Network Working Group P. Saint-Andre
Internet-Draft Cisco Systems, Inc.
Obsoletes: 3921 (if approved) July 12, 2010
Intended status: Standards Track
Expires: January 13, 2011
Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and
Presence
draft-ietf-xmpp-3921bis-08
Abstract
This document defines extensions to core features of the Extensible
Messaging and Presence Protocol (XMPP) that provide basic instant
messaging (IM) and presence functionality in conformance with RFC
2779. This document obsoletes RFC 3921.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 13, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2. History . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3. Requirements . . . . . . . . . . . . . . . . . . . . . . 6
1.4. Functional Summary . . . . . . . . . . . . . . . . . . . 8
1.5. Conventions . . . . . . . . . . . . . . . . . . . . . . . 9
1.6. Acknowledgements . . . . . . . . . . . . . . . . . . . . 9
1.7. Discussion Venue . . . . . . . . . . . . . . . . . . . . 10
2. Managing the Roster . . . . . . . . . . . . . . . . . . . . . 10
2.1. Syntax and Semantics . . . . . . . . . . . . . . . . . . 10
2.1.1. Ver Attribute . . . . . . . . . . . . . . . . . . . . 10
2.1.2. Roster Items . . . . . . . . . . . . . . . . . . . . 11
2.1.2.1. Ask Attribute . . . . . . . . . . . . . . . . . . 11
2.1.2.2. JID Attribute . . . . . . . . . . . . . . . . . . 11
2.1.2.3. Name Attribute . . . . . . . . . . . . . . . . . 11
2.1.2.4. Subscription Attribute . . . . . . . . . . . . . 11
2.1.2.5. Group Element . . . . . . . . . . . . . . . . . . 12
2.1.3. Roster Get . . . . . . . . . . . . . . . . . . . . . 12
2.1.4. Roster Result . . . . . . . . . . . . . . . . . . . . 13
2.1.5. Roster Set . . . . . . . . . . . . . . . . . . . . . 14
2.1.6. Roster Push . . . . . . . . . . . . . . . . . . . . . 15
2.2. Retrieving the Roster on Login . . . . . . . . . . . . . 15
2.3. Adding a Roster Item . . . . . . . . . . . . . . . . . . 17
2.3.1. Request . . . . . . . . . . . . . . . . . . . . . . . 17
2.3.2. Success Case . . . . . . . . . . . . . . . . . . . . 17
2.3.3. Error Cases . . . . . . . . . . . . . . . . . . . . . 18
2.4. Updating a Roster Item . . . . . . . . . . . . . . . . . 23
2.4.1. Request . . . . . . . . . . . . . . . . . . . . . . . 23
2.4.2. Success Case . . . . . . . . . . . . . . . . . . . . 25
2.4.3. Error Cases . . . . . . . . . . . . . . . . . . . . . 25
2.5. Deleting a Roster Item . . . . . . . . . . . . . . . . . 25
2.5.1. Request . . . . . . . . . . . . . . . . . . . . . . . 25
2.5.2. Success Case . . . . . . . . . . . . . . . . . . . . 25
2.5.3. Error Cases . . . . . . . . . . . . . . . . . . . . . 26
2.6. Roster Versioning . . . . . . . . . . . . . . . . . . . . 27
2.6.1. Stream Feature . . . . . . . . . . . . . . . . . . . 27
2.6.2. Request . . . . . . . . . . . . . . . . . . . . . . . 27
2.6.3. Success Case . . . . . . . . . . . . . . . . . . . . 28
3. Managing Presence Subscriptions . . . . . . . . . . . . . . . 31
3.1. Requesting a Subscription . . . . . . . . . . . . . . . . 32
3.1.1. Client Generation of Outbound Subscription Request . 32
3.1.2. Server Processing of Outbound Subscription Request . 33
3.1.3. Server Processing of Inbound Subscription Request . . 35
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3.1.4. Client Processing of Inbound Subscription Request . . 37
3.1.5. Server Processing of Outbound Subscription Approval . 38
3.1.6. Server Processing of Inbound Subscription Approval . 39
3.2. Cancelling a Subscription . . . . . . . . . . . . . . . . 41
3.2.1. Client Generation of Subscription Cancellation . . . 41
3.2.2. Server Processing of Outbound Subscription
Cancellation . . . . . . . . . . . . . . . . . . . . 41
3.2.3. Server Processing of Inbound Subscription
Cancellation . . . . . . . . . . . . . . . . . . . . 42
3.3. Unsubscribing . . . . . . . . . . . . . . . . . . . . . . 43
3.3.1. Client Generation of Unsubscribe . . . . . . . . . . 43
3.3.2. Server Processing of Outbound Unsubscribe . . . . . . 44
3.3.3. Server Processing of Inbound Unsubscribe . . . . . . 45
4. Exchanging Presence Information . . . . . . . . . . . . . . . 46
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 46
4.2. Initial Presence . . . . . . . . . . . . . . . . . . . . 47
4.2.1. Client Generation of Initial Presence . . . . . . . . 47
4.2.2. Server Processing of Outbound Initial Presence . . . 48
4.2.3. Server Processing of Inbound Initial Presence . . . . 48
4.2.4. Client Processing of Initial Presence . . . . . . . . 49
4.3. Presence Probes . . . . . . . . . . . . . . . . . . . . . 49
4.3.1. Server Generation of Outbound Presence Probe . . . . 50
4.3.2. Server Processing of Inbound Presence Probe . . . . . 51
4.4. Subsequent Presence Broadcast . . . . . . . . . . . . . . 53
4.4.1. Client Generation of Subsequent Presence Broadcast . 53
4.4.2. Server Processing of Outbound Presence . . . . . . . 54
4.4.3. Server Processing of Inbound Presence . . . . . . . . 55
4.4.4. Client Processing of Subsequent Presence . . . . . . 55
4.5. Unavailable Presence . . . . . . . . . . . . . . . . . . 56
4.5.1. Client Generation of Unavailable Presence . . . . . . 56
4.5.2. Server Processing of Outbound Unavailable Presence . 56
4.5.3. Server Processing of Inbound Unavailable Presence . . 58
4.5.4. Client Processing of Unavailable Presence . . . . . . 58
4.6. Directed Presence . . . . . . . . . . . . . . . . . . . . 59
4.6.1. Client Generation of Directed Presence . . . . . . . 59
4.6.2. Server Processing of Outbound Directed Presence . . . 59
4.6.3. Server Processing of Inbound Directed Presence . . . 60
4.6.4. Client Processing of Inbound Directed Presence . . . 60
4.7. Presence Syntax . . . . . . . . . . . . . . . . . . . . . 60
4.7.1. Type Attribute . . . . . . . . . . . . . . . . . . . 60
4.7.2. Child Elements . . . . . . . . . . . . . . . . . . . 62
4.7.2.1. Show Element . . . . . . . . . . . . . . . . . . 62
4.7.2.2. Status Element . . . . . . . . . . . . . . . . . 62
4.7.2.3. Priority Element . . . . . . . . . . . . . . . . 64
4.7.3. Extended Content . . . . . . . . . . . . . . . . . . 64
5. Exchanging Messages . . . . . . . . . . . . . . . . . . . . . 65
5.1. One-to-One Chat Sessions . . . . . . . . . . . . . . . . 65
5.2. Message Syntax . . . . . . . . . . . . . . . . . . . . . 66
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5.2.1. To Attribute . . . . . . . . . . . . . . . . . . . . 66
5.2.2. Type Attribute . . . . . . . . . . . . . . . . . . . 67
5.2.3. Body Element . . . . . . . . . . . . . . . . . . . . 68
5.2.4. Subject Element . . . . . . . . . . . . . . . . . . . 69
5.2.5. Thread Element . . . . . . . . . . . . . . . . . . . 70
5.3. Extended Content . . . . . . . . . . . . . . . . . . . . 71
6. Exchanging IQ Stanzas . . . . . . . . . . . . . . . . . . . . 72
7. A Sample Session . . . . . . . . . . . . . . . . . . . . . . 72
8. Server Rules for Processing XML Stanzas . . . . . . . . . . . 80
8.1. No 'to' Address . . . . . . . . . . . . . . . . . . . . . 81
8.2. Remote Domain . . . . . . . . . . . . . . . . . . . . . . 81
8.3. Local Domain . . . . . . . . . . . . . . . . . . . . . . 82
8.3.1. No Such User . . . . . . . . . . . . . . . . . . . . 82
8.3.2. Full JID at Local Domain . . . . . . . . . . . . . . 83
8.3.2.1. Resource Matches . . . . . . . . . . . . . . . . 83
8.3.2.2. No Resource Matches . . . . . . . . . . . . . . . 83
8.3.3. Bare JID at Local Domain . . . . . . . . . . . . . . 85
8.3.3.1. Available or Connected Resources . . . . . . . . 85
8.3.3.2. No Available or Connected Resources . . . . . . . 86
8.3.4. Summary of Message Delivery Rules . . . . . . . . . . 87
9. Handling of URIs . . . . . . . . . . . . . . . . . . . . . . 88
10. Internationalization Considerations . . . . . . . . . . . . . 89
11. Security Considerations . . . . . . . . . . . . . . . . . . . 89
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 90
12.1. Instant Messaging SRV Protocol Label Registration . . . . 90
12.2. Presence SRV Protocol Label Registration . . . . . . . . 90
13. Conformance Requirements . . . . . . . . . . . . . . . . . . 90
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 93
14.1. Normative References . . . . . . . . . . . . . . . . . . 93
14.2. Informative References . . . . . . . . . . . . . . . . . 94
Appendix A. Subscription States . . . . . . . . . . . . . . . . 97
A.1. Defined States . . . . . . . . . . . . . . . . . . . . . 97
A.2. Server Processing of Outbound Presence Subscription
Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 98
A.2.1. Subscribe . . . . . . . . . . . . . . . . . . . . . . 99
A.2.2. Unsubscribe . . . . . . . . . . . . . . . . . . . . . 99
A.2.3. Subscribed . . . . . . . . . . . . . . . . . . . . . 100
A.2.4. Unsubscribed . . . . . . . . . . . . . . . . . . . . 101
A.3. Server Processing of Inbound Presence Subscription
Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 101
A.3.1. Subscribe . . . . . . . . . . . . . . . . . . . . . . 102
A.3.2. Unsubscribe . . . . . . . . . . . . . . . . . . . . . 102
A.3.3. Subscribed . . . . . . . . . . . . . . . . . . . . . 103
A.3.4. Unsubscribed . . . . . . . . . . . . . . . . . . . . 104
Appendix B. Blocking Communication . . . . . . . . . . . . . . . 105
Appendix C. vCards . . . . . . . . . . . . . . . . . . . . . . . 105
Appendix D. XML Schemas . . . . . . . . . . . . . . . . . . . . 105
D.1. jabber:client . . . . . . . . . . . . . . . . . . . . . . 105
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D.2. jabber:server . . . . . . . . . . . . . . . . . . . . . . 110
D.3. jabber:iq:roster . . . . . . . . . . . . . . . . . . . . 114
Appendix E. Differences From RFC 3921 . . . . . . . . . . . . . 116
Appendix F. Copying Conditions . . . . . . . . . . . . . . . . . 116
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 117
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1. Introduction
1.1. Overview
The Extensible Messaging and Presence Protocol (XMPP) is an
application profile of the Extensible Markup Language [XML] that
enables the near-real-time exchange of structured yet extensible data
between any two or more network entities. The core features of XMPP
defined in [XMPP-CORE] provide the building blocks for many types of
near-real-time applications, which can be layered on top of the core
by sending application-specific data qualified by particular XML
namespaces (refer to [XML-NAMES]). This document defines XMPP
extensions that provide the basic functionality expected of an
instant messaging (IM) and presence application as described in
[IMP-REQS].
1.2. History
The basic syntax and semantics of XMPP were developed originally
within the Jabber open-source community, mainly in 1999. In late
2002, the XMPP Working Group was chartered with developing an
adaptation of the core Jabber protocol that would be suitable as an
IETF instant messaging (IM) and presence technology in accordance
with [IMP-REQS]. In October 2004, [RFC3920] and [RFC3921] were
published, representing the most complete definition of XMPP at that
time.
Since 2004 the Internet community has gained extensive implementation
and deployment experience with XMPP, including formal
interoperability testing carried out under the auspices of the XMPP
Standards Foundation (XSF). This document incorporates comprehensive
feedback from software developers and service providers, including a
number of backward-compatible modifications summarized under
Appendix E. As a result, this document reflects the rough consensus
of the Internet community regarding the instant messaging and
presence features of XMPP 1.0, thus obsoleting RFC 3921.
1.3. Requirements
Traditionally, instant messaging applications have combined the
following factors:
1. The central point of focus is a list of one's contacts or
"buddies" (in XMPP this list is called a ROSTER).
2. The purpose of using such an application is to exchange
relatively brief text messages with particular contacts in close
to real time -- often relatively large numbers of such messages
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in rapid succession, in the form of a one-to-one CHAT SESSION as
described under Section 5.1.
3. The catalyst for exchanging messages is PRESENCE -- i.e.,
information about the network availability of particular contacts
(thus knowing who is online and available for a one-to-one chat
session).
4. Presence information is provided only to contacts that one has
authorized by means of an explicit agreement called a PRESENCE
SUBSCRIPTION.
Thus at a high level this document assumes that a user needs to be
able to complete the following use cases:
o Manage items in one's contact list
o Exchange messages with one's contacts
o Exchange presence information with one's contacts
o Manage presence subscriptions to and from one's contacts
Detailed definitions of these functionality areas are contained in
RFC 2779 [IMP-REQS], and the interested reader is referred to that
document regarding detailed requirements. While the XMPP instant
messaging and presence extensions specified herein meet the
requirements of RFC 2779, they were not designed explicitly with that
specification in mind, since the base protocol evolved through an
open development process within the Jabber open-source community
before RFC 2779 was written. Although XMPP protocol extensions
addressing many other functionality areas have been defined in the
XMPP Standards Foundation's XEP series (e.g., multi-user text chat as
specified in [XEP-0045]), such extensions are not specified in this
document because they are not mandated by RFC 2779.
Implementation Note: RFC 2779 stipulates that presence services
must be separable from instant messaging services and vice-versa;
i.e., it must be possible to use the protocol to provide a
presence service, an instant messaging service, or both. Although
the text of this document assumes that implementations and
deployments will want to offer a unified instant messaging and
presence service, it is not mandatory for an XMPP service to offer
both a presence service and an instant messaging service, and the
protocol makes it possible to offer separate and distinct services
for presence and for instant messaging. (For example, a presence-
only service could return a <service-unavailable/> stanza error if
a client attempts to send a <message/> stanza.)
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1.4. Functional Summary
This non-normative section provides a developer-friendly, functional
summary of XMPP-based instant messaging and presence features;
consult the sections that follow for a normative definition of these
features.
[XMPP-CORE] specifies how an XMPP client connects to an XMPP server.
In particular, it specifies the preconditions that need to be
fulfilled before a client is allowed to send XML stanzas (the basic
unit of meaning in XMPP) to other entities on an XMPP network. These
preconditions comprise negotiation of the XML stream and include
exchange of XML stream headers, optional channel encryption via
Transport Layer Security [TLS], mandatory authentication via Simple
Authentication and Security Layer [SASL], and binding of a resource
to the stream for client addressing. The reader is referred to
[XMPP-CORE] for details regarding these preconditions, and knowledge
of [XMPP-CORE] is assumed herein.
Interoperability Note: [RFC3921] specified one additional
precondition: formal establishment of an instant messaging and
presence session. Implementation and deployment experience has
shown that this additional step is unnecessary. However, for
backward compatibility an implementation SHOULD still offer that
feature. This enables older software to connect while letting
newer software skip a round trip.
Upon fulfillment of the preconditions specified in [XMPP-CORE], an
XMPP client has a long-lived XML stream with an XMPP server, which
enables the user controlling that client to send and receive a
potentially unlimited number of XML stanzas over the stream. Such a
stream can be used to exchange messages, share presence information,
and engage in structured request-response interactions in close to
real time. After negotiation of the XML stream, the typical flow for
an instant messaging and presence session is as follows:
1. Retrieve one's roster. (See Section 2.2.)
2. Send initial presence to the server for broadcasting to all
subscribed contacts, thus "going online" from the perspective of
XMPP communication. (See Section 4.2.)
3. Exchange messages, manage presence subscriptions, perform roster
updates, and in general process and generate other XML stanzas
with particular semantics throughout the life of the session.
(See Section 5, Section 3, Section 2, and Section 6.)
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4. Terminate the session when desired by sending unavailable
presence and closing the underlying XML stream. (See
Section 4.5.)
1.5. Conventions
This document inherits the terminology defined in [XMPP-CORE].
The following capitalized keywords are to be interpreted as described
in [KEYWORDS]: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT";
"SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY",
"OPTIONAL".
For convenience, this document employs the term "user" to refer to
the owner of an XMPP account; however, account owners need not be
natural persons and can be bots, devices, or other automated
applications.
Following the "XML Notation" used in [IRI] to represent characters
that cannot be rendered in ASCII-only documents, some examples in
this document use the form "&#x...." as a notational device to
represent Unicode characters (e.g., the string "ř" stands for
the Unicode character LATIN SMALL LETTER R WITH CARON).
In examples, lines have been wrapped for improved readability,
"[...]" means elision, and the following prepended strings are used
(these prepended strings are not to be sent over the wire):
o C: = client
o CC: = contact's client
o CS: = contact's server
o S: = server
o UC: = user's client
o US: = user's server
1.6. Acknowledgements
The editor of this document finds it impossible to appropriately
acknowledge the many individuals who have provided comments regarding
the protocols defined in this specification. However, thanks are due
to those who have provided implementation feedback, bug reports,
requests for clarification, and suggestions for improvement since the
publication of the RFC this document supersedes. The editor has
endeavored to address all such feedback, but is solely responsible
for any remaining errors and ambiguities.
Some of the text about roster versioning was borrowed from [XEP-0237]
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and some of the text about message threads was borrowed from
[XEP-0201].
1.7. Discussion Venue
The document editor and the broader XMPP developer community welcome
discussion and comments related to the topics presented in this
document. The primary and preferred venue is the <xmpp@ietf.org>
mailing list, for which archives and subscription information are
available at <https://www.ietf.org/mailman/listinfo/xmpp>. Related
discussions often occur on the <standards@xmpp.org> mailing list, for
which archives and subscription information are available at
<http://mail.jabber.org/mailman/listinfo/standards>.
2. Managing the Roster
In XMPP, a user's roster contains any number of specific contacts. A
user's roster is stored by the user's server on the user's behalf so
that the user can access roster information from any device.
Security Note: Because the user's roster can contain confidential
data, the server MUST restrict access to this data so that only
authorized entities (typically limited to the account owner) are
able to retrieve, modify, or delete it.
2.1. Syntax and Semantics
Rosters are managed using IQ stanzas, specifically by means of a
<query/> child element qualified by the 'jabber:iq:roster' namespace.
The detailed syntax and semantics are defined in the following
sections.
2.1.1. Ver Attribute
The 'ver' attribute is a string that identifies a particular version
of the roster information. The value MUST be generated only by the
server and MUST be treated by the client as opaque. The server can
use any appropriate method for generating the version ID, such as a
hash of the roster data or a strictly-increasing sequence number.
