Network Working Group P. Saint-Andre, Ed.
Internet-Draft XMPP Standards Foundation
Obsoletes: 3921 (if approved) October 29, 2007
Intended status: Standards Track
Expires: May 1, 2008
Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and
Presence
draft-saintandre-rfc3921bis-04
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Copyright Notice
Copyright (C) The IETF Trust (2007).
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 . . 21
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 . 24
3.1.6. Server Processing of Inbound Subscription Approval . . 25
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 . . . . . . . . . . . . . . . 30
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 30
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 . . . . . . . . 31
4.2.3. Server Processing of Inbound Presence . . . . . . . . 32
4.2.4. Client Processing of Inbound Presence . . . . . . . . 32
4.3. Presence Probes . . . . . . . . . . . . . . . . . . . . . 33
4.3.1. Server Generation of Outbound Presence Probe . . . . . 33
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 . . . . . . . . 35
4.4.3. Server Processing of Inbound Presence . . . . . . . . 36
4.4.4. Client Processing of Inbound Presence . . . . . . . . 36
4.5. Unavailable Presence . . . . . . . . . . . . . . . . . . . 37
4.5.1. Client Generation of Unavailable Presence . . . . . . 37
4.5.2. Server Processing of Outbound Unavailable Presence . . 37
4.5.3. Server Processing of Inbound Unavailable Presence . . 38
4.5.4. Client Processing of Inbound Unavailable Presence . . 39
4.6. Directed Presence . . . . . . . . . . . . . . . . . . . . 39
4.6.1. Client Generation of Directed Presence . . . . . . . . 39
4.6.2. Server Processing of Outbound Directed Presence . . . 39
4.6.3. Server Processing of Inbound Directed Presence . . . . 40
4.6.4. Client Processing of Inbound Directed Presence . . . . 40
4.7. Presence Syntax . . . . . . . . . . . . . . . . . . . . . 40
4.7.1. Type Attribute . . . . . . . . . . . . . . . . . . . . 40
4.7.2. Child Elements . . . . . . . . . . . . . . . . . . . . 41
4.7.3. Show Element . . . . . . . . . . . . . . . . . . . . . 42
4.7.4. Status Element . . . . . . . . . . . . . . . . . . . . 42
4.7.5. Priority Element . . . . . . . . . . . . . . . . . . . 43
4.7.6. Extended Content . . . . . . . . . . . . . . . . . . . 44
5. Exchanging Messages . . . . . . . . . . . . . . . . . . . . . 44
5.1. Attributes . . . . . . . . . . . . . . . . . . . . . . . . 45
5.1.1. To Attribute . . . . . . . . . . . . . . . . . . . . . 45
5.1.2. Type Attribute . . . . . . . . . . . . . . . . . . . . 45
5.2. Child Elements . . . . . . . . . . . . . . . . . . . . . . 47
5.2.1. Body . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.2.2. Subject . . . . . . . . . . . . . . . . . . . . . . . 48
5.2.3. Thread . . . . . . . . . . . . . . . . . . . . . . . . 48
5.3. Extended Content . . . . . . . . . . . . . . . . . . . . . 49
6. Exchanging IQ Stanzas . . . . . . . . . . . . . . . . . . . . 49
7. A Sample Session . . . . . . . . . . . . . . . . . . . . . . . 50
8. Server Rules for Processing XML Stanzas . . . . . . . . . . . 56
8.1. No Such User . . . . . . . . . . . . . . . . . . . . . . . 56
8.2. Full JID at Local Domain . . . . . . . . . . . . . . . . . 56
8.2.1. Available Resource Matches . . . . . . . . . . . . . . 56
8.2.2. No Available Resource Matches . . . . . . . . . . . . 57
8.3. Bare JID at Local Domain . . . . . . . . . . . . . . . . . 57
8.3.1. Available Resources . . . . . . . . . . . . . . . . . 57
8.3.1.1. Message . . . . . . . . . . . . . . . . . . . . . 57
8.3.1.2. Presence . . . . . . . . . . . . . . . . . . . . . 58
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8.3.1.3. IQ . . . . . . . . . . . . . . . . . . . . . . . . 58
8.3.2. No Available Resources . . . . . . . . . . . . . . . . 58
8.3.2.1. Message . . . . . . . . . . . . . . . . . . . . . 59
8.3.2.2. Presence . . . . . . . . . . . . . . . . . . . . . 59
8.3.2.3. IQ . . . . . . . . . . . . . . . . . . . . . . . . 59
8.4. Foreign Domain . . . . . . . . . . . . . . . . . . . . . . 59
9. IM and Presence Compliance Requirements . . . . . . . . . . . 61
9.1. Servers . . . . . . . . . . . . . . . . . . . . . . . . . 61
9.2. Clients . . . . . . . . . . . . . . . . . . . . . . . . . 61
10. Internationalization Considerations . . . . . . . . . . . . . 62
11. Security Considerations . . . . . . . . . . . . . . . . . . . 62
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 62
12.1. Instant Messaging SRV Protocol Label Registration . . . . 63
12.2. Presence SRV Protocol Label Registration . . . . . . . . . 63
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 63
13.1. Normative References . . . . . . . . . . . . . . . . . . . 63
13.2. Informative References . . . . . . . . . . . . . . . . . . 64
Appendix A. Subscription States . . . . . . . . . . . . . . . . . 65
A.1. Defined States . . . . . . . . . . . . . . . . . . . . . . 66
A.2. Server Processing of Outbound Presence Subscription
Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 67
A.2.1. Subscribe . . . . . . . . . . . . . . . . . . . . . . 67
A.2.2. Unsubscribe . . . . . . . . . . . . . . . . . . . . . 68
A.2.3. Subscribed . . . . . . . . . . . . . . . . . . . . . . 68
A.2.4. Unsubscribed . . . . . . . . . . . . . . . . . . . . . 69
A.3. Server Processing of Inbound Presence Subscription
Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 69
A.3.1. Subscribe . . . . . . . . . . . . . . . . . . . . . . 70
A.3.2. Unsubscribe . . . . . . . . . . . . . . . . . . . . . 70
A.3.3. Subscribed . . . . . . . . . . . . . . . . . . . . . . 71
A.3.4. Unsubscribed . . . . . . . . . . . . . . . . . . . . . 72
Appendix B. Blocking Communication . . . . . . . . . . . . . . . 73
Appendix C. vCards . . . . . . . . . . . . . . . . . . . . . . . 73
Appendix D. XML Schemas . . . . . . . . . . . . . . . . . . . . . 73
D.1. jabber:client . . . . . . . . . . . . . . . . . . . . . . 73
D.2. jabber:server . . . . . . . . . . . . . . . . . . . . . . 77
D.3. jabber:iq:roster . . . . . . . . . . . . . . . . . . . . . 81
Appendix E. Differences From RFC 3921 . . . . . . . . . . . . . . 83
Appendix F. Copying Conditions . . . . . . . . . . . . . . . . . 83
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 84
Intellectual Property and Copyright Statements . . . . . . . . . . 86
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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".
