Subclassing a private (support) class in AVM2

I am developing a dynamic mocking framework for Flex/AS3 and am having trouble with private/support types (ie. those declared outside the package {} in a class file).

In my ABC "file", I am declaring the instance with the PROTECTED_NAMESPACE class flag and with a PRIVATE_NS multiname. I have also experimented with giving it the same namespace as the class it is subclassing (eg. PRIVATE_NS("ContainerClass.as$123")).

No matter what I do, I always get the following error after loadBytes:

VerifyError: Error #1014: Class ContainerClass.as$123::PrivateClass could not be found.

I have experimented with loading the generated bytecode into the same ApplicationDomain as the private class (I use a child domain by default). I even tried registering a class alias before the load (though that was a bit of a stretch).

Am I forgetting anything or is it simply a restriction of the AVM?

Please note that I am fully aware that this is illegal in ActionScript 3.0, I am looking for whether this is actually possible in the AVM.

Edit: For those interested in the work so far, the project is asmock and is on sourceforge.

I have actually developed a dynamic proxy framework and it works well (with package classes/interfaces). The only major outstanding feature of the framework is mocking 'private' classes (declared outside the package).

Richard Szalay 2009-02-09 15:19:22

Wow, then I must really check that out! I'm assuming you did not do this with the standard AS3 capabilities?

Christophe Herreman 2009-02-09 15:35:14

Actually, I'm just using Loader.loadBytes(). Generating a dynamic SWF/ABC at runtime was the tricky part ;)

Richard Szalay 2009-02-09 15:39:13

Awesome! I can imagine you had a hard time with the bytecode. I looked at it a while ago, but got so scared, I ran away ;-)

Christophe Herreman 2009-02-09 15:42:24

Alot of determination helped.

Richard Szalay 2009-02-09 15:44:40

4.4.1 designates that SYSTEM namespaces are empty (ie. String, int, etc), but private namespaces (ie. those with a multiname kind of PrivateNs/0x5) still have names) still have values. <file>.as$<number> is automatically allocated as the (private) multiname to nested classes.

Richard Szalay 2009-03-09 09:09:47

Also, the framework that I'm working does generate a loading swf and supports generation of all types of classes (including Vector.<T>). It's only the "nested" classes that are causing me grief. If you are interested in the work so far, the source is available at http://asmock.sourceforge.net

Richard Szalay 2009-03-09 09:10:44

"User-defined namespaces have kind CONSTANT_Namespace orCONSTANT_ExplicitNamespace and a non-empty name. System namespaces have empty names and one of the other kinds" is the text I'm thinking of here. This implies CONSTANT_PrivateNs is a system NS, and has no stored name.

Simon Buchan 2009-03-10 05:01:29

And I'm thinking you might have to parse in the abc tag from the swf, merge in your generated code and splice it back into the swf (in memory). Of course, you won't be able to do this within the swf you are mocking :(.

Simon Buchan 2009-03-10 05:04:37

I guess it will have to wait for when I refactor my reflection lib to parse the abc tag. I wonder if the type assignment will work if it's declared in multiple application domains.

Richard Szalay 2009-03-18 13:48:22

I might not have been clear: from my understanding, PrivateNs's are private because they are not referenceable outside the tag. You would have to parse the incoming swf, and modify the abc tag to include your mock class *before* loading: meaning only one App Domain.

Simon Buchan 2009-03-19 23:38:49

Ah, I see what you mean. Unfortunately that's not feasible as the swf in question would have already been loaded (it's a runtime dynamic mocking framework). Thanks for the clarification!

Richard Szalay 2009-03-23 20:04:45

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Subclassing a private (support) class in AVM2

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