1 /*
2 * Copyright 2009 Red Hat, Inc.
3 *
4 * Red Hat licenses this file to you under the Apache License, version 2.0
5 * (the "License"); you may not use this file except in compliance with the
6 * 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}(new {@link OrderedMemoryAwareThreadPoolExecutor}(16, 1048576, 1048576)));
172 * pipeline.addLast("handler", new MyBusinessLogicHandler());
173 * </pre>
174 *
175 * <h3>Thread safety</h3>
176 * <p>
177 * A {@link ChannelHandler} can be added or removed at any time because a
178 * {@link ChannelPipeline} is thread safe. For example, you can insert a
179 * {@link SslHandler} when sensitive information is about to be exchanged,
180 * and remove it after the exchange.
181 *
182 * <h3>Pitfall</h3>
183 * <p>
184 * Due to the internal implementation detail of the current default
185 * {@link ChannelPipeline}, the following code does not work as expected if
186 * <tt>FirstHandler</tt> is the last handler in the pipeline:
187 * <pre>
188 * public class FirstHandler extends {@link SimpleChannelUpstreamHandler} {
189 *
190 * {@code @Override}
191 * public void messageReceived({@link ChannelHandlerContext} ctx, {@link MessageEvent} e) {
192 * // Remove this handler from the pipeline,
193 * ctx.getPipeline().remove(this);
194 * // And let SecondHandler handle the current event.
195 * ctx.getPipeline().addLast("2nd", new SecondHandler());
196 * ctx.sendUpstream(e);
197 * }
198 * }
199 * </pre>
200 * To implement the expected behavior, you have to add <tt>SecondHandler</tt>
201 * before the removal or make sure there is at least one more handler between
202 * <tt>FirstHandler</tt> and <tt>SecondHandler</tt>.
203 *
204 * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
205 * @author <a href="http://gleamynode.net/">Trustin Lee</a>
206 *
207 * @version $Rev: 2153 $, $Date: 2010-02-17 17:24:25 +0900 (Wed, 17 Feb 2010) $
208 *
209 * @apiviz.landmark
210 * @apiviz.composedOf org.jboss.netty.channel.ChannelHandlerContext
211 * @apiviz.owns org.jboss.netty.channel.ChannelHandler
212 * @apiviz.uses org.jboss.netty.channel.ChannelSink - - sends events downstream
213 */
214 public interface ChannelPipeline {
215
216 /**
217 * Inserts a {@link ChannelHandler} at the first position of this pipeline.
218 *
219 * @param name the name of the handler to insert first
220 * @param handler the handler to insert first
221 *
222 * @throws IllegalArgumentException
223 * if there's an entry with the same name already in the pipeline
224 * @throws NullPointerException
225 * if the specified name or handler is {@code null}
226 */
227 void addFirst (String name, ChannelHandler handler);
228
229 /**
230 * Appends a {@link ChannelHandler} at the last position of this pipeline.
231 *
232 * @param name the name of the handler to append
233 * @param handler the handler to append
234 *
235 * @throws IllegalArgumentException
236 * if there's an entry with the same name already in the pipeline
237 * @throws NullPointerException
238 * if the specified name or handler is {@code null}
239 */
240 void addLast (String name, ChannelHandler handler);
241
242 /**
243 * Inserts a {@link ChannelHandler} before an existing handler of this
244 * pipeline.
245 *
246 * @param baseName the name of the existing handler
247 * @param name the name of the handler to insert before
248 * @param handler the handler to insert before
249 *
250 * @throws NoSuchElementException
251 * if there's no such entry with the specified {@code baseName}
252 * @throws IllegalArgumentException
253 * if there's an entry with the same name already in the pipeline
254 * @throws NullPointerException
255 * if the specified baseName, name, or handler is {@code null}
256 */
257 void addBefore(String baseName, String name, ChannelHandler handler);
258
259 /**
260 * Inserts a {@link ChannelHandler} after an existing handler of this
261 * pipeline.
262 *
263 * @param baseName the name of the existing handler
264 * @param name the name of the handler to insert after
265 * @param handler the handler to insert after
266 *
267 * @throws NoSuchElementException
268 * if there's no such entry with the specified {@code baseName}
269 * @throws IllegalArgumentException
270 * if there's an entry with the same name already in the pipeline
271 * @throws NullPointerException
272 * if the specified baseName, name, or handler is {@code null}
273 */
274 void addAfter (String baseName, String name, ChannelHandler handler);
275
276 /**
277 * Removes the specified {@link ChannelHandler} from this pipeline.
278 *
279 * @throws NoSuchElementException
280 * if there's no such handler in this pipeline
281 * @throws NullPointerException
282 * if the specified handler is {@code null}
283 */
284 void remove(ChannelHandler handler);
285
286 /**
287 * Removes the {@link ChannelHandler} with the specified name from this
288 * pipeline.
289 *
290 * @return the removed handler
291 *
292 * @throws NoSuchElementException
293 * if there's no such handler with the specified name in this pipeline
294 * @throws NullPointerException
295 * if the specified name is {@code null}
296 */
297 ChannelHandler remove(String name);
298
299 /**
300 * Removes the {@link ChannelHandler} of the specified type from this
301 * pipeline
302 *
303 * @param <T> the type of the handler
304 * @param handlerType the type of the handler
305 *
306 * @return the removed handler
307 *
308 * @throws NoSuchElementException
309 * if there's no such handler of the specified type in this pipeline
310 * @throws NullPointerException
311 * if the specified handler type is {@code null}
312 */
313 <T extends ChannelHandler> T remove(Class<T> handlerType);
314
315 /**
316 * Removes the first {@link ChannelHandler} in this pipeline.
