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Re: [soapbuilders] Multiple WS-Addresses in multiple namespaces

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  • Glen Daniels
    Hi Paul! ... While I don t necessarily disagree with this (and believe me, the discussion as to processing order was a big one back in the early days of XMLP),
    Message 1 of 14 , Jan 30, 2007
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      Hi Paul!

      You wrote:
      > Hi Steve
      > > But what happens if someone sends your stack a message with multiple
      > > wsa headers in different xml namespaces?
      > >
      > > <wsa2005:To />
      > > <wsa2003:To />
      > > <wsa2004:To />
      > I raised this very issue in my position paper [1] to the W3C Workshop
      > on Enterprise computing, and see it as a fundamental consequence
      > of SOAP not having a "stack", but a "bag" (actually a graph with WSS)
      > which requires meta-data such as the much trumpeted WS-Policy to
      > unravel.
      > [...]
      > The order of SOAP headers should have been made significant IMO.

      While I don't necessarily disagree with this (and believe me, the
      discussion as to processing order was a big one back in the early days
      of XMLP), I'm also not sure how having a processing order would save you
      here.

      There are two cases when you have two headers. Either you understand
      them both (i.e. have both versions installed) or you only understand
      one. Assuming nothing is marked MU=true here, the second case is simple
      in that you'll only process one and therefore order doesn't matter.

      In the first case, which is the interesting one, you'd still have an
      issue even if SOAP said "process in lexical order". The problem is that
      the WSA specs would need to say something like "if you support both this
      and previous versions, you MUST NOT process the earlier version's
      headers if you see them". Otherwise you'd still just process the first
      WSA header then you'd process the second one, since you understand both.
      The SOAP spec itself can't (and arguably shouldn't) handle this kind
      of thing itself.

      Lexical ordering, or hierarchical headers, can help with things like
      "encrypt then compress" vs "compress then encrypt", but not really with
      versioning, as far as I can tell.

      Thanks,
      --Glen
    • Steve Loughran
      ... or you understand none, which again, is unimportant. ... Well, then -why didnt WS-A to have some guidelines for the problem. Given that the WS-RF 1.0 spec
      Message 2 of 14 , Jan 30, 2007
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        On 1/30/07, Glen Daniels <glen@...> wrote:
        > There are two cases when you have two headers. Either you understand
        > them both (i.e. have both versions installed) or you only understand
        > one. Assuming nothing is marked MU=true here, the second case is simple
        > in that you'll only process one and therefore order doesn't matter.
        >

        or you understand none, which again, is unimportant.

        > In the first case, which is the interesting one, you'd still have an
        > issue even if SOAP said "process in lexical order". The problem is that
        > the WSA specs would need to say something like "if you support both this
        > and previous versions, you MUST NOT process the earlier version's
        > headers if you see them". Otherwise you'd still just process the first
        > WSA header then you'd process the second one, since you understand both.
        > The SOAP spec itself can't (and arguably shouldn't) handle this kind
        > of thing itself.

        Well, then -why didnt WS-A to have some guidelines for the problem.

        Given that the WS-RF 1.0 spec depends on two different drafts of WS-A,
        surely it should have been obvious that there were going to be legacy
        addresses out there.

        Life is so much simpler with URLs. You cannot post a request to three
        different URLs, and if you use the element in the message body to
        select your action, its inherently impossible to hae duplicate
        payloads.

        -steve
      • Glen Daniels
        Hi Steve: ... I agree, and I would suggest that feedback/errata be offered to the WSA working group. I haven t had time to scan the archives, but I m sure
        Message 3 of 14 , Feb 1 6:53 AM
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          Hi Steve:

          Steve Loughran wrote:
          > > The SOAP spec itself can't (and arguably shouldn't) handle this kind
          > > of thing itself.
          >
          > Well, then -why didnt WS-A to have some guidelines for the problem.
          >
          > Given that the WS-RF 1.0 spec depends on two different drafts of WS-A,
          > surely it should have been obvious that there were going to be legacy
          > addresses out there.

          I agree, and I would suggest that feedback/errata be offered to the WSA
          working group. I haven't had time to scan the archives, but I'm sure
          this came up during the course of the WG discussions (not that you'd
          know it by reading the specs). It would be nice to see some mention of
          how to deal with multiple versions in there.

          > Life is so much simpler with URLs. You cannot post a request to three
          > different URLs, and if you use the element in the message body to
          > select your action, its inherently impossible to hae duplicate
          > payloads.

