An alternative approach to make anon reply-to and sync rm work

[Paul Fremantle <paul@wso2.com>]

The biggest issue with the two way reliable HTTP + anonURI case is the 
requirement to replay request messages to get responses.

Why is this a problem? Because it means that the client has to store 
requests (if and only if the interaction is two-way) beyond getting an ack 
for that request.

This means that the RMS has to "know" if this particular message 
interaction is one-way or two way. This means that for example, a dumb 
gateway can't do it without looking at WSDLs etc.

Why do we need to do this: because WSA states:

"For instance, the SOAP 1.2 
HTTP binding puts the reply message in the HTTP response."

So I agree we should not put an application reply to message A in an 
HTTP response to application message B.

However, if we added the following text to our spec:

"In the case where an offered sequence is used, the RMS may send an 
<wsrm:AckRequested> header together with an empty SOAP body. A valid 
response to this message MAY either contain an empty SOAP body, or MAY 
contain a message for the *offered* sequence".

The result of this would be that the response message on the HTTP reply 
would be a valid reply to the request message and therefore would not break the 
WS-Addressing text above. Effectively WSRM would be defining what 
the SOAP request/reply would be, and therefore "making it right" 
with respect to the HTTP binding.

So, when things are going well the HTTP reply to any given request message would be the 
correct response message. But in the case that this message got lost or 
delayed, the RMS would have a choice. If it still had the message, and it 
"knew" that the MEP was two-way, it could choose to resend the 
original request OR it could send an empty body with an ackRequested 
header. 

This also gives the offered sequence a message onto which to 
piggyback Close and TerminateSequence requests, solving another problem.

More importantly it removes the need for 
the RMS to "know" the MEP, because by the repeated application of empty-body ackRequests, 
the RMS can get the offered sequence into a decent state.

The only compulsory implementation change I see is that the RMD would 
have to be coded to know what this empty body + ackrequest means. 

From the RMS I see this as optional. It is completely up to the RMS 
whether it initiates a CS with Offer+AnonURI. So if an implementation doesn't support this, 
it will never initiate such a channel. And if the RMS does initiate such 
a channel, it will "know" it is in this mode, that it needs to send 
occasional empty ackrequests until it can close down the offered sequence.

In addition we would have to remove the words that say Offer is simply an optimization, 
because this usage makes a specific correlation between a sequence and offered sequence.

Paul

-- 

Paul Fremantle
VP/Technology, WSO2 and OASIS WS-RX TC Co-chair

http://feeds.feedburner.com/bloglines/pzf
paul@wso2.com

"Oxygenating the Web Service Platform", www.wso2.com