Network Working Group P. Saint-Andre
Internet-Draft Jabber Software Foundation
Expires: February 20, 2004 T. Bamonti
Jabber, Inc.
August 22, 2003
XMPP CPIM Mapping
draft-ietf-xmpp-cpim-02
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes a mapping of the Extensible Messaging and
Presence Protocol (XMPP) to the Common Presence and Instant Messaging
(CPIM) specifications.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Conventions Used in this Document . . . . . . . . . . . . 5
1.4 Discussion Venue . . . . . . . . . . . . . . . . . . . . . 5
1.5 Intellectual Property Notice . . . . . . . . . . . . . . . 5
2. Approach . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Mapping of Instant Messages . . . . . . . . . . . . . . . 7
3.1 Identification of Instant Inboxes . . . . . . . . . . . . 7
3.2 Message Syntax Mapping from XMPP to CPIM Specifications . 7
3.2.1 From Address . . . . . . . . . . . . . . . . . . . . . . . 7
3.2.2 To Address . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2.3 CPIM Courtesy Copy . . . . . . . . . . . . . . . . . . . . 8
3.2.4 XMPP Stanza ID . . . . . . . . . . . . . . . . . . . . . . 8
3.2.5 XMPP Message Type . . . . . . . . . . . . . . . . . . . . 8
3.2.6 XMPP Message Thread . . . . . . . . . . . . . . . . . . . 9
3.2.7 CPIM DateTime Header . . . . . . . . . . . . . . . . . . . 9
3.2.8 Message Subject . . . . . . . . . . . . . . . . . . . . . 9
3.2.9 CPIM Header Extensions . . . . . . . . . . . . . . . . . . 9
3.2.10 CPIM Required Headers . . . . . . . . . . . . . . . . . . 10
3.2.11 MSGFMT MIME Content-type . . . . . . . . . . . . . . . . . 10
3.2.12 MSGFMT MIME Content-ID . . . . . . . . . . . . . . . . . . 10
3.2.13 Message Body . . . . . . . . . . . . . . . . . . . . . . . 10
3.2.14 XMPP Message Extensions . . . . . . . . . . . . . . . . . 11
3.3 Message Syntax Mapping from CPIM Specifications to XMPP . 11
3.3.1 From Address . . . . . . . . . . . . . . . . . . . . . . . 11
3.3.2 To Address . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3.3 CPIM Courtesy Copy . . . . . . . . . . . . . . . . . . . . 12
3.3.4 XMPP Message Type . . . . . . . . . . . . . . . . . . . . 12
3.3.5 CPIM DateTime Header . . . . . . . . . . . . . . . . . . . 12
3.3.6 Message Subject . . . . . . . . . . . . . . . . . . . . . 12
3.3.7 CPIM Header Extensions . . . . . . . . . . . . . . . . . . 13
3.3.8 CPIM Required Headers . . . . . . . . . . . . . . . . . . 13
3.3.9 MSGFMT MIME Content-type . . . . . . . . . . . . . . . . . 13
3.3.10 MSGFMT MIME Content-ID . . . . . . . . . . . . . . . . . . 13
3.3.11 Message Body . . . . . . . . . . . . . . . . . . . . . . . 14
4. Mapping of Presence . . . . . . . . . . . . . . . . . . . 15
4.1 Identification of Presentities . . . . . . . . . . . . . . 15
4.2 Presence Syntax Mapping from XMPP to CPIM Specifications . 15
4.2.1 From Address . . . . . . . . . . . . . . . . . . . . . . . 15
4.2.2 To Address . . . . . . . . . . . . . . . . . . . . . . . . 16
4.2.3 CPIM Courtesy Copy . . . . . . . . . . . . . . . . . . . . 17
4.2.4 XMPP Stanza ID . . . . . . . . . . . . . . . . . . . . . . 17
4.2.5 CPIM DateTime Header . . . . . . . . . . . . . . . . . . . 17
4.2.6 CPIM Subject Header . . . . . . . . . . . . . . . . . . . 17
4.2.7 CPIM Header Extensions . . . . . . . . . . . . . . . . . . 17
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4.2.8 CPIM Required Headers . . . . . . . . . . . . . . . . . . 18
4.2.9 PIDF MIME Content-type . . . . . . . . . . . . . . . . . . 18
4.2.10 PIDF MIME Content-ID . . . . . . . . . . . . . . . . . . . 18
4.2.11 XMPP Presence Type . . . . . . . . . . . . . . . . . . . . 18
4.2.12 XMPP Show Element . . . . . . . . . . . . . . . . . . . . 19
4.2.13 XMPP Status Element . . . . . . . . . . . . . . . . . . . 20
4.2.14 PIDF Contact Element . . . . . . . . . . . . . . . . . . . 21
4.2.15 Presence Priority . . . . . . . . . . . . . . . . . . . . 21
4.2.16 PIDF Timestamp Element . . . . . . . . . . . . . . . . . . 22
4.2.17 XMPP Presence Extensions . . . . . . . . . . . . . . . . . 22
4.3 Presence Syntax Mapping from CPIM Specifications to XMPP . 22
4.3.1 From Address . . . . . . . . . . . . . . . . . . . . . . . 22
4.3.2 To Address . . . . . . . . . . . . . . . . . . . . . . . . 23
4.3.3 CPIM Courtesy Copy . . . . . . . . . . . . . . . . . . . . 23
4.3.4 CPIM DateTime Header . . . . . . . . . . . . . . . . . . . 23
4.3.5 CPIM Subject Header . . . . . . . . . . . . . . . . . . . 24
4.3.6 CPIM Header Extensions . . . . . . . . . . . . . . . . . . 24
4.3.7 CPIM Required Headers . . . . . . . . . . . . . . . . . . 24
4.3.8 PIDF MIME Content-type . . . . . . . . . . . . . . . . . . 24
4.3.9 PIDF MIME Content-ID . . . . . . . . . . . . . . . . . . . 24
4.3.10 PIDF Basic Presence Status . . . . . . . . . . . . . . . . 25
4.3.11 PIDF Extended Status Information . . . . . . . . . . . . . 26
4.3.12 PIDF Note Element . . . . . . . . . . . . . . . . . . . . 26
4.3.13 PIDF Contact Element . . . . . . . . . . . . . . . . . . . 27
4.3.14 Presence Priority . . . . . . . . . . . . . . . . . . . . 28
4.3.15 PIDF Timestamp Element . . . . . . . . . . . . . . . . . . 28
5. XMPP-CPIM Gateway as Presence Service . . . . . . . . . . 29
5.1 Requesting a Subscription . . . . . . . . . . . . . . . . 29
5.2 Receiving a Subscription Request . . . . . . . . . . . . . 30
5.3 Subscription Durations . . . . . . . . . . . . . . . . . . 31
5.4 The Notify Operation . . . . . . . . . . . . . . . . . . . 31
5.4.1 Multiple Resources . . . . . . . . . . . . . . . . . . . . 32
5.4.2 Zero Resources . . . . . . . . . . . . . . . . . . . . . . 32
5.5 Unsubscribing . . . . . . . . . . . . . . . . . . . . . . 33
5.6 Cancelling a Subscription . . . . . . . . . . . . . . . . 33
6. Mapping of Character Encodings . . . . . . . . . . . . . . 35
7. Security Considerations . . . . . . . . . . . . . . . . . 36
Normative References . . . . . . . . . . . . . . . . . . . 37
Informative References . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 38
A. Revision History . . . . . . . . . . . . . . . . . . . . . 39
A.1 Changes from draft-ietf-xmpp-cpim-01 . . . . . . . . . . . 39
A.2 Changes from draft-ietf-xmpp-cpim-00 . . . . . . . . . . . 39
Intellectual Property and Copyright Statements . . . . . . 40
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1. Introduction
1.1 Overview
The Instant Messaging and Presence (IMPP) Working Group has defined
an abstract framework for interoperability among instant messaging
(IM) and presence systems that are compliant with RFC 2779 [1]. This
framework is commonly called Common Presence and Instant Messaging or
"CPIM". The CPIM specifications include a Common Profile for Instant
Messaging [2] (also called CPIM), a Common Profile for Presence [3]
(CPP), a CPIM Message Format [4] (MSGFMT), and a Common Presence
Information Data Format [5] (PIDF). (Note: to prevent confusion,
Common Presence and Instant Messaging is referred to herein
collectively as "the CPIM specifications", whereas the Common Profile
for Instant Messaging is referred to as "CPIM". However, the term
"XMPP-CPIM Gateway" is used to refer to a gateway between an XMPP
service and a non-XMPP service, where the common format is defined by
the CPIM specifications.)
This document describes how the Extensible Messaging and Presence
Protocol (XMPP Core [6], XMPP IM [7]) maps to the abstract model
contained in the CPIM specifications, mainly for the purpose of
establishing gateways between XMPP services and non-XMPP services
that conform to RFC 2779 [1]. Such gateways may be established to
interpret the protocols of one service and translate them into the
protocols of the other service. We can visualize this relationship as
follows:
+-------------+ +-------------+ +------------+
| | | | | |
| XMPP | | XMPP-CPIM | | Non-XMPP |
| Service | <----> | Gateway | <----> | Service |
| | | | | |
+-------------+ +-------------+ +------------+
This document defines a mapping for use by a gateway that translates
between XMPP and a non-XMPP protocol via the CPIM specifications.
Such a gateway is not an intermediate hop on a network of non-XMPP
servers (whose native formats may or may not be defined by the CPIM
specifications), but a dedicated translator between XMPP and a
non-XMPP protocol, where the CPIM specifications define the common
formats into which the protocols are translated for purposes of
interworking.
The mapping defined herein applies to instant messages and presence
information that are not encrypted or signed for end-to-end security.
For information about secure communications to or from an XMPP
service through an XMPP-CPIM gateway, refer to End-to-End Object
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Encryption in XMPP [8].
1.2 Terminology
This memo inherits vocabulary defined in RFC 2778 [9]. Terms such as
CLOSED, INSTANT INBOX, INSTANT MESSAGE, OPEN , PRESENCE SERVICE,
PRESENTITY, SUBSCRIPTION, and WATCHER are used in the same meaning as
defined therein.
This memo also inherits vocabulary defined in XMPP Core [6]. Terms
such as ENTITY, JID, NODE IDENTIFIER, DOMAIN IDENTIFIER, RESOURCE
IDENTIFIER, MESSAGE STANZA, and PRESENCE STANZA are used in the same
meaning as defined therein.
1.3 Conventions Used in this Document
The capitalized 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 [10].
1.4 Discussion Venue
The authors welcome discussion and comments related to the topics
presented in this document. The preferred forum is the
<xmppwg@jabber.org> mailing list, for which archives and subscription
information are available at <http://www.jabber.org/cgi-bin/mailman/
listinfo/xmppwg/>.
1.5 Intellectual Property Notice
This document is in full compliance with all provisions of Section 10
of RFC 2026. Parts of this specification use the term "jabber" for
identifying namespaces and other protocol syntax. Jabber[tm] is a
registered trademark of Jabber, Inc. Jabber, Inc. grants permission
to the IETF for use of the Jabber trademark in association with this
specification and its successors, if any.
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2. Approach
XMPP and CPIM are distinctly foreign technologies. Therefore, care
must be taken in mapping between XMPP and the abstract syntax defined
by the CPIM specifications.
At root, XMPP is a data transport protocol for streaming XML
fragments (called "stanzas") between any two endpoints on the
network; message and presence stanzas are two of the core data
elements defined in XMPP and are often used to exchange instant
messages and presence information between IM users (although the
inherent extensibility of XML enables applications to use the general
semantics of these stanza types for other purposes). XMPP is not
based on MIME [11]; instead, XMPP Core [6] defines XML schemas for
both message and presence stanzas (for example, the <body/> child of
a message stanza contains XML character data that is usually intended
to be read by a human user).
The CPIM specifications provide common formats for instant messaging
and presence through two MIME [11] content-types: "Message/CPIM" for
messages (MSGFMT [4]) and "application/pidf+xml" for presence (PIDF
[5]). The syntax of "Message/CPIM" objects is similar to but stricter
than that of RFC 2822 [12], and includes the ability to include
arbitrary MIME media types [13]. By contrast, each "application/
pidf+xml" object is a complete XML document whose structure is
defined by an XML schema.
The approach taken herein is to specify mappings from XMPP elements
and attributes to the headers and MIME formats defined by MSGFMT [4]
and PIDF [5] in order to comply with the semantics defined by CPIM
[2] and CPP [3]. Naturally, mappings in the opposite direction are
provided as well.
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3. Mapping of Instant Messages
This section describes how a gateway SHOULD map instant messages
between an XMPP service and a non-XMPP service using a "Message/CPIM"
object as the bearer of encapsulated text content in order to comply
with the instant messaging semantics defined by CPIM [2].
3.1 Identification of Instant Inboxes
There is a one-to-one relationship between an XMPP entity and a CPIM
instant inbox when the JID of the entity contains only a node
identifier and domain identifier, and the node identifier uniquely
corresponds to an IM user who possesses an account on an XMPP server.
However, the syntax for addressing an instant inbox is specified as
including the 'im:' URI scheme, whereas an XMPP address does not
include that scheme, so any mapping between an instant inbox address
and a JID must add or remove the 'im:' URI scheme as appropriate.
3.2 Message Syntax Mapping from XMPP to CPIM Specifications
This section defines the mapping of syntax primitives from XMPP
message stanzas to "Message/CPIM" objects with encapsulated text
content.
3.2.1 From Address
The 'from' attribute of an XMPP message stanza maps to the 'From'
header of a "Message/CPIM" object. In XMPP, the sender MUST NOT
include a 'from' attribute; instead, the sender's server stamps the
"from" address and sets its value to the full authzid (including
resource identifier) provided by the client when authenticating. Thus
an XMPP-CPIM gateway will receive from the sender's XMPP server a
message stanza containing a "from" address of the form <node@domain/
resource>. To map the 'from' attribute of an XMPP message stanza to
the 'From' header of a "Message/CPIM" object, the gateway MUST remove
the resource identifier, MUST append the "im:" Instant Messaging URI
scheme to the front of the address, and MAY include a CPIM
"Formal-name" for the sender (if known).
Example: From Address Mapping
XMPP 'from' attribute
<message from='juliet@capulet.com/balcony'>
...
</message>
CPIM 'From' header
From: Juliet Capulet <im:juliet@capulet.com>
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3.2.2 To Address
The 'to' attribute of an XMPP message stanza maps to the 'To' header
of a "Message/CPIM" object. In XMPP, the sender SHOULD include a 'to'
attribute on a message stanza, and MUST include it if the message is
intended for delivery to another user. Thus an XMPP-CPIM gateway will
receive from the sender's XMPP server a message stanza containing a
"to" address of the form <node@domain> or <node@domain/resource>. To
map the 'to' attribute of an XMPP message stanza to the 'To' header
of a "Message/CPIM" object, the gateway MUST remove the resource
identifier (if included), MUST append the "im:" Instant Messaging URI
scheme to the front of the address, and MAY include a CPIM
"Formal-name" for the recipient (if known).
Example: To Address Mapping
XMPP 'to' attribute
<message to='romeo@montague.net/orchard'>
...
</message>
CPIM 'To' header
To: Romeo Montague <im:romeo@montague.net>
3.2.3 CPIM Courtesy Copy
The core XMPP specification does not include syntax for specifying a
"courtesy copy" (non-primary addressee) for a message stanza.
Therefore, an XMPP-CPIM gateway MUST NOT generate the 'cc' header of
a "Message/CPIM" object.
3.2.4 XMPP Stanza ID
An XMPP message stanza MAY possess an 'id' attribute, which is used
by the sending application for the purpose of tracking stanzas. There
is no mapping of an XMPP 'id' attribute to a "Message/CPIM" header,
common MIME features, or encapsulated text content. Therefore if an
XMPP stanza received by an XMPP-CPIM gateway possesses an 'id'
attribute, the gateway SHOULD ignore the value provided.
3.2.5 XMPP Message Type
An XMPP message stanza MAY possess a 'type' attribute, which is used
by the sending application to capture the conversational context of
the message. There is no mapping of an XMPP 'type' attribute to a
"Message/CPIM" header, common MIME features, or encapsulated text
content. Therefore if an XMPP stanza received by an XMPP-CPIM gateway
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possesses a 'type' attribute, the gateway SHOULD ignore the value
provided.
3.2.6 XMPP Message Thread
An XMPP message stanza MAY contain a <thread/> child element to
specify the conversation thread in which the message is situated.
There is no mapping of an XMPP <thread/> element to a "Message/CPIM"
header, common MIME features, or encapsulated text content. Therefore
if an XMPP message stanza received by an XMPP-CPIM gateway contains a
<thread/> child element, the gateway SHOULD ignore the value
provided.
3.2.7 CPIM DateTime Header
The core XMPP specification does not include syntax for specifying
the datetime at which a message stanza was sent. However, an
XMPP-CPIM gateway MAY include a 'DateTime' header in the "Message/
CPIM" object it generates, the value of which SHOULD be the datetime
at which the message stanza was received for processing by the
gateway.
3.2.8 Message Subject
An XMPP message stanza MAY include a <subject/> child element. If
included, it maps to the 'Subject' header of a "Message/CPIM" object.
The <subject/> element MAY include an 'xml:lang' attribute specifying
the language in which the subject is written. To map the XMPP
<subject/> element to the 'Subject' header of a "Message/CPIM"
object, the gateway SHOULD simply map the XMPP CDATA to the value of
the 'Subject' header. If an 'xml:lang' attribute is provided, it MUST
be mapped by including ';lang=tag' after the header name and colon,
where 'tag' is the value of the 'xml:lang' attribute.
Example: Subject Mapping
XMPP <subject/> element
<subject>Hi!</subject>
<subject xml:lang='cz'>Ahoj!</subject>
CPIM 'Subject' header
Subject: Hi!
Subject:;lang=cz Ahoj!
3.2.9 CPIM Header Extensions
A "Message/CPIM" object MAY include an optional 'NS' header to
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specify the namespace of a feature extension. An XMPP-CPIM gateway
SHOULD NOT generate such headers.
3.2.10 CPIM Required Headers
A "Message/CPIM" object MAY include an optional 'Required' header to
specify mandatory-to-recognize features. An XMPP-CPIM gateway SHOULD
NOT generate such headers.
3.2.11 MSGFMT MIME Content-type
RFC 2045 [11] specifies that the default Content-type of a MIME
object is "Content-type: text/plain; charset=us-ascii". Because XMPP
uses a different character encoding (either UTF-8 or UTF-16 depending
on stream negotiation), the encapsulated MIME object generated by an
XMPP-CPIM gateway MUST set the 'Content-type' header for that object.
The "Content-type" MUST be set to "text/plain" and the charset MUST
be set to the character encoding negotiated for the XML stream used
by the sender, i.e., either UTF-8 or UTF-16.
Example: Content-type for Encapsulated Object
Content-type: text/plain; charset=utf-8
3.2.12 MSGFMT MIME Content-ID
RFC 2045 [11] specifies that the Content-ID is OPTIONAL for MIME
objects. While an XMPP-CPIM gateway MAY generate a Content-ID for
encapsulated MIME objects, it is NOT REQUIRED to do so. If included,
Content-ID values MUST be generated to be world-unique.
Example: Content-ID for Encapsulated Object
Content-ID: <123456789@montague.net>
3.2.13 Message Body
The <body/> child element of an XMPP message stanza is used to
provide the primary meaning of the message. The CDATA of the XMPP
<body/> element maps to the encapsulated text message content.
Example: Message Body
XMPP message <body/>
<message>
<body>Wherefore art thou, Romeo?</body>
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</message>
Encapsulated MIME text content
Content-type: text/plain; charset=utf-8
Content-ID: <123456789@montague.net>
Wherefore art thou, Romeo?
3.2.14 XMPP Message Extensions
As defined in XMPP Core [6], an XMPP message stanza may contain
"extended" content in any namespace in order to supplement or extend
the semantics of the core message stanza. With the exception of
extended information qualified by the
'urn:ietf:params:xml:ns:xmpp-e2e' namespace as defined in End-to-End
Object Encryption in XMPP [8], an XMPP-CPIM gateway SHOULD ignore
such information and not pass it through the gateway to the intended
recipient. No mapping for such information is defined.
3.3 Message Syntax Mapping from CPIM Specifications to XMPP
This section defines the mapping of syntax primitives from "Message/
CPIM" objects with encapsualted text content to XMPP message stanzas.
3.3.1 From Address
The 'From' header of a "Message/CPIM" object maps to the 'from'
attribute of an XMPP message stanza. To map the CPIM 'From' header to
the XMPP 'from' attribute, the gateway MUST remove the "im:" Instant
Messaging URI scheme from the front of the address and MUST remove
the CPIM "Formal-name" (if provided).
Example: From Address Mapping
CPIM 'From' header
From: Romeo Montague <im:romeo@montague.net>
XMPP 'from' attribute
<message from='romeo@montague.net'>
...
</message>
3.3.2 To Address
The 'To' header of a "Message/CPIM" object maps to the 'to' attribute
of an XMPP message stanza. To map the CPIM 'To' header to the XMPP
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'to' attribute, the gateway MUST remove the "im:" Instant Messaging
URI scheme from the front of the address and MUST remove the CPIM
"Formal-name" (if provided). If the gateway possesses knowledge of
the resource identifier in use by the XMPP entity, the gateway MAY
append the resource identifier to the address.
Example: To Address Mapping
CPIM 'To' header
To: Juliet Capulet <im:juliet@capulet.com>
XMPP 'to' attribute
<message to='juliet@capulet.com/balcony'>
...
</message>
3.3.3 CPIM Courtesy Copy
The core XMPP specification does not include syntax for specifying a
"courtesy copy" (non-primary addressee) for a message stanza.
Therefore, if an XMPP-CPIM gateway receives a "Message/CPIM" object
that contains a 'cc' header, it MUST NOT pass that information on to
the XMPP recipient.
3.3.4 XMPP Message Type
MSGFMT does not possess the concept of a message type that can map to
the XMPP 'type' attribute for message stanzas. Therefore an XMPP-CPIM
gateway SHOULD NOT include the 'type' attribute on the messages it
sends to XMPP recipients.
3.3.5 CPIM DateTime Header
The core XMPP specification does not include syntax for specifying
the datetime at which a message stanza was sent. Therefore, if an
XMPP-CPIM gateway receives a "Message/CPIM" object that contains a
'DateTime' header, it SHOULD NOT pass that information on to the XMPP
recipient.
3.3.6 Message Subject
The 'Subject' header of a "Message/CPIM" object maps to the <subject/
> child element of an XMPP message stanza. The 'Subject' header MAY
specify the "lang" in which the subject is written. To map the CPIM
'Subject' header to the XMPP <subject/> element, the gateway SHOULD
simply map the value of the 'Subject' header to the XMPP CDATA. If
"lang" information is provided, it MUST be mapped to the 'xml:lang'
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attribute of the <subject/> element, where the value of the
'xml:lang' attribute is the the "tag" value supplied in the string
';lang=tag' included CPIM 'Subject' header name and colon.
Example: Subject Mapping
CPIM 'Subject' header
Subject: Hi!
Subject:;lang=cz Ahoj!
XMPP <subject/> element
<subject>Hi!</subject>
<subject xml:lang='cz'>Ahoj!</subject>
3.3.7 CPIM Header Extensions
"Message/CPIM" objects MAY include an optional 'NS' header to specify
the namespace of a feature extension. An XMPP-CPIM gateway MUST NOT
pass such headers through to the XMPP recipient, and no mapping for
such headers is defined.
3.3.8 CPIM Required Headers
"Message/CPIM" objects MAY include an optional 'Required' header to
specify mandatory-to-recognize features. An XMPP-CPIM gateway MUST
NOT pass such headers through to the XMPP recipient, and no mapping
for such headers is defined.
3.3.9 MSGFMT MIME Content-type
CPIM [4] specifies that a "Message/CPIM" object MAY contain any
arbitrary MIME content. However, support for arbitrary content types
is not a requirement in XMPP; in particular, the <body/> child
element of an XMPP message stanza MUST contain XML character data
only. Therefore, an XMPP-CPIM gateway MUST NOT map to an XMPP message
stanza a "Message/CPIM" object whose encapsulated MIME object has a
Content-type other than "text/plain" (with the exception of
multi-part MIME objects used for End-to-End Object Encryption in XMPP
[8]).
3.3.10 MSGFMT MIME Content-ID
XMPP does not include an element or attribute that captures a
globally unique ID as is defined for the Content-ID MIME header as
specified in RFC 2045 [11]. If an XMPP-CPIM gateway receives a MIME
object that includes a Content-ID, it MAY provide the Content-ID as
the value of the message stanza's 'id' attribute but is NOT REQUIRED
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to do so.
Example: Content-ID for Encapsulated Object
MIME header
Content-ID: <123456789@montague.net>
XMPP 'id' attribute (OPTIONAL)
<message id='123456789@montague.net'>
...
</message>
3.3.11 Message Body
If the Content-type of an encapsulated MIME object is "text/plain",
then the encapsulated text message content maps to the CDATA of the
<body/> child element of an XMPP message stanza.
Example: Message Body
Encapsulated MIME text content
Content-type: text/plain; charset=utf-8
Content-ID: <123456789@montague.net>
Wherefore art thou?
XMPP message <body/>
<message id='123456789@montague.net'>
<body>Wherefore art thou?</body>
</message>
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4. Mapping of Presence
This section describes how a gateway SHOULD map presence information
between an XMPP service and a non-XMPP service using a "Message/CPIM"
object as the bearer of an encapsulated PIDF [5] object in order to
comply with the presence semantics defined by CPP [3].
4.1 Identification of Presentities
There is a one-to-one relationship between an XMPP entity and a CPP
presentity when the JID of the entity contains only a node identifier
and domain identifier, and the node identifier uniquely corresponds
to an IM user who possesses an account on an XMPP server. However,
the syntax of presentities is specified as including the 'pres:' URI
scheme, whereas XMPP addresses do not include that scheme, so any
mapping between presentities and JIDs must add or remove the 'pres:'
URI scheme as appropriate.
4.2 Presence Syntax Mapping from XMPP to CPIM Specifications
This section defines the mapping of syntax primitives from XMPP
presence stanzas to "Message/CPIM" objects with encapsulated
"application/pidf+xml" objects.
4.2.1 From Address
The 'from' attribute of an XMPP presence stanza maps to the 'From'
header of a "Message/CPIM" object. In XMPP, the sender MUST NOT
include a 'from' attribute; instead, the sender's server stamps the
"from" address and sets its value to the full authzid (including
resource identifier) provided by the client when authenticating. Thus
an XMPP-CPIM gateway will receive from the sender's XMPP server a
presence stanza containing a "from" address of the form <node@domain/
resource>. To map the 'from' attribute of an XMPP presence stanza to
the 'From' header of a "Message/CPIM" object, the gateway MUST remove
the resource identifier, MUST append the "im:" Instant Messaging URI
scheme to the front of the address, and MAY include a CPIM
"Formal-name" for the sender (if known).
Example: From Address Mapping
XMPP 'from' attribute
<presence from='juliet@capulet.com/balcony'>
...
</presence>
CPIM 'From' header
From: Juliet Capulet <im:juliet@capulet.com>
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In addition, the 'from' attribute of an XMPP presence stanza maps to
the 'entity' attribute of a PIDF <presence/> root element. To map the
XMPP 'from' attribute to the PIDF 'entity' attribute, the gateway
MUST remove the resource identifier and MUST append the "pres:"
Instant Messaging URI scheme to the front of the address.
Example: From Address Mapping (PIDF)
XMPP 'from' attribute
<presence from='juliet@capulet.com/balcony'>
...
</presence>
PIDF 'entity' attribute
<presence entity='pres:juliet@capulet.com'>
...
</presence>
Finally, an XMPP-CPIM gateway SHOULD map the resource identifier of
the JID contained in the XMPP 'from' attribute to the 'id' attribute
of the PIDF <tuple/> child element.
Example: Resource Identifier Mapping
XMPP 'from' attribute
<presence from='juliet@capulet.com/balcony'>
...
</presence>
PIDF 'id' for <tuple/>
<presence entity='pres:juliet@capulet.com'>
<tuple id='balcony'>
...
</tuple>
</presence>
4.2.2 To Address
The 'to' attribute of an XMPP presence stanza maps to the 'To' header
of a "Message/CPIM" object. In XMPP, the sender SHOULD include a 'to'
attribute on a presence stanza, and MUST include it if the presence
is intended for delivery to another user. Thus an XMPP-CPIM gateway
will receive from the sender's XMPP server a presence stanza
containing a "to" address of the form <node@domain> or <node@domain/
resource>. To map the 'to' attribute of an XMPP presence stanza to
the 'To' header of a "Message/CPIM" object, the gateway MUST remove
the resource identifier (if included), MUST append the "im:" Instant
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Messaging URI scheme to the front of the address, and MAY include a
CPIM "Formal-name" for the recipient (if known).
Example: To Address Mapping
XMPP 'to' attribute
<presence to='romeo@montague.net/orchard'>
...
</presence>
CPIM 'To' header
To: Romeo Montague <im:romeo@montague.net>
4.2.3 CPIM Courtesy Copy
The core XMPP specification does not include syntax for specifying a
"courtesy copy" (non-primary addressee) for a presence stanza.
Therefore, an XMPP-CPIM gateway MUST NOT generate the 'cc' header of
a "Message/CPIM" object.
4.2.4 XMPP Stanza ID
An XMPP presence stanza MAY possess an 'id' attribute, which is used
by the sending application for the purpose of tracking stanzas. There
is no mapping of an XMPP 'id' attribute to a "Message/CPIM" header,
common MIME features, or PIDF elements and attributes. Therefore if
an XMPP stanza received by an XMPP-CPIM gateway possesses an 'id'
attribute, the gateway SHOULD ignore the value provided.
4.2.5 CPIM DateTime Header
The core XMPP specification does not include syntax for specifying
the datetime at which a presence stanza was sent. However, an
XMPP-CPIM gateway MAY include a 'DateTime' header in the "Message/
CPIM" object it generates, the value of which SHOULD be the datetime
at which the presence stanza was received for processing by the
gateway.
4.2.6 CPIM Subject Header
An XMPP presence stanza contains no information that can be mapped to
the 'Subject' header of a "Message/CPIM" object. Therefore an
XMPP-CPIM gateway SHOULD NOT generate such headers when mapping XMPP
presence stanzas.
4.2.7 CPIM Header Extensions
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A "Message/CPIM" object MAY include an optional 'NS' header to
specify the namespace of a feature extension. An XMPP-CPIM gateway
SHOULD NOT generate such headers.
4.2.8 CPIM Required Headers
A "Message/CPIM" object MAY include an optional 'Required' header to
specify mandatory-to-recognize features. An XMPP-CPIM gateway SHOULD
NOT generate such headers.
4.2.9 PIDF MIME Content-type
RFC 2045 [11] specifies that the default Content-type of a MIME
object is "Content-type: text/plain; charset=us-ascii". Because XMPP
uses a different character encoding (either UTF-8 or UTF-16 depending
on stream negotiation) and because PIDF specifies the "application/
pidf+xml" MIME time, the encapsulated MIME object generated by an
XMPP-CPIM gateway for presence information MUST set the
'Content-type' header for that object. The "Content-type" MUST be set
to "application/pidf+xml" and the charset MUST be set to the
character encoding negotiated for the XML stream used by the sender,
i.e., either UTF-8 or UTF-16.
Example: Content-type for Encapsulated PIDF Object
Content-type: application/pidf+xml; charset=utf-8
4.2.10 PIDF MIME Content-ID
RFC 2045 [11] specifies that the Content-ID is OPTIONAL for MIME
objects. While an XMPP-CPIM gateway MAY generate a Content-ID for
encapsulated MIME objects, it is NOT REQUIRED to do so. If included,
Content-ID values MUST be generated to be world-unique.
Example: Content-ID for Encapsulated Object
Content-ID: <123456789@montague.net>
4.2.11 XMPP Presence Type
An XMPP presence stanza MAY possess a 'type' attribute. If no 'type'
attribute is included, the presence stanza indicates that the sender
is available; this state maps to the PIDF basic presence type of
OPEN. If the 'type' attribute has a value of "unavailable", the
presence stanza indicates that the sender is no longer available;
this state maps to the PIDF basic presence type of CLOSED. Thus both
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the absence of a 'type' attribute and a 'type' attribute set to a
value of "unavailable" correspond to the CPP [3] "notify operation".
All other presence types are used to manage presence subscriptions or
probe for current presence; mappings for these other presence types
are defined under XMPP-CPIM Gateway as Presence Service (Section 5).
Example: Available Presence
XMPP available presence
<presence from='juliet@capulet.com/balcony'/>
PIDF basic presence (OPEN)
<?xml version='1.0' encoding='UTF-8'?>
<presence xmlns='urn:ietf:params:xml:ns:pidf'
entity='pres:juliet@capulet.com'>
<tuple id='balcony'>
<status>
<basic>open</basic>
</status>
</tuple>
</presence>
Example: Unavailable Presence
XMPP unavailable presence
<presence from='juliet@capulet.com/balcony' type='unavailable'/>
PIDF basic presence (CLOSED)
<?xml version='1.0' encoding='UTF-8'?>
<presence xmlns='urn:ietf:params:xml:ns:pidf'
entity='pres:romeo@montague.net'>
<tuple id='balcony'>
<status>
<basic>closed</basic>
</status>
</tuple>
</presence>
4.2.12 XMPP Show Element
The <show/> child element of an XMPP presence stanza provides
additional information about the sender's availability. The CDATA of
the XMPP <show/> element maps to extended <status/> content in PIDF.
The defined values of the <show/> element are 'away', 'chat', 'dnd',
and 'xa'; as soon as values are specified for extended status states
in the 'urn:ietf:params:xml:ns:pidf:im' namespace, the XMPP values
will be mapped to the PIDF values.
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Example: Show Element
XMPP <show/> element
<presence from='juliet@capulet.com/balcony'>
<show>away</show>
</presence>
PIDF extended presence information
<?xml version='1.0' encoding='UTF-8'?>
<presence xmlns='urn:ietf:params:xml:ns:pidf'
xmlns:im='urn:ietf:params:xml:ns:pidf:im'
entity='pres:juliet@capulet.com'>
<tuple id='balcony'>
<status>
<basic>open</basic>
<im:im>away</im:im>
</status>
</tuple>
</presence>
4.2.13 XMPP Status Element
The <status/> child element of an XMPP presence stanza provides a
user-defined, natural-language description of the sender's detailed
availability state. The XMPP <status/> element maps to the PIDF
<note/> child of the PIDF <tuple/> element.
Example: Status Element
XMPP <status/> element
<presence from='juliet@capulet.com/balcony'>
<show>away</show>
<status>retired to the chamber</status>
</presence>
PIDF <note/> element
<?xml version='1.0' encoding='UTF-8'?>
<presence xmlns='urn:ietf:params:xml:ns:pidf'
xmlns:im='urn:ietf:params:xml:ns:pidf:im'
entity='pres:juliet@capulet.com'>
<tuple id='balcony'>
<status>
<basic>open</basic>
<im:im>away</im:im>
</status>
<note>retired to the chamber</note>
</tuple>
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</presence>
4.2.14 PIDF Contact Element
The core XMPP specification does not include syntax for specifying
the URL of a contact address, since the contact address is implicit
in the 'from' attribute of the XMPP presence stanza. However, an
XMPP-CPIM gateway MAY include the <contact/> child of the <tuple/>
element, the value of which SHOULD be the bare JID (<user@domain>) of
the XMPP sender, prepended by the "im:" Instant Messaging URI scheme.
Example: PIDF Contact Element
XMPP presence stanza
<presence from='juliet@capulet.com/balcony'/>
PIDF <contact/> element
<?xml version='1.0' encoding='UTF-8'?>
<presence xmlns='urn:ietf:params:xml:ns:pidf'
entity='pres:juliet@capulet.com'>
<tuple id='balcony'>
...
<contact>im:juliet@capulet.com</contact>
</tuple>
</presence>
4.2.15 Presence Priority
An XMPP presence stanza MAY contain a <priority/> child element whose
value is an integer between -128 and +127. The value of this element
MAY be mapped to the 'priority' attribute of the <contact/> child of
the PIDF <tuple/> element. If the value of the XMPP <priority/>
element is negative, an XMPP-CPIM gateway MUST NOT map the value. The
range of allowable values for the PIDF 'priority' attribute is any
decimal number from zero to one inclusive, with a maximum of three
decimal places. If an XMPP-CPIM gateway maps these values, it SHOULD
treat XMPP <priority>0</priority> as PIDF priority='0' and XMPP
<priority>127</priority> as PIDF priority='1', mapping intermediate
values appropriately so that they are unique (e.g., XMPP priority 1
to PIDF priority 0.007, XMPP priority 2 to PIDF priority 0.015, and
so on up through mapping XMPP priority 126 to PIDF priority 0.992;
note that this is an example only, and that the exact mapping shall
be determined by the XMPP-CPIM gateway).
Example: Presence Priority
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XMPP <status/> element
<presence from='juliet@capulet.com/balcony'>
<priority>13</priority>
</presence>
PIDF <note/> element
<?xml version='1.0' encoding='UTF-8'?>
<presence xmlns='urn:ietf:params:xml:ns:pidf'
entity='pres:juliet@capulet.com'>
<tuple id='balcony'>
...
<contact priority='0.102'>im:juliet@capulet.com</contact>
</tuple>
</presence>
4.2.16 PIDF Timestamp Element
The core XMPP specification does not include syntax for specifying
the datetime at which a presence stanza was sent. However, an
XMPP-CPIM gateway MAY include a <timestamp/> element within the PIDF
document it generates, the value of which SHOULD be the datetime at
which the presence stanza was received for processing by the gateway.
4.2.17 XMPP Presence Extensions
As defined in XMPP Core [6], an XMPP presence stanza may contain
"extended" content in any namespace in order to supplement or extend
the semantics of the core presence stanza. With the exception of
extended information qualified by the
'urn:ietf:params:xml:ns:xmpp-e2e' namespace as defined in End-to-End
Object Encryption in XMPP [8], an XMPP-CPIM gateway SHOULD ignore
such information and not pass it through the gateway to the intended
recipient. No mapping for such information is defined.
4.3 Presence Syntax Mapping from CPIM Specifications to XMPP
This section defines the mapping of syntax primitives from "Message/
CPIM" objects with encapsulated "application/pidf+xml" objects to
XMPP presence stanzas.
4.3.1 From Address
The 'From' header of a "Message/CPIM" object maps to the 'from'
attribute of an XMPP presence stanza. To map the CPIM 'From' header
to the XMPP 'from' attribute, the gateway MUST remove the "im:"
Instant Messaging URI scheme from the front of the address and MUST
remove the CPIM "Formal-name" (if provided).
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Example: From Address Mapping
CPIM 'From' header
From: Romeo Montague <im:romeo@montague.net>
XMPP 'from' attribute
<presence from='romeo@montague.net'>
...
</presence>
4.3.2 To Address
The 'To' header of a "Message/CPIM" object maps to the 'to' attribute
of an XMPP presence stanza. To map the CPIM 'To' header to the XMPP
'to' attribute, the gateway MUST remove the "im:" Instant Messaging
URI scheme from the front of the address and MUST remove the CPIM
"Formal-name" (if provided). If the gateway possesses knowledge of
the resource identifier in use by the XMPP entity, the gateway MAY
append the resource identifier to the address.
Example: To Address Mapping
CPIM 'To' header
To: Juliet Capulet <im:juliet@capulet.com>
XMPP 'to' attribute
<presence to='juliet@capulet.com/balcony'>
...
</presence>
4.3.3 CPIM Courtesy Copy
The core XMPP specification does not include syntax for specifying a
"courtesy copy" (non-primary addressee) for a presence stanza.
Therefore, if an XMPP-CPIM gateway receives a "Message/CPIM" object
with encapsulated PIDF object that contains a 'cc' header, it MUST
NOT pass that information on to the XMPP recipient.
4.3.4 CPIM DateTime Header
The core XMPP specification does not include syntax for specifying
the datetime at which a presence stanza was sent. Therefore, if an
XMPP-CPIM gateway receives a "Message/CPIM" object with encapsulated
PIDF object that contains a 'DateTime' header, it SHOULD NOT pass
that information on to the XMPP recipient.
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4.3.5 CPIM Subject Header
An XMPP presence stanza contains no information that can be mapped to
the 'Subject' header of a "Message/CPIM" object. Therefore, if an
XMPP-CPIM gateway receives a "Message/CPIM" object with encapsulated
PIDF object that contains a 'Subject' header, it SHOULD NOT pass that
information on to the XMPP recipient.
4.3.6 CPIM Header Extensions
"Message/CPIM" objects MAY include an optional 'NS' header to specify
the namespace of a feature extension. An XMPP-CPIM gateway MUST NOT
pass such headers through to the XMPP recipient, and no mapping for
such headers is defined.
4.3.7 CPIM Required Headers
"Message/CPIM" objects MAY include an optional 'Required' header to
specify mandatory-to-recognize features. An XMPP-CPIM gateway MUST
NOT pass such headers through to the XMPP recipient, and no mapping
for such headers is defined.
4.3.8 PIDF MIME Content-type
CPIM [4] specifies that a "Message/CPIM" object MAY contain any
arbitrary MIME content. However, support for arbitrary content types
is not a requirement in XMPP. An XMPP-CPIM gateway MUST NOT map to an
XMPP presence stanza a "Message/CPIM" object whose encapsulated MIME
object has a Content-type other than "application/pidf+xml" (with the
exception of multi-part MIME objects used for End-to-End Object
Encryption in XMPP [8]).
4.3.9 PIDF MIME Content-ID
XMPP does not include an element or attribute that captures a
globally unique ID as is defined for the Content-ID MIME header as
specified in RFC 2045 [11]. If an XMPP-CPIM gateway receives a MIME
object that includes a Content-ID, it MAY provide the Content-ID as
the value of the presence stanza's 'id' attribute but is NOT REQUIRED
to do so.
Example: Content-ID for Encapsulated Object
MIME header
Content-ID: <123456789@montague.net>
XMPP 'id' attribute (OPTIONAL)
<presence id='123456789@montague.net'>
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...
</presence>
4.3.10 PIDF Basic Presence Status
The basic presence status types defined in PIDF are OPEN and CLOSED.
The PIDF basic presence status of OPEN maps to an XMPP presence
stanza that possesses no 'type' attribute (indicating default
availability). The PIDF basic presence status of CLOSED maps to an
XMPP presence stanza that possesses a 'type' attribute with a value
of "unavailable".
Example: OPEN Presence
PIDF basic presence (OPEN)
<?xml version='1.0' encoding='UTF-8'?>
<presence xmlns='urn:ietf:params:xml:ns:pidf'
entity='pres:romeo@montague.net'>
<tuple id='orchard'>
<status>
<basic>open</basic>
</status>
</tuple>
</presence>
XMPP available presence
<presence from='romeo@montague.net/orchard'/>
Example: CLOSED Presence
PIDF basic presence (CLOSED)
<?xml version='1.0' encoding='UTF-8'?>
<presence xmlns='urn:ietf:params:xml:ns:pidf'
entity='pres:romeo@montague.net'>
<tuple id='orchard'>
<status>
<basic>closed</basic>
</status>
</tuple>
</presence>
XMPP unavailable presence
<presence from='romeo@montague.net/orchard'
type='unavailable'/>
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4.3.11 PIDF Extended Status Information
PIDF documents may contain extended <status/> content. As of this
writing there are no pre-defined extended status states that
correspond to the defined values of the XMPP <show/> element ('away',
'chat', 'dnd', and 'xa'); as soon as values are specified for
extended status states in the 'urn:ietf:params:xml:ns:pidf:im'
namespace, the PIDF values will be mapped to the relevant XMPP
values.
Example: Extended Status Information (provisional)
PIDF extended presence information
<?xml version='1.0' encoding='UTF-8'?>
<presence xmlns='urn:ietf:params:xml:ns:pidf'
xmlns:im='urn:ietf:params:xml:ns:pidf:im'
entity='pres:romeo@montague.net'>
<tuple id='orchard'>
<status>
<basic>open</basic>
<im:im>busy</im:im>
</status>
</tuple>
</presence>
XMPP <show/> element
<presence from='romeo@montague.net/orchard'>
<show>dnd</show>
</presence>
4.3.12 PIDF Note Element
A PIDF <tuple/> element may contain a <note/> child that provides a
user-defined, natural-language description of the sender's detailed
availability state. The PIDF <note/> element maps to the XMPP
<status/> element.
Example: Note Element
PIDF <note/> element
<?xml version='1.0' encoding='UTF-8'?>
<presence xmlns='urn:ietf:params:xml:ns:pidf'
xmlns:im='urn:ietf:params:xml:ns:pidf:im'
entity='pres:romeo@montague.net'>
<tuple id='orchard'>
<status>
<basic>open</basic>
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<im:im>busy</im:im>
</status>
<note>Wooing Juliet</note>
</tuple>
</presence>
XMPP <status/> element
<presence from='romeo@montague.net/orchard'>
<show>dnd</show>
<status>Wooing Juliet</status>
</presence>
A PIDF document with zero tuples MAY contain one or more <note/>
elements as direct children of the PIDF <presence/> element. There is
no mapping of such a PIDF document to an XMPP presence stanza; an
entity on the non-XMPP side of an XMPP-CPIM gateway SHOULD NOT send
such a PIDF document to an XMPP recipient if possible, and an
XMPP-CPIM gateway MUST NOT map such a PIDF document to an XMPP
presence stanza (see Zero Resources (Section 5.4.2)).
4.3.13 PIDF Contact Element
The core XMPP specification does not include syntax for specifying
the URL of a contact address, since the contact address is implicit
in the 'from' attribute of the XMPP presence stanza. Therefore, if an
XMPP-CPIM gateway receives a "Message/CPIM" object with encapsulated
PIDF object that contains a <contact/> element, it SHOULD NOT pass
the CDATA of the <contact/> element on to the XMPP recipient.
However, the gateway MAY map the 'priority' element as specified in
the following section.
Example: PIDF Contact Element
PIDF <contact/> element
<?xml version='1.0' encoding='UTF-8'?>
<presence xmlns='urn:ietf:params:xml:ns:pidf'
entity='pres:romeo@montague.net'>
<tuple id='orchard'>
...
<contact>im:romeo@montague.net</contact>
</tuple>
</presence>
XMPP presence stanza
<presence from='romeo@montague.net/orchard'/>
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4.3.14 Presence Priority
The <contact/> child of the PIDF <tuple/> element MAY possess a
'priority' attribute whose value is a decimal number between zero and
one (with a maximum of three decimal places). The value of this
attribute MAY be mapped to the <priority/> child element of an XMPP
presence stanza. An XMPP-CPIM gateway MUST NOT map PIDF priority
values to negative values of the XMPP <priority/> element. If an
XMPP-CPIM gateway maps these values, it SHOULD treat PIDF
priority='0' as XMPP <priority>0</priority> and PIDF priority='1' as
<priority>127</priority>, mapping intermediate values appropriately
so that they are unique (e.g., PIDF priorities between 0.001 and
0.007 to XMPP priority 1, PIDF priorities between 0.008 and 0.015 to
XMPP priority 2, and so on up through mapping PIDF priorities between
0.992 and 0.999 to XMPP priority 126; note that this is an example
only, and that the exact mapping shall be determined by the XMPP-CPIM
gateway).
4.3.15 PIDF Timestamp Element
The core XMPP specification does not include syntax for specifying
the datetime or timestamp at which a presence stanza was sent.
Therefore, if an XMPP-CPIM gateway receives a "Message/CPIM" object
with encapsulated PIDF object that contains a <timestamp/> element,
it SHOULD NOT pass that information on to the XMPP recipient.
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5. XMPP-CPIM Gateway as Presence Service
CPP [3] defines semantics for an abstract presence service. An
XMPP-CPIM gateway MAY function as such a presence service, and if so
an XMPP entity can use defined XMPP syntax to interact with the
gateway's presence service. Because PIDF [5] does not specify syntax
for semantic operations such as subscribe, this section defines only
the XMPP interactions with the presence service offered by an
XMPP-CPIM gateway, not the translation of such XMPP syntax into PIDF.
(Note: detailed information about XMPP presence services can be found
in XMPP IM [7]; as much as possible, an XMPP-CPIM gateway SHOULD
implement the syntax, semantics, and server business rules defined
therein.)
5.1 Requesting a Subscription
If an XMPP entity wants to subscribe to the presence information of a
non-XMPP presentity through an XMPP-CPIM gateway, it MUST send a
presence stanza of type "subscribe" to the target presentity. The
syntax mapping is as follows:
o The XMPP 'from' attribute (node@domain) MUST be mapped to the CPP
"watcher parameter" field (pres:node@domain). The XMPP-CPIM
gateway MUST append the "pres:" Presence URI scheme to the front
of the address.
o The XMPP 'to' attribute (node@domain) MUST be mapped to the CPP
"target parameter" field (pres:node@domain). The XMPP-CPIM gateway
MUST append the "pres:" Presence URI scheme to the front of the
address.
o There is no XMPP mapping for the CPP "duration parameter", since
XMPP subscriptions are active until they have been explicitly
"unsubscribed" (see Subscription Durations (Section 5.3)).
o The XMPP 'id' attribute SHOULD be mapped to the CPP "TransID"
field.
If the target presentity approves the subscription request (through
whatever protocol it uses to interact with the gateway), the
XMPP-CPIM gateway MUST return a presence stanza of type "subscribed"
to the XMPP entity and notify the XMPP entity of the target's current
available presence. Thereafter, until the subscription is cancelled,
the gateway MUST notify the subscribing XMPP entity every time the
target's presence information changes.
If the target presentity denies the subscription request, the
XMPP-CPIM gateway MUST return a presence stanza of type
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"unsubscribed" to the XMPP entity and MUST NOT invoke the notify
operation.
In addition to the approval and denial cases, one of the following
exceptions MAY occur:
o The target parameter (XMPP "to" address) does not refer to a valid
presentity; if this exception occurs, the XMPP-CPIM gateway MUST
return an <item-not-found/> stanza error to the XMPP entity.
o Access control rules do not permit the entity to subscribe to the
target; if this exception occurs, the XMPP-CPIM gateway MUST
return a <forbidden/> stanza error to the XMPP entity.
o There exists a pre-existing subscription or in-progress subscribe
operation between the XMPP entity and the target presentity; if
this exception occurs, the XMPP-CPIM gateway SHOULD return a
<conflict/> stanza error to the XMPP entity.
5.2 Receiving a Subscription Request
If a non-XMPP presentity wants to subscribe to the presence
information of an XMPP entity through an XMPP-CPIM gateway, it MUST
use whatever protocol it uses to interact with the gateway in order
to request the subscription; subject to local access rules, the
gateway MUST then send a presence stanza of type "subscribe" to the
XMPP entity from the non-XMPP watcher. The syntax mapping is as
follows:
o The CPP "watcher parameter" field (pres:node@domain) MUST be
mapped to the XMPP 'from' attribute (node@domain). The XMPP-CPIM
gateway MUST remove the "pres:" Presence URI scheme from the front
of the address.
o The CPP "target parameter" field (pres:node@domain) MUST be mapped
to the XMPP 'to' attribute (node@domain). The XMPP-CPIM gateway
MUST remove the "pres:" Presence URI scheme from the front of the
address.
o There is no XMPP mapping for the CPP "duration parameter", since
XMPP subscriptions are active until they have been explicitly
"unsubscribed" (see Subscription Durations (Section 5.3)).
o The XMPP 'id' attribute SHOULD be mapped to the CPP "TransID"
field.
If the target XMPP entity approves the subscription request, it MUST
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send a presence stanza of type "subscribed" to the watcher
presentity. The XMPP-CPIM gateway MUST then notify the watcher
presentity of the target XMPP entity's current available presence.
Thereafter, until the subscription is cancelled, the gateway MUST
notify the watcher presentity every time the target's presence
information changes.
If the target XMPP entity denies the subscription request, it MUST
send a presence stanza of type "unsubscribed" to the watcher
presentity. The XMPP-CPIM gateway MUST NOT invoke the notify
operation.
In addition to the approval and denial cases, one of the following
exceptions MAY occur:
o The target parameter (XMPP "to" address) does not refer to a valid
XMPP entity
o Access control rules do not permit the watcher presentity to
subscribe to the target XMPP entity
o There exists a pre-existing subscription or in-progress subscribe
operation between the watcher presentity and the target XMPP
entity
If any of these exceptions occurs, the XMPP-CPIM gateway MUST inform
the watcher presentity of failure.
5.3 Subscription Durations
XMPP services assume that a subscription is active until it is
explicitly terminated. With the exception of handling duration
parameters whose value is zero, handling duration parameters will be
highly dependent on the implementation and requirements of the
XMPP-CPIM gateway. Since there are no explicit requirements for
supporting a "duration parameter" specified in either RFC 2778 [9] or
RFC 2779 [1], duration parameter mapping is a local issue that falls
outside the scope of this document.
5.4 The Notify Operation
An XMPP-CPIM gateway invokes the CPP "notify operation" whenever the
presence information associated with an XMPP entity or CPP presentity
changes and there are subscribers to that information on the other
side of the gateway. The syntax mapping for presence information
related to a notify operation is defined under Mapping for Presence
(Section 4).
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5.4.1 Multiple Resources
Semantically, PIDF contains the notion of multiple presence "tuples".
Normally, a PIDF document will contain at least one tuple but MAY
contain more than one tuple (or zero tuples, for which see next
section). In the terminology of XMPP, each tuple would map to
presence information for a separate resource. However, XMPP does not
include the ability to send presence information about more than one
resource at a time, since the resource that generates the presence
information is contained in the 'from' address of a presence stanza.
Therefore, an XMPP-CPIM gateway that acts as a presence service
SHOULD split a PIDF document that contains multiple tuples into
multiple XMPP presence stanzas, and SHOULD generate only one PIDF
document (with multiple tuples) if an XMPP user currently has
multiple connected resources.
In the interest of not multiplying XMPP stanzas beyond necessity, an
XMPP-CPIM gateway SHOULD generate an XMPP presence stanza only if the
presence information contained in a PIDF tuple communicates a change
in the availability status of the device or application associated
with that tuple ID.
In the interest of complying with the PIDF recommendation to provide
information about multiple "resources" in multiple tuples rather than
in multiple PIDF documents, an XMPP-CPIM gateway SHOULD include
information about all of an XMPP user's resources in one PIDF
document (with one tuple for each resource), even if the availability
status of only one resource has changed.
5.4.2 Zero Resources
A PIDF document may contain zero tuples. For example:
PIDF Document with Zero Tuples
<presence entity='pres:juliet@capulet.com'
xmlns='urn:ietf:params:xml:ns:pidf'/>
Because (1) the 'entity' attribute of a PIDF <presence/> element maps
to the <user@host> portion of an XMPP JID and (2) the 'id' attribute
of a PIDF <tuple/> element maps to the resource identifier portion of
an XMPP JID, a PIDF document that contains zero tuples would provide
presence information about a <user@host> rather than a <user@host/
resource> when mapped to XMPP. However, the notion of presence about
a user rather than a user's resources is meaningless in the XMPP
context. Therefore, an XMPP-CPIM gateway MUST NOT map a PIDF document
with zero tuples into an XMPP presence stanza, and MUST NOT generate
such a PIDF document when receiving a presence stanza from an XMPP
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entity (i.e., all PIDF documents generated by the gateway MUST
contain at least one <tuple/> element).
5.5 Unsubscribing
If an XMPP entity wants to unsubscribe from the presence of a
non-XMPP presentity through an XMPP-CPIM gateway, it MUST send a
presence stanza of type "unsubscribe" to the target presentity. The
syntax mapping is as follows:
o The XMPP 'from' attribute (node@domain) MUST be mapped to the CPP
"watcher parameter" field (pres:node@domain). The XMPP-CPIM
gateway MUST append the "pres:" Presence URI scheme to the front
of the address.
o The XMPP 'to' attribute (node@domain) MUST be mapped to the CPP
"target parameter" field (pres:node@domain). The XMPP-CPIM gateway
MUST append the "pres:" Presence URI scheme to the front of the
address.
o The CPP "duration parameter" MUST be set to zero.
o The XMPP 'id' attribute SHOULD be mapped to the CPP "TransID"
field.
If the target parameter (XMPP "to" address) does not refer to a valid
presentity, the XMPP-CPIM gateway MUST return an <item-not-found/>
stanza error to the XMPP entity.
Upon receiving the presence stanza of type "unsubscribe" from the
XMPP entity, the XMPP-CPIM gateway MUST NOT send further presence
notifications to the XMPP entity.
5.6 Cancelling a Subscription
If an XMPP entity wants to cancel a non-XMPP presentity's
subscription to the entity's presence through an XMPP-CPIM gateway,
it MUST send a presence stanza of type "unsubscribed" to the target
presentity. The syntax mapping is as follows:
o The CPP "watcher parameter" field (pres:node@domain) MUST be
mapped to the XMPP 'from' attribute (node@domain). The XMPP-CPIM
gateway MUST remove the "pres:" Presence URI scheme from the front
of the address.
o The CPP "target parameter" field (pres:node@domain) MUST be mapped
to the XMPP 'to' attribute (node@domain). The XMPP-CPIM gateway
MUST remove the "pres:" Presence URI scheme from the front of the
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address.
o The CPP "duration parameter" MUST be set to zero.
o The XMPP 'id' attribute SHOULD be mapped to the CPP "TransID"
field.
Upon receiving the presence stanza of type "unsubscribed" from the
XMPP entity, the XMPP-CPIM gateway MUST NOT send further presence
notifications to the watcher presentity.
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6. Mapping of Character Encodings
The following rules apply to the mapping of character encodings
(charsets):
1. A gateway SHOULD NOT map a "Message/CPIM" object whose charset is
other than "us-ascii", "utf-8", or "utf-16".
2. A gateway SHOULD map a "Message/CPIM" object whose charset is
"us-ascii" no matter whether the character encoding negotiated
for the XMPP recipient's XML stream is UTF-8 or UTF-16.
3. A gateway SHOULD map a "Message/CPIM" object whose charset is
"utf-8" if the character encoding negotiated for the XMPP
recipient's XML stream is UTF-8.
4. A gateway SHOULD map a "Message/CPIM" object whose charset is
"utf-16" if the character encoding negotiated for the XMPP
recipient's XML stream is UTF-16.
5. A gateway SHOULD NOT map a "Message/CPIM" object whose charset is
"utf-8" if the character encoding negotiated for the XMPP
recipient's XML stream is UTF-16.
6. A gateway SHOULD NOT map a "Message/CPIM" object whose charset is
"utf-16" if the character encoding negotiated for the XMPP
recipient's XML stream is UTF-8.
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7. Security Considerations
Detailed security considerations for instant messaging and presence
protocols are given in RFC 2779 [1], specifically in Sections 5.1
through 5.4.
This document specifies methods for exchanging instant messages and
presence information through a gateway that implements CPIM [2] and
CPP [3]. Such a gateway MUST be compliant with the minimum security
requirements of the instant messaging and presence protocols with
which it interfaces. The introduction of gateways to the security
model of instant messaging and presence in RFC 2779 also introduces
some new risks. In particular, end-to-end security properties
(especially confidentiality and integrity) between instant messaging
and presence user agents that interface through an XMPP-CPIM gateway
can be provided only if common formats are supported; these formats
are specified fully in End-to-End Object Encryption in XMPP [8].
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Normative References
[1] Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging /
Presence Protocol Requirements", RFC 2779, February 2000.
[2] Crocker, D. and J. Peterson, "Common Profile for Instant
Messaging (CPIM)", draft-ietf-impp-im-02 (work in progress),
March 2003.
[3] Crocker, D. and J. Peterson, "Common Profile for Presence
(CPP)", draft-ietf-impp-pres-02 (work in progress), March 2003.
[4] Atkins, D. and G. Klyne, "Common Presence and Instant Messaging
Message Format", draft-ietf-impp-cpim-msgfmt-08 (work in
progress), January 2003.
[5] Fujimoto, S., Sugano, H., Klyne, G., Bateman, A., Carr, W. and
J. Peterson, "CPIM Presence Information Data Format",
draft-ietf-impp-cpim-pidf-08 (work in progress), May 2003.
[6] Saint-Andre, P. and J. Miller, "XMPP Core",
draft-ietf-xmpp-core-17 (work in progress), August 2003.
[7] Saint-Andre, P. and J. Miller, "XMPP Instant Messaging",
draft-ietf-xmpp-im-16 (work in progress), August 2003.
[8] Saint-Andre, P., "End-to-End Object Encryption in XMPP",
draft-ietf-xmpp-e2e-04 (work in progress), June 2003.
[9] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000, <http://
www.ietf.org/rfc/rfc2778.txt>.
[10] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[11] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
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Informative References
[12] Resnick, P., "Internet Message Format", RFC 2822, April 2001.
[13] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, November
1996.
Authors' Addresses
Peter Saint-Andre
Jabber Software Foundation
EMail: stpeter@jabber.org
Tony Bamonti
Jabber, Inc.
EMail: tbamonti@jabber.com
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Appendix A. Revision History
Note to RFC Editor: please remove this entire appendix, and the
corresponding entries in the table of contents, prior to publication.
A.1 Changes from draft-ietf-xmpp-cpim-01
o Added subsection about handling presence notifications for
multiple XMPP resources and multiple PIDF tuples.
o Added subsection about PIDF documents that contain zero tuples.
o Further specified mapping between XMPP JIDs and CPIM instant
inboxes and presentities.
A.2 Changes from draft-ietf-xmpp-cpim-00
o Updated references.
o Made several small editorial changes.
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