Internet-Draft                                                Mark Baker
                                                        Planetfred, Inc.
                                                         Mark Nottingham

                                                        January 14, 2002

                 The "application/soap+xml" media type

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 10 of RFC2026.

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   This document defines the "application/soap+xml" media type which can
   be used to describe SOAP 1.2 messages serialized as XML.

1. Introduction

   SOAP 1.2 is an XML Infoset[INFOSET] based protocol at the core of
   which is an envelope that defines a framework for describing what is
   in a message and how to process it, and a binding framework for
   exchanging messages using an underlying protocol.

   By being based on the XML Infoset, and not XML 1.0 [XML] itself, SOAP
   permits alternate serializations of messages.  The
   "application/soap+xml" media type can be used to describe those SOAP
   messages produced with the XML 1.0 serialization.

   Feedback or discussion about this draft should be directed to the
   XML Protocol Working Group public mailing list,
   with archives at

2. Registration

   MIME media type name:      application
   MIME subtype name:         soap+xml
   Required parameters:       none
   Optional parameters:

       This parameter has identical semantics to the charset parameter
       of the "application/xml" media type as specified in [XMLMIME].

       See Section 6 of this document.

  Encoding considerations:
     Identical to those of "application/xml" as described in [XMLMIME],
     Section 3.2.

  Security considerations:
     See Section 3 of this document.

  Interoperability considerations:
     See Section 4 of this document.

  Published specification:
     See [SOAP12P1] and [SOAP12P2].

  Applications which use this media type:
     No known applications currently use this media type.

  Additional information:

     Magic number:
       There is no single initial byte sequence that is always present
       for SOAP messages.  Section 5 below gives some context for why
       recognizing a SOAP message without any metadata is problematic,
       and some guidelines on how the XML 1.0 serialization of the SOAP
       envelope may be recognized.

     File extension:
       SOAP messages are not required or expected to be stored as

     Macintosh File Type code: TEXT

   Person & email address to contact for further information:
     Mark Baker <>

   Intended usage: COMMON

   Author/Change controller:
     The SOAP 1.2 specification set is a work product of the World Wide
     Web Consortium's XML Protocol Working Group.  The W3C has change
     control over these specifications.

3. Security considerations

3.1 Traditional considerations

  An obvious target for security considerations is the SOAP processing
  model.  It accomodates intermediaries, so is potentially prone to
  typical intermediary style attacks.  SOAP itself provides no specific
  protection from these attacks, but instead leaves that to SOAP
  extensions, or to the underlying protocol(s) to which it is bound.

  For example, portions of a SOAP envelope could be encrypted with XML
  Encryption [XMLENC], protecting the chain from some "man in the
  middle" attacks.

  The SOAP envelope includes two features that form the basis of the
  intermediary model.  Those features are;

    o "actor", used to target headers to SOAP intermediaries that
      understand its URI value
    o "mustUnderstand", used to require that a SOAP header must be
      understood by a SOAP intermediary, or the message rejected

  "actor" values are URIs, however there are no requirements that a SOAP
  processor attempt to resolve them, so no security issues should result
  from their use.

  "mustUnderstand" has no known security issues, outside the generic
  concerns about intermediaries, that enforcing the end to end model
  requires extensions, or using features provided by the underlying

3.2 Considerations of the different uses of SOAP

  From a security perspective, SOAP can be seen to be used in two
  different ways; tunneled, and non-tunneled.

3.2.1 Non-tunneled

  The non-tunneled use of SOAP is as an XML Infoset based envelope whose
  hop-by-hop transfer semantics are inherited from the application
  protocol used for that hop.

  In this use, the binding of SOAP to that protocol extends the
  application semantics of the protocol without modifying or otherwise
  disrupting the existing semantics.  This includes the safety provided
  by the fixed interface of the application protocol.  For example, when
  bound to HTTP using the SOAP 1.2 default HTTP binding, the transfer of
  a SOAP envelope is performed with HTTP POST semantics, and the
  safety implications are the same as for any other HTTP POST.

3.2 Tunneled

  Another use of SOAP is as a framework for building and deploying new
  protocols, tunneled over the underlying protocol to which it is
  bound.  If the underlying protocol is an application protocol, then
  any safety afforded by the fixed interface of that protocol would be
  disregarded (by definition of "tunnel").  It will be up to the
  designer of the new protocol to ensure that its semantics are safe.

  That SOAP explicitly supports tunneling would at first glance appear
  to be a problem.  However, as tunneling over application protocols is
  already fairly common (including IPP [IPP], on the IETF Internet
  standards track), the possibility of consolidating future tunneling
  practice within a framework such as SOAP should help security in the
  long run.

