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package org.eclipse.jetty.continuation;

import javax.servlet.FilterChain;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.ServletResponseWrapper;

/**
 * Continuation.
 * 

* A continuation is a mechanism by which an HTTP Request can be suspended and * restarted after a timeout or an asynchronous event has occurred. *

* The continuation mechanism is a portable mechanism that will work * asynchronously without additional configuration of all jetty-7, * jetty-8 and Servlet 3.0 containers. With the addition of * the {@link ContinuationFilter}, the mechanism will also work * asynchronously on jetty-6 and non-asynchronously on any * servlet 2.5 container. *

* The Continuation API is a simplification of the richer async API * provided by the servlet-3.0 and an enhancement of the continuation * API that was introduced with jetty-6. *

*

Continuation Usage

*

* A continuation object is obtained for a request by calling the * factory method {@link ContinuationSupport#getContinuation(ServletRequest)}. * The continuation type returned will depend on the servlet container * being used. *

*

* There are two distinct style of operation of the continuation API. *

*

Suspend/Resume Usage

*

The suspend/resume style is used when a servlet and/or * filter is used to generate the response after a asynchronous wait that is * terminated by an asynchronous handler. *

*
 * Filter/Servlet:
 *   // if we need to get asynchronous results
 *   Object results = request.getAttribute("results);
 *   if (results==null)
 *   {
 *     Continuation continuation = ContinuationSupport.getContinuation(request);
 *     continuation.suspend();
 *     myAsyncHandler.register(continuation);
 *     return; // or continuation.undispatch();
 *   }
 *
 * async wait ...
 *
 * Async Handler:
 *   // when the waited for event happens
 *   continuation.setAttribute("results",event);
 *   continuation.resume();
 *
 * Filter/Servlet:
 *   // when the request is redispatched
 *   if (results==null)
 *   {
 *     ... // see above
 *   }
 *   else
 *   {
 *     response.getOutputStream().write(process(results));
 *   }
 * 
*

Suspend/Complete Usage

*

* The suspend/complete style is used when an asynchronous handler is used to * generate the response: *

*
 * Filter/Servlet:
 *   // when we want to enter asynchronous mode
 *   Continuation continuation = ContinuationSupport.getContinuation(request);
 *   continuation.suspend(response); // response may be wrapped
 *   myAsyncHandler.register(continuation);
 *   return; // or continuation.undispatch();
 *
 * Wrapping Filter:
 *   // any filter that had wrapped the response should be implemented like:
 *   try
 *   {
 *     chain.doFilter(request,wrappedResponse);
 *   }
 *   finally
 *   {
 *     if (!continuation.isResponseWrapped())
 *       wrappedResponse.finish()
 *     else
 *       continuation.addContinuationListener(myCompleteListener)
 *   }
 *
 * async wait ...
 *
 * Async Handler:
 *   // when the async event happens
 *   continuation.getServletResponse().getOutputStream().write(process(event));
 *   continuation.complete()
 * 
* *

Continuation Timeout

*

* If a continuation is suspended, but neither {@link #complete()} or {@link #resume()} is * called during the period set by {@link #setTimeout(long)}, then the continuation will * expire and {@link #isExpired()} will return true. *

*

* When a continuation expires, the {@link ContinuationListener#onTimeout(Continuation)} * method is called on any {@link ContinuationListener} that has been registered via the * {@link #addContinuationListener(ContinuationListener)} method. The onTimeout handlers * may write a response and call {@link #complete()}. If {@link #complete()} is not called, * then the container will redispatch the request as if {@link #resume()} had been called, * except that {@link #isExpired()} will be true and {@link #isResumed()} will be false. *

* * @see ContinuationSupport * @see ContinuationListener * @deprecated use Servlet 3.0 {@link javax.servlet.AsyncContext} instead */ @Deprecated public interface Continuation { String ATTRIBUTE = "org.eclipse.jetty.continuation"; /** * Set the continuation timeout. * * @param timeoutMs The time in milliseconds to wait before expiring this * continuation after a call to {@link #suspend()} or {@link #suspend(ServletResponse)}. * A timeout of <=0 means the continuation will never expire. */ void setTimeout(long timeoutMs); /** * Suspend the processing of the request and associated * {@link ServletResponse}. * *

* After this method has been called, the lifecycle of the request will be * extended beyond the return to the container from the * {@link javax.servlet.Servlet#service(ServletRequest, ServletResponse)} method and * {@link javax.servlet.Filter#doFilter(ServletRequest, ServletResponse, FilterChain)} * calls. When a suspended request is returned to the container after * a dispatch, then the container will not commit the associated response * (unless an exception other than {@link ContinuationThrowable} is thrown). *

* *

* When the thread calling the filter chain and/or servlet has returned to * the container with a suspended request, the thread is freed for other * tasks and the request is held until either: *

    *
  • a call to {@link #resume()}.
  • *
  • a call to {@link #complete()}.
  • *
  • the timeout expires.
  • *
*

* Typically suspend with no arguments is uses when a call to {@link #resume()} * is expected. If a call to {@link #complete()} is expected, then the * {@link #suspend(ServletResponse)} method should be used instead of this method. *

* * @throws IllegalStateException If the request cannot be suspended */ void suspend(); /** * Suspend the processing of the request and associated * {@link ServletResponse}. * *

* After this method has been called, the lifecycle of the request will be * extended beyond the return to the container from the * {@link javax.servlet.Servlet#service(ServletRequest, ServletResponse)} method and * {@link javax.servlet.Filter#doFilter(ServletRequest, ServletResponse, FilterChain)} * calls. When a suspended request is returned to the container after * a dispatch, then the container will not commit the associated response * (unless an exception other than {@link ContinuationThrowable} is thrown). *

