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From Polar Humenn <phum...@iona.com>
Subject Re: [PROPOSAL] Client and Conduit changes
Date Mon, 19 Mar 2007 20:23:10 GMT
Glynn, Eoghan wrote:
>  
>
>   
>> -----Original Message-----
>> From: Polar Humenn [mailto:phumenn@iona.com] 
>> Sent: 19 March 2007 14:25
>> To: cxf-dev@incubator.apache.org
>> Subject: Re: [PROPOSAL] Client and Conduit changes
>>
>> I've got a couple of CXF architectural questions.
>>
>> Must be a Client in order for there to be an invocation 
>> request/response/fault/ack protocol? 
>>     
>
>
> Nope, a Client is not currently required for an invocation to occur.
>   
An "invocation" or  "sending a Message"?

I would classify an "invocation" as an abstract element that is composed 
of by two other abstract elements, a "request" and a "response" that are 
correlated with each other.

It would appear that the Client is the object in CXF that performs 
invocations. (i.e. sends a "request" and collects the "response" 
realized as CXF Messages.

The "request" messages seems to get sent out over a Conduit, which is an 
abstract element that seems to suggest a "connection" to a particular 
server (for lack of a better word).

In this model, the "response" can come back by some other means 
(protocol, address, connection orientation, etc), and as a result of 
being by any other means, the response quite possibly completely 
uncorrelated, except for the thing that correlates the request and 
resposne, ie. the Client.

So, I surmise if you are going to do "invocations" in CXF, you get the 
Client to do the work of the correlation of request and response. 
Therefore The Client should be setting the "response" endpoints 
(Destination? BackChannel? DecoupledEndpoint?), shouldn't it?

Your description of the JAX-WS Dispatch stuff being used means that  CXF 
is used underneath where the Client would use it. So if there is a 
correlation of request and response by JAX-WS Dispatch its 
implementation should be taking care of it. So, why isn't it using a Client?

Right now, I see the Conduit as a one way tunnel in which a Message is 
sent from a client to any server. I assume that abstract element on 
which Messages are received is a "Destination".

These two things are only very loosely coupled at best, and the fact 
that a response may come back on the same underlying transport (i.e. 
URLConnection) is merely coincidence.

 From what I can gather, is that  a Client composes an invocation by 
placing a "request" Message on a Conduit, through a bunch of special 
interceptors, and receives a correlated "response" message by picking it 
up off a predetermined Destination (listen point? Queue?).

You want these two things to be correlated at the outset so that 
addressing information can be injected into the message headers (in the 
case of http). Right?

If the JAX-WS Dispatch doesn't use a client, then what does it use? If 
it's suppose to correlate its own responses, then perhaps it's operating 
at a lower level and has to do more of the work the client does.

> We discussed a couple of these scenarios in the "Client API, EPRs" thread, specifically
where the JAX-WS Dispatch mechanism is used, or where the application wires together the interceptor
chains itself.
>
>
>
>   
>> Does the client that 
>> send the invocation request get notified of the response, 
>> fault, or ack? 
>>     
>
>
> Whatever the MessageObserver is set on the Conduit gets to process the response(s).
>   
This is a lower level mechanism that notices the messages and gets them 
to go somewhere to get processed. Should this really be a thing some 
application code should be using?

