SIMPLE J. Rosenberg
Internet-Draft Cisco
Intended status: Standards Track J. Urpalainen
Expires: August 5, 2010 Nokia
February 1, 2010
An Extensible Markup Language (XML) Document Format for Indicating A
Change in XML Configuration Access Protocol (XCAP) Resources
draft-ietf-simple-xcap-diff-14
Abstract
This specification defines a document format that can be used to
indicate that a change has occurred in a document managed by the
Extensible Markup Language (XML) Configuration Access Protocol
(XCAP). This format reports which document has changed and its
former and new entity tags. It can report the differences between
versions of the document, using an XML patch format. It can report
existing element and attribute content when versions of an XCAP
server document change. XCAP diff documents can be delivered to diff
clients using a number of means, including a Session Initiation
Protocol (SIP) event package.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 5, 2010.
Copyright Notice
Rosenberg & Urpalainen Expires August 5, 2010 [Page 1]
Internet-Draft XCAP Diff Format February 2010
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Rosenberg & Urpalainen Expires August 5, 2010 [Page 2]
Internet-Draft XCAP Diff Format February 2010
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Structure of an XCAP Diff Document . . . . . . . . . . . . . . 6
4. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Example Document . . . . . . . . . . . . . . . . . . . . . . . 12
6. Basic Requirements For a System Exchanging XCAP Diff
Documents . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8.1. application/xcap-diff+xml MIME Type . . . . . . . . . . . 15
8.2. URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:xcap-diff . . . . . . . . . . . . . 16
8.3. Schema Registration . . . . . . . . . . . . . . . . . . . 16
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
10.1. Normative References . . . . . . . . . . . . . . . . . . . 17
10.2. Informative References . . . . . . . . . . . . . . . . . . 18
Appendix A. Informative Examples . . . . . . . . . . . . . . . . 19
A.1. Indicating Existing, Changed or Removed Documents . . . . 19
A.2. Indicating Actual Changes of Documents . . . . . . . . . . 22
A.3. Indicating XCAP Component Contents . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
Rosenberg & Urpalainen Expires August 5, 2010 [Page 3]
Internet-Draft XCAP Diff Format February 2010
1. Introduction
The Extensible Markup Language (XML) Configuration Access Protocol
(XCAP) [RFC4825] is a protocol that allows XCAP clients to manipulate
XML documents stored on a server. These XML documents serve as
configuration information for application protocols. As an example,
resource list [RFC4662] subscriptions (also known as presence lists)
allow a SIP client to have a single SIP subscription to a list of
users, where the list is maintained on a server. The server will
obtain presence for those users and report it back to the SIP client.
This application requires the server, called a Resource List Server
(RLS), to have access to the list of presentities [RFC2778]. This
list needs to be manipulated by XCAP clients so they can add and
remove their friends as they desire.
Complexities arise when multiple XCAP clients attempt to
simultaneously manipulate a document, such as a presence list.
Frequently, an XCAP client will keep a copy of the current list in
memory, so it can render it to users. However, if another XCAP
client modifies the document, the cached version becomes stale. This
modification event must be made known to all clients which have
cached copies of the document, so that they can fetch the most recent
one.
To deal with this problem, clients can use a Session Initiation
Protocol (SIP) [RFC3261] event package [RFC3265] to subscribe to
change events [I-D.ietf-sip-xcapevent] in XCAP documents. This
notification needs to indicate the specific resource that changed,
and how it changed. One solution for the format of such a change
notification would be a content indirection object [RFC4483]. Though
content indirection can tell a client that a document has changed, it
provides it with MIME Content-ID indicating the new version of the
document. The MIME Content-ID is not the same as the entity tag,
which is used by XCAP for document versioning. As such, a client
cannot easily ascertain whether an indication of a change in a
document is due to a change it just made, or due to a change another
XCAP client made at around the same time. Furthermore, content
indirections don't indicate how a document changed; they would only
be able to indicate that it did change.
To resolve these problems, this document defines a data format which
can convey the fact that an XML document managed by XCAP has changed.
This data format is an XML document format, called an XCAP diff
document. This format reports which document has changed and its
former and new entity tags. It can report the differences between
versions of the document, using an XML patch format [RFC5261], which
indicate how to transform the locally cached XCAP document from the
version prior to the change, to the version after it. Its intent is
Rosenberg & Urpalainen Expires August 5, 2010 [Page 4]
Internet-Draft XCAP Diff Format February 2010
to reduce the required overall bandwidth and the number of separate
transmissions. It can also report existing element and attribute
content when versions of an XML document change at an XCAP server.
XML documents that are equivalent for the purposes of many
applications may differ in their physical representation. Similar to
XCAP, the canonical form with comments [W3C.REC-xml-c14n-20010315] of
an XML document determines the logical equivalence when this format
is used to patch locally cached XCAP documents.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119] and
indicate requirement levels for compliant implementations.