Inclusion of the 'ver' attribute is RECOMMENDED.
Use of the 'ver' attribute is described more fully under Section 2.6.
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2.1.2. Roster Items
The <query/> element inside a roster set (Section 2.1.5) contains one
<item/> child, and a roster result (Section 2.1.4) typically contains
multiple <item/> children. Each <item/> element describes a unique
ROSTER ITEM or "contact".
The syntax of the <item/> element is described in the following
sections.
2.1.2.1. Ask Attribute
The 'ask' attribute is used to specify certain subscription sub-
states; for details, see Section 3.1.2.
Inclusion of the 'ask' attribute is OPTIONAL.
2.1.2.2. JID Attribute
The 'jid' attribute specifies the Jabber Identifier (JID) that
uniquely identifies the roster item.
Inclusion of the 'jid' attribute is REQUIRED.
2.1.2.3. Name Attribute
The 'name' attribute specifies the "handle" to be associated with the
JID, as determined by the user (not the contact). Although the value
of the 'name' attribute MAY have meaning to a human user, it is
opaque to the server. However, the 'name' attribute MAY be used by
the server for matching purposes within the context of various XMPP
extensions (one possible comparison method is that described for XMPP
resourceparts in [XMPP-ADDR]).
Inclusion of the 'name' attribute is OPTIONAL.
2.1.2.4. Subscription Attribute
The state of the presence subscription is captured in the
'subscription' attribute of the <item/> element. The defined
subscription-related values are:
none: the user does not have a subscription to the contact's
presence, and the contact does not have a subscription to the
user's presence; this is the default value, so if the subscription
attribute is not included then the state is to be understood as
"none"
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to: the user has a subscription to the contact's presence, but the
contact does not have a subscription to the user's presence
from: the contact has a subscription to the user's presence, but the
user does not have a subscription to the contact's presence
both: the user and the contact have subscriptions to each other's
presence (also called a "mutual subscription")
In a roster result (Section 2.1.4), the client MUST ignore values of
the 'subscription' attribute other than "none", "to", "from", or
"both".
In a roster push (Section 2.1.6), the client MUST ignore values of
the 'subscription' attribute other than "none", "to", "from", "both",
or "remove".
In a roster set (Section 2.1.5), the 'subscription' attribute MAY be
included with a value of "remove", which indicates that the item is
to be removed from the roster; in a roster set the server MUST ignore
all values of the 'subscription' attribute other than "remove".
Inclusion of the 'subscription' attribute is OPTIONAL.
2.1.2.5. Group Element
The <group/> child element specifies a category or "bucket" into
which the roster item is to be grouped by a client. An <item/>
element MAY contain more than one <group/> element, which means that
roster groups are not exclusive. Although the XML character data of
the <group/> element MAY have meaning to a human user, it is opaque
to the server. However, the <group/> element MAY be used by the
server for matching purposes within the context of various XMPP
extensions (one possible comparison method is that described for XMPP
resourceparts in [XMPP-ADDR]).
Inclusion of the <group/> element is OPTIONAL. If a roster set
(Section 2.1.5) includes no <group/> element, then the item is to be
interpreted being affiliated with no group.
2.1.3. Roster Get
A ROSTER GET is a client's request for the server to return the
roster; syntactically it is an IQ stanza of type "get" sent from
client to server and containing a <query/> element qualified by the
'jabber:iq:roster' namespace, where the <query/> element MUST NOT
contain any <item/> child elements.
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C: <iq from='juliet@example.com/balcony'
id='bv1bs71f'
type='get'>
<query xmlns='jabber:iq:roster'/>
</iq>
The expected outcome of sending a roster get is for the server to
return a roster result.
2.1.4. Roster Result
A ROSTER RESULT is the server's response to a roster get;
syntactically it is an IQ stanza of type "result" sent from server to
client and containing a <query/> element qualified by the 'jabber:iq:
roster' namespace.
The <query/> element in a roster result contains one <item/> element
for each contact and therefore can contain more than one <item/>
element.
S: <iq id='bv1bs71f'
to='juliet@example.com/chamber'
type='result'>
<query xmlns='jabber:iq:roster' ver='ver7'>
<item jid='nurse@example.com'/>
<item jid='romeo@example.net'/>
</query>
</iq>
If the roster exists but there are no contacts in the roster, then
the server MUST return an IQ-result containing a child <query/>
element that in turn contains no <item/> children (i.e. , the server
MUST NOT return an empty <iq/> stanza of type 'error').
S: <iq id='bv1bs71f'
to='juliet@example.com/chamber'
type='result'>
<query xmlns='jabber:iq:roster' ver='ver9'/>
</iq>
If the roster does not exist, then the server MUST return a stanza
error with a condition of <item-not-found/>.
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S: <iq id='bv1bs71f'
to='juliet@example.com/chamber'
type='error'>
<error type='auth'>
<item-not-found
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
2.1.5. Roster Set
A ROSTER SET is a client's request for the server to modify (i.e.,
create, update, or delete) a roster item; syntactically it is an IQ
stanza of type "set" sent from client to server and containing a
<query/> element qualified by the 'jabber:iq:roster' namespace.
The following rules apply to roster sets:
1. The <query/> element MUST contain one and only one <item/>
element.
2. The server MUST ignore any value of the 'subscription' attribute
other than "remove" (see Section 2.1.2.4).
Note: Traditionally, the IQ stanza of the roster set included no
'to' address, with the result that all roster sets were sent from
an authenticated resource of the account whose roster was being
updated. Furthermore, the predecessor to this specification
required a server to perform special-case checking of roster set
stanzas to ignore the 'to' address; however, this specification
has removed that special-casing, which means that a roster set
stanza might include a 'to' address other than that of the sender.
Therefore, the server MUST verify that the sender of the roster
set stanza is authorized to update the roster, and if not return a
<forbidden/> error.
C: <iq from='juliet@example.com/balcony'
id='rs1'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'/>
</query>
</iq>
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2.1.6. Roster Push
A ROSTER PUSH is a newly created, updated, or deleted roster item
that is sent from the server to the client; syntactically it is an IQ
stanza of type "set" sent from server to client and containing a
<query/> element qualified by the 'jabber:iq:roster' namespace.
The following rules apply to roster pushes:
1. The <query/> element in a roster push MUST contain one and only
one <item/> element.
2. A receiving client MUST ignore the stanza unless it has no 'from'
attribute (i.e., implicitly from the user's bare JID) or it has a
'from' attribute whose value matches the user's bare JID
<user@domain>.
S: <iq id='a78b4q6ha463'
to='juliet@example.com/chamber'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'/>
</query>
</iq>
As mandated by the semantics of the IQ stanza as defined in
[XMPP-CORE], each resource that receives a roster push MUST reply
with an IQ stanza of type "result" (or "error").
C: <iq from='juliet@example.com/balcony'
id='a78b4q6ha463'
type='result'/>
C: <iq from='juliet@example.com/chamber'
id='a78b4q6ha463'
type='result'/>
Note: There is no error case for client processing of roster
pushes; if the server receives an IQ of type "error" in response
to a roster push it SHOULD ignore the error.
2.2. Retrieving the Roster on Login
Upon authenticating with a server and binding a resource (thus
becoming a connected resource as defined in [XMPP-CORE]), a client
SHOULD request the roster before sending initial presence (however,
because receiving the roster is not necessarily desirable for all
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resources, e.g., a connection with limited bandwidth, the client's
request for the roster is not mandatory). After a connected resource
sends initial presence (see Section 4.2), it is referred to as an
AVAILABLE RESOURCE. If a connected resource or available resource
requests the roster, it is referred to as an INTERESTED RESOURCE.
The server MUST send roster pushes to all interested resources.
Implementation Note: Presence subscription requests are sent to
available resources, whereas the roster pushes associated with
subscription state changes are sent to interested resources.
Therefore if a resource wishes to receive both subscription
requests and roster pushes, it MUST both send initial presence and
request the roster.
A client requests the roster by sending a roster get over its stream
with the server.
C: <iq from='juliet@example.com/balcony'
id='hu2bac18'
type='get'>
<query xmlns='jabber:iq:roster'/>
</iq>
S: <iq id='hu2bac18'
to='juliet@example.com/balcony'
type='result'>
<query xmlns='jabber:iq:roster' ver='ver11'>
<item jid='romeo@example.net'
name='Romeo'
subscription='both'>
<group>Friends</group>
</item>
<item jid='mercutio@example.com'
name='Mercutio'
subscription='from'/>
<item jid='benvolio@example.net'
name='Benvolio'
subscription='both'/>
</query>
</iq>
If the server cannot process the roster get, it MUST return an
appropriate stanza error as described in [XMPP-CORE] (such as
<service-unavailable/> if the roster namespace is not supported or
<internal-server-error/> if the server experiences trouble processing
or returning the roster).
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2.3. Adding a Roster Item
2.3.1. Request
At any time, a client can add an item to the roster. This is done by
sending a roster set containing a new item.
C: <iq from='juliet@example.com/balcony'
id='ph1xaz53'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'>
<group>Servants</group>
</item>
</query>
</iq>
2.3.2. Success Case
If the server can successfully process the roster set for the new
item (i.e., if no error occurs), it MUST create the roster item in
persistent storage.
The server MUST then return an IQ stanza of type "result" to the
connected resource that sent the roster set.
S: <iq id='ph1xaz53'
to='juliet@example.com/balcony'
type='result'/>
The server MUST also send a roster push containing the new roster
item to all of the user's interested resources, including the
resource that generated the roster set.
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S: <iq to='juliet@example.com/balcony'
id='a78b4q6ha463'
type='set'>
<query xmlns='jabber:iq:roster' ver='ver13'>
<item jid='nurse@example.com'
name='Nurse'
subscription='none'>
<group>Servants</group>
</item>
</query>
</iq>
S: <iq to='juliet@example.com/chamber'
id='x81g3bdy4n19'
type='set'>
<query xmlns='jabber:iq:roster' ver='ver13'>
<item jid='nurse@example.com'
name='Nurse'
subscription='none'>
<group>Servants</group>
</item>
</query>
</iq>
As mandated by the semantics of the IQ stanza as defined in
[XMPP-CORE], each resource that receives a roster push MUST reply
with an IQ stanza of type "result" (or "error").
C: <iq from='juliet@example.com/balcony'
id='a78b4q6ha463'
type='result'/>
C: <iq from='juliet@example.com/chamber'
id='x81g3bdy4n19'
type='result'/>
2.3.3. Error Cases
If the server cannot successfully process the roster set, it MUST
return a stanza error. The following error cases are defined
(naturally, other stanza errors can occur, such as <internal-server-
error/>).
The server MUST return a <forbidden/> stanza error to the client if
the sender of the roster set is not authorized to update the roster
(where typically only an authenticated resource of the account itself
is so authorized).
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The server SHOULD return a <bad-request/> stanza error to the client
if the roster set contains any of the following violations:
1. The <query/> element contains more than one <item/> child
element.
2. The <item/> element contains more than one <group/> element, but
there are duplicate groups (one possible comparison method for
determining duplicates is that described for XMPP resourceparts
in [XMPP-ADDR]).
The server SHOULD return a <not-acceptable/> stanza error to the
client if the roster set contains any of the following violations:
1. The value of the 'name' attribute is greater than a server-
configured limit.
2. The XML character data of the <group/> element is of zero length
(to remove an item from all groups, the client instead needs to
exclude any <group/> element from the roster set).
3. The XML character data of the <group/> element is greater than a
server-configured limit.
As an alternative to returning a <bad-request/> or <not-acceptable/>
stanza error, the server MAY ignore the foregoing violations and
process the roster set as best as possible (e.g., process only the
first <item/> element, ignore duplicate <group/> elements, place the
roster item in no group or a default group if the <group/> element is
empty, and truncate 'name' attributes and <group/> elements that are
too long).
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Error: Roster set initiated by unauthorized entity
C: <iq from='juliet@example.com/balcony'
id='ix7s53v2'
to='romeo@example.net'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'/>
</query>
</iq>
S: <iq id='ix7s53v2'
to='juliet@example.com/balcony'
type='error'>
<error type='auth'>
<forbidden xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
Error: Roster set contains more than one item
C: <iq from='juliet@example.com/balcony'
id='nw83vcj4'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'>
<group>Servants</group>
</item>
<item jid='mother@example.com'
name='Mom'>
<group>Family</group>
</item>
</query>
</iq>
S: <iq id='nw83vcj4'
to='juliet@example.com/balcony'
type='error'>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
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Error: Roster set contains item with oversized handle
C: <iq from='juliet@example.com/balcony'
id='yl491b3d'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='[ ... some-very-long-handle ... ]'>
<group>Servants</group>
</item>
</query>
</iq>
S: <iq id='yl491b3d'
to='juliet@example.com/balcony'
type='error'>
<error type='modify'>
<not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
Error: Roster set contains duplicate groups
C: <iq from='juliet@example.com/balcony'
id='tk3va749'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'>
<group>Servants</group>
<group>Servants</group>
</item>
</query>
</iq>
S: <iq id='tk3va749'
to='juliet@example.com/balcony'
type='error'>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
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Error: Roster set contains empty group
C: <iq from='juliet@example.com/balcony'
id='fl3b486u'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'>
<group></group>
</item>
</query>
</iq>
S: <iq id='fl3b486u'
to='juliet@example.com/balcony'
type='error'>
<error type='modify'>
<not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
Error: Roster set contains oversized group name
C: <iq from='juliet@example.com/balcony'
id='qh3b4v19'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'>
<group>[ ... some-very-long-group-name ... ]</group>
</item>
</query>
</iq>
S: <iq id='qh3b4v19'
to='juliet@example.com/balcony'
type='error'>
<error type='modify'>
<not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
The server MUST return a <not-allowed/> stanza error to the client if
the value of the <item/> element's 'jid' attribute matches the bare
JID <node@domain> portion of the <iq/> element's 'from' attribute
(i.e., a JID MUST NOT be allowed to add itself to its own roster).
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Error: Roster set contains sender's JID
C: <iq from='juliet@example.com/balcony'
id='ry3vs714'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'/>
</query>
</iq>
S: <iq id='ry3vs714'
to='juliet@example.com/balcony'
type='error'>
<error type='cancel'>
<not-allowed xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
2.4. Updating a Roster Item
2.4.1. Request
Updating an existing roster item is done in the same way as adding a
new roster item, i.e., by sending a roster set to the server.
Because a roster item is atomic, the item MUST be updated exactly as
provided in the roster set.
There are several reasons why a client might update a roster item:
1. Adding a group
2. Deleting a group
3. Changing the handle
4. Deleting the handle
Consider a roster item that is defined as follows:
<item jid='romeo@example.net'
name='Romeo'>
<group>Friends</group>
</item>
The user who has this item in her roster might want to add the item
to another group.
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C: <iq from='juliet@example.com/balcony'
id='di43b2x9'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
name='Romeo'>
<group>Friends</group>
<group>Lovers</group>
</item>
</query>
</iq>
Sometime later, the user might want to remove the item from the
original group.
C: <iq from='juliet@example.com/balcony'
id='lf72v157'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
name='Romeo'>
<group>Lovers</group>
</item>
</query>
</iq>
The user might want to remove the item from all groups.
C: <iq from='juliet@example.com/balcony'
id='ju4b62a5'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'/>
</query>
</iq>
The user might also want to change the handle for the item.
C: <iq from='juliet@example.com/balcony'
id='gb3sv487'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
name='MyRomeo'/>
</query>
</iq>
The user might then want to remove the handle altogether.
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Implementation Note: Including an empty 'name' attribute is
equivalent to including no 'name' attribute; both actions set the
name to the empty string.
C: <iq from='juliet@example.com/balcony'
id='o3bx66s5'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
name=''/>
</query>
</iq>
2.4.2. Success Case
As with adding a roster item, if the roster item can be successfully
processed then the server MUST update the roster information in
persistent storage, send a roster push to all of the user's
interested resources, and send an IQ result to the initiating
resource; for details, see Section 2.3.
2.4.3. Error Cases
The error cases described under Section 2.3.3 also apply to updating
a roster item.
2.5. Deleting a Roster Item
2.5.1. Request
At any time, a client can delete an item from his or her roster by
sending a roster set and specifying a value of "remove" for the
'subscription' attribute.
C: <iq from='juliet@example.com/balcony'
id='hm4hs97y'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
subscription='remove'/>
</query>
</iq>
2.5.2. Success Case
As with adding a roster item, if the server can successfully process
the roster set then it MUST update the roster information in
persistent storage, send a roster push to all of the user's
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interested resources (with the 'subscription' attribute set to a
value of "remove"), and send an IQ result to the initiating resource;
for details, see Section 2.3.
In addition, the user's server might need to generate one or more
subscription-related presence stanzas, as follows:
1. If the user has a presence subscription to the contact, then the
user's server MUST send a presence stanza of type "unsubscribe"
to the contact (to unsubscribe from the contact's presence).
2. If the contact has a presence subscription to the user, then the
user's server MUST send a presence stanza of type "unsubscribed"
to the contact (to cancel the contact's subscription to the
user), or both.
3. If the presence subscription is mutual, then the user's server
MUST send both a presence stanza of type "unsubscribe" and a
presence stanza of type "unsubscribed" to the contact.
S: <presence from='juliet@example.com'
to='nurse@example.com'
type='unsubscribe'/>
S: <presence from='juliet@example.com'
to='nurse@example.com'
type='unsubscribed'/>
2.5.3. Error Cases
If the value of the 'jid' attribute specifies an item that is not in
the roster, then the server MUST return an <item-not-found/> stanza
error.
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Error: Roster item not found
C: <iq from='juliet@example.com/balcony'
id='uj4b1ca8'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='[ ... non-existent-jid ... ]'
subscription='remove'/>
</query>
</iq>
S: <iq id='uj4b1ca8'
to='juliet@example.com/balcony'
type='error'>
<error type='modify'>
<item-not-found
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
2.6. Roster Versioning
2.6.1. Stream Feature
If a server supports roster versioning, then it MUST advertise the
following stream feature during stream negotiation.
<ver xmlns='urn:xmpp:features:rosterver'>
<optional/>
</ver>
The roster versioning stream feature SHOULD always be voluntary
(advertised by means of the <optional/> child element), not mandatory
(advertised by means of the <required/> child element).
2.6.2. Request
If a client supports roster versioning and the server to which it has
connected advertises support for roster versioning as described in
the foregoing section, then the client MUST include the 'ver' element
in its request for the roster. If the server does not advertise
support for roster versioning, the client MUST NOT include the 'ver'
attribute. If the client includes the 'ver' attribute in its roster
get, it sets the attribute's value to the version ID associated with
its last cache of the roster.
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C: <iq from='romeo@example.net/home'
id='r1h3vzp7'
to='romeo@example.net'
type='get'>
<query xmlns='jabber:iq:roster' ver='ver14'/>
</iq>
If the client has not yet cached the roster or the cache is lost or
corrupted, but the client wishes to bootstrap the use of roster
versioning, it MUST set the 'ver' attribute to the empty string
(i.e., ver="").
Naturally, if the client does not support roster versioning or does
not wish to bootstrap the use of roster versioning, it will not
include the 'ver' attribute.
