Re: [Knobot-devel] a question on the ordering of TypeHandler

[dbu <db...@us...>]

hi reto,

thanks for this excplications. now i see better how requests are processed.
the problem with caching is that firefox ignores the header.
Vary: Cookies
what i am trying to do now is adding a flag to the Response object 
telling whether it may be cached or not. the IEFixFilter could check it 
and only add the no-cache headers if the response is not cachable. 
although it is not the most elegant solution, this would solve the 
biggest problems with caching today: images which do not exist in 
different language variants and the css files would be cached, really 
improving user experience when surfing the page.

i could create a post-filter chain that is used after the 
typechainfilter finished using the handlers and move the IEFixFilter 
there. do you think this is a good idea? or is there a better way?
i could also put a method to the response to remove headers and remove 
all cache-related headers in the fileserverfilter if the response is 
cachable - but this is definitely not the proper way...

david



Reto Bachmann-Gmür wrote:
> hi david,
> 
> - FileServerFilter is a rwcf:TypeHandler
> - IEFixFilter is a rwcf:Filter
> - rwcf:TypeHandlerS get executed by the TypeChainFilter which is an
> rwcf:Filter.
> 
> What happens is the following:
> 1. the rwcf:FilterS gets ordered by priority, higher priority are
> excecuted first, lower if and only if the higher-priority filters
> forward the request
> 2. With prirority 500 the TypeHandlerFilter comes into action, this
> creates a chain of TypeHandler so that what's returned by one
> TypeHandler is the input-type for the next, the goal is to create a
> chain which return a content-type acceptable by the client agent.
> 
> From: http://development.osar.ch/documentation (this should be moved to
> a wymiwyg-site...)
> 
> The Type Handler Filter is a filter which creates a list of
> TypeHandlers  and forwards the request to this list. TypeHanlers are
> itself very similar to Filters, in fact they implement the same java class.
> 
>     * The description of a TypeHandler contains the media type it
> returns, if the handler requires some input data the media-types such
> data must be is specified. (an exception for TypeBlindHandlers as well
> as for TypeHandlers implementing the Java Interface TypeHandler, this
> rarely used features need some redesign)
>     * The desciption of a TypeHandler may force authentification by
> being of type rwcf:PermissionEnforcer
> 
> 
> The Type Hanlder Filter constructs the chain of TypeHandlers  by
> iterating through the available TypeHandlers  in descending order of
> rwcf:priority, when a TypeHandlers matches the current request and  has
> the desired target-typeit if added to the chainand the iteration through
> the available TypeHandlers starts over omiting  those already in the
> chain. This processed is repeated till a terminal chain is found, a
> terminal chain is one that ends with a TypeHandler which needs no input
> data.
> basing on the request it receives so that the changes made by previous
> Filters inluence the selection of TypeHandlers.
> 
> 3. If no type-handler chain can be created the request is forwarded to
> the next rwcf:Filter after TypeHandlerFilter, possibly getting at a
> filter generating a 404 or a method-not-supported error page.
> 
> 
> So setting a low priority to IEFixFilter will cause the filter to be
> executed iff no previous filter can handle the request, which includes
> that no type-handler filter chain can be created, which in turn includes
> that FileServerFilter cannot serve a file.
> 
> reto
> 
> PS: http://jena.hpl.hp.com/juc2006/proceedings/bachmann-gmur/paper.pdf
> also has some infos about FilterS and TypeHandlerS
> 
> dbu wrote:
>> hi,
>>
>> i am experimenting with caching and the IEFixFilter.
>> i realised that the FileServerFilter gets called after the IEFixFilter. 
>> the iefix-section.rdf defines the priority of the iefix, fs-section.rdf 
>> that of the fileserver.
>> i tried to put iefixfilter priority lower than that of the filefilter, 
>> but this results in iefixfilter not being used at all.
>> how can i control which filters are used on a request and in what order? 
>> or can't i use several handlers on one request?
>>
>> cheers,david
>>
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