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1   /*
2    * Copyright 2012 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package org.jboss.netty.channel;
17  
18  import java.io.InputStream;
19  import java.io.OutputStream;
20  import java.util.List;
21  import java.util.Map;
22  import java.util.NoSuchElementException;
23  
24  import org.jboss.netty.buffer.ChannelBuffer;
25  import org.jboss.netty.handler.execution.ExecutionHandler;
26  import org.jboss.netty.handler.execution.OrderedMemoryAwareThreadPoolExecutor;
27  import org.jboss.netty.handler.ssl.SslHandler;
28  
29  
30  /**
31   * A list of {@link ChannelHandler}s which handles or intercepts
32   * {@link ChannelEvent}s of a {@link Channel}.  {@link ChannelPipeline}
33   * implements an advanced form of the
34   * <a href="http://java.sun.com/blueprints/corej2eepatterns/Patterns/InterceptingFilter.html">Intercepting
35   * Filter</a> pattern to give a user full control over how an event is handled
36   * and how the {@link ChannelHandler}s in the pipeline interact with each other.
37   *
38   * <h3>Creation of a pipeline</h3>
39   *
40   * For each new channel, a new pipeline must be created and attached to the
41   * channel.  Once attached, the coupling between the channel and the pipeline
42   * is permanent; the channel cannot attach another pipeline to it nor detach
43   * the current pipeline from it.
44   * <p>
45   * The recommended way to create a new pipeline is to use the helper methods in
46   * {@link Channels} rather than calling an individual implementation's
47   * constructor:
48   * <pre>
49   * import static org.jboss.netty.channel.{@link Channels}.*;
50   * {@link ChannelPipeline} pipeline = pipeline(); // same with Channels.pipeline()
51   * </pre>
52   *
53   * <h3>How an event flows in a pipeline</h3>
54   *
55   * The following diagram describes how {@link ChannelEvent}s are processed by
56   * {@link ChannelHandler}s in a {@link ChannelPipeline} typically.
57   * A {@link ChannelEvent} can be handled by either a {@link ChannelUpstreamHandler}
58   * or a {@link ChannelDownstreamHandler} and be forwarded to the closest
59   * handler by calling {@link ChannelHandlerContext#sendUpstream(ChannelEvent)}
60   * or {@link ChannelHandlerContext#sendDownstream(ChannelEvent)}.  The meaning
61   * of the event is interpreted somewhat differently depending on whether it is
62   * going upstream or going downstream. Please refer to {@link ChannelEvent} for
63   * more information.
64   * <pre>
65   *                                       I/O Request
66   *                                     via {@link Channel} or
67   *                                 {@link ChannelHandlerContext}
68   *                                           |
69   *  +----------------------------------------+---------------+
70   *  |                  ChannelPipeline       |               |
71   *  |                                       \|/              |
72   *  |  +----------------------+  +-----------+------------+  |
73   *  |  | Upstream Handler  N  |  | Downstream Handler  1  |  |
74   *  |  +----------+-----------+  +-----------+------------+  |
75   *  |            /|\                         |               |
76   *  |             |                         \|/              |
77   *  |  +----------+-----------+  +-----------+------------+  |
78   *  |  | Upstream Handler N-1 |  | Downstream Handler  2  |  |
79   *  |  +----------+-----------+  +-----------+------------+  |
80   *  |            /|\                         .               |
81   *  |             .                          .               |
82   *  |     [ sendUpstream() ]        [ sendDownstream() ]     |
83   *  |     [ + INBOUND data ]        [ + OUTBOUND data  ]     |
84   *  |             .                          .               |
85   *  |             .                         \|/              |
86   *  |  +----------+-----------+  +-----------+------------+  |
87   *  |  | Upstream Handler  2  |  | Downstream Handler M-1 |  |
88   *  |  +----------+-----------+  +-----------+------------+  |
89   *  |            /|\                         |               |
90   *  |             |                         \|/              |
91   *  |  +----------+-----------+  +-----------+------------+  |
92   *  |  | Upstream Handler  1  |  | Downstream Handler  M  |  |
93   *  |  +----------+-----------+  +-----------+------------+  |
94   *  |            /|\                         |               |
95   *  +-------------+--------------------------+---------------+
96   *                |                         \|/
97   *  +-------------+--------------------------+---------------+
98   *  |             |                          |               |
99   *  |     [ Socket.read() ]          [ Socket.write() ]      |
100  *  |                                                        |
101  *  |  Netty Internal I/O Threads (Transport Implementation) |
102  *  +--------------------------------------------------------+
103  * </pre>
104  * An upstream event is handled by the upstream handlers in the bottom-up
105  * direction as shown on the left side of the diagram.  An upstream handler
106  * usually handles the inbound data generated by the I/O thread on the bottom
107  * of the diagram.  The inbound data is often read from a remote peer via the
108  * actual input operation such as {@link InputStream#read(byte[])}.
