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From "Dan Diephouse" <...@envoisolutions.com>
Subject Re: JaxwsInterceptorRemoverInterceptor and RM
Date Mon, 08 Jan 2007 01:28:57 GMT
this is very dangerous and way too common of a problem to rely on catching
exceptions that might occur during processing. Making interceptors more
fault tolerant this way complicates development for advanced users,
integrators, etc. Lets say I as a user write an interceptor which verifies
that an authentication header is present and throws a fault if it is not
present. I now need to add logic now to look for WS-* messages.

Also, it is dangerous because I think it could give into situations where it
isn't clear if we should throw an error or if we should be catching it. What
if the incoming message is formatted wrong and that is what throws the
ClassCastException? Now our fault tolerance has turned into fault
swallowing.

I would much prefer a more sophisticated dispatching maechanism. Here's a
look at our incoming interceptor flow with RM and Addressing enabled:

  receive [AttachmentInInterceptor, InMessageRecorder]
  pre-stream []
  user-stream [StreamHandlerInterceptor]
  post-stream [StaxInInterceptor]
  read [ReadHeadersInterceptor]
  pre-protocol [MustUnderstandInterceptor, MAPCodec, SOAPHandlerInterceptor,
RMSoapInterceptor]
  user-protocol []
  post-protocol []
  unmarshal [URIMappingInterceptor, WrappedInInterceptor,
SoapHeaderInterceptor]
  pre-logical [OutgoingChainSetupInterceptor, RMInInterceptor,
MAPAggregator]
  user-logical [LogicalHandlerInterceptor]
  post-logical []
  pre-invoke []
  invoke [ServiceInvokerInterceptor]
  post-invoke [OutgoingChainInterceptor]

We can recognize that a message isn't destined to the original endpoint (and
is destined to RM) after we've parsed the headers for the most part. I think
it is at this point that we should be re-dispatching off to the RM service
or wherever it needs to go (by redispatching I mean creating a new chain
with the actual service's interceptors and starting it at the current
phase).  Since interceptors at the beginning of the chain work with the
message itself and shouldn't make assumptions about what Service is being
invoked for the most part, this is a good breaking point to re- dispatch.

Another option to handle these scenarios would be to implement a more
advanced dispatching mechansim which dispatches to the service later in the
chain and not at the front. I outlined some ways to do this in [1]. One of
the ways involves creating a MessageObserver for the soap binding itself.
The soap binding would then contain some logic on how to find the correct
service given the URL/soap version/etc. In theory the RM layer could then
override/preempt this logic at some point in the chain.

I'm not sure if I prefer the redispatching or the delaying Service
resolution, but I don't think I'm cool with just doing a
catch(ClassCastException).

- Dan

1.
http://mail-archives.apache.org/mod_mbox/incubator-cxf-dev/200612.mbox/%3c7b774c950612021343x513c2783o128a032ba93923bb@mail.gmail.com%3e

On 1/5/07, Glynn, Eoghan <eoghan.glynn@iona.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Andrea Smyth [mailto:andrea.smyth@iona.com]
> > Sent: 05 January 2007 15:59
> > To: cxf-dev@incubator.apache.org
> > Subject: Re: JaxwsInterceptorRemoverInterceptor and RM
> >
> > >>Can you elaborate on how exactly you see this thing working?
> > >>
> > >>
> > >
> > >Well I was thinking of something even more simple ... the
> > interceptors
> > >should be coded defensively to "expect the unexpected" and
> > simply step
> > >out of the way when that occurs ... e.g. instead of the
> > >HolderOutInterceptor just doing a straight cast of the
> > message parts to
> > >Holder and barfing with ClassCastException on any other
> > type, it would
> > >first check with instanceof to ensure the cast succeeds and
> > otherwise
> > >bail out from handleMessage() immediately.
> > >
> > >
> > I'd be very much in favour of this - hence my question: Is it
> > OK to make the HolderInInterceptor robust by performing a
> > type check before casting to Holder? Or is there a more
> > efficient way, e.g. check the parameter type for INOUT first,
> > and only then attempt the cast?
> >
> > Andrea.
>
> Well if you're worried about the runtime cost of doing the instanceof
> check for every single message dispatch, then we could make an
> assumption that in practice out-of-band RM protocol messages will
> generally only constitute a small minority of the messages dispatched
> (assuming RM sequences have a reasonable lifespan).
>
> If this assumption holds, we could dispense with the instanceof check
> and instead do the Holder cast inside a try ... catch
> (ClassCastException) block, bailing out of handleMessage() in the catch
> block. That way we'd take the performance hit of throwing and catching
> the ClassCastException only when an RM protocol message is actually
> being dispatched (presumably relatively rare) and incurr no extra cost
> in the normal case.
>
> /Eoghan
>



-- 
Dan Diephouse
Envoi Solutions
http://envoisolutions.com | http://netzooid.com/blog

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