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From Polar Humenn <phum...@iona.com>
Subject Re: Proposal for chaning CXF Interceptor APIs. WAS: RE: When should we close the handlers in CXF?
Date Thu, 08 Feb 2007 16:19:38 GMT
Liu, Jervis wrote:
> You are right in saying statelessness is only a sufficient condition. But I would say
it is recommended that the CXF interceptors are implemented as statelessness unless the developer
are fully aware of the implication of writing a stateful interceptor as our current interceptor
calling semantics are not enough to guarantee thread safety in this case.
>   
Exactly, so the call semantics have to be nailed down, documented and 
adhered to. What are the intended invariants on each call?
>> ....
>>
>> I don't like the idea of an onFinish(Message) because it 
>> requires me to 
>> *wait* in my interceptor to make sure that my message popped out the 
>> other end.  The handleFault() which is the result of an interceptor 
>> thrown Fault, gives me the "exception" to my *assumption* that the 
>> message will pop out the other end. Assuming messages make it 
>> out or in 
>> is the most abundant normal case.
>>
>>     
>
> onFinish() was proposed to address the subchain issue, i.e., we want the interceptor
has the capability to register some sort of terminal actions with the InterceptorChain to
be executed when the chain traversal is complete, more details on this discussion can be found
from [1] [2] [3]. onFinish is not designed to address fault handling issues.
>   
Okay, so I read what was below. I was not yet familiar with the subChain 
semantics, but now I am getting it. I see some problems with the 
subChain semantics (which are below), and I almost grasp what you are 
looking for,  which may alleviate my concerns, so please correct me if 
am totally off base.

The goal of an outbound message is to get from the application to the wire,

          Application ----> Wire

is it not? Interceptor traversal happens on that arrow. An interceptor 
chain is NOT *finished* until that message is out on the wire, (unless 
some fault occurs). Correct?

          Application  ---- InterceptorChainTraversal ----> Wire

The basic requirement you are looking for is to have some backward 
actions planned after the chain is traversed in one direction to do some 
clean up, or write end messages, trade output streams, in the backward 
direction. Correct?

I understand from your explanation of the SoapOutHandler interceptor in 
[1], than on the proposed onFinish() call that the message hasn't yet 
been written to the wire, but is about to be written (after adding 
ending tags, etc). Finally the at the end the MessageSenderInterceptor 
calls the "conduit.close(message)", which I presume actually writes the 
message out on the wire.

I surmise that the interceptor chain is NOT *finished* at the last 
interceptor in the chain, because the intended goal of the interceptor 
chain is to get the message out on the wire, and that has not been 
achieved.

I believe you really want is to describe a two phase interceptor 
traversal to *complete* the chain.  I realize the the execution trace 
would be the same, yet the proverbial semantics are subtly different 
(maybe suggesting different name for the operations).

For an interceptor chain of A,B,C,D we would get the following execution.

        Application   ---- A, B, C, D, D, C, B, A -> Wire

Is this the trace you intend? I suggest on the backward trace that the 
interceptor is still "handling" the message. Therefore, I would suggest 
different names.

interface Interceptor<T extends Message> {
    void handleMessageP1(T message);
    void handleMessageP2(T message);
    // fault handing is another topic.
}

Where P1 and P2  distinguish the "forward" phase and the "backward" 
phase of message handling, respectively. Suggestions?

Now, for my concerns about the subchain logic;

The doInterceptInSubChain and finishSubChain is a way for two 
interceptors to communicate (that coordinated with each other), yet have 
the unknowing possibly of being subverted by other injected interceptors 
in unfortunate places that call doInterceptSubChain and finishSubChain 
as well, and thereby two seemingly coordinated interceptors are 
mis-coordinated.

I surmise that this approach will eliminate the need 
for"doInterceptSubChain" and "finishSubChain" calls, and also will 
eliminate ability to call "doIntercept" for anything but the CXF 
internal processing (i.e. interceptors cannot call it).

> As far as the fault handling is concerned, I agree with you that our current fault handling
logics are bit confusing. This has been raised by Eoghan couple months ago, see [4]. Can I
suggest we separate this thread into two topics? One is the proposal of adding onFinish()
into interceptor interface, which is to address subchain and terminal actions issues. One
is about the fault handling. For the former, I would like to see if there are any objections?
If there is no different voice, at least we can start working on this and keep our discussion
for the later going until it is fully baked.
>   
I agree. We should discuss on another thread.