109  * If an upstream event goes beyond the top upstream handler, it is discarded
110  * silently.
111  * <p>
112  * A downstream event is handled by the downstream handler in the top-down
113  * direction as shown on the right side of the diagram.  A downstream handler
114  * usually generates or transforms the outbound traffic such as write requests.
115  * If a downstream event goes beyond the bottom downstream handler, it is
116  * handled by an I/O thread associated with the {@link Channel}. The I/O thread
117  * often performs the actual output operation such as {@link OutputStream#write(byte[])}.
118  * <p>
119  * For example, let us assume that we created the following pipeline:
120  * <pre>
121  * {@link ChannelPipeline} p = {@link Channels}.pipeline();
122  * p.addLast("1", new UpstreamHandlerA());
123  * p.addLast("2", new UpstreamHandlerB());
124  * p.addLast("3", new DownstreamHandlerA());
125  * p.addLast("4", new DownstreamHandlerB());
126  * p.addLast("5", new UpstreamHandlerX());
127  * </pre>
128  * In the example above, the class whose name starts with {@code Upstream} means
129  * it is an upstream handler.  The class whose name starts with
130  * {@code Downstream} means it is a downstream handler.
131  * <p>
132  * In the given example configuration, the handler evaluation order is 1, 2, 3,
133  * 4, 5 when an event goes upstream.  When an event goes downstream, the order
134  * is 5, 4, 3, 2, 1.  On top of this principle, {@link ChannelPipeline} skips
135  * the evaluation of certain handlers to shorten the stack depth:
136  * <ul>
137  * <li>3 and 4 don't implement {@link ChannelUpstreamHandler}, and therefore the
138  *     actual evaluation order of an upstream event will be: 1, 2, and 5.</li>
139  * <li>1, 2, and 5 don't implement {@link ChannelDownstreamHandler}, and
140  *     therefore the actual evaluation order of a downstream event will be:
141  *     4 and 3.</li>
142  * <li>If 5 extended {@link SimpleChannelHandler} which implements both
143  *     {@link ChannelUpstreamHandler} and {@link ChannelDownstreamHandler}, the
144  *     evaluation order of an upstream and a downstream event could be 125 and
145  *     543 respectively.</li>
146  * </ul>
147  *
148  * <h3>Building a pipeline</h3>
149  * <p>
150  * A user is supposed to have one or more {@link ChannelHandler}s in a
151  * pipeline to receive I/O events (e.g. read) and to request I/O operations
152  * (e.g. write and close).  For example, a typical server will have the following
153  * handlers in each channel's pipeline, but your mileage may vary depending on
154  * the complexity and characteristics of the protocol and business logic:
155  *
156  * <ol>
157  * <li>Protocol Decoder - translates binary data (e.g. {@link ChannelBuffer})
158  *                        into a Java object.</li>
159  * <li>Protocol Encoder - translates a Java object into binary data.</li>
160  * <li>{@link ExecutionHandler} - applies a thread model.</li>
161  * <li>Business Logic Handler - performs the actual business logic
162  *                              (e.g. database access).</li>
163  * </ol>
164  *
165  * and it could be represented as shown in the following example:
166  *
167  * <pre>
168  * {@link ChannelPipeline} pipeline = {@link Channels#pipeline() Channels.pipeline()};
169  * pipeline.addLast("decoder", new MyProtocolDecoder());
170  * pipeline.addLast("encoder", new MyProtocolEncoder());
171  * pipeline.addLast("executor", new {@link ExecutionHandler}(
172  *         new {@link OrderedMemoryAwareThreadPoolExecutor}(16, 1048576, 1048576)));
173  * pipeline.addLast("handler", new MyBusinessLogicHandler());
174  * </pre>
175  *
176  * <h3>Thread safety</h3>
177  * <p>
178  * A {@link ChannelHandler} can be added or removed at any time because a
179  * {@link ChannelPipeline} is thread safe.  For example, you can insert a
180  * {@link SslHandler} when sensitive information is about to be exchanged,
181  * and remove it after the exchange.