This specification also defines the following additional terms:
Document: When the term document is used without the "(XCAP) diff"
in front of it, it refers to the XCAP document resource about whom
the XCAP diff document is reporting a change.
Diff document: The XML document defined by this specification that
reports on a set of changes in an XCAP document resource. It is
delivered from a server to a diff client by a transport which is
not defined by this specification.
XCAP server: A protocol entity that manages XCAP documents and their
entity tags. It usually contains an integrated diff notifier.
Diff notifier: This is the entity of a server which generates XCAP
diff documents based on its knowledge of a set of XCAP documents
and their changes, and it transmits the generated diff documents
to a diff client within a session.
Diff client: A client which consumes XCAP diff documents in order to
construct a locally cached document that is equivalent to a
specific version of a document resource stored at an XCAP server.
It is typically a SIP User Agent (UA) and an XCAP client.
XCAP Client: A client which updates and retrieves documents stored
at an XCAP server. It can also patch element and attribute
content of XCAP documents located at an XCAP server.
Rosenberg & Urpalainen Expires August 5, 2010 [Page 5]
Internet-Draft XCAP Diff Format February 2010
Locally cached resource: A resource which has typically been
downloaded by HTTP from an XCAP server to a diff client. It may
have been patched locally by a diff client based on the XCAP diff
document information. It is equivalent to a single version in its
change history at an XCAP server. Version history of XCAP
documents is indicated by HTTP entity tags (ETag).
ETag: A strong HTTP entity tag whose value is set by an XCAP server.
Documents at an XCAP server are updated by XCAP clients. The XCAP
server assigns a new ETag value to each document version according
to the HTTP specification.
3. Structure of an XCAP Diff Document
An XCAP diff document is an XML [W3C.REC-xml-20060816] document that
MUST be well-formed and SHOULD be valid. XCAP diff documents MUST be
based on XML 1.0 and MUST be encoded using UTF-8. This specification
makes use of XML namespaces for identifying XCAP diff documents and
document fragments. The namespace URI for elements defined by this
specification is a URN [RFC2141], using the namespace identifier
'ietf' defined by [RFC2648] and extended by [RFC3688]. This URN is:
urn:ietf:params:xml:ns:xcap-diff
An XCAP diff document begins with the root element tag <xcap-diff>.
This element has a single mandatory attribute, "xcap-root". The
value of this attribute is the XCAP root URI for the documents in
which the changes have taken place. A single XCAP diff document can
only represent changes in documents within the same XCAP root. The
content of the <xcap-diff> element is a sequence of <document>,
<element> and <attribute> elements followed by any number of elements
from other namespaces for the purposes of extensibility. Wherever
the XML schema (see Section 4) allows extension elements or
attributes, any such unknown content MUST be ignored by the diff
client.
Each <document> element specifies changes in a specific document
within the XCAP root. If several <document> elements pinpoint to the
same specific document, i.e., for example, the full entity tag (ETag)
change history is indicated, the corresponding patches MUST be able
to be applied in the given XCAP diff document order.
Note: This requirement simplifies applications that process XCAP
diff documents since there's no need to sort patch instructions
when applying them.
The <document> element has one mandatory attribute, "sel", and a two
Rosenberg & Urpalainen Expires August 5, 2010 [Page 6]
Internet-Draft XCAP Diff Format February 2010
optional attributes, "new-etag" and "previous-etag". The "sel"
attribute of the <document> element identifies the specific document
within the XCAP root for which changes are indicated. Its content
MUST be a relative path reference, with the base URI being equal to
the XCAP root URI. The "new-etag" attribute provides the entity tag
(ETag) for the document after the application of the changes,
assuming the document exists after those changes. The "previous-
etag" attribute provides an identifier for the document instance
prior to the change. If the change being reported is the removal of
a document, only the "previous-etag" MUST be included and the "new-
etag" attribute MUST NOT be present. The "new-etag" attribute MUST
only exist alone when the document either exists or it was just
created (no patch included). Both attributes are present when a
patch (or series of XCAP operations) has been applied to the
resource. Also both attributes MAY be used to indicate an ETag
change without any document modifications (patches).
The "previous-etag" and "new-etag" need not have been sequentially
assigned ETags at the server. An XCAP diff document can indicate
changes that have occurred over a series of XCAP operations. The
only requirement then is that, the sequence of events, when executed
serially, will result in the transformation of the document with the
ETag "previous-etag" to the one whose ETag is "new-etag". Also the
series of operations do not have to be the same exact series of
operations that occurred at the server.
