/
void addBefore(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
* @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, name, or handler is {@code null}
*/
void addAfter(String baseName, String name, ChannelHandler handler);
/**
* Removes the specified {@link ChannelHandler} from this pipeline.
*
* @throws NoSuchElementException
* if there's no such handler in this pipeline
* @throws NullPointerException
* if the specified handler is {@code null}
*/
void remove(ChannelHandler handler);
/**
* Removes the {@link ChannelHandler} with the specified name from this
* pipeline.
*
* @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.
*
* @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, new name, or new handler is
* {@code null}
*/
void replace(ChannelHandler oldHandler, String newName, ChannelHandler newHandler);
/**
* Replaces the {@link ChannelHandler} of the specified name with a new
* handler in this pipeline.
*
* @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, new name, 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.
*
* @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, new name, 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 getFirst();
/**
* Returns the last {@link ChannelHandler} in this pipeline.
*
* @return the last handler. {@code null} if this pipeline is empty.
*/
ChannelHandler getLast();
/**
* 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 getContext(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 getContext(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 getContext(Class<? extends ChannelHandler> handlerType);
/**
* Sends the specified {@link ChannelEvent} to the first
* {@link ChannelUpstreamHandler} in this pipeline.
*
* @throws NullPointerException
* if the specified event is {@code null}
*/
void sendUpstream(ChannelEvent e);
/**
* Sends the specified {@link ChannelEvent} to the last
* {@link ChannelDownstreamHandler} in this pipeline.
*
* @throws NullPointerException
* if the specified event is {@code null}
*/
void sendDownstream(ChannelEvent e);
/**
* Schedules the specified task to be executed in the I/O thread associated
* with this pipeline's {@link Channel}.
*/
ChannelFuture execute(Runnable task);
/**
* Returns the {@link Channel} that this pipeline is attached to.
*
* @return the channel. {@code null} if this pipeline is not attached yet.
*/
Channel getChannel();
/**
* Returns the {@link ChannelSink} that this pipeline is attached to.
*
* @return the sink. {@code null} if this pipeline is not attached yet.
*/
ChannelSink getSink();
/**
* Attaches this pipeline to the specified {@link Channel} and
* {@link ChannelSink}. Once a pipeline is attached, it can't be detached
* nor attached again.
*
* @throws IllegalStateException if this pipeline is attached already
*/
void attach(Channel channel, ChannelSink sink);
/**
* Returns {@code true} if and only if this pipeline is attached to
* a {@link Channel}.
*/
boolean isAttached();
/**
* Returns the {@link List} of the handler names.
*/
List<String> getNames();
/**
* Converts this pipeline into an ordered {@link Map} whose keys are
* handler names and whose values are handlers.
*/
Map<String, ChannelHandler> toMap();
}