1 //
2 // ========================================================================
3 // Copyright (c) 1995-2013 Mort Bay Consulting Pty. Ltd.
4 // ------------------------------------------------------------------------
5 // All rights reserved. This program and the accompanying materials
6 // are made available under the terms of the Eclipse Public License v1.0
7 // and Apache License v2.0 which accompanies this distribution.
8 //
9 // The Eclipse Public License is available at
10 // http://www.eclipse.org/legal/epl-v10.html
11 //
12 // The Apache License v2.0 is available at
13 // http://www.opensource.org/licenses/apache2.0.php
14 //
15 // You may elect to redistribute this code under either of these licenses.
16 // ========================================================================
17 //
18
19 package org.eclipse.jetty.continuation;
20
21 import javax.servlet.Filter;
22 import javax.servlet.FilterChain;
23 import javax.servlet.Servlet;
24 import javax.servlet.ServletRequest;
25 import javax.servlet.ServletResponse;
26 import javax.servlet.ServletResponseWrapper;
27
28 /* ------------------------------------------------------------ */
29 /**
30 * Continuation.
31 *
32 * A continuation is a mechanism by which a HTTP Request can be suspended and
33 * restarted after a timeout or an asynchronous event has occurred.
34 * <p>
35 * The continuation mechanism is a portable mechanism that will work
36 * asynchronously without additional configuration of all jetty-7,
37 * jetty-8 and Servlet 3.0 containers. With the addition of
38 * the {@link ContinuationFilter}, the mechanism will also work
39 * asynchronously on jetty-6 and non-asynchronously on any
40 * servlet 2.5 container.
41 * <p>
42 * The Continuation API is a simplification of the richer async API
43 * provided by the servlet-3.0 and an enhancement of the continuation
44 * API that was introduced with jetty-6.
45 * </p>
46 * <h1>Continuation Usage</h1>
47 * <p>
48 * A continuation object is obtained for a request by calling the
49 * factory method {@link ContinuationSupport#getContinuation(ServletRequest)}.
50 * The continuation type returned will depend on the servlet container
51 * being used.
52 * </p>
53 * <p>
54 * There are two distinct style of operation of the continuation API.
55 * </p>
56 * <h3>Suspend/Resume Usage</h3>
57 * <p>The suspend/resume style is used when a servlet and/or
58 * filter is used to generate the response after a asynchronous wait that is
59 * terminated by an asynchronous handler.
60 * </p>
61 * <pre>
62 * <b>Filter/Servlet:</b>
63 * // if we need to get asynchronous results
64 * Object results = request.getAttribute("results);
65 * if (results==null)
66 * {
67 * Continuation continuation = ContinuationSupport.getContinuation(request);
68 * continuation.suspend();
69 * myAsyncHandler.register(continuation);
70 * return; // or continuation.undispatch();
71 * }
72 *
73 * async wait ...
74 *
75 * <b>Async Handler:</b>
76 * // when the waited for event happens
77 * continuation.setAttribute("results",event);
78 * continuation.resume();
79 *
80 * <b>Filter/Servlet:</b>
81 * // when the request is redispatched
82 * if (results==null)
83 * {
84 * ... // see above
85 * }
86 * else
87 * {
88 * response.getOutputStream().write(process(results));
89 * }
90 * </pre>
91 * <h3>Suspend/Complete Usage</h3>
92 * <p>
93 * The suspend/complete style is used when an asynchronous handler is used to
94 * generate the response:
95 * </p>
96 * <pre>
97 * <b>Filter/Servlet:</b>
98 * // when we want to enter asynchronous mode
99 * Continuation continuation = ContinuationSupport.getContinuation(request);
100 * continuation.suspend(response); // response may be wrapped
101 * myAsyncHandler.register(continuation);
102 * return; // or continuation.undispatch();
103 *
104 * <b>Wrapping Filter:</b>
105 * // any filter that had wrapped the response should be implemented like:
106 * try
107 * {
108 * chain.doFilter(request,wrappedResponse);
109 * }
110 * finally
111 * {
112 * if (!continuation.isResponseWrapped())
113 * wrappedResponse.finish()
114 * else
115 * continuation.addContinuationListener(myCompleteListener)
116 * }
117 *
118 * async wait ...
