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PROPOSED STANDARD
Network Working Group P. Saint-Andre
Request for Comments: 3922 Jabber Software Foundation
Category: Standards Track October 2004
Mapping the Extensible Messaging and Presence Protocol (XMPP) to
Common Presence and Instant Messaging (CPIM)
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
This memo describes a mapping between the Extensible Messaging and
Presence Protocol (XMPP) and the Common Presence and Instant
Messaging (CPIM) specifications.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Address Mapping . . . . . . . . . . . . . . . . . . . . . . . 4
4. Syntax Mapping of Instant Messages . . . . . . . . . . . . . . 5
5. Syntax Mapping of Presence Information . . . . . . . . . . . . 13
6. XMPP-CPIM Gateway as Presence Service . . . . . . . . . . . . 26
7. Security Considerations . . . . . . . . . . . . . . . . . . . 31
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 33
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 34
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RFC 3922 XMPP to CPIM October 2004
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".)
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 a gateway, referred to herein as an
"XMPP-CPIM gateway", 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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RFC 3922 XMPP to CPIM October 2004
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].
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
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.
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RFC 3922 XMPP to CPIM October 2004
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. Address Mapping
3.1. Overview
Address mapping may be required since the address formats used to
identify XMPP entities (specified in [XMPP-CORE]) are different from
those used to identify instant inboxes (the im: URI scheme specified
in [CPIM]) and presentities (the pres: URI scheme specified in
[CPP]). In particular, different characters are allowed in im: and
pres: URIs than are allowed in XMPP addresses:
o The following [US-ASCII] characters are allowed in im:/pres: URIs
but not in XMPP addresses: #26; (&), #27; ('), and #2f; (/).
o Many non-US-ASCII (specifically, UTF-8) characters are allowed in
XMPP addresses but not allowed in im:/pres: URIs, since XMPP
allows internationalized local-part addresses.
Note: In this document we discuss characters allowed in local-part
addresses only (i.e., we have ruled the mapping of domain names as
out of scope for the initial version of this document, since it is a
matter for the Domain Name System and the translation of fully
internationalized domain names).
3.2. XMPP to CPIM
The following is a high-level algorithm for mapping an XMPP address
to an im: or pres: URI:
1. Split XMPP address into node identifier (local-part; mapping
described in remaining steps), domain identifier (hostname;
mapping is out of scope), and resource identifier (specifier for
particular device or connection; discard this for cross-system
interoperability)
2. Apply Nodeprep profile of [STRINGPREP] (as specified in
[XMPP-CORE]) for canonicalization (OPTIONAL)
3. Translate #26; to &, #27; to ', and #2f; to / respectively
4. For each byte, if the byte is not in the set A-Za-z0-9!$*.?_~+=
then change to %hexhex as described in Section 2.2.5 of
[URL-GUIDE]
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5. Combine resulting local-part with mapped hostname to form
local@domain address
6. Prepend with 'im:' scheme (for XMPP <message/> stanzas) or
'pres:' scheme (for XMPP <presence/> stanzas)
3.3. CPIM to XMPP
The following is a high-level algorithm for mapping an im: or pres:
URI to an XMPP address:
1. Remove URI scheme
2. Split at the first '@' character into local-part and hostname
(mapping the latter is out of scope)
3. Translate %hexhex to equivalent octets as described in Section
2.2.5 of [URL-GUIDE]
4. Treat result as a UTF-8 string
5. Translate & to #26;, ' to #27;, and / to #2f respectively
6. Apply Nodeprep profile of [STRINGPREP] (as specified in
[XMPP-CORE]) for canonicalization (OPTIONAL)
7. Recombine local-part with mapped hostname to form local@domain
address
4. Syntax 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].
4.1. 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.
Note: 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
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RFC 3922 XMPP to CPIM October 2004
"Content-type" MUST be set to "text/plain" and the charset MUST be
set to "utf-8".
4.1.1. 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>
4.1.2. 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).