Each <document> element contains either a sequence of patching
instructions or an indication that the body hasn't semantically
changed. The latter means that the document has been assigned a new
ETag but its content is unchanged and it is indicated by the <body-
not-changed> element. Patching instructions are described by the
<add>, <replace> and <remove> elements. These elements use the
corresponding add, replace and remove types defined in [RFC5261], and
define a set of patch operations that can be applied to transform the
locally cached document. See [RFC5261] for instructions on how this
transformation is effected. The <document> element can also contain
elements from other namespaces for the purposes of extensibility.
The <add>, <replace> and <remove> elements allow extension attributes
from any namespace.
Rosenberg & Urpalainen Expires August 5, 2010 [Page 7]
Internet-Draft XCAP Diff Format February 2010
Figure 1 shows <document> element content and how the corresponding
resource or metadata changes. An external document retrieval means
in practice HTTP GET requests for target resources. The asterisk
character '*' means that a <document> element has child element(s):
<add>, <replace> or <remove>, or alternatively only a <body-not-
changed> element. The hyphen character '-' means that the
corresponding content (attribute or element) doesn't exist in a
<document> element. The 'xxx' and 'yyy' are values of entity tags
(ETag) of an XCAP document.
+-----------+----------+-----------+----------+-------------------+
| previous- | new- | <add> | <body- | locally cached |
| etag | etag | <replace> | not- | XCAP resource/ |
| | | <remove> | changed> | metadata change |
+-----------+----------+-----------+----------+-------------------+
| xxx | yyy | * | - | resource patched, |
| | | | | patch included |
+-----------+----------+-----------+----------+-------------------+
| xxx | yyy | - | - | resource patched, |
| | | | | external document |
| | | | | retrieval |
+-----------+----------+-----------+----------+-------------------+
| xxx | yyy | - | * | only ETag changed |
+-----------+----------+-----------+----------+-------------------+
| - | yyy | - | - | resource created |
| | | | | or exists, |
| | | | | external document |
| | | | | retrieval |
+-----------+----------+-----------+----------+-------------------+
| xxx | - | - | - | resource removed |
+-----------+----------+-----------+----------+-------------------+
Figure 1: <document> element content / corresponding resource changes
Each <element> element indicates the existing element content of an
XCAP document. It has one mandatory attribute, "sel", and
optionally, an "exists" attribute and extension attributes from any
namespace. The "sel" attribute of the <element> element identifies
an XML element of an XCAP document. It is a percent encoded relative
URI following XCAP conventions when selecting elements. The XCAP
Node Selector MUST always locate a unique node, the "exists"
attribute thus shows whether an element exists or not in the XCAP
document. When the "exists" attribute is absent from the <element>
element, the indicated element still exists in the XCAP document.
The located element exists as a child element of the <element>
element. In a corner case where the content of this element cannot
Rosenberg & Urpalainen Expires August 5, 2010 [Page 8]
Internet-Draft XCAP Diff Format February 2010
be presented for some reason (e.g. too large payload), although it
exists in the XCAP document, the <element> element MUST NOT have any
child nodes.
As the located XML element is typically namespace qualified, all
needed namespace declarations MUST exist within the <xml-diff>
document. The possible local namespace declarations within the
located element exist unmodified as in the source document, similar
to XCAP conventions. Other namespace references MUST be resolved
from the context of the <element> or its parent elements. The
prefixes of qualified names (QName) [W3C.REC-xml-names-20060816] of
XML nodes also remain as they exist originally in the source XCAP
document.
Each <attribute> element indicates the existing attribute content of
an XCAP document. It has one mandatory attribute, "sel", and
optionally, an "exists" attribute and extension attributes from any
namespace. The "sel" attribute of the <attribute> element identifies
an XML attribute of an XCAP document. It is a percent encoded
relative URI following XCAP conventions when selecting attributes.
The "exists" attribute indicates whether an attribute exists or not
in the XCAP document. When the "exists" attribute is absent from the
<attribute> element, the indicated attribute still exists in the XCAP
document. The child text node of the <attribute> element indicates
the value of the located attribute. Note that if the attribute is
namespace qualified, the query parameter of the XCAP URI indicates
the attached namespace URI and the prefix in the XCAP source
document.
Namespaces of the "sel" attribute of the <attribute> and <element>
elements MUST also be resolved properly. The Section 6.4. of
[RFC4825] describes the rules when using namespace prefixes in XCAP
Node Selectors. Without a namespace prefix in an element selector,
an XCAP Default Document Namespace MUST be applied. The namespace
resolving rules of Patch operation elements: <add>, <replace> and
<remove> are described in Section 4.2.1 of [RFC5261].
4. XML Schema
The XML Schema for the XCAP diff format.
