Internet DRAFT - draft-saintandre-rfc3921bis
draft-saintandre-rfc3921bis
Network Working Group P. Saint-Andre, Ed.
Internet-Draft XMPP Standards Foundation
Obsoletes: 3921 (if approved) June 6, 2008
Intended status: Standards Track
Expires: December 8, 2008
Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and
Presence
draft-saintandre-rfc3921bis-05
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Abstract
This document describes 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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Requirements . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Functional Summary . . . . . . . . . . . . . . . . . . . . 6
1.4. Conventions . . . . . . . . . . . . . . . . . . . . . . . 7
1.5. Discussion Venue . . . . . . . . . . . . . . . . . . . . . 7
2. Managing the Roster . . . . . . . . . . . . . . . . . . . . . 8
2.1. Syntax and Semantics . . . . . . . . . . . . . . . . . . . 8
2.1.1. Items . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.2. Roster Get . . . . . . . . . . . . . . . . . . . . . . 8
2.1.3. Roster Set . . . . . . . . . . . . . . . . . . . . . . 9
2.1.4. Roster Push . . . . . . . . . . . . . . . . . . . . . 9
2.1.5. Roster Result . . . . . . . . . . . . . . . . . . . . 10
2.1.6. Subscription Attribute . . . . . . . . . . . . . . . . 10
2.2. Retrieving the Roster on Login . . . . . . . . . . . . . . 11
2.3. Adding a Roster Item . . . . . . . . . . . . . . . . . . . 12
2.3.1. Success Case . . . . . . . . . . . . . . . . . . . . . 12
2.3.2. Error Cases . . . . . . . . . . . . . . . . . . . . . 14
2.4. Updating a Roster Item . . . . . . . . . . . . . . . . . . 17
2.4.1. Success Case . . . . . . . . . . . . . . . . . . . . . 17
2.4.2. Error Cases . . . . . . . . . . . . . . . . . . . . . 19
2.5. Deleting a Roster Item . . . . . . . . . . . . . . . . . . 19
2.5.1. Success Case . . . . . . . . . . . . . . . . . . . . . 19
2.5.2. Error Cases . . . . . . . . . . . . . . . . . . . . . 20
3. Managing Presence Subscriptions . . . . . . . . . . . . . . . 20
3.1. Requesting a Subscription . . . . . . . . . . . . . . . . 21
3.1.1. Client Generation of Outbound Subscription Request . . 21
3.1.2. Server Processing of Outbound Subscription Request . . 22
3.1.3. Server Processing of Inbound Subscription Request . . 23
3.1.4. Client Processing of Inbound Subscription Request . . 24
3.1.5. Server Processing of Outbound Subscription Approval . 25
3.1.6. Server Processing of Inbound Subscription Approval . . 26
3.2. Cancelling a Subscription . . . . . . . . . . . . . . . . 27
3.2.1. Client Generation of Subscription Cancellation . . . . 27
3.2.2. Server Processing of Outbound Subscription
Cancellation . . . . . . . . . . . . . . . . . . . . . 27
3.2.3. Server Processing of Inbound Subscription
Cancellation . . . . . . . . . . . . . . . . . . . . . 28
3.3. Unsubscribing . . . . . . . . . . . . . . . . . . . . . . 29
3.3.1. Client Generation of Unsubscribe . . . . . . . . . . . 29
3.3.2. Server Processing of Outbound Unsubscribe . . . . . . 29
3.3.3. Server Processing of Inbound Unsubscribe . . . . . . . 30
4. Exchanging Presence Information . . . . . . . . . . . . . . . 31
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2. Initial Presence . . . . . . . . . . . . . . . . . . . . . 31
4.2.1. Client Generation of Initial Presence . . . . . . . . 31
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4.2.2. Server Processing of Outbound Presence . . . . . . . . 32
4.2.3. Server Processing of Inbound Presence . . . . . . . . 33
4.2.4. Client Processing of Inbound Presence . . . . . . . . 33
4.3. Presence Probes . . . . . . . . . . . . . . . . . . . . . 33
4.3.1. Server Generation of Outbound Presence Probe . . . . . 34
4.3.2. Server Processing of Inbound Presence Probe . . . . . 34
4.4. Subsequent Presence Broadcast . . . . . . . . . . . . . . 35
4.4.1. Client Generation of Presence Broadcast . . . . . . . 35
4.4.2. Server Processing of Outbound Presence . . . . . . . . 36
4.4.3. Server Processing of Inbound Presence . . . . . . . . 37
4.4.4. Client Processing of Inbound Presence . . . . . . . . 37
4.5. Unavailable Presence . . . . . . . . . . . . . . . . . . . 37
4.5.1. Client Generation of Unavailable Presence . . . . . . 37
4.5.2. Server Processing of Outbound Unavailable Presence . . 38
4.5.3. Server Processing of Inbound Unavailable Presence . . 39
4.5.4. Client Processing of Inbound Unavailable Presence . . 39
4.6. Directed Presence . . . . . . . . . . . . . . . . . . . . 40
4.6.1. Client Generation of Directed Presence . . . . . . . . 40
4.6.2. Server Processing of Outbound Directed Presence . . . 40
4.6.3. Server Processing of Inbound Directed Presence . . . . 41
4.6.4. Client Processing of Inbound Directed Presence . . . . 41
4.7. Presence Syntax . . . . . . . . . . . . . . . . . . . . . 41
4.7.1. Type Attribute . . . . . . . . . . . . . . . . . . . . 41
4.7.2. Child Elements . . . . . . . . . . . . . . . . . . . . 42
4.7.3. Show Element . . . . . . . . . . . . . . . . . . . . . 42
4.7.4. Status Element . . . . . . . . . . . . . . . . . . . . 43
4.7.5. Priority Element . . . . . . . . . . . . . . . . . . . 44
4.7.6. Extended Content . . . . . . . . . . . . . . . . . . . 44
5. Exchanging Messages . . . . . . . . . . . . . . . . . . . . . 45
5.1. Attributes . . . . . . . . . . . . . . . . . . . . . . . . 45
5.1.1. To Attribute . . . . . . . . . . . . . . . . . . . . . 45
5.1.2. Type Attribute . . . . . . . . . . . . . . . . . . . . 46
5.2. Child Elements . . . . . . . . . . . . . . . . . . . . . . 47
5.2.1. Body . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.2.2. Subject . . . . . . . . . . . . . . . . . . . . . . . 48
5.2.3. Thread . . . . . . . . . . . . . . . . . . . . . . . . 49
5.3. Extended Content . . . . . . . . . . . . . . . . . . . . . 50
5.4. One-to-One Chat Sessions . . . . . . . . . . . . . . . . . 51
6. Exchanging IQ Stanzas . . . . . . . . . . . . . . . . . . . . 51
7. A Sample Session . . . . . . . . . . . . . . . . . . . . . . . 52
