atom feed3 messages in org.apache.qpid.protonRe: Python wrapper - SASL and SSL cla...
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Ken GiustiDec 11, 2013 6:35 am 
Rafael SchlomingDec 11, 2013 6:43 am 
Ken GiustiDec 11, 2013 6:58 am 
Subject:Re: Python wrapper - SASL and SSL class API
From:Rafael Schloming (rh@alum.mit.edu)
Date:Dec 11, 2013 6:43:59 am
List:org.apache.qpid.proton

On Wed, Dec 11, 2013 at 9:35 AM, Ken Giusti <kgiu@redhat.com> wrote:

Hi all - just wanted to get some opinions on $Subject:

While I was trying to implement a fix for https://issues.apache.org/jira/browse/PROTON-476 I found that the lifecycle model for the python SASL and SSL objects differs for the C engine. I think the python wrapper's impl is buggy.

In the C engine, these objects are singletons with respect to their associated transport - there can only be one SSL and SASL object associated with a given transport. This is enforce by the C api - the transport provides factory classes for these objects.

The python wrapper doesn't enforce this. For both objects, a "public" constructor is supplied (I say "public" because it is exported by the wrapper's __all__ list). This makes it trivial for an application to construct multiple instances of SASL/SSL objects that reference the same underlying C object. While this can technically be done safely using reference counting, I think it may lead to unanticipated behavior - not to mention that it differs from the object model provide by the C engine.

I'd like to fix this by modifying the python wrapper to remove the SSL and SASL objects from the __all__ list, and provide factory methods on the Transport class for creating instances of these objects.

This would result in a change to the public API.

Why exactly do you need to change the API to do this? I would expect there should be a number of ways to keep it the same, e.g. rename the class and use a factory function with the same name as the class, or override __new__ if you want to keep the class name the same. Am I missing something?

--Rafael