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns="urn:ietf:params:xml:ns:xcap-diff"
targetNamespace="urn:ietf:params:xml:ns:xcap-diff"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
Rosenberg & Urpalainen Expires August 5, 2010 [Page 9]
Internet-Draft XCAP Diff Format February 2010
<!-- include patch-ops -->
<xs:include
schemaLocation="urn:ietf:params:xml:schema:patch-ops"/>
<!-- document root -->
<xs:element name="xcap-diff">
<xs:complexType>
<xs:sequence minOccurs="0">
<xs:sequence minOccurs="0" maxOccurs="unbounded">
<xs:choice>
<xs:element name="document" type="documentType"/>
<xs:element name="element" type="elementType"/>
<xs:element name="attribute" type="attributeType"/>
</xs:choice>
</xs:sequence>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="xcap-root" type="xs:anyURI" use="required"/>
<xs:anyAttribute processContents="lax"/>
</xs:complexType>
</xs:element>
<!-- xcap document type -->
<xs:complexType name="documentType">
<xs:choice minOccurs="0">
<xs:element name="body-not-changed" type="emptyType"/>
<xs:sequence minOccurs="0" maxOccurs="unbounded">
<xs:choice>
<xs:element name="add">
<xs:complexType mixed="true">
<xs:complexContent>
<xs:extension base="add">
<xs:anyAttribute processContents="lax"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:element>
<xs:element name="remove">
<xs:complexType>
<xs:complexContent>
<xs:extension base="remove">
<xs:anyAttribute processContents="lax"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:element>
<xs:element name="replace">
Rosenberg & Urpalainen Expires August 5, 2010 [Page 10]
Internet-Draft XCAP Diff Format February 2010
<xs:complexType mixed="true">
<xs:complexContent>
<xs:extension base="replace">
<xs:anyAttribute processContents="lax"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:element>
<xs:any namespace="##other" processContents="lax"/>
</xs:choice>
</xs:sequence>
</xs:choice>
<xs:attribute name="sel" type="xs:anyURI" use="required"/>
<xs:attribute name="new-etag" type="xs:string"/>
<xs:attribute name="previous-etag" type="xs:string"/>
<xs:anyAttribute processContents="lax"/>
</xs:complexType>
<!-- xcap element type -->
<xs:complexType name="elementType">
<xs:complexContent mixed="true">
<xs:restriction base="xs:anyType">
<xs:sequence>
<xs:any processContents="lax" namespace="##any"
minOccurs="0" maxOccurs="1"/>
</xs:sequence>
<xs:attribute name="sel" type="xs:string"
use="required"/>
<xs:attribute name="exists" type="xs:boolean"/>
<xs:anyAttribute processContents="lax"/>
</xs:restriction>
</xs:complexContent>
</xs:complexType>
<!-- xcap attribute type -->
<xs:complexType name="attributeType">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="sel" type="xs:string"
use="required"/>
<xs:attribute name="exists" type="xs:boolean"/>
<xs:anyAttribute processContents="lax"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<!-- empty type -->
<xs:complexType name="emptyType"/>
Rosenberg & Urpalainen Expires August 5, 2010 [Page 11]
Internet-Draft XCAP Diff Format February 2010
</xs:schema>
5. Example Document
The following is an example of a document compliant to the schema.
<?xml version="1.0" encoding="UTF-8"?>
<d:xcap-diff xmlns:d="urn:ietf:params:xml:ns:xcap-diff"
xmlns="urn:ietf:params:xml:ns:rls-services"
xcap-root="http://xcap.example.com/root/">
<d:document new-etag="7ahggs"
sel="resource-lists/users/sip:joe@example.com/coworkers"
previous-etag="8a77f8d"/>
<d:element sel="rls-services/users/sip:joe@example.com/index/~~
/*/service%5b@uri='sip:marketing@example.com'%5d"
xmlns:rl="urn:ietf:params:xml:ns:resource-lists"
><service uri="sip:marketing@example.com">
<list name="marketing">
<rl:entry uri="sip:joe@example.com"/>
<rl:entry uri="sip:sudhir@example.com"/>
</list>
<packages>
<package>presence</package>
</packages>
</service></d:element>
<d:attribute
sel="rls-services/users/sip:joe@example.com/index/~~/*/service/@uri"
>sip:marketing@example.com</d:attribute>
</d:xcap-diff>
This indicates that the document with URI "http://xcap.example.com/
root/resource-lists/users/sip:joe@example.com/coworkers" has changed.
Its previous entity tag is "8a77f8d" and its new one is "7ahggs" but
actual changes are not shown. The <service> element exists in the
rls-services "index" document and its full content is shown. Note
that the <service> element is attached with a default namespace
declaration within the original document. Similarly, a "uri"
attribute content is shown from the same "index" document as an
illustrative example.