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 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
error if a client attempt to send a
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
mailing list, for which archives and
subscription information are available at
<>.
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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
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 element MAY contain one or more children, each
describing a unique roster item or "contact".
The syntax of the 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). The value of the
'name' attribute is typicall opaque to the server but may have
meaning to a human user.
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 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 MAY more than one
element. The XML character data of the element is
typicall 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 element qualified by the 'jabber:iq:roster'
namespace.
The element in a roster get MUST NOT contain any
child elements.
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C:
2.1.3. Roster Set
A ROSTER SET is an IQ stanza of type "set" sent from client to server
and containing a element qualified by the 'jabber:iq:roster'
namespace.
The following rules apply to roster sets:
1. The element MUST contain one and only one
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:
2.1.4. Roster Push
A ROSTER PUSH is an IQ stanza of type "set" sent from server to
client and containing a element qualified by the 'jabber:iq:
roster' namespace.
The following rules apply to roster pushes:
1. The element in a roster get MUST contain one and only
one 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 .
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S:
2.1.5. Roster Result
A ROSTER RESULT is an IQ stanza of type "result" sent from server to
client and containing a element qualified by the 'jabber:iq:
roster' namespace.
The element in a roster result contains one element
for each contact and therefore MAY contain more than one
element.
S:
If there are no contacts in the roster, the element MUST be
empty.
S:
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 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:
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S:
-
Friends
If the server cannot process the roster get, it MUST return an
appropriate stanza error as described in [XMPP-CORE] (such as
if the roster namespace is not supported or
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 rather a full
JID , 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:
-
Servants
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:
-
Servants
S:
-
Servants
The server MUST also return an IQ stanza of type "result" to the
connected resource that sent the roster set.
S:
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:
C:
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., ).
The server SHOULD return a error to the client if the
roster set violates any of the following conditions:
1. The element contains more than one child
element.
2. The element contains more than one 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 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 element is of zero length.
3. The XML character data of the 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 element, ignore duplicate elements, place the
roster item in no group or a default group if the element is
empty, and truncate 'name' attributes and elements that are
too long).
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Error: Roster set contains more than one item
C:
-
Servants
-
Family
S:
Error: Roster set contains item with oversized handle
C:
-
Servants
S:
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Error: Roster set contains duplicate groups
C:
-
Servants
Servants
S:
Error: Roster set contains empty group
C:
-
S:
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Error: Roster set contains oversized group
C:
-
[ ... some-very-long-group-name ... ]
S:
The server MUST return a error to the client if the
value of the element's 'jid' attribute matches the bare JID
portion of the 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:
S:
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:
-
Friends
The user who has this item in her roster may want to add the item to
another group.
C:
-
Friends
Lovers
The user may then want to remove the item from the original group.
C:
-
Lovers
The user may then want to change the handle for the item.
C:
-
Lovers
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:
-
Lovers
The user may then want to remove the item from all groups.
C:
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:
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:
S:
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 error.
Error: Roster item not found
C:
S:
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").
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 of the sending entity, not the full
JID . 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 .
UC:
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.
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 of the user.
US:
If the potential contact is hosted on the same server, the server
MUST adhere to the rules specified in the next section in processing
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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:
US:
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
MAY choose to 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.
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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:
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).
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, 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
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deliver only one of the requests when the contact next has an
interested resource; this helps to prevent "subscription request
spam".)
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:
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
"unsubscribed", which is processed as described under Section 3.2 for
both the contact's server and the user's server.
CC:
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
of the contact and route or deliver the stanza to
the user.
CS:
The contact's server then MUST send a roster push to all of the
contact's interested resources.
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CS:
CS:
The contact's server MUST then also send current presence to the user
from each of the contact's available resources.
CS:
CS:
From the perspective of the contact, there now exists a subscription
from the user.
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
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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:
US:
From the perspective of the user, there now exists a subscription to
the contact's presence.
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.
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[ ... to resource1 ... ]
US:
[ ... to resource2 ... ]
US:
[ ... to resource1 ... ]
US:
[ ... to resource2 ... ]
US:
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:
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 of the
contact.
CS:
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.
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.
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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:
CS:
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).
US:
US:
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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:
3.3.2. Server Processing of Outbound Unsubscribe
As mentioned, the user's server MUST stamp the outbound unsubscribe
with the bare JID of the user.
US:
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).
US:
US:
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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:
CS:
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
stanza with no 'type' attribute, and an entity's lack of availability
is signalled when a client generates a 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"
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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
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:
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
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
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benvolio@example.com.
US:
US:
US:
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:
US:
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.
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:
[ ... to resource2 ... ]
CS:
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
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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).
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 of the probing user and the value of the
'to' address SHOULD be the bare JID of the contact
whose availability the user wants to discover.
US:
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.
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
of the user to the bare JID
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).
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US:
US:
US:
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
"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:
2. Else, if the contact has no available resources, the server MUST
either (1) 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, or (2) 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:
CS:
away
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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:
away
Note: A user SHOULD NOT send a presence update to broadcast
information that changes independently of the user's availability for
communication.
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".
US:
away
US:
away
US:
away
Note: As an optimization, if the subscription state is "both" then
the user's server MAY choose to broadcast subsequent presence only if
the server has received available presence from the contact at some
point during the user's session; i.e., if the server never received
available presence from the contact and the user has a mutual
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presence subscription with the contact, it MAY decline to send
subsequent presence to the contact.
The user's server MUST also send the presence stanza to all of the
user's available resources.
US:
away
US:
away
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:
away
[ ... to resource2 ... ]
CS:
away
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).