          I don't think this is a particularly valid comparison. It would be more
          like adding multiple versioned HTTP headers rather than posting to
          different URLs. The point of SOAP headers is that they modify, not
          replace, the (potentially non-extensible) content of a message.

          --Glen
        • Steve Loughran
          ... well, I shall modify my servlet engine to support multiple Host fields in the get request to make its http layer more consistent :)
          Message 4 of 14 , Feb 1 12:11 PM
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            On 2/1/07, Glen Daniels <glen@...> wrote:
            >
            > > Life is so much simpler with URLs. You cannot post a request to three
            > > different URLs, and if you use the element in the message body to
            > > select your action, its inherently impossible to hae duplicate
            > > payloads.
            >
            > I don't think this is a particularly valid comparison. It would be more
            > like adding multiple versioned HTTP headers rather than posting to
            > different URLs. The point of SOAP headers is that they modify, not
            > replace, the (potentially non-extensible) content of a message.
            >

            well, I shall modify my servlet engine to support multiple Host fields
            in the get request to make its http layer more consistent :)
          • noah_mendelsohn@us.ibm.com
            ... One of my great regrets about the SOAP Recommendation is that it does not make crystal clear an aspect of the design that I considered to be very
            Message 5 of 14 , Feb 6 5:16 PM
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              Paul Downey writes:

              > I raised this very issue in my position paper [1] to the W3C Workshop
              > on Enterprise computing, and see it as a fundamental consequence
              > of SOAP not having a "stack", but a "bag" (actually a graph with WSS)
              > which requires meta-data such as the much trumpeted WS-Policy to
              > unravel.

              One of my great regrets about the SOAP Recommendation is that it does not
              make crystal clear an aspect of the design that I considered to be very
              important. Still, the crucial function is there IMO:

              First of all, it's not true that what SOAP has is a "bag"; the header
              elements are siblings in an envelope Infoset, and the Infoset is ordered.
              Also, headers may have interacting semantics [1] :

              "Mandatory SOAP header blocks are presumed to somehow modify the semantics
              of other SOAP header blocks or SOAP body elements."

              Furthermore, and this is crucial, while SOAP itself mandates no fixed
              order when processing, headers can be defined to control the order [1]:

              "The processing of one or more SOAP header blocks MAY control or determine
              the order of processing for other SOAP header blocks and/or the SOAP body.
              For example, one could create a SOAP header block to force processing of
              other SOAP header blocks in lexical order. In the absence of such a
              controlling SOAP header block, the order of header and body processing is
              at the discretion of the SOAP node. Header blocks MAY be processed in
              arbitrary order. Header block processing MAY precede, MAY be interleaved
              with, or MAY follow processing of the SOAP body. For example, processing
              of a "begin transaction" header block would typically precede body
              processing, a "logging" function might run concurrently with body
              processing and a "commit transaction" header block might be honored
              following completion of all other work."

              This is not an accident. It's why we require that all mustUnderstand
              checking be done before any other work. That's what ensures you that if
              you have an mU header that says "do the headers in reverse order" or
              "alphabetical order" or more likely "do signatures first" then that
              header or those headers will necessarily be checked in time to determine
              an order.

              Furthermore, and this is the part I really wish had been highlighted a bit
              more, nothing says these must be separate headers. So, IMO, if you want
              to say >in the specification for wsa:To< "if there are multiple wsa:To
              headers, here's the rule for how to process them all in the presence of
              the others", you can do so. If they are marked mU then you can be sure
              that, at least per the SOAP spec, their specifications can conspire to
              determine an order.

              In fact, what I really wanted to see in the recommendation would be a
              statement along the lines of: "The specifications for headers that may
              coexist in a SOAP message must collectively describe the correct
              interpretation of the headers in combination as well as in isolation.
              Thus, specifications may be written for families of headers designed to be
              used together, to determine operation in the case where multiple instances
              of the same header appear etc. Such specifications may call for a given
              header to be "understood" only when accompanied or only if not accompanied
              by certain other headers. etc."

              I think that is in fact implicit in what is there, but obviously many
              users have missed it. Whether the typical stacks out there provide much
              help in supporting such combined interpretation and ordering is a
              different question, but the spec definitely anticipates it IMO.