119 *
120 * <b>Async Handler:</b>
121 * // when the async event happens
122 * continuation.getServletResponse().getOutputStream().write(process(event));
123 * continuation.complete()
124 * </pre>
125 *
126 * <h1>Continuation Timeout</h1>
127 * <p>
128 * If a continuation is suspended, but neither {@link #complete()} or {@link #resume()} is
129 * called during the period set by {@link #setTimeout(long)}, then the continuation will
130 * expire and {@link #isExpired()} will return true.
131 * </p>
132 * <p>
133 * When a continuation expires, the {@link ContinuationListener#onTimeout(Continuation)}
134 * method is called on any {@link ContinuationListener} that has been registered via the
135 * {@link #addContinuationListener(ContinuationListener)} method. The onTimeout handlers
136 * may write a response and call {@link #complete()}. If {@link #complete()} is not called,
137 * then the container will redispatch the request as if {@link #resume()} had been called,
138 * except that {@link #isExpired()} will be true and {@link #isResumed()} will be false.
139 * </p>
140 *
141 * @see ContinuationSupport
142 * @see ContinuationListener
143 *
144 */
145 public interface Continuation
146 {
147 public final static String ATTRIBUTE = "org.eclipse.jetty.continuation";
148
149 /* ------------------------------------------------------------ */
150 /**
151 * Set the continuation timeout.
152 *
153 * @param timeoutMs
154 * The time in milliseconds to wait before expiring this
155 * continuation after a call to {@link #suspend()} or {@link #suspend(ServletResponse)}.
156 * A timeout of <=0 means the continuation will never expire.
157 */
158 void setTimeout(long timeoutMs);
159
160 /* ------------------------------------------------------------ */
161 /**
162 * Suspend the processing of the request and associated
163 * {@link ServletResponse}.
164 *
165 * <p>
166 * After this method has been called, the lifecycle of the request will be
167 * extended beyond the return to the container from the
168 * {@link Servlet#service(ServletRequest, ServletResponse)} method and
169 * {@link Filter#doFilter(ServletRequest, ServletResponse, FilterChain)}
170 * calls. When a suspended request is returned to the container after
171 * a dispatch, then the container will not commit the associated response
172 * (unless an exception other than {@link ContinuationThrowable} is thrown).
173 * </p>
174 *
175 * <p>
176 * When the thread calling the filter chain and/or servlet has returned to
177 * the container with a suspended request, the thread is freed for other
178 * tasks and the request is held until either:
179 * <ul>
180 * <li>a call to {@link #resume()}.</li>
181 * <li>a call to {@link #complete()}.</li>
182 * <li>the timeout expires.</li>
183 * </ul>
184 * <p>
185 * Typically suspend with no arguments is uses when a call to {@link #resume()}
186 * is expected. If a call to {@link #complete()} is expected, then the
187 * {@link #suspend(ServletResponse)} method should be used instead of this method.
188 * </p>
189 *
190 * @exception IllegalStateException
191 * If the request cannot be suspended
192 */
193 void suspend();
194
195
196 /* ------------------------------------------------------------ */
197 /**
198 * Suspend the processing of the request and associated
199 * {@link ServletResponse}.
200 *
201 * <p>
202 * After this method has been called, the lifecycle of the request will be
203 * extended beyond the return to the container from the
204 * {@link Servlet#service(ServletRequest, ServletResponse)} method and
205 * {@link Filter#doFilter(ServletRequest, ServletResponse, FilterChain)}
206 * calls. When a suspended request is returned to the container after
207 * a dispatch, then the container will not commit the associated response
208 * (unless an exception other than {@link ContinuationThrowable} is thrown).