Otherwise, the client SHOULD ignore the presence information and not
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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:
Optionally, the final presence stanza MAY contain one or more
elements specifying the reason why the user is no longer
available.
US:
going on vacation
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 contact has at least one resource that is online according to
the user's server.
3. The last presence stanza received from the contact during the
user's presence session was not of type "error" or "unsubscribe".
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.
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US:
US:
US:
The user's server MUST also send the unavailable presence stanza to
all of the user's remaining available resources.
US:
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:
[ ... to resource2 ... ]
CS:
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.
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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.
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 or a 'type' attribute whose value
is "unavailable".
If a user exchanges messages or 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, subject to user approval
(either explicitly for this entity 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.
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
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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
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).
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A 'type' attribute with a value of "unavailable" signals that the
relevant entity is not available for communication (see Section 4.5).
The XMPP presence stanza is also used to negotiate and manage
subscriptions to the presence of other entities. These tasks are
completed via presence stanzas of type "subscribe", "unsubscribe",
"subscribed", and "unsubscribed" as described under Section 3.
If a user and contact are associated with different XMPP servers,
those servers also use a special presence stanza of type "probe" in
order to determine the availability of the entity on the peer server;
for details, see Section 4.3. Clients SHOULD NOT send presence
stanzas of type "probe".
The values of the 'type' attribute can be summarized as follows:
o error -- An error has occurred regarding processing of a
previously-sent presence stanza; if the presence stanza is of type
"error", it MUST include an 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 .
Note: There is no default value for the 'type' attribute of the
element. Therefore if the intended recipient or
intermediate router receives a element whose 'type' value
is undefined, it SHOULD return a stanza error of .
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 , , and
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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 element specifies the particular availability
sub-state of an entity or a specific resource thereof. A presence
stanza MUST NOT contain more than one element. The
element MUST NOT possess any attributes. The XML character data of
the 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):
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 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 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.
dnd
Wooing Juliet
The element MUST NOT possess any attributes, with the
exception of the 'xml:lang' attribute. Multiple instances of the
element MAY be included, but only if each instance
possesses an 'xml:lang' attribute with a distinct language value
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(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]).
dnd
Wooing Juliet
Dvořím se Julii
A presence stanza of type "unavailable" MAY also include a
element to provide detailed information about why the entity is going
offline.
Busy IRL
The 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 to a human user (see
Section 11).
Hi, Juliet said I should add you to my buddy list.
4.7.5. Priority Element
The OPTIONAL 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 element. The
element MUST NOT possess any attributes.
dnd
Wooing Juliet
Dvořím se Julii
1
If no priority is provided, the processing server or client SHOULD
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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]).)
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 .
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 stanza.
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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 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 rather than of the form
.
Art thou not Romeo, and a Montague?
If the message is being sent in reply to a message previously
received from an address of the form (e.g.,
within the context of a chat session), the value of the 'to' address
SHOULD be of the form rather than of the form
unless the sender has knowledge (via presence) that the
intended recipient's resource is no longer available.
Neither, fair saint, if either thee dislike.
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:
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o chat -- The message is sent in the context of a one-to-one chat
conversation. A receiving client SHOULD present the message in an
interface enabling one-to-one chat between the two parties,
including an appropriate conversation history. (For detailed
recommendations regarding chat sessions, refer to [XEP-0201].)
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
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').
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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 element contains human-readable XML character data that
specifies the textual contents of the message; this child element is
normally included but is OPTIONAL.
Wherefore art thou, Romeo?
The element MUST NOT possess any attributes, with the
exception of the 'xml:lang' attribute. Multiple instances of the
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]).
Wherefore art thou, Romeo?
PročeŽ jsi ty, Romeo?
The element MUST NOT contain mixed content (as defined in
Section 3.2.2 of [XML]).
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5.2.2. Subject
The element contains human-readable XML character data
that specifies the topic of the message.
I implore you!
Wherefore art thou, Romeo?
The element MUST NOT possess any attributes, with the
exception of the 'xml:lang' attribute. Multiple instances of the
element MAY be included for the purpose of providing
alternate versions of the same subject, but only if each instance
possesses an 'xml:lang' attribute with a distinct language value
(either explicitly or by inheritance from the 'xml:lang' value of an
element farther up in the XML hierarchy, which may include the XML
stream header as described in [XMPP-CORE]).
I implore you!
Úpěnlivě prosím!
Wherefore art thou, Romeo?
Pročež jsi ty, Romeo?
The 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 element is to uniquely identify
a conversation thread or "chat session" between two entities
instantiated by stanzas of type 'chat'. However, the XMPP
element may also be used to uniquely identify an analogous
thread between two entities instantiated by stanzas of
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type 'headline' or 'normal', or among multiple entities in the
context of a multi-user chat room instantiated by stanzas
of type 'groupchat'. It may also be used for stanzas not
related to a conversation, such as a game session or between plugins.
The value of the element MUST be a universally unique
identifier (UUID) as described in [UUID].
The use of the element is OPTIONAL. The element
is not used to identify individual messages, only conversations. A
message stanza MUST NOT contain more than one element. The
element MUST NOT possess any attributes. The value of the
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 element MUST
NOT contain mixed content (as defined in Section 3.2.2 of [XML]).
For detailed recommendations regarding use of the 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]).)
Wherefore art thou, Romeo?
Wherefore art
thou, Romeo?
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],
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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
define any children of IQ stanzas other than the 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:
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Example 2: User receives roster from server:
US:
-
Friends
Now the user begins a presence session.
Example 3: User sends initial presence:
UC:
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:
US:
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:
US:
Example 6: Contacts' servers reply to presence probe on behalf of all
available resources:
CS:
away
be right back
0
CS:
1
CS:
dnd
gallivanting
Example 7: Contacts' servers deliver user's initial presence to all
available resources or return unsubscribed to user:
CS:
CS:
CS:
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Example 8: User sends directed presence to another user not in his
roster:
UC:
dnd
courting Juliet
0
Now the user has a threaded conversation (chat session) with one of
his contacts.
Example 9: A threaded conversation
CC:
Art thou not Romeo, and a Montague?
e0ffe42b28561960c6b12b944a092794b9683a38
UC:
Neither, fair saint, if either thee dislike.
e0ffe42b28561960c6b12b944a092794b9683a38
CC:
How cam'st thou hither, tell me, and wherefore?
e0ffe42b28561960c6b12b944a092794b9683a38
And so on.
