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/*
 * Copyright 2008 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.google.gwt.http.client;

import com.google.gwt.core.shared.GWT;
import com.google.gwt.user.client.Timer;
import com.google.gwt.xhr.client.XMLHttpRequest;

/**
 * An HTTP request that is waiting for a response. Requests can be queried for
 * their pending status or they can be canceled.
 * 
 * 

Required Module

Modules that use this class should inherit * com.google.gwt.http.HTTP. * * {@gwt.include * com/google/gwt/examples/http/InheritsExample.gwt.xml} * */ public class Request { /** * Native implementation associated with {@link Request}. User classes should not use this class * directly. */ static class RequestImpl { /** * Creates a {@link Response} instance for the given JavaScript XmlHttpRequest object. * * @param xmlHttpRequest xmlHttpRequest object for which we need a response * @return a {@link Response} object instance */ Response createResponse(final XMLHttpRequest xmlHttpRequest) { return new ResponseImpl(xmlHttpRequest); } } /** * Special {@link RequestImpl} for IE8, IE9 to work around some IE specialities. */ static class RequestImplIE8And9 extends RequestImpl { @Override Response createResponse(XMLHttpRequest xmlHttpRequest) { return new ResponseImpl(xmlHttpRequest) { @Override public int getStatusCode() { /* * http://code.google.com/p/google-web-toolkit/issues/detail?id=5031 * * The XMLHTTPRequest object in IE will return a status code of 1223 and drop some * response headers if the server returns a HTTP/204. * * This issue is fixed in IE10. */ int statusCode = super.getStatusCode(); return (statusCode == 1223) ? SC_NO_CONTENT : statusCode; } }; } } /* * Although Request is a client-side class, it's a transitive dependency of * some GWT servlet code. Because GWT.create() isn't safe to call on the * server, we use the "Initialization On Demand Holder" idiom to lazily * initialize the RequestImpl. */ private static class ImplHolder { private static final RequestImpl impl = GWT.create(RequestImpl.class); public static RequestImpl get() { return impl; } } /** * Creates a {@link Response} instance for the given JavaScript XmlHttpRequest * object. * * @param xmlHttpRequest xmlHttpRequest object for which we need a response * @return a {@link Response} object instance */ private static Response createResponse(final XMLHttpRequest xmlHttpRequest) { return ImplHolder.get().createResponse(xmlHttpRequest); } private final RequestCallback callback; /** * The number of milliseconds to wait for this HTTP request to complete. */ private final int timeoutMillis; /** * Timer used to force HTTPRequest timeouts. If the user has not requested a * timeout then this field is null. */ private final Timer timer = new Timer() { @Override public void run() { fireOnTimeout(); } }; /** * JavaScript XmlHttpRequest object that this Java class wraps. This field is * not final because we transfer ownership of it to the HTTPResponse object * and set this field to null. */ private XMLHttpRequest xmlHttpRequest; /** * Only used for building a * {@link com.google.gwt.user.client.rpc.impl.FailedRequest}. */ protected Request() { callback = null; timeoutMillis = 0; xmlHttpRequest = null; } /** * Constructs an instance of the Request object. * * @param xmlHttpRequest JavaScript XmlHttpRequest object instance * @param timeoutMillis number of milliseconds to wait for a response * @param callback callback interface to use for notification * * @throws IllegalArgumentException if timeoutMillis < 0 * @throws NullPointerException if xmlHttpRequest, or callback are null */ Request(XMLHttpRequest xmlHttpRequest, int timeoutMillis, RequestCallback callback) { if (xmlHttpRequest == null) { throw new NullPointerException(); } if (callback == null) { throw new NullPointerException(); } if (timeoutMillis < 0) { throw new IllegalArgumentException(); } this.callback = callback; this.timeoutMillis = timeoutMillis; this.xmlHttpRequest = xmlHttpRequest; if (timeoutMillis > 0) { timer.schedule(timeoutMillis); } } /** * Cancels a pending request. If the request has already been canceled or if * it has timed out no action is taken. */ public void cancel() { if (xmlHttpRequest == null) { return; } timer.cancel(); /* * There is a strange race condition that occurs on Mozilla when you cancel * a request while the response is coming in. It appears that in some cases * the onreadystatechange handler is still called after the handler function * has been deleted and during the call to XmlHttpRequest.abort(). So we * null the xmlHttpRequest here and that will prevent the * fireOnResponseReceived method from calling the callback function. * * Setting the onreadystatechange handler to null gives us the correct * behavior in Mozilla but crashes IE. That is why we have chosen to fixed * this in Java by nulling out our reference to the XmlHttpRequest object. */ final XMLHttpRequest xhr = xmlHttpRequest; xmlHttpRequest = null; xhr.clearOnReadyStateChange(); xhr.abort(); } /** * Returns true if this request is waiting for a response. * * @return true if this request is waiting for a response */ public boolean isPending() { if (xmlHttpRequest == null) { return false; } int readyState = xmlHttpRequest.getReadyState(); /* * Because we are doing asynchronous requests it is possible that we can * call XmlHttpRequest.send and still have the XmlHttpRequest.getReadyState * method return the state as XmlHttpRequest.OPEN. That is why we include * open although it is nottechnically true since open implies that the * request has not been sent. */ switch (readyState) { case XMLHttpRequest.OPENED: case XMLHttpRequest.HEADERS_RECEIVED: case XMLHttpRequest.LOADING: return true; } return false; } /* * Method called when the JavaScript XmlHttpRequest object's readyState * reaches 4 (LOADED). */ void fireOnResponseReceived(RequestCallback callback) { if (xmlHttpRequest == null) { // the request has timed out at this point return; } timer.cancel(); /* * We cannot use cancel here because it would clear the contents of the * JavaScript XmlHttpRequest object so we manually null out our reference to * the JavaScriptObject */ final XMLHttpRequest xhr = xmlHttpRequest; xmlHttpRequest = null; Response response = createResponse(xhr); callback.onResponseReceived(this, response); } /* * Method called when this request times out. */ private void fireOnTimeout() { if (xmlHttpRequest == null) { // the request has been received at this point return; } cancel(); callback.onError(this, new RequestTimeoutException(this, timeoutMillis)); } }




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