501 lines
20 KiB
Java
501 lines
20 KiB
Java
/*
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* Copyright 2009 Red Hat, Inc.
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*
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* Red Hat licenses this file to you under the Apache License, version 2.0
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* (the "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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package io.netty.channel;
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import java.io.InputStream;
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import java.io.OutputStream;
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import java.util.List;
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import java.util.Map;
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import java.util.NoSuchElementException;
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import io.netty.buffer.ChannelBuffer;
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import io.netty.handler.execution.ExecutionHandler;
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import io.netty.handler.execution.OrderedMemoryAwareThreadPoolExecutor;
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import io.netty.handler.ssl.SslHandler;
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/**
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* A list of {@link ChannelHandler}s which handles or intercepts
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* {@link ChannelEvent}s of a {@link Channel}. {@link ChannelPipeline}
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* implements an advanced form of the
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* <a href="http://java.sun.com/blueprints/corej2eepatterns/Patterns/InterceptingFilter.html">Intercepting
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* Filter</a> pattern to give a user full control over how an event is handled
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* and how the {@link ChannelHandler}s in the pipeline interact with each other.
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*
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* <h3>Creation of a pipeline</h3>
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*
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* For each new channel, a new pipeline must be created and attached to the
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* channel. Once attached, the coupling between the channel and the pipeline
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* is permanent; the channel cannot attach another pipeline to it nor detach
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* the current pipeline from it.
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* <p>
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* The recommended way to create a new pipeline is to use the helper methods in
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* {@link Channels} rather than calling an individual implementation's
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* constructor:
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* <pre>
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* import static io.netty.channel.{@link Channels}.*;
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* {@link ChannelPipeline} pipeline = pipeline(); // same with Channels.pipeline()
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* </pre>
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*
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* <h3>How an event flows in a pipeline</h3>
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*
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* The following diagram describes how {@link ChannelEvent}s are processed by
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* {@link ChannelHandler}s in a {@link ChannelPipeline} typically.
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* A {@link ChannelEvent} can be handled by either a {@link ChannelUpstreamHandler}
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* or a {@link ChannelDownstreamHandler} and be forwarded to the closest
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* handler by calling {@link ChannelHandlerContext#sendUpstream(ChannelEvent)}
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* or {@link ChannelHandlerContext#sendDownstream(ChannelEvent)}. The meaning
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* of the event is interpreted somewhat differently depending on whether it is
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* going upstream or going downstream. Please refer to {@link ChannelEvent} for
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* more information.
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* <pre>
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* I/O Request
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* via {@link Channel} or
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* {@link ChannelHandlerContext}
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* |
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* +----------------------------------------+---------------+
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* | ChannelPipeline | |
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* | \|/ |
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* | +----------------------+ +-----------+------------+ |
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* | | Upstream Handler N | | Downstream Handler 1 | |
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* | +----------+-----------+ +-----------+------------+ |
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* | /|\ | |
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* | | \|/ |
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* | +----------+-----------+ +-----------+------------+ |
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* | | Upstream Handler N-1 | | Downstream Handler 2 | |
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* | +----------+-----------+ +-----------+------------+ |
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* | /|\ . |
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* | . . |
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* | [ sendUpstream() ] [ sendDownstream() ] |
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* | [ + INBOUND data ] [ + OUTBOUND data ] |
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* | . . |
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* | . \|/ |
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* | +----------+-----------+ +-----------+------------+ |
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* | | Upstream Handler 2 | | Downstream Handler M-1 | |
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* | +----------+-----------+ +-----------+------------+ |
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* | /|\ | |
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* | | \|/ |
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* | +----------+-----------+ +-----------+------------+ |
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* | | Upstream Handler 1 | | Downstream Handler M | |
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* | +----------+-----------+ +-----------+------------+ |
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* | /|\ | |
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* +-------------+--------------------------+---------------+
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* | \|/
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* +-------------+--------------------------+---------------+
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* | | | |
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* | [ Socket.read() ] [ Socket.write() ] |
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* | |
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* | Netty Internal I/O Threads (Transport Implementation) |
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* +--------------------------------------------------------+
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* </pre>
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* An upstream event is handled by the upstream handlers in the bottom-up
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* direction as shown on the left side of the diagram. An upstream handler
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* usually handles the inbound data generated by the I/O thread on the bottom
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* of the diagram. The inbound data is often read from a remote peer via the
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* actual input operation such as {@link InputStream#read(byte[])}.
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* If an upstream event goes beyond the top upstream handler, it is discarded
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* silently.
