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Re: Proposal for new last call issue: Some unprocessed headers should stay

From: Jacek Kopecky <jacek@systinet.com>
Date: 16 Oct 2002 14:54:40 +0200
To: Noah Mendelsohn <noah_mendelsohn@us.ibm.com>
Cc: XMLP Dist App <xml-dist-app@w3.org>
Message-Id: <1034772880.1544.38.camel@krava>

Hi Noah,

we (the group) thought about this problem a few times before. IIRC the
answer always was that a particular header may be defined so that it is
relayed. The example of the digital signature is a good one, its
definition would just say "if you know that, you may check the
signature, and you SHOULD (or MUST) reinsert the header so that others
down the line may do so too".

I really think that the questions of relay and of role targeting are
orthogonal. This would suggest some resolution like the new attributes
you proposed below. Furthermore, I think that the question of relaying a
header after processing is tied to the semantics of the header, which in
turn hints at the answer above.

So, I don't like the proposal because:

 1) it uses an exceptional role to change header processing rules which
is too much of an overload IMHO, and
 2) it attempts to solve something that can already be solved by a
header specification (and which should be specified there anyway).

Best regards,

                   Jacek Kopecky

                   Senior Architect, Systinet Corporation

> At 02:11 PM 10/14/02 -0400, noah_mendelsohn@us.ibm.com wrote:
> >At the face-to-face on the West Coast at SAS, several us noticed and
> >began privately discussing what we now believe is a problem that needs
> >at least some attention in the specification.  Specifically, there is
> >a use case that more or less all of us have come to believe is
> >important, and for which the specification is at best ambiguous and at
> >worst incapable of meeting without republication.  Several of us have
> >come up with a proposed resolution that we believe to be
> >straightforward, low risk, and within the bounds of what we can
> >reasonably do without going back to last call. I am indebted to Mark
> >Jones for first pointing this out, and to numerous others including
> >Henrik and Marc Hadley for helpful discussion and comment.  Particular
> >thanks to Henrik for helping me to refine early drafts of this note.
> >The responsibility for the formulation in this note, and for raising
> >this now, is mine.
> >
> >The Problem
> >-----------
> >
> >Among the reasons that we have the "next" role is for headers that
> >carry information to be available to all downstream nodes.  One of the
> >simplest scenarios would be to have such a header that would travel
> >with the message, to be available to those nodes that "understand" the
> >header, and to be ignored and passed on by nodes that do not
> >understand it.  As a simple example, I might want to put in the header
> >indicating the time at which the message was originally sent. More
> >substantively, I might wish to put in a digital signature, to be
> >checked by those who care, and ignored but retained by others.
> >
> >SOAP 1.2 as proposed cannot support these simple scenarios. Why?
> >Because section 2.7.1[1] makes clear that a forwarding intermediary
> >MUST remove from the message all headers targeted to it, and can
> >trigger reinsertion only by processing and understanding a header.  In
> >the case where you don't understand the header, you must remove it.
> >It's essential to note that we are considering the case of
> >mustUnderstand='false'; there is no problem with the 'true' case.
> >
> >Approaches to Resolving the Problem
> >-----------------------------------
> >
> >Discussion of this problem has been going on at a low level for
> >awhile, in part because some of us have been trying to decide whether
> >the existing specification can somehow be made to do the right thing.
> >Given that we are in last call, that would obviously be a desirable
> >approach.  So, here I briefly outline some of the approaches that were
> >considered, and then in the next section I propose one that seems to
> >some of us to be the best.
> >
> >It is tempting to ask whether a user might be able to design specific
> >headers and/or roles that would meet the need.  In other words: if I
> >define a role and some headers to use with it, then I could say that
> >you wouldn't assume that role unless you knew the specification for at
> >least one of the headers, and that specification would implement a
> >feature to change the relay rules for that role.  My personal
> >conclusion is that this is possible in principle, but would not be
> >practical when one considers the way that most SOAP software will in
> >fact be built.  Reason: the core rules regarding the relaying of
> >headers are baked into section 2.7.1, and in practice will often be
> >implemented by general-purpose SOAP middleware.  The key point is that
> >such middleware will in general be written to treat all user-defined
> >roles identically.  Allowing particular roles to change the relay
> >rules requires that such middleware have pluggable handlers that key
> >on specific role names, and this is something that few of us
> >anticipate doing.
> >
> >There is another alternative which is also coherent, and indeed is