Cheers,
-Polar
> [1]. http://mail-archives.apache.org/mod_mbox/incubator-cxf-dev/200701.mbox/%3c9A4696F35B459043970EE4A85A3173900665B6@amer-ems1.IONAGLOBAL.COM%3e
> [2]. http://mail-archives.apache.org/mod_mbox/incubator-cxf-dev/200701.mbox/%3c9A4696F35B459043970EE4A85A3173900665B1@amer-ems1.IONAGLOBAL.COM%3e
> [3]. http://mail-archives.apache.org/mod_mbox/incubator-cxf-dev/200701.mbox/%3cFA1787F64A095C4090E76EBAF8B183E071FB84@owa-emea.iona.com%3e
> [4] http://mail-archives.apache.org/mod_mbox/incubator-cxf-dev/200611.mbox/%3cFA1787F64A095C4090E76EBAF8B183E071FADE@emea-ems1.dublin.emea.iona.com%3e
>
>   
>> Unfortunately, after a discussion with Eoghan, I find that some 
>> interceptor chains are just not completed. If that is the 
>> case, when or 
>> if would you call "onFinish()"?
>>
>> I would suggest:
>>
>>     void handleMessage(Message m) throws Fault;
>>
>>     void handleFault(
>>          Message m, String phase, String interceptor, Fault f
>>     );
>>
>> naming the phase and interceptor that threw the particular fault.
>> or maybe even
>>
>>     class InterceptorFault {
>>         String phase; String interceptor; Fault fault;
>>     }
>>     void handleFault(
>>         Message m, List<InterceptorFault> faults
>>     ) throw Fault;
>>
>> which allows handleMessage to throw a fault, and 
>> handleFault() to throw 
>> Faults, but is given a list of faults and the names of 
>> interceptors that 
>> throw them back along the way. The chain collects Faults and adds the 
>> faults to the list.
>>
>> Cheers,
>> -Polar
>>
>> Liu, Jervis wrote:
>>     
>>> Hi Polar, comments in-line.
>>>
>>> Cheers,
>>> Jervis
>>>
>>>   
>>>       
>>>> -----Original Message-----
>>>> From: Polar Humenn [mailto:phumenn@iona.com]
>>>> Sent: 2007?2?7? 6:05
>>>> To: cxf-dev@incubator.apache.org
>>>> Subject: Re: Proposal for chaning CXF Interceptor APIs. WAS: 
>>>> RE: When should we close the handlers in CXF?
>>>>
>>>>
>>>> I'm still trying to find out how this interceptor stuff works. So 
>>>> forgive me if I seem naive. :-[
>>>>
>>>> You say CXF interceptors are stateless. Are you saying that 
>>>> "statelessness" is a requirement to be a CXF interceptor? 
>>>>         
>> Or are you 
>>     
>>>> saying that the processing interceptors that are currently 
>>>> used in CXF 
>>>> are stateless and that's all that need to be supported?
>>>>
>>>> I can definitely see a use case for CXF interceptors 
>>>> maintaining state.
>>>>
>>>> A simple one is an outbound message counter. The interceptor 
>>>> increments 
>>>> a counter on handleMessage() assuming the message makes out 
>>>> the end (has 
>>>> no way of knowing). So the interceptor must decrement its 
>>>>         
>> counter on 
>>     
>>>> handleFault() because that tells the interceptor that the 
>>>> message never 
>>>> made it out the end because of some interceptor downstream in 
>>>> the chain.
>>>>
>>>>     
>>>>         
>>> Once interceptors are created (eg, in 
>>>       
>> SoapBindingFactory.java), their instances are shared across 
>> all interceptor chains and threads. Interceptors have to be 
>> stateless for the sake of thread safe. If you really have to 
>> have some states that you want to be shared among 