8. Server Rules for Processing XML Stanzas . . . . . . . . . . . 59
8.1. No Such User . . . . . . . . . . . . . . . . . . . . . . . 59
8.2. Full JID at Local Domain . . . . . . . . . . . . . . . . . 59
8.2.1. Available Resource Matches . . . . . . . . . . . . . . 59
8.2.2. No Available Resource Matches . . . . . . . . . . . . 60
8.3. Bare JID at Local Domain . . . . . . . . . . . . . . . . . 60
8.3.1. Available Resources . . . . . . . . . . . . . . . . . 60
8.3.1.1. Message . . . . . . . . . . . . . . . . . . . . . 60
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8.3.1.2. Presence . . . . . . . . . . . . . . . . . . . . . 61
8.3.1.3. IQ . . . . . . . . . . . . . . . . . . . . . . . . 61
8.3.2. No Available Resources . . . . . . . . . . . . . . . . 61
8.3.2.1. Message . . . . . . . . . . . . . . . . . . . . . 62
8.3.2.2. Presence . . . . . . . . . . . . . . . . . . . . . 62
8.3.2.3. IQ . . . . . . . . . . . . . . . . . . . . . . . . 62
8.4. Foreign Domain . . . . . . . . . . . . . . . . . . . . . . 63
9. IM and Presence Compliance Requirements . . . . . . . . . . . 64
9.1. Servers . . . . . . . . . . . . . . . . . . . . . . . . . 64
9.2. Clients . . . . . . . . . . . . . . . . . . . . . . . . . 64
10. Internationalization Considerations . . . . . . . . . . . . . 65
11. Security Considerations . . . . . . . . . . . . . . . . . . . 65
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 66
12.1. Instant Messaging SRV Protocol Label Registration . . . . 66
12.2. Presence SRV Protocol Label Registration . . . . . . . . . 66
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 67
13.1. Normative References . . . . . . . . . . . . . . . . . . . 67
13.2. Informative References . . . . . . . . . . . . . . . . . . 68
Appendix A. Subscription States . . . . . . . . . . . . . . . . . 69
A.1. Defined States . . . . . . . . . . . . . . . . . . . . . . 69
A.2. Server Processing of Outbound Presence Subscription
Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 70
A.2.1. Subscribe . . . . . . . . . . . . . . . . . . . . . . 71
A.2.2. Unsubscribe . . . . . . . . . . . . . . . . . . . . . 71
A.2.3. Subscribed . . . . . . . . . . . . . . . . . . . . . . 72
A.2.4. Unsubscribed . . . . . . . . . . . . . . . . . . . . . 72
A.3. Server Processing of Inbound Presence Subscription
Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 73
A.3.1. Subscribe . . . . . . . . . . . . . . . . . . . . . . 73
A.3.2. Unsubscribe . . . . . . . . . . . . . . . . . . . . . 73
A.3.3. Subscribed . . . . . . . . . . . . . . . . . . . . . . 74
A.3.4. Unsubscribed . . . . . . . . . . . . . . . . . . . . . 75
Appendix B. Blocking Communication . . . . . . . . . . . . . . . 76
Appendix C. vCards . . . . . . . . . . . . . . . . . . . . . . . 76
Appendix D. XML Schemas . . . . . . . . . . . . . . . . . . . . . 76
D.1. jabber:client . . . . . . . . . . . . . . . . . . . . . . 76
D.2. jabber:server . . . . . . . . . . . . . . . . . . . . . . 80
D.3. jabber:iq:roster . . . . . . . . . . . . . . . . . . . . . 85
Appendix E. Differences From RFC 3921 . . . . . . . . . . . . . . 86
Appendix F. Copying Conditions . . . . . . . . . . . . . . . . . 86
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 87
Intellectual Property and Copyright Statements . . . . . . . . . . 89
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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] for
streaming XML data in close to real time between any two (or more)
network-aware entities. XMPP is typically used to exchange messages,
share presence information, and engage in structured request-response
interactions. The core features of XMPP defined in [XMPP-CORE]
provide the building blocks for many types of near-real-time
applications, which may be layered on top of the core by sending
application-specific data qualified by particular XML namespaces
(refer to [XML-NAMES]). This document describes XMPP extensions that
provide the basic functionality expected of an instant messaging (IM)
and presence application as defined in [IMP-REQS].
This document obsoletes RFC 3921.
1.2. 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 each of one's contacts in
close to real time -- often relatively large numbers of such
messages in rapid succession, in the form of one-to-one chat
sessions as described under Section 5.4.
3. The catalyst for exchanging messages is PRESENCE -- i.e.,
information about the network availability of each of one's
contacts (thus knowing who is online and available for a one-to-
one chat session).
4. Presence information is provided only to contacts that a user has
authorized via a presence subscription.
Thus at a high level this document assumes that a user must 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
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document regarding the requirements addressed herein. 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 required by RFC 2779.
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, there is no
requirement that a service must 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/> error if a client attempt to send a <message/>
stanzas.)
1.3. Functional Summary
This non-normative section provides a developer-friendly, functional
summary of XMPP-based instant messaging and presence features; refer
to 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 must 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 XML
stream establishment, 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.
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 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
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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 communications. (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.)
4. Terminate the session when desired by sending unavailable
presence and closing the underlying XML stream. (See
Section 4.5.)
1.4. Conventions
This document inherits the terminology defined in [XMPP-CORE].
