DDevelopment & Design

GWT Hosted mode on 64bit linux

GWT for linux is build against 32bit architecture. It contains some SWT/GTK 32bit modules. So if you try to run it with 64bit java it failsException in thread “main” java.lang.UnsatisfiedLinkError: /opt/tools/sdk/gwt/gwt-linux-1.5.3/libswt-pi-gtk-3235….

GWT for linux is build against 32bit architecture. It contains some SWT/GTK 32bit modules. So if you try to run it with 64bit java it fails

Exception in thread “main” java.lang.UnsatisfiedLinkError: /opt/tools/sdk/gwt/gwt-linux-1.5.3/libswt-pi-gtk-3235.so: /opt/tools/sdk/gwt/gwt-linux-1.5.3/libswt-pi-gtk-3235.so: wrong ELF class: ELFCLASS32 (Possible cause: architecture word width mismatch)
    at java.lang.ClassLoader$NativeLibrary.load(Native Method)
    at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1807)
    at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1703)
    at java.lang.Runtime.load0(Runtime.java:770)
    at java.lang.System.load(System.java:1003)
    at org.eclipse.swt.internal.Library.loadLibrary(Library.java:132)
    at org.eclipse.swt.internal.gtk.OS.(OS.java:22)
    at org.eclipse.swt.internal.Converter.wcsToMbcs(Converter.java:63)
    at org.eclipse.swt.internal.Converter.wcsToMbcs(Converter.java:54)
    at org.eclipse.swt.widgets.Display.(Display.java:126)
    at com.google.gwt.dev.GWTShell.(GWTShell.java:301)
Could not find the main class: com.google.gwt.dev.GWTShell.  Program will exit.
[INFO] ————————————————————————
[ERROR] BUILD ERROR

You have two choices. Find 64bit SWT/GTK modules with same build version (3235 in this case) – good luck! or download 32bit JRE.

I chose second option and it took me 3 mins to resolve the problem.
Find proper JRE version on Oracle site I suggest bin file instead rpm. It unpacks jre to own dir. Move that directory to some convenient location (it doesn’t matter where). Edit gwt.properties *and set java.executable* to java exec located in 32bit JRE.
Now run your GWT hosted mode and be unstoppable developer!

You may have some warnings from GTK, such as

/usr/lib/gtk-2.0/2.10.0/menuproxies/libappmenu.so: wrong ELF class: ELFCLASS64
(GWT:351): Gtk-WARNING **: Failed to load type module: /usr/lib/gtk-2.0/2.10.0
/menuproxies/libappmenu.so
**

But it has no consequences for me, so far…

Some sources say that you should set an environment var:

export LIBXCB_ALLOW_SLOPPY_LOCK=1

to block bugs in X display layer but I don’t know what does it mean :)

In this case I had to hadle with GWT version 1.5.3 (old corporate project)

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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.