              Noah

              [1] http://www.w3.org/TR/soap12-part1/#muprocessing
              [2] http://www.w3.org/TR/soap12-part1/#procsoapmsgs
              --------------------------------------
              Noah Mendelsohn
              IBM Corporation
              One Rogers Street
              Cambridge, MA 02142
              1-617-693-4036
              --------------------------------------
            • Steve Loughran
              On 2/7/07, noah_mendelsohn@us.ibm.com wrote: . ... aah. Soap1.2. Soap 1.1 says nothing about where the headers are validated,
              Message 6 of 14 , Feb 8 7:58 AM
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                On 2/7/07, noah_mendelsohn@... <noah_mendelsohn@...> wrote:
                ."
                >
                > Furthermore, and this is crucial, while SOAP itself mandates no fixed
                > order when processing, headers can be defined to control the order [1]:
                >
                > "The processing of one or more SOAP header blocks MAY control or determine
                > the order of processing for other SOAP header blocks and/or the SOAP body.
                > For example, one could create a SOAP header block to force processing of
                > other SOAP header blocks in lexical order. In the absence of such a
                > controlling SOAP header block, the order of header and body processing is
                > at the discretion of the SOAP node. Header blocks MAY be processed in
                > arbitrary order. Header block processing MAY precede, MAY be interleaved
                > with, or MAY follow processing of the SOAP body. For example, processing
                > of a "begin transaction" header block would typically precede body
                > processing, a "logging" function might run concurrently with body
                > processing and a "commit transaction" header block might be honored
                > following completion of all other work."
                >
                > This is not an accident. It's why we require that all mustUnderstand
                > checking be done before any other work. That's what ensures you that if
                > you have an mU header that says "do the headers in reverse order" or
                > "alphabetical order" or more likely "do signatures first" then that
                > header or those headers will necessarily be checked in time to determine
                > an order.
                >

                aah. Soap1.2. Soap 1.1 says nothing about where the headers are
                validated, only that they must be validated

                "A env:mustUnderstand value of "true" means that the SOAP node must
                process the header with the semantics described in that header's
                specification, or else generate a SOAP fault. Processing the header
                appropriately may include removing the header from any generated SOAP
                message, reinserting the header with the same or altered value, or
                inserting a new header. The inability to process a mandatory header
                requires that all further processing of the SOAP message cease, and a
                SOAP fault be generated. The message is not forwarded any further."

                This is why the release of Axis (1.0?) that didnt do mU checking until
                after the message had been handled was within the spirit of the spec,
                and not the law.

                SOAP1.2 implies that I must check all mu headers before having any
                side effect at all. hmm. My current stack lets you declare handlers in
                a chain, as axis has done forever, and sun's stack has done since last
                week:

                AddressedEchoEndpoint extends AlpineEndpoint {
                name "wsa-echo";
                handlers [
                LogCurrentMessageHandler:classname,
                AddressHandler:classname,
                MustUnderstandChecker:classname,
                EchoHandler:classname,
                LogCurrentMessageHandler:classname
                ];
                }

                There's no way with this chain-of-resposibility design to do advance
                checking of handling, or guarantee that there are no side effects (I
                log the message -is that a side effect?), before the message is handed
                for processing.

                I suppose I could modify the handler interface to add an extra method
                in which every handler indicates if it will process a specific mU
                header. But if every handler is empowered to transform the incoming
                message during its work phase, things get complex. You need to create
                a provisionally transformed doc (transform, without side effects) just
                to make sure the mu headers get processed right.

                Or I ignore that part of the spec on the grounds that its pretty much
                impossible for interop tests to catch and retain my existing
                SOAP1.1-compatible mU processing algorithm.

                > Furthermore, and this is the part I really wish had been highlighted a bit
                > more, nothing says these must be separate headers. So, IMO, if you want
                > to say >in the specification for wsa:To< "if there are multiple wsa:To
                > headers, here's the rule for how to process them all in the presence of
                > the others", you can do so. If they are marked mU then you can be sure
                > that, at least per the SOAP spec, their specifications can conspire to
                > determine an order.
                >

                well, its a shame they dont.