182  *
183  * <h3>Pitfall</h3>
184  * <p>
185  * Due to the internal implementation detail of the current default
186  * {@link ChannelPipeline}, the following code does not work as expected if
187  * <tt>FirstHandler</tt> is the last handler in the pipeline:
188  * <pre>
189  * public class FirstHandler extends {@link SimpleChannelUpstreamHandler} {
190  *
191  *     {@code @Override}
192  *     public void messageReceived({@link ChannelHandlerContext} ctx, {@link MessageEvent} e) {
193  *         // Remove this handler from the pipeline,
194  *         ctx.getPipeline().remove(this);
195  *         // And let SecondHandler handle the current event.
196  *         ctx.getPipeline().addLast("2nd", new SecondHandler());
197  *         ctx.sendUpstream(e);
198  *     }
199  * }
200  * </pre>
201  * To implement the expected behavior, you have to add <tt>SecondHandler</tt>
202  * before the removal or make sure there is at least one more handler between
203  * <tt>FirstHandler</tt> and <tt>SecondHandler</tt>.
204  *
205  * @apiviz.landmark
206  * @apiviz.composedOf org.jboss.netty.channel.ChannelHandlerContext
207  * @apiviz.owns       org.jboss.netty.channel.ChannelHandler
208  * @apiviz.uses       org.jboss.netty.channel.ChannelSink - - sends events downstream
209  */
210 public interface ChannelPipeline {
211 
212     /**
213      * Inserts a {@link ChannelHandler} at the first position of this pipeline.
214      *
215      * @param name     the name of the handler to insert first
216      * @param handler  the handler to insert first
217      *
218      * @throws IllegalArgumentException
219      *         if there's an entry with the same name already in the pipeline
220      * @throws NullPointerException
221      *         if the specified name or handler is {@code null}
222      */
223     void addFirst(String name, ChannelHandler handler);
224 
225     /**
226      * Appends a {@link ChannelHandler} at the last position of this pipeline.
227      *
228      * @param name     the name of the handler to append
229      * @param handler  the handler to append
230      *
231      * @throws IllegalArgumentException
232      *         if there's an entry with the same name already in the pipeline
233      * @throws NullPointerException
234      *         if the specified name or handler is {@code null}
235      */
236     void addLast(String name, ChannelHandler handler);
237 
238     /**
239      * Inserts a {@link ChannelHandler} before an existing handler of this
240      * pipeline.
241      *
242      * @param baseName  the name of the existing handler
243      * @param name      the name of the handler to insert before
244      * @param handler   the handler to insert before
245      *
246      * @throws NoSuchElementException
247      *         if there's no such entry with the specified {@code baseName}
248      * @throws IllegalArgumentException
249      *         if there's an entry with the same name already in the pipeline
250      * @throws NullPointerException
251      *         if the specified baseName, name, or handler is {@code null}
252      */
253     void addBefore(String baseName, String name, ChannelHandler handler);
254 
255     /**
256      * Inserts a {@link ChannelHandler} after an existing handler of this
257      * pipeline.