The following keywords are to be interpreted as described in [TERMS]:
"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
human persons and may be bots, devices, or other non-human
applications.
In examples, lines have been wrapped for improved readability,
"[...]" means elision, and the following prepended strings are used:
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
1.5. Discussion Venue
The editor welcomes discussion and comments related to the topics
presented in this document. The preferred forum is the
<standards@xmpp.org> mailing list, for which archives and
subscription information are available at
<<http://mail.jabber.org/mailman/listinfo/standards>>.
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2. Managing the Roster
In XMPP, one'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 may access roster information from any resource.
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. Items
The <query/> element MAY contain one or more <item/> children, each
describing a unique roster item or "contact".
The syntax of the <item/> is as follows:
1. The 'jid' attribute is REQUIRED; the value of this attribute is
Jabber Identifier (JID) that uniquely identifies the roster item.
2. The 'name' attribute is OPTIONAL; the value of this attribute
specifies the "handle" to be associated with the JID, as
determined by the user (not the contact). While the value of the
'name' attribute may have meaning to a human user, typically it
is opaque to the server (although it MAY be used by the server
for matching purposes within the context of various XMPP
extensions).
3. The 'subscription' attribute is OPTIONAL; see Section 2.1.6.
4. The 'ask' attribute is OPTIONAL and is used to specify certain
subscription sub-states; for details, see Section 3.1.2.
5. The <group/> element is OPTIONAL; the XML character data of this
element specifies a category into which the roster item should be
grouped by a client. The <item/> MAY contain more than one
<group/> element. The XML character data of the <group/> element
is typically opaque to the server but may have meaning to a human
user.
2.1.2. Roster Get
A ROSTER GET is an IQ stanza of type "get" sent from client to server
and containing a <query/> element qualified by the 'jabber:iq:roster'
namespace.
The <query/> element in a roster get MUST NOT contain any <item/>
child elements.
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C: <iq from='juliet@example.com/balcony'
type='get'
id='roster_get'>
<query xmlns='jabber:iq:roster'/>
</iq>
2.1.3. Roster Set
A ROSTER SET 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. A receiving server MUST ignore any value of the 'subscription'
attribute other than "remove" (see Section 2.1.6).
3. A receiving server MUST ignore any 'to' address specified on the
IQ stanza and MUST handle the IQ stanza as if it included no 'to'
attribute.
C: <iq from='juliet@example.com/balcony'
type='set'
id='roster_set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'/>
</query>
</iq>
2.1.4. Roster Push
A ROSTER PUSH 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 server) or it has a 'from'
attribute whose value matches the user's bare JID <user@domain>.
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S: <iq to='juliet@example.com/chamber'
type='set'
id='roster_push'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'/>
</query>
</iq>
2.1.5. Roster Result
A ROSTER RESULT 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 MAY contain more than one <item/>
element.
S: <iq to='juliet@example.com/chamber'
type='result'
id='roster_result'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'/>
<item jid='romeo@example.net'/>
</query>
</iq>
If there are no contacts in the roster, the <query/> element MUST be
empty.
S: <iq to='juliet@example.com/chamber'
type='result'
id='roster_result'>
<query xmlns='jabber:iq:roster'/>
</iq>
2.1.6. Subscription Attribute
The state of the presence subscription in relation to a roster item
is captured in the 'subscription' attribute of the <item/> element.
Allowable subscription-related values for this attribute are:
o "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
o "to" -- the user has a subscription to the contact's presence, but
the contact does not have a subscription to the user's presence
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o "from" -- the contact has a subscription to the user's presence,
but the user does not have a subscription to the contact's
presence
o "both" -- both the user and the contact have subscriptions to each
other's presence (also called a "mutual subscription")
In a roster result, a receiving client MUST ignore values of the
'subscription' attribute other than "none", "to", "from", or "both".
In a roster push, a receiving client MUST ignore values of the
'subscription' attribute other than "none", "to", "from", "both", or
"remove".
In a roster set, the value of the 'subscription' attribute MAY be
"remove", which indicates that the item is to be removed from the
roster; a receiving server MUST ignore all values of the
'subscription' attribute other than "remove".
2.2. Retrieving the Roster on Login
Upon authenticating with a server and binding a resource (thus
becoming a connected resource), a client SHOULD request the roster
before sending initial presence (however, because receiving the
roster may not be desirable for all resources, e.g., a connection
with limited bandwidth, the client's request for the roster is
recommended and not required). After a connected resource sends
initial presence (see Section 4.2), it is referred to as an available
resource. If a connected resource requests the roster but does not
send initial presence, the server MUST NOT send it presence
subscription requests and SHOULD NOT send it associated roster
pushes. If an available resource does not request the roster during
a session, the server SHOULD NOT send it presence subscription
requests and MUST NOT send it associated roster pushes. Therefore,
if a client wishes to engage in the full range of interactions
related to contact lists (rosters) and presence subscriptions, it
SHOULD both request the roster and send initial presence. For the
sake of brevity, the term INTERESTED RESOURCE is used herein to refer
to the concept of "an available resource that has requested the
roster".
A client requests the roster by sending a roster get over its stream
to the server.
C: <iq from='juliet@example.com/balcony' type='get' id='roster_1'>
<query xmlns='jabber:iq:roster'/>
</iq>
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S: <iq to='juliet@example.com/balcony' type='result' id='roster_1'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
name='Romeo'
subscription='both'>
<group>Friends</group>
</item>
<item jid='mercutio@example.org'
name='Mercutio'
subscription='from'/>
<item jid='nurse@example.com'
name='Nurse'
subscription='to'/>
<item jid='benvolio@example.org'
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).
2.3. Adding a Roster Item
2.3.1. Success Case
At any time, a client may add an item to the roster by sending a
roster set to the server.
Note: When the item added represents another IM user, the value of
the 'jid' 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.
C: <iq from='juliet@example.com/balcony' type='set' id='roster_2'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'>
<group>Servants</group>
</item>
</query>
</iq>
If the server can successfully process the roster set (i.e., if none
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of the error cases occurs), it MUST create the roster item in
persistent storage and send a roster push containing the new roster
item to all of the user's interested resources.