The user can also send subsequent broadcasted presence.
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Example 10: User sends updated available presence for broadcasting:
UC:
away
I shall return!
1
Example 11: User's server broadcasts updated presence only to one
contact:
US:
away
I shall return!
1
Example 12: Contact's server delivers updated presence to all of the
contact's available resources ("balcony" and "chamber"):
CS:
away
I shall return!
1
CS:
away
I shall return!
1
Example 13: One of the contact's resources broadcasts unavailable
presence:
CC:
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Example 14: Contact's server sends unavailable presence to user:
CS:
Now the user ends his presence session.
Example 15: User sends unavailable presence:
UC:
gone home
Example 16: User's server broadcasts unavailable presence to contact
as well as to the person to whom the user sent directed presence:
US:
gone home
US:
gone home
Finally the user closes his stream and the server responds in kind.
Example 17: User closes stream:
UC:
Example 18: User's server closes stream:
US:
THE END
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8. Server Rules for Processing XML Stanzas
Basic server rules for processing XML stanzas are defined in
[XMPP-CORE]. This section defines supplementary rules for XMPP
instant messaging and presence servers; in the absence of a
supplementary rule defined below (e.g., for stanzas without a 'to'
address), the rule defined in [XMPP-CORE] shall apply.
8.1. No Such User
If the user account does not exist, how the stanza shall be processed
depends on the stanza type.
o For a message stanza, the server SHOULD return a stanza error to the sender.
o For a presence stanza with no 'type' attribute or a 'type'
attribute of "unavailable", the server SHOULD silently ignore the
stanza (i.e., not return an error or a presence stanza of type
"unsubscribed").
o For a presence stanza of type "subscribe", "subscribed",
"unsubscribe", or "unsubscribed", the server MUST follow the
guidelines provided under Section 3.
o For an IQ stanza, the server MUST return a
stanza error to the sender.
8.2. Full JID at Local Domain
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute of an inbound stanza matches one of the
configured hostnames of the server itself and the JID contained in
the 'to' attribute is of the form , the server
MUST adhere to the following rules.
8.2.1. Available Resource Matches
If an available resource exactly matches the full JID, the
recipient's server MUST deliver the stanza to that resource.
However, for IQ stanzas of type "get" or "set", if the intended
recipient does not share presence with the requesting entity either
by means of a presence subscription of type "both" or "from" or by
means of directed presence, then the server SHOULD NOT deliver the IQ
stanza but instead SHOULD return a stanza
error to the requesting entity. This policy helps to prevent
presence leaks (see Section 11).
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8.2.2. No Available Resource Matches
If no connected or available resource exactly matches the full JID,
how the stanza shall be processed depends on the stanza type.
o For a message, the server SHOULD treat the stanza as if it were
addressed to as described in the next section.
o For a presence stanza with no 'type' attribute or a 'type'
attribute of "unavailable", the server SHOULD silently ignore the
stanza (i.e., not return an error or a presence stanza of type
"unsubscribed").
o For a presence stanza of type "subscribe", "subscribed",
"unsubscribe", or "unsubscribed", the server MUST follow the
guidelines provided under Section 3.
o For an IQ stanza, the server MUST return a
stanza error to the sender.
8.3. Bare JID at Local Domain
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute of an inbound stanza matches one of the
configured hostnames of the server itself and the JID contained in
the 'to' attribute is of the form , the server MUST
adhere to the following rules.
8.3.1. Available Resources
If there is at least one available resource, how the stanza shall be
processed depends on the stanza type.
8.3.1.1. Message
For a message stanza of type "headline", the server SHOULD deliver
the stanza to all available resources.
For a message stanza of type "chat", "error", "groupchat", or
"normal", the server SHOULD deliver the stanza to the highest-
priority available resource. If there is not one highest-priority
available resource but instead the highest priority is asserted by
two or more available resources, these resources are said to form a
"delivery tie". In the case of a delivery tie, a server SHOULD
deliver the message to all of the tied resources. However, before
delivering the message, a server MAY remove one or more resources
from the tie. Methods for doing so are outside the scope of this
specification, but could include factors such as the resource's time
of connection, time of last network or application activity,
availability as determined by some hierarchy of values, or
user-configured rules. Nevertheless, a server MUST NOT remove all
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resources from the tie, and MUST deliver the message to at least one
of the highest-priority resources.
However, for any message type the server MUST NOT deliver the stanza
to any available resource with a negative priority; if the only
available resource has a negative priority, the server SHOULD handle
the message as if there were no available resources as described
under Section 8.3.2.
In all cases, the server MUST NOT rewrite the 'to' attribute (i.e.,
it MUST leave it as rather than change it to
).
8.3.1.2. Presence
For a presence stanza of type "probe", the server MUST handle it
directly as described under Section 4.3.
For a presence stanza with no type or of type "unavailable", the
server MUST deliver the stanza to all available resources.
For a presence stanza of type "subscribe", "subscribed",
"unsubscribe", or "unsubscribed", the server MUST adhere to the rules
defined under Section 3 and summarized under Appendix A.
In all cases, the server MUST NOT rewrite the 'to' attribute (i.e.,
it MUST leave it as rather than change it to
).
8.3.1.3. IQ
For an IQ stanza, the server itself MUST reply on behalf of the user
with either an IQ result or an IQ error, and MUST NOT deliver the IQ
stanza to any of the user's available resources. Specifically, if
the semantics of the qualifying namespace define a reply that the
server can provide on behalf of the user, the server MUST reply to
the stanza on behalf of the user by returning either an IQ stanza of
type "result" or an IQ stanza of type "error" that is appropriate to
the original payload; if not, the server MUST reply with a stanza error.
8.3.2. No Available Resources
If there are no available resources associated with the user, how the
stanza shall be processed depends on the stanza type.
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8.3.2.1. Message
For a message stanza of type "headline", the server SHOULD NOT store
the stanza on behalf of the user and deliver it when the user next
becomes available, but instead SHOULD either forward the stanza to
the user via a non-XMPP messaging system (e.g., to the user's email
account) or return a stanza error to the
sender.