2.6.3. Success Case
Whether or not the roster has been modified since the version ID
enumerated by the client, the server MUST either return the complete
roster as described under Section 2.1.4 (including a 'ver' attribute
that signals the latest version) or return an empty IQ-result (thus
indicating that any roster modifications will be sent via roster
pushes, as described below). In general, unless returning the
complete roster would (1) use less bandwidth than sending individual
roster pushes to the client (e.g., if the roster contains only a few
items) or (2) the server cannot associate the version ID with any
previous version it has on file, the server SHOULD send an empty IQ-
result and then send the modifications (if any) via roster pushes.
S: <iq from='romeo@example.net'
id='r1h3vzp7'
to='romeo@example.net/home'
type='result'/>
Implementation Note: This empty IQ-result is different from an
empty <query/> element, thus disambiguating this usage from an
empty roster.
If roster versioning is enabled and the roster has not been modified
since the version ID enumerated by the client, the server will simply
not send any roster pushes to the client (until and unless some
relevant event triggers a roster push during the lifetime of the
client's session).
If the roster has been modified since the version ID enumerated by
the client, the server MUST then send one roster push to the client
for each roster item that has been modified since the version ID
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enumerated by the client. (We call a roster push that is sent for
purposes of roster version synchronization an "interim roster push".)
Definition: A ROSTER MODIFICATION is any modification to the
roster data that would result in a roster push to a connected
client. Therefore internal states related to roster processing
within the server that would not result in a roster push to a
connected client do not necessitate a change to the version.
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S: <iq from='romeo@example.net'
id='ah382g67'
to='romeo@example.net/home'
type='set'>
<query xmlns='jabber:iq:roster' ver='ver34'>
<item jid='tybalt@example.org' subscription='remove'/>
</query>
</iq>
S: <iq from='romeo@example.net'
id='b2gs90j5'
to='romeo@example.net/home'
type='set'>
<query xmlns='jabber:iq:roster' ver='ver42'>
<item jid='bill@example.org' subscription='both'/>
</query>
</iq>
S: <iq from='romeo@example.net'
id='c73gs419'
to='romeo@example.net/home'
type='set'>
<query xmlns='jabber:iq:roster' ver='ver72'>
<item jid='nurse@example.org'
name='Nurse'
subscription='to'>
<group>Servants</group>
</item>
</query>
</iq>
S: <iq from='romeo@example.net'
id='dh361f35'
to='romeo@example.net/home'
type='set'>
<query xmlns='jabber:iq:roster' ver='ver96'>
<item jid='juliet@example.org'
name='Juliet'
subscription='both'>
<group>VIPs</group>
</item>
</query>
</iq>
These "interim roster pushes" can be understood as follows:
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1. Imagine that the client had an active presence session for the
entire time between its cached roster version (say, "ver14") and
the new roster version (say, "ver96").
2. During that time, the client might have received roster pushes
related to various roster versions (which might have been, say,
"ver27" and "ver49"). However, some of those roster pushes might
have contained intermediate updates to the same roster item
(e.g., modifications to the subscription state for
bill@example.org from "none" to "to" and from "to" to "both").
3. The interim roster pushes would not include all of the
intermediate steps, only the final result of all modifications
applied to each item while the client was in fact offline (which
might have been, say, "ver34", "ver42", "ver72", and "ver96").
The client MUST handle an "interim roster push" in the same way it
handles any roster push (indeed, from the client's perspective it
cannot tell the difference between an "interim" roster push and a
"live" roster push). If the client's session ends before it receives
all of the interim roster pushes, when requesting the roster after
reconnection it SHOULD request the version associated with the last
roster push it received during the session that was disconnected, not
the version associated with the roster result it received at the
start of that session.
When roster versioning is enabled, the server MUST include the
updated roster version with each roster push. Roster pushes MUST
occur in order of modification and the version contained in a roster
push MUST be unique. Even if the client has not included the 'ver'
attribute in its roster gets or sets, the server SHOULD include the
'ver' attribute on all roster pushes and results that it sends to the
client.
Implementation Note: Guidelines and more detailed examples for
roster versioning are provided in [XEP-0237].
3. Managing Presence Subscriptions
In order to protect the privacy of instant messaging users, presence
information is disclosed only to other entities that a user has
approved. When a user has agreed that another entity is allowed to
view its presence, the entity is said to have a SUBSCRIPTION to the
user's presence. An entity that has a subscription to a user's
presence or to which a user has a presence subscription is called a
CONTACT (in this document the term "contact" is also used in a less
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strict sense to refer to a potential contact or any item in a user's
roster).
In XMPP, a subscription lasts across presence sessions; indeed, it
lasts until the contact unsubscribes or the user cancels the
previously-granted subscription.
Subscriptions are managed within XMPP by sending presence stanzas
containing specially-defined attributes ("subscribe", "unsubscribe",
"subscribed", and "unsubscribed").
Implementation Note: When a server processes or generates an
outbound presence stanza of type "subscribe", "subscribed",
"unsubscribe", or "unsubscribed", the server MUST stamp the
outgoing presence stanza with the bare JID <node@domain> of the
sending entity, not the full JID <node@domain/resource>.
Enforcement of this rule simplifies the presence subscription
model and helps to prevent presence leaks; for information about
presence leaks, refer to the security considerations of
[XMPP-CORE].
Subscription states are reflected in the rosters of both the user and
the contact. Complete details regarding these subscription states
can be found Appendix A; those details are not provided in this
section, which simply narrates the protocol flows for common use
cases related to presence subscriptions.
3.1. Requesting a Subscription
A SUBSCRIPTION REQUEST is a request from a user for authorization to
permanently subscribe to a contact's presence information;
syntactically it is a presence stanza whose 'type' attribute has a
value of "subscribe". A subscription request is generated by a
user's client, processed by the (potential) contact's server, and
acted on by the contact via the contact's client. The workflow is
described in the following sections.
Implementation Note: Presence subscription requests are sent to
available resources, whereas the roster pushes associated with
subscription state changes are sent to interested resources.
Therefore if a resource wishes to receive both subscription
requests and roster pushes, it MUST both send initial presence and
request the roster.
3.1.1. Client Generation of Outbound Subscription Request
A user's client generates a subscription request by sending a
presence stanza of type "subscribe" and specifying a 'to' address of
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the potential contact's bare JID <contact@domain>.
UC: <presence id='xk3h1v69'
to='juliet@example.com'
type='subscribe'/>
When a user sends a presence subscription request to a potential
instant messaging and presence contact, the value of the 'to'
attribute MUST be a bare JID <contact@domain> rather a full JID
<contact@domain/resource>, since the desired result is for the user
to receive presence from all of the contact's resources, not merely
the particular resource specified in the 'to' attribute. Use of bare
JIDs also simplifies subscription processing, presence probes, and
presence notifications by the user's server and the contact's server.
For tracking purposes, a client SHOULD include an 'id' attribute in a
presence subscription request.
Note: Many XMPP clients prompt the user for information about the
potential contact (e.g., "handle" and desired roster group) when
generating an outbound presence subscription request and therefore
send a roster set before sending the outbound presence
subscription request. This behavior is OPTIONAL, because a client
MAY instead wait until receiving the initial roster push from the
server before uploading user-provided information about the
contact. A server MUST process a roster set and outbound presence
subscription request in either order.
3.1.2. Server Processing of Outbound Subscription Request
Upon receiving the outbound presence subscription request, the user's
server MUST proceed as follows.
1. Before processing the request, the user's server SHOULD check the
syntax of the JID contained in the 'to' attribute. If the JID is
of the form <contact@domain/resource> instead of
<contact@domain>, the user's server SHOULD treat it as if the
request had been directed to the contact's bare JID and modify
the 'to' address accordingly. The server MAY also verify that
the JID adheres to the format defined in [XMPP-ADDR] and possibly
return a <jid-malformed/> stanza error.
2. If the potential contact is hosted on the same server as the
user, then the server MUST adhere to the rules specified in the
next section in processing the subscription request and
delivering it to the (local) contact.
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3. If the potential contact is hosted on a remote server, subject to
local service policies the user's server MUST then route the
stanza to that remote domain in accordance with core XMPP stanza
processing rules. (This can result in returning an appropriate
stanza error to the user, such as <remote-server-timeout/>.)
As mentioned, before locally delivering or remotely routing the
presence subscription request, the user's server MUST stamp the
outbound subscription request with the bare JID <user@domain> of the
user.
US: <presence from='romeo@example.net'
id='xk3h1v69'
to='juliet@example.com'
type='subscribe'/>
If the presence subscription request cannot be locally delivered or
remotely routed (e.g., because the request is malformed, the local
contact does not exist, the remote server does not exist, an attempt
to contact the remote server times out, or any other error determined
or experienced by the user's server), then the user's server MUST
return an appropriate error stanza to the user. An example follows.
US: <presence from='juliet@example.com'
id='xk3h1v69'
to='romeo@example.net'
type='error'>
<error type='modify'>
<remote-server-not-found
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</presence>
After locally delivering or remotely routing the presence
subscription request, the user's server MUST then send a roster push
to all of the user's interested resources, containing the potential
contact with a subscription state of "none" and with notation that
the subscription is pending (via an 'ask' attribute whose value is
"subscribe").
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US: <iq id='b89c5r7ib574'
to='romeo@example.net/foo'
type='set'>
<query xmlns='jabber:iq:roster'>
<item ask='subscribe'
jid='juliet@example.com'
subscription='none'/>
</query>
</iq>
US: <iq id='b89c5r7ib575'
to='romeo@example.net/bar'
type='set'>
<query xmlns='jabber:iq:roster'>
<item ask='subscribe'
jid='juliet@example.com'
subscription='none'/>
</item>
</query>
</iq>
If a remote contact does not approve or deny the subscription request
within some configurable amount of time, the user's server SHOULD
resend the subscription request to the contact based on an
implementation-specific algorithm (e.g., whenever a new resource
becomes available for the user, or after a certain amount of time has
elapsed); this helps to recover from transient, silent errors that
might have occurred when the original subscription request was routed
to the remote domain.
3.1.3. Server Processing of Inbound Subscription Request
Before processing the inbound presence subscription request, the
contact's server SHOULD check the syntax of the JID contained in the
'to' attribute. If the JID is of the form <contact@domain/resource>
instead of <contact@domain>, the contact's server SHOULD treat it as
if the request had been directed to the contact's bare JID and modify
the 'to' address accordingly. The server MAY also verify that the
JID adheres to the format defined in [XMPP-ADDR] and possibly return
a <jid-malformed/> stanza error.
When processing the inbound presence subscription request, the
contact's server MUST adhere to the following rules:
1. Above all, the contact's server MUST NOT automatically approve
subscription requests on the contact's behalf (unless the contact
has configured its account to automatically approve subscription
requests or has accepted an agreement with its service provider
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that allows such behavior, for instance via an employment
agreement within an enterprise deployment). Instead, if a
subscription request requires approval then the contact's server
MUST deliver that request to the contact's available resource(s)
for approval or denial by the contact.
2. If the contact does not exist, then the contact's server MUST
automatically return a presence stanza of type "unsubscribed" to
the user.
CS: <presence from='juliet@example.com'
id='xk3h1v69'
to='romeo@example.net'
type='unsubscribed'/>
3. If the contact exists and the user already has a subscription to
the contact's presence, then the contact's server MUST auto-reply
on behalf of the contact by sending a presence stanza of type
"subscribed" from the contact's bare JID to the user's bare JID.
Likewise, if the contact previously sent a presence stanza of
type "subscribed" and the contact's server treated that as
indicating "pre-approval" for the user's presence subscription
(see Appendix A), then the contact's server SHOULD also auto-
reply on behalf of the contact.
CS: <presence from='juliet@example.com'
id='xk3h1v69'
to='romeo@example.net'
type='subscribed'/>
4. Otherwise, if there is at least one available resource associated
with the contact when the subscription request is received by the
contact's server, then the contact's server MUST broadcast that
subscription request to all available resources in accordance
with Section 8.
As a way of acknowledging receipt of the presence subscription
request, the contact's server MAY send a presence stanza of type
"unavailable" from the bare JID of the contact to the bare JID of
the user (the user's client MUST NOT assume that this ack
provides presence information about the contact, since it comes
from the contact's bare JID and is received before the
subscription request has been approved).
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5. Otherwise, if the contact has no available resources when the
subscription request is received by the contact's server, then
the contact's server MUST keep a record of the complete presence
stanza comprising the subscription request, including any
extended content contained therein, and deliver the request when
the contact next has an available resource. The contact's server
MUST continue to deliver the subscription request whenever the
contact creates an available resource, until the contact either
approves or denies the request. (The contact's server MUST NOT
deliver more than one subscription request from any given user
when the contact next has an available resource; e.g., if the
user sends multiple subscription requests to the contact while
the contact is offline, the contact's server SHOULD store only
one of those requests, such as the first request or last request,
and MUST deliver only one of the requests when the contact next
has an available resource; this helps to prevent "subscription
request spam".)
As a way of acknowledging receipt of the presence subscription
request, the contact's server MAY send a presence stanza of type
"unavailable" from the bare JID of the contact to the bare JID of
the user, since it comes from the contact's bare JID and is
received before the subscription request has been approved).
Security Note: Until and unless the contact approves the
subscription request as described under Section 3.1.4, the
contact's server MUST NOT add an item for the user to the
contact's roster.
3.1.4. Client Processing of Inbound Subscription Request
When the contact's client receives a subscription request from the
user, it MUST present the request to the contact for approval (unless
the contact has explicitly configured the client to automatically
approve or deny some or all subscription requests).
A subscription request is approved by sending a presence stanza of
type "subscribed", which is processed as described under
Section 3.1.5 for the contact's server and Section 3.1.6 for the
user's server.
CC: <presence to='romeo@example.net' type='subscribed'/>
A subscription request is denied by sending a presence stanza of type
"unsubscribed", which is processed as described under Section 3.2 for
both the contact's server and the user's server.
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CC: <presence to='romeo@example.net' type='unsubscribed'/>
3.1.5. Server Processing of Outbound Subscription Approval
When the contact's client sends the subscription approval, the
contact's server MUST stamp the outbound stanza with the bare JID
<contact@domain> of the contact and locally deliver or remotely route
the stanza to the user.
CS: <presence from='juliet@example.com'
to='romeo@example.net'
type='subscribed'/>
The contact's server then MUST send an updated roster push to all of
the contact's interested resources, with the 'subscription' attribute
set to a value of "from".
CS: <iq id='a78b4q6ha463'
to='juliet@example.com/balcony'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='from'/>
</query>
</iq>
CS: <iq id='x81g3bdy4n19'
to='juliet@example.com/chamber'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='from'/>
</query>
</iq>
From the perspective of the contact, there now exists a subscription
from the user (which is why the 'subscription' attribute is set to a
value of "from").
The contact's server MUST then also send current presence to the user
from each of the contact's available resources.
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'/>
CS: <presence from='juliet@example.com/chamber'
to='romeo@example.net'/>
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In order to subscribe to the user's presence, the contact would then
need to send a subscription request to the user. (XMPP clients will
often automatically send the subscription request instead of
requiring the contact to initiate the subscription request, since it
is assumed that the desired end state is a mutual subscription.)
Naturally, when the contact sends a subscription request to the user,
the subscription states will be different from those shown in the
foregoing examples (see Appendix A) and the roles will be reversed.
3.1.6. Server Processing of Inbound Subscription Approval
When the user's server receives the subscription approval, it MUST
first check if the contact is in the user's roster with
subscription='none' or subscription='from' and the 'ask' flag set to
"subscribe" (i.e., a subscription state of "None + Pending Out",
"None + Pending Out+In", or "From + Pending Out"; see Appendix A).
If this check is successful, then the user's server MUST:
1. Deliver the inbound subscription approval to all of the user's
interested resources (this helps to give the user's client(s)
proper context regarding the subscription approval so that they
can differentiate between a roster push originated by another of
the user's resources and a subscription approval received from
the contact). This MUST occur before sending the roster push
described in the next step.
US: <presence from='juliet@example.com'
to='romeo@example.net'
type='subscribed'/>
2. Initiate a roster push to all of the user's interested resources,
containing an updated roster item for the contact with the
'subscription' attribute set to a value of "to" (if the
subscription state was "None + Pending Out" or "None + Pending
Out+In") or "both" (if the subscription state was "From + Pending
Out").
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US: <iq id='b89c5r7ib576'
to='romeo@example.net/foo'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='to'/>
</query>
</iq>
US: <iq id='b89c5r7ib577'
to='romeo@example.net/bar'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='to'/>
</item>
</query>
</iq>
3. The user's server MUST also deliver the available presence stanza
received from each of the contact's available resources to each
of the user's available resources.
[ ... to resource1 ... ]
US: <presence from='juliet@example.com/balcony'
to='romeo@example.net'/>
[ ... to resource2 ... ]
US: <presence from='juliet@example.com/balcony'
to='romeo@example.net'/>
[ ... to resource1 ... ]
US: <presence from='juliet@example.com/chamber'
to='romeo@example.net'/>
[ ... to resource2 ... ]
US: <presence from='juliet@example.com/chamber'
to='romeo@example.net'/>
Otherwise -- that is, if the user does not exist, if the contact is
not in the user's roster, or if the contact is in the user's roster
with a subscription state other than those described in the foregoing
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check -- then the user's server MUST silently ignore the subscription
approval stanza by not delivering it to the user, not modifying the
user's roster, and not generating a roster push to the user's
interested resources.
From the perspective of the user, there now exists a subscription to
the contact's presence (which is why the 'subscription' attribute is
set to a value of "to").
3.2. Cancelling a Subscription
3.2.1. Client Generation of Subscription Cancellation
If a contact would like to cancel a subscription that it has
previously granted to a user (or deny a subscription request), it
sends a presence stanza of type "unsubscribed".
CC: <presence to='romeo@example.net' type='unsubscribed'/>
3.2.2. Server Processing of Outbound Subscription Cancellation
Upon receiving the outound subscription cancellation, the contact's
server MUST proceed as follows.
1. If the user is hosted on the same server as the contact, then the
server MUST adhere to the rules specified in the next section in
processing the subscription cancellation.
2. If the user is hosted on a remote server, subject to local
service policies the contact's server MUST then route the stanza
to that remote domain in accordance with core XMPP stanza
processing rules. (This can result in returning an appropriate
stanza error to the contact, such as <remote-server-timeout/>.)
As mentioned, before locally delivering or remotely routing the
stanza, the contact's server MUST stamp the outbound subscription
cancellation with the bare JID <contact@domain> of the contact.
CS: <presence from='juliet@example.com'
to='romeo@example.net'
type='unsubscribed'/>
The contact's server then MUST send a roster push with the updated
roster item to all of the contact's interested resources, where the
subscription state is now either "none" or "to" (see Appendix A).
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CS: <iq id='pw3f2v175b34'
to='juliet@example.com/balcony'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='none'/>
</query>
</iq>
CS: <iq id='zu2y3f571v35'
to='juliet@example.com/chamber'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='none'/>
</query>
</iq>
The contact's server then MUST send a presence stanza of type
"unavailable" from all of the contact's online resources to the user.