258      *
259      * @param baseName  the name of the existing handler
260      * @param name      the name of the handler to insert after
261      * @param handler   the handler to insert after
262      *
263      * @throws NoSuchElementException
264      *         if there's no such entry with the specified {@code baseName}
265      * @throws IllegalArgumentException
266      *         if there's an entry with the same name already in the pipeline
267      * @throws NullPointerException
268      *         if the specified baseName, name, or handler is {@code null}
269      */
270     void addAfter(String baseName, String name, ChannelHandler handler);
271 
272     /**
273      * Removes the specified {@link ChannelHandler} from this pipeline.
274      *
275      * @throws NoSuchElementException
276      *         if there's no such handler in this pipeline
277      * @throws NullPointerException
278      *         if the specified handler is {@code null}
279      */
280     void remove(ChannelHandler handler);
281 
282     /**
283      * Removes the {@link ChannelHandler} with the specified name from this
284      * pipeline.
285      *
286      * @return the removed handler
287      *
288      * @throws NoSuchElementException
289      *         if there's no such handler with the specified name in this pipeline
290      * @throws NullPointerException
291      *         if the specified name is {@code null}
292      */
293     ChannelHandler remove(String name);
294 
295     /**
296      * Removes the {@link ChannelHandler} of the specified type from this
297      * pipeline
298      *
299      * @param <T>          the type of the handler
300      * @param handlerType  the type of the handler
301      *
302      * @return the removed handler
303      *
304      * @throws NoSuchElementException
305      *         if there's no such handler of the specified type in this pipeline
306      * @throws NullPointerException
307      *         if the specified handler type is {@code null}
308      */
309     <T extends ChannelHandler> T remove(Class<T> handlerType);
310 
311     /**
312      * Removes the first {@link ChannelHandler} in this pipeline.
313      *
314      * @return the removed handler
315      *
316      * @throws NoSuchElementException
317      *         if this pipeline is empty
318      */
319     ChannelHandler removeFirst();
320 
321     /**
322      * Removes the last {@link ChannelHandler} in this pipeline.
323      *
324      * @return the removed handler
325      *
326      * @throws NoSuchElementException
327      *         if this pipeline is empty
328      */
329     ChannelHandler removeLast();
330 
331     /**
332      * Replaces the specified {@link ChannelHandler} with a new handler in
333      * this pipeline.
334      *
335      * @throws NoSuchElementException
336      *         if the specified old handler does not exist in this pipeline
337      * @throws IllegalArgumentException
338      *         if a handler with the specified new name already exists in this
339      *         pipeline, except for the handler to be replaced
340      * @throws NullPointerException
341      *         if the specified old handler, new name, or new handler is
342      *         {@code null}
343      */
344     void replace(ChannelHandler oldHandler, String newName, ChannelHandler newHandler);
345 
346     /**
347      * Replaces the {@link ChannelHandler} of the specified name with a new
348      * handler in this pipeline.
349      *
350      * @return the removed handler
351      *
352      * @throws NoSuchElementException
353      *         if the handler with the specified old name does not exist in this pipeline
354      * @throws IllegalArgumentException
355      *         if a handler with the specified new name already exists in this
356      *         pipeline, except for the handler to be replaced
357      * @throws NullPointerException
358      *         if the specified old handler, new name, or new handler is
359      *         {@code null}
360      */
361     ChannelHandler replace(String oldName, String newName, ChannelHandler newHandler);
362 
363     /**
364      * Replaces the {@link ChannelHandler} of the specified type with a new
365      * handler in this pipeline.
366      *
367      * @return the removed handler
368      *
369      * @throws NoSuchElementException
370      *         if the handler of the specified old handler type does not exist
371      *         in this pipeline
372      * @throws IllegalArgumentException
373      *         if a handler with the specified new name already exists in this
374      *         pipeline, except for the handler to be replaced
375      * @throws NullPointerException
376      *         if the specified old handler, new name, or new handler is
377      *         {@code null}
378      */
379     <T extends ChannelHandler> T replace(Class<T> oldHandlerType, String newName, ChannelHandler newHandler);
380 
381     /**
382      * Returns the first {@link ChannelHandler} in this pipeline.