>> interceptors, you can put them into Message. 
>>     
>>>   
>>>       
>>>> So, if I have this right, what you are proposing is to alter the 
>>>> semantics, and only call this onFinish() method on the unwind 
>>>> chain when 
>>>> the message makes finally makes it out the end of the chain.
>>>>
>>>> This changes the semantics quite a bit. With the 
>>>>         
>> handleFault approach 
>>     
>>>> one can assume that the message will be successful in 
>>>>         
>> negotiating the 
>>     
>>>> chain *unless* it is told otherwise, (handleFault), which leads to 
>>>> optimistic processing. The latter onFinish() approach 
>>>>         
>> requires me to 
>>     
>>>> *wait* to see *if* the message was successful, which is a 
>>>> pessimistic, 
>>>> possibly more expensive approach.
>>>>
>>>> It seems to me, that "fault" processing is the exceptional 
>>>> case, and one 
>>>> should be able to assume optimistic processing, unless 
>>>>         
>> told otherwise.
>>     
>>>>     
>>>>         
>>> Actually what has been proposed does not change the 
>>>       
>> semantics a lot. We only want to do two changes:
>>     
>>> 1. Remove handlerFault(). The reason for this has been 
>>>       
>> presented in the previous discussion, just quoted again 
>> below: "However, the difference is CXF interceptors are not 
>> designed to hook in user logic as these JAX-WS handlers do, 
>> thus handleFault is not needed in CXF interceptors (correct 
>> me if I am wrong, but I believe this is the purpose that 
>> JAX-WS handlers's handleFault method designed for. I.e., when 
>> a known exception - ProtocolException occurs, handleFault() 
>> gives handler developer a hook to clean up sth, for example, 
>> roll back a transaction, this is different from what close() 
>> is supposed to do. The latter is designed to clean things up 
>> under a succeeded situation). For any Runtime exceptions 
>> thrown by interceptors, we just wrap it as soap exception 
>> then dispatch it back calling handleMessage."
>>     
>>> 2. Add a onFinish(Message) or onComplete(Message) method 
>>>       
>> (using name DanD suggested): this method is called in a 
>> reversed direction when chain completes, can be used to 
>> remove the sub-chain or interceptor re-entrance. For example, 
>> SoapOutInterceptor can use onComplete to write the end 
>> element of SoapBody SoapEnvelop, this way SoapOutInterceptor 
>> does not need to wrap its following interceptors in a sub chain.
>>     
>>>
>>>   
>>>       
>>>> Thoughts?
>>>>
>>>> The other thing I don't get, is what constitutes an Inbound Fault 
>>>> Message as opposed to an Inbound Message? Why does this make a 
>>>> difference in Interceptors of inbound and outbound messages?
>>>>
>>>> Cheers,
>>>> -Polar
>>>>
>>>>
>>>> Dan Diephouse wrote:
>>>>     
>>>>         
>>>>> Could I offer just once suggestion? Could we rename the 
>>>>> postHandleMessage to
>>>>> onFinish(Message) or onComplete(Message)?
>>>>>
>>>>> - Dan
>>>>>
>>>>> On 2/6/07, Unreal Jiang <sinbad_jia@yahoo.com> wrote:
>>>>>       
>>>>>           
>>>>>> Hi,
>>>>>>
>>>>>>   Looks like there has no opponent for jervis' proposal,  I will