CS: <presence from='juliet@example.com/balcony'
type='unavailable'/>
CS: <presence from='juliet@example.com/chamber'
type='unavailable'/>
3.2.3. Server Processing of Inbound Subscription Cancellation
When the user's server receives the inbound subscription
cancellation, it MUST first check if the contact is in the user's
roster with subscription='to' or subscription='both' (see
Appendix A). If this check is successful, then the user's server
MUST:
1. Deliver the inbound subscription cancellation to all of the
user's interested resources (this helps to give the user's
client(s) proper context regarding the subscription cancellation
so that they can differentiate between a roster push originated
by another of the user's resources and a subscription
cancellation received from the contact). This MUST occur before
sending the roster push described in the next step.
US: <presence from='juliet@example.com'
to='romeo@example.net'
type='unsubscribed'/>
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2. Initiate a roster push to all of the user's interested resources,
containing an updated roster item for the contact with the
'subscription' attribute set to a value of "none" (if the
subscription state was "To" or "To + Pending In") or "from" (if
the subscription state was "Both").
US: <iq id='h37h3u1bv400'
to='romeo@example.net/foo'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='none'/>
</query>
</iq>
US: <iq id='h37h3u1bv401'
to='romeo@example.net/bar'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='none'/>
</item>
</query>
</iq>
The user's server MUST also deliver the inbound presence stanzas of
type "unavailable".
Otherwise -- that is, if the user does not exist, if the contact is
not in the user's roster, or if the contact is in the user's roster
with a subscription state other than those described in the foregoing
check -- then the user's server MUST silently ignore the subscription
cancellation stanza by not delivering it to the user, not modifying
the user's roster, and not generating a roster push to the user's
interested resources.
3.3. Unsubscribing
3.3.1. Client Generation of Unsubscribe
If a user would like to unsubscribe from a contact's presence, it
sends a presence stanza of type "unsubscribe".
UC: <presence to='juliet@example.com' type='unsubscribe'/>
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3.3.2. Server Processing of Outbound Unsubscribe
Upon receiving the outbound unsubscribe, the user's server MUST
proceed as follows.
1. If the contact is hosted on the same server as the user, then the
server MUST adhere to the rules specified in the next section in
processing the subscription request.
2. If the contact is hosted on a remote server, subject to local
service policies the user's server MUST then route the stanza to
that remote domain in accordance with core XMPP stanza processing
rules. (This can result in returning an appropriate stanza error
to the user, such as <remote-server-timeout/>.)
As mentioned, before locally delivering or remotely routing the
unsubscribe, the user's server MUST stamp the stanza with the bare
JID <user@domain> of the user.
US: <presence from='romeo@example.net'
to='juliet@example.com'
type='unsubscribe'/>
The user's server then MUST send a roster push with the updated
roster item to all of the user's interested resources, where the
subscription state is now either "none" or "from" (see Appendix A).
US: <iq id='h37h3u1bv402'
to='romeo@example.net/foo'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='none'/>
</query>
</iq>
US: <iq to='romeo@example.net/bar'
type='set'
id='h37h3u1bv403'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='none'/>
</item>
</query>
</iq>
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3.3.3. Server Processing of Inbound Unsubscribe
When the contact's server receives the unsubscribe notification, it
MUST first check if the user is in the contact's roster with
subscription='from' or subscription='both' (i.e., a subscription
state of "From", "From + Pending Out", or "Both"; see Appendix A).
If this check is successful, then the contact's server MUST:
1. Deliver the inbound unsubscribe to all of the contact's
interested resources (this helps to give the contact's client(s)
proper context regarding the unsubscribe so that they can
differentiate between a roster push originated by another of the
contact's resources and an unsubscribe received from the user).
This MUST occur before sending the roster push described in the
next step.
CS: <presence from='romeo@example.net'
to='juliet@example.com'
type='unsubscribe'/>
2. Initiate a roster push to all of the contact's interested
resources, containing an updated roster item for the contact with
the 'subscription' attribute set to a value of "none" (if the
subscription state was "From" or "From + Pending Out") or "to"
(if the subscription state was "Both").
CS: <iq id='tn2b5893g1s4'
to='juliet@example.com/balcony'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='none'/>
</query>
</iq>
CS: <iq id='sp3b56n27hrp'
to='juliet@example.com/chamber'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='none'/>
</query>
</iq>
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3. Generate an outbound presence stanza of type "unavailable" from
each of the contact's available resources to the user.
CS: <presence from='romeo@example.net'
to='juliet@example.com'
type='unavailable'/>
Otherwise -- that is, if the contact does not exist, if the user is
not in the contact's roster, or if the user is in the contact's
roster with a subscription state other than those described in the
foregoing check -- then the contact's server MUST silently ignore the
unsubscribe stanza by not delivering it to the contact, not modifying
the contact's roster, and not generating a roster push to the
contact's interested resources. However, if the contact's server is
keeping track of an inbound presence subscription request from the
user to the contact but the user is not yet in the contact's roster
(functionally equivalent to a subscription state of "None + Pending
In" where the contact never added the user to the contact's roster),
then the contact's server MUST simply remove any record of the
inbound presence subscription request (it cannot remove the user from
the contact's roster because the user was never added to the
contact's roster).
Implementation Note: The user's client MUST NOT depend on
receiving the unavailable presence notification, since it MUST
consider its presence subscription to the contact, and its
presence information about the contact, to be null and void when
it sends the presence stanza of type "unsubscribe" or when it
receives the roster push triggered by the unsubscribe request.
4. Exchanging Presence Information
4.1. Overview
The concept of presence refers to an entity's availability for
communication over a network. At the most basic level, presence is a
boolean "on/off" variable that signals whether an entity is available
or unavailable for communication (the terms "online" and "offline"
are also used). In XMPP, an entity's availability is signalled when
its client generates a <presence/> stanza with no 'type' attribute,
and an entity's lack of availability is signalled when its client
generates a <presence/> stanza whose 'type' attribute has a value of
"unavailable".
XMPP presence typically follows a "publish-subscribe" or "observer"
pattern, wherein an entity sends presence to its server, and its
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server then broadcasts that information to all of the entity's
contacts who have a subscription to the entity's presence (in the
terminology of [IMP-MODEL], an entity that generates presence is a
"presentity" and the entities that receive presence are
"subscribers"). A client generates presence for broadcasting to all
subscribed entities by sending a presence stanza to its server with
no 'to' address, where the presence stanza has either no 'type'
attribute or a 'type' attribute whose value is "unavailable". This
kind of presence is called BROADCAST PRESENCE. (A client can also
send DIRECTED PRESENCE, i.e., a presence stanza with a 'to' address;
this is less common but is sometimes used to send presence to
entities that are not subscribed to the user's presence; see
Section 4.6.)
After a client completes the preconditions specified in [XMPP-CORE],
it can establish a PRESENCE SESSION at its server by sending initial
presence (Section 4.2), where the presence session is terminated by
sending unavailable presence (Section 4.5). For the duration of its
presence session, a connected resource (in the terminology of
[XMPP-CORE]) is said to be an AVAILABLE RESOURCE.
In XMPP applications that combine messaging and presence
functionality, the default type of communication for which presence
signals availability is messaging; however, it is not necessary for
XMPP applications to combine messaging and presence functionality,
and they can provide standalone presence features without messaging
(in addition, XMPP servers do not require information about network
availability in order to successfully route message and IQ stanzas).
Informational Note: In the examples that follow, the user is
<juliet@example.com>, she has two available resources ("balcony"
and "chamber"), and she has three contacts in her roster with a
subscription state of "from" or "both": <romeo@example.net>,
<mercutio@example.com>, and <benvolio@example.net>.
4.2. Initial Presence
4.2.1. Client Generation of Initial Presence
After completing the preconditions described in [XMPP-CORE]
(REQUIRED) and requesting the roster (RECOMMENDED), a client signals
its availability for communication by sending INITIAL PRESENCE to its
server, i.e., a presence stanza with no 'to' address (indicating that
it is meant to be broadcast by the server on behalf of the client)
and no 'type' attribute (indicating the user's availability).
UC: <presence/>
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The initial presence stanza MAY contain the <priority/> element, the
<show/> element, and one or more instances of the <status/> element,
as well as extended content; see Section 4.7 for details.
4.2.2. Server Processing of Outbound Initial Presence
Upon receiving initial presence from a client, the user's server MUST
send the initial presence stanza from the full JID
<user@domain/resource> of the user to all contacts that are
subscribed to the user's presence; such contacts are those for which
a JID is present in the user's roster with the 'subscription'
attribute set to a value of "from" or "both".
US: <presence from='juliet@example.com/balcony'
to='romeo@example.net'/>
US: <presence from='juliet@example.com/balcony'
to='mercutio@example.com'/>
US: <presence from='juliet@example.com/balcony'
to='benvolio@example.net'/>
The user's server MUST also broadcast initial presence from the
user's newly available resource to all of the user's available
resources, including the resource that generated the presence
notification in the first place (i.e., an entity is implicitly
subscribed to its own presence).
[... to the "balcony" resource ...]
US: <presence from='juliet@example.com/balcony'
to='juliet@example.com'/>
[... to the "chamber" resource ...]
US: <presence from='juliet@example.com/balcony'
to='juliet@example.com'/>
In the absence of presence information about the user's contacts, the
user's server MUST also send presence probes to the user's contacts
on behalf of the user as specified under Section 4.3.
4.2.3. Server Processing of Inbound Initial Presence
Upon receiving presence from the user, the contact's server MUST
deliver the user's presence stanza to all of the contact's available
resources.
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[ ... to resource1 ... ]
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'/>
[ ... to resource2 ... ]
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'/>
4.2.4. Client Processing of Initial Presence
When the contact's client receives presence from the user, it SHOULD
proceed as follows:
1. If the user is in the contact's roster, the client MUST display
the presence information in an appropriate roster interface.
2. If the user is not in the contact's roster but the contact and
the user are actively exchanging message or IQ stanzas, the
contact's client SHOULD display the presence information in the
user interface for that communication session (see also
Section 4.6 and Section 5.1).
3. Otherwise, the client MUST ignore the presence information and
not display it to the contact.
4.3. Presence Probes
A PRESENCE PROBE is a request for a contact's current presence
information, sent on behalf of a user by the user's server;
syntactically it is a presence stanza whose 'type' attribute has a
value of "probe". In the context of presence subscriptions, the
value of the 'from' address MUST be the bare JID of the subscribed
user and the value of the 'to' address MUST be the bare JID of the
contact to which the user is subscribed, since presence subscriptions
are based on the bare JID. Probes can also be sent outside the
context of a presence subscription, e.g. when the contact has sent
directed presence to an entity as described under Section 4.6; in
this case the value of the 'from' or 'to' address can be a full JID
instead of a bare JID.
US: <presence from='juliet@example.com'
id='ign291v5'
to='romeo@example.net'
type='probe'/>
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Implementation Note: Although presence probes MAY be sent by a
client, in general a client will not need to send them since the
task of gathering presence from a user's contacts is managed by
the user's server. However, if a client generates an outbound
presence probe then the user's server SHOULD route the probe (if
the contact is at another server) or process the probe (if the
contact is at the same server) and MUST NOT return a stanza or
stream error to the client.
4.3.1. Server Generation of Outbound Presence Probe
When a server needs to discover the availability of a user's contact,
it sends a presence probe from the bare JID <user@domain> of the user
to the bare JID <contact@domain> of the contact. The server MUST NOT
send a probe to a contact if the user is not subscribed to the
contact's presence (i.e., if the contact is not in the user's roster
with the 'subscription' attribute set to a value of "to" or "both"),
unless the user has sent directed presence to the contact and has
received presence information in return.
The user's server SHOULD send a presence probe whenever the user
starts a new presence session by sending initial presence; however,
the server MAY choose not to send the probe at that point if it has
what it deems to be reliable and up-to-date presence information
about the user's contacts (e.g., because the user has another
available resource or because the user briefly logged off and on
before the new presence session began). In addition, a server MAY
periodically send a presence probe to a contact if it has not
received presence information or other traffic from the contact in
some configurable amount of time; this can help to prevent "ghost"
contacts who appear to be online but in fact are not.
US: <presence from='juliet@example.com'
id='ign291v5'
to='romeo@example.net'
type='probe'/>
US: <presence from='juliet@example.com'
id='xv291f38'
to='mercutio@example.com'
type='probe'/>
Naturally, the user's server does not need to send a presence probe
to a contact if the contact's account resides on the same server as
the user, since the server possesses the contact's information
locally.
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4.3.2. Server Processing of Inbound Presence Probe
Upon receiving a presence probe to the contact's bare JID from the
user's server on behalf of the user, the contact's server MUST reply
as follows:
1. If the contact account does not exist or the user is in the
contact's roster with a subscription state other than "From",
"From + Pending Out", or "Both" (as defined under Appendix A) and
the contact has not sent directed presence to the user (as
defined under Section 4.6), then the contact's server MUST return
a presence stanza of type "unsubscribed" in response to the
presence probe. Here the 'from' address MUST be the bare JID of
the contact, since specifying a full JID would constitute a
presence leak as described in [XMPP-CORE].
CS: <presence from='mercutio@example.com'
id='xv291f38'
to='juliet@example.com'
type='unsubscribed'/>
However, if a server receives a presence probe from a configured
hostname of the server itself or another such trusted service, it
MAY provide presence information about the user to that entity.
2. Else, if the contact has moved temporarily or permanently to
another address, then the server SHOULD return a presence stanza
of type "error" with a stanza error condition of <redirect/>
(temporary) or <gone/> (permanent) that includes the new address
of the contact.
CS: <presence from='mercutio@example.com'
id='xv291f38'
to='juliet@example.com'
type='error'>
<error type='modify'>
<gone xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
xmpp:la-mer@example.com
</gone>
</error>
</presence>
3. Else, if the contact has no available resources, then the server
SHOULD reply to the presence probe by sending to the user a
presence stanza of type "unavailable" (although sending
unavailable presence here is preferable because it results in a
deterministic answer to the probe, it is not mandatory because it
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can greatly increase the number of presence notifications
generated by the contact's server). Here the 'from' address is
the bare JID because there is no available resource associated
with the contact.
If appropriate in accordance with local security policies this
presence notification MAY include the full XML of the last
unavailable presence stanza that the server received from the
contact (including the 'id' of the original stanza), but if not
then the presence notification SHOULD simply indicate that the
contact is unavailable without any of the details originally
provided. In any case the presence notification returned to the
probing entity SHOULD include information about the time when the
last unavailable presence stanza was generated (formatted using
the XMPP delayed delivery extension [DELAY]).
CS: <presence from='mercutio@example.com'
id='xv291f38'
to='juliet@example.com'
type='unavailable'>
<delay xmlns='urn:xmpp:delay'
stamp='2002-09-10T23:41:07Z'/>
</presence>
4. Else, if the contact has at least one available resource, then
the server MUST reply to the presence probe by sending to the
user the full XML of the last presence stanza with no 'to'
attribute received by the server from each of the contact's
available resources. Here the 'from' addresses are the bare JIDs
of each available resource.
CS: <presence from='romeo@example.net/foo'
id='hzf1v27k'
to='juliet@example.com'/>
CS: <presence from='romeo@example.net/bar'
id='ps6t1fu3'
to='juliet@example.com'>
<show>away</show>
</presence>
If the contact's server receives a presence probe addressed to a full
JID of the contact, the server MUST NOT return presence information
about any resource except the resource specified by the 'to' address
of the probe. Rules #1 and #2 for a bare JID probe apply equally to
the case of a full JID probe. If there is a resource matching the
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full JID and (a) the probing entity has authorization via a presence
subscription to see the contact's presence or (b) the contact has
sent directed available presence to the probing entity, then the
server MUST return an available presence notification, which SHOULD
communicate only the fact that the resource is available (not
detailed information such as the <show/>, <status/>, <priority/>, or
presence extensions).
CS: <presence from='romeo@example.net/bar'
to='lobby@chat.example.com'/>
Implementation Note: The handling of the 'id' attribute in
relation to presence probes was unspecified in the predecessor to
this specification. Although the pattern of "send a probe and
receive a reply" might seem like a request-response protocol, in
fact it is not because the response to a probe might consist of
multiple presence stanzas (one for each available resource
currently active for the contact). For this reason, if the
contact currently has available resources then the contact's
server SHOULD preserve the 'id' attribute of the contact's
original presence stanza (if any) when sending those presence
notifications to the probing entity; however, if the contact
currently has no available resources, the probing entity is not
authorized (via presence subscription) to see the contact's
presence, or an error occurs in relation to the proble, then the
contact's server SHOULD mirror the 'id' of the user's presence
probe when replying to the probing entity.
4.4. Subsequent Presence Broadcast
4.4.1. Client Generation of Subsequent Presence Broadcast
After sending initial presence, at any time during its session the
user's client can update its availability for broadcasting by sending
a presence stanza with no 'to' address and no 'type' attribute.
UC: <presence>
<show>away</show>
</presence>
The presence broadcast MAY contain the <priority/> element, the
<show/> element, and one or more instances of the <status/> element,
as well as extended content; see Section 4.7 for details.
However, a user SHOULD send a presence update only to broadcast
information that is relevant to the user's availability for
communication or the communication capabilities of the connected
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resource. Information that is not relevant in this way might be of
interest to the user's contacts but SHOULD be sent via other means,
such as the XMPP message stanza.
4.4.2. Server Processing of Outbound Presence
Upon receiving a presence stanza expressing updated availability, the
user's server MUST broadcast the full XML of that presence stanza to
the contacts who meet all of the following criteria:
1. The contact is in the user's roster with a subscription type of
"from" or "both".
2. The last presence stanza received from the contact during the
user's presence session was not of type "error" or "unsubscribe".
As an optimization, if the subscription type is "both", then the
server SHOULD send subsequent presence notifications to a contact
only if the contact is online according to the user's server. That
is, if the user's server never received a positive indication that
the contact is online in response to the presence probe it sent to
the contact or if the last presence stanza it received from the
contact during the user's presence session was of type "unavailable",
the user's server SHOULD NOT send subsequent presence notifications
from the user to the contact. This optimization helps to save
bandwidth, since most presence subscriptions are bidirectional and
many contacts will not be online at any given time.
US: <presence from='juliet@example.com/balcony'
to='romeo@example.net'>
<show>away</show>
</presence>
US: <presence from='juliet@example.com/balcony'
to='benvolio@example.net'>
<show>away</show>
</presence>
US: <presence from='juliet@example.com/balcony'
to='mercutio@example.com'>
<show>away</show>
</presence>
Implementation Note: See Section 4.6 regarding rules that
supplement the foregoing for handling of directed presence.
The user's server MUST also send the presence stanza to all of the
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user's available resources (including the resource that generated the
presence notification in the first place).
US: <presence from='juliet@example.com/balcony'
to='juliet@example.com/chamber'>
<show>away</show>
</presence>
US: <presence from='juliet@example.com/balcony'
to='juliet@example.com/balcony'>
<show>away</show>
</presence>
4.4.3. Server Processing of Inbound Presence
Upon receiving presence from the user, the contact's server MUST
deliver the user's presence stanza to all of the contact's available
resources.
