Internet-Draft Mark Baker
Planetfred, Inc.
Mark Nottingham
January 14, 2002
The "application/soap+xml" media type
draft-baker-soap-media-reg-00.txt
Status of this Memo
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Abstract
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, xml-dist-app@w3.org
with archives at http://lists.w3.org/Archives/Public/xml-dist-app/.
2. Registration
MIME media type name: application
MIME subtype name: soap+xml
Required parameters: none
Optional parameters:
charset
This parameter has identical semantics to the charset parameter
of the "application/xml" media type as specified in [XMLMIME].
action
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
files.
Macintosh File Type code: TEXT
Person & email address to contact for further information:
Mark Baker <mbaker@planetfred.com>
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
protocol.
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
today.
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
URI
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
recognized.
The root element of the message will always be named "envelope" with
the namespace "http://www.w3.org/2001/12/soap-envelope". 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
tel:+1-613-789-1818
mailto:mbaker@planetfred.com
Mark Nottingham
mailto:mnot@mnot.net
9. References
[XML] "Extensible Markup Language (XML) 1.0", W3C Recommendation,
February 1998. Available at <http://www.w3.org/TR/REC-xml>
(or <http://www.w3.org/TR/2000/REC-xml-20001006>).
[INFOSET] "XML Information Set", W3C Recommendation, 24 October 2001,
Available at <http://www.w3.org/TR/xml-infoset> (or
<http://www.w3.org/TR/2001/REC-xml-infoset-20011024>).
[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.
<http://www.w3.org/TR/2000/NOTE-SOAP-20000508>.
[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.
<http://www.w3.org/TR/soap12-part1/>.
[SOAP12P2] "SOAP Version 1.2 Part 2: Adjuncts", W3C Working Draft (work
in progress), December 2001. Gudgin, M., Hadley, M.,
Moreau, J., Nielsen, H. <http://www.w3.org/TR/soap12-part2/>.
[XMLBASE] "XML Base", W3C Recommendation, 27 June 2001. Available at
<http://www.w3.org/TR/xml-base/> (or
<http://www.w3.org/TR/2001/REC-xmlbase-20010627/>).
[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.
<http://www.w3.org/TR/xmlenc-core/>.