More thoughts at the bottom.
Simon Nash wrote:
Raymond Feng wrote:
At this moment, the "From" of the Message is used for the reference
of the source component. And if the interface is bidirectional, the
"From" EPR will contain a callback EPR.
The current code only sets "From" in the Message for a bidirectional
interface. This means that outbound interceptors don't currently get any
"From" endpoint information for calls across a unidirectional interface.
What's going to happen if the user customize the callback object by
calling ServiceReference.setCallback() with a ServiceReference?
Should we replace the callback EPR under the From or carry it as part
of the reference parameters of the To?
In this case, the current code in JDKInvocationHandler replaces the
"From"
EPR with the custom ServiceReference. Again, this means that outbound
interceptors don't have access to the "From" reference endpoint.
So the value of holding the callback endpoint information somewhere other
than the Message's "From" endpoint is that outbound interceptors can have
access to the actual calling reference endpoint if they need it.
Simon
Thanks,
Raymond
----- Original Message ----- From: "Jean-Sebastien Delfino"
<[EMAIL PROTECTED]>
To: <tuscany-dev@ws.apache.org>
Sent: Friday, September 07, 2007 4:09 PM
Subject: Re: WS-Addressing mapping (was Re: What is
Message.set/getCallableReference used for?)
Simon Nash wrote:
Until now we have always held this information in the wsa:From
element.
However, in thinking about what is really going on here in
WS-Addressing
terms, I believe we should be putting it in the wsa:To element
instead.
The wsa:To element is mandatory for WS-Addressing, but we are not
sending it currently. Here's how this would look:
<wsa:To>
<wsa:EndpointReference xmlns:wsa="..." xmlns:tuscany="...">
<!-- I'm not sure if we should use sca or tuscany ns here -->
<wsa:Address>...URI of the service being
invoked...</wsa:Address>
<wsa:ReferenceParameters>
<tuscany:CallbackID>callback-A01</tuscany:CallbackID>
<tuscany:ConversationID>conversation-006</tuscany:ConversationID>
<tuscany:CallbackReference>
<wsa:EndpointReference>
<wsa:Address>...URI of the service for the
callback...</wsa:Address>
<wsa:EndpointReference>
</tuscany:CallbackReference>
</wsa:ReferenceParameters>
</wsa:EndpointReference>
</wsa:To>
(Note: I have capitalized the first letters of CallbackID,
ConversationID
and CallbackReference to match the WS-Addressing "house style")
This has a few advantages:
1. It makes us fully compliant with WS-Addressing.
2. WS-Addressing has the notion of a stateful endpoint reference,
where
the endpoint address is augmented with other information that
represents a particular "instance" of the endpoint. This is
exactly
what is happening here. Invocations to the same SCA service that
differ only in their conversation and callback information are
very
nicely modelled as different WS-Addressing endpoint references for
the same endpoint address.
3. It allows the wsa:To infomation to be exactly the same as the
information that would be serialized to represent the
CallableReference
for the invocation. This is a very neat solution to the question
of how a CallableReference should be serialized. It might even
give us a decent chance of being interoperable with some non-SCA
environments.
The callback message would be as follows:
<wsa:To>
<wsa:EndpointReference xmlns:wsa="..." xmlns:tuscany="...">
<!-- I'm not sure if we should use sca or tuscany ns here -->
<wsa:Address>...URI of the service for the
callback...</wsa:Address>
<wsa:ReferenceParameters>
<tuscany:CallbackID>callback-A01</tuscany:CallbackID>
<tuscany:ConversationID>conversation-006</tuscany:ConversationID>
</wsa:ReferenceParameters>
</wsa:EndpointReference>
</wsa:To>
Regarding the sca or tuscany namespace question, the code currently
uses the sca namespace but it may be better to use tuscany until we
get spec endorsement that this is the correct SCA-approved mapping for
SCA conversations and callbacks to Web service protocols. This
would be defined in the WS Binding specification.
For comparison, this is what the current code does for forward calls,
with the From address directly representing the callback endpoint:
<wsa:From>
<wsa:EndpointReference xmlns:wsa="..." xmlns:tuscany="...">
<!-- I'm not sure if we should use sca or tuscany ns here -->
<wsa:Address>...The URI of the service for the
callback...</wsa:Address>
<wsa:ReferenceParameters>
<tuscany:CallbackID>callback-A01</tuscany:CallbackID>
<tuscany:ConversationID>conversation-006</tuscany:ConversationID>
</wsa:ReferenceParameters>
</wsa:EndpointReference>
</wsa:From>
Simon
Raymond Feng wrote:
Hi,
I'm thinking of this syntax:
<wsa:From>
<wsa:EndpointReference xmlns:wsa="..." xmlns:tuscany="...">
<!-- I'm not sure if we should use sca or tuscany ns here -->
<wsa:Address>...sourceComponentURI#referenceName...</wsa:Address>
<wsa:ReferenceParameters>
<tuscany:callbackID>callback-A01</tuscany:conversationID>
<tuscany:conversationID>conversation-006</tuscany:conversationID>
<tuscany:callbackReference>
<wsa:EndpointReference>
<wsa:Address>...The URI of the service for
the callback...</wsa:Address>
<wsa:EndpointReference>
</tuscany:callbackReference>
</wsa:ReferenceParameters>
</wsa:EndpointReference>
</wsa:From>
+1 to flow callback ID and conversation ID in parameters of the "to"
endpoint reference.
I don't understand the technical reason for flowing the callback
endpoint reference - nested!! - in a parameter of the "to" endpoint
reference.
Can you help me understand why we cannot just use the "from"
endpoint reference to identify the callback endpoint?
--
Jean-Sebastien
I've reviewed this thread and - unless I missed something - I think we
have consensus on:
- conversationID flows as a reference parameter of the "to" epr
- callbackObject does not flow in the message at all
We don't have consensus on how to flow the callbackID, as I'm not sure
yet that flowing it as a parameter of the "to" epr is right.
And we're still discussing the following how to flow the callback epr:
- as the replyTo epr?
- the from epr?
- as a callback epr nested in a parameter of the from or to eprs?
- as another epr, a callback epr, peer of the from, to and replyTo?
(another option that I'd like to consider)
I think that the "WS-addressing mapping" exercise helped us make
progress. How about another similar exercise now to help close this :)
IMO the SCA callback APIs provide built-in support for one of a more
general category of message exchange patterns where partners exchange
messages back and forth and communicate their service references and
context data relevant to the interaction as part of the exchanged
business data.
Let's take an example with 2 components, a Client component is wired to
a Writer component, invokes the Writer to write some data, the writer
sends another message to the client when the data has been written. I
hope that the following pseudo-code will be clear enough to illustrate
the scenario.
@Service(Client.class)
class Client {
ComponentContext componentContext;
Writer writer;
write(inputData) {
self = componentContext.createSelfReference();
id = new UUID();
writer.asyncWrite(self, id, inputData);
}
written(id) {
// data <id> has been written
}
}
@Service(Writer.class)
class Writer {
@OneWay
asyncWrite(clientReference, id, inputData) {
// actually write the data
clientReference.getService().written(id);
}
}
Another variation of this could do self.setCallbackID(id) in the Client
and id = clientReference.getCallbackID() in the Writer to pass the id as
part of the reference instead of a business method parameter, but I
don't think it really changes the pattern.
Assuming that a WS binding is used, what do people think the SOAP
messages for the request and callback should look like?
--
Jean-Sebastien
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