Rosenberg & Urpalainen Expires August 5, 2010 [Page 12]
Internet-Draft XCAP Diff Format February 2010
6. Basic Requirements For a System Exchanging XCAP Diff Documents
Documents at an XCAP server are identified by URIs, and updated by
XCAP clients with HTTP (PUT and DELETE) methods. The XCAP server
assigns a new entity tag value for each document version. An entity
tag value is defined by the Section 3.11 of RFC 2616 [RFC2616]: an
entity tag MUST be unique across all versions of all entities
associated with a particular resource. These entity tags are used to
protect requests from making overriding changes when multiple XCAP
clients update the same XCAP document. An entity tag value can be
interpreted as a unique identifier to a specific version of an XCAP
document in its change history.
The entity tag values of XCAP resources enable also a reliable way to
update the locally cached XCAP resource copies in an XCAP diff
implementation. When a diff client applies XCAP diff document
changes, it MUST apply a resource state change only if entity tag
values match with octet-by-octet equivalence according to the table
defined in Figure 1. If a diff client notices inconsistencies and/or
errors when it applies reported resource changes, it SHOULD tear down
the session.
State changes of an XCAP document MUST be delivered reliably from a
diff notifier to a diff client, and a diff client MUST be able to
apply all changes of an XCAP document in the same chronological order
that occurred at an XCAP server. When using an unreliable transport
with retransmissions, the application protocol used with XCAP diff
MUST ensure that duplicates are dropped. If an XCAP diff delivery is
lost, the diff session MUST be torn down. Note that a diff notifier
can easily notice a lost notification when a diff client must respond
to each XCAP diff delivery.
A diff notifier doesn't necessarily report all of these XCAP document
updates with ETags, it MAY skip over some intermediate version of a
document, for example with rapidly changing resources. However, it
MUST always report changes consistently to a diff client so that it
can properly update the latest state (content and ETag) of its
locally cached resources.
As an example, an XCAP document is updated by different 'a', 'b'
and 'c' versions identified with the same corresponding ETag
values in a relatively short period. The first reported
notification contains the 'a' "new-tag" information (no "previous-
etag" attribute), and the diff notifier decides to skip the update
notification identified by the 'b' ETag value. The second
notification to a diff client MUST then contain the 'a' "previous-
etag" and 'c' "new-etag" values with optional corresponding
content changes (from version 'a' to 'c').
Rosenberg & Urpalainen Expires August 5, 2010 [Page 13]
Internet-Draft XCAP Diff Format February 2010
Since XCAP documents are typically confidential, diff notifiers MUST
obey the XCAP authorization rules. In practice, this means following
the read privilege rules of XCAP resources when notifying changes to
authenticated diff clients. Transport SHOULD be secured by
encryption.
Note: This format specification doesn't define how to select the
resources whose differences a diff notifier should report. It
also doesn't define whether actual content changes should be
reported. Typically however, a diff client starts a session by
sending a resource listing request. Then it compares the remote
resource listings with locally cached ones, and probably downloads
those resources which aren't locally cached, or whose entity tags
differ. When a diff client receives an XCAP diff with a
"previous-etag" value that matches its current cached copy of a
document, it can apply the diffs to the cached copy. As it takes
some time to download reference documents, and diff notifications
appear after actual resource state changes, several round-trips
may be needed before a full synchronization is achieved,
especially with rapidly changing resources.
7. Security Considerations
XCAP diff documents can include changes from one version of a
document to another version. As a consequence, if the document
itself is sensitive and requires confidentiality, integrity or
authentication, then the same applies to the XCAP diff format.
Therefore, protocols which transport XCAP diff documents must provide
sufficient security capabilities for transporting the document
itself. Confidential XCAP documents are typically transported using
TLS-encrypted [RFC5246] communication; see RFC 4825 [RFC4825] for
further security details.
When this format is used to report content changes of XCAP documents,
all security considerations of RFC 5261 [RFC5261] apply. Very
frequent updates of XCAP documents and/or many diff clients per
subscribed resource impose a Denial-of-Service attack possibility to
the servers processing XCAP diff documents. An efficient patch
processing and throttling can however, decrease the required overall
processings and transactions.
The SIP event package framework specified in RFC 3265 [RFC3265] is
the most typical use-case for this format. Then an end-to-end SIP
encryption mechanism, such as S/MIME described in Section 26.2.4 of
RFC 3261 [RFC3261], SHOULD be used. If that is not available, it is
RECOMMENDED that TLS [RFC5246] be used between elements to provide
hop-by-hop authentication and encryption mechanisms described in
Rosenberg & Urpalainen Expires August 5, 2010 [Page 14]
Internet-Draft XCAP Diff Format February 2010
Section 26.2.2 "SIPS URI Scheme" and Section 26.3.2.2 "Interdomain
Requests" of RFC 3261 [RFC3261]. Event packages MAY also have other
specific threats which MUST be considered on an application-by-
application basis.
8. IANA Considerations
There are several IANA considerations associated with this
specification.