Cheers,
-Polar
> This *may* be the Client instance. Or something else entirely.
>
>
>   
>> How are the responses (many?) are correlated 
>> to the client invocation.
>>     
>
> Zero, or 1 depending on the MEP (whether oneway or twoway).
>
> There's also the issue of partial responses (lets not go there on the detail, you can
look in the archive for lengthy discussions on this subject). But there 
>
>  
>   
>> Is there actually an object called a "Request" that does this 
>> correlation? Should there be?
>>
>> When I send a "reply-To" or "fault-To" or "ack-To" property 
>> is that on single message? Or is it on a single connection 
>> (for many messages)? 
>> What is the request/response correction based on? Is there an 
>> object in CXF that represents it, or is that done by the 
>> Client, the Conduit, or something else?
>>
>> Cheers,
>> -Polar
>>
>> Glynn, Eoghan wrote:
>>     
>>> My position is that the Conduit should continue to hold to 
>>>       
>> the reference to, and manage the lifecycle of, the decoupled 
>> response endpoint (DRE).
>>     
>>> Without rehashing the entire thread, my reasons briefly are:
>>>
>>> 1. Separation of concernsApache CXF - logged to 
>>> http://dev.rectang.com/logs/codehaus/%23cxf/
>>>
>>> The DRE is an aspect of the transport and thus should be 
>>>       
>> created and referenced from within the realm of the transport.
>>     
>>> On the other hand, the purpose of the Client is to set up 
>>>       
>> interceptor chains and dispatch the invocation. Such 
>> invocations may NOT require a DRE, or even a Conduit for that 
>> matter. Thus I think it inappropriate for the Client to be 
>> concerned with the creation of the DRE, and would even go one 
>> step further and move the Conduit creation to the 
>> MessageSenderInterceptor, so that a Conduit comes into being 
>> only if it really is needed.    
>>     
>>> 2. Avoid forcing the usage of a Client instance
>>>
>>> In general, if A is to be responsible for maintaining a 
>>>       
>> reference to B, then its reasonable to expect that the 
>> existence of a B implies the existence of an A. Otherwise, in 
>> some cases an instance of A will have be artificially 
>> created, solely to manage the reference to B.  
>>     
>>> But if a DRE is in use, then the *only* other thing we're 
>>>       
>> guaranteed also exists is the corresponding Conduit.
>>     
>>> IMO we should neither require the usage of a Client 
>>>       
>> instance to mediate invocations, nor impose any undue burden 
>> on applications that choose to wire up the interceptor chains 
>> directly and initiate dispatch themselves.
>>     
>>> An example of an undue burden would be forcing such 
>>>       
>> applications to either always create the DRE 
>> *programmatically* via DestinationFactory.getDestination(), 
>> or if they want the DRE to be specified declaratively, to 
>> manage this configuration themselves.  
>>     
>>> 3. Suitability for JMS
>>>
>>> In order to setup a Destination, JMS may require more 
>>>       
>> information than can be easily shoe-horned into an EPR. Stuff 
>> like a JNDI provider, ConnectionFactory username/password etc. 
>>     
>>> Now I don't accept the JMS as odd-man-out argument, especially when 
>>> most of the counter-examples wheeled out (i.e. XMPP, TCP, 
>>>       
>> FTP) do not 
>>     
>>> currently even exist as CXF transports. I could just as 
>>>       
>> easily make up 
>>     
>>> a list of non-existent transports that suggests that the 
>>> URI-friendliness of HTTP is the exceptional case, but 
>>>       
>> obviously you'd 
>>     
>>> argue my list was hypothetical and proved nothing. And 
>>>       
>> you'd be right 
>>     
>>> :)
>>>
>>> Neither does the "most people just use HTTP" line wash with 
>>>       
>> me. One of the design centres of CXF is to be a 
>> multi-transport stack, and that in my book amounts to more 
>> than just paying lip-service to non-HTTP transports.  
>>     
>>> Also I'd like to respond quickly to a couple of specific 
>>>       
>> points that Dan makes in his proposal:
>>     
>>> "Right now if you want to create different endpoints for 
>>>       
>> receiving ReplyTos and FaultTos you have configure the 
>> ReplyTos using the Conduit API and the FaultTos using the 
>> destination API. Creating those endpoints in different ways 
>> is bad IMO."
>>     
>>> So how would this be any different under your proposal? Is 
>>>       
>> the implication that in addition to a 
>> Client.setAsynchronousEndpoint() API, you'd also add 
>> Client.setFaultToEndpoint() and Client.setAcksToEndpoint(), 
>> and similarly expose <faultToEndpoint> and <acksToEndpoint> 
>> elements in your proposed <client> bean?
>>     
>>> If so, this would expose *way* too much of WS-A and WS-RM 
>>>       
>> semantics directly in the Client, which should IMO be 
>> independent of such QoS concerns. The CXF WS-A and WS-RM 
>> layers were specifically designed to be pluggable, so that 
>> they could slotted into the runtime without impact on the 
>> core APIs. I would be strongly against a move that breaks 
>> this ... I mean, what next, Client.setSecurityPolicyToken()??
>>     
>>> If on the other hand, if you're not suggesting polluting 
>>>       
>> the Client with those aspects of WS-A & WS-RM, can you 
>> explain how your proposal provides a consistent mechanism for 
>> specifying the faultTo & acksTo vis-à-vis the replytTo?
>>     
>>> Another point which I strongly disagree with:
>>>
>>> "If all Conduits share the same code for setting up 
>>>       
>> decoupled destinations, that is a sign to me that we can take 
>> it out of the Conduit."
>>     
>>> I've never come across a design principle that suggests 
>>>       
>> having common code in a common base class is a sign that such 
>> code should be moved elsewhere. In fact what purpose do 
>> common base classes serve, other than to factor out 
>> commonality from sub-classes?
>>     
>>> Cheers,
>>> Eoghan
>>>
>>>   
>>>       
>>>> -----Original Message-----
>>>> From: Dan Diephouse [mailto:dan@envoisolutions.com]
>>>> Sent: 16 March 2007 22:20
>>>> To: cxf-dev@incubator.apache.org
>>>> Subject: [PROPOSAL] Client and Conduit changes
>>>>
>>>> For those of you who haven't been following the long discussion 
>>>> Eoghan and I have been having, I'm going to take a moment to 
>>>> summarize my proposal here.
>>>> I consider it rather important. If we don't reach any consensus on 
>>>> the proposal (it sucks/doesn't suck) or if Eoghan & I are the only 
>>>> ones who participate, I'll probably start a vote. So do 
>>>>         
>> your communal 
>>     
>>>> duty and participate so I don't have to do that! :-)
>>>>
>>>> I propose the following:
>>>>
>>>> 1. API to set an Asynchronous EndpointReference I believe 
>>>>         
>> we should 
>>     
>>>> create a simple method on the Client which allows the user 
>>>>         
>> to specify 
>>     
>>>> the asynchronous endpoint that they wish to have used for 
>>>>         
>> decoupled 
>>     
>>>> responses:
>>>>
>>>> Client.getAsynchronousEndpoint(EndpointReferenceType epr);
>>>>
>>>> The Client would check to see if this EPR was set. If so, it would 
>>>> call
>>>> DestinationFactory.getDestination(epr) for the EPR and use that as 
>>>> the asynchronous destination. This would result in a 
>>>>         
>> standard way to 
>>     
>>>> automatically set up the decoupled destination when using the API.
>>>>
>>>> While it has been said that this isn't generic enough for JMS, I 
>>>> don't agree. First, I believe that JMS will eventually get a self 
>>>> contained IRI format which can be stuck in an EPR.
>>>> We could even create our own proprietary format. Second, JMS is an 
>>>> edge case. There are other transports beside just JMS and 
>>>>         
>> HTTP, like 
>>     
>>>> XMPP or TCP or FTP which work just fine with URIs. JMS is the odd 
>>>> ball in the sense that historically it has needed stuff 
>>>>         
>> outside the 
>>     
>>>> EPR.
>>>>
>>>> 2. Access to the Conduits and Destinations I would like to add the 
>>>> following methods to the Client:
>>>>
>>>> void setConduit(Conduit) - this allows a user to easily specify an 
>>>> alternate Conduit.
>>>> void setAsynchronousDestination(Destination) - this allows 
>>>>         
>> a user to 
>>     
>>>> easily specify a decoupled endpoint. It's address would be 
>>>>         
>> used for 
>>     
>>>> WS-Addressing interactions. If no Async destination 
>>>>         
>> exists, then the 
>>     
>>>> Client will only listen on the Conduit.
>>>> Destination getAsynchronousDestination() - utility method 
>>>>         
>> to easily 
>>     
>>>> get the asynchronous destination
>>>>
>>>> 3. Client.close();
>>>> We need a way to shutdown the decouled endpoints (regardless of 
>>>> whether or not #1 & #2 are adopted). I think there is pretty good 
>>>> conensus we need a
>>>> Client.close() method which will do this. It will call
>>>> getConduit().close() and getAsynchronousDestination().shutdown().
>>>>
>>>> (Ideally we'd like to be able to shut down RM at this same 
>>>>         
>> time. I'm 
>>     
>>>> going to guess that this would require the addition of a client 
>>>> lifecycle interface which allows RM to listen for Client.close(). 
>>>> This is an issue no matter which route we go though, so I'll defer 
>>>> this conversation for another
>>>> thread)
>>>>
>>>> 4. Remove the setup of decoupled destinations from inside 
>>>>         
>> the Conduit 
>>     
>>>> Currently, the Conduits are responsible for setting up the 
>>>>         
>> decoupled 
>>     
>>>> destinations. We've already got a perfectly good API for creating 
>>>> destinations, lets use it! Creating another API to create 
>>>>         
>> decoupled 
>>     
>>>> destinations introduces inconsistencies into our APIs. 
>>>>         
>> Right now if 
>>     
>>>> you want to create different endpoints for receiving ReplyTos and 
>>>> FaultTos you have configure the ReplyTos using the Conduit API and 
>>>> the FaultTos using the destination API. Creating those 
>>>>         
>> endpoints in 
>>     
>>>> different ways is bad IMO.
>>>>
>>>> Putting in decoupled destinations inside the Conduit also makes it 
>>>> more complex for transport writers or people trying to 
>>>>         
>> understand the 
>>     
>>>> API. IMO, people intuitively expect this to be outside the Conduit 
>>>> class.
>>>>
>>>> 5. Client Configuration
>>>> I would propose that we make the decoupled destination 
>>>>         
>> configuration 
>>     
>>>> part of the Client
>>>>
>>>> <jaxws:client id="...SomePort">
>>>>   <jaxws:asynchronousEndpoint>
>>>>     <wsa:Address>http://my.decoupled/endpoint</wsa:Address>
>>>>   </jaxws:asynchronousEndpoint>
>>>> </jaxws:client>
>>>>
>>>> <jaxws:client id="...SomePort">
>>>>
>>>> <jaxws:asynchronousDestination><http:destination...></jaxws:as
>>>> ynchronousDestination>
>>>> </jaxws:client>
>>>>
>>>> As an added bonus, we can now wire together clients and 
>>>>         
>> destinations 
>>     
>>>> however we want. I wouldn't *have* to create a <conduit> config 
>>>> element with the port name inside it.
>>>> Instead I could simply do:
>>>>
>>>> <jaxws:client id="...SomePort">
>>>>    <jaxws:conduit> <http:conduit... /> </jaxws:conduit>