>>>>>> create a
>>>>>> jira task for this proposal and sign it me.
>>>>>>
>>>>>>   Cheers
>>>>>>   Unreal
>>>>>>
>>>>>> "Liu, Jervis" <jliu@iona.com> wrote:
>>>>>>
>>>>>> ________________________________
>>>>>>
>>>>>> From: Dan Diephouse [mailto:dan@envoisolutions.com]
>>>>>> Sent: Tue 1/23/2007 1:02 AM
>>>>>> To: cxf-dev@incubator.apache.org
>>>>>> Subject: Re: Proposal for chaning CXF Interceptor APIs. 
>>>>>>         
>>>>>>             
>>>> WAS: RE: When
>>>>     
>>>>         
>>>>>> should we close the handlers in CXF?
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 1/22/07, Liu, Jervis  wrote:
>>>>>>         
>>>>>>             
>>>>>>> Hi, I would like to summarize what we have been 
>>>>>>>           
>>>>>>>               
>>>> discussed in this 
>>>>     
>>>>         
>>>>>> thread
>>>>>>         
>>>>>>             
>>>>>>> (including Eoghan's proposal posted last Oct [1]) regarding 
>>>>>>>           
>>>>>>>               
>>>>>> Interceptor
>>>>>> API
>>>>>>         
>>>>>>             
>>>>>>> changes. Any comments would be appreciated.
>>>>>>>
>>>>>>> Currently our Interceptor APIs look like below:
>>>>>>>
>>>>>>> public interface Interceptor {
>>>>>>>      void handleMessage(T message) throws Fault;
>>>>>>>      void handleFault(T message);
>>>>>>> }
>>>>>>>
>>>>>>> Also in the interceptor chain, we have a notion of sub-chain
or
>>>>>>> interceptor chain reentrance by calling 
>>>>>>>           
>>>>>>>               
>>>> message.getInterceptorChain
>>>>     
>>>>         
>>>>>> ().doIntercept(message)
>>>>>>         
>>>>>>             
>>>>>>> or message.getInterceptorChain().doInterceptInSubChain(message).
>>>>>>>
>>>>>>> The main issues we have with the current implementation are:
>>>>>>>
>>>>>>> 1. Fault handling. See Eoghag's email [1]
>>>>>>>
>>>>>>> 2. Sub-chain reentrance. See previous discussion in this thread.
>>>>>>>
>>>>>>> We propose to change Interceptor API as below:
>>>>>>>
>>>>>>> public interface Interceptor {
>>>>>>>      void handleMessage(T message) throws Fault;
>>>>>>>      void handleFault(T message);
>>>>>>>      void close(T message);
>>>>>>> }
>>>>>>>
>>>>>>> handleFault(T message) method is used to process fault message