S: <iq to='juliet@example.com/balcony'
type='set'
id='a78b4q6ha463'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'
subscription='none'>
<group>Servants</group>
</item>
</query>
</iq>
S: <iq to='juliet@example.com/chamber'
type='set'
id='a78b4q6ha464'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'
subscription='none'>
<group>Servants</group>
</item>
</query>
</iq>
The server MUST also return an IQ stanza of type "result" to the
connected resource that sent the roster set.
S: <iq to='juliet@example.com/balcony' type='result' id='roster_2'/>
As required by the semantics of the IQ stanza as defined in
[XMPP-CORE], each resource that received the roster push MUST reply
with an IQ stanza of type "result" (or "error").
C: <iq from='juliet@example.com/balcony'
type='result'
id='a78b4q6ha463'/>
C: <iq from='juliet@example.com/chamber'
type='result'
id='a78b4q6ha464'/>
Note: There is no error case for client replies to roster pushes, and
if the server receives an IQ of type "error" in response to a roster
push it SHOULD ignore the error.
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2.3.2. Error Cases
If the server cannot successfully process the roster set, it MUST
return an error. The following error cases are defined (naturally,
other stanza errors may occur, e.g., <internal-server-error/>).
The server SHOULD return a <bad-request/> error to the client if the
roster set violates any of the following conditions:
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 (where duplicates are determined using
the Resourceprep profile of stringprep as defined in
[XMPP-CORE]).
The server SHOULD return a <not-acceptable/> error to the client if
the roster set violates any of the following conditions:
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.
3. The XML character data of the <group/> element is greater than a
server-configured limit.
Alternatively, 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 contains more than one item
C: <iq from='juliet@example.com/balcony' type='set' id='roster_3'>
<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 to='juliet@example.com/balcony' type='error' id='roster_3'>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
Error: Roster set contains item with oversized handle
C: <iq from='juliet@example.com/balcony' type='set' id='roster_4'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='[ ... some-very-long-handle ... ]'>
<group>Servants</group>
</item>
</query>
</iq>
S: <iq to='juliet@example.com/balcony' type='error' id='roster_4'>
<error type='modify'>
<not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
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Error: Roster set contains duplicate groups
C: <iq from='juliet@example.com/balcony' type='set' id='roster_5'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'>
<group>Servants</group>
<group>Servants</group>
</item>
</query>
</iq>
S: <iq to='juliet@example.com/balcony' type='error' id='roster_5'>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
Error: Roster set contains empty group
C: <iq from='juliet@example.com/balcony' type='set' id='roster_6'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'>
<group></group>
</item>
</query>
</iq>
S: <iq to='juliet@example.com/balcony' type='error' id='roster_6'>
<error type='modify'>
<not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
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Error: Roster set contains oversized group
C: <iq from='juliet@example.com/balcony' type='set' id='roster_7'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'>
<group>[ ... some-very-long-group-name ... ]</group>
</item>
</query>
</iq>
S: <iq to='juliet@example.com/balcony' type='error' id='roster_7'>
<error type='modify'>
<not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
The server MUST return a <not-allowed/> 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).
Error: Roster set contains sender's JID
C: <iq from='juliet@example.com/balcony' type='set' id='roster_8'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'/>
</query>
</iq>
S: <iq to='juliet@example.com/balcony' type='error' id='roster_8'>
<error type='cancel'>
<not-allowed xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
2.4. Updating a Roster Item
2.4.1. Success Case
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 shall be updated exactly as
provided in the roster set.
There are several reasons why a client might update a roster item:
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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 may want to add the item to
another group.
C: <iq from='juliet@example.com/chamber' type='set' id='update_1'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
name='Romeo'>
<group>Friends</group>
<group>Lovers</group>
</item>
</query>
</iq>
The user may then want to remove the item from the original group.
C: <iq from='juliet@example.com/chamber' type='set' id='update_2'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
name='Romeo'>
<group>Lovers</group>
</item>
</query>
</iq>
The user may then want to change the handle for the item.
C: <iq from='juliet@example.com/chamber' type='set' id='update_3'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
name='MyRomeo'>
<group>Lovers</group>
</item>
</query>
</iq>
The user may then want to remove the handle altogether (note:
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including an empty 'name' attribute is equivalent to including no
'name' attribute).
C: <iq from='juliet@example.com/chamber' type='set' id='update_4'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
name=''>
<group>Lovers</group>
</item>
</query>
</iq>
The user may then want to remove the item from all groups.
C: <iq from='juliet@example.com/chamber' type='set' id='update_5'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'/>
</query>
</iq>
As with adding a roster item, when updating a roster item 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.
2.4.2. Error Cases
The error cases described under Section 2.3.2 also apply to updating
a roster item.
2.5. Deleting a Roster Item
2.5.1. Success Case
At any time, a client may delete an item from his or her roster by
sending a roster set and specifying the value of the 'subscription'
attribute to be "remove".
C: <iq from='juliet@example.com/balcony' type='set' id='delete_1'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com' subscription='remove'/>
</query>
</iq>
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
interested resources (with the 'subscription' attribute set to a
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value of "remove"), and send an IQ result to the initiating resource;
for details, see Section 2.3.
The server MUST also generate a presence stanza of type "unsubscribe"
and a presence stanza of type "unsubscribed" from the user 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'/>
2.5.2. Error Cases
If the value of the 'jid' attribute specifies an item that is not in
the roster, the server MUST return an <item-not-found/> error.
Error: Roster item not found
C: <iq from='juliet@example.com/balcony'
type='set'
id='delete_2'>
<query xmlns='jabber:iq:roster'>
<item jid='[ ... non-existent-jid ... ]'
subscription='remove'/>
</query>
</iq>
S: <iq to='juliet@example.com/balcony' type='error' id='delete_2'>
<error type='modify'>
<item-not-found xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
3. Managing Presence Subscriptions
In order to protect the privacy of instant messaging users, presence
information is disclosed only to other entities that the user has
approved. When a user has agreed that another entity may 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 less strict sense to
refer to a potential contact or an item in a user's roster).
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In XMPP, a subscription lasts across 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").
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.
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>. This rule helps to prevent presence
leaks; for details, see the security considerations of [XMPP-CORE].
3.1. Requesting a Subscription
A SUBSCRIPTION REQUEST 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.
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
the potential contact's bare JID <contact@domain>.
UC: <presence to='juliet@example.com' type='subscribe'/>
A user's client SHOULD NOT send a presence subscription to a full JID
<contact@domain/resource>.
Typically the user's client prompts the user for information about
the potential contact ("handle" and desired roster group) and
generates a roster set with that information before sending the
subscription request, but that behavior is recommended rather than
required.
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3.1.2. Server Processing of Outbound Subscription Request
As mentioned, 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'
to='juliet@example.com'
type='subscribe'/>
Note: If the subscription request is directed to a full JID
<contact@domain/resource> instead of a bare JID <contact@domain>, the
user's server MAY treat it as if the request had been directed to the
contact's bare JID and modify the 'to' address accordingly. This
simplifies processing of presence subscriptions.
If the potential contact is hosted on the same server, the server
MUST adhere to the rules specified in the next section in processing
the subscription request and delivering it to the (local) contact.
If the potential contact is hosted on a different server, the user's
server then routes the stanza to that foreign domain in accordance
with core XMPP stanza processing rules.
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").
US: <iq to='romeo@example.net/foo'
type='set'
id='b89c5r7ib574'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='none'
ask='subscribe'/>
</query>
</iq>
US: <iq to='romeo@example.net/bar'
type='set'
id='b89c5r7ib575'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='none'
ask='subscribe'/>
</item>
</query>
</iq>
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Note: Because the server must send this roster push, a client MAY
simply wait for the roster push rather than proactively adding the
contact to the user's roster before sending the subscription request.
Note: If the contact does not approve or deny the subscription
request within some configurable amount of time, the user's server
SHOULD re-send 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
may have occurred in relation to the original subscription request.
3.1.3. Server Processing of Inbound Subscription Request
The contact's server MUST adhere to the following rules when
processing the inbound subscription request:
1. Above all, the contact's server MUST NOT automatically approve
subscription requests on the contact's behalf; instead, if a
subscription request requires approval then the contact's server
MUST deliver that request to the contact's interested resource(s)
for approval or denial by the contact.
2. If the contact does not exist, the contact's server MUST
automatically return a presence stanza of type "unsubscribed" to
the user.
CS: <presence from='juliet@example.com'
to='romeo@example.net'
type='unsubscribed'/>
3. If the contact exists and the user already has a subscription to
the user's presence, then the contact's server SHOULD 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.
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 MAY also auto-reply on
behalf of the contact.
4. If the contact exists, the user does not already have a
subscription to the contact's presence, and there is at least one
interested resource associated with the contact when the
subscription request is received by the contact's server, the
contact's server MUST broadcast that subscription request to all
interested resources in accordance with Server Rules for
Processing XML Stanzas (Section 8).
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5. If the contact exists, the user does not already have a
subscription to the contact's presence, and the contact has no
interested resources when the subscription request is received by
the contact's server, 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 interested resource. The
contact's server MUST continue to deliver the subscription
request whenever the contact creates an interested resource,
until the contact either approves or denies the request. (Note:
The contact's server MUST NOT deliver more than one subscription
request from any given user when the contact next has an
interested 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
interested resource; this helps to prevent "subscription request
spam".)
Note: If the subscription request is directed to a full JID
<contact@domain/resource> instead of a bare JID <contact@domain>, the
contact's server MAY treat it as if the request had been directed to
the contact's bare JID. This simplifies processing of presence
subscriptions.
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 in the following
sections for both the contact's server and the user's server.
CC: <presence to='romeo@example.net' type='subscribed'/>
Note: Before approving a presence subscription, the contact MAY
generate a roster set that includes a handle for the user and that
places the user in one or more roster groups; see Section 2.3.
A subscription request is denied by sending a presence stanza of type
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"unsubscribed", which is processed as described under Section 3.2 for
both the contact's server and the user's server.
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 route or deliver the stanza to
the user.
CS: <presence from='juliet@example.com'
to='romeo@example.net'
type='subscribed'/>
The contact's server then MUST send a roster push to all of the
contact's interested resources.
CS: <iq to='juliet@example.com/balcony'
type='set'
id='a78b4q6ha463'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='from'/>
</query>
</iq>
CS: <iq to='juliet@example.com/chamber'
type='set'
id='a78b4q6ha464'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='from'/>
</query>
</iq>
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'/>
From the perspective of the contact, there now exists a subscription
from the user.
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In order to subscribe to the user's presence, the contact would then
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 a
subscription='none' or subscription='from' and the 'ask' flag set to
"subscribe" (i.e., a subscription states of "None + Pending Out" or
"From + Pending Out"; see Appendix A). If the contact is not in the
user's roster with either of those states, the user's server MUST
silently ignore the presence stanza of type "subscribed" (i.e., it
MUST NOT route it to the user, modify the user's roster, or generate
a roster push to the user's interested resources).
If the foregoing check is successful, the user's server MUST 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".
US: <iq to='romeo@example.net/foo'
type='set'
id='b89c5r7ib576'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='to'/>
</query>
</iq>
US: <iq to='romeo@example.net/bar'
type='set'
id='b89c5r7ib577'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='to'/>
</item>
</query>
</iq>
From the perspective of the user, there now exists a subscription to
the contact's presence.
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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'/>
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
As mentioned, 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'/>
If the user is hosted on the same server, the server MUST adhere to
the rules specified in the next section when processing the
subscription cancellation.
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If the user is hosted on a different server, the contact's server
then routes the stanza to that foreign domain in accordance with core
XMPP stanza processing rules.
If the user is in the contact's roster, 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).
CS: <iq to='juliet@example.com/balcony'
type='set'
id='a78b4q6ha465'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='none'/>
</query>
</iq>
CS: <iq to='juliet@example.com/chamber'
type='set'
id='a78b4q6ha466'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='none'/>
</query>
</iq>
3.2.3. Server Processing of Inbound Subscription Cancellation
When the user's server receives the inbound subscription
cancellation, it MUST modify the subscription state and send a roster
push to the user's interested resources, where the subscription state
is now either "none" or "from" (see Appendix A).