[ ... to resource1 ... ]
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'>
<show>away</show>
</presence>
[ ... to resource2 ... ]
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'>
<show>away</show>
</presence>
4.4.4. Client Processing of Subsequent Presence
When the contact's client receives presence from the user, it SHOULD
proceed as follows:
1. If the user is in the contact's roster, the client MUST display
the presence information in an appropriate roster interface.
2. If the user is not in the contact's roster but the contact and
the user are actively exchanging message or IQ stanzas, the
contact's client SHOULD display the presence information in the
user interface for that communication session (see also
Section 4.6 and Section 5.1).
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3. Otherwise, the client MUST ignore the presence information and
not display it to the contact.
4.5. Unavailable Presence
4.5.1. Client Generation of Unavailable Presence
Before ending its presence session with a server, the user's client
SHOULD gracefully become unavailable by sending UNAVAILABLE PRESENCE,
i.e., a presence stanza that possesses no 'to' attribute and that
possesses a 'type' attribute whose value is "unavailable".
UC: <presence type='unavailable'/>
Optionally, the unavailable presence stanza MAY contain one or more
<status/> elements specifying the reason why the user is no longer
available.
UC: <presence type='unavailable'>
<status>going on vacation</status>
</presence>
However, the unavailable presence stanza MUST NOT contain the
<priority/> element or the <show/> element, since these elements
apply only to available resources.
4.5.2. Server Processing of Outbound Unavailable Presence
The user's server MUST NOT depend on receiving unavailable presence
from an available resource, since the resource can become unavailable
ungracefully (e.g., the resource can be timed out by the server
because of inactivity).
If an available resource becomes unavailable for any reason (either
gracefully or ungracefully), the user's server MUST broadcast
unavailable presence to all contacts that meet all of the following
criteria:
1. The contact is in the user's roster with a subscription type of
"from" or "both".
2. The last presence stanza received from the contact during the
user's presence session was not of type "error" or "unsubscribe".
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Implementation Note: See Section 4.6 regarding rules that
supplement the foregoing for handling of directed presence.
Implementation Note: The optimization employed for subsequent
presence broadcast during a user's presence session (see
Section 4.4.2) MUST NOT be employed for unavailable presence
broadcast; if it were, the last presence received by the contact's
server would be the user's initial presence for the presence
session, with the result that the contact would consider the user
to be online.
If the unavailable notification was gracefully received from the
client, then the server MUST broadcast the full XML of the presence
stanza.
US: <presence from='juliet@example.com/balcony'
to='romeo@example.net'
type='unavailable'/>
<status>going on vacation</status>
</presence>
US: <presence from='juliet@example.com/balcony'
to='benvolio@example.net'
type='unavailable'>
<status>going on vacation</status>
</presence>
US: <presence from='juliet@example.com/balcony'
to='mercutio@example.com'
type='unavailable'>
<status>going on vacation</status>
</presence>
The user's server MUST also send the unavailable notification to all
of the user's available resources (including the resource that
generated the presence notification in the first place).
US: <presence from='juliet@example.com/balcony'
to='juliet@example.com/chamber'
type='unavailable'>
<status>going on vacation</status>
</presence>
If the server detects that the user has gone offline ungracefully,
then the server MUST generate the unavailable presence broadcast on
the user's behalf.
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Implementation Note: Any presence stanza with no 'type' attribute
and no 'to' attribute that the client sends after the server
broadcasts or generates an unavailable presence notification MUST
be routed or delivered by the user's server to all subscribers
(i.e., MUST be treated as equivalent to initial presence for a new
presence session).
4.5.3. Server Processing of Inbound Unavailable Presence
Upon receiving an unavailable notification from the user, the
contact's server MUST deliver the user's presence stanza to all of
the contact's available resources.
[ ... to resource1 ... ]
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'
type='unavailable'>
<status>going on vacation</status>
</presence>
[ ... to resource2 ... ]
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'
type='unavailable'>
<status>going on vacation</status>
</presence>
If the contact's server is optimizing subsequent presence delivery as
described under Section 4.4.2, it MUST also note that the user is
unavailable and appropriately update its internal representation of
which entities are online.
4.5.4. Client Processing of Unavailable Presence
When the contact's client receives an unavailable notification from
the user, it SHOULD proceed as follows:
1. If the user is in the contact's roster, the client MUST display
the unavailable notification in an appropriate roster interface.
2. If the user is not in the contact's roster but the contact and
the user are actively exchanging message or IQ stanzas, the
contact's client SHOULD display the unavailable notification in
the user interface for that chat session (see also Section 4.6
and Section 5.1).
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3. Otherwise, the client MUST ignore the unavailable notification
and not display it to the contact.
Typically, presence provides availability information about a
particular connected resource. However, it is possible for the
contact to receive an unavailable notification from the bare JID of
the user. In this case, the presence notification SHOULD be treated
as related to a resource identifier of zero length, which does not
supersede or overshadow other resources associated with the same bare
JID.
4.6. Directed Presence
This section supplements and in some respects modifies the rules for
client and server processing of presence notifications, but only for
the special case of directed presence.
4.6.1. Client Generation of Directed Presence
As noted, directed presence is a client-generated presence stanza
with a 'to' attribute whose value is the bare JID or full JID of the
other entity and with either no 'type' attribute (indicating
availability) or a 'type' attribute whose value is "unavailable".
Information about the use of directed presence in the context of a
one-to-one chat session is provided under Section 5.1.
4.6.2. Server Processing of Outbound Directed Presence
When the user's server receives a directed presence stanza, it SHOULD
process it according to the following rules.
1. If the user sends directed available or unavailable presence to a
contact that is in the user's roster with a subscription type of
"from" or "both" after having sent initial presence and before
sending unavailable presence broadcast (i.e., during the user's
presence session), the user's server MUST locally deliver or
remotely route the full XML of that presence stanza but SHOULD
NOT otherwise modify the contact's status regarding presence
broadcast (i.e., it SHOULD include the contact's JID in any
subsequent presence broadcasts initiated by the user).
2. If the user sends directed presence to an entity that is not in
the user's roster with a subscription type of "from" or "both"
after having sent initial presence and before sending unavailable
presence broadcast (i.e., during the user's presence session),
the user's server MUST locally deliver or remotely route the full
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XML of that presence stanza to the entity but MUST NOT modify the
contact's status regarding available presence broadcast (i.e., it
MUST NOT include the entity's JID in any subsequent broadcasts of
available presence initiated by the user); however, if the
available resource from which the user sent the directed presence
becomes unavailable, the user's server MUST route that
unavailable presence to the entity (if the user has not yet sent
directed unavailable presence to that entity).
3. If the user sends directed presence without first sending initial
presence or after having sent unavailable presence broadcast
(i.e., the resource is connected but not available), the user's
server MUST treat the entity to which the user sends directed
presence as in case #2 above.
4.6.3. Server Processing of Inbound Directed Presence
From the perspective of the contact's server, there is no difference
between presence broadcast and directed presence, so the contact's
server follows the rules for processing of inbound presence defined
under Section 4.3.2, Section 4.4.3, and Section 4.5.3.
4.6.4. Client Processing of Inbound Directed Presence
When the contact's client receives directed presence from the user,
it SHOULD proceed as follows:
1. If the user is in the contact's roster, the client MUST display
the presence information in an appropriate roster interface.
2. If the user is not in the contact's roster but the contact and
the user are actively exchanging message or IQ stanzas, the
contact's client SHOULD display the presence information in the
user interface for that communication session (see also
Section 4.6 and Section 5.1).
3. Otherwise, the client MUST ignore the presence information and
not display it to the contact.
4.7. Presence Syntax
4.7.1. Type Attribute
The absence of a 'type' attribute signals that the relevant entity is
available for communication (see Section 4.2 and Section 4.4).
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A 'type' attribute with a value of "unavailable" signals that the
relevant entity is not available for communication (see Section 4.5).
The XMPP presence stanza is also used to negotiate and manage
subscriptions to the presence of other entities. These tasks are
completed via presence stanzas of type "subscribe", "unsubscribe",
"subscribed", and "unsubscribed" as described under Section 3.
If a user and contact are associated with different XMPP servers,
those servers also use a special presence stanza of type "probe" in
order to determine the availability of the entity on the peer server;
for details, see Section 4.3. Clients SHOULD NOT send presence
stanzas of type "probe".
The values of the 'type' attribute can be summarized as follows:
o error -- An error has occurred regarding processing of a
previously-sent presence stanza; if the presence stanza is of type
"error", it MUST include an <error/> child element (refer to
[XMPP-CORE]).
o probe -- A request for an entity's current presence; SHOULD be
generated only by a server on behalf of a user.
o subscribe -- The sender wishes to subscribe to the recipient's
presence.
o subscribed -- The sender has allowed the recipient to receive
their presence.
o unavailable -- The sender is no longer available for
communication.
o unsubscribe -- The sender is unsubscribing from the receiver's
presence.
o unsubscribed -- The subscription request has been denied or a
previously-granted subscription has been cancelled.
If the value of the 'type' attribute is not one of the foregoing
values, the recipient or an intermediate router SHOULD return a
stanza error of <bad-request/>.
Implementation Note: There is no default value for the 'type'
attribute of the <presence/> element; in particular, there is no
value of "available".
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4.7.2. Child Elements
In accordance with the default namespace declaration, a presence
stanza is qualified by the 'jabber:client' or 'jabber:server'
namespace, which defines certain child elements of presence stanzas,
in particular the <show/>, <status/>, and <priority/> elements.
These child elements are used to provide more detailed information
about an entity's availability. Typically these child elements are
included only if the presence stanza possesses no 'type' attribute,
although exceptions are noted in the text that follows.
4.7.2.1. Show Element
The OPTIONAL <show/> element specifies the particular availability
sub-state of an entity or a specific resource thereof. A presence
stanza MUST NOT contain more than one <show/> element. There are no
attributes defined for the <show/> element. The XML character data
of the <show/> element is not human-readable. The XML character data
MUST be one of the following (additional availability states could be
defined through a child element of the presence stanza that is
qualified by a namespace other than the default namespace):
o away -- The entity or resource is temporarily away.
o chat -- The entity or resource is actively interested in chatting.
o dnd -- The entity or resource is busy (dnd = "Do Not Disturb").
o xa -- The entity or resource is away for an extended period (xa =
"eXtended Away").
If no <show/> element is provided, the entity is assumed to be online
and available.
Any specialized processing of availability states by recipients and
intermediate routers is up to the implementation (e.g., incorporation
of availability states into stanza routing and delivery logic).
4.7.2.2. Status Element
The OPTIONAL <status/> element contains human-readable XML character
data specifying a natural-language description of an entity's
availability. It is normally used in conjunction with the show
element to provide a detailed description of an availability state
(e.g., "In a meeting") when the presence stanza has no 'type'
attribute.
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<presence from='romeo@example.net/orchard'
xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
</presence>
There are no attributes defined for the <status/> element, with the
exception of the 'xml:lang' attribute inherited from [XML]. Multiple
instances of the <status/> element MAY be included, but only if each
instance possesses an 'xml:lang' attribute with a distinct language
value (either explicitly or by inheritance from the 'xml:lang' value
of an element farther up in the XML hierarchy, which from the
sender's perspective can include the XML stream header as described
in [XMPP-CORE]).
<presence from='romeo@example.net/orchard'
id='jx62vs97'
xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
<status xml:lang='cs'>Dvořím se Julii</status>
</presence>
A presence stanza of type "unavailable" MAY also include a <status/>
element to provide detailed information about why the entity is going
offline.
<presence from='romeo@example.net/orchard'
id='oy6sb241'
type='unavailable'
xml:lang='en'>
<status>Busy IRL</status>
</presence>
The <status/> child MAY also be sent in a subscription-related
presence stanza (i.e., type "subscribe", "subscribed", "unsubscribe",
or "unsubscribed") to provide a description of the action. The
receiving client MAY present this <status/> information to a human
user (see Section 11).
<presence from='romeo@example.net'
id='uc51xs63'
to='nurse@example.com'
type='subscribe'>
<status>Hi, Juliet told me to add you to my buddy list.</status>
</presence>
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4.7.2.3. Priority Element
The OPTIONAL <priority/> element contains non-human-readable XML
character data that specifies the priority level of the resource.
The value MUST be an integer between -128 and +127. A presence
stanza MUST NOT contain more than one <priority/> element. There are
no attributes defined for the <priority/> element.
<presence xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
<status xml:lang='cs'>Dvořím se Julii</status>
<priority>1</priority>
</presence>
If no priority is provided, the processing server or client MUST
consider the priority to be zero ("0").
The client's server MAY override the priority value provided by the
client (e.g., in order to impose a message handling rule of
delivering a message intended for the account's bare JID to all of
the account's available resources); if the server does so, it MUST
include the modified priority value (typically zero) when it echoes
the client's presence back to itself.
For information regarding the semantics of priority values in stanza
processing within instant messaging and presence applications, refer
to Section 8.
4.7.3. Extended Content
As described in [XMPP-CORE], an XML stanza MAY contain any child
element that is qualified by a namespace other than the default
namespace; this applies to the presence stanza as well.
(In the following example, the presence stanza includes entity
capabilities information as defined in [XEP-0115]).)
<presence from='romeo@example.net'>
<c xmlns='http://jabber.org/protocol/caps'
hash='sha-1'
node='http://psi-im.org'
ver='q07IKJEyjvHSyhy//CH0CxmKi8w='/>
</presence>
Any extended content included in a presence stanza SHOULD represent
aspects of an entity's availability for communication or provide
information about communication-related capabilities.
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5. Exchanging Messages
Once a client has authenticated with a server and bound a resource to
an XML stream as described in [XMPP-CORE], an XMPP server will route
XML stanzas to and from that client. One kind of stanza that can be
exchanged is <message/> (if, that is, messaging functionality is
enabled on the server). Exchanging messages is a basic use of XMPP
and occurs when a user generates a message stanza that is addressed
to another entity. As defined under Section 8, the sender's server
is responsible for delivering the message to the intended recipient
(if the recipient is on the same local server) or for routing the
message to the recipient's server (if the recipient is on a remote
server). Thus a message stanza is used to "push" information to
another entity.
5.1. One-to-One Chat Sessions
In practice, instant messaging activity between human users tends to
occur in the form of a conversational burst that we call a CHAT
SESSION: the exchange of at least several messages between two
parties in relatively rapid succession within a relatively brief
period of time.
When a human user intends to engage in such a chat session with a
contact (rather than sending a single message to which no reply is
expected), the message type generated by the user's client SHOULD be
"chat" and the contact's client SHOULD preserve that message type in
subsequent replies. The user's client also SHOULD include a
<thread/> element with its initial message, which the contact's
client SHOULD also preserve during the life of the chat session (see
Section 5.2.5.
The user's client MUST address the initial message in a chat session
to the bare JID <contact@domain> of the contact (rather than
attempting to guess an appropriate full JID <contact@domain/resource>
based on the <show/>, <status/>, or <priority/> value of any presence
notifications it has received from the contact). Until and unless
the user's client receives a reply from the contact, it MUST send any
further messages to the contact's bare JID. The contact's client
SHOULD address its replies to the user's full JID
<user@domain/resource> as provided in the 'from' address of the
initial message. Once the user's client receives a reply from the
contact's full JID, it SHOULD address its subsequent messages to the
contact's full JID as provided in the 'from' address of the contact's
replies, thus "locking in" on that full JID. A client SHOULD
"unlock" after having received a <message/> or <presence/> stanza
from any other resource controlled by the peer (or a presence stanza
from the locked resource); as a result, it SHOULD address its next
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message(s) in the chat session to the bare JID of the peer (thus
"unlocking" the previous "lock") until it receives a message from one
of the peer's full JIDs.
When two parties engage in a chat session but do not share presence
with each other based on a presence subscription, they SHOULD send
directed presence to each other so that either party can easily
discover if the peer changes its availability or goes offline during
the course of the chat session. However, a client MUST provide a way
for a user to disable such presence sharing globally or to enable it
only with particular entities. Furthermore, a party SHOULD send
directed unavailable presence to the peer when it has reason to
believe that the chat session is over (e.g., if, after some
reasonable amount of time, no subsequent messages have been exchanged
between the parties).
An example of a chat session is provided under Section 7.
5.2. Message Syntax
The following sections describe the syntax of the <message/> stanza.
5.2.1. To Attribute
An instant messaging client specifies an intended recipient for a
message by providing the JID of the intended recipient in the 'to'
attribute of the <message/> stanza.
If the message is being sent outside the context of any existing chat
session or received message, the value of the 'to' address SHOULD be
of the form <user@domain> rather than of the form
<user@domain/resource> (see Section 5.1).
<message
from='juliet@example.com/balcony'
id='ktx72v49'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<body>Art thou not Romeo, and a Montague?</body>
</message>
If the message is being sent in reply to a message previously
received from an address of the form <user@domain/resource> (e.g.,
within the context of a one-to-one chat session as described under
Section 5.1), the value of the 'to' address SHOULD be of the form
<user@domain/resource> rather than of the form <user@domain> unless
the sender has knowledge (e.g., via presence) that the intended
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recipient's resource is no longer available.
<message
from='romeo@example.net/orchard'
id='sl3nx51f'
to='juliet@example.com/balcony'
type='chat'
xml:lang='en'>
<body>Neither, fair saint, if either thee dislike.</body>
</message>
5.2.2. Type Attribute
Common uses of the message stanza in instant messaging applications
include: single messages; messages sent in the context of a one-to-
one chat session; messages sent in the context of a multi-user chat
room; alerts, notifications, or other information to which no reply
is expected; and errors. These uses are differentiated via the
'type' attribute. Inclusion of the 'type' attribute is RECOMMENDED.
If included, the 'type' attribute MUST have one of the following
values:
o chat -- The message is sent in the context of a one-to-one chat
session. Typically a receiving client will present a message of
type "chat" in an interface that enables one-to-one chat between
the two parties, including an appropriate conversation history.
Detailed recommendations regarding one-to-one chat sessions are
provided under Section 5.1.
o error -- The message is generated by an entity that experiences an
error in processing a message received from another entity (for
details regarding stanza error syntax, refer to [XMPP-CORE]). A
client that receives a message of type "error" SHOULD present an
appropriate interface informing the sender of the nature of the
error.
o groupchat -- The message is sent in the context of a multi-user
chat environment (similar to that of [IRC]). Typically a
receiving client will present a message of type "groupchat" in an
interface that enables many-to-many chat between the parties,
including a roster of parties in the chatroom and an appropriate
conversation history. For detailed information about XMPP-based
groupchat, refer to [XEP-0045].
o headline -- The message provides an alert, a notification, or
other transient information to which no reply is expected (e.g.,
news headlines, sports updates, near-real-time market data, and
syndicated content). Because no reply to the message is expected,
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typically a receiving client will present a message of type
"headline" in an interface that appropriately differentiates the
message from standalone messages, chat messages, or groupchat
messages (e.g., by not providing the recipient with the ability to
reply). The receiving server SHOULD deliver the message to all of
the recipient's available resources, or silently ignore it if
there are no available resources (see Section 8).
o normal -- The message is a standalone message that is sent outside
the context of a one-to-one conversation or groupchat, and to
which it is expected that the recipient will reply. Typically a
receiving client will present a message of type "normal" in an
interface that enables the recipient to reply, but without a
conversation history. The default value of the 'type' attribute
is "normal".
