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

From: Graham Klyne <GK@ninebynine.org>
Date: Tue, 15 Oct 2002 12:08:03 +0100
Message-Id: <>
To: noah_mendelsohn@us.ibm.com
Cc: xml-dist-app@w3.org

I agree that this is an important use-case (e.g. for diagnostic tracing) 
and that the proposed solution looks reasonable.

Question:  does the proposed new "relay" role apply to the final 
recipient?  The name suggests not, but the description suggests that it can.


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:
>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.
>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.
>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.
>[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

Graham Klyne
Received on Tuesday, 15 October 2002 09:21:49 GMT

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