                -steve
              • noah_mendelsohn@us.ibm.com
                ... Well, my reading of the ws-i basic profile is that it says the same thing regarding SOAP 1.1 [1]: R1025 A RECEIVER MUST handle messages in such a way
                Message 7 of 14 , Feb 8 9:09 AM
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                  Steve Loughran writes:

                  > On 2/7/07, noah_mendelsohn@...
                  > <noah_mendelsohn@...> wrote: ."
                  >
                  > > Furthermore, and this is crucial, while SOAP
                  > > itself mandates no fixed order when processing,
                  > > headers can be defined to control the order [1]:
                  >
                  > > "The processing of one or more SOAP header
                  > > blocks MAY control or determine the order of
                  > > processing for other SOAP header blocks and/or
                  > > the SOAP body. For example, one could create a
                  > > SOAP header block to force processing of other
                  > > SOAP header blocks in lexical order. In the
                  > > absence of such a controlling SOAP header block,
                  > > the order of header and body processing is at
                  > > the discretion of the SOAP node. Header blocks
                  > > MAY be processed in arbitrary order. Header
                  > > block processing MAY precede, MAY be interleaved
                  > > with, or MAY follow processing of the SOAP
                  > > body. For example, processing of a "begin
                  > > transaction" header block would typically
                  > > precede body processing, a "logging" function
                  > > might run concurrently with body processing and
                  > > a "commit transaction" header block might be
                  > > honored following completion of all other work."
                  >
                  > > This is not an accident. It's why we require
                  > > that all mustUnderstand checking be done before
                  > > any other work. That's what ensures you that if
                  > > you have an mU header that says "do the headers
                  > > in reverse order" or "alphabetical order" or
                  > > more likely "do signatures first" then that
                  > > header or those headers will necessarily be
                  > > checked in time to determine an order.
                  > >
                  >
                  > aah. Soap1.2. Soap 1.1 says nothing about where
                  > the headers are validated, only that they must be
                  > validated

                  Well, my reading of the ws-i basic profile is that it says the same thing
                  regarding SOAP 1.1 [1]:

                  "R1025 A RECEIVER MUST handle messages in such a way that it appears
                  that all checking of mandatory header blocks is performed before any
                  actual processing. "

                  Like so much in the basic profile, it takes the SOAP 1.2 refinements to
                  the processing model, and mandates their use with SOAP 1.1.

                  > > "A env:mustUnderstand value of "true" means that
                  > > the SOAP node must process the header with the
                  > > semantics described in that header's
                  > > specification, or else generate a SOAP
                  > > fault. Processing the header appropriately may
                  > > include removing the header from any generated
                  > > SOAP message, reinserting the header with the same
                  > > or altered value, or inserting a new header. The
                  > > inability to process a mandatory header requires
                  > > that all further processing of the SOAP message
                  > > cease, and a SOAP fault be generated. The message
                  > > is not forwarded any further."
                  >
                  > This is why the release of Axis (1.0?) that didnt
                  > do mU checking until after the message had been
                  > handled was within the spirit of the spec, and not
                  > the law.
                  >
                  > SOAP1.2 implies that I must check all mu headers
                  > before having any side effect at all. hmm. My
                  > current stack lets you declare handlers in a
                  > chain, as axis has done forever, and sun's stack
                  > has done since last week:

                  Well, I'm not sure what to say. The spec is clear that you must inspect
                  the headers first, and I think there are defensible reasons for that. I
                  believe most of the commercial implementations (not speaking for my
                  employer, IBM here) are moving toward a model in which headers are
                  buffered so that mU checking can be done and header processing
                  appropriately ordered, but the body is not necessarily parsed and
                  processed in advance. Thus, the body can be streamed, but not the
                  headers.

                  > AddressedEchoEndpoint extends AlpineEndpoint {
                  > name "wsa-echo";
                  > handlers [
                  > LogCurrentMessageHandler:classname,
                  > AddressHandler:classname,
                  > MustUnderstandChecker:classname,
                  > EchoHandler:classname,
                  > LogCurrentMessageHandler:classname
                  > ];
                  > }
                  >
                  > There's no way with this chain-of-resposibility
                  > design to do advance checking of handling, or
                  > guarantee that there are no side effects (I log
                  > the message -is that a side effect?), before the
                  > message is handed for processing.
                  >
                  > I suppose I could modify the handler interface to
                  > add an extra method in which every handler
                  > indicates if it will process a specific mU
                  > header. But if every handler is empowered to
                  > transform the incoming message during its work
                  > phase, things get complex. You need to create a
                  > provisionally transformed doc (transform, without
                  > side effects) just to make sure the mu headers get
                  > processed right.

                  To be precise, headers are empowered to change the interpretation of other
                  parts of the message, or to affect whether you can "understand" other
                  headers in the message, but NOT to transform the message. In particular,
                  I don't see anything that says a header can cause parts of the message to
                  be decrypted or decompressed in a manner that would lead to the appearance
                  of new headers that were processed as if they were there from the start.