383      *
384      * @return the first handler.  {@code null} if this pipeline is empty.
385      */
386     ChannelHandler getFirst();
387 
388     /**
389      * Returns the last {@link ChannelHandler} in this pipeline.
390      *
391      * @return the last handler.  {@code null} if this pipeline is empty.
392      */
393     ChannelHandler getLast();
394 
395     /**
396      * Returns the {@link ChannelHandler} with the specified name in this
397      * pipeline.
398      *
399      * @return the handler with the specified name.
400      *         {@code null} if there's no such handler in this pipeline.
401      */
402     ChannelHandler get(String name);
403 
404     /**
405      * Returns the {@link ChannelHandler} of the specified type in this
406      * pipeline.
407      *
408      * @return the handler of the specified handler type.
409      *         {@code null} if there's no such handler in this pipeline.
410      */
411     <T extends ChannelHandler> T get(Class<T> handlerType);
412 
413     /**
414      * Returns the context object of the specified {@link ChannelHandler} in
415      * this pipeline.
416      *
417      * @return the context object of the specified handler.
418      *         {@code null} if there's no such handler in this pipeline.
419      */
420     ChannelHandlerContext getContext(ChannelHandler handler);
421 
422     /**
423      * Returns the context object of the {@link ChannelHandler} with the
424      * specified name in this pipeline.
425      *
426      * @return the context object of the handler with the specified name.
427      *         {@code null} if there's no such handler in this pipeline.
428      */
429     ChannelHandlerContext getContext(String name);
430 
431     /**
432      * Returns the context object of the {@link ChannelHandler} of the
433      * specified type in this pipeline.
434      *
435      * @return the context object of the handler of the specified type.
436      *         {@code null} if there's no such handler in this pipeline.
437      */
438     ChannelHandlerContext getContext(Class<? extends ChannelHandler> handlerType);
439 
440     /**
441      * Sends the specified {@link ChannelEvent} to the first
442      * {@link ChannelUpstreamHandler} in this pipeline.
443      *
444      * @throws NullPointerException
445      *         if the specified event is {@code null}
446      */
447     void sendUpstream(ChannelEvent e);
448 
449     /**
450      * Sends the specified {@link ChannelEvent} to the last
451      * {@link ChannelDownstreamHandler} in this pipeline.
452      *
453      * @throws NullPointerException
454      *         if the specified event is {@code null}
455      */
456     void sendDownstream(ChannelEvent e);
457 
458     /**
459      * Schedules the specified task to be executed in the I/O thread associated
460      * with this pipeline's {@link Channel}.
461      */
462     ChannelFuture execute(Runnable task);
463 
464     /**
465      * Returns the {@link Channel} that this pipeline is attached to.
466      *
467      * @return the channel. {@code null} if this pipeline is not attached yet.
468      */
469     Channel getChannel();
470 
471     /**
472      * Returns the {@link ChannelSink} that this pipeline is attached to.
473      *
474      * @return the sink. {@code null} if this pipeline is not attached yet.
475      */
476     ChannelSink getSink();
477 
478     /**
479      * Attaches this pipeline to the specified {@link Channel} and
480      * {@link ChannelSink}.  Once a pipeline is attached, it can't be detached
481      * nor attached again.
482      *
483      * @throws IllegalStateException if this pipeline is attached already
484      */
485     void attach(Channel channel, ChannelSink sink);
486 
487     /**
488      * Returns {@code true} if and only if this pipeline is attached to
489      * a {@link Channel}.
490      */
491     boolean isAttached();
492 
493     /**
494      * Returns the {@link List} of the handler names.
495      */
496     List<String> getNames();
497 
498     /**
499      * Converts this pipeline into an ordered {@link Map} whose keys are
500      * handler names and whose values are handlers.
501      */
502     Map<String, ChannelHandler> toMap();
503 }