For a message stanza of type "chat", "error", "groupchat", or
"normal", the server MAY choose to store the stanza on behalf of the
user and deliver it when the user next becomes available, or forward
the message to the user via a non-XMPP messaging system (e.g., to the
user's email account). However, if offline message storage or
message forwarding is not enabled, the server MUST return a stanza error to the sender.
Note: Offline message storage and message forwarding are not defined
in XMPP, since they are strictly a matter of implementation and
service provisioning. However, for recommendations regarding offline
message storage refer to [XEP-0160].
8.3.2.2. Presence
For a presence stanza with no type or of type "unavailable" or
"probe", the server SHOULD silently ignore the stanza by not storing
it for later delivery and not replying to it on behalf of the user.
For a presence stanza of type "subscribe", "subscribed",
"unsubscribe", or "unsubscribed", the server MUST adhere to the rules
defined under Section 3 and summarized under Appendix A.
8.3.2.3. IQ
For an IQ stanza, the server itself MUST reply on behalf of the user
with either an IQ result or an IQ error. Specifically, if the
semantics of the qualifying namespace define a reply that the server
can provide on behalf of the user, the server MUST reply to the
stanza on behalf of the user by returning either an IQ stanza of type
"result" or an IQ stanza of type "error" that is appropriate to the
original payload; if not, the server MUST reply with a stanza error.
8.4. Foreign Domain
If the hostname of the domain identifier portion of the address
contained in the 'to' attribute of an outbound stanza does not match
a configured hostname of the server itself, the server MUST attempt
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to route the stanza to the foreign domain. If there exists an active
stream between the two peers, the server shall route the stanza over
that stream for processing by the peer server. If not, the server
MUST do the following.
First, resolve the hostname of the foreign domain (or use a cached
resolution of the foreign domain to an IP address). The recommended
order of attempted resolutions is as follows:
1. Attempt to resolve the foreign hostname using a DNS service
location record [SRV] Service of "xmpp-server" and Proto of
"tcp", resulting in resource records such as "_xmpp-
server._tcp.example.com.", as specified in [XMPP-CORE].
2. If the "xmpp-server" address record resolution fails, attempt to
resolve the "_im" or "_pres" SRV Service as specified in
[IMP-SRV], using the "_im" Service for stanzas and the
"_pres" Service for stanzas (it is up to the
implementation how to handle stanzas). This will result in
one or more resolutions of the form "_im..example.com." or
"_pres..example.com.", where "" would be a label
registered in the Instant Messaging SRV Protocol Label registry
or the Presence SRV Protocol Label registry: either "_xmpp" for
an XMPP-aware domain or some other IANA-registered label (e.g.,
"_simple") for a non-XMPP-aware domain.
3. If both SRV address record resolutions fail, attempt to perform a
normal IPv4/IPv6 address record resolution to determine the IP
address using the "xmpp-server" port of 5269 registered with the
IANA, as specified in [XMPP-CORE].
If the server cannot resolve the foreign domain, it SHOULD return a
stanza error.
Second, negotiate XML streams with the foreign domain by following
the process defined in [XMPP-CORE]. If the server can resolve the
foreign domain but cannot establish streams with the XMPP service at
that domain, it SHOULD return a stanza
error.
Third, route the stanza to the foreign domain for processing by the
peer server.
Note: Administrators of server deployments are strongly encouraged to
keep the _im._xmpp, _pres._xmpp, and _xmpp._tcp SRV records properly
synchronized, since different implementations might perform the "_im"
and "_pres" lookups before the "xmpp-server" lookup.
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9. IM and Presence Compliance Requirements
This section summarizes the specific aspects of the Extensible
Messaging and Presence Protocol that MUST be supported by instant
messaging and presence servers and clients in order to be considered
compliant implementations. All such applications MUST comply with
the requirements specified in [XMPP-CORE]. The text in this section
specifies additional compliance requirements for instant messaging
and presence servers and clients (the requirements described here
supplement but do not supersede the core requirements).
Note: A server or client MAY support only presence or instant
messaging, and is not required to support both if only a presence
service or an instant messaging service is desired.
9.1. Servers
In addition to core server compliance requirements, an instant
messaging and presence server MUST additionally support all server-
related instant messaging and presence syntax and semantics defined
in this document, including:
o Presence broadcast on behalf of clients as specified under
Section 4
o Presence subscriptions as specified under Section 3
o Roster storage and management as specified under Section 2
o IM-specific routing and delivery rules as specified under
Section 8
9.2. Clients
In addition to core client compliance requirements, an instant
messaging and presence client MUST additionally support the following
protocols:
o Generation and processing of the IM-specific semantics of XML
stanzas as defined by the XML schemas, including the 'type'
attribute of message and presence stanzas as well as their child
elements (see Section 5 and Section 4)
o All client-related instant messaging syntax and semantics defined
in this document, including presence subscriptions and roster
management (see Section 3 and Section 2)
o End-to-end object signing and encryption as defined in [XMPP-E2E]
A client MUST also handle addresses that are encoded as "im:" URIs as
specified in [CPIM] and "pres:" URIs as specified in [CPP], although
it MAY do so by removing the "im:" or "pres:" scheme and entrusting
address resolution to the server as specified under Section 8.4.
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10. Internationalization Considerations
For internationalization considerations, refer to the relevant
section of [XMPP-CORE].
11. Security Considerations
Core security considerations for XMPP are defined in the relevant
section of [XMPP-CORE].
Additional considerations that apply only to instant messaging and
presence applications of XMPP are defined in several places within
this document; specifically:
o When a server processes an inbound presence stanza of type "probe"
whose intended recipient is a user associated with one of the
server's hostnames, the server MUST NOT reveal the user's presence
if the sender is an entity that is not authorized to receive that
information as determined by presence subscriptions (see
Exchanging Presence Information (Section 4)).
o A user's server MUST NOT leak the user's network availability to
entities who are not authorized to know the user's presence,
either via an explicit subscription as described herein or via an
existing trust relationship (such as presence-enabled user
directories within organizations).
o When a server processes an outbound presence stanza with no type
or of type "unavailable", it MUST follow the rules defined under
Exchanging Presence Information (Section 4) in order to ensure
that such presence information is not broadcasted to entities that
are not authorized to know such information.
o When a server generates an error stanza in response to receiving a
stanza for a user who does not exist, the use of the error condition helps protect against well-known
dictionary attacks, since this is the same error condition that is
returned if, for instance, the namespace of an IQ child element is
not understood, or if offline message storage or message
forwarding is not enabled for a domain.
o A client MAY ignore the element when contained in a
presence stanza of type "subscribe", "unsubscribe", "subscribed",
or "unsubscribed" in order to help prevent "presence subscription
spam".