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US: <iq to='romeo@example.net/foo'
type='set'
id='h37h3u1bv400'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='none'/>
</query>
</iq>
US: <iq to='romeo@example.net/bar'
type='set'
id='h37h3u1bv401'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='none'/>
</item>
</query>
</iq>
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'/>
3.3.2. Server Processing of Outbound Unsubscribe
As mentioned, the user's server MUST stamp the outbound unsubscribe
with the bare JID <user@domain> of the user.
US: <presence from='romeo@example.net'
to='juliet@example.com'
type='unsubscribe'/>
If the contact is hosted on the same server, the server MUST adhere
to the rules specified in the next section when processing the
unsubscribe.
If the contact is hosted on a different server, the user's server
then routes the stanza to that foreign domain in accordance with core
XMPP stanza processing rules.
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).
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US: <iq to='romeo@example.net/foo'
type='set'
id='h37h3u1bv402'>
<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>
3.3.3. Server Processing of Inbound Unsubscribe
When the contact's server receives the inbound unsubscribe, it MUST
modify the subscription state and send a roster push to the contact's
interested resources, where the subscription state is now either
"none" or "to" (see Appendix A).
CS: <iq to='juliet@example.com/balcony'
type='set'
id='a78b4q6ha467'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='none'/>
</query>
</iq>
CS: <iq to='juliet@example.com/chamber'
type='set'
id='a78b4q6ha468'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='none'/>
</query>
</iq>
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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, a principal's availability is signalled
when a client controlled by the principal generates a <presence/>
stanza with no 'type' attribute, and an entity's lack of availability
is signalled when a client generates a <presence/> stanza whose
'type' attribute has a value of "unavailable". In XMPP-based
applications that combine messaging and presence functionality, the
default type of communication for which presence signals availability
is messaging; however, XMPP-based applications are not required to
combine messaging and presence functionality, and 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).
XMPP presence typically follows a "publish-subscribe" or "observer"
pattern, wherein an entity sends presence to its server, and its
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 BROADCASTED PRESENCE. (A client MAY 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 principal'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). Such a presence session is terminated by
sending unavailable presence (Section 4.5).
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 SHOULD
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signal 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 broadcasted by the server on
behalf of the client) and no 'type' attribute (indicating the user's
availability). After sending initial presence, a connected resource
(in the terminology of [XMPP-CORE]) is said to be an AVAILABLE
RESOURCE.
UC: <presence/>
4.2.2. Server Processing of Outbound 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".
Note: In the following examples, the "user" is juliet@example.com and
the user has three contacts in her roster with a subscription state
of "from" or "both": romeo@example.net, mercutio@example.com, and
benvolio@example.com.
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.com'/>
The user's server MUST also broadcast initial presence from the
user's newly available resource to all of the user's available
resources.
US: <presence from='juliet@example.com/balcony'
to='juliet@example.com/balcony'/>
US: <presence from='juliet@example.com/balcony'
to='juliet@example.com/chamber'/>
In the absence of presence information about the user's contacts, the
user's server SHOULD also send presence probes to the user's contacts
on behalf of the user as specified under Section 4.3.
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4.2.3. 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'/>
[ ... to resource2 ... ]
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'/>
4.2.4. Client Processing of Inbound Presence
When the contact's client receives presence from the user and the
user is in the contact's roster, it SHOULD display the presence
information in an appropriate roster interface.
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 chat session (see also Section 4.6 and Section 5.4).
Otherwise, the client SHOULD ignore the presence information and not
display it to the contact.
4.3. Presence Probes
A PRESENCE PROBE is a presence stanza whose 'type' attribute has a
value of "probe". The value of the 'from' address SHOULD be the full
JID <user@domain/resource> of the probing user and the value of the
'to' address SHOULD be the bare JID <contact@domain> of the contact
whose availability the user wants to discover.
US: <presence from='juliet@example.com/balcony'
to='romeo@example.net'
type='probe'/>
A presence probe SHOULD NOT be sent by a client. Instead, it is
designed to be sent by a user's server on the user's behalf in order
to discover the availability of the user's contacts.
If a server receives a presence probe intended for a full JID
<contact@domain/resource>, it SHOULD treat the probe as if the 'to'
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address was a bare JID, but MAY instead handle it on behalf of the
connected resource by returning only the presence information for
that particular resources (and in any case MUST NOT deliver it to the
resource).
4.3.1. Server Generation of Outbound Presence Probe
When a server needs to discover the availability of a user's contact,
it SHOULD send a presence probe from the full JID
<user@domain/resource> of the user to the bare JID <contact@domain>
of the contact. The server SHOULD send a probe to a contact only if
the contact is in the user's roster with the 'subscription' attribute
set to a value of "to" or "both" (i.e., if the user is subscribed to
the contact's presence).
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/balcony'
to='romeo@example.net'
type='probe'/>
US: <presence from='juliet@example.com/balcony'
to='benvolio@example.com'
type='probe'/>
US: <presence from='juliet@example.com/balcony'
to='nurse@example.com'
type='probe'/>
4.3.2. Server Processing of Inbound Presence Probe
Upon receiving a presence probe from the user's server on behalf of
the user, the contact's server SHOULD 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),
the contact's server MUST return a presence stanza of type
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"unsubscribed" in response to the presence probe (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).
CS: <presence from='mercutio@example.com'
to='juliet@example.com'
type='unsubscribed'/>
2. Else, if the contact has no available resources, the server
SHOULD reply to the presence probe by sending to the user the
full XML of the last presence stanza of type "unavailable"
received by the server from the contact (but MAY not reply at
all).
3. Else, if the contact has at least one available resource, 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.
CS: <presence from='romeo@example.net/foo'
to='juliet@example.com'/>
CS: <presence from='romeo@example.net/bar'
to='juliet@example.com'>
<show>away</show>
</presence>
4.4. Subsequent Presence Broadcast
4.4.1. Client Generation of Presence Broadcast
After sending initial presence, the user's client may update its
availability for broadcasting at any time during its session by
sending a presence stanza with no 'to' address and no 'type'
attribute.