>>>>>>>           
>>>>>>>               
>>>>>> (which is
>>>>>>         
>>>>>>             
>>>>>>> done by handleMessage() in fault-chain currently).
>>>>>>>           
>>>>>>>               
>>>>>>         
>>>>>>             
>>>>>>> I'm not sure I understand how you want to use this. I 
>>>>>>>           
>>>>>>>               
>>>> guess I could 
>>>>     
>>>>         
>>>>>> see
>>>>>> two
>>>>>>         
>>>>>>             
>>>>>>> ways
>>>>>>>           
>>>>>>> 1. Remove In/OutFault interceptors and call handleFault 
>>>>>>>           
>>>>>>>               
>>>> on the In/Out
>>>>     
>>>>         
>>>>>>> interceptors. I don't know that mapping works especially 
>>>>>>>           
>>>>>>>               
>>>> well though.
>>>>     
>>>>         
>>>>>>> 2. Don't call handleFault on in/out interceptors, but 
>>>>>>>               
>> only on the
>>     
>>>>>>> in/outFault interceptors - this would mean, for example, 
>>>>>>>           
>>>>>>>               
>>>> that the 
>>>>     
>>>>         
>>>>>> logic
>>>>>> from
>>>>>>         
>>>>>>             
>>>>>>> Soap11OutFaultInterceptor would be moved from the 
>>>>>>>           
>>>>>>>               
>>>> handleMessage to
>>>>     
>>>>         
>>>>>>> handleFault.
>>>>>>>           
>>>>>>> Can you be more specific about what you mean?
>>>>>>>           
>>>>>>>               
>>>>>> Sorry, after rethinking about this, I've changed my mind 
>>>>>>         
>>>>>>             
>>>> slightly, so 
>>>>     
>>>>         
>>>>>> here
>>>>>> is the idea:
>>>>>>
>>>>>> CXF Interceptor API will be similiar to JAX-WS API, 
>>>>>>         
>>>>>>             
>>>> section 9.3.2.1.
>>>>     
>>>>         
>>>>>> Throw ProtocolException or a subclass This indicates that 
>>>>>>         
>>>>>>             
>>>> normal message
>>>>     
>>>>         
>>>>>> processing should cease.
>>>>>> Subsequent actions depend on whether the MEP in use requires a 
>>>>>> response to
>>>>>> the message currently
>>>>>> being processed or not:
>>>>>>
>>>>>> Response: Normal message processing stops, fault message 
>>>>>>             
>> processing
>>     
>>>>>> starts. The message direction
>>>>>> is reversed, if the message is not already a fault message 
>>>>>>         
>>>>>>             
>>>> then it is
>>>>     
>>>>         
>>>>>> replaced with a fault message4,
>>>>>> and the runtime invokes handleFault on the next handler or 
>>>>>>         
>>>>>>             
>>>> dispatches 
>>>>     
>>>>         
>>>>>> the
>>>>>> message (see
>>>>>> section 9.1.2.2) if there are no further handlers.
>>>>>>
>>>>>> No response: Normal message processing stops, close is 
>>>>>>         
>>>>>>             
>>>> called on each
>>>>     
>>>>         
>>>>>> previously invoked handler
>>>>>> in the chain, the exception is dispatched (see section 9.1.2.3).
>>>>>>
>>>>>>
>>>>>> Throw any other runtime exception This indicates that 
>>>>>>         
>>>>>>             
>>>> normal message
>>>>     
>>>>         
>>>>>> processing should cease. Subse-
>>>>>> quent actions depend on whether the MEP in use includes a 
>>>>>>         
>>>>>>             
>>>> response to 
>>>>     
>>>>         
>>>>>> the
>>>>>> message currently being
>>>>>> processed or not:
>>>>>>
>>>>>> Response: Normal message processing stops, close is 
>>>>>>             
>> called on each
>>     
>>>>>> previously invoked handler in
>>>>>> the chain, the message direction is reversed, and the 
>>>>>>             
>> exception is
>>     
>>>>>> dispatched (see section 9.1.2.3).
>>>>>>
>>>>>>
>>>>>> No response: Normal message processing stops, close is 
>>>>>>         
>>>>>>             
>>>> called on each
>>>>     
>>>>         
>>>>>> previously invoked handler
>>>>>> in the chain, the exception is dispatched (see section 9.1.2.3).
>>>>>>
>>>>>> However,  the difference is CXF interceptors are not 
>>>>>>         
>>>>>>             
>>>> designed to hook in
>>>>     
>>>>         
>>>>>> user  logic as these JAX-WS handlers do, thus handleFault 
>>>>>>         
>>>>>>             
>>>> is not needed
>>>>     
>>>>         
>>>>>> in  CXF interceptors (correct me if I am wrong, but I 
>>>>>>         
>>>>>>             
>>>> believe this is
>>>>     
>>>>         
>>>>>> the  purpose that JAX-WS handlers's handleFault method 
>>>>>>         
>>>>>>             
>>>> designed for. 
>>>>     
>>>>         
>>>>>> I.e,  when
>>>>>> a known exception - ProtocolException occurs, 
>>>>>>             
>> handleFault() gives  
>>     
>>>>>> handler
>>>>>> developer a hook to clean up sth, for example, roll back a 
>>>>>>         
>>>>>>             
>>>>  transaction,
>>>>     
>>>>         
>>>>>> this is different from what close() is supposed to do. The 
>>>>>>         
>>>>>>             
>>>>  latter is
>>>>     
