RE: [ws-rx] AnonURI and Offer and WS-Addressing

[Doug Davis <dug@us.ibm.com>]

The WSA spec is very clear what anon
replyTo means - this is a contract that both the client and server need
to follow.  This means that (for anon replyTo + HTTP)  the server
MUST send it back on 'this http response' and that the client MUST look
for it on 'this http response'.  Sending it back on some other http
connection, or looking for it on some other http connection is not compliant
with WSA's defintion of what anon ReplyTo means.  Composing RM into
the picture can not change what WSA says - RM can cause the messages to
be resent but for any individual message exchange the WSA rules must be
adhered to.

I believe all of the options I listed
are valid - spec wise.  You can dislike some of them but I believe
that are all compliant with WSA.

Marc said: On point 3 I see
that as being different only if you’ve only been looking at this from
a point of view of 1 way messages exclusively. If you get an ack for a
request you sent without the corresponding response you obviously still
have the request available for retransmitting. I don’t see the difficulty.
I don’t see how out only applies in this discussion though. 

You 'obviously still have the request'
only until the request is acked.  After that point the RM spec does
not manadate anything - so replaying an ACked message, as I said, is something
I believe is new to most people.  'Out only' applies because I'd like
our RM to be used in more than the most simple of use-cases.

Marc said: On point 4 you
seem to have an async response in mind. In a synchronous req/resp MEP the
ack for the request message would be on the response message. The thing
we’re discussing is what to do when that response message is lost and
the ack is detected in a ack range on a subsequent response message to
the client. It helps to think of this without complications. Imagine that
the request comes in and the response (with the ack) is lost. The client
hasn’t sent any other requests. What does it do? Why it resends the request.
The service should be prepared for this as it never got an ack for the
response either. Just extend that model and it is easy to see that when
the client sees an ack on a response to another message that contains an
ack for a request it never got a response from it can resend the request
to get the unacknowledged response. What is the problem?

The problem is that the RMS MUST know
about the MEP - something we haven't required up to now, and it links the
request and response sequences - something, again, we haven't done.  Once
we head down this path I don't see how we can't be required then to examine
how the lifecycle of the two sequences might be linked.  Again, as
I've said many times, no one has been able to explain how the full RM protocol
works - for example, how a Close or Terminate can be sent from the RMD
back to the RMS.   Or how RM can be used in one direction but not
the other - e.g. non-RM-request/RM-response.  The longer we talk about
this the more questions we get.

thanks,
-Doug

"Marc Goodner" <mgoodner@microsoft.com>

03/14/2006 12:50 PM

To	Doug Davis/Raleigh/IBM@IBMUS, <ws-rx@lists.oasis-open.org>
cc
Subject	RE: [ws-rx] AnonURI and Offer and WS-Addressing

I would point out that the
definition of anonymous uri is: 
“Some endpoints cannot be
located with a meaningful IRI; this URI is used to allow such endpoints
to send and receive messages. The precise meaning of this URI is defined
by the binding of Addressing to a specific protocol and/or the context
in which the EPR is used.”
 
The section you quote below
is from section 5.1 Use of Anonymous Address in SOAP Response Endpoints.
The SOAP 1.2 binding text you quote does not cover RM, rather it covers
a vanilla SOAP 1.2 endpoint only. WS-A leaves us the flexibility to clarify
any points on its use when RM is in use.
 
I’m still surprised to see
suggestions to the effect that anon can not be used with RM followed by
suggestions that amount to defining our own anon uri (essential anonymous
uri redux). I think it makes far more sense to clarify any points on the
use of anon when the RM protocol is being used rather than forbid its use
as it seems the WS-A WG left us the latitude to do so. So I disagree with
your points 1, 2 and 5 below.
 
On point 3 I see that as
being different only if you’ve only been looking at this from a point
of view of 1 way messages exclusively. If you get an ack for a request
you sent without the corresponding response you obviously still have the
request available for retransmitting. I don’t see the difficulty. I don’t
see how out only applies in this discussion though. 
 
On point 4 you seem to have
an async response in mind. In a synchronous req/resp MEP the ack for the
request message would be on the response message. The thing we’re discussing
is what to do when that response message is lost and the ack is detected
in a ack range on a subsequent response message to the client. It helps
to think of this without complications. Imagine that the request comes
in and the response (with the ack) is lost. The client hasn’t sent any
other requests. What does it do? Why it resends the request. The service
should be prepared for this as it never got an ack for the response either.
Just extend that model and it is easy to see that when the client sees
an ack on a response to another message that contains an ack for a request
it never got a response from it can resend the request to get the unacknowledged
response. What is the problem?
 
Finally I’d like to point
out that this and many other recent posts conflates i090 and i089 together.
I don’t understand why so much emphasis is being placed on the use of
anonymous with an Offered sequence to simultaneously justify removing Offer
and prove that anonymous should be forbidden when using WS-RM because of
perceived problems when used with Offer.
 