  As a worst case from a security perspective, if SOAP were used only
  for tunneling, it would be no worse than the tunneling that exists

4. Interoperability considerations

  There are several factors affecting a SOAP processor's ability to
  successfully process a SOAP message.  These are itemized in Section
  4.4.5 of [SOAP12P1];

    o version mismatch; the SOAP envelope uses an unrecognized namespace
    o mustUnderstand; the SOAP envelope contained a header tagged as
      "mustUnderstand", but the recipient processor didn't understand or
      could not obey them
    o DTD not supported; the SOAP message contained a Document Type
      Definition, which SOAP 1.2 does not support
    o Data encoding unknown; a header or body targetted at the current
      SOAP node is scoped with a data encoding that the current node
      does not support

  SOAP defines faults for these, and requires that conformant processors
  send the appropriate fault when encountered.

5. Recognizing SOAP messages

  SOAP 1.2 does not require or assume that SOAP 1.2 messages have any
  particular serialization, making it impossible to determine (in the
  absence of other information) when a chunk of data is a SOAP 1.2
  message or not.

  However, for the case of the XML 1.0 serialization of SOAP 1.2
  messages, the following best describes how these messages may be

  The root element of the message will always be named "envelope" with
  the namespace "".  However,
  this may be expressed in two ways;

    o  with an xmlns declaration on the root element
    o  with a prefix-adorned xmlns declaration on the root element
       where "envelope" is so prefixed

6. The "action" parameter

  SOAP 1.1 [SOAP11] introduced the HTTP SOAPAction header, which was
  designed to be used to indicate the "intent" of the SOAP message.  Its
  value is a URI reference, and its existence was to be used to
  unambiguously identify SOAP messages tranferred with HTTP.  It was
  required because SOAP 1.1 used the generic "text/xml" media type,
  preventing that same information from being communicated on the media
  type where it might normally reside.

  As SOAP 1.2 is defining its own media type, the possibility of using
  a parameter on that media type to convey the same information as is
  done with SOAPAction, now exists.  "action" is that parameter.

  Its semantics are identical to that of the SOAPAction header of SOAP
  1.2, not SOAP 1.1 (a key difference being that it is optional in SOAP
  1.2).  The following is a mapping of the meanings of the various uses
  of SOAPAction (as described in [SOAP12P2]) to the "action" parameter;

                  SOAPAction use    |    "action" parameter
       SOAPAction: "http://foo/bar" |  action="http://foo/bar"
       SOAPAction: "myapp.sdl"      |  action="myapp.sdl"
       SOAPAction: ""               |  action=""
7. Fragment identifiers

   No meaning is associated with fragment identifiers for content
   described by the "application/soap+xml" media type.

8. Authors' Addresses

   Mark A. Baker
   Planetfred, Inc.
   44 Byward Market, Suite 240
   Ottawa, Ontario, CANADA. K1N 7A2

   Mark Nottingham

9. References

[XML]    "Extensible Markup Language (XML) 1.0", W3C Recommendation,
         February 1998.  Available at <>
         (or <>).

[INFOSET] "XML Information Set", W3C Recommendation, 24 October 2001,
         Available at <> (or

[XMLMIME] "XML Media Types", RFC 3023, January 2001.  Murata, M.,
         St.Laurent, S., Kohn, D.

[SOAP11] "Simple Object Access Protocol", Box, D., Ehnebuske, D.,
         Kakivaya, G., Layman, A., Mendelsohn, N., Nielsen, H.,
         Thatte, S. and D. Winer, May 2000.

[SOAP12P1] "SOAP Version 1.2 Part 1: Messaging Framework", W3C Working
         Draft (work in progress), December 2001.  Gudgin, M.,
         Hadley, M., Moreau, J., Nielsen, H.

[SOAP12P2] "SOAP Version 1.2 Part 2: Adjuncts", W3C Working Draft (work
         in progress), December 2001.  Gudgin, M., Hadley, M.,
         Moreau, J., Nielsen, H.  <>.

[XMLBASE] "XML Base", W3C Recommendation, 27 June 2001.  Available at
         <> (or

[IPP]    "Internet Printing Protocol/1.1: Encoding and Transport", RFC
         2910, September 2000.  Herriot, R., Butler, S., Moore, P.,
         Turner, R. and J.  Wenn.

[XMLENC] "XML Encryption Syntax and Processing", W3C Working Draft (work
         in progress), October 2001.  Eastlake, D., Reagle, J., Editors.