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* <p>
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* A downstream event is handled by the downstream handler in the top-down
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* direction as shown on the right side of the diagram. A downstream handler
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* usually generates or transforms the outbound traffic such as write requests.
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* If a downstream event goes beyond the bottom downstream handler, it is
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* handled by an I/O thread associated with the {@link Channel}. The I/O thread
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* often performs the actual output operation such as {@link OutputStream#write(byte[])}.
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* <p>
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* For example, let us assume that we created the following pipeline:
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* <pre>
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* {@link ChannelPipeline} p = {@link Channels}.pipeline();
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* p.addLast("1", new UpstreamHandlerA());
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* p.addLast("2", new UpstreamHandlerB());
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* p.addLast("3", new DownstreamHandlerA());
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* p.addLast("4", new DownstreamHandlerB());
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* p.addLast("5", new UpstreamHandlerX());
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* </pre>
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* In the example above, the class whose name starts with {@code Upstream} means
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* it is an upstream handler. The class whose name starts with
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* {@code Downstream} means it is a downstream handler.
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* <p>
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* In the given example configuration, the handler evaluation order is 1, 2, 3,
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* 4, 5 when an event goes upstream. When an event goes downstream, the order
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* is 5, 4, 3, 2, 1. On top of this principle, {@link ChannelPipeline} skips
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* the evaluation of certain handlers to shorten the stack depth:
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* <ul>
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* <li>3 and 4 don't implement {@link ChannelUpstreamHandler}, and therefore the
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* actual evaluation order of an upstream event will be: 1, 2, and 5.</li>
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* <li>1, 2, and 5 don't implement {@link ChannelDownstreamHandler}, and
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* therefore the actual evaluation order of a downstream event will be:
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* 4 and 3.</li>
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* <li>If 5 extended {@link SimpleChannelHandler} which implements both
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* {@link ChannelUpstreamHandler} and {@link ChannelDownstreamHandler}, the
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* evaluation order of an upstream and a downstream event could be 125 and
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* 543 respectively.</li>
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* </ul>
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*
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* <h3>Building a pipeline</h3>
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* <p>
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* A user is supposed to have one or more {@link ChannelHandler}s in a
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* pipeline to receive I/O events (e.g. read) and to request I/O operations
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* (e.g. write and close). For example, a typical server will have the following
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* handlers in each channel's pipeline, but your mileage may vary depending on
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* the complexity and characteristics of the protocol and business logic:
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*
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* <ol>
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* <li>Protocol Decoder - translates binary data (e.g. {@link ChannelBuffer})
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* into a Java object.</li>
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* <li>Protocol Encoder - translates a Java object into binary data.</li>
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* <li>{@link ExecutionHandler} - applies a thread model.</li>
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* <li>Business Logic Handler - performs the actual business logic
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* (e.g. database access).</li>
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* </ol>
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*
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* and it could be represented as shown in the following example:
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*
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* <pre>
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* {@link ChannelPipeline} pipeline = {@link Channels#pipeline() Channels.pipeline()};
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* pipeline.addLast("decoder", new MyProtocolDecoder());
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* pipeline.addLast("encoder", new MyProtocolEncoder());
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* pipeline.addLast("executor", new {@link ExecutionHandler}(new {@link OrderedMemoryAwareThreadPoolExecutor}(16, 1048576, 1048576)));
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* pipeline.addLast("handler", new MyBusinessLogicHandler());
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* </pre>
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*
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* <h3>Thread safety</h3>
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* <p>
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* A {@link ChannelHandler} can be added or removed at any time because a
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* {@link ChannelPipeline} is thread safe. For example, you can insert a
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* {@link SslHandler} when sensitive information is about to be exchanged,
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* and remove it after the exchange.
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*
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* <h3>Pitfall</h3>
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* <p>
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* Due to the internal implementation detail of the current default
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* {@link ChannelPipeline}, the following code does not work as expected if
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* <tt>FirstHandler</tt> is the last handler in the pipeline:
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* <pre>
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* public class FirstHandler extends {@link SimpleChannelUpstreamHandler} {
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*
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* {@code @Override}
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* public void messageReceived({@link ChannelHandlerContext} ctx, {@link MessageEvent} e) {
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* // Remove this handler from the pipeline,
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* ctx.getPipeline().remove(this);
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* // And let SecondHandler handle the current event.
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* ctx.getPipeline().addLast("2nd", new SecondHandler());
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* ctx.sendUpstream(e);
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* }
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* }
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* </pre>
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* To implement the expected behavior, you have to add <tt>SecondHandler</tt>
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* before the removal or make sure there is at least one more handler between
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* <tt>FirstHandler</tt> and <tt>SecondHandler</tt>.