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RFC 3922 XMPP to CPIM October 2004
Example: To Address Mapping
XMPP 'to' attribute
<message to='romeo@example.net/orchard'>
...
</message>
CPIM 'To' header
To: Romeo Montague <im:romeo@example.net>
4.1.3. Stanza ID
An XMPP message stanza MAY possess an 'id' attribute, which is used
by the sending application for the purpose of tracking stanzas and is
not a globally-unique identifier such as is defined by the MIME
Content-ID header. Because the XMPP 'id' attribute does not have the
same meaning as the MIME Content-ID header, it SHOULD NOT be mapped
to that header; however, if the 'id' is known to be unique (e.g., if
it is generated to be unique by the XMPP server and that fact is
known by the XMPP-CPIM gateway), then it SHOULD be so mapped.
4.1.4. 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.
4.1.5. 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.
4.1.6. 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
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RFC 3922 XMPP to CPIM October 2004
'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!
4.1.7. 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?
4.1.8. 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.
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RFC 3922 XMPP to CPIM October 2004
4.1.9. Gateway-Generated CPIM Syntax
CPIM specifies the existence of "Message/CPIM" headers in addition to
those described above, but there is no exact analogue for those
headers in the core XMPP specifications. These include:
o cc -- specifies the address of an entity that is to receive a
"courtesy copy" of the message (i.e., a non-primary addressee)
o DateTime -- specifies the datetime at which the message was sent
o NS -- specifies the namespace of a feature extension
o Require -- specifies mandatory-to-recognize features
An XMPP-CPIM gateway MAY independently generate such headers based on
its own information (e.g., the datetime at which it received a
message stanza from an XMPP entity) or based on data encoded in
non-core XMPP extensions, but rules for doing so are out of scope for
this memo.
4.2. 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.
4.2.1. 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>
4.2.2. 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
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RFC 3922 XMPP to CPIM October 2004
"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>
4.2.3. 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 the information
contained in that header on to the XMPP recipient.
4.2.4. 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 the information contained in
that header on to the XMPP recipient.
4.2.5. 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 "tag" value supplied in the string
';lang=tag' included after the CPIM 'Subject' header name and colon.
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Example: Subject Mapping
CPIM 'Subject' header
Subject: Hi!
Subject:;lang=cz Ahoj!
XMPP <subject/> element
<subject>Hi!</subject>
<subject xml:lang='cz'>Ahoj!</subject>
4.2.6. 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.
4.2.7. Require Header
"Message/CPIM" objects MAY include an optional 'Require' header to
specify mandatory-to-recognize features. In general, such a header
would be included by the non-XMPP sending application to (1) insist
that the receiving application needs to understand functionality
specified by a particular header or (2) indicate that some non-header
semantics need to be implemented by the receiving application in
order to understand the contents of the message (e.g.,
"Locale.MustRenderKanji"). Because the mandatory-to-recognize
features would be required of the XMPP receiving application rather
than the XMPP-CPIM gateway itself, the gateway cannot properly handle
the 'Require' header without detailed knowledge about the
capabilities of the XMPP receiving application. Therefore, it seems
appropriate that the XMPP-CPIM gateway SHOULD return a warning or
error to the non-XMPP sending application if it includes one or more
'Require' headers in a "Message/CPIM" object; the exact nature of the
warning or error will depend on the nature of the non-XMPP technology
used by the foreign system, and is not defined herein. Furthermore,
any mapping of the 'Require' header into XMPP or an XMPP extension is
left up to the implementation or to a future specification.
4.2.8. 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 this is OPTIONAL.
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Example: Content-ID for Encapsulated Object
MIME header
Content-ID: <123456789@example.net>
XMPP 'id' attribute (OPTIONAL)
<message id='123456789@example.net'>
...
</message>
4.2.9. 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>
Wherefore art thou?
XMPP message <body/>
<message id='123456789@example.net'>
<body>Wherefore art thou?</body>
</message>
If the Content-Type is not "text/plain", the XMPP-CPIM gateway MAY
map the content to an XMPP extension but MUST NOT map it to the
<body/> child of the XMPP message stanza, which is allowed to contain
XML character data only. The only exception to this rule is a
multi-part MIME object of the kind specified in [XMPP-E2E], which is
to be mapped as described in that memo.
If the charset is "US-ASCII" or "UTF-8", the gateway MUST map the
"Message/CPIM" object; otherwise it SHOULD NOT.
4.2.10. Gateway-Generated XMPP Syntax
XMPP specifies the existence of a 'type' attribute for XMPP message
stanzas, which enables the sender to define the conversational
context of the message. There is no exact analogue for this
attribute in CPIM. An XMPP-CPIM gateway MAY independently generate
the 'type' attribute based on its own information, but this is
OPTIONAL and rules for doing so are out of scope for this memo.
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5. Syntax Mapping of Presence Information
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].
5.1. 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.
Note: 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 type, 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".
5.1.1. 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
XMPP 'from' attribute
<presence from='juliet@example.com/balcony'>
...
</presence>
CPIM 'From' header
From: Juliet Capulet <im:juliet@example.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@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>
5.1.2. To Address
The 'to' attribute of an XMPP presence stanza maps to the 'To' header
of a "Message/CPIM" object. In XMPP, the sender 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
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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>
5.1.3. Stanza ID
An XMPP presence stanza MAY possess an 'id' attribute, which is used
by the sending application for the purpose of tracking stanzas and is
not a globally-unique identifier such as is defined by the MIME
Content-ID header. Because the XMPP 'id' attribute does not have the
same meaning as the MIME Content-ID header, it SHOULD NOT be mapped
to that header; however, if the 'id' is known to be unique (e.g., if
it is generated to be unique by the XMPP server and that fact is
known by the XMPP-CPIM gateway), then it SHOULD be so mapped.
5.1.4. 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 6).
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'>
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<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>
5.1.5. 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>
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<im:im>away</im:im>
</status>
</tuple>
</presence>
5.1.6. 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'?>
<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>
5.1.7. 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
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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>
5.1.8. 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.
5.1.9. Gateway-Generated CPIM and PIDF Syntax
5.1.9.1. CPIM Message Headers
CPIM specifies the existence of "Message/CPIM" headers in addition to
those described above, but there is no exact analogue for those
headers in the core XMPP specifications. These include:
o cc -- specifies the address of an entity that is to receive a
"courtesy copy" of the presence information (i.e., a non-primary
addressee)
o DateTime -- specifies the datetime at which the presence
information was sent
o NS -- specifies the namespace of a feature extension
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o Subject -- specifies the subject or topic of the encapsulated
"Message/CPIM" object
o Require -- specifies mandatory-to-recognize features
An XMPP-CPIM gateway MAY independently generate such headers based on
its own information (e.g., the datetime at which it received a
presence stanza from an XMPP entity) or based on data encoded in
non-core XMPP extensions, but rules for doing so are out of scope for
this memo.
5.1.9.2. PIDF Elements
PIDF specifies the existence of XML elements in addition to those
described above, but there is no exact analogue for those XML
elements in the core XMPP specifications. These include:
o <contact/> -- specifies an address (e.g., an im:, tel:, or mailto:
URI) at which one may communicate with the presentity; an
XMPP-CPIM gateway MAY include this element, in which case it
SHOULD set its value to the <user@host> of the XMPP sender,
prepended by the "im:" Instant Messaging URI scheme.
o <timestamp/> -- specifies the datetime at which the presence
information was sent; an XMPP-CPIM gateway MAY independently
generate this element based on its own information (e.g., the
datetime at which it received the presence stanza from an XMPP
entity) or based on data encoded in non-core XMPP extensions, but
rules for doing so are out of scope for this memo.
5.2. 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.
Note: 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]).