12. IANA Considerations
The following sections update the registrations provided in
[RFC3921].
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For a number of related IANA considerations, refer to the relevant
section of [XMPP-CORE].
12.1. Instant Messaging SRV Protocol Label Registration
Address Resolution for Instant Messaging and Presence [IMP-SRV]
defines an Instant Messaging SRV Protocol Label registry for
protocols that can provide services that conform to the "_im" SRV
Service label. Because XMPP is one such protocol, the IANA registers
the "_xmpp" protocol label in the appropriate registry, as follows:
Protocol label: _xmpp
Specification: XXXX
Description: Instant messaging protocol label for the Extensible
Messaging and Presence Protocol (XMPP) as defined by XXXX.
Registrant Contact: IETF, XMPP Working Group,
12.2. Presence SRV Protocol Label Registration
Address Resolution for Instant Messaging and Presence [IMP-SRV]
defines a Presence SRV Protocol Label registry for protocols that can
provide services that conform to the "_pres" SRV Service label.
Because XMPP is one such protocol, the IANA registers the "_xmpp"
protocol label in the appropriate registry, as follows:
Protocol label: _xmpp
Specification: XXXX
Description: Presence protocol label for the Extensible Messaging
and Presence Protocol (XMPP) as defined by XXXX.
Registrant Contact: IETF, XMPP Working Group,
13. References
13.1. Normative References
[IMP-REQS]
Day, M., Aggarwal, S., and J. Vincent, "Instant Messaging
/ Presence Protocol Requirements", RFC 2779,
February 2000.
[IMP-SRV] Peterson, J., "Address Resolution for Instant Messaging
and Presence", RFC 3861, August 2004.
[SRV] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
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[TERMS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[UUID] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
July 2005.
[XML] Paoli, J., Maler, E., Sperberg-McQueen, C., Yergeau, F.,
and T. Bray, "Extensible Markup Language (XML) 1.0 (Fourth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20060816, August 2006,
.
[XML-NAMES]
Bray, T., Hollander, D., and A. Layman, "Namespaces in
XML", W3C REC-xml-names, January 1999,
.
[XMPP-CORE]
Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", draft-saintandre-rfc3920bis-04
(work in progress), October 2007.
[XMPP-E2E]
Saint-Andre, P., "End-to-End Signing and Object Encryption
for the Extensible Messaging and Presence Protocol
(XMPP)", RFC 3923, October 2004.
13.2. Informative References
[CPIM] Peterson, J., "Common Profile for Instant Messaging
(CPIM)", RFC 3860, August 2004.
[CPP] Peterson, J., "Common Profile for Presence (CPP)",
RFC 3859, August 2004.
[IMP-MODEL]
Day, M., Rosenberg, J., and H. Sugano, "A Model for
Presence and Instant Messaging", RFC 2778, February 2000.
[IRC] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
April 2000.
[RFC3921] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
RFC 3921, October 2004.
[SASL] Melnikov, A. and K. Zeilenga, "Simple Authentication and
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Security Layer (SASL)", RFC 4422, June 2006.
[TLS] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
[XEP-0016]
Millard, P. and P. Saint-Andre, "Privacy Lists", XSF
XEP 0016, February 2007.
[XEP-0045]
Saint-Andre, P., "Multi-User Chat", XSF XEP 0045,
April 2007.
[XEP-0054]
Saint-Andre, P., "vcard-temp", XSF XEP 0054, March 2003.
[XEP-0071]
Saint-Andre, P., "XHTML-IM", XSF XEP 0071, August 2007.
[XEP-0115]
Hildebrand, J., Saint-Andre, P., and R. Troncon, "Entity
Capabilities", XSF XEP 0115, August 2007.
[XEP-0160]
Saint-Andre, P., "Best Practices for Handling Offline
Messages", XSF XEP 0160, January 2006.
[XEP-0201]
Saint-Andre, P., Paterson, I., and K. Smith, "Best
Practices for Message Threads", XSF XEP 0201, August 2007.
[XML-SCHEMA]
Thompson, H., Maloney, M., Mendelsohn, N., and D. Beech,
"XML Schema Part 1: Structures Second Edition", World Wide
Web Consortium Recommendation REC-xmlschema-1-20041028,
October 2004,
.
[VCARD] Dawson, F. and T. Howes, "vCard MIME Directory Profile",
RFC 2426, September 1998.
Appendix A. Subscription States
This section provides detailed information about subscription states
and server processing of subscription-related presence stanzas (i.e.,
presence stanzas of type "subscribe", "subscribed", "unsubscribe",
and "unsubscribed").
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A.1. Defined States
There are four primary subscription states (note: these states are
described from the perspective of the user, not the contact):
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
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 (i.e., the union of 'from' and 'to')
These states are supplemented by various pending sub-states to yield
nine possible subscription states:
1. "None" = contact and user are not subscribed to each other, and
neither has requested a subscription from the other; this is
reflected in the user's roster by subscription='none'
2. "None + Pending Out" = contact and user are not subscribed to
each other, and user has sent contact a subscription request but
contact has not replied yet; this is reflected in the user's
roster by subscription='none' and ask='subscribe'
3. "None + Pending In" = contact and user are not subscribed to each
other, and contact has sent user a subscription request but user
has not replied yet (note: contact's server SHOULD NOT push or
deliver roster items in this state, but instead SHOULD wait until
user has approved subscription request from contact); this is
reflected in the user's roster by subscription='none'
4. "None + Pending Out+In" = contact and user are not subscribed to
each other, contact has sent user a subscription request but user
has not replied yet, and user has sent contact a subscription
request but contact has not replied yet; this is reflected in the
user's roster by subscription='none' and ask='subscribe'
5. "To" = user is subscribed to contact (one-way); this is reflected
in the user's roster by subscription='to'
6. "To + Pending In" = user is subscribed to contact, and contact
has sent user a subscription request but user has not replied
yet; this is reflected in the user's roster by subscription='to'
7. "From" = contact is subscribed to user (one-way); this is
reflected in the user's roster by subscription='from'
8. "From + Pending Out" = contact is subscribed to user, and user
has sent contact a subscription request but contact has not
replied yet; this is reflected in the user's roster by
subscription='none' and ask='subscribe'
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9. "Both" = user and contact are subscribed to each other (two-way);
this is reflected in the user's roster by subscription='both'
A.2. Server Processing of Outbound Presence Subscription Stanzas
Outbound presence subscription stanzas enable the user to manage his
or her subscription to the contact's presence (via the "subscribe"
and "unsubscribe" types), and to manage the contact's access to the
user's presence (via the "subscribed" and "unsubscribed" types).