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*
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* @author <a href="http://netty.io/">The Netty Project</a>
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* @author <a href="http://gleamynode.net/">Trustin Lee</a>
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*
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* @apiviz.landmark
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* @apiviz.composedOf io.netty.channel.ChannelHandlerContext
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* @apiviz.owns io.netty.channel.ChannelHandler
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* @apiviz.uses io.netty.channel.ChannelSink - - sends events downstream
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*/
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public interface ChannelPipeline {
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/**
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* Inserts a {@link ChannelHandler} at the first position of this pipeline.
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*
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* @param name the name of the handler to insert first
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* @param handler the handler to insert first
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*
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* @throws IllegalArgumentException
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* if there's an entry with the same name already in the pipeline
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* @throws NullPointerException
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* if the specified name or handler is {@code null}
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*/
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void addFirst (String name, ChannelHandler handler);
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/**
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* Appends a {@link ChannelHandler} at the last position of this pipeline.
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*
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* @param name the name of the handler to append
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* @param handler the handler to append
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*
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* @throws IllegalArgumentException
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* if there's an entry with the same name already in the pipeline
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* @throws NullPointerException
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* if the specified name or handler is {@code null}
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*/
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void addLast (String name, ChannelHandler handler);
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/**
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* Inserts a {@link ChannelHandler} before an existing handler of this
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* pipeline.
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*
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* @param baseName the name of the existing handler
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* @param name the name of the handler to insert before
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* @param handler the handler to insert before
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*
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* @throws NoSuchElementException
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* if there's no such entry with the specified {@code baseName}
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* @throws IllegalArgumentException
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* if there's an entry with the same name already in the pipeline
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* @throws NullPointerException
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* if the specified baseName, name, or handler is {@code null}
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*/
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void addBefore(String baseName, String name, ChannelHandler handler);
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/**
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* Inserts a {@link ChannelHandler} after an existing handler of this
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* pipeline.
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*
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* @param baseName the name of the existing handler
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* @param name the name of the handler to insert after
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* @param handler the handler to insert after
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*
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* @throws NoSuchElementException
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* if there's no such entry with the specified {@code baseName}
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* @throws IllegalArgumentException
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* if there's an entry with the same name already in the pipeline
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* @throws NullPointerException
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* if the specified baseName, name, or handler is {@code null}
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*/
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void addAfter (String baseName, String name, ChannelHandler handler);
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/**
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* Removes the specified {@link ChannelHandler} from this pipeline.
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*
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* @throws NoSuchElementException
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* if there's no such handler in this pipeline
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* @throws NullPointerException
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* if the specified handler is {@code null}
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*/
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void remove(ChannelHandler handler);
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/**
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* Removes the {@link ChannelHandler} with the specified name from this
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* pipeline.
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*
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* @return the removed handler
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*
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* @throws NoSuchElementException
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* if there's no such handler with the specified name in this pipeline
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* @throws NullPointerException
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* if the specified name is {@code null}
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*/
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ChannelHandler remove(String name);
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/**
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* Removes the {@link ChannelHandler} of the specified type from this
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* pipeline
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*
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* @param <T> the type of the handler
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* @param handlerType the type of the handler
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*
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* @return the removed handler
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*
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* @throws NoSuchElementException
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* if there's no such handler of the specified type in this pipeline
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* @throws NullPointerException
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* if the specified handler type is {@code null}
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*/
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<T extends ChannelHandler> T remove(Class<T> handlerType);
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/**
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* Removes the first {@link ChannelHandler} in this pipeline.
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*
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* @return the removed handler
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*
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* @throws NoSuchElementException
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* if this pipeline is empty
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*/
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ChannelHandler removeFirst();
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/**
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* Removes the last {@link ChannelHandler} in this pipeline.
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*
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* @return the removed handler
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*
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* @throws NoSuchElementException
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* if this pipeline is empty
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*/
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ChannelHandler removeLast();
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/**
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* Replaces the specified {@link ChannelHandler} with a new handler in
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* this pipeline.
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*
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* @throws NoSuchElementException
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* if the specified old handler does not exist in this pipeline
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* @throws IllegalArgumentException
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* if a handler with the specified new name already exists in this
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* pipeline, except for the handler to be replaced
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* @throws NullPointerException
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* if the specified old handler, new name, or new handler is
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* {@code null}
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*/
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void replace(ChannelHandler oldHandler, String newName, ChannelHandler newHandler);
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/**
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* Replaces the {@link ChannelHandler} of the specified name with a new
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* handler in this pipeline.
