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Bug 335373

Summary: NPE when changing iFrame url via SWT browser evaluate() method
Product: [Eclipse Project] Platform Reporter: Michael Burkhart <mikelb>
Component: SWTAssignee: Grant Gayed <grant_gayed>
Status: RESOLVED FIXED QA Contact:
Severity: major    
Priority: P3 CC: eclipse.felipe
Version: 3.5.2   
Target Milestone: 3.7 M6   
Hardware: All   
OS: All   
Whiteboard:
Attachments:
Description Flags
SWT Snippet Testcase
none
HTML/javascript file for testing
none
3.7-stream patch none

Description Michael Burkhart CLA 2011-01-25 15:05:02 EST 
Build Identifier: SWT 3.5.2.v3557f

We are developing a an app that leverages iFrames to manage a collection of different pieces of browser content and are trying to dynamically manage the separate iFrame data with a call from the SWT browser evaluate() method to a javascript method we have created to change the iFrames in the browser.

When testing this we ran into NPE's quite quickly after attempting to make the call several times in a row.

Here is the stack we are getting:

Exception in thread "main" java.lang.NullPointerException
	at org.eclipse.swt.browser.Mozilla.execute(Mozilla.java:1810)
	at org.eclipse.swt.browser.Mozilla.OnStateChange(Mozilla.java:2903)
	at org.eclipse.swt.browser.Mozilla$9.method3(Mozilla.java:1557)
	at org.eclipse.swt.internal.mozilla.XPCOMObject.callback3(XPCOMObject.java:266)
	at org.eclipse.swt.internal.mozilla.XPCOM._JS_EvaluateUCScriptForPrincipals(Native Method)
	at org.eclipse.swt.internal.mozilla.XPCOM.JS_EvaluateUCScriptForPrincipals(XPCOM.java:163)
	at org.eclipse.swt.browser.Mozilla.execute(Mozilla.java:1837)
	at org.eclipse.swt.browser.WebBrowser.evaluate(WebBrowser.java:378)
	at org.eclipse.swt.browser.Browser.evaluate(Browser.java:539)
	at org.eclipse.swt.snippets.Snippet308$1.widgetSelected(Snippet308.java:53)
	at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:228)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1003)
	at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3910)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3503)
	at org.eclipse.swt.snippets.Snippet308.main(Snippet308.java:62)

The line generating the NPE is this a de-reference of the "script" variable that is passed into the Mozilla.execute() method. In this specific case execute it called by the OnStateChange method with a null due to the fact that the specific function that the code is attempting to "re-install" does not have a functionString defined because it appears to be an internal function and for whatever reason it was not assigned a functionString value when it was dynamically created.

I will attach a simple testcase based on Snippet308 that can be used to recreate the problem.

Reproducible: Always

Steps to Reproduce:
1. Import the attached snippet project into your workspace
2. Place the offers.html file into a dir on your PC (defaults to c:/tempy )
3. If the location of the offers.html is not c:/tempy then update the test code to point to the location on your PC where you placed it.
2. Run ( SWT snippet )
3. When the UI appears click on the button on the right called "Change UrL". You will see that yahoo is loaded in to the browser frame on the left. 
4. Click this button several more times and your application will crash with the exception provided.

While this may seem to be a strange case, it is an important piece of our application and is critical for us. When this NPE is generated we have been unable to recover the browser instance.
Comment 1 Michael Burkhart CLA 2011-01-25 15:05:44 EST 
Created attachment 187566 [details]
SWT Snippet Testcase
Comment 2 Michael Burkhart CLA 2011-01-25 15:06:20 EST 
Created attachment 187567 [details]
HTML/javascript file for testing
Comment 3 Grant Gayed CLA 2011-02-22 16:01:50 EST 
I see the NPE sometimes and will look into this.  However, note that if your snippet reflects what your app is doing then you can probably get around this bug simply by changing your Browser.evaluate() invocation to Browser.execute().  These should be functionally equivalent since the JS function is not returning anything, but will eliminate the BrowserFunction that is used by the Browser behind-the-scenes.
Comment 4 Grant Gayed CLA 2011-02-22 16:32:25 EST 
Created attachment 189544 [details]
3.7-stream patch

Patch with fix for 3.7 stream.  I see that you're based on 3.5.x, but I'm assuming that you can avoid this problem by using Browser.execute() instead of evaluate(), and therefore don't really need this fix in 3.5.x.  If I'm wrong about this then you can follow up here.
Comment 5 Grant Gayed CLA 2011-02-22 16:33:11 EST 
fixed > 20110222
Comment 6 Michael Burkhart CLA 2011-02-23 16:23:06 EST 
execute() will work fine for us, thanks for the hint, and thanks for the fix in the 3.7 stream.