对于单独的Web app应用来说，加载进来的url一般不能保证它的安全性。那么如何来处理url安全性的问题呢。
让我们来看看PhoneGap是如何做的。
PhoneGap采用了白名单的形式，认为在白名单中的url认为是安全的，不在白名单中的url是不安全的。对于安全的url，PhoneGap的Web app会直接打开，对于不安全的url，会通过浏览器打开。
那么怎么增加白名单呢？PhoneGap是需要在配置文件res/xml/config.xml中设置，如下：
<cordova>
- <!-- access elements control the Android whitelist.
Domains are assumed blocked unless set otherwise
-->
<access origin="http://127.0.0.1*" />
- <!-- allow local pages
-->
- <!-- <access origin="https://example.com" /> allow any secure requests to example.com
-->
- <!-- <access origin="https://example.com" subdomains="true" /> such as above, but including subdomains, such as www
-->
<access origin=".*" />
<log level="DEBUG" />
<preference name="useBrowserHistory" value="false" />
<preference name="exit-on-suspend" value="false" />
- <plugins>
<plugin name="App" value="org.apache.cordova.App" />
<plugin name="Geolocation" value="org.apache.cordova.GeoBroker" />
<plugin name="Device" value="org.apache.cordova.Device" />
<plugin name="Accelerometer" value="org.apache.cordova.AccelListener" />
<plugin name="Compass" value="org.apache.cordova.CompassListener" />
<plugin name="Media" value="org.apache.cordova.AudioHandler" />
<plugin name="Camera" value="org.apache.cordova.CameraLauncher" />
<plugin name="Contacts" value="org.apache.cordova.ContactManager" />
<plugin name="File" value="org.apache.cordova.FileUtils" />
<plugin name="NetworkStatus" value="org.apache.cordova.NetworkManager" />
<plugin name="Notification" value="org.apache.cordova.Notification" />
<plugin name="Storage" value="org.apache.cordova.Storage" />
<plugin name="Temperature" value="org.apache.cordova.TempListener" />
<plugin name="FileTransfer" value="org.apache.cordova.FileTransfer" />
<plugin name="Capture" value="org.apache.cordova.Capture" />
<plugin name="Battery" value="org.apache.cordova.BatteryListener" />
<plugin name="SplashScreen" value="org.apache.cordova.SplashScreen" />
<plugin name="Echo" value="org.apache.cordova.Echo" />
<plugin name="Globalization" value="org.apache.cordova.Globalization" />
</plugins>
</cordova>
其中，<access origin="http://127.0.0.1*" />就是加的白名单，我们只需要将网址后面加上*，上格式加进配置文件即可。
那么PhoneGap又是如何实现白名单的呢？让我们看一下源代码：CordovaWebView.java。CordovaWebView是显示的WebView的基类。它在初始化时，会加载配置文件的配置项，源代码如下：
/**
* Load Cordova configuration from res/xml/cordova.xml.
* Approved list of URLs that can be loaded into DroidGap
* <access origin="http://server regexp" subdomains="true" />
* Log level: ERROR, WARN, INFO, DEBUG, VERBOSE (default=ERROR)
* <log level="DEBUG" />
*/
private void loadConfiguration() {
int id = getResources().getIdentifier("config", "xml", this.cordova.getActivity().getPackageName());
if(id == 0)
{
id = getResources().getIdentifier("cordova", "xml", this.cordova.getActivity().getPackageName());
Log.i("CordovaLog", "config.xml missing, reverting to cordova.xml");
}
if (id == 0) {
LOG.i("CordovaLog", "cordova.xml missing. Ignoring...");
return;
}
XmlResourceParser xml = getResources().getXml(id);
int eventType = -1;
while (eventType != XmlResourceParser.END_DOCUMENT) {
if (eventType == XmlResourceParser.START_TAG) {
String strNode = xml.getName();
if (strNode.equals("access")) {
String origin = xml.getAttributeValue(null, "origin");
String subdomains = xml.getAttributeValue(null, "subdomains");
if (origin != null) {
this.addWhiteListEntry(origin, (subdomains != null) && (subdomains.compareToIgnoreCase("true") == 0));
}
}
else if (strNode.equals("log")) {
String level = xml.getAttributeValue(null, "level");
LOG.i("CordovaLog", "Found log level %s", level);
if (level != null) {
LOG.setLogLevel(level);
}
}
else if (strNode.equals("preference")) {
String name = xml.getAttributeValue(null, "name");
String value = xml.getAttributeValue(null, "value");
LOG.i("CordovaLog", "Found preference for %s=%s", name, value);
Log.d("CordovaLog", "Found preference for " + name + "=" + value);
// Save preferences in Intent
this.cordova.getActivity().getIntent().putExtra(name, value);
}
}
try {
eventType = xml.next();
} catch (XmlPullParserException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
// Init preferences
