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Posted to dev@cocoon.apache.org by Jeremy Quinn <je...@media.demon.co.uk> on 2003/10/29 12:36:22 UTC

NPEs in FlowLayer

Hi All

I am getting mysterious NPEs in the flowlayer, while working with the  
flow version of  'authentication-fw'.

Not only are they odd, they are completely inconsistent.
They tend to happen after a script redirects after eg. a bad login.


eg.

"file:/Users/jermq/Checkouts/Secure/cocoon-2.1/build/webapp/arches- 
public/flow/authentication.js", line 91: uncaught JavaScript exception:
at failure  
(file:/Users/jermq/Checkouts/Secure/cocoon-2.1/build/webapp/arches- 
public/flow/authentication.js, Line 91):
java.lang.NullPointerException

line 91 is:	cocoon.log.info ("FAILED");

HUH? Other log calls in my script are working fine!

the stacktrace is:

Original Exception: java.lang.NullPointerException
         at  
org.apache.cocoon.components.flow.javascript.fom.FOM_Cocoon$FOM_Log.jsFu 
nction_info(FOM_Cocoon.java:757)
         at inv4.invoke()
         at  
org.mozilla.javascript.FunctionObject.doInvoke(FunctionObject.java:523)
         at  
org.mozilla.javascript.FunctionObject.call(FunctionObject.java:438)
         at  
org.mozilla.javascript.ScriptRuntime.call(ScriptRuntime.java:1244)

etc.

is FOM_Cocoon getting a null logger under certain circumstances ?

I also had a null logger in a component I am writing .....

The logger was null during all the lifecycle methods : configure,  
service, initialise, dispose etc.

I am also getting inconsistent NPEs while calling: cocoon.sendPage

I also get a weird exception while throwing errors from flowscript:

	"file:/Users/jermq/Checkouts/Secure/cocoon-2.1/build/webapp/arches- 
public/flow/authentication.js", line 104: Invalid JavaScript value of  
type org.mozilla.javascript.UniqueTag

line 104 is:		throw new Error("No failure redirection parameter given");


I have a fully up-to date CVS and apart from the 'throw new Error()'  
business, these problems were not happening last week.

	
Thanks for any help ....

regards Jeremy

Re: NPEs in FlowLayer

Posted by Ugo Cei <u....@cbim.it>.

Christopher Oliver wrote:
> Ugo Cei wrote:
> Sorry, but I don't agree. NPE's are indications of bugs. Hiding those 
> with checks for null doesn't help matters, IMO.

I have my share of doubts when it comes to these matters. This is my 
line of reasoning:

The Flowscript is a core component of Cocoon. We should apply defensive 
programming in order to protect the core from potentially buggy or 
malicious client code.

I am assuming that:

1. JXForms is "client code" and not part of the core.
2. The bug is in JXForms.

In any case, it is clearly a prerequisite of FOM_Cocoon.invalidate that 
the "request" member variable is not null. Given that, even if we find 
the bug that is causing the present problems, we cannot guarantee that 
there aren't more lurking somewhere, how do we verify that the 
prerequisite always holds?

A. Do we add a null check and log a message if the check fails?
B. Do we let the code throw an NPE without an explaining message?
C. Do we catch the NPE and rethrow some other kind of runtime exception?
D. Do we "assert request != null" and hope everybody is using Java 1.4? 
(just joking)

I agree with you that option A might hide some bugs, but I don't like 
option B either. While we wait for Java 1.3 to be considered obsolete 
and unsupported, maybe option C is the best one. What do you think?

	Ugo