*

* When the thread calling the filter chain and/or servlet has returned to * the container with a suspended request, the thread is freed for other * tasks and the request is held until either: *

    *
  • a call to {@link #resume()}.
  • *
  • a call to {@link #complete()}.
  • *
  • the timeout expires.
  • *
*

* Typically suspend with a response argument is uses when a call to {@link #complete()} * is expected. If a call to {@link #resume()} is expected, then the * {@link #suspend()} method should be used instead of this method. *

*

* Filters that may wrap the response object should check {@link #isResponseWrapped()} * to decide if they should destroy/finish the wrapper. If {@link #isResponseWrapped()} * returns true, then the wrapped request has been passed to the asynchronous * handler and the wrapper should not be destroyed/finished until after a call to * {@link #complete()} (potentially using a {@link ContinuationListener#onComplete(Continuation)} * listener). * * @param response The response to return via a call to {@link #getServletResponse()} * @throws IllegalStateException If the request cannot be suspended */ void suspend(ServletResponse response); /** * Resume a suspended request. * *

* This method can be called by any thread that has been passed a reference * to a continuation. When called the request is redispatched to the * normal filter chain and servlet processing with {@link #isInitial()} false. *

*

* If resume is called before a suspended request is returned to the * container (ie the thread that called {@link #suspend()} is still * within the filter chain and/or servlet service method), then the resume * does not take effect until the call to the filter chain and/or servlet * returns to the container. In this case both {@link #isSuspended()} and * {@link #isResumed()} return true. Multiple calls to resume are ignored. *

*

* Typically resume() is used after a call to {@link #suspend()} with * no arguments. The dispatch after a resume call will use the original * request and response objects, even if {@link #suspend(ServletResponse)} * had been passed a wrapped response. *

* * @throws IllegalStateException if the request is not suspended. * @see #suspend() */ void resume(); /** * Complete a suspended request. * *

* This method can be called by any thread that has been passed a reference * to a suspended request. When a request is completed, the associated * response object committed and flushed. The request is not redispatched. *

* *

* If complete is called before a suspended request is returned to the * container (ie the thread that called {@link #suspend()} is still * within the filter chain and/or servlet service method), then the complete * does not take effect until the call to the filter chain and/or servlet * returns to the container. In this case both {@link #isSuspended()} and * {@link #isResumed()} return true. *

* *

* Typically resume() is used after a call to {@link #suspend(ServletResponse)} with * a possibly wrapped response. The async handler should use the response * provided by {@link #getServletResponse()} to write the response before * calling {@link #complete()}. If the request was suspended with a * call to {@link #suspend()} then no response object will be available via * {@link #getServletResponse()}. *

* *

* Once complete has been called and any thread calling the filter chain * and/or servlet chain has returned to the container, the request lifecycle * is complete. The container is able to recycle request objects, so it is * not valid hold a request or continuation reference after the end of the * life cycle. * * @throws IllegalStateException if the request is not suspended. * @see #suspend() */ void complete(); /** * @return true after {@link #suspend()} has been called and before the * request has been redispatched due to being resumed, completed or * timed out. */ boolean isSuspended(); /** * @return true if the request has been redispatched by a call to * {@link #resume()}. Returns false after any subsequent call to * suspend */ boolean isResumed(); /** * @return true after a request has been redispatched as the result of a * timeout. Returns false after any subsequent call to suspend. */ boolean isExpired(); /** * @return true while the request is within the initial dispatch to the * filter chain and/or servlet. Will return false once the calling * thread has returned to the container after suspend has been * called and during any subsequent redispatch. */ boolean isInitial(); /** * Is the suspended response wrapped. *

* Filters that wrap the response object should check this method to * determine if they should destroy/finish the wrapped response. If * the request was suspended with a call to {@link #suspend(ServletResponse)} * that passed the wrapped response, then the filter should register * a {@link ContinuationListener} to destroy/finish the wrapped response * during a call to {@link ContinuationListener#onComplete(Continuation)}. * * @return True if {@link #suspend(ServletResponse)} has been passed a * {@link ServletResponseWrapper} instance. */ boolean isResponseWrapped(); /** * Get the suspended response. * * @return the {@link ServletResponse} passed to {@link #suspend(ServletResponse)}. */ ServletResponse getServletResponse(); /** * Add a ContinuationListener. * * @param listener the listener */ void addContinuationListener(ContinuationListener listener); /** * Set a request attribute. * This method is a convenience method to call the {@link ServletRequest#setAttribute(String, Object)} * method on the associated request object. * This is a thread safe call and may be called by any thread. * * @param name the attribute name * @param attribute the attribute value */ void setAttribute(String name, Object attribute); /** * Get a request attribute. * This method is a convenience method to call the {@link ServletRequest#getAttribute(String)} * method on the associated request object. * This is a thread safe call and may be called by any thread. * * @param name the attribute name * @return the attribute value */ Object getAttribute(String name); /** * Remove a request attribute. * This method is a convenience method to call the {@link ServletRequest#removeAttribute(String)} * method on the associated request object. * This is a thread safe call and may be called by any thread. * * @param name the attribute name */ void removeAttribute(String name); /** * Undispatch the request. *

* This method can be called on a suspended continuation in order * to exit the dispatch to the filter/servlet by throwing a {@link ContinuationThrowable} * which is caught either by the container or the {@link ContinuationFilter}. * This is an alternative to simply returning from the dispatch in the case * where filters in the filter chain may not be prepared to handle a suspended * request. *

* This method should only be used as a last resort and a normal return is a prefereable * solution if filters can be updated to handle that case. * * @throws ContinuationThrowable thrown if the request is suspended. The instance of the * exception may be reused on subsequent calls, so the stack frame may not be accurate. */ void undispatch() throws ContinuationThrowable; }




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