8.1. application/xcap-diff+xml MIME Type
MIME media type name: application
MIME subtype name: xcap-diff+xml
Mandatory parameters: none
Optional parameters: Same as charset parameter application/xml as
specified in RFC 3023 [RFC3023].
Encoding considerations: Same as encoding considerations of
application/xml as specified in RFC 3023 [RFC3023].
Security considerations: See Section 10 of RFC 3023 [RFC3023] and
Section 7 of RFCXXXX [[NOTE TO RFC-EDITOR/IANA: Please replace
XXXX with the RFC number of this specification.]].
Interoperability considerations: none.
Published specification: This document.
Applications which use this media type: This document type has
been used to support manipulation of resource lists [RFC4826]
using XCAP.
Additional Information:
Magic Number: None
File Extension: .xdf
Macintosh file type code: "TEXT"
Rosenberg & Urpalainen Expires August 5, 2010 [Page 15]
Internet-Draft XCAP Diff Format February 2010
Personal and email address for further information: Jonathan
Rosenberg, jdrosen@jdrosen.net
Intended usage: COMMON
Author/Change controller: The IETF.
8.2. URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:xcap-diff
This section registers a new XML namespace, as per the guidelines in
[RFC3688]
URI: The URI for this namespace is
urn:ietf:params:xml:ns:xcap-diff.
Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org),
Jonathan Rosenberg (jdrosen@jdrosen.net).
XML:
BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>XCAP Diff Namespace</title>
</head>
<body>
<h1>Namespace for XCAP Diff</h1>
<h2>urn:ietf:params:xml:ns:xcap-diff</h2>
<p>See <a href="[URL of published RFC]">RFCXXXX[[NOTE
TO IANA/RFC-EDITOR: Please replace XXXX with the RFC number of this
specification.]]</a>.</p>
</body>
</html>
END
8.3. Schema Registration
This section registers a new XML schema per the procedures in
[RFC3688].
Rosenberg & Urpalainen Expires August 5, 2010 [Page 16]
Internet-Draft XCAP Diff Format February 2010
URI: urn:ietf:params:xml:schema:xcap-diff
Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org),
Jonathan Rosenberg (jdrosen@jdrosen.net).
The XML for this schema can be found as the sole content of
Section 4.
9. Acknowledgments
The authors would like to thank Pavel Dostal, Jeroen van Bemmel,
Martin Hynar, Anders Lindgren, Mary Barnes, Ben Campbell, Francis
Dupont, David Harrington, Alexey Melnikov, Dan Romascanu and Robert
Sparks for their valuable comments.
10. References
10.1. Normative References
[W3C.REC-xml-20060816]
Maler, E., Paoli, J., Bray, T., Yergeau, F., and C.
Sperberg-McQueen, "Extensible Markup Language (XML) 1.0
(Fourth Edition)", World Wide Web Consortium
Recommendation REC-xml-20060816, August 2006,
<http://www.w3.org/TR/2006/REC-xml-20060816>.
[W3C.REC-xml-c14n-20010315]
Boyer, J., "Canonical XML Version 1.0", World Wide Web
Consortium Recommendation REC-xml-c14n-20010315,
March 2001,
<http://www.w3.org/TR/2001/REC-xml-c14n-20010315>.
[W3C.REC-xml-names-20060816]
Hollander, D., Bray, T., Layman, A., and R. Tobin,
"Namespaces in XML 1.0 (Second Edition)", World Wide Web
Consortium Recommendation REC-xml-names-20060816,
August 2006,
<http://www.w3.org/TR/2006/REC-xml-names-20060816>.
[RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Rosenberg & Urpalainen Expires August 5, 2010 [Page 17]
Internet-Draft XCAP Diff Format February 2010
Types", RFC 3023, January 2001.
[RFC2648] Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
August 1999.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4825] Rosenberg, J., "The Extensible Markup Language (XML)
Configuration Access Protocol (XCAP)", RFC 4825, May 2007.
[RFC5261] Urpalainen, J., "An Extensible Markup Language (XML) Patch
Operations Framework Utilizing XML Path Language (XPath)
Selectors", RFC 5261, September 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
10.2. Informative References
[I-D.ietf-sip-xcapevent]
Urpalainen, J. and D. Willis, "An Extensible Markup
Language (XML) Configuration Access Protocol (XCAP) Diff
Event Package", draft-ietf-sip-xcapevent-08 (work in
progress), July 2009.
[RFC2778] Day, M., Rosenberg, J., and H. Sugano, "A Model for
Presence and Instant Messaging", RFC 2778, February 2000.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific
Event Notification", RFC 3265, June 2002.
[RFC4662] Roach, A., Campbell, B., and J. Rosenberg, "A Session
Initiation Protocol (SIP) Event Notification Extension for
Resource Lists", RFC 4662, August 2006.
[RFC4826] Rosenberg, J., "Extensible Markup Language (XML) Formats
for Representing Resource Lists", RFC 4826, May 2007.