5.2.1. From Address
The 'From' header of a "Message/CPIM" object maps to the <user@host>
portion of the 'from' attribute of an XMPP presence stanza, and the
'id' attribute of the PIDF <tuple/> child element maps to the
resource identifier portion XMPP 'from' attribute. Therefore, to map
the CPIM and PIDF information to the XMPP 'from' attribute, the
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RFC 3922 XMPP to CPIM October 2004
gateway MUST remove the "im:" Instant Messaging URI scheme from the
front of the address and MUST remove the CPIM "Formal-name" (if
provided) in order to generate the <user@host> portion of the XMPP
'from' attribute, then add a '/' character followed by the value of
the PIDF <tuple/> element's 'id' attribute.
Example: From Address Mapping
CPIM 'From' header
From: Romeo Montague <im:romeo@example.net>
XMPP 'from' attribute
<presence from='romeo@example.net'>
...
</presence>
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>
5.2.2. 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.
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RFC 3922 XMPP to CPIM October 2004
Example: To Address Mapping
CPIM 'To' header
To: Juliet Capulet <im:juliet@example.com>
XMPP 'to' attribute
<presence to='juliet@example.com/balcony'>
...
</presence>
5.2.3. 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 SHOULD
NOT pass the information contained in that header on to the XMPP
recipient.
5.2.4. 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 the
information contained in that header on to the XMPP recipient.
5.2.5. 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 the
information contained in that header on to the XMPP recipient.
5.2.6. 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.
5.2.7. Require Header
"Message/CPIM" objects MAY include an optional 'Require' 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.
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RFC 3922 XMPP to CPIM October 2004
5.2.8. 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 presence stanza's 'id' attribute, but this is OPTIONAL.
Example: Content-ID for Encapsulated Object
MIME header
Content-ID: <123456789@example.net>
XMPP 'id' attribute (OPTIONAL)
<presence id='123456789@example.net'>
...
</presence>
5.2.9. 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'/>
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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>
<basic>closed</basic>
</status>
</tuple>
</presence>
XMPP unavailable presence
<presence from='romeo@example.net/orchard'
type='unavailable'/>
5.2.10. Extended Status Information
PIDF documents may contain extended <status/> content. As of this
writing there are no pre-defined extended status states that can be
mapped to the defined values of the XMPP <show/> element ('away',
'chat', 'dnd', and 'xa'). Once PIDF extensions for such extended
status states are defined within the Internet Standards Process, a
gateway SHOULD map those extensions; however, any such mapping is out
of scope for this memo, since the relevant PIDF extensions have not
yet been defined.
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>
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5.2.11. 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@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 6.3.2)).
5.2.12. Contact Element
A PIDF document may contain a <contact/> element specifying the URI
of an address at which the principal can be contacted (e.g., an im:,
tel:, or mailto: URI). The core XMPP specification does not include
syntax for specifying the URI 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/>
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RFC 3922 XMPP to CPIM October 2004
element, it SHOULD NOT pass the XML character data of the <contact/>
element on to the XMPP recipient. (However, see Inclusion of
Complete PIDF Document (Section 5.2.15) below.)
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'>
...
<contact>im:romeo@example.net</contact>
</tuple>
</presence>
XMPP presence stanza
<presence from='romeo@example.net/orchard'/>
5.2.13. 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).
5.2.14. 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 the XML character data of the <timestamp/> element
on to the XMPP recipient.
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5.2.15. Inclusion of Complete PIDF Document
Certain PIDF elements do not map to XMPP presence stanza syntax
(e.g., the XML character data of the <contact/> element). However,
an XMPP client may be able to handle such information by parsing a
native PIDF document. To make this possible, an XMPP-CPIM gateway
MAY include the complete PIDF document as a child element of the
presence stanza, as described in [XMPP-PIDF]. If an XMPP client does
not understand this extended data, it naturally MUST ignore it.
6. 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.)
6.1. 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".
o The XMPP 'id' attribute SHOULD be mapped to the CPP "TransID"
field.
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RFC 3922 XMPP to CPIM October 2004
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.
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.
XMPP services assume that a subscription is active until it is
explicitly terminated. However, non-XMPP services may implement
subscriptions of limited duration, which must be periodically
refreshed in order to mimic the permanence of XMPP subscriptions.