if ("true".equals(this.getProperty("useBrowserHistory", "false"))) {
this.useBrowserHistory = true;
}
else {
this.useBrowserHistory = false;
}
if ("true".equals(this.getProperty("fullscreen", "false"))) {
this.cordova.getActivity().getWindow().clearFlags(WindowManager.LayoutParams.FLAG_FORCE_NOT_FULLSCREEN);
this.cordova.getActivity().getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
}
}
在解析xml文件时，会将origin标签中的内容加入白名单，调用的是addWhiteListEntry方法。下面我们来看看addWhiteListEntry方法的源代码：
public void addWhiteListEntry(String origin, boolean subdomains) {
try {
// Unlimited access to network resources
if (origin.compareTo("*") == 0) {
LOG.d(TAG, "Unlimited access to network resources");
this.whiteList.add(Pattern.compile(".*"));
} else { // specific access
// check if subdomains should be included
// TODO: we should not add more domains if * has already been added
if (subdomains) {
// XXX making it stupid friendly for people who forget to include protocol/SSL
if (origin.startsWith("http")) {
this.whiteList.add(Pattern.compile(origin.replaceFirst("https?://", "^https?://(.*\\.)?")));
} else {
this.whiteList.add(Pattern.compile("^https?://(.*\\.)?" + origin));
}
LOG.d(TAG, "Origin to allow with subdomains: %s", origin);
} else {
// XXX making it stupid friendly for people who forget to include protocol/SSL
if (origin.startsWith("http")) {
this.whiteList.add(Pattern.compile(origin.replaceFirst("https?://", "^https?://")));
} else {
this.whiteList.add(Pattern.compile("^https?://" + origin));
}
LOG.d(TAG, "Origin to allow: %s", origin);
}
}
} catch (Exception e) {
LOG.d(TAG, "Failed to add origin %s", origin);
}
}
我们可以看到，它用正则表达式解析后将白名单中的url加入到whiteList这个属性中，而whiteList是个ArrayList类型的属性。
那么PhoneGap的Web app在显示网页时又是如何利用白名单的呢？让我们继续来看下面的源代码，这是加载网页时会调用的方法：
/**
* Load the specified URL in the Cordova webview or a new browser instance.
*
* NOTE: If openExternal is false, only URLs listed in whitelist can be loaded.
*
* @param url The url to load.
* @param openExternal Load url in browser instead of Cordova webview.
* @param clearHistory Clear the history stack, so new page becomes top of history
* @param params DroidGap parameters for new app
*/
public void showWebPage(String url, boolean openExternal, boolean clearHistory, HashMap<String, Object> params) {
LOG.d(TAG, "showWebPage(%s, %b, %b, HashMap", url, openExternal, clearHistory);
// If clearing history
if (clearHistory) {
this.clearHistory();
}
// If loading into our webview
if (!openExternal) {
// Make sure url is in whitelist
if (url.startsWith("file://") || url.indexOf(this.baseUrl) == 0 || isUrlWhiteListed(url)) {
// TODO: What about params?
// Clear out current url from history, since it will be replacing it
if (clearHistory) {
this.urls.clear();
}
// Load new URL
this.loadUrl(url);
}
// Load in default viewer if not
else {
LOG.w(TAG, "showWebPage: Cannot load URL into webview since it is not in white list. Loading into browser instead. (URL=" + url + ")");
try {
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setData(Uri.parse(url));
cordova.getActivity().startActivity(intent);
} catch (android.content.ActivityNotFoundException e) {
LOG.e(TAG, "Error loading url " + url, e);
}
}
}
// Load in default view intent
else {
try {
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setData(Uri.parse(url));
cordova.getActivity().startActivity(intent);
} catch (android.content.ActivityNotFoundException e) {
LOG.e(TAG, "Error loading url " + url, e);
}
}
}
我们可以看到，里面会用isUrlWhiteListed等方法判断该url是否在白名单中，或者是否安全，然后对安全的url直接通过loadUrl来 加载进该Web app，对于PhoneGap认为不安全的url会通过发Intent的形式打开浏览器加载该网页。
下面再贴一段isUrlWhiteListed方法的源代码：
/**
* Determine if URL is in approved list of URLs to load.
*
* @param url
* @return
*/
public boolean isUrlWhiteListed(String url) {
// Check to see if we have matched url previously
if (this.whiteListCache.get(url) != null) {
return true;
}
// Look for match in white list
Iterator<Pattern> pit = this.whiteList.iterator();
while (pit.hasNext()) {
Pattern p = pit.next();
Matcher m = p.matcher(url);
// If match found, then cache it to speed up subsequent comparisons
if (m.find()) {
this.whiteListCache.put(url, true);
return true;
}
}
return false;
}