Marc Goodner
Technical Diplomat
Microsoft Corporation
Tel: (425) 703-1903
Blog: http://spaces.msn.com/mrgoodner/

---

From: Doug Davis [mailto:dug@us.ibm.com]
Sent: Monday, March 13, 2006 6:03 AM
To: ws-rx@lists.oasis-open.org
Subject: Re: [ws-rx] AnonURI and Offer and WS-Addressing
 

Paul, 
  please see:  http://dev.w3.org/cvsweb/~checkout~/2004/ws/addressing/ws-addr-soap.html?content-type=text/html;%20charset=utf-8#anonaddress
which is the latest editor's copy of WSA, and in particular:
When "http://www.w3.org/2005/08/addressing/anonymous" is specified
for the response endpoint and the message is the http://www.w3.org/2003/05/soap/mep/InboundMessage
property of a SOAP request-response MEP [SOAP
1.2 Part 2: Adjuncts],
then any response MUST be the http://www.w3.org/2003/05/soap/mep/OutboundMessage
property of the same instance of the SOAP request-response MEP [SOAP
1.2 Part 2: Adjuncts].

They've added quite a bit of clarifying text since the submitted version.
 I think the "same instance" part makes it clear that the
response MUST flow over the same http connection as the request. 

Perhaps it would help if we summarized the list of options:

1 - prohibit anon replyTo if the response is expected to be sent using
RM 
2 - prohibit the use of RM when the wsa:To is anonymous - or said another
way, when replyTo is anon the response is not sent using RM
3 - resend request until response is delivered/acked even if the request
is acked 
4 - don't ack a request until the response is sent
5 - define a new URI that allows a polling flow like Paul described in
his previous note 

Here are some comments on each:
1 and 2 might actually be the same thing but my intention was to say that
in '1' you can't use anon replyTo if the response is sent reliably - so
perhaps a Fault is generated.  In '2', if the replyTo is anon then
no matter what the wsdl/policy... says, RM needs to be turned off for the
response - it can still be sent but just not as part of an RM sequence.
 Slightly different. 
'3' is a change to what I believe is most people current view of the RM
processing model because we'll resend ACKed messages.  It also will
only work for one-req/one-res MEPs.  Out-only, or single-req/multiple-res
may have issues. 
'4' is a change to the RM processing model because the RMD will not ACK
a message even if it is received.  Depending on how you view things
this could mean that the RMD needs to lie about what it has and could cause
messages to be resent because the RMD is waiting for a response before
it will ACK the request.  Now, since the RMD gets to choose when it
ACKs (meaning is it simply 'I got it' or something else it up to it), so
to some this may not be lying but just a change to the ACK model of that
RMD. 
'5' doesn't require a change to the RM processing model but heads in the
direction of ws-polling and can work w/o a change to the RM processing
model and can work for all MEPs.  Even if we did pick this option
we'd still need to say something in the RM spec about what should happen
when anon replyTo is used (I'm guessing 1 or 2).

Are there any other options people think we need to add to the list?  Having
all of the known choices in front of us might help focus the discussions.

thanks, 
-Doug

Paul Fremantle <paul@wso2.com>

03/12/2006 04:43 AM

To	Bob Freund-Hitachi <bob.freund@hitachisoftware.com>
cc	Doug Davis/Raleigh/IBM@IBMUS, wsrx <ws-rx@lists.oasis-open.org>
Subject	[ws-rx] AnonURI and Offer and WS-Addressing

 

Bob et al.

I've attached a document that outlines the flow and shows message exchanges for a given interaction. The key question is whether the interaction:

  RMD.AckRequested_EmptyBody -> EchoResponse_World_ackSeq_1_2_3

breaks the WS-Addressing spec.

Paul

Bob Freund-Hitachi wrote:
Just another log for the fire…
In reading HTTP 1.1, I do not see anything that specifies that the response entity cannot be interpreted prior to its completion.  In principle, it seems to me that both ack and response could be sent on the same connection backchannel provided that it was not closed prematurely.  Is this how the implementations that work do it?
Thanks
-bob
 

 

---

From: Doug Davis [mailto:dug@us.ibm.com]
Sent: Friday, March 10, 2006 1:36 AM
To: Paul Fremantle
Cc: wsrx
Subject: Re: [ws-rx] An alternative approach to make anon reply-to
and sync rm work 
  

Paul, 

I think there are some problems with this - I still think this violates
WSA.  There's a reason anon replyTo means, in essence, the http response
flow of the request message.  The connection becomes the correlator
between the request and the response - meaning if several anon requests
come in the only way the server knows which client gets which response
is thru the http connection.  In your scenario if there are two anon
requests sent to the server using the same sequence and no responses sent,
when the third connection is made (to carry the ackReq) how does the server
know which client is initiating the request.  It can not simply assume
that just because they shared the same sequence that they also share WSA
state and that any response can be sent to any client.  The correlation
is now lost.   

thanks, 
-Doug

Paul Fremantle <paul@wso2.com>

03/09/2006 06:53 PM

 

To	wsrx <ws-rx@lists.oasis-open.org>
cc
Subject	[ws-rx] An alternative approach to make anon reply-to and sync rm work

 

 

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

--

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[attachment "AnonURI+Offer.doc" deleted by Doug Davis/Raleigh/IBM]