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Date: Mon, 14 Mar 2005 14:42:11 +0100
From: Sylvain Wallez <sylvain@apache.org>
Organization: Anyware Technologies
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To: dev@cocoon.apache.org
Subject: Re: [VOTE] Internal Pipelines Error Handling
References: <4234DFFF.80609@reverycodes.com> <423547EA.3010809@apache.org>
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Vadim Gritsenko wrote:

> Sylvain Wallez wrote:
>
>> Vadim Gritsenko wrote:
>>
>>>     <map:pipeline internal-error-handling="true">
>>
>>
>> Or even better, let's put this information on the handle-error 
>> statement itself, because it's really where it belongs:
>
>
> Only problem I see with it is that it opens up a scenario:
>
> <map:pipeline>
>   ...
>   <map:handle-errors when="internal">
>     ...
>   </map:handle-errors>
>   <map:handle-errors when="external">
>     ...
>   </map:handle-errors>
> </map:pipeline>
>
> And I'm not sure we want to go there. Hence, attribute on the pipeline 
> itself is better, IMHO. It indicates that this is a feature of the 
> pipeline (similar to internal-only="true").


The easy solution is to consider that there can be only one 
<map:handle-errors> per <map:pipeline>! Currently, and for historical 
reasons, there can be a combination of either :
    <map:handle-errors> where the handler will need to have its own 
generator
or
    <map:handle-errors type="404">
    <map:handle-errors type="500">
    where the ErrorGenerator is automatically added.

The second form can be considered to be a deprecated legacy feature 
(need to add logs for it, BTW), and we can therefore safely put the 
"when" attribute on the first form (with no "type" attribute).

> OTOH, using handle-errors attribute allows for:
> <map:pipelines>
>   <map:pipeline>
>     ...
>   </map:pipeline>
>   <map:handle-errors when="always">
>     ...
>   </map:handle-errors>
> </map:pipeline>
>
> Which otherwise would require attribute on map:pipelines, if that 
> feature is needed at all.


Yep. And that shows that it's really a feature of <handle-errors> and 
not of <pipeline>.

>>  <map:handle-errors when="external|internal|always">
>
>
> Isn't <map:handle-errors when="internal"> FS? What would be the 
> scenario for having error handler for internal but not external requests?


Maybe a scenario where you want to have errors be handled by the servlet 
engine?

>>> When attribute is missing or set to false, error handling behaviour 
>>> is as it is currently. Limitation of current implementation of the 
>>> feature is that only one, the inner most one error handler will be 
>>> used for error handling. Implementation can be extended to support 
>>> hierarchical error handlers, but I followed KISS and YAGNI approaches.
>>
>>
>>
>> Internal requests have the problem that pipeline execution occurs out 
>> of the control of the sitemap engine. Does the above restriction 
>> apply to pipeline build-time or pipeline execution-time?
>
>
> Yes, good catch. I implemented single error handler for pipeline 
> processing time. Pipeline assembly stage can use hierarchical handlers.


Ok, cool.

Sylvain

-- 
Sylvain Wallez                                  Anyware Technologies
http://www.apache.org/~sylvain           http://www.anyware-tech.com
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