Re: [sca-bindings] ISSUE 2 - Callback support over the Web Service binding

[Simon Nash <NASH@uk.ibm.com>]

Using the wsa:ReplyTo header for the callback endpoint does not seem to 
exactly match SCA callback semantics, which allow callback messages to be 
directed to a different endpoint from the endpoint that receives the reply 
to the original request (by calling setCallbackObject() with a 
ServiceReference).  Using wsa:ReplyTo also requires a message ID to be 
added to the original request and the same message ID to be returned on 
the reply and any callbacks in the wsa:RelatesTo header.  This is more of 
an observation than a problem, though it does require extra state to be 
maintained for the message IDs being exchanged.

In Tuscany, we did not use wsa:Reply To.  Instead we used the 
WS-Addressing wsa:To endpoint reference with reference parameters to 
represent the callback endpoint (as a wsa:EndpointReference), the callback 
ID, and the conversation ID for stateful callbacks.

I did not propose a specific solution when opening this issue because I 
wanted to open this up to as many suggestions and options as possible. The 
discussion around wsa:ReplyTo has been interesting.  Perhaps someone will 
have an idea on we can overcome the semantic mismatch that I mentioned 
above.  I agree that defining a new header for SCA callbacks would be 
undesirable.  Even the use of SCA-specific reference parameters seems less 
than ideal, but without them I'm not sure how additional information like 
the callback ID could be transmitted.  We can't use wsa:MessageID for 
this, because of the statement in the WS-Addressing spec that "No two 
messages with a distinct application intent may share a [message id] 
property."  Perhaps the callback ID could be mapped into a wsa:MessageID 
by adding a unique discriminator, so different callback requests could use 
distinct message IDs from which the same callback ID could be extracted.

    Simon

Simon C. Nash, IBM Distinguished Engineer
Member of the IBM Academy of Technology
Tel. +44-1962-815156  Fax +44-1962-818999



Khanderao Kand <khanderao.kand@oracle.com> 
01/10/2007 22:47

To
Michael Rowley <mrowley@bea.com>
cc
sca-bindings@lists.oasis-open.org
Subject
Re: [sca-bindings] ISSUE 2 - Callback support over the Web Service binding






Michael Rowley wrote:
> One problem with using WS-Addressing wsa:ReplyTo is that it is usually
> used to send the response message of a request/response pair.  I don't
> think that WS-Address forbids its use for subsequent messages
> (callbacks), but it would at least be unconventional.
> 
[khanderao] IMHO WS-Addressing does not make any assumptions on the 
number of returned messages. It is upto the integration scenario to have 
one or many.
> However, if we can't use wsa:ReplyTo, that would seem to imply that we
> have to devise our own header to use, but that would be getting
> dangerously close to inventing a wire-level protocol, which we don't
> want to be doing.
> 
[khanderao] Introducing SCA specific correlation / replyTo parameters 
would not be essential. As far as possible we should be using the 
available standards,  like WSA / WS-Coordination etc..
> Michael
>
> -----Original Message-----
> From: Eric Johnson [mailto:eric@tibco.com] 
> Sent: Monday, October 01, 2007 12:16 PM
> To: sca-bindings@lists.oasis-open.org
> Subject: Re: [sca-bindings] NEW ISSUE: Callback support over the Web
> Service binding
>
> Created as: http://www.osoa.org/jira/browse/BINDINGS-2
>
> -Eric.
>
> Simon Nash wrote:
> 
>> TARGET:
>>
>> Web Service Binding specification, section TBD
>>
>> DESCRIPTION:
>> 
>> The Web Service binding provides no example or suggestion for how SCA 
>> callback semantics could be carried over Web services.  There is an 
>> example in section 2.2.3 for how conversation semantics could be 
>> supported.  It would be good to give some guidance (somewhere in the
>> 
> range 
> 
>> between example and normative) for what could be done for callbacks.
>> 
> One 
> 
>> possibility is to make use of the capabilities provided by
>> 
> WS-Addressing.
> 
>> PROPOSAL:
>>
>> None yet.
>>
>>
>>
>>
>>
>>
>> Unless stated otherwise above:
>> IBM United Kingdom Limited - Registered in England and Wales with
>> 
> number 
> 
>> 741598. 
>> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
>> 
> 3AU
> 
>>
>>
>>
>>
>> 
>> 








Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU