XMPP Working Group P. Saint-Andre
Internet-Draft Jabber Software Foundation
Expires: May 20, 2004 November 20, 2003
Mapping the Extensible Messaging and Presence Protocol (XMPP) to
Common Presence and Instant Messaging (CPIM)
draft-ietf-xmpp-cpim-03
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 memo 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Mapping of Instant Messages . . . . . . . . . . . . . . . . . 5
4. Mapping of Presence . . . . . . . . . . . . . . . . . . . . . 13
5. XMPP-CPIM Gateway as Presence Service . . . . . . . . . . . . 26
6. Internationalization Considerations . . . . . . . . . . . . . 31
7. Security Considerations . . . . . . . . . . . . . . . . . . . 32
Normative References . . . . . . . . . . . . . . . . . . . . . 32
Informative References . . . . . . . . . . . . . . . . . . . . 33
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 34
A. Revision History . . . . . . . . . . . . . . . . . . . . . . . 34
Intellectual Property and Copyright Statements . . . . . . . . 35
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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 [IMP-REQS]. This
framework is commonly called Common Presence and Instant Messaging or
"CPIM". The CPIM family of specifications include a Common Profile
for Instant Messaging [CPIM] (also called CPIM), a Common Profile for
Presence [CPP], a CPIM Message Format [MSGFMT], and a Common Presence
Information Data Format [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". In order to refer to a gateway
between an Extensible Messaging and Presence Protocol (XMPP) service
and a non-XMPP service where the common format is defined by the CPIM
specifications, the term "XMPP-CPIM Gateway" is used herein.)
This memo describes how the Extensible Messaging and Presence
Protocol ([XMPP-CORE], [XMPP-IM]) 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 [IMP-REQS]. 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 memo 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 [XMPP-E2E].
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1.2 Terminology
This memo inherits vocabulary defined in [IMP-MODEL]. 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]. Terms
such as ENTITY, 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
[TERMS].
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.
1.6 Contributors
Tony Bamonti contributed to the first version of this memo.
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 elements
(called "stanzas") between any two endpoints on the network; message
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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]; instead,
[XMPP-CORE] 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] content-types: "Message/CPIM" for
messages ([MSGFMT]) and "application/pidf+xml" for presence ([PIDF]).
The syntax of "Message/CPIM" objects is similar to but stricter than
that defined in [RFC2822], and provides the ability to include
arbitrary MIME media types [MIMETYPES]. 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]
and [PIDF] in order to comply with the semantics defined by [CPIM]
and [CPP]. Naturally, mappings in the opposite direction are
provided as well.
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].
3.1 Identification of Instant Inboxes
There is a one-to-one relationship between an XMPP entity and a CPIM
instant inbox when the address of the XMPP 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 as defined in [CPIM],
whereas an XMPP address does not include that scheme, so any mapping
between an instant inbox address and an XMPP address 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.
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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's server
stamps or validates the "from" address and sets its value to the full
<user@host/resource> negotiated between client and server during
authentication and resource binding as defined in [XMPP-CORE]. Thus
an XMPP-CPIM gateway will receive from the sender's XMPP server a
message stanza containing a "from" address of the form <user@host/
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@example.com/balcony'>
...
</message>
CPIM 'From' header
From: Juliet Capulet <im:juliet@example.com>
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 <user@host> or <user@host/
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@example.net/orchard'>
...
</message>
CPIM 'To' header
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To: Romeo Montague <im:romeo@example.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 SHOULD 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 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.
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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.
To map the XMPP <subject/> element to the 'Subject' header of a
"Message/CPIM" object, the gateway SHOULD simply map the XML
character data of the XMPP <subject/> element to the value of the
'Subject' header. The <subject/> element MAY include an 'xml:lang'
attribute specifying the language in which the subject is written.
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
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
As specified in [MIME], the default Content-type of a MIME object is
"Content-type: text/plain; charset=us-ascii". Because XMPP uses the
[UTF-8] character encoding exclusively, 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 UTF-8.
Example: Content-type for Encapsulated Object
Content-type: text/plain; charset=utf-8
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3.2.12 MSGFMT MIME Content-ID
As specified in [MIME], 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@example.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 XML character data
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>
</message>
Encapsulated MIME text content
Content-type: text/plain; charset=utf-8
Content-ID: <123456789@example.net>
Wherefore art thou, Romeo?
3.2.14 XMPP Message Extensions
As defined in [XMPP-CORE], 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 [XMPP-E2E],
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.
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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@example.net>
XMPP 'from' attribute
<message from='romeo@example.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
'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@example.com>
XMPP 'to' attribute
<message to='juliet@example.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 SHOULD NOT pass that information on
to the XMPP recipient.
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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. To map the CPIM 'Subject'
header to the XMPP <subject/> element, the gateway SHOULD simply map
the value of the 'Subject' header to the XML character data of the
XMPP <subject/> element. The 'Subject' header MAY specify the "lang"
in which the subject is written. If "lang" information is provided,
it MUST be mapped to the 'xml:lang' 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
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"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
As specified in [MSGFMT], 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 as specified in [XMPP-E2E]).
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 [MIME]. 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 to
do so.
Example: Content-ID for Encapsulated Object
MIME header
Content-ID: <123456789@example.net>
XMPP 'id' attribute (OPTIONAL)
<message id='123456789@example.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 XML character
data 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@example.net>
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Wherefore art thou?
XMPP message <body/>
<message id='123456789@example.net'>
<body>Wherefore art thou?</body>
</message>
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] object in order to
comply with the presence semantics defined by [CPP].
4.1 Identification of Presentities
There is a one-to-one relationship between an XMPP entity and a CPP
presentity when the address of the XMPP 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 as defined in [CPP], whereas XMPP addresses do not
include that scheme, so any mapping between presentities and XMPP
addresses 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's server
stamps or validates the "from" address and sets its value to the
<user@host/resource> negotiated between client and server during
authenticating and resource binding as defined in [XMPP-CORE]. Thus
an XMPP-CPIM gateway will receive from the sender's XMPP server a
presence stanza containing a "from" address of the form <user@host/
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
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XMPP 'from' attribute
<presence from='juliet@example.com/balcony'>
...
</presence>
CPIM 'From' header
From: Juliet Capulet <im:juliet@example.com>
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@example.com/balcony'>
...
</presence>
PIDF 'entity' attribute
<presence entity='pres:juliet@example.com'>
...
</presence>
Finally, an XMPP-CPIM gateway SHOULD map the resource identifier of
the XMPP address 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@example.com/balcony'>
...
</presence>
PIDF 'id' for <tuple/>
<presence entity='pres:juliet@example.com'>
<tuple id='balcony'>
...
</tuple>
</presence>
4.2.2 To Address
The 'to' attribute of an XMPP presence stanza maps to the 'To' header
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of a "Message/CPIM" object. In XMPP, the sender MAY include a 'to'
attribute on a presence stanza, and MUST include it if the presence
stanza is intended for delivery directly to another user (presence
stanzas intended for broadcasting are stamped with a 'to' address by
the sender's server). Thus an XMPP-CPIM gateway will receive from
the sender's XMPP server a presence stanza containing a "to" address
of the form <user@host> or <user@host/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 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@example.net/orchard'>
...
</presence>
CPIM 'To' header
To: Romeo Montague <im:romeo@example.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 SHOULD 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
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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
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
As specified in [MIME], the default Content-type of a MIME object is
"Content-type: text/plain; charset=us-ascii". Because XMPP uses the
[UTF-8] character encoding exclusively 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
UTF-8.
Example: Content-type for Encapsulated PIDF Object
Content-type: application/pidf+xml; charset=utf-8
4.2.10 PIDF MIME Content-ID
As specified in [MIME], 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@example.net>
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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
the absence of a 'type' attribute and a 'type' attribute set to a
value of "unavailable" correspond to the [CPP] "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@example.com/balcony'/>
PIDF basic presence (OPEN)
<?xml version='1.0' encoding='UTF-8'?>
<presence xmlns='urn:ietf:params:xml:ns:pidf'
entity='pres:juliet@example.com'>
<tuple id='balcony'>
<status>
<basic>open</basic>
</status>
</tuple>
</presence>
Example: Unavailable Presence
XMPP unavailable presence
<presence from='juliet@example.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@example.net'>
<tuple id='balcony'>
<status>
<basic>closed</basic>
</status>
</tuple>
</presence>
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4.2.12 XMPP Show Element
The <show/> child element of an XMPP presence stanza provides
additional information about the sender's availability. The XML
character data 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.
Example: Show Element
XMPP <show/> element
<presence from='juliet@example.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@example.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@example.com/balcony'>
<show>away</show>
<status>retired to the chamber</status>
</presence>
PIDF <note/> element
<?xml version='1.0' encoding='UTF-8'?>
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<presence xmlns='urn:ietf:params:xml:ns:pidf'
xmlns:im='urn:ietf:params:xml:ns:pidf:im'
entity='pres:juliet@example.com'>
<tuple id='balcony'>
<status>
<basic>open</basic>
<im:im>away</im:im>
</status>
<note>retired to the chamber</note>
</tuple>
</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 <user@host> of the XMPP
sender, prepended by the "im:" Instant Messaging URI scheme.
Example: PIDF Contact Element
XMPP presence stanza
<presence from='juliet@example.com/balcony'/>
PIDF <contact/> element
<?xml version='1.0' encoding='UTF-8'?>
<presence xmlns='urn:ietf:params:xml:ns:pidf'
entity='pres:juliet@example.com'>
<tuple id='balcony'>
...
<contact>im:juliet@example.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
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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
XMPP <status/> element
<presence from='juliet@example.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@example.com'>
<tuple id='balcony'>
...
<contact priority='0.102'>im:juliet@example.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], 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 [XMPP-E2E],
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/
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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).
Example: From Address Mapping
CPIM 'From' header
From: Romeo Montague <im:romeo@example.net>
XMPP 'from' attribute
<presence from='romeo@example.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@example.com>
XMPP 'to' attribute
<presence to='juliet@example.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
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with encapsulated PIDF object that contains a 'cc' header, it SHOULD
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.
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
As specified in [MSGFMT], 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 as specified in
[XMPP-E2E]).
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 [MIME]. If an XMPP-CPIM gateway receives a MIME object
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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@example.net>
XMPP 'id' attribute (OPTIONAL)
<presence id='123456789@example.net'>
...
</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@example.net'>
<tuple id='orchard'>
<status>
<basic>open</basic>
</status>
</tuple>
</presence>
XMPP available presence
<presence from='romeo@example.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@example.net'>
<tuple id='orchard'>
<status>
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<basic>closed</basic>
</status>
</tuple>
</presence>
XMPP unavailable presence
<presence from='romeo@example.net/orchard'
type='unavailable'/>
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@example.net'>
<tuple id='orchard'>
<status>
<basic>open</basic>
<im:im>busy</im:im>
</status>
</tuple>
</presence>
XMPP <show/> element
<presence from='romeo@example.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.
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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@example.net'>
<tuple id='orchard'>
<status>
<basic>open</basic>
<im:im>busy</im:im>
</status>
<note>Wooing Juliet</note>
</tuple>
</presence>
XMPP <status/> element
<presence from='romeo@example.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 XML character data 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@example.net'>
<tuple id='orchard'>
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...
<contact>im:romeo@example.net</contact>
</tuple>
</presence>
XMPP presence stanza
<presence from='romeo@example.net/orchard'/>
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.
5. XMPP-CPIM Gateway as Presence Service
[CPP] 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] 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]; as much as possible, an XMPP-CPIM gateway SHOULD
implement the syntax, semantics, and server business rules defined
therein.)
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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 (user@host) MUST be mapped to the CPP
"watcher parameter" field (pres:user@host). The XMPP-CPIM gateway
MUST append the "pres:" Presence URI scheme to the front of the
address.
o The XMPP 'to' attribute (user@host) MUST be mapped to the CPP
"target parameter" field (pres:user@host). 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
"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.
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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:user@host) MUST be mapped
to the XMPP 'from' attribute (user@host). The XMPP-CPIM gateway
MUST remove the "pres:" Presence URI scheme from the front of the
address.
o The CPP "target parameter" field (pres:user@host) MUST be mapped
to the XMPP 'to' attribute (user@host). 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
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:
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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 [IMP-MODEL] or
[IMP-REQS], duration parameter mapping is a local issue that falls
outside the scope of this memo.
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).
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.
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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@example.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 address and (2) the 'id'
attribute of a PIDF <tuple/> element maps to the resource identifier
portion of an XMPP address, 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 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 (user@host) MUST be mapped to the CPP
"watcher parameter" field (pres:user@host). The XMPP-CPIM gateway
MUST append the "pres:" Presence URI scheme to the front of the
address.
o The XMPP 'to' attribute (user@host) MUST be mapped to the CPP
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"target parameter" field (pres:user@host). 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:user@host) MUST be mapped
to the XMPP 'from' attribute (user@host). The XMPP-CPIM gateway
MUST remove the "pres:" Presence URI scheme from the front of the
address.
o The CPP "target parameter" field (pres:user@host) MUST be mapped
to the XMPP 'to' attribute (user@host). The XMPP-CPIM gateway
MUST remove the "pres:" Presence URI scheme from 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.
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.
6. Internationalization Considerations
6.1 Addresses
Although XMPP enables full internationalization of XMPP addresses
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(see [XMPP-CORE]), there is no guarantee that non-XMPP addresses can
include characters other than [US-ASCII]. If an XMPP user attempts to
communicate with a non-XMPP user through an XMPP-CPIM gateway, the
XMPP user SHOULD NOT assume that the non-XMPP service supports fully
internationalized addresses.
6.2 Character Encodings
The following rules apply to the mapping of character encodings
(charsets):
1. A gateway SHOULD map a "Message/CPIM" object whose charset is
"US-ASCII" or "UTF-8".
2. A gateway SHOULD NOT map a "Message/CPIM" object whose charset is
other than "US-ASCII" or "UTF-8".
7. Security Considerations
Detailed security considerations for instant messaging and presence
protocols are given in [IMP-REQS], 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] and
[CPP]. 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 [XMPP-E2E].
Normative References
[CPIM] Peterson, J., "Common Profile for Instant Messaging
(CPIM)", draft-ietf-impp-im-04 (work in progress), August
2003.
[CPP] Peterson, J., "Common Profile for Presence (CPP)",
draft-ietf-impp-pres-04 (work in progress), August 2003.
[IMP-MODEL]
Day, M., Rosenberg, J. and H. Sugano, "A Model for
Presence and Instant Messaging", RFC 2778, February 2000,
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Internet-Draft XMPP CPIM November 2003
<http://www.ietf.org/rfc/rfc2778.txt>.
[IMP-REQS]
Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging /
Presence Protocol Requirements", RFC 2779, February 2000.
[MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[MSGFMT] Atkins, D. and G. Klyne, "Common Presence and Instant
Messaging Message Format", draft-ietf-impp-cpim-msgfmt-08
(work in progress), January 2003.
[PIDF] 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.
[TERMS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[US-ASCII]
Cerf, V., "ASCII format for network interchange", RFC 20,
October 1969.
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 2279, January 1998.
[XMPP-CORE]
Saint-Andre (ed.), P., "Extensible Messaging and Presence
Protocol (XMPP): Core", draft-ietf-xmpp-core-20 (work in
progress), November 2003.
[XMPP-E2E]
Saint-Andre (ed.), P., "End-to-End Object Encryption in
the Extensible Messaging and Presence Protocol (XMPP)",
draft-ietf-xmpp-e2e-06 (work in progress), November 2003.
[XMPP-IM] Saint-Andre (ed.), P., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
draft-ietf-xmpp-im-19 (work in progress), November 2003.
Informative References
[RFC2822] Resnick, P., "Internet Message Format", RFC 2822, April
2001.
[MIMETYPES]
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Internet-Draft XMPP CPIM November 2003
Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996.
Author's Address
Peter Saint-Andre
Jabber Software Foundation
EMail: stpeter@jabber.org
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-02
o Removed references to UTF-16.
o Changed MUST NOT to SHOULD NOT for mapping of courtesy copy data.
o Added information about internationalization of addresses.
o Completed formatting changes to meet RFC Editor requirements.
A.2 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 addresses and CPIM instant
inboxes and presentities.
A.3 Changes from draft-ietf-xmpp-cpim-00
o Updated references.
o Made several small editorial changes.
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