317 *
318 * @return the removed handler
319 *
320 * @throws NoSuchElementException
321 * if this pipeline is empty
322 */
323 ChannelHandler removeFirst();
324
325 /**
326 * Removes the last {@link ChannelHandler} in this pipeline.
327 *
328 * @return the removed handler
329 *
330 * @throws NoSuchElementException
331 * if this pipeline is empty
332 */
333 ChannelHandler removeLast();
334
335 /**
336 * Replaces the specified {@link ChannelHandler} with a new handler in
337 * this pipeline.
338 *
339 * @throws NoSuchElementException
340 * if the specified old handler does not exist in this pipeline
341 * @throws IllegalArgumentException
342 * if a handler with the specified new name already exists in this
343 * pipeline, except for the handler to be replaced
344 * @throws NullPointerException
345 * if the specified old handler, new name, or new handler is
346 * {@code null}
347 */
348 void replace(ChannelHandler oldHandler, String newName, ChannelHandler newHandler);
349
350 /**
351 * Replaces the {@link ChannelHandler} of the specified name with a new
352 * handler in this pipeline.
353 *
354 * @return the removed handler
355 *
356 * @throws NoSuchElementException
357 * if the handler with the specified old name does not exist in this pipeline
358 * @throws IllegalArgumentException
359 * if a handler with the specified new name already exists in this
360 * pipeline, except for the handler to be replaced
361 * @throws NullPointerException
362 * if the specified old handler, new name, or new handler is
363 * {@code null}
364 */
365 ChannelHandler replace(String oldName, String newName, ChannelHandler newHandler);
366
367 /**
368 * Replaces the {@link ChannelHandler} of the specified type with a new
369 * handler in this pipeline.
370 *
371 * @return the removed handler
372 *
373 * @throws NoSuchElementException
374 * if the handler of the specified old handler type does not exist
375 * in this pipeline
376 * @throws IllegalArgumentException
377 * if a handler with the specified new name already exists in this
378 * pipeline, except for the handler to be replaced
379 * @throws NullPointerException
380 * if the specified old handler, new name, or new handler is
381 * {@code null}
382 */
383 <T extends ChannelHandler> T replace(Class<T> oldHandlerType, String newName, ChannelHandler newHandler);
384
385 /**
386 * Returns the first {@link ChannelHandler} in this pipeline.
387 *
388 * @return the first handler. {@code null} if this pipeline is empty.
389 */
390 ChannelHandler getFirst();
391
392 /**
393 * Returns the last {@link ChannelHandler} in this pipeline.
394 *
395 * @return the last handler. {@code null} if this pipeline is empty.
396 */
397 ChannelHandler getLast();
398
399 /**
400 * Returns the {@link ChannelHandler} with the specified name in this
401 * pipeline.
402 *
403 * @return the handler with the specified name.
404 * {@code null} if there's no such handler in this pipeline.
405 */
406 ChannelHandler get(String name);
407
408 /**
409 * Returns the {@link ChannelHandler} of the specified type in this
410 * pipeline.
411 *
412 * @return the handler of the specified handler type.
413 * {@code null} if there's no such handler in this pipeline.
414 */
415 <T extends ChannelHandler> T get(Class<T> handlerType);
416
417 /**
418 * Returns the context object of the specified {@link ChannelHandler} in
419 * this pipeline.
420 *
421 * @return the context object of the specified handler.
422 * {@code null} if there's no such handler in this pipeline.
423 */
424 ChannelHandlerContext getContext(ChannelHandler handler);
425
426 /**
427 * Returns the context object of the {@link ChannelHandler} with the
428 * specified name in this pipeline.
429 *
430 * @return the context object of the handler with the specified name.
431 * {@code null} if there's no such handler in this pipeline.
432 */
433 ChannelHandlerContext getContext(String name);
434
435 /**
436 * Returns the context object of the {@link ChannelHandler} of the
437 * specified type in this pipeline.
438 *
439 * @return the context object of the handler of the specified type.
440 * {@code null} if there's no such handler in this pipeline.
441 */
442 ChannelHandlerContext getContext(Class<? extends ChannelHandler> handlerType);
443
444
445 /**
446 * Sends the specified {@link ChannelEvent} to the first
447 * {@link ChannelUpstreamHandler} in this pipeline.
448 *
449 * @throws NullPointerException
450 * if the specified event is {@code null}
451 */
452 void sendUpstream(ChannelEvent e);
453
454 /**
455 * Sends the specified {@link ChannelEvent} to the last
456 * {@link ChannelDownstreamHandler} in this pipeline.
457 *
458 * @throws NullPointerException
459 * if the specified event is {@code null}
460 */
461 void sendDownstream(ChannelEvent e);
462
463 /**
464 * Returns the {@link Channel} that this pipeline is attached to.
465 *
466 * @return the channel. {@code null} if this pipeline is not attached yet.
467 */
468 Channel getChannel();
469
470 /**
471 * Returns the {@link ChannelSink} that this pipeline is attached to.
472 *
473 * @return the sink. {@code null} if this pipeline is not attached yet.
474 */
475 ChannelSink getSink();
476
477 /**
478 * Attaches this pipeline to the specified {@link Channel} and
479 * {@link ChannelSink}. Once a pipeline is attached, it can't be detached
480 * nor attached again.
481 *
482 * @throws IllegalStateException if this pipeline is attached already
483 */
484 void attach(Channel channel, ChannelSink sink);
485
486 /**
487 * Returns {@code true} if and only if this pipeline is attached to
488 * a {@link Channel}.
489 */
490 boolean isAttached();
491
492 /**
493 * Returns the {@link List} of the handler names.
494 */
495 List<String> getNames();
496
497 /**
498 * Converts this pipeline into an ordered {@link Map} whose keys are
499 * handler names and whose values are handlers.
500 */
501 Map<String, ChannelHandler> toMap();
502 }