The following rules apply to outbound routing of the stanza as well
as changes to the user's roster.
Note: The rules for server processing of outbound presence
subscription stanzas are described from the perspective of the user,
not the contact.
Note: In the following tables, "S.N." stand for SHOULD NOT.
A.2.1. Subscribe
Table 1: Processing of outbound "subscribe" stanzas
+-----------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+-----------------------------------------------------------------+
| "None" | MUST | "None + Pending Out" [1] |
| "None + Pending Out" | MUST | no state change |
| "None + Pending In" | MUST | "None + Pending Out+In" |
| "None + Pending Out+In" | MUST | no state change |
| "To" | MUST | no state change |
| "To + Pending In" | MUST | no state change |
| "From" | MUST | "From + Pending Out" [1] |
| "From + Pending Out" | MUST | no state change |
| "Both" | MUST | no state change |
+-----------------------------------------------------------------+
[1] A state change to "pending out" includes setting the 'ask' flag
to a value of "subscribe" in the user's roster.
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A.2.2. Unsubscribe
Table 2: Processing of outbound "unsubscribe" stanzas
+-----------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+-----------------------------------------------------------------+
| "None" | MUST | no state change |
| "None + Pending Out" | MUST | "None" |
| "None + Pending In" | MUST | no state change |
| "None + Pending Out+In" | MUST | "None + Pending In" |
| "To" | MUST | "None" |
| "To + Pending In" | MUST | "Pending In" |
| "From" | MUST | no state change |
| "From + Pending Out" | MUST | "From" |
| "Both" | MUST | "From" |
+-----------------------------------------------------------------+
A.2.3. Subscribed
Table 3: Processing of outbound "subscribed" stanzas
+-----------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+-----------------------------------------------------------------+
| "None" | S.N. | no state change [1] |
| "None + Pending Out" | S.N. | no state change |
| "None + Pending In" | MUST | "From" |
| "None + Pending Out+In" | MUST | "From + Pending Out" |
| "To" | S.N. | no state change |
| "To + Pending In" | MUST | "Both" |
| "From" | S.N. | no state change |
| "From + Pending Out" | S.N. | no state change |
| "Both" | S.N. | no state change |
+-----------------------------------------------------------------+
[1] A server MAY note the fact that the user wishes to allow the
contact to be subscribed to the user's presence and automatically
approve any subscription request received from the contact; if it
does so, upon the receiving presence stanza of type "subscribed" from
the user's client it MUST add a roster item for the contact to the
user's roster and set the 'ask' flag to a value of "subscribed".
However, the user's server still SHOULD NOT route the presence stanza
of type "subscribed" to the contact. This optional functionality
applies only if the contact is not already in the user's roster or if
the contact is in the user's roster with a state of "None" (not
including a state of "None + Pending Out").
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A.2.4. Unsubscribed
Table 4: Processing of outbound "unsubscribed" stanzas
+-----------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+-----------------------------------------------------------------+
| "None" | S.N. | no state change |
| "None + Pending Out" | S.N. | no state change |
| "None + Pending In" | MUST | "None" |
| "None + Pending Out+In" | MUST | "None + Pending Out" |
| "To" | S.N. | no state change |
| "To + Pending In" | MUST | "To" |
| "From" | MUST | "None" |
| "From + Pending Out" | MUST | "None + Pending Out" |
| "Both" | MUST | "To" |
+-----------------------------------------------------------------+
A.3. Server Processing of Inbound Presence Subscription Stanzas
Inbound presence subscription stanzas request a subscription-related
action from the user (via the "subscribe" type), inform the user of
subscription-related actions taken by the contact (via the
"unsubscribe" type), or enable the user to manage the contact's
access to the user's presence information (via the "subscribed" and
"unsubscribed" types).
The following rules apply to delivery of the inbound stanza as well
as changes to the user's roster.
Note: The rules for server processing of inbound presence
subscription stanzas are described from the perspective of the user,
not the contact.
Note: In the following tables, "S.N." stand for SHOULD NOT.
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A.3.1. Subscribe
Table 5: Processing of inbound "subscribe" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | MUST [1] | "None + Pending In" |
| "None + Pending Out" | MUST | "None + Pending Out+In" |
| "None + Pending In" | S.N. | no state change |
| "None + Pending Out+In" | S.N. | no state change |
| "To" | MUST | "To + Pending In" |
| "To + Pending In" | S.N. | no state change |
| "From" | S.N. [2] | no state change |
| "From + Pending Out" | S.N. [2] | no state change |
| "Both" | S.N. [2] | no state change |
+------------------------------------------------------------------+
[1] If the user previously sent presence of type "subscribed" as
described under Appendix A.2.3, then the server MAY auto-reply with
"subscribed" and change the state to "From" rather than "None +
Pending In".
[2] Server SHOULD auto-reply with "subscribed".
A.3.2. Unsubscribe
When the user's server receives a presence stanza of type
"unsubscribe" for the user from the contact, if the stanza results in
a subscription state change from the user's perspective then the
user's server MUST change the state and SHOULD auto-reply by sending
a presence stanza of type "unsubscribed" to the contact on behalf of
the user. Otherwise the user's server MUST NOT change the state and
SHOULD NOT deliver the stanza. These rules are summarized in the
following table.