An IM application SHOULD support all of the foregoing message types.
If an application receives a message with no 'type' attribute or the
application does not understand the value of the 'type' attribute
provided, it MUST consider the message to be of type "normal" (i.e.,
"normal" is the default).
Guidelines for server handling of different message types is provided
under Section 8.
Although the 'type' attribute is OPTIONAL, it is considered polite to
mirror the type in any replies to a message; furthermore, some
specialized applications (e.g., a multi-user chat service) MAY at
their discretion enforce the use of a particular message type (e.g.,
type='groupchat').
5.2.3. Body Element
The <body/> element contains human-readable XML character data that
specifies the textual contents of the message; this child element is
normally included but is OPTIONAL.
<message
from='juliet@example.com/balcony'
id='b4vs9km4'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<body>Wherefore art thou, Romeo?</body>
</message>
There are no attributes defined for the <body/> element, with the
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exception of the 'xml:lang' attribute. Multiple instances of the
<body/> element MAY be included in a message stanza, but only if each
instance possesses an 'xml:lang' attribute with a distinct language
value (either explicitly or by inheritance from the 'xml:lang' value
of an element farther up in the XML hierarchy, which from the
sender's perspective can include the XML stream header as described
in [XMPP-CORE]).
<message
from='juliet@example.com/balcony'
id='z94nb37h'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<body>Wherefore art thou, Romeo?</body>
<body xml:lang='cs'>
PročeŽ jsi ty, Romeo?
</body>
</message>
The <body/> element MUST NOT contain mixed content (as defined in
Section 3.2.2 of [XML]).
5.2.4. Subject Element
The <subject/> element contains human-readable XML character data
that specifies the topic of the message.
<message
from='juliet@example.com/balcony'
id='c8xg3nf8'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<subject>I implore you!</subject>
<body>Wherefore art thou, Romeo?</body>
</message>
There are no attributes defined for the <subject/> element, with the
exception of the 'xml:lang' attribute inherited from [XML]. Multiple
instances of the <subject/> element MAY be included for the purpose
of providing alternate versions of the same subject, but only if each
instance possesses an 'xml:lang' attribute with a distinct language
value (either explicitly or by inheritance from the 'xml:lang' value
of an element farther up in the XML hierarchy, which from the
sender's perspective can include the XML stream header as described
in [XMPP-CORE]).
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<message
from='juliet@example.com/balcony'
id='jk3v47gw'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<subject>I implore you!</subject>
<subject xml:lang='cs'>
Úpěnlivě prosím!
</subject>
<body>Wherefore art thou, Romeo?</body>
<body xml:lang='cs'>
Pročež jsi ty, Romeo?
</body>
</message>
The <subject/> element MUST NOT contain mixed content (as defined in
Section 3.2.2 of [XML]).
5.2.5. Thread Element
The primary use of the XMPP <thread/> element is to uniquely identify
a conversation thread or "chat session" between two entities
instantiated by <message/> stanzas of type 'chat'. However, the XMPP
<thread/> element MAY also be used to uniquely identify an analogous
thread between two entities instantiated by <message/> stanzas of
type 'headline' or 'normal', or among multiple entities in the
context of a multi-user chat room instantiated by <message/> stanzas
of type 'groupchat'. It MAY also be used for <message/> stanzas not
related to a human conversation, such as a game session or an
interaction between plugins. The <thread/> element is not used to
identify individual messages, only conversations or messaging
sessions.
The inclusion of the <thread/> element is OPTIONAL. Because the
<thread/> element identifies the particular conversation thread to
which a message belongs, a message stanza MUST NOT contain more than
one <thread/> element.
The <thread/> element MAY possess a 'parent' attribute that
identifies another thread of which the current thread is an offshoot
or child; the value of the 'parent' attribute MUST conform to the
syntax of the <thread/> element itself.
The value of the <thread/> element is not human-readable and MUST be
treated as opaque by entities; no semantic meaning can be derived
from it, and only exact comparisons can be made against it. The
value of the <thread/> element MUST uniquely identify the
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conversation thread either between the conversation partners or more
generally (one way to ensure uniqueness is by generating a
universally unique identifier (UUID) as described in [UUID]).
The <thread/> element MUST NOT contain mixed content (as defined in
Section 3.2.2 of [XML]).
<message
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<subject>I implore you!</subject>
<subject xml:lang='cs'>
Úpěnlivě prosím!
</subject>
<body>Wherefore art thou, Romeo?</body>
<body xml:lang='cs'>
Pročež jsi ty, Romeo?
</body>
<thread parent='e0ffe42b28561960c6b12b944a092794b9683a38'>
0e3141cd80894871a68e6fe6b1ec56fa
</thread>
</message>
For detailed recommendations regarding use of the <thread/> element,
refer to [XEP-0201].
5.3. Extended Content
As described in [XMPP-CORE], an XML stanza MAY contain any child
element that is qualified by a namespace other than the default
namespace; this applies to the message stanza as well.
(In the following example, the message stanza includes an XHTML-
formatted version of the message as defined in [XEP-0071]).)
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<message
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<body>Wherefore art thou, Romeo?</body>
<html xmlns='http://jabber.org/protocol/xhtml-im'>
<body xmlns='http://www.w3.org/1999/xhtml'>
<p>Wherefore <span style='font-style: italic'>art</span>
thou, <span style='color:red'>Romeo</span>?</p>
</body>
</html>
</message>
6. Exchanging IQ Stanzas
As described in [XMPP-CORE], IQ stanzas provide a structured request-
response mechanism. The basic semantics of that mechanism (e.g.,
that the 'id' attribute is mandatory) are defined in [XMPP-CORE],
whereas the specific semantics needed to complete particular use
cases are defined in all instances by the extended namespace that
qualifies the direct child element of an IQ stanza of type "get" or
"set". The 'jabber:client' and 'jabber:server' namespaces do not
define any children of IQ stanzas other than the <error/> element
common to all stanza types. This document defines one such extended
namespace, for Managing the Roster (Section 2). However, an IQ
stanza MAY contain structured information qualified by any extended
namespace.
As noted under Section 4.6, if a user exchanges IQ stanzas with
another entity but does not share presence with the entity based on a
presence subscription, it is RECOMMENDED for the user's client to
send directed presence to the other entity.
7. A Sample Session
The examples in this section illustrate a possible instant messaging
and presence session. The user is <romeo@example.net>, he has an
available resource whose resource identifier is "orchard", and he has
the following individuals in his roster:
o <juliet@example.com> (subscription="both" and she has two
available resources, "chamber" and "balcony")
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o <benvolio@example.net> (subscription="to")
o <mercutio@example.org> (subscription="from")
First, the user completes the preconditions (stream establishment,
TLS and SASL negotiation, and resource binding) described in
[XMPP-CORE]; those protocol flows are not reproduced here.
Next, the user requests his roster.
Example 1: User requests current roster from server:
UC: <iq from='romeo@example.net/orchard'
id='hf61v3n7'
type='get'>
<query xmlns='jabber:iq:roster'/>
</iq>
Example 2: User receives roster from server:
US: <iq id='hf61v3n7'
to='romeo@example.net/orchard'
type='result'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
name='Juliet'
subscription='both'>
<group>Friends</group>
</item>
<item jid='benvolio@example.org'
name='Benvolio'
subscription='to'/>
<item jid='mercutio@example.org'
name='Mercutio'
subscription='from'/>
</query>
</iq>
Now the user begins a presence session.
Example 3: User sends initial presence:
UC: <presence/>
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Example 4: User's server sends presence probes to contacts with
subscription="to" and subscription="both" on behalf of the user:
US: <presence
from='romeo@example.net'
to='juliet@example.com'
type='probe'/>
US: <presence
from='romeo@example.net'
to='benvolio@example.org'
type='probe'/>
Example 5: User's server sends initial presence to contacts with
subscription="from" and subscription="both" on behalf of the user's
available resource:
US: <presence
from='romeo@example.net/orchard'
to='juliet@example.com'/>
US: <presence
from='romeo@example.net/orchard'
to='mercutio@example.org'/>
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Example 6: Contacts' servers reply to presence probe on behalf of all
available resources:
CS: <presence
from='juliet@example.com/balcony'
to='romeo@example.net'
xml:lang='en'>
<show>away</show>
<status>be right back</status>
<priority>0</priority>
</presence>
CS: <presence
from='juliet@example.com/chamber'
to='romeo@example.net'>
<priority>1</priority>
</presence>
CS: <presence
from='benvolio@example.org/pda'
to='romeo@example.net'
xml:lang='en'>
<show>dnd</show>
<status>gallivanting</status>
</presence>
Example 7: Contacts' servers deliver user's initial presence to all
available resources:
CS: <presence
from='romeo@example.net/orchard'
to='juliet@example.com'/>
CS: <presence
from='romeo@example.net/orchard'
to='juliet@example.com'/>
CS: <presence
from='romeo@example.net/orchard'
to='mercutio@example.org'/>
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Example 8: User sends directed presence to another user not in his
roster:
UC: <presence
from='romeo@example.net/orchard'
to='nurse@example.com'
xml:lang='en'>
<show>dnd</show>
<status>courting Juliet</status>
<priority>0</priority>
</presence>
Now the user engages in a chat session with one of his contacts.
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Example 9: A threaded conversation
CC: <message
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<body>My ears have not yet drunk a hundred words</body>
<thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
</message>
CC: <message
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<body>Of that tongue's utterance, yet I know the sound:</body>
<thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
</message>
CC: <message
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<body>Art thou not Romeo, and a Montague?</body>
<thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
</message>
UC: <message
from='romeo@example.net/orchard'
to='juliet@example.com/balcony'
type='chat'
xml:lang='en'>
<body>Neither, fair saint, if either thee dislike.</body>
<thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
</message>
CC: <message
from='juliet@example.com/balcony'
to='romeo@example.net/orchard'
type='chat'
xml:lang='en'>
<body>How cam'st thou hither, tell me, and wherefore?</body>
<thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
</message>
And so on.
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The user can also send subsequent presence broadcast.
Example 10: User sends updated available presence for broadcasting:
UC: <presence xml:lang='en'>
<show>away</show>
<status>I shall return!</status>
<priority>1</priority>
</presence>
Example 11: User's server broadcasts updated presence to the contacts
who hvae a subscription of type "both" or "from" (but not to the
entity to which the user sent directed presence):
US: <presence
from='romeo@example.net/orchard'
to='juliet@example.com'
xml:lang='en'>
<show>away</show>
<status>I shall return!</status>
<priority>1</priority>
</presence>
US: <presence
from='romeo@example.net/orchard'
to='mercutio@example.org'
xml:lang='en'>
<show>away</show>
<status>I shall return!</status>
<priority>1</priority>
</presence>
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Example 12: Contacts' servers deliver updated presence:
CS: <presence
from='romeo@example.net/orchard'
to='juliet@example.com'
xml:lang='en'>
<show>away</show>
<status>I shall return!</status>
<priority>1</priority>
</presence>
CS: <presence
from='romeo@example.net/orchard'
to='juliet@example.com'
xml:lang='en'>
<show>away</show>
<status>I shall return!</status>
<priority>1</priority>
</presence>
CS: <presence
from='romeo@example.net/orchard'
to='mercutio@example.org'
xml:lang='en'>
<show>away</show>
<status>I shall return!</status>
<priority>1</priority>
</presence>
Example 13: One of the contact's resources broadcasts unavailable
notification:
CC: <presence from='juliet@example.com/chamber' type='unavailable'/>
Example 14: Contact's server sends unavailable notification to user:
CS: <presence
from='juliet@example.com/chamber'
to='romeo@example.net'
type='unavailable'/>
Now the user ends his presence session.
Example 15: User sends unavailable notification:
UC: <presence type='unavailable' xml:lang='en'>
<status>gone home</status>
</presence>
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Example 16: User's server broadcasts unavailable notification to
contacts as well as to the entity to whom the user sent directed
presence:
US: <presence
from='romeo@example.net/orchard'
to='juliet@example.com'
type='unavailable'
xml:lang='en'>
<status>gone home</status>
</presence>
US: <presence
from='romeo@example.net/orchard'
to='mercutio@example.org'
type='unavailable'
xml:lang='en'>
<status>gone home</status>
</presence>
US: <presence
from='romeo@example.net/orchard'
to='nurse@example.com'
type='unavailable'
xml:lang='en'>
<status>gone home</status>
</presence>
Finally the user closes his stream and the server responds in kind.
Example 17: User closes stream:
UC: </stream:stream>
Example 18: User's server closes stream:
US: </stream:stream>
THE END
8. Server Rules for Processing XML Stanzas
Basic server rules for processing XML stanzas are defined in
[XMPP-CORE]. This section defines supplementary rules for XMPP
instant messaging and presence servers.
Some delivery rules defined in this section specify the use of
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OFFLINE STORAGE, i.e., the server's storing a message stanza on
behalf of the user and delivering it when the user next becomes
available. For recommendations regarding offline message storage
refer to [XEP-0160].
8.1. No 'to' Address
If the stanza possesses no 'to' attribute, the rules defined in
[XMPP-CORE] apply.
8.2. Remote Domain
If the hostname of the domain identifier portion of the address
contained in the 'to' attribute of an outbound stanza does not match
a configured hostname of the server itself, then the server MUST
attempt to route the stanza to the remote domain. If there exists an
active stream between the two peers, then the server MUST route the
stanza over that stream for processing by the peer server. If not,
then the server MUST do the following.
First, resolve the hostname of the remote domain (or use a cached
resolution of the remote domain to an IP address). The RECOMMENDED
order of attempted resolutions is as follows:
1. Attempt to resolve the remote hostname using a DNS service
location record [SRV] Service of "xmpp-server" and a Proto of
"tcp", resulting in resource records such as "_xmpp-
server._tcp.example.com.", as specified in [XMPP-CORE].
2. If the "xmpp-server" address record resolution fails, attempt to
resolve the "_im" or "_pres" SRV Service as specified in
[IMP-SRV], using the "_im" Service for <message/> stanzas and the
"_pres" Service for <presence/> stanzas (it is up to the
implementation how to handle <iq/> stanzas). This will result in
one or more resolutions of the form "_im.<proto>.example.com." or
"_pres.<proto>.example.com.", where "<proto>" would be a label
registered in the Instant Messaging SRV Protocol Label registry
or the Presence SRV Protocol Label registry: either "_xmpp" for
an XMPP-aware domain or some other IANA-registered label (e.g.,
"_simple") for a non-XMPP-aware domain.
3. If both SRV address record resolutions fail, attempt to perform a
normal IPv4/IPv6 address record resolution to determine the IP
address using the "xmpp-server" port of 5269 registered with the
IANA, as specified in [XMPP-CORE].
If the server cannot resolve the remote domain, it MUST return a
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<remote-server-not-found/> stanza error.
Second, negotiate XML streams with the remote domain by following the
process defined in [XMPP-CORE]. If the server can resolve the remote
domain but cannot establish streams with the XMPP service at that
domain, it MUST return a <remote-server-timeout/> stanza error.
Third, route the stanza to the remote domain for processing by the
peer server.
Note: Administrators of server deployments are strongly encouraged
to keep the _im._xmpp, _pres._xmpp, and _xmpp._tcp SRV records
properly synchronized, since different implementations might
perform the "_im" and "_pres" lookups before the "xmpp-server"
lookup.
8.3. Local Domain
If the hostname of the domainpart of the JID contained in the 'to'
attribute matches one of the configured hostnames of the server and
the hostname is serviced by the server itself (not a specialized
local service), the server MUST proceed as follows.
8.3.1. No Such User
If the user account identified by the 'to' attribute does not exist,
how the stanza is processed depends on the stanza type.
o For an IQ stanza, the server MUST return a <service-unavailable/>
stanza error to the sender.
o For a message stanza, the server MUST return a <service-
unavailable/> stanza error to the sender.
o For a presence stanza with no 'type' attribute or a 'type'
attribute of "unavailable", the server MUST silently ignore the
stanza.
o For a presence stanza of type "subscribe", the server MUST return
a presence stanza of type "unsubscribed".
o For a presence stanza of type "subscribed", "unsubscribe", or
"unsubscribed", the server MUST silently ignore the stanza.
o For a presence stanza of type "probe", the server MUST return a
presence stanza of type "unsubscribed".
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8.3.2. Full JID at Local Domain
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute of an inbound stanza matches one of the
configured hostnames of the server itself and the JID contained in
the 'to' attribute is of the form <user@domain/resource>, then the
server MUST adhere to the following rules (subject to enforcement of
relevant privacy and security policies, such as those deployed by
means of [XEP-0016] or [XEP-0191]).
8.3.2.1. Resource Matches
If an available or connected resource exactly matches the full JID,
how the stanza is processed depends on the stanza type.
o For an IQ stanzas of type "get" or "set", if the intended
recipient does not share presence with the requesting entity
either by means of a presence subscription of type "both" or
"from" or by means of directed presence, then the server SHOULD
NOT deliver the IQ stanza but instead SHOULD return a <service-
unavailable/> stanza error to the requesting entity. This policy
helps to prevent presence leaks (see Section 11).
o For a message stanza, the server MUST deliver the stanza to the
resource.
o For a presence stanza with no 'type' attribute or a 'type'
attribute of "unavailable", the server MUST deliver the stanza to
the resource.
o For a presence stanza of type "subscribe", the server MUST follow
the guidelines provided under Section 3.1.3.
o For a presence stanza of type "subscribe", "subscribed",
"unsubscribe", or "unsubscribed", the server MUST follow the
guidelines provided under Section 3.
o For a presence stanza of type "probe", the server MUST follow the
guidelines provided under Section 4.3.
8.3.2.2. No Resource Matches
If no connected or available resource exactly matches the full JID,
how the stanza is processed depends on the stanza type.
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8.3.2.2.1. Message
For a message stanza of type "normal", the server SHOULD return a
stanza error to the sender, which SHOULD be <service-unavailable/>.
For a message stanza of type "chat":
o If the only available resource has a negative presence priority
then the server SHOULD store the message offline for later
delivery or return a stanza error to the sender, which SHOULD be
<service-unavailable/>.
o If the only available resource has a non-negative presence
priority then the server SHOULD deliver the message to that
resource.
o If there is more than one resource with a non-negative presence
priority then the server SHOULD deliver the message to the "most
available" resource or resources (according to the server's
implementation-specific algorithm) but it MAY instead deliver it
to all of the non-negative resources that have opted in to receive
chat messages.
For a message stanza of type "groupchat", the server MUST return a
stanza error to the sender, which SHOULD be <service-unavailable/>.
For a message stanza of type "headline", the server SHOULD silently
ignore the stanza.
For a message stanza of type "error", the server MUST silently ignore
the stanza.
8.3.2.2.2. Presence
For a presence stanza with no 'type' attribute or a 'type' attribute
of "unavailable", the server MUST silently ignore the stanza.
For a presence stanza of type "subscribe", the server MUST follow the
guidelines provided under Section 3.1.3.
For a presence stanza of type "subscribed", "unsubscribe", or
"unsubscribed", the server MUST ignore the stanza.
For a presence stanza of type "probe", the server MUST follow the
guidelines provided under Section 4.3.
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8.3.2.2.3. IQ
For an IQ stanza, the server MUST return a <service-unavailable/>
stanza error to the sender.
