/*
* Copyright 2009 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.core.client.impl;
import com.google.gwt.core.client.GWT;
import com.google.gwt.core.client.JavaScriptObject;
import com.google.gwt.core.client.impl.AsyncFragmentLoader.LoadTerminatedHandler;
import com.google.gwt.core.client.impl.AsyncFragmentLoader.LoadingStrategy;
/**
* Load runAsync code using a script tag. The
* {@link com.google.gwt.core.linker.XSLinker} sets
* <code>__gwtModuleFunction</code> to point at the function that wraps the
* initially downloaded code. On that function is a property
* <code>installCode</code> that can be invoked to eval more code in a scope
* nested somewhere within that function. The loaded script for fragment 123 is
* expected to invoke __gwtModuleFunction.runAsyncCallback123 with the code to
* be installed.
*/
public class CrossSiteLoadingStrategy implements LoadingStrategy {
/**
* A trivial JavaScript map from ints to ints.
*/
private static final class IntToIntMap extends JavaScriptObject {
public static IntToIntMap create() {
return (IntToIntMap) JavaScriptObject.createArray();
}
protected IntToIntMap() {
}
/**
* Get an entry. If there is no such entry, return 0.
*/
public native int get(int x) /*-{
return this[x] ? this[x] : 0;
}-*/;
public native void put(int x, int y) /*-{
this[x] = y;
}-*/;
}
private static RuntimeException LoadTerminated = new RuntimeException(
"Code download terminated");
/**
* Clear callbacks on script objects. This is important on IE 6 and 7 to
* prevent a memory leak. If the callbacks aren't cleared, there is a cyclical
* chain of references between the script tag and the function callback, and
* IE 6/7 can't garbage collect them.
*/
private static native void clearCallbacks(JavaScriptObject script) /*-{
var nop = new Function('');
script.onerror = script.onload = script.onreadystatechange = nop;
}-*/;
/**
* Clear the success callback for fragment <code>fragment</code>.
*/
private static native void clearOnSuccess(int fragment) /*-{
delete __gwtModuleFunction['runAsyncCallback'+fragment];
}-*/;
private static native JavaScriptObject createScriptTag(String url) /*-{
var head = document.getElementsByTagName('head').item(0);
var script = document.createElement('script');
script.src = url;
return script;
}-*/;
private static native void installScriptTag(JavaScriptObject script) /*-{
var head = document.getElementsByTagName('head').item(0);
head.appendChild(script);
}-*/;
private static native JavaScriptObject removeTagAndCallErrorHandler(
int fragment, JavaScriptObject tag,
LoadTerminatedHandler loadFinishedHandler) /*-{
return function(exception) {
if (tag.parentNode == null) {
// onSuccess or onFailure must have already been called.
return;
}
var head = document.getElementsByTagName('head').item(0);
@com.google.gwt.core.client.impl.CrossSiteLoadingStrategy::clearOnSuccess(*)(fragment);
@com.google.gwt.core.client.impl.CrossSiteLoadingStrategy::clearCallbacks(*)(tag);
head.removeChild(tag);
function callLoadTerminated() {
loadFinishedHandler.@com.google.gwt.core.client.impl.AsyncFragmentLoader.LoadTerminatedHandler::loadTerminated(*)(exception);
}
$entry(callLoadTerminated)();
}
}-*/;
private static native JavaScriptObject removeTagAndEvalCode(int fragment,
JavaScriptObject tag) /*-{
return function(code) {
var head = document.getElementsByTagName('head').item(0);
@com.google.gwt.core.client.impl.CrossSiteLoadingStrategy::clearOnSuccess(*)(fragment);
@com.google.gwt.core.client.impl.CrossSiteLoadingStrategy::clearCallbacks(*)(tag);
head.removeChild(tag);
__gwtModuleFunction.installCode(code);
}
}-*/;
private static native void setOnFailure(JavaScriptObject script,
JavaScriptObject callback) /*-{
var exception = @com.google.gwt.core.client.impl.CrossSiteLoadingStrategy::LoadTerminated;
script.onerror = function() {
callback(exception);
}
script.onload = function() {
callback(exception);
}
script.onreadystatechange = function () {
if (script.readyState == 'loaded' || script.readyState == 'complete') {
script.onreadystatechange = function () { }
callback(exception);
}
}
}-*/;
/**
* Set the success callback for fragment <code>fragment</code>
* to the supplied JavaScript function.
*/
private static native void setOnSuccess(int fragment, JavaScriptObject callback) /*-{
__gwtModuleFunction['runAsyncCallback'+fragment] = callback;
}-*/;
private final IntToIntMap serialNumbers = IntToIntMap.create();
public void startLoadingFragment(int fragment,
LoadTerminatedHandler loadFinishedHandler) {
JavaScriptObject tag = createScriptTag(getUrl(fragment));
setOnSuccess(fragment, removeTagAndEvalCode(fragment, tag));
setOnFailure(tag, removeTagAndCallErrorHandler(fragment, tag,
loadFinishedHandler));
installScriptTag(tag);
}
protected String getDeferredJavaScriptDirectory() {
return "deferredjs/";
}
private int getSerial(int fragment) {
int ser = serialNumbers.get(fragment);
serialNumbers.put(fragment, ser + 1);
return ser;
}
/**
* The URL to retrieve a fragment of code from. NOTE: this function is not
* stable. It tweaks the URL with each call so that browsers are not tempted
* to cache a download failure.
*/
private String getUrl(int fragment) {
return GWT.getModuleBaseURL() + getDeferredJavaScriptDirectory()
+ GWT.getPermutationStrongName() + "/" + fragment + ".cache.js?serial="
+ getSerial(fragment);
}
}