DDevelopment & Design

Phonegap / Cordova and cross domain ssl request problem on android.

In one app I have participated, there was a use case: User fill up a form. User submit the form. System send data via https to server and show a response. During development there wasn’t any problem, but when we were going to release production version then some unsuspected situation occurred. I prepare the production version accordingly with standard flow for Android environment: ant release align signing During conduct tests on that version, every time I try to submit the form, a connection error appear. In that situation, at the first you should check whitelist in cordova settings. Every URL you want to connect to, must be explicit type in: res/xml/cordova.xml If whitelist looks fine, the error is most likely caused by inner implementation of Android System. The Android WebView does not allow by default self-signed SSL certs. When app is debug-signed the SSL error is ignored, but if app is release-signed connection to untrusted services is blocked. Workaround You have to remember that secure connection to service with self-signed certificate is risky and unrecommended. But if you know what you are doing there is some workaround of the security problem. Behavior of method CordovaWebViewClient.onReceivedSslError must be changed. Thus add new class extended CordovaWebViewClient and override ‘onReceivedSslError’. I strongly suggest to implement custom onReceiveSslError as secure as possible. I know that the problem occours when app try connect to example.domain.com and in spite of self signed certificate the domain is trusted, so only for that case the SslError is ignored. public class MyWebViewClient extends CordovaWebViewClient {   private static final String TAG = MyWebViewClient.class.getName();   private static final String AVAILABLE_SLL_CN = "example.domain.com";   public MyWebViewClient(DroidGap ctx) {       super(ctx);   }   @Override   public void onReceivedSslError(WebView view, SslErrorHandler handler, android.net.http.SslError error) { String errorSourceCName = error.getCertificate(). getIssuedTo().getCName();       if( AVAILABLE_SLL_CN.equals(errorSourceCName) ) {           Log.i(TAG, "Detect ssl connection error: " + error.toString() + „ so the error is ignored”);           handler.proceed();           return;       }       super.onReceivedSslError(view, handler, error);   }} Next step is forcing yours app to  use custom implementation of WebViewClient. public class Start extends DroidGap{   private static final String TAG = Start.class.getName();   @Override   public void onCreate(Bundle savedInstanceState)   {       super.onCreate(savedInstanceState);       super.setIntegerProperty("splashscreen", R.drawable.splash);       super.init();       MyWebViewClient myWebViewClient = new MyWebViewClient(this);       myWebViewClient.setWebView(this.appView);       this.appView.setWebViewClient(myWebViewClient);        // yours code   }} That is all ypu have to do if minSdk of yours app is greater or equals 8. In older version of Android there is no class android.net.http.SslError So in class MyCordovaWebViewClient class there are errors because compliator doesn’t see SslError class. Fortunately Android is(was) open source, so it is easy to find source of the class. There is no inpediments to ‘upgrade’ app and just add the file to project. I suggest to keep original packages. Thus after all operations the source tree looks like: Class SslError placed in source tree.   Now the app created in release mode can connect via https to services with self-signed SSl certificates.

In one app I have participated, there was a use case:
* User fill up a form.
* User submit the form.
* System send data via https to server and show a response.During development there wasn’t any problem, but when we were going to release production version then some unsuspected situation occurred. I prepare the production version accordingly with standard flow for Android environment:

  • ant release
  • align
  • signingDuring conduct tests on that version, every time I try to submit the form, a connection error appear. In that situation, at the first you should check whitelist in cordova settings. Every URL you want to connect to, must be explicit type in:

    res/xml/cordova.xml
    If whitelist looks fine, the error is most likely caused by inner implementation of Android System. The Android WebView does not allow by default self-signed SSL certs. When app is debug-signed the SSL error is ignored, but if app is release-signed connection to untrusted services is blocked.

Workaround

 

You have to remember that secure connection to service with self-signed certificate is risky and unrecommended. But if you know what you are doing there is some workaround of the security problem. Behavior of method

CordovaWebViewClient.onReceivedSslErrormust be changed.