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Table 6: Processing of inbound "unsubscribe" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | S.N. | no state change |
| "None + Pending Out" | S.N. | no state change |
| "None + Pending In" | S.N. [1] | "None" |
| "None + Pending Out+In" | S.N. [1] | "None + Pending Out" |
| "To" | S.N. | no state change |
| "To + Pending In" | S.N. [1] | "To" |
| "From" | S.N. [1] | "None" |
| "From + Pending Out" | S.N. [1] | "None + Pending Out |
| "Both" | S.N. [1] | "To" |
+------------------------------------------------------------------+
[1] Server SHOULD auto-reply with "unsubscribed".
A.3.3. Subscribed
When the user's server receives a presence stanza of type
"subscribed" for the user from the contact, if there is no pending
outbound request for access to the contact's presence information,
then it MUST NOT change the subscription state and SHOULD NOT deliver
the stanza to the user. If there is a pending outbound request for
access to the contact's presence information and the inbound presence
stanza of type "subscribed" results in a subscription state change,
then the user's server MUST change the subscription state but SHOULD
NOT deliver the stanza to the user. If the user already has access
to the contact's presence information, the inbound presence stanza of
type "subscribed" does not result in a subscription state change;
therefore the user's server MUST NOT change the subscription state
and SHOULD NOT deliver the stanza to the user. These rules are
summarized in the following table.
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Table 7: Processing of inbound "subscribed" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | S.N. | no state change |
| "None + Pending Out" | S.N. | "To" |
| "None + Pending In" | S.N. | no state change |
| "None + Pending Out+In" | S.N. | "To + Pending In" |
| "To" | S.N. | no state change |
| "To + Pending In" | S.N. | no state change |
| "From" | S.N. | no state change |
| "From + Pending Out" | S.N. | "Both" |
| "Both" | S.N. | no state change |
+------------------------------------------------------------------+
A.3.4. Unsubscribed
When the user's server receives a presence stanza of type
"unsubscribed" for the user from the contact, if there is a pending
outbound request for access to the contact's presence information or
if the user currently has access to the contact's presence
information, then the user's server MUST change the subscription
state but SHOULD NOT deliver the stanza to the user. Otherwise, the
user's server MUST NOT change the subscription state and SHOULD NOT
deliver the stanza. These rules are summarized in the following
table.
Table 8: Processing of inbound "unsubscribed" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | S.N. | no state change |
| "None + Pending Out" | S.N. | "None" |
| "None + Pending In" | S.N. | no state change |
| "None + Pending Out+In" | S.N. | "None + Pending In" |
| "To" | S.N. | "None" |
| "To + Pending In" | S.N. | "None + Pending In" |
| "From" | S.N. | no state change |
| "From + Pending Out" | S.N. | "From" |
| "Both" | S.N. | "From" |
+------------------------------------------------------------------+
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Appendix B. Blocking Communication
Sections 2.3.5 and 5.4.10 of [IMP-REQS] require that a compliant
instant messaging and presence technology must enable a user to block
communications from selected users. A protocol for doing so is
specified in [XEP-0016].
Appendix C. vCards
Sections 3.1.3 and 4.1.4 of [IMP-REQS] require that it be possible to
retrieve out-of-band contact information for other users (e.g.,
telephone number or email address). An XML representation of the
vCard specification defined in RFC 2426 [VCARD] is in common use
within the Jabber community to provide such information but is out of
scope for XMPP (documentation of this protocol is contained in
[XEP-0054]).
Appendix D. XML Schemas
Because validation of XML streams and stanzas is optional, the
following XML schemas are provided for descriptive purposes only.
These schemas are not normative.
The following schemas formally define various XML namespaces used in
the core XMPP protocols, in conformance with [XML-SCHEMA]. For
schemas defining namespaces for XML streams and other core aspects of
XMPP, refer to [XMPP-CORE].
D.1. jabber:client
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D.2. jabber:server
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D.3. jabber:iq:roster
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Appendix E. Differences From RFC 3921
Based on consensus derived from implementation and deployment
experience as well as formal interoperability testing, the following
substantive modifications were made from RFC 3921.
o The protocol for session establishment was determined to be
unnecessary and therefore the content previously defined in
Section 3 of RFC 3921 was removed. However, server
implementations may still want to advertise support for the
feature in order to ensure backward-compatibility, even though
session establishment is a "no-op".
o The protocol for communications blocking specified in Section 10
of RFC 3921 has been moved to [XEP-0016].
o In order to more seamlessly repair lack of synchronization in
subscription states between rosters located at different servers,
error handling related to presence probes and presence
notifications was modified to return presence stanzas of type
"unsubscribe" or "unsubscribed" rather than error stanzas.
o Added optional server support for pre-approved presence
subscriptions via presence stanzas of type "subscribed" and the
optional "subscribed" value for the 'ask' flag.
In addition, numerous changes of an editorial nature were made in
order to more fully specify and clearly explain the protocols.
Appendix F. Copying Conditions
The Contributor grants third parties the irrevocable right to copy,
use and distribute the Contribution, with or without modification, in
any medium, without royalty, provided that, unless separate
permission is granted, redistributed modified works:
1. do not contain misleading author, version, name of work, or
endorsement information, and
2. do not claim endorsement of the modified work by the Contributor,
or any organization the Contributor belongs to, the Internet
Engineering Task Force (IETF), Internet Research Task Force
(IRTF), Internet Engineering Steering Group (IESG), Internet
Architecture Board (IAB), Internet Assigned Numbers Authority
(IANA), Internet Society (ISOC), Request For Comments (RFC)
Editor, or any combination or variation of such terms (including
without limitation the IETF "4 diamonds" logo), or any terms that
are confusingly similar thereto, and
3. remove any claims of status as an Internet Standard, including
without limitation removing the RFC boilerplate.
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The IETF suggests that any citation or excerpt of unmodified text
reference the RFC or other document from which the text is derived.
Index
A
Available Resource 31
B
Broadcasted Presence 31
C
Contact 20
D
Directed Presence 31
I
Initial Presence 31
Interested Resource 11
P
Presence 5
Presence Probe 33
Presence Session 31
Presence Subscription 20
R
Roster 5
Roster Get 8
Roster Push 9
Roster Result 10
Roster Set 9
S
Subscription Request 21
U
Unavailable Presence 37
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Author's Address
Peter Saint-Andre (editor)
XMPP Standards Foundation
Email: stpeter@jabber.org
URI: https://stpeter.im/
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Full Copyright Statement
Copyright (C) The IETF Trust (2007).
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contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
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