209 * </p>
210 * <p>
211 * When the thread calling the filter chain and/or servlet has returned to
212 * the container with a suspended request, the thread is freed for other
213 * tasks and the request is held until either:
214 * <ul>
215 * <li>a call to {@link #resume()}.</li>
216 * <li>a call to {@link #complete()}.</li>
217 * <li>the timeout expires.</li>
218 * </ul>
219 * <p>
220 * Typically suspend with a response argument is uses when a call to {@link #complete()}
221 * is expected. If a call to {@link #resume()} is expected, then the
222 * {@link #suspend()} method should be used instead of this method.
223 * </p>
224 * <p>
225 * Filters that may wrap the response object should check {@link #isResponseWrapped()}
226 * to decide if they should destroy/finish the wrapper. If {@link #isResponseWrapped()}
227 * returns true, then the wrapped request has been passed to the asynchronous
228 * handler and the wrapper should not be destroyed/finished until after a call to
229 * {@link #complete()} (potentially using a {@link ContinuationListener#onComplete(Continuation)}
230 * listener).
231 *
232 * @param response The response to return via a call to {@link #getServletResponse()}
233 * @exception IllegalStateException
234 * If the request cannot be suspended
235 */
236 void suspend(ServletResponse response);
237
238 /* ------------------------------------------------------------ */
239 /**
240 * Resume a suspended request.
241 *
242 * <p>
243 * This method can be called by any thread that has been passed a reference
244 * to a continuation. When called the request is redispatched to the
245 * normal filter chain and servlet processing with {@link #isInitial()} false.
246 * </p>
247 * <p>
248 * If resume is called before a suspended request is returned to the
249 * container (ie the thread that called {@link #suspend()} is still
250 * within the filter chain and/or servlet service method), then the resume
251 * does not take effect until the call to the filter chain and/or servlet
252 * returns to the container. In this case both {@link #isSuspended()} and
253 * {@link #isResumed()} return true. Multiple calls to resume are ignored.
254 * </p>
255 * <p>
256 * Typically resume() is used after a call to {@link #suspend()} with
257 * no arguments. The dispatch after a resume call will use the original
258 * request and response objects, even if {@link #suspend(ServletResponse)}
259 * had been passed a wrapped response.
260 * </p>
261 *
262 * @see #suspend()
263 * @exception IllegalStateException if the request is not suspended.
264 *
265 */
266 void resume();
267
268 /* ------------------------------------------------------------ */
269 /**
270 * Complete a suspended request.
271 *
272 * <p>
273 * This method can be called by any thread that has been passed a reference
274 * to a suspended request. When a request is completed, the associated
275 * response object committed and flushed. The request is not redispatched.
276 * </p>
277 *
278 * <p>
279 * If complete is called before a suspended request is returned to the
280 * container (ie the thread that called {@link #suspend()} is still
281 * within the filter chain and/or servlet service method), then the complete
282 * does not take effect until the call to the filter chain and/or servlet
283 * returns to the container. In this case both {@link #isSuspended()} and
284 * {@link #isResumed()} return true.
285 * </p>
286 *
287 * <p>
288 * Typically resume() is used after a call to {@link #suspend(ServletResponse)} with
289 * a possibly wrapped response. The async handler should use the response
290 * provided by {@link #getServletResponse()} to write the response before
291 * calling {@link #complete()}. If the request was suspended with a
292 * call to {@link #suspend()} then no response object will be available via
293 * {@link #getServletResponse()}.
294 * </p>
295 *
296 * <p>
297 * Once complete has been called and any thread calling the filter chain
298 * and/or servlet chain has returned to the container, the request lifecycle
299 * is complete. The container is able to recycle request objects, so it is
300 * not valid hold a request or continuation reference after the end of the
301 * life cycle.
302 *
303 * @see #suspend()
304 * @exception IllegalStateException
305 * if the request is not suspended.
