[Engine-devel] Issue with XML namespaces in engine-setup

[Juan Hernandez]

On 04/12/2012 07:18 AM, Daniel Veillard wrote:
> On Tue, Apr 10, 2012 at 01:54:51PM +0200, Juan Hernandez wrote:
>> Hello,
>>
>> The code that we use in engine-setup to modify JBoss AS XML
>> configuration files uses the following pattern:
>>
>> datasourceStr = '''
>>     <datasource ...>
>>        ...
>>     </datasource>
>> '''
>>
>> xmlObj.addNodes("//datasource:subsystem/datasource:datasources",
>> datasourceStr)
>>
>> This looks correct but is in fact generating a incorrect XML document,
>> as the tags being added are not associated to a namespace. The resulting
>> XML file will be correct, but the temporary representation in memory is
>> not. This causes problems if you later, before writing out the modified
>> file, try to use xpath expressions matching the added nodes: there will
>> be no match.
>>
>> I would suggest that we change the pattern to something like this:
>>
>> datasourceStr = '''
>>   <any_dummy_tag xmlns="urn:jboss:domain:datasources:1.0">
>>     <datasource ...>
>>        ...
>>     </datasource>
>>   </any_dummy_tag>
>> '''
>> datasourceNodes = libxml2.parseDoc(datasourceStr).getRootElement().children
>>
>> xmlObje.addNodes("//datasource:subsystem/datasource:datasources",
>> datasourceNodes)
>>
>> This way both the representation in memory and the resulting file are
>> correct.
>>
>> Le me know what you think.
> 
>   I think it's dangerous to move nodes from one document to another
> especially if there is namespaces (I assume you're operating in an
> environment on top of libxml2 as I saw a reference to it ;-)
> 
>   For libxml2 there is an API in C:
>     http://xmlsoft.org/html/libxml-parser.html#xmlParseInNodeContext
> which could do what you expect. Maybe there is a binding/wrapper
> available you could use.

Thanks Daniel, that looks certainly better/easier than what I am
proposing. We use libxml2-python, but I can't locate that method there.
Do you know if it is possible to use it from python?

> Also your "//datasource:subsystem/datasource:datasources" XPath query
> could lead to multiple result nodes, I would suggest to pick the first
> result only, I suppose you don't want to add the set of nodes to
> multiple places
> 
>   xmlObje.addNodes("(//datasource:subsystem/datasource:datasources)[1]",
>                    datasourceNodes)
> 
>  or something equivalent (unless addNodes() takes care to handle that
>  properly ...)

Yes, the addNodes method takes care of that.