                  What I do think is there implicitly for such cases is for the
                  specification of a header to say: when I am present, the SOAP processing
                  model is to be rerun from the start on a new infoset constructed in the
                  following way (e.g. by decrypting parts of the current.) In a given
                  single use of the SOAP processing model, the input envelope infoset is
                  invariant, but the interpretations of the headers present may interact.
                  Indeed, it's crucial that they do. Surely a digital signature header
                  affects the semantics of that which is signed, in the sense that if the
                  dsig doesn't check, you may want to act as if none of the other headers
                  are there (since they may be the result of tampering.) SOAP is designed
                  to enable such scenarios, as long as the specification for the header (in
                  this case a dsig header) is written properly.

                  > Or I ignore that part of the spec on the grounds
                  > that its pretty much impossible for interop tests
                  > to catch and retain my existing SOAP1.1-compatible
                  > mU processing algorithm.

                  Whether you wish your implementation to expose that full power is up to
                  you. HOWEVER, if you do not, then the only conforming response is for you
                  to act as if you do not in fact "understand" any headers that might
                  conceivably have such interacting semantics that you can't handle. So,
                  unless you know that a header doesn't affect others, then if it's mU
                  you'll either have to mU fault or be nonconforming to ws-i basic profile
                  and/or SOAP 1.2.


                  > > Furthermore, and this is the part I really wish
                  > > had been highlighted a bit more, nothing says
                  > > these must be separate headers. So, IMO, if you
                  > > want to say >in the specification for wsa:To<
                  > > "if there are multiple wsa:To headers, here's
                  > > the rule for how to process them all in the
                  > > presence of the others", you can do so. If they
                  > > are marked mU then you can be sure that, at
                  > > least per the SOAP spec, their specifications
                  > > can conspire to determine an order.
                  > >
                  >
                  > well, its a shame they dont.

                  Yes, well, I have many concerns about how the higher level WS* specs were
                  written, and whether they took sufficient care to use SOAP's details
                  properly. I'm sorry that's in fact causing you trouble.

                  > -steve
                  >

                  Noah

                  [1]
                  http://www.ws-i.org/Profiles/BasicProfile-1.0-2004-04-16.html#refinement16468312



                  --------------------------------------
                  Noah Mendelsohn
                  IBM Corporation
                  One Rogers Street
                  Cambridge, MA 02142
                  1-617-693-4036
                  --------------------------------------
                • Steve Loughran
                  ... Sometimes I suspect complexity is the underlying problem. Like WSDL. Its almost impossible for humans to write, so what you get is a mess, compared to,
                  Message 8 of 14 , Feb 8 10:51 AM
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                    On 2/8/07, noah_mendelsohn@... <noah_mendelsohn@...> wrote:
                    > Steve Loughran writes:
                    >
                    > > On 2/7/07, noah_mendelsohn@...
                    > > <noah_mendelsohn@...> wrote: ."
                    >
                    >
                    > > > Furthermore, and this is the part I really wish
                    > > > had been highlighted a bit more, nothing says
                    > > > these must be separate headers. So, IMO, if you
                    > > > want to say >in the specification for wsa:To<
                    > > > "if there are multiple wsa:To headers, here's
                    > > > the rule for how to process them all in the
                    > > > presence of the others", you can do so. If they
                    > > > are marked mU then you can be sure that, at
                    > > > least per the SOAP spec, their specifications
                    > > > can conspire to determine an order.
                    > > >
                    > >
                    > > well, its a shame they dont.
                    >
                    > Yes, well, I have many concerns about how the higher level WS* specs were
                    > written, and whether they took sufficient care to use SOAP's details
                    > properly. I'm sorry that's in fact causing you trouble.
                    >

                    Sometimes I suspect complexity is the underlying problem. Like WSDL.
                    Its almost impossible for humans to write, so what you get is a mess,
                    compared to, say, COM IDL interfaces.

                    As for the higher order specs, well, I relish their inconsistency,
                    epecially WSRF, that has explicit dependencies on two different draft
                    WSA versions, and punts on the whole problem of whether not bulk
                    attribute read/write operations are atomic or not.

                    But that's an OASIS problem so I won't be giving my local TAG
                    representative a hard time, about it, or you. Liked your W3C
                    submission to the web of enterprisey services; interesting contrast to
                    the IBM 'we want a single stack' story.

                    -steve
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