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/*
 * Copyright (c) 2010-2012 Sonatype, Inc. All rights reserved.
 *
 * This program is licensed to you under the Apache License Version 2.0,
 * and you may not use this file except in compliance with the Apache License Version 2.0.
 * You may obtain a copy of the Apache License Version 2.0 at http://www.apache.org/licenses/LICENSE-2.0.
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the Apache License Version 2.0 is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the Apache License Version 2.0 for the specific language governing permissions and limitations there under.
 */
package com.ning.http.client;

import com.ning.http.client.Response.ResponseBuilder;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.Semaphore;

/**
 * An AsyncHandler that returns Response (without body, so status code and
 * headers only) as fast as possible for inspection, but leaves you the option
 * to defer body consumption.
 * 

* This class introduces new call: getResponse(), that blocks caller thread as * long as headers are received, and return Response as soon as possible, but * still pouring response body into supplied output stream. This handler is * meant for situations when the "recommended" way (using * client.prepareGet("http://foo.com/aResource").execute().get() * would not work for you, since a potentially large response body is about to * be GETted, but you need headers first, or you don't know yet (depending on * some logic, maybe coming from headers) where to save the body, or you just * want to leave body stream to some other component to consume it. *

* All these above means that this AsyncHandler needs a bit of different * handling than "recommended" way. Some examples: *

*

 *     FileOutputStream fos = ...
 *     BodyDeferringAsyncHandler bdah = new BodyDeferringAsyncHandler(fos);
 *     // client executes async
 *     Future<Response> fr = client.prepareGet("http://foo.com/aresource").execute(
 * 	bdah);
 *     // main thread will block here until headers are available
 *     Response response = bdah.getResponse();
 *     // you can continue examine headers while actual body download happens
 *     // in separate thread
 *     // ...
 *     // finally "join" the download
 *     fr.get();
 * 
*

*

 *     PipedOutputStream pout = new PipedOutputStream();
 *     BodyDeferringAsyncHandler bdah = new BodyDeferringAsyncHandler(pout);
 *     // client executes async
 *     Future<Response> fr = client.prepareGet("http://foo.com/aresource").execute(bdah);
 *     // main thread will block here until headers are available
 *     Response response = bdah.getResponse();
 *     if (response.getStatusCode() == 200) {
 *      InputStream pin = new BodyDeferringInputStream(fr,new PipedInputStream(pout));
 *      // consume InputStream
 *      ...
 *     } else {
 *      // handle unexpected response status code
 *      ...
 *     }
 * 
*/ public class BodyDeferringAsyncHandler implements AsyncHandler { private final ResponseBuilder responseBuilder = new ResponseBuilder(); private final CountDownLatch headersArrived = new CountDownLatch(1); private final OutputStream output; private boolean responseSet; private volatile Response response; private volatile Throwable throwable; private final Semaphore semaphore = new Semaphore(1); public BodyDeferringAsyncHandler(final OutputStream os) { this.output = os; this.responseSet = false; } public void onThrowable(Throwable t) { this.throwable = t; // Counting down to handle error cases too. // In "premature exceptions" cases, the onBodyPartReceived() and // onCompleted() // methods will never be invoked, leaving caller of getResponse() method // blocked forever. try { semaphore.acquire(); } catch (InterruptedException e) { // Ignore } finally { headersArrived.countDown(); semaphore.release(); } try { closeOut(); } catch (IOException e) { // ignore } } public STATE onStatusReceived(HttpResponseStatus responseStatus) throws Exception { responseBuilder.reset(); responseBuilder.accumulate(responseStatus); return STATE.CONTINUE; } public STATE onHeadersReceived(HttpResponseHeaders headers) throws Exception { responseBuilder.accumulate(headers); return STATE.CONTINUE; } public STATE onBodyPartReceived(HttpResponseBodyPart bodyPart) throws Exception { // body arrived, flush headers if (!responseSet) { response = responseBuilder.build(); responseSet = true; headersArrived.countDown(); } bodyPart.writeTo(output); return STATE.CONTINUE; } protected void closeOut() throws IOException { try { output.flush(); } finally { output.close(); } } public Response onCompleted() throws IOException { if (!responseSet) { response = responseBuilder.build(); responseSet = true; } // Counting down to handle error cases too. // In "normal" cases, latch is already at 0 here // But in other cases, for example when because of some error // onBodyPartReceived() is never called, the caller // of getResponse() would remain blocked infinitely. // By contract, onCompleted() is always invoked, even in case of errors headersArrived.countDown(); closeOut(); try { semaphore.acquire(); if (throwable != null) { IOException ioe = new IOException(throwable.getMessage()); ioe.initCause(throwable); throw ioe; } else { // sending out current response return responseBuilder.build(); } } catch (InterruptedException e) { return null; } finally { semaphore.release(); } } /** * This method -- unlike Future.get() -- will block only as long, * as headers arrive. This is useful for large transfers, to examine headers * ASAP, and defer body streaming to it's fine destination and prevent * unneeded bandwidth consumption. The response here will contain the very * 1st response from server, so status code and headers, but it might be * incomplete in case of broken servers sending trailing headers. In that * case, the "usual" Future.get() method will return complete * headers, but multiple invocations of getResponse() will always return the * 1st cached, probably incomplete one. Note: the response returned by this * method will contain everything except the response body itself, * so invoking any method like Response.getResponseBodyXXX() will result in * error! Also, please not that this method might return null * in case of some errors. * * @return a {@link Response} * @throws InterruptedException */ public Response getResponse() throws InterruptedException, IOException { // block here as long as headers arrive headersArrived.await(); try { semaphore.acquire(); if (throwable != null) { IOException ioe = new IOException(throwable.getMessage()); ioe.initCause(throwable); throw ioe; } else { return response; } } finally { semaphore.release(); } } // == /** * A simple helper class that is used to perform automatic "join" for async * download and the error checking of the Future of the request. */ public static class BodyDeferringInputStream extends FilterInputStream { private final Future future; private final BodyDeferringAsyncHandler bdah; public BodyDeferringInputStream(final Future future, final BodyDeferringAsyncHandler bdah, final InputStream in) { super(in); this.future = future; this.bdah = bdah; } /** * Closes the input stream, and "joins" (wait for complete execution * together with potential exception thrown) of the async request. */ public void close() throws IOException { // close super.close(); // "join" async request try { getLastResponse(); } catch (Exception e) { IOException ioe = new IOException(e.getMessage()); ioe.initCause(e); throw ioe; } } /** * Delegates to {@link BodyDeferringAsyncHandler#getResponse()}. Will * blocks as long as headers arrives only. Might return * null. See * {@link BodyDeferringAsyncHandler#getResponse()} method for details. * * @return a {@link Response} * @throws InterruptedException */ public Response getAsapResponse() throws InterruptedException, IOException { return bdah.getResponse(); } /** * Delegates to Future#get() method. Will block * as long as complete response arrives. * * @return a {@link Response} * @throws InterruptedException * @throws ExecutionException */ public Response getLastResponse() throws InterruptedException, ExecutionException { return future.get(); } } }




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