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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 IE6-9 to work around some IE specialities. */ static class RequestImplIE6To9 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); } /** * 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; /* * 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() { timeoutMillis = 0; xmlHttpRequest = null; timer = 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, final RequestCallback callback) { if (xmlHttpRequest == null) { throw new NullPointerException(); } if (callback == null) { throw new NullPointerException(); } if (timeoutMillis < 0) { throw new IllegalArgumentException(); } this.timeoutMillis = timeoutMillis; this.xmlHttpRequest = xmlHttpRequest; if (timeoutMillis > 0) { // create and start a Timer timer = new Timer() { @Override public void run() { fireOnTimeout(callback); } }; timer.schedule(timeoutMillis); } else { // no Timer required timer = null; } } /** * Cancels a pending request. If the request has already been canceled or if * it has timed out no action is taken. */ public void 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. */ if (xmlHttpRequest != null) { XMLHttpRequest xmlHttp = xmlHttpRequest; xmlHttpRequest = null; xmlHttp.clearOnReadyStateChange(); xmlHttp.abort(); cancelTimer(); } } /** * 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; } cancelTimer(); /* * 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; String errorMsg = getBrowserSpecificFailure(xhr); if (errorMsg != null) { Throwable exception = new RuntimeException(errorMsg); callback.onError(this, exception); } else { Response response = createResponse(xhr); callback.onResponseReceived(this, response); } } /* * Stops the current HTTPRequest timer if there is one. */ private void cancelTimer() { if (timer != null) { timer.cancel(); } } /* * Method called when this request times out. * * NOTE: this method is called from JSNI */ private void fireOnTimeout(RequestCallback callback) { if (xmlHttpRequest == null) { // the request has been received at this point return; } cancel(); callback.onError(this, new RequestTimeoutException(this, timeoutMillis)); } /** * Tests if the JavaScript XmlHttpRequest.status property is * readable. This can return failure in two different known scenarios: * *
    *
  1. On Mozilla, after a network error, attempting to read the status code * results in an exception being thrown. See https://bugzilla.mozilla.org/show_bug.cgi?id=238559.
  2. *
  3. On Safari, if the HTTP response does not include any response text. See * http://bugs.webkit.org * /show_bug.cgi?id=3810.
  4. *
* * @param xhr the JavaScript XmlHttpRequest object to test * @return a String message containing an error message if the * XmlHttpRequest.status code is unreadable or null if * the status code could be successfully read. */ private native String getBrowserSpecificFailure(XMLHttpRequest xhr) /*-{ try { if (xhr.status === undefined) { return "XmlHttpRequest.status == undefined, please see Safari bug " + "http://bugs.webkit.org/show_bug.cgi?id=3810 for more details"; } return null; } catch (e) { return "Unable to read XmlHttpRequest.status; likely causes are a " + "networking error or bad cross-domain request. Please see " + "https://bugzilla.mozilla.org/show_bug.cgi?id=238559 for more " + "details"; } }-*/; }




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