UC: <presence>
<show>away</show>
</presence>
Note: A user SHOULD NOT send a presence update to broadcast
information that changes independently of the user's availability for
communication.
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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", the server
MAY 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 received from the contact during the
user's presence session was of type "unavailable", the user's server
MAY opt not to send subsequent presence notifications from the user
to the contact.
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.com'>
<show>away</show>
</presence>
US: <presence from='juliet@example.com/balcony'
to='mercutio@example.com'>
<show>away</show>
</presence>
The user's server MUST also send the presence stanza to all of the
user's available resources.
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>
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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 Inbound Presence
When the contact's client receives presence from the user and the
user is in the contact's roster, it SHOULD display the presence
information in an appropriate roster interface.
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 chat session (see also Section 4.6 and Section 5.4).
Otherwise, the client SHOULD 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 final presence stanza MAY contain one or more
<status/> elements specifying the reason why the user is no longer
available.
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US: <presence type='unavailable'>
<status>going on vacation</status>
</presence>
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 may become unavailable
ungracefully (e.g., the resource may 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".
As an optimization, if the subscription type is "both", the server
MAY send the unavailable presence notification 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 received from the contact
during the user's presence session was of type "unavailable", the
user's server MAY opt not to send the unavailable presence
notification from the user to the contact.
See Section 4.6 regarding rules that supplement the foregoing.
If the unavailable presence stanza was gracefully received from the
client, the server MUST broadcast the full XML of the presence
stanza.
US: <presence from='juliet@example.com/balcony'
to='romeo@example.net'
type='unavailable'/>
US: <presence from='juliet@example.com/balcony'
to='benvolio@example.com'
type='unavailable'/>
US: <presence from='juliet@example.com/balcony'
to='mercutio@example.com'
type='unavailable'/>
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The user's server MUST also send the unavailable presence stanza to
all of the user's remaining available resources.
US: <presence from='juliet@example.com/balcony'
to='juliet@example.com/chamber'
type='unavailable'/>
Note: Any presence stanza with no 'type' attribute and no 'to'
attribute that is sent after sending broadcasted unavailable presence
MUST be broadcasted by the 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 unavailable 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'
type='unavailable'/>
[ ... to resource2 ... ]
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'
type='unavailable'/>
If the server is optimizing subsequent presence delivery as described
under Section 4.4, it SHOULD also note that the user is unavailable
and appropriately update its internal representation of which users
are online.
4.5.4. Client Processing of Inbound Unavailable Presence
When the contact's client receives unavailable presence from the user
and the user is in the contact's roster, it SHOULD display the
unavailable presence information in an appropriate roster interface.
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 presence information in the
user interface for that chat session (see also Section 4.6 and
Section 5.4).
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Otherwise, the client SHOULD ignore the unavailable presence
information and not display it to the contact.
4.6. Directed Presence
This section supplements and in some respects modifies the rules
defined above, but only for the special case of directed presence.
4.6.1. Client Generation of Directed Presence
As noted, directed presence is a 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 5.4.
4.6.2. Server Processing of Outbound Directed Presence
When the user's server receives the 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 broadcasted unavailable presence (i.e., during the user's
presence session), the user's server MUST route or deliver the
full XML of that presence stanza but SHOULD NOT otherwise modify
the contact's status regarding broadcasted presence (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 broadcasted
unavailable presence (i.e., during the user's presence session),
the user's server MUST route or deliver the full 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
become 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
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server MUST treat the entities to which the user sends directed
presence in the same way that it treats the entities listed 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 broadcasted presence and directed presence, so the contact's
server follows the existing rules for processing of inbound presence.
4.6.4. Client Processing of Inbound Directed Presence
When the contact's client receives presence from the user and the
user is in the contact's roster, it SHOULD display the presence
information in an appropriate roster interface.
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 an appropriate user
interface.
Otherwise, the client SHOULD 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).
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:
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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 unsubscribe -- The sender is unsubscribing from another entity's
presence.
o unsubscribed -- The subscription request has been denied or a
previously-granted subscription has been cancelled.
o unavailable -- Signals that the entity is no longer available for
communication.
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/>.
Note: There is no default value for the 'type' attribute of the
<presence/> element. Therefore if the intended recipient or
intermediate router receives a <presence/> element whose 'type' value
is undefined, it SHOULD return a stanza error of <bad-request/>.
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 allowable children 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 provided only if the presence stanza possesses no 'type'
attribute, although exceptions are noted in the text that follows.
4.7.3. 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. The <show/>
element MUST NOT possess any attributes. 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 properly-namespaced child element of the presence
stanza):
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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 server routing and delivery logic).
4.7.4. 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.
<presence from='romeo@example.net/orchard'
xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
</presence>
The <status/> element MUST NOT possess any attributes, with the
exception of the 'xml:lang' attribute. 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 may include the XML
stream header as described in [XMPP-CORE]).
<presence from='romeo@example.net/orchard'
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.
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<presence from='romeo@example.net/orchard'
type='unavailable'>
<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/> to a human user (see
Section 11).
<presence from='romeo@example.net'
to='nurse@example.com'
type='subscribe'>
<status>Hi, Juliet said I should add you to my buddy list.</status>
</presence>
4.7.5. 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. The
<priority/> element MUST NOT possess any attributes.
<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 SHOULD
consider the priority to be zero.
For information regarding the semantics of priority values in stanza
processing within instant messaging and presence applications, refer
to Server Rules for Processing XML Stanzas (Section 8).
4.7.6. Extended Content
As described in [XMPP-CORE], an XML stanza MAY contain any properly-
namespaced child element; this applies to the presence stanza as
well.
(In the following example, the presence stanza includes entity
capabilities information as defined in [XEP-0115]).)
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<presence from='romeo@example.net'>
<c xmlns='http://jabber.org/protocol/caps'
node='http://psi-im.org/caps'
ver='0.11'/>
</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.
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 (if, that is, messaging
functionality is enabled and the server is not a presence-only
service). One kind of stanza that may be exchanged is <message/>.
