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

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  • Paul Downey
    Hi Steve ... 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
    Message 1 of 14 , Jan 30, 2007
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      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.

      I guess you could send all three to handle versioning in the recipient,
      but mostly it's going to spell doom, especially if

      wsa2004:Action says "getCustomerInfo",
      wsa2005:Action says "fireNuclearMissiles",

      and your XML Gateway and Service are out of sync .. boom!

      It gets worse if you consider the old Action could have been
      signed and the new one does the deed.

      The order of SOAP headers should have been made significant IMO.

      Paul
      --
      http://blog.whatfettle.com

      [1] http://www.w3.org/2007/01/wos-papers/bt


      --
      http://blog.whatfettle.com
    • 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 2 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 3 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 4 of 14 , Feb 1, 2007
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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 5 of 14 , Feb 1, 2007
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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 6 of 14 , Feb 6, 2007
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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 7 of 14 , Feb 8, 2007
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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 8 of 14 , Feb 8, 2007
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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 9 of 14 , Feb 8, 2007
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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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