Therefore, an XMPP-to-CPIM gateway may need to send such refreshes to
the non-XMPP entity on behalf of the XMPP entity to that the
subscription does not expire. Whether such refreshes are necessary
depends on the native protocol implemented by the CPIM-aware non-XMPP
service to which the gateway is translating.
6.2. 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:
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RFC 3922 XMPP to CPIM October 2004
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".
o The CPP "TransID" field SHOULD be mapped to the XMPP 'id'
attribute.
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:
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.
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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. However, an XMPP-CPIM gateway MAY
keep track of the duration parameter if received from an entity on
the non-XMPP service and delete the subscription after that duration
parameter expires.
6.3. 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 5).
6.3.1. 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
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RFC 3922 XMPP to CPIM October 2004
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.
6.3.2. 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. Although the notion of
presence notifications about a mere user rather than one of the
user's resources is nearly meaningless in the XMPP context, an
XMPP-CPIM gateway SHOULD map a PIDF document with zero tuples to an
XMPP presence stanza whose 'from' address is the user@host of the
non-XMPP entity. However, an XMPP-CPIM gateway MUST NOT generate a
PIDF document with zero <tuple/> children when receiving a presence
stanza from an XMPP entity (i.e., all PIDF documents communicated by
the gateway to a non-XMPP service MUST contain at least one <tuple/>
element).
6.4. 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
"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.
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RFC 3922 XMPP to CPIM October 2004
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.
6.5. 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 XMPP 'from' attribute (user@host) MUST be mapped to the CPP
"watcher parameter" field (pres:user@host). The XMPP-CPIM gateway
MUST add 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 add 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.
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.
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
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RFC 3922 XMPP to CPIM October 2004
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].
8. References
8.1. Normative References
[CPIM] Peterson, J., "Common Profile for Instant Messaging
(CPIM)", RFC 3860, August 2004.
[CPP] Peterson, J., "Common Profile for Presence (CPP)", RFC
3859, August 2004.
[IMP-MODEL] Day, M., Rosenberg, J., and H. Sugano, "A Model for
Presence and Instant Messaging", RFC 2778, February
2000.
[IMP-REQS] Day, M., Aggarwal, S., Mohr, G., 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] Klyne, G. and D. Atkins, "Common Presence and Instant
Messaging (CPIM): Message Format", RFC 3862, August
2004.
[PIDF] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr,
W., and J. Peterson, "Presence Information Data Format
(PIDF)", RFC 3863, August 2004.
[STRINGPREP] Hoffman, P. and M. Blanchet, "Preparation of
Internationalized Strings (stringprep)", RFC 3454,
December 2002.
[TERMS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[URL-GUIDE] Masinter, L., Alvestrand, H., Zigmond, D., and R. Petke,
"Guidelines for new URL Schemes", RFC 2718, November
1999.
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RFC 3922 XMPP to CPIM October 2004
[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", STD 63, RFC 3629, November 2003.
[XMPP-CORE] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, October 2004.
[XMPP-E2E] Saint-Andre, P., Ed., "End-to-End Signing and Object
Encryption in the Extensible Messaging and Presence
Protocol (XMPP)", RFC 3923, October 2004.
[XMPP-IM] Saint-Andre (ed.), P., "Extensible Messaging and
Presence Protocol (XMPP): Instant Messaging and
Presence", RFC 3921, October 2004.
8.2. Informative References
[RFC2822] Resnick, P., Ed., "Internet Message Format", RFC 2822,
April 2001.
[MIMETYPES] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996.
[XMPP-PIDF] Saint-Andre, P., "Transporting Presence Information
Data/Format (PIDF) over the Extensible Messaging and
Presence Protocol (XMPP)", Work in Progress, February
2004.
Author's Address
Peter Saint-Andre
Jabber Software Foundation
EMail: stpeter@jabber.org
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RFC 3922 XMPP to CPIM October 2004
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