306 *
307 */
308 void complete();
309
310 /* ------------------------------------------------------------ */
311 /**
312 * @return true after {@link #suspend()} has been called and before the
313 * request has been redispatched due to being resumed, completed or
314 * timed out.
315 */
316 boolean isSuspended();
317
318 /* ------------------------------------------------------------ */
319 /**
320 * @return true if the request has been redispatched by a call to
321 * {@link #resume()}. Returns false after any subsequent call to
322 * suspend
323 */
324 boolean isResumed();
325
326 /* ------------------------------------------------------------ */
327 /**
328 * @return true after a request has been redispatched as the result of a
329 * timeout. Returns false after any subsequent call to suspend.
330 */
331 boolean isExpired();
332
333 /* ------------------------------------------------------------ */
334 /**
335 * @return true while the request is within the initial dispatch to the
336 * filter chain and/or servlet. Will return false once the calling
337 * thread has returned to the container after suspend has been
338 * called and during any subsequent redispatch.
339 */
340 boolean isInitial();
341
342 /* ------------------------------------------------------------ */
343 /**
344 * Is the suspended response wrapped.
345 * <p>
346 * Filters that wrap the response object should check this method to
347 * determine if they should destroy/finish the wrapped response. If
348 * the request was suspended with a call to {@link #suspend(ServletResponse)}
349 * that passed the wrapped response, then the filter should register
350 * a {@link ContinuationListener} to destroy/finish the wrapped response
351 * during a call to {@link ContinuationListener#onComplete(Continuation)}.
352 * @return True if {@link #suspend(ServletResponse)} has been passed a
353 * {@link ServletResponseWrapper} instance.
354 */
355 boolean isResponseWrapped();
356
357
358 /* ------------------------------------------------------------ */
359 /**
360 * Get the suspended response.
361 * @return the {@link ServletResponse} passed to {@link #suspend(ServletResponse)}.
362 */
363 ServletResponse getServletResponse();
364
365 /* ------------------------------------------------------------ */
366 /**
367 * Add a ContinuationListener.
368 *
369 * @param listener
370 */
371 void addContinuationListener(ContinuationListener listener);
372
373 /* ------------------------------------------------------------ */
374 /** Set a request attribute.
375 * This method is a convenience method to call the {@link ServletRequest#setAttribute(String, Object)}
376 * method on the associated request object.
377 * This is a thread safe call and may be called by any thread.
378 * @param name the attribute name
379 * @param attribute the attribute value
380 */
381 public void setAttribute(String name, Object attribute);
382
383 /* ------------------------------------------------------------ */
384 /** Get a request attribute.
385 * This method is a convenience method to call the {@link ServletRequest#getAttribute(String)}
386 * method on the associated request object.
387 * This is a thread safe call and may be called by any thread.
388 * @param name the attribute name
389 * @return the attribute value
390 */
391 public Object getAttribute(String name);
392
393 /* ------------------------------------------------------------ */
394 /** Remove a request attribute.
395 * This method is a convenience method to call the {@link ServletRequest#removeAttribute(String)}
396 * method on the associated request object.
397 * This is a thread safe call and may be called by any thread.
398 * @param name the attribute name
399 */
400 public void removeAttribute(String name);
401
402 /* ------------------------------------------------------------ */
403 /**
404 * Undispatch the request.
405 * <p>
406 * This method can be called on a suspended continuation in order
407 * to exit the dispatch to the filter/servlet by throwing a {@link ContinuationThrowable}
408 * which is caught either by the container or the {@link ContinuationFilter}.
409 * This is an alternative to simply returning from the dispatch in the case
410 * where filters in the filter chain may not be prepared to handle a suspended
411 * request.
412 * </p>
413 * This method should only be used as a last resort and a normal return is a prefereable
414 * solution if filters can be updated to handle that case.
415 *
416 * @throws ContinuationThrowable thrown if the request is suspended. The instance of the
417 * exception may be reused on subsequent calls, so the stack frame may not be accurate.
418 */
419 public void undispatch() throws ContinuationThrowable;
420 }