> >more powerful than the one proposed below, but which seems to be
> >overkill and would probably take us back to last call.  That
> >alternative would be to introduce a new attribute for use on header
> >entries along the lines of relayIfNotProcessed='true'.  Thus:
> >
> >         <soap:Header>
> >                 <nrm:myHeader role="..any role you like..."
> >                                 mustUnderstand="false"
> >                                 relayIfNotProcessed="true">
> >                         ...
> >                 </nrm:myHeader>
> >         </soap:Header>
> >
> >This seems to work, and has the capability of working with any role.
> >It just seems like more power and complexity than we need to deal with
> >the specific use case.  If we were to get serious about this proposal,
> >there would be several details requiring refinement, but for now I am
> >just suggesting that this is not the direction to go.
> >
> >Another possibility that has been raised would be to change the
> >default behavior to be: "leave in place any header entries that are
> >not processed".  Optionally, we could additionally define a
> >relayIfProcessed override if the group felt it to be worth the
> >trouble.  My impression is that some who have considered changing the
> >default rules like the idea, but some feel that it doesn't meet a need
> >to have headers that do indeed disappear when unprocessed.  For the
> >record, I quite like the idea, but (a) am not ready to take the lead in
> >pushing it in the face of any significant opposition and (b) would not
> >want to go back to last call if this were deemed a serious change--
> >I'm not sure it is.
> >
> >A Proposal
> >----------
> >
> >Anyway, having done the above analysis, several of us conclude that:
> >
> >* The use case is important that we must find a way to meet it
> >* The draft as written doesn't give explanation of how
> >* We need a simple, minimally invasive fix to what we have
> >
> >We propose one new builtin role to be called:
> >http://www.w3.org/2002/06/soap-envelope/role/relay .  In most
> >respects, this role would be like any other.  Any intermediary or
> >ultimate receiver MAY choose to assume this role.  The one significant
> >difference, and it is one that we believe has to be baked into the
> >specification from day one (I.e. would be an incompatible change if
> >made later) is that section 2.7.1 will be changed as follows:
> >
> ><original>
> >Forwarding SOAP intermediaries MUST process the message
> >according to the SOAP processing model defined in 2.6
> >Processing SOAP Messages. They MUST also remove from
> >the SOAP message all SOAP header blocks targeted at
> >themselves, prior to forwarding, regardless of whether
> >these header blocks were processed or ignored.
> >
> >In addition, forwarding SOAP intermediaries MUST also
> >obey the specification for the SOAP forwarding feature
> >being used. The specification for such a feature MUST
> >describe the required semantics, including the rules
> >describing how the forwarded message is
> >constructed. Such rules MAY describe placement of
> >inserted or reinserted SOAP header blocks. Inserted
> >SOAP header blocks might be indistinguishable from one
> >or more of the header blocks removed above.
> ></original>
> >
> ><proposed>
> >Forwarding SOAP intermediaries MUST process the message
> >according to the SOAP processing model defined in
> >2.6 Processing SOAP Messages. In addition, when
> >generating a SOAP message for the purpose of forwarding,
> >they MUST:
> >
> >* For any processed SOAP header block, as well as for
> >   ignored SOAP header blocks targeted to the node
> >   using a role other than
> >   http://www.w3.org/2002/06/soap-envelope/role/relay:
> >   remove the header block prior to forwarding
> >
> >* Retain all SOAP header blocks that were targeted at
> >   the forwarding node using the role
> >   "http://www.w3.org/2002/06/soap-envelope/role/relay"
> >   but ignored during processing.
> >
> >
> >In addition, forwarding SOAP intermediaries MUST also obey the
> >specification for the SOAP forwarding feature being used. The
> >specification for such a feature MUST describe the required semantics,
> >including the rules describing how the forwarded message is
> >constructed. Such rules MAY describe placement of inserted or
> >reinserted SOAP header blocks. Inserted SOAP header blocks might be
> >indistinguishable from one or more of the header blocks removed above.
> ></proposed>
> >
> >I wish to reiterate that I understand it is late in the last call
> >process, and that I would strongly prefer that we not do anything that
> >would delay our progress for weeks or months, just to deal with this
> >one concern.  That said, I think this is a significant use case that
> >deserves at least some consideration.  Thank you.
> >
> >Noah
> >
> >[1] http://www.w3.org/2000/xp/Group/2/06/LC/soap12-part1.html#forwardinter
> >
> >------------------------------------------------------------------
> >Noah Mendelsohn                              Voice: 1-617-693-4036
> >IBM Corporation                                Fax: 1-617-693-8676
> >One Rogers Street
> >Cambridge, MA 02142
Received on Wednesday, 16 October 2002 08:54:45 UTC

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