[RFC4483] Burger, E., "A Mechanism for Content Indirection in
Rosenberg & Urpalainen Expires August 5, 2010 [Page 18]
Internet-Draft XCAP Diff Format February 2010
Session Initiation Protocol (SIP) Messages", RFC 4483,
May 2006.
Appendix A. Informative Examples
These informative examples illustrate basic features of XCAP diff
format.
The following documents exist at an XCAP server (xcap.example.com)
with an imaginary "tests" application usage (there's no default
document namespace defined in this imaginary application usage).
http://xcap.example.com/tests/users/sip:joe@example.com/index:
<?xml version="1.0" encoding="UTF-8"?>
<doc id="bar">
<note>This is a sample document</note>
</doc>
and then
http://xcap.example.com/tests/users/sip:john@example.com/index:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<note>This is another sample document</note>
</doc>
A.1. Indicating Existing, Changed or Removed Documents
Firstly, an XCAP diff document can indicate what documents exist in a
collection. An XCAP diff document may then be:
Rosenberg & Urpalainen Expires August 5, 2010 [Page 19]
Internet-Draft XCAP Diff Format February 2010
<?xml version="1.0" encoding="UTF-8"?>
<xcap-diff xmlns="urn:ietf:params:xml:ns:xcap-diff"
xcap-root="http://xcap.example.com/">
<document new-etag="7ahggs"
sel="tests/users/sip:joe@example.com/index"/>
<document new-etag="terteer"
sel="tests/users/sip:john@example.com/index"/>
</xcap-diff>
This listing indicates current ETags of existing documents and their
relative URIs.
Let's say that Joe adds a new document to his collection:
PUT /tests/users/sip:joe@example.com/another_document HTTP/1.1
Host: xcap.example.com
....
Content-Type: application/xml
Content-Length: [XXX]
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<note>This is another sample document</note>
</doc>
The requests result header has an HTTP ETag "terteer" for this new
document.
Then an XCAP diff document may then indicate only the creation of
this single new document:
<?xml version="1.0" encoding="UTF-8"?>
<xcap-diff xmlns="urn:ietf:params:xml:ns:xcap-diff"
xcap-root="http://xcap.example.com/">
<document new-etag="terteer"
sel="tests/users/sip:joe@example.com/another_document"/>
</xcap-diff>
Rosenberg & Urpalainen Expires August 5, 2010 [Page 20]
Internet-Draft XCAP Diff Format February 2010
A "new-etag" without a "previous-etag" attribute indicates a creation
of a new document.
Then Joe decides to modify an existing resource:
PUT /tests/users/sip:joe@example.com/another_document HTTP/1.1
Host: xcap.example.com
....
Content-Type: application/xml
Content-Length: [XXX]
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<note>This is a modified document</note>
</doc>
The reported new HTTP ETag is "huwiias".
Then an XCAP diff document may be:
<?xml version="1.0" encoding="UTF-8"?>
<xcap-diff xmlns="urn:ietf:params:xml:ns:xcap-diff"
xcap-root="http://xcap.example.com/">
<document previous-etag="terteer" new-etag="huwiias"
sel="tests/users/sip:joe@example.com/another_document"/>
</xcap-diff>
Both "previous-etag" and "new-etag" attributes signal that a
modification has happened to a resource, but actual changes are not
shown.
Let's say that Joe then removes a document from his collection:
DELETE /tests/users/sip:joe@example.com/another_document HTTP/1.1
Host: xcap.example.com
This HTTP DELETE request results in the unlinking of the resource,
and the XCAP diff may be:
Rosenberg & Urpalainen Expires August 5, 2010 [Page 21]
Internet-Draft XCAP Diff Format February 2010
<?xml version="1.0" encoding="UTF-8"?>
<xcap-diff xmlns="urn:ietf:params:xml:ns:xcap-diff"
xcap-root="http://xcap.example.com/">
<document previous-etag="huwiias"
sel="tests/users/sip:joe@example.com/another_document"/>
</xcap-diff>
Thus a "previous-etag" without "new-etag" attribute indicates the
removal of a resource.
A.2. Indicating Actual Changes of Documents
Secondly, XCAP diff documents are capable of showing actual changes
to documents with [RFC5261] patching semantics.
Now Joe's XCAP client utilizes XCAP patching capability to add a new
element to a document:
PUT /tests/users/sip:joe@example.com/index/~~/doc/foo HTTP/1.1
Host: xcap.example.com
....
Content-Type: application/xcap-el+xml
Content-Length: [XXX]
<foo>this is a new element</foo>
Since the insertion of the element is successful, Joe's XCAP client
receives the new HTTP ETag "fgherhryt3" of the updated "index"
document.