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*
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* @return the removed handler
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*
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* @throws NoSuchElementException
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* if the handler with the specified old name does not exist in this pipeline
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* @throws IllegalArgumentException
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* if a handler with the specified new name already exists in this
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* pipeline, except for the handler to be replaced
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* @throws NullPointerException
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* if the specified old handler, new name, or new handler is
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* {@code null}
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*/
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ChannelHandler replace(String oldName, String newName, ChannelHandler newHandler);
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/**
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* Replaces the {@link ChannelHandler} of the specified type with a new
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* handler in this pipeline.
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*
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* @return the removed handler
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*
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* @throws NoSuchElementException
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* if the handler of the specified old handler type does not exist
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* in this pipeline
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* @throws IllegalArgumentException
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* if a handler with the specified new name already exists in this
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* pipeline, except for the handler to be replaced
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* @throws NullPointerException
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* if the specified old handler, new name, or new handler is
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* {@code null}
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*/
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<T extends ChannelHandler> T replace(Class<T> oldHandlerType, String newName, ChannelHandler newHandler);
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/**
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* Returns the first {@link ChannelHandler} in this pipeline.
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*
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* @return the first handler. {@code null} if this pipeline is empty.
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*/
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ChannelHandler getFirst();
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/**
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* Returns the last {@link ChannelHandler} in this pipeline.
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*
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* @return the last handler. {@code null} if this pipeline is empty.
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*/
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ChannelHandler getLast();
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/**
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* Returns the {@link ChannelHandler} with the specified name in this
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* pipeline.
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*
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* @return the handler with the specified name.
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* {@code null} if there's no such handler in this pipeline.
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*/
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ChannelHandler get(String name);
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/**
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* Returns the {@link ChannelHandler} of the specified type in this
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* pipeline.
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*
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* @return the handler of the specified handler type.
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* {@code null} if there's no such handler in this pipeline.
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*/
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<T extends ChannelHandler> T get(Class<T> handlerType);
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/**
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* Returns the context object of the specified {@link ChannelHandler} in
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* this pipeline.
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*
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* @return the context object of the specified handler.
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* {@code null} if there's no such handler in this pipeline.
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*/
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ChannelHandlerContext getContext(ChannelHandler handler);
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/**
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* Returns the context object of the {@link ChannelHandler} with the
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* specified name in this pipeline.
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*
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* @return the context object of the handler with the specified name.
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* {@code null} if there's no such handler in this pipeline.
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*/
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ChannelHandlerContext getContext(String name);
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/**
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* Returns the context object of the {@link ChannelHandler} of the
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* specified type in this pipeline.
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*
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* @return the context object of the handler of the specified type.
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* {@code null} if there's no such handler in this pipeline.
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*/
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ChannelHandlerContext getContext(Class<? extends ChannelHandler> handlerType);
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/**
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* Sends the specified {@link ChannelEvent} to the first
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* {@link ChannelUpstreamHandler} in this pipeline.
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*
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* @throws NullPointerException
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* if the specified event is {@code null}
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*/
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void sendUpstream(ChannelEvent e);
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/**
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* Sends the specified {@link ChannelEvent} to the last
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* {@link ChannelDownstreamHandler} in this pipeline.
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*
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* @throws NullPointerException
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* if the specified event is {@code null}
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*/
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void sendDownstream(ChannelEvent e);
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/**
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* Returns the {@link Channel} that this pipeline is attached to.
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*
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* @return the channel. {@code null} if this pipeline is not attached yet.
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*/
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Channel getChannel();
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/**
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* Returns the {@link ChannelSink} that this pipeline is attached to.
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*
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* @return the sink. {@code null} if this pipeline is not attached yet.
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*/
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ChannelSink getSink();
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/**
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* Attaches this pipeline to the specified {@link Channel} and
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* {@link ChannelSink}. Once a pipeline is attached, it can't be detached
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* nor attached again.
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*
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* @throws IllegalStateException if this pipeline is attached already
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*/
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void attach(Channel channel, ChannelSink sink);
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/**
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* Returns {@code true} if and only if this pipeline is attached to
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* a {@link Channel}.
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*/
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boolean isAttached();
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/**
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* Returns the {@link List} of the handler names.
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*/
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List<String> getNames();
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/**
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* Converts this pipeline into an ordered {@link Map} whose keys are
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* handler names and whose values are handlers.
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*/
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Map<String, ChannelHandler> toMap();
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}
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