>>>>         
>>>>>> designed to clean things up under a succeeded 
>>>>>>             
>> situation). For  any 
>>     
>>>>>> Runtime
>>>>>> exceptions thrown by interceptors, we just wrap it as soap 
>>>>>>         
>>>>>>             
>>>>  exception 
>>>>     
>>>>         
>>>>>> then
>>>>>> dispatch it back calling handleMessage.
>>>>>>
>>>>>> So here is the change we need to make:
>>>>>>
>>>>>> 1. Add a postHandleMessage() into Interceptor interface
>>>>>>
>>>>>> 2.  Remove handleFault() method from Interceptor 
>>>>>>         
>>>>>>             
>>>> interface. Or we can
>>>>     
>>>>         
>>>>>> still  keep it for a while until we are absolutely sure we 
>>>>>>         
>>>>>>             
>>>> wont need
>>>>     
>>>>         
>>>>>> this  method, but I presume there is nothing we need to 
>>>>>>             
>> do in this 
>>     
>>>>>> method.
>>>>>>
>>>>>> 3.  We will NOT add a close() method into Interceptor 
>>>>>>             
>> interface, as
>>     
>>>>>> CXF  interceptors are stateless, there is no resources 
>>>>>>             
>> need to be 
>>     
>>>>>> closed.
>>>>>>
>>>>>> public interface Interceptor {
>>>>>>       void handleMessage(T message) throws Fault;
>>>>>>       void postHandleMessage(T message);
>>>>>> }
>>>>>>
>>>>>> When  an interceptor chain ends normally, we need to call
>>>>>> postHandleMessage()  on each previously traversed 
>>>>>>             
>> interceptor in a 
>>     
>>>>>> reversed
>>>>>> direction.
>>>>>>
>>>>>> When  a fault occurs on the in-bound chain, an exception 
>>>>>>         
>>>>>>             
>>>> will be thrown
>>>>     
>>>>         
>>>>>> from  the interceptor, after catching the exception in
>>>>>> PhaseInterceptorChain,  we unwind the current chain by calling
>>>>>> postHandleMessage() on each  previously traversed 
>>>>>>             
>> interceptor and 
>>     
>>>>>> then jump
>>>>>> to the out-fault-chain,  calling handleMessage() on each 
>>>>>>         
>>>>>>             
>>>> interceptor 
>>>>     
>>>>         
>>>>>> with
>>>>>> the fault message.
>>>>>>
>>>>>> Any thoughs?
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>         
>>>>>>             
>>>>>>> close(T message) method is called on a reverse direction 
>>>>>>>           
>>>>>>>               
>>>> at the end of
>>>>     
>>>>         
>>>>>>> interceptor chain or when a fault or exception occurs. 
>>>>>>>           
>>>>>>>               
>>>> Take the fault
>>>>     
>>>>         
>>>>>>> handling case as an example, below is how handleFault 
>>>>>>>           
>>>>>>>               
>>>> and close work
>>>>     
>>>>         
>>>>>>> together
>>>>>>>           
>>>>>>>               
>>>>>>         
>>>>>>             
>>>>>>> +1 to close() - Although I think Eoghan has a good point 
>>>>>>>           
>>>>>>>               
>>>> about the
>>>>     
>>>>         
>>>>>> ordering
>>>>>>         
>>>>>>             
>>>>>>> not necessarily being the same. I think we need to do a 
>>>>>>>           
>>>>>>>               
>>>> little bit 
>>>>     
>>>>         
>>>>>> more
>>>>>>         
>>>>>>             
>>>>>>> digging before we can know whether or not sub chains can 
>>>>>>>           
>>>>>>>               
>>>> be removed.
>>>>     
>>>>         
>>>>>>> when a fault occurs on the in-chain, we unwind the 
>>>>>>>           
>>>>>>>               
>>>> current chain by
>>>>     
>>>>         
>>>>>> calling
>>>>>>         
>>>>>>             
>>>>>>> close() on each previously traversed interceptor and 
>>>>>>>           
>>>>>>>               
>>>> then jump to the
>>>>     
>>>>         
>>>>>>> out-fault-chain, calling handleFault() on each 
>>>>>>>           
>>>>>>>               
>>>> interceptor with the
>>>>     
>>>>         
>>>>>> fault
>>>>>>         
>>>>>>             
>>>>>>> message.
>>>>>>>
>>>>>>> Close method is also used to remove the sub-chain 
>>>>>>>           
>>>>>>>               
>>>> reentrance. See the
>>>>     
>>>>         
>>>>>>> SOAPHandlerInterceptor example I posted previously.
>>>>>>>
>>>>>>> Cheers,
>>>>>>> Jervis
>>>>>>>
>>>>>>> [1]
>>>>>>>
>>>>>>>           
>>>>>>>               
>>>> http://mail-archives.apache.org/mod_mbox/incubator-cxf-dev/200
>>>>     
>>>>         
>> 611.mbox/%3cFA1787F64A095C4090E76EBAF8B183E071FADE@emea-ems1.d
>>     
> ublin.emea.iona.com%3e 
>   
>>>   
>>>       
>>>>>>         
>>>>>>             
>>>>> -- 
>>>>> Dan Diephouse
>>>>> Envoi Solutions
>>>>> http://envoisolutions.com   | http://netzooid.com/blog
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ---------------------------------
>>>>> Access over 1 million songs - Yahoo! Music Unlimited.
>>>>>       
>>>>>           
>>>>     
>>>>         
>>>   
>>>       
>>     


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