8.3.3. Bare JID at Local Domain
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute of an inbound stanza matches one of the
configured hostnames of the server itself and the JID contained in
the 'to' attribute is of the form <user@domain>, then the server MUST
adhere to the following rules.
8.3.3.1. Available or Connected Resources
If there is at least one available or connected resource, how the
stanza is processed depends on the stanza type.
8.3.3.1.1. Message
For a message stanza of type "normal" or "chat":
o If the only available resource has a negative presence priority
then the server SHOULD store the message offline for later
delivery or return a stanza error to the sender, which SHOULD be
<service-unavailable/>.
o If the only available resource has a non-negative presence
priority then the server SHOULD deliver the message to that
resource.
o If there is more than one resource with a non-negative presence
priority then the server SHOULD deliver the message to the "most
available" resource or resources (according to the server's
implementation-specific algorithm) but it MAY instead deliver it
to all of the non-negative resources that have opted in to receive
chat messages.
For a message stanza of type "groupchat", the server MUST NOT deliver
the stanza to any of the available resources but instead MUST return
a stanza error to the sender, which SHOULD be <service-unavailable/>.
For a message stanza of type "headline", the server MUST deliver the
stanza to all available resources.
For a message stanza of type "error", the server MUST silently ignore
the message.
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However, for any message type the server MUST NOT deliver the stanza
to any available resource with a negative priority; if the only
available resource has a negative priority, the server SHOULD handle
the message as if there were no available or connected resources as
described under Section 8.3.3.2.
In all cases, the server MUST NOT rewrite the 'to' attribute (i.e.,
it MUST leave it as <user@domain> rather than change it to
<user@domain/resource>).
8.3.3.1.2. Presence
For a presence stanza with no type or of type "unavailable", the
server MUST deliver it to all available resources.
For a presence stanza of type "subscribe", "subscribed",
"unsubscribe", or "unsubscribed", the server MUST adhere to the rules
defined under Section 3 and summarized under Appendix A.
For a presence stanza of type "probe", the server MUST handle it
directly as described under Section 4.3.
In all cases, the server MUST NOT rewrite the 'to' attribute (i.e.,
it MUST leave it as <user@domain> rather than change it to
<user@domain/resource>).
8.3.3.1.3. IQ
For an IQ stanza, the server itself MUST reply on behalf of the user
with either an IQ result or an IQ error, and MUST NOT deliver the IQ
stanza to any of the user's available resources. Specifically, if
the semantics of the qualifying namespace define a reply that the
server can provide on behalf of the user, then the server MUST reply
to the stanza on behalf of the user by returning either an IQ stanza
of type "result" or an IQ stanza of type "error" that is appropriate
to the original payload; if not, then the server MUST reply with a
<service-unavailable/> stanza error.
8.3.3.2. No Available or Connected Resources
If there are no available or connected resources associated with the
user, how the stanza is processed depends on the stanza type.
8.3.3.2.1. Message
For a message stanza of type "normal" or "chat", the server SHOULD
add the message to offline storage or return a stanza error to the
sender, which SHOULD be <service-unavailable/>.
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For a message stanza of type "groupchat", the server MUST return an
error to the sender, which SHOULD be <service-unavailable/>.
For a message stanza of type "headline", the server MUST silently
ignore the message.
For a message stanza of type "error", the server MUST silently ignore
the message.
8.3.3.2.2. Presence
For a presence stanza with no type or of type "unavailable", the
server SHOULD silently ignore the stanza by not storing it for later
delivery and not replying to it on behalf of the user.
For a presence stanza of type "subscribe", "subscribed",
"unsubscribe", or "unsubscribed", the server MUST adhere to the rules
defined under Section 3 and summarized under Appendix A.
For a presence stanza of type "probe", the server MUST handle it
directly as described under Section 4.3.
8.3.3.2.3. IQ
For an IQ stanza, the server itself MUST reply on behalf of the user
with either an IQ result or an IQ error. Specifically, if the
semantics of the qualifying namespace define a reply that the server
can provide on behalf of the user, then the server MUST reply to the
stanza on behalf of the user by returning either an IQ stanza of type
"result" or an IQ stanza of type "error" that is appropriate to the
original payload; if not, then the server MUST reply with a <service-
unavailable/> stanza error.
8.3.4. Summary of Message Delivery Rules
The following table summarizes the message delivery rules described
earlier in this section. The left column shows various combinations
of available resources (no resource, one resource with a negative
presence priority, one resource with a non-negative presence
priority, or more than one resource with a non-negative presence
priority) and 'to' addresses (bare JID, full JID matching an
available resource, or full JID matching no available resource). The
subsequent columns list the four message types (normal, chat,
groupchat, or headline) along with six possible delivery options:
storing the message offline (O), bouncing the message with a stanza
error (E), silently ignoring the message (S), delivering the message
to the resource specified in the 'to' address (D), delivering the
message to the "most available" resource or resources according to
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the server's implementation-specific algorithm (M), or delivering the
message to all resources with non-negative presence priority that
have opted in to receive chat messages (A). The '/' character stands
for "or".
Table 1: Message Delivery Rules
+----------------------------------------------------------+
| Resources | Normal | Chat | Groupchat | Headline |
+----------------------------------------------------------+
| NONE | O/E | O/E | E | S |
+----------------------------------------------------------+
| 1 NEG |
| bare | O/E | O/E | E | S |
| full match | D | D | D | D |
| full no match | E | O/E | E | S |
+----------------------------------------------------------+
| 1 NON-NEG |
| bare | D | D | E | D |
| full match | D | D | D | D |
| full no match | E | D | E | S |
+----------------------------------------------------------+
| 1+ NON-NEG |
| bare | M/A | M/A | E | M/A |
| full match | D | D/A* | D | D |
| full no match | E | M/A | E | S |
+----------------------------------------------------------+
* A server SHOULD NOT act in accordance with option (A) unless
clients can explicitly opt in to receiving all chat messages;
however, methods for opting in are outside the scope of this
specification.
9. Handling of URIs
The addresses of XMPP entities as used in communication over an XMPP
network (e.g., in the 'from' and 'to' addresses of an XML stanza)
MUST NOT be prepended with a Uniform Resource Identifier [URI]
scheme. However, an application that is external to XMPP itself
(e.g., a page on the World Wide Web) might need to identify an XMPP
entity either as a URI or as an Internationalized Resource Identifier
[IRI], and an XMPP client might need to interact with such an
external application (for example, an XMPP client might be invoked by
clicking a link provided on a web page).
In the context of such interactions, an XMPP client SHOULD handle
addresses that are encoded as "xmpp:" URIs and IRIs as specified in
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[XMPP-URI] and further described in [XEP-0147]. A client SHOULD also
handle addresses that are encoded as "im:" URIs as specified in
[CPIM] and "pres:" URIs as specified in [CPP], although it MAY do so
by removing the "im:" or "pres:" scheme and entrusting address
resolution to the server as specified under Section 8.2.
10. Internationalization Considerations
For internationalization considerations, refer to the relevant
section of [XMPP-CORE].
11. Security Considerations
Core security considerations for XMPP are defined in the relevant
section of [XMPP-CORE].
Additional considerations that apply only to instant messaging and
presence applications of XMPP are defined in several places within
this document; specifically:
o When a server processes an inbound presence stanza of type "probe"
whose intended recipient is a user associated with one of the
server's hostnames, the server MUST NOT reveal the user's presence
if the sender is an entity that is not authorized to receive that
information as determined by presence subscriptions (see
Section 4).
o A user's server MUST NOT leak the user's network availability to
entities who are not authorized to know the user's presence,
either via an explicit subscription as described herein or via an
existing trust relationship (such as presence-enabled user
directories within organizations).
o When a server processes an outbound presence stanza with no type
or of type "unavailable", it MUST follow the rules defined under
Section 4 in order to ensure that such presence information is not
sent to entities that are not authorized to know such information.
o A client MAY ignore the <status/> element when contained in a
presence stanza of type "subscribe", "unsubscribe", "subscribed",
or "unsubscribed"; this can help prevent "presence subscription
spam".
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12. IANA Considerations
The following sections update the registrations provided in
[RFC3921].
For a number of related IANA considerations, refer to the relevant
section of [XMPP-CORE].
12.1. Instant Messaging SRV Protocol Label Registration
Address Resolution for Instant Messaging and Presence [IMP-SRV]
defines an Instant Messaging SRV Protocol Label registry for
protocols that can provide services that conform to the "_im" SRV
Service label. Because XMPP is one such protocol, the IANA registers
the "_xmpp" protocol label in the appropriate registry, as follows:
Protocol label: _xmpp
Specification: XXXX
Description: Instant messaging protocol label for the Extensible
Messaging and Presence Protocol (XMPP) as defined by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmpp@ietf.org>
12.2. Presence SRV Protocol Label Registration
Address Resolution for Instant Messaging and Presence [IMP-SRV]
defines a Presence SRV Protocol Label registry for protocols that can
provide services that conform to the "_pres" SRV Service label.
Because XMPP is one such protocol, the IANA registers the "_xmpp"
protocol label in the appropriate registry, as follows:
Protocol label: _xmpp
Specification: XXXX
Description: Presence protocol label for the Extensible Messaging
and Presence Protocol (XMPP) as defined by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmpp@ietf.org>
13. Conformance Requirements
This section describes a protocol feature set that summarizes the
conformance requirements of this specification. This feature set is
appropriate for use in software certification, interoperability
testing, and implementation reports. For each feature, this section
provides the following information:
o A human-readable name
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o An informational description
o A reference to the particular section of this document that
normatively defines the feature
o Whether the feature applies to the Client role, the Server role,
or both (where "N/A" signifies that the feature is not applicable
to the specified role)
o Whether the feature MUST or SHOULD be implemented, where the
capitalized terms are to be understood as described in [KEYWORDS]
The feature set specified here attempts to adhere to the concepts and
formats proposed by Larry Masinter within the IETF's NEWTRK Working
Group in 2005, as captured in [INTEROP]. Although this feature set
is more detailed than called for by [REPORTS], it provides a suitable
basis for the generation of implementation reports to be submitted in
support of advancing this specification from Proposed Standard to
Draft Standard in accordance with [PROCESS].
Feature: message-body
Description: Support the <body/> child element of the <message/>
stanza.
Section: Section 5.2.3
Roles: Client MUST, Server N/A.
Feature: message-subject
Description: Support the <subject/> child element of the <message/>
stanza.
Section: Section 5.2.4
Roles: Client SHOULD, Server N/A.
Feature: message-thread
Description: Support the <thread/> child element of the <message/>
stanza.
Section: Section 5.2.5
Roles: Client SHOULD, Server N/A.
Feature: message-type
Description: Differentiate between messages of type "normal",
"chat", "groupchat", "headline", and "error".
Section: Section 5.2.2
Roles: Client MUST, Server MUST.
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Feature: presence-notype
Description: Treat a presence stanza with no 'type' attribute as
indicating availability.
Section: Section 4.7.1
Roles: Client MUST, Server MUST.
Feature: presence-probe
Description: Send and receive presence stanzas with a 'type'
attribute of "probe" for the discovery of presence information.
Section: Section 4.7.1
Roles: Client N/A, Server MUST.
Feature: presence-sub-approval
Description: Treat an outbound presence stanza of type "subscribed"
as the act of approving a presence subscription request previously
received from another entity, and treat an inbound presence stanza
of type "subscribed" as a subscription approval from another
entity.
Section: Section 3.1
Roles: Client MUST, Server MUST.
Feature: presence-sub-cancel
Description: Treat an outbound presence stanza of type
"unsubscribed" as the act of denying a subscription request
received from another entity or cancelling a subscription approval
previously granted to another entity, and treat an inbound
presence stanza of type "unsubscribed" as an subscription denial
or cancellation from another entity.
Section: Section 3.2
Roles: Client MUST, Server MUST.
Feature: presence-sub-request
Description: Treat an outbound presence stanza of type "subscribe"
as the act of requesting a subscription to the presence
information of another entity, and treat an inbound presence
stanza of type "subscribe" as a presence subscription request from
another entity.
Section: Section 3.1
Roles: Client MUST, Server MUST.
Feature: presence-sub-unsubscribe
Description: Treat an outbound presence stanza of type "unsubscribe"
as the act of unsubscribing from another entity, and treat an
inbound presence stanza of type "unsubscribe" as an unsubscribe
notification from another entity.
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Section: Section 3.3
Roles: Client MUST, Server MUST.
Feature: presence-unavailable
Description: Treat a presence stanza with a 'type' attribute of
"unavailable" as indicating lack of availability.
Section: Section 4.7.1
Roles: Client MUST, Server MUST.
Feature: roster-get
Description: Treat an IQ stanza of type "get" containing an empty
<query/> element qualified by the 'jabber:iq:roster' namespace as
a request to retrieve the roster information associated with an
account on a server.
Section: Section 2.1.3
Roles: Client MUST, Server MUST.
Feature: roster-set
Description: Treat an IQ stanza of type "set" containing a <query/>
element qualified by the 'jabber:iq:roster' namespace as a request
to add or update the item contained in the <query/> element.
Section: Section 2.1.5
Roles: Client MUST, Server MUST.
Feature: roster-push
Description: Send a roster push to each interested resource whenever
the server-side representation of the roster information
materially changes, or handle such a push when received from the
server.
Section: Section 2.1.6
Roles: Client MUST, Server MUST.
Feature: roster-version
Description: Treat the 'ver' attribute of the <query/> element
qualified by the 'jabber:iq:roster' namespace as an identifier of
the particular version of roster information being sent or
received.
Section: Section 2.1.1
Roles: Client SHOULD, Server MUST.
14. References
14.1. Normative References
[DELAY] Saint-Andre, P., "Delayed Delivery", XSF XEP 0203,
September 2009.
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[IMP-SRV] Peterson, J., "Address Resolution for Instant Messaging
and Presence", RFC 3861, August 2004.
[KEYWORDS]
Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[SRV] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[XML] Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J.,
and T. Bray, "Extensible Markup Language (XML) 1.0 (Fifth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20081126, November 2008,
<http://www.w3.org/TR/2008/REC-xml-20081126>.
[XML-NAMES]
Bray, T., Hollander, D., and A. Layman, "Namespaces in
XML", W3C REC-xml-names, January 1999,
<http://www.w3.org/TR/REC-xml-names>.
[XMPP-CORE]
Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", draft-ietf-xmpp-3920bis-10 (work
in progress), July 2010.
[XMPP-URI]
Saint-Andre, P., "Internationalized Resource Identifiers
(IRIs) and Uniform Resource Identifiers (URIs) for the
Extensible Messaging and Presence Protocol (XMPP)",
RFC 5122, February 2008.
14.2. Informative 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., and J. Vincent, "Instant Messaging
/ Presence Protocol Requirements", RFC 2779,
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February 2000.
[INTEROP] Masinter, L., "Formalizing IETF Interoperability
Reporting", draft-ietf-newtrk-interop-reports-00 (work in
progress), October 2005.
[IRC] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
April 2000.
[IRI] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[PROCESS] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.
[REPORTS] Dusseault, L. and R. Sparks, "Guidance on Interoperation
and Implementation Reports for Advancement to Draft
Standard", BCP 9, RFC 5657, September 2009.
[RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, October 2004.
[RFC3921] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
RFC 3921, October 2004.
[SASL] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.
[TLS] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[UUID] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
July 2005.
[XEP-0016]
Millard, P. and P. Saint-Andre, "Privacy Lists", XSF
XEP 0016, February 2007.
[XEP-0045]
Saint-Andre, P., "Multi-User Chat", XSF XEP 0045,
July 2008.
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[XEP-0054]
Saint-Andre, P., "vcard-temp", XSF XEP 0054, July 2008.
[XEP-0071]
Saint-Andre, P., "XHTML-IM", XSF XEP 0071, September 2008.
[XEP-0115]
Hildebrand, J., Saint-Andre, P., and R. Troncon, "Entity
Capabilities", XSF XEP 0115, February 2008.
[XEP-0147]
Saint-Andre, P., "XMPP URI Scheme Query Components", XSF
XEP 0147, September 2006.
[XEP-0160]
Saint-Andre, P., "Best Practices for Handling Offline
Messages", XSF XEP 0160, January 2006.
[XEP-0191]
Saint-Andre, P., "Simple Communications Blocking", XSF
XEP 0191, February 2007.
[XEP-0201]
Saint-Andre, P., Paterson, I., and K. Smith, "Best
Practices for Message Threads", XSF XEP 0201, May 2010.
[XEP-0237]
Saint-Andre, P. and D. Cridland, "Roster Versioning", XSF
XEP 0237, March 2010.
[XML-SCHEMA]
Thompson, H., Maloney, M., Mendelsohn, N., and D. Beech,
"XML Schema Part 1: Structures Second Edition", World Wide
Web Consortium Recommendation REC-xmlschema-1-20041028,
October 2004,
<http://www.w3.org/TR/2004/REC-xmlschema-1-20041028>.
[XMPP-ADDR]
Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Address Format",
draft-ietf-xmpp-address-01 (work in progress), July 2010.
[VCARD] Dawson, F. and T. Howes, "vCard MIME Directory Profile",
RFC 2426, September 1998.
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Appendix A. Subscription States
This section provides detailed information about subscription states
and server processing of subscription-related presence stanzas (i.e.,
presence stanzas of type "subscribe", "subscribed", "unsubscribe",
and "unsubscribed").
A.1. Defined States
There are four primary subscription states (these states are
described from the perspective of the user, not the contact):
None: the user does not have a subscription to the contact's
presence, and the contact does not have a subscription to the
user's presence
To: the user has a subscription to the contact's presence, but the
contact does not have a subscription to the user's presence
From: the contact has a subscription to the user's presence, but the
user does not have a subscription to the contact's presence
Both: both the user and the contact have subscriptions to each
other's presence (i.e., the union of 'from' and 'to')
These states are supplemented by various pending sub-states to yield
nine possible subscription states:
1. "None" = contact and user are not subscribed to each other, and
neither has requested a subscription from the other; this is
reflected in the user's roster by subscription='none'
2. "None + Pending Out" = contact and user are not subscribed to
each other, and user has sent contact a subscription request but
contact has not replied yet; this is reflected in the user's
roster by subscription='none' and ask='subscribe'
3. "None + Pending In" = contact and user are not subscribed to each
other, and contact has sent user a subscription request but user
has not replied yet; this state might or might not be reflected
in the user's roster, as follows: if the user has created a
roster item for the contact then the server MUST maintain that
roster item and also note the existence of the inbound presence
subscription request, whereas if the user has not created a
roster item for the contact then the user's server MUST note the
existence of the inbound presence subscription request but MUST
NOT create a roster item for the contact (instead, the server
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MUST wait until the user has approved the subscription request
before adding the contact to the user's roster).