>>>> </jaxws:client>
>>>>
>>>> It also creates a central place to embed Client configuration
>>>> - such as enabling MTOM or configuring WS-*:
>>>> <jaxws:client id="...SomePort">
>>>>    <jaxws:conduit>...</jaxws:conduit>
>>>>    <jaxws:binding mtomEnabled="true">
>>>>      <jaxws:requestContext>
>>>>        <map><entry key="javax.xml.ws.session.maintain" 
>>>> value="true"/></map>
>>>>      </jaxws:requestContext>
>>>>    </jaxws:binding>
>>>>    <jaxws:features>
>>>>      <wsrm:reliability timeout="10000" .../>
>>>>    </jaxws:features>
>>>> </jaxws:client>
>>>>
>>>> Users could still use the <http:conduit id="PORT"/> syntax if they

>>>> wanted to though.
>>>>
>>>> (Note: I haven't written the jaxws:client Spring schema 
>>>>         
>> yet, but its 
>>     
>>>> on my todo list. The feature stuff will hopefully be part of my 
>>>> commit with
>>>> WS-Security)
>>>>
>>>> 6. Bring back Destination.getDestination(EndpointReferenceType)
>>>> This method would be needed for the API that I propose in #1.
>>>>
>>>> 7. Make the JAX-WS dispatch use the client.
>>>>
>>>> ----
>>>>
>>>> In summary:
>>>> a) This simplifies the API. We've created an API to set up 
>>>>         
>> decoupled 
>>     
>>>> endpoints easily. We've reduced the complexity inside Conduits and 
>>>> have avoided introducing new complexity onto the Conduit 
>>>>         
>> interface to 
>>     
>>>> specify a decoupled destination.
>>>>
>>>> b) It creates a consistent API for working with decoupled 
>>>>         
>> endpoints. 
>>     
>>>> There is no reason to go writing a new API for setting up 
>>>>         
>> decoupled 
>>     
>>>> endpoints - which is only used sometimes.
>>>>
>>>> c) Dependency Injenction: By putting the Conduit & 
>>>>         
>> Destination on the 
>>     
>>>> Client we've made it much friendlier to people using 
>>>>         
>> Spring or other 
>>     
>>>> DI containers.
>>>>
>>>> d) Improved configuration: I think the jaxws:client is a 
>>>>         
>> more natural 
>>     
>>>> place to setup the conduit and destination configuration 
>>>>         
>> as opposed 
>>     
>>>> to nesting the destination configuration inside the conduit.
>>>>
>>>> e) Setting up decoupled destinations is not the job of the conduit 
>>>> IMO.
>>>> We're giving Conduits a dual task unnecessarily. If all Conduits 
>>>> share the same code for setting up decoupled destinations, 
>>>>         
>> that is a 
>>     
>>>> sign to me that we can take it out of the Conduit.
>>>>
>>>> I of course would be volunteering to do all this work.
>>>> --
>>>>
>>>> Alternatives: While Eoghan can elaborate, I believe he 
>>>>         
>> would rather 
>>     
>>>> see 1. The decoupled endpoint remain part of the conduit. 
>>>>         
>> He views a 
>>     
>>>> decoupled endpoint as part of the Conduit contract.
>>>> 2. An API on the Conduit to set up the decoupled endpoint like so:
>>>> Client.get(Conduit.class
>>>> ).getClientPolicy().setDecoupledEndpoint(EndpointReferenceType)
>>>> 3. The Client.getConduit/setConduit methods go away and have the 
>>>> Conduit be an optional part of the Client 4. No 
>>>> Client.setAsynchronousDestination method.
>>>> 5. Keep the decoupled endpoint configuration as part of 
>>>>         
>> the conduit 
>>     
>>>> instead of the client.
>>>>
>>>> Regards,
>>>> - Dan
>>>>
>>>> --
>>>> Dan Diephouse
>>>> Envoi Solutions
>>>> http://envoisolutions.com | http://netzooid.com/blog
>>>>
>>>>     
>>>>         
>>     


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