Immediately thereafter, Joe's XCAP client issues another HTTP request
(this request could even be pipe-lined):
PUT /tests/users/sip:joe@example.com/index/~~/doc/bar HTTP/1.1
Host: xcap.example.com
....
Content-Type: application/xcap-el+xml
Content-Length: [XXX]
<bar>this is a bar element
Rosenberg & Urpalainen Expires August 5, 2010 [Page 22]
Internet-Draft XCAP Diff Format February 2010
</bar>
The reported new HTTP ETag of "index" is now "dgdgdfgrrr".
And then Joe's XCAP client issues yet another HTTP request:
PUT /tests/users/sip:joe@example.com/index/~~/doc/foobar HTTP/1.1
Host: xcap.example.com
....
Content-Type: application/xcap-el+xml
Content-Length: [XXX]
<foobar>this is a foobar element</foobar>
The reported new ETag of "index" is now "63hjjsll".
XCAP diff format document may then indicate these XCAP Component
changes by:
<?xml version="1.0" encoding="UTF-8"?>
<d:xcap-diff xmlns:d="urn:ietf:params:xml:ns:xcap-diff"
xcap-root="http://xcap.example.com/">
<d:document previous-etag="7ahggs3"
sel="tests/users/sip:joe@example.com/index"
new-etag="63hjjsll">
<d:add sel="*"
><foo>this is a new element</foo><bar>this is a bar element
</bar><foobar>this is a foobar element</foobar></d:add>
</d:document>
</d:xcap-diff>
Note how several XCAP component modifications were aggregated
together, and full history information got lost.
Alternatively, the content could have been:
Rosenberg & Urpalainen Expires August 5, 2010 [Page 23]
Internet-Draft XCAP Diff Format February 2010
<?xml version="1.0" encoding="UTF-8"?>
<d:xcap-diff xmlns:d="urn:ietf:params:xml:ns:xcap-diff"
xcap-root="http://xcap.example.com/">
<d:document previous-etag="7ahggs"
sel="tests/users/sip:joe@example.com/index"
new-etag="fgherhryt3">
<d:add sel="*"
><foo>this is a new element</foo></d:add></d:document>
<d:document previous-etag="fgherhryt3"
sel="tests/users/sip:joe@example.com/index"
new-etag="dgdgdfgrrr">
<d:add sel="*"
><bar>this is a bar element
</bar></d:add></d:document>
<d:document previous-etag="dgdgdfgrrr"
sel="tests/users/sip:joe@example.com/index"
new-etag="63hjjsll">
<d:add sel="*"
><foobar>this is a foobar element</foobar></d:add></d:document>
</d:xcap-diff>
This shows the full ETag change history of a document, and ETags
change chronologically in the reported XML document order.
A.3. Indicating XCAP Component Contents
Lastly, the XCAP diff format can also indicate the existing full
contents of XCAP Components, i.e. elements or attributes:
<?xml version="1.0" encoding="UTF-8"?>
<d:xcap-diff xmlns:d="urn:ietf:params:xml:ns:xcap-diff"
xcap-root="http://xcap.example.com/">
<d:attribute sel="tests/users/sip:joe@example.com/index/~~/doc/@id"
>bar</d:attribute>
<d:element sel="tests/users/sip:joe@example.com/index/~~/*/foo"
><foo>this is a new element</foo></d:element>
</d:xcap-diff>
Rosenberg & Urpalainen Expires August 5, 2010 [Page 24]
Internet-Draft XCAP Diff Format February 2010
Note that the HTTP ETag value of the new document is not shown as it
is irrelevant for this use-case.
Then Joe's XCAP client removes the "id" attribute:
DELETE /tests/users/sip:joe@example.com/index/~~/doc/@id HTTP/1.1
Host: xcap.example.com
....
Content-Length: 0
And the XCAP diff document may then be:
<?xml version="1.0" encoding="UTF-8"?>
<xcap-diff xmlns="urn:ietf:params:xml:ns:xcap-diff"
xcap-root="http://xcap.example.com/">
<attribute sel="tests/users/sip:joe@example.com/index/~~/doc/@id"
exists="0"/>
</xcap-diff>
This indicates that the subscribed attribute was removed from the
document. The element content in this use-case may be discarded from
the XCAP diff document, for example when the size of XCAP diff
document would be impractically large to the transport layer.
Authors' Addresses
Jonathan Rosenberg
Cisco
Edison, NJ
USA
Email: jdrosen@cisco.com
URI: http://www.jdrosen.net
Rosenberg & Urpalainen Expires August 5, 2010 [Page 25]
Internet-Draft XCAP Diff Format February 2010
Jari Urpalainen
Nokia
Itamerenkatu 11-13
Helsinki 00180
Finland
Phone: +358 7180 37686
Email: jari.urpalainen@nokia.com
Rosenberg & Urpalainen Expires August 5, 2010 [Page 26]