4. "None + Pending Out+In" = contact and user are not subscribed to
each other, contact has sent user a subscription request but user
has not replied yet, and user has sent contact a subscription
request but contact has not replied yet; this is reflected in the
user's roster by subscription='none' and ask='subscribe'
5. "To" = user is subscribed to contact (one-way); this is reflected
in the user's roster by subscription='to'
6. "To + Pending In" = user is subscribed to contact, and contact
has sent user a subscription request but user has not replied
yet; this is reflected in the user's roster by subscription='to'
7. "From" = contact is subscribed to user (one-way); this is
reflected in the user's roster by subscription='from'
8. "From + Pending Out" = contact is subscribed to user, and user
has sent contact a subscription request but contact has not
replied yet; this is reflected in the user's roster by
subscription='from' and ask='subscribe'
9. "Both" = user and contact are subscribed to each other (two-way);
this is reflected in the user's roster by subscription='both'
A.2. Server Processing of Outbound Presence Subscription Stanzas
Outbound presence subscription stanzas enable the user to manage his
or her subscription to the contact's presence (via the "subscribe"
and "unsubscribe" types), and to manage the contact's access to the
user's presence (via the "subscribed" and "unsubscribed" types).
The following rules apply to outbound routing of the stanza as well
as changes to the user's roster. (These rules are described from the
perspective of the user, not the contact. In addition, "S.N." stands
for SHOULD NOT.)
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A.2.1. Subscribe
Table 2: Processing of outbound "subscribe" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+------------------------------------------------------------------+
| "None" | MUST [1] | "None + Pending Out" |
| "None + Pending Out" | MUST | no state change |
| "None + Pending In" | MUST [1] | "None + Pending Out+In" |
| "None + Pending Out+In" | MUST | no state change |
| "To" | MUST | no state change |
| "To + Pending In" | MUST | no state change |
| "From" | MUST [1] | "From + Pending Out" |
| "From + Pending Out" | MUST | no state change |
| "Both" | MUST | no state change |
+------------------------------------------------------------------+
[1] A state change to "pending out" includes setting the 'ask'
flag to a value of "subscribe" in the user's roster.
A.2.2. Unsubscribe
Table 3: Processing of outbound "unsubscribe" stanzas
+-----------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+-----------------------------------------------------------------+
| "None" | MUST | no state change |
| "None + Pending Out" | MUST | "None" |
| "None + Pending In" | MUST | no state change |
| "None + Pending Out+In" | MUST | "None + Pending In" |
| "To" | MUST | "None" |
| "To + Pending In" | MUST | "None + Pending In" |
| "From" | MUST | no state change |
| "From + Pending Out" | MUST | "From" |
| "Both" | MUST | "From" |
+-----------------------------------------------------------------+
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A.2.3. Subscribed
Table 4: Processing of outbound "subscribed" stanzas
+-----------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+-----------------------------------------------------------------+
| "None" | S.N. | no state change [1] |
| "None + Pending Out" | S.N. | no state change |
| "None + Pending In" | MUST | "From" |
| "None + Pending Out+In" | MUST | "From + Pending Out" |
| "To" | S.N. | no state change |
| "To + Pending In" | MUST | "Both" |
| "From" | S.N. | no state change |
| "From + Pending Out" | S.N. | no state change |
| "Both" | S.N. | no state change |
+-----------------------------------------------------------------+
[1] A server MAY note the fact that the user wishes to allow the
contact to be subscribed to the user's presence and automatically
approve any subscription request received from the contact; if it
does so, upon the receiving presence stanza of type "subscribed"
from the user's client it MUST add a roster item for the contact
to the user's roster and set the 'ask' flag to a value of
"subscribed". However, the user's server still SHOULD NOT route
the presence stanza of type "subscribed" to the contact. This
optional functionality applies only if the contact is not already
in the user's roster or if the contact is in the user's roster
with a state of "None" (not including a state of "None + Pending
Out").
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A.2.4. Unsubscribed
Table 5: Processing of outbound "unsubscribed" stanzas
+-----------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+-----------------------------------------------------------------+
| "None" | S.N. | no state change |
| "None + Pending Out" | S.N. | no state change |
| "None + Pending In" | MUST | "None" |
| "None + Pending Out+In" | MUST | "None + Pending Out" |
| "To" | S.N. | no state change |
| "To + Pending In" | MUST | "To" |
| "From" | MUST | "None" |
| "From + Pending Out" | MUST | "None + Pending Out" |
| "Both" | MUST | "To" |
+-----------------------------------------------------------------+
A.3. Server Processing of Inbound Presence Subscription Stanzas
Inbound presence subscription stanzas request a subscription-related
action from the user (via the "subscribe" type), inform the user of
subscription-related actions taken by the contact (via the
"unsubscribe" type), or enable the user to manage the contact's
access to the user's presence information (via the "subscribed" and
"unsubscribed" types).
The following rules apply to delivery of the inbound stanza as well
as changes to the user's roster. (These rules for server processing
of inbound presence subscription stanzas are described from the
perspective of the user, not the contact. In addition, "S.N." stands
for SHOULD NOT.)
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A.3.1. Subscribe
Table 6: Processing of inbound "subscribe" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | MUST [1] | "None + Pending In" |
| "None + Pending Out" | MUST | "None + Pending Out+In" |
| "None + Pending In" | S.N. | no state change |
| "None + Pending Out+In" | S.N. | no state change |
| "To" | MUST | "To + Pending In" |
| "To + Pending In" | S.N. | no state change |
| "From" | S.N. [2] | no state change |
| "From + Pending Out" | S.N. [2] | no state change |
| "Both" | S.N. [2] | no state change |
+------------------------------------------------------------------+
[1] If the user previously sent presence of type "subscribed" as
described under Appendix A.2.3, then the server MAY auto-reply
with "subscribed" and change the state to "From" rather than "None
+ Pending In".
[2] Server SHOULD auto-reply with "subscribed".
A.3.2. Unsubscribe
When the user's server receives a presence stanza of type
"unsubscribe" for the user from the contact, if the stanza results in
a subscription state change from the user's perspective then the
user's server MUST change the state, MUST deliver the presence stanza
from the contact to the user, and SHOULD auto-reply by sending a
presence stanza of type "unsubscribed" to the contact on behalf of
the user. Otherwise the user's server MUST NOT change the state and
(because there is no state change) SHOULD NOT deliver the stanza.
These rules are summarized in the following table.
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Table 7: Processing of inbound "unsubscribe" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | S.N. | no state change |
| "None + Pending Out" | S.N. | no state change |
| "None + Pending In" | MUST [1] | "None" |
| "None + Pending Out+In" | MUST [1] | "None + Pending Out" |
| "To" | S.N. | no state change |
| "To + Pending In" | MUST [1] | "To" |
| "From" | MUST [1] | "None" |
| "From + Pending Out" | MUST [1] | "None + Pending Out |
| "Both" | MUST [1] | "To" |
+------------------------------------------------------------------+
[1] Server SHOULD auto-reply with "unsubscribed".
A.3.3. Subscribed
When the user's server receives a presence stanza of type
"subscribed" for the user from the contact, if there is no pending
outbound request for access to the contact's presence information,
then it MUST NOT change the subscription state and (because there is
no state change) SHOULD NOT deliver the stanza to the user. If there
is a pending outbound request for access to the contact's presence
information and the inbound presence stanza of type "subscribed"
results in a subscription state change, then the user's server MUST
change the subscription state and MUST deliver the stanza to the
user. If the user already is subscribed to the contact's presence
information, the inbound presence stanza of type "subscribed" does
not result in a subscription state change; therefore the user's
server MUST NOT change the subscription state and (because there is
no state change) SHOULD NOT deliver the stanza to the user. These
rules are summarized in the following table.
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Table 8: Processing of inbound "subscribed" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | S.N. | no state change |
| "None + Pending Out" | MUST | "To" |
| "None + Pending In" | S.N. | no state change |
| "None + Pending Out+In" | MUST | "To + Pending In" |
| "To" | S.N. | no state change |
| "To + Pending In" | S.N. | no state change |
| "From" | S.N. | no state change |
| "From + Pending Out" | MUST | "Both" |
| "Both" | S.N. | no state change |
+------------------------------------------------------------------+
A.3.4. Unsubscribed
When the user's server receives a presence stanza of type
"unsubscribed" for the user from the contact, if there is a pending
outbound request for access to the contact's presence information or
if the user currently is subscribed to the contact's presence
information, then the user's server MUST change the subscription
state and MUST deliver the stanza to the user. Otherwise, the user's
server MUST NOT change the subscription state and (because there is
no state change) SHOULD NOT deliver the stanza. These rules are
summarized in the following table.
Table 9: Processing of inbound "unsubscribed" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | S.N. | no state change |
| "None + Pending Out" | MUST | "None" |
| "None + Pending In" | S.N. | no state change |
| "None + Pending Out+In" | MUST | "None + Pending In" |
| "To" | MUST | "None" |
| "To + Pending In" | MUST | "None + Pending In" |
| "From" | S.N. | no state change |
| "From + Pending Out" | MUST | "From" |
| "Both" | MUST | "From" |
+------------------------------------------------------------------+
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Appendix B. Blocking Communication
Sections 2.3.5 and 5.4.10 of [IMP-REQS] require that a compliant
instant messaging and presence technology needs to enable a user to
block communications from selected users. Protocols for doing so are
specified in [XEP-0016] and [XEP-0191].
Appendix C. vCards
Sections 3.1.3 and 4.1.4 of [IMP-REQS] require that it be possible to
retrieve out-of-band contact information for other users (e.g.,
telephone number or email address). An XML representation of the
vCard specification defined in RFC 2426 [VCARD] is in common use
within the XMPP community to provide such information but is out of
scope for this specification (documentation of this protocol is
contained in [XEP-0054]).
Appendix D. XML Schemas
Because validation of XML streams and stanzas is optional, the
following XML schemas are provided for descriptive purposes only.
These schemas are not normative.
The following schemas formally define various XML namespaces used in
the core XMPP protocols, in conformance with [XML-SCHEMA]. For
schemas defining namespaces for XML streams and other core aspects of
XMPP, refer to [XMPP-CORE].
D.1. jabber:client
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='jabber:client'
xmlns='jabber:client'
elementFormDefault='qualified'>
<xs:import
namespace='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<xs:element name='message'>
<xs:complexType>
<xs:sequence>
<xs:choice minOccurs='0' maxOccurs='unbounded'>
<xs:element ref='subject'/>
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<xs:element ref='body'/>
<xs:element ref='thread'/>
</xs:choice>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error'
minOccurs='0'/>
</xs:sequence>
<xs:attribute name='from'
type='xs:string'
use='optional'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute name='to'
type='xs:string'
use='optional'/>
<xs:attribute name='type'
use='optional'
default='normal'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='chat'/>
<xs:enumeration value='error'/>
<xs:enumeration value='groupchat'/>
<xs:enumeration value='headline'/>
<xs:enumeration value='normal'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='body'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='subject'>
<xs:complexType>
<xs:simpleContent>
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<xs:extension base='xs:string'>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='thread'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:NMTOKEN'>
<xs:attribute name='parent'
type='xs:NMTOKEN'
use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='presence'>
<xs:complexType>
<xs:sequence>
<xs:choice minOccurs='0' maxOccurs='unbounded'>
<xs:element ref='show'/>
<xs:element ref='status'/>
<xs:element ref='priority'/>
</xs:choice>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error'
minOccurs='0'/>
</xs:sequence>
<xs:attribute name='from'
type='xs:string'
use='optional'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute name='to'
type='xs:string'
use='optional'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='error'/>
<xs:enumeration value='probe'/>
<xs:enumeration value='subscribe'/>
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<xs:enumeration value='subscribed'/>
<xs:enumeration value='unavailable'/>
<xs:enumeration value='unsubscribe'/>
<xs:enumeration value='unsubscribed'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='show'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='away'/>
<xs:enumeration value='chat'/>
<xs:enumeration value='dnd'/>
<xs:enumeration value='xa'/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name='status'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='string1024'>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:simpleType name='string1024'>
<xs:restriction base='xs:string'>
<xs:minLength value='1'/>
<xs:maxLength value='1024'/>
</xs:restriction>
</xs:simpleType>
<xs:element name='priority' type='xs:byte'/>
<xs:element name='iq'>
<xs:complexType>
<xs:sequence>
<xs:any namespace='##other'
minOccurs='0'/>
<xs:element ref='error'
minOccurs='0'/>
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</xs:sequence>
<xs:attribute name='from'
type='xs:string'
use='optional'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='required'/>
<xs:attribute name='to'
type='xs:string'
use='optional'/>
<xs:attribute name='type' use='required'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='error'/>
<xs:enumeration value='get'/>
<xs:enumeration value='result'/>
<xs:enumeration value='set'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='error'>
<xs:complexType>
<xs:sequence xmlns:err='urn:ietf:params:xml:ns:xmpp-stanzas'>
<xs:group ref='err:stanzaErrorGroup'/>
<xs:element ref='err:text'
minOccurs='0'/>
</xs:sequence>
<xs:attribute name='by'
type='xs:string'
use='optional'>
<xs:attribute name='type' use='required'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='auth'/>
<xs:enumeration value='cancel'/>
<xs:enumeration value='continue'/>
<xs:enumeration value='modify'/>
<xs:enumeration value='wait'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
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</xs:schema>
D.2. jabber:server
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='jabber:server'
xmlns='jabber:server'
elementFormDefault='qualified'>
<xs:import
namespace='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<xs:element name='message'>
<xs:complexType>
<xs:sequence>
<xs:choice minOccurs='0' maxOccurs='unbounded'>
<xs:element ref='subject'/>
<xs:element ref='body'/>
<xs:element ref='thread'/>
</xs:choice>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error'
minOccurs='0'/>
</xs:sequence>
<xs:attribute name='from'
type='xs:string'
use='required'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute name='to'
type='xs:string'
use='required'/>
<xs:attribute name='type'
use='optional'
default='normal'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='chat'/>
<xs:enumeration value='error'/>
<xs:enumeration value='groupchat'/>
<xs:enumeration value='headline'/>
<xs:enumeration value='normal'/>
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</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='body'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='subject'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='thread'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:NMTOKEN'>
<xs:attribute name='parent'
type='xs:NMTOKEN'
use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='subject'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:NMTOKEN'>
<xs:attribute name='parent'
type='xs:NMTOKEN'
use='optional'/>
</xs:extension>
</xs:simpleContent>
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</xs:complexType>
</xs:element>
<xs:element name='presence'>
<xs:complexType>
<xs:sequence>
<xs:choice minOccurs='0' maxOccurs='unbounded'>
<xs:element ref='show'/>
<xs:element ref='status'/>
<xs:element ref='priority'/>
</xs:choice>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error'
minOccurs='0'/>
</xs:sequence>
<xs:attribute name='from'
type='xs:string'
use='required'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute name='to'
type='xs:string'
use='required'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='error'/>
<xs:enumeration value='probe'/>
<xs:enumeration value='subscribe'/>
<xs:enumeration value='subscribed'/>
<xs:enumeration value='unavailable'/>
<xs:enumeration value='unsubscribe'/>
<xs:enumeration value='unsubscribed'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='show'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='away'/>
<xs:enumeration value='chat'/>
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<xs:enumeration value='dnd'/>
<xs:enumeration value='xa'/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name='status'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='string1024'>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:simpleType name='string1024'>
<xs:restriction base='xs:string'>
<xs:minLength value='1'/>
<xs:maxLength value='1024'/>
</xs:restriction>
</xs:simpleType>
<xs:element name='priority' type='xs:byte' default='0'/>
<xs:element name='iq'>
<xs:complexType>
<xs:sequence>
<xs:any namespace='##other'
minOccurs='0'/>
<xs:element ref='error'
minOccurs='0'/>
</xs:sequence>
<xs:attribute name='from'
type='xs:string'
use='required'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='required'/>
<xs:attribute name='to'
type='xs:string'
use='required'/>
<xs:attribute name='type' use='required'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='error'/>
<xs:enumeration value='get'/>
<xs:enumeration value='result'/>
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<xs:enumeration value='set'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='error'>
<xs:complexType>
<xs:sequence xmlns:err='urn:ietf:params:xml:ns:xmpp-stanzas'>
<xs:group ref='err:stanzaErrorGroup'/>
<xs:element ref='err:text'
minOccurs='0'/>
</xs:sequence>
<xs:attribute name='by'
type='xs:string'
use='optional'>
<xs:attribute name='type' use='required'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='auth'/>
<xs:enumeration value='cancel'/>
<xs:enumeration value='continue'/>
<xs:enumeration value='modify'/>
<xs:enumeration value='wait'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
</xs:schema>
D.3. jabber:iq:roster
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='jabber:iq:roster'
xmlns='jabber:iq:roster'
elementFormDefault='qualified'>
<xs:element name='query'>
<xs:complexType>
<xs:sequence>
<xs:element ref='item'
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minOccurs='0'
maxOccurs='unbounded'/>
</xs:sequence>
<xs:attribute name='ver'
type='xs:string'
use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='item'>
<xs:complexType>
<xs:sequence>
<xs:element ref='group'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:sequence>
<xs:attribute name='ask' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='subscribe'/>
<xs:enumeration value='subscribed'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name='jid'
type='xs:string'
use='required'/>
<xs:attribute name='name'
type='xs:string'
use='optional'/>
<xs:attribute name='subscription'
use='optional'
default='none'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='both'/>
<xs:enumeration value='from'/>
<xs:enumeration value='none'/>
<xs:enumeration value='remove'/>
<xs:enumeration value='to'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name='group' type='xs:string'/>
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</xs:schema>
Appendix E. Differences From RFC 3921
Based on consensus derived from implementation and deployment
experience as well as formal interoperability testing, the following
substantive modifications were made from [RFC3921].
o The protocol for session establishment was determined to be
unnecessary and therefore the content previously defined in
Section 3 of RFC 3921 was removed. However, for the sake of
backward-compatibility server implementations are encouraged to
advertise support for the feature, even though session
establishment is a "no-op".
o In order to more seamlessly repair lack of synchronization in
subscription states between rosters located at different servers,
clarified and modified error handling related to presence
subscription requests, presence probes and presence notifications.
o Explicitly specified that a server is allowed to deliver a message
stanza of type "normal" or "chat" to all resources.
o Added optional versioning of roster information to save bandwidth
in cases where the roster has not changed (or has changed very
little) between sessions; the relevant protocol interactions were
originally described in [XEP-0237].
o Added optional server support for pre-approved presence
subscriptions via presence stanzas of type "subscribed" and the
optional "subscribed" value for the 'ask' flag.
o Added optional 'parent' attribute to <thread/> element
o Moved the protocol for communications blocking (specified in
Section 10 of RFC 3921) back to [XEP-0016], from which it was
originally taken.
o Recommended returning presence unavailable in response to probes.
o Clarified handling of presence probes sent to full JIDs.
o Explicitly specified that the default value for the presence
<priority/> element is zero.
In addition, numerous changes of an editorial nature were made in
order to more fully specify and clearly explain the protocols.
Appendix F. Copying Conditions
Regarding this entire document or any portion of it, the author makes
no guarantees and is not responsible for any damage resulting from
its use. The author grants irrevocable permission to anyone to use,
modify, and distribute it in any way that does not diminish the
rights of anyone else to use, modify, and distribute it, provided
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that redistributed derivative works do not contain misleading author
or version information. Derivative works need not be licensed under
similar terms.
Author's Address
Peter Saint-Andre
Cisco Systems, Inc.
1899 Wyknoop Street, Suite 600
Denver, CO 80202
USA
Phone: +1-303-308-3282
Email: psaintan@cisco.com
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