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 Server Rules for Processing XML Stanzas (Section 8),
the sender's server is responsible for delivering the message to the
intended recipient (if the recipient is on the same server) or for
routing the message to the recipient's server (if the recipient is on
a different server). Thus a message stanza is used to "push"
information to another entity.
As noted under Section 4.6, if a user exchanges messages 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.
The following sections describe the syntax of the <message/> stanza.
5.1. Attributes
5.1.1. To Attribute
An instant messaging client SHOULD specify an intended recipient for
a message by providing the JID of an entity other than the sender 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>.
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<message
from='juliet@example.com/balcony'
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 chat session), 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 (via presence) that the
intended recipient's resource is no longer available.
<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>
</message>
5.1.2. Type Attribute
Common uses of the message stanza in instant messaging applications
include single messages, messages sent in the context of a chat
conversation, messages sent in the context of a multi-user chat room,
headlines and other alerts, 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. A receiving client SHOULD present the message in an
interface enabling one-to-one chat between the two parties,
including an appropriate conversation history. Detailed
recommendations regarding chat sessions are provided under
Section 5.4.
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]). A receiving client
SHOULD present the message in an interface enabling many-to-many
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chat between the parties, including a roster of parties in the
chatroom and an appropriate conversation history. Full definition
of XMPP-based groupchat protocols is out of scope for this
document (for details, refer to [XEP-0045]).
o headline -- The message is probably generated by an automated
service that delivers or broadcasts content (news, sports, market
information, syndicated content, alerts, etc.), or the sender
wishes the message to be delivered as if it were so generated. No
reply to the message is expected, and a receiving client SHOULD
present the message in an interface that appropriately
differentiates the message from standalone messages, chat
sessions, or groupchat sessions (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.
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. A receiving
client SHOULD present the message in an interface enabling the
recipient to reply, but without a conversation history. This is
the default value of the 'type' attribute.
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).
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. Child Elements
An XMPP message stanza MAY contain any allowable child elements
qualified by the 'jabber:client' (or 'jabber:server') namespace, as
well as any other properly-namespaced child element that consists of
extended content. The defined payloads are described in the
following sections and extended content payloads are described in the
appropriate XMPP extension specifications (not herein).
5.2.1. Body
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.
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<message
to='romeo@example.net'
from='juliet@example.com/balcony'
type='chat'
xml:lang='en'>
<body>Wherefore art thou, Romeo?</body>
</message>
The <body/> element MUST NOT possess any attributes, with the
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 may include the
XML stream header as described in [XMPP-CORE]).
<message
to='romeo@example.net'
from='juliet@example.com/balcony'
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]).
5.2.2. Subject
The <subject/> element contains human-readable XML character data
that specifies the topic of the message.
<message
to='romeo@example.net'
from='juliet@example.com/balcony'
type='chat'
xml:lang='en'>
<subject>I implore you!</subject>
<body>Wherefore art thou, Romeo?</body>
</message>
The <subject/> element MUST NOT possess any attributes, with the
exception of the 'xml:lang' attribute. 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
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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 may include the XML
stream header as described in [XMPP-CORE]).
<message
to='romeo@example.net'
from='juliet@example.com/balcony'
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]).
5.2.3. Thread
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 conversation, such as a game session or between plugins.
The <thread/> element is not used to identify individual messages,
only conversations.
The inclusion of the <thread/> element is OPTIONAL. Because the
<thread/> element uniquely identifies the particular conversation
thread to which a message belongs, a message stanza MUST NOT contain
more than one <thread/> element.
The value of the <thread/> element is not human-readable and MUST be
treated as opaque by entities; no semantic meaning may be derived
from it, and only exact comparisons may be made against it. The
value of the <thread/> element MUST be a universally unique
identifier (UUID) as described in [UUID].
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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' MUST conform to the syntax of the
<thread/> element itself. The <thread/> element MUST NOT contain
mixed content (as defined in Section 3.2.2 of [XML]).
<message
to='romeo@example.net'
from='juliet@example.com/balcony'
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 properly-
namespaced child element; 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]).)
<message
to='romeo@example.net'
from='juliet@example.com/balcony'
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'>
Wherefore <span style='font-style: italic'>art</span>
thou, <span style='color:red'>Romeo</span>?
</body>
</html>
</message>
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5.4. One-to-One Chat Sessions
In practice, instant messaging activity between human users tends to
occur in 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 user's client SHOULD send a message of type "chat" and
the contact's client SHOULD preserve that message type in subsequent
replies. The user's client also SHOULD include a <thread/> element
on its initial message, which the contact's client SHOULD also
preserve during the life of the chat session.
The user's client MUST address the initial message in a chat session
to the bare JID <contact@domain> (rather than attempting to guess an
appropriate full JID <contact@domain/resource>). Until and unless
the user's client receives a reply from the contact, it MUST continue
sending any further messages to the contact's bare JID. The
contact's client SHOULD address its subsequent 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.
If a user exchanges messages with a contact but the user does not
normally share presence with the contact via a presence subscription,
it is RECOMMENDED for the user's client to send directed presence to
the contact, subject to user approval (either explicitly for this
contact or implicitly via a configuration setting). If a client
supports this feature, it MUST allow the user to disable the feature
in order to prevent presence sharing with unknown entities.
An example of a chat session as described above is provided under
Section 7.
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 required) are defined in [XMPP-CORE],
whereas the specific semantics required to complete particular use
cases are defined in all cases 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
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define any children of IQ stanzas other than the <error/> 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, one whose resource identifier is "chamber" and another
whose resource identifier is "balcony")
o benvolio@example.org (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/balcony' type='get' id='ex1'>
<query xmlns='jabber:iq:roster'/>
</iq>
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Example 2: User receives roster from server:
US: <iq to='romeo@example.net/balcony' type='result' id='ex1'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@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 from='romeo@example.net/orchard'/>
Example 4: User's server sends presence probes to contacts with
subscription="to" and subscription="both" on behalf of the user's
available resource:
US: <presence
type='probe'
from='romeo@example.net/orchard'
to='juliet@example.com'/>
US: <presence
type='probe'
from='romeo@example.net/orchard'
to='benvolio@example.org'/>
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'
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