 

Thus add new class extended CordovaWebViewClient and override ‘onReceivedSslError’. I strongly suggest to implement custom onReceiveSslError as secure as possible. I know that the problem occours when app try connect to example.domain.com and in spite of self signed certificate the domain is trusted, so only for that case the SslError is ignored.

public class MyWebViewClient extends CordovaWebViewClient {

   private static final String TAG = MyWebViewClient.class.getName();
   private static final String AVAILABLE_SLL_CN
= "example.domain.com";

   public MyWebViewClient(DroidGap ctx) {
       super(ctx);
   }

   @Override
   public void onReceivedSslError(WebView view,
SslErrorHandler handler,
android.net.http.SslError error) {

String errorSourceCName = error.getCertificate().
getIssuedTo().getCName();

       if( AVAILABLE_SLL_CN.equals(errorSourceCName) ) {
           Log.i(TAG, "Detect ssl connection error: " +
error.toString() +
„ so the error is ignored”);

           handler.proceed();
           return;
       }

       super.onReceivedSslError(view, handler, error);
   }
}Next step is forcing yours app to  use custom implementation of WebViewClient. public class Start extends DroidGap
{
   private static final String TAG = Start.class.getName();

   @Override
   public void onCreate(Bundle savedInstanceState)
   {
       super.onCreate(savedInstanceState);
       super.setIntegerProperty("splashscreen", R.drawable.splash);
       super.init();

       MyWebViewClient myWebViewClient = new MyWebViewClient(this);
       myWebViewClient.setWebView(this.appView);

       this.appView.setWebViewClient(myWebViewClient);
       
// yours code

   }
}

That is all ypu have to do if minSdk of yours app is greater or equals 8. In older version of Android there is no class android.net.http.SslErrorSo in class MyCordovaWebViewClient class there are errors because compliator doesn’t see SslError class. Fortunately Android is(was) open source, so it is easy to find source of the class. There is no inpediments to ‘upgrade’ app and just add the file to project. I suggest to keep original packages. Thus after all operations the source tree looks like:

Class SslError placed in source tree.

Now the app created in release mode can connect via https to services with self-signed SSl certificates.

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Private fields and methods are not private in groovy

I used to code in Java before I met groovy. Like most of you, groovy attracted me with many enhancements. This was to my surprise to discover that method visibility in groovy is handled different than Java!

Consider this example:

class Person {
private String name
public  String surname

private Person() {}

private String signature() { "${name?.substring(0, 1)}. $surname" }

public String toString() { "I am $name $surname" }
}

How is this class interpreted with Java?

  1. Person has private constructor that cannot be accessed
  2. Field "name" is private and cannot be accessed
  3. Method signature() is private and cannot be accessed

Let's see how groovy interpretes Person:

public static void main(String[] args) {
def person = new Person()   // constructor is private - compilation error in Java
println(person.toString())

    person.@name = 'Mike'       // access name field directly - compilation error in Java
println(person.toString())

    person.name = 'John'        // there is a setter generated by groovy
println(person.toString())

    person.@surname = 'Foo'     // access surname field directly
println(person.toString())

    person.surname = 'Bar'      // access auto-generated setter
println(person.toString())

println(person.signature()) // call private method - compilation error in Java
}

I was really astonished by its output:

I am null null
I am Mike null
I am John null
I am John Foo
I am John Bar
J. Bar

As you can see, groovy does not follow visibility directives at all! It treats them as non-existing. Code compiles and executes fine. It's contrary to Java. In Java this code has several errors, pointed out in comments.

I've searched a bit on this topic and it seems that this behaviour is known since version 1.1 and there is a bug report on that: http://jira.codehaus.org/browse/GROOVY-1875. It is not resolved even with groovy 2 release. As Tim Yates mentioned in this Stackoverflow question: "It's not clear if it is a bug or by design". Groovy treats visibility keywords as a hint for a programmer.

I need to keep that lesson in mind next time I want to make some field or method private!